Pace-making mode switching in ventricular pacemaker

Abstract

An intracardiac ventricular pacemaker configured to operate in a selected one of an atrial tracking ventricular pacing mode and a non-atrial tracking ventricular pacing mode. A control circuit of the pacemaker: determines at least one motion signal metric from a motion signal; comparing the at least one motion signal metric to a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switching from a selected one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to the other of the non-atrial tracking pacing mode and the atrial tracking pacing mode, a ventricular pacing pulse is controlled for controlling ventricular pacing pulses delivered by the pacemaker.

Description

[0001] This application is a divisional application of an invention patent application with an international application date of 2019-06-28, international application number PCT / US2019 / 039738, and application number 201980042732.8 entering the Chinese national phase, entitled "Pacing Mode Switching in Ventricular Pacemakers". Technical Field

[0002] The present disclosure relates to a ventricular pacemaker and related methods for switching between an atrial tracking ventricular pacing mode and a non-atrial tracking ventricular pacing mode based on a motion sensor signal. Background Art

[0003] An implantable cardiac pacemaker is typically placed in a pocket under the skin and connected to one or more intravenous medical electrical leads with pacing and sensing electrodes placed in the heart. A subcutaneously implanted cardiac pacemaker may be a single-chamber pacemaker, coupled to one intravenous medical lead for electrodes to be placed in one atrium or ventricle, or a dual-chamber pacemaker, coupled to two intracardiac leads for electrodes to be placed in both the atria and ventricles. Multi-chamber pacemakers are also available, which may be connected to three leads, for example, to position electrodes for pacing and sensing in one atrium and in both the left and right ventricles.

[0004] Recently, intracardiac pacemakers have been introduced that can be implanted in the ventricular chambers of a patient's heart to deliver ventricular pacing pulses. Such pacemakers can sense the R-wave signal that accompanies 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 may be adequate for some patients' conditions, other conditions may require the provision of atrial-synchronized ventricular pacing by atrial and ventricular (bi-chamber) sensing to maintain a regular heart rhythm. Summary of the invention

[0005] In general, the present disclosure is directed to a ventricular pacemaker and techniques for controlling a ventricular pacing mode by switching between an atrial tracking pacing mode and a non-atrial tracking pacing mode. The ventricular pacemaker may be an intracardiac pacemaker and may be configured to detect an atrial contraction event based on a motion signal generated by a motion sensor included in the intracardiac ventricular pacemaker. A ventricular pacemaker operating according to the techniques disclosed herein automatically switches between an atrial tracking pacing mode and a non-atrial tracking pacing mode based on a mode switching criterion to provide an appropriate ventricular pacing rate to support the metabolic needs of a patient.

[0006] In one embodiment, the present disclosure provides an intracardiac ventricular pacemaker, comprising: a pulse generator, a motion sensor, a control circuit and a housing, wherein the housing is implantable in a cardiac chamber and encloses the pulse generator, the motion sensor and the control circuit. The pulse generator is configured to generate pacing pulses via electrodes coupled to the pacemaker and deliver the pacing pulses to the ventricles of a patient's heart. The motion sensor is configured to generate a motion signal. The control circuit is coupled to the motion sensor and the pulse generator, and is configured to detect an atrial contraction event from the motion signal. The control circuit is also configured to operate in a mode selected from an atrial tracking ventricular pacing mode or a non-atrial tracking ventricular pacing mode. The control circuit: determines at least one motion signal metric from the motion signal; compares the at least one motion signal metric with a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switches from a selected one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to another one of the non-atrial tracking pacing mode and the atrial tracking pacing mode for controlling the pacing pulse delivered by the pulse generator.

[0007] In another embodiment, the present disclosure provides a method performed by a ventricular pacemaker in a heart having a motion sensor configured to generate a motion signal. The pacemaker is capable of detecting atrial contraction events from the motion signal and switching between an atrial tracking pacing mode and a non-atrial tracking pacing mode. The method includes: operating in a mode selected from the atrial tracking ventricular pacing mode or the non-atrial tracking ventricular pacing mode; determining at least one motion signal metric from the motion signal; comparing the at least one motion signal metric with a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switching from a mode selected from the non-atrial tracking pacing mode and the atrial tracking pacing mode to another mode from the non-atrial tracking pacing mode and the atrial tracking pacing mode for controlling the ventricular pacing pulses delivered by the pulse generator.

[0008] In another embodiment, the present disclosure provides a non-transitory computer-readable medium storing an instruction set, which, when executed by a control circuit of a ventricular pacemaker in a heart having a motion sensor configured to generate a motion signal, causes the pacemaker to detect an atrial contraction event from the motion signal and operate in a mode selected from an atrial tracking ventricular pacing mode or a non-atrial tracking ventricular pacing mode. The instructions also cause the pacemaker to: determine at least one motion signal metric from the motion signal; compare the at least one motion signal metric with a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switch from one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to another of the non-atrial tracking pacing mode and the atrial tracking pacing mode for controlling the ventricular pacing pulses delivered by the pulse generator.

[0009] 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

[0010] Figure 1 is a conceptual diagram showing an intracardiac pacing system that can be used to sense cardiac electrical signals and motion signals caused by cardiac motion and flowing blood and provide pacing therapy to a patient's heart.

[0011] Figure 2A yes Figure 1 A conceptual diagram of a ventricular pacemaker within the heart is shown.

[0012] Figure 2B yes Figure 1 A conceptual diagram of another embodiment of an intraventricular pacemaker is shown.

[0013] Figure 3 yes Figure 2A Schematic diagram of an example configuration of a pacemaker.

[0014] Figure 4 can be included in Figure 1 An embodiment of a motion sensor signal acquired by a motion sensor in a ventricular intracardiac pacemaker during a cardiac cycle.

[0015] Figure 5 is a flow chart of a method performed by a cardiac ventricular pacemaker for detecting atrial contraction events from a motion sensor signal and controlling ventricular pacing.

[0016] Figure 6 is an example of a motion sensor signal acquired over two different ventricular cycles.

[0017] Figure 7 is the average motion sensor signal.

[0018] Figure 8 is a flow chart of a method performed by a cardiac ventricular pacemaker for detecting atrial events and controlling ventricular synchronous ventricular pacing according to another embodiment.

[0019] Fig. 9 is a flow chart of a method for controlling a ventricular pacing mode by an intracardiac ventricular pacemaker according to one embodiment.

[0020] Fig. 10A is a flow chart of a method performed by an intracardiac ventricular pacemaker for switching from an atrial tracking pacing mode to a non-atrial tracking pacing mode, according to one embodiment.

[0021] Fig. 10B is a flow chart of a method for controlling a pacing mode switch from an atrial tracking pacing mode to a non-atrial tracking mode according to another embodiment.

[0022] Fig.11 is a flow chart of a method for controlling a pacing mode switch from a non-atrial tracking pacing mode to an atrial tracking pacing mode in an intracardiac pacemaker according to one embodiment.

[0023] Fig.12 is a flow chart of a method that may be performed for controlling a pacing mode switch from a non-atrial tracking mode to an atrial tracking mode according to another embodiment.

[0024] Fig.13 is a flow chart of a method for controlling pacing mode switching by an intraventricular pacemaker according to yet another embodiment.

[0025] Fig.14 is a flow chart of a method for controlling pacing mode switching performed by a pacemaker according to another embodiment.

[0026] Fig.15 is a flow chart of a method for controlling ventricular pacing by a ventricular pacemaker in the heart according to another embodiment. DETAILED DESCRIPTION

[0027] During atrial-synchronized ventricular pacing, atrial pacing pulses are delivered at atrioventricular (AV) pacing intervals following an atrial fibrillation event to provide proper synchronization between ventricular contraction and ventricular contraction. In order for the intraventricular pacemaker to provide atrial-synchronized ventricular pacing, the intraventricular pacemaker needs to sense or detect an atrial event to initiate the AV pacing interval. As the atrial rate increases or decreases, the ventricular pacing rate tracks the atrial rate. This atrial-synchronized ventricular pacing is referred to as an "atrial tracking" pacing mode. In a non-atrial tracking ventricular pacing mode, ventricular pacing pulses are delivered at ventricular low-rate (LR) pacing intervals that are unrelated to atrial events and do not track the atrial rate. Typically, an atrial tracking ventricular pacing mode is desirable when the heart's sinoatrial node is functioning normally when the intrinsic atrial rate is set or when the atria are paced at an appropriate pacing rate for the patient's level of physical activity.

[0028] However, in some cases, such as during atrial tachycardias, such as atrial fibrillation or atrial flutter, tracking the atrial rate is undesirable. Thus, a method of switching between an atrial-tracking ventricular pacing mode and a non-atrial-tracking ventricular pacing mode is needed to enable an intracardiac ventricular pacemaker to deliver ventricular pacing that tracks the atrial rate without tracking the atrial rate at appropriate times and at other times, based on the patient's need for ventricular pacing, and without causing pacemaker-mediated ventricular tachycardia.

[0029] Disclosed herein are techniques for controlling switching between an atrial tracking ventricular pacing mode and a non-atrial tracking ventricular pacing mode in an intraventricular pacemaker. The intraventricular pacemaker has a motion sensor for detecting an atrial contraction mechanical event. During the atrial tracking pacing mode, in response to detecting an atrial contraction mechanical event, an AV pacing interval is initiated. The detection of an atrial contraction mechanical event during the atrial tracking mode and the non-atrial tracking mode can be used to determine whether a pacing mode switching criterion is met to control when the pacemaker switches between the atrial tracking pacing mode and the non-atrial tracking pacing mode.

[0030] Figure 1 is a conceptual diagram illustrating an intracardiac pacing system 10 that can be used to sense cardiac electrical signals and motion signals caused by cardiac motion and flowing blood, and to provide pacing therapy to a patient's heart 8. In some embodiments, the IMD system 10 includes a right ventricular (RV) intracardiac pacemaker 14, and can optionally include a right atrial (RA) intracardiac pacemaker 12. The pacemakers 12 and 14 are transcatheter intracardiac pacemakers that can be adapted to be completely implanted in a cardiac chamber, such as completely implanted in the RV, completely implanted in the left ventricle (LV), completely implanted in the RA, or completely implanted in the left atrium (LA) of the heart 8.

[0031] exist Figure 1In an embodiment, the pacemaker 12 is placed along the endocardial wall of the RA, such as along the RA lateral wall or the RA septum. The pacemaker 14 is positioned along the endocardial wall of the RV, such as near the RV apex, although other locations are possible. The technology disclosed herein is not limited to Figure 1 The pacemaker positions shown in the embodiment of FIG. 8 are not limited to those shown in FIG. 1 , but other positions and relative positions in the heart 8 and relative positions to each other are possible. For example, a ventricular intracardiac pacemaker 14 can be positioned in the LV using the techniques disclosed herein and configured to detect cardiac motion signals and deliver ventricular synchronized ventricular pacing to the LV.

[0032] Pacemakers 12 and 14 are reduced in size compared to subcutaneously implanted pacemakers and are generally cylindrical in shape to enable intravenous implantation via a delivery catheter. In other examples, pacemakers 12 and 14 may be positioned at any other location within heart 8. For example, pacemaker 12 may be positioned outside or inside the right atrium or left atrium to provide corresponding right atrial or left atrial pacing. Pacemaker 14 may be positioned within the right ventricle or left ventricle to provide corresponding right ventricular or left ventricular pacing and to sense motion signals via motion sensors within the ventricular chambers.

[0033] Each of the pacemakers 12 and 14 is capable of generating electrical stimulation pulses, such as pacing pulses, which are delivered to the heart 8 via one or more electrodes on the housing of the pacemaker. The RA pacemaker 12 is configured to sense cardiac electrical signals from within the RA, which can be used to generate RA intracardiac electrogram (EGM) signals. The RV pacemaker 14 is configured to deliver RV pacing pulses and sense RV cardiac electrical signals using housing-based electrodes to generate RV EGM signals. The cardiac pacemaker 12 or 14 can sense cardiac electrical signals using housing-based electrodes, which are also used to deliver pacing pulses to the respective RA or RV.

[0034] In some embodiments, a patient may only require the RV pacemaker 14 for ventricular pacing. In other embodiments, depending on the needs of the individual patient, the RA pacemaker 12 may be required for atrial pacing. The RV pacemaker 14 is configured to control the delivery of ventricular pacing pulses to the RV in a manner that promotes synchronization between RA activation and RV activation, such as by maintaining a target AV pacing interval between atrial events and ventricular pacing pulses. That is, the RV pacemaker 14 controls the delivery of RV pacing pulses to maintain a desired AV interval between atrial activation (intrinsic or pacing-induced) corresponding to cardiac contractions and a ventricular pacing pulse that causes ventricular depolarization.

[0035] According to the techniques described herein, the RV pacemaker 14 detects atrioventricular activation from motion sensor signals that include motion signals caused by ventricular and atrial events. For example, the RV pacemaker 14 detects the acceleration of blood flowing between the RA and RV through the tricuspid valve 16 into the RV due to atrial activation (sometimes referred to as "atrial kick") from signals generated by a motion sensor, such as an accelerometer included in the RV pacemaker 14. Other motion signals detected by the RV pacemaker 14, such as motion caused by ventricular contraction, motion caused by ventricular relaxation, and motion caused by passive filling of the ventricles, will be discussed below in conjunction with the present disclosure. Figure 4 Give a description.

[0036] 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 RV cardiac electrical signal received by the pacemaker 14, and therefore it may be difficult to reliably detect the cardiac electrical signal acquired by the RV pacemaker 14 therefrom. Thus, ventricular-synchronous ventricular pacing performed by the RV pacemaker 14 may be unreliable when based solely on the cardiac electrical signal received by the RV pacemaker 14. According to the technology disclosed herein, the RV pacemaker 14 includes a motion sensor, such as an accelerometer, and is configured to use a signal from the motion sensor to detect an atrial event associated with atrial mechanical activation or cardiac contraction. The ventricular pacing pulse is synchronized with the atrial event detected from the accelerometer signal by setting a programmable atrioventricular (AV) pacing interval that controls the timing of the ventricular pacing pulse relative to the detected atrial contraction event. As described below, the detection of an atrial contraction event for synchronizing the ventricular pacing pulse with the heartbeat may include the detection of other cardiac event motion signals in order to positively identify the atrial contraction event.

[0037] The target AV interval may be a programmed value selected by the 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 fiducial point of an atrial contraction event signal. The target AV interval may be determined to be 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 identified by cardiac electrical signals received from the RV pacemaker 14 and motion sensor signals received by the RV pacemaker 14.

[0038] Both pacemakers 12 and 14 can communicate bidirectionally with an external device 20 wirelessly to program AV pacing intervals and other pacing control parameters and mechanical event sensing parameters for detecting ventricular mechanical events and atrial contraction event signals from motion sensors. Aspects of the external device 20 may generally correspond to an external programming / monitoring unit disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.), which is incorporated herein by reference in its entirety. The external device 20 is often referred to as a "programmer" because it is often used by physicians, technicians, nurses, clinicians, or other qualified users to program operating parameters in the pacemakers 12 and 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 can be used in a medical institution, a patient's home, or other location. The operating parameters, including sensing and therapy delivery control parameters and pacing mode switching criteria, may be programmed into the pacemaker 14 using the external device 20.

[0039] The external device 20 is configured to communicate bidirectionally with implantable telemetry circuitry contained in the RV pacemaker 14 and the RA pacemaker 12 (if present). The external device 20 establishes a wireless radio frequency (RF) communication link 22 with the RA pacemaker 12 and a wireless RF communication link 24 with the RV pacemaker 14 using a communication protocol that appropriately addresses the target pacemaker 12 or 14. The RF link (such as The external device 20 may include a programming header that is placed near the pacemaker 12 or 14 to establish and maintain the communication link, and in other examples, the external device 20 and the pacemakers 12 and 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.), which is hereby incorporated by reference in its entirety.

[0040] The external device 20 can display data and information related to the function of the pacemaker to the user, allowing the user to view the operation and programmed parameters of the pacemaker, as well as EGM signals sent from the pacemaker 14 or pacemaker 12, or motion sensor signals acquired by the pacemaker 14, or other physiological data acquired by the pacemakers 12 and / or 14 during the interrogation process.

[0041] It is contemplated that the external device 20 may be connected to a communication network in a wired or wireless manner via telemetry circuitry including a transceiver and an antenna or via a hard-wired communication line for transmitting data to a remote database or computer to allow remote management of the patient. A remote patient management system including a remote patient database may be configured to utilize the presently disclosed techniques to enable a clinician to review EGM, motion sensor, and marker channel data and authorize programming of sensing and therapy control parameters in the RV pacemaker 14 to view visual representations of the EGM, motion sensor signals, and marker channel data.

[0042] The pacemaker 12 and the pacemaker 14 may or may not be configured to communicate directly with each other. When the pacemakers 12 and 14 are configured to communicate with each other, the communication may be minimized to conserve battery life of the intracardiac pacemakers 12 and 14. Thus, there may be no beat-to-beat communication between the RA pacemaker 12 and the RV pacemaker 14 when the other pacemaker senses a cardiac event or when it delivers a pacing pulse. However, as disclosed herein, the RV pacemaker 14 is configured to detect atrial events from a motion sensor signal on a beat-to-beat basis without a communication signal from the RA pacemaker 12 to provide atrial event detection for controlling ventricular pacing for ventricular synchronization and for determining when to switch to a non-atrial tracking pacing mode.

[0043] Figure 2A yes Figure 1 1. Conceptual diagram of an intracardiac RV pacemaker 14 is shown. The RV 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 middle portion of the housing 150 (e.g., adjacent the proximal end 104). 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 (e.g., a catheter) and in close proximity to a target pacing site.

[0044] 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 other locations along the pacemaker 14 than those shown.

[0045] The housing 150 is formed of a biocompatible material, such as stainless steel or a titanium alloy. In some embodiments, the housing 150 may include an insulating coating. Examples of insulating coatings include polyparaxylene, urethane, PEEK, or polyimide. The entirety of the housing 150 may be insulated, but only electrodes 162 and 164 are not insulated. Electrode 164 may serve as a cathode and be coupled to an internal circuit, such as a pacing pulse generator and a cardiac electrical signal sensing circuit, which is enclosed by the housing 150 via an electrical feedthrough passing through the housing 150. Electrode 162 may be formed as a conductive portion of the housing 150 as a ring electrode that is electrically isolated from other portions of the housing 150, such as Figure 2A In other embodiments, instead of providing a localized annular electrode such as anode electrode 162, the entire periphery of housing 150 may be used as an electrode electrically insulated from tip electrode 164. Electrode 162 formed along a conductive portion of housing 150 serves as a return anode during pacing and sensing.

[0046] Housing 150 includes control electronics 152, which houses electronics for sensing cardiac signals, generating pacing pulses, and controlling other functions of pacemaker 14, as described below in conjunction with Figure 3 In some embodiments, the motion sensor can be implemented as an accelerometer enclosed within housing 150. The accelerometer provides signals to a processor included in control electronics 152 for signal processing and analysis to detect ventricular mechanical events and ventricular contractile events to time ventricular pacing pulses, as described below.

[0047] Housing 150 also includes a battery subassembly 160 that provides power to control electronics subassembly 152. 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.

[0048] 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 the ventricular trabeculae. The fixation tines 166 are configured to anchor the pacemaker 14 to position the electrode 164 in operable proximity to the target tissue to deliver 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. Patent No. 9,775,982 (Grubac et al.), which is hereby incorporated by reference in its entirety.

[0049] The pacemaker 14 may optionally include a delivery tool interface 158. The delivery tool interface 158 may be located at the proximal end 104 of the pacemaker 14 and configured to connect to a delivery device (e.g., a catheter) used to position the pacemaker 14 at an implantation site during implantation, such as within a cardiac chamber.

[0050] Figure 2B is a conceptual diagram of another embodiment of the RV pacemaker 14. Figure 2B In the embodiment of the present invention, the RV pacemaker 14 includes a proximal sensing extension 165 extending away from the housing 150 and carrying a pair of sensing electrodes 167 and 168. The proximal sensing extension 165 can be coupled to the housing 150 to position the return sensing electrode 168 or 167 to be paired with the distal electrode 164 at an increased inter-electrode distance compared to the inter-electrode spacing of the housing-based electrodes 162 and 164. The increased inter-electrode distance can facilitate sensing of far-field atrial signals, such as the P wave accompanying atrial depolarization.

[0051] Alternatively, electrodes 167 and 168 can form a sensing electrode pair for sensing atrial P waves. When distal end 102 is fixed along the RV apex, sensing extension 165 can extend toward the RA, thereby positioning electrodes 167 and 168 closer to atrial tissue to sense far-field atrial P waves. One electrode 167 can be connected to a sensing circuit enclosed in housing 150 via an electrical feedthrough through housing 150, and one electrode 168 can be connected to housing 150 to serve as a ground electrode.

[0052] Figure 3 yes Figure 1 Schematic diagram of an example configuration of a pacemaker 14 is shown. The pacemaker 14 includes a pulse generator 202, a sensing circuit 204, a control circuit 206, a memory 210, a telemetry circuit 208, a motion sensor 212, and a power supply 214. In the embodiments described herein, the motion sensor 212 is implemented as an accelerometer and may also be referred to herein as "accelerometer 212." The motion sensor 212 is not limited to being an accelerometer, but other motion sensors may be successfully used in the pacemaker 14 to detect cardiac motion signals in accordance with the techniques described herein. Examples of motion sensors that may be implemented in the pacemaker 14 include piezoelectric sensors and micro-electromechanical systems (MEMS) devices.

[0053] The motion sensor 212 can be a multi-axis sensor, such as a two-dimensional or three-dimensional sensor, wherein each axis provides a signal that can be analyzed individually or in combination to detect a cardiac mechanical event. The motion sensor 212 generates an electrical signal related to the motion or vibration of the sensor 212 (and the pacemaker 14), for example, when subjected to blood flow and cardiac motion. The motion sensor 212 can be a one-dimensional single-axis accelerometer, a two-dimensional or three-dimensional multi-axis accelerometer. One embodiment of an accelerometer for an implantable medical device is generally disclosed in U.S. Pat. No. 5,885,471 (Ruben et al.), which is incorporated herein by reference in its entirety. An implantable medical device arrangement including a piezoelectric accelerometer for detecting patient motion is disclosed in, for example, 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 herein by reference in their entirety. Embodiments of three-dimensional accelerometers that can be implemented in a pacemaker 14 using the techniques disclosed herein 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), both of which are incorporated herein by reference in their entirety. Other accelerometer designs can be used to generate electrical signals related to the motion imposed on the pacemaker 14 due to ventricular and atrial events.

[0054] In addition to being subjected to cardiac motion, motion sensor 212 is also subjected to the patient's body motion during physical activities such as walking, driving, exercising, changing body posture, housework, and other daily activities. The motion sensor signal can be used by control circuit 206 to detect cardiac mechanical events (as described in more detail below), as well as to determine the patient's body posture and / or the patient's physical activity level (e.g., stationary, not stationary but in the normal range of activities of daily life, submaximal exercise, or maximal exercise). Techniques for monitoring the patient's body posture and the patient's physical activity based on accelerometer signals are generally disclosed in the above-mentioned references.

[0055] Figure 3 The various circuits represented may be combined on one or more integrated circuit boards, which may include: a specific integrated circuit (ASIC); an electronic circuit; a processor (shared, dedicated, or grouped) and memory that executes one or more software or firmware programs; a combinational logic circuit; a state machine; or other suitable components that provide the above-mentioned functionality.

[0056] The sensing circuit 204 is configured to receive the cardiac electrical signal via 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 for removing DC offset, such as a high-pass filter of 2.5 to 5 Hz, 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 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, such as P waves. The identification of cardiac electrical events can be used in an algorithm for detecting atrial contraction events from motion sensor signals. The digital signal from 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 .

[0057] The R-wave detector 224 may include a sense amplifier or other detection circuit that compares the input rectified cardiac electrical signal to an R-wave detection threshold, which may be an automatically adjusted threshold. When the input signal exceeds the R-wave detection threshold, the R-wave detector 224 generates an R-wave detection event signal (R-sense), which is transmitted to the control circuit 206. In other embodiments, 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 R-wave sensed event signal transmitted from the R-wave detector 224 to the control circuit 206 may be used to schedule ventricular pacing pulses by the pace 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 from the signal received from the motion sensor 212.

[0058] Control circuit 206 includes atrial event detector circuit 240, pacing timing circuit 242, and processor 244. Atrial event detector circuit 240 is configured to detect atrial mechanical events based on signals received from motion sensor 212. As described below, one or more ventricular mechanical events may be detected from the motion sensor signal in a given cardiac cycle to facilitate actively detecting ventricular contraction events from the motion sensor signal in the ventricular cycle.

[0059] The control circuit 206 may receive R-wave sensed event signals and / or digital cardiac electrical signals from the sensing circuit 204 for use in 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 signals may be transmitted to the pacing timing circuit 242 to inhibit a predetermined ventricular pacing pulse or a predetermined ventricular pacing pulse. The R-wave sensed event signals may also be transmitted to the atrial event detector circuit 240 for use in setting a ventricular event detection window and / or an atrial event refractory period, for example in conjunction with a ventricular event detection window. Figure 6 Shown and described.

[0060] Some R-wave sensed event signals may be caused by premature ventricular contractions (PVCs). Control circuit 206 may be configured to detect PVCs based on the timing of the R-wave sensed event signals since a previous R-wave or ventricular pacing pulse and / or based on the signal morphology of the R-wave. PVCs may be distinguished from normally conducted R-waves to avoid scheduling pacing pulses based on PVCs. Fig.12 As described, a PVC detected during a non-atrial tracking pacing mode may trigger a prolongation of the LR pacing interval to facilitate detection of an atrial contractile event from the motion sensor signal during a long compensatory pause following the PVC.

[0061] Atrial event detector circuit 240 receives motion signals from motion sensor 212 and initiates an atrial refractory period in response to a ventricular electrical event (e.g., an event signal from R-wave sensing of sensing circuit 204 or a pacing pulse delivered by pulse generator 202). Atrial event detector circuit 240 determines whether the motion sensor signal meets atrial mechanical contraction event detection criteria outside of the refractory period. In order to detect a ventricular mechanical event, the motion sensor signal during the refractory period can be monitored by atrial event detector circuit 240, which ventricular mechanical event can be used to confirm or confirm atrial contraction event detection and / or set atrial contraction event detection control parameters. In this way, a ventricular mechanical event detection window can be set during the atrial refractory period, and the ventricular mechanical event detection window can be set according to a predetermined time interval after the ventricular electrical event is identified. Atrial event detector circuit 240 can be configured to detect one or more ventricular mechanical events during each ventricular event detection window in the atrial refractory period. The timing and detection of a ventricular mechanical event may be used to update the atrial refractory period and / or ventricular contraction detection threshold amplitude, and may be used to confirm detection of a ventricular contraction event that occurs after an expected ventricular mechanical event.

[0062] Atrial event detector circuit 240 communicates an atrial event detection signal to processor 244 and / or pacing timing circuit 242. Pacing timing circuit 242 (or processor 244) may additionally receive an R-wave sensed event signal from R-wave detector 224 for use in controlling the timing of pacing pulses delivered by pulse generator 202. Processor 244 may include one or more clocks for generating a clock signal used by pace 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 pacing 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 use in setting the AV pacing interval used by pacing timing circuit 242). Techniques for controlling atrial-synchronous ventricular pacing using motion sensor signals are generally disclosed in US Pat. No. 9,399,140 (Yong et al.), which is incorporated herein by reference in its entirety.

[0063] The pacing timing circuit 242 may additionally include a lower rate (LR) pacing interval timer for controlling the minimum ventricular pacing rate in the absence of a detected atrial event. For example, if a ventricular contraction event is detected without triggering a ventricular pacing pulse at the programmed AV pacing interval from the motion sensor signal, then upon expiration of the LR pacing interval, the pulse generator 202 may send a ventricular pacing pulse to prevent ventricular beats and maintain a minimum ventricular rate.

[0064] In the non-atrial tracking pacing mode, the LR pacing interval timer is used to control the frequency of ventricular pacing pulses delivered independently of the atrial rate. The LR pacing interval can be set to a minimum or basic LR pacing interval to maintain a minimum ventricular rate, and can be adjusted to a temporary LR pacing interval based on providing rate-responsive pacing. The sensor indication rate (SIR) can be determined based on the patient's physical activity level, which can be determined from the motion sensor signal. The temporary LR pacing interval set based on the SIR provides ventricular pacing pulses at a rate greater than the minimum or basic pacing rate. During non-resting physical exercise based on the SIR, higher ventricular rate support can be provided based on the patient's metabolic needs. The use of accelerometers in intracardiac pacemakers to obtain patient activity signals is generally disclosed in U.S. Patent No. 9,814,887 (Nikolski et al.), which is incorporated herein by reference in its entirety. The use of patient activity signals to determine SIR and provide rate-responsive pacing is generally disclosed in US Pat. Nos. 5,720,769 (van Oort) and 7,031,772 (Condie et al.), both of which are incorporated herein by reference in their entirety.

[0065] Processor 244 can retrieve other programmable pacing control parameters, such as pacing pulse amplitude and pacing pulse width, which are passed to pulse generator 202 for controlling pacing pulse delivery. In addition to providing control signals to pacing timing circuit 242 and pulse generator 202 for controlling pacing pulse delivery, processor 244 can also: provide sensing control signals to sensing circuit 204 (e.g., R-wave sensing threshold, sensitivity, various blanking and refractory intervals applied to cardiac electrical signals); and provide atrial event detection control signals to atrial event detector circuit 240 for detecting and confirming atrial contraction events (e.g., ventricular event detection window, atrial refractory period, detection threshold amplitude applied to motion sensor signals, and any other atrial event detection criteria applied by circuits included in atrial event detector circuit 240).

[0066] The functionality 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 circuits is intended to highlight different functional aspects and does not necessarily imply that such functionality must be implemented by separate hardware, firmware, or software components or any particular circuit structure. Rather, the functionality 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.

[0067] As disclosed herein, the operation of the circuits included in the pacemaker 14 should not be construed as reflecting a specific form of hardware, firmware, and software necessary to practice the described techniques. It is believed that the specific form of the software, hardware, and / or firmware will be determined primarily by the specific system architecture employed in the pacemaker 14, as well as by the specific sensing and therapy delivery circuits employed in the pacemaker 14. Given the disclosure herein, it is within the ability 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] The pulse generator 202 generates electrical pacing pulses that are delivered to the RV of the patient's heart via the cathode electrode 164 and the return anode electrode 162. The pulse generator 202 may include a charging circuit 230, a switching circuit 232, and an output circuit 234. 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 switching circuit 232 may control when the holding capacitor of the charging circuit 230 is coupled to the output circuit 234 for delivering a pacing pulse. For example, the switching circuit 232 may include a switch that is activated by a timing signal received from the pacing timing circuit 242 at the expiration of the AV pacing interval (or the LR pacing interval) and remains closed for the programmed pacing pulse duration 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 between electrodes 162 and 164 through the output capacitor of output circuit 234. Embodiments of pacing circuitry generally disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.) and commonly assigned U.S. Pat. No. 8,532,785 (Crutchfield et al.), both of which are incorporated herein by reference in their entireties, may be implemented in pacemaker 14 to charge the pacing capacitor to a predetermined pacing pulse amplitude and deliver pacing pulses under the control of control circuit 206.

[0069] The memory 210 may include 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 include any non-volatile 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 intervals; and other data used by the control circuit 206 to control the ventricular pacing mode and the delivery of pacing pulses by the pulse generator 202 (e.g., by detecting atrial contraction events from the motion sensor signal by the atrial event detector circuit 240, and setting the pacing escape interval timer included in the pacing timing circuit 242).

[0070] The power source 214 provides power to each of the other circuits and components of the pacemaker 14 when needed. The control circuit 206 may perform power control operations to control when various circuits or components are powered to perform various pacemaker functions. 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 Shown in.

[0071] Telemetry circuit 208 includes transceiver 209 and antenna 211 for transmitting and receiving data via a radio frequency (RF) communication link. As described above, telemetry circuit 208 can communicate with external device 20 ( Figure 1 ) for two-way communication. The motion sensor signals and cardiac electrical signals and / or data derived therefrom may be transmitted by telemetry circuit 208 to external device 20. Telemetry circuit 208 may receive programmable control parameters and algorithms for performing atrial event detection and ventricular pacing control and store them in memory 210 for access by control circuit 206.

[0072] Figure 4 is an example of a motion sensor signal 250 that can be acquired by the motion sensor 212 over the cardiac cycle. The vertical dashed lines 252 and 262 represent the timing of two consecutive ventricular events (intrinsic ventricular depolarization or ventricular pace), marking the beginning and end of the ventricular cycle 251, respectively. The motion signals include: A1 event 254, A2 event 256, A3 event 258, and A4 event 260. A1 event 254 is an acceleration signal that occurs during ventricular contraction and marks the approximate onset of ventricular mechanical contraction (in this example, when the motion sensor 250 is implemented as an accelerometer). A1 events are also referred to herein as "ventricular contraction events." A2 events 265 are acceleration signals that occur during ventricular diastole and mark the approximate offset or end of ventricular mechanical contraction. A2 events are also referred to herein as "ventricular relaxation events." A3 events 258 are acceleration signals that occur during passive ventricular filling and mark ventricular mechanical relaxation. A3 events are also referred to herein as "ventricular passive filling events." Since the A2 event occurs at the end of ventricular systole, it is an indicator of the onset of ventricular diastole. The A3 event occurs during ventricular diastole. Thus, the A2 and A3 events can be collectively referred to as ventricular mechanical diastolic events, as they are both indicators of ventricular diastole.

[0073] The A4 event 260 is an acceleration signal that occurs during atrial contraction and active ventricular filling and marks atrial mechanical contraction. The A4 event 260 is also referred to herein as an "atrial contraction event" or simply an "atrial event". The A4 event 260 is an atrial contraction event detected by the atrial event detector circuit 240 from the motion sensor signal 250 when the pacemaker 14 is operating in the atrial tracking ventricular pacing mode, for controlling the pacing timing circuit 242 to trigger ventricular pacing pulse delivery by starting the AV pacing interval in response to detecting the A4 event 260. As described below, 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 in at least some ventricular cardiac cycles for actively 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 erroneous detection of the A4 event and to facilitate reliable A4 event detection to achieve correct atrial synchronized ventricular pacing pulse timing.

[0074] Figure 5 Flowchart 300 of a method performed by the pacemaker 14 for detecting A4 events and controlling ventricular pacing during an atrial tracking pacing mode. At block 302, the control circuit 206 identifies a ventricular event. The ventricular event can be an event signal detected from an R wave received from the sensing circuit 204 or a ventricular pacing pulse delivered by the pulse generator 202. Because ventricular A1, A2, and A3 events during an intrinsic ventricular rhythm may have different characteristics than during a ventricular paced rhythm, the methods described herein for determining the amplitude, time interval, or other characteristics of the A1, A2, and A3 events are used to set A4 detection control parameters or confirm A4 event detection for both intrinsic ventricular rhythms and ventricular paced rhythms.

[0075] For example, as described in conjunction with the flowcharts and timing diagrams presented herein, various time intervals, sensing windows, atrial refractory periods, and atrial event detection threshold amplitudes may be set based on characterizations of one or more of the A1, A2, and A3 events. A set of A4 detection control parameters and characteristics of the A1, A2, and A3 events may be determined and stored for use during an episode of ventricular sensing (intrinsic ventricular rhythm), and another set of A4 detection control parameters and characteristics of the A1, A2, and A3 events may be determined and stored for use during an episode of ventricular pacing.

[0076] During ventricular sensing, control circuit 206 may be configured to distinguish normal sinus R waves from premature ventricular contractions (PVCs) such that the ventricular events identified at block 302 to initiate a search for A1 to A4 events from the motion sensor signal do not include PVCs. When a sensed or paced ventricular event that is not a PVC is identified at block 302, pacing timing circuit 242 may set the escape interval timer to the ventricular LR pacing interval. If the LR pacing interval expires (as described below in conjunction with block 315), a ventricular pacing pulse may be delivered, asynchronous with atrial activity, to maintain some minimum basal ventricular rate.

[0077] At block 304, atrial event detector 240 detects A1 to A3 motion signals. In short, atrial event detector 240 may compare motion sensor signals to one or more predetermined detection threshold amplitudes during one or more set time windows in response to identifying a ventricular event at block 302 to detect A1 to A3 events. In some examples, an A4 event may also be detected at block 304 to increase confidence in the positive identification of each of the four motion sensor signals A1 to A4 in a given cardiac cycle. In this example, A1 to A3 events, and optionally A4, may be detected beat by beat.

[0078] After the A1 to A3 events are detected, the A1-A3 time interval is determined as the time interval from the detection of the A1 event to the detection of the A3 event at block 304. The A1-A3 time interval may be used to update the A1-A3 interval trend at block 308. For example, a running average A1-A3 time interval may be updated at block 308 using the most recent A1-A3 time interval measurement, e.g., the most recent three to twelve A1-A3 time intervals.

[0079] At box 310, the A1-A3 time interval is used to set a post-ventricular atrial refractory period. The atrial refractory period is also referred to herein as the "A4 refractory period" because, in some examples, A4 event detection may be suppressed or ignored during the atrial refractory period. When a ventricular electrical event is identified at box 302, the atrial event detector 240 may start an atrial refractory period at box 310. The atrial refractory period may be set based on the A1-A3 time interval, for example, a fixed interval that is greater than or longer than the A1-A3 time interval. For example, the atrial refractory period may be set to 50 to 150 ms longer than the A1-A3 time interval, although a shorter or longer fixed interval may be added to the A1-A3 time interval to set the atrial refractory period. In some examples, the fixed time interval used to set the atrial refractory period may vary depending on the heart rate.

[0080] During the atrial refractory period, any motion sensor event detected or exceeding a detection threshold magnitude will be ignored for the purpose of triggering a ventricular pacing pulse and initiating an AV pacing interval. As shown in block 304, ventricular mechanical events A1 to A3 may be detected during the atrial refractory period to determine an A1-A3 time interval and update the A1-A3 interval trend periodically or beat-to-beat (blocks 306 and 308).

[0081] At block 312, atrial event detector circuit 240 monitors the motion sensor signal to detect an A4 event after the atrial refractory period expires. If an A4 event is not detected before the LR pacing interval expires (block 315), a ventricular pacing pulse is delivered at block 316 to ensure a minimum ventricular rate, e.g., at least 40 to 60 beats per minute (bpm). Further, it should be appreciated that if an intrinsic R wave is sensed before an A4 event is detected, then Figure 5 The process may return to block 302, where the sensed R wave is identified as a ventricular electrical event and the control circuit 206 restarts the process of detecting an A4 event in the next ventricular cycle.

[0082] If an A4 event is detected before the LR pacing interval expires, control circuit 206 sets an AV pacing interval in response to the detection of the A4 event at block 314. If no intrinsic R-wave is sensed from the cardiac electrical signal by sensing circuit 204 during the AV pacing interval (the "NO" branch of block 316), then upon expiration of the AV pacing interval, a ventricular pacing pulse is delivered by pulse generator 202 at block 318. At block 302, if a ventricular pacing pulse is delivered, and otherwise a sensed R-wave, it is identified as the next ventricular event, and the process repeats.

[0083] In this way, A1 to A3 events can be detected from the motion sensor signal on a beat-to-beat (or less frequent) basis to update the A1-A3 time interval trend used to set the atrial refractory period, thereby providing a high probability of positively detecting an A4 event and correctly timing the ventricular pacing pulse in sync with the atrial event. By applying the atrial refractory period set based on the A1-A3 timing, other motion sensor signal events A1 to A3 are less likely to be erroneously detected as A4 events.

[0084] In some examples, the time interval to the A2 event may be determined instead of determining the A1-A3 time interval, thereby setting the atrial refractory period based on the A1-A2 time interval to extend at least through the A2 event and terminate before the A3 event. In this example, the A4 detection threshold amplitude may be set higher than the expected A3 event amplitude to allow detection of the A4 event earlier in the ventricular cycle, for example, as the atrial frequency increases. In other cases, the time interval from the identified ventricular electrical event to the A1, A2, or A3 event may be determined and used to set the atrial refractory period.

[0085] In some examples, the processes of blocks 304 to 308 are performed periodically rather than beat by beat. For example, once every third cardiac cycle, every eighth cardiac cycle, or other predetermined schedule for updating the A1-A3 time interval (or other ventricular event time intervals as discussed above) for setting the atrial refractory period at block 310, detection of A1-A3 events can be performed during the atrial refractory period. In some cases, when the heart rate changes by more than a predetermined amount, the paced or intrinsic heart rate can be monitored, and A1-A3 events can be detected to update the A1-A3 interval trend. For example, at block 302, when a ventricular event is identified, the ventricular event interval between consecutive ventricular events can be determined. The ventricular event interval may be the RR interval between consecutive sensed intrinsic R waves, or the VV interval between consecutive delivered ventricular pacing pulses, and may include the RV interval between sensed intrinsic R waves and consecutive delivered pacing pulses and the VR interval between delivered pacing pulses and consecutive sensed R waves. For example, when the pacemaker 14 is a rate-responsive pacemaker, both the intrinsic heart rate and the pacing rate may change. If the ventricular event interval changes or the trend of the ventricular event interval changes by more than a predetermined amount, the control circuit may execute blocks 304 to 308 to update the A1-A3 interval trend used to set the atrial refractory period.

[0086] In other examples, if an A4 event is not detected at box 312 after the atrial refractory period and before the next ventricular event (intrinsic or paced) is identified at box 302, the control circuit 206 may perform the processes of boxes 304 to 306 for a predetermined number of consecutive or non-consecutive cardiac cycles to update the A1-A3 interval trend used to set the atrial refractory period to restore A4 detection.

[0087] Figure 6 is an example of motion sensor signals 400 and 410 acquired over two different cardiac cycles. At time 0.0 seconds in both cardiac cycles, a ventricular pacing pulse is delivered. The top sensor signal 400 is received over one cardiac cycle, while the bottom sensor signal 401 is received over a different cardiac cycle. The two signals 400 and 410 are aligned in time with time 0.0 seconds of the ventricular pacing pulse being delivered.

[0088] It is observed that the A1 events 402 and 412 of the respective 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 (occurring during ventricular diastole) 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, ventricular diastole, and 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 be different after a ventricular pacing pulse than after a sensed intrinsic R wave, but, under stable pacing or intrinsic rhythm, the relative timing of the A1, A2, and A3 events is consistent with each other and the preceding ventricular electrical event for a given heart rate.

[0089] The A4 events 408 and 418 of the first motion sensor signal 400 and the second motion sensor signal 410 are not aligned in time. The A4 event occurs during ventricular systole, so the time interval between the immediately preceding ventricular electrical event (a sensed R wave or ventricular pacing pulse) and the A4 event after the preceding A1 to A3 events may vary between cardiac cycles.

[0090] The timing of the A1 to A3 events relative to each other and the timing coherence of the immediately preceding ventricular electrical events can be used to determine the atrial refractory period and increase confidence in the reliable detection of the A4 events 408 and 418. In some examples, the A1 sensing window 420 can be set based on the expected Vpace-A1 time interval. When the motion sensor signal 400 or 410 exceeds the A1 sensing threshold amplitude 440, the Vpace-A1 time interval 430 can be measured. The A1 sensing window 420 can be adjusted on the next cardiac cycle based on the Vpace-A1 time interval 430 determined on the current cardiac cycle or a running average Vpace-A1 time interval.

[0091] The A2 sensing window 422 may be set based on an expected Vpace-A2 time interval (not explicitly shown, but understood to be the total time from 0.0 seconds to A2 event detection) or an A1-A2 time interval 432 (from the time of the start of A1 detection to the time of A2 detection). An A2 event 404 or 414 may be detected at the first positive crossing of the A2 sensing threshold amplitude 442 by the motion sensor signal 400 or 410 during the A2 sensing window 422. The A2 sensing window 422 may be adjusted on the next cardiac cycle based on the Vpace-A2 time interval or the A1-A2 time interval 432 determined on the current cardiac cycle.

[0092] Similarly, the A3 sensing window 424 can be set based on an expected Vpace-A3 time interval (not explicitly labeled, but understood to be the sum of time intervals 430 and 434), an A1-A3 time interval 434, or an A2-A3 time interval (not explicitly labeled, but understood to be the time interval from a sensed A2 event 404 or 414 to a sensed A3 event 406 or 416). An A3 event 406 or 416 can be detected during the A3 sensing window 424 when the motion sensor signal 400 or 410 exceeds the A3 sensing threshold amplitude 444, respectively. The threshold crossing that results in the detection of an A3 event can be the first positive-going threshold crossing of the A3 event signal, the last negative-going threshold crossing (of the rectified signal), or another reference point. The A3 sensing window 424 can be adjusted on the next cardiac cycle based on the Vpace-A3 time interval, the A1-A3 time interval 434, or the A2-A3 time interval determined during the current cardiac cycle.

[0093] Each of the sensing windows 420, 422, and 424 or 416 may be set based on a history of time intervals determined from a ventricular pacing pulse or sensed intrinsic R-wave to the corresponding A1 event 402 or 412, A2 event 404 or 414, and A3 event 406, or based on a history of time intervals between detected A1, A2, and A3 events, or any combination thereof. For example, the A2 sensing window 422 may be set to the beginning based on the time interval measured between the ventricular pacing pulse or sensed R-wave and the detected A1 event. The end of the A2 sensing window 422 may be set to the beginning based on the A1-A2 time interval 432 or based on the A1-A3 time interval 434. It should be appreciated that a variety of methods of setting the A1, A2, and A3 sensing windows 420, 422, and 424, respectively, may be contemplated based on the consistency of expected time intervals between any combination of ventricular electrical events (pacing or sensing) and subsequent A1, A2, and A3 events. Furthermore, it is contemplated that these sensing windows 420, 422, and 424 may be set according to different control parameters, such as different fixed time intervals being added to or subtracted from the measured event time intervals depending on whether the ventricular electrical event is a paced or sensed event and / or depending on the heart rate. The event time intervals that may be measured and used to set the start, offset, and duration of the sensing windows 420, 422, and 424 may include any one or combination of the Vpace-A1, Vpace-A2, Vpace-A3, Rsense-A1, Rsense-A2, Rsense-A3, A1-A2, A1-A3, and / or A2-A3 time intervals determined during a paced and / or intrinsic rhythm.

[0094] The sensing threshold amplitudes 440, 442, and 444 may be uniquely set during each of the respective sensing windows 420, 422, and 424, or set to a fixed common value for all sensing windows. The sensing threshold amplitudes 440, 442, and 444 may be fixed thresholds or decaying thresholds, and may be automatically adjusted to be set as starting thresholds based on the peak motion sensor signal amplitude detected during each respective window 420, 422, and 424. The motion sensor signals 400 and 410 are shown as raw signals, but the motion sensor signals may be filtered, amplified, and rectified by circuits included in the motion sensor 212 to provide rectified signals to the control circuit 206 for detecting A1 to A4 events.

[0095] The post-ventricular atrial refractory period 436 may be set based on the A1-A3 time interval 434 or based on the Vpace-A3 time interval (the sum of the Vpace-A1 interval 430 and the A1-A3 time interval 434). In some embodiments, the atrial refractory period 436 ends when the A3 sensing window 424 expires. In other embodiments, the atrial refractory period 436 ends after the A3 sensing window 424 expires. The A4 event 408 or 418 may be detected by the rectified motion sensor signal in response to a crossing (e.g., the first positive crossing or the last negative crossing) of the A4 sensing threshold amplitude 446.

[0096] In some examples, an A4 detection is confirmed when an A1, A2, and A3 event, respectively, is detected during the atrial refractory period 436. If none of the A1, A2, or A3 events are detected during the atrial refractory period 436, then an A4 event detection based on the crossing of the threshold 446 may not be confirmed and not used to initiate an AV pacing interval. In other examples, at least one of the A1, A2, or A3 events may need to be detected on a beat-to-beat basis during each sensing window 420, 422, or 424 to confirm an A4 detection 436 after the atrial refractory period.

[0097] The A1, A2, and / or A3 events sensed during the corresponding A1 sensing window 420, A2 sensing window 422, and A3 sensing window 424 may be used as combined with Figure 5 The atrial refractory period 436 is updated beat by beat or less frequently as described, without the need for positive detection of each of A1, A2, and / or A3 for confirming A4 detection on every beat. The atrial refractory period is set based on the detection and relative timing of the A1 to A3 events so that the atrial refractory period can be set based on consistent timing of ventricular motion sensor signal events, thereby allowing A4 events to be detected with high reliability when the timing of A4 events relative to A1-A3 events and previous ventricular electrical events is variable.

[0098] In some embodiments, an A3-A4 event interval 445 is determined and used to adjust the A4 refractory period 436. For example, an A3 event 406 may be detected by detecting the last negative-going crossing of an A3 event detection threshold magnitude 444 during an A3 sensing window 424. After the A4 refractory period 436 ends, an A4 event 408 may be detected by the first positive-going crossing of an A4 event detection threshold magnitude 446. An A3-A4 event interval 445 is determined as the time from the A3 event detection and the time of the A4 event detection. The A3-A4 event time may be compared to a previous A3-A4 event time, for example, to one or more previous A3-A4 event times that may be determined during a corresponding one or more previous cardiac cycles, or to a running average A3-A4 event time determined from two to five or other predetermined number of previously determined A3-A4 event times. If a change in the A3-A4 event time interval compared to one or more previous A3-A4 event times is detected, the A4 refractory period 436 may be adjusted. When a decrease or increase in the A3-A4 event time is detected, the control circuit 206 may decrease or increase the A4 refractory period, respectively, to account for changes in the time interval between ventricular diastolic events and atrial contractile events as the atrial rate changes.

[0099] Figure 7 is a motion sensor signal that can be obtained by the control circuit 206 by averaging over multiple cardiac cycles (e.g., Figure 6 The average motion sensor signal 500 can be determined by combining the signals 400 and 410 of the present invention. The average motion sensor signal 500 can represent an average value of 3 to 20 or other predetermined number of cardiac cycles. The raw motion sensor signal or the filtered, amplified and / or rectified motion sensor signal can be buffered starting from a ventricular electrical event, pacing pulse or sensed R-wave at time 0.0 seconds until the next ventricular electrical event. The buffered motion sensor signal obtained over one cardiac cycle can be averaged with the buffered motion sensor signals obtained over a predetermined number of other cardiac cycles to produce the average motion sensor signal 500.

[0100] A ventricular electrical signal 510 is shown aligned in time with the average motion sensor signal 500. The ventricular electrical signal 510 may be transmitted from the sensing circuit 204 to the control module 206 and includes an R wave 512 (which may be an induced or intrinsic R wave) and a T wave 514. The R wave 512 is followed by a ventricular contraction A1 event 502. Ventricular relaxation A2 event 504 occurs during the T wave 514. Passive ventricular filling A3 event 506 occurs after the T wave 514.

[0101] Because the A1, A2, and A3 events are ventricular mechanical events, they occur at consistent time intervals relative to each other and relative to ventricular electrical events (R wave 512 and T wave 514). Figure 6 The signal-to-noise ratio of A1 signal 502, A2 signal 504, and A3 signal 506 in averaged motion sensor signal 500 is improved compared to single-cycle motion sensor signals 400 and 410. Averaged A1 events 502, A2 events 504, and A3 events 506 have an improved signal-to-noise ratio compared to A1, A2, and A3 events observed in motion sensor signals 400 or 410 of a single cardiac cycle, as shown in FIG. Figure 6 As shown, the detection of the A1, A2 and A3 events from the average motion signal 500 is made more reliable.

[0102] A single event detection threshold amplitude 540 may be defined such that crossings of the threshold 540 with the average rectified motion sensor signal 500 within the A1 sensing window 520, the A2 sensing window 522, and the A3 sensing window 524 are detected as respective A1 events 502, A2 events 504, and A3 events 506. In various examples, the threshold crossing may be the first positive-going crossing or the last negative-going crossing. Alternatively, a unique detection threshold amplitude may be defined for each sensing window 520, 522, and 524 to detect respective A1, A2, and A3 events. The sensing windows 520, 522, and 524 may be initially set based on the expected A1, A2, and A3 event timing following the ventricular pacing pulse or R-wave 512, and may be adjusted based on the actual detection time of each respective A1 event 502, A2 event 504, and A3 event 506 based on the threshold crossing. Sensing windows 520, 522, and 524 may be set based on the ventricular pacing rate or the atrial event rate, such as based on the A4-A4 event interval. Since the timing of the A1, A2, and A3 events and the T wave 514 may vary during the comparison of ventricular pacing, the sensing windows 520, 522, and 524 may also be set differently during intrinsic arrhythmias after a ventricular pacing pulse than after an intrinsic R-wave sensing event.

[0103] The timing of the atrial systolic A4 event, which is independent of the timing of the ventricular electrical events, may vary more from one cardiac cycle to the next than the timing of the ventricular electrical and mechanical events, as shown, for example, by the relative timing of the A4 events 408 and 418 of signals 400 and 410 ( Figure 6 ). As a result, Figure 7The improved signal-to-noise ratio of the A1 to A3 events and the attenuation of the A4 event in the average motion signal 500 enable the control circuit 206 to reliably detect the signal averaged A1 event 502, A2 event 504, and A3 event 506 to determine one or more ventricular event time intervals for setting the A1, A2, and A3 detection windows 420, 422, and 424, respectively, setting the detection threshold amplitude for detecting the A1, A2, A3, and / or A4 events, and / or setting the atria should not be as Figure 6 As shown, cycle A436 is used on a beat-by-beat basis to detect A4 events.

[0104] For example, the ventricular R wave or pacing pulse to A1 time interval 530, the A1-A3 time interval 534, the A1-A2 time interval 536, the ventricular R wave or pacing pulse to A3 time interval 516, and / or the control circuit 206 can determine the T wave to A3 time interval 518 from the average motion signal 500 and the cardiac electrical signal 510. The ventricular refractory period 436 begins when the ventricular pacing pulse is delivered or the intrinsic R wave is sensed. The atrial refractory period 436 can be set to expire after a predetermined time interval (e.g., 30 to 100 ms) after the A3 time interval 516. For example, if the time interval 516 is 700 ms, the atrial refractory period 436 can be set to expire 750 ms after the ventricular pacing pulse or sensed R wave that starts the atrial refractory period. Instead of using a time interval ending with an A3 event detection, a time interval ending with an A2 event detection can be determined and used to control the duration of the atrial refractory period 436. As described above, the A2 event occurring during the T wave 514 is indicative of the end of ventricular mechanical contraction and the onset of ventricular mechanical relaxation. The A3 event occurs during the period of ventricular mechanical relaxation, the period of passive ventricular filling. Thus, the timing of the A2 event 504 or the timing of the A3 event 506 relative to another ventricular electrical event (a ventricular pacing pulse, an R wave 512 or a T wave 514) can be used to control the duration of the atrial refractory period 436 and the exhalation time. In other words, the timing of the ventricular mechanical relaxation event, the A2 event 504 or the A3 event 506 can be determined and used to set the atrial refractory period 436, which is used to detect the A4 event on a beat-to-beat basis.

[0105] T wave 514 may be detected by detection circuit 206 on a beat-to-beat basis by control circuit 206 or by detection circuit 204 from cardiac electrical signal 510. T wave 514 may be sensed at the maximum peak amplitude of the rectified cardiac electrical signal or the maximum absolute peak amplitude in the unrectified cardiac signal received by control circuit 206 from sensing circuit 204. Alternatively, sensing circuit 204 may sense T wave 514 in response to the cardiac electrical signal crossing a T wave sensing threshold amplitude following an ECG pacing pulse or an R-wave sensed event signal. In some cases, a T wave sensing window may be applied following an R-wave sensed event signal or a delivered pacing pulse to facilitate T wave sensing.

[0106] The T wave 514 may be sensed during the atrial refractory period 436. The control circuit 206 may terminate the atrial refractory period 436 at a predetermined time interval after the T wave 514 is sensed. For example, if it is determined that the time interval 518 from the average motion signal 500 to the T wave to A3 is 150 ms, the control circuit 206 may terminate the atrial refractory period 436 at 180 ms after the T wave is sensed to facilitate reliable sensing of an A4 event.

[0107] Atrial event detector circuit 240 may be a processor-based circuit that determines an average motion sensor signal 500 over a plurality of cardiac cycles, detects A1, A2, and A3 events 502, 504, and 506 from the average motion sensor signal 500, and sets the atrial refractory period 436 based on the timing of at least one ventricular mechanical diastolic event (e.g., A3 event 506) detected from the average motion sensor signal 500. In other examples, the A2 event is used as a ventricular diastolic mechanical event to mark the approximate time of the onset of ventricular diastole. After the expiration of the atrial refractory period 436, an A4 event, such as event 408 or 418 ( Figure 6 ).

[0108] Figure 8 600 is a flow chart of a method for detecting atrial events and controlling ventricular synchronous ventricular pacing during an atrial tracking pacing mode performed by a pacemaker 14 according to one example. At block 602, a ventricular electrical event is identified, which may be a sensed intrinsic R wave or a delivered ventricular pacing pulse. Figure 5 As described, once a ventricular electrical event is identified, the LR pacing interval may be set at block 602 to maintain a minimum basal ventricular rate in the absence of an A4 event detection.

[0109] At block 604, the motion sensor signal is buffered over the cardiac cycle, e.g., until the next ventricular electrical event is identified. At block 606, the buffered motion signal is averaged with the buffered motion sensor signal acquired over a predetermined number of cardiac cycles to obtain an A4 signal having improved A1, A2, and A3 signal-to-noise ratios and an attenuated A4 signal compared to the non-averaged motion sensor signal.

[0110] At block 608, the A1, A2 and A3 events are averaged by the detection signal, as described above in conjunction with Figure 7 As described, the A1-A3 time interval or the ventricular electrical event to A3 time interval is determined from the averaged motion sensor signal. In box 610, the atrial event detector circuit 240 uses the A3 time interval to set the atrial refractory period. As described above, the atrial refractory period can be set to a predetermined percentage or fixed time interval longer than the A1-A3 time interval, or the ventricular electrical event can be set to the A3 time interval, or it can be set to expire when the A3 sensing window defined below expires. The relative timing of A1, A2 and A3 events expires. In other examples, the A2 time interval is determined at box 608 for setting the A4 refractory period. The A2 and A3 events are ventricular mechanical diastolic event markers that can be used to control the time when the A4 refractory period occurs at the beginning or before the passive ventricular filling phase or before the active ventricular filling phase associated with ventricular contraction.

[0111] After the ventricular electrical event is identified at box 602, the atrial refractory period is started at box 610. In some examples, signal averaging and determination of the A3 time interval (or A2 time interval) for setting the atrial refractory period can occur on a beat-by-beat basis using the average motion signal. In other examples, the A3 time interval is periodically determined or determined in response to changes in the atrial rate, for example, determined according to the A4-A4 interval, or changes between the sensed heart rhythm and the paced heart rhythm. The most recently updated A3 time interval (or A2 time interval) determined from the average motion sensor signal can be used to set the atrial refractory period at box 610. The expiration of the atrial refractory period can be set instantly in the atrial refractory period that has already begun based on the A3 time interval determined in the current ventricular cycle. In other examples, the A3 time interval determined in the previous ventricular cycle is used to set the atrial refractory period of the current ventricular cycle so that the atrial refractory period ends during or after the expected time of the A3 event, or in some cases to the expected A3 event, but after the expected A2 event.

[0112] In other embodiments, the duration of the atrial refractory period may be controlled on a beat-to-beat basis by initiating the atrial refractory period upon a recognized ventricular event, sensing a T wave during the atrial refractory period, and terminating the atrial refractory period within a predetermined duration time interval after the T wave is sensed, wherein the predetermined time interval is based on a T wave to A3 time interval 518 ( Figure 7 ).

[0113] If an A4 event is detected from the non-averaged motion sensor signal at box 612, an AV pacing interval is set at box 614 after the atrial refractory period expires. The A4 event may be detected based on an A4 detection threshold amplitude crossing of the raw motion sensor signal or the rectified signal. The rhythm timing circuit 242 sets the AV pacing interval at box 614 in response to the detected A4 signal. If an intrinsic R wave is not sensed before the AV pacing interval expires, as determined at box 616, a planned ventricular pacing pulse is delivered at box 620. In some cases, an A4 event may not be detected before a lower rate pacing interval expires at box 615. If a lower rate pacing interval expires before an A4 event is detected to maintain a programmed minimum ventricular basal rate, an atrial asynchronous ventricular pacing pulse may be delivered at box 620, returning the process to box 602, where a ventricular pacing pulse is identified as the next ventricular electrical event.

[0114] Fig. 9 650 is a flow chart of a method for controlling a ventricular pacing mode by a pacemaker 14 according to an example. The control circuit 206 is configured to control the pacemaker 14 to operate in a first pacing mode, to control an atrial tracking pacing mode or a non-atrial tracking pacing mode of ventricular pacing pulses, and to determine when to switch to a second pacing mode, the other of the atrial tracking pacing mode or the non-atrial tracking pacing mode based on an analysis of a motion sensor signal.

[0115] like Fig. 9 As shown, at box 652, ventricular pacing pulses are delivered according to the selected pacing mode. For example, the pacemaker 14 can operate in an atrial tracking VDD pacing mode in which ventricular pacing pulses are scheduled at AV pacing intervals in response to detecting an A4 event. In the absence of a detected A4 event, if an intrinsic R wave is not detected before the LR interval expires, ventricular pacing pulses are sent at VDD lower rate (LR) intervals to prevent ventricular contraction. At other times, the pacemaker 14 can operate in a non-atrial tracking VVIR or VDIR pacing mode in which pacing pulses are scheduled at ventricular LR pacing intervals, which can be permanent VVIR or VDIR LR intervals corresponding to the basal pacing rate or temporary LR intervals set based on a patient physical activity indicator determined from a motion sensor signal (or other sensor signals related to the patient's metabolic needs).

[0116] During operation in the selected ventricular pacing mode, at box 654, the control circuit 206 is configured to determine one or more motion signal metrics from the motion signal. At box 656, the one or more motion signal metrics are compared to a first pacing mode switching criterion. If the first pacing mode switching criterion is met, the control circuit switches from the current first pacing mode (atrial tracking pacing mode or non-atrial tracking pacing mode) to a second pacing mode. Depending on which pacing mode the control circuit 206 switches from, the second pacing mode is the other of the atrial tracking pacing mode or the non-atrial tracking pacing mode.

[0117] During the second pacing mode, the control circuit 206 determines one or more motion signal metrics, which may be the same or multiple motion signal metrics or different motion signal metrics determined during the first pacing mode, at block 654. The control circuit 206 determines whether the motion signal metrics satisfy a second pacing mode switching criterion during the second pacing mode, and switches back to the first pacing mode in response to satisfying the second pacing mode switching criterion.

[0118] Among the motion signal metrics that may be determined at box 654 are metrics related to patient physical activity and / or related to a loss of reliable A4 event detection. The motion signal metric related to patient physical activity may be a patient activity metric related to the patient's metabolic needs, such as an activity count or a sensor-indicated pacing rate determined based on the patient activity metric. Patient posture may be determined from the motion signal as an indirect indication of patient activity, for example, by detecting a non-upright posture as a stationary or inactive posture, and an upright posture as a non-stationary or active posture. Because patient posture may affect A4 signal strength and the reliability of A4 event detection, patient posture may also be determined as a motion signal metric related to a loss of reliable A4 event detection. For example, a specific patient posture, such as left lateral decubitus or other recognized posture, may be determined to confound A4 event detection in a single patient and as a criterion for pacing mode switching.

[0119] A motion signal metric that may be determined at block 654 and that is associated with a loss of reliable A4 event detection may be a count of ventricular cycles that occur without a detected A4 event. Another motion signal metric that may be associated with a loss of reliable A4 event detection may be an A3-A4 time interval. Shortening the A3-A4 time interval, e.g. Figure 6 Interval 445 in, or a change in the time interval from another ventricular event to A4 may indicate an increase in atrial tachycardia, may result in fusion of A3 and A4 events and / or be associated with increased patient physical activity, both of which may confound A4 event detection.

[0120] A motion signal metric that can be determined at box 654 and is associated with the patient's physical activity and the loss of reliable A4 event detection can be determined by processing motion signal samples acquired over a predetermined time period of the motion signal. For example, the average amplitude of all samples over the predetermined time period, the sum of the amplitudes of the samples over the predetermined time period, the average frequency over the time period, the average slope, or other metrics of motion signal energy or entropy during motion over the entire predetermined time period can indicate a potential decrease in the reliability of patient body motion, non-cardiac motion, increased signal noise, and / or A4 event detection due to an increase in motion signal peaks present in the motion signal. The time period used to determine the motion signal metric can be a cardiac cycle or a portion thereof, or can be timed independently of the cardiac cycle, for example, any 500ms, 1 second, 2 seconds, or other predetermined time period or multiple predetermined time periods of the motion sensor signal.

[0121] Thus, the one or more motion signal metrics determined at block 654 may include direct or indirect metrics of non-cardiac, patient body motion and / or A4 event detection reliability. The motion signal metrics determined based on the motion sensor signals included in the pacemaker 14 may include metrics of patient body activity; e.g., motion metrics. Patient body posture; A4 event detection counts; time intervals, amplitudes, and / or other characteristics of cardiac mechanical events (A1, A2, A3, and / or A4); motion signal metrics determined by processing motion signal sampling points over a predetermined time period to obtain metrics related to motion signal energy and / or entropy over the entire time period.

[0122] Fig. 10A 700 is a flow chart of a method performed by the pacemaker 14 for switching from an atrial tracking pacing mode to a non-atrial tracking pacing mode based on a motion signal measure, according to one example. Figure 5 and Figure 8 The method depicted by the flowchart of generally represents an atrial tracking ventricular pacing mode, such as a VDD pacing mode, in which ventricular pacing pulses (at least ventricular R waves and atrial A4 events) are delivered based on dual chamber (atrial and ventricular) sensing of cardiac events (e.g., atria), and a dual pacing response of triggered and suppressed pacing pulses is provided by the RV pacemaker 14. In response to detecting an A4 event from a motion sensor signal, a ventricular pacing pulse is triggered. In response to sensing a ventricular R wave, a ventricular pacing pulse is suppressed.

[0123] Respectively Figure 5 and Figure 8The LR pacing interval set at blocks 302 and 602 of can be a VDD LR pacing interval that provides ventricular pacing at a minimum or basal ventricular rate in the absence of a sensed A4 event and a sensed R wave during the LR pacing interval. The VDD LR pacing interval can be set to provide a basal pacing rate of 40 bpm. Whenever an A4 event is sensed, ventricular pacing is provided at the atrial rate in synchronization with the ventricular contraction event, which can be paced by the atrial pacemaker 12 or the intrinsic atrial rate. As the patient's heart rate changes due to changes in the patient's physical activity or metabolic demands, the ventricular pacing rate will track changes in the rate of A4 events.

[0124] However, in some cases, an A4 event may go unnoticed. For example, the A4 signal may sometimes have a lower signal strength and therefore go undetected. In some patients, posture changes, changes between pacing and intrinsic rhythm, or other factors may affect the A4 event amplitude. A patient may have normal sinus rhythm, but the pacemaker 14 does not detect the ventricular contraction event. In this case, atrial tracking of the ventricular pacing pulse is required, but the atrial rate is unknown. In this way, switching to a non-atrial pacing mode may be warranted. In other cases, an A4 event may go undetected due to atrial tachycardia. During atrial fibrillation, the A4 signal may become too small to be detected. In this case, non-atrial tracking ventricular pacing is appropriate to avoid pacemaker-mediated tachycardia.

[0125] In both cases, an A4 event is not detected in normal sinus rhythm or atrial tachyarrhythmia, and in a patient with atrioventricular block, ventricular pacing is required at a rate sufficient to support the patient's physical activity. The method of flowchart 700 provides a technique for switching a ventricular pacing mode from an atrial tracking VDD pacing mode to a non-atrial tracking pacing mode based on meeting a mode switching criteria. Mode switching criteria are defined to facilitate switching to non-atrial tracking ventricular pacing when no A4 event is detected and ventricular rate support is required. Mode switching criteria can be defined to preferentially provide ventricular synchronous ventricular pacing in a VDD pacing mode when an A4 event is detected or when no A4 event is detected but ventricular pacing is being performed at a programmed lower VDD rate sufficient to support the patient's physical activity level, such as a resting state.

[0126] exist Fig. 10A At block 702 of , a first LR interval is established for an atrial tracking pacing mode (e.g., a VDD pacing mode), and a second LR interval is established for a non-atrial tracking mode (e.g., a VVIR or VDIR pacing mode). Fig.11 and Fig.12As described, the non-atrial pacing mode can be a VVIR pacing mode in which sensing of A4 events is disabled most of the time to conserve pacemaker battery life, but can be temporarily re-enabled to check whether pacemaker mode switching criteria associated with A4 event detection are met. In other examples, such as in combination with Fig.13 As described, a non-atrial tracking pacing mode may be a VDIR pacing mode that still detects and monitors for A4 events, which may be done on a beat-to-beat basis, but does not trigger ventricular pacing pulses in response to detection of an A4 event.

[0127] Atrial tracking LR pacing intervals and non-atrial tracking LR pacing intervals may be established by control circuitry 206 at box 702 based on respective atrial tracking and non-atrial tracking lower rates programmed in memory 210. The LR intervals established at box 702 are sometimes referred to as "permanent" LR intervals because they correspond to a programmed basal or minimum pacing rate. In some cases, the permanent LR intervals may be adjusted to temporary LR intervals. For example, during rate-responsive VVIR pacing, the permanent VVIR LR intervals may be shortened to temporary LR intervals to meet the patient's physical activity needs. As described below, when pacing mode switching criteria are met, the pacemaker 14 switches from an atrial tracking pacing mode (e.g., as described in the accompanying drawings) to a temporary LR interval. Figure 5 or Figure 8 as shown) switches to a non-atrial tracking pacing mode to provide ventricular pacing in a rate-responsive pacing mode in order to maintain an appropriate ventricular rate to meet the patient's physical activity level.

[0128] The non-atrial tracking LR interval can be set to provide pacing at a lower rate that is different from the atrial tracking LR interval. For example, the atrial tracking LR interval can be established at box 702 to provide VDD pacing at a basic pacing rate of 40 pulses per minute. The non-atrial tracking LR interval can be established at box 702 to provide a basic pacing rate of 60 pulses per minute. By providing a longer LR pacing interval in the atrial tracking pacing mode, more time can be left in each ventricular pacing cycle to detect A4 events to promote ventricular synchronous ventricular pacing. When A4 events are intermittently undetectable, a basic pacing rate of 40 pulses per minute corresponding to the atrial tracking LR interval can provide pacing. Rate smoothing can be provided to avoid sudden changes in ventricular rate. When A4 events are consistently not adequately detected over multiple ventricular cycles, switching to a non-atrial tracking pacing mode with a higher basic pacing rate of 60 pulses per minute can provide adequate rate support for the patient during rest or relatively low physical activity states.

[0129] At box 704, the pacemaker 14 operates in a VDD pacing mode. In some patients, the atrial rate may be intrinsically controlled by the sinoatrial node and increase and decrease physiologically in response to changes in the patient's physical activity. In other embodiments, the atrial rhythm may be paced by the atrial pacemaker 12, which may be a rate-responsive pacemaker that includes a patient activity sensor for determining a sensor-indicated pacing rate that matches the patient's metabolic needs. In either case, the ventricular pacemaker 14 is configured to detect intrinsic or paced A4 contractile events on a beat-by-beat basis. In response to detecting an A4 event at box 706, an AV pacing interval begins, and upon its expiration, a ventricular pacing pulse is delivered at box 708. It is recognized that if an intrinsic R wave is sensed prior to the expiration of the AV pacing interval, then, for example, as described above in conjunction with Figure 8 Maintain ventricular pacing pulses as described.

[0130] At block 709, the count of A4 event detections is updated. For example, X of a Y counter included in the control circuit 206 for counting the number of A4 event detections in a predetermined total number of Y ventricular cycles may be updated. In other examples, a counter may be used to track the number of consecutive ventricular cycles that occurred without detecting an A4 event. In this case, the counter may be reset to zero at block 709 in response to an A4 event detected at block 706. A counter for tracking A4 event detections (or ventricular cycles without A4 detection) may be determined as a motion signal metric for controlling pacing mode switching, and the counter may or may not be required to be on consecutive ventricular cycles.

[0131] If an A4 event is not detected before the VDD LR interval expires, a ventricular pacing pulse is delivered at box 710. The VDD LR interval may be adjusted according to a rate smoothing algorithm to avoid sudden changes in ventricular rate. The ventricular pacing pulse delivered at box 710 may be delivered at a pacing interval between the expected A4 event time and the VDD LR pacing interval corresponding to the minimum basal rate established at box 702. For example, at box 710, the VDD LR interval may be adjusted from the VDD LR pacing interval to the expected A4 event time plus the delay interval to provide rate smoothing. To illustrate, rather than waiting for the VDD LR interval, which may be set to 1.5 seconds for a minimum basal rate of 40 pulses per minute, the pace timing circuit 242 may set a rate smoothing adjusted LR interval whose delay time is longer than the nearest ventricular pacing cycle length. For example, if the two previous ventricular pacing pulses were delivered 800 ms apart (approximately 75 bpm), the ventricular pacing pulse delivered at block 712 may be delivered at 1000 ms (e.g., 800 ms plus a 200 ms delay interval) if an A4 event has not yet been detected. In this way, some additional time is allowed to detect an A4 event, but by using an adjusted LR interval of 1000 ms (60 bpm), asystole may be prevented without a sudden large change in ventricular rate from 75 bpm to 40 bpm.

[0132] The count of A4 events detected from the predetermined number of ventricular cycles is updated at block 711. At block 712, the control circuit 206 determines whether the count of A4 detections obtained in the predetermined number of ventricular cycles is less than a mode switching threshold. A threshold number of X A4 detections in a predetermined number of Y ventricular cycles may be required to remain in the VDD pacing mode. In various examples, the control circuit 206 may determine whether less than a threshold number of X A4 events have been detected in the most recent Y ventricular cycles where X and Y are equal (consecutive ventricular cycles) or X is less than Y (non-continuous cycles). Less than a threshold number of A4 events in Y ventricular cycles may be set as a motion signal metric to switch from the VDD atrial tracking pacing mode to the non-atrial tracking pacing mode.

[0133] The X of the Y standard can be programmable and can be based in part on the patient's history of atrial fibrillation. For example, if the patient has no history of atrial fibrillation, the atria may be in sinus rhythm, but no A4 event signals are detected. In patients without a history of atrial fibrillation, it may be desirable to remain in VDD pacing mode for a relatively long time to enable detection of A4 events and facilitate atrial synchronized ventricular pacing. In cases with little or no history of atrial fibrillation, a relatively large number of ventricular cycles without A4 event detection may be required before switching pacing modes. For example, less than 10 A4 event detections in 20 ventricular cycles or less than 12 A4 event detections in 24 ventricular cycles may be required at box 712 before switching to a non-atrial tracking pacing mode at box 718.

[0134] However, in patients with a strong history of atrial fibrillation, it may be desirable to switch to a non-atrial pacing mode relatively quickly because the loss of A4 event detection may be due to atrial fibrillation. The X criteria for Y may be set to be relatively less stringent to more quickly switch to a non-atrial tracking pacing mode to provide ventricular rate support pacing than in patients with no or minimal history of atrial fibrillation. For example, the X criteria for Y may be set to less than 6 A4 event detections in 10 ventricular cycles or less than 10 A4 event detections in 16 ventricular cycles. If the count of A4 event detections outside of Y ventricular cycles is less than the pacing mode switching threshold, then at box 718, the control circuit 206 may immediately switch to a non-atrial tracking pacing mode. If the threshold number of A4 event detections is met or exceeded, then at box 712, the pacemaker 14 may remain in the VDD mode and return to box 704.

[0135] However, other mode switching criteria may be applied to enable the control circuit 206 to switch from VDD to a non-atrial tracking pacing mode. For example, if the Y pacing mode switching criteria associated with the detection of an A4 event are not met, the control circuit 206 may apply other criteria at box 716 to cause the pacing mode to switch to a non-atrial tracking pacing mode. In one embodiment, the control circuit 206 may determine the patient's body posture as a motion signal metric at box 714 to compare to the pacing mode switching criteria at box 716. When the motion sensor 212 is implemented as an accelerometer, the patient's body posture may be determined based on an analysis of the motion sensor signal, or a dedicated accelerometer may be included in the pacemaker 14 to detect the patient's body posture. Example techniques for determining patient posture from one or three-dimensional accelerometers are generally disclosed in U.S. Patent No. 9,814,887 (Nikolski et al.) incorporated herein by reference in its entirety, and U.S. Publication No. 2017 / 0113051 (Sheldon et al.) (which disclosure is also incorporated herein by reference in its entirety), as well as U.S. Patent Nos. 5,593,431 and 6,044,297 incorporated herein by reference.

[0136] As determined at box 716, if the detected body posture of the patient meets the pacing mode switching criteria, then at box 718, the control circuit 206 switches to the non-atrial tracking pacing mode. In some patients, posture changes may affect the motion sensor signal. Specific postures can be identified in which A4 event detection is poor or unreliable for atrial tracking for ventricular pacing. The control circuit 206 can actively switch to the non-atrial tracking pacing mode even if the number of A4s detected at box 712 is greater than the pacing mode switching threshold. If the patient's body posture is determined to be a posture known to be associated with poor A4 detection, the control circuit 206 can switch to the non-atrial tracking mode in the expectation of a loss of A4 event detection.

[0137] In other examples, the control circuit 206 may determine the patient's body posture at box 714 even if the A4 event detection count is equal to or greater than the pacing mode switching threshold at box 712. In other words, the "yes" branch of box 712 may alternatively lead to box 714 for determining the patient's body posture. The patient posture mode switching criteria may require that the patient be in an upright position before switching to the non-atrial pacing mode, even when the switching criteria is detected less than X A4 in at least Y ventricular cycles. If no A4 events are detected and the patient is upright, such as sitting, standing, walking, etc., ventricular rate support may be required and can be provided by switching to the non-atrial tracking pacing mode. The upright posture generally represents a non-stationary posture in which the patient is assumed to be awake and may be physically active, requiring a rate of ventricular pacing support greater than the VDD lower rate. If the patient posture meets the mode switching criteria at box 716, such as an upright position or a non-stationary position, then at box 718, the control circuit 206 switches to the non-atrial pacing mode.

[0138] However, if the patient posture does not satisfy the mode switching criteria, the pacemaker 14 remains in the VDD pacing mode even though the A4 detection count is less than the mode switching threshold at box 712. If the patient is in a non-upright or resting position, such as in any lying or tilted position that is typically indicative of a sleeping or resting posture, the lower VDD rate can provide adequate ventricular rate support for the resting patient. The VDD LR pacing interval established at box 702 allows more time to detect A4 events between pacing pulses than the relatively shorter non-atrial tracking LR interval. By remaining in the VDD pacing mode when the patient is at rest, and a higher pacing rate is not required, an earlier return to A4 event detection and atrial synchronized ventricular pacing when the patient is at rest can be facilitated. In this case, the control circuit 206 can remain in the VDD pacing mode by returning to box 704.

[0139] Fig. 10B 750 is a flow chart of a method that may be performed by the pacemaker 14 for controlling a pacing mode switch from a VDD pacing mode to a non-atrial tracking mode according to another embodiment. At block 704, the pacemaker 14 operates in the VDD pacing mode. In this embodiment, block 704 corresponds to Fig. 10A The same numbered box 704 of flowchart 750 is shown to indicate that the technique of flowchart 750 can be performed in parallel, simultaneously, or sequentially with the technique of flowchart 700. The technique of flowchart 750 provides additional or alternative pacing mode switching criteria that can be used to control when the pacemaker 14 switches from the atrial tracking pacing mode to the non-atrial tracking pacing mode. Fig. 10B The process of flowchart 750 in FIG. 1 is used to control pacing mode switching based on motion signal metrics without executing Fig. 10AIn various implementations, Fig. 10A and Fig. 10B The processes are combined and can be executed separately Fig. 10A process rather than Fig. 10B and vice versa.

[0140] exist Fig. 10B In block 752, the control circuit 206 monitors the motion signal metric determined at block 752 for use in applying the mode switching criteria to determine whether to switch from VDD pacing to a non-atrial tracking pacing mode. Fig. 10B technology to cause a change in pacing pattern in response to increases in the frequency and / or amplitude of non-cardiac motion signals due to elevated patient physical activity or motion signal noise, even in Fig. 10A The mode switching criteria related to insufficient A4 detection are not met during the process. The motion signal metric determined at box 752 can be a patient physical activity metric determined based on one or more sensor signals related to the patient's physical activity. If the motion sensor 212 is implemented as an accelerometer, an activity count or other activity metric related to the patient's physical activity (and the patient's metabolic needs) can be determined from the motion sensor signal. Methods for determining patient activity metrics from an accelerometer included in the pacemaker 14 are generally disclosed in U.S. Publication No. 2017 / 0113051 (Sheldon et al.) and U.S. Patent No. 9,724,518 (Sheldon et al.), which are incorporated herein by reference in their entirety.

[0141] When the pacemaker 14 is operating in the atrial tracking VDD pacing mode, it is not necessary to determine the patient's physical activity and the corresponding SIR for providing a rate-responsive pacing rate. However, at block 754, the control circuit 206 may perform a determination of at least a patient activity metric and a SIR during the VDD pacing mode to determine whether the pacing mode switching criteria are met.

[0142] Other motion signal metrics that may be used to determine whether the switching criteria are met may include a metric indicative of the patient's posture or a metric determined from a predetermined time period of the motion signal by processing sample points over a predetermined time period to obtain a metric indicative of: signal energy, signal entropy, or noise. The motion signal metric determined by processing the motion signal sample points over a predetermined time period may indicate that A4 event sensing may be unreliable due to an increase in the frequency and / or amplitude of non-cardiac signals in the motion signal over the predetermined time period. The motion sensor metric may be determined by summing the absolute amplitudes of consecutive motion signal sample points over a predetermined time period or during a specified window (e.g., during an A3 sensing window, during an A4 refractory period, outside an A4 refractory period, during an A4 window, during an A4-A4 cardiac cycle, during a ventricular cardiac cycle, or over a time period defined independently of cardiac event timing). An average slope, average amplitude, average frequency, or other motion signal metric may be determined that indicates an increase in motion signal energy that may interfere with reliable A4 event sensing.

[0143] At box 754, the control circuit 206 can compare the motion signal metric with the motion signal metric threshold to trigger the pacing mode switch. If the motion signal metric is determined to be a patient body activity metric, the patient body activity metric can be compared with the pacing mode switch activity threshold. The comparison of the patient activity metric with the mode switching threshold can be performed each time the patient activity metric is determined or on a less frequent basis. In one embodiment, the patient activity metric is determined from the motion sensor signal at regular time intervals (e.g., every two seconds, every six seconds, every thirty seconds, every minute, etc.). The patient activity metric can be determined from the motion sensor signal that is also used to detect the A4 event signal. If the patient's physical activity increases, resulting in an increase in the frequency of signal spikes in the motion sensor signal due to patient body movement (in addition to heart movement), these patient body activity signals may be mistakenly detected as A4 events. In some cases, as the atrial rate increases, the A4 event may move earlier in the ventricular cycle and be undetected during the atrial refractory period or merge with the A3 event and be more difficult to detect. As the patient's physical activity increases, the control circuit 206 can switch to a non-atrial pacing mode to provide ventricular pacing rate support appropriate for the patient's physical activity level, regardless of A4 events sensed from the motion sensor signal, which may be less reliable during periods of increased patient activity.

[0144] At box 754, one or a combination of metrics may be determined and compared to the pacing mode switching criteria. In one example, if the patient's physical activity metric is determined as a motion signal metric at box 754 and is greater than the mode switching activity threshold, the control circuit 206 may proceed directly to box 718 to switch to the non-atrial tracking pacing mode. The patient's physical activity metric may be determined as a SIR. For example, if an activity count is determined from an activity sensor signal as described in the reference incorporated above, a transfer function may be used to convert the activity count to a SIR. At box 754, the SIR may be compared to a mode switching activity threshold. The mode switching activity threshold may be a SIR corresponding to a particular level of the patient's physical activity, for example, daily living activities (e.g., driving, moving around the house, etc.) or a higher level of the patient's physical activity that occurs with exercise or physical exertion greater than daily daily activities. For example, the pacing mode switching threshold may be a SIR of 90 pulses per minute. In another example, the pacing mode switching threshold is a SIR of 100 pulses per minute. If the SIR is determined as a motion signal metric at box 752 and exceeds the pacing mode switch activity threshold at box 754, then at box 718, the pacemaker 14 can immediately switch to a non-atrial tracking pacing mode.

[0145] In addition to or in lieu of the patient physical activity metric, other motion signal metrics may be compared to respective pacing mode switching thresholds. For example, the sum of the amplitude, average amplitude, average slope, average frequency, or other motion signal metrics may be compared to respective pacing mode switching thresholds. If the threshold is reached, then A4 event sensing may be deemed unreliable and the process may proceed directly to block 718 to switch to a non-atrial tracking pacing mode.

[0146] However, in the example shown, at box 754, in response to the motion signal metric satisfying the pacing mode switching criteria, the control circuit 206 may analyze the A4 event rate and / or the motion sensor signal stability. Thus, the control circuit 206 may be configured to determine the A4 event rate at box 756. The A4 event rate may be determined by determining the time interval between the detected A4 event and the most recent previous A4 event as the A4 event interval. One or more A4 event intervals may be determined and averaged for comparison to the SIR, or individually compared to the SIR pacing intervals, to determine whether the A4 event rate is within an acceptable range (e.g., +10bpm) matches the SIR. Three, five, eight or other predetermined number of A4 event intervals can be averaged, or individually compared to the SIR intervals. For example, if the SIR is determined to be 120 pulses per minute (which can be set as the maximum upper limit pace), the SIR pacing interval is 500ms. If the average of two or more A4 event intervals is greater than or less than 500ms and is greater than an acceptable rate response threshold margin, such as greater than 600ms or less than 400ms, it can be determined that the A4 rate does not meet the patient's physical activity needs at box 758.

[0147] In other examples, it may be required that the M of the most recent N A4 event intervals be within a threshold margin of the SIR pacing interval, e.g., within 10%, 20%, or other percentage of the SIR pacing interval. The threshold margin may be a variable margin that allows for a larger difference between the SIR pacing interval and the A4 event interval at a relatively low SIR when the need for pacing rate is high, and a smaller difference between the SIR pacing interval and the A4 event interval at a relatively high SIR when support may be more critical to preventing the patient from experiencing symptoms. For example, if the SIR is within a range corresponding to activities of daily living, such as a pacing rate of 80 bpm (temporary LR interval of 750 ms), the threshold margin may be 20%, so that if the A4 event interval is between 600 ms and 900 ms, the A4 event rate is determined to meet the patient's activity needs at box 758. If the SIR is greater than the range corresponding to activities of daily living, indicating that the patient is exercising, the threshold margin may be 10%. For example, if the SIR is 100 pulses per minute (600 msec temporary LR interval), then the A4 event interval may be required to fall between 540 msec and 660 msec to meet the patient's physical activity needs (block 758).

[0148] If, as determined at block 758, A4 events are detected and occur at a rate that supports the patient's current physical activity needs, which can be based on a comparison of the A4 event rate to the SIR, the pacemaker 14 can remain in the atrium tracking VDD pacing mode to continue ventricular synchronous ventricular pacing by appropriately tracking the heart rate. If the A4 event rate is slower or faster than the SIR by a predetermined margin, the A4 event tracking used to control ventricular pacing will no longer provide ventricular pacing rate support suitable for meeting the patient's physical activity needs. At block 718, the control circuit 206 can switch to the non-atrial tracking pacing mode.

[0149] Additionally or alternatively, the control circuit 206 may determine whether the motion sensor signal stability meets the pacing mode switching criteria. If, at block 758, the A4 event rate meets or matches the patient's physical activity demand, the control circuit 206 may determine the motion sensor stability metric at block 760. In other examples, if the motion signal metric meets the switching criteria at block 754, the motion signal stability metric may be determined at block 760 without checking the A4 event rate (blocks 756 and 758 are omitted in some examples).

[0150] In one example, the motion sensor stability metric is the A4 event amplitude. Stability of the A4 event amplitude indicates that reliable A4 event detection is possible, and therefore the VDD pacing mode is still applicable. Large changes in the A4 event signal amplitude may indicate erroneous A4 event detection (e.g., due to erroneous detection of a patient's body activity signal spike as an A4 event) and loss of reliable A4 event sensing mode for atrial tracking purposes of VDD pacing.

[0151] The motion sensor signal stability metric can be determined at box 760 by determining the difference between the peak amplitude of each of a predetermined number of detected A4 events and a moving average A4 event amplitude or other statistic of previously determined A4 event amplitudes. In another embodiment, for three or more consecutively determined A4 event amplitude differences, the cumulative amplitude difference between consecutively detected A4 events can be determined at box 760 by determining the absolute value of the difference between the current A4 event amplitude and the most recent previous A4 event amplitude, and adding the absolute values ​​of the determined differences. If the cumulative amplitude difference is greater than a stability threshold, it is determined that the motion sensor signal does not meet the stability criteria required to remain in the VDD pacing mode. In other examples, M of the N most recent A4 events may be required to be within an amplitude difference threshold of each other or within an average A4 event amplitude of the N events.

[0152] Other features of the detected A4 event may be determined at block 760 and analyzed at block 762 to determine whether the motion sensor signal stability criteria are met. For example, the A4 event interval variability or A4 timing relative to a previous ventricular pacing pulse, sensed R-wave, or ventricular mechanical event (e.g., an A1, A2, or A3 event) may be determined to assess whether the A4 event is stable or presents an expected trend relative to a ventricular event (e.g., gradually moving earlier in the ventricular cycle). The slope, width, polarity, or other morphological features of the A4 event may be determined at block 762 for comparative analysis to assess the stability of the A4 event features as an indication of a true A4 event detection as opposed to a false A4 event detection.

[0153] In addition to or in lieu of the A4 event features, other motion sensor signal stability metrics associated with the A1, A2, and / or A3 events may be determined at block 760. The criteria applied at block 762 for confirming motion sensor signal stability may include stability of the A1, A2, and / or A3 morphological features and / or timing. It should be appreciated that a number of comparative analyses may be performed to apply criteria for determining stability and consistency of the cardiac mechanical signal for the A1, A2, A3, and / or A4 events to increase confidence that a detected A4 event is a true A4 event and not a signal spike caused by patient physical activity or other non-cardiac motion or motion sensor signal noise.

[0154] If the motion sensor signal stability criteria are not met at box 762, the control circuit 206 switches to the non-atrial pacing mode at box 718. If the A4 event rate meets the patient's physical activity needs ("yes" branch of box 758) and the motion sensor signal stability criteria are met at box 762, then at box 704, the pacemaker 14 remains in the VDD pacing mode.

[0155] The foregoing examples of determining whether the A4 rate meets the patient's physical activity needs at box 758 and determining whether the motion sensor signal stability meets the stability criteria at box 762 are provided for illustrative purposes and are not intended to be limiting. It should be appreciated that other threshold margins and rate threshold criteria can be applied at box 758 to determine whether the detected A4 rate matches the patient's metabolic needs in order to track the A4 rate in providing ventricular pacing. When the A4 rate is too low (or too high) compared to the SIR based on the patient's activity, atrial tracking of atrial rhythm pacing cannot provide a rhythm that matches the patient's metabolic needs. Thus, when the A4 rate does not meet the SIR rate according to the criteria applied at box 758, switching to a non-atrial pacing mode is guaranteed at box 718.

[0156] Additionally, in other examples, at block 758, the motion signal stability criteria may be applied regardless of whether the A4 event rate meets the patient's physical activity requirements. In some cases, if the motion signal stability criteria are not met at block 762, the control circuit 206 may switch to a non-atrial pacing mode at block 718 even if the A4 event rate matches the patient's physical activity at block 758.

[0157] Fig.11 800 is a flow chart of a method performed by a pacemaker 14 for controlling a pacing mode switch from a non-atrial tracking pacing mode back to a cardiac rhythm tracking pacing mode according to an example. At block 802, the pacemaker 14 operates in a non-atrial pacing mode. In this embodiment, the non-atrial tracking pacing mode is a VVIR pacing mode. Fig. 10A or Fig. 10B The VVIR pacing mode of block 802 is achieved by satisfying the pacing mode switching criteria during the VDD pacing mode of block 802. For example, the VVIR pacing mode of block 802 may be achieved in response to insufficient detection of A4 and / or mode switching criteria based on the patient's posture (e.g., in combination with Fig. 10A described) or in response to motion signal metrics, A4 rate mismatch physical activity and / or motion sensor signal stability (such as in combination with Fig. 10B described) to initiate VVIR pacing mode 802.

[0158] In VVIR pacing mode, A4 event detection is disabled most of the time, which can save pacemaker battery life. For example, A4 event detection can be disabled by turning off power to atrial event detector circuit 240 or disabling processing functions performed to detect A4 events. However, motion sensor 212 can remain enabled to generate motion sensor signals for use by control circuit 206 to determine the patient's physical activity metric and SIR to control the ventricular pacing rate during VVIR pacing. A4 event detection from the motion sensor signal can be periodically enabled to determine whether mode switching criteria associated with A4 event detection are met in order to switch back to VDD pacing mode.

[0159] exist Fig.11 In the embodiment of the present invention, a patient activity metric for determining a SIR for controlling the VVIR pacing rate is determined at block 804. The patient activity metric determined at block 804 may be equivalent to Fig. 10B The patient activity metric determined at block 752 of is used as a motion signal metric, but may be a different metric. The SIR is determined based on the patient activity metric, and the pacemaker 14 sets the ventricular LR interval based on the SIR. The LR interval may be set to a temporary LR interval that is shorter than the basic rate LR interval to provide ventricular pacing at the SIR.

[0160] At box 806, the control circuit 206 determines whether the SIR based on the patient activity metric has decreased from a previously determined SIR. The previously determined SIR may have been determined during the VDD pacing mode and caused the pacing mode to switch to the VVIR pacing mode. In other cases, the previously determined SIR may be determined after switching to the VVIR pacing mode. If the SIR has decreased due to detection of the previously determined SIR, A4 event detection may be enabled during the VVIR pacing mode at box 807. A4 event detection may enable one or more ventricular pacing cycles.

[0161] After enabling A4 event detection, to facilitate detection of A4 events, the LR pacing rate interval may be extended at box 808 to a pacing interval that is longer than the LR interval set based on the currently determined SIR. For example, if the SIR is initially 100 pulses per minute (ppm) and drops to 90 ppm, the temporary LR interval may be increased from 600 ms (SIR of 100) to 670 ms (SIR of 90). The 670 ms temporary LR interval may be extended at box 808 by a predetermined extended interval, or adjusted to reduce the heart rate by 10 bpm or other rate less than the SIR. In the above embodiment where the SIR is 90 and the LR interval is 670 ms, the temporary LR interval may be extended to 750 to 1000 ms (pacing rate between 80 and 60 ppm) so that there is more time to detect A4 events during the extended LR pacing interval. In one example, the pacing rate is 10 ppm lower than the SIR for a predetermined number of pacing cycles, decreasing from 90 ppm in the above example to 80 ppm.

[0162] At box 808, the likelihood of detecting an A4 event before the next ventricular pacing pulse is increased by extending the LR interval by 50, 100, 200, or even up to 500 ms or longer for one or more pacing cycles. In some examples, the temporary LR interval can be extended at box 808 by a fixed extended interval of, for example, 100 ms, over one or more pacing cycles. In other examples, the temporary LR interval can be increased by a continuously increasing extended interval over each of a predetermined number of consecutive pacing cycles. For illustration, the temporary LR interval can be increased by an extended interval of 50 ms over each consecutive pacing cycle, for example, an extended interval of 50 ms, 100 ms, 150 ms, 200 ms, and 250 ms can be added to the LR interval of each of the temporary five consecutive pacing cycles to facilitate A4 detection. Alternatively, the pacing interval can be continuously increased until an A4 event is detected up to the maximum extended interval. If an A4 event is detected, the extended LR interval at which the A4 event was first detected can be maintained for a predetermined number of ventricular pacing cycles to determine whether reliable A4 event detection has been returned. The maximum prolongation of the transient LR interval may be limited by the currently established SIR to avoid a mismatch between the patient's metabolic needs and the ventricular pacing rate.

[0163] It will be appreciated that if the SIR has been reduced to the basal pacing rate (minimum VVIR pacing rate) at block 806, then Fig. 10AThe temporary LR pacing interval set for the previously determined SIR may be adjusted at box 702 to the permanent LR interval established for the non-atrial tracking mode. For example, if the patient activity measure drops to a resting level, e.g., an amount of activity less than a daily activity threshold, the VVIR permanent LR pacing interval may take effect at box 804. The VVIR LR interval may be extended to, for example, the VDD LR interval, or between the VDD LR and VVIR LR intervals. In other examples, if the SIR is at a basal or minimum pacing rate, e.g., 60 ppm, the VVIR LR interval may not be extended at box 808 to maintain the heart rate at the minimum VVIR pacing rate. Thus, in some examples, a temporary LR interval set based on a non-stationary SIR may be extended at box 808, but an LR interval set during a SIR equal to the basal pacing rate may not be extended at box 808.

[0164] If no A4 events are detected in one or more of the extended LR pacing intervals (the "No" branch) of box 810, then at box 812, the extended LR intervals are adjusted back to the permanent or temporary LR intervals corresponding to the currently determined SIR. If at least one A4 event or other predetermined threshold number of A4 events is detected at box 810, the control circuit 206 may determine at box 814 whether a pacing mode switching criterion is met. The pacing mode switching criterion applied at box 814 may require that a threshold number of A4 events be detected in consecutive or non-consecutive ventricular pacing cycles. A4 events may be detected during a temporary LR interval, a permanent LR, or an extended LR rate interval to meet X A4 events that meet the Y ventricular cycle criterion. X of the Y criterion applied at box 814 may be defined as the number of A4 events that meet the Y ventricular cycle criterion. Fig. 10A The X of the Y criterion applied at block 712 of is the same or different to determine whether under-detection of A4 occurs during the VDD pacing mode, thereby controlling the switch from atrial tracking to non-atrial tracking pacing mode.

[0165] In some examples, the X criteria of Y can be conditional criteria that are defined differently for different conditions (e.g., different patient activity levels and / or different patient body postures). The X in the Y criteria can be defined to require a relatively low threshold number of A4 event detections, such as 4 of 8 ventricular cycles or 8 of 16 ventricular cycles, to facilitate switching to a VDD pacing mode when the patient's body activity is low and / or when the patient's posture is a static posture, such as lying or a non-upright static posture. When the patient's body posture is known to be associated with reliable A4 event sensing (or at least not associated with unreliable A4 event sensing), the X criteria of Y can be defined to be relatively low to facilitate switching to a VDD pacing mode.

[0166] The X criterion of Y may be defined as relatively high, e.g., 14 A4 events detected in 16 ventricular cycles, to bias the patient to remain in the non-atrial pacing mode when the patient's body activity is high and / or the patient's body position is upright. When the patient's body posture is known to be associated with unreliable A4 event detection, the X criterion of Y may be defined as relatively high to bias the patient to remain in the non-atrial pacing mode. Thus, the X criterion in Y may be applied at block 814, where a threshold number of A4 event detections in at least or greater than Y ventricular cycles to be detected is required, where the control circuit 206 determines the threshold number of A4 events based on the patient's body activity and / or the patient's body posture. The X criterion of Y used under specific activity and / or posture conditions may be retrieved from the memory 210, e.g., from a lookup table stored in the memory 210.

[0167] In addition to or in lieu of at least a threshold number of A4 event detections, other pacing mode criteria may be applied at box 814. For example, the incidence of detected A4 events may be required to be within a predetermined range of a currently determined SIR, a patient activity metric or SIR may be required to be below a threshold activity level, and / or a patient posture may be determined and required to match a posture known to be associated with reliable A4 event sensing (or at least not match a posture known to be associated with unreliable A4 event sensing). Motion sensor stability criteria may also be applied at box 814 to increase confidence in reliable A4 event detection before switching back to VDD pacing. At box 814, one or more other motion signal metrics may be determined and compared to the mode switching criteria, such as an average motion signal amplitude, frequency, slope, or other signal feature determined over a predetermined time period of the motion signal. The motion signal metric may be compared to a threshold value to switch back to VDD pacing. For example, a metric of motion signal energy, entropy, frequency, or other metric including non-cardiac motion signals in the motion signal may be determined and required to be below a corresponding threshold value in order to control the atrial tracking pacing mode in dependence on A4 event detection.

[0168] exist Fig.11In an embodiment, during the non-atrial tracking pacing mode, A4 detection is required at box 810 and then switched back to the VDD pacing mode at box 816. In this way, A4 event detection that was disabled during the VVIR pacing mode is temporarily enabled. However, in other examples, in response to meeting other mode switching criteria, the control circuit 206 may switch back to the VDD pacing mode at box 816, and A4 event detection is not required during the VVIR pacing mode. A4 event detection may remain disabled throughout the VVIR pacing mode. For example, during the VVIR pacing mode, a motion signal metric may be periodically determined at box 814 without determining whether A4 event detection has returned. At box 814, a motion signal metric (which may be a metric of the patient's physical activity) or a combination of the above may be used to determine whether A4 event detection has returned. Fig. 10B The other motion signal measure is compared to the mode switching threshold.At block 816, the control circuit 206 may switch back to the VDD pacing mode and then re-enable A4 event detection.

[0169] In another example, if the control circuit 206 detects a quiescent activity level and / or detects a non-upright posture of lying or resting based on a patient activity metric or SIR at block 814, the control circuit 206 may switch to a VDD pacing mode without enabling A4 event detection in the VVIR pacing mode. Ventricular pacing may be performed as needed at the VDD basal rate (permanent VDD LR interval) until A4 event detection is reacquired. Rate smoothing may be applied to derive the VDD basal rate from the last VVIR pacing rate.

[0170] Fig.12 850 is a flow chart of a method that may be performed by the pacemaker 14 for controlling a pacing mode switch from a non-atrial tracking mode to an atrial tracking mode according to another embodiment. Blocks 802, 804, and 808 to 816 generally correspond to the above combined Fig.11 Description of the same numbered boxes. Fig.11 and Fig.12 The techniques and methods may be performed independently or in combination.

[0171] exist Fig.12In an embodiment of the present invention, instead of waiting for a decrease in the SIR before enabling A4 event detection, the control circuit 206 can periodically enable A4 event detection at box 807 based on a predetermined scheduling basis determined at box 805. Periodic A4 event monitoring can be scheduled at a predetermined frequency. The frequency can be a predetermined number of ventricular pacing pulses (or a combination of ventricular pacing pulses and sensed R waves) or a predetermined time interval. For example, A4 event detection can be checked after every 16, 24, 30, or other predetermined number of pacing pulses. In one example, the temporary LR interval can be extended at box 808 to reduce the ventricular pacing rate by 10 ppm after every 16 pacing pulses. In other examples, A4 event detection can be scheduled every minute, every thirty minutes, every hour, or other scheduled time interval.

[0172] In some examples, the frequency of periodic monitoring can depend on the SIR and / or the conditions that caused the switch from the VDD to the VVIR pacing mode. For example, as the SIR decreases, more frequent monitoring for A4 events can be enabled compared to when the SIR is higher. To illustrate, if the SIR is at a maximum pacing rate, such as 120 ppm, then A4 event monitoring is enabled only when the SIR decreases from the maximum pacing rate, as described above in conjunction with Fig.12 If the SIR is greater than 100 ppm but less than the maximum 120 ppm, A4 event monitoring may be performed every five minutes. If the SIR is greater than 80 and less than 100 ppm, A4 event monitoring may be performed more frequently (e.g., once every two minutes). If the SIR drops below daily living activities, such as 80 ppm or below, A4 event monitoring may be performed every minute to facilitate switching back to VDD pacing when high rate pacing support is no longer required and reliable A4 events are more likely to be detected during relatively long pacing intervals, and physical exercise contributes less to the motion sensor signal. As combined Fig.11 As described, A4 event detection may be enabled when the SIR decreases by a threshold amount and then scheduled to be re-enabled at a predetermined frequency.

[0173] In other embodiments, the control circuit 206 may determine whether to check for A4 detection at this time at block 805 and enable A4 event detection at a frequency determined based on the reason for switching from the VDD pacing mode to the VVIR pacing mode at block 807. For example, if the control circuit 206 switches from the VDD pacing mode to the VVIR pacing mode due to instability of the A4 signal, A4 event monitoring may be enabled relatively frequently, such as once per minute, because transient motion sensor signal noise may have caused the A4 signal to be unstable.

[0174] At any time during the VVIR pacing mode, if a premature ventricular contraction (PVC) is detected (block 818), the pacing timing circuit 242 may extend the temporary LR interval at block 808 to allow detection of an A4 event during a longer compensatory pause following the PVC. The temporary LR interval may be extended to a programmed permanent LR interval or other backup pacing interval to allow a relatively long time interval for detecting an A4 event. If an A4 event is detected at block 810, an additional extended LR interval may be applied during the long compensatory pause following the PVC to determine whether at least X out of Y A4 event detections have occurred and / or other mode switching criteria (e.g., posture, activity level, SIR, motion signal stability, and / or other motion signal metrics) may be checked at block 814, as described above in conjunction with Fig.11 As described.

[0175] Thus, in some examples, in response to detecting a PVC, A4 event detection is enabled during the VVIR pacing mode at block 807. PVCs may be detected from cardiac electrical signals based on the timing of an R-wave sensed event following a prior ventricular pacing pulse or sensed R-wave and / or based on an analysis of the R-wave morphology according to a PVC detection algorithm implemented in the pacemaker 14.

[0176] exist Fig.12 In an embodiment of the present invention, the control circuit 206 may determine the patient's body posture at box 820. The control circuit 206 may monitor the patient's body posture to detect a non-upright posture (indicating a stationary state) and / or detect a change in posture. The patient's body posture determination may be performed periodically on a planned basis and / or in response to a change in the SIR. If a stationary body posture is detected at box 822, the control circuit 206 may switch to the VDD pacing mode. A stationary body posture may be detected when any lying posture or tilted posture is detected instead of an upright sitting, standing, walking, or running posture. Such upright postures may be collectively referred to as non-stationary body postures.

[0177] A resting posture may not require ventricular rate support. In some examples, in addition to detecting a resting body posture, the control circuit 206 may also verify that the patient's activity metric or SIR is at a resting level, e.g., activity less than a daily living threshold. When the patient is expected to be at rest based on a non-upright body posture, the control circuit 206 may actively switch to an atrial tracking VDD pacing mode at block 816.

[0178] It may not be necessary to verify A4 event detection prior to switching to VDD pacing mode. The ventricular pacing rate may be adjusted down to a rate lower than VDD until A4 event detection and atrial synchronized ventricular pacing are restored. Thus, in some examples, the pacing mode switching criteria applied during VVIR pacing mode may not require enabling A4 event detection. Without enabling A4 event detection, the control circuit 206 may make the decision to switch back to VDD pacing mode based on other analysis of the motion sensor signals, such as the patient's physical activity and / or body posture and / or motion sensor metrics.

[0179] If the patient's body posture is determined to be a non-stationary or upright position, then at the "No" branch of box 822, the control circuit 206 can determine at box 824 whether the patient's body posture has changed since the previously determined body posture. If no change in body posture is detected, the pacemaker 14 remains in the VVIR pacing mode (box 802). If a change in body posture is detected, then at the "Yes" branch of box 824, the control circuit 206 can proceed to box 807 to enable A4 event detection, and extend the temporary LR interval at box 808 to look for A4 events. Changes in body posture may affect motion sensor signals. In certain body positions, the signal-to-noise ratio of the A4 event signal may be lower than the signal-to-noise ratio in other body positions. In this way, if an A4 event was not detected in a previous body posture, a change in the patient's body posture can restore reliable A4 event sensing.

[0180] If an A4 event is detected at box 810 after a posture change is detected, a mode switching criterion may be applied at box 814. The mode switching criterion may typically require a motion signal metric to meet a corresponding threshold requirement for switching back to the VDD pacing mode. The motion signal metric may be required to be greater than or less than a corresponding threshold. For example, a motion signal metric indicating signal energy or signal entropy may need to be less than a corresponding threshold. In other examples, the mode switching criterion may include requiring X undetected A4 events greater than a threshold number in Y ventricular cycles, as previously described herein. The X of the Y criterion may depend on the determined posture. If a posture known to be associated with reliable A4 event detection is detected, the X criterion for Y may be relatively low, for example, five A4 event detections were made in eight consecutive ventricular cycles. If the posture change detected at box 824 is a change in body posture associated with unreliable A4 event detection, or is not known to be associated with reliable A4 event detection, a higher X criterion in Y may be required, for example, 12 out of 15, or 18 out of 22. In this way, when the patient's body posture is determined to be associated with reliable A4 event sensing, the mode switching criteria may be biased toward returning to the atrial pacing mode more quickly, while when the patient's body posture is determined to be associated with unreliable A4 event sensing or unknown reliability of A4 event sensing, the mode switching criteria may be biased toward returning to the atrial pacing mode less quickly.

[0181] Therefore, it should be understood that Fig.11 and Fig.12 As described, A4 event monitoring may be enabled on a periodically scheduled basis and / or in response to a triggering event such as PVC detection, posture change, and / or SIR reduction. Fig.11 and Fig.12 The mode switching criteria applied at box 814 can be conditional criteria that favor (set relatively low) pacing in the VDD mode when A4 detection is expected to be reliable and / or when ventricular pacing in the rate-responsive mode is not required to provide ventricular rate support (e.g., during stationary activity and / or stationary posture), and favor (set relatively high) pacing in the VVIR pacing mode when A4 event detection is expected to be unreliable (e.g., during certain postures) and / or when ventricular rate support is required during non-stationary body activity levels and / or non-stationary patient postures.

[0182] Additionally, mode switching criteria for controlling a switch from a VVIR pacing mode back to a VDD pacing mode can be defined such that A4 event detection need not be enabled during the VVIR pacing mode. In some examples, the mode switching criteria applied during the VVIR pacing mode can be based solely on patient activity, solely on patient posture, solely on a motion signal metric determined within a predetermined time interval that is not necessarily an indicator of patient activity or patient posture, or based on a combination of two or more patient physical activity, patient posture, or other motion signal indicators without requiring A4 event detection to satisfy the pacing mode switching criteria for switching back to the VDD pacing mode.

[0183] Fig.13 1 is a flow chart of a method for controlling pacing mode switching by the pacemaker 14 according to another embodiment. When the mode switching criteria for switching from the VDD pacing mode to the non-atrial tracking pacing mode are met ( Fig. 10A or Fig. 10B , the control circuit 206 may switch from the VDD pacing mode to the VDIR pacing mode. Fig.11 and 12 The VVIR pacing mode described.

[0184] exist Fig.13 At block 902 of , the pacemaker 14 operates in the VDIR pacing mode. Similar to the VVIR pacing mode, during VDIR pacing, non-atrial tracking ventricular pacing is delivered in a rate-responsive pacing mode. Ventricular pacing pulses are delivered at a temporary LR interval set according to the SIR and are disabled when an intrinsic R wave is sensed before the LR interval expires. One difference between the VVIR pacing mode and the VDIR pacing mode is that in the VDIR pacing mode, A4 event detection remains enabled for atrial mechanical contraction event sensing. When switching to the VVIR pacing mode, A4 event detection is disabled, but may be enabled in conjunction with the SIR as described above. Fig.11 and Fig.12 As described, it is periodically re-enabled to check for A4 event detection.

[0185] If an A4 event is detected during VDIR pacing mode, Fig.13 At block 903 of pacing mode, an A4 event does not trigger a ventricular pacing pulse. A4 event detection is used to determine whether pacing mode switching criteria are met (block 914), but is not used to schedule ventricular pacing pulses during the VDIR pacing mode. If an A4 event is detected at block 903, then at block 914, the control circuit 206 may determine whether a threshold number X of A4 events have been detected in the most recent Y ventricular cycles. If A4 event detection has become reliable based on X criteria being met for Y, then at block 916, the pacemaker 14 may switch back to VDD pacing.

[0186] The X of the Y criterion can be a conditional criterion set based on the SIR, patient posture, or other factors. For example, the X of the Y criterion can be set as a measure of patient activity or as a proportion of the SIR so that as the patient's physical activity increases, more A4 event detections are required before switching back to VDD pacing mode.

[0187] In some examples, when the A4 event detection criteria have been met prior to switching to VDD pacing, patient body posture criteria and / or patient body activity criteria or other motion signal metrics may need to be met at box 914. For example, if X out of Y A4 event detection criteria are met, the control circuit 206 can verify that the patient posture is not a posture associated with unreliable A4 event detection and / or the SIR or other motion signal metric is not greater than the mode switching limit. If the patient is in a posture associated with unreliable A4 event detection, or the SIR is greater than the daily living SIR or other threshold activity level, the pacemaker 14 can remain in the VDIR pacing mode by returning to box 902.

[0188] In some examples, the motion sensor signal stability criteria may need to be met at block 914 before switching back to VDD pacing. Fig. 10B The motion sensor signal stability requirements for remaining in the VDD pacing mode described at block 758 of FIG. 204 may be applied at block 914 to meet the mode switching criteria for switching back to the VDD pacing mode. For example, before the control circuit 206 switches to the VDD pacing mode, it may be verified that the A4 event time interval, A4 event amplitude, A4 event slope, A4 event width, or other A4 event feature or combination of features is stable within predetermined limits over a plurality of ventricular cycles. In other embodiments, any combination of one or more time intervals and / or morphological features of any of the A1, A2, A3, and A4 events may be analyzed to determine whether the motion sensor signal is stable.

[0189] In some embodiments, the control module 206 may Fig. 10A The switch to the non-atrial tracking pacing mode is controlled at box 718 of or 10B by first switching to a temporary non-atrial tracking pacing mode at a ventricular pacing rate based on the most recently determined atrial rate. The atrial rate can be determined from one or more A4-A4 event intervals determined just before the switch to the non-atrial tracking mode. In this case, the pacemaker 14 can operate in the temporary VDI pacing mode at a ventricular pacing rate set based on the previously determined A4 event rate. The control module 206 can set a temporary VDI pacing mode timer or enable a counter to count the number of ventricular pacing pulses delivered at a rate based on the A4 events.

[0190] If no A4 event detection occurs based on the ventricular rate of the A4 event rate during the temporary VDI mode, or the pacing mode switching criteria are still not met at box 914, the control module 206 determines whether the temporary non-atrial tracking mode has expired at box 904. If the temporary mode timer expires or the ventricular pacing pulse counter reaches the maximum temporary mode count, the control module 206 can switch to the VDIR mode at box 905, during which the pacemaker 14 controls the ventricular pacing rate according to the programmed VDIR lower rate interval and the SIR transfer function for determining the SIR using a patient activity metric determined based on the motion sensor signal. The ventricular pacing rate is no longer controlled based on the most recent A4 event rate, but is instead controlled based on the patient's activity.

[0191] In this manner, the control module 206 switches to the first non-atrial tracking pacing mode for a predetermined time interval or number of ventricular cycles during which the interval or ventricular cycle is based on the most recently determined atrial rate. If the temporary non-atrial tracking pacing mode has not expired (block 904), the pacemaker 14 returns to block 902 and remains in the VDI pacing mode at a ventricular pacing rate based on the A4 rate. For example, the pacing rate can be set to match the most recent A4 event rate, or to a rate that is at least 10 to 20 pulses per minute slower than the most recent A4 event rate.

[0192] At box 905, when the temporary non-atrial tracking pacing mode expires at box 904, for example, based on a predetermined time interval or a maximum number of ventricular pacing pulses based on the pacing rate of the temporary A4 event rate, the control module 206 switches to a second non-atrial tracking pacing mode. The second non-atrial tracking pacing mode can have no time limit. The second non-atrial tracking pacing mode can last for an indefinite time or number of ventricular cycles until the pacing mode switching criteria for switching back to the atrial tracking pacing mode are met. In the second non-atrial tracking pacing mode, the ventricular pacing rate is not based on the most recent A4 event rate. The ventricular pacing rate during the second non-tracking pacing mode can be based on a programmed VDI lower rate interval and / or SIR.

[0193] If no A4 event detection is made during the VDIR permanent LR interval at box 903 or during the temporary LR interval set according to the SIR during the second non-atrial tracking pacing mode, the control circuit 206 may extend the interval at which the temporary (or permanent) LR is currently effective at box 910. The LR interval may be extended to facilitate A4 event detection between ventricular pacing pulses. If the control circuit 206 detects a decrease in the SIR at box 906, the LR interval may be extended at box 910. The control circuit 206 may additionally or alternatively extend the LR interval periodically on a scheduled basis. The control circuit determines whether it is time to perform a periodic check for A4 event detection at box 908 based on a predetermined frequency, which may depend on the SIR. For example, the LR interval may be extended every 16 pacing pulses to reduce the pacing rate by 10 ppm. A lower SIR may extend the LR interval more frequently than a higher SIR. If an A4 event is detected during the extended LR interval, the extended LR interval may be applied to additional pacing cycles at box 914 to determine whether the pacing mode switching criteria are met. As given in the previous embodiments, the X out of Y A4 event detection criteria may be applied at block 914 along with other motion sensor signal stability, patient body posture, patient body activity level, or SIR or motion signal metrics determined as a running average or over a predetermined time interval. One or more other motion signal metrics may be determined and compared to corresponding thresholds for determining whether to switch back to VDD pacing mode.

[0194] If the mode switching criteria are met at block 914, the control circuit 206 switches to the VDD pacing mode at block 916. If the mode switching criteria are not met, the LR interval is restored at block 918 from the expanded LR interval applied at block 910. By returning to block 902, the pacemaker 14 remains in the VDIR pacing mode.

[0195] Fig.14 950 is a flowchart of a method for controlling pacing mode switching performed by the pacemaker 14 according to another embodiment. At block 952, for example, using the above combination Figures 5 to 8 The A4 refractory period may be set by any of the techniques described herein. At block 956, an A3-A4 time interval is determined. The A3-A4 time interval may be determined on a beat-by-beat basis or less frequently, such as every three beats, every five beats, etc. The A3-A4 time interval may be used to update a running average of A3-A4 time intervals stored in the memory 210 and / or a buffer stored in the memory 210 that stores a series of consecutive or non-consecutive A3-A4 time intervals. In some embodiments, the A3-A4 time interval may be determined as the time from the last negative A3 threshold amplitude crossing to the first positive A4 threshold amplitude crossing, such as the A3-A4 time interval 445, as shown in FIG. Figure 6 In other examples, other reference points or threshold crossings for the A3 and A4 events may be used to determine the A3-A4 time interval.

[0196] The A3-A4 time interval determined at box 956 can be used additionally or alternatively as a motion signal metric to determine whether the mode switching criteria are met. At box 958, the A3-A4 time interval can be compared to the interval shortening criteria to detect the shortening of the A3-A4 time interval by the control circuit 206. The current A3-A4 time interval can be compared with one or more previously determined A3-A4 time intervals, which can be individually or combined together, for example as a running average or median. The ratio or difference between the current A3-A4 time interval and one or more previously determined A3-A4 time intervals can be compared with a shortening threshold. In other examples, a downward trend in the running order of three or more consecutive or discontinuous A3-A4 time intervals can be detected as a shortening of the A3-A4 time interval.

[0197] If a shortening of the A3-A4 time interval is detected at box 958, the shortening amount is compared to a pacing mode switching criterion at box 960. For example, at box 960, the difference between the currently detected A3-A4 time interval and the previous time interval or the running average A3-A4 time interval can be compared to a switching threshold. If the pacing mode switching criterion is not met, one or more A4 detection control parameters can be adjusted in response to detecting a shortened A3-A4 time interval at box 962. The A4 refractory period can be shortened and / or the A4 detection threshold amplitude can be adjusted. For example, the A4 detection threshold amplitude can be adjusted to enable detection of a fused A3-A4 event. Early detection of A4 events during the A4 refractory period may be enabled, or other adjustments may be made to the A4 detection control parameters, for example, as generally disclosed in U.S. patent application Ser. No. 15 / 280,538 (Sheldon et al.), U.S. patent application Ser. No. 15 / 280,339 (Splett et al.), and U.S. patent application Ser. No. 15 / 342,699 (Demmer et al.), all of which are incorporated herein by reference in their entirety. At block 954, the ventricular pacing mode is maintained in the VDD pacing mode.

[0198] If the shortening of the A3-A4 time interval satisfies the pacing mode switching criteria in box 960, the control circuit 206 switches to a non-tracking pacing mode, e.g., VVIR or VDIR pacing, at box 964. When operating in a non-atrial tracking pacing mode, the control circuit 206 may continue to monitor the A3-A4 time interval at box 966. The A3-A4 time interval may be determined on a beat-by-beat basis during the VDIR pacing mode, or periodically during the VVIR or VDIR pacing mode. If an increase in the A3-A4 time interval is detected at box 968, the increase in the A3-A4 time interval may be compared to the pacing mode switching criteria at box 970. If the pacing mode switching criteria are met at box 970, the control circuit 206 may switch back to the VDD pacing mode at box 954. If the A3-A4 time interval is greater than the threshold time interval, or the A3-A4 time interval is trending upward, reliable A4 detection is expected to return, so that VDD pacing can be resumed. In other examples, other mode switching criteria described herein may also be applied at block 970 .

[0199] If the extension of the A3-A4 time interval does not satisfy the pacing mode switching criteria in block 970, the pacemaker 14 remains in the non-atrial pacing mode in block 964. In some examples, at block 972, the increase in the A3-A4 time interval can result in an adjustment to the A4 refractory period, the A4 detection threshold amplitude, or other A4 detection control parameters or a combination of A4 detection control parameters.

[0200] The operations performed in the method of flowchart 950 may be combined with Fig. 9 , 10A , 10B, 11, 12 and 13 are performed in combination to control pacing mode switching. Thus, in some examples, in addition to detecting a change in the A3-A4 time interval before switching the pacing mode, any other pacing mode switching criteria described herein can be applied at blocks 960 and / or 970.

[0201] Fig.151001 is a flow chart of a method for controlling ventricular pacing by an intracardiac ventricular pacemaker according to another embodiment. At block 1002, the control circuit 206 operates in an atrial tracking ventricular pacing mode (e.g., VDDR). During the atrial tracking ventricular pacing mode, the control circuit 206 detects an A4 event as a cardiac contraction event from a motion signal received from a motion sensor 212 implanted in the ventricular chamber. The control circuit 206 starts an AV pacing interval in response to detecting the A4 event. The control circuit 206 detects a ventricular intrinsic event in response to each R sense signal received from the sensing circuit 204. As described above, the sensing circuit 204 generates an R sense signal in response to an R wave sensing threshold crossing a cardiac electrical signal received via electrodes 162 and 164. In the absence of receiving an R sense signal before the expiration of the AV pacing interval, the control circuit 206 controls the pulse generator 202 to deliver an atrial synchronized ventricular pacing pulse.

[0202] During the atrial tracking ventricular pacing mode, at block 1004, the control circuit 206 determines the SIR based on the motion signal generated by the motion sensor 212. The SIR is not used to adjust the pacing rate during the atrial tracking pacing mode because ventricular pacing pulses are triggered in response to detecting A4, thereby tracking a heart rate that is considered to be appropriate to meet the patient's metabolic needs. The SIR is determined during the atrial tracking pacing mode, but is compared to the pacing mode switching criteria.

[0203] The pacing mode switching criteria can be based on the actual ventricular rate, which can include the sensed rhythm and the paced rhythm. In one example, the control circuit 206 determines the median RR interval as a measure of the ventricular rate at box 1006. The median RR interval can be determined from the RR interval determined at one or more consecutive time intervals, which corresponds to the time interval of the motion signal applied to determine the SIR. For example, a patient activity metric can be determined based on the motion signal within a predetermined time interval and then used to determine the SIR. In the illustrative embodiment proposed herein and described in U.S. Patent No. 9,814,887 incorporated above, an activity metric can be derived from the accelerometer signal by integrating the absolute value of the selected accelerometer axis signal within a predetermined time interval (e.g., 2 seconds). The metric is referred to herein as an "activity count" and represents the amount of activity detected within a predetermined time interval. The 2-second interval counts can be averaged or summed over multiple time intervals to determine the patient's activity level at a specific monitoring interval. In another embodiment, activity counts for rate-responsive pacing are generally disclosed in U.S. Pat. No. 5,562,711 (Yerich et al.), which is hereby incorporated by reference in its entirety. Briefly, an activity count is determined as a count of the number of times an accelerometer signal peak is greater than a predetermined threshold within a predetermined time interval.

[0204] The median RR interval determined at block 1006 may be determined over one or more time intervals for determining a patient activity metric or activity count. In one example, an activity count is determined after every two second time intervals, and the SIR is updated at block 1004 based on the activity count determined after five two-second time intervals. The median RR interval determined at block 1006 may be the median of all RR intervals determined during the five two-second time intervals. Each RR interval within a two-second time interval is determined as a time interval between two consecutive ventricular events, which may be two consecutive R sense signals received from sensing circuit 204, two consecutive ventricular pacing pulses transmitted by pulse generator 202, or one R sense signal received from sensing circuit 204 and one ventricular pacing pulse.

[0205] In other embodiments, the median RR interval can be determined from a predetermined number of ventricular cycles, for example, from the most recent eight, ten, twelve, or other selected number of RR intervals. Although the median RR interval is described in the illustrative examples presented herein, in other examples, another measure of ventricular rate can be used instead of the median RR interval. For example, an average, trimmed mean, or other measure of the actual ventricular rate over the time interval corresponding to the time interval from which the SIR is derived can be determined at block 1006.

[0206] The control circuit 206 sets a pacing mode switching threshold at box 1008 based on the ventricular rate, for example, based on the median RR interval. In one example, the pacing mode switching threshold is set by converting the median RR interval to a heart rate and adding a tolerance. For example, the pacing mode switching threshold can be set to 20 bpm greater than the median RR interval rate. To illustrate, if the median RR interval is 600 ms, the median RR interval rate is 100 bpm, and the pacing mode switching threshold can be set to 120 bpm. The tolerance added to the median RR interval heart rate can be zero to 20 bpm or higher and can be a fixed value or a programmable value.

[0207] At block 1010, the control circuit 206 determines whether the pacing mode switching criteria are met. In one embodiment, the pacing mode switching criteria require that the SIR updated at block 1004 is greater than the pacing mode switching threshold set at block 1008. If the SIR is within the tolerance range of the median RR interval rate, it is determined that the atrial tracking ventricular pacing mode can provide a sufficient rate response to support the patient's physical needs. In some examples, in addition to comparing the SIR to the pacing mode switching threshold based on the RR interval, additional pacing mode switching criteria can be applied at block 1010. For example, the SIR may be required to be greater than a second switching threshold, which, in addition to being greater than the pacing mode switching threshold set based on the actual ventricular rate, can also correspond to the daily living activities (ADL) rate. The ADL rate can be a heart rate that is defined as the lower and upper limits of the range of heart rhythms expected to occur when the patient is engaged in normal activities of daily life (e.g., moving around the house, personal hygiene, chores or tasks, or other non-strenuous activities). The ADL rate can be greater than the patient's resting heart rate or basal pacing rate, and can be, for example, 80 bpm. If the SIR is less than the ADL rate, the pacing mode switching criteria may not be met, and the control circuit 206 continues to operate in the atrial tracking ventricular pacing mode.

[0208] If the SIR is greater than the ADL rate and greater than the ventricular rate-based pacing mode switching threshold, the pacing mode switching criteria may be met at box 1010. The SIR is considered to be significantly greater than the actual heart rate, demonstrating that the pacing mode switch can provide non-atrial tracking ventricular pacing at a rate that supports the patient's physical activity. In the atrial tracking pacing mode, insufficient perception of A4 events by the motion signal may cause the ventricular rate to be slower than the rate required to support the patient's physical activity level. In some cases, even if the perception of A4 events is insufficient, the actual ventricular rate (which may include pacing and intrinsic beats) may still provide sufficient rate support for the patient's physical activity level, for example, depending on the frequency of unperceived A4 events. In this way, the ventricular rate-based pacing mode switching threshold can be used to determine whether the actual ventricular rate meets the SIR within the allowable range. If so, the control circuit 206 can remain in the atrial tracking ventricular pacing mode. If not, at box 1012, the control circuit 206 switches to the non-atrial tracking ventricular pacing mode.

[0209] Upon switching to the non-atrial tracking pacing mode, the LR pacing interval may be initially set at box 1014 to a temporary LR pacing interval equal to the median RR interval (or other ventricular rate metric) determined at box 1006 to avoid a sudden change from the current ventricular rate to the pacing rate. The LR pacing interval may be adjusted from the median RR interval set at box 1014 to the SIR using a rate smoothing acceleration time constant at box 1016. Time constant-based rate smoothing limits the rate at which the pacing rate can be increased, which may be between 50 and 100 milliseconds, for example. During the non-atrial tracking pacing mode, the SIR will continue to be determined and updated to provide rate responsive pacing by adjusting the LR pacing interval as needed based on the SIR interval, which may include rate smoothing constants based on the acceleration time constant and the deceleration time.

[0210] At block 1018, the control circuit 206 determines whether a minimum mode switching time interval has expired. The control circuit 206 may operate in the non-atrial tracking ventricular pacing mode for at least a predetermined minimum time interval before determining whether pacing mode switching criteria for switching back to the atrial tracking pacing mode are met. By requiring at least one minimum time interval in the non-atrial tracking pacing mode, frequent pacing mode switching may be avoided. In one embodiment, the control circuit 206 may wait for at least five two-second time intervals (corresponding to the activity count determination intervals and the times when the SIR is re-determined) before determining whether criteria for returning to the atrial tracking pacing mode are met.

[0211] If the minimum time interval has expired at box 1018, the motion signal metric is compared to the pacing mode switching criteria at box 1020 by comparing the SIR most recently determined from the motion signal to a threshold rate. In one embodiment, the threshold rate can be a predetermined ADL rate. If the SIR is less than or equal to the ADL rate, the control circuit 206 can switch back to the atrial pacing mode at box 1002. If the SIR is still greater than the ADL rate, the control circuit 206 remains in the non-atrial tracking pacing mode by returning to box 1016 and adjusting the VV interval as needed based on the SIR interval. If the minimum mode switching interval requirement at box 1018 has been met, the control circuit 206 can compare the next updated value of the SIR to the threshold rate at box 1020 without waiting for the minimum mode switching time interval to expire again. Other examples of motion signal metrics and pacing mode switching criteria described above can be used at box 1020 to determine whether the pacing mode switching criteria are met and cause the control circuit 206 to switch back to the atrial tracking ventricular pacing mode.

[0212] Thus, various methods for controlling pacing mode switching in a cardiac ventricular pacemaker configured to deliver ventricular pacing in atrial tracking and non-atrial tracking pacing modes have been described according to illustrative embodiments. In other examples, the various methods described herein may include steps performed in a different order or combination than the illustrative examples shown and described herein. Furthermore, other circuits for implementing the techniques disclosed herein may be conceived by one of ordinary skill in the art; the specific embodiments described herein are illustrative in nature and not limiting.

[0213] An example implementation of the techniques described herein is provided below.

[0214] Embodiment 1. A method performed by a ventricular pacemaker in a heart having a motion sensor configured to generate a motion signal, the method comprising: receiving the motion signal by a control circuit of the pacemaker; detecting an atrial contraction event from the motion signal; operating in a mode selected from an atrial tracking ventricular pacing mode and a non-atrial tracking ventricular pacing mode, wherein operating in the atrial tracking ventricular pacing mode comprises: setting an atrioventricular pacing interval in response to detecting an atrial contraction event from the motion signal, and controlling a pulse generator of the pacemaker in response to expiration of the atrioventricular pacing interval. delivering ventricular pacing pulses; determining at least one motion signal metric from the motion signal while operating in a selected one of the atrial tracking ventricular pacing mode and the non-atrial tracking ventricular pacing mode; comparing the at least one motion signal metric with a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switching from a selected one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to another one of the non-atrial tracking pacing mode and the atrial tracking pacing mode for controlling pacing pulses delivered by the pulse generator.

[0215] Embodiment 2. A method according to embodiment 1, wherein determining the at least one motion signal metric includes determining a patient physical activity metric.

[0216] Embodiment 3. A method according to embodiment 1 or 2, wherein determining the at least one motion signal metric includes determining a patient posture from the motion signal.

[0217] Example 4. The method according to any one of Examples 1-3 further includes: receiving cardiac electrical signals through a sensing circuit; sensing intrinsic ventricular electrical events from the cardiac electrical signals; determining a ventricular event rate from a plurality of at least one of the sensed intrinsic ventricular events and delivered ventricular pacing pulses; and establishing a first switching threshold for the pacing mode switching criterion based on at least the ventricular event rate.

[0218] Example 5. The method according to Example 4 further includes: while operating in the atrial tracking ventricular pacing mode, determining the motion signal metric by determining the sensor-indicated pacing rate from the motion signal; comparing the sensor-indicated pacing rate with the first switching threshold; and switching from the atrial tracking ventricular pacing mode to the non-atrial tracking ventricular pacing mode in response to at least the sensor-indicated pacing rate being greater than the first switching threshold.

[0219] Example 6. The method according to Example 5 further includes: comparing the pacing rate indicated by the sensor with a second switching threshold corresponding to daily life heart rate activities; and switching from the atrial tracking pacing mode to the non-atrial tracking pacing mode in response to the pacing rate indicated by the sensor being greater than the second pacing mode switching threshold and greater than the first pacing mode switching threshold.

[0220] Example 7. The method according to Example 6 further includes: determining the motion signal metric by determining the pacing rate indicated by the sensor while operating in the non-atrial tracking pacing mode; comparing the pacing rate indicated by the sensor with the second pacing mode switching threshold; and switching back to the atrial pacing mode in response to the pacing rate indicated by the sensor being less than the second pacing mode switching threshold.

[0221] 7 Example 8. The method according to any one of Examples 4-7 also includes determining the ventricular event rate by determining the median ventricular event interval.

[0222] Embodiment 9. The method of any one of embodiments 1-8, wherein determining the at least one motion signal metric comprises processing the motion signal within a predetermined time period.

[0223] Example 10. The method according to any one of Examples 1-9 further includes: extending the ventricular pacing rate interval by at least one ventricular cycle; detecting an atrial contraction event during the extended ventricular pacing rate interval; and determining whether the pacing mode switching criteria are met in response to detecting the atrial contraction event.

[0224] Example 11. The method according to Example 10 also includes: detecting at least one of the following: detecting premature ventricular contraction from the cardiac electrical signal received by the sensing circuit of the pacemaker, detecting a decrease in patient body activity from the motion signal, and detecting a change in patient body posture from the motion signal; and extending the ventricular pacing rate interval in response to detecting at least one of premature ventricular contraction, decreased patient body activity and a change in patient posture.

[0225] Example 12. The method according to Example 11 also includes: determining a patient physical activity metric; and periodically extending the ventricular pacing rate interval at a frequency that depends on the patient physical activity metric.

[0226] Example 13. The method according to any one of Examples 1-12 also includes setting the pacing mode switching criteria based on a patient condition determined from the motion signal.

[0227] Example 14. A method according to any one of Examples 1-13, wherein switching from the atrial tracking pacing mode to the non-atrial tracking pacing mode comprises: switching from the atrial tracking pacing mode to a first non-atrial tracking pacing mode within a temporary interval; and switching from the first non-atrial tracking pacing mode to a second non-atrial tracking pacing mode in response to expiration of the temporary interval.

[0228] Example 15. The method of any one of Examples 1-14, further comprising delivering the ventricular pacing pulses via at least one electrode carried by a housing, the housing enclosing the pulse generator, the motion sensor, and the control circuit of the pacemaker.

[0229] Embodiment 16. A non-transitory computer-readable medium storing a set of instructions, which, when executed by a control circuit of a ventricular pacemaker in a heart having a motion sensor configured to generate a motion signal, causes the pacemaker to perform the following operations: detecting an atrial contraction event from the motion signal; operating in a mode selected from an atrial tracking ventricular pacing mode and a non-atrial tracking ventricular pacing mode, wherein operating in the atrial tracking ventricular pacing mode includes: setting an atrioventricular pacing interval in response to detecting an atrial contraction event from the motion signal, and controlling the pacemaker in response to expiration of the atrioventricular pacing interval. A pulse generator delivers ventricular pacing pulses; while operating in a selected one of the atrial tracking ventricular pacing mode and the non-atrial tracking ventricular pacing mode, determining at least one motion signal metric from the motion signal; comparing the at least one motion signal metric with a pacing mode switching criterion; and in response to satisfying the pacing mode switching criterion, switching from a selected one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to another one of the non-atrial tracking pacing mode and the atrial tracking pacing mode to control the pacing pulses delivered by the pulse generator.

[0230] It will be appreciated that various modifications may be made to the referenced embodiments without departing from the scope of the disclosure and the appended claims.

Claims

1. A medical device comprising: a motion sensor (212) configured to generate a motion signal; a pulse generator configured to deliver ventricular pacing pulses; as well as A control circuit (206) configured to: determining a first sensor-indicated pacing rate from the motion signal sensed during a first time interval; determining a first ventricular rate from at least a ventricular pacing pulse delivered by the pulse generator during the first time interval; determining a first threshold rate by adding a tolerance to the determined first ventricular rate; determining that the pacing rate indicated by the first sensor is less than the first threshold rate determined by adding the tolerance to the determined first ventricular rate; as well as In response to at least the first sensor indicating a pacing rate less than the first threshold rate, the pulse generator is controlled to deliver ventricular pacing pulses according to an atrial tracking pacing mode.

2. The medical device according to claim 1, wherein: The control circuit is further configured to: determining that the pacing rate indicated by the first sensor is greater than an activity threshold rate corresponding to a threshold level of patient activity; and In response to the pacing rate indicated by the first sensor being less than the first threshold rate and greater than the activity threshold rate, the pulse generator is controlled to deliver ventricular pacing pulses according to the atrial tracking pacing mode.

3. The medical device of claim 2, wherein: The control circuit is further configured to determine that the pacing rate indicated by the first sensor is greater than the activity threshold by determining that the pacing rate indicated by the first sensor is greater than a daily living activity rate.

4. The medical device according to any one of claims 1 to 3, wherein: The control circuit is further configured to: determining a second sensor-indicated pacing rate from the motion signal sensed during a second time interval; determining a second ventricular rate from at least a ventricular pacing pulse delivered by the pulse generator during the second time interval; determining a second threshold rate by adding the tolerance to the determined second ventricular rate; determining that the pacing rate indicated by the second sensor is greater than the second threshold rate determined by adding the tolerance to the determined second ventricular rate; as well as In response to at least the second sensor indicating a pacing rate greater than the second threshold rate, the pulse generator is controlled to deliver ventricular pacing pulses according to a non-atrial tracking pacing mode.

5. The medical device of claim 4, wherein: The control circuit is further configured to: determining that the pacing rate indicated by the second sensor is greater than an activity threshold rate corresponding to a threshold level of patient activity; and In response to the pacing rate indicated by the second sensor being greater than the second threshold rate and greater than the activity threshold rate, the pulse generator is controlled to deliver ventricular pacing pulses according to the non-atrial tracking pacing mode.

6. The medical device according to claim 4 or 5, wherein: The control circuit is further configured to: The pulse generator is controlled to begin delivering the ventricular pacing pulses at the second ventricular rate according to the non-atrial tracking pacing mode.

7. The medical device according to any one of claims 1 to 6, wherein: The control circuit is further configured to: determining a second sensor-indicated pacing rate from the motion signal sensed during a second time interval; determining a second ventricular rate from at least a ventricular pacing pulse delivered by the pulse generator during the second time interval; determining a second threshold rate by adding the tolerance to the determined second ventricular rate; determining that the pacing rate indicated by the second sensor is less than an activity threshold rate corresponding to a threshold level of patient activity and greater than the second threshold rate determined by adding the tolerance to the determined second ventricular rate; as well as In response to the pacing rate indicated by the second sensor being greater than the second threshold rate and less than the activity threshold rate, the pulse generator is controlled to deliver ventricular pacing pulses according to the atrial tracking pacing mode.

8. The medical device of any one of claims 1-7, further comprising a cardiac electrical signal sensing circuit configured to sense intrinsic ventricular electrical events; in, The control circuit is also configured to determine the first ventricular rate from at least the ventricular pacing pulses delivered by the pulse generator during the first time interval and one or more intrinsic ventricular electrical events sensed by the cardiac electrical signal sensing circuit during the first time interval.

9. The medical device according to any one of claims 1 to 8, wherein: The control circuit is further configured to determine the first threshold rate by adding the tolerance by adding up to twenty beats per minute to the first ventricular rate.

10. The medical device according to any one of claims 1 to 9, wherein: The control circuit is further configured to: determining an atrial contraction event from the motion signal; and In response to detecting the atrial contraction event from the motion signal, the pulse generator is controlled to deliver a ventricular pacing pulse according to the atrial tracking pacing mode by initiating an atrioventricular pacing interval.

11. A non-transitory computer readable medium storing a set of instructions which, when executed by control circuitry of a medical device, cause the medical device to: A motion signal is generated by a motion sensor; The ventricular pacing pulses are delivered by the pulse generator; determining a sensor-indicated pacing rate from the motion signal sensed during the time interval; determining a ventricular rate from at least a ventricular pacing pulse delivered by said pulse generator during said time interval; determining a threshold rate by adding a tolerance to the determined ventricular rate; determining that the pacing rate indicated by the sensor is less than the threshold rate determined by adding the tolerance to the determined ventricular rate; as well as In response to at least the sensor indicating a pacing rate less than the threshold rate, ventricular pacing pulses are delivered according to an atrial tracking pacing mode.

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