Method and apparatus for adjusting control parameters for cardiac event sensing

Abstract

A medical device includes a motion sensor configured to generate a motion signal and a control circuit configured to set a sensing control parameter and sense an atrial event from the motion signal during a ventricular cycle in accordance with the sensing control parameter. In some examples, the control circuit is configured to determine a characteristic of the motion signal for at least some ventricular cycles, determine a metric of the motion signal based on the determined characteristic, and adjust at least one of the sensing control parameter based on the metric.

Description

Technical Field

[0001] This disclosure relates to a medical device and method for adjusting control parameters for sensing cardiac events from motion sensor signals. Background Technology

[0002] Implantable pacemakers are typically placed in a subcutaneous pouch and coupled to one or more transvenous medical leads carrying pacing and sensing electrodes positioned within the heart. A subcutaneously implanted pacemaker can be a single-chamber pacemaker coupled to one transvenous medical lead to position the electrode in one heart chamber (atrium or ventricle) or a dual-chamber pacemaker coupled to two intracardiac leads to position the electrode in both the atrium and ventricle. Multi-chamber pacemakers are also available, which can be coupled to three leads, for example, to position the electrodes for pacing and sensing in one atrium and both the left and right ventricles.

[0003] Intracardiac pacemakers have been introduced that can be implanted within the ventricular chambers of a patient's heart to deliver ventricular pacing pulses. These pacemakers can sense the R-wave signal accompanying inherent ventricular depolarization and deliver ventricular pacing pulses even in the absence of a sensed R-wave. While single-chamber ventricular sensing and pacing via an intracardiac ventricular pacemaker can adequately address the condition in some patients, some may benefit from atrial and ventricular (dual-chamber) sensing to provide atrial-synchronized ventricular pacing in order to maintain a regular heart rhythm. Summary of the Invention

[0004] This disclosure generally relates to a pacemaker having a motion sensor that generates motion signals, which may include signals representing ventricular and atrial mechanical events. The pacemaker is configured to sense atrial events from the motion signals, for example, atrial mechanical event signals corresponding to atrial contractions occurring during atrial systole. In some instances, the sensed atrial events can be used to control atrial-synchronized ventricular pacing pulses delivered by the pacemaker. A pacemaker operating according to the disclosed technique adjusts sensing control parameters for sensing atrial event signals from the motion sensor signals. The sensing control parameters may include one or more of a sensing window start time, a sensing window end time, and / or a sensing threshold amplitude applied to the motion sensor signals for sensing atrial events.

[0005] In one example, this disclosure provides a medical device comprising a motion sensor and control circuitry. The motion sensor is configured to generate a motion signal. The control circuitry is configured to set sensing control parameters and, based on the sensing control parameters, sense atrial events from the motion signal during a plurality of ventricular cycles. The control circuitry is configured to determine characteristics of the motion signal for each ventricular cycle, for at least a portion of the plurality of ventricular cycles, determine a metric of the motion signal based on the determined characteristics, and adjust at least one of the sensing control parameters based on the metric. The control circuitry is configured to sense atrial events from the motion signal according to the adjusted sensing control parameters and, in response to sensing the atrial event, generate an atrial sensing event signal.

[0006] In another example, this disclosure provides a method comprising generating a motion signal from a motion sensor, setting a plurality of sensing control parameters, and sensing an atrial event from the motion signal during a plurality of ventricular cycles based on the sensing control parameters. The method may include: determining characteristics of the motion signal for each ventricular cycle of at least a portion of the plurality of ventricular cycles; determining a metric of the motion signal based on the determined characteristics; adjusting at least one of the sensing control parameters based on the metric; and sensing an atrial event from the motion signal based on the adjusted sensing control parameters. The method may also include generating an atrial sensing event signal in response to sensing the atrial event based on the adjusted sensing control parameters.

[0007] In another example, this disclosure provides a non-transitory computer-readable storage medium comprising a set of instructions, which, when executed by control circuitry of a medical device, cause the medical device to: generate a motion signal via a motion sensor; set a plurality of sensing control parameters; and sense an atrial event from the motion signal during a plurality of ventricular cycles according to the sensing control parameters. The instructions further cause the device to determine characteristics of the motion signal for each ventricular cycle of at least some of the plurality of ventricular cycles; determine a metric of the motion signal based on the determined characteristics; adjust at least one of the sensing control parameters based on the metric; and sense an atrial event from the motion signal according to the adjusted sensing control parameters. The instructions can cause the device to generate an atrial sensing event signal in response to sensing the atrial event according to the adjusted sensing control parameters.

[0008] Details of one or more aspects of this disclosure are set forth in the accompanying drawings and the following description. Other features, objects, and advantages described in this disclosure will become apparent from the description and drawings and from the claims. Attached Figure Description

[0009] Figure 1This is a conceptual diagram of a medical device system that can be used to sense electrical and kinematic signals induced by cardiac movement and blood flow and to provide pacing therapy to a patient's heart.

[0010] Figure 2 yes Figure 1 The diagram shown is a conceptual illustration of an intracardiac pacemaker.

[0011] Figure 3 yes Figure 1 A schematic diagram of an exemplary configuration of the pacemaker shown.

[0012] Figure 4 This is an example of motion sensor signals that can be generated by a motion sensor during the cardiac cycle.

[0013] Figure 5 This is an example of motion sensor signals generated during two different cardiac cycles.

[0014] Figure 6 This is a flowchart illustrating methods for adjusting atrial event sensing control parameters based on some examples.

[0015] Figure 7 This is a diagram illustrating a method for determining control parameter metrics during atrial tracking of ventricular pacing modes, based on an example.

[0016] Figure 8 It is a diagram representing four ventricular cycles that can occur during a ventricular cycle with defined control parameters.

[0017] Figure 9 This is a flowchart of a method for determining the control parameter metric used in adjusting the low sensing threshold of atrial events, based on an example.

[0018] Figure 10 This is a flowchart of a method for determining the adjustment of the low sensing threshold amplitude for atrial events, based on an example.

[0019] Figure 11 This is a flowchart illustrating an example of a method for determining when the low sensing threshold adjustment criteria for atrial events are met.

[0020] Figure 12 It is a graph of the electrogram (EGM) signal, the motion sensor signal, and various features of the motion sensor signal that can be used to determine the A4 sensing control parameter measure.

[0021] Figure 13 This is a flowchart illustrating a method performed by a medical device, based on an example, for determining A4 sensing control parameter measurements and adjusting the sensing window end time.

[0022] Figure 14 This is a flowchart of a method that can be executed by a medical device to determine when the sensing window end time adjustment criteria are met.

[0023] Figure 15 This is a flowchart of a method performed by a medical device, based on an example, for adjusting the amplitude of atrial event high sensing threshold.

[0024] Figure 16 This is a flowchart 900 of a method, according to another example, that can be executed by control circuitry 206 to adjust the amplitude of the high A4 sensing threshold.

[0025] Figure 17 Figure 950 shows a histogram of the A3 event amplitude that can be determined by the control circuit 206 and stored in the memory 210 for setting the high A4 sensing threshold amplitude, based on some examples.

[0026] Figure 18 This is a flowchart of a method for adjusting atrial event sensing control parameters from initial values ​​to operational values, based on an example. Detailed Implementation

[0027] Generally, this disclosure describes techniques for adjusting cardiac event sensing parameters via an implantable medical device. As described below, motion sensor signals, such as accelerometer signals, can contain cardiac event signals accompanying the mechanical contraction and relaxation (and filling) of the heart chambers. Cardiac event signals can be sensed from signals generated by the motion sensor. The motion sensor signal can contain cardiac event signals corresponding to ventricular and atrial events. For example, an atrial contraction event signal corresponding to the mechanical contraction of the atrium and the active filling phase of the ventricle (sometimes referred to as an "atrial kick") can be present in the motion sensor signal implanted in the ventricular chamber. Atrial events can be sensed from the motion sensor signal using atrial event sensing control parameters, which can include one or more sensing threshold amplitudes and / or time windows. Atrial events can be sensed based on sensing control parameters from other cardiac event signals that may occur in the motion sensor signal during the cardiac cycle. The techniques disclosed herein provide methods for sensing cardiac events (e.g., atrial events) from motion sensor signals and adjusting cardiac event sensing control parameters to improve cardiac event sensing performance via a medical device.

[0028] In some instances, the medical device is a ventricular pacemaker, which can be fully implanted within the ventricle of the heart and has motion sensors for generating intraventricular motion signals. Atrial contraction events can be sensed from the motion sensor signals within the ventricle for use, for example, in controlling atrial synchronizing ventricular pacing. Atrial-synchronized ventricular pacing pulses can be delivered by the pacemaker implanted in the ventricle, eliminating the need for sensors located in or on the atria of the patient's heart for detecting atrial events.

[0029] Figure 1 This is a conceptual diagram of an implantable medical device (IMD) system 10 that can be used to sense cardiac electrical and kinematic signals induced by cardiac motion and blood flow and to deliver pacing therapy to a patient's heart 8. The IMD system 10 includes an intraventricular pacemaker 14. The pacemaker 14 may be a transcatheter intraventricular pacemaker adapted to be implanted entirely within the heart chambers (e.g., entirely within the right ventricle (RV) or entirely within the left ventricle (LV) of the heart 8) for sensing cardiac signals and delivering ventricular pacing pulses. The size of the pacemaker 14 can be reduced compared to a subcutaneously implanted pacemaker, and its shape may be generally cylindrical to allow for transvenous implantation via a delivery catheter.

[0030] Although other locations are possible, pacemaker 14 is shown positioned along the endocardial wall within the RV, for example, near the apex of the RV. The techniques disclosed herein are not limited to... Figure 1 The pacemaker location shown in the examples is possible, but other locations within the heart 8 are also possible. For example, the intraventricular pacemaker 14 can be located in the LV and configured to detect cardiac motion signals using the techniques disclosed herein and deliver atrial-synchronized ventricular pacing to the LV. The pacemaker 14 can be located within the RV or LV to provide corresponding right or left ventricular pacing and to sense cardiac mechanical event signals from signals generated by motion sensors passing through the ventricular chambers. In other examples, the pacemaker 14 does not necessarily need to be implanted inside the heart chambers but can be located outside the heart, for example, along the epicardium in the RV or LV.

[0031] The pacemaker 14 is capable of generating electrical stimulation pulses (e.g., pacing pulses) delivered to the heart 8 via one or more electrodes on the outer casing of the pacemaker. The pacemaker 14 is configured to deliver RV pacing pulses and sense RV cardiac electrical signals using casing-based electrodes to generate an RV electrogram (EGM) signal. In some embodiments, the cardiac electrical signals can be sensed using casing-based electrodes that deliver the pacing pulses to the RV.

[0032] The pacemaker 14 is configured to control the delivery of ventricular pacing pulses to the RV in a manner that promotes synchronization between atrial and ventricular activation (e.g., by maintaining a target atrial-ventricular (AV) interval between atrial events and ventricular pacing pulses). That is, the pacemaker 14 controls pacing pulse delivery to maintain a desired AV interval between atrial contractions corresponding to atrial systole and ventricular pacing pulses delivered to induce ventricular depolarization and ventricular systole.

[0033] According to the technology described herein, an atrial systolic event that generates the active ventricular filling phase is detected by pacemaker 14 from motion sensor signals (e.g., accelerometer signals), generated by a motion sensor that can be surrounded by a housing of pacemaker 14. The motion signal generated by the accelerometer implanted within the ventricular chamber (which may be referred to as the “intraventricular motion signal”) includes motion signals caused by ventricular and atrial events. For example, the acceleration of blood flowing through the tricuspid valve 16 between the RA and RV, referred to as an “atrial jump”, caused by atrial systole, can be detected by pacemaker 14 from signals generated by the accelerometer contained within pacemaker 14. The following is combined with… Figure 4 Other motion signals that can be detected by pacemaker 14 are described, such as motion caused by ventricular contraction and passive ventricular filling.

[0034] The atrial P wave accompanying atrial depolarization is a relatively low-amplitude signal in the near-field ventricular cardiac electrical signal received by pacemaker 14 (e.g., compared to the near-field R wave accompanying ventricular depolarization) and therefore may be difficult to reliably detect from the cardiac electrical signal acquired by pacemaker 14 when implanted in the ventricular chamber. When based solely on the cardiac electrical signal received by pacemaker 14, atrial-synchronized ventricular pacing performed by pacemaker 14 or other functions relying on atrial sensing may be unreliable. According to the techniques disclosed herein, pacemaker 14 includes a motion sensor (such as an accelerometer) and is configured to detect atrial events corresponding to atrial mechanical activation or atrial systole from signals generated by the motion sensor. By setting a programmable AV pacing interval that controls the timing of the ventricular pacing pulse relative to the detected atrial systole event, the ventricular pacing pulse can be synchronized with the atrial event detected from the motion sensor signal. As described below, the detection of atrial contraction events used to synchronize ventricular pacing pulses with atrial systole may include the detection of motion signals from other cardiac events in order to definitively identify atrial contraction events and / or adjust atrial contraction event sensing control parameters.

[0035] The target AV interval can be a default value or a programmed value selected by the clinician, and is the time interval from the detection of an atrial event until the delivery of the immediately following ventricular pacing pulse. In some cases, the target AV interval can begin from the time when an atrial contraction event is detected based on motion sensor signals, or from a reference point identified by the atrial event signal. Based on the patient's clinical tests or assessments, or based on clinical data from a patient population, the target AV interval can be identified as hemodynamically optimal for a given patient. The target AV interval can be determined to be optimal based on the relative timing of electrical and mechanical events identified in the cardiac electrical signals received from pacemaker 14 and the motion sensor signals received from pacemaker 14. For example, the AV interval can be programmed from 10 milliseconds to 50 milliseconds.

[0036] The pacemaker 14 may be capable of bidirectional wireless communication with the external device 20 to program the AV pacing interval and other pacing control parameters and mechanical event sensing parameters that can be used to detect ventricular mechanical events and atrial contraction events from motion sensor signals. Aspects of the external device 20 may generally correspond to the external programming / monitoring unit disclosed in U.S. Patent No. 5,507,782 (Kieval et al.), which is incorporated herein by reference in its entirety. The external device 20 is generally referred to as a “programmer” because it is typically used by a physician, technician, nurse, clinician, or other qualified user to program the operating parameters in the pacemaker 14. The external device 20 may be located in a clinic, hospital, or other medical facility. Alternatively, the external device 20 may be embodied as a home monitor or handheld device that can be used in a medical facility, a patient’s home, or another location. Operating parameters, including sensing and therapy delivery control parameters, can be programmed into the pacemaker 14 by a user interacting with the external device 20.

[0037] External device 20 may include processor 52, memory 53, display unit 54, user interface 56, and telemetry unit 58. Processor 52 controls the operation of external device and processes data and signals received from pacemaker 14. Display unit 54 may generate displays of data and information relating to pacemaker function (the displays may include a graphical user interface) for the user to review pacemaker operation and programmed parameters, as well as cardiac electrical signals, cardiac motion signals, or other physiological data that can be acquired by pacemaker 14 and transmitted to external device 20 during an inquiry session.

[0038] User interface 56 may include a mouse, touchscreen, keyboard, etc., to enable a user to interact with external device 20 to initiate a telemetry session with pacemaker 14 for retrieving and / or transmitting data to pacemaker 14, including programmable parameters for controlling cardiac event sensing and therapy delivery. Telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with telemetry circuitry included in pacemaker 14, and is configured to operate in conjunction with processor 52 to send and receive data relating to pacemaker functionality via communication link 24.

[0039] At the time of implantation, during patient follow-up, or at any time after pacemaker implantation, pacemaker 14 can execute a setup procedure to establish parameters for detecting atrial events from motion sensor signals. During the procedure, the patient can be standing, sitting, lying down, or not in bed. The setup procedure may include acquiring motion sensor signal data and generating a distribution of motion sensor signal characteristics to establish atrial event sensing parameters. In some instances, the motion sensor signal data can be transmitted to external device 20 and displayed as a histogram on display unit 54 of external device 20. The atrial event sensing parameters established based on the motion sensor signal data can be automatically set or transmitted to external device 20 to generate a display on display unit 54 as recommended parameters, allowing clinicians to review and accept or modify the recommended parameters, for example, using user interface 56.

[0040] In some instances, the external device processor 52 can perform operations for establishing initial values ​​for atrial event sensing parameters based on data retrieved from the pacemaker 14. The processor 52 can cause the display unit 54 to generate a display of data relating to motion sensor signals, including a histogram distribution of metrics determined from cardiac motion signals, for selecting initial values ​​for the atrial event sensing control parameters. The display unit 54 can be a graphical user interface that allows a user to interact with the display, for example, to select various displays or information for viewing. In some instances, the user can select one or more atrial event sensing control parameter settings to be automatically established by the pacemaker 14 and / or can program the initial sensing control parameters or other programmable parameters for controlling sensor operation and therapy delivery. In some instances, the processing circuitry and / or processor 52 included in the pacemaker 14 can determine initial values ​​for one or more atrial contraction event sensing control parameters based on data acquired from acceleration signals generated by an accelerometer included in the pacemaker 14, and various thresholds and criteria (which may include user-programmable thresholds or criteria used to set the initial parameter values).

[0041] One or more initial values ​​for the sensing control parameters can be adjusted by the pacemaker 14 according to the techniques disclosed herein. After establishing initial values ​​for the sensing control parameters used to sense cardiac event signals from cardiac motion signals, signal variability due to various factors such as patient posture, patient physical activity, and patient heart rate may cause these initial values ​​to no longer be optimal. To facilitate reliable sensing of cardiac mechanical events from motion signals over time, the pacemaker 14 is configured to adjust the sensing control parameters. This automatic adjustment adapts to and optimizes the sensing control parameters as patient or signal sensing conditions change over time, improving the reliability of sensing cardiac mechanical events and delivery of pacing therapy even in walking patients, and reducing the burden on clinicians to manually adjust the sensing control parameters.

[0042] The external telemetry unit 58 is configured for bidirectional communication with the implantable telemetry circuitry system included in the pacemaker 14. The telemetry unit 58 establishes a wireless communication link 24 with the pacemaker 14. The communication link 24 can use methods such as... The communication link 24 may be established using Wi-Fi, Medical Implantable Communication Service (MICS), or other radio frequency (RF) links of varying bandwidths. In some examples, external device 20 may include a programming head positioned close to pacemaker 14 to establish and maintain the communication link 24. In other examples, external device 20 and pacemaker 14 may be configured to communicate using distance telemetry algorithms and circuitry that do not require the use of a programming head and do not require user intervention to maintain the communication link.

[0043] Consideration has been made that the external device 20 can be connected to a communication network, either wired or wirelessly, via telemetry circuitry including a transceiver and antenna or via hardwired communication lines for transmitting data to a centralized database or computer, to allow for remote patient management. A remote patient management system containing a centralized patient database can be configured to utilize currently disclosed technologies to enable clinicians to review, for example, EGM, motion sensor signals, and marker channel data after viewing a visual representation of the data, and to authorize the programming of sensing and therapy control parameters in the pacemaker 14.

[0044] Figure 2 It is based on an instance. Figure 1The diagram shows an intracardiac pacemaker 14. The pacemaker 14 includes electrodes 162 and 164 spaced apart along a housing 150 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 164 is shown as a tip electrode extending from the distal end 102 of the pacemaker 14, and electrode 162 is shown as a ring-shaped electrode along a middle portion of the housing 150 (e.g., adjacent to the proximal end 104). The distal end 102 is referred to as the "distal end" because it is expected to become the tip as the pacemaker 14 advances through a delivery tool (such as a catheter) and is placed against the target pacing site.

[0045] Electrodes 162 and 164 form an anode and cathode pair for bipolar cardiac pacing and sensing. In an alternative embodiment, pacemaker 14 may include two or more annular electrodes, two tip electrodes, and / or other types of electrodes exposed along pacemaker housing 150 for delivering electrical stimulation to the heart 8 and sensing cardiac electrical signals. Electrodes 162 and 164 may be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and may include low-polarity coatings such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc. Electrodes 162 and 164 may be positioned along pacemaker 14 at locations other than those shown.

[0046] The housing 150 is formed of a biocompatible material, such as stainless steel or titanium alloy. In some instances, the housing 150 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide. The entire housing 150 may be insulating, except for electrodes 162 and 164. Electrode 164 may act as a cathode electrode and be coupled via an electrical feedthrough across the housing 150 to an internal circuitry system enclosed by the housing 150, such as a pacemaker pulse generator and cardiac electrical signal sensing circuitry. Electrode 162 may be formed as a definition of the housing 150, such as... Figure 2 The conductive portion of the annular electrode, generally shown, is electrically isolated from the rest of the housing 150. In other examples, instead of providing a local annular electrode such as anode electrode 162, the entire periphery of the housing 150 can serve as an electrode electrically isolated from the tip electrode 164. Electrode 162, formed along the conductive portion of the housing 150, acts as a return anode during pacing and sensing.

[0047] The housing 150 may include a control electronics subassembly 152 and a battery subassembly 160 that supplies power to the control electronics subassembly 152. The control electronics subassembly 152 accommodates, as described below... Figure 3The described electronic devices are used to sense cardiac signals, generate pacing pulses, and control the therapy delivery and other functions of pacemaker 14. In some examples, the motion sensor may be implemented as an accelerometer encapsulated within housing 150. The accelerometer provides signals to a processor included in control electronics subassembly 152 for signal processing and analysis to detect atrial contraction events, such as those used to control timing ventricular pacing pulses, as described below.

[0048] An accelerometer can be a three-dimensional accelerometer. In some instances, an accelerometer may have a "longitudinal" axis parallel to or aligned with the longitudinal axis 108 of the pacemaker 14 and two orthogonal axes extending radially relative to the longitudinal axis 108. However, the practice of the techniques disclosed herein is not limited to a specific orientation of the accelerometer within or along the housing 150. In other instances, a one-dimensional accelerometer may be used to obtain intracardiac motion signals from which cardiac mechanical events can be detected. In other instances, a two-dimensional accelerometer or other multi-dimensional accelerometers may be used. Each axis of a one-dimensional or multi-dimensional accelerometer may be defined by a piezoelectric element, microelectromechanical system (MEMS) device, or other sensor element capable of generating an electrical signal in response to a change in acceleration applied to a sensor element (e.g., by converting acceleration into a force or displacement that has been converted into an electrical signal). In a multi-dimensional accelerometer, the sensor elements may be arranged orthogonally, with each sensor element axis orthogonal to the other sensor element axes. However, an orthogonal arrangement of the elements of a multi-axis accelerometer is not necessarily required.

[0049] Each sensor element or axis can generate an acceleration signal corresponding to a vector aligned with the axis of the sensor element. The vector signal of a multidimensional accelerometer (also known as a "multi-axis" accelerometer) used to sense cardiac mechanical events can be selected to include a single-axis signal or a combination of two or more axis signals. In some cases, one, two, or all three axis signals generated by a three-dimensional accelerometer can be selected as vector signals for detecting atrial contraction events, for example, for controlling ventricular pacing synchronized with atrial contraction delivered by pacemaker 14. When two or more axis signals are selected, the axis signals can be added or combined in another manner to generate a motion signal from which atrial contraction events can be sensed.

[0050] The pacemaker 14 may include features for facilitating deployment and fixation of the pacemaker 14 at the implantation site. For example, the pacemaker 14 may include a set of fixation teeth 166 to fix the pacemaker 14 to patient tissue, for example, by active engagement with the ventricular endocardium and / or interaction with ventricular trabeculae. The fixation teeth 166 are configured to anchor the pacemaker 14 to position the electrode 164 operatively close to the target tissue for delivery of therapeutic electrical stimulation pulses. Various types of active and / or passive fixation components may be employed to anchor or stabilize the pacemaker 14 in the implantation location. The pacemaker 14 may optionally include a delivery tool interface 158. The delivery tool interface 158 may be located at the proximal end 104 of the pacemaker 14 and is configured to connect to a delivery device (such as a catheter) for positioning the pacemaker 14 at the implantation site (e.g., within a cardiac chamber) during the implantation procedure.

[0051] Figure 3 yes Figure 1 The diagram shows a conceptual configuration of an exemplary pacemaker 14. The pacemaker 14 includes a pulse generator 202, cardiac electrical signal sensing circuitry 204, control circuitry 206, memory 210, telemetry circuitry 208, motion sensor 212, and power supply 214. Figure 3 The various circuits represented herein can be combined on one or more integrated circuit boards, which include: application-specific integrated circuits (ASICs), electronic device circuits, processors (shared, dedicated, or grouped) and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components that provide the described functions.

[0052] In the examples described herein, motion sensor 212 may include an accelerometer. However, motion sensor 212 is not limited to an accelerometer, and other motion sensors can be successfully used in pacemaker 14 to detect cardiac motion signals according to the techniques described herein. Examples of motion sensors that can be implemented in motion sensor 212 include piezoelectric sensors and MEMS devices.

[0053] Motion sensor 212 may comprise a multi-axis sensor, such as a two-dimensional or three-dimensional sensor, where each axis provides an axis signal for detecting cardiac mechanical events that can be analyzed independently or in combination. Motion sensor 212 generates, for example, electrical signals associated with motion or vibration of sensor 212 (and pacemaker 14) in response to flowing blood and cardiac motion. Motion sensor 212 may include one or more filters, amplifiers, rectifiers, analog-to-digital converters (ADCs), and / or other components for generating motion signals that are passed to control circuitry 206. For example, each signal generated by each individual axis of the multi-axis accelerometer may be filtered by a high-pass filter (e.g., a 10Hz high-pass filter). The filtered signal may be digitized by the ADC and rectified for use by atrial event detector circuitry 240 to detect atrial contraction events. If detection of atrial signals with lower frequency content is required, the high-pass filter may be reduced (e.g., to 5Hz). In some examples, high-pass filtering is performed without low-pass filtering. In other examples, each accelerometer axis signal is filtered by a low-pass filter (e.g., a 30Hz low-pass filter) with or without a high-pass filter.

[0054] An example of an accelerometer used in an implantable medical device that can be implemented in conjunction with the techniques disclosed herein is generally disclosed in U.S. Patent No. 5,885,471 (Ruben et al.), which is incorporated herein by reference in its entirety. Implantable medical device arrangements including piezoelectric accelerometers for detecting patient motion are disclosed, for example, in U.S. Patent Nos. 4,485,813 (Anderson et al.) and 5,052,388 (Sivula et al.), both of which are incorporated herein by reference in their entirety. Embodiments of a three-dimensional accelerometer that can be implemented in a pacemaker 14 using the techniques disclosed herein and used for detecting cardiac mechanical events are generally disclosed in U.S. Patent Nos. 5,593,431 (Sheldon) and 6,044,297 (Sheldon), both of which are incorporated herein by reference in their entirety. Other accelerometer designs can be used to generate electrical signals related to motion applied to the pacemaker 14 due to ventricular and atrial events.

[0055] Sensing circuit 204 is configured to receive cardiac electrical signals via electrodes 162 and 164 through pre-filter and amplifier circuit 220. Pre-filter and amplifier circuit 220 may include a high-pass filter to remove DC offset, such as a 2.5 to 5 Hz high-pass filter, or a broadband filter with a passband of 2.5 Hz to 100 Hz to remove DC offset and high-frequency noise. Pre-filter and amplifier circuit 220 may further include an amplifier to amplify the “raw” cardiac electrical signal passed to analog-to-digital converter (ADC) 226. ADC 226 may pass a multi-bit digital electrogram (EGM) signal to control circuit 206 for use by atrial event detector circuit 240 to identify ventricular electrical events (e.g., R waves or T waves) and / or atrial electrical events (e.g., P waves). The identification of cardiac electrical events can be used in algorithms used to establish atrial sensing control parameters and to detect atrial contraction events from motion sensor signals. The digital signal from the ADC 226 can be passed to a rectifier and amplifier circuit 222, which may include a rectifier, a bandpass filter, and an amplifier for passing the cardiac signal to the R-wave detector 224.

[0056] R-wave detector 224 may include a sensing amplifier or other detection circuitry that compares an incoming rectified cardiac electrical signal with an R-wave sensing threshold (which may be an automatically adjusted threshold). When the incoming signal exceeds the R-wave sensing threshold, R-wave detector 224 generates an R-wave sensing event signal (R-sensing) that is passed to control circuitry 206. In other instances, R-wave detector 224 may receive the digital output of ADC 226 for detecting R-waves via comparators, morphological signal analysis of digital EGM signals, or other R-wave detection techniques. Processor 244 may provide sensing control signals to sensing circuitry 204, such as the R-wave sensing threshold, sensitivity, and various blanking and refractory periods applied to the cardiac electrical signal to control R-wave sensing. The R-wave sensing event signal passed from R-wave detector 224 to control circuitry 206 may be used by pacing timing circuitry 242 to schedule ventricular pacing pulses and to identify the timing of ventricular electrical events in an algorithm executed by atrial event detector circuitry 240 for detecting atrial contraction events based on signals received from motion sensor 212.

[0057] Control circuitry 206 includes atrial event detector circuitry 240, pacing timing circuitry 242, and processor 244. Control circuitry 206 can receive R-wave sensed event signals and / or digital cardiac electrical signals from sensing circuitry 204 for detecting and confirming cardiac events associated with each heartbeat (e.g., inherent ventricular depolarization) and controlling ventricular pacing. For example, when pacemaker 14 operates in a non-atrial tracking ventricular pacing mode, the R-wave sensed event signal (which may correspond to inherent ventricular depolarization) can be passed to pacing timing circuitry 242 to suppress or schedule ventricular pacing pulses. The R-wave sensed event signal can also be passed to atrial event detector circuitry 240 to set the time window used by control circuitry 206 in detecting atrial contraction events from motion sensor signals.

[0058] Atrial event detector circuit 240 is configured to detect atrial contraction events based on signals received from motion sensor 212. Techniques for setting a time window for detecting atrial contraction events are described below. In some instances, one or more ventricular mechanical events can be detected from the motion sensor signal during a given cardiac cycle to facilitate definitive detection of atrial contraction events from the motion sensor signal during the ventricular cycle and to adjust atrial contraction event sensing control parameters.

[0059] The atrial event detector circuit 240 receives motion signals from the motion sensor 212 and can initiate an atrial “silencing” period in response to a ventricular electrical event (e.g., an R-wave sensing event signal from the sensing circuit 204 or a pacing pulse delivered by the pulse generator 202). The silence period can correspond to a time period following a ventricular electrical event during which a ventricular mechanical event, such as the opening and / or closing of a semilunar valve, is expected to occur. When ventricular pacing is properly synchronized with the atrial event, an atrial event corresponding to ventricular systole is not expected to occur during the atrial silence period. Therefore, a motion signal peak occurring during the atrial silence period will not be sensed as an atrial event. The atrial “silencing” period can also be used to define a time period following a ventricular electrical event during which the atrial event detector circuit 240 will not sense an atrial systole event. However, in some instances, the motion sensor signal is not necessarily blanked during this period, because the control circuit 206 can still receive the motion sensor signal during the atrial blanking period and process the motion signal for sensing ventricular events during the atrial blanking period.

[0060] For example, in some instances, motion sensor signals during the atrial event detection period can be monitored by the atrial event detector circuit 240 for the purpose of detecting ventricular mechanical events that can be used to confirm or verify the detection of atrial contraction events. Therefore, the ventricular mechanical event detection window can be set during the atrial event disappearance period and can be set according to a predetermined time interval following a ventricular electrical event. The atrial event detector circuit 240 can be configured to detect one or more ventricular mechanical events during a corresponding ventricular event detection window during the atrial event disappearance period. The timing and detection of ventricular mechanical events can be used to update the atrial event disappearance period and / or can be used to confirm the detection of an atrial event that occurred after an expected ventricular mechanical event.

[0061] Atrial event detector circuit 240 determines whether the motion sensor signal meets the detection criteria for an atrial contraction event outside the atrial blanking period. In some instances, atrial event detector circuit 240 may be set to begin after the sensed or paced ventricular electrical event, representing an atrial refractory period. Atrial event detector circuit 240 may be set to time windows corresponding to the passive ventricular filling phase and the active ventricular filling phase (atrial systole) based on the timing of the preceding ventricular electrical event (R-wave sensed event signal or ventricular pacing pulse). The motion sensor signal crossing the atrial event sensing threshold during either of these windows and outside the atrial blanking period can be detected as an atrial contraction event. As described below, two different atrial event sensing thresholds may be established for application during the passive filling phase window and after the passive filling phase window (during the active filling phase window, also referred to below as the "A4 window").

[0062] Atrial event detector circuit 240 may, in response to the detection of an atrial event, transmit an atrial event detection signal to processor 244 and / or pacing timing circuit 242. Pacing timing circuit 242 (or processor 244) may additionally receive an R-wave sensed event signal from R-wave detector 224 for controlling the timing of pacing pulses delivered by pulse generator 202. Processor 244 may include one or more clocks for generating a clock signal used by pacing timing circuit 242 to cause an AV pacing interval timeout that begins upon receiving an atrial event detection signal from atrial event detector circuit 240. In some instances, atrial events sensed outside the atrial blanking period but within the atrial refractory period are classified as atrial refractory sense. Atrial refractory sense may not cause the pacing timing circuit to initiate the AV pacing interval, therefore atrial refractory sensed events are not tracked by ventricular pacing pulses. However, in some cases, atrial refractory sensed events may be used, for example, to adjust atrial event sensing control parameters or to determine the atrial rate.

[0063] The pacing timing circuit 242 may include one or more escape interval timers or counters for timeouts of the AV pacing interval (which may be a programmable interval stored in memory 210 and retrievable by processor 244) to set the AV pacing interval used by the pacing timing circuit 242. One application of the atrial sensing event signal generated by the atrial event detector circuit 240 is to set the AV pacing interval for controlling the timing of ventricular pacing pulses. However, the control circuit 206 may use the atrial sensing event signal for other purposes.

[0064] The pacing timing circuit 242 may additionally include a lower pacing rate interval timer for controlling the minimum ventricular pacing rate. For example, if no atrial contraction event is detected from the motion sensor signal that triggers the ventricular pacing pulse at the programmed AV pacing interval, the ventricular pacing pulse can be delivered by the pulse generator 202 when the lower pacing rate interval expires to prevent ventricular arrest and maintain the minimum ventricular rate. Sometimes, the control circuit 206 may control the pulse generator 202 in a non-atrial tracking ventricular pacing mode (which may also be referred to as "asynchronous ventricular pacing") during the process of establishing sensing parameters for detecting atrial contraction events from the motion signal. The non-atrial tracking ventricular pacing mode can be described as a VDI pacing mode in which the ventricular pacing pulse is delivered in the absence of a sensed R wave and is suppressed in response to an R wave sensing event signal from the sensing circuit 204. Dual-chamber sensing can be performed during non-atrial tracking ventricular pacing modes by sensing ventricular electrical events by sensing circuitry 204 and sensing atrial contraction events from motion signals received from motion sensor 212 by atrial event detector circuitry 240. As an example, atrial event sensing parameters established during VDI pacing modes may include the end time of the passive ventricular filling window, the atrial event sensing threshold amplitude applied during and after the passive ventricular filling window, and the postventricular atrial refractory period. These atrial event sensing parameters established during VDI pacing modes can be applied during VDD pacing modes, in which ventricular pacing pulses track sensed atrial events with AV intervals.

[0065] The pulse generator 202 generates electrical pacing pulses for the ventricular pacing (RV) to be delivered to the patient's heart via the cathode electrode 164 and the return anode electrode 162. In addition to providing control signals to the pacing timing circuit 242 and the pulse generator 202 to control the timing of the ventricular pacing pulses, the processor 244 can also retrieve programmable pacing control parameters, such as pacing pulse amplitude and pacing pulse width, delivered to the pulse generator 202 to control the delivery of the pacing pulses. The pulse generator 202 may include a charging circuit 230, a switching circuit 232, and an output circuit 234.

[0066] Charging circuit 230 may include a holding capacitor that can be charged to the pacing pulse amplitude at a multiple of the battery voltage signal of power supply 214 under the control of a voltage regulator. The pacing pulse amplitude may be set based on a control signal from control circuit 206. Switching circuit 232 can control when the holding capacitor of charging circuit 230 is coupled to output circuit 234 for pacing pulse delivery. For example, switching circuit 232 may include a switch that is activated by a timing signal received from pacing timing circuit 242 when the AV pacing interval (or VV lower rate pacing interval) expires and remains closed for a programmed pacing pulse width so that the holding capacitor of charging circuit 230 can discharge. During the programmed pacing pulse duration, the holding capacitor, pre-charged to the pacing pulse voltage amplitude, discharges across electrodes 162 and 164 through the output capacitor of output circuit 234. Examples of pacing circuits generally disclosed in U.S. Patent No. 5,507,782 (Kieval et al.) and U.S. Patent No. 8,532,785 (Crutchfield et al.) (both patents are incorporated herein by reference in their entirety) may be implemented in pacemaker 14 for charging the pacing capacitor to a predetermined pacing pulse amplitude under the control of control circuitry 206 and for delivering the pacing pulse.

[0067] Memory 210 may contain computer-readable instructions that, when executed by control circuitry 206, cause control circuitry 206 to perform various functions attributed to pacemaker 14 throughout this disclosure. The computer-readable instructions may be encoded within memory 210. Memory 210 may contain any non-transitory computer-readable storage medium, including any volatile, non-volatile, magnetic, optical, or electrical medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or other digital media, with the sole exception of transient propagation signals. Memory 210 may store: timing intervals; and other data used by control circuitry 206 to control the delivery of pacing pulses via pulse generator 202 (e.g., by detecting atrial events from motion sensor signals by atrial event detector circuitry 240 and setting the pacing escape interval timer included in pacing timing circuitry 242 according to the techniques disclosed herein). The memory 210 may include various buffers for storing threshold crossing time and / or amplitude of motion sensor signals for adjusting atrial event sensing control parameters, as described below.

[0068] Power source 214 supplies power to each of the other circuits and components of pacemaker 14 when needed. Power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. For clarity, the connections between power source 214 and other pacemaker circuits and components are not shown in the diagram. Figure 3 As shown in the text, but should be obtained from... Figure 3 The overall block diagram is understood. For example, power supply 214 can supply power as needed to the charging and switching circuitry, amplifier, ADC 226, and other components included in pulse generator 202, such as sensing circuit 204, telemetry circuit 208, memory 210, and motion sensor 212.

[0069] Telemetry circuit 208 includes a transceiver 209 and an antenna 211 for transmitting and receiving data via a radio frequency (RF) communication link. As described above, telemetry circuit 208 may be able to communicate with external device 20 ( Figure 1 Two-way communication is enabled. Motion sensor signals and cardiac electrical signals and / or data derived therefrom can be transmitted by telemetry circuit 208 to external device 20. Programmable control parameters and algorithms for performing atrial event detection and ventricular pacing control can be received by telemetry circuit 208 and stored in memory 210 for access by control circuit 206.

[0070] The functions attributed to pacemaker 14 herein may be embodied in one or more processors, controllers, hardware, firmware, software, or any combination thereof. Describing different features as specific circuit systems is intended to highlight different functional aspects and does not necessarily imply that such functions must be implemented by separate hardware, firmware, or software components or by any particular circuit architecture. Rather, the functions associated with one or more circuits described herein may be performed by separate hardware, firmware, or software components, or integrated within general-purpose hardware, firmware, or software components. For example, atrial contraction event detection from motion sensor signals and ventricular pacing control operations performed by pacemaker 14 may be implemented in control circuitry 206 that executes instructions stored in memory 210 and depends on inputs from sensing circuitry 204 and motion sensor 212. Given the disclosure herein, providing software, hardware, and / or firmware to perform the described functions in the context of any modern pacemaker is within the capabilities of those skilled in the art.

[0071] Figure 4An example of motion sensor signal 250 acquired by motion sensor 212 during the cardiac cycle is shown. Vertical dashed lines 252 and 262 represent the timing of two consecutive ventricular electrical events (inherent ventricular depolarization or ventricular pacing pulses), marking the corresponding start and end of the ventricular cycle 251. The motion signal includes events A1 254, A2 256, A3 258, and A4 260. Event A1 254 is an acceleration signal that occurs during ventricular systole and marks an approximate onset of the mechanical systolic phase of the ventricle (in this example, when motion sensor 212 is implemented as acceleration timing). Event A1 is also referred to herein as a “ventricular systolic event.” Event A2 256 is an acceleration signal that may occur with the closure of the aortic and pulmonary valves and marks an approximate shift or end of the mechanical systolic phase of the ventricle. Event A2 can also mark the isovolumetric relaxation phase of the ventricle that occurs with the closure of the aortic and pulmonary valves.

[0072] Event A3 (258) is an acceleration signal that occurs during passive ventricular filling and marks the mechanical diastolic phase of the ventricle. Event A3 is also referred to as a "ventricular diastolic event" in this paper. Since event A2 occurs at the end of ventricular systole, it can be an indicator of ventricular diastole. Event A3 occurs during ventricular diastole. Therefore, events A2 and A3 can be collectively referred to as mechanical diastolic events because both are indicators of ventricular diastole.

[0073] Event A4 260 is an acceleration signal that occurs during atrial contraction and active ventricular filling and marks the mechanical contraction phase of the atrium. Event A4 260 is also referred to herein as an “atrial event” detected from motion sensor signal 250. Atrial event detector circuit 240 detects event A4 260 using atrial event sensing control parameters as disclosed herein. Processor 244 can control pacing timing circuit 242 to trigger a ventricular pacing pulse by activating an AV pacing interval in response to the detection of event A4 260, for example, when it occurs outside the postventricular atrial blanking period and after the postventricular atrial refractory period. Control circuit 206 can be configured to detect one or more of events A1, A2, and A3 from motion sensor signal 250 for at least some ventricular cardiac cycles to affirmatively detect event A4 260 and set atrial event detection control parameters. In some instances, A1, A2, and / or A3 events can be detected and characterized to avoid false detection of A4 events and to facilitate reliable A4 event detection for proper timing of ventricular pacing pulses for atrial synchronization.

[0074] The techniques described below, in conjunction with the flowcharts and illustrations presented herein, can be executed by pacemaker 14 to adjust sensing control parameters for sensing events A4, without necessarily requiring the identification and differentiation of events A1–A4. The motion signal can be characterized by determining features of the motion signal during and after the passive ventricular filling window, outside of the atrial concealment period. These features are used by control circuitry 206 to establish atrial event sensing parameters.

[0075] Figure 5 This is an example of motion sensor signals 400 and 410 acquired during two different cardiac cycles. The ventricular pacing pulse is delivered at time 0.0 seconds within both cardiac cycles. The top motion sensor signal 400 is received within one cardiac cycle, and the bottom motion sensor signal 410 is received in different cardiac cycles. The two signals 400 and 410 are time-aligned at 0.0 seconds (the time of ventricular pacing pulse delivery). Although... Figure 4 Motion signals 400 and 410 and motion signal 250 are shown as raw accelerometer signals, but it should be recognized that control circuit 206 can receive digitized, filtered, amplified and rectified signals from motion sensor 212 for processing and analysis as described in conjunction with the accompanying drawings.

[0076] Events 402 and 412 of the corresponding motion sensor signals 400 and 410, occurring during ventricular systole, were observed to be well-aligned temporally at 0.0 seconds after the ventricular pacing pulse. Similarly, events 404 and 414 (which may mark the end of ventricular systole and the isovolumetric ventricular diastolic phase) and events 406 and 416 (occurring during passive ventricular filling) were well-aligned temporally. Since events A1, A2, and A3 are ventricular events occurring during ventricular systole, at the end of ventricular systole, and during passive ventricular filling, respectively, these events are expected to occur at relatively consistent intervals after the ventricular electrical event (in this example, the ventricular pacing pulse) and relative to each other. The timing relationships of events A1, A2, and A3 may differ after a ventricular pacing pulse compared to after a sensed intrinsic R wave. However, during a stable pacing or intrinsic ventricular rhythm, the relative timing of ventricular events A1, A2, and A3 with each other and immediately following the preceding ventricular electrical event is expected to be consistent between heartbeats.

[0077] The A4 events 408 and 418 of the first motion sensor signal 400 and the second motion sensor signal 410 are not aligned in time. The A4 event occurs during atrial systole, and therefore, the time interval between the A4 event immediately following the previous ventricular electrical event (sensed R wave or ventricular pacing pulse) and the previous A1 to A3 events may vary between cardiac cycles.

[0078] The timing consistency of events A1 through A3 relative to each other and immediately preceding ventricular electrical events can be used to determine the atrial silencing period 436 and increase the confidence in reliably detecting events A4 408 and 418. In some examples, no atrial systolic event is detected during the atrial silencing period 436, which may extend from the ventricular electrical event (at time 0.0) to the estimated onset of ventricular diastole, such that the atrial silencing period 436 includes both events A1 and A2. The A3 window 424 can be set with a start time 420 corresponding to the end of the post-ventricular atrial silencing period 436 and an end time 422. The end time 422 can be used, for example, in conjunction with the following... Figures 12 to 14 The described technique is used for adjustment. The end time 422 can also be considered as the start time of the A4 sensing window 450, although in some cases the A4 event can be sensed during the A3 window. The A3 window 424 is also referred to herein as the "ventricular diastolic event window", and the end time 422 is also referred to herein as the "ventricular diastolic event window end time" because the A3 event (a ventricular diastolic event) corresponding to passive ventricular filling is expected to occur during the A3 window, before the end time 422.

[0079] A4 events 408 and 418 can be detected based on a multi-level A4 sensing threshold 444. As can be seen from the lower motion sensor signal 410, A4 event 418 may occur earlier than A3 window 424 due to changes in atrial rate. In some cases, A4 event 418 may occur within A3 window 424 as atrial rate increases. When this occurs, A3 event 416 and A4 event 418 may fuse when passive and active ventricular filling occur together. The fused A3 / A4 events may have high amplitudes, even greater than the amplitudes of A3 event 416 or A4 event 418 when they occur individually. Therefore, in some examples, a first higher A4 sensing threshold amplitude 446 can be established for detecting early A4 events fused with A3 events during A3 window 424. A second lower A4 sensing threshold amplitude 448 can be established for detecting relatively late A4 events during A4 window 450 after the end time 422 of A3 window 424. The A4 window 450 extends from the end time 422 of the A3 window 424 to the next ventricular electrical event (sensed or paced). The motion sensor signal that first crosses the A4 sensing threshold 444 after the start time 420 of the A3 window (or after the atrial blanking period 436 expires) can be detected as an atrial contraction event. The atrial event detector circuit 240 can sense the A4 event in response to the earliest crossing time of either a high or low A4 sensing threshold amplitude. (The following is in conjunction with...) Figure 7-15The technique described is for adjusting the high A4 sensing threshold amplitude 446 used during A3 window 424 and the low A4 sensing threshold amplitude 448 used after the end time 422 of A3 window 424 during A4 window 450.

[0080] In some examples, control circuitry 206 can set a postventricular atrial refractory period (PVARP) 438. PVARP 438 can extend from a ventricular electrical event (a sensed R wave or ventricular pacing pulse) for a time interval longer than the postventricular atrial blanking period 436. Depending on the end time 422 of A3 window 424, PVARP 438 will typically expire during A3 window 424. Atrial event detector circuitry 240 can perform refractory period A4 sensing when the motion sensor signal crosses a high A4 sensing threshold amplitude 446 during PVARP 438 but outside the blanking period 436. Pacing timing circuitry 242 does not respond to refractory period A4 sensing to set the AV pacing interval, but control circuitry 206 can use refractory period A4 sensing to adjust A4 sensing control parameters. When the motion sensor signal crosses the A4 sensing threshold 444 after the PVARP 438 period expires, the atrial event detector circuit 240 senses an atrial contraction event, and the pacing timing circuit 242 begins the AV pacing interval ( Figure 5 (Not shown in the image). At the end of the AV pacing interval, the pulse generator 202 generates a pacing pulse delivered to the ventricle to track non-reactive atrial events.

[0081] Figure 6 This is a flowchart 300 illustrating a method for adjusting atrial event sensing control parameters according to some examples. Control circuitry 206 can execute the method of flowchart 300 to automatically adjust the values ​​of the atrial event sensing control parameters (also referred to herein as “A4 sensing control parameters”) used in sensing an A4 event from a motion sensor signal. In some examples, the A4 event is sensed during an atrial-tracking ventricular pacing mode (e.g., VDD pacing mode). The VDD pacing mode can be a temporary or permanent pacing mode. For example, pacemaker 14 can operate in a permanent VDD pacing mode that temporarily switches to a non-atrial-tracking ventricular pacing mode, such as a VDI(R) or VVI(R) pacing mode. When control circuitry 206 is not operating in an atrial-tracking ventricular pacing mode, adjustment of one or more atrial event sensing control parameters can be disabled, as defined at block 302.

[0082] In some cases, at box 302, pacemaker 14 can operate in a temporary VDI pacing mode, for example, during pacemaker 14 implantation, to allow determining initial values ​​for atrial sensing control parameters and adjusting them to values ​​suitable for the patient. (The following is in conjunction with...) Figure 18An example describing the adjustment process of the A4 sensing control parameters is provided. The initial value of the atrial event sensing control parameters can be set according to a user-programmed or default nominal value. In other instances, the initial value of the atrial event sensing control parameters can be established during an automatic setup process performed by the pacemaker 14, during which motion signal characteristics are determined over a period of time to generate a distribution and / or median or other measure of the signal characteristics. The initial atrial event sensing control parameters can be established based on the generated distribution and median. Exemplary techniques for establishing initial values ​​for atrial event sensing control parameters are generally disclosed in commonly assigned U.S. Patent Application Publication No. 2020 / 0179707 (Splett et al.) and U.S. Patent Application Publication No. 2020 / 0179708 (Splett et al.), both of which are incorporated herein by reference in their entirety. Figure 18 The initial values ​​of at least some A4 sensing control parameters can be adjusted during non-atrial tracking ventricular pacing modes (e.g., VDI pacing modes) that include atrial and ventricular (dual-chamber) sensing.

[0083] When control circuitry 206 operates at block 302 in a specified pacing mode (e.g., VDI or VDD), control circuitry 206 can enable and perform adjustments to one or more A4 sensing control parameters. In some instances, automatic adjustment of the A4 sensing control parameters can be enabled or disabled by a user, for example, via a programmed command sent by external device 20 and received by telemetry circuitry 208. Adjustment of the A4 sensing control parameters can be programmed to be enabled or disabled individually or as a group. Thus, in some instances, control circuitry 206 can determine at block 302 that automatic adjustment of a given A4 sensing control parameter is programmed to be "on" or enabled by a user, and that the current pacing mode is a specified pacing mode during which A4 sensing control parameter adjustments can be performed.

[0084] At block 304, control circuitry 206 determines a sensing control parameter metric from the motion signal over a predetermined number of cardiac cycles. The sensing control parameter metric is a characteristic or property of the motion sensor signal determined by control circuitry 206, used to set or adjust an A4 sensing control parameter that distinguishes an A4 event (which may be fused with an A3 event) from A1, A2, and A3 events. As described in detail below, the sensing control parameter metric can be determined based on the amplitude of the motion sensor signal (e.g., maximum peak amplitude or a predetermined threshold amplitude) during a specified time window of the ventricular cycle. Control circuitry 206 can adjust the A4 sensing control parameter based on the control parameter metric determined from the motion sensor signal over a predetermined number of ventricular cycles. Some control parameter metrics are characteristics or properties of the motion sensor signal that provide information about the expected timing and / or amplitude of atrial contraction events so that the A4 sensing control parameter can be appropriately adjusted. Other control parameter measures are characteristics or properties of the motion sensor signal that provide information about the expected timing and / or amplitude of other characteristics of the motion signal (e.g., the A3 event signal), which can enable the control circuit 206 to adjust the A4 sensing control parameters in a manner that avoids oversensing the A3 event signal or other motion signals that are not the A4 event signal.

[0085] In the illustrative examples presented herein, the sensing control parameter metric is determined from a predetermined number of consecutive ventricular cycles (e.g., 8 consecutive ventricular cycles). In other examples, the sensing control parameter metric may be determined based on a predetermined number of ventricular cycles including an A4 window. An A4 window may not initiate in a given ventricular cycle if an A4 event is sensed during an A3 window or if an intrinsic R wave is sensed before the A4 window. The term "applicable cycle" is used herein to refer to a ventricular cycle that includes an A4 window that begins after the end time of the A3 window. In some examples, the sensing control parameter metric is determined by a predetermined number of applicable cycles (e.g., 8 applicable cycles), which may or may not be consecutive ventricular cycles.

[0086] In various instances, determining the A4 sensing control parameter measure within one or more ventricular cycles of the motion signal may include determining the maximum amplitude of the motion signal during the A4 window, the time of the maximum amplitude relative to the most recent previous ventricular electrical event during the A4 window, the maximum amplitude of the motion signal during the A3 window, and the most recent time the low threshold amplitude was crossed during the A3 window. Other control parameter measures that can be determined may involve the number or count of ventricular cycles in which an A4 event is sensed during the A4 window, the number or count of ventricular cycles in which an A4 event is sensed during the A3 window, the number or count of ventricular cycles with an A4 window (e.g., the number of cycles longer than the end time of the A3 window), the number or count of ventricular cycles in which an A4 event is sensed earlier during the A4 window, the number or count of ventricular cycles in which an A4 event is sensed later during the A4 window, or other parameters counted over a predetermined number of ventricular cycles. Examples are given below. Figure 7-8 This describes an exemplary method for determining a control parameter metric. The control parameter metric can be determined from one or more ventricular cycles as the average, median, highest or lowest value at a specified sequence number (nth), or frequency or count of specified events across multiple ventricular cycles.

[0087] At block 306, control circuitry 206 can verify that other adjustment criteria are met before performing A4 sensing control parameter adjustment based on the control parameter metric determined at block 304. Various criteria may require the sensing control parameter to be within a predetermined range before adjusting the sensing control parameter, for example, less than or equal to a maximum adjustable value or greater than or equal to a minimum adjustable value. Other criteria may verify that a minimum number of A4 events are detected for a predetermined number of ventricular cycles, such that the given control parameter metric determined at block 304 over the predetermined number of ventricular cycles is considered a valid metric on which the adjustment is based. Other criteria may require that the A4 sensing control parameter metric determined at block 304 from the motion sensor signal indicates changes in the timing and / or amplitude of atrial contraction events and / or changes in the timing and / or amplitude of A3 events. As further described below, control circuitry 206 can determine whether the adjustment criteria are met by comparing the A4 sensing control parameter metric determined at block 304 with various criteria used to detect evidence of undersensing of A4 events and / or oversensing of A3 events or other motion signals as evidence of false A4 events.

[0088] When the adjustment criteria are not met, as determined by control circuitry 206 at block 306, the A4 sensing control parameter adjustment may not be performed (or the adjustment may be set to zero). Control circuitry 206 returns to block 302. When the adjustment criteria are met at block 306, control circuitry 206 determines the adjustment value at block 308. As described below, the A4 sensing control parameter metric determined from the motion sensor can be evaluated to determine whether a given A4 sensing control parameter should be increased or decreased from its current value. In some instances, a target value for the A4 sensing control parameter can be determined at block 308 based on the A4 sensing control parameter metric determined at block 304, such that the A4 sensing control parameter can be appropriately increased or decreased toward the target value or remain unchanged.

[0089] At box 310, control circuit 206 adjusts the A4 sensing control parameter according to the determined adjustment. The A4 sensing control parameter may be the A3 window end time (e.g., Figure 5 The end time 422), and the high A4 threshold magnitude applied during the A3 window (e.g., Figure 5 The high A4 threshold 446), and the low A4 sensing threshold magnitude applied after the A3 window (e.g., Figure 5 The low A4 threshold (448) and / or PVARP (e.g., Figure 5 The exemplary method performed by control circuitry 206 for determining A4 sensing control parameter metrics from motion sensor signals (at block 304), determining whether adjustment criteria are met (at block 306), and determining appropriate adjustments for adjusting each of the exemplary A4 sensing control parameters listed above (at block 308) is described below in conjunction with the accompanying flowcharts and illustrations.

[0090] Figure 7 Figure 320 illustrates a method for determining an A4-sensing control parameter metric from a motion sensor signal during atrial-tracked ventricular pacing mode, according to one example. In this example, eight ventricular cycles are shown, each beginning with a ventricular pacing pulse (VP) 322, tracked by an AV pacing interval 340 to a previously A4-sensing event signal 328. The end of the eight ventricular cycles is indicated by 332, which is the final, ending VP of the eight-cycle group. The AV pacing interval 340 is a pacing interval set by the pacing timing circuit 242 in response to the A4-sensing event signal 328, and extends from the A4-sensing event signal 328 to the subsequent ventricular pacing pulse 322 delivered by the pulse generator 202 when the AV pacing interval 340 expires.

[0091] In response to each VP 322, control circuitry 206 initiates A3 window 324 according to a predetermined A3 window start time (e.g., 600 milliseconds after VP 322). A4 window 326 begins at A3 window end time 325 when A3 window 324 expires and extends until an A4 signal 330 is sensed or a ventricular pacing rate interval (VV interval) expires, thereby generating a ventricular pacing pulse if no A4 signal is sensed. Figure 7 In this example, during each of the eight ventricular cycles shown, an A4 event 330 is sensed in response to the crossing of a low A4 sensing threshold amplitude 338 (during the A4 window 326). The A4-sensed event signal 328 can be generated by the atrial event detector circuit 240 in response to the earliest crossing of the A4 sensing threshold amplitude during each ventricular cycle (outside of the postventricular blanking period). The next VP 322 is generated by the pulse generator 202 when the AV pacing interval 340, which was initiated by the pacing timing circuit 242 in response to the A4-sensed event signal 328, expires.

[0092] It should be noted that the durations of windows A3 324, A4 326, and the AV pacing interval 340 are shown for illustrative purposes and are not necessarily shown according to the time scales relative to each other or the ventricular cycle length as a whole in Figure 320. For example, the AV pacing interval 340 can be 10 to 30 milliseconds (e.g., 20 milliseconds), while window A3 324 can be 200 to 300 milliseconds long, and window A4 326 can be even longer, for example, 400 milliseconds or longer in some instances. For illustrative and convenience purposes, in Figure 7 The relative durations of A3 window 324, A4 window 326, and AV pacing interval 340 are shown without any intended limitation.

[0093] The control circuit 208 can, for example, be in Figure 7 At the end of VP 332 of the eight ventricular cycles shown, an A4 sensing control parameter metric is determined every eight (or other selected number) ventricular cycles. Figure 7 In the example shown, the A4 sensing control parameter metric determined by control circuitry 206 is the minimum detected A4 amplitude. The maximum motion signal amplitude during A4 window 326 can be determined as the A4 signal amplitude during each ventricular cycle, which includes the A4-sensed event signal 328 after the A3 window end time 326. The minimum maximum amplitude value 334 determined over eight ventricular cycles is determined as the minimum detected A4 amplitude at the end of eight ventricular cycles (at VP 332). As described below, this minimum detected A4 amplitude is a characteristic of the motion sensor signal, which is determined by control circuitry 206 over a specified number of ventricular cycles as the A4 sensing control parameter metric used in adjusting the low A4 sensing threshold amplitude 338.

[0094] For example, if the minimum detected A4 amplitude 334 is at least 1.5 times the low A4 sensing threshold amplitude 338, the low A4 sensing threshold amplitude 338 can be increased. Sufficient safety margin exists between the minimum detected A4 amplitude 334 and the low A4 sensing threshold amplitude 338, allowing control circuitry 206 to increase the low A4 sensing threshold amplitude 338. When control circuitry 206 determines that the peak amplitude of the sensed A4 event is relatively high (based on the minimum detected A4 amplitude 334) and that A4 events are sensed regularly during most ventricular cycles (e.g., at least 75% of ventricular cycles), the low A4 sensing threshold amplitude 338 can be increased to avoid oversensing of other motion signals (which could be cardiac or body motion or other signal noise), while still providing a reasonable safety margin between the minimum detected A4 amplitude 334 and the low A4 sensing threshold amplitude 338.

[0095] Other multiples of the low A4 sensing threshold amplitude 338 can be compared to the minimum detected A4 amplitude 334 to determine if there is a safety margin exceeding the minimum expected value between the low A4 sensing threshold amplitude 338 and the minimum detected A4 amplitude, justifying an increase in the low A4 sensing threshold amplitude. In other instances, 1.25 times up to 2 times the low A4 sensing threshold amplitude 338 can be used as adjustment thresholds applied to the minimum detected A4 amplitude 334. The low A4 sensing threshold amplitude 338 can be safely increased by control circuitry 206 when the minimum detected A4 amplitude 334 is at least a selected multiple greater than the current value of the low A4 sensing threshold amplitude 338. Relatively lower multiples, such as 1.25 times the low A4 sensing threshold amplitude 338, tend to allow control circuitry 206 to increase the low A4 sensing threshold amplitude 338 more frequently and toward higher values, while maintaining a relatively low safety margin between the low A4 sensing threshold amplitude 338 and the minimum detected A4 amplitude 334. A relatively high multiplier, such as twice the low A4 sensing threshold amplitude 338, tends to cause the control circuit 206 to increase the low A4 sensing threshold amplitude less often, keeping the low A4 sensing threshold amplitude at a relatively low value over time, with a large safety margin between the low A4 sensing threshold amplitude 338 and the minimum detected A4 amplitude 334.

[0096] Figure 8Figure 350 shows four ventricular cycles labeled I, II, III, and IV, representing various scenarios that may occur during eight (or other predetermined number) ventricular cycles, during which A4 sensing control parameter measurements are determined from motion sensor signals. In some instances, each ventricular cycle may be classified as an "applicable" or "inapplicable" cycle by control circuitry 206, depending on whether the A4 window is activated. Control circuitry 206 may, for example, in... Figure 6 Box 306 determines whether the adjustment criteria are met based on the number of applicable cycles during a consecutive series of a predetermined number of ventricular cycles.

[0097] exist Figure 7 In this instance, the A4 signal was detected during A4 window 326 in each ventricular cycle. However, this may not always be the case. For example, in Figure 8 During the first ventricular cycle I, VP 352 is followed by A3 windows 354 and A4 windows 356. However, the motion sensor signal 351 does not cross the high A4 sensing threshold 376 or the low A4 sensing threshold 368 before the ventricular pacing interval (VV interval) 358 expires. The VV interval 358 can be a programmed lower ventricular rate interval or can be adjusted from a lower ventricular rate interval to a rate smoothing interval based on a recently determined actual ventricular rate. VP 362 is generated by the pulse generator 202 when the VV interval 358 expires. Since no A4 signal is sensed, the amplitude of the A4 event cannot be determined during the first ventricular cycle I. However, for the purpose of determining when the A4 sensing control parameter adjustment criteria are met (e.g., in...), the motion sensor signal 351 does not cross the high A4 sensing threshold 376 or the low A4 sensing threshold 368. Figure 6 (At box 306), ventricular cycle I can be considered the applicable cycle. For example, the A4 sensing control parameter adjustment standard may require the A4 window to be activated within at least a threshold number of a predetermined number of ventricular cycles. Since the A4 window 356 is activated, even if no A4 signal is sensed, the first ventricular cycle I can be determined to be the applicable cycle by the control circuit 206.

[0098] The second ventricular cycle II begins with VP 362 and ends with VP 372, which is generated by pulse generator 202 with an AV pacing interval 370 based on the event signal 365 sensed by A4. The A4 window 366 begins at the end time 325 of the A3 window, and the A4 signal 360 is sensed during the A4 window 366 because the motion signal crosses the low A4 sensing threshold amplitude 368. The second ventricular cycle II is counted as applicable cycles by control circuitry 206 as the A4 window 366 is initiated. The maximum amplitude of the motion sensor signal during the A4 window 366 can be determined by control circuitry 206 to determine the minimum detected A4 amplitude over a predetermined number of ventricular cycles, as a measure of an A4 sensing control parameter determined by control circuitry 206 based on the motion sensor signal.

[0099] The third ventricular cycle III begins at VP 372 and ends at VP 382. During this cycle, the A4 signal 380 crosses the high A4 sensing threshold 376 during the A3 window 374. Therefore, the A4 window is never activated. VP 382 is delivered with an event signal 375 sensed from A4 at a VA pacing interval 370. Since the A4 window is not activated, the third ventricular cycle III can be classified as an inapplicable cycle by control circuitry 206 for the purposes of determining the applicable cycle count and applying criteria for adjusting the A4 sensing control parameters and / or for determining the adjustments applied to the A4 sensing control parameters. An applicable cycle can be any ventricular cycle longer than the A3 window end time 325.

[0100] In some instances, when an A4 event is sensed during A3 window 374, such as in ventricular cycle III, control circuit 206 extends the A3 window end time 325. Control circuit 206 initiates an AV pacing interval 370, which may expire after the normally scheduled A3 window end time 325. Thus, control circuit 206 can extend the A3 window end time from the scheduled end time 325 to an extended end time 327 that occurs simultaneously with the expiration of the AV pacing interval 370, preventing the A4 window from being initiated. In this case, the extended A3 window end time 327 expires with the AV pacing interval 270 that begins during A3 window 374, but may end later than the normal A3 window end time 325 if an A4 event is sensed later in A3 window 374. The extended A3 window end time 327 ends with a ventricular pacing pulse 382, ​​which excludes the initiation of the A4 window, preventing ventricular cycle III from being counted as an applicable cycle.

[0101] The fourth ventricular cycle IV begins at VP 382 and ends at ventricular-sensed event 392. In this example, window A3 384 is initiated, but prior to the start of window A4, the inherent R wave (which may be a premature ventricular contraction (PVC)) is sensed by cardiac electrical signal sensing circuit 204, as indicated by ventricular-sensed event signal (VS) 392 during window A3 384. The fourth ventricular cycle IV is classified as an inapplicable cycle by control circuit 206 because window A4 is not initiated.

[0102] Therefore, in some instances, each ventricular cycle out of a predetermined number of ventricular cycles (e.g., eight ventricular cycles) (within which the A4 sensing control parameter metric is determined from the motion signal) can be categorized as "applicable" when the A4 window is activated (regardless of whether an A4 signal is sensed) or "not applicable" when the A4 window is not activated. In some instances, in Figure 6The adjustment criteria at box 306 may require reaching a minimum number of applicable cycles during each group of N ventricular cycles. When the control circuit 206 classifies and counts applicable cycles that are less than the threshold number, it can be determined that the adjustment criteria at box 306 are not met because there may not be enough A4 signal amplitude and timing information available.

[0103] like Figure 7 As shown, Figure 8 The durations of the A3 window, A4 window, AV pacing interval 370, and ventricular cycles I, II, III, and IV shown are illustrative and conceptual in nature and not intended to be restrictive. The relative durations of the A3 window, A4 window, AV pacing interval, and total ventricular cycle may not be shown according to their relative time scales. For example, an A4 window 356 that begins in ventricular cycle I and ends with a ventricular pacing pulse 362 in the VV pacing interval 358 will tend to be a relatively long A4 window (when no A4 event is sensed) compared to an A4 window 366 where an A4 event is sensed in ventricular cycle II. An A4 window may be longer or shorter than an A3 window, depending on when and whether an A4 event is detected. Therefore, it should be noted that the relative durations of the A3 and A4 windows can vary between different cycles and can differ relative to each other, as can the ventricular cycle length and AV pacing interval. Figure 8 The examples shown are different.

[0104] Figure 9 This is a flowchart 500 illustrating a method, according to one example, for determining an A4 sensing control parameter metric by control circuitry 206 to adjust a low A4 sensing threshold. In some instances, the A4 sensing threshold is automatically adjusted by control circuitry 206 only during atrial-tracking ventricular pacing modes (e.g., VDD pacing modes, which can be temporary or permanent VDD pacing modes). When the pacing mode is a non-atrial-tracking pacing mode (e.g., VDI(R) or VVI(R)), the adjustment of the low A4 sensing threshold can be disabled or paused. Figure 5 As shown, the low A4 sensing threshold (e.g., threshold 448) is the threshold amplitude applied to the motion sensor signal after the end of the A3 window for sensing an A4 event. If the pacing mode at block 502 is an atrial tracking pacing mode, then control circuitry 206 determines the A4 event amplitude and time at block 504 for each A4 event sensed during the A4 window following each ventricular pacing pulse, or an R wave sensed within a predetermined number of ventricular cycles (e.g., eight cycles). The predetermined number of ventricular cycles can be consecutive cycles, e.g., as... Figure 7 As shown, however, A4 events may or may not be detected within the A4 window of each consecutive ventricular cycle.

[0105] For each A4 event sensed over N ventricular cycles, the A4 event amplitude can be determined as the maximum peak amplitude of the motion sensor signal after a low A4 sensing threshold is crossed (and before the next ventricular electrical event) that occurs later than the end of the A3 window. The A4 event time can be determined as the sample number or timestamp of the maximum peak amplitude since the most recent previous ventricular electrical event (the most recent previous ventricular pacing pulse or sensed R wave).

[0106] Control circuit 206 continues to determine the A4 event amplitude and duration (box 504) for each A4 event sensed during the A4 window, until N ventricular cycles have elapsed (box 506). In some cases, as described above... Figure 8 As stated, for each of the N ventricular cycles, an A4 event may not be sensed during the A4 window, or the A4 window may not occur (due to an R wave or an early sensed A4 event during the A3 window). Therefore, in some instances, after N ventricular cycles have passed, for N ventricular cycles, the control circuit 206 can determine up to N A4 event amplitudes and A4 event durations, but sometimes less than N A4 event amplitudes and A4 event durations, and buffer them in memory 210.

[0107] Once N ventricular cycles have elapsed (the "Yes" branch of box 506), control circuitry 206 can determine one or more A4-sensing control parameter metrics based on the motion sensor signals over the N ventricular cycles. At box 508, control circuitry 206 can determine the applicable cycle count. The applicable cycle count is the number of cycles out of the N ventricular cycles, where, as described above... Figure 8 The A4 window is initiated. A buffer in memory 210 can store flags for each ventricular cycle containing the A4 window during N ventricular cycles to facilitate determining the applicable cycle count at block 508. Even if the A4 window is initiated during a ventricular cycle, an A4 event may or may not be sensed during the A4 window. Another buffer in memory 210 can store flags for each of the N ventricular cycles in which an A4 event is sensed during the A4 window to facilitate determining the detected A4 count at block 510. Control circuitry 206 can count the number of flags set in the buffer in response to each A4 sensed event signal generated by the atrial contraction event detector circuitry 240 during the A4 window within N ventricular cycles.

[0108] At box 511, the minimum detected A4 amplitude within N ventricular cycles is determined as the lowest value of the A4 event amplitude determined at box 504. At box 512, control circuitry 206 can determine the early A4 count. A4 events sensed during the A4 window within a predetermined threshold time interval of the end time of the A3 window are classified as early A4 events. For example, each A4 sensed event signal occurring within 50 milliseconds (or other selected time interval) of the end time of the A3 window can be counted as an early A4 event. Control circuitry 206 can subtract the end time of the A3 window from the A4 event time determined at box 504 and compare the difference with the threshold time interval (e.g., 50 milliseconds). If the difference is less than the threshold time interval, an early A4 event flag can be stored in a buffer in memory 206 for the corresponding ventricular cycle. Control circuitry 206 can determine the early A4 count at box 512 by counting the number of early A4 event flags set within N ventricular cycles.

[0109] At block 514, control circuit 206 determines a normal A4 count by counting the number of A4-sensor event signals generated by atrial contraction event detector circuit 240 during or after the early event threshold time interval. For example, control circuit 206 may set a flag in a buffer for each ventricular cycle during which an A4-sensor event signal is generated 50 milliseconds or more after the end time of the A3 window. At block 514, control circuit 206 may count the number of normal A4 event flags set over N ventricular cycles.

[0110] At block 518, control circuitry 206 determines the A3 window detection count. Whenever an A4 event is sensed during the A3 window, in response to the motion sensor signal crossing a high A4 sensing threshold amplitude, the A4 event may merge with or overlap with the A3 event, or the A3 event may be oversensed as an A4 event. In some cases, atrioventricular synchrony may be lost due to the loss of regular A4 event sensing, which may occur when the A3 event is oversensed as an A4 event before the A4 signal actually occurs during the ventricular cycle. Loss of atrial tracking caused by ventricular pacing pulses may occur in combination with A3 event oversensing, as demonstrated by the frequent A4 sensing event signals generated by atrial contraction event detector circuitry 240 during and / or early after the end of the A3 window. The ventricular pacing pulse may be tracking an oversensed A3 event, rather than a true A4 event. In this case, reducing the low A4 sensing threshold amplitude during the A4 window may result in A3 event oversensing, accompanied by a related loss of atrial tracking of the ventricular pacing pulse. Thus, for each ventricular cycle during N ventricular cycles in which the atrial contraction event detector circuit 240 generates an event signal sensed by A4 during the A3 window, the control circuit 206 can set an A3 window detection flag in a buffer in the memory 210 to determine the A3 window detection count at block 518. This count of A4 events sensed within the A3 window can be used to verify conditions of A3 event oversensing and / or possible A4 event undersensing due to A3 event oversensing.

[0111] At block 520, control circuitry 206 can determine whether the low A4 sensing threshold amplitude should be adjusted, and if so, determine the adjustment to be made based on various A4 sensing control parameter measures determined over N ventricular cycles at blocks 508-518. For example, the low A4 sensing threshold amplitude can be increased when the currently set low A4 sensing threshold amplitude does not exceed the adjustment upper limit and the number of early A4 events has been counted. The low A4 sensing threshold can be decreased to restore the desired safety margin between the minimum detected A4 amplitude and the low A4 sensing threshold amplitude when the minimum detected A4 amplitude is less than or equal to a predetermined factor of the currently set low A4 sensing threshold amplitude. The low A4 sensing threshold can be increased when the minimum detected A4 amplitude is greater than a predetermined factor of the currently set low A4 sensing threshold amplitude. The following is in conjunction with... Figure 10 Various criteria based on A4 sensing control parameter metrics are described, which can be applied at box 520 to determine whether to increment, decrement, or keep the low A4 sensing threshold unchanged.

[0112] When the adjustment criteria are met and an appropriate increment or decrement is determined at block 520, control circuitry 206 adjusts the low A4 sensing threshold amplitude at block 522. In some instances, the low A4 sensing threshold amplitude is increased or decreased by predetermined increments or decrements when specified conditions are met. In other instances, the low A4 sensing threshold amplitude can be adjusted to a value determined based on one or more control parameter metrics. For example, the low A4 sensing threshold amplitude can be adjusted to a value set based on the minimum detected A4 amplitude. For example, the low A4 sensing threshold amplitude can be adjusted directly to a fraction or percentage of the minimum detected A4 amplitude to achieve the desired safety margin, rather than through predetermined increments or decrements.

[0113] After adjusting the low A4 sensing threshold amplitude at box 522, control circuitry 206 can return to box 502 to continue determining the A4 sensing control parameter metric for the next series of N ventricular cycles, as long as the atrial tracking pacing mode remains active (as determined at box 502). In some instances, the pacing mode can be switched only every eight ventricular cycles, simultaneously determining the A4 sensing control parameter metric and any resulting A4 sensing control parameter adjustments. Thus, if a pacing mode switch occurs, for example, to a rate-response pacing mode or a non-atrial tracking ventricular pacing mode, automatic adjustment of the low A4 sensing threshold amplitude can be paused or disabled until control module 206 switches back to atrial tracking ventricular pacing mode. In other instances, the pacing mode can be switched over N ventricular cycles. When this occurs, if the new pacing mode is not atrial tracking ventricular pacing mode, control circuitry 206 can pause and disable A4 sensing threshold amplitude adjustment without determining the A4 sensing control parameter metric after N cycles.

[0114] Furthermore, while flowchart 500 (and other flowcharts presented herein) involves some A4 sensing control parameters (based on A4 sensing control parameter measurements determined from N cycles) being adjusted after every N cycles, it should be understood that adjustments can be paused within a predetermined time interval or number of ventricular cycles between sets of N cycles to provide periodic adjustments to one or more A4 sensing control parameters. The number of ventricular cycles between each set of N cycles can be greater than, less than, or equal to N. For illustration, a low A4 sensing threshold (or another A4 sensing control parameter) can be adjusted after 8 ventricular cycles. Control circuitry 206 can pause adjustments for the next 8 to 16 cycles, and then adjust the low A4 sensing threshold again after the next 8 ventricular cycles. In this way, the magnitude of the low A4 sensing threshold can be adjusted based on the most recent 8 ventricular cycles, but for example, once every 16 to 24 cycles.

[0115] Figure 10This is a flowchart 520 illustrating a method for determining the adjustment of the low A4 sensing threshold amplitude, based on an example. The process in flowchart 520 can correspond to the control circuit 206 in... Figure 9 The determination is performed at box 520, which is similarly numbered. Therefore, once an adjustment decision is made at box 538 (decrease), box 544 (increment), or box 546 (no adjustment) according to the process described in flowchart 520 below, the control circuit 206 can proceed to... Figure 9 Box 522 is adjusted accordingly. During the process of flowchart 520, adjustments can be made based on the above combination. Figure 9 The analysis of the determined A4 sensing control parameter metrics is performed by control circuit 206 to analyze various conditions related to the timing and / or amplitude of motion signal characteristics and / or sensed A4 events. When specified conditions / criteria are met, control circuit 206 can determine that... Figure 9 Adjustments should be applied at box 522, such as predetermined increments or decrements.

[0116] For example, control circuit 206 can be configured to detect evidence of oversensing of A3 event or other motion signals, causing erroneous A4-sensed event signals to be generated by atrial contraction event detector circuit 240. At block 530, control circuit 206 can detect evidence of oversensing of A3 event when early A4 window sensing conditions are met. Control circuit 206 can determine that the generated A4-sensed event signal occurs earlier in the A4 window at a relatively high frequency. When an A4 event is sensed relatively quickly after the end of the A3 window, for example, within 50 to 100 milliseconds, the low A4 sensing threshold amplitude applied during the A4 window may be lower than optimal. When this occurs, the A4 event signal may actually occur later in the A4 window, but due to the low value of the low A4 sensing threshold amplitude, the A3 event or other motion signals may be oversensed as A4 events in the A4 window before the actual A4 event signal. Therefore, at block 530, control circuit 206 can check the A4 sensing control parameter metric to determine whether the A4 sensed event signal occurs relatively early and frequently in the A4 window, indicating possible oversensing of A3 events or other motion signals.

[0117] At box 530, control circuit 206 can apply various criteria to determine whether the A4 event signal is sensed earlier in the A4 window, thus satisfying the earlier A4 window sensing condition. This indicates that the A3 event signal is sensed earlier than the end time of the A3 window, or the end of the A3 event signal, or other baseline motion signal noise is used as the A4 event. In one example, control circuit 206 will... Figure 9The early A4 count determined at box 512 is compared with an early A4 count threshold. For example, if the early A4 count (the number of A4-sensed event signals generated within 50 milliseconds after the end of the A3 window or other predetermined time intervals) is at least 1, 2, 3, 4, or other selected number (or percentage) out of N ventricular cycles, evidence of possible oversensing of A3 events or other motion signals can be detected at least based on the early A4 window sensing condition being met at box 530.

[0118] Control circuit 206 can additionally or alternatively compare the early A4 count with the normal A4 count. At block 514 ( Figure 9 The defined normal A4 count is the number of A4 events sensed after a predetermined time interval following the end of the A3 window (e.g., 50 milliseconds or later after the end of the A3 window). When the early A4 count is at least equal to or greater than the normal A4 count, the control circuit 206 can detect evidence of frequent A3 events or oversensing of other motion signals, which leads to the generation of erroneous A4 sensed event signals early in the A4 window.

[0119] In some instances, a combination of conditions may need to be met, such as requiring a threshold for early A4 counts and that the early A4 count is greater than or equal to the normal A4 count, for control circuitry 206 to determine at block 530 that the early A4 window sensing condition is met. In an illustrative example, control circuitry 206 may determine at block 530 that the early A4 window sensing condition is met when the early A4 count is at least 25% of N ventricular cycles (e.g., 2 out of 8 ventricular cycles) and the early A4 count is greater than or equal to the normal A4 count. In other instances, one or more amplitude conditions may need to be met at block 530, which would indicate that erroneous A4 event sensing may be occurring. For example, if for each counted early A4 event, the maximum motion sensor signal amplitude during the A4 window occurs more frequently than the threshold time interval following the low A4 sensing threshold crossover time (and the generation of the A4 sensing event signal), this amplitude condition could indicate premature A4 event signal sensing due to oversensing of the A3 event signal and / or other motion signals.

[0120] At block 530, various early A4 window sensing conditions can be applied via control circuitry 206. Such criteria can be time-based and / or amplitude-based. For example, control circuitry 206 can compare the time of a sensed A4 event (e.g., the time it takes for a low A4 sensing threshold amplitude to cross during the A4 window) with an early A4 window sensing criterion, compare the time it takes for the amplitude to cross from the low A4 sensing threshold to the maximum motion sensor signal amplitude during the A4 window with an early A4 window sensing criterion, and compare the difference between the maximum motion sensor signal amplitude and the low A4 sensing threshold amplitude during the A4 window with the early A4 window sensing criterion and / or other timing and / or amplitude-related criteria indicating that non-A4 events may be sensed prematurely during the A4 window, such as due to oversensing of an earlier A3 event within the A4 window. When an early A4 window sensing condition / criterion is met, control circuitry 206 can determine at block 532 whether the criteria for incrementing the low A4 threshold are met.

[0121] Control circuit 206 can apply an incremental standard at block 532 to avoid increasing the low A4 sensing threshold beyond its maximum limit, and / or increasing a low A4 sensing threshold that is already at a relatively high value. For example, the adjusted low A4 sensing threshold amplitude can be limited to no greater than the maximum limit of the low A4 threshold, which may correspond to 5 m / s. 2 The upper limit of acceleration or other selected values. It should be understood that the acceleration thresholds or examples of maximum and minimum values ​​given herein can be implemented in the ADC unit of the atrial event detector circuit 240. For example, each ADC unit may correspond to 11.8 mg (where 1 g is gravitational acceleration), while 100 mg may correspond to 1 m / s². 2 Acceleration. When control circuit 206 determines that adjusting the low A4 sensing threshold by a predetermined increment would cause the low A4 sensing threshold amplitude to exceed the maximum limit, the increment criterion at block 532 is not met. Control circuit 206 can then determine at block 546 that adjustment should not be made.

[0122] Additionally or alternatively, control circuitry 206 may compare the current value of the low A4 sensing threshold amplitude with an adjustment threshold at block 532. For example, the current value of the low A4 sensing threshold amplitude may need to be less than or equal to twice (or other multiples of) the minimum limit of the low A4 sensing threshold amplitude. For illustration, if the minimum available low A4 sensing threshold amplitude is set to 0.8 m / s... 2 Therefore, the current low A4 sensing threshold amplitude may need to be equal to or less than twice the minimum setting, or in this example, 1.6 m / s. 2This is to ensure that the incremental criterion is met at block 532. If the currently set low A4 sensing threshold amplitude is greater than the adjustment threshold, the control circuit 206 can determine at block 532 that the incremental criterion is not met, and at block 546 determine that no adjustment will be made.

[0123] In other instances, control circuitry 206 may compare the current value of the low A4 sensing threshold amplitude with half (or other fraction) of the maximum available setting for the low A4 sensing threshold amplitude. Typically, control circuitry 206 may determine at block 532 that an incremental criterion is met when the current setting of the low A4 sensing threshold amplitude is relatively low within the range of available settings (e.g., in the lower half of the range of available settings).

[0124] In other instances, control circuitry 206 may additionally or alternatively compare the current value of the low A4 sensing threshold amplitude with one or more previous values ​​of the low A4 sensing threshold amplitude. The maximum (or minimum) allowable setting of the low A4 sensing threshold amplitude may be based on one or more historical values ​​of the low A4 sensing threshold amplitude. For example, the low A4 sensing threshold amplitude may be limited to a maximum value, which is set as a percentage of the maximum, average, or median value of the low A4 sensing threshold amplitude settings that can be buffered in memory 210, such as the most recent four, eight, twelve, or other recent values. In other instances, historical values ​​of the A4 sensing threshold amplitude settings may be stored from the time of implantation and when the pacemaker 14 begins operation.

[0125] When control circuit 206 determines that the early A4 window sensing condition is met at block 530 and the increment criterion is met at block 532, control circuit 206 can determine that the low A4 sensing threshold amplitude will be adjusted by a predetermined increment of the ADC unit, such as one or more ADC units, which may correspond to 0.1 m / s. 2 0.2m / s 2 0.25m / s 2 0.3m / s 2 The acceleration increment or other predetermined acceleration increment. Control circuit 206 can be set at block 544 to adjust the increment for use in... Figure 9 Adjust the amplitude of the low A4 sensing threshold at box 422. The increment can be a fixed increment (e.g., 0.3 m / s). 2 The fixed increment is used at any time when the early A4 window sensing condition is met at box 530 and the increment criterion is met at box 532. It should be understood that the adjustment may be part of a predetermined increment when increasing the entire increment would exceed the maximum upper limit of the low A4 sensing threshold amplitude.

[0126] In other instances, the increment set at box 544 can be an adjustable increment, which can be relatively larger or smaller depending on the current value of the low A4 sensing threshold amplitude, the value of the A4 sensing control parameter metric, and the conditions met at box 530. For example, a relatively high increment can be set at box 544 when the early A4 count is relatively high or significantly greater than the normal A4 count and / or the current value of the low A4 sensing threshold amplitude is at or near the minimum limit. A relatively low increment can be set at box 544 if the early A4 count is relatively low or equal to the normal A4 count, or the current value of the low A4 sensing threshold amplitude is near the maximum limit or in the higher range of available settings. In this way, the adjustment increment set at box 544 can be scaled based on one or more factors, such as the current value of the low A4 sensing threshold amplitude, the frequency of A4 events sensed earlier in the A4 window, and / or the difference between the current value of the low A4 sensing threshold amplitude and the minimum detected A4 amplitude during the A4 window over N ventricular cycles.

[0127] When the early A4 window sensing conditions are not met at box 530 (the "No" branch of box 530), control circuit 206 can determine whether conditions / criteria indicating possible undersensitivity of the A4 event signal during the A4 window are met. If no A4 event is sensed during the A3 window, causing the A4 window to be initiated at the end of the A3 window, and no A4 event signal is detected before the next ventricular pacing pulse or sensed R wave, the A4 event signal may not be sufficiently sensed due to the low A4 sensing threshold amplitude being set too high. Therefore, at box 534, control circuit 206 can compare one or more A4 sensing control parameter measures determined over N ventricular cycles with criteria used to detect evidence of undersensitivity of the A4 event during the A4 window.

[0128] In one example, control circuit 206 will count the detected A4 (in Figure 9 (determined at box 510) and applicable cycle count (the number of ventricular cycles in which window A3 ends and window A4 begins, as shown in...) Figure 9The comparison is defined at box 508. When the detected A4 count is less than the applicable cycle count by more than a threshold difference (or percentage), at box 534, control circuit 206 can detect evidence of undersensitivity within the A4 window. Various comparisons can be performed by control circuit 206 to determine whether the number of A4 events sensed during the A4 window occurring within N ventricular cycles is relatively low, indicating possible undersensitivity of the A4 event signal. For example, the ratio of the detected A4 count to the applicable cycle count can be compared to a threshold ratio or percentage. When the detected A4 count is less than 100%, 90%, 80%, 75%, 70%, or other selected percentages of the applicable cycle count, control circuit 206 can detect evidence of undersensitivity of A4.

[0129] In some instances, the applicable cycle count may need to be greater than or equal to a specified threshold, such as at least 3, 4, 5, or other selected number (or percentage) of N ventricular cycles, in order to detect evidence of insufficient A4 sensing during the A4 window. Control circuitry 206 can determine when to begin a minimum threshold number of A4 windows within N ventricular cycles (ending before the A3 window ends) to satisfy the conditions for detecting evidence of insufficient A4 sensing at box 534. When a small fraction of N ventricular cycles has an A4 window beginning, such as only one of eight ventricular cycles or less than 20% (or other threshold percentage) of N ventricular cycles, there may not be sufficient evidence to detect possible insufficient A4 sensing. (The above is combined with...) Figure 8 Conditions that may result in no A4 window being activated during a ventricular cycle are described. In some instances, control circuitry 206 determines whether the number of applicable cycles within N ventricular cycles is less than 50%, 40%, 30%, 25%, 20%, or 15% of the N ventricular cycles, in order to meet the criteria used at block 534 to determine insufficient A4 sensing during the A4 window period.

[0130] When the detected A4 count is less than a threshold percentage of the applicable cycle count or the difference between the applicable cycle count and the applicable cycle count, and the applicable cycle count is at least the threshold count, control circuitry 206 can determine evidence at block 534 that the criteria for insufficient A4 event sensing are met. For example, when at least five of the eight ventricular cycles are applicable cycles (with an initial A4 window) and an A4 event is sensed during fewer than two cycles less than the number of applicable cycles, the criteria for detecting insufficient A4 event sensing during the A4 window period can be met at block 534. Additionally or alternatively, control circuitry 206 can compare a normal A4 count to a threshold at block 534. When an applicable cycle of the threshold number occurs but no normal A4 event is sensed, which is an A4 event sensed at least a predetermined time interval (e.g., 50 milliseconds) after the end of the A3 window, insufficient A4 event sensing during the A4 window period may be occurring, possibly due to a low A4 threshold amplitude set too high.

[0131] In other instances, control circuit 206 can detect a minimum A4 amplitude (in Figure 9 The minimum detected A4 amplitude (defined at box 511) is compared with a threshold, which can be based on the current setting of the low A4 sensing threshold amplitude. When the minimum detected A4 amplitude is less than the threshold amplitude, the likelihood of insufficient A4 event sensing may increase due to insufficient safety margin between the low A4 sensing threshold amplitude and the minimum detected A4 amplitude. The minimum detected A4 amplitude threshold can be set to a multiple of the current low A4 sensing threshold amplitude value, such as 1.1, 1.2, 1.25, 1.5, 2.0, or other chosen multiples. The likelihood of insufficient A4 event sensing may increase when the minimum detected A4 amplitude threshold is at least not greater than the safety margin of the current low A4 sensing threshold amplitude.

[0132] At box 534, control circuitry 206 can examine a combination of two or more criteria (including any of the criteria described above) to determine whether the conditions for detecting insufficient A4 event sensing are met. In an illustrative example, control circuitry 206 detects evidence of insufficient A4 event sensing at box 534 when the applicable cycle count is at least 5 out of 8 ventricular cycles, the detected A4 count is less than twice the applicable cycle count, and the minimum detected A4 amplitude is less than or equal to 1.5 times the current low A4 sensing threshold amplitude setting, or the normal A4 count is zero. When these criteria are met, control circuitry 206 can determine that insufficient A4 event sensing is possible, and the low A4 sensing threshold amplitude should be reduced. Control circuitry 206 can then proceed to box 536 to determine whether the reduction criteria are met.

[0133] By detecting evidence of insufficient A4 event sensing at box 534, control circuit 206 can adjust the low A4 threshold amplitude when it is set too high to reliably sense A4 events. However, in some cases, the low A4 threshold amplitude can be appropriately set, but true A4 events may not be sensed because earlier A3 events during the ventricular cycle are oversensed, thus excluding the sensing of later true A4 events. When the reason for insufficient A4 event sensing is solely due to the low A4 threshold amplitude being set too high, few or no A4 events are expected to be detected during the A3 window. However, oversensing of A3 events may lead to insufficient sensing of true A4 events during the A4 window when the A3 window end time is set too early or the high A4 threshold amplitude is set too low. In this case, adjusting the high A4 threshold amplitude and / or the A3 window end time can restore reliable A4 sensing without requiring adjustment of the low A4 threshold amplitude.

[0134] Therefore, in some instances, when determining at block 534 that the criteria for insufficient A4 event sensing during the A4 window period are met, control circuit 206 can apply a criterion for verifying that oversensing of the A3 event did not occur within N ventricular cycles and resulted in insufficient sensing of the subsequent A4 event. In some cases, for example, due to variations in heart rate or other factors, the A3 window end time can be set near or slightly before the end of the A3 event. In this case, it may be necessary to adjust the A3 window end time before adjusting the amplitude of the low A4 threshold. The criteria applied at block 534 may include counting the A3 window detections (in... Figure 9 The threshold is compared (as determined at box 518). In some instances, control circuit 206 may require zero A4 events to be detected during the A3 window (the A3 window detection count is zero over N ventricular cycles) to meet the criterion of insufficient A4 event sensing at box 534, thereby resulting in a possible reduction in the amplitude of the low A4 threshold at box 538.

[0135] Another condition, which can be applied at box 534, for verifying that oversensing of A3 events does not lead to undersensing of A4 events, may require that relatively few A4 events be sensed earlier in the A4 window (e.g., within 50 milliseconds of the end of the A3 window or other specified time intervals). When the A3 event signal occurs after the end of the A3 window, several early A4-sensing event signals can occur within N ventricular cycles, causing the A3 event to be oversensed as an early A4 event. If this occurs, the amplitude of the low A4 sensing threshold should not be reduced, otherwise A3 event oversensing may occur more frequently. Moreover, the A3 window end time may need to be adjusted. An example of a criterion applied by control circuitry 206 for verifying that no A3 oversensing has occurred could include requiring early A4 counts (within 50 milliseconds of the end of the A3 window or other specified time intervals) to be sensed. Figure 9 (As determined at box 512) The number is less than the threshold number, for example, less than 2 out of 8 ventricular cycles and / or the early A4 count is less than the normal A4 count.

[0136] When all criteria for determining insufficient A4 sensing during the A4 window are met at box 534 (which may include criteria for verifying that A3 oversensing has not occurred), control circuitry 206 may determine at box 536 whether a reduction criterion is met. The low A4 sensing threshold amplitude can be reduced when the reduction does not result in the low A4 sensing threshold amplitude falling below a minimum. When the current low A4 sensing threshold amplitude is close to the minimum available setting and / or close to the minimum detected A4 amplitude, additional criteria related to the current setting of the minimum detected A4 amplitude and / or the low A4 sensing threshold amplitude may be applied to avoid reducing the low A4 sensing threshold amplitude.

[0137] When the reduction criterion is met at box 536, the control circuit 206 sets a reduction at box 538, which is used to reduce the amount of material removed from the material. Figure 9 The amplitude of the low A4 sensing threshold is adjusted at box 522. The reduction can be a fixed predetermined value, such as 0.3 ms / s for one or more ADC units. 2 In other instances, the reduction can be adjustable or proportional. Control circuitry 206 can determine the reduction based on the current setting of the low A4 sensing threshold amplitude and / or the minimum detected A4 amplitude.

[0138] When the reduction criterion is not met at block 536, control circuit 206 can determine that the low A4 sensing threshold amplitude should not decrease from its current value, even if evidence of insufficient A4 event sensing is detected at block 534 without evidence of oversensing of A3 events. Control circuit 206 can proceed to block 546, such that... Figure 9 No adjustments will be made at position 522 of the frame.

[0139] If the criteria for determining insufficient A4 event sensing during the A4 window are not met at block 534, control circuitry 206 may proceed to block 540 to determine whether regular A4 sensing with a high A4 event amplitude criterion is met. When A4 events with high amplitudes are sensed periodically, the increase in the low A4 sensing threshold amplitude can be justified. The high A4 event amplitude criterion is met when control circuitry 206 determines that regular A4 event sensing and / or the amplitude of sensed A4 events during the A4 window over N ventricular cycles is relatively high compared to the current low A4 sensing threshold amplitude. For example, A4 event sensing can be determined to be regular when most of the N ventricular cycles consist of A4 events sensed during the A4 window. At block 540, control circuitry 206 can determine that the high A4 amplitude criterion is met when the peak amplitude of each periodically sensed A4 event is greater than a predetermined margin exceeding the currently set low A4 sensing threshold amplitude.

[0140] In one instance, control circuitry 206 can determine whether regular A4 sensing meets a high A4 amplitude criterion by determining that the applicable cycle count is greater than a threshold, that the detected A4 count is equal to the applicable cycle count, that the normal A4 event count is at least the threshold number, and that the minimum detected A4 event amplitude is greater than an adjustment threshold. In some instances, the applicable cycle count threshold may be greater than half of N ventricular cycles. For example, the applicable cycle count may need to be at least five of the eight ventricular cycles analyzed. When the detected A4 count equals the applicable cycle count, an A4 event is sensed in each A4 window and determined to be a regular sensing. It may be required that the threshold number of detected A4 events is a normal A4 event (i.e., sensed at least for a predetermined time interval after the A3 window ends). For example, the normal A4 cycle count may need to be greater than one. The adjustment threshold applied to the minimum detected A4 event amplitude can be set to the current low A4 sensing threshold amplitude multiplied by an adjustment factor. For example, the adjustment factor may be 1.25, 1.5, 2.0, or other factors that provide the required safety margin between the minimum detected A4 amplitude and the low A4 sensing threshold. For example, when the minimum detected A4 amplitude, as determined in box 511, is greater than 1.5 times the current low A4 sensing threshold amplitude setting, the low A4 sensing threshold amplitude can be increased.

[0141] When control circuit 206 determines that A4 event sensing occurs regularly and reliably during the A4 window (e.g., for at least 50% or more of N ventricular cycles) and the minimum detected A4 amplitude is greater than a multiple of the low A4 sensing threshold amplitude, control circuit 206 determines at block 540 that a criterion is met and proceeds to block 542. At block 542, control circuitry determines whether the low A4 threshold amplitude increment criterion is met. For example, the current setting of the low A4 sensing threshold amplitude may need to be a threshold amount smaller than the maximum upper limit (e.g., smaller by at least one ADC unit or more). Other increment criteria may be applied based on the minimum detected A4 event amplitude and / or the current setting of the low A4 sensing threshold amplitude to avoid introducing insufficient A4 event sensing due to incrementing the low A4 sensing threshold amplitude.

[0142] When the incremental criterion is met at block 542, control circuit 206 can proceed to block 544 to determine what needs to be done. Figure 9 The adjustment increment is applied at box 522. The adjustment increment can be set to correspond to 0.1 m / s. 2 0.2m / s 2 0.25m / s 2 0.3m / s 2 Or other selected fixed predetermined values. As described above, the adjustment increment can be adjusted or scaled based on the minimum detected A4 amplitude, the current setting of the low A4 sensing threshold amplitude, the difference between the current setting of the low A4 sensing threshold amplitude and the maximum or minimum limit, the difference between the minimum detected A4 amplitude and the maximum or minimum limit, the detected A4 count, the normal A4 count, the early A4 count and / or other A4 sensing control parameter measures or any combination thereof.

[0143] When control circuit 206 determines that the criteria for detecting a regular A4 event with a high A4 amplitude are not met (box 540) or the incremental criteria are not met (box 542), control circuit 206 can set the adjustment to zero at box 546, so that in Figure 9 The low A4 sensing threshold amplitude is not adjusted at box 522.

[0144] It should be understood that when the low A4 sensing threshold amplitude is increased by a predetermined fixed increment (which would cause the low A4 sensing threshold amplitude to exceed the maximum permissible setting), the control circuit 206 can set the adjustment increment as a part of the fixed increment, so that the low A4 sensing threshold amplitude is adjusted to the maximum limit without exceeding that maximum limit. Similarly, in some cases, when adjusting by a fixed decrement would cause the low A4 sensing threshold amplitude to be less than the minimum limit, the adjustment decrement set at block 538 can be a part of a predetermined fixed decrement. For example, the minimum setting could be 0.8 m / s. 2 The acceleration. When the predetermined fixed deceleration is 0.3 m / s².2 Furthermore, the current value of the low A4 sensing threshold amplitude is 0.9 m / s. 2 At this point, reducing the A4 sensing threshold amplitude by a fixed amount will bring it below the minimum limit. In this case, the low A4 sensing threshold amplitude can be reduced to 0.8 m / s. 2 Instead of reducing a full, predetermined fixed reduction value, the minimum allowed setting is used.

[0145] Combination Figure 10 The various criteria and conditions described in flowchart 420 are described as being applied to A4 sensing control parameter metrics in a specific order. However, it should be understood that the criteria may be applied in a different order than that shown herein. For example, one or more incremental criteria in block 532 may be applied before and / or after determining whether an earlier A4 window sensing criterion is met, or vice versa. Similarly, one or more decremental criteria may be applied before and / or after determining whether an A4 sensing insufficiency criterion is met at block 534, or vice versa. For example, control circuit 206 may check whether the low A4 sensing threshold amplitude is already at its maximum or minimum limit before checking the conditions that would respectively lead to an increment or decrement. Furthermore, control circuit 206 is expected to be configured to evaluate multiple criteria sequentially, simultaneously, or in a parallel combination to reach a decision to increment, decrement, or not adjust the low A4 sensing threshold amplitude.

[0146] When blocks 530, 534, and 540 are executed in the order shown, control circuitry 206 can prioritize checking for A3 event oversensing by verifying that the early A4 window sensing condition is met at block 530. During VDD pacing mode, A3 event oversensing causes the ventricular pacing pulse to lose atrial tracking. Ventricular pacing pulses tracking A3 events (which are ventricular events) can be delivered with relatively short ventricular cycles, resulting in a rapid pacing rate. Therefore, a first priority could be ensuring that A3 event oversensing does not occur starting from the criteria described in conjunction with block 530.

[0147] The second priority could be detecting insufficient A4 event sensing when oversensing of A3 event does not occur, as determined when the criterion is met at box 534. In this case, the ventricular pacing pulse can be delivered asynchronously with the A4 event because the VV pacing interval expires without generating an A4 sensing event signal to trigger the AV pacing interval. Therefore, while providing ventricular rate support, atrioventricular synchrony may be lost during periods of insufficient A4 event sensing. Therefore, detecting insufficient A4 event sensing within the A4 window when oversensing of A3 event does not occur could be a second priority criterion used by control circuitry 206 when making a decision to adjust the amplitude of the low A4 sensing threshold.

[0148] The lowest priority condition for adjusting the low A4 sensing threshold amplitude can be applied at block 540 to increase the low A4 sensing threshold amplitude in response to regular sensing of high-amplitude A4 events. In this case, ventricular pacing can correctly track A4 events with a reliable A4-sensed event signal. Under these conditions, the adjustment of the low A4 sensing threshold amplitude may be optional, but the increment can promote continuous, reliable A4 event sensing while reducing any possibility of oversensing A3 events or other motion signals occurring within the A4 window. However, as stated above, although blocks 530, 534, and 540 are shown in a specific order, which may correspond to a priori hierarchy based on how A3 oversensing, A4 undersensing, and reliable A4 sensing can affect ventricular tracking of atrial events, it should be recognized that these criteria can be applied in parallel or simultaneous operation to arrive at the adjustment decision. Once the adjustment decision is made at block 538, 544, or block 546, control circuitry 206 can proceed to Figure 9 The flowchart 500, block 522, is used to perform an adjustment of the low A4 sensing threshold amplitude accordingly.

[0149] Figure 11 This is a flowchart 600 illustrating an example of a method for determining when a low A4 sensing threshold adjustment criterion is met and setting an adjustment increment or decrement. Control circuitry 206 can execute instructions stored in memory 210 to combine... Figure 11 This is combined with other flowcharts presented herein to perform various comparisons and decisions attributed to control circuitry 206. This functionality can be implemented in any combination of hardware, firmware, and / or software. The process in flowchart 600 can be performed after every N ventricular cycles using A4-sensored control parameter metrics determined from N ventricular cycles, as described above. Figure 9 As an example, the A4 sensing control parameter metric may include the count of all sensed A4 events, early A4 events, normal A4 events, the count of A4 events sensed during the A3 window, and the minimum detected A4 event amplitude. The process of flowchart 600 is executed by control circuit 206, which operates in an atrial-tracking ventricular pacing mode (e.g., VDD pacing mode).

[0150] At block 602, control circuit 206 compares the early A4 count with a threshold and a normal A4 count. Control circuit 206 can detect A3 event oversensing in response to an early A4 event count exceeding a threshold, for example, exceeding a predetermined percentage of N (the number of ventricular cycles) and exceeding the normal A4 event count. When the early A4 count exceeds the threshold (e.g., 2 or more) and is greater than or equal to the normal A4 count, at block 604, control circuit 206 compares the current low A4 sensing threshold amplitude with an incremental threshold. When the low A4 sensing threshold amplitude is less than or equal to the incremental threshold, control circuit 206 increases the low A4 sensing threshold amplitude at block 606, which can be increased by an increment (e.g., 0.3 m / s). 2 () to not exceed the maximum limit (e.g., 5.0 m / s) 2 When the low A4 sensing threshold amplitude is already greater than a multiple of the minimum set low A4 sensing threshold amplitude, such as twice the minimum, the control circuit 206 can prevent the low A4 sensing threshold amplitude from being increased. In one example, when the low A4 sensing threshold amplitude is greater than 1.6 m / s... 2 That is, 0.8 m / s 2 When the minimum setting is doubled, the amplitude of the low A4 sensing threshold does not increase.

[0151] Boxes 602 and 604 typically correspond to evidence of potential oversensing of A3 events and criteria for meeting the early A4 sensing criteria, respectively. The likelihood of persistent oversensing of A3 events can be reduced by increasing the amplitude of the low A4 sensing threshold in response to detected frequent early A4 sensing events. Thus, the criteria applied at boxes 602 and 604 reflect a trade-off between preventing oversensing of A3 events (by increasing the low A4 sensing threshold) and avoiding an excessive increase in the amplitude of the low A4 sensing threshold that could lead to undersensing of intermittent or persistent A4 events. It is desirable to increase the amplitude of the low A4 sensing threshold sufficiently to avoid oversensing of A3 events or other motion signals, while keeping it low enough to reliably sense A4 events during the A4 window, especially when heart rate is relatively high and / or the A4 event signal has a relatively low amplitude.

[0152] When either of the criteria at boxes 602 or 604 is not met, control circuitry 206 proceeds to box 608 to compare the applicable cycle count with a threshold count, for example, a threshold count of 5 when evaluating N = 8 ventricular cycles to determine an A4 sensing control parameter metric. An A4 event sensing insufficiency criterion may be met when control circuitry 206 determines that at least a threshold number of ventricular cycles are applicable cycles (cycles at the start of the A4 window), and the A4 count detected at box 610 is less than the applicable cycle count minus X (e.g., the detected A4 count is less than the applicable cycle count minus 2). In other instances, the detected A4 count as a percentage of the applicable cycle count may be compared to a threshold percentage (e.g., 80%, 70%, or other percentages). When the detected A4 count is less than a threshold percentage of the applicable cycle count, A4 sensing insufficiency may be suspected, and a reduction in the magnitude of the low A4 sensing threshold may be warranted.

[0153] At block 612, control circuitry 206 can determine whether over-sensing of the A3 event is possible by comparing the early A4 count with a threshold count and / or comparing the early A4 count with a normal A4 count. A3 over-sensing is less likely when the early A4 count is less than 2 or another selected threshold, or when the early A4 count is less than the normal A4 count, supporting the determination of insufficient A4 sensing during the A4 window and the need to reduce the magnitude of the low A4 sensing threshold.

[0154] At block 612, control circuitry 206 may additionally or alternatively determine whether the A3 window detection count (the number of sensed A4 events occurring during the A3 window) is less than a threshold, for example, less than 1 or zero A3 window detection count. When zero A4 events are sensed during the A3 window and the early A4 count is less than the threshold count and less than the normal A4 count, the A3 oversensing condition is not met, supporting the determination that the criteria for detecting insufficient A4 sensing are met, and guaranteeing a reduced low A4 sensing threshold magnitude.

[0155] Before reducing the low A4 sensing threshold amplitude, control circuit 206 may determine at block 614 whether the minimum detected A4 amplitude is less than the threshold amplitude. For example, control circuit 206 may determine that the minimum detected A4 amplitude is less than or equal to the current low A4 sensing threshold amplitude multiplied by a safety factor, such as 1.5. In some instances, control circuit 206 may determine at block 614 that the normal A4 count is zero, which justifies reducing the low A4 sensing threshold amplitude even when the minimum detected A4 amplitude is not greater than the current low A4 sensing threshold amplitude multiplied by the safety factor.

[0156] The standards applied at boxes 608, 610, and 612 typically correspond to... Figure 10The criteria applied at box 534 are used to determine insufficient A4 sensing without excessive A3 sensing. When the criteria at boxes 608, 610, and 612 are met and the reduction criterion is met at box 614, control circuit 206 can reduce the low A4 sensing threshold amplitude by one ADC unit or other selected reduction at box 616, but not less than the minimum permissible low A4 sensing threshold amplitude, for example, 0.8 m / s. 2 .

[0157] When A4 sensing and atrial tracking of ventricular pacing pulses may be temporarily lost, control circuitry 206 may apply the A3 oversensing criterion at block 612 and the reduction criterion at block 614 to avoid reducing the amplitude of the low A4 sensing threshold. The low A4 sensing threshold amplitude may be reduced only if the detected A4 count is less than at least 2 of the applicable cycle count (or other selected difference threshold) and the minimum detected A4 amplitude is low (less than the threshold) or the normally detected A4 count is zero; all of these criteria support the detection of insufficient A4 event sensing associated with low-amplitude A4 event signals. A3 oversensing may be occurring when the A3 window detection count is above the threshold, or when an early A4 count is above the threshold (e.g., above the normal A4 count), which may result in relatively late A4 event signals not being sensed in some ventricular cycles. However, reducing the low A4 sensing threshold amplitude may be unnecessary if transient conditions lead to temporary A3 event oversensing associated with a temporary loss of A4 sensing during the current N ventricular cycles. The control circuit 206 can be configured to avoid decreasing the low A4 sensing threshold under such conditions, for example, by checking the amplitude of the A4 event signal at block 614 using the minimum detected A4 amplitude or another A4 signal amplitude metric.

[0158] Temporary loss of A4 sensing may occur when premature ventricular contractions (PVCs) occur during N ventricular cycles, when the patient changes position, or in other situations. In an illustrative example, if two discontinuous PVCs occur within eight ventricular cycles, the applicable cycle count may reach six. When a PVC occurs during the A3 window, the A4 window may not initiate between the two PVC cycles. An A4 event may not be sensed in the next ventricular cycle after each PVC because the A4 window may not correspond to the atrial rate of the first cycle after the PVC. If an A4 event is missed only in another cycle, the number of A4 events detected in eight ventricular cycles may be only three. In this case, the A4 event sensing insufficiency criterion of at least five applicable cycle counts (six applicable cycles) and two fewer detected A4 counts than the applicable cycle count (only three sensed A4 events) is met. However, the reduction criterion may not be met by applying the minimum detected A4 amplitude criterion in box 614. Of the three detected A4 event signals, the smallest detected A4 amplitude may be greater than the safety factor multiplied by the low A4 sensing threshold amplitude, indicating that the low A4 sensing threshold amplitude is at an appropriate value, but other factors may have caused the temporary, transient A4 sensing insufficiency criterion to be met, in which case there are two PVCs.

[0159] Therefore, this check on the minimum detected A4 amplitude when the A4 sensing insufficiency criterion is met avoids reducing the low A4 sensing threshold amplitude when the A4 event signal has a relatively high amplitude, although other factors such as PVC could be potential causes of meeting the A4 sensing insufficiency criterion over N ventricular cycles. Maintaining the low A4 sensing threshold amplitude at its current value allows for the restoration of regular A4 sensing over the next N ventricular cycles, where AV synchronization is restored via atrial-tracking ventricular pacing, without needing to adjust to the low A4 sensing threshold amplitude. In this example, the application of the minimum detected A4 amplitude criterion (box 614) avoids reducing the low A4 sensing threshold amplitude even when the detected A4 count is low (at box 610), for example, due to temporary loss of sensing A4 events caused by other transient, non-continuous changes in PVC or rhythm, patient position or activity, or other factors.

[0160] If any criterion at boxes 608, 610, 612, or 614 is not met, control circuitry 206 proceeds to box 618 to determine whether a regular A4 sensing is occurring with a relatively high A4 event signal amplitude. At boxes 618 and 620, control circuitry 206 determines whether a regular A4 event sensing is occurring by comparing the detected A4 count to the applicable cycle count and by comparing the normal A4 count to a threshold count, respectively. In one instance, control circuitry 206 determines that a regular A4 sensing is occurring when the detected A4 count equals the applicable cycle count (the A4 sensing event signal generated in each A4 window occurring within N ventricular cycles) and the normal A4 count is at least 1. The criteria applied at boxes 618 and 620 typically correspond to those that can be used to... Figure 10 The criteria applied at block 540 are used to determine a conventional A4 sensing with a high A4 amplitude. When these criteria are met, control circuitry 206 proceeds to block 622 to determine whether an incremental criterion is met.

[0161] At block 622, control circuitry 206 can compare the minimum detected A4 amplitude with a threshold. The threshold can be based on a current setting of the low A4 sensing threshold amplitude multiplied by a safety factor, such as 1.5. When the minimum detected A4 amplitude at block 622 is greater than the threshold, control circuitry 206 determines at block 606 that it is safe to increase the low A4 sensing threshold amplitude without impairing or interrupting regular A4 event sensing. Control circuitry 206 can increase the low A4 sensing threshold amplitude by a predetermined increment, such as 0.3 m / s. 2 Or other selected increments. (As mentioned above) Figure 7 The other multiples of the low A4 sensing threshold amplitude can be used as thresholds for comparison with the minimum detected A4 amplitude. The multiples used to set the incremental standard at block 622 effectively set the minimum safety margin required between the low A4 sensing threshold amplitude and the minimum detected A4 amplitude to facilitate reliable A4 event sensing.

[0162] In some cases, control circuit 206 may determine that the criteria applied in blocks 602, 604, 608, 610, 612, 614, 618, 620, and 622 are not met, causing no adjustment to be performed in block 624. In this case, A4 events can be periodically sensed, and a low A4 sensing threshold amplitude is considered appropriate based on the minimum detected A4 amplitude being at least an acceptable safety margin of the current low A4 sensing threshold amplitude.

[0163] However, at other times, due to oversensing of A3 events during or after the A3 window, A4 events may be undersensed, potentially failing to meet the increment or decrement criteria. In such cases, adjusting the A4 sensing threshold amplitude to a low level may not correct the oversensing of A3 events. Instead, adjusting the A4 sensing threshold amplitude applied during the A3 window and / or adjusting the A3 window end time may be a more appropriate response to restore reliable A4 event sensing. Techniques for automatically adjusting the high A4 sensing threshold amplitude and the A3 window end time are described below.

[0164] Figure 12 Figure 700 is a schematic diagram 700 of an EGM signal 702 generated by sensing circuit 204 and a motion signal 710 generated by motion sensor 212, shown here as an acceleration signal (ACC). Figure 700 depicts A4 sensing control parameters and A4 sensing control parameter measures that can be determined by control circuit 206 from motion signal 710 for adjusting at least some of the A4 sensing control parameters. Figure 12 The A4 sensing control parameters depicted include the A3 window end time 744, the high A4 sensing threshold amplitude 720 applied to the motion signal 710 during the A3 window 740, and the low A4 sensing threshold amplitude 722 applied after the A3 window end time 744 during the A4 window 750. The A4 sensing control parameters further include a postventricular atrial refractory period 730 and a postventricular atrial refractory period 732. A4 sensing control parameter measures that can be determined by the control circuit 206 from the motion signal 710 include the A3 event time 726, the A3 event amplitude 760, the A4 event time 728, and the A4 event amplitude 762. Each of these A4 sensing control parameter measures can be determined for use by the control circuit 206 when adjusting the A3 window end time 744 and / or the high A4 sensing threshold amplitude 720.

[0165] EGM signal 702 includes an R wave 704, which can be an inherent R wave sensed by sensing circuit 204. Sensing circuit 204 can generate an event signal 706 that senses the R wave, initiating a post-ventricular atrial refractory period 730 (during which no A4 event is sensed) and a post-ventricular atrial refractory period (PVARP) 732, during which the A4 event can be sensed after the expiration 742 of the ventricular refractory period 730, but without triggering a response from pacing timing circuit 242. Figure 3The AV pacing interval is initiated. In some instances, PVARP 732 can be adjusted every N ventricular cycles based on the ventricular rate over N ventricular cycles. In some instances, the postventricular atrial blanking period 730 can be extended to 550 milliseconds. PVARP 732 can be set to at least blanking period 730 and no longer than the A3 window end time 744, but will typically expire earlier than the A3 window end time 744. For example, the A3 window 740 can be initiated at 550 milliseconds (the end of blanking period 730) and extended to end time 744, i.e., 600 to 1000 milliseconds after ventricular event 706. PVARP 732 can expire 550 to 600 milliseconds after the R-wave sensed event signal 706.

[0166] PVARP 732 can be adjusted based on a ventricular rate metric determined to be the median or the Nth longest ventricular cycle interval over N ventricular cycles (e.g., the fourth longest ventricular cycle out of eight ventricular cycles). Ventricular cycle intervals, such as RR intervals, can each begin and end with a sensed R wave or ventricular pacing pulse. In one example, control circuitry 206 sets PVARP 732 to subtract an offset ventricular rate metric, for example, subtracting the median ventricular cycle interval from 100 to 200 milliseconds. In another example, PVARP 732 is adjusted after every N (e.g., 8) ventricular cycles to the Nth longest (e.g., the fourth longest) ventricular cycle interval minus 130 milliseconds, but not less than the minimum PVARP (e.g., 500 milliseconds) and not greater than the maximum PVARP (e.g., 600 milliseconds). As an example, the offset used to set the PVARP 732 based on ventricular rate measurements can include a PVARP adjustment offset, such as 100 milliseconds, plus the AV pacing interval, such as 10 milliseconds, 20 milliseconds, or 30 milliseconds. In this way, the PVARP 732 can be shortened during fast heart rates but will not be prolonged beyond a maximum value, such as 600 milliseconds, during slow heart rates to facilitate non-refractory period sensing of A4 event signals.

[0167] During the blanking period 730, events A1 712 and A2 714 occur but are not sensed by the atrial event detector circuit 240. At the end of the blanking period 730, control circuit 206 initiates an A3 window 740 that extends to the A3 window end time 744. Event A3 716 occurs during the A3 window 740. In the illustrated example, event A3 716 is not sensed as an A4 event because the motion signal 710 does not cross the high A4 sensing threshold amplitude 720 applied during the A3 window 740. However, control circuit 206 can be set to a low A3 threshold amplitude 724 applied during the A3 window 740 to determine the timing of event A3 716 as a measure of the A4 sensing control parameters used to adjust the A3 window end time 744. The low A3 threshold amplitude 724 (also referred to herein as the “ventricular diastolic event threshold amplitude”) can be set equal to or lower than the low A4 sensing threshold amplitude 722, for example, 75% of the low A4 sensing threshold amplitude. The A3 event 716 crosses the low A3 threshold amplitude 724 at time 726 of the event signal 706 (the start of the ventricular cycle) sensed from the R wave. This low A3 sensing threshold crossing time 726 can be referred to as the "A3 event time" 726. The low A3 sensing threshold crossing time 726 is shown as the most recent negative crossing time of the A3 sensing threshold 724. In other instances, the positive crossing time of the A3 sensing threshold 724 can be determined as the A3 event time.

[0168] During some ventricular cycles, the motion signal 710 may cross the low A3 threshold amplitude 724 more than once during the A3 window 740. Therefore, in some instances, the A3 event time 726 can be determined as the latest crossing time of the low A3 threshold amplitude 724 during the A3 window 740, which may be the latest negative crossing of the low A3 threshold amplitude 724. The control circuit 206 can adjust the A3 window end time 744 based on the latest crossing time of the low A3 threshold amplitude 724 to avoid setting the A3 window end time 744 too early, which could lead to oversensing of the A3 event 716 during the A4 window 750. As further described below, the control circuit 206 can determine the A3 event time 726 during each of N ventricular cycles to adjust the A3 window end time 744 as needed after every N ventricular cycles or less. Therefore, the control circuit 206 can be configured to determine the latest time when the motion signal 710 in the A3 window 740 is greater than the low A3 threshold amplitude 724, such that the A3 window end time 744 can be appropriately set after the A3 event signal 716 has ended (or at least return to a low amplitude that will not be oversensed as an A4 event).

[0169] In other ventricular cycles, the motion sensor signal 710 may not cross the low A3 threshold amplitude 724. In this case, the A3 event time may not be determined. The control circuit 206 may count the number of ventricular cycles in which the A3 event time is not determined due to the absence of a low A3 sensing threshold. In other instances, the A3 event time may be set to a minimum predetermined value or a default value, such as 550 milliseconds, to indicate that the A3 window end time 744 can be adjusted to a relatively early time after the ventricular event 706, regardless of the A3 event signal 716 having an amplitude greater than the low A4 sensing threshold amplitude 722. In other ventricular cycles, premature ventricular contractions or other rapid ventricular beats may occur before the A3 window 740 or before the A3 window end time 744, causing the A3 window 740 to not be initiated or at least not completed during the ventricular cycle. In some instances, when the A3 window 740 is not initiated or the A3 window end time 744 is not reached, the A3 event time may not be determined by the control circuit 206 for the ventricular cycle. The control circuit 206 can count the number of ventricular cycles in which the A3 event time is not determined due to the absence of an A3 window or an incomplete A3 window.

[0170] In some instances, the low A3 threshold amplitude 724 applied during the A3 window 740 for detecting the A3 event time 726 can be set based on the low A4 sensing threshold amplitude 722. For example, the low A3 threshold amplitude 724 can be set to 60%, 70%, 75%, 80%, 90%, 100%, or other selected percentages of the low A4 sensing threshold amplitude 722 applied after the A3 window end time 744 and during the A4 window 750. In one instance, the low A3 threshold amplitude 724 is set to 75% of the low A4 sensing threshold amplitude 722 and can be adjusted upward or downward every N ventricular cycles, as per the above combination. Figure 9-11 Any instance given.

[0171] Control circuit 206 can be configured to determine the A3 event amplitude 760 during each of N ventricular cycles. Control circuit 206 can determine the A3 event amplitude 760 to adjust the high A4 sensing threshold amplitude 720, as further described below. The A3 event amplitude 760 can be determined as the maximum peak amplitude of the motion signal 710 during the A3 window 740. In some cases, the A3 event amplitude 760 is determined as the maximum sample point amplitude that occurs after the low A3 threshold amplitude 724 is crossed by the motion sensor signal 710. However, the maximum peak amplitude 760 does not necessarily always occur after the latest motion sensor signal crossing time of the low A3 threshold amplitude, especially when the latest negative crossing time is determined to be the A3 event time 726. Therefore, the A3 event amplitude 760 may occur earlier or later in the A3 window 740 than the A3 event time 726. The timing of the A3 event amplitude 760 can be independent of the A3 event time 726. However, in some instances, the A3 event amplitude 760 can be determined to be the maximum amplitude greater than or equal to the low A3 threshold amplitude 724, such that in some cases, the A3 event amplitude 760 and the A3 event time 726 can occur at the same sample point.

[0172] During some ventricular cycles, the motion signal 710 may not cross the lower A3 threshold amplitude 724, making it impossible to determine the A3 event time. When it does not cross the lower A3 threshold amplitude 724, the A3 event amplitude 760 may or may not be determined as the maximum sample point amplitude during the A3 window 740. When it does not cross the lower A3 threshold amplitude 724, the control circuit 206 can determine that the A3 event amplitude is unknown. Therefore, in some instances, the control circuit 206 determines the A3 event amplitude as the maximum amplitude greater than (or equal to) the lower A3 threshold amplitude 724.

[0173] In addition to determining the A3 event amplitude 760 and A3 event duration 726, control circuitry 206 can be configured to determine the A4 event amplitude 762 and A4 event duration 728 during the A4 window 750 of each ventricular cycle (N ventricular cycles) in which the A4 window 750 is initiated. The A4 window 750 is initiated when the A3 window 740 ends without a sensed A4 event or a sensed R wave. The A4 event duration 728 can be determined as the time interval from the start of the ventricular electrical event 706 (the event signal 706 sensed by the R wave in this cycle, but a ventricular pacing pulse in other cycles) until the maximum amplitude 762 of the motion signal 710 during the A4 window 750 (after the end time 744 of the A3 window). In other instances, control circuitry 206 can determine the A4 event duration 728 as the time interval from the most recent ventricular electrical event to the earliest time span of the low A4 sensing threshold amplitude 722. The control circuit 206 can determine the A4 event time 728 alone or in combination with the A3 event time 726, for adjusting the A3 window end time 744 as described below.

[0174] In some ventricular cycles, even if the A4 window 750 is activated, the motion signal 710 may not cross the low A4 sensing threshold amplitude 722. The low A4 sensing threshold amplitude 722 may be set too high, ventricular pacing or the sensed R wave may occur before the low A4 sensing threshold amplitude 722 is crossed, or atrial beating may not occur during the A4 window to result in an A4 event 718. Thus, for each ventricular cycle containing the A4 window, the A4 event time may not be determined by the control circuit 206. When the A4 event time is not determined for a given ventricular cycle, the control circuit 206 may or may not determine the A4 event amplitude 762. The control circuit 206 may determine the A4 event amplitude 762 as the maximum sample point amplitude greater than the low A4 sensing threshold amplitude 722 during the A4 window 750.

[0175] like Figure 12 As shown, when event A4 718 is detected by the external atrial event detector circuit 240 of PVARP 732 ( Figure 3 When a motion signal 710 is sensed, for example, in response to the motion signal 710 crossing a low A4 sensing threshold amplitude 722, the pacing timing circuit 242 initiates an AV pacing interval 764. The pulse generator 202 generates a ventricular pacing pulse 708 in response to the expiration of the AV pacing interval 764, which terminates the ventricular cycle and the A4 window 750. During other ventricular cycles, the atrial event detector circuit 240 can sense an A4 event in response to the motion signal 710 crossing a high A4 sensing threshold amplitude 720 during the A3 window 740, for example, when the heart rate is high and the A4 event signal merges with the A3 event signal, resulting in a combined high-amplitude fused A3 / A4 event signal.

[0176] If an A4 event is sensed during the A3 window 740 outside of PVARP 732, the AV pacing interval 764 is initiated by the pacing timing circuit 242. The pulse generator 202 generates a pacing pulse when the AV pacing interval 764 expires to provide atrial tracking of the A4 event sensed after PVARP 732 during either the A3 window 740 or the A4 window 750.

[0177] It should be noted that when the atrial event detector circuit 240 senses an A4 event during the A3 window 740, the A3 window 740 can be extended until the next ventricular event. For example, the pacing timing circuit 242 can initiate an AV pacing interval 764 in response to an A4 event sensed during the A3 window 740. The AV pacing interval 764 can be extended beyond the scheduled end time 744 of the A3 window. However, to avoid another A4 sensing threshold being crossed during the ventricular cycle, the control circuit 206 can extend the A3 window 740 until the AV pacing interval expires and a ventricular pacing pulse is delivered. The control circuit 206 can extend the A3 window 740 until the next ventricular event is sensed or paced, at which point the high A4 sensing threshold amplitude 720 is crossed, so that the A4 window 750 is not initiated during the same ventricular cycle. The A3 window is extended to avoid another A4 sensing threshold amplitude being crossed in the same ventricular cycle. In this scenario, since the A4 window 750 is not activated, the A4 event time 728 and the A4 event amplitude 762 are not determined. By maintaining a high A4 sensing threshold amplitude 720 until the next ventricular electrical event, the A3 window 740 can be effectively extended without lowering the A4 sensing threshold to a low A4 sensing threshold amplitude 722.

[0178] Figure 13 This is a flowchart 760 of a method performed by control circuitry 206 according to an example for determining the A4 sensing control parameter metric from a motion signal and adjusting the A3 window end time. At block 762, control circuitry 206 determines that the current operating mode includes atrial event sensing. For example, control circuitry 206 may operate in an atrial-tracking ventricular pacing mode (e.g., a temporary or permanent VDD pacing mode including A4 event sensing). At other times, control circuitry 206 may operate in a non-atrial-tracking ventricular pacing mode, but with atrial sensing (dual-chamber sensing), such as VDI pacing mode. During VDD or VDI pacing modes, adjustment of the A3 window end time may be enabled. When the pacing mode is a rate-response pacing mode (e.g., VDIR pacing mode) or a single-chamber sensing mode (e.g., VVI or VVIR pacing mode), control circuitry 206 may disable the determination of the A4 sensing control parameter metric and the adjustment of the A3 window end time.

[0179] Referring to the above and combining Figure 12 The described A4 sensing control parameter metric, in response to a ventricular electrical event (sensed R wave or ventricular pacing pulse) initiating a new ventricular cycle, allows control circuitry 206 to determine the A3 event time 726 at block 764. When the A4 window 750 is activated and a low A4 sensing threshold amplitude is crossed, control circuitry 206 can determine the A4 event time 728 of the ventricular cycle at block 766. At block 768, control circuitry 206 determines whether N ventricular cycles have elapsed, for example, 8 ventricular cycles in the example given above. If not, control circuitry 206 returns to block 764 to continue determining the A3 and A4 event times for each ventricular cycle.

[0180] As described above, for some ventricular cycles, the A3 event time and / or A4 event time may be indeterminate, for example, when an early R wave is sensed such that the A3 and / or A4 windows are not initiated, or when the motion signal does not cross the low A3 threshold amplitude or the low A4 sensing threshold amplitude. When the motion signal does not cross the low A3 threshold amplitude during a ventricular cycle, the control circuit 206 can determine the A3 event time for that cycle as unknown. In other instances, when the low A3 threshold amplitude is not crossed, the A3 event time can be set according to a specified value. For example, the control circuit 206 can set the A3 event time to the minimum available setting of the A3 window end time or the minimum available setting of the A3 window minus a specified interval, such as minus 50 milliseconds. In one instance, the minimum A3 window end time is 600 milliseconds, such that when the low A3 threshold amplitude is not crossed by the motion signal, the control circuit 206 sets the A3 event time to 550 milliseconds. When the amplitude of the motion signal remains below the low A3 threshold amplitude throughout the A3 window, the A3 window can be set to the minimum end time because the risk of oversensing A3 events is minimized.

[0181] When the A4 window is not activated during a ventricular cycle, the timing of the A4 event in that ventricular cycle is unknown. The above describes an example where the A4 window 750 is not activated, for example, when a ventricular electrical event occurs before the end time 744 of the A3 window or when the A3 window 740 is extended due to an A4 sensing event during the A3 window 740.

[0182] When the A4 window is activated but the motion sensor signal does not cross the low A4 sensing threshold amplitude during the A4 window, control circuit 206 can set the A4 event time of that ventricular cycle to a default value. The default value can be based on a programmed lower ventricular pacing rate or rate smoothing rate. Control circuit 206 can set the rate smoothing rate interval based on the actual ventricular rate, such that the VV pacing interval can be set to the rate smoothing rate interval, which can be shorter than the lower ventricular pacing rate interval to avoid a sudden change in ventricular rate to a lower ventricular pacing rate when no A4 event is sensed. When no A4 event is sensed, the rate smoothing interval can be gradually adjusted towards a lower rate interval. When the motion sensor signal 710 does not cross the low A4 sensing threshold amplitude 722 during the A4 window 750, the A4 event time can be set to the rate smoothing interval plus an offset (which can be zero or other selected values) indicating a relatively long A4 event time after the VV pacing interval. In other instances, the A4 event time can be set to a lower rate interval. In this way, the A4 event time can be determined by the control circuit 206 when the A4 window begins to be at least the VV pacing interval, or even when the motion sensor signal 710 does not cross the low A4 sensing threshold amplitude 722 before the VV pacing interval expires.

[0183] After N ventricular cycles (the "Yes" branch of box 768), control circuit 206 can determine the A3 time metric at box 770 and the A4 time metric at box 772. The A3 time metric is determined by the individual A3 event times determined within the N ventricular cycles, while the A4 time metric is determined by the individual A4 event times determined within the N ventricular cycles. In various instances, as further described below, the A3 window end time can be adjusted based on one or both of the A3 and A4 time metrics. For example, the A3 window end time can be adjusted to be at least later than a threshold time interval of the A3 time metric, at least earlier than a threshold time interval of the A4 time metric, or some interval between the A3 and A4 time metrics.

[0184] The A3 time metric can be determined by control circuitry 206 as the average or median of all A3 event times determined from N ventricular cycles. In other instances, the A3 time metric can be determined as the specified nth shortest (or longest) A3 event time determined from N ventricular cycles. For example, when evaluating eight ventricular cycles, the fourth shortest A3 event time can be determined as the A3 time metric at box 770. When fewer than four A3 event times are obtained from N ventricular cycles, the A3 time metric may be determined as unknown, for example, due to too few A3 windows being activated. In other instances, the longest A3 event time among any determined A3 event times can be determined as the A3 event time metric.

[0185] At block 772, control circuitry 206 determines an A4 time metric from the A4 event times determined over N ventricular cycles. The A4 time metric can be determined as the average, median, or the nth shortest (or longest) A4 event time. In one instance, the A4 time metric is set to the fourth shortest A4 event time determined over eight ventricular cycles. When fewer than four (or other specified necessary number) A4 event times are determined for N ventricular cycles, control circuitry 206 can determine the A4 time metric as unknown.

[0186] At block 774, control circuitry 206 determines the target A3 window end time based on the A3 time metric and / or the A4 time metric. In one instance, the target A3 window end time is determined as the A3 time metric plus a fraction or percentage of the difference between the A3 and A4 time metrics. For example, control circuitry 206 may determine the difference between the A3 and A4 time metrics at block 774 and then add 20%, 25%, 30%, 33%, 40%, or other selected percentage of that difference to the A3 time metric to determine the target A3 window end time. In this way, the target A3 window end time is set to a safety margin later than the expected A3 event time. In one instance, the target A3 window end time is the A3 time metric plus one-third of the difference between the A3 and A4 time metrics. When either the A3 or A4 time metric is determined to be unknown, the target A3 window end time may be determined by control circuitry 206 to be unknown or remain at a previously determined value.

[0187] In some instances, the percentage or fraction of the difference between the A3 and A4 time measures used to set the target A3 window end time can be adjustable, for example, based on the current ventricular rate and / or based on the magnitude of the difference. In some instances, the ventricular rate measure can be determined over N ventricular cycles, which is used to determine the rate-smoothing pacing interval. When the ventricular rate measure is less than a heart rate threshold, the target A3 window end time can be set to the A3 time measure plus a first percentage of the difference between the A3 and A4 time measures. When the ventricular rate measure is greater than or equal to the heart rate threshold, the target A3 window end time can be set to the A3 time measure plus a second percentage of the difference (different from the first percentage). For example, a higher percentage of the difference (e.g., 30%) can be used during relatively low ventricular rates (e.g., less than 80, 90, or 100 beats per minute) compared to a percentage of the difference (e.g., 15%) during relatively high ventricular rates (e.g., greater than 80, 90, or 100 beats per minute).

[0188] In some instances, the method used by control circuitry 206 to determine the target A3 window end time is selected based on the effective pacing mode. For example, the target A3 window end time can be determined differently when the pacing mode is VDD compared to when the pacing mode is VDI. During VDD pacing mode, control circuitry 206 can determine the target A3 window end time based on a combination of A3 and A4 time measures as described above. During VDI pacing mode, control circuitry 206 can determine the target A3 window end time based on the A3 time measure instead of the A4 time measure. For example, control circuitry 206 can determine the target A3 window end time as the A3 time measure plus a specified offset, such as 50 ms, 100 ms, 150 ms, or other selected offset. In some instances, the offset can be scaled or adjusted based on the actual ventricular rate. During non-atrial tracking VDI pacing mode, the atrial rate may differ from the ventricular rate, making the A4 event signal unreliable during the A4 window. The A3 event time can be determined, but any A4 event time may be unreliable. Therefore, during VDI pacing mode, when the control circuit 206 determines the target A3 window end time at block 774, it can use only the A3 time metric and not the A4 time metric.

[0189] At block 776, control circuit 206 determines whether the A3 window end time adjustment criterion is met. To determine whether the adjustment criterion is met, control circuit 206 can be configured to determine whether the target A3 end time is known or unknown, and for what reason (e.g., the A3 window is too small during N ventricular cycles or the A3 threshold amplitude spans too little during the A3 window within N ventricular cycles). Control circuit 206 can additionally or alternatively determine whether the A4 time metric is known or unknown. Control circuit 206 can be configured to compare the A3 time metric with the A4 time metric or compare their difference with a difference threshold to determine whether the adjustment criterion is met at block 776. Additionally or alternatively, control circuit 206 can be configured to compare the current value of the A3 window end time 744 with the target A3 window end time at block 776 to determine whether the adjustment criterion is met. The following is in conjunction with... Figure 14 This describes an example of a method that the control circuit 206 can perform to determine at block 776 whether the adjustment criteria are met.

[0190] When the adjustment criteria are met at box 776, the control circuit 206 determines at box 778 what the adjustment should be (increase, decrease, or no adjustment) and performs the adjustment at box 780. The following is in conjunction with... Figure 14The technique used to determine whether to increase, decrease, or keep the A3 window end time constant is described. When control circuitry 206 determines that the adjustment criteria are not met (the "No" branch of block 776), control circuitry returns to block 762 to determine the A4 sensing control parameter measurement for the next set of N ventricular cycles, as long as the operating mode still includes atrial event sensing. If the operating mode has changed, control circuitry 206 may pause determining the A4 sensing control parameter measurement used to adjust the A3 window end time and / or pause adjusting the A3 window end time.

[0191] As described above Figure 12 The low A3 threshold amplitude used to determine the A3 event time at box 764 can be based on the low A4 sensing threshold amplitude. For example, according to the above combination Figure 9-11 The described technique allows adjustment of the low A4 sensing threshold amplitude after every N ventricular cycles, as described in any of the examples given in 9-11. Thus, before determining the A3 event time during the next N ventricular cycles, control circuitry 206 can determine at block 775 whether the low A4 sensing threshold amplitude has been adjusted after the current N ventricular cycles. If the low A4 sensing threshold amplitude has been adjusted, for example, based on the just-ended N ventricular cycles (the "Yes" branch of block 775), then control circuitry 206 can adjust the low A3 threshold amplitude at block 777. The low A3 threshold amplitude is adjusted based on the adjusted low A4 sensing threshold amplitude, for example, to 75% of or equal to the new low A4 sensing threshold amplitude. Otherwise, if the low A4 sensing threshold amplitude has not been adjusted, control circuitry 206 returns to block 762 without adjusting the low A3 threshold amplitude.

[0192] Figure 14 This is a flowchart 776 of a method according to an example, the method being controlled by control circuit 206 in... Figure 13 The same procedure is performed at box 776, which determines when the A3 window end time adjustment criteria are met. At box 782, control circuitry 206 can determine whether the A3 time metric is known. As described above, the A3 time metric may be unknown when two small A3 event times are available after N ventricular cycles. Too few A3 event times may be available when the A3 window is activated due to too many rapid ventricular events, or when the motion signal does not cross a low A3 threshold amplitude during the threshold number of A3 window periods.

[0193] If the A3 time metric is unknown, control circuit 206 can determine at block 784 whether the unknown A3 time metric is due to too few A3 windows during the N ventricular events. Control circuit 206 can compare the number of A3 windows occurring over the N ventricular events to a threshold number. When the number of A3 windows is less than the threshold number, for example, less than 50% of the N ventricular cycles, the A4 sensing control parameter metric may be insufficient to support adjustment of the A3 window end time because the A3 event time is unknown. Control circuit 206 can set the adjustment to zero at block 792 in response to too few A3 windows being initiated during the N ventricular cycles. In some instances, control circuit 206 can count initiated A3 windows even if they do not reach their end time, for example, due to early ventricular contractions sensed as R waves during the A3 window. In other instances, control circuit can count A3 windows only at the beginning and end of their ventricular cycles.

[0194] When at least a threshold number of A3 windows occur during N ventricular cycles (the "No" branch of box 784), control circuitry 206 can determine at box 786 that the A3 time metric is unknown because too few A3 event times have been determined over N ventricular cycles. For example, when A3 event times are determined in less than 50% of N ventricular cycles, the A3 time metric may be unknown due to the limited number of A3 event times. In this case, control circuitry 206 can determine at box 788 that the A3 window end time should be reduced. Since motion signals rarely cross the low A3 threshold amplitude, the risk of oversensing A3 events is low if the number of A3 events is small. The A3 window end time can be shortened to facilitate A4 sensing during the A4 window period.

[0195] Since the target A3 window end time is unknown when the A3 time metric is unknown, control circuit 206 can determine at block 778 to adjust the A3 window end time by a predetermined decrease, such as 10 milliseconds, 20 milliseconds, 30 milliseconds, 50 milliseconds, or other selected time intervals. If the predetermined decrease would result in the A3 window end time being less than the minimum A3 window end time, the adjustment determined at block 778 can be an adjustment to the minimum A3 window end time (not less than the minimum A3 window end time).

[0196] In other instances, instead of determining the A3 event time as unknown and subsequently the A3 time metric as unknown, the A3 event time can be set to a specified value, for example, Y milliseconds less than the minimum A3 window end time, when the motion signal does not cross the low A3 threshold amplitude. Y milliseconds could be 50 milliseconds or other predetermined values. When the motion signal remains low during the A3 window, for example, less than the low A3 threshold amplitude, the likelihood of oversensing the A3 event is small. Therefore, the A3 window end time can be set to a relatively short time interval after a ventricular electrical event, with a low probability of oversensing the A3 event as an A4 event. Thus, when the motion signal does not cross the low A3 threshold amplitude in a given ventricular cycle, the A3 event time is set to a relatively short default time interval. Then, based on the A3 time metric known for all A3 event times determined over N ventricular cycles, which may include cycles in which the A3 event time is set to the low default value, control circuitry 206 can use the A3 time metric to set a target A3 window end time for determining A3 window end time adjustments. In this case, the criteria used in box 786 to determine why the A3 time metric is unknown due to the small number of A3 events can be omitted.

[0197] When control circuit 206 determines at block 782 that the A3 time metric is known ("Yes" branch), control circuit 206 can determine at block 790 whether the pacing mode is an atrial tracking pacing mode and whether the A4 time metric is known. If neither of these conditions is met, for example, if the pacing mode is a non-atrial tracking pacing mode (e.g., VDI, VVIR, etc.) or the A4 time metric is unknown (e.g., due to two limited A4 windows or too few A4 event times determined over N ventricular cycles), control circuit 206 determines at block 791 whether the current operating mode is a VDI pacing mode.

[0198] Combined with the following text Figure 18Prior to initiating operation in the atrial-tracking ventricular pacing mode, control circuitry 206 can operate in VDI pacing mode to adjust the A3 window end time from an initial start A3 window end time value, for example, during pacemaker implantation. If VDI pacing mode is active at box 791, control circuitry 206 can proceed to box 796. Otherwise, when the A4 time metric is unknown and the pacing mode is neither atrial-tracking pacing mode nor VDI pacing mode (the "No" branches of boxes 790 and 791), at box 792, the A3 window end time is not adjusted by control circuitry 206. Similarly, when the pacing mode is atrial-tracking ventricular pacing mode (e.g., VDD) but the A4 time metric is unknown (the "No" branches of boxes 790 and 791), the A3 window end time is not adjusted at box 792 because any adjustment might not correctly set the A3 window end time earlier than the A4 event time when the A4 event time is unknown.

[0199] When the operating mode is atrial tracking pacing mode and the A4 time measure is known (the "Yes" branch of box 790), control circuitry 206 can determine whether there is a sufficient difference between the A4 and A3 time measures to move the end time of the A3 window. For example, as an example, control circuitry 206 can determine whether the difference between the A4 and A3 time measures is less than a threshold difference, such as less than 100 milliseconds. In some instances, the threshold difference can be a predetermined fixed value. In other instances, the threshold difference can be an adjustable or variable threshold difference, for example, scaled to the actual ventricular rate. For example, the threshold difference can be a percentage of the actual ventricular rate interval, such that the threshold difference decreases as the ventricular rate increases and increases as the ventricular rate decreases.

[0200] If the difference between the A4 time measure and the A3 time measure is less than the threshold difference (the "Yes" branch of box 794), then control circuit 206 determines at box 792 not to adjust the A3 window end time. In this case, sufficient A3 event time and sufficient A4 event time are known from N ventricular cycles, such that both the A3 and A4 time measures are known. These known A3 and A4 time measures indicate that the current A3 window end time is set to a value that allows the A3 window to reliably end before the A4 event, such that the A3 and A4 events are separated by their end times and the event times are reliably detected. However, the separation between the A3 and A4 event signals is relatively small, so there is no need to change the A3 window end time.

[0201] When the difference between the A4 time metric and the A3 time metric is relatively large, for example, at least 100 milliseconds or more, as determined by control circuitry 206 based on a comparison with the threshold difference at block 794, control circuitry 206 proceeds to block 796 (the "No" branch of block 794). In this case, the time difference from the A3 event to the A4 event is large enough that an offset (increase or decrease) in the A3 window end time can be reasonable.

[0202] At box 796, control circuit 206 determines whether the end time of window A3 is less than or equal to the target end time of window A3. (As per the above...) Figure 13 The control circuit 206 can determine the target A3 window end time based on the A3 time metric during VDI pacing mode or based on both the A3 and A4 time metrics during VDD pacing mode. When the current A3 window end time is greater than the target A3 window end time, at block 788, the control circuit 206 determines that the A3 window end time should be reduced.

[0203] For example, when the A3 time metric is determined to be relatively short, such as when the A3 event time is set to a default minimum (e.g., minimum A3 window end time minus 50 milliseconds) because it does not cross the low A3 threshold amplitude, the current value of the A3 window end time may be greater than the target A3 end time. In this case, the target A3 window end time may be at or near the minimum A3 window end time. If control circuit 206 determines at block 788 that the A3 window end time should be reduced, it adjusts the A3 window end time toward or to the minimum A3 sensing window end time. In this way, the A3 window is shortened when the likelihood of oversensing of A3 events is low due to relatively low amplitude A3 events (less than the low A3 threshold amplitude) or due to A3 events occurring very early in the A3 window. Control circuit 206 shortens the A3 window end time toward or to the minimum A3 window end time to facilitate reliable A4 event sensing, even when the ventricular rate increases. Shortening the end time of the A3 window effectively enables the A4 window to start earlier, where a low A4 sensing threshold amplitude is effective, increasing the likelihood of sensing A4 events.

[0204] When control circuit 206 determines at block 788 that the end time of window A3 should be reduced, control circuit 206 can adjust the time based on the current value of the end time of window A3. Figure 13Adjustments are confirmed at box 778. The A3 window end time can be reduced by a predetermined amount, such as 10 milliseconds, 15 milliseconds, 20 milliseconds, or other selected reductions, but not less than the target A3 window end time or the minimum available setting for the target A3 window end time. As an example, the minimum A3 window end time could be 600 milliseconds after the most recent previous ventricular electrical event.

[0205] If the A3 window time is less than (or equal to) the target A3 window end time as determined at box 796 (“Yes” branch), then control circuit 206 determines at box 798 that the A3 window end time should increase toward (or remain at) the target A3 window end time (not exceeding the target A3 window end time). It is understood that when control circuit 206 determines that the A3 window end time is equal to the target end time, control circuit 206 determines not to adjust the end time, for example, to 0 milliseconds.

[0206] When the control circuit 206 is Figure 14 When the end time adjustment of window A3 is increased at box 798, control circuit 206 can... Figure 13 At box 778, the adjustment is determined to be a predetermined increment, such as 10 milliseconds, 20 milliseconds, or other selected values, but not greater than the target A3 window end time or the maximum allowed setting for the A3 window end time, for example, not greater than the maximum value of 1000 milliseconds after the most recent ventricular event. In some instances, the minimum and maximum limits of the A3 window end time can be programmable and tailored to a given patient, and can be selected to be at least 100 milliseconds apart. For example, in a given patient, the minimum to maximum range of the A3 window end time could be 600 milliseconds to 700 milliseconds or 700 milliseconds to 800 milliseconds. In another patient, the minimum to maximum range might be larger, for example, 700 milliseconds to 1000 milliseconds. Figure 13 At box 780, control circuit 206 adjusts the end time of window A3 based on the adjustment determined at box 778, and on which adjustment criterion (increase, decrease, or maintain) is met at box 776, such as in combination with... Figure 14 As stated above.

[0207] Figure 15This is a flowchart 800 of a method for adjusting the amplitude of a high A4 sensing threshold, performed by control circuitry 206 according to an example. When the A4 event signal is fused with the A3 event signal from the motion sensor signal, a high A4 sensing threshold amplitude is applied during the A3 window for detecting the A4 event. The high A4 sensing threshold amplitude may also be referred to as the first or early A4 sensing threshold because it is applied during the A3 window before the low A4 sensing threshold amplitude, and the low A4 sensing threshold amplitude may also be referred to as the second or late A4 sensing threshold because it is applied after the end of the A3 window. The high A4 sensing threshold amplitude may be based on the A3 event amplitude determined over N ventricular cycles (e.g., Figure 12 The A3 event amplitude (760) shown in the figure can be adjusted.

[0208] When control circuit 206 operates in a pacing mode that includes atrial event sensing (e.g., a VDD or VDI pacing mode as defined at box 802), control circuit 206 determines the A3 event amplitude for each ventricular cycle at box 804 until N ventricular cycles have elapsed (as defined at box 806). It should be understood that the A3 event amplitude and other A4 sensing control parameter measures can be determined during or at the end of each ventricular cycle. In other instances, control circuit 206 may buffer motion sensor signals in memory 210 for N ventricular cycles. Upon the expiration of N ventricular cycles, control circuit 206 can determine the A3 event amplitude (and / or other A4 sensing control parameter measures) from the motion sensor signals buffered in memory 210. As described above, when A3 window 740 (see...) Figure 12 If the event does not occur, for example, due to the sensing of an R-wave during the blanking period 730, the control circuit 206 may not be certain of the amplitude of the A3 event. When the A3 window 740 is activated, the control circuit 206 determines the amplitude of the maximum motion sensor signal during the A3 window as the amplitude of the A3 event.

[0209] In some instances, control circuitry 206 may determine the A3 event amplitude only during ventricular cycles containing A4 events detected during the A4 window. Alternatively, the A3 event amplitude may be determined for all ventricular cycles, but when no A4 event is detected during the A4 window, the A3 event amplitude may be ignored for the purpose of determining an A3 amplitude metric at block 808. In some instances, the A3 event amplitude determined only during ventricular cycles containing normal A4 event detection is used by control circuitry 206 to adjust the high A4 sensing threshold amplitude as described below. Normal A4 event detection is an A4 event detected at least a threshold time interval (e.g., 50 ms to 100 ms) after the end of the A3 window. When it is known that the A4 event was detected later during the A4 window, the A3 event amplitude can more accurately reflect the amplitude of the true A3 event. When an A4 event is detected early, a fusion of A3 and A4 events may occur, such that the A4 event contributes to the A3 event amplitude determined by control circuitry 206. Thus, when an A4 event is detected during the A3 window, the control circuit 206 can reject the amplitude of the A3 event occurring during the ventricular cycle as an early A4 event within the threshold time interval at the end of the A3 window, or it can be completely ignored.

[0210] In other instances, the amplitude of the A3 event can be determined for all ventricular cycles; however, different A3 event amplitude measures can be determined by control circuit 206 based on the timing of A4 event detection. Therefore, control circuit 206 can store the A3 event amplitude in different buffers in memory 210 based on when the A4 event is detected. For example, control circuit 206 can determine the A3 event amplitude for all ventricular cycles and store it in memory 210, and can also mark or store the A3 event amplitude determined for ventricular cycles containing only normal A4 event detection in different buffers.

[0211] After N ventricular cycles have elapsed (box 806), control circuitry 206 determines an A3 amplitude metric at box 808 based on individually determined A3 event amplitudes. As an example, the A3 amplitude metric could be the average, median, maximum, or nth highest A3 event amplitude. When determining A3 event amplitudes over eight ventricular cycles, as an example, the A3 amplitude metric could be determined at the fourth highest A3 event amplitude. If fewer than four A3 event amplitudes are known, for example, due to fewer than four A3 windows being initiated during eight ventricular cycles or the motion signal not crossing the low A3 threshold amplitude, the A3 amplitude metric can be determined as unknown.

[0212] As described above, the A3 event amplitude can be determined as the maximum motion signal amplitude greater than the low A3 threshold amplitude during the A3 window, which can be set as a percentage of the low A4 sensing threshold amplitude. If the motion signal does not cross the low A3 threshold amplitude during the A3 window, the A3 event amplitude may be unknown for that ventricular cycle. When adjusting the low A4 sensing threshold amplitude (e.g., once every N ventricular cycles), the low A3 threshold amplitude can be adjusted based on the adjusted low A4 sensing threshold amplitude. Thus, the low A3 threshold amplitude is adjusted using the low A4 sensing threshold amplitude, but the high A4 sensing threshold amplitude applied during the A3 window can be adjusted less frequently, as described below.

[0213] As described above, the A3 amplitude metric can be determined solely based on the A3 event amplitude determined for a ventricular cycle with normal A4 event detection. For example, the A3 amplitude metric can be set as the maximum A3 event amplitude, a predetermined percentile of the A3 event amplitude associated with a normal A4 event detection cycle, or the nth highest A3 event amplitude. In other instances, the A3 amplitude metric can be determined based on a combination of the A3 event amplitude determined for a ventricular cycle with normal A4 event detection and the A3 event amplitude determined for all ventricular cycles. For example, the A3 amplitude metric can be set as the percentile of all A3 event amplitudes greater than the A3 event amplitude associated with a normal A4 event detection cycle.

[0214] At block 810, control circuitry 206 determines the target high A4 sensing threshold amplitude based on the A3 amplitude metric determined at block 808. In some instances, the target high A4 sensing threshold amplitude can be determined based on a combination of the current low A4 sensing threshold amplitude and the A3 amplitude metric. For example, control circuitry 206 can determine the target high A3 sensing threshold amplitude as the sum of the current low A4 sensing threshold amplitude plus the A3 amplitude metric multiplied by a threshold factor. The threshold factor can be 1, 1.2, 1.5, 1.8, or other selected values. In some instances, the target high A4 sensing threshold amplitude is set to the low A4 sensing threshold amplitude plus 1.5 times the A3 amplitude metric plus an offset. Since the actual A4 event signal during the A3 window can be fused with the A3 event signal, the fused A3 / A4 amplitude can be the sum of two separate events. Therefore, the target high A4 sensing threshold amplitude can be set based on a combination of the low A4 sensing threshold amplitude (or the minimum detected A4 amplitude) and the A3 amplitude metric. The offset can be set to zero, but it can also be set to other positive or negative values ​​to fine-tune the high A4 sensing threshold amplitude. In other instances, the target high A4 sensing threshold amplitude can be set to the maximum programmable low A4 sensing threshold amplitude plus the A3 amplitude metric multiplied by a selected factor, such as 1.5. When the A3 amplitude metric is unknown, the target high A4 sensing threshold amplitude can be determined as unknown at box 810.

[0215] At block 812, control circuit 206 can adjust the high A4 threshold adjustment counter based on the target value determined at block 810. When the target high A4 sensing threshold amplitude is greater than the current high A4 sensing threshold amplitude, the adjustment counter is incremented by 1. When the target high A4 sensing threshold amplitude is less than the current high A4 sensing threshold amplitude, control circuit 206 decrements the high A4 adjustment counter by 1. If the target value and the current value of the high A4 sensing threshold amplitude are equal, control circuit 206 does not change the value of the high A4 adjustment counter at block 812.

[0216] At block 814, control circuitry 206 determines whether the adjustment counter has reached a threshold. The adjustment counter can be increased up to a predetermined maximum value and decreased to a predetermined minimum value. In other instances, instead of using an adjustment counter, control circuitry 206 can set a timer or counter to adjust the high A4 sensing threshold amplitude on a scheduled basis, such as once per hour, once every four hours, once every eight hours, once every twelve hours, once per day, or other selected frequencies. When the adjustment counter reaches the maximum or minimum threshold, or when a scheduled adjustment time is reached, control circuitry 206 can determine at block 815 whether any other desired high A4 sensing threshold adjustment criteria are met.

[0217] In some instances, control circuitry 206 may determine at block 815 whether the heart rate and / or A3 window detection count is less than an adjustment threshold. During high heart rates, the large amplitude of the fused A3 / A4 events will be determined as the A3 event amplitude and contribute to the A3 amplitude metric. Since the target value for the high A4 sensing threshold amplitude includes the A3 amplitude metric (combined with the low A4 sensing threshold amplitude), the target value will be increased during fused A3 / A4 events. In some cases, this increased target value may cause the high A4 sensing threshold amplitude to be increased above the fused A3 / A4 amplitude, resulting in undersensitivity of the fused A3 / A4 events. Therefore, in some instances, the high A4 sensing threshold may be maintained at its current value (without adjustment) when continuous sensing occurs within the A3 window. Thus, the adjustment criteria applied at block 815 may require the A3 window detection count to be less than a threshold for one or more sets of N ventricular cycles and / or the actual ventricular rate to be less than a threshold rate, e.g., less than 90 heartbeats per minute, to indicate the adjustment criteria to be met. When the A3 window detection count exceeds a threshold count (e.g., greater than 3) and / or the heart rate exceeds 90 beats per minute, there is a possibility of fused A3 / A4 events leading to increased A3 event amplitude and increased target high A4 sensing threshold amplitude. Under these conditions, control circuitry 206 stops adjusting to the high A4 sensing threshold amplitude. Therefore, the frequency of adjustment to the high A4 sensing threshold amplitude can be controlled by setting maximum and minimum adjustment counter thresholds, and this frequency can be further reduced when the A3 window detection count reaches the threshold within one or more sets of N ventricular cycles.

[0218] When the adjustment counter reaches its maximum value and meets any other adjustment criteria at block 815, the high A4 sensing threshold amplitude can be increased at block 816. When the adjustment counter reaches its minimum value, the high A4 sensing threshold amplitude can be decreased at block 816. The range of the maximum and minimum values ​​of the adjustment counter controls the frequency of adjustments to the high A4 sensing threshold. The high A4 sensing threshold amplitude is increased or decreased only after the high A4 adjustment counter has been gradually increased or decreased a certain number of times. For example, whenever the target high A4 sensing threshold amplitude is greater than the current high A4 sensing threshold amplitude, the high A4 adjustment counter can be increased by 1 until the maximum count is positive 8. When the maximum positive count of 8 is reached (block 814) because the target high A4 sensing threshold amplitude is always greater than the current setting of the high A4 sensing threshold, the high A4 sensing threshold can be increased at block 816 by control circuitry 206.

[0219] In some instances, whenever the target high A4 sensing threshold amplitude is less than the current high A4 sensing threshold amplitude, the adjustment counter can be decremented by 1, down to a minimum value of -8. When the threshold count of -8 is reached (box 814), at box 816, control circuitry 206 can reduce the high A4 sensing threshold amplitude. In this way, the high A4 sensing threshold amplitude can be adjusted less than the low A4 sensing threshold amplitude, but will slowly track changes in the low A4 sensing threshold amplitude and the A3 amplitude metric. Other thresholds besides +8 and -8 can be applied to the high A4 adjustment counter, such as... + 2. + 4. + A value of 6 or other chosen values ​​can be used to control the frequency of adjusting the high A4 sensing threshold amplitude relative to the low A4 sensing threshold amplitude. In addition to the adjustment counter described herein, other techniques such as timers or ventricular cycle counters can be used to limit or control the frequency of adjusting the high A4 sensing threshold amplitude.

[0220] When the adjustment counter reaches its maximum threshold at block 814, the control circuit 206 increases the high A4 sensing threshold amplitude towards the target high A4 sensing threshold amplitude at block 816. This adjustment can be a predetermined increment, such as one ADC unit or 0.12 m / s. 2 0.2m / s 2 0.3m / s 2 Or other selected increments. In other instances, the high A4 sensing threshold amplitude is adjusted to a target value, or adjusted in scaled increments based on the difference between the target value and the current high A4 sensing threshold amplitude.

[0221] When the counter is adjusted to the minimum threshold at block 814, at block 816, control circuit 206 reduces the high A4 sensing threshold amplitude toward the target value. The high A4 sensing threshold amplitude can be reduced by a predetermined amount (e.g., 0.3 m / s). 2 The high A4 sensing threshold amplitude can be reduced to the target value either proportionally or by an adjustable reduction. The high A4 sensing threshold amplitude can be adjusted within a specified range, for example, up to the upper limit of the A4 sensing threshold and down to the lower limit of the high A4 sensing threshold, and it can be adjustable and based on or equal to the low A4 sensing threshold. After adjusting the high A4 sensing threshold amplitude, at box 820, the adjustment counter is reset to zero (or an intermediate value between its maximum and minimum thresholds).

[0222] If the adjustment counter at box 814 does not reach the maximum or minimum threshold (“No” branch), control circuitry 206 can return to box 802 without adjusting the high A4 sensing threshold amplitude. As long as the pacing mode includes atrial sensing, control circuitry 206 can continue to determine the A3 amplitude measurement for the next N ventricular cycles. In some instances, before returning to box 802, control circuitry 206 can check at box 818 whether the high A4 sensing threshold or low A4 sensing threshold amplitude has been reprogrammed to a new value by the user. If the high A4 sensing threshold or low A4 sensing threshold has been programmed, the adjustment counter can be reset at box 820 to a starting value of zero or to an intermediate value within the range between the minimum and maximum thresholds.

[0223] At block 819, control circuitry 206 can determine whether the low A4 sensing threshold amplitude has been adjusted after the most recent N ventricular cycles. If so, the low A3 threshold amplitude is adjusted at block 821. As described above, the low A3 threshold amplitude can be set based on the low A4 sensing threshold amplitude, for example, to 75% of the low A4 sensing threshold amplitude or another specified percentage. Similarly, as described above... Figure 12 The A3 event amplitude determined at block 804 can be determined by control circuitry 206 as the maximum amplitude of a motion signal greater than the low A3 threshold amplitude during the A3 window. Therefore, in some instances, the low A3 threshold amplitude can be adjusted in response to any programming change to the low A4 sensing threshold amplitude and in response to any adjustment to the low A4 sensing threshold amplitude after N ventricular cycles, so that the A3 event amplitude can be appropriately determined.

[0224] Additionally or alternatively, at block 822, control circuitry 206 can compare the high A4 sensing threshold amplitude with the low A4 sensing threshold amplitude to verify that if the low A4 sensing threshold amplitude increases, the high A4 sensing threshold amplitude is always at least equal to or greater than the low A4 sensing threshold amplitude. If control circuitry 206 determines at block 822 that the low A4 sensing threshold amplitude has been adjusted to be higher than the high A4 sensing threshold amplitude, then at block 824, control circuitry 206 can adjust the high A4 sensing threshold amplitude to be at least equal to or greater than the low A4 sensing threshold amplitude. This adjustment at block 822 can be made before the adjustment counter reaches its maximum or minimum threshold. After verifying that the operating mode still includes atrial event sensing, control circuitry 206 can return to block 802 to continue determining the A3 amplitude metric used to update the target high A4 sensing threshold amplitude.

[0225] Typically, the high A4 sensing threshold amplitude will be larger than the A3 event amplitude because it is set based on a combination of the A3 amplitude metric and a multiple of the low A4 sensing threshold amplitude. Setting the high A4 sensing threshold amplitude in this way avoids oversensing of A3 events during the A3 window. However, as heart rate increases and the A3 and A4 event signals become fused, the fused A3 / A4 event signal may cross the high A4 sensing threshold amplitude to properly sense the A4 event. By adjusting the high A4 sensing threshold amplitude less than the low A4 sensing threshold amplitude, oversensing of A3 events is avoided, while allowing sensing of the duration of the fused A3 / A4 event signal within the A3 window. For example, adjusting the maximum and minimum thresholds of the counter can be set to limit the adjustment to approximately 0.1 m / sec per minute. 2 The high A4 sensing threshold amplitude.

[0226] In the illustrative example disclosed herein, control circuitry 206 determines an A4 sensing control parameter metric from motion sensor signals over a non-overlapping set of N consecutive ventricular cycles. After each set of N ventricular cycles (or, in the case of a high A4 sensing threshold amplitude, after the adjustment counter reaches the threshold), control circuitry 206 determines an adjustment (incremental, decremental, or no adjustment) to the A4 sensing control parameter based on the control parameter metric. However, it should be understood that control circuitry 206 may update the A4 sensing control parameter metric according to other schedules or frequencies, for example, on a beat-by-beat basis or after an overlapping number of N ventricular cycles. For example, the A4 sensing control parameter metric may be updated after every four ventricular cycles based on the most recent eight ventricular cycles. It should be recognized that the A4 sensing control parameter metric may be updated according to various schedules based on various selected numbers of ventricular cycles (e.g., one, two, three, four, five, eight, twelve, sixteen, twenty-four, or any other selected number of cycles).

[0227] Furthermore, it is recognized that the timeline and / or number of ventricular cycles required to update one A4 sensing control parameter metric may differ from the timeline and / or number required to update another A4 sensing control parameter metric. Different control parameter metrics may be updated at different frequencies. (As in combination...) Figure 15 The method described above involves implementing an adjustment counter that tracks the difference between the target's high A4 sensing threshold amplitude and the current high A4 sensing threshold amplitude. This results in the high A4 sensing threshold amplitude being adjusted less frequently than the low A4 sensing threshold amplitude and the A3 window end time. It is understood that various timers and / or counters can be implemented to control the timing and frequency of adjustments to different A4 sensing control parameters.

[0228] The predetermined frequency or number of ventricular cycles at which a given A4 sensing control parameter is adjusted can be fixed or adjustable. For example, if a given A4 sensing control parameter is not adjusted within a threshold time interval (e.g., within a set of a specified number of N ventricular cycles) because it does not meet the adjustment criteria, the number N can be increased, making the determination of the A4 sensing control parameter metric and the A4 sensing control parameter adjustment less frequent. To illustrate, if control circuitry 206 determines that a low A4 sensing threshold amplitude is not adjusted in response to the last six, eight, ten, or other specified number of N ventricular cycles, the number N can be doubled, for example, from eight ventricular cycles to sixteen ventricular cycles. As an example, the A4 sensing control parameter metric determined for adjusting the low A4 sensing threshold amplitude can be determined after every 16 ventricular cycles instead of every 8 ventricular cycles.

[0229] When control circuit 206 determines that the low A4 sensing threshold amplitude has been adjusted twice consecutively (or other specified number of times) after 16 ventricular cycles, the number N can be reduced, for example, back to 8 ventricular cycles, to allow for more frequent adjustments to the low A4 sensing threshold amplitude. In some instances, the number of ventricular cycles used to determine the A4 sensing control parameter metric and adjust the A4 sensing control parameter can be increased one or more times based on the stability of the A4 sensing control parameter, and can be reduced one or more times based on the frequency of adjustments to the A4 sensing control parameter. For example, in Figure 6 At box 304, control circuit 206 can adjust the number N of ventricular cycles based on one or more A4 sense control parameters to measure the frequency of adjustment. Adjustment to a specified number of ventricular cycles allows the current drain of power supply 214 required for motion signal processing and analysis by control circuit 206 to be conserved during periods of stable motion signal and heart rhythm (when frequent adjustments are not required), while providing adjustments at an increased frequency when the motion signal and / or heart rhythm changes due to changes in the patient's condition. Thus, it should be understood, for example, in... Figure 9 Frame 506 Figure 13 The frame 768 and Figure 15 At box 806, when determining whether N ventricular cycles have been reached, control circuit 206 can adjust N (the number of ventricular cycles) used to determine the A4 sensing control parameter metric.

[0230] Among the A4 sensing control parameter measures that can be determined by control circuit 206 for adjusting the A4 sensing control parameters, without any intentional limitation, are applicable cycle count (ventricular cycle including the A4 window), detected A4 count, minimum detected A4 amplitude or other A4 amplitude measure, early A4 count, normal A4 count, A3 window detection count (the number of A4 events sensed during the A3 window), low A3 threshold amplitude, A3 time measure, A4 time measure, target A3 window end time, target A3 amplitude measure, and target A4 high sensing threshold amplitude, all of which are described above in conjunction with the accompanying drawings.

[0231] The A4 sensing control parameter adjustment described herein involves determining A4 sensing control parameter metrics during a ventricular cycle, which may begin with a sensed R wave or a ventricular pacing pulse. In some instances, control circuitry 206 may be configured to determine a first set of A4 sensing control parameter metrics corresponding to a ventricular cycle beginning with a sensed R wave, and a second set of A4 sensing control parameter metrics corresponding to a ventricular cycle beginning with a ventricular pacing pulse. In this way, one set of A4 sensing control parameters can be adjusted for sensing an A4 event following a sensed R wave, and the second set of A4 sensing control parameters can be adjusted for sensing an A4 event following a ventricular pacing pulse. For example, the end time of the post-sensing A3 window can be adjusted based on an A3 time metric and an A4 time metric determined after a sensed R wave. This end time of the post-sensing A3 window can be applied after the sensed R wave. The end time of the post-pacing A3 window can be adjusted based on an A3 time metric and an A4 time metric determined after and applied after a ventricular pacing pulse. Similarly, the amplitudes of the high A4 sensing threshold after pacing and after sensing, as well as the amplitudes of the low A4 sensing threshold after pacing and after sensing, can be adjusted separately based on the corresponding pacing-after A4 sensing control parameter metric and sensing-after A4 sensing control parameter metric.

[0232] The examples presented herein demonstrate that an A4 sensing control parameter adjustment method can be performed during a specified pacing operation mode to control A4 sensing during atrial-tracking ventricular pacing modes. In some cases, the telemetry circuitry 208 of pacemaker 14 may receive or transmit telemetry signals or perform other temporary operations. During at least some temporary operations, for example, when adjusting the A4 sensing control parameter during a temporary operation might interfere with or confuse the temporary operation or other functions of pacemaker 14, the determination of A4 sensing control parameter measurement and adjustment can be paused via control circuitry 206.

[0233] Furthermore, it is anticipated that the A4 sensing control parameters can be adjusted by the medical device during and when used in sensing operation modes that do not necessarily include ventricular pacing. A4 sensing can be used to monitor atrial rate or rhythm, differentiate between ventricular tachyarrhythmias and supraventricular tachyarrhythmias, or in other applications requiring atrial systolic event sensing but not necessarily including ventricular pacing. Therefore, the techniques disclosed herein are not limited to implementations used in conjunction with ventricular pacing or in ventricular pacemakers or other medical devices that must include ventricular pacing operation modes.

[0234] Figure 16 This is a flowchart 900 of a method, according to another example, that can be executed by control circuitry 206 to adjust the amplitude of a high A4 sensing threshold. When control circuitry 206 operates in an operating mode that includes atrial event sensing, as determined at block 902, an A4 sensing control parameter metric can be determined from the motion signal for adjusting the amplitude of the high A4 sensing threshold. At block 904, control circuitry 206 determines the amplitude of the A3 event. Figure 16 In this method, the control circuit 206 can adjust the amplitude of the high A4 sensing threshold during the scheduled adjustment time interval, rather than based on, as in combination with... Figure 15 The aforementioned adjustment counter. Thus, control circuit 206 can determine the A3 event amplitude for each ventricular cycle until the adjustment time interval expires (at box 908).

[0235] During the adjustment time interval (which in various instances can be minutes, hours, or days), the A3 event amplitude can be determined at box 904 for each ventricular cycle with an A3 window by determining the maximum amplitude of the motion sensor signal during the A3 window. In some instances, the A3 event amplitude is determined for a given ventricular cycle only when the A3 window reaches its end time. In other instances, the A3 event amplitude is determined for all ventricular cycles in which the A3 window is initiated. (The above is combined...) Figure 12 It may be necessary for the maximum amplitude of the motion signal to be greater than the low A3 threshold in order to be identified as the A3 event amplitude.

[0236] At block 906, control circuitry 206 can store the A3 event amplitude in histogram bins allocated in memory 210. In some instances, the A3 event amplitude is stored in two different histograms, each with multiple histogram bins assigned to different amplitude values ​​or ranges. All determined A3 event amplitudes can be stored in one histogram, independent of the timing of A4 event detection. In the second histogram, A3 event amplitudes determined only for ventricular cycles containing normal A4 event detection can be stored. When an A4 event is sensed during the A4 window or at least a threshold time interval later than the end of the A3 window, the ventricular cycle can be determined as a “normal” A4 event cycle because the A4 event was not sensed early in or during the A3 window. During these normal A4 event cycles, the maximum amplitude during the A3 window is most likely an A3 event, rather than a fused A3 / A4 event, and therefore represents the true A3 event amplitude with a high degree of confidence. Therefore, a histogram could be a normal A4 event histogram that is assigned to store the amplitude of A3 events for all ventricular cycles, all of which have normal A4 events sensed at least a threshold time interval (e.g., 0-100 milliseconds) later than the end of the A3 window.

[0237] In another example, within a histogram, control circuitry 206 may store only the amplitude of A3 events determined to occur within a predetermined range of the A3 time metric or within a currently determined median (or similar metric) of the A3 event time determined over an adjustment time interval. For example, when the maximum amplitude during the A3 window is within 10 to 20 milliseconds of the median A3 event time, control circuitry 206 may store that maximum amplitude in the corresponding bin of the histogram. In this way, a portion of the A3 event amplitude can be identified for determining the A3 amplitude metric, where each A3 event amplitude is determined as the maximum amplitude of a motion signal during the A3 window and within a threshold time range of the A3 time metric. This A3 amplitude metric, based on the maximum amplitude within the threshold time range of the A3 time metric, is more likely to correspond to a true A3 event.

[0238] At block 908, control circuitry 206 can determine when the scheduled adjustment time interval for adjusting the high A4 sensing threshold amplitude expires. In some instances, the high A4 sensing threshold amplitude is adjusted every 24 hours. In other instances, the scheduled adjustment time may be more or less frequent and may be set to a variable time interval by control circuitry 206 based on time since pacemaker 14 implantation, relative changes in A3 event amplitude, A4 event amplitude, changes in the target high A4 threshold, the difference between the target high A4 threshold and the current setting of the high A4 threshold, or other factors. If the scheduled adjustment time interval for adjusting the high A4 sensing threshold has not expired, control circuitry 206 returns to block 902 to continue accumulating A3 event amplitudes for use in the histogram stored in memory 210.

[0239] If the operating mode has changed from atrial event sensing mode, control circuitry 206 can wait until atrial event sensing mode resumes. A3 event amplitudes accumulated in memory 210 can be retained until the scheduled time for adjusting the high A4 sensing threshold arrives, where additional A3 event amplitudes are added to the histogram in memory 210 whenever the operating mode includes atrial event sensing. Alternatively, if the operating mode changes to a mode without atrial event sensing, A3 event amplitudes can be cleared from memory 210. Collection of A3 event amplitudes in memory 210 can resume the next time control circuitry 206 begins operating in an operating mode that includes atrial event sensing.

[0240] When control circuit 206 determines at block 908 that it is time to adjust the high A4 sensing threshold amplitude, control circuit 206 can determine at block 909 whether the histogram is sufficiently filled. In some cases, there may be insufficient ventricular cycle lengths with normal A4 event detection, resulting in a low or sparse distribution of the A3 event amplitude in the histogram for normal A4 event cycles. It may be necessary to store a threshold number of A3 event amplitudes in the normal A4 event histogram to utilize the accumulated data to determine the A3 amplitude metric as described below. When control circuit 206 determines at block 909 that fewer than a threshold number of ventricular cycles are identified as normal A4 event ventricular cycles, control circuit 206 can stop determining the A3 amplitude metric. When insufficient data exists, for example, for normal A4 event ventricular cycles, less than the stored threshold number of A3 event amplitudes, control circuit 206 can return to block 902 to continue accumulating A3 event amplitudes without adjusting the high A4 sensing threshold amplitude. In various instances, the high A4 sensing threshold amplitude can be adjusted when the next adjustment time interval expires, or when the amplitude of the A3 events of the threshold number fills the normal A4 event histogram, or based on the first occurrence.

[0241] In some instances, the limited number of A3 event amplitudes stored in a normal A4 event histogram may be due to oversensing of A3 events. As mentioned above, for example, combined with Figure 10 When an A3 event is oversensed as an A4 event, for example, because the high A4 sensing threshold amplitude is set too low, the A4 window is not activated. This excludes the determination and storage of the A3 event amplitude in the normal A4 event histogram. Thus, control circuit 206 can determine at box 916 whether the A3 event oversensing criterion is met in response to a number of A3 event amplitudes less than the threshold number stored in the normal A4 event histogram (as determined at box 909).

[0242] The A3 event oversensing criterion can be met at box 916 when the histogram stores a number of A3 event amplitudes greater than a threshold for all ventricular cycles but a number of amplitudes less than a threshold for only normal A4 event ventricular cycles. In other instances, control circuitry 206 can track the number of applicable cycles (the number of cycles with A4 windows starting after the A3 window expires). The A3 event oversensing criterion can be met at box 916 when fewer than a threshold number of ventricular cycles are applicable cycles within a scheduled adjustment time interval. In other instances, control circuitry 206 can determine the early A4 count (the number of A4 events sensed within a threshold time interval after the ventricular window ends) and / or the A3 window detection count within the adjustment time interval. The A3 event oversensing criterion can be met at box 916 when either or the sum of these A3 window and early A4 counts is greater than a threshold. For example, control circuitry 206 can compare the early A4 count, the A3 window detection count, or the sum of these two counts with the applicable cycle count or with the detected A4 count determined within the adjustment time interval. When the ratio or difference between the A3 window detection count, the early A4 count, or the sum of both, and the applicable cycle count (or the detected A4 count) is greater than a threshold, the control circuit 206 can determine at block 916 that the A3 event oversensing criterion is met.

[0243] If the A3 event oversensing criterion is not met (the "No" branch of block 916), control circuitry 206 can return to block 902. When the A3 event oversensing criterion is met, control circuitry 206 can increase the high A4 sensing threshold at block 918, for example, by a predetermined increment. By increasing the magnitude of the high A4 sensing threshold, oversensing of A3 events can be reduced or avoided, allowing the histogram storing A3 event amplitudes determined from normal A4 event ventricular cycles to be adequately filled within the next scheduled adjustment time interval. In some examples, control circuitry 206 increases the high A4 threshold magnitude (as determined at block 909) at block 918 in response to a number of A3 event amplitudes less than a threshold stored in the normal A4 event histogram, without needing to meet any additional A3 event oversensing criterion at block 916.

[0244] When the time for adjusting the high A4 sensing threshold is reached at block 908 and the histogram is sufficiently filled (block 909), control circuitry 206 determines an A3 amplitude metric at block 910 based on the A3 event amplitude stored in memory 210. In some instances, the A3 amplitude metric may be a predetermined percentile of the A3 event amplitude stored for a ventricular cycle containing normal A4 event detection. For example, the A3 amplitude metric may be determined as the 80th, 85th, 90th, or 95th percentile of the A3 event amplitude determined from a ventricular cycle containing normal A4 event detection.

[0245] At block 912, control circuitry 206 can determine the target high A4 sensing threshold amplitude. The target high A4 sensing threshold amplitude can be determined based on an A3 amplitude metric. In other instances, the target high A4 sensing threshold amplitude is determined based on the A3 amplitude metric and all accumulated A3 event amplitudes stored in memory 210 during the scheduled adjustment period, regardless of whether the A4 event is detected early or late in the relevant ventricular cycle. In one instance, the target high A4 sensing threshold amplitude is determined as a predetermined percentile of all A3 event amplitudes greater than the A3 amplitude metric. The following is in conjunction with… Figure 17 An exemplary method is described for determining the A3 amplitude metric and the target high A4 sensing threshold amplitude based on a histogram of the A3 event amplitude.

[0246] At block 914, control circuitry 206 adjusts the high A4 sensing threshold amplitude toward a target high A4 threshold. In some instances, control circuitry 206 adjusts the high A4 sensing threshold amplitude directly to the target value defined at block 912. In other instances, control circuitry 206 may adjust the high A4 sensing threshold amplitude toward the target value by a predetermined adjustment value, which may be an increment or decrement toward the target value as needed. If the current high A4 sensing threshold amplitude is equal to the target value, no adjustment is made.

[0247] The adjustment value, applied incrementally or subtractively to the current high A4 sensing threshold amplitude to adjust towards the target high A4 sensing threshold, can be fixed or variable. For example, the adjustment value can be fixed at 0.2 m / s. 2 0.4m / s 2 0.6m / s 2 0.8m / s 2 Or other selected values. In other instances, the adjustment value can be variable. For example, the adjustment increment / decrement can be set by control circuitry 206 based on the time since pacemaker 14 implantation. In the initial days, weeks, or months after implantation, the adjustment increment / decrement can be set larger to allow adjustments toward the target high A4 threshold to occur more quickly. The magnitude of the adjustment increment / decrement can be gradually or incrementally reduced after a specified time since pacemaker implantation (e.g., after a week, a month, or other selected time period). In other instances, the adjustment value of the increment / decrement can be variably adjusted by control circuitry 206 based on the difference between the target high A4 threshold and the current setting of the high A4 threshold. In other instances, the adjustment value can be adjusted based on a scheduled adjustment time interval that determines the frequency of high A4 sensing threshold adjustments. For example, a smaller increment / decrement can be used when the scheduled adjustment time interval is relatively short (e.g., less than every 12 hours), and a larger increment / decrement can be used when the scheduled adjustment time interval is relatively long (e.g., every 12 hours or longer).

[0248] After making appropriate adjustments at box 914, control circuit 206 can clear the histogram box (or a portion thereof) and return to box 902 to restart accumulating A3 event amplitudes when the operating mode includes atrial event sensing. Control circuit 206 can schedule the next adjustment of the high A4 sensing threshold amplitude, for example, at a fixed time interval or an adjustable time interval. As described above, control circuit 206 can schedule the time for adjusting the high A4 threshold amplitude according to a variable adjustment time interval, which can be set based on the difference between the current target high A4 sensing threshold amplitude and a previously determined target high A4 sensing threshold amplitude, the time since pacemaker 14 implantation, the difference between the target high A4 sensing threshold amplitude and the current setting of the high A4 sensing threshold amplitude, or other factors.

[0249] The histogram storing A3 event amplitudes can be completely cleared after adjusting the high A4 sensing threshold amplitude or on a first-in, first-out basis, so that a portion of the most recent A3 event amplitude can be retained in the histogram bin and included in the next determination of the A3 amplitude metric and the target high A4 sensing threshold amplitude. For example, the A3 event amplitude histogram bin can store data over a first time interval, such as 24 hours, but the high A4 sensing threshold can be adjusted after a second time interval, which can be shorter than the first time interval, such as every 12 hours based on the most recent 24 hours of data. After adjusting the high A4 sensing threshold amplitude at box 914, the oldest 12 hours of A3 event amplitude data can be cleared, and the most recent 12 hours of A3 event amplitude data can be saved in the histogram and compiled together with the new data for the next 12 hours. Alternatively, multiple histograms can be allocated in memory 210 to allow data to be stored in histogram form over different overlapping time periods. Storing A3 event amplitude data over a relatively long period can represent significant variations in heart rate, physical activity, or other factors that can affect the timing of A4 events and / or motion signal amplitude during the ventricular cycle. Adjusting the high A4 sensing threshold amplitude based on a longer data collection interval with a relatively shorter adjustment interval allows the threshold amplitude to more frequently and appropriately track any changes in motion signal amplitude.

[0250] Figure 17 Figure 950 shows histograms 952 and 962 of the A3 event amplitude based on some examples. The A3 event amplitude can be determined by control circuit 206 and stored in memory 210 for adjusting the high A4 sensing threshold amplitude. The A3 event amplitude is plotted along the horizontal axis as a measure of m / s. 2 The measured speed is 0.1 m / s. 2 The acceleration within the range of the box. The frequency of occurrence of each amplitude box range is plotted along the y-axis.

[0251] Top histogram 952 is a histogram of A3 event amplitudes determined only from ventricular cycles containing normal A4 event detection. In these ventricular cycles, an A4 event is detected in response to a motion signal crossing a low A4 sensing threshold amplitude (not crossing a high A4 sensing threshold amplitude during the A3 window) later than a threshold time interval (e.g., 0 ms to 100 ms) after the end of the A3 window. In some instances, all ventricular cycles with A4 events sensed at least 50 ms later than the end of the A3 window are classified by control circuitry 206 as normal A4 event cycles. In these ventricular cycles, the determined A3 event amplitude is less likely to be affected by A4 events (which occur later in the ventricular cycle than A3 events) and is more likely to correspond to a true A3 event not fused with an A4 event.

[0252] Control circuit 206 can Figure 16 Box 910 defines the A3 amplitude metric as a predetermined percentile of the A3 event amplitude contained in the normal A4 event histogram 952. In the illustrated example, the A3 amplitude metric is defined as the 95th percentile of the A3 event amplitude stored in the normal A4 event histogram 952. Line 954 marks the 95th percentile of the A3 event amplitude contained in the histogram 952 and is referred to hereinafter as the A3 amplitude metric 954 of this illustrative example. In some examples, control circuitry 206 may set a target high A4 sensing threshold amplitude based on the A3 amplitude metric 954, for example, by setting it to a percentage greater than the A3 amplitude metric 954, or by adding an offset to the A3 amplitude metric 954 and / or adding a low A4 sensing threshold amplitude to the value of the A3 amplitude metric 954. For example, the added offset could be 0.2 m / s. 2 0.3m / s 2 0.5m / s 2 0.8m / s 2 or 1.0m / s 2 During atrial-tracking ventricular pacing mode, all or most of the peak amplitudes of motion sensor signals represented in the normal A4 event histogram 952 should not be detected as A4 events by the atrial event detector circuit 240. Therefore, the control circuit 206 can be configured to set the high A4 sensing threshold amplitude to be equal to or higher than the value of the A3 amplitude metric 954 to avoid oversensing A3 events.

[0253] The second bottom histogram 962 represents all A3 event amplitudes determined within a predetermined time period for accumulating histogram data. Histogram 962 can therefore include A3 event amplitudes determined from the ventricular cycle, where A4 events are detected during the A3 window, A4 events are detected early after the end of the A3 window, and “normal” A4 events are detected at a threshold time interval after the end of the A3 window (as well as ventricular cycles where A4 events may not have been detected). As observed by histograms 952 and 962, when all A3 event amplitudes are stored in histogram 962, a higher frequency of higher A3 event amplitudes larger than A3 amplitude metric 954 may occur, presumably due to the influence of earlier A4 events and A4 events sensed during the A3 window period that contributes to the A3 event amplitude. Therefore, higher A3 event amplitudes larger than A3 amplitude metric 954 included in histogram 962 can represent ventricular cycles with fused A3 / A4 events occurring during or near the end of the A3 window.

[0254] Control circuit 206 can be configured to determine the magnitude of A3 events greater than A3 magnitude 954 based on the magnitude of A3 events stored in histogram 962. Figure 16The target high A4 sensing threshold amplitude 964 is located at box 912. A3 event amplitudes above the A3 amplitude metric are displayed on range 966. In the illustrative example shown, the target high A4 sensing threshold amplitude 964 is set as a percentile of the A3 event amplitudes on range 966. For example, the target high A4 sensing threshold amplitude 964 can be set to the 10th, 20th, 25th, 30th, or 35th percentile of A3 event amplitudes greater than the A3 amplitude metric 954, as shown by range 966. In some cases, an offset and / or a lower A4 sensing threshold amplitude can be added to the value of a predetermined percentile 964 to determine the target high A4 sensing threshold amplitude. In other instances, the target high A4 sensing threshold amplitude can be set based on the percentiles of all amplitudes stored in histogram 962. For example, control circuitry 206 may set the target high A4 sensing threshold amplitude to a predetermined percentile of all A3 event amplitudes stored in histogram 962, such as the 60th, 65th, 70th, or 75th percentile, and may optionally add an offset and / or a low A4 sensing threshold amplitude to the value of the specified percentile amplitude. Thus, in some instances, one of histograms 952 or 962 may be populated to determine the target high A4 sensing threshold amplitude, but not both simultaneously. In other instances, both are populated as described above to determine an A3 amplitude measure from a first portion of the A3 event amplitude (e.g., those identified from normal A4 event ventricular cycles), and to determine the target high A4 sensing threshold amplitude based on a second portion of the A3 event amplitude (e.g., those greater than the A3 amplitude measure).

[0255] Figure 18This is a flowchart 1100 of a method for adjusting selected atrial event sensing control parameters according to an example. The initial value of the A4 sensing control parameter can be programmed by a clinician or can be automatically selected by control circuitry 206. For example, control circuitry 206 can determine the initial value of one or more A4 sensing control parameters, such as the A3 window end time and a first higher A4 sensing threshold amplitude value and a second lower A4 sensing threshold amplitude value, at block 1101 by determining an A4 sensing control parameter metric over an extended time interval or number of ventricular cycles when the pacemaker 14 is initially implanted. The initial value can be selected by determining the A4 sensing control parameter metric during a non-atrial tracking ventricular pacing mode that includes atrial sensing using motion sensor signals (e.g., VDI mode as shown in block 1101). This pacing mode allows analysis of motion sensor signal characteristics to determine the control parameter metric over a relatively extended time period (e.g., one minute, two minutes, or five minutes), thereby selecting an appropriate initial value for the A4 sensing control parameter for the patient. Techniques that can be used to select a value for the start-up control parameter at box 1101 are generally disclosed in U.S. Patent Application No. 62 / 776,027, provisionally filed December 6, 2018, and the corresponding non-provisional U.S. Patent Application No. 16 / 703,047, filed December 4, 2019 (now published as U.S. Patent Application Publication No. 2020 / 0179707 (Splett et al.)), and in U.S. Patent Application No. 62 / 776,034, provisionally filed December 6, 2018, and the corresponding non-provisional U.S. Patent Application No. 16 / 703,320, filed December 4, 2019 (now published as U.S. Patent Publication No. 2020 / 0179708 (Splett et al.)), all of which are incorporated herein by reference in their entirety.

[0256] The initial value of the A4 sensing control parameter can be based on motion sensor signal characteristics determined over a relatively long period of time compared to the N ventricular cycles used to adjust the A4 sensing control parameter using the techniques disclosed herein. For example, the motion sensor signal characteristics used to set the initial value may have been several minutes or even hours ago when the initial value is selected. Furthermore, when the initial value is selected during VDI pacing mode, the A4 event will not continue to occur during the A4 window. Thus, after selecting the initial value at box 1101, before the control circuit 206 switches from VDI pacing mode to permanent atrial tracking ventricular pacing mode (e.g., VDD pacing mode), the control circuit 206 can use the adjustment techniques disclosed herein to adjust the initial value of one or more A4 sensing control parameters within a relatively short time interval (e.g., one to two minutes) or within one or more sets of N ventricular cycles. In this way, the A4 sensing control parameter, which is set as an initial value based on “historical” data that may be several minutes or hours ago, can be further optimized to an operating value based on the most recently determined, simultaneously determined A4 sensing control parameter metric. Just before switching to permanent VDD pacing mode to deliver atrial-synchronous ventricular pacing, adjust the starting value to the working value to facilitate optimal A4 sensing control parameter settings when switching to permanent VDD pacing mode.

[0257] After selecting initial values ​​for one or more A4 sensing control parameters at box 1101, control circuitry 206 proceeds to boxes 1102 and 1104 to adjust the high A4 sensing threshold amplitude and the A3 window end time, respectively, from their initial values. It should be understood that boxes 1102 and 1104 can operate in parallel, simultaneously. The determination of the A4 sensing control parameter metrics required to determine the adjustment of the high A4 sensing threshold amplitude and the A3 window end time can be entirely determined within every N ventricular cycles, and subsequently, the high A4 sensing threshold amplitude and the A3 window end time are adjusted at the end of every N ventricular cycles.

[0258] At boxes 1102 and 1104, control circuitry 206 can continue operating in non-atrial tracking ventricular pacing modes (e.g., VDI pacing mode) for a predetermined time interval, such as one minute, two minutes, three minutes, or other relatively short time intervals or the number of ventricular cycles of choice, to adjust the high A4 sensing threshold amplitude and A3 window end time from initial values ​​determined during a relatively long setup process to current relevant values, which may be referred to as the "adjusted starting values". At box 1102, control circuitry 206 determines the A4 sensing control parameter metric and uses the above-mentioned combination Figure 12 and 15The described technique is used to adjust the initial value of the high A4 sensing threshold amplitude. For example, the A3 amplitude measure can be determined as the median maximum amplitude occurring during an A3 window over N consecutive ventricular cycles. The high A4 sensing threshold amplitude value can be adjusted after every eight ventricular cycles based on the fourth highest A3 event amplitude during those eight ventricular cycles. During this process of adjusting the high A4 sensing threshold amplitude from the initial value during VDI pacing mode, the high A4 sensing threshold amplitude can be adjusted over N ventricular cycles without having to combine... Figure 15 The described waiting period is until the adjustment threshold is reached.

[0259] Control circuit 206 can determine a target value for the high A4 sensing threshold amplitude based on the A3 amplitude metric. The initial value of the high A4 sensing threshold amplitude determined during the setup process at block 1101 can be adjusted towards the target value by a predetermined increment or decrement (or as combined) every N ventricular cycles. Figure 15 (As described, controlled by an adjustment counter). When operating in VDI pacing mode, this process of adjusting the high A4 sensing threshold amplitude can be performed for adjustment time intervals (e.g., for one minute, two minutes, five minutes, or other selected time intervals). Control circuitry 206 can store the adjusted high A4 sensing threshold amplitude during temporary VDI pacing mode without applying the high A4 sensing threshold amplitude for A4 event sensing during VDI pacing mode. The adjusted initial high A4 sensing threshold amplitude value may not take effect until control circuitry 206 switches to atrial-tracking ventricular pacing mode, so that A4 events are not detected by atrial event detector circuitry 240, until all A4 sensing control parameters are adjusted from initial values ​​to operating values.

[0260] At box 1104, control circuitry 206 can determine the A3 event time, for example, the latest low A3 threshold amplitude of the motion sensor signal crossing during the A3 window, which can be a negative crossing (set to end at the start A3 window end time). The A3 event time can be determined for N ventricular cycles. Control circuitry 206 can determine the A3 time metric from the A3 event time and the target A3 window end time, as described above. Figure 12 and 13 As described. During VDI pacing mode, the target A3 window end time can be based solely on the A3 time metric instead of the A4 time metric, because a reliable A4 time metric may be unknown during non-atrial tracking ventricular pacing mode. At box 1104, the initial value of the A3 window end time set in box 1101 can be adjusted based on the A3 time metric and the target A3 window end time per N ventricular cycles.

[0261] The end time of the A3 window established during the setup procedure at box 1101 can be based on the most recent crossover of a test value with a low A3 threshold amplitude. The test value can be set to a predetermined, fixed, or default value, such as 0.9 m / s. 2 However, the low A3 threshold amplitude used at box 1104 to determine the A3 event time is better suited to the patient when it is set by control circuitry 206 as a percentage (e.g., 75%) of the initial value of the low A4 sensing threshold amplitude determined during the setup procedure executed at box 1101, rather than the default value. Since the initial low A4 sensing threshold amplitude determined during the setup process at box 1101 is more suitable for the patient, the low A3 threshold amplitude set at box 1104 is also more suitable for the patient than the default value. At box 1104, when determining the A3 event time and A3 time metric to adjust the A3 window end time to the currently relevant value, a low A3 threshold amplitude set as a percentage of the initial low A4 sensing threshold amplitude may be a more appropriate threshold for a given patient.

[0262] For example, if the initial value of the low A4 sensing threshold amplitude is set to 2.5 m / s at the end of the setup process at box 1101. 2 The low A3 threshold amplitude, which is set to 75% of the initial low A4 sensing threshold amplitude, is 1.9 m / s. 2 Instead of the default 0.9m / s 2 Threshold. This more relevant, patient-tailored low A3 threshold amplitude can be used during the A3 window over N ventricular cycles at box 1104 to detect the latest low A3 threshold crossing time and adjust the A3 window end time. In this way, the A3 window end time at box 1104 is better optimized for the patient from its initial value. At box 1104, the A3 window end time can be adjusted for 2 minutes (or other adjustment intervals) every 8th ventricular cycle or other selected number of ventricular cycles to reach the adjusted initial A3 window end time, which takes effect as the operational A3 window end time when switching to an atrial-tracking ventricular pacing mode (e.g., VDD pacing mode).

[0263] After adjusting the start A3 window end time and / or start high A4 sensing threshold amplitude to the operating values ​​during the temporary VDI pacing mode at boxes 1102 and 1104, control circuitry 206 can switch to a temporary atrial tracking pacing mode (e.g., VDD pacing mode) at box 1106. The operating values ​​of the early A4 sensing threshold amplitude and A3 window end value can take effect when switching to temporary VDD pacing mode.

[0264] The low A4 sensing threshold amplitude can be adjusted at box 1108 from its initial value (selected during the setup process performed at box 1101). During this temporary VDD pacing mode, the above can be used in combination. Figure 7-11 The technique described in general is based on adjusting the low A4 sensing threshold amplitude from its initial value using A4 sensing control parameter metrics determined every N ventricular cycles. With the concurrently optimized A3 window end time determined at box 1104 now in effect, the adjustment of the low A4 sensing threshold amplitude during temporary VDD pacing mode is expected to tune the low A4 sensing threshold amplitude to an optimized value based on the A4 sensing control parameter metrics determined during temporary VDD pacing mode. For example, at box 1108, the early A4 count, applicable cycle count, detected A4 count, and A3 window detection count can be determined by control circuitry 206 for adjusting the low A4 sensing threshold amplitude. In practice, these A4 sensing control parameter metrics are determined using the operating A3 window end time and operating high A4 threshold amplitude determined at boxes 1104 and 1102, respectively.

[0265] At block 1110, control circuitry 206 can determine the rate smoothing interval based on one or more ventricular cycle lengths occurring during the temporary VDD pacing mode. In some instances, the initial rate smoothing interval is set to a programmed lower rate interval. At block 1110, control circuitry 206 can determine the median ventricular cycle length over N ventricular cycles (e.g., eight ventricular cycles). The adjusted rate smoothing interval can be set by control circuitry 206 to a predetermined interval longer than the median ventricular cycle length (e.g., 100 to 150 milliseconds longer than the median ventricular cycle length). At block 1110, during the temporary VDD pacing mode, the rate smoothing interval can be updated every N ventricular cycles for a predetermined time interval, such as two minutes.

[0266] Control circuit 206 can enable rate smoothing during temporary VDD mode to facilitate and maintain atrioventricular synchronization while determining an A4 sensing control parameter metric for adjusting the low A4 sensing threshold. In some instances, the rate smoothing interval can be adjusted at a higher frequency than the low A4 sensing threshold during temporary VDD pacing mode at block 1110. For example, the median or fourth fastest ventricular cycle length can be determined from the most recent eight ventricular cycles on a rolling basis after each ventricular cycle. The rate smoothing interval can be set by control circuit 206 to the updated median ventricular cycle length plus a specified offset. In some instances, control circuit 206 can update the rate smoothing interval with each ventricular cycle, such that the VV pacing interval is set to the updated rate smoothing interval on a beat-by-beat basis. If the VV pacing interval set as the rate smoothing interval expires, it is desirable to maintain atrioventricular synchronization at appropriate timing within the A4 window covering the A4 event signal. By maintaining atrioventricular synchronization during the temporary VDD pacing mode, the A4 sensing control parameter metric determined at box 1108 for adjusting the low A4 sensing threshold amplitude will enable control circuitry 206 to adjust the low A4 sensing threshold amplitude to an optimal value for the patient.

[0267] Thus, it should be understood that blocks 1108 and 1110 can be executed in simultaneous parallel operation. For example, every N ventricular cycles, control circuit 206 can determine the A4 sensing control parameter metric required to determine the adjustment of the low A4 sensing threshold amplitude. Simultaneously, for each ventricular cycle, control circuit 206 can determine an updated ventricular cycle length metric for adjusting the rate smoothing interval as frequently as per ventricular cycle. The final adjusted values ​​of the A4 sensing control parameters determined at blocks 1102, 1104, and / or 1108, and the most recently updated rate smoothing interval, can both take effect as operating values ​​when switching to permanent VDD pacing mode at block 1112.

[0268] After adjusting the initial value of the low A4 sensing threshold amplitude and adjusting the rate smoothing interval over predetermined time intervals or ventricular cycle counts during temporary VDD pacing mode, control circuitry 206 can switch at block 1112 to a permanent atrial-tracking ventricular pacing mode, such as VDD pacing mode, where the operating values ​​of the A4 sensing control parameters and the adjusted rate smoothing interval are effective. In this way, the initial value of the A4 sensing control parameters, which can be programmed by the user or determined over a relatively long period during the setup process at block 1101, can be adjusted to a more relevant operating value based on newer motion sensor signal amplitude and timing characteristics used to determine the A4 sensing control parameter metric. The rate smoothing interval is set to a currently relevant value based on the current ventricular rate. These operating values ​​of the A4 sensing control parameter metric and the rate smoothing interval take effect when switching to VDD pacing mode to provide optimized atrial-tracking ventricular pacing.

[0269] The following exemplary terms are consistent with the technology described in this disclosure.

[0270] Clause 1: A method comprising: generating a motion signal via a motion sensor; setting a plurality of sensing control parameters; sensing a first atrial event from the motion signal during a plurality of ventricular cycles according to the sensing control parameters; determining characteristics of the motion signal for each ventricular cycle for at least a portion of the plurality of ventricular cycles; determining a metric of the motion signal based on the determined characteristics; adjusting the sensing control parameters among the plurality of sensing control parameters based on the metric; sensing a second atrial event from the motion signal according to the adjusted sensing control parameters; and generating an atrial sensing event signal in response to sensing the second atrial event.

[0271] Clause 2: The method according to Clause 1, wherein: setting the plurality of control parameters includes: setting a ventricular diastolic event window end time; setting a high sensing threshold amplitude extending to the event window end time; and setting a low sensing threshold amplitude starting from the end time of the ventricular diastolic event window after the high sensing threshold amplitude; sensing the first atrial event during the plurality of ventricular cycles includes: sensing each of the first atrial events in response to the earliest crossing of a motion signal of one of the high sensing threshold amplitude and the low sensing threshold amplitude during a corresponding ventricular cycle in the plurality of ventricular cycles; and adjusting the sensing control parameters includes adjusting at least one of the ventricular diastolic event window end time, the high sensing threshold amplitude, or the low sensing threshold amplitude.

[0272] Clause 3: The method according to Clause 2 includes: determining the feature by determining the time of each first atrial event sensed during the plurality of ventricular cycles; and determining the metric based on the determined time of each first atrial event sensed during the plurality of ventricular cycles by determining at least one of the following: an early atrial event count by counting each first atrial event sensed after the end time of the ventricular diastolic event window and before a threshold time interval; a normal atrial event count by counting each first atrial event sensed at or after the early event threshold time interval; and a ventricular diastolic window atrial event count by counting each first atrial event sensed before the end time of the ventricular diastolic event window.

[0273] Clause 4: The method according to Clause 3 includes: determining, at least based on the early atrial event count, that the ventricular diastolic event oversensing criteria are met; and, in response to meeting the ventricular diastolic event oversensing criteria, adjusting the sensing control parameters based on the early atrial event count by increasing the amplitude of the low sensing threshold.

[0274] Clause 5: The method according to Clause 3 or 4 includes: determining that a conventional atrial event sensing criterion is met based at least on a normal atrial event count; and adjusting the sensing control parameter based on the normal atrial event count by increasing the low sensing threshold amplitude in response to meeting the conventional atrial event sensing criterion.

[0275] Clause 6: The method according to any one of Clauses 3 to 5 includes: determining, at least based on the normal atrial event count, that a criterion for insufficient atrial event sensing is met; and adjusting the sensing control parameter based on the normal atrial event count by reducing the magnitude of the low sensing threshold in response to meeting the criterion for insufficient atrial event sensing.

[0276] Clause 7: The method according to any one of Clauses 2 to 6, comprising: determining the feature by determining the maximum amplitude of the motion signal after the end time of the ventricular diastolic event window for each of the plurality of ventricular cycles, the maximum amplitude being longer than the end time of the ventricular diastolic event window; determining the metric by determining the minimum amplitude among the maximum amplitudes; and adjusting the sensing control parameter by adjusting the low sensing threshold amplitude based on the minimum amplitude among the maximum amplitudes.

[0277] Clause 8: The method according to any one of Clauses 2 to 7, comprising: determining the feature by determining the most recent crossing time of a threshold amplitude of a ventricular diastolic event occurring before the end time of the ventricular diastolic event window; determining the metric by determining the ventricular diastolic event time based on the determined most recent crossing time; and adjusting the sensing control parameter by adjusting the end time of the ventricular diastolic event window based on the ventricular diastolic event time.

[0278] Clause 9: The method described in Clause 8 includes setting the ventricular diastolic event threshold amplitude based on the low sensing threshold amplitude.

[0279] Clause 10: The method according to Clause 8 or 9 includes: determining the feature by determining the earliest crossing time of the low sensing threshold amplitude; determining the metric by determining the atrial event time based on the determined earliest crossing time; and adjusting the ventricular diastolic event window end time based on the ventricular diastolic event time and the atrial event time.

[0280] Clause 11: The method according to any one of Clauses 1 to 10, comprising: determining the feature by determining the maximum amplitude of the motion signal prior to the end time of the ventricular diastolic event window; determining the metric by determining the ventricular diastolic event amplitude based on the determined maximum amplitude; and adjusting the sensing control parameter by adjusting the high sensing threshold amplitude based on the ventricular diastolic event amplitude and the low sensing threshold amplitude.

[0281] Clause 12: The method according to Clause 11 includes: determining a target high threshold amplitude based on a combination of the ventricular diastolic event amplitude and the low sensing threshold amplitude; determining a difference between the target high threshold amplitude and the high sensing threshold amplitude; adjusting a counter value based on the difference; determining that the counter value is equal to one of a maximum threshold and a minimum threshold; and adjusting the high sensing threshold amplitude toward the target high threshold amplitude in response to the counter value being equal to one of the maximum threshold or the minimum threshold.

[0282] Clause 13: The method according to any one of Clauses 2 to 12, comprising: determining the feature by determining a first plurality of maximum amplitudes of the motion signal prior to the end time of the ventricular diastolic event window for each of the plurality of ventricular cycles having one of the first atrial events sensed after the end time of the ventricular diastolic event window; determining the metric by determining a first percentile of the first plurality of maximum amplitudes; determining a second plurality of maximum amplitudes of the motion signal prior to the end time of the ventricular diastolic event window for each of the plurality of ventricular cycles; determining a target high sensing threshold by determining a second percentile of the second plurality of maximum amplitudes greater than the metric; and adjusting the sensing control parameter by adjusting the high sensing threshold amplitude based on the target high sensing threshold.

[0283] Clause 14: The method according to any one of Clauses 1 to 13, comprising: determining that the atrial sensing event signal is generated before the expiration of the ventricular diastolic event window end time; and in response to determining that the atrial sensing event signal is generated before the expiration of the ventricular diastolic event window end time, extending the ventricular diastolic event window end time until a subsequent ventricular electrical event.

[0284] Clause 15: The method according to any one of Clauses 1 to 14 includes generating a pacing pulse in response to the atrial sensing event signal.

[0285] Clause 16: A non-transitory computer-readable storage medium comprising a set of instructions, which, when executed by control circuitry of a medical device, cause the medical device to: generate a motion signal via a motion sensor; set a plurality of sensing control parameters; sense a first atrial event from the motion signal during a plurality of ventricular cycles according to the sensing control parameters; determine characteristics of the motion signal for each ventricular cycle for at least a portion of the plurality of ventricular cycles; determine a metric of the motion signal based on the determined characteristics; adjust one of the plurality of sensing control parameters based on the metric; sense a second atrial event from the motion signal according to the adjusted sensing control parameters; and generate an atrial sensing event signal in response to sensing the second atrial event.

[0286] It should be understood that, depending on the examples, certain actions or events in any of the methods described herein may be performed in a different order, may be added, combined, or may be omitted entirely (e.g., not all described actions or events are necessary for practicing the methods). Furthermore, in some examples, actions or events may be performed simultaneously rather than sequentially, for example, through multithreaded processing, interrupt handling, or multiple processors. Additionally, for clarity, although some aspects of this disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of this disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0287] In one or more examples, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored on a computer-readable medium in the form of one or more instructions or code and may be executed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store the required program code in the form of instructions or data structures and is accessible by a computer).

[0288] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPLAs), or other equivalent integrated or discrete logic circuit systems. Therefore, the term "processor" as used herein can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, these techniques can be implemented entirely within one or more circuit or logic elements.

[0289] Therefore, specific examples have been presented in the foregoing description with reference to them. It should be understood that the various aspects disclosed herein can be combined in different combinations than those shown in the accompanying drawings. It should be understood that various modifications can be made to the reference examples without departing from the scope of this disclosure and the following claims.

Claims

1. A medical device comprising: A motion sensor configured to generate motion signals; as well as Control circuit, the control circuit being configured to: Multiple sensing control parameters are set, including the end time of the ventricular diastolic event window; A first atrial event is sensed from the motion signal during multiple ventricular cycles based on the sensing control parameters. The characteristics of the motion signal are determined for each ventricular cycle, which is at least a portion of the plurality of ventricular cycles; The metric of the motion signal is determined based on the identified features, wherein the metric involves the number of ventricular cycles longer than the end time of the ventricular diastolic event window; The sensing control parameters among the plurality of sensing control parameters are adjusted based on the metric. The second atrial event is sensed from the motion signal based on the adjusted sensing control parameters; as well as An atrial sensing event signal is generated in response to sensing the second atrial event.

2. The medical device according to claim 1, wherein the control circuit is configured to: The multiple control parameters are set as follows: Set the end time of the ventricular diastolic event window; Set the high sensing threshold amplitude for the expiration time that extends to the end time of the event window; as well as A low sensing threshold amplitude is set after the high sensing threshold amplitude, starting from the expiration of the end time of the ventricular diastolic event window; In response to the earliest crossing of the motion signal to one of the high sensing threshold amplitude and the low sensing threshold amplitude, each of the first atrial events is sensed during the plurality of ventricular cycles; as well as The sensing control parameters are adjusted by adjusting at least one of the ventricular diastolic event window end time, the high sensing threshold amplitude, or the low sensing threshold amplitude.

3. The medical device according to claim 2, wherein the control circuit is configured as follows: The feature is determined by determining the timing of each first atrial event sensed during the plurality of ventricular cycles; The metric is determined based on the determined time of each first atrial event sensed during the plurality of ventricular cycles by determining at least one of the following: Early atrial event count is performed by counting each of the first atrial events sensed after the end of the ventricular diastolic event window and before the threshold time interval. Normal atrial event count is performed by counting each first atrial event sensed at or after the early event threshold time interval; as well as Atrial event count is performed by counting each of the first atrial events sensed before the end time of the ventricular diastolic event window.

4. The medical device according to claim 3, wherein the control circuit is configured as follows: At least based on the early atrial event count, the criteria for excessive sensing of ventricular diastolic events must be met; and The sensing control parameters are adjusted based on the early atrial event count by increasing the low sensing threshold amplitude in response to meeting the oversensing criteria for ventricular diastolic events.

5. The medical device according to claim 3 or 4, wherein the control circuit is configured to: At least based on the normal atrial event count, it is determined that the standard atrial event sensing criteria are met; and The sensing control parameters are adjusted based on the normal atrial event count by increasing the low sensing threshold amplitude in response to meeting the conventional atrial event sensing criteria.

6. The medical device according to any one of claims 3 to 5, wherein the control circuit is configured to: At least based on the normal atrial event count, it is determined that the atrial event sensing insufficiency criterion is met; and The sensing control parameters are adjusted based on the normal atrial event count by reducing the magnitude of the low sensing threshold in response to meeting the insufficient atrial event sensing criteria.

7. The medical device according to any one of claims 2 to 6, wherein the control circuit is configured to: The feature is determined by the maximum amplitude of the motion signal after determining the end time of the ventricular diastolic event window for each of the plurality of ventricular cycles, wherein the maximum amplitude is longer than the end time of the ventricular diastolic event window; The metric is determined by identifying the minimum amplitude among the maximum amplitudes; as well as The sensing control parameters are adjusted by adjusting the low sensing threshold amplitude based on the minimum amplitude of the maximum amplitude.

8. The medical device according to any one of claims 2 to 7, wherein the control circuit is configured to: The feature is determined by determining the most recent crossover time of the threshold amplitude of a ventricular diastolic event that occurred before the end time of the ventricular diastolic event window; The metric is determined by determining the ventricular diastolic event time based on the determined most recent crossing time; as well as The sensing control parameters are adjusted by adjusting the end time of the ventricular diastolic event window based on the ventricular diastolic event time.

9. The medical device of claim 8, wherein the control circuitry is configured to set the ventricular diastolic event threshold amplitude based on the low sensing threshold amplitude.

10. The medical device according to claim 8 or 9, wherein the control circuit is configured to: The feature is determined by determining the earliest time across the low sensing threshold amplitude; The metric is determined by determining the atrial event time based on the earliest determined crossing time; as well as The ventricular diastolic event window end time is adjusted based on the ventricular diastolic event time and the atrial event time.

11. The medical device according to any one of claims 2 to 10, wherein the control circuit is configured to: The feature is determined by determining the maximum amplitude of the motion signal prior to the end of the ventricular diastolic event window. The metric is determined by determining the amplitude of the ventricular diastolic event based on the determined maximum amplitude; as well as The sensing control parameters are adjusted by adjusting the high sensing threshold amplitude based on the amplitude of the ventricular diastolic event and the amplitude of the low sensing threshold.

12. The medical device of claim 11, wherein the control circuit is configured to: The target high threshold amplitude is determined based on a combination of the ventricular diastolic event amplitude and the low sensing threshold amplitude. Determine the difference between the target high threshold amplitude and the high sensing threshold amplitude; Adjust the counter value based on the difference; The counter value is determined to be equal to one of the maximum threshold and the minimum threshold; as well as In response to the counter being equal to either the maximum threshold or the minimum threshold, the high sensing threshold amplitude is adjusted toward the target high threshold amplitude.

13. The medical device according to any one of claims 2 to 12, wherein the control circuit is configured to: The feature is determined by determining a first plurality of maximum amplitudes of the motion signal prior to the end of the ventricular diastolic event window for each of the plurality of ventricular cycles having one of the first atrial events sensed after the end of the ventricular diastolic event window; The metric is determined by determining the first percentile of the first plurality of maximum amplitudes; For each of the plurality of ventricular cycles, a second plurality of maximum amplitudes of the motion signal prior to the end time of the ventricular diastolic event window are determined; The target high sensing threshold is determined by determining the second percentile of the second plurality of maximum amplitudes that is greater than the metric. as well as The sensing control parameters are adjusted by adjusting the magnitude of the high sensing threshold based on the target high sensing threshold.

14. The medical device according to any one of claims 2 to 13, wherein the control circuit is configured to: Determine that the atrial sensing event signal is generated before the end of the ventricular diastolic event window; and In response to determining that the atrial sensing event signal is generated before the expiration of the ventricular diastolic event window end time, the ventricular diastolic event window end time is extended until a subsequent ventricular electrical event.

15. The medical device according to any one of claims 1 to 14, further comprising a pulse generator configured to generate pacing pulses in response to the atrial sensing event signal.

16. The medical device of claim 15, further comprising: A housing that encloses the motion sensor, the control circuitry, and the pulse generator; as well as A pair of electrodes located on the housing and coupled to the pulse generator.

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