Medical system for heart pacing

Abstract

A medical system configured to deliver a plurality of pacing signals to a heart of patient. In examples, the medical system is configured to provide at least first pacing signal to cause or assist in causing a first cardiac cycle of the heart and a second pacing signal to cause and / or assist in causing a second cardiac cycle of the heart. The medical system the medical system includes processing circuitry configured to control an interval separating the first pacing signal and the second pacing signal to cause the second pacing signal to be subsequent to a diastole indicator of the first cardiac cycle.

Description

Docket No: A0011909W001MEDICAL SYSTEM FOR HEART PACINGTECHNICAL FIELD

[0001] This disclosure is related to a medical system for the pacing of a heart of a patient.

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 687,973, filed August 28, 2024, the entire content of which is incorporated herein by reference.BACKGROUND

[0003] Medical devices are often placed in a subcutaneous pocket and coupled to one or more transvenous medical electrical leads carrying pacing and sensing electrodes positioned in the heart. Intracardiac pacemakers have recently been introduced that are implantable within a ventricular chamber of a patient’s heart for delivering ventricular pacing pulses without the use of electrical leads. Such pacemakers or other implantable medical devices may also be able to detect the occurrence of arrhythmias, such as fibrillation, tachycardia and bradycardia, in the patient’s heart. An implantable cardiac defibrillator may deliver electrical shocks to the patient’s heart in response to detection of a tachycardia or fibrillation to restore a normal heartbeat in the patient. In some cases, a single implantable medical device functions as both an implantable pacemaker and implantable cardiac defibrillator.

[0004] Implantable medical devices may include electrodes and / or other elements for physiological sensing and / or therapy delivery. The electrodes and / or other elements may be implanted at target locations selected to detect a physiological condition of the patient and / or deliver one or more therapies. For example, the electrodes and / or other elements may be delivered to a target location within an atrium or ventricle to sense intrinsic cardiac signals and deliver pacing or antitachyarrhythmia shock therapy from a medical device coupled to a lead. An implantable medical device may be associated with leads that position electrodes at a desired location, or may be leadless with electrodes integrated with and / or attached to a device housing (e.g., rather than medical leads). The implantable medical device may have the ability to wirelessly transmit data either to another device implanted in the patient or to another instrument located externally of the patient, or both.

[0005] An implantable medical device may be a pacemaker system configured to sense the electrical activity of the heart and deliver cardiac pacing based on the sensed electrical activity, via electrodes. In some examples, a pacemaker may be configured to provide dualDocket No: A0011909W001 chamber functionality, by sensing and / or stimulating the activity of both atria and ventricles, or other multi-chamber functionality. The pacemaker system may provide multi-chamber functionality via leads that extend to respective heart chambers, and / or the pacemaker system my include multiple pacemakers to provide multi-chamber functionality through implantation in respective chambers. In some examples, a pacemaker sized for implantation in a heart chamber may be configured with electrodes that enable multi-chamber functionality.SUMMARY

[0006] In an example, a medical system comprises: processing circuitry configured to control an interval of a medical device to limit a heart rate of a heart of a patient, the interval extending from a first pacing signal delivered by the medical device to cause or assist in causing a first cardiac cycle of the heart to a second pacing signal delivered by the medical device to cause or assist in causing a second cardiac cycle of the heart, wherein the processing circuitry is configured to: define an onset point within the first cardiac cycle, wherein the onset point is indicative of a cardiac indication of the heart occurring during the first cardiac cycle, and wherein the onset point precedes or is substantially concurrent with a diastole indicator indicative of a diastole of the first cardiac cycle, define an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and control the interval of the medical device to cause the second pacing signal to be subsequent to the end point, thereby limiting the heart rate of the heart.

[0007] In an example, a medical system comprises: a medical device is configured to deliver a first pacing signal to cause or assist in causing a first cardiac cycle of a heart of a patient and deliver second pacing signal to cause or assist in causing a second cardiac cycle of the heart, wherein the medical device is configured to deliver the second pacing signal following elapse of an interval after the delivery of the first pacing signal; a detector configured to detect one or more of a cardiac indication of the heart occurring during the first cardiac cycle or a diastole indicator indicative of a diastole of the first cardiac cycle, wherein the detector is configured to communicate a signal indicative of the detection; processing circuitry configured to: define an onset point within the first cardiac cycle using the signal, wherein the onset point precedes or is substantially concurrent with the diastole indicator, define an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and control the interval of the medical device to cause the second pacing signal to be subsequent to the end point, thereby limiting a heart rate of the heart.Docket No: A0011909W001

[0008] In an example, a method comprises: defining, by processing circuitry, an onset point within a first cardiac cycle, wherein the onset point is indicative of a cardiac indication of a heart of a patient occurring during the first cardiac cycle, wherein the onset point precedes or is substantially concurrent with a diastole indicator indicative of a diastole of the first cardiac cycle, and wherein the first cardiac cycle is caused or assisted by a first pacing signal delivered by a medical device, the medical device configured to deliver a second pacing signal to cause or assist in causing a second cardiac cycle of the heart following the delivery of the first pacing signal, and the medical device configured to separate the first pacing signal and the second pacing signal by an interval, defining, by the processing circuitry, an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and controlling, by the processing circuitry, the interval to cause the second pacing signal to be subsequent to the end point.

[0009] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. l is a conceptual diagram illustrating an example medical system including a medical device.

[0011] FIG. 2 is a schematic illustration of one or more signals provided by the medical system.

[0012] FIG. 3 is a schematic illustration of one or more signals provided by the medical system over a plurality of cardiac cycles of a heart.

[0013] FIG. 4 is a schematic illustration of one or more parameters defined by the medical signals using one or more signals provided by the medical system.

[0014] FIG. 5 illustrates an example technique for using the medical system.DETAILED DESCRIPTION

[0015] This disclosure describes a medical system configured to implant at least one electrode within tissue of a patient, such as a septal wall of the heart. The medical system is configured such that at least some portion positions within a heart of a patient, such as within an atrium, ventricle, coronary sinus, or other portions of the heart. The medical system includes a medical device configured to provide a pacing signal to cause pacing of the heart.Docket No: A0011909W001The medical device includes therapy delivery circuitry configured to deliver the pacing signal. In examples, the therapy delivery system includes pulse generator circuitry configured to generate the pacing signal. The medical system includes one or more electrodes configured to establish electrical communication with tissues of the heart to deliver the pacing signal to the heart and / or sense cardiac signals generated by the heart.

[0016] The medical device (e.g., a housing of the medical device) supports the therapy delivery circuitry. In some examples, the housing is sufficiently small such that the housing may be implanted within an anatomical volume defined by the patient’s heart (e.g., within a right ventricle (RV), right atrium (RA), coronary sinus (CS), or another area of the heart). The medical device may be configured such that the housing supports an electrode (e.g., one of the one or more electrodes). In examples, the medical system (e.g., the medical device) includes a fixation element configured to engage tissues of the heart when the medical device is implanted within the heart. The medical device may be configured such that, when the fixation element engages the tissue, the electrode is electrically coupled to the tissues of the heart and / or to a conduction system of the heart. The medical device may be configured to deliver the pacing signal via the electrode.

[0017] In some examples (e.g., when the housing may not be configured for implantation within a heart), the medical system includes one or more elongate bodies (e.g., leads) configured to deliver the pacing signal. An elongate body may be electrically coupled to the medical device (e.g., to the processing circuitry) and the electrode. The elongate body may be configured to extend from the medical device (e.g., when the medical device is subcutaneously implanted on the patient) to a location in the heart (e.g., a location within an anatomical volume of the heart). For example, the elongate body may be configured to extend from the medical device and through a vein of the heart (e.g., an innominate vein, an interior vena cava (IVC), and / or a superior vena cava (SVC)) to the location. In examples, the elongate body supports the electrode and / or the fixation element. The elongate body may be configured such that, when the fixation element engages the tissue, the electrode is electrically coupled to the tissues of the heart and / or to the conduction system of the heart.

[0018] The therapy delivery circuitry of the medical device is configured to deliver pacing signals to the heart. A pacing signal is configured to cause and / or assist in causing a cardiac cycle of the heart. The therapy delivery circuitry is configured to deliver the pacing signals at a pacing rate to cause the heart to provide a plurality of successive cardiac cycles. For example, the therapy delivery circuitry may provide a first pacing signal to the heart to cause or assist in causing a first cardiac cycle, followed by a second pacing signal to causeDocket No: A0011909 WO01 and / or assist in causing a second cardiac cycle, and so on. The therapy delivery circuitry may be configured to separate the first pacing signal and the second pacing signal (and, e.g., successive pacing signals) by an interval (e.g., a pacing interval). The therapy delivery circuitry may be configured to alter the pacing rate (e.g., the pacing interval) to support higher or lower heart rates of the patient.

[0019] The medical system disclosed herein includes processing circuitry configured to limit the interval of the therapy delivery circuitry based on one or more diastolic indicators detected in a cardiac cycle. A diastolic indicator may be indicative of one or more physiological events and / or occurrences expected to occur during a diastole of a cardiac cycle, such as a heart valve closure, a heart sound, and / or other physiological events and / or occurrences. The processing circuitry may limit the interval to mitigate a heart rate of a patient in order to, for example, encourage, enhance, and / or cause one or more desirable outcomes over the course of a cardiac cycle. For example, the processing circuitry may limit the interval of the therapy delivery circuity (and, e.g., limit the heart rate of the patient) to enhance the perfusion of blood in cardiac muscle of the heart during a cardiac cycle (e.g., during diastole of the cardiac cycle). In examples, the processing circuitry is a portion of the therapy delivery circuitry.

[0020] The medical system may be configured to deliver the pacing signal to tissues of the heart at any of one or more locations, such as a right ventricle (RV) of the heart, right atrium (RA) of the heart, left ventricle (LV) of the heart, and / or another area of the heart. For example, the medical system (e.g., the medical device, the therapy delivery circuitry, the one or more elongate bodies, and / or the one or more electrodes) may be configured to perform as a single chamber pacemaker which delivers the pacing signal to a location in the right atrium or right ventricle to cause the cardiac cycle.

[0021] In some examples, the medical system may be configured to perform as an atrioventricular (e.g., dual chamber) pacemaker which delivers an atrial pacing signal to a location in the right atrium and a ventricular pacing signal to location in the right ventricle to cause the cardiac cycle. The medical system may be configured to deliver the atrial pacing signal over a first time domain and deliver the ventricular pacing signal over a second time domain different from the first time domain. In examples, the first time domain commences prior to the second time domain. The therapy delivery circuitry may be configured to synchronize the second time domain relative to the first time domain and vice-versa (e.g., for A / V synchrony).

[0022] In some examples, the medical system may be configured to perform as an biDocket No: A0011909W001 ventricular pacemaker which delivers a primary pacing signal to a location in the right ventricle, a secondary pacing signal to a location in the left ventricle, and / or a tertiary pacing signal to a location in the right atrium to cause the cardiac cycle. The therapy delivery circuitry may be configured to deliver the primary pacing signal over a primary time domain, deliver the secondary pacing signal over a secondary time domain different from or substantially concurrent with the primary time domain, and / or deliver the tertiary pacing signal over a tertiary domain different from the primary time domain and the secondary time domain. In some examples, the tertiary time domain commences prior to the primary time domain and / or the secondary time domain. The therapy delivery circuitry may be configured to synchronize the primary time domain relative to the second time domain and / or the tertiary time domain, synchronize the secondary time domain relative to the primary time domain and / or the tertiary time domain, and / or synchronize the tertiary time domain relative to the primary time domain and / or the secondary time domain.

[0023] A cardiac cycle of the heart may generally include a series of pressure changes taking place within the heart and causing movement of blood through the heart and the body as a whole. The cardiac cycle (e.g., with or without a pacemaker) is generally divided into diastole and systole. Diastole generally begins with the closing of a semilunar valve (e.g., an aortic and / or pulmonary valve) of the heart and ends with the closing of a atrioventricular valve ( e.g., a mitral and / or tricuspid valve) of the heart. Diastole typically encompasses a ventricular relaxation and filling of the heart. For example, diastole may be generally indicative of blood vessels of the patient returning blood to the heart prior to (e.g., in preparation for) the next ventricular contraction. Systole generally begins with atrioventricular valve closure and ends with the closure of the semilunar valves. Systole typically represents ventricular contraction, which forces blood into the arteries of the patient.

[0024] The heart of the patient may produce heart sounds as the cardiac valves open and close during the cardiac cycle. The heart sounds may result from, for example, vibrations of the cardiac valves and / or other structures of the heart as the blood flows through the heart. The heart sounds may be generally grouped into an SI sound, an S2 sound, an S3 sound, and an S4 sound. The SI sound is indicative of closure of the atrioventricular (mitral and tricuspid) valves, and generally signals the end of diastole and the commencement of systole. The S2 sound represents closure of the semilunar (aortic and pulmonary) valves and generally signals the end of systole and / or the commencement of diastole. The S3 sound is typically an early diastolic sound occurring during the (e.g., relatively rapid) entry of blood from the atrium to the ventricle (e.g., during passive ventricular filling). The S4 sound mayDocket No: A0011909W001 be a later diastolic sound that corresponds to late ventricular filling through atrial contraction.

[0025] The SI sound, S2 sound, S3 sound, and / or S4 sound are thus generally indicative of physiological events expected to occur in the heart over a cardiac cycle. Hence, detection of the SI sound, the S2 sound, the S3 sound, and / or the S4 sound, and / or their timing with respect to each other, may serve as indications of where a given heart may be within a particular cardiac cycle. Further, expected and / or desired events during the cardiac cycle may be substantially mapped to the SI sound, S2 sound, S3 sound, and / or S4 sound. For example, as noted above, diastole and systole phases of the cardiac cycle (as well as other events over the cardiac cycle) may generally be tracked using the SI sound, S2 sound, S3 sound, and / or S4 sound.

[0026] The medical system may be configured to utilize the SI sound, S2 sound, S3 sound, and / or S4 heart, and / or their timing with respect to each other, to indicate periods during a cardiac cycle in which the blood is expected to perfuse in the cardiac muscle of the heart. For example, contraction of the myocardium during systole generally compresses the dense network of arteriole and capillaries present within cardiac muscle (e.g., the myocardium) of the heart. This compression may increase a resistance to blood flow during systole. During diastole, the myocardium substantially relaxes and the compression is relieved, such that blood may flow more freely into the arteriole and capillaries of the cardiac muscle (e.g., for delivery of oxygen to cardiac muscle). Correspondingly, heart muscles are mainly perfused with blood during diastole. Further, the cardiac timing of the cardiac cycle (e.g., the time required to complete a cardiac cycle) decreases as the heart rate of the heart increases, causing a decrease in the duration of diastole during cardiac cycles. Hence, at higher heart rates (for some patients), the decreased duration of diastole may negatively impact and / or result in low and / or inadequate coronary perfusion, potentially leading to myocardial ischemia, myocardial infarction (e.g., a heart attack), and / or other detrimental issues to the heart and patient. In examples, the medical system (e.g., the processing circuitry) is configured to cause the medical device (e.g., the therapy delivery circuitry) to limit a maximum heart rate of the patient to, among other reasons, assist in ensuring that a duration of diastole is sufficient to provide for adequate coronary perfusion during a cardiac cycle.

[0027] The medical system may be configured to limit the maximum heart rate (e.g., limit a pacing rate of the medical device) such that a diastole indicator indicative of diastole occurs over the cardiac cycle. For example, the diastole indicator may be an S2 indication indicative of the S2 sound, an S3 indication indicative of the S3 sound, an S4 indication indicative of the S4 sound, or another cardiac indication indicative of diastole. The processing circuitry isDocket No: A0011909W001 configured to limit an interval of the medical device extending from a first pacing signal to a second pacing signal (e.g., to limit the heart rate of the patient), such that a cardiac cycle includes at least the diastole indicator. In examples, the interval is a pacing interval defined by the medical device and intended to cause a particular heart rate of the patient. Thus, the processing circuitry may be configured to control the medical device such that an interval utilized by the medical device does not cause a heart rate that decreases the duration of diastole to where potentially inadequate coronary perfusion could result.

[0028] As an example, therapy delivery circuitry of the medical device may be configured to deliver an initial pacing signal to cause and / or assist in causing an initial cardiac cycle of a heart, and subsequently deliver a subsequent pacing signal to cause and / or assist in causing a subsequent cardiac cycle of the heart, as well as deliver further pacing signals following the subsequent pacing signal. The therapy delivery circuitry may be configured to separate the initial pacing signal and the subsequent pacing signal by an interval (e.g., a pacing interval). The therapy delivery circuitry may be configured to alter the interval to support higher or lower heart rates of the patient based on, for example, an assessment of the patient’s physical activity. In examples, the interval is associated with a base heart rate of the heart. The interval may be, for example, indicative of an elapsed time between delivery of the initial pacing signal and the subsequent pacing signal.

[0029] The processing circuitry is configured to control the therapy delivery circuitry such that the interval is likely to include (e.g., extend over) the diastole indicator of the first cardiac cycle. Stated similarly, the processing circuitry is configured to limit the interval such the subsequent pacing signal is not delivered at least until the diastole indicator of the initial cardiac cycle occurs or is expected to occur. For example, the diastole indicator (e.g., an S2 indication and / or an S3 indication) may occur or be expected to occur within an interlude defined by the processing circuitry and extending over at least some portion of the initial cardiac cycle caused and / or assisted by the initial pacing signal. The interlude may be used to define a minimum interval where, at intervals less than the minimum interval, delivery of the subsequent pacing signal may tend to truncate or even prevent the occurrence of the diastole indicator within the initial cardiac cycle, and / or truncate the elapsed time following the diastole indicator such that coronary perfusion during the initial cardiac cycle might be less than desired.

[0030] A pacing signal as used herein may refer to any pacing signal delivered by the therapy delivery circuitry and configured to cause and / or assist in causing a cardiac cycle of a heart. Medical system 100 may be configured to deliver the pacing signal to a right ventricleDocket No: A0011909W001(RV) of the heart, right atrium (RA) of the heart, a left ventricle (LV) of the heart, and / or another area of the heart. In some examples, such when the medical system is configured to deliver an atrial pacing signal to a location in the right atrium and deliver a ventricular pacing signal to location in the right ventricle to cause the cardiac cycle (e.g., configured as an atrioventricular pacemaker), the pacing signal may be either of the atrial pacing signal or the ventricular pacing signal. In some examples, such as when the medical system is configured to deliver a primary pacing signal to a location in the right ventricle, deliver a secondary pacing signal to a location in the left ventricle, and / or deliver a tertiary pacing signal to a location in the right atrium (e.g., configured as a bi-ventricular pacemaker), the pacing signal may any of the primary pacing signal, the secondary pacing signal, or the tertiary pacing signal.

[0031] In examples, an initial pacing signal and / or first pacing signal may refer to one of a particular pacing signal configured to be delivered to a particular location in a heart (e.g., an atrium or ventricle). A subsequent pacing signal and / or second pacing signal may refer to another of the particular pacing signal configured to be delivered to the particular location in the heart, wherein the subsequent and / or second pacing signal is delivered after (e.g., chronologically subsequent to) the initial pacing signal and / or first pacing signal. For example, the initial pacing signal and / or first pacing signal may refer to one of a pacing signal configured to be delivered to an atrium of a heart and the subsequent pacing signal and / or second pacing signal may refer to another of a pacing signal configured to be delivered to the atrium of the heart. In examples, the initial pacing signal and / or first pacing signal may refer to one of a pacing signal configured to be delivered to an ventricle of the heart and the subsequent pacing signal and / or second pacing signal may refer to another of a pacing signal configured to be delivered to the ventricle of the heart.

[0032] In some examples, within a given cardiac cycle caused and / or assisted by an initial pacing signal, the interlude commences at an onset point within the given cardiac cycle which precedes and / or coincides with the diastole indicator of the given cardiac cycle. The interlude may conclude at an end point within the given cardiac cycle which is subsequent to the diastole indicator. Stated similarly, the interlude may be defined such that a range (e.g., a chronological range) between the onset point and the end point includes the diastole indicator of the cardiac cycle. In some examples, the onset point is referenced to a heart sound indicator which occurs or is expected to occur over the given cardiac cycle, such as one of an SI indication, an S2 indication, and S3 indication, and / or an S4 indication. In some examples, the onset point may be defined by an initial pace signal (e.g., an atrial pacing signal)Docket No: A0011909W001 delivered to an atrium of the heart, wherein the initial pace signal is configured to cause the heart to initiate and / or experience the given cardiac cycle. The end point may be referenced to another heart sound indicator which occurs or is expected to occur during a diastole phase of the given cardiac cycle, such as the S3 indication and / or the S4 indication. In some examples, the end point is defined by a time window which commences at the onset point and elapses at the end point.

[0033] The processing circuitry is configured to control the interval of the medical device to cause delivery of a subsequent pacing signal to be subsequent to the end point of the interlude, such that the subsequent pacing signal is not delivered until the diastole indicator of a preceding cycle occurs or is expected to occur. Stated similarly, the processing circuitry is configured to control the medical device such that the interval between a first pacing pulse and a second pacing pulse is sufficient to allow the interlude within a first cardiac cycle caused by the first pacing pulse to complete prior to delivery of the second pacing pulse. Allowing the interlude to complete assists in ensuring that a diastole indicator of a first cardiac cycle caused by the first pacing signal occurs prior to delivery of the second pacing signal. Thus, the processing circuitry may be configured to cause the medical device (e.g., the therapy delivery circuitry) to limit a maximum heart rate of the patient such that the second pacing pulse to follows completion of the interlude within of the first cardiac cycle, such that a duration of diastole within the first cardiac cycle provides for adequate coronary perfusion during the first cardiac cycle.

[0034] In examples, the processing circuitry is configured to define the onset point of an interlude based on physiological characteristics of a specific patient. For example, the processing circuitry and / or medical device may be configured to detect one or more of the SI indication, S2 indication, S3 indication, and / or S4 indication as the medical device delivers pacing signals to the heart of the specific patient. The processing circuitry may be configured to define the onset point based on the SI indication, S2 indication, S3 indication, and / or S4 indication. For example, during a given cardiac cycle, the processing circuitry may be configured to detect the SI indication and / or the S2 indication and define the onset point relative to the SI indication and / or the S2 indication. In some examples, the processing circuitry may be configured to define the end point based on the SI indication, S2 indication, S3 indication, and / or S4 indication. For example, during the given cardiac cycle, the processing circuitry may be configured to detect the S3 indication and / or the S4 indication and define the end point relative to the S3 indication and / or the S4 indication. In some examples, the processing circuitry may be configured to define the end point using a timeDocket No: A0011909W001 window which commences at the onset point and chronologically extends over a time when the diastole indicator occurs or is expected to occur. The processing circuitry may be configured to define the end point by monitoring the elapse of the time window and defining the end point when the time window elapses.

[0035] The processing circuitry may be configured to control the interval (e.g., the pacing interval) of the medical device using the interlude. The processing circuitry may be configured to control the interval such that, following delivery of the first pacing pulse by the medical device, the pacing interval between the first pacing pulse and the second pacing pulse is such that the second pacing pulse is delivered subsequent to the end point of the interlude. In examples, the processing circuitry is configured to define a minimum interval based on the interlude and cause the medical device to utilize a pacing interval which is at least equal to the minimum interval. Hence, by limiting a pacing interval used by the medical device to deliver pacing signals to the heart, the processing circuitry may be configured to limit a heart rate of the heart. Limiting the heart rate of the heart may assist in with coronary perfusion during a diastole of cardiac cycles caused by the pacing signals.

[0036] As used here, an SI indication may be an indication of an SI sound produced by the heart over a cardiac cycle. An S2 indication may be an indication of an S2 sound produced by the heart over the cardiac cycle. An S3 indication may be an indication of an S3 sound produced by the heart over the cardiac cycle. An S4 indication may be an indication of an S4 sound produced by the heart over the cardiac cycle. In examples, the SI indication is produced by a detector. In examples, the medical system includes a detector configured to detect the indication of the SI sound, the indication of the S2 sound, the indication of the S3 sound, and / or the indication of the S4 sound. The detector may be configured to provide the SI indication, the S2 indication, the S3 indication, and / or the S4 indication to the processing circuitry.

[0037] For example, the detector may include an accelerometer configured to detect an acceleration caused by movement of the heart during the SI sound, the S2 sound, the S3 sound, and / or the S4 sound. Processing circuitry of the detector, the medical device, and / or another component of the system may be configured to define the SI indication, the S2 indication, the S3 indication, and / or the S4 indication based on the acceleration. In some examples, the detector may include a microphone configured to detect a sound caused by movement of the heart during the SI sound, the S2 sound, the S3 sound, and / or the S4 sound. The processing circuitry of the detector, the medical device, and / or another component of the system may be configured to define the SI indication, the S2 indication, the S3 indication,Docket No: A0011909W001 and / or the S4 indication based on the sound. In some examples, the detector may be configured to detect an electrocardiogram of the heart during the SI sound, the S2 sound, the S3 sound, and / or the S4 sound. The processing circuitry of the detector, the medical device, and / or another component of the system may be configured to define the SI indication, the S2 indication, the S3 indication, and / or the S4 indication based on the electrocardiogram. The detector may be configured to detect the indication of the SI sound, the indication of the S2 sound, the indication of the S3 sound, and / or the indication of the S4 sound in other ways in other examples.

[0038] FIG. l is a conceptual diagram illustrating a portion of an example medical system 100 configured to deliver therapy (e.g., pacing) to a heart 102 of a patient. The medical system includes a medical device 104 which includes therapy delivery circuitry 106 configured to provide pacing signals to cause pacing of heart 102. Medical device 104 includes a housing 108 supporting therapy delivery circuitry 106. Although depicted in FIG.1 with housing 108 positioned outside of heart 102 (e.g., outside of an anatomical volume defined by heart 102), in some examples, housing 108 may be sufficiently small such that medical device 104 may be implanted within an anatomical volume of heart 102 (e.g., within a right ventricle (RV), a right atrium (RA), a left ventricle (LV), a left atrium (LA), a coronary sinus (CS), or another area of heart 102).

[0039] Medical system 100 includes one or more electrodes such as an electrode 110 configured to deliver the pacing signal from therapy delivery circuitry 106 to heart 102. Electrode 110 may be electrically coupled to therapy delivery circuitry 106 (e.g., via one or more conductors (not shown)). Electrode 110 may be configured to establish electrical communication with tissues of heart 102 to deliver the pacing signal to heart 102 and / or sense cardiac signals generated by heart 102. In some examples, medical system 100 includes a return electrode 111 electrically coupled to therapy delivery circuitry 106 (e.g., via one or more conductors (not shown)). Medical system 100 (e.g., therapy delivery circuitry 106) may be configured to deliver pacing signals to and / or sense physiological parameters of heart 102 using electrode 110, return electrode 111, and / or other electrodes of medical system 100.

[0040] In examples, medical system 100 includes a fixation element 112 configured to engage tissues of heart 102 in proximity to a target site 114 when at least some portion of medical system 100 (e.g., electrode 110) is implanted within heart 102. For example, fixation element 112 may be configured to penetrate cardiac tissue of a septal wall in the RV, RA, LV, and / or LA of heart 102, or penetrate cardiac tissue in another area of heart 102. Medical system 100 may be configured such that, when fixation element 112 engages the tissue,Docket No: A0011909W001 electrode 110 is electrically coupled to the tissues of heart 102. In examples, fixation element 112 mechanically supports electrode 110. In some examples, electrode 110 may be mechanically supported by another portion of medical system 100. In some examples, for example when housing 108 is configured to position within an anatomical volume of heart 102, housing 108 may support electrode 110 and / or fixation element 112.

[0041] In some examples, for example when housing 108 is configured to position outside of heart 102, such as configured to be subcutaneously implanted on a patient, medical system 100 may include one or more elongate bodies (e.g., leads) such as medical lead 116. Medical lead 116 may be configured to extend from medical device 104 through vasculature of the patient. Medical lead 116 may include a lead body 118 defining a distal portion 120 of lead body 118 (“lead body distal portion 120”) and a proximal portion 122 of lead body 118 (“lead body proximal portion 122) substantially opposite lead body distal portion 120. Medical system 100 may be configured such that lead body proximal portion 122 is attached to housing 108 when lead body distal portion 120 is positioned in the vicinity of target site 114. Medical system 100 may include other leads coupled to medical device 104 and extending into heart 102 instead of or in addition to medical lead 116. For example, medical system 100 may include a lead coupled to medical device 104 and extending into the RA of heart 102, a lead coupled to medical device 104 and extending into the LV of heart 102, and / or a lead coupled to medical device 104 and extending into another portion (e.g., another anatomical volume) of heart 102. In some examples, lead body 118 (e.g., lead body distal portion 120) supports fixation element 112 and / or electrode 110. In some examples, fixation element 112 extends distal to lead body distal portion 120.

[0042] Therapy delivery circuitry 106 and / or other circuitry of medical system 100 is configured to deliver pacing signals and / or receive sensing signals from electrodes 110, 111 and / or other electrodes and / or sensors within medical system 100. A pacing signal may be configured to cause a cardiac cycle of heart 102. Therapy delivery circuitry 106 is configured to deliver the pacing signals at a pacing rate to cause heart 102 to provide a plurality of successive cardiac cycles. For example, therapy delivery circuitry 106 may deliver a first pacing signal (e.g., via electrode 110, 111) to heart 102 to cause a first cardiac cycle of heart 102, followed by delivery of a second pacing signal to heart 102 cause a second cardiac cycle of heart 102, and so on. In examples, therapy delivery circuitry 106 is configured to separate the first pacing signal and the second pacing signal (and, e.g., successive pacing signals) by an interval (e.g., a pacing interval). Therapy delivery circuitry 106 may be configured to alter the pacing rate (e.g., the pacing interval) to support higher or lower heart rates of heart 102.Docket No: A0011909W001

[0043] Therapy delivery circuitry 106 may be configured to deliver the pacing signal to heart 102 at any of one or more locations, such as the RV, the RA, the LV, and / or another portion of the heart. For example, therapy delivery circuitry 106 may be configured to perform as a single chamber pacemaker which delivers the pacing signal to a location in the RA or RV to cause and / or assist a cardiac cycle of heart 102. Therapy delivery circuitry 106 may be configured to perform as an atrio-ventricular (e.g., dual chamber) pacemaker which delivers the pacing signal to a location in the RA and a location in the RV to cause and / or assist the cardiac cycle. In some examples, therapy circuitry 106 is configured to perform as an bi-ventricular pacemaker which delivers the pacing signal to a location in the RV, the LV, and / or the RA to cause and / or assist the cardiac cycle.

[0044] Medical system 100 is configured to limit the interval of therapy delivery circuitry 106 based on one or more diastole indicators detected in a cardiac cycle. A diastole indicator may be indicative of one or more physiological events and / or occurrences expected to occur during a diastole of a cardiac cycle, such as a heart valve closure, a heart sound, and / or other physiological events and / or occurrences. In examples, the diastole indicator is one or more of an S2 indication indicative of an S2 sound of heart 102, an S3 indication indicative of an S3 sound of heart 102, and / or an S4 indication indicative of an S4 sound of heart 102. Medical system 100 may be configured to limit the interval of therapy delivery circuitry 106 to mitigate a heart rate of heart 102 in order to, for example, encourage, enhance, and / or cause one or more desirable outcomes over the course of a cardiac cycle. For example, medical system 100 may limit the interval of therapy delivery circuity 106 (and, e.g., limit the heart rate of heart 102) to enhance the perfusion of blood in cardiac muscle of heart 102 during the cardiac cycle (e.g., during diastole of the cardiac cycle).

[0045] Medical system 100 includes processing circuitry 124 is configured to control therapy delivery circuitry 106 such that an interval between a first pacing signal delivered by therapy delivery circuitry 106 and a subsequent second pacing signal delivered by therapy delivery circuitry 106 is likely to include (e.g., extend over) the diastole indicator of the first cardiac cycle caused by the first pacing signal. Hence, processing circuitry 124 may be configured to limit the interval such the second pacing signal is not delivered at least until the diastole indicator of the first cardiac cycle occurs or is expected to occur. In examples, the diastole indicator occurs or is expected to occur within an interlude extending from an onset point within the first cardiac cycle to an end point within the first cardiac cycle. The interlude may be used to define a minimum interval where, at intervals less than the minimum interval, delivery of the second pacing pulse may tend to truncate or even prevent the occurrence ofDocket No: A0011909W001 the diastole indicator within the first cardiac cycle, and / or truncate the elapsed time following the diastole indicator such that coronary perfusion during the first cardiac cycle might be less than desired. In examples, processing circuitry 124 is configured to control therapy delivery circuitry 106 using a communication link 127.

[0046] Processing circuitry 124 may be configured to define the interlude based on physiological characteristics of a specific patient. For example, medical system 100 may be configured to detect a cardiac indication which occurs over a cardiac cycle of heart 102, such as an SI sound, an S2 sound, and S3 sound, and S4 sound, and / or another cardiac indication. In examples, medical system 100 includes a detector 126 configured to detect the cardiac indication. Detector 126 may be configured to communicate a signal to processing circuitry 124 (e.g., using a communication link 128) indicative of the cardiac indication. In examples, detector 126 is configured to detect an SI sound produced by heart 102 and communicate an SI indication to processing circuitry 124 in response to the SI sound detection. Detector 126 may be configured to detect an S2 sound produced by heart 102 and communicate an S2 indication to processing circuitry 124 in response to the S2 sound detection. Detector 126 may be configured to detect an S3 sound produced by heart 102 and communicate an S3 indication to processing circuitry 124 in response to the S3 sound detection. Detector 126 may be configured to detect an S4 sound produced by heart 102 and communicate an S4 indication to processing circuitry 124 in response to the S4 sound detection. Detector 126 may be configured to detect other cardiac indications of heart 102 and communicate other communications to processing circuitry 124 in response to detecting the other cardiac indications. Processing circuitry 124 may be configured to define the interlude based on one or more of the SI indication, the S2 indication, the S3 indication, the S4 indication, and / or the other cardiac indications, such that processing circuitry 124 defines the interlude based on physiological characteristics of a specific patient.

[0047] Processing circuitry 124 is configured to limit the interval (e.g., a pacing interval) of therapy delivery circuitry 106 to allow time for coronary perfusion of heart 102 following delivery of a first pacing signal prior to a subsequent delivery of a second pacing signal. In examples, processing circuitry 124 is configured to define an interlude which includes a diastole indicator to limit the interval. In examples, during a given cardiac cycle, processing circuitry 124 is configured to define the onset point of the interlude relative to the SI indication, the S2 indication, the S3 indication, the S4 indication, and / or another indication of a cardiac indication received from detector 126. For example, in some examples, processing circuitry 124 may define the onset point to be substantially concurrent with or subsequent toDocket No: A0011909W001 any one of the SI indication, the S2 indication, the S3 indication, the S4 indication, or the other indication. In some examples, processing circuitry 124 may define the onset point based on an initial pace signal (e.g., an atrial pacing signal) delivered to an atrium (e.g., the RA) of heart 102. The initial pace signal may be configured to cause heart 101 to initiate and / or experience a cardiac cycle. Hence, processing circuitry 124 may define the onset point for a given cardiac cycle of heart 102 such that the onset point precedes or coincides with a diastole indicator indicative of a diastole phase of the given cardiac cycle.

[0048] Processing circuitry 124 is configured to define the end point of the interlude such that the end point of the given cardiac cycle is subsequent to (e.g., chronologically subsequent to) the onset point of the given cardiac cycle. In some examples, during the given cardiac cycle, processing circuitry 124 is configured to define the end point of the interlude relative to the S3 indication, the S4 indication, and / or an additional indication of a cardiac indication received from detector 126. For example, processing circuitry 124 may define the end point to be substantially concurrent with or subsequent to one of the S3 indication, the S4 indication, or the additional indication. Hence, processing circuitry 124 may define the end point for the given cardiac cycle of heart 102 such that the end point is subsequent to commencement of the diastole phase of the given cardiac cycle. The interlude between the onset point and the end point within the given cardiac cycle may thus provide for adequate and / or increased cardiac perfusion within heart 102 during the diastole phase of the given cardiac cycle.

[0049] In some examples, processing circuitry 124 may be configured to define the end point of the given cardiac cycle using a time window which commences at the onset point and chronologically extends over a time when a diastole indicator (e.g., one of the S2 indication, the S3 indication, and / or the S4 indication) occurs or is expected to occur. Processing circuitry 124 may define the end point by monitoring the elapse of the time window subsequent to defining the onset point, and defining the end point when the time window elapses. In examples, the time window commences at the onset point and concludes at the end point.

[0050] Processing circuitry 124 is configured to control therapy delivery circuitry 106 such that, when therapy delivery circuitry 106 delivers an initial pacing signal causing the given cardiac cycle and a subsequent pacing signal causing a subsequent cardiac cycle following the given cardiac cycle, therapy delivery circuitry 106 delivers the subsequent pacing signal following (e.g., subsequent to) the end point defined for the given cardiac cycle. Thus, processing circuitry 124 may use the interlude within the given cardiac cycle to avoidDocket No: A0011909W001 and / or limit a truncation of the diastole phase of the given cardiac cycle by controlling when therapy delivery circuitry 106 may deliver the subsequent pacing signal. Limiting the delivery of the subsequent pacing signal may assist in ensuring that a duration of the diastole phase of the given cardiac cycle is sufficient for coronary perfusion of heart 102 during the given cardiac cycle.

[0051] In some examples, processing circuitry 124 is configured to define the onset point for each cardiac cycle of heart 102. Processing circuitry 124 may be configured to define an end point corresponding to each onset point. For example, processing circuitry 124 may define a first onset point (e.g., based on an SI indication, and S2 indication, an S3 indication, or an S4 indication) and a first end point (e.g., based on the S3 indication, the S4 indication, or a time window) for a first cardiac cycle caused by a first pacing signal delivered to heart 102. Processing circuitry 124 may control therapy delivery circuitry 106 such that therapy delivery circuitry 106 delivers a second pacing signal subsequent to the first end point. Processing circuitry 124 may define a second onset point and a second end point for a second cardiac cycle caused by the second pacing signal. Processing circuitry 124 may control therapy delivery circuitry 106 such that therapy delivery circuitry 106 delivers a third pacing signal subsequent to the second end point. Processing circuitry 124 may define a third onset point and a third end point for a third cardiac cycle caused by the third pacing signal and cause therapy delivery circuitry 106 to deliver a fourth pacing signal subsequent to the third end point, and so on for successive pacing signals to heart 102.

[0052] In some examples, for example when processing circuitry 124 defines an end point based on a time window which elapses following an onset point, processing circuitry 124 may be configured to define the time window based on the cardiac indications of heart 102. Hence, processing circuitry 124 may be configured to define the time window based on specific physiological characteristics of heart 102. For example, during an initial period, processing circuitry 124 may be configured to define an onset point for a specific cardiac cycle and monitor for the occurrence of a diastole indicator (e.g., an S2 indication, an S3 indication, or an S4 indication) of the specific cardiac cycle. Processing circuitry 124 may define a reference window (e.g., a reference time window) commencing at the reference onset point and chronologically extending at least to (e.g., extending to some period after) the diastole indicator. Processing circuitry 124 may utilize the thus defined reference window as the time window for successive pacing signals delivered to heart 102, such that the time window is specific to heart 102. In some examples, processing circuity 124 is configured to define a plurality of reference windows by defining a reference window for each of aDocket No: A0011909W001 plurality of cardiac cycles during the initial period. Processing circuitry 124 may define the time window using the plurality of reference windows (e.g., as an average of and / or some other function of the plurality of reference windows).

[0053] In some examples, processing circuitry 124 is configured to associate the reference window thus determined with a heart rate of heart 102. For example, processing circuitry 124 may be configured to determine and / or detect a heart rate of heart 102 based on a communication from detector 126 or another portion of medical system 100 as processing circuitry 124 determines the reference window. Processing circuitry 124 may be configured to store the reference window and the associated heart rate in, for example, a memory of processing circuitry 124 and / or medical system 100. Processing circuitry 124 may be configured to define an interlude (e.g., define a time window) using the reference window when system 100 indicates that heart 102 is experiencing the associated heart rate. In some examples, processing circuitry 124 is configured to determine a heart rate of heart 102 and select a reference window (e.g., from a set of reference windows) based on the heart rate.

[0054] For example, processing circuitry 124 may be configured to select a first reference window when processing circuitry 124 determines (e.g., based on a communication from detector 126 or another portion of medical system 100) that heart 102 has a first heart rate. Processing circuitry 124 may be configured to select a second reference window when processing circuitry 124 determines heart 102 has a second heart rate, select a third reference window when processing circuitry 124 determines heart 102 has a third heart rate, and so on. Processing circuitry 124 may define the time window based on the thus selected reference window. Selecting the reference window based on a heart rate of heart 102 may allow therapy delivery circuitry 106 to alter (e.g., increase) the heart rate of heart 102 based on, for example, an activity level of a patient, while also continuing to maintain a duration of diastole to enhance coronary perfusion.

[0055] Processing circuitry 124 may be configured to define the set of reference windows, such that the set of reference windows are relatively specific to a patient. For example, during the initial period, processing circuitry 124 may be configured to define the first reference window based on the cardiac indications of heart 102 when heart 102 has the first heart rate (e.g., when the patient has a first activity level), define the second reference window when heart 102 has the second heart rate (e.g., when the patient has a second activity level), define the third reference window when heart 102 has the third heart rate (e.g., when the patient has a third activity level), and so on. Processing circuitry 124 may associate the first reference window with the first heart rate, associate the second reference window withDocket No: A0011909W001 the second heart rate, associate the third reference window with the third heart rate, and associate each of other determined reference windows with a particular heart rate, such that processing circuitry 124 defines the set of reference windows for the patient. Processing circuitry 124 may be configured to utilize the set of reference windows by determining a present heart rate of the patient (e.g., a heart rate of heart 102) and selecting the reference window associated with the present heart rate. Processing circuitry 124 may define the time window used to define the end point of an interlude using the thus selected reference window, such that processing circuitry 124 utilizes a time window determined using the physiological characteristics of the patient.

[0056] In some examples, processing circuitry 124 may be configured to associate a reference time window with a particular onset point defined by processing circuitry 124. For example, processing circuitry 124 may be configured to define the first reference window, the second reference window, and the third reference window when processing circuitry 124 is defining the onset point using a first cardiac indication (e.g., one of the SI indication, the S2 indication, the S3 indication, and / or the S4 indication of heart 102). Processing circuitry 124 may be configured to define a fourth reference window, a fifth reference window, and a sixth reference window when processing circuitry 124 is defining the onset point using a second cardiac indication (e.g., another of the SI indication, the S2 indication, the S3 indication, and / or the S4 indication of heart 102). Processing circuitry 124 may associate the first reference window, the second reference window, and the third reference window with the first cardiac indication and associate the fourth reference window, the fifth reference window, and the sixth reference window with the second cardiac indication. Processing circuitry 124 may be configured to select a reference time window based on the cardiac indication used to determine the onset point (e.g., in addition to the heart rate of heart 102). Selecting a reference time window based on a cardiac indication used to define the onset point may provide additional flexibility for processing circuitry 124 if, for example, processing circuitry 124 uses a combination of cardiac indications to define the onset point, and / or shifts from defining the onset point using a first cardiac indication (e.g., during a first cardiac cycle) to defining the onset point using a second cardiac indication (e.g., during a second cardiac cycle).

[0057] Detector 126 may be configured to detect a cardiac indication of heart 102 (e.g., an SI sound, an S2 sound, an S3 sound, an S4 sound, and / or other cardiac indications) in any manner. In examples, detector 126 includes a housing 130 (“detector housing 130”) supporting an accelerometer 132. Accelerometer 132 may be configured to sense anDocket No: A0011909W001 acceleration (e.g., of accelerometer 132 and / or detector housing 130) caused by the cardiac indication and produce a signal indicative of the acceleration. Processing circuitry 124 and / or other circuitry of medical system 100 may be configured to identify the cardiac indication (e.g., the SI sound, the S2 sound, the S3 sound, the S4 sound, and / or the other cardiac indication) using the signal indicative of the acceleration. In some examples, detector housing 130 supports an electrode 134 configured to sense an electrocardiogram of heart 102. Detector 126 may be configured to produce a signal indicative of the electrocardiogram. Processing circuitry 124 and / or other circuitry of medical system 100 may be configured to identify the cardiac indication using the signal indicative of the electrocardiogram. In some examples, detector housing 130 supports a microphone 136 configured to sense sound waves produced by heart 102. Detector 126 may be configured to produce a signal indicative of the sound waves. Processing circuitry 124 and / or other circuitry of medical system 100 may be configured to identify the cardiac indication using the signal indicative of the sound waves. Detector 126 may be configured to detect a cardiac indication of heart 102 in other manners in other examples.

[0058] Although detector 126, accelerometer 132, electrode 134, and microphone 136 are depicted as supported by detector housing 130 in FIG. 1, this is not required in other examples. In some examples, any of detector 126, accelerometer 132, electrode 134, and / or microphone 136, and / or any circuitry (e.g., operating circuitry and / or processing circuitry) associated with detector 126, accelerometer 132, electrode 134, and / or microphone 136 may be supported by housing 108 of medical device 104, medical lead 116, another medical lead of medical system 100 (e.g., another medical lead not depicted in FIG. 1), and / or another component of medical system 100 (e.g., another component not depicted in FIG. 1). Further, although depicted as positioned outside of an anatomical volume (e.g., a chamber) defined by heart 102. Medical device 104 and housing 108 may be configured to be positioned within an anatomical volume (e.g., a chamber) defined by heart 102. In some examples, housing 108 may support electrode 110.

[0059] Hence, medical system 100 is configured to limit the maximum heart rate (e.g., limit a pacing rate of therapy delivery circuitry 106) such that a diastole indicator indicative of diastole occurs over a cardiac cycle caused by therapy delivery circuitry 106. The diastole indicator may be an S2 indication indicative of the S2 sound, an S3 indication indicative of the S3 sound, an S4 indication indicative of the S4 sound, or another cardiac indication indicative of diastole. Processing circuitry 124 is configured to limit an interval (e.g., a pacing interval) of therapy delivery circuitry 106 intended to cause a particular heart rate ofDocket No: A0011909W001 heart 102, such that an interval utilized by therapy delivery circuitry 106 does not cause a heart rate that decreases a duration of diastole to where potentially inadequate coronary perfusion could result.

[0060] As an example, FIG. 2 illustrates signals 138 which might be generated by detector 126 in response to cardiac activity of heart 102. Signals 138 may include, for example, one or more of an accelerometer signal 140 produced using accelerometer 132, a sound signal 142 produced using microphone 136, an electrocardiogram signal 144 (“ECG signal 144”) produced using electrode 134, and / or other signals indicative of one or more cardiac indications of heart 102 (e.g., one or more of an SI indication, an S2 indication, an S3 indication, an S4 indication, and / or indicative of another cardiac indication). Signals 138 are illustrated using an axis MG and a chronological axis TIME. The axis MG indicates relative magnitudes between a first portion of a particular signal of signals 138 (e.g., one of accelerometer signal 140, sound signal 142, or ECG signal 144) and a second portion of the particular signal, and is not intended to indicate relative magnitudes between a first signal (e.g., one of accelerometer signal 140, sound signal 142, or ECG signal 144) and a second signal (e.g., another of accelerometer signal 140, sound signal 142, or ECG signal 144).

[0061] FIG. 3 illustrates a representative signal 145 generated by detector 126 in response to cardiac activity of heart 102 over a plurality of cardiac cycles. FIG. 4 illustrates a representative signal 146 generated by detector 126 over a first cardiac cycle Cl and a second cardiac cycle C2. Although representative signal 145, 146 is illustrated as similar to sound signal 142 for clarity, representative signal 145, 146 may be accelerometer signal 140, sound signal 142, ECG signal 144, and / or another signal indicative of one or more cardiac indications of heart 102. Representative signal 145 may be an example of representative signal 146.

[0062] Referring largely to FIG. 2, signals 138 extend chronologically over a first cardiac cycle Cl, a second cardiac cycle C2, and into a third cardiac cycle C3. Detector 126 produces at least one of signals 138 such that the at least one of signals 138 delineates one or more of an SI indication over a cardiac cycle, an S2 indication over the cardiac cycle, an S3 indication over the cardiac cycle, an S4 indication over the cardiac cycle, and / or another cardiac indication over the cardiac cycle. For example, detector 126 may be configured such that accelerometer signal 140 delineates an indication Pl indicative of an SI sound produced by heart 102 during first cardiac cycle Cl (“S 1 (1)”), an indication P2 indicative of an S2 sound produced by heart 102 during first cardiac cycle Cl (“S2(l)”), an indication P3 indicative of an S3 sound produced by heart 102 during first cardiac cycle Cl (“S3 (1)”),Docket No: A0011909W001 and / or an indication P4 indicative of an S4 sound produced by heart 102 during first cardiac cycle Cl (“S4(l)”). Detector 126 may be configured such that sound signal 142 delineates an indication P5 indicative of S 1 (1), an indication P6 indicative of S2(l), an indication P7 indicative of S3 (1), and / or an indication P8 indicative of S4(l). Detector 126 may be configured such that ECG signal 144 delineates an indication P9 indicative of S 1(1), an indication PIO indicative of S2(l), an indication Pl 1 indicative of S3( 1 ), and / or an indication P12 indicative of S4(l) during first cardiac cycle Cl.

[0063] In examples, detector 126 produces at least one of signals 138 such that the at least one of signals 138 delineates one or more of another cardiac indication such as a first cardiac indication Bl and / or a second cardiac indication B2 over the cardiac cycle. First cardiac indication Bl and / or second cardiac indication B2 may be indicative of any cardiac indication produced by heart 102 over a cardiac cycle. For example, detector 126 may be configured such that accelerometer signal 140 delineates an indication P13 indicative of first cardiac indication Bl produced by heart 102 during first cardiac cycle Cl (“Bl(l)”) and / or an indication P14 indicative of second cardiac indication B2 produced by heart 102 during first cardiac cycle Cl (“B2(l)”). Detector 126 may be configured such that sound signal 142 delineates an indication P15 indicative of Bl(l), and / or an indication P16 indicative of B2(l). Detector 126 may be configured such that ECG signal 142 delineates an indication P17 indicative of Bl(l), and / or an indication P18 indicative of B2(l).

[0064] Therapy delivery circuitry 106 is configured to deliver one or more pacing signals (e.g., via medical lead 116) to cause heart 102 (FIG. 1) to undergo first cardiac cycle Cl and / or second cardiac cycle C2. For example, therapy delivery circuitry 106 may be configured to deliver a first pacing signal at a first time T1 to cause and / or assist in causing heart 102 to produce first cardiac cycle Cl, a second pacing signal at a second time T2 to cause and / or assist in causing heart 102 to produce second cardiac cycle C2, and / or a third pacing signal at a third time T3 to cause and / or assist in causing heart 102 to produce third cardiac cycle C3. In examples, therapy delivery circuitry 106 is configured to separate the first pacing signal and the second pacing signal by an interval INTI (e.g., a pacing interval) and / or separate the second pacing signal and the third pacing signal by an interval INT2 (e.g., a pacing interval).

[0065] Detector 126 may be configured such that signals 138 delineate the at least one or more of the SI indication, the S2 indication, the S3 indication, the S4 indication, and / or another cardiac indication (e.g., first cardiac indication Bl and / or second cardiac indication B2) on an ongoing basis as heart 102 produces successive cardiac cycles. For example,Docket No: A0011909W001 detector 126 may be configured such that accelerometer signal 140 delineates an SI sound produced by heart 102 during second cardiac cycle Cl (“SI (2)”), delineates an S2 sound produced by heart 102 during second cardiac cycle C2 (“S2(2)”), delineates an S3 sound produced by heart 102 during second cardiac cycle C2 (“S3 (2)”), delineates an S4 sound produced by heart 102 during second cardiac cycle C2 (“S4(2)”), delineates a first cardiac indication produced by heart 102 during second cardiac cycle C2 (“Bl(2)”), and / or delineates a second cardiac indication produced by heart 102 during second cardiac cycle C2 (“B2(2)”). Detector 126 may be configured such that sound signal 142 delineates SI (2), S2(2), S3 (2), S4(2), Bl(2), and / or B2(2), and / or be configured such that ECG 142 delineates Sl(2), S2(2), S3(2), S4(2), Bl(2), and / or B2(2). Detector 126 may be configured such that signals 138 delineate the at least one or more of the SI indication, the S2 indication, the S3 indication, the S4 indication, the first cardiac indication, and / or the second cardiac indication in cardiac cycles subsequent to second cardiac cycle C2, such as within third cardiac cycle C3 and other subsequent cardiac cycles.

[0066] In some examples, therapy delivery circuitry 106 may be configured to define INTI as a first chronological interval over which a certain amount of time elapses. In some examples, therapy delivery circuitry 106 may be configured to define INTI based on a first detection of one or more cardiac indications of heart 102 during first cardiac cycle Cl (e.g., a detection of one or more of Sl(l), S2(l), S3(l), S4(l), Bl(l), and / or B2(l)). Therapy delivery circuitry 106 may be configured to define INT2 as a second chronological interval (which may, for example, be substantially equal to the first chronological interval) over which an amount of time elapses. In examples, therapy delivery circuitry 106 may be configured to define INT2 based on detection of one or more cardiac indications of heart 102 during second cardiac cycle C2 (e.g., a detection of one or more of SI (2), S2(2), S3 (2), S4(2), Bl (2), and / or B2(2)). In examples, therapy delivery circutiryl06 is configured to deliver a pacing signal intended to prompt heart 102 to commence a cardiac cycle commencing with an SI sound such that, for example, the SI sound is produced shortly after delivery of the pacing pulse. Therapy delivery circuitry 106 may be configured to alter a pacing rate (e.g., to alter the interval between successive pacing signals) to support higher or lower heart rates of the patient.

[0067] Medical system 100 (e.g., therapy delivery circuitry 106, processing circuitry 124, and / or processing circuitry of detector 126) may be configured to detect (e.g., to identify) the SI indication, the S2 indication, the S3 indication, and / or the S4 indication using signals 138. In some examples, the processing circuitry of detector 126 detects the SI indication, the S2Docket No: A0011909W001 indication, the S3 indication, and / or the S4 indication using signals 138 and provides a communication to processing circuitry 124 to indicate the detection. In some examples, therapy delivery circuitry 106 detects the SI indication, the S2 indication, the S3 indication, and / or the S4 indication using signals 138 and provides a communication to processing circuitry 124 to indicate the detection. In some examples, another portion of medical system 100 detects the SI indication, the S2 indication, the S3 indication, and / or the S4 indication using signals 138 and provides a communication to processing circuitry 124 to indicate the detection. In some examples, processing circuitry 124 detects the SI indication, the S2 indication, the S3 indication, and / or the S4 indication using signals 138. Hence, processing circuitry 124 may determine that one or more cardiac indications of heart 102 (e.g., one of more of the SI sound, the S2 sound, the S3 sound, and / or the S4 sound) have occurred based on one or more communications from the processing circuitry of detector 126, therapy delivery circuitry 106, another portion of medical system 100, and / or through detection of the SI indication, the S2 indication, the S3 indication, and / or the S4 indication using signals 138.

[0068] In some examples, therapy delivery circuitry 106 is configured such that a pacing signal substantially causes and / or prompts heart 102 to produce an SI heart sound. Medical system 100 may be configured to delineate (e.g., distinguish) the cardiac cycles of heart 102 based on the SI heart sound, the S2 heart sound, the S3 heart sound, the S4 heart sound, the first cardiac indication, the second cardiac indication, and / or another cardiac indication of heart 102 occurring during a cardiac cycle. In examples, medical system 100 (e.g., detector 126, processing circuitry 124, and / or therapy delivery circuitry 106) is configured to distinguish an initial cardiac cycle from a subsequent cardiac cycle based on a detection of particular type of cardiac indication during the initial cardiac cycle and a detection of the particular type of cardiac indication during the subsequent cardiac cycle. For example, the particular type of cardiac indication may be the SI indication. Medical system 100 may be configured to distinguish the initial cardiac cycle from the subsequent cardiac cycle based on a detection of the SI indication during the initial cardiac cycle and a detection of SI indication during the subsequent cardiac cycle. The particular type of cardiac indication may be another cardiac indication (e.g., the S2 indication, the S3 indication, the S4 indication, the first cardiac indication Bl, the second cardiac indication B2, and / or another cardiac indication) in other examples.

[0069] FIG. 3 depicts representative signal 145 extending over first cardiac cycle Cl, second cardiac cycle C2, third cardiac cycle C3, a fourth cardiac cycle C4, a fifth cardiac cycle C5, and into a sixth cardiac cycle C6. Therapy delivery circuitry 106 is configured toDocket No: A0011909W001 deliver the first pacing signal at first time Tl, deliver the second pacing signal at second time T2, and deliver the third pacing signal at third time T3 such that heart 102 produces first cardiac cycle Cl, second cardiac cycle C2, and third cardiac cycle C3 respectively. Therapy delivery circuitry 106 is further configured to deliver a fourth pacing signal at a fourth time T4 to cause and / or assist in causing heart 102 to produce fourth cardiac cycle C4, deliver a fifth pacing signal at a fifth time T5 to cause and / or assist in causing heart 102 to produce fifth cardiac cycle C5, and deliver a sixth pacing signal at a sixth time T6 to cause and / or assist in causing heart 102 to produce sixth cardiac cycle C6. Therapy delivery circuitry 106 may be configured to deliver additional pacing signals subsequent (e.g., chronologically subsequent) to the sixth pacing signal to cause and / or assist in causing heart 102 to produce additional cardiac cycles subsequent to sixth cardiac cycle C6.

[0070] Processing circuitry 124 is configured to limit a maximum heart rate (e.g., limit a pacing rate of therapy delivery circuitry 106) such that a diastole indicator indicative of diastole occurs over one or more of (e.g., over substantially all of) first cardiac cycle Cl, second cardiac cycle C2, third cardiac cycle C3, fourth cardiac cycle C4, fifth cardiac cycle C5, sixth cardiac cycle C6, and / or cardiac cycles subsequent to sixth cardiac cycle C6. For example, the diastole indicator may be the S2 indication indicative of the S2 sound during a cardiac cycle, the S3 indication indicative of the S3 sound during the cardiac cycle, the S4 indication indicative of the S4 sound during the cardiac cycle, the first cardiac indication Bl indicative of the first cardiac indication during the cardiac cycle, the second cardiac indication B2 indicative of the second cardiac indication during the cardiac cycle, or another cardiac indication indicative of a diastole phase of heart 102 during the cardiac cycle.

[0071] Processing circuitry 124 is configured to limit an interval (e.g., INTI) used by therapy delivery circuitry 106 to separate an initial pacing signal (e.g., the first pacing signal) and a subsequent pacing signal (e.g., the second pacing signal) such that a cardiac cycle (e.g., first cardiac cycle Cl) includes at least the diastole indicator (e.g., includes the S2(l) indication, S3(l) indication, S4(l) indication, Bl(l) indication, and / or B2(l) indication). Stated similarly, Processing circuitry is configured to limit the interval such that the second pacing signal is not delivered at least until the diastole indicator of first cardiac cycle Cl occurs or is expected to occur. In examples, processing circuitry 124 defines an interlude I over which the diastole indicator occurs or is expected to occur. Interlude I may be used to define a minimum interval where, at intervals less than the minimum interval, delivery of the second pacing pulse may tend to truncate or even prevent the occurrence of the diastoleDocket No: A0011909W001 indicator within first cardiac cycle Cl, such that coronary perfusion during the diastole phase of heart 102 during first cardiac cycle Cl might be less than desired.

[0072] In examples, therapy delivery circuitry 106 is configured to alter the interval (e.g., alter a duration of the interval) to alter a heart rate of heart 102. For example, therapy delivery circuitry 106 may be configured to decrease the interval to support an increase in a heart rate of heart 102 (e.g., based on a determination that a patient activity level has increased). Therapy delivery circuitry 106 may be configured to increase the interval to support a decrease in the heart rate of heart 102 (e.g., based on a determination that a patient activity level has decreased). Processing circuitry 124 is configured to limit the interval using interlude I such that, as therapy delivery circuitry 106 decreases a duration of the interval (e.g., to support higher heart rates of heart 102), therapy delivery circuitry 106 is limited from (e.g., prevented from) establishing an interval whereby a subsequent pacing signal following an initial pacing signal would be delivered prior to completion of interlude I during a cardiac cycle caused and / or assisted by the initial pacing signal. Hence, processing circuitry 124 may use interlude I to limit and / or prevent truncation of a diastole phase of heart 102 by the subsequent pacing signal to, for example, assist with coronary perfusion during the diastole phase of heart 102.

[0073] For example, as discussed, and referring largely to FIG. 3, therapy delivery circuitry 106 may be configured to separate delivery of the first pacing signal and the second pacing signal by the interval INTI and separate delivery of the second pacing signal and the third pacing signal by the interval INT2. In examples, therapy delivery circuitry 106 is configured to separate delivery of the third pacing signal and the fourth pacing signal by an interval INT3, separate delivery of the fourth pacing signal and the fifth pacing signal by an interval INT4, and separate delivery of the fifth pacing signal and the sixth pacing signal by an interval INT5. Therapy delivery circuitry 106 may be configured to separate pacing signals subsequent to the sixth pacing signals using one or more intervals subsequent to interval INT 5.

[0074] Therapy delivery circuitry 106 may be configured to alter an interval (e.g., alter a duration of the interval) to alter a heart rate of heart 102. For example, medical system 100 may be configured to determine and / or detect an indication (e.g., an activity level of a patient) indicating an increase in the heart rate of heart 102 might be occurring or be beneficial for the patient. Therapy delivery circuitry 106 may be configured to decrease the interval to support the increase in the heart rate of heart 102. For example, therapy delivering circuitry may be configured to alter the interval such that INT3 has a lesser duration thanDocket No: A0011909W001INT2, INT 4 has a lesser duration than INT3, and INT 5 has a lesser duration than INT 4, such that the interval between pacing signals decreases and the heart rate of heart 102 increases.

[0075] Processing circuitry 124 is configured to limit the interval using interlude I such that therapy delivery circuitry 106 is limited from (e.g., prevented from) establishing an interval that would result in the delivery of a pacing pulse prior to conclusion of the interlude I during a preceding cardiac cycle. As an example, processing circuitry 124 may be configured to control therapy delivery circuitry 106 such that INT4 and INT5 are not decreased to an extent whereby completion of interlude I is precluded (e.g., due to the delivery of the fifth pacing signal or the sixth pacing signal). Hence, processing circuitry 124 may be configured to limit the interval (e.g., INT4, INT5) of therapy delivery circuitry 106 using interlude I, such that a heart rate caused and / or assisted by therapy delivery circuitry 106 avoids and / or mitigates possible truncation of a diastole phase of heart 102 by a subsequent pacing signal. In examples, processing circuitry 124 defines a maximum heart rate of heart 102 based on the interlude. Processing circuitry 124 may control therapy delivery circuitry 106 such that therapy delivery circuitry 106 is limited from establishing a pacing rate that might cause heart 102 to exceed the maximum heart rate.

[0076] In some examples, processing circuitry 124 may be configured such that, in a first mode, processing circuitry 124 acts to limit the interval of therapy delivery circuitry 106 (e.g., using interval I), and in a second mode, processing circuitry 124 does not act to limit the interval of therapy delivery circuitry 106. Processing circuitry 124 may be configured to operate in the first mode or the second mode based on a heart rate of heart 101. For example, at lower heart rates such as during INTI and / or INT2, processing circuitry 124 may be configured to operate in the second mode (e.g., to not limit the interval of therapy delivery circuitry 106). At higher heart rates such as during INT4 and / or INT5, processing circuitry 124 may be configured to operate in the first mode (e.g., to limit the interval of therapy delivery circuitry 106 using interlude I).

[0077] In examples, processing circuitry 124 is configured to shift between the first mode and the second mode based on the heart rate of heart 101. For example, processing circuitry 124 may be configured to receive an indication of the heart rate of heart 101 from detector 126, medical device 104 (e.g., therapy delivery circuitry 106), and / or another portion of medical system 106. Processing circuitry 124 may be configured to transition from the second mode to the first mode when the heart rate is equal to or greater than a threshold heart rate. Processing circuitry 124 may be configured to transition from the first mode to theDocket No: A0011909W001 second mode when the heart rate is less than the threshold heart rate.

[0078] In examples, processing circuitry 124 is configured to define interlude I using an onset point O defined in a given cardiac cycle and an end point E defined in the given cardiac cycle. End point E is subsequent (e.g., chronologically subsequent) onset point O. Processing circuitry 124 may define interlude I as extending (e.g., chronologically extending) from the onset point O defined for the given cardiac cycle to the end point E defined for the given cardiac cycle. In examples, the onset point O chronologically precedes or is substantially concurrent with the diastole indicator. The end point E may be subsequent to the diastole indicator.

[0079] Processing circuitry 124 may be configured to define the onset point O based on a determination that a specific cardiac indication (e.g., the SI indication, the S2 indication, the S3 indication, the S4 indication, the Bl indication, or the B2 indication) has occurred during the given cardiac cycle. In some examples, processing circuitry 124 is configured to define end point E based on the elapse of a time window subsequent to onset point O (e.g., a time window during which the diastole indicator occurs or is expected to occur). The time window may be greater than about 40 milliseconds (ms) in some examples, and / or greater than about 50 ms in some examples. In some examples, processing circuitry 124 may be configured to define the time window based on a heart rate of heart 102. For example, processing circuitry 124 may be configured to define a first time window when heart 101 experiences a first heart rate and define a second time window less than (e.g., shorter than ) the first time window when heart 101 experiences a second heart rate greater than the first heart rate. In some examples, processing circuitry 124 is configured to define end point E based on a determination that another cardiac indication (e.g., the S3 indication, the S4 indication, the Bl indication, or the B2 indication) has occurred during the given cardiac cycle.

[0080] For example, FIG. 4 depicts representative signal 146 extending over first cardiac cycle Cl, second cardiac cycle C2, and into third cardiac cycle C3. As stated, representative signal 146 may be an example of accelerometer signal 140, sound signal 142, ECG signal 144, and / or another signal produced by medical system 100 and delineating an SI indication indicative of an SI heart sound during a given cardiac cycle, an S2 indication indicative of an S2 heart sound during the given cardiac cycle, an S3 indication indicative of an S3 heart sound during the given cardiac cycle, an S4 indication indicative of an S4 heart sound during the given cardiac cycle, and / or another indication indicative of another cardiac indication during the given cardiac cycle. For example, detector 126 may be configured such that representative signal 146 delineates an indication P18 indicative of S 1 (1), an indication P19Docket No: A0011909W001 indicative of S2(l), an indication P20 indicative of S3 (1), an indication P21 indicative of S4(l), an indication P22 indicative of B 1(1), and / or an indication P22 indicative of B2(l). Indication P18 may be an example of indication Pl, P5, P9 (FIG. 2), indication P19 may be an example of indication P2, P6, PIO, indication P20 may be an example of indication P3, P7, Pl 1, indication P21 may be an example of indication P4, P8, P12, indication P21 may be an example of indication P13, P15, P17, and / or indication P22 may be an example of indication P14, P16, P18.

[0081] Processing circuitry 124 is configured to control therapy delivery circuitry 106 such that INTI between the first pacing signal delivered by therapy delivery circuitry 106 and the second pacing signal delivered by therapy delivery circuitry 106 is likely to include (e.g., extend over) a diastole indicator of first cardiac cycle Cl caused by the first pacing signal. Processing circuitry 124 is configured to define an interlude which extends from an onset point within first cardiac cycle Cl to an end point within cardiac cycle Cl, with the end point subsequent (e.g., chronologically subsequent) to the onset point. Processing circuitry 124 may control therapy delivery circuitry 106 such that the second pacing signal is delivered subsequent to the end point to, for example, control a duration of the diastole phase of heart 102.

[0082] Processing circuitry 124 may be configured to define the onset point for a given cardiac cycle relative to an SI indication, an S2 indication, an S3 indication, an S4 indication, and / or another cardiac indication received during the given cardiac cycle. In some examples, processing circuitry 124 may define the onset point to be substantially concurrent with or subsequent to any one of the SI indication, the S2 indication, the S3 indication, the S4 indication, or the other indication. Processing circuitry 124 may be configured to define the onset point based on determining one or more of the SI indication, the S2 indication, the S3 indication, the S4 indication, the Bl indication, or the B2 indication has occurred during the given cardiac cycle.

[0083] In some examples, processing circuitry 124 is configured to determine an end point corresponding to the onset point using a time window which commences at the onset point and elapses at the end point. Processing circuitry 124 may be configured to monitor the passing of the time window and define the end point based on the elapse. In some examples, Processing circuitry 124 may be configured to define the end point based on determining a cardiac indication subsequent to the onset point has occurred during the given cardiac cycle. For example, processing circuitry 124 may be configured to define an onset point based on determining one of the SI indication, the S2 indication, the S3 indication, the S4 indication,Docket No: A0011909W001 the Bl indication, or the B2 indication has occurred during the given cardiac cycle, and define the end point based on determining another of the SI indication, the S2 indication, the S3 indication, the S4 indication, the Bl indication, or the B2 indication has occurred during the given cardiac cycle and subsequent to the defined onset point.

[0084] In examples, and referring largely to FIG. 4, processing circuitry 124 may be configured to define an onset point for cardiac cycle Cl (“Cl onset point”) using one of a first onset point 01, a second onset point 02, a third onset point 03, a fourth onset point 04, a fifth onset point 05, or another onset point defined using signal 146 during cardiac cycle Cl. Processing circuitry 124 may be configured to define an interlude for cardiac cycle Cl (“Cl interlude”) which commences at the Cl onset point and extends to an end point for cardiac cycle Cl (“Cl end point”). In examples, processing circuitry 124 is configured to define the Cl end point using one of a first end point El, a second end point E2, a third end point E3, a fourth end point E4, or another end point defined during cardiac cycle Cl. In examples, processing circuitry 124 defines the Cl end point such that the Cl end point is subsequent (e.g., chronologically subsequent) to the Cl onset point. First onset point 01, second onset point 02, third onset point 03, fourth onset point 04, and fifth onset point 05 are examples of onset point O (FIG. 3). First end point El, second end point E2, third end point E3, and fourth end point E4 and examples of end point E (FIG. 3).

[0085] In some examples, first onset point 01 is based on (e.g., defined in relation to) the S 1 (1 ) indication. For example, first onset point 01 may be substantially concurrent with the S 1 (1) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define first onset point 01 such that first onset point 01 is subsequent to the S 1 (1) indication. For example, first onset point 01 may be based on an elapse of a first time period following the S 1(1) indication. Processing circuitry 124 may be configured to track the first time period following the S 1(1) indication and define first onset point 01 based on the elapse of the first time period. In examples, first onset point 01 precedes or is expected to precede the S2(l) indication.

[0086] In some examples, second onset point 02 is based on (e.g., defined in relation to) the S2(l) indication. For example, second onset point 02 may be substantially concurrent with the S2(l) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define second onset point 02 such that second onset point 02 is subsequent to the S2(l) indication. For example, second onset point 02 may be based on an elapse of a second time period following the S2(l) indication. Processing circuitry 124 may be configured to track the second time period following the S2(l) indication and defineDocket No: A0011909W001 second onset point 02 based on the elapse of the second time period. In examples, second onset point 02 precedes or is expected to precede the S3 (1 ) indication.

[0087] In some examples, third onset point 03 is based on (e.g., defined in relation to) the S3 (1) indication. For example, third onset point 03 may be substantially concurrent with the S3 (1) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define third onset point 03 such that third onset point 03 is subsequent to the S3 ( 1 ) indication. For example, third onset point 03 may be based on an elapse of a third time period following the S3( 1 ) indication. Processing circuitry 124 may be configured to track the third time period following the S3 (1) indication and define third onset point 03 based on the elapse of the third time period. In examples, third onset point 03 precedes or is expected to precede the S4(l) indication.

[0088] In some examples, fourth onset point 04 is based on (e.g., defined in relation to) the S4(l) indication. For example, fourth onset point 04 may be substantially concurrent with the S4(l) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define fourth onset point 04 such that fourth onset point 04 is subsequent to the S4(l) indication. For example, fourth onset point 04 may be based on an elapse of a fourth time period following the S4(l) indication. Processing circuitry 124 may be configured to track the fourth time period following the S4(l) indication and define fourth onset point 03 based on the elapse of the fourth time period. In examples, fourth onset point 04 precedes or is expected to precede the Sl(2) indication of second cardiac cycle C2.

[0089] In some examples, fifth onset point 05 is based on (e.g., defined in relation to) the Bl(l) indication. For example, fifth onset point 05 may be substantially concurrent with the Bl(l) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define fifth onset point 05 such that fifth onset point 05 is subsequent to the B 1(1) indication. For example, fifth onset point 05 may be based on an elapse of a fifth time period following the B 1(1) indication. Processing circuitry 124 may be configured to track the fifth time period following the B 1(1) indication and define fifth onset point 05 based on the elapse of the fifth time period. In examples, fifth third onset point 03 precedes or is expected to precede the S2(l) indication, the S3 (1 ) indication, the S4(l) indication, and / or the Sl(2) indication.

[0090] Processing circuitry 124 may be configured to define the Cl end point using one of first end point El, second end point E2, third end point E3, fourth end point E4, or another end point defined using signal 146 during cardiac cycle Cl. In examples, first end point El is based on (e.g., defined in relation to) the S2(2) indication. For example, in some examples (asDocket No: A0011909W001 depicted in FIG. 3), processing circuitry 124 may define first end point El such that first end point El is subsequent to the S2(l) indication. In some examples, first end point El is based on an elapse of an additional first time period following the S2(l) indication. Processing circuitry 124 may be configured to track the other first time period following the S2(l) indication and define first end point El based on the elapse of the additional first time period. In examples, first end point El precedes or is expected to precede the S3 (1 ) indication.

[0091] In some examples, second end point E2 is based on (e.g., defined in relation to) the S3 ( 1 ) indication. For example, second end point E2 may be substantially concurrent with the S3 (1) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define second end point E2 such that second end point E2 is subsequent to the S3 ( 1 ) indication. For example, second end point E2 may be based on an elapse of an additional second time period following the S3 (1) indication. Processing circuitry 124 may be configured to track the additional second time period following the S3 (1 ) indication and define second end point E2 based on the elapse of the additional second time period. In examples, second end point E2 precedes or is expected to precede the S4(l) indication.

[0092] In some examples, third end point E3 is based on (e.g., defined in relation to) the S4(l) indication. For example, third end point E3 may be substantially concurrent with the S4(l) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define third end point E3 such that third end point E3 is subsequent to the S4(l) indication. For example, third end point E3 may be based on an elapse of an additional third time period following the S4(l) indication. Processing circuitry 124 may be configured to track the additional third time period following the S4(l) indication and define third end point E3 based on the elapse of the additional third time period. In examples, third end point E3 precedes or is expected to precede the SI (2) indication of second cardiac cycle C2.

[0093] In some examples, fourth end point E4 is based on (e.g., defined in relation to) the B2(l) indication. For example, fourth end point E4 may be substantially concurrent with the B2(l) indication in some examples (as depicted in FIG. 3). In other examples, processing circuitry 124 may define fourth end point E4 such that fourth end point E4 is subsequent to the B2(l) indication. For example, fourth end point E4 may be based on an elapse of an additional fourth time period following the B2(l) indication. Processing circuitry 124 may be configured to track the additional fourth time period following the B2(l) indication and define fourth end point E4 based on the elapse of the additional fourth time period. In examples, fourth end point E4 precedes or is expected to precede the S3 (1 ) indication, the S4(l) indication, and / or the Sl(2) indication.Docket No: A0011909W001

[0094] Processing circuitry 124 may be configured to define the Cl interlude using (e.g., based on) the Cl onset point. The Cl interlude may commence at the Cl onset point and extend to the Cl end point. For example, processing circuitry 124 may be configured to define the Cl interlude using a first interlude II which commences at first onset point 01 and extends to one of end point El, end point E2, end point E3, end point E4, or another endpoint defined by processing circuitry 124 (e.g., using signal 146) during first cardiac cycle Cl. Processing circuitry 124 may be configured to define the Cl interlude using a second interlude 12 which commences at second onset point 02 and extends to one of end point El, end point E2, end point E3, end point E4, or another endpoint defined by processing circuitry 124 (e.g., using signal 146) during first cardiac cycle Cl. Processing circuitry 124 may be configured to define the Cl interlude using a third interlude 13 which commences at third onset point 03 and extends to one of end point E3, end point E4, or another endpoint defined by processing circuitry 124 (e.g., using signal 146) during first cardiac cycle Cl. Processing circuitry 124 may be configured to define the Cl interlude using a fourth interlude 14 which commences at fourth onset point 04 and extends to one of end point E3 (e.g., when end point E3 is based on the elapse of the additional third time period) or another endpoint defined by processing circuitry 124 (e.g., using signal 146) during first cardiac cycle Cl. Processing circuitry 124 may be configured to define the Cl interlude using a fifth interlude 15 which commences at fifth onset point 05 and extends (depending on where in first cardiac cycle Cl the first cardiac indication Bl occurs) to one of any of end point El, end point E2, end point E3, end point E4, or another endpoint defined by processing circuitry 124 (e.g., using signal 146) during first cardiac cycle Cl.

[0095] Processing circuitry 124 may be configured to control INTI using the Cl interlude (e.g., one of interlude II, interlude 12, interlude 13, interlude 14, interlude 15, or another interlude). In some examples, processing circuitry 124 is configured to define a minimum INTI for therapy delivery circuitry 106 using the Cl interlude. For example, processing circuitry 124 may be configured to define the minimum INTI such that the minimum INTI is greater than or equal to the Cl interlude. Processing circuitry 124 may be configured to control therapy delivery circuitry 106 such that therapy delivery circuitry 106 does not cause INTI to be less than the minimum INTI. Hence, processing circuitry 124 may assist in providing a duration of a diastole phase of heart 102 during first cardiac cycle Cl which is at least equal to the Cl interlude, such that, for example, coronary perfusion of heart 102 may occur over at least over the Cl interlude.

[0096] Stated similarly, processing circuitry 124 may be configured to control the intervalDocket No: A0011909W001INTI between the first pacing signal delivered by therapy delivery circuitry 106 and the second pacing signal delivered by therapy delivery circuitry 106 such that the second pacing signal is delivered subsequent to or substantially concurrent with the Cl end point (e.g., one of end point El, end point E2, end point E3, end point E4, or another end point) defined by processing circuitry 124 during first cardiac cycle Cl. Processing circuitry 124 may limit the delivery of the second pacing pulse by therapy delivery circuitry 106 and / or limit a pacing rate of therapy delivery circuitry 106 such that the Cl interlude (e.g., one of interlude II, interlude 12, interlude 13, interlude 14, interlude 15, or another interlude) provides a duration of a diastole phase of heart 102 during first cardiac cycle Cl which promotes coronary perfusion of heart 102 during first cardiac cycle Cl.

[0097] Processing circuitry 124 may be configured to define an onset point for each cardiac cycle of heart 102. Processing circuitry 124 may be configured to define an end point corresponding to each onset point. For example, processing circuitry 124 may define the Cl onset point and the Cl end point for first cardiac cycle Cl caused and / or assisted by a first pacing signal delivered by therapy delivery circuitry 106. Processing circuitry 124 may subsequently define a C2 onset point (e.g., onset point O-N) for second cardiac cycle C2, a C2 end point (e.g., end point E-N) for second cardiac cycle C2, and define an interlude (e.g., interlude I-N) extending from the C2 onset point to the C2 end point. Processing circuitry 124 may define the C2 onset point during second cardiac cycle C2 using one of the methodologies described for defining the Cl onset point during cardiac cycle Cl, and / or define the C2 end point during second cardiac cycle C2 using one of the methodologies described for defining the Cl end point during cardiac cycle Cl. Processing circuitry 124 may be configured to control the interval INT2 between the second pacing signal and a third pacing signal delivered by therapy delivery circuitry 106, such that the third pacing signal is delivered subsequent to or substantially concurrent with the C2 end point.

[0098] In some examples, for example when processing circuitry 124 defines an end point based on a time window which elapses following an onset point, processing circuitry 124 is configured to define the time window based on the cardiac indications of heart 102. Hence, processing circuitry 124 may be configured to define the time window based on specific physiological characteristics of heart 102.

[0099] For example, referring largely to FIG. 3, first cardiac cycle Cl, second cardiac cycle C2, third cardiac cycle C3, fourth cardiac cycle C4, and fifth cardiac cycle C5 may occur during an initial period (e.g., a learning period) during which processing circuitry 124 is configured to determine a time window appropriate for heart 102. Processing circuitry 124Docket No: A0011909W001 may be configured to define a reference onset point O-R for a specific cardiac cycle (e.g., first cardiac cycle Cl) and monitor for the occurrence of a diastole indicator DS (e.g., based on or another cardiac indication) during the specific cardiac cycle. Diastole indicator DS occurs subsequent to reference onset point O-R. For example, when the reference onset O-R is defined based on the S2(l) indication (as depicted in FIG. 3), diastole indicator DS may be based on the S3 (1 ) indication, the S4(l) indication, or another cardiac indication which occurs during cardiac cycle Cl subsequent to the S2(l) indication. In other examples, for example when the reference onset O-R is defined based on the S 1 (1), diastole indicator DS may be based on the S2(l) indication, the S3 (1 ) indication, the S4(l) indication, or another cardiac indication which occurs during cardiac cycle Cl and subsequent to the S 1 (1 ) indication. When the reference onset O-R is defined based on the S3 (1 ), diastole indicator DS may be based on the S4(l) indication or another cardiac indication which occurs during cardiac cycle Cl and subsequent to the S4(l) indication.

[0100] In some examples, processing circuitry 124 may be configured to define a plurality of reference windows 148 (e.g., a plurality of reference time windows), including a first reference window Rl, a second reference window R2, a third reference window R3, and so on to an Nth reference window RN. Processing circuitry 124 may be configured to monitor the elapse of each reference window in the plurality of reference windows 148 subsequent to the occurrence of reference onset point O-R during a cardiac cycle, such as first cardiac cycle Cl. In examples, processing circuitry 124 is configured to begin monitoring the elapse of each reference window substantially concurrently with the occurrence of reference onset point O-R during the cardiac cycle.

[0101] Programming circuitry 124 may be configured to determine if the elapse of a reference window occurs prior to, substantially concurrent with, or subsequent to the occurrence of diastole indicator DS during the cardiac cycle. Processing circuitry 124 may be configured to determine and / or select one of the reference windows which elapses subsequent to the occurrence of diastole indicator DS during the cardiac cycle. For example, as depicted in FIG. 3, processing circuitry 124 may determine and / or select Nth reference window RN based on its elapse occurring subsequent to the occurrence of diastole indicator DS during the cardiac cycle.

[0102] Processing circuitry 124 may be configured to use the selected reference window (e.g., Nth reference window RN) to define a reference end point E-R based on reference onset point O-R of the cardiac cycle. Programming circuitry 124 may be configured to define a reference interlude I-R using reference onset point O-R of the cardiac cycle and reference endDocket No: A0011909W001 point E-R. Processing circuitry 124 may be configured to define onset point O using reference onset point O-R of second cardiac cycle C2, define end point E using reference end point E-R, and define interlude I using reference interlude I-R. Hence, processing circuitry 124 may utilize the thus defined reference window as the time window for successive pacing signals delivered to heart 102, such that the time window is specific to heart 102.

[0103] It is understood that, rather than monitoring the elapse of each reference window in the plurality of reference windows 148 during a single cardiac cycle, such as first cardiac cycle Cl, processing circuitry 124 may monitor the elapse of each reference window over a plurality of cardiac cycles. For example, processing circuitry 124 may determine the elapse of first time interval R1 during first cardiac cycle Cl, with reference onset point O-R and diastole indicator DS occurring during first cardiac cycle Cl. Processing circuitry 124 may determine the elapse of second time interval R2 during second cardiac cycle C2, with reference onset point O-R and diastole indicator DS occurring during second cardiac cycle C2. Processing circuitry 124 may determine the elapse of third time interval R3 during third cardiac cycle C3 with reference onset point O-R and diastole indicator DS occurring during third cardiac cycle C3, and so on.

[0104] In some examples, processing circuitry 124 is configured to associate the defined reference window determined with a heart rate of heart 102. For example, processing circuitry 124 may be configured to determine and / or detect a heart rate of heart 102 based on a communication from detector 126 or another portion of medical system 100 as processing circuitry 124 determines the defined reference window. Processing circuitry 124 may be configured to store the defined reference window and the associated heart rate in, for example, a memory of processing circuitry 124 and / or medical system 100. For example, processing circuitry 124 may determine a first defined reference window as heart 102 experiences a first heart rate (e.g., during first cardiac cycle Cl) and associate the first defined reference window and the first heart rate. Processing circuitry 124 may determine a second defined reference window as heart 102 experiences a second heart rate (e.g., during third cardiac cycle C3) different from the first heart rate, and associate the second defined reference window and the second heart rate. Processing circuitry 124 may determine a third defined reference window as heart 102 experiences a third heart rate (e.g., during fifth cardiac cycle C3) different from the first heart rate and the second heart rate, and associate the third defined reference window and the third heart rate.

[0105] Following the initial period during which the first defined reference window, the second defined reference window, and the third defined reference window are defined,Docket No: A0011909W001 processing circuitry 124 may be configured to define interlude I based on a heart rate of heart 102. For example, processing circuitry 124 may be configured to define interlude I using the first defined reference window when system 100 indicates that heart 102 is experiencing and / or has a heart rate within a certain range of the first heart rate. Processing circuitry 124 may be configured to define interlude I using the second defined reference window when system 100 indicates that heart 102 is experiencing and / or has a heart rate within a particular range of the second heart rate. Processing circuitry 124 may be configured to define interlude I using the third defined reference window when system 100 indicates that heart 102 is experiencing and / or has a heart rate within a specific range of the third heart rate. Thus, processing circuitry 124 may define interlude I using the thus selected reference window, such that processing circuitry 124 utilizes a time window determined based on physiological characteristics of the patient.

[0106] In some examples, processing circuitry 124 may be configured to associate a reference time window with a particular reference onset point O-R defined by processing circuitry 124. For example, processing circuitry 124 may be configured to define a one reference window (e.g., one of first reference window, second reference window, or third reference window) when processing circuitry 124 defines reference onset point O-R using a first cardiac indication (e.g., one of the SI indication, the S2 indication, the S3 indication, and / or the S4 indication of heart 102). Processing circuitry 124 may be configured to define another reference window (e.g., another of the first reference window, second reference window, or third reference window) when processing circuitry 124 defines reference onset point O-R using a second cardiac indication (e.g., another of the SI indication, the S2 indication, the S3 indication, and / or the S4 indication of heart 102). Processing circuitry 124 may associate the one reference window with the first cardiac indication and associate the other reference window with the second cardiac indication.

[0107] Processing circuitry 124 may be configured to select a reference time window based on a cardiac indication used to determine an onset point (e.g., used to determine one of onset point 01, onset point 02, onset point 03, onset point 05, or another onset point). Selecting a reference time window based on the cardiac indication used to define the onset point may provide additional flexibility for processing circuitry 124 if, for example, processing circuitry 124 uses a combination of cardiac indications to define the onset point, and / or shifts from defining the onset point using a first cardiac indication (e.g., during first cardiac cycle Cl) to defining the onset point using a second cardiac indication (e.g., during second cardiac cycle C2).Docket No: A0011909W001

[0108] In examples, and referring to FIG. 2, the indication Pl may be indicative of (e.g., defined by) a first segment of accelerometer signal 140 and / or a first magnitude of accelerometer signal occurring within a first time range over which accelerometer signal 140 occurs. The indication P2 may be indicative of (e.g., defined by) a second segment of accelerometer signal 140 and / or a second magnitude of accelerometer signal 140 occurring within a second time range over which accelerometer signal 140 occurs and different from the first time range. The indication P3 may be indicative of (e.g., defined by) a third segment of accelerometer signal 140 and / or a third magnitude of accelerometer signal 140 occurring within a third time range over which accelerometer signal 140 occurs and different from the first time range and the second time range. The indication P4 may be indicative of (e.g., defined by) a fourth segment of accelerometer signal 140 and / or a fourth magnitude of accelerometer signal 140 occurring within a fourth time range over which accelerometer signal 140 occurs and different from the first time range, the second time range, and the third time range. The indication P13 may be indicative of (e.g., defined by) a fifth segment of accelerometer signal 140 and / or a fifth magnitude of accelerometer signal 140 occurring within a fifth time range over which accelerometer signal 140 occurs and different from the first time range, the second time range, the third time range, and the fourth time range. The indication P14 may be indicative of (e.g., defined by) a sixth segment of accelerometer signal 140 and / or a sixth magnitude of accelerometer signal 140 occurring within a sixth time range over which accelerometer signal 140 occurs and different from the first time range, the second time range, the third time range, the fourth time range, and the fifth time range.

[0109] In examples, the indication P5 may be indicative of (e.g., defined by) a first segment of sound signal 142 and / or a first magnitude of accelerometer signal occurring within a first time range over which sound signal 142 occurs. The indication P6 may be indicative of (e.g., defined by) a second segment of sound signal 142 and / or a second magnitude of sound signal 142 occurring within a second time range over which sound signal 142 occurs and different from the first time range. The indication P7 may be indicative of (e.g., defined by) a third segment of sound signal 142 and / or a third magnitude of sound signal 142 occurring within a third time range over which sound signal 142 occurs and different from the first time range and the second time range. The indication P8 may be indicative of (e.g., defined by) a fourth segment of sound signal 142 and / or a fourth magnitude of sound signal 142 occurring within a fourth time range over which sound signal 142 occurs and different from the first time range, the second time range, and the third time range. The indication Pl 5 may be indicative of (e.g., defined by) a fifth segment of soundDocket No: A0011909W001 signal 142 and / or a fifth magnitude of sound signal 142 occurring within a fifth time range over which sound signal 142 occurs and different from the first time range, the second time range, the third time range, and the fourth time range. The indication P16 may be indicative of (e.g., defined by) a sixth segment of sound signal 142 and / or a sixth magnitude of sound signal 142 occurring within a sixth time range over which sound signal 142 occurs and different from the first time range, the second time range, the third time range, the fourth time range, and the fifth time range.

[0110] In examples, the indication P9 may be indicative of (e.g., defined by) a first segment of ECG signal 144 and / or a first magnitude of accelerometer signal occurring within a first time range over which ECG signal 144 occurs. The indication PIO may be indicative of (e.g., defined by) a second segment of ECG signal 144 and / or a second magnitude of ECG signal 144 occurring within a second time range over which ECG signal 144 occurs and different from the first time range. The indication Pl 1 may be indicative of (e.g., defined by) a third segment of ECG signal 144 and / or a third magnitude of ECG signal 144 occurring within a third time range over which ECG signal 144 occurs and different from the first time range and the second time range. The indication P 12 may be indicative of (e.g., defined by) a fourth segment of ECG signal 144 and / or a fourth magnitude of ECG signal 144 occurring within a fourth time range over which ECG signal 144 occurs and different from the first time range, the second time range, and the third time range. The indication P17 may be indicative of (e.g., defined by) a fifth segment of ECG signal 144 and / or a fifth magnitude of ECG signal 144 occurring within a fifth time range over which ECG signal 144 occurs and different from the first time range, the second time range, the third time range, and the fourth time range. The indication Pl 8 may be indicative of (e.g., defined by) a sixth segment of ECG signal 144 and / or a sixth magnitude of ECG signal 144 occurring within a sixth time range over which ECG signal 144 occurs and different from the first time range, the second time range, the third time range, the fourth time range, and the fifth time range.[oni] A technique for controlling a medical device is illustrated in FIG. 5. Although the technique is described mainly with reference to medical system 100 of FIGS. 1-4, the technique may be applied to other medical systems in other examples.

[0112] The technique includes defining, by processing circuitry 124, an onset point O, 01, 02, 03, 04, 05, O-N within a first cardiac cycle Cl (502). Onset point O, 01, 02, 03, 04, 05, O-N may be indicative of a cardiac indication of a heart 102 of a patient occurring during first cardiac cycle Cl. Onset point O, 01, 02, 03, 04, 05, O-N may precede or be substantially concurrent with a diastole indicator DS indicative of a diastole of first cardiacDocket No: A0011909W001 cycle Cl. First cardiac cycle Cl may be caused or assisted by a first pacing signal delivered by a medical device 104 (e.g., therapy delivery circuitry 106). Medical device 104 (e.g., therapy delivery circuitry 106) may deliver a second pacing signal to cause or assist in causing second cardiac cycle C2 following the delivery of the first pacing signal. Medical device 104 (e.g., therapy delivery circuitry 106) may separate the first pacing signal and the second pacing signal by an interval.

[0113] The technique includes defining, by processing circuitry 124, an end point E, El, E2, E3, E4, E-N within the first cardiac cycle, wherein end point E, El, E2, E3, E4, E-N occurs subsequent to the diastole indicator. The technique includes controlling, by processing circuitry 124, the interval of medical device 104 to cause the second pacing signal to be subsequent to end point E, El, E2, E3, E4, E-N (504).

[0114] In examples, processing circuitry 124 defines onset point O, 01, 02, 03, 04, 05, O-N based on a heart sound of heart 102 produced during the first cardiac cycle. In examples, processing circuitry 124 defines onset point O, 01, 02, 03, 04, 05, O-N based on one of an SI indication indicative of an SI sound of heart 102, an S2 indication indicative of an S2 sound of heart 102, an S3 indication indicative of an S3 sound of heart 102, or an S4 indication indicative of an S4 sound of heart 102. In some examples, processing circuitry 124 defines end point E, El, E2, E3, E4, E-N based on the elapse of a time window which commences at onset point O, 01, 02, 03, 04, 05, O-N. Processing circuitry 124 may define end point E, El, E2, E3, E4, E-N based on an expiration of the time window. In some examples, processing circuitry 124 defines end point E, El, E2, E3, E4, E-N based on another heart sound of heart 102 produced during the first cardiac cycle. In examples, processing circuitry 124 defines end point E, El, E2, E3, E4, E-N based on one of the S2 indication, the S3 indication, or the S4 indication.

[0115] In examples, processing circuitry 124 defines a minimum interval extending from the delivery of the first pacing signal by medical device 104 to end point E, El, E2, E3, E4, E-N. Processing circuitry 124 may control medical device 104 to cause the interval to be greater than or equal to the minimum interval. In examples, processing circuitry 124 defines an interlude I, II, 12, 13, 14, 15, 1-N commencing at onset point O, 01, 02, 03, 04, 05, O-N and extending to end point E, El, E2, E3, E4, E-N. Processing circuitry 124 may define the minimum interval using interlude I, II, 12, 13, 14, 15, 1-N.

[0116] In some examples, processing circuitry 124 determines a heart rate of heart 102 and defines interlude I, II, 12, 13, 14, 15, 1-N using a reference time window associated with the heart rate. In some examples, processing circuitry 124 defines a plurality of referenceDocket No: A0011909W001 time windows 148. Processing circuitry 124 may define reference end point E-R using a reference time window of the plurality of reference time windows 148. Processing circuitry 124 may determine whether reference end point E-R occurs subsequent to diastole indicator DS. Processing circuitry 124 may, if reference end point E-R occurs subsequent to diastole indicator DS, use the reference end point E-R as end point E, El, E2, E3, E4. Processing circuitry 124 may, if reference end point E-R does not occur subsequent to diastole indicator DS, select another time window of the plurality of reference time windows 148 and update reference end point E-R based on the other time window. Processing circuitry 124 may, if reference the updated end point E-R occurs subsequent to diastole indicator DS, use the updated reference end point E-R as end point E, El, E2, E3, E4.

[0117] Medical system 100 may comprise a pacemaker such as a leadless and / or wholly intracardiac pacemaker. Electrode 110, 134 and / or other electrodes of medical system 100 may be electrically connected to therapy delivery circuitry 106, processing circuitry 124, and / or detector 126. Medical device 104, processing circuitry 124, and / or detector 126 may be operably connected to operating circuitry configured to deliver therapy to a patient and / or sense physiological signals of the patient using electrode 110, 134, and / or other electrodes of medical system 100.

[0118] Processing circuitry 124 and / or therapy delivery circuitry 106 may include fixed function circuitry and / or programmable operating circuitry. In examples, processing circuitry 124 and / or therapy delivery circuitry 106 includes circuitry configured to perform one or more functions of operating circuitry, such as therapy delivery circuitry, sensing circuitry, processing circuitry, switching circuitry, communication circuitry, and / or other circuitries. Processing circuitry 124 and / or therapy delivery circuitry 106, as well as other processors, operating circuitry, controllers, control circuitry, and the like, described herein, may include any combination of integrated circuitry, discrete logic circuity, analog circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs). In some examples, processing circuitry 124 and / or therapy delivery circuitry 106 includes multiple components, such as any combination of one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry, and / or analog circuitry.

[0119] Functions attributed to processing circuitry 124 and / or therapy delivery circuitry 106 may be embodied as software, firmware, hardware or any combination thereof.Processing circuitry 124 and / or therapy delivery circuitry 106 may include, for instance, a variety of capacitors, transformers, switches, and the like configured to perform the functionsDocket No: A0011909W001 of processing circuitry 124 and / or therapy delivery circuitry 106. In examples, processing circuitry 124 and / or therapy delivery circuitry 106 may be configured to communicate with another device, such as a patient input / output device, a clinician input / output device, and / or others. Processing circuitry 124 and / or therapy delivery circuitry 106 may include any suitable hardware, firmware, software or any combination thereof for communicating with another device. In addition, processing circuitry 124 and / or therapy delivery circuitry 106 may communicate with a networked computing device and a computer network. In examples, processing circuitry 124 and / or therapy delivery circuitry 106 is configured to deliver stimulation signals to and / or receive sensing signals from electrodes 110, 134, and / or other electrodes and / or sensors within medical system 100 or external to medical system 100. Processing circuitry 124 and / or therapy delivery circuitry 106 may be configured to provide electrical signals, e.g., pacing therapy, to electrode 110, 134 and / or other electrodes within medical system 100. Processing circuitry 124 and / or therapy delivery circuitry 106 may be configured to receive electrical signals, e.g., sensed cardiac electrical signals, from electrodes 110, 134, and / or other electrodes within medical system 100.

[0120] Medical system 100 (e.g., processing circuitry 124 and / or therapy delivery circuitry 106) can also include a memory configured to store program instructions, such as software, which may include one or more program modules, which are executable by processing circuitry 124 and / or therapy delivery circuitry 106. The program instructions may be embodied in software and / or firmware. The memory can include any volatile, nonvolatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), ferroelectric RAM (FRAM), flash memory, or any other digital media. In some examples, the memory includes computer-readable instructions that, when executed by processing circuitry 124 and / or therapy delivery circuitry 106 cause processing circuitry 124 and / or therapy delivery circuitry 106 to perform various functions described herein and / or other functions of processing circuitry 124 and / or therapy delivery circuitry 106.

[0121] Housing 108 may enclose processing circuitry 124 and / or therapy delivery circuitry 106 and / or other circuitry within medical system 100. Housing 108 may be configured to fluidly isolate processing circuitry 124 and / or therapy delivery circuitry 106 and / or other circuitry from an environment in contact with an exterior surface of housing 108. In examples, housing 108 is configured to hermetically seal an enclosure defined by medical device 103 and holding processing circuitry 124, therapy delivery circuitry 106, and / or otherDocket No: A0011909W001 circuitry. Housing 108 may be configured to define shapes that are easily accepted by the patient's body while minimizing patient discomfort. For example, housing 108 may define shapes in which comers and edges are designed with relatively large radii, in order to present a housing having smoothly contoured exterior surfaces.

[0122] Communication links 127, 128 may be hard-line and / or wireless communications links. In some examples, communication links 127, 128 may comprise some portion of processing circuitry 124 and / or therapy delivery circuitry 106. In some examples, communication links 127, 128 comprise a wired connection, a wireless Internet connection, a direct wireless connection such as wireless LAN, Bluetooth™, Wi-Fi™, and / or an infrared connection. Communication links 127, 128 may utilize any wireless or remote communication protocol.

[0123] As used here, when a first event (e.g., a first cardiac indication, a first cardiac cycle) precedes a second event (e.g., a second cardiac indication, a second cardiac cycle), this may mean that the first event occurs during a first time period that elapses chronologically earlier than a second time period during which the second event occurs. When a subsequent event (e.g., a second cardiac indication, a second cardiac cycle) is subsequent to an initial event (e.g., a first cardiac indication, a first cardiac cycle), this may mean that the subsequent event occurs during a subsequent period that elapses chronologically later than an initial time period during which the initial event occurs.

[0124] As used here, when a first portion of a system (e.g., medical system 100) supports a second portion of the system, this means that when the second portion causes a first force to be exerted on the first portion, the first portion causes a second force to be exerted on the second portion in response to the first force. The first force and / or second force may be a contact force and / or an action-at-a-distance force. For example, first force and / or second force may be mechanical force, a magnetic force, a gravitational force, or some other type of force. The first portion of the system may be a portion of the system or a portion of a component of the system. The second portion of the system may be another portion of the system or another portion of the same component or a different component. In some examples, when the first portion of the system supports the second portion of the system, this may mean the second portion is mechanically supported by and / or mechanically connected to the first portion.

[0125] Various examples of the disclosure have been described. Any combination of the described systems, operations, or functions is contemplated. These and other examples are within the scope of the following claims.Docket No: A0011909W001

[0126] The following are illustrative of the techniques described herein.

[0127] Example 1. A medical system, comprising: processing circuitry configured to control an interval of a medical device to limit a heart rate of a heart of a patient, the interval extending from a first pacing signal delivered by the medical device to cause or assist in causing a first cardiac cycle of the heart to a second pacing signal delivered by the medical device to cause or assist in causing a second cardiac cycle of the heart, wherein the processing circuitry is configured to: define an onset point within the first cardiac cycle, wherein the onset point is indicative of a cardiac indication of the heart occurring during the first cardiac cycle, and wherein the onset point precedes or is substantially concurrent with a diastole indicator indicative of a diastole of the first cardiac cycle, define an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and control the interval of the medical device to cause the second pacing signal to be subsequent to the end point, thereby limiting the heart rate of the heart.

[0128] Example 2. The medical system of example 1, wherein the cardiac indication is indicative of a heart sound of the heart during the first cardiac cycle.

[0129] Example 3. The medical system of example 2, wherein the cardiac indication includes at least one of at least one of an SI indication indicative of an SI sound of the heart, an S2 indication indicative of an S2 sound of the heart, an S3 indication indicative of an S3 sound of the heart, or an S4 indication indicative of an S4 sound of the heart

[0130] Example 4. The medical system of any of examples 1-3, wherein the processing circuitry is configured to define the onset point using one or more of the SI indication or the52 indication.

[0131] Example 5. The medical system of any of examples 1-4, wherein the diastole indicator includes at least one of an S2 indication indicative of an S2 sound of the heart, an53 indication indicative of an S3 sound of the heart, or an S4 indication indicative of an S4 sound of the heart.Docket No: A0011909W001

[0132] Example 6. The medical system of any of examples 1-5, wherein the processing circuitry is configured to define the end point using one or more of the S3 indication or the S4 indication.

[0133] Example 7. The medical system of any of examples 1-5, wherein the processing circuitry is configured to define the end point by monitoring the elapse of a time window which commences at the onset point and concludes at the end point.

[0134] Example 8. The medical system of any of examples 1-7, wherein the processing circuitry is configured to define a minimum interval extending from the delivery of the first pacing signal to the end point, and where the processing circuitry is configured to control the medical device to cause the interval to be greater than or equal to the minimum interval.

[0135] Example 9. The medical system of example 7, wherein the processing circuitry is configured to define a maximum pacing rate of the medical device based on the minimum interval, wherein the maximum pacing rate defines a quantity of pacing signals delivered by the medical device over a time period, and cause the medical device to limit a number of pacing signals delivered over the time period to less than or equal to the maximum pacing rate.

[0136] Example 10. The medical system of any of example 8 or example 9, wherein the processing circuitry is configured to define an interlude commencing at the onset point and extending to the end point, wherein the processing circuitry is configured to define the minimum interval using the interlude.

[0137] Example 11. The medical system of example 10, wherein the processing circuitry is configured to: determine a heart rate of the heart, define the interlude using a reference time window associated with the heart rate.

[0138] Example 12. The medical system of any of examples 8-11, wherein: the medical device is configured to deliver a plurality of pacing signals subsequent to the second pacing signal, the medical device is configured to separate each pacing signal in the plurality of pacing signals from another signal in the plurality of pacing signals at least by the minimum pacing interval.Docket No: A0011909W001

[0139] Example 13. The medical system of any of examples 1-12, wherein the processing circuitry is configured to: control the interval of the medical device for a plurality of cardiac cycles, determine a heart rate of the heart for each cardiac cycle of the plurality of cardiac cycles, and associate the interval controlled for the each cardiac cycle with the heart rate determined for the each cardiac cycle.

[0140] Example 14. The medical system of any of examples 1-13, wherein the processing circuitry is configured to: define a plurality of reference time windows, define a reference end point using a reference time window of the plurality of reference time windows, wherein the reference time window separates the onset point and the reference end point, determine if the reference end point occurs subsequent to the diastole indicator, and use, if the reference end point occurs subsequent to the diastole indicator, the reference end point as the end point.

[0141] Example 15. The medical system of any of examples 1-14, further comprising the medical device, wherein the medical device is configured to deliver the first pacing signal and deliver second pacing signal following elapse of the interval after the delivery of the first pacing signal.

[0142] Example 16. The medical system of example 15, wherein the medical device comprises therapy delivery circuitry configured to produce the first pacing signal and the second pacing signal, and wherein the medical system includes an electrode electrically coupled to the therapy delivery circuitry, wherein the electrode is configured to deliver the first pacing signal and the second pacing signal to the heart.

[0143] Example 17. The medical system of example 16, further comprising a medical lead configured to position within an anatomical volume of the heart, where the medical lead is configured to electrically couple the electrode and the therapy delivery circuitry.

[0144] Example 18. The medical system of example 16 or example 17, wherein the medical device comprises a housing supporting at least the therapy delivery circuitry.

[0145] Example 19. The medical system of example 18, wherein the housing is configured to position within an anatomical volume of the heart.Docket No: A0011909W001

[0146] Example 20. The medical system of any of examples 1-19, further comprising a detector configured to communicate a signal indicative of the cardiac indication to at least one of the processing circuitry or the medical device, and wherein the at least one of the processing circuitry or the medical device is configured to detect the cardiac indication using the signal.

[0147] Example 21. The medical system of example 20, wherein the detector comprises an accelerometer configured to detect an acceleration of the accelerometer caused by at least one of a sound produced by the heart or a movement of the heart, and wherein the signal is indicative of the acceleration.

[0148] Example 22. The medical system of example 20 or example 21, wherein the detector comprises a microphone configured to detect a heart sound, and wherein the signal is indicative of the heart sound.

[0149] Example 23. The medical system of any of examples 20-22, wherein the detector is configured to detect an electrocardiogram of the heart, and wherein the signal is indicative of the electrocardiogram.

[0150] Example 24. The medical system of any of examples 20-23, wherein the processing circuitry is configured to detect the cardiac indication by identifying a segment of the signal, wherein the segment is indicative of the cardiac indication.

[0151] Example 25. A medical system, comprising: a medical device is configured to deliver a first pacing signal to cause or assist in causing a first cardiac cycle of a heart of a patient and deliver second pacing signal to cause or assist in causing a second cardiac cycle of the heart, wherein the medical device is configured to deliver the second pacing signal following elapse of an interval after the delivery of the first pacing signal; a detector configured to detect one or more of a cardiac indication of the heart occurring during the first cardiac cycle or a diastole indicator indicative of a diastole of the first cardiac cycle, wherein the detector is configured to communicate a signal indicative of the detection; processing circuitry configured to: define an onset point within the first cardiac cycle using the signal, wherein the onset point precedes or is substantially concurrent with the diastole indicator,Docket No: A0011909W001 define an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and control the interval of the medical device to cause the second pacing signal to be subsequent to the end point, thereby limiting a heart rate of the heart.

[0152] Example 26. The medical system of example 25, wherein the cardiac indication or the diastole indicator is indicative of a heart sound of the heart during the first cardiac cycle.

[0153] Example 27. The medical system of example 15 or example 16, wherein the processing circuitry is configured to: define a plurality of reference time windows, define a reference end point using a reference time window of the plurality of reference time windows, wherein the reference time window separates the onset point and the reference end point, determine if the reference end point occurs subsequent to the diastole indicator, and use, if the reference end point occurs subsequent to the diastole indicator, the reference end point as the end point.

[0154] Example 28. A method, comprising: defining, by processing circuitry, an onset point within a first cardiac cycle, wherein the onset point is indicative of a cardiac indication of a heart of a patient occurring during the first cardiac cycle, wherein the onset point precedes or is substantially concurrent with a diastole indicator indicative of a diastole of the first cardiac cycle, and wherein the first cardiac cycle is caused or assisted by a first pacing signal delivered by a medical device, the medical device configured to deliver a second pacing signal to cause or assist in causing a second cardiac cycle of the heart following the delivery of the first pacing signal, and the medical device configured to separate the first pacing signal and the second pacing signal by an interval, defining, by the processing circuitry, an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and controlling, by the processing circuitry, the interval to cause the second pacing signal to be subsequent to the end point.

[0155] Example 29. The method of example 28, wherein the cardiac indication is indicative of a heart sound of the heart during the first cardiac cycle.

[0156] Example 28. The medical system of example 29, wherein the cardiac indication includes at least one of at least one of an SI indication indicative of an SI sound of the heart,Docket No: A0011909W001 an S2 indication indicative of an S2 sound of the heart, an S3 indication indicative of an S3 sound of the heart, or an S4 indication indicative of an S4 sound of the heart

[0157] Example 29. The method of any of examples 26-28, further comprising defining, by the processing circuitry, the end point using one or more of the S3 indication or the S4 indication.

[0158] Example 30. The method of any of examples 26-28, further comprising defining, by the processing circuitry, the end point by monitoring the elapse of a time window which commences at the onset point and concludes at the end point.

[0159] Example 31. The method of any of examples 26-30, further comprising: defining, by the processing circuitry, a minimum interval extending from the delivery of the first pacing signal to the end point, controlling, by the processing circuitry, the medical device to cause the interval to be greater than or equal to the minimum interval.

[0160] Example 32. The method of example 31, further comprising: defining, by the processing circuitry, an interlude commencing at the onset point and extending to the end point, defining, by the processing circuitry, the minimum interval using the interlude.

[0161] Example 33. The method of example 32, further comprising: determining, by the processing circuitry, a heart rate of the heart, defining, by the processing circuitry, the interlude using a reference time window associated with the heart rate.

[0162] Example 34. The method of any of examples 26-33, further comprising: controlling, by the processing circuitry, the interval of the medical device for a plurality of cardiac cycles, determining, by the processing circuitry, a heart rate of the heart for each cardiac cycle of the plurality of cardiac cycles, and associating, by the processing circuitry, the interval controlled for the each cardiac cycle with the heart rate determined for the each cardiac cycle.

[0163] Example 35. The method of any of examples26-34, further comprising defining, by the processing circuitry, a plurality of reference time windows, defining, by the processing circuitry, a reference end point using a reference time window of the plurality of referenceDocket No: A0011909W001 time windows, wherein the reference time window separates the onset point and the reference end point, determining, by the processing circuitry, if the reference end point occurs subsequent to the diastole indicator, and using, by the processing circuitry, and if the reference end point occurs subsequent to the diastole indicator, the reference end point as the end point.

[0164] Example 36. The method of any of examples 26-35, further comprising controlling, by the processing circuitry, the interval to cause the second pacing signal to be subsequent to the end point when the processing circuitry operates in a first mode, wherein the processing circuitry is configured to operate in the first mode based on a heart rate of the heart.

Claims

Docket No: A0011909W001What is claimed:

1. A medical system, comprising: processing circuitry configured to control an interval of a medical device to limit a heart rate of a heart of a patient, the interval extending from a first pacing signal delivered by the medical device to cause or assist in causing a first cardiac cycle of the heart to a second pacing signal delivered by the medical device to cause or assist in causing a second cardiac cycle of the heart, wherein the processing circuitry is configured to: define an onset point within the first cardiac cycle, wherein the onset point is indicative of a cardiac indication of the heart occurring during the first cardiac cycle, and wherein the onset point precedes or is substantially concurrent with a diastole indicator indicative of a diastole of the first cardiac cycle, define an end point within the first cardiac cycle, wherein the end point occurs subsequent to the diastole indicator, and control the interval of the medical device to cause the second pacing signal to be subsequent to the end point, thereby limiting the heart rate of the heart.

2. The medical system of claim 1, wherein the cardiac indication is indicative of a heart sound of the heart during the first cardiac cycle.

3. The medical system of claim 1 or claim 2, wherein the cardiac indication includes at least one of an SI indication indicative of an SI sound of the heart, an S2 indication indicative of an S2 sound of the heart, an S3 indication indicative of an S3 sound of the heart, or an S4 indication indicative of an S4 sound of the heart4. The medical system of claim 3, wherein the processing circuitry is configured to define the onset point using one or more of the SI indication or the S2 indication.

5. The medical system of any of claims 1-4, wherein the diastole indicator includes at least one of an S2 indication indicative of an S2 sound of the heart, an S3 indication indicative of an S3 sound of the heart, or an S4 indication indicative of an S4 sound of the heart.Docket No: A0011909W0016. The medical system of claim 5, wherein the processing circuitry is configured to define the end point using one or more of the S3 indication or the S4 indication.

7. The medical system of any of claims 1-6, wherein the processing circuitry is configured to define the end point by monitoring the elapse of a time window which commences at the onset point and concludes at the end point.

8. The medical system of any of claims 1-7, wherein the processing circuitry is configured to define a minimum interval extending from the delivery of the first pacing signal to the end point, and where the processing circuitry is configured to control the medical device to cause the interval to be greater than or equal to the minimum interval.

9. The medical system of claim 8, wherein the processing circuitry is configured to define a maximum pacing rate of the medical device based on the minimum interval, wherein the maximum pacing rate defines a quantity of pacing signals delivered by the medical device over a time period, and cause the medical device to limit a number of pacing signals delivered over the time period to less than or equal to the maximum pacing rate.

10. The medical system of claim 8 or claim 9, wherein the processing circuitry is configured to define an interlude commencing at the onset point and extending to the end point, and wherein the processing circuitry is configured to define the minimum interval using the interlude.

11. The medical system of claim 10, wherein the processing circuitry is configured to: determine a heart rate of the heart, and define the interlude using a reference time window associated with the heart rate.

12. The medical system of any of claims 8-11, wherein: the medical device is configured to deliver a plurality of pacing signals subsequent to the second pacing signal,Docket No: A0011909W001 the medical device is configured to separate each pacing signal in the plurality of pacing signals from another signal in the plurality of pacing signals at least by the minimum interval.

13. The medical system of any of claims 1-12, wherein the processing circuitry is configured to: control the interval of the medical device for a plurality of cardiac cycles, determine the heart rate of the heart for each cardiac cycle of the plurality of cardiac cycles, and associate the interval controlled for the each cardiac cycle with the heart rate determined for the each cardiac cycle.

14. The medical system of any of claims 1-13, wherein the processing circuitry is configured to: define a plurality of reference time windows, define a reference end point using a reference time window of the plurality of reference time windows, wherein the reference time window separates the onset point and the reference end point, determine if the reference end point occurs subsequent to the diastole indicator, and use, if the reference end point occurs subsequent to the diastole indicator, the reference end point as the end point.

15. The medical system of any of claims 1-14, further comprising a detector configured to communicate a signal indicative of the cardiac indication to at least one of the processing circuitry or the medical device, and wherein the at least one of the processing circuitry or the medical device is configured to detect the cardiac indication using the signal.

Images