Rate smoothing for enhanced atrial synchronous pacing in ventricular pacemakers

Abstract

A ventricular pacemaker is configured to determine a ventricular rate interval by determining at least one ventricular event interval between two consecutive ventricular events and to determine a rate-smoothed ventricular pacing interval based on the ventricular rate interval. The pacemaker is further configured to detect an atrial event from a sensor signal and deliver a ventricular pacing pulse in response to detecting an atrial event from the sensor signal. The pacemaker may start a rate-smoothed ventricular pacing interval to schedule a next pacing pulse to be delivered upon expiration of the rate-smoothed ventricular pacing interval.

Description

Technical Field

[0001] The present disclosure relates to a ventricular pacemaker and method for controlling the timing of ventricular pacing pulses for facilitating atrial synchronous ventricular pacing. Background Art

[0002] Implantable cardiac pacemakers are often placed in a subcutaneous pouch and are coupled to one or more transvenous medical electrical leads that carry pacing and sensing electrodes positioned in the heart. Subcutaneously implanted cardiac pacemakers can be single-chamber pacemakers, which are coupled to one transvenous medical lead for positioning electrodes in one heart chamber (atrium or ventricle), or dual-chamber pacemakers, which are coupled to two transvenous intracardiac leads for positioning electrodes in both the atrial and ventricular chambers. Multi-chamber pacemakers are also available, which can be coupled to, for example, three leads for positioning electrodes for pacing and sensing in one atrial chamber and in both the right and left ventricles.

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

[0004] The technology disclosed herein generally relates to controlling ventricular pacing pulses delivered by a ventricular pacemaker for enhancing atrial synchronization of the ventricular pacing pulses. The ventricular pacemaker can be a cardiac ventricular pacemaker configured to sense an atrial contraction event from within a ventricular chamber and deliver a ventricular pacing pulse synchronized with the sensed atrial contraction event. The ventricular pacemaker is configured to perform the technology disclosed herein to set a rate smoothing pacing interval based on an actual ventricular rate interval determined according to a time interval (a time interval determined between consecutive ventricular events). When a ventricular pacing pulse is delivered synchronously with an atrial contraction event, the pacemaker starts a rate smoothing pacing interval and delivers the next ventricular pacing pulse at the expiration of the rate smoothing pacing interval in the event that the sensed atrial contraction event is missing during the rate smoothing pacing interval.

[0005] In one example, the present disclosure provides a pacemaker comprising: a pulse generator configured to deliver ventricular pacing pulses via electrodes coupled to the pacemaker; a sensor configured to generate a signal including an atrial event signal; and a control circuit coupled to the sensor and the pulse generator. The control circuit is configured to determine a ventricular rate interval by determining at least one ventricular event interval between two consecutive ventricular events, and to determine a frequency-smoothed ventricular pacing interval based on the ventricular rate interval. The control circuit is further configured to: detect an atrial event from the sensor signal; control the pulse generator to deliver a ventricular pacing pulse in response to detecting an atrial event from the sensor signal; and start a frequency-smoothed ventricular pacing interval to schedule a next pacing pulse to be delivered by the pulse generator when the frequency-smoothed ventricular pacing interval expires.

[0006] In another example, the present disclosure provides a method comprising: determining a ventricular rate interval by determining at least one ventricular event interval between two consecutive ventricular events; determining a frequency-smoothed ventricular pacing interval based on the ventricular rate interval; detecting an atrial event from a sensor signal; delivering a ventricular pacing pulse in response to detecting the atrial event from the sensor signal; and starting the frequency-smoothed ventricular pacing interval to schedule the next pacing pulse to be delivered when the frequency-smoothed ventricular pacing interval expires.

[0007] In yet another example, the present disclosure provides a non-transitory computer-readable storage medium, comprising a set of instructions, which, when executed by a control circuit of a pacemaker, causes the pacemaker to determine a ventricular rate interval by determining at least one ventricular event interval between two consecutive ventricular events, and to determine a rate-smoothed ventricular pacing interval based on the ventricular rate interval. The instructions further cause the pacemaker to perform the following operations: detect an atrial event from a sensor signal; deliver a ventricular pacing pulse in response to detecting an atrial event from the sensor signal; and start a rate-smoothed ventricular pacing interval to schedule a next pacing pulse for delivery when the rate-smoothed ventricular pacing interval expires.

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

[0009] Figure 1 is a conceptual diagram illustrating an intracardiac pacing system that may be used to sense cardiac electrical signals and motion signals caused by cardiac motion and flowing blood and to deliver pacing therapy to a patient's heart.

[0010] Figure 2A yes Figure 1 A conceptual diagram of an intracardiac pacemaker is shown in FIG.

[0011] Figure 2B yes Figure 1 A conceptual diagram of another example of a pacemaker.

[0012] Figure 3 yes Figure 1 Schematic diagram of an example configuration of a pacemaker is shown in .

[0013] Figure 4 is an example of a motion sensor signal that may be acquired by an intracardiac pacemaker during the cardiac cycle.

[0014] Figure 5 is an example of motion sensor signals acquired during two different cardiac cycles.

[0015] Figure 6 According to one example, a method for controlling a ventricular pacemaker (such as Figure 1 Flow chart of a method for delivering ventricular pacing pulses using an intraventricular pacemaker (IVP).

[0016] Figure 7 is a graph of motion sensor signals, electrocardiogram signals and marker channels, and ventricular EGM signals depicting the frequency smoothed ventricular pacing technique disclosed herein.

[0017] Figure 8 is a graph of the motion sensor signal, ECG signal and marker channels, and the ventricular EGM signal including premature ventricular beats.

[0018] Fig. 9 is a flow chart of a method that may be performed by a pacemaker according to another example.

[0019] Fig.10 is a flow chart of a method that may be performed by pacemaker 14 for updating a rate smoothing interval, according to some examples.

[0020] Fig.11 is a timing diagram depicting sensed atrial contraction events, ventricular pacing pulses, and corresponding pacing control time intervals for providing pacing rate smoothing during atrial synchronized ventricular pacing according to one example. DETAILED DESCRIPTION

[0021] In general, the present disclosure describes techniques for controlling ventricular pacing, generally referred to as "frequency smoothing," for avoiding sudden changes in ventricular rate and facilitating atrial synchronous ventricular pacing. In the illustrative examples presented herein, a cardiac ventricular pacemaker is configured to sense atrial contraction events for synchronizing ventricular pacing pulses with the atrial rate. As described below, atrial contraction events may be sensed from a signal generated by a motion sensor, the signal including atrial contraction event signals corresponding to atrial mechanical contraction and ventricular active filling phases, sometimes referred to as "atrial drive." In other examples, atrial contraction event sensing may be performed using other techniques, such as sensing atrial contraction events from another cardiac mechanical signal (e.g., a pressure signal, an acoustic signal, an impedance signal, etc.) or sensing a P wave of a cardiac electrical signal accompanying atrial depolarization.

[0022] The techniques disclosed herein provide rate smoothing by controlling the timing of ventricular pacing pulses in the absence of an atrial sensed event. By controlling the delivery of ventricular pacing pulses according to the rate smoothing interval, the ventricular pacing pulse is less likely to interfere with the sensing of the next atrial event, thereby increasing the likelihood of an atrial-synchronous ventricular pacing pulse occurring on the next cardiac cycle. In this way, the rate smoothing techniques disclosed herein tend to increase the percentage of ventricular pacing pulses delivered synchronously with the atrial rate, thereby providing the patient with the benefits of atrial-synchronous ventricular pacing without the need to place electrodes or other sensors in or on the atrial chambers.

[0023] Figure 1 is a conceptual diagram showing 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. The IMD system 10 includes a right ventricular (RV) intracardiac pacemaker 14. The pacemaker 14 can be a transcatheter intracardiac pacemaker that is adapted to be implanted entirely within a cardiac chamber, for example, entirely within the RV of the heart 8 or entirely within the left ventricle (LV) of the heart 8 for sensing cardiac signals and delivering ventricular pacing pulses. The pacemaker 14 is reduced in size compared to subcutaneously implanted pacemakers and can be generally cylindrical in shape to enable transvenous implantation via a delivery catheter.

[0024] The pacemaker 14 is positioned along the endocardial wall of the RV, for example, near the RV apex, but other locations are possible. The technology disclosed herein is not limited to Figure 1The pacemaker positions shown in the example of , and other positions within the heart 8 are possible. For example, a ventricular intracardiac pacemaker 14 can be positioned in the LV and configured to detect cardiac motion signals and deliver atrial synchronized ventricular pacing to the LV using the techniques disclosed herein. The pacemaker 14 can be positioned in the right ventricle or left ventricle to provide corresponding right ventricular or left ventricular pacing and to sense motion signals via a motion sensor within the ventricular chamber.

[0025] The pacemaker 14 is capable of generating electrical stimulation pulses, e.g., pacing pulses, that are delivered to the heart 8 via one or more electrodes on the external housing of the pacemaker. The pacemaker 14 is configured to deliver RV pacing pulses and sense RV cardiac electrical signals using the housing-based electrodes for generating an RV electrogram (EGM) signal. The cardiac electrical signals may be sensed using the housing-based electrodes that are also used to deliver pacing pulses to the RV.

[0026] The pacemaker 14 is configured to control the delivery of ventricular pacing pulses to the RV in a manner that promotes synchronization between atrial activation and ventricular activation (e.g., by maintaining a target atrioventricular (AV) interval between an atrial event and a ventricular pacing pulse). That is, the pacemaker 14 controls the delivery of pacing pulses to maintain a desired AV interval between atrial contraction corresponding to atrial contraction and a ventricular pacing pulse delivered to cause ventricular depolarization and ventricular contraction.

[0027] According to the techniques described herein, atrial contraction events during the active ventricular filling phase are detected by the pacemaker 14 from a motion sensor such as an accelerometer enclosed by the housing of the pacemaker 14. The motion signal generated by the accelerometer implanted in the RV includes motion signals caused by ventricular and atrial events. For example, the acceleration of blood flowing into the RV through the tricuspid valve 16 between the RA and the RV caused by atrial contraction is detected by the pacemaker 14 from the signal generated by the accelerometer included in the pacemaker 14. Figure 4 Other motion signals detected by the pacemaker 14 are described, such as motion caused by ventricular contraction, motion caused by ventricular relaxation, and motion caused by passive filling of the ventricles.

[0028] In other examples, the pacemaker 14 may sense an atrial contraction event by sensing an atrial P wave that accompanies atrial depolarization. The P wave is a signal of relatively low amplitude (e.g., compared to the near-field R wave signal) in the near-field RV electrical signal received by the pacemaker 14, and is therefore difficult to always detect from the cardiac electrical signal acquired by the pacemaker 14 implanted in the ventricular chamber. When based solely on the cardiac electrical signal received by the pacemaker 14, the atrial synchronized ventricular pacing of the pacemaker 14 may be unreliable. According to the technology disclosed herein, the pacemaker 14 may include a motion sensor (such as an accelerometer) and may be configured to use a signal from the motion sensor to detect an atrial event corresponding to atrial mechanical excitation or atrial contraction. However, it is contemplated that other types of sensors of cardiac mechanical or hemodynamic function may be used to generate a cardiac mechanical signal and sense an atrial contraction event from the cardiac mechanical signal. Such sensors may include an impedance sensor (which generates a signal related to the blood volume in the ventricle), a pressure sensor, an acoustic sensor, or other sensors that generate a signal related to the mechanical contraction of the cardiac chamber.

[0029] The ventricular pacing pulse is synchronized with an atrial event that may be detected from an accelerometer signal as described below by setting a programmable atrioventricular (AV) pacing interval that controls the timing of the ventricular pacing pulse relative to a detected atrial contraction event. As described below, the detection of an atrial contraction event for synchronizing the ventricular pacing pulse with atrial contraction may include the detection of other cardiac event motion signals in order to positively identify an atrial contraction event and / or to set sensing parameters for distinguishing an atrial contraction event from other cardiac motion events.

[0030] The target AV interval may be a programmed value selected by a clinician and is the time interval from detection of an atrial event until delivery of a ventricular pacing pulse. In some instances, the target AV interval may start from the time an atrial contraction event is detected based on a motion sensor signal, or from an identified reference point of an atrial event signal. The target AV interval may be identified as being 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 from cardiac electrical signals received by the pacemaker 14 and motion sensor signals received by the pacemaker 14. In some examples, the AV interval may be set to approximately 10 to 200 ms for controlling the pacemaker 14 to deliver ventricular pacing pulses synchronized with atrial events sensed from the motion signal.

[0031] The pacemaker 14 may be capable of bidirectional wireless communication with an external device 20 for programming AV pacing intervals and other pacing control parameters and both electrical event sensing parameters and mechanical event sensing parameters for detecting ventricular events and atrial contraction events from cardiac electrical signals and / or motion sensor signals. Aspects of the external device 20 may generally correspond to the external programming / monitoring unit disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.), which is incorporated herein by reference in its entirety. The external device 20 is often referred to as a "programmer" because it is typically used by a physician, technician, nurse, clinician, or other qualified user to program operating parameters in the pacemaker 14. The external device 20 may be located in a clinic, hospital, or other medical facility. The external device 20 may alternatively be implemented as a home monitor or handheld device that may be used in a medical facility, in a patient's home, or in another location. The operating parameters (including sensing and therapy delivery control parameters) may be programmed into the pacemaker 14 using the external device 20.

[0032] The external device 20 is configured to communicate bidirectionally with implanted telemetry circuitry included in the pacemaker 14. The external device 20 establishes a wireless communication link 24 with the pacemaker 14. The external device 20 may include a programming head that is placed proximate to the pacemaker 14 to establish and maintain the communication link 24, and in other examples, the external device 20 and the pacemaker 14 may be configured to communicate using a distance telemetry algorithm and circuitry that does not require the use of a programming head and does not require user intervention to maintain the communication link.

[0033] The external device 20 can display data and information related to pacemaker function to the user for viewing pacemaker operation and programmed parameters as well as EGM signals transmitted from the pacemaker 14, motion sensor signals acquired by the pacemaker 14, or other physiological data acquired by and retrieved from the pacemaker 14 during an interrogation session.

[0034] It is contemplated that the external device 20 may be wired or wirelessly connected to a communication network via telemetry circuitry including a transceiver and antenna or via hardwired communication lines for transmitting data to a central 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 view EGM, motion sensor, and marker channel data, and, for example, authorize programming of sensing and therapy control parameters in the pacemaker 14 after viewing visual representations of the EGM, motion sensor signals, and marker channel data.

[0035] Figure 2A yes Figure 1 . The pacemaker 14 includes electrodes 162 and 164 spaced apart along a housing 150 of the pacemaker 14 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 164 is shown as a tip electrode extending from a distal end 102 of the pacemaker 14, and electrode 162 is shown as a ring electrode along a 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 (such as a catheter) and placed against a target pacing site.

[0036] 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 various locations along the pacemaker 14 other than those shown.

[0037] The housing 150 is formed of a biocompatible material, such as stainless steel or a titanium alloy. In some examples, the housing 150 may include an insulating coating. Examples of insulating coatings include polyparaxylene, polyurethane, PEEK, or polyimide, among others. The entire housing 150 may be insulated, but only electrodes 162 and 164 are uninsulated. Electrode 164 may serve as a cathode electrode and be coupled to an internal circuit system enclosed by the housing 150, such as a pacing pulse generator and a cardiac electrical signal sensing circuit system, via an electrical feedthrough passing through the housing 150. Electrode 162 may be formed as a conductive portion of the housing 150, defining a ring electrode that is electrically isolated from other portions of the housing 150, such as Figure 2A In other examples, rather than providing a localized annular electrode such as anode electrode 162, the entire perimeter of housing 150 can be used as an electrode electrically isolated from tip electrode 164. Electrode 162 formed along a conductive portion of housing 150 serves as a return anode during pacing and sensing.

[0038] Housing 150 includes control electronics subassembly 152 which houses components for sensing cardiac signals, generating pacing pulses and controlling therapy delivery as well as for incorporating the following: Figure 3The motion sensor may be implemented as an accelerometer enclosed within housing 150. The accelerometer provides a signal to a processor included in control electronics subassembly 152 for signal processing and analysis as described below for detecting ventricular mechanical events and atrial contractile events for timing ventricular pacing pulses.

[0039] Housing 150 further 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 incorporated herein by reference in their entirety.

[0040] 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 operably adjacent to the target tissue for delivery of therapeutic electrical stimulation pulses. Many 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 disclosed in commonly assigned U.S. Pat. No. 9,775,872 (Grubac et al.), which is incorporated herein by reference in its entirety.

[0041] The pacemaker 14 may optionally include a delivery tool interface 158. The delivery tool interface 158 may be located at the proximal end 104 of the pacemaker 14 and is configured to connect to a delivery device, such as a catheter, used to position the pacemaker 14 at an implantation site, e.g., within a heart chamber, during an implantation procedure.

[0042] Figure 2B is a conceptual diagram of another example of the pacemaker 14. Figure 2B In the embodiment of the present invention, the 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 for positioning a return sensing electrode 168 or 167, which can 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 far-field signals, which can include P waves accompanying atrial depolarization.

[0043] 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 tip, sensing extension 165 can be extended toward the RA, thereby positioning electrodes 167 and 168 closer to atrial tissue for sensing atrial P waves. One electrode 167 can be coupled to sensing circuitry enclosed in housing 150 via an electrical feedthrough through housing 150, and one electrode 168 can be coupled to housing 150 to serve as a ground electrode.

[0044] Figure 3 yes Figure 1 Schematic diagram of an example configuration of a pacemaker 14 shown in . 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. The motion sensor 212 is implemented as an accelerometer in the examples described herein, and may also be referred to as "accelerometer 212" herein. However, the motion sensor 212 is not limited to being an accelerometer, and other motion sensors or mechanical sensors may be successfully utilized in the pacemaker 14 to detect cardiac motion signals according to the techniques described herein. Examples of motion sensors that may be implemented in the motion sensor 212 include piezoelectric sensors and MEMS devices.

[0045] The motion sensor 212 can be a multi-axis sensor (e.g., a two-dimensional or three-dimensional sensor), where each axis provides a signal that can be analyzed separately or in combination for detecting cardiac mechanical events. For example, when subjected to flowing blood and cardiac motion, the motion sensor 212 generates an electrical signal related to the motion or vibration of the sensor 212 (and the pacemaker 14). The motion sensor 212 may include filters, amplifiers, rectifiers, ADCs, and / or other components for generating motion signals that are transmitted to the control circuit 206. For example, each vector signal corresponding to each axis of the multi-axis accelerometer can be filtered by a high pass filter (e.g., a 10 Hz high pass filter) and rectified for use by the atrial event detection circuit 240 for detecting atrial contraction events. If necessary, the high pass filter can be reduced (e.g., to 5 Hz) for detecting atrial signals with lower frequency content. In some examples, high pass filtering is performed without low pass filtering. In other examples, each accelerometer axis signal is filtered by a low pass filter (eg, a 30 Hz low pass filter) with or without a high pass filter.

[0046] The motion sensor 212 can be a one-dimensional, single-axis accelerometer, a two-dimensional, or three-dimensional multi-axis accelerometer. An example 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. Implantable medical device arrangements including piezoelectric accelerometers for detecting patient motion are disclosed, for example, in U.S. Pat. No. 4,485,813 (Anderson et al.) and U.S. Pat. No. 5,052,388 (Sivula et al.), both of which are hereby incorporated by reference in their entirety. Examples of three-dimensional accelerometers that can be implemented in a pacemaker 14 and used to detect cardiac mechanical events using the presently disclosed technology are generally described 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 may be used to generate electrical signals related to the motions imposed on the pacemaker 14 due to ventricular and atrial events.

[0047] Figure 3 The various circuits represented may be combined on one or more integrated circuit boards including application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or groups) and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components that provide the described functionality.

[0048] The sensing circuit 204 is configured to receive cardiac electrical signals via electrodes 162 and 164 through a pre-filter and amplifier circuit 220. The pre-filter and amplifier circuit may include a high pass filter (e.g., a 2.5 to 5 Hz high pass filter) for removing DC offset, or a wideband filter having 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 signals that are passed to an 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 an 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 may be used in an algorithm for detecting atrial contraction events from motion sensor signals. The digital signal from the ADC 226 may be passed to a rectifier and amplifier circuit 222 , which may include a rectifier, a bandpass filter, and an amplifier for passing the cardiac signal to an R-wave detector 224 .

[0049] The cardiac event detector 224 may include a sense amplifier or other detection circuit system 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 crosses the R-wave detection threshold, the cardiac event detector 224 generates an R-wave sense event signal (R-sense), which is transmitted to the control circuit 206. In other examples, the cardiac event detector 224 may receive the digital output of the ADC 226 for detecting R waves through a comparator, morphological signal analysis of the digital EGM signal, or other R-wave detection techniques. The R-wave sense event signal transmitted from the R-wave detector 224 to the control circuit 206 may be used to schedule ventricular pacing pulses through the pacing timing circuit 242 and to identify the timing of ventricular electrical events in the algorithm executed by the atrial event detector circuit 240 for detecting atrial contraction events from the signal received from the motion sensor 212.

[0050] In some examples, cardiac event detector 224 is configured to receive signals from electrodes 162 and 164 (and / or electrodes carried by a sensing extension, such as Figure 2B The cardiac event detector 224 may sense a P wave from a cardiac electrical signal received from a motion sensor (e.g., an extension 165 shown in FIG. 1 ). The cardiac event detector 224 may compare the incoming signal to a P wave sensing threshold and, in response to crossing the threshold, generate a P-wave sensed event signal that is transmitted to the control circuit 206. When the pacemaker 14 is configured to sense R waves and P waves, the sensing circuit 204 may include two different sensing channels, each including a pre-filter / amplifier, an ADC, a rectifier / amplifier, and a cardiac event detector, configured to amplify and filter cardiac electrical signals received via one or two different sensing electrode pairs (for sensing R waves and P waves separately from cardiac electrical signals). P wave sensing may be used to verify an atrial event sensed from a motion sensor signal, or vice versa. In some examples, the P wave sensed event signal is used by the control circuit 206 to initiate an AV interval for controlling an atrial-synchronized ventricular pacing pulse delivered by the pulse generator 202.

[0051] 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 from signals received from motion sensor 212. In some examples, one or more ventricular mechanical events can be detected from the motion sensor signals in a given cardiac cycle to facilitate positive detection of atrial contraction events from the motion sensor signals during the ventricular cycle.

[0052] The control circuit 206 may receive R-wave sensed event signals, P-wave sensed event signals, and / or digital cardiac electrical signals from the sensing circuit 204 for detecting and confirming cardiac events and controlling ventricular pacing. For example, when the pacemaker 14 is operating in a non-atrial tracking (asynchronous) ventricular pacing mode, the R-wave sensed event signal may be transmitted to the pacing timing circuit 242 for inhibiting scheduled ventricular pacing pulses or for scheduling ventricular pacing pulses. The R-wave sensed event signal may also be transmitted to the atrial event detector circuit 240 for setting a time window used by the control circuit 206 to detect atrial contraction events from the motion sensor signal.

[0053] Atrial event detector circuit 240 receives motion signals from motion sensor 212 and may initiate an atrial refractory period in response to a ventricular electrical event (e.g., an R-wave sensed event signal from sensing circuit 204 or the delivery of a ventricular pacing pulse by pulse generator 202). In some examples, atrial event detector circuit 240 determines whether the motion sensor signal meets atrial mechanical event detection criteria outside of the refractory period. The motion sensor signal during the refractory period may be monitored by atrial event detector circuit 240 to detect a ventricular mechanical event, which may be used to confirm or verify atrial contraction event detection. Thus, a ventricular mechanical event detection window may be set during the atrial refractory period and may be set according to a predetermined time interval after a ventricular electrical event is identified. Atrial event detector circuit 240 may be configured to detect one or more ventricular mechanical events during a corresponding ventricular event detection window during the atrial refractory period. The timing and detection of a ventricular mechanical event can be used to update the atrial refractory period and / or atrial contraction detection threshold amplitude, and can be used to confirm detection of an atrial contraction event that occurs after an expected ventricular mechanical event.

[0054] Atrial event detector circuit 240 can set time windows corresponding to passive ventricular filling period and active ventricular filling period based on the timing of the preceding ventricular electrical event (R wave sense event signal or ventricular pacing pulse). The crossing of the atrial event detection threshold by the motion sensor signal during any of these windows can be detected as an atrial contraction event. As described below, two different atrial event detection thresholds can be established for application during corresponding passive filling period windows and active filling period windows.

[0055] The atrial event detector circuit 240 transmits an atrial event detection signal to the processor 244 and / or the pacing timing circuit 242 in response to detecting an atrial contraction event from the motion sensor signal. In other examples, the atrial contraction event may be detected as a mechanical event from the motion sensor signal and / or as an electrical event (P wave) by the sensing circuit 204. The P wave sensed event signal may be transmitted from the cardiac event detector 224 to the atrial event detector circuit 240 or directly to the pacing timing circuit 242. In still other examples, the pacemaker 14 may be configured to receive a signal indicating the timing of the atrial contraction event from another medical device, for example, via the telemetry circuit 208. The other medical device may be an intra-atrial pacemaker or a subcutaneously or submuscularly implanted sensing device, pacemaker, or implantable cardioverter-defibrillator that is configured to sense the P wave and transmit or broadcast a signal to the pacemaker 14 indicating the timing of the sensed P wave or delivered atrial pacing pulse. Other examples of atrial event sensing or detection for atrial synchronous ventricular pacing controlled by an intracardiac ventricular pacemaker are generally disclosed in U.S. Publication No. 2018 / 0161580A1 (Demmer et al.) and U.S. Publication No. 2016 / 0144190 (Cao et al.), both of which are incorporated herein by reference in their entirety.

[0056] Pace timing circuit 242 (or processor 244) may additionally receive an R-wave sense event signal from R-wave detector 224 for use in controlling the timing of pacing pulses delivered by pulse generator 202. Processor 244 may include one or more clocks for generating clock signals used by pace timing circuit 242 to time out an AV pacing interval that is initiated upon receipt of an atrial event detection signal from atrial event detector circuit 240. Pace timing circuit 242 may include one or more paced escape interval timers or counters for timeout of an AV pacing interval, which may be a programmable interval stored in memory 210 and retrieved by processor 244 for setting the AV pacing interval used by pace timing circuit 242.

[0057] The pacing timing circuit 242 may additionally include a lower pacing frequency interval timer for controlling a lower ventricular pacing frequency. For example, if an atrial contraction event that results in triggering a ventricular pacing pulse with a programmed AV pacing interval is not detected from the motion sensor signal, a ventricular pacing pulse may be delivered by the pulse generator 202 at the expiration of the lower pacing frequency interval to prevent ventricular asystole and maintain a minimum ventricular rate. As described below, in order to avoid sudden changes in ventricular rate and to promote recovery of atrial event sensing when no atrial event is sensed during the cardiac cycle, the control circuit 206 may be configured to set the ventricular pacing interval to a frequency smoothing interval during the atrial tracking ventricular pacing mode. The frequency smoothing interval may be determined based on one or more preceding ventricular event intervals. For example, the actual pacing frequency interval (Vp-Vp interval) between consecutively delivered ventricular pacing pulses may be determined. The Vp-Vp interval may be determined as an interval between two consecutive delivered pacing pulses or an interval between corresponding two consecutive induced R waves sensed from the cardiac electrical signal by the sensing circuit 204. The rate smoothing interval may be set based on the actual Vp-Vp interval, such that a ventricular pacing pulse delivered in the absence of a sensed atrial event is delivered at an interval within a predetermined interval of the preceding Vp-Vp interval, e.g., within 150 ms or within 100 ms.

[0058] At times, control circuit 206 may control pulse generator 202 in a non-atrial tracking ventricular pacing mode (also referred to as "asynchronous ventricular pacing") during which the VV interval may be set based on a measure of patient activity determined from motion sensor 212, or may be set according to a programmed lower rate. If control circuit 206 switches from the atrial tracking ventricular pacing mode to the non-atrial tracking ventricular pacing mode, control circuit 206 may set a rate smoothing interval to control a stepwise adjustment of the ventricular pacing frequency from the atrial tracking Vp-Vp interval to the ventricular lower rate for controlling the ventricular pacing frequency during the non-atrial tracking pacing mode (e.g., VVI or VDI pacing mode).

[0059] 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 from memory 210. In addition to providing control signals to pace timing circuit 242 and pulse generator 202 for controlling pacing pulse delivery, processor 244 can provide sensing control signals to sensing circuit 204 that are applied to the cardiac electrical signals, such as R-wave sensing thresholds, P-wave sensing thresholds, sensitivity, and / or various blanking periods and refractory periods.

[0060] 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 by a plurality of battery voltage signals 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 delivery of 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 an AV pacing interval (VV frequency smoothing interval or VV lower frequency pacing interval) and remains closed for a programmed pacing pulse width to enable the holding capacitor of the charging circuit 230 to discharge. The holding capacitor previously charged to the pacing pulse voltage amplitude is discharged across electrodes 162 and 164 for the programmed pacing pulse duration through the output capacitor of output circuit 234. Examples of pacing circuit systems generally disclosed in U.S. Pat. No. 5,507,782 (Kieval et al.) and in commonly assigned U.S. Pat. No. 8,532,785 (Crutchfield et al.), both of which are incorporated herein by reference in their entirety, may be implemented in pacemaker 14 for charging the pacing capacitor to a predetermined pacing pulse amplitude and delivering pacing pulses under the control of control circuit 206.

[0061] 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-transitory, computer readable storage medium, including any volatile, non-volatile, magnetic, optical, or electrical medium, such as a random access memory (RAM), a read-only memory (ROM), a non-volatile RAM (NVRAM), an electrically erasable programmable ROM (EEPROM), a flash memory, or other digital medium. According to the techniques disclosed herein, the memory 210 may store timing periods and other data that are used by the control circuit 206 to control the delivery of pacing pulses by the pulse generator 202, for example, by detecting an atrial contraction event from a motion sensor signal by the atrial event detector circuit 240 and setting a pacing escape interval timer included in the pacing timing circuit 242.

[0062] The memory 210 may store one or more Vp-Vp intervals for determining a frequency smoothing interval. In some examples, the most recent Vp-Vp interval may be determined as the actual ventricular pacing frequency. In other examples, the memory 210 may buffer a series of ventricular event intervals, such as Vp-Vp intervals (or induced RR intervals), for determining the actual ventricular pacing frequency as an average or median Vp-Vp interval, which is used by the processor 244 to determine the VV frequency smoothing pacing interval. For example, the pacing timing circuit 242 may include a timer or counter that starts when a ventricular pacing pulse is delivered, which is used to determine the Vp-Vp time interval until the next delivered ventricular pacing pulse. The Vp-Vp time intervals may be stored in the memory 210, for example, by storing a predetermined number of Vp-Vp time intervals in a first-in, first-out buffer. In one example, up to 12 Vp-Vp intervals are stored for use in determining a median Vp-Vp interval, although more or less than 12 Vp-Vp intervals may be stored for use in determining a mean or median Vp-Vp interval.

[0063] Processor 244 may be configured to set the VV rate smoothing interval to a predetermined increment greater than the actual ventricular pacing rate, which in some examples may be determined based on a single most recent Vp-Vp interval or a median or average of multiple Vp-Vp intervals. The predetermined increment may be set to 10 ms, 25 ms, 50 ms, 75 ms, 100 ms, 150 ms, or other selected time interval. Processor 244 may control pacing timing circuit 242 to start a VV pacing interval timer or counter for counting down the VV rate smoothing interval. If the VV rate smoothing interval expires without sensing an atrial contraction event, a ventricular pacing pulse is delivered by pulse generator 202 at the rate smoothing interval.

[0064] The power source 214 provides power to each of the other circuits and components of the pacemaker 14 as needed. The power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. For purposes of clarity, the power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Figure 3 The connections between the power supply 214 and other pacemaker circuits and components are not shown, but should be understood from Figure 3 For example, power supply 214 may provide power to charging circuit 230 for charging a holding capacitor to a pacing voltage amplitude, current as needed to switch 232 and other circuitry included in pulse generator 202, power as needed to transducer 209, motion sensor 212, and ADC 226 and other circuitry of sensing circuit 204, and memory 210.

[0065] Telemetry circuit 208 includes a transceiver 209 and an antenna 211 for transmitting and receiving data via a radio frequency (RF) communication link. As described above, telemetry circuit 208 may be able to communicate with external device 20 ( Figure 1 ) for two-way communication. Motion sensor signals and cardiac electrical signals, and / or data derived therefrom, may be transmitted by telemetry circuitry 208 to external device 20. Programmable control parameters and algorithms for performing atrial event detection and ventricular pacing control may be received by telemetry circuitry 208 and stored in memory 210 for access by control circuitry 206.

[0066] The functionality of the pacemaker 14 attributed herein may be embodied as one or more processors, controllers, hardware, firmware, software, or any combination thereof. Depicting different features as specific circuit systems is intended to highlight different functional aspects and does not necessarily imply that such functionality must be implemented by separate hardware, firmware, or software components or by any particular circuit architecture. Rather, the functionality associated with one or more circuits described herein may be performed by separate hardware, firmware, or software components, or integrated within common hardware, firmware, or software components. For example, atrial contraction event detection and ventricular pacing control operations from motion sensor signals 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] The operation of the circuitry included in the pacemaker 14 as disclosed herein 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 and by the specific sensing circuitry and therapy delivery circuitry employed by the pacemaker 14. In view of the disclosure herein, it is within the capabilities of those skilled in the art to provide software, hardware, and / or firmware for accomplishing the described functions in the context of any modern pacemaker.

[0068] Figure 4is an example of a motion sensor signal 250 that can be acquired by the motion sensor 212 during a cardiac cycle. The vertical dashed lines 252 and 262 represent the timing of two consecutive ventricular events (intrinsic ventricular depolarization or ventricular pacing), marking the respective start and end of the ventricular cycle 251. The motion signal includes an A1 event 254, an A2 event 256, an A3 event 258, and an A4 event 260. The A1 event 254 is an acceleration signal that occurs during ventricular contraction and marks the approximate start of ventricular mechanical contraction (in this example, when the motion sensor 212 is implemented as an accelerometer). The A1 event is also referred to herein as a "ventricular contraction event." The A2 event 265 is an acceleration signal that occurs during ventricular relaxation and marks the approximate offset or end of ventricular mechanical contraction. The A2 event is also referred to herein as a "ventricular relaxation event." The A3 event 258 is an acceleration signal that occurs during passive ventricular filling and marks ventricular mechanical relaxation. The A3 event is also referred to herein as a "ventricular passive filling event." Since the A2 event occurs at the end of ventricular contraction, it is an indicator of the beginning of ventricular diastole. The A3 event occurs during ventricular diastole. Therefore, the A2 and A3 events can be collectively referred to as ventricular mechanical diastolic events, as they are both indicators of ventricular diastole.

[0069] The A4 event 260 is an acceleration signal that occurs during atrial contraction and active ventricular filling and marks a mechanical contraction of the atria. The A4 event 260 may also be referred to herein as an "atrial contraction event" or simply an "atrial event" and is an atrial contraction event detected by the atrial event detector circuit 240 from the motion sensor signal 250 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 for at least some ventricular cardiac cycles for positive detection of the A4 event 260 and setting an atrial event detection control parameter. The A1, A2, and / or A3 events can be detected and characterized to avoid false detection of the A4 event and to facilitate reliable A4 event detection for correct timing of atrial synchronized ventricular pacing pulses.

[0070] Figure 5 4 is an example of motion sensor signals 400 and 410 acquired during two different cardiac cycles. For both cardiac cycles, a ventricular pacing pulse is delivered at time 0.0 seconds. The top sensor signal 400 is received during one cardiac cycle, and the bottom sensor signal 401 is received during a different cardiac cycle. The two signals 400 and 410 are aligned at time 0.0 seconds, which is the time when the ventricular pacing pulse is delivered. Although the motion signals 400 and 410 are Figure 4The motion signal 250 is shown as a raw accelerometer signal, but it is recognized that the control circuit 206 may receive a filtered, amplified, and rectified signal from the motion sensor 212 for processing and analysis as described herein in conjunction with the flow charts and histogram distributions presented herein.

[0071] It is observed that the A1 events 402 and 412 of the respective motion sensor signals 400 and 410, which occur during ventricular contraction, are well aligned in time after the ventricular pacing pulse at time 0.0 seconds. Similarly, the A2 events 404 and 414 (occurring during ventricular relaxation) 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 that occur during ventricular contraction, ventricular relaxation, and passive ventricular filling, respectively, these events are expected to occur after a ventricular electrical event (in this example, a ventricular pacing pulse) and at relatively consistent intervals relative to each other. The timing of the A1, A2, and A3 events following a ventricular pacing pulse may differ compared to the timing of the A1, A2, and A3 events following a sensed intrinsic R wave, however, during a stable paced or intrinsic ventricular rhythm, the relative timing of the A1, A2, and A3 events is expected to be consistent with each other and with the immediately preceding ventricular electrical event.

[0072] The A4 events 408 and 418 of the first and second motion sensor signals 400 and 410, respectively, are not aligned in time. The A4 event occurs during atrial contraction, and thus the time interval of the A4 event after the immediately preceding ventricular electrical event (a sensed R-wave or ventricular pacing pulse) and the preceding A1 to A3 events can vary between cardiac cycles.

[0073] The consistency of the timing of the A1 to A3 events relative to each other and the A1 to A3 events with the immediately preceding ventricular electrical event can be used to determine the atrial refractory period 436 and increase the confidence that the A4 events 408 and 418 are reliably detected. No atrial contraction events are detected during the atrial refractory period 436 extending from the ventricular electrical event (at time 0.0) to the estimated start of ventricular contraction. The A3 sensing window 424 can be set with a start time 420 corresponding to the end of the post-ventricular atrial refractory period 436, and an end time 422.

[0074] A4 events 408 and 418 may be detected based on a multi-level A4 detection threshold 444. As seen by the lower motion sensor signal 410, the A4 event 418 may occur earlier after the A3 window 424 due to changes in the atrial rate. In some instances, as the atrial rate increases, the A4 event 418 may occur within the A3 window 424. When this occurs, the A3 event 416 and the A4 event 418 may fuse together as passive and active ventricular filling. The fused A3 / A4 event may have a high amplitude, even greater than the amplitude when the A3 event 416 or the A4 event 418 occurs separately. Therefore, in some examples, a first higher A4 threshold amplitude 446 may be established for detecting early A4 events that fuse with the A3 event during the A3 window 424. A second lower A4 threshold amplitude 448 may be established for detecting relatively late A4 events after the end time 422 of the A3 window 424. The earliest crossing of the A4 detection threshold 444 by the motion sensor signal after the start time 420 of the A3 window (or after the expiration of the atrial refractory period 436) may be detected as an atrial contraction event. Various examples of intracardiac pacemakers configured to detect atrial contraction events from motion sensor signals for delivering atrial synchronized ventricular pacing are disclosed in commonly assigned U.S. Patent Publication No. 2018 / 0085589 (Splett et al.), U.S. Patent Publication No. 2018 / 0085588 (Splett et al.), U.S. Patent Publication No. 2018 / 0117337 (Demmer et al.), U.S. Patent Publication No. 2018 / 0161580 (Demmer et al.), and U.S. Patent No. 10,207,116 (Sheldon et al.), all of which are incorporated herein by reference in their entirety. The techniques disclosed herein for controlling the timing of ventricular pacing pulses using frequency smoothed pacing intervals may be implemented in any of the examples presented in the aforementioned incorporated references.

[0075] Figure 6300 is a flow chart of a method for controlling ventricular pacing pulses delivered by a ventricular pacemaker (such as the intracardiac ventricular pacemaker 14) according to one example. At box 302, the control circuit 206 identifies a ventricular electrical event. The ventricular event may be a sensed intrinsic R wave, for example, when the control circuit 206 receives an R wave sense event signal from the sensing circuit 204. In this case, the control circuit 206 starts a VV lower frequency pacing interval (box 306). Generally speaking, atrial synchronized ventricular pacing is delivered in patients with AV block. Atrial depolarization is not conducted, or may be conducted with a very long delay. Some patients with some degree of AV block may experience AV conduction and / or premature ventricular contractions (PVC) episodes. If a sensed intrinsic ventricular event occurs, the control circuit 206 sets the VV pacing interval to a lower frequency interval, for example, 1.5 to 1.0 seconds, corresponding to a lower frequency of 40 to 60 pulses per minute. In this way, the relatively long pacing interval facilitates sensing of the next atrial event during the long pacing interval.

[0076] If the ventricular electrical event identified at box 302 is a ventricular pacing pulse (V pace) delivered by pulse generator 202 (or a subsequently induced R wave sensed by sensing circuit 204), control circuit 206 may update the actual ventricular pacing rate interval at box 308. The actual ventricular pacing rate may be the most recent preceding Vp-Vp interval (or sensed R wave to V pace interval), which may or may not include an intervening sensed A4 event. In another example, the median Vp-Vp interval is determined as the median of the last twelve Vp-Vp intervals. Each Vp-Vp interval is the time interval between a pair of consecutively delivered ventricular pacing pulses (or corresponding induced R waves). In some examples, the sensed intrinsic ventricular R waves may be ignored to determine the Vp-Vp interval. Because the patient may have AV block, any intrinsic sensed R wave may be a PVC. The short interval before the PVC and the long interval after the PVC may be ignored because they do not represent a regular ventricular rate. In other examples, all ventricular event intervals, including sensed and paced intervals, may be used in updating the ventricular rate intervals at block 308. PVCs may be identified based on short-long intervals and / or morphology differences from normally conducted R waves and excluded from updating the actual ventricular event intervals at block 308, while other intrinsically sensed R waves that appear to be conducted from the atria may be used to determine ventricular event intervals that are used to update the actual ventricular rate intervals.

[0077] The control circuit 206 uses the actual ventricular rate interval updated at box 308 (or updated on a preceding ventricular pacing event) to set the frequency smoothing interval at box 310 in response to the delivered ventricular pacing pulse. The frequency smoothing interval is the VV pacing interval that is used to control the timing of the next ventricular pacing pulse in the absence of a sensed atrial event. As described below, when no atrial event is sensed, rather than delivering a ventricular pacing pulse at a programmed lower frequency interval after each V pacing, the frequency smoothing interval allows ventricular pacing to occur close to the expected atrial rate based on the preceding actual atrial tracking ventricular pacing frequency. The frequency smoothing interval avoids sudden changes in ventricular rate and preserves the timing of the post-ventricular atrial refractory period and the start and end of the A3 window relative to the preceding ventricular pacing pulse to facilitate rapid return to atrial sensing.

[0078] In some examples, a frequency smoothing interval is initiated only in response to a delivered ventricular pacing pulse, which may be delivered at an AV interval after a sensed A4 event, or may be delivered at a lower frequency interval or a frequency smoothing interval. When an intrinsic R wave is sensed, the control circuit 206 may only initiate a programmed lower frequency interval without applying a frequency smoothing interval. In other examples, a frequency smoothing interval may be initiated in response to a sensed intrinsic R wave. For example, a frequency smoothing interval may be initiated in response to a sensed intrinsic R wave when the sensed intrinsic R wave occurs at a ventricular event frequency interval close to the expected atrial rate.

[0079] In conjunction with initiating a VV lower rate interval in response to an intrinsic ventricular sensed event at block 306, or in conjunction with initiating a rate smoothing interval in response to a ventricular pacing pulse at block 310, control circuit 206 initiates a post-ventricular atrial refractory period at block 312. Any events sensed during the post-ventricular atrial refractory period are not used to initiate an AV pacing interval. Upon expiration of the atrial refractory period, control circuit 206 may initiate an A3 (passive ventricular filling) window that is set based on the A3 window end time (e.g., Figure 5 Terminates at the position shown in .

[0080] If an R wave is sensed before rate smoothing or the VV lower rate interval expires, as determined at block 314, the control circuit 206 returns to block 302. The scheduled pacing pulse is suppressed and the VV lower rate interval may be restarted at block 306. Some patients may experience a series of PVCs that are not used to update the actual ventricular rate interval. In other cases, R wave sensing may indicate the return of AV conduction.

[0081] As long as no R wave is sensed at box 314, the control circuit 206 waits for an atrial event to be sensed at box 316. If no atrial event is sensed (the "No" branch of box 316), the frequency smoothing interval (or the VV lower frequency interval) continues to run (box 324). If an atrial event is sensed at box 316, the control circuit 206 responds by starting the AV interval at box 318. An atrial event can be sensed from the motion sensor signal in response to an A4 threshold crossing. As described above, a higher A4 threshold crossing can be applied during the A3 window, and a lower A4 threshold can be applied starting at the end of the A3 window until an A4 event is sensed or a ventricular pacing pulse is delivered (or an intrinsic R wave is sensed). In other examples, the atrial event can be a P wave sensed from the cardiac electrical signal. In yet other examples, the atrial event sensed at box 316 can be a communication signal or trigger signal that is transmitted by another co-implanted medical device and received by the pacemaker 14 to indicate that an atrial P wave or an atrial pacing pulse has occurred.

[0082] At box 322, the control circuit 206 delivers a ventricular pacing pulse at the expiration of the AV interval. The rate smoothing interval is canceled, and the ventricular pacing pulse scheduled at the expiration of the rate smoothing interval is suppressed. The control circuit 206 returns to box 302, and updates the actual ventricular rate interval using the most recent Vp-Vp interval at box 308. It is to be understood that in some examples, an R wave may be sensed during the AV interval at box 318, in which case the AV interval may be suspended and the corresponding scheduled ventricular pacing pulse may be suppressed. In this case, the process returns to box 302 without delivering an atrial synchronized ventricular pacing pulse.

[0083] If no atrial event is sensed ("NO" branch of block 316), and the rate smoothing interval (or VV lower rate interval) expires at block 324, a ventricular pacing pulse is delivered at the rate smoothing interval (or VV lower rate interval). When a ventricular pacing pulse is delivered at the rate smoothing interval from a preceding ventricular pacing pulse, the rate smoothing interval will be used to update the actual pacing rate interval at block 308. The actual pacing rate may be updated to be equal to a single preceding Vp-Vp interval, or the actual pacing rate may be determined based on a plurality of preceding Vp-Vp intervals, e.g., the actual pacing rate is determined as an average or median value. If multiple ventricular pacing pulses are delivered at a frequency smoothing interval over multiple consecutive cycles without an atrial sensing event, or multiple ventricular pacing pulses are delivered at increasing Vp-Vp intervals that include an atrial sensing event (where V pacing is delivered at the AV interval), the frequency smoothing interval will gradually increase because each frequency smoothing interval is based on the updated actual pacing frequency interval plus a predetermined increment, such as 8 to 200 ms. If atrial sensing is lost for multiple cardiac cycles, the frequency smoothing interval gradually increases and approaches the VV lower frequency interval. If the VV lower frequency interval is reached, the frequency smoothing interval set in response to the ventricular pacing pulse is not set to be greater than the VV lower frequency interval. In other words, the maximum frequency smoothing interval may be equal to the VV lower frequency interval.

[0084] Figure 7 5 is a graph 500 of a motion sensor signal 502, an electrocardiogram signal and marker channel 504, and a ventricular EGM signal 506. Figure 7 In the example of FIG. 5 , the motion sensor signal 502 is shown as an unrectified signal, however, it is understood that the motion sensor signal 502 may be filtered and rectified for sensing an A4 signal representing a mechanical contraction of the atria. The motion sensor signal 502 includes A4 signals 510, 512, 514, and 516. An early A4 sensing threshold 515a may be applied during the A3 window 526, and a late A4 sensing threshold 515b may be applied to the motion sensor signal 502 after the end of the A3 window 528. The early and late A4 sensing thresholds 515a and 515b are collectively referred to as A4 sensing thresholds 515. The A4 signals 510, 512, and 516 each cross the A4 sensing threshold 515, resulting in a corresponding atrial sensed event signal 520 shown on the ECG and marker channel signal 504. The A4 signal 514 does not cross the A4 sensing threshold 515 and is not sensed by the atrial event detector circuit 240.

[0085] The ECG and marker channel signals 504 show the ventricular pacing pulses 522 delivered in response to each atrial sensed event signal 520. In response to the atrial event detector circuit 240 generating the atrial sensed event signal 520, the control circuit 206 sets the AV interval 555, for example, as short as 10 ms. The pulse generator 202 delivers the ventricular pacing pulse 522 at the expiration of the AV interval, resulting in the appearance of an induced R wave 518 on both the ECG signal (504) and the ventricular EGM signal 506. In response to delivering the ventricular pacing pulse 522, the actual pacing interval 530 between the current and immediately preceding pacing pulses is used to update the actual ventricular rate interval. The actual ventricular rate interval may be set to the current Vp-Vp interval 530; to the current Vp-Vp interval plus or minus an adjustment interval for tracking trends in the Vp-Vp interval; or to an actual rate interval determined based on a plurality of Vp-Vp intervals, for example, to the median of 12 (or other predetermined number of) consecutive Vp-Vp intervals. It is to be understood that consecutive Vp-Vp intervals used to update the actual pacing rate interval may not represent consecutive ventricular event intervals, as intervening PVCs or intrinsically conducted R-waves may occur. For purposes of updating the actual ventricular rate interval, cardiac cycle intervals that begin or end with a sensed intrinsic R-wave may be ignored. The actual ventricular rate interval updated when the ventricular pacing pulse 522 is delivered (or the immediately preceding updated actual ventricular rate interval) is used by the control circuit 206 to set the rate smoothing interval 532. The rate smoothing interval may be set, for example, to be longer by an increment 552 than the updated actual ventricular rate interval 550, the increment being, for example, 100 ms.

[0086] In response to delivering the ventricular pacing pulse 522, the control circuit 206 sets a post-ventricular atrial refractory period 524, followed by an A3 window 526, which ends at an A3 window end 528. The frequency smoothing interval 532 expires due to undersensing of the A4 signal 514. The control circuit 206 controls the pulse generator 202 to deliver a ventricular pacing pulse 536 at the expiration of the frequency smoothing interval 532, which begins another atrial refractory period 524, followed by an A3 window 526. The ventricular pacing pulse 536 is delivered at a rate close to the actual ventricular rate interval, which is the previously tracked atrial rate (e.g., the frequency of the sensed A4 signals 510 and 512). Therefore, the next atrial event (in this case, the A4 signal 516) is expected to be outside the atrial refractory period 524 and may be after the next A3 window end 528. By delivering ventricular pacing pulses 536 at frequency smoothing intervals set based on the actual ventricular rate intervals, rather than delivering ventricular pacing pulses 536 at VV lower frequency intervals, the likelihood of sensing the next A4 signal 516 during or after the A3 window is increased.

[0087] The improved likelihood of sensing an A4 signal after a ventricular pacing pulse delivered at a frequency smoothing interval is demonstrated by the dashed VV lower frequency interval 540. If the VV lower frequency interval 540 is initiated in response to the ventricular pacing pulse 522, the next ventricular pacing pulse will be delivered much later in the atrial cycle, potentially precluding or interfering with atrial event sensing. If a pacing pulse is delivered at the expiration of the VV lower frequency interval 540, the subsequent atrial refractory period 524 (shown by the dashed line) and the end of the A3 window 528 will occur much later in time. The next atrial event 516 may occur (and not be detected) after the VV lower frequency interval 540 during the post-ventricular atrial refractory period 524, or may occur during the A3 window 526 but be too small to be detected. Several cycles of ventricular pacing pulses may be delivered at the VV lower frequency interval 540 before an atrial event is sensed outside the atrial refractory period 524. The timing of the end of the A3 window 528 is substantially preserved relative to the actual atrial rate by setting the frequency smoothing interval 532 based on the actual ventricular rate interval, thereby facilitating a rapid return to A4 sensing, in this example, as early as the next cardiac cycle (A4 event 516). In this way, the percentage of ventricular pacing pulses delivered synchronously with atrial contraction events can be increased by using the frequency smoothing interval based on the actual ventricular rate interval to control the timing of ventricular pacing pulses in the absence of atrial sensed events. Rapidly reacquire atrial event sensing after single cycle or scattered or intermittent atrial event undersensing.

[0088] Figure 8 6 is a graph 600 of a motion sensor 602, an ECG signal and marker channel 604, and a ventricular EGM signal 606 including a PVC 630. The motion sensor signal 602 is a rectified signal including A4 signals 610, 612, 614, and 616. The A4 signal 610 is sensed by the control circuit 206, and an atrial sensed event signal 620 is generated. In response to the A4 sensed event signal 620, the control circuit 206 delivers a ventricular pacing pulse 622 after the AV interval (which may be as short as 10 ms and therefore not in the AV interval). Figure 8 6, but it is understood that it is the time interval between the atrial sensed event signal 620 and the ventricular pacing pulse 622). In response to delivering the ventricular pacing pulse 622, the control circuit 206 may set an atrial refractory period followed by the A3 window, as described above in conjunction with Figure 6 and Figure 7 The control circuit 206 may update the actual ventricular rate interval and set the frequency smoothing interval based on the actual ventricular rate interval, as described above in conjunction with Figure 6 and Figure 7 as described.

[0089] exist Figure 8In the example of FIG. 6 , PVC 630 occurs before the end of the A3 window following the ventricular pacing pulse 622. PVC 630 is sensed by the sensing circuit 204. An R-wave sense event signal 632 is generated and communicated to the control circuit 206. The PVC may interfere with A4 event sensing due to the presence of a ventricular event motion signal in the motion sensor signal 602 near the time of the A4 signal and / or the PVC before the end of the A3 window, and may result in the initiation of a post-ventricular atrial refractory period.

[0090] In some examples, the ventricular event interval that begins with a ventricular pacing pulse 622 and ends with a ventricular sensed event 632 is not used to update the actual ventricular rate interval. The control circuit 206 does not initiate a frequency smoothing interval in response to the ventricular sensed event signal 632. Instead, a VV lower frequency interval 640 is initiated in response to the ventricular sensed event signal 632. Since the sensed event may be a PVC occurring in a patient with AV block, a long pause is expected to occur after the PVC. If a frequency smoothing interval 642 (shown in dashed lines) set based on a previously updated actual ventricular rate interval is initiated in response to the ventricular sensed event signal 632, the frequency smoothing interval 642 may expire before the next atrial cycle, resulting in a pacing pulse before the next expected atrial event 612. Thus, frequency smoothing is suppressed in response to an intrinsic ventricular sensed event to facilitate sensing of the next atrial event 612 without interfering with the ventricular pacing pulse.

[0091] In response to the ventricular sensed event signal 632, an atrial refractory period 624 is initiated and followed by an A3 window 626. The next atrial event 612 is sensed after the end of the A3 window 628 and before the expiration of the relatively long VV lower frequency interval 640. The ventricular pacing pulse scheduled to occur at the expiration of the VV lower frequency interval 640 is inhibited or canceled. Alternatively, a ventricular pacing pulse 636 is delivered after the start of the AV interval that begins in response to the atrial sensed event signal 634. In this way, in this example, atrial synchronized ventricular pacing is reacquired on the next atrial event after the PVC.

[0092] The ventricular event interval ending with the ventricular pacing pulse 636 may not be used to update the actual ventricular rate interval because the ventricular event interval is initiated by the intrinsic ventricular sensed event 632 and does not affect the true atrial synchronized ventricular event interval. The most recently determined rate smoothing interval 642 based on the most recently updated actual ventricular rate interval using only the Vp-Vp interval may be initiated in response to the delivered ventricular pacing pulse 636. The rate smoothing interval 642 does not expire before the next A4 signal 614 is sensed, thereby facilitating the delivery of atrial synchronized ventricular pacing pulses 650, 652, each delivered in response to the sensed atrial events 614 and 616, respectively.

[0093] In a ventricular pacing system in which an atrial event signal has a relatively low or variable amplitude, applying a frequency smoothing interval after a ventricular pacing pulse and suppressing the frequency smoothing interval (and applying a lower frequency pacing interval instead) after an intrinsic ventricular sensed event facilitates recovery of atrial event sensing after an atrial event undersensing. The frequency smoothing techniques disclosed herein can be implemented in a variety of ventricular pacing systems and are particularly useful in ventricular pacing systems that include sensors (such as motion sensors or electrodes) for sensing atrial events from signals acquired within a ventricular chamber. Atrial event signals in a cardiac signal acquired within a ventricular chamber will have a relatively low signal-to-noise ratio compared to ventricular event signals.

[0094] Fig. 9 is a flow chart 700 of a method that may be performed by the pacemaker 14 according to another example. Fig. 9 The boxes marked with the same reference numerals in Figure 6 The same marked boxes shown in and combined above Figure 6 Described in Fig. 9 In an example of , the control circuit 206 is configured to determine at box 702 whether the sensed atrial event that triggers the delivery of a ventricular pacing pulse at box 322 is an early atrial event. An early atrial event can be detected based on sensing the atrial event within a threshold time interval after a preceding ventricular pacing pulse (or sensed R wave). In one example, the early atrial event is before 50 ms after the end of the A3 window, but other criteria for detecting early atrial events can also be defined. An early atrial event (e.g., an early atrial event after the end of the A3 window or during the A3 window) can be a premature atrial contraction (PAC). A PAC generates a short atrial cycle followed by a long atrial cycle corresponding to a compensatory pause that typically follows the PAC.

[0095] Therefore, to facilitate sensing of the next atrial event that ends the long interval, the control circuit 206 may adjust the rate smoothing increment to an extended increment at block 704 in response to identifying the sensed atrial event at the early event at block 702. At block 310, the extended increment is used to set an extended rate smoothing interval that begins after a ventricular pacing pulse delivered at the AV interval following the early atrial sensing event.

[0096] In other examples, oversensing may result in false detection of atrial contraction events. For example, if an A3 event (see Figure 4) occurs after the A3 window and crosses the A4 sensing threshold, it can be detected as an A4 event. A3 events typically occur earlier than A4 events after a ventricular pacing pulse (provided the atrial rate is relatively stable), such that an early atrial sensed event can be an indication of an over-sensed A3 event. By extending the rate smoothing interval by a longer increment after an early atrial sensed event, the time at which a true A4 event is sensed on the next cycle is not terminated prematurely by a rate smoothing interval that starts earlier after the ventricular pacing pulse that is synchronized to the early atrial sensed event. If the early event is an over-sensed A3 event, A4 event sensing can be reacquired during the extended rate smoothing interval on the next cardiac cycle, thereby returning to proper atrial synchronization to the ventricular pacing pulse.

[0097] At box 308, the control circuit 206 identifies the V pace delivered at box 322 immediately after the sensed atrial event, which is identified as an early atrial event at box 702. The V pace following the early atrial event is identified as a ventricular event that ends the ventricular rate interval, which is used to update the actual ventricular rate interval at box 308. After the frequency smoothing interval is set at box 310, after the ventricular pacing pulse delivered immediately after the early atrial event, the frequency smoothing interval can be set by adding (box 704) the extended frequency smoothing increment to the updated actual ventricular rate interval (box 308). For illustrative purposes, if the frequency smoothing interval is typically set to 100 ms longer than the updated actual ventricular rate interval at box 310, the extended frequency smoothing increment can be 150 ms or 200 ms. In some examples, the extended frequency smoothing increment is twice the normal increment added to the actual ventricular rate interval to set the frequency smoothing interval.

[0098] When the sensed A4 event is not identified as an early event (the "NO" branch of block 702), the control circuit 206 may return directly to block 308 without triggering the use of the extended rate smoothing increment at block 704. Thus, the control circuit 206 may add one rate smoothing increment to the actual ventricular rate interval for setting the rate smoothed pacing interval following an atrial event that is not identified as an early atrial event, and add another longer rate smoothing increment to the actual ventricular rate interval when the atrial event is identified as an early event (possibly a PAC or an over-sensed A3 signal).

[0099] In other examples, an extended frequency smoothing increment may be determined based on the early onset of an early atrial event. For example, if the Vp-Vp interval including the early atrial event is X ms shorter than the most recently updated actual ventricular rate interval, X ms may be added to the frequency smoothing interval. In some examples, the extended frequency smoothing interval following an early atrial event is determined as the updated actual ventricular rate interval plus a fixed frequency smoothing increment plus an extended frequency smoothing increment determined based on the early onset of the early atrial event.

[0100] Fig.10 800 is a flow chart of a method that may be executed by pacemaker 14 for updating a rate-smoothed base interval based on an actual ventricular rate interval, for example, after each Vp-Vp interval. Fig.10 The method can be found in Figure 6 and Fig. 9 Executed at block 310 of for setting the rate smoothing interval. In the example described above, the rate smoothing interval may be set by adding a predetermined increment (which may be extended in response to an early atrial sensing event) to an actual ventricular pacing rate interval determined based on a predetermined number of ventricular event intervals. Fig.10 In the example of , the rate smoothing base interval is determined based on the actual ventricular rate interval, and in Figure 6 and Fig. 9 The frequency smoothing interval is set by adding a delta to the frequency smoothing base interval at block 310 of . The frequency smoothing base interval may be determined using a single most recent Vp-Vp interval. After each Vp-Vp interval, the frequency smoothing base interval is adjusted based on a comparison between the frequency smoothing base interval and the Vp-Vp interval to track the actual Vp-Vp interval.

[0101] At block 802, the control circuit 206 may set the frequency smoothing basal interval to an initial value. In some examples, the frequency smoothing basal interval is initially set to a programmed lower frequency interval, such as the lower frequency interval minus a frequency smoothing increment. In the absence of an actual pacing frequency history, such as at initial implant, no actual ventricular pacing frequency may be used as a basis for the frequency smoothing interval. Therefore, the frequency smoothing basal interval may be initialized at block 801 based on a programmed lower frequency interval (LRI). Referring now to Fig. 9 , the actual ventricular rate interval based solely on the Vp-Vp interval cannot be updated at block 308 before the first ventricular pacing interval. Control circuit 206 may begin a rate smoothing interval initially set to the LRI in response to Vpacing (block 304). Thereafter, the rate smoothing interval set at block 310 may be adjusted based on the actual ventricular rate interval updated at block 308 in response to the Vp-Vp interval.

[0102] exist Fig.10At box 802, the ventricular event interval is identified. If the ventricular event interval includes a sensed intrinsic R wave, resulting in an R sense-R sense interval, an R sense-Vp interval, or a Vp-R sense interval, the Vp-Vp interval is not identified at box 804. The frequency smoothing base interval is not adjusted at box 805. The frequency smoothing interval may remain unchanged, i.e., equal to the previously set frequency smoothing interval, and not start in response to the sensed intrinsic R wave. However, when two consecutive ventricular pacing pulses occur, i.e., when the Vp-Vp interval occurs, as determined at box 804, the control circuit 206 determines the actual Vp-Vp interval as the actual ventricular rate interval and compares it with the current value of the frequency smoothing base interval at box 806. The frequency smoothing base interval is the frequency smoothing interval minus the frequency smoothing increment, (e.g., minus 100 ms or other frequency smoothing increment used to set the frequency smoothing interval). Initially, the rate smoothing base interval may be set to the lower rate interval minus the rate smoothing increment. Based on the comparison at block 806, the control circuit 206 updates the rate smoothing base interval to track the actual Vp-Vp interval, thereby causing the rate smoothing interval to track the actual ventricular pacing rate during atrial synchronous ventricular pacing.

[0103] The Vp-Vp interval identified at box 804 can end with a ventricular pacing pulse that is delivered at the current frequency smoothing interval (no sensed A4 event) or at the AV interval after the sensed A4 event. After the A4 event is sensed, the Vp-Vp interval identified at box 804 can be equal to, greater than, or less than the frequency smoothing basal interval, depending on the timing of the sensed A4 event after the leading V pace and the duration of the AV interval. The control circuit 206 can start the AV interval in response to the sensed A4 event and suppress the ventricular pacing pulse scheduled at the expiration of the frequency smoothing interval. In this way, a ventricular pacing pulse is delivered synchronously with the sensed A4 event, which can be earlier or later than the frequency smoothing basal interval or at the frequency smoothing basal interval.

[0104] If the actual Vp-Vp interval identified at block 804 is greater than the current frequency smoothed basal interval ("yes" branch of block 806), the A4 event may be sensed relatively late (e.g., slow atrial rate) and / or the AV interval may be relatively long, such that the V pace that ends the Vp-Vp interval is longer than the frequency smoothed basal interval. When the Vp-Vp interval is greater than the frequency smoothed basal interval, the frequency smoothed basal interval is updated at block 810 to the current frequency smoothed basal interval plus an adjustment interval, e.g., plus 7.8 ms, to account for possible slowing of the atrial rate. The frequency smoothed basal interval is used to set the frequency smoothed basal interval at 810. Fig. 9The frequency smoothing interval is set to be equal to the base interval plus the frequency smoothing increment, e.g., plus 100 to 200 ms. The frequency smoothing base interval is updated and used to set the next frequency smoothing interval based on a comparison between the actual Vp-Vp interval and the current frequency smoothing base interval, even if a ventricular pacing pulse scheduled at the frequency smoothing interval is suppressed due to a sensed A4 event starting the AV interval.

[0105] When no A4 event is sensed, the Vp-Vp interval may be equal to the frequency smoothing interval, in which case the actual Vp-Vp interval identified at box 804 is greater than the frequency smoothing base interval by the frequency smoothing increment (the "yes" branch of box 806). The frequency smoothing base interval is increased by an adjustment interval, for example, 7.8 ms or more, to effectively increase the frequency smoothing interval and facilitate A4 event sensing on the next ventricular cycle. The frequency smoothing base interval may be increased to up to, but not greater than, the lower frequency interval minus the frequency smoothing increment, in which case the frequency smoothing interval is set to the lower frequency interval. In other examples, the frequency smoothing base interval may be increased to up to the lower frequency interval, however, the frequency smoothing interval is limited to the maximum interval of the lower frequency interval, and the frequency smoothing interval is not set using an increment that would cause the frequency smoothing interval to exceed the lower frequency interval.

[0106] When the Vp-Vp interval is not greater than the frequency smoothed basal interval (the "No" branch of box 806), the Vp-Vp interval may include a sensed A4 event, and the actual Vp-Vp interval may be shorter than or equal to the frequency smoothed basal interval. When the Vp-Vp interval is equal to the frequency smoothed basal interval at box 814 (the "No" branch), no adjustment is made to the frequency smoothed basal interval at box 805. The frequency smoothed interval remains unchanged. When the Vp-Vp interval is less than the frequency smoothed basal interval (the "Yes" branch of box 814), the control circuit 206 updates the frequency smoothed basal interval at box 816 by reducing the current frequency smoothed basal interval by the adjustment interval (e.g., the current basal interval minus 7.8 ms or more). In this case, the sensed A4 event triggers V pacing at an interval shorter than the frequency smoothed basal interval, which may indicate an increased atrial rate. The frequency smoothed basal interval is updated to a shortened interval and Figure 6 and Fig. 9 Block 310 of is used to set the next rate smoothing interval for avoiding sudden changes in ventricular rate while still facilitating A4 event sensing.

[0107] In this manner, the frequency smoothing interval is updated based on the actual ventricular pacing rate (each Vp-Vp interval), and the frequency smoothing interval is initiated at each V pacing delivery. The actual ventricular pacing rate can be determined as a Vp-Vp interval that is used to update the frequency smoothing basal interval for each pacing cycle. By tracking the actual ventricular pacing rate by adjusting the frequency smoothing basal interval, the frequency smoothing interval can be increased on a beat-by-beat basis (excluding beats that include a sensed intrinsic R wave) until the LRI is reached as long as the actual Vp-Vp interval is increasing. The frequency smoothing interval can be decreased on a beat-by-beat basis as long as the actual Vp-Vp interval is less than the frequency smoothing interval (which corresponds to an increasing atrial rate). If the current ventricular cycle is not a Vp-Vp interval, for example, one or both of the leading or ending ventricular events are sensed R waves, the control circuit 206 can return to box 802 without adjusting the frequency smoothing basal interval. The rate smoothing basal interval may not be adjusted based on an interval that includes a sensed R wave, or when the actual Vp-Vp interval is equal to the rate smoothing basal interval (e.g., within a predetermined range of the rate smoothing basal interval), the rate smoothing basal interval may not be adjusted. In both cases, the rate smoothing basal interval and subsequent rate smoothing intervals set in response to delivered V pacing may be maintained at their current values.

[0108] Fig.11 900 is a timing diagram depicting sensed atrial contraction events, ventricular pacing pulses, and corresponding pacing control time intervals for providing pacing rate smoothing during atrial synchronous ventricular pacing according to one example. The control circuit 206 starts an AV interval 910 in response to each sensed atrial contraction event 902, 904, and 908, which can be an A4 event sensed from the motion signal. A first Vp-Vp interval 922 is defined by a leading V pace 912 and an ending V pace 914, which is delivered in the AV interval 910 after the sensed A4 event 902. The Vp-Vp interval 922 is determined as the actual ventricular rate interval. A first rate smoothed base interval (RSBI) 930 is compared to the actual Vp-Vp interval 922. Because RSBI 930 is greater than Vp-Vp interval 922, the next RSBI 932 is reduced by subtracting the adjustment interval (AI) from the first RSBI 930, such as RSBI=RSBI(i-1)-7.8 ms in one example.

[0109] The new RSBI 932 is used to set the rate smoothing interval (RSI) 940 equal to the adjusted RSBI 932 plus the rate smoothing increment 938. Because another A4 event 904 is sensed before the RSI 940 expires, the next V pace 916 is delivered after the sensed A4 event 904 at the AV interval 910. The resulting actual Vp-Vp interval 924 is compared to the current RSBI 932. Because the current RSBI 932 is greater than the actual Vp-Vp interval 924, the next RSBI 934 is also reduced by subtracting the adjustment interval. The next RSI 942 is set to the adjusted RSBI 934 plus the rate smoothing increment 938.

[0110] In this example, the decrease in atrial rate on the next beat causes the next A4 event 906 to occur later than the expiration of the RSI 942 and is not sensed by the control circuit 206. V pacing 918 is delivered at the expiration of the RSI 942. The resulting actual Vp-Vp 926 is longer than the current RSBI 934 (longer by the rate smoothing increment 938). Therefore, the next RSBI 936 is increased by adding the adjustment interval. The next RSI 944 is set to the increased RSBI 936 plus the rate smoothing increment 938. This increased RSI 944 allows the next A4 event 908 to be sensed before the expiration of the RSI 944, thereby making Fig.11 The final V pace 920 shown in FIG. 1 is delivered synchronously with the sensed A4 event 908 during the AV interval 910 .

[0111] like Fig.11 As shown in , the RSBI tracks the actual ventricular rate interval (determined as a single Vp-Vp interval in this example), and the RSI is set to the RSBI plus a frequency smoothing increment. The RSBI can be increased or decreased depending on the actual Vp-Vp interval, thereby causing the RSI to track the actual ventricular pacing rate during A4 event sensing as well, but the RSI is set to a longer frequency smoothing increment than the RSBI, which can facilitate the sensing of A4 events when sensing of (multiple) A4 events is temporarily lost due to atrial rate changes. It is recognized that in other examples, the current RSBI can be compared to the actual ventricular rate interval determined based on more than one Vp-Vp interval. For example, the current RSBI can be compared to the median or average of two or more recent Vp-Vp intervals.

[0112] The adjustment interval for adjusting RSBI based on a comparison with the actual ventricular rate interval may be programmable and, as an example, may be in the range of 5 ms to 20 ms. The adjustment interval may be fixed (until reprogrammed by the user) or may be automatically adjusted in some examples. For example, after a continuous increase in a threshold number of times in RSBI occurs due to pacing with RSI, the AI ​​may be increased to provide a larger step increase in RSI to facilitate recovery of A4 sensing. After a continuous decrease in a threshold number of times in RSBI occurs due to a shortening of the Vp-Vp interval including an A4 sensing event, the AI ​​may be increased so that when the atrial rate increases relatively rapidly, the RSBI shortens at a faster rate. In other examples, the adjustment interval for reducing RSBI and the adjustment interval for increasing RSBI may be set to different intervals and / or one of them is variable and the other is fixed. For example, the adjustment interval for increasing RSBI may be adjustable to allow RSI to increase faster when A4 sensing is lost, but the adjustment interval for decreasing RSBI may remain fixed to avoid rapid shortening of RSI, which may prevent A4 event sensing during atrial rate changes.

[0113] Additionally or alternatively, rate smoothing increment 938 may be a fixed, user programmable, or automatically adjusted interval. As described above, when a sensed A4 event is determined to occur early after a ventricular pacing pulse, rate smoothing increment 938 may be extended, such as doubled. In other examples, rate smoothing increment 938 may be automatically increased or decreased after a threshold number of ventricular pacing pulses delivered with RSI to facilitate more rapid adjustment of the Vp-Vp interval in the absence of a sensed A4 event, and thereby facilitate earlier resumption of A4 event sensing.

[0114] It should be understood that, depending on the example, certain actions or events in any of the methods described herein may be performed in a different order, may be added, merged, or omitted entirely (e.g., not all described actions or events are necessary to practice the method). In addition, in some examples, actions or events may be performed simultaneously rather than sequentially, for example, through multithreading, interrupt processing, or multiple processors. In addition, although for clarity, certain aspects of the present disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of the present disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0115] In one or more examples, the described functions can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, these functions can be stored as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium, such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer).

[0116] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuit systems. Accordingly, the term "processor" as used herein may refer to any of the above structures or any other structure suitable for implementing the techniques described herein. In addition, these techniques may be fully implemented in one or more circuits or logic elements.

[0117] Thus, pacemakers have been presented in the foregoing specification with reference to specific examples. It will be understood that the various aspects disclosed herein may be combined in combinations other than the specific combinations presented in the drawings. It will be understood that various modifications may be made to the referenced examples without departing from the scope of the present disclosure and the appended claims.

Claims

1. A pacemaker, comprising: a pulse generator configured to deliver ventricular pacing pulses via electrodes coupled to the pacemaker; a sensor configured to generate a signal including an atrial event signal; as well as a control circuit coupled to the sensor and the pulse generator and configured to: determining a ventricular rate interval during an atrial synchronized ventricular pacing mode by determining at least one ventricular event interval between two consecutive ventricular events; determining a rate-smoothed ventricular pacing interval based on the ventricular rate interval; detecting atrial events from the sensor signal; controlling the pulse generator to deliver a first ventricular pacing pulse in response to detecting the atrial event from the sensor signal; and The rate-smoothed ventricular pacing interval is initiated to schedule a next pacing pulse to be delivered by the pulse generator upon expiration of the rate-smoothed ventricular pacing interval.

2. The pacemaker according to claim 1, characterized in that: further comprising a sensing circuit including an R-wave detector for sensing an R-wave from a cardiac electrical signal via electrodes coupled to the pacemaker, Wherein, the control circuit is further configured to suppress setting of a next frequency smoothed ventricular pacing interval in response to the sensing circuit sensing an R wave.

3. The pacemaker according to claim 1 or 2, characterized in that: The control circuit is configured to determine the ventricular rate interval by determining at least one ventricular pacing interval extending from one ventricular pacing pulse delivered by the pulse generator to a next successively delivered ventricular pacing pulse.

4. The pacemaker according to claim 3, characterized in that: The control circuit is configured to: Set the frequency smoothing basic interval; comparing the ventricular rate interval to the rate-smoothed base interval; adjusting the frequency smoothing base interval based on the comparison; and The rate-smoothed ventricular pacing interval is set to the adjusted rate-smoothed base interval plus the rate-smoothed increment.

5. The pacemaker according to claim 4, characterized in that: The control circuit is configured to adjust the frequency smoothing basis interval based on the comparison by one of: In response to the ventricular rate interval being greater than the frequency smoothing base interval, increasing the frequency smoothing base interval; In response to the frequency smoothed base interval being equal to the ventricular rate interval, maintaining the frequency smoothed base interval at a current value; as well as In response to the ventricular rate interval being less than the frequency smoothing base interval, the frequency smoothing base interval is decreased.

6. The pacemaker according to any one of claims 1-2, characterized in that: The sensor is configured to generate a cardiac mechanical signal including an atrial contraction event signal; The control circuit is further configured to: detecting atrial contraction events from the cardiac mechanical signal, and The pulse generator is controlled to deliver the first ventricular pacing pulse in response to detecting the atrial contraction event.

7. The pacemaker according to any one of claims 1-2, characterized in that: The sensor comprises a motion sensor configured to generate a motion signal comprising an atrial contraction event signal; The control circuit is further configured to: responsive to delivering the first ventricular pacing pulse, setting a passive ventricular filling window; detecting an atrial contraction event from the motion signal after a start time of the passive ventricular filling window and during the rate-smoothed ventricular pacing interval; In response to detecting the atrial contraction event during the rate-smoothed ventricular pacing interval, inhibiting a next scheduled pacing pulse; and The pulse generator is controlled to deliver an atrial synchronized ventricular pacing pulse in response to detecting the atrial contraction event.

8. The pacemaker according to claim 7, characterized in that: The control circuit is further configured to: determining a ventricular pacing interval between the first ventricular pacing pulse and the atrial synchronized ventricular pacing pulse; updating the ventricular rate interval using the ventricular pacing interval; updating the rate-smoothed ventricular pacing interval based on the updated ventricular rate interval; and The updated rate-smoothed ventricular pacing interval begins with the atrial synchronized ventricular pacing pulse.

9. The pacemaker according to claim 8, characterized in that: The control circuit is configured to set the rate-smoothed ventricular pacing interval to the updated ventricular rate interval plus a predetermined increment.

10. The pacemaker according to any one of claims 1-2, characterized in that: The control circuit is configured to: determining whether the detected atrial event is an early atrial event that occurred before a threshold time interval from a preceding ventricular event; In response to the detected atrial event not being an early atrial event, determining the rate-smoothed ventricular pacing interval using a first increment; and In response to the detected atrial event being an early atrial event, the rate-smoothed ventricular pacing interval is determined using a second increment, the second increment being greater than the first increment.

11. The pacemaker according to claim 10, characterized in that: The control circuit is further configured to: In response to determining that the detected atrial event is an early atrial event, determining an early onset of the early atrial event; and Based on the determined early onset, the second increment is set.

12. The pacemaker according to any one of claims 1-2, characterized in that: The control circuit is further configured to: responsive to delivering the first ventricular pacing pulse, setting a first end time of a passive ventricular filling window, the first end time being a first time interval after the first ventricular pacing pulse; applying an atrial event sensing threshold to the sensor signal beginning at the first end time of the passive ventricular filling window; in response to expiration of the rate-smoothed ventricular pacing interval without the sensor signal crossing the atrial event sensing threshold, delivering a next pacing pulse; and In response to delivering the next pacing pulse, a second end time of the passive ventricular filling window is set, the second end time being a second time interval after the next ventricular pacing pulse, wherein the second time interval is within a predetermined frequency smoothing increment of the first time interval.

13. The pacemaker according to any one of claims 1-2, characterized in that: Further including: a housing enclosing the pulse generator, the sensor, and the control circuit and configured to be implanted within a ventricular heart chamber; Wherein, the sensor is configured to acquire the signals including atrial event signals from within the ventricular heart chamber.

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