Method and apparatus for establishing parameters for performing cardiac event detection

Abstract

A pacemaker having a motion sensor is configured to set an atrial event sensing parameter for sensing an atrial contraction event from a motion signal generated by the motion sensor. The pacemaker sets at least one atrial event sensing parameter by identifying ventricular electrical events and setting a sensing window after each of the ventricular electrical events. The pacemaker may determine a characteristic of the motion signal generated by the motion sensor during each of the sensing windows and set the atrial event sensing parameter based on the determined characteristic.

Description

Technical Field

[0001] The present disclosure relates to a medical device and method for establishing parameters for detecting cardiac events from motion sensor signals. Background Art

[0002] An implantable cardiac pacemaker is typically placed in a subcutaneous pocket and coupled to one or more transvenous medical electrical leads that carry pacing and sensing electrodes positioned in the heart. A subcutaneously implanted cardiac pacemaker may be a single-chamber pacemaker that is coupled to one transvenous medical lead to position the electrodes in one heart chamber (atrium or ventricle) or a dual-chamber pacemaker that is coupled to two intracardiac leads to position the electrodes in both the atrial and ventricular chambers. Multi-chamber pacemakers that may be connected to three leads, for example, to position electrodes for pacing and sensing in one atrial chamber and both the left and right ventricles may also be used.

[0003] Intracardiac pacemakers that can be implanted within the ventricular chamber of a patient's heart to deliver ventricular pacing pulses have recently been introduced. Such pacemakers can sense the R-wave signal accompanying intrinsic ventricular depolarization and deliver ventricular pacing pulses in the absence of a sensed R-wave. While single-chamber ventricular sensing and pacing by an intracardiac ventricular pacemaker can adequately address some patient conditions, some patients may benefit from atrial and ventricular (dual-chamber) sensing for providing atrial synchronized ventricular pacing to maintain a regular heart rhythm. Summary of the invention

[0004] The technology disclosed herein generally relates to a pacemaker having a motion sensor that generates a motion signal that includes ventricular and atrial event signals. The pacemaker is configured to sense atrial events from the motion signal. 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 technology disclosed herein determines one or more atrial event sensing parameters for sensing the atrial event signals by determining characteristics of the motion signal and setting the atrial event sensing parameters based on the determined characteristics over multiple ventricular cycles. In some instances, the atrial event sensing parameters are set based on a distribution of the characteristics (e.g., based on a percentile or median or other central measure of the distribution).

[0005] In one example, the present disclosure provides a pacemaker, comprising: a pulse generator configured to generate a pacing pulse to be delivered to a ventricle of a patient's heart through electrodes coupled to the pacemaker; a sensing circuit including an R-wave detector for sensing an R-wave from a cardiac electrical signal received through electrodes coupled to the pacemaker; a motion sensor configured to generate a motion signal, the motion signal including an atrial event signal corresponding to an atrial contraction event; and a control circuit coupled to the motion sensor, the sensing circuit, and the pulse generator. The control circuit is configured to identify a ventricular electrical event, which may be a sensed R-wave and / or a generated ventricular pacing pulse. After each of the ventricular electrical events, the control circuit may set a sensing window, determine a feature of the motion signal during each of the sensing windows in the sensing window, and set an atrial event sensing parameter based on the determined feature. The pacemaker may sense the atrial contraction event from the motion signal based on the atrial event sensing parameter, and generate an atrial sensed event signal in response to sensing the atrial contraction event. In some examples, the control circuit may start an atrioventricular pacing interval in response to sensing the atrial contraction event, and control the pulse generator to generate a ventricular pacing pulse in response to expiration of the atrioventricular pacing interval.

[0006] In another example, the present disclosure provides a method performed by a pacemaker. The method includes generating a motion signal including an atrial event signal corresponding to an atrial contraction event; identifying a ventricular electrical event; and setting a sensing window after each of the ventricular electrical events. The method further includes determining the characteristics of the motion signal generated by the motion sensor of the pacemaker during each of the sensing windows and setting an atrial event sensing parameter based on the determined characteristics. The method may further include sensing an atrial contraction event from the motion signal based on the atrial event sensing parameter, and generating an atrial sensing event signal in response to sensing the atrial contraction event. In some examples, the method includes: starting an atrioventricular pacing interval in response to sensing the atrial event; and delivering a ventricular pacing pulse in response to expiration of the atrioventricular pacing interval.

[0007] In another example, the present disclosure provides a non-transitory computer-readable storage medium, comprising a set of instructions that, when executed by a control circuit of a pacemaker, cause the pacemaker to generate a motion signal including an atrial event signal corresponding to an atrial contraction event, identify ventricular electrical events, set a sensing window after each of the ventricular electrical events, determine a characteristic of the motion signal generated by a motion sensor of the pacemaker during each of the sensing windows, and set an atrial event sensing parameter based on the determined characteristic. The instructions further cause the pacemaker to sense the atrial contraction event from the motion signal based on the atrial event sensing parameter, and generate an atrial sensed event signal in response to sensing the atrial contraction event. In some examples, the instructions further cause the pacemaker to start an atrioventricular pacing interval in response to the atrial sensed event signal, and to generate a ventricular pacing pulse in response to expiration of the atrioventricular pacing interval.

[0008] The details of one or more aspects of the disclosure are set forth in the drawings and description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 2 yes Figure 1 A conceptual illustration of a pacemaker inside the heart is shown in .

[0011] Figure 3 yes Figure 1 Schematic diagram of an example configuration of a pacemaker is shown in .

[0012] Figure 4 It is possible through Figure 1 An example of a motion sensor signal acquired by a motion sensor included in a pacemaker during a cardiac cycle.

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

[0014] Figure 6 is a flow chart of a method for establishing atrial event sensing parameters.

[0015] Figure 7 is a flow chart of a method for selecting an atrial event sensing vector according to one example.

[0016] Figure 8Depicted are two example histograms generated for two different motion sensor signal vectors.

[0017] Fig. 9 is a flow chart of a method for establishing an end time for a passive ventricular filling window (also referred to herein as the "A3 window").

[0018] Fig.10 is an example of a histogram of recent threshold amplitudes spanning time during an extended A3 window.

[0019] Fig.11 is a flow chart of a method for establishing early and late values ​​of an atrial event sensing threshold amplitude applied during and after the passive ventricular filling window, respectively.

[0020] Fig.12 is an example of a histogram of the maximum amplitude of the motion signal used to establish the threshold amplitude for early atrial event sensing.

[0021] Fig.13 is an example of a histogram of the maximum amplitude of the motion signal used to establish the threshold amplitude for late atrial event sensing.

[0022] Fig.14 is a flow chart of a method for controlling atrial synchronized ventricular pacing according to one example.

[0023] Fig.15 is a flow chart of a process performed by a pacemaker for setting atrial event sensing parameters according to another example.

[0024] Fig.16 is a flow chart of a method for setting and adjusting atrial event sensing control parameters according to one example. DETAILED DESCRIPTION

[0025] In general, the present disclosure describes techniques for establishing cardiac event sensing parameters by an implantable medical device. As described below, an atrial contraction event (sometimes referred to as an "atrial beat") can be sensed from a signal generated by a motion sensor, the signal comprising an atrial contraction event signal corresponding to a mechanical contraction of the atria and an active filling phase of the ventricles. Atrial event sensing parameters can include a vector signal for selecting a motion sensor, a sensing threshold amplitude, and a time window during which an atrial event can be sensed. The technology disclosed herein provides techniques for sensing atrial events by a ventricular pacemaker, which can be completely implanted in a ventricular heart chamber and has a motion sensor for generating an intraventricular motion signal. In this way, atrial events can be detected, for example, from the ventricles for controlling atrial synchronized ventricular pacing. Atrial synchronized ventricular pacing pulses can be delivered by a pacemaker implanted in the ventricles without the need for a sensor for detecting atrial events located in or on the atria of the patient's heart.

[0026] Figure 1 is a conceptual diagram showing an implantable medical device (IMD) system 10 that can be used to sense cardiac electrical signals and motion signals induced by cardiac motion and flowing blood and provide pacing therapy to a patient's heart 8. The IMD system 10 includes a ventricular intracardiac pacemaker 14. The pacemaker 14 can be a transcatheter intracardiac pacemaker adapted to be fully implanted in a cardiac chamber (e.g., fully implanted in the right ventricle (RV) of the heart 8 or fully implanted in the left ventricle (LV)) 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 can be generally cylindrical to enable transvenous implantation via a delivery catheter.

[0027] The pacemaker 14 is shown positioned in the RV along the endocardial wall, for example near the RV apex, although other locations are possible. The technology disclosed herein is not limited to Figure 1 The pacemaker locations shown in the examples of and other locations within the heart 8 are possible. For example, a ventricular intracardiac pacemaker 14 can be positioned in the LV and configured to detect cardiac motion signals and deliver atrial synchronized ventricular pacing to the LV using the techniques disclosed herein. The pacemaker 14 can be positioned in the RV or LV to provide respective right ventricular or left ventricular pacing and for sensing cardiac motion signals via motion sensors within the ventricular chambers.

[0028] The pacemaker 14 is capable of generating electrical stimulation pulses (e.g., pacing pulses) that are delivered to the heart 8 via one or more electrodes on the external housing of the pacemaker. The pacemaker 14 is configured to deliver RV pacing pulses and sense RV cardiac electrical signals using the housing-based electrodes to generate an RV electrogram (EGM) signal. The cardiac electrical signals may be sensed using the housing-based electrodes that are also used to deliver pacing pulses to the RV.

[0029] The pacemaker 14 is configured to control the delivery of ventricular pacing pulses to the RV in a manner that promotes synchronization between atrial activation and ventricular activation (e.g., by maintaining a target atrial-ventricular (AV) interval between an atrial event and a ventricular pacing pulse. That is, the pacemaker 14 controls the delivery of pacing pulses to maintain a desired AV interval between atrial contraction corresponding to atrial contraction and a ventricular pacing pulse delivered to induce ventricular depolarization and ventricular contraction.

[0030] According to the techniques described herein, atrial contraction events that produce the active ventricular filling phase are detected by the pacemaker 14 from a motion sensor (e.g., an accelerometer) enclosed by the housing of the pacemaker 14. The motion signal generated by the accelerometer implanted within the ventricular chamber (which may be referred to as an "intraventricular motion signal") contains motion signals caused by both ventricular and atrial events. For example, the acceleration of blood flowing through the tricuspid valve 16 between the RA and RV into the RV caused by atrial contraction and referred to as an "atrial beat" can be detected by the pacemaker 14 from a signal generated by the accelerometer contained in the pacemaker 14. Figure 4 Other motion signals that may be detected by pacemaker 14 are described, such as motion caused by ventricular contraction and passive ventricular filling.

[0031] The atrial P wave accompanying atrial depolarization is a relatively low amplitude signal (e.g., compared to the near-field R wave) in the near-field ventricular cardiac electrical signal received by the pacemaker 14 and may therefore be difficult to reliably detect from the cardiac electrical signal acquired by the pacemaker 14 implanted in the ventricular chamber. When based solely on the cardiac electrical signal received by the pacemaker 14, atrial-synchronized ventricular pacing or other functions that rely on atrial sensing by the pacemaker 14 may be unreliable. According to the technology disclosed herein, the pacemaker 14 includes a motion sensor (such as an accelerometer) and is configured to detect an atrial event corresponding to atrial mechanical activation or atrial contraction from a signal 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 contraction event, the ventricular pacing pulse can be synchronized with the atrial event detected from the motion sensor signal. As described below, the detection of an atrial contraction event for synchronizing the ventricular pacing pulse with the atrial contraction can include the detection of other cardiac event motion signals in order to positively identify the atrial contraction event.

[0032] The target AV interval may be a default or programmed value selected by a clinician and is the time interval from detection of an atrial event to delivery of a ventricular pacing pulse. In some cases, the target AV interval may begin at the time an atrial contraction event is detected based on a motion sensor signal, or from an identified reference point of an atrial event signal. The target AV interval may be identified as hemodynamically optimal for a given patient based on clinical testing or evaluation of the patient or based on clinical data from a patient population. The target AV interval may be determined to be optimal based on the relative timing of electrical and mechanical events as identified from cardiac electrical signals received by the pacemaker 14 and motion sensor signals received by the pacemaker 14.

[0033] The pacemaker 14 may be capable of bidirectional wireless communication with an external device 20 to program AV pacing intervals and other pacing control parameters that may be used to detect ventricular mechanical events and atrial contraction events from motion sensor signals, as well as mechanical event sensing parameters. Aspects of the external device 20 may generally correspond to the external programming / monitoring unit disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.). The external device 20 is often referred to as a "programmer" because it is often used by a physician, technician, nurse, clinician, or other qualified user to program operating parameters in the pacemaker 14. The external device 20 may be located in a clinic, hospital, or other medical facility. The external device 20 may alternatively be embodied as a home monitor or handheld device that may be used in a medical facility, in a patient's home, or in another location. Operating parameters including sensing and therapy delivery control parameters may be programmed into the pacemaker 14 using the external device 20.

[0034] The external device 20 may include a processor 52, a memory 53, a display 54, a user interface 56, and a telemetry unit 58. The processor 52 controls the operation of the external device and processes data and signals received from the pacemaker 14. The display unit 54 may generate a display of data and information related to the function of the pacemaker to the user (the display may include a graphical user interface) to review the operation and programmed parameters of the pacemaker, as well as cardiac electrical signals, cardiac motion signals, or other physiological data that may be acquired by the pacemaker 14 and transmitted to the external device 20 during an interrogation session.

[0035] The user interface 56 may include a mouse, touch screen, keyboard, etc. to enable a user to interact with the external device 20 to initiate a telemetry session with the pacemaker 14 to retrieve data from and / or transmit data to the pacemaker 14, including programmable parameters for controlling cardiac event sensing and therapy delivery. The telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with telemetry circuitry included in the pacemaker 14, and is configured to operate in conjunction with the processor 52 to send and receive data related to pacemaker function over the communication link 24.

[0036] At the time of implantation, during patient follow-up, or at any time after pacemaker implantation, the pacemaker 14 can perform a setup procedure to establish parameters for detecting atrial events from the motion sensor signal. During the procedure, the patient can be standing, sitting, lying down, or ambulatory. The setup procedure can 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 the external device 20 and displayed on the display unit 54 of the external device 20 in the form of a histogram. The atrial event sensing parameters established based on the motion sensor signal data can be automatically set or can be transmitted to the external device 20 to generate a display on the display unit 54 as recommended parameters, thereby allowing a clinician to review and accept or modify the recommended parameters, for example using the user interface 56.

[0037] In some examples, the external device processor 52 may perform operations disclosed herein for establishing starting values ​​for atrial event sensing parameters based on data retrieved from the pacemaker 14. The processor 52 may cause the display unit 54 to generate a display of data related to the motion sensor signal, including a histogram distribution of metrics determined from the cardiac motion signal for use in selecting starting values ​​for atrial event sensing control parameters. The display unit 54 may be a graphical user interface that enables a user to interact with the display, for example, to select various displays or information for viewing. In some examples, the user may select one or more atrial event sensing control parameter settings to be automatically established by the pacemaker 14 and / or may program starting sensing control parameters or other programmable parameters for controlling sensor operation and therapy delivery. The processing circuitry and / or processor 52 included in the pacemaker 14 may determine starting values ​​for one or more atrial contraction event sensing control parameters based on data acquired from the motion sensor signal generated by the accelerometer included in the pacemaker 14 and various thresholds and criteria (which may include user programmable thresholds or criteria used in setting starting parameter values).

[0038] The external device telemetry unit 58 is configured for bidirectional communication with implantable telemetry circuitry contained in the pacemaker 14. The telemetry unit 58 establishes a wireless communication link 24 with the pacemaker 14. The communication link 24 may be implemented using, for example, The external device 20 may be configured to establish a wireless communication link 24 using a Wi-Fi, Medical Implant Communications Service (MICS), or other radio frequency (RF) link of a communication bandwidth. In some instances, the external device 20 may include a programming header that is placed proximate to the pacemaker 14 to establish and maintain the communication link 24, and in other instances, the external device 20 and the pacemaker 14 may be configured to communicate using a distance telemetry algorithm and circuitry that does not require the use of a programming header and does not require user intervention to maintain the communication link. An example RF telemetry communication system that may be implemented in the system 10 is generally disclosed in U.S. Pat. No. 5,683,432 (Goedeke et al.).

[0039] It is contemplated that the external device 20 may be wired or wirelessly connected to a communication network via telemetry circuitry including a transceiver and antenna or via hardwired communication lines for transmitting data to a centralized database or computer to allow remote management of the patient. A remote patient management system including a centralized patient database may be configured to utilize the presently disclosed techniques to enable a clinician to review the EGM, motion sensor signals, and marker channel data and authorize programming of sensing and therapy control parameters in the pacemaker 14, for example, after viewing a visual representation of the EGM, motion sensor signals, and marker channel data.

[0040] Figure 2 yes Figure 1 1. A conceptual diagram of an intracardiac pacemaker 14 is shown in FIG. The pacemaker 14 includes electrodes 162 and 164 spaced apart along a housing 150 of the pacemaker 14 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 164 is shown as a tip electrode extending from a distal end 102 of the pacemaker 14, and electrode 162 is shown as a ring electrode along a mid-portion (e.g., adjacent the proximal end 104) of the housing 150. The distal end 102 is referred to as "distal" because it is expected to be the leading end when the pacemaker 14 is advanced through a delivery tool (such as a catheter) and placed against a target pacing site.

[0041] Electrodes 162 and 164 form an anode and cathode pair for bipolar cardiac pacing and sensing. In alternative embodiments, the pacemaker 14 may include two or more ring electrodes, two tip electrodes, and / or other types of electrodes exposed along the 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 polarization coatings such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc. Electrodes 162 and 164 may be positioned at locations along the pacemaker 14 other than those shown.

[0042] The housing 150 is formed of a biocompatible material such as stainless steel or a titanium alloy. In some instances, the housing 150 may include an insulating coating. Examples of insulating coatings include polyparaxylene, urethane, PEEK, or polyimide, etc. The entire housing 150 may be insulated, but only electrodes 162 and 164 are not insulated. Electrode 164 may act as a cathode electrode and be coupled to an internal circuit system enclosed by the housing 150, such as a pacing pulse generator and a cardiac electrical signal sensing circuit system, through an electrical feedthrough across the housing 150. Electrode 162 may be formed as a confinement of the housing 150 such as Figure 2 164 is a conductive portion of a ring electrode generally shown in FIG. 16A that is electrically isolated from the rest of the housing 150. In other examples, instead of providing a localized ring electrode such as anode electrode 162, the entire perimeter of the housing 150 can serve as an electrode that is electrically isolated from the tip electrode 164. The electrode 162 formed along the conductive portion of the housing 150 serves as a return anode during pacing and sensing.

[0043] The housing 150 contains a housing for accommodating the following combination Figure 3 A control electronics subassembly 152 is described for electronics used to sense cardiac signals, generate pacing pulses, and control therapy delivery and other functions of the pacemaker 14. In some examples, the motion sensor can be implemented as an accelerometer enclosed within the housing 150. The accelerometer provides signals to a processor contained in the control electronics subassembly 152 for signal processing and analysis to detect atrial contraction events, e.g., for controlling timed ventricular pacing pulses, as described below.

[0044] The accelerometer may be a three-dimensional accelerometer. In some instances, the accelerometer may have a "longitudinal" axis parallel or aligned with the longitudinal axis 108 of the pacemaker 14 and two orthogonal axes extending in a radial direction relative to the longitudinal axis 108. However, the practice of the technology 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 an intracardiac motion signal from which an atrial contraction event is detected. In other instances, a two-dimensional accelerometer or other multi-dimensional accelerometer may be used. Each axis of a one-dimensional or multi-dimensional accelerometer may be defined by a piezoelectric element, a microelectromechanical system (MEMS) device, or other sensor element capable of generating an electrical signal in response to a change in acceleration applied to the sensor element (e.g., by converting the acceleration into a force or displacement that is converted into an electrical signal). In a multi-dimensional accelerometer, the sensor elements may be arranged orthogonally, with each sensor element axis being orthogonal relative to the other sensor element axes. However, an orthogonal arrangement of the elements of a multi-axis accelerometer is not necessarily required.

[0045] Each sensor element can generate an acceleration signal corresponding to a vector aligned with an axis of the sensor element. As described below, the techniques disclosed herein include selecting a vector signal of a multi-dimensional accelerometer (also referred to as a "multi-axis" accelerometer) for sensing atrial contraction events. 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 atrial synchronized ventricular pacing delivered by pacemaker 14.

[0046] The housing 150 further includes a battery subassembly 160 that provides power to the control electronics subassembly 152. The battery subassembly 160 may include features of the batteries disclosed in commonly assigned U.S. Pat. No. 8,433,409 (Johnson et al.) and U.S. Pat. No. 8,541,131 (Lund et al.), both of which are hereby incorporated by reference in their entireties.

[0047] The pacemaker 14 may include a set of fixation tines 166 to secure the pacemaker 14 to patient tissue, for example, by actively engaging the ventricular endocardium and / or interacting with ventricular trabeculae. The fixation tines 166 are configured to anchor the pacemaker 14 to position the electrode 164 operatively proximate to the target tissue for delivery of therapeutic electrical stimulation pulses. Various types of active and / or passive fixation members may be employed to anchor or stabilize the pacemaker 14 in an implanted position. The pacemaker 14 may include a set of fixation tines as disclosed in commonly assigned U.S. Pat. No. 9,775,872 (Grubac et al.).

[0048] The pacemaker 14 may optionally include a delivery tool interface 158. The delivery tool interface 158 may be positioned at the proximal end 104 of the pacemaker 14 and configured to connect to a delivery device (such as a catheter) used to position the pacemaker 14 at an implantation site (e.g., within a heart chamber) during an implantation procedure.

[0049] Figure 3 yes Figure 1 Schematic diagram of an example configuration of a pacemaker 14 is shown in . The pacemaker 14 includes a pulse generator 202, a cardiac electrical signal sensing circuit 204, a control circuit 206, a memory 210, a telemetry circuit 208, a motion sensor 212, and a power source 214. Figure 3 The various circuits represented may be combined on one or more integrated circuit boards including: 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 functionality.

[0050] 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 may be successfully used in pacemaker 14 to detect cardiac motion signals according to the techniques described herein. Examples of motion sensors that may be implemented in motion sensor 212 include piezoelectric sensors and MEMS devices.

[0051] The motion sensor 212 may include a multi-axis sensor, such as a two-dimensional or three-dimensional sensor, wherein each axis provides an axis signal for detecting a cardiac mechanical event that can be analyzed independently or in combination. The motion sensor 212 generates an electrical signal related to the motion or vibration of the sensor 212 (and the pacemaker 14) when subjected to flowing blood and cardiac motion, for example. The 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 transmitted to the control circuit 206. For example, each vector signal generated by each individual axis of the multi-axis accelerometer may be filtered by a high-pass filter (e.g., a 10 Hz high-pass filter). The filtered signal may be digitized by the ADC and rectified for use by the atrial event detector circuit 240 to detect atrial contraction events. If it is necessary to detect an atrial signal with a lower frequency content, the high-pass filter may be reduced (e.g., to 5 Hz). In some instances, high-pass filtering is performed without low-pass filtering. In other examples, each accelerometer axis signal is filtered by a low pass filter (eg, a 30 Hz low pass filter) with or without high pass filtering.

[0052] One example of an accelerometer for use in an implantable medical device that may be implemented in conjunction with the techniques disclosed herein is generally disclosed in U.S. Pat. No. 5,885,471 (Ruben et al.). Implantable medical device arrangements that include piezoelectric accelerometers for detecting patient motion are disclosed, for example, in U.S. Pat. No. 4,485,813 (Anderson et al.) and U.S. Pat. No. 5,052,388 (Sivula et al.), both of which are hereby incorporated by reference in their entireties. Examples of three-dimensional accelerometers that may be implemented in a pacemaker 14 using the presently disclosed techniques and used to detect cardiac mechanical events are generally disclosed in U.S. Pat. No. 5,593,431 (Sheldon) and U.S. Pat. No. 6,044,297 (Sheldon). Other accelerometer designs may be used to generate electrical signals related to motion imposed on the pacemaker 14 due to ventricular and atrial events.

[0053] The sensing circuit 204 is configured to receive the cardiac electrical signal through the electrodes 162 and 164 through the pre-filter and amplifier circuit 220. The pre-filter and amplifier circuit may include a high pass filter (e.g., a 2.5 to 5 Hz high pass filter) for removing DC offset or a wideband filter with a passband of 2.5 Hz to 100 Hz to remove DC offset and high frequency noise. The pre-filter and amplifier circuit 220 may further include an amplifier to amplify the "raw" cardiac electrical signal that is passed to the analog-to-digital converter (ADC) 226. The ADC 226 may pass a multi-bit digital electrogram (EGM) signal to the control circuit 206 for use by the 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 may be used in algorithms for establishing atrial sensing control parameters and for detecting atrial contraction events from the motion sensor signal. The digital signal from the ADC 226 may 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 an R-wave detector 224 .

[0054] The R-wave detector 224 may include a sense amplifier or other detection circuitry that compares the incoming rectified cardiac electrical signal to an R-wave sensing threshold (which may be an automatically adjusted threshold). When the incoming signal exceeds the R-wave sensing threshold, the R-wave detector 224 generates an R-wave sensing event signal (R-sense) that is transmitted to the control circuit 206. In other examples, the R-wave detector 224 may receive the digital output of the ADC 226 for detecting the R-wave by a comparator, morphological signal analysis of the digital EGM signal, or other R-wave detection techniques. The processor 244 may provide sensing control signals to the sensing circuit 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 transmitted from the R-wave detector 224 to the control circuit 206 may be used to schedule ventricular pacing pulses by the pacing timing circuit 242 and to identify the timing of ventricular electrical events in the algorithm executed by the atrial event detector circuit 240 for detecting atrial contraction events based on the signal received from the motion sensor 212.

[0055] The control circuit 206 includes an atrial event detector circuit 240, a pacing timing circuit 242, and a processor 244. The control circuit 206 can receive an R-wave sensed event signal and / or a digital cardiac electrical signal from the sensing circuit 204 for detecting and confirming cardiac events and controlling ventricular pacing. For example, when the pacemaker 14 is operating in a non-atrial tracking ventricular pacing mode, the R-wave sensed event signal can be transmitted to the pacing timing circuit 242 for inhibiting scheduled ventricular pacing pulses or scheduling ventricular pacing pulses. The R-wave sensed event signal can also be transmitted to the atrial event detector circuit 240 for setting a time window used by the control circuit 206 in detecting an atrial contraction event from the motion sensor signal.

[0056] Atrial event detector circuit 240 is configured to detect atrial contraction events based on signals received from motion sensor 212. Figure 9-10 Techniques for setting a time window for use in detecting atrial contraction events are described. In some examples, one or more ventricular mechanical events can be detected from a motion sensor signal in a given cardiac cycle to facilitate positive detection of an atrial contraction event from the motion sensor signal during the ventricular cycle.

[0057] Atrial event detector circuit 240 receives motion signals from motion sensor 212 and may initiate an atrial "blanking" period in response to a ventricular electrical event (e.g., an R-wave sensed event signal from sensing circuit 204 or a pacing pulse delivered by pulse generator 202). The blanking period may correspond to a time period following a ventricular electrical event during which ventricular mechanical events corresponding to ventricular contraction and isovolumetric relaxation are expected to occur. When ventricular pacing is properly synchronized with atrial events, atrial events corresponding to ventricular contraction are not expected to occur during the atrial blanking period. Thus, motion signal peaks occurring during the atrial blanking period are not sensed as atrial events. The atrial "blanking" period may be used to define a time period following a ventricular electrical event during which atrial event detector circuit 240 does not sense an atrial contraction event. However, in some instances, the motion sensor signal is not necessarily blanked during this time period because control circuit 206 may still receive the motion sensor signal during the atrial blanking period and may process the motion signal for sensing a ventricular event during the atrial blanking period.

[0058] The atrial event detector circuit 240 determines whether the motion sensor signal meets the atrial contraction event detection criteria outside of the atrial blanking period. In some instances, the motion sensor signal during the blanking period can be monitored by the atrial event detector circuit 240 for the purpose of detecting a ventricular mechanical event that can be used to confirm or verify the detection of an atrial contraction event. Therefore, a ventricular mechanical event detection window can be set during the atrial blanking period and can be set according to a predetermined time interval after the identification of a ventricular electrical event. The atrial event detector circuit 240 can be configured to detect one or more ventricular mechanical events during corresponding ventricular event detection windows during the atrial blanking period. The timing and detection of ventricular mechanical events can be used to update the atrial blanking period and / or can be used to confirm the detection of an atrial event that occurs after an expected ventricular mechanical event.

[0059] The atrial event detector circuit 240 can set time windows corresponding to the passive ventricular filling phase and the active ventricular filling phase based on the timing of previous ventricular electrical events (R-wave sensing event signals or ventricular pacing pulses). The crossing of the atrial event sensing threshold by the motion sensor signal during any of these windows can be detected as an atrial contraction event. As described below, two different atrial event sensing thresholds can be established for application during the passive filling phase window and after the passive filling phase window (during the active filling phase window (hereinafter also referred to as the "A4 window")).

[0060] Atrial event detector circuit 240 communicates an atrial event detection signal to processor 244 and / or pacing timing circuit 242 in response to detecting an atrial event. Pacing timing circuit 242 (or processor 244) may additionally receive an R-wave sensed event signal from R-wave detector 224 for use in controlling the timing of pacing pulses delivered by pulse generator 202. Processor 244 may include one or more clocks for generating clock signals used by pacing timing circuit 242 to time out an AV pacing interval that begins upon receipt of an atrial event detection signal from atrial event detector circuit 240. Pacing timing circuit 242 may include one or more escape interval timers or counters for timeout of an AV pacing interval (which may be a programmable interval stored in memory 210 and retrievable by processor 244) for setting the AV pacing interval used by pacing timing circuit 242. One application of the atrial sensed event signal generated by atrial event detector circuit 240 is for setting an AV pacing interval for controlling the timing of ventricular pacing pulses. However, the control circuit 206 may use the atrial sensed event signals for other purposes.

[0061] The pacing timing circuit 242 may additionally include a lower pacing rate interval timer for controlling the minimum ventricular pacing rate. For example, if an atrial contraction event is not detected from the motion sensor signal that triggers a ventricular pacing pulse at a programmed AV pacing interval, a ventricular pacing pulse may be delivered by the pulse generator 202 at the expiration of the lower pacing rate interval to prevent ventricular asystole 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 (also 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 represented as a VDI pacing mode in which a ventricular pacing pulse is delivered in the absence of a sensed R wave and is suppressed in response to an R wave sense event signal from the sensing circuit 204. Dual chamber sensing may be performed during a non-atrial tracking ventricular pacing mode by sensing ventricular electrical events by sensing circuit 204 and sensing atrial contraction events from motion signals received from motion sensor 212 by atrial event detector circuit 240. Figure 7-14 As described, atrial event sensing parameters established during a VDI pacing mode may include an atrial event sensing vector of a motion sensor that generates a signal from which an atrial contraction event is detected, the end of a passive ventricular filling window, and an atrial event sensing threshold amplitude value applied during and after the passive ventricular filling window.

[0062] The pulse generator 202 generates electrical pacing pulses that are delivered to the RV of the patient's heart through 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 that are delivered to the pulse generator 202 to control the delivery of the pacing pulses. The pulse generator 202 can include a charging circuit 230, a switching circuit 232, and an output circuit 234.

[0063] The charging circuit 230 may include a holding capacitor that may be charged to a pacing pulse amplitude at a multiple of the battery voltage signal of the power supply 214 under the control of a voltage regulator. The pacing pulse amplitude may be set based on a control signal from the control circuit 206. The switch circuit 232 may control when the holding capacitor of the charging circuit 230 is coupled to the output circuit 234 for delivery of a pacing pulse. For example, the switch circuit 232 may include a switch that is activated by a timing signal received from the pacing timing circuit 242 at the expiration of an AV pacing interval (or a VV lower rate pacing interval) and remains closed for a programmed pacing pulse width to enable the holding capacitor of the charging circuit 230 to discharge. During the programmed pacing pulse duration, the holding capacitor, which is pre-charged to the pacing pulse voltage amplitude, is discharged across the electrodes 162 and 164 through the output capacitor of the output circuit 234. Examples of pacing circuit systems generally disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.) and U.S. Pat. No. 8,532,785 (Crutchfield et al.) can be implemented in a pacemaker 14 to charge a pacing capacitor to a predetermined pacing pulse amplitude and deliver pacing pulses under the control of a control circuit 206.

[0064] The memory 210 may contain computer readable instructions that, when executed by the control circuit 206, cause the control circuit 206 to perform various functions attributed to the pacemaker 14 throughout the present disclosure. The computer readable instructions may be encoded within the memory 210. The 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 propagating signals. According to the techniques disclosed herein, the memory 210 may store: timing periods; and other data used by the control circuit 206 to control the pulse generator 202 to deliver pacing pulses (e.g., by detecting atrial events from the motion sensor signal by the atrial event detector circuit 240 and setting the escape interval timer included in the pacing timing circuit 242).

[0065] The power source 214 provides power to each of the other circuits and components of the pacemaker 14 as needed. The 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 the power source 214 and the other pacemaker circuits and components are not shown. Figure 3 However, it should be Figure 3For example, the power supply 214 can provide power to the charging and switching circuitry, amplifier, ADC 226, and other components of the sensing circuit 204, telemetry circuit 208, memory 210, and motion sensor 212 contained in the pulse generator 202 as needed.

[0066] 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 ) for two-way communication. Motion sensor signals and cardiac electrical signals and / or data derived therefrom may be transmitted by telemetry circuitry 208 to external device 20. Programmable control parameters and algorithms for performing atrial event detection and ventricular pacing control may be received by telemetry circuitry 208 and stored in memory 210 for access by control circuitry 206.

[0067] The functions attributed to the pacemaker 14 herein may be embodied as one or more processors, controllers, hardware, firmware, software, or any combination thereof. Depicting 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. Instead, the functions associated with one or more circuits described herein may be performed by separate hardware, firmware, or software components, or integrated within general hardware, firmware, or software components. For example, atrial contraction event detection from motion sensor signals and ventricular pacing control operations performed by the pacemaker 14 may be implemented in a control circuit 206 that executes instructions stored in a memory 210 and relies on inputs from a sensing circuit 204 and a motion sensor 212. Given the disclosure herein, it is within the capabilities of those skilled in the art to provide software, hardware, and / or firmware to accomplish the described functions in the context of any modern pacemaker.

[0068] Figure 4is an example of a motion sensor signal 250 that can be acquired by the motion sensor 212 during the cardiac cycle. The vertical dashed lines 252 and 262 represent the timing of two consecutive ventricular events (intrinsic ventricular depolarization or ventricular pacing pulses), which mark the corresponding start and end of the ventricular cycle 251. The motion signal includes an A1 event 254, an A2 event 256, an A3 event 258, and an A4 event 260. The A1 event 254 is an acceleration signal that occurs during ventricular contraction and marks the approximate onset of the mechanical contraction period of the ventricle (in this example, when the motion sensor 212 is implemented as an accelerometer). The A1 event is also referred to as a "ventricular contraction event" in this article. The A2 event 256 is an acceleration signal that may occur and marks the approximate offset or end of the mechanical contraction period of the ventricle when the aortic valve and the pulmonary valve are closed. The A2 event can also mark the beginning of the isovolumetric relaxation phase of the ventricle that occurs when the aortic valve and the pulmonary valve are closed.

[0069] The A3 event 258 is an acceleration signal that occurs during passive ventricular filling and marks the ventricular mechanical diastole. The A3 event is also referred to herein as the "A3 signal" and "ventricular passive filling event." Since the A2 event occurs at the end of the ventricular systole, it is an indicator of the onset of ventricular diastole. The A3 event occurs during ventricular diastole. Therefore, the A2 and A3 events can be collectively referred to as ventricular mechanical diastolic events because both of them are indicators of ventricular diastole.

[0070] The A4 event 260 is an acceleration signal that occurs during atrial contraction and active ventricular filling and marks the atrial mechanical contraction period. The A4 event 260 is also referred to herein as an "A4 signal" and is an "atrial contraction event" or just an "atrial event" detected from the motion sensor signal 250. The atrial event detector circuit 240 detects the A4 event 260. The processor 244 can control the pacing timing circuit 242 to trigger a ventricular pacing pulse by starting an AV pacing interval in response to detecting the A4 event 260. The control circuit 206 can be configured to detect one or more of the A1, A2, and A3 events from the motion sensor signal 250 for at least some ventricular cardiac cycles for positively detecting the A4 event 260 and setting the atrial event detection control parameters. The A1, A2, and / or A3 events can be detected and characterized to avoid false detection of the A4 event and promote reliable A4 event detection to properly time the atrial synchronized ventricular pacing pulse.

[0071] Combined diagram Figure 6-13The described techniques may be performed by the pacemaker 14 to establish parameters for detecting A4 events without necessarily identifying and distinguishing A1-A4 events. Instead, motion signals acquired during a non-atrial tracking ventricular pacing mode may be characterized by determining features of the motion signal during the sensing window and / or outside of the atrial blanking period. The distribution of features is used to establish atrial event sensing parameters.

[0072] Figure 5 is an example of motion sensor signals 400 and 410 acquired during two different cardiac cycles. A ventricular pacing pulse is delivered at time 0.0 seconds during both cardiac cycles. The top sensor signal 400 is received during one cardiac cycle, and the bottom sensor signal 410 is received during a different cardiac cycle. The two signals 400 and 410 are aligned in time at 0.0 seconds (the time of delivery of the ventricular pacing pulse). 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 flowchart and histogram distribution presented in the accompanying drawings.

[0073] It is observed that the A1 events 402 and 412 of the corresponding motion sensor signals 400 and 410 occurring during ventricular contraction are well aligned in time at time 0.0 seconds after the ventricular pacing pulse. Similarly, the A2 events 404 and 414 (which may mark the end of the ventricular contraction period and the isovolumetric ventricular relaxation phase) and the A3 events 406 and 416 (occurring during passive ventricular filling) are well aligned in time. Since the A1, A2, and A3 events are ventricular events occurring during ventricular contraction, at the end of the ventricular contraction period and the beginning of isovolumetric ventricular relaxation, and during passive ventricular filling, respectively, these events are expected to occur at relatively consistent intervals after a ventricular electrical event (in this example, a ventricular pacing pulse) and relative to each other. The temporal relationship of the A1, A2, and A3 events may differ after a ventricular pacing pulse compared to after a sensed intrinsic R-wave; however, during a stable paced or intrinsic ventricular rhythm, the relative timing of the ventricular A1, A2, and A3 events to each other and to the immediately preceding ventricular electrical event is expected to be consistent from beat to beat.

[0074] The A4 events 408 and 418 of the first and second motion sensor signals 400 and 410, respectively, 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 (a sensed R-wave or ventricular pacing pulse) and the previous A1 to A3 events may vary between cardiac cycles.

[0075] The timing consistency of the A1 to A3 events relative to each other and the immediately preceding ventricular electrical event can be used to determine the atrial blanking period 436 and increase the confidence that the A4 events 408 and 418 are reliably detected. No atrial contraction events are detected during the atrial blanking period 436, which extends from the ventricular electrical event (at time 0.0) to the estimated onset of ventricular diastole, such that the atrial blanking period 436 contains both the A1 event and the A2 event. The A3 window 424 can be set with a start time 420 and an end time 422 corresponding to the end of the post-ventricular atrial blanking period 436. The following can be used in conjunction with Fig. 9 and 10 The described techniques are used to establish the end time 422. The end time 422 may also be considered as the start time of the A4 sensing window 450, although in some cases an A4 signal may be sensed during the A3 window.

[0076] A4 events 408 and 418 can be detected based on a multi-level A4 sensing threshold 444. As seen by the lower motion sensor signal 410, the A4 event 418 can occur earlier after the A3 window 424 due to changes in the atrial rate. In some cases, the A4 event 418 can occur within the A3 window 424 when the atrial rate increases. When this occurs, the A3 event 416 and the A4 event 418 can fuse when passive and active ventricular filling occur together. The fused A3 / A4 event can have a high amplitude, even greater than the amplitude of the A3 event 416 or the A4 event 418 when they occur separately. Therefore, in some instances, a first higher A4 sensing threshold amplitude 446 can be established for detecting early A4 signals that fuse with the A3 signal during the A3 window 424. A second lower A4 sensing threshold amplitude 448 can be established for detecting relatively late A4 events after the end time 422 of the A3 window 424 during the A4 window 450. The A4 window 450 extends from the end time of the A3 window 424 to the next ventricular electrical event (sensed or paced). The earliest crossing of the A4 sensing threshold 444 by the motion sensor signal after the start time 420 of the A3 window (or after the expiration of the atrial blanking period 436) can be detected as an atrial contraction event. Figure 11-13 Techniques for establishing an early A4 sensing threshold amplitude 446 for use during the A3 window 424 and a late A4 sensing threshold amplitude 448 for use after the end time 422 of the A3 window 424 during the A4 window 450 are described.

[0077] Figure 6300 is a flow chart of a method for establishing atrial event sensing parameters. The control circuit 206 may perform the method of the flow chart 300 to automatically select and set starting values ​​of atrial event sensing parameters for sensing A4 events from motion sensor signals during an atrial tracking ventricular pacing mode. The process of the flow chart 300 may be performed by the control circuit 206 when the pacemaker 14 is implanted and may be performed at other post-implantation times to update or reset the A4 sensing parameters.

[0078] At box 302, the control circuit 206 sets the pacing mode to a non-atrial tracking ventricular pacing mode (e.g., VDI) so that ventricular pacing pulses are delivered asynchronously to atrial events. The pacing rate can be set to a nominal rate, such as 50 pulses per minute. In some instances, the ventricular pacing mode can be a rate-responsive mode (e.g., VDIR), but the method for establishing atrial event sensing parameters can be performed when the pacing rate is at or near a programmed lower rate (e.g., 40 to 60 pulses per minute). In patients with AV block, during the non-atrial tracking pacing mode, atrial contraction events occur asynchronously with ventricular electrical events. In patients with AV block, ventricular electrical events will typically be delivered ventricular pacing pulses, but in some cases and in patients with intact AV conduction, may include intrinsic R waves. Therefore, atrial events may experience the ventricular cardiac cycle at different times during the VDI pacing mode.

[0079] For each available sensing vector of the multi-axis motion sensor, motion sensor signal data is acquired during the non-atrial tracking ventricular pacing mode. Aspects of the motion sensor signal outside the post-ventricular atrial blanking period (or later than the minimum A3 window start time) can be determined to characterize the motion sensor signal characteristics within the passive and active filling phases of each ventricular cycle for each available sensing vector. For example, at box 304, the control circuit 206 can determine at least one maximum motion sensor signal amplitude in each ventricular cycle (outside the post-ventricular atrial blanking period) and the time when the motion sensor signal most recently crossed the nominal threshold amplitude. The data acquired at box 304 can be acquired during each ventricular cycle or during a predetermined number of ventricular cycles within a predetermined time interval. For example, the control circuit 206 can acquire data from the motion sensor signal over a few minutes, up to one hour, or up to 24 hours to characterize various aspects of the motion sensor signal in each sensing vector in one or more sensing vectors of the motion sensor. In other examples, at least N values ​​of the motion signal characteristics during a corresponding number of N ventricular cycles are determined.

[0080] At block 306, control circuit 206 generates one or more distributions of the amplitude and / or timing data acquired at block 304. In some examples, the one or more distributions are generated as one or more histograms. A histogram of maximum amplitude data may be generated for each available sensing vector, for example, to be used to select a sensing vector or combination of vectors of a motion sensor from which to perform atrial event sensing during an atrial tracking ventricular pacing mode. Figure 7 and 8 Techniques for generating a distribution of motion sensor maximum amplitude data and selecting sensing vectors are described.

[0081] In another example, a histogram of the most recent crossing times of the amplitude threshold during each ventricular cycle may be generated at block 306 for use in establishing the end time of the A3 window (also referred to as the passive ventricular filling window). Fig. 9 and 10 Example techniques for generating distributions and establishing A3 window end times are described.

[0082] A distribution of the maximum amplitude data in the form of a histogram may be generated at block 306 for use in establishing an early A4 sensing threshold amplitude value and a late A4 sensing threshold amplitude value for a multi-level A4 sensing threshold for sensing an A4 event during an atrial tracking ventricular pacing mode. Techniques for generating a histogram to establish an atrial event sensing threshold are described below in conjunction with FIGS. 11-13.

[0083] At block 308, the control circuit 206 analyzes one or more distributions of the motion sensor signal characteristic data to establish one or more atrial event sensing control parameters. Based on the distribution analysis, the control circuit 206 may select atrial event sensing parameters that may include a motion sensor vector signal or a combination of vector signals from which an A4 signal was sensed during an atrial tracking pacing mode. Other atrial event sensing parameters that may be derived from the generated one or more distributions of the motion signal characteristics include an end time of the A3 window and an early sensing threshold amplitude and a late sensing threshold amplitude of a multi-level A4 sensing threshold. Various examples of techniques for acquiring data from a motion signal, generating distributions of motion signal data, and deriving one or more atrial event sensing parameters from the distributions are described below in conjunction with 7-13.

[0084] Figure 7500 is a flow chart of a method for selecting an A4 sensing vector according to one example. The control circuit 206 can control the process of flow chart 500 to set an initial sensing vector during the early postoperative period after pacemaker implantation, and can repeat the process to reset the A4 sensing vector selection after a specified time interval or when insufficient sensing of A4 events is being performed (e.g., when a threshold number of ventricular pacing pulses are delivered at a rate smoothing interval during an atrial tracking ventricular pacing mode). The A4 sensing vector selection process of flow chart 500 is performed to determine which vector signal (from one axis or a combination of axes) of a multi-axis motion sensor produces a motion signal from which an atrial event can be most reliably sensed, for example, based on atrial event signal strength.

[0085] At box 502, the control circuit 206 sets the pacing mode of the pacemaker 14 to a non-atrial tracking ventricular pacing mode (e.g., VDI). The control circuit 206 can set the ventricular pacing interval (VV interval) according to the nominal pacing rate (e.g., 50 pulses per minute) to maintain a minimum lower ventricular rate. During the asynchronous pacing mode, the A4 event can occur at different times during the ventricular cycle. The control circuit 206 can set a nominal or default A4 window at box 504 during which the motion signal peak amplitude is detected to characterize the motion signal. In one example, for a pacing rate of 50 pulses per minute, the A4 window can be set to start at 800 to 900 milliseconds after the delivered ventricular pacing pulse (or sensed R wave) and extend until the next ventricular pacing pulse (or sensed R wave).

[0086] In other examples, the end of the A3 window and the start of the A4 window can be set as a percentage of the ventricular rate interval. For example, the control circuit 206 can determine the ventricular cycle length of a specified number of recent ventricular cycles (which can be paced or sensed). The control circuit 206 can determine the average or median of the determined ventricular cycle lengths and set the A4 window to start at a percentage of the average or median. In one example, the median ventricular cycle length of the eight most recent ventricular cycles is determined, and the A3 window is set to end and the A4 window is set to start at 80% of the median ventricular cycle length or the 4th longest ventricular cycle length in 8 ventricular cycles. The end of the A3 window and the start of the A4 window can be set between a specified minimum time interval and a maximum time interval, for example, in some examples, not less than 650 milliseconds and not more than 900 milliseconds. When the specified percentage of the median ventricular cycle length exceeds the limit range, the minimum or maximum value can be used.

[0087] In some examples, setting the A4 window at block 504 can be performed by setting a long post-ventricular atrial blanking period from the start of a ventricular pacing pulse. The A4 window extends from the end of the long post-ventricular atrial blanking period until the next ventricular pacing pulse. The post-ventricular atrial blanking period can be set to an extended time interval that is expected to cover the motion sensor signal that is expected to occur at a relatively predictable interval after the ventricular pacing pulse (e.g., Figure 5 In this way, any relatively large amplitude peak in the motion signal that occurs after the extended atrial blanking period is more likely to be an A4 signal and less likely to be a ventricular event (A1, A2, or A3).

[0088] At box 506, the control circuit 206 determines the maximum amplitude of the motion sensor signal during each A4 window for each motion sensor vector signal selected for analysis during the automatic sensing parameter selection process. The motion sensor vector signals selected for analysis can include one, two, or all three single-axis vector signals; one, two, or all three combinations of two-axis vector signals; and / or a combination of all three accelerometer axes in a three-axis vector signal. The maximum amplitude of each of the vector signals analyzed can be determined for each ventricular cycle occurring during a predetermined time interval or within a predetermined number of ventricular cycles. For example, as an example, the maximum amplitude can be determined from each vector signal during each ventricular cycle or over 50 to 1000 ventricular cycles over a minute, several minutes, an hour, or longer period.

[0089] The control circuit 206 determines the distribution of maximum amplitude values ​​at box 508, for example, by populating a histogram of the maximum amplitude determined during the A4 window for each vector signal selected for analysis. For example, as described above, a histogram of maximum amplitudes can be generated for a longitudinal vector and two radial vectors of a three-dimensional accelerometer whose one axis is aligned with the long axis of the pacemaker 14. In other instances, a histogram of maximum amplitudes can be generated for each single-axis vector signal and / or each two-axis vector signal and / or three-axis vector signal. When a combination of two or all three axes is used to generate a vector signal, the acceleration signal sampling points of the two or all three axis signals can be summed to generate a two-axis or three-axis vector signal. In other instances, vector mathematics can be used to determine the generated vector signal. The maximum amplitude can be determined from the rectified vector signal, or it can be the maximum peak-to-peak amplitude of the unrectified vector signal.

[0090] Figure 8Two example histograms 600 and 620 generated for two different motion sensor vector signals are depicted. Along the horizontal axis 604 of each of the histograms 600 and 620 is plotted the maximum amplitude of the vector signal detected during the A4 window. In the example shown, the horizontal axis 604 is shown in ADC units, where each ADC unit is 11.8 milli-g (acceleration due to gravity). The histograms of amplitudes determined from the motion sensor vector signals received by the control circuit 206 from the ADC included in the motion sensor 212 may be generated in ADC units, but may optionally be converted to units of acceleration (e.g., meters per second squared (meters per second)). 2 )) to be displayed on an external device (e.g., external device 20). For example, the acceleration conversion rate may be 1 m / s 2 / 100milli-g.

[0091] The maximum amplitude during each A4 window is matched to a histogram bin value or range. For each matching maximum amplitude value, the matching histogram bin count is increased by one to track the frequency of occurrence of each maximum amplitude value or range. The frequency or count of the binned maximum amplitude values ​​obtained within a predetermined time interval of a given vector signal is plotted along the y-axis 602 in each histogram. Since the ventricular cycle is asynchronous with the atrial rhythm, many ventricular cycles during which no true A4 event occurs during the A4 window may occur. Therefore, when the atrial contraction period does not happen to coincide with the nominal A4 window, relatively high counts 612 and 622 of relatively low maximum amplitudes may occur. In this example, a low maximum amplitude can be defined as a maximum amplitude of less than 5 ADC units detected during the A4 window. The high frequency of A4 windows with relatively low maximum amplitudes of the vector signal reflects a relatively large number of ventricular cycles during which the atrial contraction period does not happen to coincide with the A4 window.

[0092] As shown in the example histogram 600, the reliable sensing vector signal contains relatively high counts 614 at relatively high maximum amplitude values ​​(e.g., in the range of 7 to 15 ADC units). A moderately high frequency (counts 614) of higher maximum amplitudes (e.g., 8 ADC units or more) during the A4 window indicates the occurrence of A4 signals that happen to coincide with the A4 window during the non-atrial tracking pacing mode. Because these A4 signals have relatively high amplitudes, the vector signal used to generate the histogram 600 can be a highly reliable vector signal for sensing atrial events.

[0093] In contrast, example histogram 620 shows a relatively low or zero count 624 of a relatively high maximum amplitude signal during the A4 window. The vector signal used to generate histogram 620 is considered unreliable for use in detecting atrial events because most or all of the maximum amplitudes during the A4 window are relatively low, e.g., within the range of the baseline noise of the vector signal. This means that even on periods where the A4 signal coincides with the A4 window, the A4 amplitude is substantially within the range of the baseline noise of the vector signal, e.g., less than 5 ADC units. The orientation of one or more axes used to generate the vector signal associated with histogram 620 may result in a null signal during atrial systole.

[0094] Reference again Figure 7 And continue to refer to Figure 8 , at block 510, histogram bins corresponding to relatively low maximum amplitudes may be rejected due to low level noise in the vector signal. Figure 8 In the example of , the histogram bins storing counts of maximum amplitudes less than a noise threshold 606 (e.g., 5 ADC units) are discarded due to noise. In other examples, the noise threshold 606 can be set to a value greater than or less than 5 ADC units and can be set based on the baseline noise of the vector signal. In some examples, the noise threshold 606 is optional, or the noise threshold can be set to zero.

[0095] At box 512, the control circuit 206 can determine whether the maximum amplitude meets the vector selection criteria for each vector signal tested. In one example, at box 512, the total number of maximum amplitudes greater than the noise threshold 606 (e.g., all maximum amplitudes counted within ranges 616 and 626 in histograms 600 and 620, respectively) is determined by the control circuit 206. At box 512, the number of high maximum amplitudes greater than the high amplitude threshold 608 is also determined by the control circuit 206. In the example shown, the high amplitude threshold 608 is set to 8 ADC units. The number of maximum amplitudes greater than 8 ADC units is determined as the high maximum amplitude count. At box 512, the ratio of the high maximum amplitude count to the count of all maximum amplitudes greater than the noise threshold 606 is determined as the high maximum amplitude ratio. This high maximum amplitude ratio is determined for each A4 sense vector signal tested and is the frequency of high amplitude signals that occur during the A4 window and are likely to be actual A4 signals because they occur outside the post-ventricular atrial blanking period (as determined by Figure 8 614 in general).

[0096] The control circuit 206 can compare this high maximum amplitude ratio determined for each single-axis vector signal analyzed of the number of high maximum amplitudes (greater than the threshold 608) to the number of all maximum amplitudes greater than the noise threshold 606 to the single-axis vector selection threshold at box 514. In one example, if at least 50% of the maximum amplitude values ​​are greater than the high amplitude threshold, then after rejecting the low maximum amplitude values ​​less than the noise threshold, the single-axis vector signal can be selected as an A4 sensing vector and can be used as a single-axis vector signal for reliable A4 sensing. Figure 8 In the example histogram 600, more than 50% of the maximum amplitudes acquired within the range 616 (greater than 4 ADC units) are greater than 8 ADC units (high amplitude threshold 608). Therefore, when this vector signal is a single-axis vector signal used to obtain maximum amplitude data to generate the histogram 600, at box 516, this single-axis vector signal can be selected as the A4 event sensing vector signal. Using a single-axis sensing vector signal for sensing A4 events allows a single axis of the accelerometer to be powered to generate the A4 sensing vector signal, which saves power and can extend the functional life of the pacemaker 14 compared to using a combination of two or more axes to generate a vector signal for sensing atrial events.

[0097] In the event that two or more uniaxial vector signals satisfy the criteria applied at block 514, the uniaxial vector signal with the highest high to maximum amplitude ratio may be selected as the uniaxial A4 sensing vector signal at block 516. Typically, the control circuit 206 may select a vector signal that produces a distribution of maximum amplitudes during the A4 window that is skewed to the right (its distribution tail on the right is longer than its distribution tail on the left as the amplitude increases from left to right on the x-axis). At block 516, the vector signal with the largest median maximum amplitude, the highest rightward skewness of the maximum amplitude distribution, or other measure indicative of rightward skewness of the maximum amplitude distribution may be selected as the sole vector signal for sensing an A4 event during an atrial tracking ventricular pacing mode.

[0098] In some instances, the maximum amplitude determined for each vector signal can be compared with the rejection criteria. When the maximum amplitude of all vector signals meets the rejection criteria, an alarm can be generated. For example, if the high maximum amplitude ratio (the ratio of the number of maximum amplitudes greater than the high amplitude threshold 608 to the number of maximum amplitudes greater than the noise threshold 606) is less than the rejection threshold (as determined at box 518), the control circuit 206 can select a combination of all three axis signals at box 522 to generate an A4 sensing vector signal or select the best combination of two axis signals from the three axis signals to generate a two-axis vector signal for A4 sensing. Selecting the minimum number of accelerometer axes required to sense an A4 event can save the current demand from the power supply 214. Additionally or alternatively, an alarm can be generated to notify the clinician that no vector signal analyzed has met the reliable A4 sensing criteria. At box 522, the notification can be transmitted to the external device 20 by the telemetry circuit 208.

[0099] In some cases, all three uniaxial vector signals may have high maximum amplitude ratios less than a uniaxial vector signal threshold (the "NO" branch of box 514), but at least one, two, or all three uniaxial vector signals may have high maximum amplitude ratios greater than a rejection threshold (the "NO" branch of box 518). When at least one of the possible uniaxial vector signals has a high maximum amplitude ratio between the uniaxial vector threshold and the rejection threshold, the control circuit 206 may select two axis signals (corresponding to two different motion sensor axes) in combination for A4 event sensing at box 520. The two uniaxial vector signals with the highest high maximum amplitude ratios may be selected in combination for sensing atrial events. The two uniaxial vector signals may be summed to produce two axis vector signals. In some instances, a uniaxial vector signal aligned with the longitudinal axis of the housing 150 of the pacemaker 14 is selected along with another vector (e.g., a radial vector). The atrial event sensing vector may be selected as a combination of the longitudinal uniaxial vector signal summed with one of the radial uniaxial vector signals having the highest high maximum amplitude ratio determined at block 512 to produce a two-axis vector signal for A4 event sensing.

[0100] When two (or three) single-axis vector signals are selected in combination as the A4 event sensing vector signal, the multi-axis vector signal can be determined by vector summation of the two (or three) separate vector signals. The vector signals can be digitally summed using digitized rectified vector signals. The summation can be performed after steam flow to avoid destructive summation of two or more vector signals. In other examples, when the single-axis vector signal does not produce a high maximum amplitude ratio greater than the single-axis vector threshold, two or three separate analog vector signals can be summed.

[0101] In other examples, instead of determining a ratio as indicated at block 512, another measure of the distribution of the maximum amplitudes may be determined and compared to the vector selection and / or rejection criteria. For example, as described below in conjunction with Fig.15 As described, the median, mean, or specified percentile of all maximum amplitudes determined at box 506 can be determined (in some instances, after discarding maximum amplitudes less than a noise threshold). The medians (or other measures of distribution) of the maximum amplitudes determined for each of the vector signals being analyzed can be compared to each other, and the vector signal that produces the largest median maximum amplitude can be selected. In some instances, when a single-axis vector signal corresponds to the largest median maximum amplitude, the single-axis vector signal can be selected. However, a vector signal that is a combination of at least two axis signals will typically have a larger median maximum amplitude than a single-axis vector signal (due to the summation of the two single-axis signals). Therefore, in some instances, a two-axis vector signal with the largest median maximum amplitude can be selected as an atrial event sensing vector signal.

[0102] In the event that each of the two-axis vector signals is rejected due to the maximum amplitude meeting the rejection criteria, the combination of all three motion sensor axis signals may be selected as a three-axis vector signal for atrial event sensing. Fig.15 As further described, a two-axis vector signal (or any analyzed vector signal) may be rejected when a threshold count less than the maximum amplitude acquired for a given vector signal is greater than a minimum amplitude threshold. In some examples, the minimum amplitude threshold may be set to the minimum available A4 sensing threshold amplitude.

[0103] Fig. 9 is used to establish the end time of the A3 window (for example, Figure 5 Flowchart 700 of a method for determining an end time 422 of the window 424 shown in FIG. 4 ). At box 702, the control circuit 206 sets the pacing mode to a non-atrial tracking pacing mode. By setting the VV pacing interval, the pacing rate can be set to a nominal pacing rate, such as 50 pulses per minute. At box 704, the A4 sensing vector (a single-axis vector signal or a sum of two or more single-axis vector signals) is selected. The control circuit 206 may combine the above Figure 7 and 8The process described selects a vector signal that is established as the A4 sensing vector. The process of flowchart 700 can be performed only for the selected atrial event sensing vector signal (a single-axis vector or a two-axis or three-axis vector signal that is a summed combination of two or more single-axis vector signals), and the process can be repeated if the A4 sensing vector signal selection changes. In other examples, at least a portion of the process of flowchart 700 can be performed for all available motion sensor vector signals or multiple selected vector signals to enable simultaneous motion sensor signal data acquisition for generating a distribution of motion sensor signal features.

[0104] In some instances, Figure 7 After selecting the atrial event sensing vector at block 520 of , the non-atrial tracking pacing mode and rate remain in effect. The control circuit 206 may proceed directly to the process of flowchart 700 to establish the A3 window end time, for example, directly from Figure 7 The frame 520 to Fig. 9 In the example of the A4 sensing vector signal selection including a one-dimensional single-axis motion sensor or a fixed A4 sensing vector signal selection, Figure 7 At block 704, the process of establishing the A3 window end time according to flowchart 700 may be performed by selecting a manually programmed or default atrial event sensing vector signal without first performing the process of flowchart 500.

[0105] At block 706, a nominal A3 window is set, for example, starting 600 milliseconds after a ventricular event (sensed or paced) and extending until the next ventricular event. The nominal A3 window may be set by setting a post-ventricular atrial blanking period extending from a ventricular electrical event (sensed or paced) within a predetermined time interval (e.g., 600 milliseconds). The nominal A3 window may be set to start after the expected time of the A1 and A2 signals (e.g., Figure 4 ) and extends as late as possible to the next ventricular electrical event to increase the likelihood of capturing an A3 signal during the nominal A3 window. In some examples, at box 706, the A3 window is set to start at a fixed interval (e.g., 600 milliseconds after a ventricular event (a sensed R wave or ventricular pacing pulse)) and extend to an A3 window end time that is set to a percentage (e.g., 80% of an average or median ventricular cycle length determined based on a specified number of recent ventricular cycle lengths (e.g., 8 ventricular cycle lengths)).

[0106] At block 708, the control circuit 206 sets a nominal threshold amplitude. As an example, the nominal threshold amplitude may be 9 ADC units, which may correspond to 0.9 m / s. 2. At box 709, the time of the most recent crossing of the nominal threshold amplitude in each A3 window is determined for each vector signal being analyzed within a predetermined time period or a predetermined number of ventricular cycles. When atrial contraction (and A4 event) does not happen to occur during the A3 window, the most recent threshold crossing may be a true A3 signal, and since the A3 signal is a ventricular event signal that follows the ventricular electrical event at a relatively consistent time interval, the most recent crossing is expected to occur relatively early in the nominal A3 window. When atrial contraction does happen to occur during the A3 window, the most recent threshold crossing may be an A3 or A4 signal, depending on when the atrial contraction occurs during the A3 window. However, during an extended A3 window, a relatively late threshold crossing is more likely to be an A4 signal than an A3 signal, because the A3 signal is typically related to the timing of ventricular electrical events. In some ventricular cycles, the motion sensor vector signal may cross the nominal threshold amplitude multiple times during the A3 window. For example, a true A3 signal and a true A4 signal may cross the nominal threshold amplitude. In this case, in some instances, only the timing of the most recent threshold crossing is stored.

[0107] When threshold amplitude crossings accumulate over a large number of ventricular cycles (e.g., over at least 50 to 100 ventricular cycles or more), a relatively high frequency of recent threshold crossings will represent an A3 signal, and some frequencies will represent an A4 signal when atrial contraction happens to occur during the A3 window. In some cases, a fused A3 / A4 event may occur as the most recent threshold amplitude crossing during the A3 window. In some cases, although A1 and A2 signals may occur during the post-ventricular atrial blanking period, a relatively late threshold amplitude crossing may be an A1 signal. The distribution of the timing of the most recent threshold amplitude crossings can reveal the expected timing of A3 events and the expected timing of A4 events during the ventricular cycle.

[0108] At block 710, a histogram may be populated using the data accumulated at block 709. The most recent nominal threshold amplitude crossing times accumulated beat by beat over a predetermined time interval or a predetermined number of ventricular cycles may be binned according to a histogram bin time interval range. A count of the number of most recent threshold crossings occurring during each bin time interval range is determined.

[0109] Fig.10 It is possible to detect a sensing vector signal in Fig. 9750 . The most recent threshold amplitude crossing time is plotted in milliseconds (ms) along the x-axis 754 and represents the time at which the last nominal threshold amplitude crossing occurred during the ventricular cycle after a ventricular electrical event. The frequency or count of the most recent threshold crossing time is plotted along the y-axis 752. In the example shown, for an A3 window whose start time 756 is 600 milliseconds after a ventricular electrical event, the leftmost, lowest bin contains the most recent crossing times that occurred in the range of 601 milliseconds to 650 milliseconds after the ventricular electrical event. The rightmost bin contains the most recent crossing times that occurred in the range of 1001 to 1050 milliseconds after a ventricular electrical event (pacing pulse or sensed R wave). In this example, each bin contains a time range of 50 milliseconds, and the A3 window extends from 600 milliseconds after the previous ventricular electrical event to the next ventricular electrical event. Other start and / or end times for the A3 window may be selected (and may depend on the ventricular rate), and in other examples, other time ranges for the histogram bins may be used.

[0110] The distribution represented by histogram 750 exhibits a bimodal distribution with a left peak 772 corresponding to a possible A3 signal during the extended A3 window and a right peak 770 corresponding to a possible A4 signal during the extended A3 window. A4 confidence time threshold 758 may be set to the time after which the nominal threshold amplitude is expected to cross with high probability to be an A4 signal and very unlikely to be an A3 signal. Fig.10 In the example of , the A4 confidence time threshold 758 is set to 900 milliseconds based on the ventricular pacing rate being set to 50 pulses per minute. During the accumulation of recent threshold crossing times, the A4 confidence time threshold 758 can be set to a fixed value based on the ventricular rate. In other examples, the A4 confidence time threshold 758 can be set based on a predetermined percentage (e.g., a predetermined percentile) of all accumulated recent threshold crossing times.

[0111] After discarding bins above the A4 confidence time threshold 758, the leftmost peak of the bimodal distribution is represented by the highest bin count 772 within the remaining range 760 of the histogram bins. The leftmost peak 772 is likely to represent the occurrence of an A3 event during an extended A3 window and may contain some fused A3 / A4 signals. An appropriate end time for the A3 window may be any time from the median 762 of the most recent threshold crossing times within the range 760 to the A4 confidence time threshold 758. The A3 window end time may be selected between the median 762 and the A4 confidence time threshold 758 so that the A3 window contains an A3 signal (and a fused A3 / A4 signal) with a high probability. In some instances, the A3 window end time or A4 window start time for A4 sensing during atrial tracking ventricular pacing mode is set to the time of the left peak of the bimodal distribution based on the most recent nominal threshold crossing time. For example, the A3 window end time used during atrial tracking ventricular pacing mode can be set to the left peak of the bimodal distribution (as time increases from left to right) plus an offset, where the offset is a predetermined value ranging from zero to 200 milliseconds as an example.

[0112] return Fig. 9 , at box 712, counts in filled histogram bins that are greater than the A4 confidence time threshold are discarded. At box 714, the control circuit 206 selects an A3 window end time based on the remaining histogram bin data after discarding bins greater than the A4 confidence time threshold. The control circuit 206 can determine the median time of the most recent nominal amplitude threshold crossing for the remaining bins. The A3 window end time can be established as the median of the distribution plus an offset. The offset can be a predetermined value in the range of 0 milliseconds to 200 milliseconds (e.g., 50 milliseconds to 100 milliseconds). In other instances, after discarding histogram bins greater than the A4 confidence time threshold, the A3 window end time can be set to a percentile of the remaining histogram bin counts (in Fig.10 For example, after discarding bin counts greater than the A4 confidence time threshold 758, the A3 window end time may be set to a time at which at least 70%, 80%, 90%, or 95% of the most recent threshold spanning times are less than the A3 end time.

[0113] exist Fig.10 In the example of , the A3 window begins at the expiration of the post-atrial ventricular blanking period (e.g., 600 milliseconds after a ventricular event) until the next ventricular event (pacing pulse or sensed R wave). During this extended A3 window, both early and late threshold crossings are detected, resulting in Fig.10, which contains a left peak 772 corresponding to a possible A3 event signal and a right peak 770 corresponding to a possible A4 event signal. Instead of setting an extended A3 window and then discarding bins greater than the A4 confidence time threshold, the A3 window can be set at box 706 to extend from 600 milliseconds (or the end of the post-ventricular atrial blanking interval) until the A4 confidence time threshold 758 (which can be set as a percentage of the median ventricular cycle length as described above). For example, the A3 window can be set to extend from 600 milliseconds until 80% of the median of the eight ventricular cycle lengths and not less than 650 milliseconds or greater than 900 milliseconds when the pacing lower rate is set to 50 pulses per minute. In this way, the most recent threshold crossings during the A3 window are most likely to be A3 events because they occur before the A4 confidence time threshold 758. After the A4 confidence time threshold 758, histogram bins corresponding to even later threshold crossings do not need to be filled because they are unlikely to contain true A3 event threshold crossing times. The A3 window end time may be established as the median of the distribution of most recent threshold crossing times plus an offset.

[0114] Fig.11 800 is a flow chart of a method for establishing early and late values ​​of an A4 sensing threshold applied during and after the A3 window, respectively, for sensing an A4 signal during an atrial tracking ventricular pacing mode. At block 802, the control circuit 206 sets the pacing mode to a non-atrial tracking pacing mode and sets the VV pacing interval according to a selected pacing rate (e.g., 50 pulses per minute). At block 804, the control circuit 206 sets the A4 sensing threshold to a non-atrial tracking pacing mode and sets the VV pacing interval according to a selected pacing rate (e.g., 50 pulses per minute). Figure 7 Method to select the A4 sensing vector (as a single-axis vector signal or a combination of two or more acceleration axis signals).

[0115] In some instances, only the Figure 7 The process of flowchart 800 is performed for the A4 sensing vector signal selected by the method. In other examples, portions of the process of flowchart 800 may be performed for all available motion sensor vector signals (including single-axis, two-axis, and three-axis vector signals, or any number of vector signals selected for analysis). For example, Figure 7 The multiple vector signals used in the process of obtaining the data required to generate the histogram for setting the A4 sensing threshold amplitude value, but only corresponding to Figure 7 The data of the vector signal selected as the A4 sense vector signal at blocks 516 , 520 , or 522 may be used to set the A4 sense threshold amplitude value.

[0116] At block 806, the A3 window end time may be set. In one example, as described above, the A3 window end time is set as a percentage of the median ventricular cycle length. In other examples, the A3 window is set to a percentage of the median ventricular cycle length based on a histogram of recent threshold crossing times. Fig. 9 The A3 window may extend from a fixed start time (which may be programmable or based on empirical data) to the A3 window end time selected at block 714 of FIG. Fig. 9 and 10 The A3 window end time is automatically determined based on the distribution of the most recent nominal threshold amplitude across time as described above. In other examples, a manually programmed or default A4 sensing vector signal and / or A3 window end time is set at blocks 804 and 806, respectively. In this case, the A4 sensing threshold amplitude value need not be established in Fig.11 Execute before the process Figure 7 and Fig. 9 process.

[0117] At block 808, the control circuit 206 determines the maximum amplitude of the motion signal during the A3 window for each ventricular cycle within a predetermined number of cycles or a predetermined time interval. At block 810, for each ventricular cycle within a predetermined number of cycles or a predetermined time interval, the control circuit 206 determines the maximum amplitude of the motion signal after the end time of the A3 window and before the next ventricular electrical event (e.g., during the A4 window).

[0118] At block 812, the maximum amplitudes determined during the A3 window are used by the control circuit 206 to generate an A3 window maximum amplitude distribution, for example by populating an A3 window maximum amplitude histogram. Counts for histogram bins corresponding to maximum amplitudes less than a noise threshold may be discarded at block 814. Very low maximum amplitudes during the A3 window may not represent true A3 or A4 events and may be baseline noise of the motion signal. At block 816, the control circuit 206 selects an early A4 sensing threshold amplitude value to be applied during the A3 sensing window based on the remaining histogram data that was not discarded. Fig.12 A method for selecting an early A4 sensing threshold amplitude value based on A3 window histogram data is described.

[0119] The control circuit 206 may, for example, at block 818, use the maximum amplitude determined at block 810 during the A4 window (after the A3 window until the end of the ventricular cycle marked by the next ventricular electrical event) to generate a distribution of A4 window maximum amplitude data, for example, by populating an A4 window maximum amplitude histogram. At block 820, the histogram bins storing maximum amplitudes less than the noise threshold are discarded. At block 822, the control circuit 206 selects a late A4 sensing threshold amplitude value based on the remaining (not discarded) distributions of the maximum amplitude values. Fig.13 A method for selecting a late A4 sensing threshold amplitude value based on histogram data is described.

[0120] Fig.12 850 is an example of a histogram of the maximum amplitude of the motion sensor vector signal during the A3 window that may be generated by the control circuit 206. The maximum vector signal amplitude is plotted on the x-axis 856 (shown in ADC units in this example). The counts for each histogram bin are plotted along the y-axis 854. Although other histogram bin resolutions may be used (and may be in g or meters / second), 2 ), but each histogram bin is Fig.12 The amplitude range is shown as containing one ADC unit in . Each bin stores a count of the number of times the maximum amplitude of the vector signal during the A3 window falls within the corresponding bin range.

[0121] The noise threshold amplitude 858 can be a predetermined value or determined as a percentile of the histogram frequency distribution. The maximum amplitude during the A3 window that is less than the noise threshold amplitude 858 can be attributed to baseline noise (or very low amplitude A3 signal) during the A3 window. The histogram bins corresponding to the maximum amplitudes that are less than the noise threshold amplitude 858 can be discarded for the purpose of selecting an early A4 sensing threshold amplitude (also referred to herein as an "early atrial event sensing threshold"). Fig.12 In the example of 2 .

[0122] After discarding histogram bins that are less than (to the left of) the noise threshold amplitude 858, the control circuit 206 can determine the early A4 sensing threshold 860 as the percentile of the remaining distribution of maximum amplitudes determined during the A3 window. Since it is expected that most of the maximum amplitude values ​​determined during the A3 window and counted in the histogram 850 represent actual A3 events, most of the maximum amplitudes should be less than the early A4 sensing threshold 860 so that they are not falsely detected as A4 events.

[0123] A small percentage of relatively high maximum amplitudes (e.g., maximum amplitudes greater than the early A4 sensing threshold 860) occurring during the A3 window can represent fused A3 / A4 events that should be sensed as A4 events. According to one example, the early A4 sensing threshold 860 can be set to a relatively high percentile, for example, eighty percent, eighty-five percent, or ninety percent of the maximum amplitudes of the remainder (not discarded) of the histogram 850. In one example, the upper 15% of the maximum amplitude signals during the A3 window (after discarding the bin below the noise threshold) would meet the atrial event sensing criteria and would be sensed as A4 signals, for example, during an atrial tracking pacing mode. The lower 85% of the maximum amplitude signals during the A3 window would not be sensed as A4 signals.

[0124] Fig.13 can be controlled by the control circuit 206 in Fig.11 870 for a vector signal being analyzed. The maximum amplitude during the A4 window of the vector signal being analyzed is plotted on the x-axis 876. The counts for each histogram bin are plotted along the y-axis 874. Each histogram bin is plotted at 876, although other histogram bin resolutions may be used. Fig.13 Each bin stores a count of the number of times the maximum amplitude of the vector signal after the A3 window (during the A4 window) falls within the range of the corresponding bin.

[0125] The noise threshold amplitude 878 may be a predetermined value or determined as a percentile of the histogram frequency distribution. Histogram bin counts less than the noise threshold amplitude 878 may be discarded for the purpose of selecting a late A4 sensing threshold amplitude value. These relatively low maximum amplitude signals during the A4 window may be baseline noise and not true A4 signals. Fig.13 In this example, the noise threshold is 5 ADC units (or approximately 0.6 m / s 2 ). Counts in bins with fewer than 5 ADC units are discarded for the purpose of selecting a late A4 sensing threshold amplitude value (also referred to herein as a "late atrial event sensing threshold").

[0126] After discarding the histogram bins corresponding to maximum amplitudes less than the noise threshold amplitude 878, the control circuit 206 can determine the late A4 sensing threshold amplitude value 880 as a percentile of the remaining maximum amplitude distribution. Since it is expected that most of the maximum amplitude values ​​determined during the A4 window and counted in the histogram 870 represent actual A4 signals, most of the maximum amplitudes should be greater than the late A4 sensing threshold 880 to avoid insufficient sensing of A4 events. A small percentage of the maximum amplitudes occurring during the A4 window may be noise or even late A3 signals. The late A4 sensing threshold 880 can be set to a relatively low percentile (e.g., fifty percent) of the remaining (not discarded) maximum amplitudes of the histogram 870. In this way, after discarding the maximum amplitudes less than the noise threshold 878, the lower 5% of the remaining maximum amplitude signals during the A4 window will not be sensed, but 95% of the maximum amplitude signals will be greater than the late A4 sensing threshold 880 and meet the atrial event sensing criteria, for example, during the atrial tracking ventricular pacing mode. The example percentiles and noise thresholds given here are illustrative in nature, and it should be understood that other percentiles and noise thresholds may also be used to establish early and late A4 sensing thresholds.

[0127] A histogram generally depicted in the figures presented herein or other type of graphical representation of the distribution of motion sensor signal features determined for setting atrial event sensing parameters may be generated for display on display unit 54 of external device 20. The generated display may include values ​​or graphical depictions (e.g., a line, bar, or icon overlaid on a histogram) to indicate the determination by control circuitry 206 (or external processor 52) of atrial event sensing parameter values ​​or settings based on the distribution of the determined features.

[0128] Fig.14 is a flow chart 900 of a method for controlling atrial synchronized ventricular pacing according to one example. At block 902, the control circuit 206 selects the A4 sensing vector. The A4 sensing vector (single-axis vector signal, two-axis vector signal, or three-axis vector signal) can be used in conjunction with the above Figure 7 and 8 At block 904, the A3 window is set according to the start time and the end time. The end time can be set to the time after the previous ventricular electrical event, which is determined using the method described above in conjunction with 9 and 10. At block 906, the multi-level A4 sensing threshold is determined by using a combination of Figure 11-13 The described method establishes an early A4 sensing threshold amplitude value and a late A4 sensing threshold amplitude value to set.

[0129] At least one atrial sensing parameter of the A4 sensing vector, the A3 window end time, the early A4 sensing threshold amplitude value, and / or the late A4 sensing threshold amplitude value is established by determining a characteristic of the motion sensor signal, generating at least one histogram or one or more other representations of a distribution of the one or more determined characteristics of the motion sensor signal, and selecting a corresponding A4 sensing parameter based on an analysis of the distribution. In some examples, one or more of the atrial event sensing parameters including the A4 sensing vector, the A3 window end time, and the early and late A4 sensing thresholds are set to default or user-programmable values ​​without generating a histogram or other representative distribution of the motion signal characteristics.

[0130] In some examples, the A4 sensing vector is first determined, as shown in block 902. After the A4 sensing vector is selected, the A3 window end time can be established (block 904), and then the early and late A4 sensing threshold amplitude values ​​can be established (block 906). However, in other examples, the A4 sensing parameters can be determined in the same manner as Fig.14 , or partially or completely simultaneously. For example, when pacing in a non-atrial tracking pacing mode, a nominal A3 window end time of 800 to 900 milliseconds can be set to enable simultaneous data acquisition during multiple ventricular pacing cycles to generate a distribution of motion sensor signal data for simultaneously establishing two or more atrial event sensing parameters. The maximum amplitude during the A3 window, the maximum amplitude after the A3 window, and the most recent nominal threshold crossing that occurred after the start of the A3 window (e.g., after 600 milliseconds) can be determined based on each ventricular cycle to generate a distribution of histograms such as those shown in the accompanying drawings. Early and late values ​​of the A4 sensing vector, A3 window end time, and atrial event sensing threshold can be established based on simultaneously acquired motion sensor signal features and corresponding distributions generated therefrom.

[0131] At block 908, the control circuit 206 may set the pacing mode to an atrial tracking ventricular pacing mode, such as a VDD pacing mode. At block 910, the atrial event detector circuit 240 senses an A4 event during the ventricular cycle using the A4 sensing parameters established at blocks 902 to 906. The control circuit 206 may generate an atrial sensed event signal in response to the atrial event detector circuit 240 sensing an A4 event. The atrial sensed event signal may be used to control the timing of ventricular pacing pulses during the VDD pacing mode. The atrial tracking ventricular pacing mode set at block 908 may be referred to as an atrial synchronized ventricular pacing mode because an AV pacing interval (block 912) may be initiated in response to sensing an A4 signal (block 910) for controlling the timing of ventricular pacing pulses. If an R wave is sensed before the AV interval expires (the "yes" branch of block 918), then at block 910, the control circuit 206 senses the next A4 signal. The A4 signal is sensed in response to the earliest crossing of the multi-level atrial event sensing threshold during either the A3 window or the A4 window.

[0132] When the AV pacing interval expires ("yes" branch of block 914), a ventricular pacing pulse is generated by pulse generator 202 and delivered (block 920). In this way, the ventricular pacing pulse is synchronized with the atrial contraction event to provide a more normal heart rhythm for patients experiencing AV block.

[0133] Fig.15 1000 is a flow chart of a process for setting atrial event sensing parameters performed by a pacemaker 14 according to another example. In some examples, automatic selection of starting values ​​for atrial event sensing parameters may be initiated at block 1001 by the control circuit 206 after a time delay following a telemetry session with an external device 20. For example, in a clinic or hospital or remotely, during an implant procedure or any patient follow-up procedure, the feature of automatic selection of atrial event sensing parameters may be programmed as "on" or enabled by a user interacting with the external device 20. After the pacemaker telemetry circuit 208 is no longer receiving telemetry communications, the control circuit 206 may detect inactivity of the external device 20 or termination of a telemetry session therewith and initiate the automatic selection process at block 1001 by waiting for a time delay (e.g., after one to ten minutes or after three minutes in one example). This time delay after the receipt of telemetry communication signals has ceased may allow other programming or procedures to be completed before the automatic atrial event sensing parameter selection process is initiated, such as during an implant procedure or a programming and interrogation session.

[0134] Prior to initiating the selection process, the control circuit 206 may apply other criteria at box 1001. For example, the control circuit 206 may verify that the patient activity level is less than a threshold level, verify that the target heart rate for rate-responsive pacing is less than a threshold rate based on the patient activity level, and / or verify that the actual ventricular rate is not greater than a threshold rate. In some instances, the control circuit 206 may be configured to determine a patient activity metric based on a motion sensor signal associated with the patient's physical activity level. In some instances, this patient activity metric may be used by the control circuit to control rate-responsive ventricular pacing to provide ventricular rate support during times of increased or elevated patient activity.

[0135] Upon initiating the atrial event sensing parameter selection process, the control circuit 206 may set test values ​​for a plurality of control parameters to enable motion sensor signal analysis and data collection to generate profile data for setting atrial event sensing control parameters. At box 1002, the control circuit 206 may switch from a programmed atrial tracking ventricular pacing mode (e.g., a VDD pacing mode) to a temporary non-atrial tracking ventricular pacing mode (e.g., a VDI pacing mode) that includes generating a motion sensor signal for analysis. The control circuit 206 may set a temporary lower pacing rate to control the ventricular pacing rate during the motion sensor signal analysis. In one example, the lower pacing rate is set to 50 pulses per minute, but in various examples, may be set to 40 pulses per minute or higher.

[0136] At box 1002, the control circuit 206 can set a test value of the test A3 threshold amplitude for detecting the most recent motion signal threshold crossing during the A3 window to establish the end time of the A3 window. Additionally or alternatively, the control circuit 206 can set one or both of the early and late A4 sensing threshold amplitude values ​​to the maximum possible value to avoid actual A4 sensing during the motion sensor signal analysis. In an illustrative example, the A4 sensing threshold amplitude values ​​of the early (during the A3 window) and late (during the A4 window) can be set to the maximum limit of the ADC or to the value of the maximum bin range of the generated histogram that exceeds the maximum value of the generated distribution range or the maximum amplitude of the vector signal being analyzed. In this way, A4 event detection is avoided, which may otherwise terminate the A3 or A4 window, thereby excluding additional analysis of the motion sensor signal during a given ventricular cycle. The control circuit 206 can further set the test settings for the ventricular post-blanking period and the end time of the A3 window.

[0137] As described above, during the motion sensor signal analysis, the end of the A3 window (and the beginning of the A4 window) can be set to a percentage of the ventricular rate interval. For example, at box 1002, when switching to the VDI pacing mode, the control circuit 206 can determine the ventricular cycle lengths of a specified number of ventricular cycles (which can be paced or sensed). The control circuit 206 can determine the average or median of the determined ventricular cycle lengths and set the test end time of the A3 window to start at a percentage of the average or median ventricular cycle length. In one example, after switching to the VDI pacing mode, the test A3 window end time is set to 80% of the fourth shortest ventricular cycle length of the first eight ventricular cycles. The end of the A3 window (and the beginning of the A4 window) can be set between a specified minimum time interval and a maximum time interval, for example, in some examples, not less than 650 milliseconds and not more than 900 milliseconds from the most recent ventricular electrical event (sensed or paced). When a specified percentage of the median ventricular cycle length is outside the limits, the minimum or maximum value can be used instead.

[0138] The ventricular post-blanking period can be set to a fixed value, a value based on the lower pacing rate set during the temporary VDI pacing mode, or the median ventricular cycle length. In one example, when the lower pacing rate is set to 50 pulses per minute, the ventricular post-blanking period is set to 600 milliseconds. The A3 window begins when the ventricular post-blanking period expires and extends to the test A3 window end time.

[0139] The test A3 threshold amplitude for detecting the most recent motion sensor signal threshold crossing during the test A3 window is, for example, as combined with Fig. 9 and Fig.10 The A3 window end time described for setting the A3 window end time can be set to a relatively low amplitude that is expected to be greater than the baseline motion sensor signal noise. For example, the test A3 threshold amplitude can be set to 9 ADC units, which can correspond to approximately 106 milli-g or about 1 meter / second. 2 .

[0140] At block 1002, the control circuit 206 may establish a vector signal from the motion sensor 212 that will be analyzed to generate distribution data. In some instances, each available two-axis vector signal and three-axis vector signal is generated and analyzed to generate amplitude and timing distribution data for each of the vector signals. For example, each axis of the three-dimensional accelerometer is referred to as axis 1, axis 2, and axis 3, the combination of axis 1 and axis 2 may be referred to as a 1+2 vector signal, the combination of axis 1 and axis 3 may be referred to as a 1+3 vector signal, and the combination of axis 2 and axis 3 may be referred to as a 2+3 vector signal. The combination of all three axis signals from the motion sensor 212 may be referred to as a 1+2+3 vector signal. In one instance, each of the 1+2 vector signal, the 1+3 vector signal, the 2+3 vector signal, and the 1+2+3 vector signal may be processed and analyzed by the control circuit 206 to determine the amplitude and timing data of the corresponding vector signal for selecting at least one atrial event sensing control parameter used during the atrial tracking ventricular pacing mode.

[0141] After setting the test pacing mode, pacing rate, test vector signal, and other test control parameters, at box 1004, the control circuit 206 can begin to acquire amplitude and timing data from the vector signal being analyzed. When the four vector signals listed above are selected for analysis during the automatic atrial sensing parameter selection process, each vector signal can be analyzed on a rotating basis to remove or minimize the effects of confounding factors on a particular vector signal, such as posture-dependent changes that may occur in the vector signal due to varying patient positioning or activity. For example, one vector signal can be analyzed within a one-minute time interval to acquire amplitude and timing data, and then the next vector signal can be analyzed within the next one-minute time interval, and so on. In this way, each of the four vector signals listed above can be analyzed within one minute of each four-minute time interval. This process can be repeated a specified number of times (e.g., twice, five times, ten times, etc.) until the desired number of minutes or data points are obtained for each of the vector signals being analyzed. In one example, amplitude and timing data is obtained from each of the four vector signals listed above on a rotating basis for a total of five minutes per vector signal or a total of at least 20 minutes.

[0142] In other examples, one or more of the single-axis vector signals (e.g., axis 1 vector signal, axis 2 vector signal, and / or axis 3 vector signal) can be included as test vector signals in the analysis for obtaining vector signal data at block 1004. Any specified number of vector signals, each of which can be obtained from a single accelerometer axis, a sum of two axis signals, or a sum of all three accelerometer axis signals, can be included in the analysis for obtaining amplitude and timing data at block 1004. The number of vector signals analyzed and the accelerometer axis used to obtain each vector signal can be programmed by the user. When a combination of axes is used, the signal from each axis in the combination of axes can be sampled at a specified time slot of the sampling rate, so that the sample points from two or all three axis signals can be summed to produce the desired vector signal that is a combination of two or all three accelerometer axis signals. For example, if the vector signal is sampled once every 1 millisecond, each axis signal can be sampled within a 333 millisecond time slot, so that the sample of each axis signal can be used to sum with one or more other axis signals at each 1 millisecond sample point time.

[0143] At box 1004, amplitude and / or timing data is accumulated as needed from the vector signal being analyzed for selecting one or more atrial event sensing parameters. For example, one or more of an A4 sensing vector signal, an early A4 sensing threshold amplitude value, a late A4 sensing threshold amplitude value, and / or an A3 window end time, or any combination thereof, may be established by the control circuit 206 during the process of flowchart 1000. When the process of flowchart 1000 is executed to select an A4 sensing vector signal, a maximum amplitude during the A4 window is determined for each test vector signal for a desired number of ventricular cycles or time periods. By setting the late A4 sensing threshold amplitude value to a relatively high value (e.g., a maximum available value), the A4 window does not terminate before the next ventricular event, thereby allowing the control circuit 206 to determine the maximum vector signal amplitude until the next ventricular event (paced or sensed).

[0144] Other data determined from each of the vector signals may include the time of the most recent Test A3 threshold crossing during the Test A3 window (e.g., as combined with Fig. 9 and 10 ) and the maximum vector signal amplitude during the A3 window and / or A4 window (e.g., as combined with Figure 11-13 The amplitude and / or timing data determined from each test vector signal depends on which atrial event sensing parameter value is being set by control circuit 206 during the process of flowchart 1000.

[0145] At any time before, during, or after the determination of amplitude and / or timing data based on the motion sensor vector signal at box 1004 is completed, the control circuit 206 can detect a suspension condition as indicated by box 1006. One or more conditions may cause confounding effects on the amplitude and timing data, thereby warranting a pause or delay in obtaining the data. For example, high or variable patient physical activity and / or a high or variable heart rate may cause changes in the amplitude and timing data of a given vector signal, which confounds the distribution data generated for the vector signal. Therefore, the amplitude and / or timing data obtained at box 1004 for selecting one or more atrial event sensing control parameters can be obtained during a time interval associated with a relatively low stable heart rate (e.g., less than 80 beats per minute) and / or a patient physical activity level (e.g., less than an activity threshold corresponding to activities of daily living or rest).

[0146] The control circuit 206 can determine a patient physical activity metric based on the motion sensor signal at regular time intervals. The target heart rate and the sensor-indicated pacing rate can be determined based on the physical activity metric to provide rate-responsive pacing to support the patient's level of physical activity. The control circuit 206 can detect a termination condition based on at least one patient physical activity metric or level determined based on the motion sensor signal being greater than a threshold activity level. In another example, the control circuit 206 can detect a termination condition based on the variability of the patient's physical activity level, for example by detecting a threshold change in the physical activity level within a predetermined time interval. In other examples, the control circuit 206 can detect a termination condition in response to determining that a paced or sensed target heart rate, a sensor-indicated pacing rate, and / or an actual ventricular rate is greater than a threshold rate or is highly variable based on a threshold rate change within a predetermined time interval.

[0147] In one instance, a ventricular rate faster than 85 beats per minute can be an abort condition. The control circuit 206 can determine the ventricular cycle length during the amplitude and timing data acquisition at box 1004. After completing the data acquisition, at box 1006, the control circuit 206 can determine whether it is greater than a percentage threshold, such as more than 20% to 30% of the ventricular cycle lengths are shorter than the threshold interval. For example, if 20% or more of the ventricular cycle lengths are shorter than about 700 milliseconds (or faster than a rate of about 85 beats per minute) during the data acquisition, an abort condition may be detected at box 1006 due to a high ventricular rate. Without generating a distribution or histogram of the data, the data can be discarded. In other instances, the data can be stored and compiled with data obtained during the next data acquisition time to generate and analyze a distribution of the data.

[0148] In other instances, the threshold ventricular cycle length interval for detecting a high heart rate may be 650 to 750 milliseconds. In still other instances, the threshold ventricular cycle length interval may be set based on an average or median ventricular cycle length determined from ventricular cycle lengths stored during data acquisition. For example, the threshold cycle length may be set to the median ventricular cycle length minus 100 to 150 milliseconds, or to a ventricular rate that corresponds to 10 to 20 beats per minute faster than the median ventricular rate during data acquisition. In an illustrative example, an abort condition may be detected at box 1006 due to a variable or high ventricular rate when more than 20% (or other selected percentage) of the ventricular cycle lengths correspond to a ventricular rate that is faster than the rate of the median cycle length during data acquisition plus 10 beats per minute.

[0149] In some examples, an abort condition may be detected at block 1006 due to a variable heart rate, the abort condition comprising a threshold percentage of ventricular cycle lengths being longer than a long threshold cycle length (or slower than a corresponding ventricular rate). The control circuit 206 may set the long threshold cycle length based on a ventricular rate corresponding to a median ventricular cycle length determined from the ventricular cycle lengths stored during the data acquisition at block 1004. For example, the long threshold cycle length may be set to correspond to a median ventricular rate determined from the median ventricular cycle lengths during the data acquisition period minus a ventricular rate interval of 10 beats per minute. An abort condition may be detected at block 1006 due to a variable ventricular rate when the exceeding threshold percentage (e.g., 20%, 30%, or other percentage) of the ventricular cycle lengths is faster than a slow ventricular rate interval less than the median rate (e.g., corresponding to 10 beats per minute).

[0150] Additionally or alternatively, a high or variable patient activity level may be a termination condition detected at block 1006. A patient physical activity metric may be determined by integrating the absolute value of a selected accelerometer vector signal over a predetermined duration (e.g., 2 seconds). The metric may be referred to as an "activity count" and is related to the acceleration applied to the motion sensor due to patient body motion associated with physical activity during a predetermined time interval. In some instances, a 2-second (or other time interval) activity count may be used directly to indicate a patient physical activity level, or may be combined in further calculations to obtain other physical activity metrics. At block 1006, at least one activity count may be compared to a threshold count to determine whether the termination condition is met. In some instances, a threshold number of activity counts (e.g., 10 to 40 activity counts) greater than a threshold activity count may be detected as a termination condition. For example, when 30 activity counts (each activity count determined within a 2-second interval) are greater than a threshold activity count during data acquisition, the control circuit 206 may determine at block 1006 that the termination condition is met due to high patient activity. The activity count threshold can correspond to patient activity that exceeds activities of daily living, to brisk walking or other activity levels that can be associated with body movement and / or posture changes that can alter motion sensor signals compared to relatively low physical activity (e.g., rest or low levels of daily living activities).

[0151] In other examples, each activity count may be compared to a median activity count, and if the exceeding threshold percentage of each activity count determined during data acquisition differs from the median activity count by more than a threshold difference (positive or negative), then an abort condition may be detected due to variable patient activity at block 1006. In still other examples, a target heart rate or sensor-indicated pacing rate may be determined by the control circuit 206 based on the activity counts. In some examples, a target heart rate or sensor-indicated pacing rate determined based on a measure of patient physical activity may be compared to a threshold rate greater than the current ventricular rate (e.g., 10 beats per minute) and / or a rate variability criterion for detecting an abort condition.

[0152] In addition to or as an alternative to the heart rate and / or patient physical activity based abort condition, the control circuit 206 can detect an abort condition in response to the telemetry circuit 208 receiving a communication signal, for example, from the external device 20. For example, the control circuit 206 can detect an abort condition when a telemetry session is initiated and the telemetry circuit 208 is receiving a programming command. In some examples, the telemetry circuit 208 can be enabled to transmit motion sensor signals or related data during the atrial event sensing parameter setting procedure of flowchart 1000; however, other telemetry signals received from the external device 20, such as programming commands, can be detected as an abort condition. The programming command contains programmable control parameters used to change the use of the control circuit 206 in controlling sensing, therapy delivery, or other pacemaker functions.

[0153] When the suspension condition is detected at box 1006, the control circuit 206 can determine at box 1010 whether the maximum time period for data acquisition and atrial event sensing parameter selection has been reached. If not, the control circuit 206 can temporarily suspend data acquisition at box 1012 and return to box 1004 to restart vector signal analysis to obtain amplitude and timing data. Data acquisition can be restarted on the next processor interrupt signal or after a predetermined time interval (e.g., after one minute, five minutes or other selected time intervals). In some instances, the control circuit 206 can monitor the ventricular cycle length and / or the patient's physical activity level until the suspension condition is no longer detected, and restart data acquisition at box 1004 when a relatively stable ventricular rate and / or a relatively low stable patient's physical activity is detected. In still other instances, when the suspension condition is detected, the control circuit 206 can wait for a predetermined time interval (e.g., one minute), and then resume motion sensor signal data collection. In some cases, the data acquired before the suspension condition is detected will be discarded. In other examples, data acquired before the abort condition is detected is saved and combined with data obtained after data collection is resumed.

[0154] The data acquisition process can be restarted multiple times, up to a maximum number of attempts or within a maximum time period, such as up to one hour, four hours, 24 hours or other selected maximum attempt time period. If the maximum number of attempts or maximum time period for successfully acquiring the amplitude and timing data of all vector signals being analyzed at box 1010 expires, the process can terminate at box 1020. At box 1002, the control circuit 206 can terminate any temporary control parameters previously set to test values. For example, at box 1024, the control circuit 206 can use any default or programmed atrial sensing control parameter to switch back to a programmed pacing mode (e.g., VDD pacing mode). The control circuit 206 can generate a notification indicating the termination of the automatic sensing parameter selection process at box 1022. The notification generated at box 1022 may include the number of data acquisition attempts or restarts and / or one or more associated termination conditions detected. The telemetry circuit 208 can transmit any generated notification to the external device 20 for display on the display unit 54. The user can program atrial sensing control parameters for use during VDD pacing mode.

[0155] When data acquisition is completed within the maximum time period (e.g., five minutes per test vector signal), control circuit 206 proceeds to block 1014 to perform, for example, Figure 8 , 10 , 12 and 13. Based on the histogram distribution, one or more atrial event sensing parameter values ​​can be selected and set at box 1016. Although the detection of the abort condition is indicated at box 1106, it should be understood that the abort condition can be detected by the control circuit 206 before, during or after acquiring amplitude and timing data (box 1004), generating a histogram distribution (box 1014), or selecting A4 sensing control parameters (box 1016). Monitoring for one or more abort conditions (such as any of the examples described above) can be performed during the process of boxes 1001 to 1016, and is not limited to a specific time point during the process of setting test parameters, acquiring data, generating a distribution of data, and selecting A4 sensing control parameters.

[0156] In some instances, an A4 sensing vector signal is selected at box 1016 based on a histogram of the maximum vector signal amplitude during the A4 window generated for each vector signal. For each vector signal being analyzed, the control circuit 206 can determine a valid maximum amplitude sample count. For example, the maximum amplitude greater than a minimum threshold amplitude (e.g., the minimum programmable value of the late atrial event sensing threshold amplitude) can be counted. Any vector signal having a valid maximum amplitude sample count less than a rejection threshold number of valid maximum amplitudes may be rejected as a possible A4 sensing vector signal. For example, when it is determined that the maximum amplitude acquired for a given vector signal is less than 20 greater than the minimum programmable late atrial event sensing threshold, the vector signal may be rejected from the selection process because the maximum amplitude acquired for the vector signal meets the rejection criteria.

[0157] The control circuit 206 can determine the median maximum amplitude of all maximum amplitudes acquired that are greater than the minimum programmable late atrial event sensing threshold (or other minimum threshold). For each vector signal that is not rejected, the median maximum amplitude can be determined after discarding the maximum amplitude that is less than the noise threshold. For example, for each vector signal that does not meet the rejection criteria, the histogram bin storing the number of maximum amplitudes less than or equal to the minimum programmable A4 sensing threshold amplitude value can be discarded. The median of the maximum amplitude can be determined based on the distribution of the maximum amplitudes in the histogram bins that are greater than the minimum A4 sensing threshold amplitude value. At box 1016, the vector signal corresponding to the highest median maximum amplitude determined from the A4 window can be selected as the A4 sensing vector signal.

[0158] In the illustrative example given above of analyzing each of the four vector signals specified by the accelerometer axis combinations of 1+2, 1+3, 2+3, and 1+2+3, if the valid maximum amplitude sampling points of all three of the two-axis signals are less than the threshold number, then at box 1016, the three-axis vector signal can be selected as the A4 sensing vector signal. When at least one of the three two-axis vector signals has the necessary number of valid maximum amplitude sampling points, the two-axis vector signal with the highest median maximum amplitude can be selected as the A4 sensing vector signal (for example, to save the current consumption required to power the third accelerometer axis). When two or more of the two-axis vector signals have the same median maximum amplitude during the A4 window, the two-axis vector signal that shares a single axis for determining the patient's body activity can be selected. In other examples, the single-axis vector with the highest median maximum amplitude can be identified, and any two-axis vector signal containing the single-axis vector signal with the highest median maximum amplitude can be selected. In one example, when axis 2 is generally aligned with the longitudinal axis 108 of the pacemaker 14 (see Figure 2), when the median maximum amplitude of the A4 window matches between two or all three of the vector signals in the vector signal, priority is given to the 1+2 vector signal, then the 2+3 vector signal, then the 1+3 vector signal. A single-axis vector signal that is generally aligned with the longitudinal axis of the pacemaker 14 can correspond to the highest A4 signal amplitude, although this can vary with implant positioning and orientation. The single-axis vector signal with the highest A4 signal amplitude can be identified from empirical data, and when two or more two-axis vector signals have equal median maximum amplitudes, priority can be given to any two-axis vector signal that contains this identified single-axis vector.

[0159] At box 1016, the control circuit 206 can set a late A4 sensing threshold amplitude value (applied during the A4 window during atrial tracking ventricular pacing) based on the median value of the maximum amplitude determined for the selected A4 sensing vector signal during the A4 window. In one instance, the late A4 sensing threshold amplitude value is set to the median value of the maximum amplitude determined for the selected A4 sensing vector signal during the A4 window. In other instances, the late A4 sensing threshold amplitude value is set to a percentage of the median maximum amplitude value (e.g., 60% to 80%). In some cases, the method of setting the late A4 sensing threshold amplitude value depends on the median maximum amplitude during the A4 window. For example, if the median maximum amplitude during the A4 window is 1.2 meters per second 2 (or other threshold acceleration), the late A4 sensing threshold amplitude can be set to the median maximum amplitude. If the median maximum amplitude is greater than 1.2 m / s 2 (or other threshold acceleration), the late A4 sensing threshold amplitude can be set to 70% of the median maximum amplitude of the A4 window, but not less than 1.2 m / s 2 (or other minimum limit).

[0160] The method for setting the late A4 sensing threshold amplitude value may vary depending on the selected A4 sensing vector signal. For example, when a two-axis vector signal is selected as the A4 sensing vector signal, the late A4 sensing threshold amplitude may be set according to a percentage of the median value or at least a minimum limit. When a three-axis vector signal is selected as the A4 sensing vector signal, the late A4 sensing threshold amplitude may be set according to different percentages or limits. The late A4 sensing threshold amplitude may be set within a lower limit and an upper limit (e.g., between 0.5 m / s 2 and 5.0 m / s 2 The minimum A4 sensing threshold amplitude may vary depending on the number of accelerometer axis signals combined in the selected vector signal. For example, for a single axis vector signal, a relatively low minimum threshold amplitude (e.g., 0.6 m / s) may be enforced. 2); for two-axis vector signals, an intermediate minimum threshold amplitude can be enforced (e.g., 0.7 m / s 2 ), and for three-axis vector signals, a maximum minimum threshold amplitude (e.g., 0.8 m / s 2 ). Compared to a single-axis vector signal, a relatively higher minimum threshold amplitude setting may be permissible for a vector signal that is a combination of two or all three accelerometer axis signals because, with the addition of each axis signal, additional noise is included in the summed axis signal.

[0161] At box 1016, the control circuit 206 can set the early A4 sensing threshold amplitude (applied during the A3 window during atrial tracking ventricular pacing). The early A4 sensing threshold amplitude can be set based on the maximum amplitude determined for the selected A4 sensing vector signal during the A3 window. In one instance, the early A4 sensing threshold amplitude value can be set by determining the median maximum amplitude during the A3 window (for the selected A4 sensing vector signal), multiplying this median maximum amplitude by a multiplication factor (e.g., 1.5), and adding this product of the median maximum amplitude and the multiplication factor to the late A4 sensing threshold amplitude. In some instances, setting the early A4 sensing threshold amplitude value can include adding an offset, for example by adding 0.3 meters / second 2 The early A4 sensing threshold amplitude may be set based on the median maximum amplitude during the A4 window, the median maximum amplitude during the A3 window, or a combination of the two (which may be a weighted combination). In one example, the early A4 sensing threshold amplitude may be set within a lower limit and an upper limit (e.g., between 0.8 m / s 2 and 18.8 m / s 2 between).

[0162] The control circuit 206 can set the A3 window end time at block 1016 based on the distribution of the timing of the most recent test threshold crossings during the A3 window determined for the selected A4 sense vector signal. In one example, the A3 window end time is set based on the median time of the most recent test threshold crossings during the A3 window plus an offset (e.g., plus 50 to 150 milliseconds). The A3 window end time can be set within a minimum limit and a maximum limit (e.g., not less than 650 milliseconds and not more than 1000 milliseconds).

[0163] After completing the atrial event sensing control parameter selection at block 1016, the control circuit 206 can generate a notification of parameter selection completion at block 1022, which includes the selected parameters. The selected parameters can be transmitted to the external device 20 by the telemetry circuit 208 to generate a display of the results of the automatic setup procedure. In the event that the selected A4 sensing control parameters are valid, the control circuit 206 can switch to an atrial tracking ventricular pacing mode (e.g., VDD pacing mode) at block 1024.

[0164] In some cases, the maximum amplitude during the A4 window may be too low to reliably select the A4 sensing control parameter. For example, when less than a threshold number of sample points exceed the minimum programmable late A4 sensing threshold amplitude value for all vector signals, the control circuit 206 may set the A4 sensing control parameter to a default or previous setting and generate a notification indicating a low A4 signal amplitude at block 1022. The notification may be transmitted by the pacemaker 14 and displayed by the external device 20, thereby allowing the user to select and program pacing modes and sensing control parameters.

[0165] Fig.16 1100 is a flow chart of a method for adjusting selected atrial event sensing control parameters according to one example. The control circuit 206 may use the above combined Figure 6-15 The described techniques determine starting values ​​for one or more A4 sensing control parameters, such as the A3 window end time and early and late A4 sensing threshold amplitude values. After selecting the starting values, the starting values ​​can be adjusted to operating values ​​used when switching to a permanent atrial tracking ventricular pacing mode. At blocks 1102 and 1104, the control circuit 206 can continue to operate in a non-atrial tracking ventricular pacing mode (e.g., in a VDI pacing mode) to enable adjustment of the early A4 sensing threshold amplitude value from its selected starting value and adjustment of the A3 window end time from its selected starting value.

[0166] At box 1102, the control circuit 206 can continue to operate in the VDI pacing mode and update the early A4 threshold amplitude value based on the maximum amplitude of the selected vector signal during the A3 window determined based on one or more ventricular cycles. In one instance, the median maximum amplitude during the A3 window can be determined based on a predetermined number of consecutive ventricular cycles (e.g., 3 to 12 ventricular cycles). For example, the early A4 threshold amplitude value can be adjusted after every eight ventricular cycles based on the median maximum amplitude of the selected vector signal determined during eight ventricular cycles. In one instance, the median maximum amplitude of the A3 window can be determined as the 4th highest maximum amplitude based on 8 consecutive ventricular cycles. In some instances, a target value for the early A4 threshold amplitude value can be determined based on the determined median maximum amplitude. The starting value of the early A4 threshold amplitude determined during the setup process can be adjusted by a predetermined increase or decrease toward the target value. The predetermined increase or decrease can be 0.1 to 0.5 meters per second. 2 , and in one example, 0.3 m / s 2 When operating in the VDI pacing mode, this process may be repeated every 8 ventricular cycles (or other predetermined number of cycles) for an adjusted time interval, such as for one minute, two minutes, five minutes, or other selected time interval. The adjusted initial early A4 threshold amplitude value is not in effect until the control circuit 206 switches to the atrial tracking ventricular pacing mode, such that an A4 event is not detected until all atrial event sensing parameters are adjusted to operational values ​​from initial values ​​determined based on the distribution of data described above.

[0167] At box 1104, the control circuit 206 can determine the time of the most recent test threshold amplitude crossing of the selected vector signal during the A3 window within one or more consecutive ventricular cycles. The starting A3 window end time can be adjusted based on the most recent test threshold crossing time during the A3 window determined based on the one or more ventricular cycles. The test threshold amplitude can be set to a percentage (e.g., 75%) of the late A4 sensing threshold amplitude value set during the setup procedure described above. The A3 window end time established during the setup procedure is based on a predetermined fixed value (e.g., 0.9 m / s) that can be set. 2 ) of the test threshold of the selected vector. However, the starting late A4 threshold amplitude determined for the selected vector during the setup process is customized for the patient and the selected atrial event sensing vector and A4 signal amplitude. A test threshold set as a percentage of the starting late A4 threshold amplitude may be a more appropriate threshold for determining the most recent threshold crossing time and setting the A3 window end time. For example, if at block 1101 the starting value for the late A4 threshold amplitude is set to 2.5 m / s at the end of the setup process, 2 , then the late A4 threshold amplitude is set to 75% of the test threshold at 1.9 m / s2 This test threshold may be used during the A3 window to detect the most recent test threshold crossing time for adjusting the A3 window end time to provide patient-customized optimization of the A3 window end time for the selected sensing vector.

[0168] After every 3 to 12 ventricular cycles, the median of the most recent test threshold crossing time during the A3 window can be updated. The median time of the most recent A3 threshold amplitude crossing can be determined as the 4th shortest time in 8 ventricular cycles. The median of the most recent test threshold crossing time can be used to update the A3 window end time established during the setup procedure described above. The target A3 window end time can be set based on the median time. The A3 window end time can be adjusted toward the target value by adding or subtracting the adjustment interval from the current value of the A3 window end time. The A3 window end time can be adjusted for 2 minutes (or other adjustment time intervals) every 8 ventricular cycles or other selected number of ventricular cycles to reach the adjusted starting A3 window end time that takes effect as the operating A3 window end time when switching to the atrial tracking ventricular pacing mode (e.g., VDD pacing mode).

[0169] After adjusting the A3 window end time and / or early A4 sensing threshold from their respective set starting values ​​to operational values ​​during the VDI pacing mode, the control circuit 206 may switch to a temporary atrial tracking pacing mode (e.g., VDD pacing mode) at block 1106. The operational values ​​of the early A4 sensing threshold amplitude value and the A3 window end value may take effect upon switching to the temporary VDD pacing mode.

[0170] At box 1108, the late A4 sensing threshold amplitude value can be adjusted from its starting value. During this temporary VDD pacing mode, the late A4 sensing threshold amplitude value can be adjusted from its starting value based on the maximum amplitude of the selected sensing vector signal during one or more A4 windows. In one instance, the control circuit 206 determines the median maximum amplitude during the A4 windows of the selected vector signal after every X ventricular cycles. The adjusted late A4 sensing threshold amplitude value can be determined based on the determined median value. In some instances, the target late A4 sensing threshold amplitude value can be determined based on the median value determined every eight ventricular cycles. The starting value of the late A4 sensing threshold amplitude can be adjusted up or down toward the updated target late A4 sensing threshold by a predetermined adjustment interval (e.g., + 0.3 m / s 2 During the VDD pacing mode, this process may be repeated every X ventricular cycles for a predetermined time interval (eg, every eight ventricular cycles for two minutes) to reach the late operational A4 sensing threshold amplitude value.

[0171] At block 1110, the control circuit 206 may determine a rate smoothing interval based on one or more ventricular cycle lengths during the temporary VDD pacing mode. In some instances, the initial rate smoothing interval is set to a programmed lower rate interval. A median ventricular cycle length within X ventricular cycles (e.g., eight ventricular cycles) may be determined. The adjusted rate smoothing interval may be set to a predetermined interval that is longer than the median ventricular cycle length (e.g., 100 to 150 milliseconds longer than the median ventricular cycle length). The rate smoothing interval may be updated every X ventricular cycles within a predetermined time interval (e.g., two minutes).

[0172] After adjusting the starting value of the late A4 sensing threshold amplitude and adjusting the rate smoothing interval during the temporary VDD pacing mode, the control circuit 206 can switch to the permanent atrial tracking pacing mode with the operating value of the A4 sensing control parameter and the adjusted rate smoothing interval in effect at block 1112. In this manner, the starting value of the A4 sensing control parameter and the rate smoothing interval determined during the automatic setup process described above can be adjusted to operating values ​​that are set and in effect based on the simultaneous signal amplitude and timing characteristics of the selected vector signal and the current ventricular rate.

[0173] It should be understood that, depending on the example, certain actions or events of any method described herein may be performed in a different order, may be added, merged, or completely excluded (e.g., not all described actions and events are necessary for the method technology). In addition, in some instances, actions or events may be performed simultaneously rather than sequentially, for example, by multithreading, interrupt processing, or multiple processors. In addition, for the purpose of clarity, although certain aspects of the present disclosure are described as being performed by a single circuit or unit, it should be understood that the technology of the present disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0174] The following clauses describe example techniques of the present disclosure.

[0175] Item 1: A method comprising: generating a motion signal including an atrial event signal corresponding to an atrial contraction event; identifying a plurality of ventricular electrical events, wherein each of the plurality of ventricular electrical events is one of an intrinsic R wave or a generated ventricular pacing pulse; setting a sensing window after each of the plurality of ventricular electrical events; determining characteristics of the motion signal during each sensing window in the sensing window; setting atrial event sensing parameters based on the determined characteristics; sensing the atrial contraction event based on the atrial event sensing parameters; and generating an atrial sensing event signal in response to sensing the atrial contraction event.

[0176] Clause 2: The method of clause 1, further comprising: determining a median value of the determined characteristic; and setting the atrial event sensing parameter based on the median value.

[0177] Clause 3: The method of clause 1 or 2, further comprising: determining a distribution of the determined feature; and setting the atrial event sensing parameter based on a percentile of the distribution.

[0178] Clause 4: A method according to any one of clauses 1 to 3, further comprising: setting a non-atrial tracking pacing mode before identifying the multiple ventricular electrical events; determining the characteristics of the motion signal during each sensing window in the sensing window during the non-atrial tracking pacing mode; switching to an atrial tracking pacing mode after setting the atrial event sensing parameters; and sensing the atrial contraction event from the motion signal based on the set atrial event sensing parameters during the atrial tracking pacing mode.

[0179] Clause 5: A method according to any one of clauses 1 to 4, further comprising: determining the characteristic of the motion signal by determining the maximum amplitude of each vector signal in a plurality of vector signals during each sensing window of the sensing window, wherein each vector signal in the plurality of vector signals includes at least one axis signal generated by a multi-axis motion sensor that is generating the motion signal; determining the distribution of the maximum amplitude of each vector signal in the plurality of vector signals; determining one vector signal in the plurality of vector signals having the maximum median value of the distribution of the maximum amplitude during the sensing window; and setting the atrial event sensing parameters by selecting an atrial event sensing vector as the one vector signal in the plurality of vector signals having the maximum median value of the distribution of the maximum amplitude during the sensing window.

[0180] Clause 6: A method according to any one of clauses 1 to 5, further comprising: determining the characteristic of the motion signal by determining the most recent crossing time of a first threshold amplitude of the motion signal during each sensing window in the sensing windows; determining the distribution of the most recent crossing times; and setting the atrial event sensing parameters by setting the end time of the passive ventricular filling window based on the distribution.

[0181] Clause 7: The method according to Clause 6 further comprises: discarding the most recent crossing time of the distribution that is greater than an atrial event confidence time threshold; and setting the end time of the passive ventricular filling window based on the distribution of the most recent crossing time that is less than the atrial event confidence time threshold.

[0182] Clause 8: The method of clause 6 or 7, further comprising: determining a median value based on the most recent span time; and setting the end time to the median value plus an offset.

[0183] Clause 9: A method according to any one of clauses 6 to 8, further comprising: setting a second threshold amplitude; and sensing the atrial contraction event in response to the motion signal crossing the second sensing threshold amplitude later than the end time of the passive ventricular filling window.

[0184] Clause 10: A method according to any one of clauses 1 to 9, further comprising: setting a passive ventricular filling window after each ventricular electrical event among the multiple ventricular electrical events; setting the sensing window by setting an atrial event sensing window starting at the end time of the passive ventricular filling window; during each sensing window, determining a first maximum amplitude of the motion signal; determining a distribution of the first maximum amplitude; and setting the atrial event sensing parameters by setting a late atrial event sensing threshold amplitude based on the distribution.

[0185] Clause 11: The method according to Clause 10 further comprises: discarding a first maximum amplitude that is less than a noise threshold; determining one of a percentile and a median of the first maximum amplitude after discarding the first maximum amplitude that is less than the noise threshold; and setting the late atrial event sensing threshold amplitude based on the determined one of the percentile and the median.

[0186] Clause 12: The method according to clause 10 or 11, further comprising: determining a second maximum amplitude of the motion signal during each passive ventricular filling window; and setting an early atrial event sensing threshold based on the second maximum amplitude of the motion signal during the passive ventricular filling window.

[0187] Clause 13: The method of clause 12, wherein setting the early atrial event sensing threshold comprises determining a weighted sum of a median value of the first maximum amplitude and a median value of the second maximum amplitude.

[0188] Clause 14: A method according to any one of clauses 1 to 13, further comprising: setting a passive ventricular filling window after each of the multiple ventricular electrical events; determining the maximum amplitude of the motion signal during each passive ventricular filling window in the passive ventricular filling window; determining the distribution of the maximum amplitude; and setting the atrial event sensing parameters by setting an early atrial event sensing threshold amplitude based on the distribution of the maximum amplitude.

[0189] Clause 15: The method according to clause 14, further comprising sensing the atrial contraction event in response to the earlier of: the motion signal crossing the early atrial event sensing threshold amplitude during the passive ventricular filling window; and the motion signal crossing the late atrial event sensing threshold amplitude after the passive filling window, the late atrial event sensing threshold amplitude being less than the early atrial event sensing threshold amplitude.

[0190] Clause 16: The method of any of clauses 1 to -15, further comprising: initiating an atrioventricular pacing interval in response to the atrial sensed event signal; and generating a ventricular pacing pulse in response to expiration of the atrioventricular pacing interval.

[0191] Clause 17: A method according to any one of clauses 1 to 16, further comprising: receiving a communication signal from another medical device; waiting for a time delay after receiving the communication signal has stopped; and starting to determine the characteristics of the motion signal during each sensing window in the sensing window after the time delay.

[0192] Clause 18: The method of any one of clauses 1 to 17, further comprising: detecting a termination condition after initiating determination of the characteristic of the motion signal; and terminating determination of the characteristic of the motion signal in response to detecting the termination condition.

[0193] Clause 19: The method of clause 18, wherein the termination condition is detected by detecting one of: a change in heart rate; a change in the patient's physical activity; and a telemetry communication signal received from another medical device.

[0194] Clause 20: A method according to any one of clauses 1 to 19, further comprising: determining the characteristics of the motion signal during a predetermined number of ventricular cycles after setting the atrial event sensing parameters; adjusting the atrial event sensing parameters based on the characteristics determined during the predetermined number of ventricular cycles; and sensing the atrial contraction event from the motion signal after adjusting the atrial event sensing parameters.

[0195] Item 21: A non-transitory computer-readable storage medium comprising a set of instructions that, when executed by a control circuit of a pacemaker, cause the pacemaker to: generate a motion signal including an atrial event signal corresponding to an atrial contraction event; identify a plurality of ventricular electrical events, wherein each of the plurality of ventricular electrical events is one of an intrinsic R wave or a generated ventricular pacing pulse; set a sensing window after each of the plurality of ventricular electrical events; determine characteristics of the motion signal during each sensing window in the sensing windows; set atrial event sensing parameters based on the determined characteristics; sense the atrial contraction event based on the atrial event sensing parameters; and generate an atrial sensing event signal in response to sensing the atrial contraction event.

[0196] In one or more instances, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored in the form of one or more instructions or codes on a computer-readable medium and may be performed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium corresponding 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 desired program code in the form of instructions or data structures and can be accessed by a computer).

[0197] Instructions may 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. Thus, the term "processor" as used herein may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, the techniques may be fully implemented in one or more circuits or logic elements.

[0198] Therefore, the medical devices have been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein may be combined in different combinations other than the specific combinations presented in the drawings. It should be understood that various modifications may be made to the referenced examples without departing from the scope of the present disclosure and the appended claims.

Claims

1. A pacemaker, comprising: a pulse generator configured to generate pacing pulses; a sensing circuit comprising an R-wave detector for sensing an R-wave from a cardiac electrical signal; a motion sensor configured to generate a motion signal including an atrial event signal corresponding to an atrial contraction event; as well as a control circuit coupled to the motion sensor and the pulse generator and configured to: identifying a plurality of ventricular electrical events, wherein each of the plurality of ventricular electrical events is one of an R-wave sensed by the sensing circuit or a ventricular pacing pulse generated by the pulse generator; setting a sensing window after each ventricular electrical event in the plurality of ventricular electrical events; determining a characteristic of the motion signal during each of the sensing windows; setting atrial event sensing parameters based on the determined characteristics during each of the sensing windows; sensing the atrial contraction event based on the atrial event sensing parameter; and An atrial sensed event signal is generated in response to sensing the atrial contraction event.

2. The pacemaker of claim 1, wherein the control circuit is further configured to: determining a median value of the determined characteristic; and The atrial event sensing parameter is set based on the median value.

3. The pacemaker of claim 1, wherein the control circuit is further configured to: determining a distribution of the determined features; and The atrial event sensing parameters are set based on percentiles of the distribution.

4. The pacemaker of claim 1 , wherein the control circuit is further configured to: setting a non-atrial tracking pacing mode prior to identifying the plurality of ventricular electrical events; determining, during the non-atrial tracking pacing mode, the characteristic of the motion signal during each of the sensing windows; switching to an atrial tracking pacing mode after setting the atrial event sensing parameters; and The atrial contraction event is sensed from the motion signal using the set atrial event sensing parameters during the atrial tracking pacing mode.

5. The pacemaker according to claim 1, wherein: The motion sensor is a multi-axis motion sensor configured to generate an axis signal for each axis; The control circuit is configured to: determining the characteristic of the motion signal by determining a maximum amplitude of each of a plurality of vector signals during each of the sensing windows in the sensing windows, each of the plurality of vector signals including one or more of the axis signals; determining a distribution of the maximum amplitude of each vector signal in the plurality of vector signals; determining a vector signal among the plurality of vector signals having a maximum median value of the distribution of the maximum amplitude during the sensing window; and The atrial event sensing parameters are set by selecting an atrial event sensing vector signal as the one of the plurality of vector signals having the maximum median value of the distribution of the maximum amplitude during the sensing window.

6. The pacemaker of claim 1 , wherein the control circuit is configured to: determining the characteristic of the motion signal by determining a most recent crossing time of a first threshold amplitude of the motion signal during each of the sensing windows; determining a distribution of the most recent span times; and The atrial event sensing parameter is set by setting an end time of a passive ventricular filling window based on the distribution.

7. The pacemaker of claim 6, wherein the control circuit is configured to: discarding the most recent crossing time that is greater than an atrial event confidence time threshold; and The end time of the passive ventricular filling window is set based on the distribution of the most recent crossing times that are less than the atrial event confidence time threshold.

8. The pacemaker of claim 6, wherein the control circuit is further configured to: determining a median value based on the most recent span time; and The end time is set to the median value plus an offset.

9. The pacemaker of claim 6, wherein the control circuit is further configured to: Setting a second sensing threshold amplitude; and The atrial contraction event is sensed in response to the motion signal crossing the second sensing threshold amplitude later than the end time of the passive ventricular filling window.

10. The pacemaker of claim 1, wherein the control circuit is configured to: setting a passive ventricular filling window after each ventricular electrical event in the plurality of ventricular electrical events; Setting the sensing window by setting an atrial event sensing window beginning at an end time of the passive ventricular filling window; determining a first maximum amplitude of the motion signal during each sensing window; determining a distribution of the first maximum amplitude; and The atrial event sensing parameters are set by setting a late atrial event sensing threshold amplitude based on the distribution.

11. The pacemaker of claim 10, wherein the control circuit is configured to: Discard the first maximum amplitude that is smaller than the noise threshold; determining one of a percentile and a median of the first maximum amplitude after discarding the first maximum amplitudes that are less than the noise threshold; and The late atrial event sensing threshold amplitude is set based on the determined one of the percentile and the median.

12. The pacemaker of claim 10, wherein the control circuit is configured to: determining a second maximum amplitude of the motion signal during each passive ventricular filling window; and An early atrial event sensing threshold is set based on the maximum amplitude of the motion signal during the passive ventricular filling window.

13. The pacemaker of claim 12, wherein the control circuit is configured to set the early atrial event sensing threshold by determining a weighted sum of a median value of the first maximum amplitude and a median value of the second maximum amplitude.

14. The pacemaker of claim 1, wherein the control circuit is further configured to: setting a passive ventricular filling window after each ventricular electrical event in the plurality of ventricular electrical events; determining a maximum amplitude of the motion signal during each of the passive ventricular filling windows; determining a distribution of said maximum amplitudes; The atrial event sensing parameter is set by setting an early atrial event sensing threshold amplitude based on the distribution of the maximum amplitudes.

15. The pacemaker of claim 14, wherein the control circuit is configured to sense the atrial contraction event in response to the earlier of: The motion signal crosses the early atrial event sensing threshold amplitude during the passive ventricular filling window; and The motion signal crosses a late atrial event sensing threshold amplitude after the passive ventricular filling window, the late atrial event sensing threshold amplitude being less than the early atrial event sensing threshold amplitude.

16. The pacemaker according to any one of claims 1 to 15, wherein: The control circuit is further configured to initiate an atrioventricular pacing interval in response to the atrial sensed event signal; and The pulse generator is configured to generate a ventricular pacing pulse in response to expiration of the atrioventricular pacing interval.

17. The pacemaker of any one of claims 1 to 15, further comprising a telemetry circuit configured to receive a communication signal from another medical device; The control circuit is further configured to: waiting for a time delay after the telemetry circuit ceases to receive the communication signal; Determining the characteristic of the motion signal during each of the sensing windows begins after the time delay.

18. The pacemaker according to any one of claims 1 to 15, wherein the control circuit is further configured to: detecting a termination condition after initiating determination of said characteristic of said motion signal; and Determining the characteristic of the motion signal is discontinued in response to detecting the discontinuation condition.

19. The pacemaker of claim 18, wherein the control circuit is configured to detect the abort condition by detecting one of: Changes in heart rate; changes in the patient's physical activity; and A telemetry communication signal received from another medical device.

20. The pacemaker according to any one of claims 1 to 15, wherein the control circuit is further configured to: determining said characteristic of said motion signal during a predetermined number of ventricular cycles after setting said atrial event sensing parameters; adjusting the atrial event sensing parameters based on the characteristics determined during the predetermined number of ventricular cycles; and The atrial contraction event is sensed from the motion signal after adjusting the atrial event sensing parameters.

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