Dual chamber sensing in a medical device

Abstract

A medical device is configured to receive a first cardiac electrical signal as an atrial signal and a second cardiac electrical signal as a ventricular signal. The medical device can determine an atrial sensing signal from the atrial signal and the ventricular signal and compare the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals. The medical device may determine if a cardiac electrical stimulation pulse is needed according to a cardiac electrical stimulation therapy based on at least the sensed atrial event signal.

Description

DUAL CHAMBER SENSING IN A MEDICAL DEVICE

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 579,776, filed August 30, 2023, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The disclosure relates generally to a medical device and method for dual chamber sensing of cardiac electrical signals.BACKGROUND

[0003] Medical devices may sense electrophysiological signals from the heart, brain, nerve, muscle or other tissue. Such devices may be implantable, wearable or external devices using implantable and / or surface (skin) electrodes for sensing the electrophysiological signals. In some cases, such devices may be configured to deliver a therapy based on the sensed electrophysiological signals. For example, implantable or external cardiac pacemakers, cardioverter defibrillators, cardiac monitors and the like, sense cardiac electrical signals from a patient’s heart. The medical device may sense cardiac electrical signals from a heart chamber and deliver electrical stimulation therapies to the heart chamber using electrodes carried by a transvenous medical electrical lead that positions electrodes within the patient’s heart.

[0004] A cardiac pacemaker or cardioverter defibrillator may deliver therapeutic electrical stimulation to the heart via electrodes carried by one or more medical electrical leads coupled to the medical device. The electrical stimulation may include electrical pulses such as pacing pulses and / or cardioversion or defibrillation (CV / DF) shocks. In some cases, a medical device may sense cardiac electrical signals attendant to the intrinsic depolarizations of the myocardium and control delivery of stimulation pulses to the heart based on sensed cardiac electrical signals. Cardiac signals sensed within a heart chamber using endocardial electrodes carried by transvenous leads, for example, generally have a high signal strength and quality for reliably sensing cardiac electrical events, such as ventricular R-waves sensed from within a ventricle. Upon detection of an abnormal rhythm, such as bradycardia, tachycardia or fibrillation, an electrical stimulation pulse or pulses may be delivered to restore or maintain a more normal rhythm of the heart. For example, an implantable cardioverter dcfib''i | |;i|r»- riCD) may deliver pacing pulses to theheart of the patient upon detecting bradycardia or tachycardia or deliver CV / DF shocks to the heart upon detecting tachycardia or fibrillation.SUMMARY

[0005] In general, this disclosure is directed to a medical device and techniques for sensing cardiac electrical signals, detecting arrhythmias and delivering cardiac electrical stimulation therapies as needed. In some examples, the medical device may be coupled to an extracardiac medical lead carrying electrodes positioned outside of the heart for sensing cardiac electrical signals and delivering electrical stimulation pulses, including pacing pulses and / or CV / DF shocks. A medical device operating according to the techniques disclosed herein is configured to sense at least two different cardiac electrical signals from two different sensing electrode vectors. Based on processing and analysis of the two different cardiac electrical signals, the medical device may sense atrial P-waves and ventricular R-waves for use in detecting arrhythmias and / or delivering electrical stimulation therapies.

[0006] In some examples, paired sample points of two different cardiac electrical signals may be combined, e.g., added, subtracted, divided or multiplied, to determine an atrial sensing signal for sensing atrial P-waves. The paired sample points may or may not be time aligned sample points of the two different cardiac electrical signals. Paired sample points of the two different cardiac electrical signals may be combined to determine a ventricular sensing signal for sensing R-waves using a different operation than the operation used to determine the atrial sensing signal. In one example, the atrial sensing signal is determined as a first difference signal by subtracting the second cardiac signal, which may be a rectified signal, from the first cardiac electrical signal, which may be a rectified signal. In this example, the ventricular sensing signal may be determined as a second difference signal by subtracting the first cardiac electrical signal, which may be a rectified signal, from the second cardiac electrical signal, which may be a rectified signal. A P-wave sensing threshold may be applied to the first difference signal determined as the atrial sensing signal, which may be a non-rectified signal, for sensing atrial P-waves. An R-wave sensing threshold may be applied to the second difference signal determined as the ventricular sensing signal, which may be a non-rectified signal, for sensing ventricular R-waves. The sensed P-waves may be used in identifying ventricular event signal oversensing (e.g., P-waves falsely sensedcR-waves) that may lead to false ventriculartachyarrhythmia detection. The sensed P-waves may be used in controlling the delivery of atrial synchronous ventricular pacing. The sensed P-waves may be used in detecting atrial tachyarrhythmias and discriminating between supraventricular tachyarrhythmias and ventricular tachyarrhythmias and controlling tachyarrhythmia therapies delivered by the medical device.

[0007] In one example, the disclosure provides a medical device including a therapy delivery circuit configured to deliver a cardiac electrical stimulation therapy by generating one or more cardiac electrical stimulation pulses. The medical device includes a sensing circuit configured to receive a first cardiac electrical signal as an atrial signal and receive a second cardiac electrical signal as a ventricular signal. The sensing circuit is further configured to determine an atrial sensing signal from the atrial signal and the ventricular signal, compare the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals and sense an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The medical device further includes a control circuit in communication with the sensing circuit and the therapy delivery circuit. The control circuit being configured to determine if a cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal and control the therapy delivery circuit to either generate or not generate the cardiac electrical stimulation pulse according to the determined need for a cardiac electrical stimulation pulse.

[0008] In another example, the disclosure provides a method including receiving a first cardiac electrical signal as an atrial signal, receiving a second cardiac electrical signal as a ventricular signal and determining an atrial sensing signal from the atrial signal and the ventricular signal. The method includes comparing the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals and sensing an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The method may include determining if a cardiac electrical stimulation pulse is needed according to a cardiac electrical stimulation therapy based on at least the sensed atrial event signal and either generating or not generating the cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

[0009] In yet another example, the disclosure provides a non-transitory computer readable medium storing a set of instructions that, when executed by control circuitry of a medicaldevice, cause the medical device to receive a first cardiac electrical signal as an atrial signal, receive a second cardiac electrical signal as a ventricular signal and determine an atrial sensing signal from the atrial signal and the ventricular signal. The instructions further cause the medical device to compare the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals and sense an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The instructions may further cause the medical device to determine if a cardiac electrical stimulation pulse is needed according to a cardiac electrical stimulation therapy based on at least the sensed atrial event signal and either generate or not generate a cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

[0010] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. Further details of one or more examples are set forth in the accompanying drawings and the description below.BRIEF DESCRIPTION OF DRAWINGS

[0011] FIGs. 1A and IB are conceptual diagrams of one example of a medical device system that may be configured to sense cardiac event signals, detect arrhythmia and deliver electrical stimulation therapy according to the techniques disclosed herein.

[0012] FIGs. 2A-2C are conceptual diagrams of a patient implanted with a medical device system in a different implant configuration than the arrangement shown in FIGs. 1A-1B.

[0013] FIG. 3 is a conceptual diagram illustrating another example of an implantable medical device (IMD) that may be configured to sense cardiac signals according to the techniques disclosed herein and provide cardiac pacing.

[0014] FIG. 4 is a conceptual diagram of an implantable medical device according to one example.

[0015] FIG. 5 is a conceptual diagram of circuitry that may be included in a sensing circuit of the implantable medical device shown in FIG. 4 according to one example.

[0016] FIG. 6 is a conceptual diagram of an atrial sensing signal and a ventricular sensing signal that may be determined by the sensing circuit of FIG. 5 according to some examples.

[0017] FIG. 7 is a flow chart of a method that may be performed by a medical device for sensing cardiac event signals and controlling cardiac electrical stimulation therapies according to some examples.

[0018] FIG. 8 is a flow chart of a method for sensing cardiac event signals by a medical device according to another example.

[0019] FIG. 9 is a flow chart of a method for sensing cardiac event signals by a medical device according to another example.

[0020] FIG. 10 is a flow chart of a method for detecting ventricular tachyarrhythmia by an IMD according to some examples.

[0021] FIG. 11 is a flow chart of a method for detecting tachyarrhythmia and controlling VT / VF therapies by an IMD according to another example.DETAILED DESCRIPTION

[0022] In general, this disclosure describes a medical device and techniques for sensing cardiac event signals including ventricular event signals, e.g., R-waves attendant to ventricular depolarizations, and atrial event signals, e.g., P-waves attendant to atrial depolarizations. The medical device may control delivery of electrical stimulation therapies based on the sensed cardiac event signals. In various examples, the medical device performing the techniques disclosed herein may be included in an ICD system capable of sensing cardiac electrical signals, detecting arrhythmia based on an analysis of the sensed cardiac electrical signals, and delivering electrical stimulation therapy for treating the arrhythmia, e.g., to promote or restore a more normal heart rhythm. In some examples, the ICD is coupled to an extra-cardiovascular lead. As used herein, the term “extra-cardiovascular” refers to a position outside the blood vessels, heart, and pericardium surrounding the heart of a patient. Implantable electrodes carried by extra- cardiovascular leads may be positioned extra-thoracically (outside the ribcage and sternum) or intra-thoracically (beneath the ribcage or sternum) but generally not in intimate contact with myocardial tissue, e.g., within the heart or within the pericardium. In other examples, a transvenous extra-cardiac lead may carry implantable electrodes that can be positioned intravenously but outside the heart in an extra-cardiac location, e.g., within the internal thoracic vein, jugular vein, or other vein, for sensing cardiac electrical signals and delivering cardiac pacing pulses from a location away from the heart. In still otherexamples, electrodes used for sensing cardiac electrical signals by a medical device for sensing cardiac event signals according to the techniques disclosed herein may be carried by leads advanced into a heart chamber or positioned on a heart chamber. In still other examples, electrodes used for sensing cardiac electrical signals by a medical device for sensing cardiac event signals according to the techniques disclosed herein may be carried by the medical device housing when the device is a leadless pacemaker that can be advanced into a heart chamber or positioned on a heart chamber.

[0023] FIGs. 1A and IB are conceptual diagrams of one example of an IMD system, in this case an ICD system 10, that may be configured to sense cardiac electrical signals, detect arrhythmia and deliver electrical stimulation therapy according to the techniques disclosed herein. FIG. 1 A is a front view of ICD system 10 implanted within patient 12. FIG. IB is a side view of ICD system 10 implanted within patient 12. ICD system 10 includes an ICD 14 connected to an electrical stimulation and sensing lead 16, positioned in an extra-cardiovascular location in this example. FIGs. 1A and IB are described in the context of an ICD system 10 capable of providing high voltage CV / DF shocks and / or cardiac pacing pulses in response to detecting a cardiac arrhythmia based on processing of sensed cardiac electrical signals. The techniques for sensing cardiac event signals as disclosed herein may be implemented in a cardiac monitoring device that does not necessarily include cardiac pacing and / or CV / DF shock delivery capabilities in some examples. Furthermore, the techniques disclosed herein for sensing cardiac electrical signals and detecting arrhythmia may be implemented in a variety of medical devices including external or implantable cardiac monitors, pacemakers, and ICDs.

[0024] ICD 14 includes a housing 15 that forms a hermetic seal that protects internal components of ICD 14. The housing 15 of ICD 14 may be formed of a conductive material, such as titanium or titanium alloy. The housing 15 may function as an electrode (sometimes referred to as a “can” electrode). Housing 15 may be used as an active can electrode for use in delivering CV / DF shocks or other high voltage pulses delivered using a high voltage therapy circuit. In other examples, housing 15 may be available for use in delivering unipolar, relatively lower voltage cardiac pacing pulses and / or for sensing cardiac electrical signals in combination with electrodes carried by lead 16. In other instances, the housing 15 of ICD 14 may include a plurality of electrodes on an outer portion of the housing. The outer portion(s) of the housing 15 functioning as anelectrode(s) may be coated with a material, such as titanium nitride, e.g., for reducing post- stimulation polarization artifact.

[0025] ICD 14 includes a connector assembly 17 (also referred to as a connector block or header) that includes electrical feedthroughs crossing housing 15 to provide electrical connections between conductors extending within the lead body 18 of lead 16 and electronic components included within the housing 15 of ICD 14. As will be described in further detail herein, housing 15 may house one or more processing circuits, memories, transceivers, cardiac electrical signal sensing circuitry, therapy delivery circuitry, power sources and other components for sensing cardiac electrical signals, detecting a heart rhythm, and controlling and delivering electrical stimulation pulses to treat an abnormal heart rhythm.

[0026] Elongated lead body 18 has a proximal end 27 that includes a lead connector (not shown) configured to be connected to ICD connector assembly 17 and a distal portion 25 that includes one or more electrodes. Elongated lead body 18 has a terminal, free distal end 29. In the example illustrated in FIGs. 1A and IB, the distal portion 25 of lead body 18 includes defibrillation electrodes 24 and 26 and pace / sense electrodes 28, 30 and 31. In some cases, defibrillation electrodes 24 and 26 may together form a defibrillation electrode in that they may be configured to be activated concurrently. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes in which case each of the electrodes 24 and 26 may be activated independently.

[0027] Electrodes 24 and 26 (and in some examples housing 15) are referred to herein as “defibrillation electrodes” because they can be utilized, individually or collectively, for delivering high voltage stimulation therapy (e.g., CV / DF shocks). Electrodes 24 and 26 may be elongated coil electrodes and generally have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to pacing and sensing electrodes 28, 30 and 31. However, electrodes 24 and 26 and housing 15 may also be utilized to provide pacing functionality, sensing functionality or both pacing and sensing functionality in addition to or instead of high voltage stimulation therapy. In this sense, the use of the term “defibrillation electrode” herein should not be considered as limiting the electrodes 24 and 26 for use in only high voltage CV / DF shock therapy applications. For example, either of electrodes 24 and 26 may be used as a sensing electrode in a sensingelectrode vector for sensing cardiac electrical signals and determining a need for an electrical stimulation therapy.

[0028] Electrodes 28, 30 and 31 are relatively smaller surface area electrodes which are available for use in sensing electrode vectors for sensing cardiac electrical signals and may be used for delivering relatively low voltage pacing pulses in some configurations. Electrodes 28, 30 and 31 are referred to as pace / sense electrodes because they are generally configured for use in low voltage applications, e.g., used as either a cathode or anode for delivery of pacing pulses and / or sensing of cardiac electrical signals, as opposed to delivering high voltage CV / DF shocks. In some instances, electrodes 28, 30 and 31 may provide only pacing functionality, only sensing functionality or both.

[0029] ICD 14 may obtain cardiac electrical signals corresponding to electrical activity of heart 8 via a combination of sensing electrode vectors that include combinations of electrodes 24, 26, 28, 30 and / or 31. In some examples, housing 15 of ICD 14 is used in combination with one or more of electrodes 24, 26, 28, 30 and / or 31 in at least one sensing electrode vector. Various sensing electrode vectors utilizing combinations of electrodes 24, 26, 28, 30 and 31 and housing 15 are described below for sensing one or more cardiac electrical signals. Each cardiac electrical signal that is sensed by ICD 14 may be received using a different sensing electrode vector, which may be selected by sensing circuitry included in ICD 14. As described herein, in some examples the cardiac electrical signal(s) received via a selected sensing electrode vector may be used by ICD 14 for sensing cardiac event signals attendant to intrinsic depolarizations of the myocardium, e.g., R- waves and P-waves. Sensed cardiac event signals may be used for determining the heart rate and determining a need for cardiac pacing, e.g., for treating bradycardia or asystole for preventing a long ventricular pause, delivering atrial synchronous ventricular pacing, or for determining a need for tachyarrhythmia therapies, e.g., anti-tachycardia pacing (ATP) or CV / DF shocks.

[0030] In the example illustrated in FIGs. 1A and IB, electrode 28 is located proximal to defibrillation electrode 24, and electrode 30 is located between defibrillation electrodes 24 and 26. A third pace / sense electrode 31 may be located distal to defibrillation electrode 26, proximate to or on the distal end 29 of lead body 18. Electrodes 28, 30 and 31 are illustrated as ring electrodes; however, electrodes 28, 30 and 31 may comprise any of a number of different types of electrodes, including ring electrodes, short coil electrodes,hemispherical electrodes, directional electrodes, segmented electrodes, or the like. Distal- most electrode 31 is shown as a ring electrode circumscribing the lead body 18 adjacent to the distal end 29 of lead body 18. However, electrode 31 may take the form of a tip electrode positioned on the distal end 29 of lead body 18. In this case, electrode 31 may be a screw-in helical electrode, hook electrode, button electrode or other type of tip electrode. Electrodes 28, 30 and 31 may be positioned at other locations along lead body 18 and are not necessarily limited to the positions shown. In other examples, lead 16 may include fewer or more pace / sense electrodes and / or defibrillation electrodes than the example shown here.

[0031] In the example shown, lead 16 extends subcutaneously or submuscularly over the ribcage 32 medially from the connector assembly 27 of ICD 14 toward a center of the torso of patient 12, e.g., toward xiphoid process 20 of patient 12. At a location near xiphoid process 20, lead 16 bends or turns and extends superiorly, subcutaneously or submuscularly, over the ribcage and / or sternum, substantially parallel to sternum 22. Although illustrated in FIG. 1A as being offset laterally from and extending substantially parallel to sternum 22, the distal portion 25 of lead 16 may be implanted at other locations, such as over sternum 22, offset to the right or left of sternum 22, angled laterally from sternum 22 toward the left or the right, or the like. Alternatively, lead 16 may be placed along other subcutaneous or submuscular paths. The path of extra-cardiovascular lead 16 may depend on the location of ICD 14, the arrangement and position of electrodes carried by the lead body 18, and / or other factors. The techniques disclosed herein are not limited to a particular path of lead 16 or final locations of electrodes 24, 26, 28, 30 and 31.

[0032] Electrical conductors (not illustrated) extend through one or more lumens of the elongated lead body 18 of lead 16 from the lead connector at the proximal lead end 27 to electrodes 24, 26, 28, 30 and 31 located along the distal portion 25 of the lead body 18. The elongated electrical conductors contained within the lead body 18, which may be separate respective insulated conductors within the lead body 18, are each electrically coupled with respective defibrillation electrodes 24 and 26 and pace / sense electrodes 28,30 and 31. The respective conductors electrically couple the electrodes 24, 26, 28, 30 and31 to circuitry, such as a therapy delivery circuit and / or a sensing circuit, of ICD 14 via connections in the connector assembly 17, including associated electrical feedthroughs crossing housing 15. The electrical conductors transmit electrical stimulation pulses from atherapy delivery circuit within ICD 14 to one or more of defibrillation electrodes 24 and 26 and / or pace / sense electrodes 28, 30 and 31 and transmit electrical signals produced by the patient’s heart 8 from one or more of defibrillation electrodes 24 and 26 and / or pace / sense electrodes 28, 30 and 31 to the sensing circuit within ICD 14.

[0033] The lead body 18 of lead 16 may be formed from a non-conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and / or other appropriate materials, and shaped to form one or more lumens within which the one or more conductors extend. Lead body 18 may be tubular or cylindrical in shape. In other examples, the distal portion 25 (or all of) the elongated lead body 18 may have a flat, ribbon or paddle shape. Lead body 18 may be formed having a preformed distal portion 25 that is generally straight, curving, bending, serpentine, undulating or zig-zagging.

[0034] In the example shown, lead body 18 includes a curving distal portion 25 having two “C” shaped curves, which together may resemble the Greek letter epsilon, “s.” Defibrillation electrodes 24 and 26 are each carried by one of the two respective C-shaped portions of the lead body distal portion 25. The two C-shaped curves are seen to extend or curve in the same direction away from a central axis of lead body 18, along which pace / sense electrodes 28 and 30 are positioned. Pace / sense electrodes 28, 30 and 31 may, in some instances, be approximately aligned with the central axis of the straight, proximal portion of lead body 18 such that mid-points of defibrillation electrodes 24 and 26 are laterally offset from pace / sense electrodes 28, 30 and 31.

[0035] Other examples of extra-cardiovascular leads including one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by curving, serpentine, undulating or zig-zagging distal portion of the lead body 18 that may be implemented with the techniques described herein are generally disclosed in U.S. Patent No. 10,675,478 (Marshall, et al.), incorporated herein by reference in its entirety. The techniques disclosed herein are not limited to any particular lead body design, however. In other examples, lead body 18 is a flexible elongated lead body without any pre-formed shape, bends or curves.

[0036] ICD 14 may analyze the cardiac electrical signal(s) received from sensing electrode vectors to monitor for abnormal rhythms, such as asystole, bradycardia, supraventricular tachycardia (SVT), ventricular tachycardia (VT) and / or ventricular fibrillation (VF). ICD 14 may analyze the rate of sensed cardiac event signals, the pattern of sensed cardiac event signals, and / or morphology of the cardiac electrical signals tomonitor for a long pause, bradycardia, atrial tachyarrhythmia and ventricular tachyarrhythmia, as examples, in accordance with techniques disclosed herein. ICD 14 may generate and deliver electrical stimulation therapy in response to detecting a tachyarrhythmia, e.g., VT or VF (VT / VF), using a therapy delivery electrode vector which may be selected from any of the available electrodes 24, 26, 28, 30, 31 and / or housing 15. ICD 14 may deliver ATP in response to VT detection and in some cases may deliver ATP prior to a CV / DF shock or during high voltage capacitor charging in an attempt to avert the need for delivering a CV / DF shock. If ATP does not successfully terminate VT or when VF is detected, ICD 14 may deliver one or more CV / DF shocks via one or both of defibrillation electrodes 24 and 26 and / or housing 15.

[0037] In the absence of a sensed ventricular event signal, e.g., when a long pause in ventricular activity or asystole is detected, ICD 14 may generate and deliver a pacing pulse, such as a post-shock pacing pulse or bradycardia pacing pulse, to capture and pace the ventricles. The pacing pulses may be delivered using a pacing electrode vector that includes one or more of the electrodes 24, 26, 28, 30 and 31 and the housing 15 of ICD 14. In some examples, atrial synchronous ventricular pacing pulses may be delivered by ICD 14 in response to P-waves sensed by sensing circuitry of ICD 14 according to the techniques disclosed herein.

[0038] In some examples, at least one sensing electrode vector may be selected for sensing cardiac signal segments corresponding to one sensed R-wave and / or cardiac signal segments that extend over a specified time interval that may encompass more than one sensed R-wave for use in detecting and classifying cardiac rhythms. Morphology analysis of a sensed cardiac electrical signal may be triggered by a threshold number of R- waves sensed at tachyarrhythmia intervals. According to the techniques disclosed herein, the ICD 14 may reduce how often morphology analysis is performed for detecting ventricular tachyarrhythmia by avoiding or detecting oversensing of P-waves as false R-waves. The improved dual chamber P-wave and R-wave sensing techniques disclosed herein may enable ICD 14 to detect and discriminate SVTs and VT / VF with greater reliability based on the rate and patterns of sensed atrial event signals and sensed ventricular event signals without performing cardiac signal morphology analysis or with reduced cardiac signal morphology analysis compared to an ICD configured for only single chamber ventricular sensing. In an ICD that is configured for single chamber ventricular sensing, detection anddiscrimination of SVTs and VT / VF may require relatively greater processing burden and power associated with performing analysis of the cardiac signal waveform morphology to avoid false VT / VF detections due to P-wave oversensing and / or due to SVT that may be conducted to the ventricles.

[0039] ICD 14 is shown implanted subcutaneously on the left side of patient 12 along the ribcage 32. ICD 14 may, in some instances, be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. ICD 14 may, however, be implanted at other subcutaneous or submuscular locations in patient 12. For example, ICD 14 may be implanted in a subcutaneous pocket in the pectoral region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22 and bend or turn and extend inferiorly from the manubrium to the desired location subcutaneously or submuscularly. In yet another example, ICD 14 may be placed abdominally. Lead 16 may be implanted in other extra-cardiovascular locations as well. For instance, as described with respect to FIGs. 2A-2C, the distal portion 25 of lead 16 may be implanted underneath the sternum / ribcage in the substernal space. FIGs. 1A and IB are illustrative in nature and should not be considered limiting in the practice of the techniques disclosed herein.

[0040] A medical device operating according to techniques disclosed herein may be coupled to a transvenous or non-transvenous lead in various examples for carrying electrodes for sensing cardiac electrical signals and delivering electrical stimulation therapy. For example, the medical device, such as ICD 14, may be coupled to an extra- cardiovascular lead as illustrated in the accompanying drawings, referring to a lead that positions electrodes outside the blood vessels, heart, and pericardium surrounding the heart of a patient. Implantable electrodes carried by extra-cardiovascular leads may be positioned extra- thoracic ally (outside the ribcage and sternum), subcutaneously or submuscularly, or intra-thoracically (beneath the ribcage or sternum, sometimes referred to as a sub-sternal position) and may not necessarily be in intimate contact with myocardial tissue. An extra-cardiovascular lead may also be referred to as a “non-transvenous” lead. In some examples, a non-transvenous lead coupled to ICD 14 may be advanced to position the distal portion of the lead carrying one or more electrodes or on or within the pericardium.

[0041] In other examples, the medical device may be coupled to a transvenous lead that positions electrodes within a blood vessel, which may remain outside the heart in an “extra-cardiac” location or be advanced to position electrodes within a heart chamber. For instance, a transvenous medical lead may be advanced along a venous pathway to position electrodes in an extra-cardiac location within the internal thoracic vein (ITV), an intercostal vein, the superior epigastric vein, or the azygos, hemiazygos, or accessory hemiazygos veins, as examples. In still other examples, a transvenous lead may be advanced to position electrodes within the heart, e.g., within an atrial and / or ventricular heart chambers. In still other examples, a leadless medical device may be implanted within a heart chamber carrying housing-based electrodes for sensing cardiac electrical signals and delivering electrical stimulation pulses according to a therapy protocol based at least in part on the cardiac event signals sensed according to the techniques disclosed herein.

[0042] An external device 40 is shown in telemetric communication with ICD 14 by a wireless communication link 42 in FIG. 1A. External device 40 may include a processor 52, memory 53, display 54, user interface 56 and telemetry unit 58. Processor 52 controls external device operations and processes data and signals received from ICD 14. Display unit 54, which may include a graphical user interface, displays data and other information to a user for reviewing ICD operation and programmed parameters as well as cardiac electrical signals retrieved from ICD 14.

[0043] User interface 56 may include a mouse, touch screen, keypad or the like to enable a user to interact with external device 40 to initiate a telemetry session with ICD 14 for retrieving data from and / or transmitting data to ICD 14, including programmable parameters for controlling cardiac event signal sensing, arrhythmia detection and therapy delivery. Telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with a telemetry circuit included in ICD 14 and is configured to operate in conjunction with processor 52 for sending and receiving data relating to ICD functions via communication link 42.

[0044] Communication link 42 may be established between ICD 14 and external device 40 using a radio frequency (RF) link such as BLUETOOTH®, Wi-Fi, or Medical Implant Communication Service (MICS) or other RF or communication frequency bandwidth or communication protocols. Data stored or acquired by ICD 14, including physiological signals or associated data derived therefrom, results of device diagnostics, battery status,and histories of detected rhythm episodes and delivered therapies, etc., may be retrieved from ICD 14 by external device 40 following an interrogation command.

[0045] External device 40 may be embodied as a programmer used in a hospital, clinic or physician’s office to retrieve data from ICD 14 and to program operating parameters and algorithms in ICD 14 for controlling ICD functions. External device 40 may alternatively be embodied as a home monitor or handheld device. External device 40 may be used to program cardiac signal sensing parameters, cardiac rhythm detection parameters and therapy control parameters used by ICD 14. At least some control parameters used in sensing cardiac event signals and detecting arrhythmias according to the techniques disclosed herein as well as therapy delivery may be programmed into ICD 14 using external device 40 in some examples.

[0046] FIGs. 2A-2C are conceptual diagrams of patient 12 implanted with extra- cardiovascular ICD system 10 in a different implant configuration than the arrangement shown in FIGs. 1A-1B. FIG. 2A is a front view of patient 12 implanted with ICD system 10. FIG. 2B is a side view of patient 12 implanted with ICD system 10. FIG. 2C is a transverse view of patient 12 implanted with ICD system 10. In this arrangement, extra- cardiovascular lead 16 of system 10 is implanted at least partially underneath sternum 22 of patient 12. Eead 16 extends subcutaneously or submuscularly from ICD 14 toward xiphoid process 20 and at a location near xiphoid process 20 bends or turns and extends superiorly within anterior mediastinum 36 (see FIG. 2C) in a substemal position.

[0047] Anterior mediastinum 36 may be viewed as being bounded laterally by pleurae 39, posteriorly by pericardium 38, and anteriorly by sternum 22 (see FIG. 2C). The distal portion 25 of lead 16 may extend along the posterior side of sternum 22 substantially within the loose connective tissue and / or substernal musculature of anterior mediastinum 36. A lead implanted such that the distal portion 25 is substantially within anterior mediastinum 36, may be referred to as a “substemal lead.”

[0048] In the example illustrated in FIGS. 2A-2C, lead 16 is located substantially centered under sternum 22. In other instances, however, lead 16 may be implanted such that it is offset laterally from the center of sternum 22. In some instances, lead 16 may extend laterally such that distal portion 25 of lead 16 is undemeath / below the ribcage 32 in addition to or instead of sternum 22. In other examples, the distal portion 25 of lead 16may be implanted in other extra-cardiac, intra-thoracic locations, including in the pleural cavity or around the perimeter of and adjacent to or within the pericardium 38 of heart 8.

[0049] In the various example implant locations of lead 16 and electrodes 24, 26, 28 30 and 31 shown and described herein, cardiac signals sensed by ICD 14 may have a relatively low and / or variable signal strength, e.g., caused by postural changes, respiration or other body movement, and / or may be contaminated by skeletal muscle myopotentials and / or environmental EMI. Undersensing of R-waves or fibrillation waves may result in an undetected tachyarrhythmia when ATP or CV / DF therapy may be needed. Oversensing of P-waves, T- waves, skeletal muscle myopotentials or other noise as false R-waves may lead to a false tachyarrhythmia detection resulting in unnecessary ATP or CV / DF shock delivery. In other instances, oversensing of cardiac signals (e.g., falsely sensing P-waves or T-waves as being R-waves) or non-cardiac noise (skeletal muscle myopotentials, EMI or other electrical noise) may result in withholding of pacing pulses when cardiac pacing is needed to prevent a long ventricular pause or asystole. Undersensing of R-waves or fibrillation waves may cause unneeded ventricular pacing pulse delivery that could confound VT / VF detection. Techniques disclosed herein provide improvements in sensing cardiac event signals (e.g., R-waves and P-waves) and detecting arrhythmias by an implantable medical device. Improvements in sensing and detecting arrhythmias with high sensitivity and specificity can improve the performance of the implantable medical device in monitoring for arrhythmias and for delivering appropriate electrical stimulation therapy for successfully treating the detected arrhythmia.

[0050] FIG. 3 is a conceptual diagram illustrating another example of an implantable medical device (IMD) that may be configured to sense cardiac signals according to the techniques disclosed herein and provide cardiac pacing. In this example, the IMD is shown as a pacemaker 114, implanted within the right atrium (RA) of a patient’s heart. In some examples, pacemaker 114 is a transcatheter, leadless pacemaker that can be implanted wholly within a heart chamber. Pacemaker 114 may be reduced in size compared to subcutaneously implanted pacemakers or ICDs and may be generally cylindrical in shape to facilitate transvenous implantation via a delivery catheter. For example, pacemaker housing 115 may have a generally cylindrical, longitudinal sidewall extending from a distal end 170 to a proximal end 172 of pacemaker 114. Distal end 170 is referred to as “distal” in that it is expected to be the leading end as pacemaker 114 is advanced through adelivery tool, such as a catheter, and placed against a targeted pacing site. In other examples, housing 115 may have a generally prismatic shape. The housing 115 encloses the electronics and a power supply for sensing cardiac signals, producing pacing pulses and controlling therapy delivery and other functions of pacemaker 114 as described herein.

[0051] Pacemaker 114 may be configured to sense atrial and ventricular event signals, e.g., P-waves attendant to atrial depolarizations and R-waves attendant to ventricular depolarizations, according to the techniques disclosed herein. Pacemaker 114 may be configured as a dual chamber pacemaker capable of sensing both atrial and ventricular event signals and delivering atrial pacing pulses and ventricular pacing pulses as needed based on the sensed atrial and / or ventricular event signals. In other examples, pacemaker 114 may be configured as a single chamber pacemaker capable of delivering only atrial pacing pulses or capable of delivering only ventricular pacing pulses but may still be capable of dual chamber sensing of both atrial and ventricular event signals. In still other examples, pacemaker 114 may be configured to sense and pace a single heart chamber, atrial or ventricular, using the techniques disclosed herein to determine an atrial sensing signal or a ventricular sensing signal using two different cardiac electrical signals, one atrial signal and one ventricular signal, received by sensing circuitry of pacemaker 114.

[0052] Pacemaker 114 may be a leadless pacemaker that includes electrodes carried on the pacemaker housing without requiring medical electrical leads extending from pacemaker 114 for sensing cardiac electrical signals and delivering cardiac pacing pulses. Pacemaker 114 is shown including electrodes 162, 164 and 165, spaced apart along the housing 115 of pacemaker 114, for sensing cardiac electrical signals and delivering pacing pulses. In other examples, pacemaker 114 may include more than three electrodes as shown here, but at least three electrodes may be provided for sensing an atrial signal and a ventricular signal using two different sensing electrode vectors. Electrode 164 is shown as a tip electrode extending from distal end 170 of housing 115. Electrodes 162 and 165 are shown as ring electrodes along the lateral sidewall of housing 115. Electrodes 162 and 165 may be ring electrodes circumscribing the lateral sidewall, for example adjacent proximal end 172 and adjacent distal end 170, respectively.

[0001] In the example shown, pacemaker 114 is implanted in the RA for providing ventricular pacing from an atrial location. Pacemaker 114 may be configured for delivering ventricular pacing pulses via the heart’s native conduction system and / orventricular myocardium from a RA approach. For example, the distal end of pacemaker 114 may be positioned at the inferior end of the interatrial septum, beneath the atrioventricular (AV) node and near the tricuspid valve annulus, generally in the Triangle of Koch, to position a tip electrode 164 for advancement into the interatrial septum toward the His bundle of the native His-Purkinje conduction system. Tip electrode 164 is shown as a screw-in helical electrode which may provide fixation of pacemaker 114 at an implant site as well as serving as a pacing and sensing electrode. Electrode 164 can be advanced from within the right atrial chamber to a ventricular pacing site, e.g., for delivering pacing to the His-Purkinje conduction system and / or for pacing of ventricular septal myocardial tissue.

[0053] A second electrode, e.g., a ring electrode 162 or ring electrode 165, may be spaced proximally from the tip electrode 164 for use with the tip electrode 164 for bipolar pacing of the right and left ventricles via the His-Purkinje system and / or ventricular myocardium. Ventricular pacing pulses delivered by pacemaker 114 may capture at least a portion of the His bundle and / or ventricular myocardium for delivering ventricular pacing to the ventricles, e.g., the right ventricle (RV) and / or left ventricle (LV), from an atrial implant location of pacemaker 114. The techniques disclosed herein are not necessarily limited to a particular implant location of pacemaker 114, however, and may be practiced in a pacemaker implanted in a variety of operative locations for providing cardiac signal sensing of atrial and / or ventricular events and, at least in some examples, delivering cardiac pacing to at least one heart chamber.

[0054] Pacemaker 114 may receive a first cardiac electrical signal as an atrial signal via the distal ring electrode 165 paired with the proximal ring electrode 162. Pacemaker 114 may receive a second cardiac electrical signal as a ventricular signal via the distal tip electrode 164 paired with the proximal ring electrode 162. As described below, paired sample points of the atrial signal and the ventricular signal may be combined in a first combination to determine an atrial sensing signal that is used for sensing atrial P-waves and / or combined in a second combination different than the first combination to determine a ventricular sensing signal that is used for sensing ventricular R-waves according to the techniques disclosed herein.

[0055] Electrodes 162, 164 and 165 may be, without limitation, titanium, platinum, iridium or alloys thereof and may include a low polarizing coating, such as titaniumnitride, iridium oxide, ruthenium oxide, platinum black, among others. Electrodes 162,164 and 165 may be positioned at locations along pacemaker 114 other than the locations shown. Electrodes 162, 164, 165 may be provided as other types of electrodes, such as button, fishhook, hemispherical, segmented, and are not necessarily limited to being a combination of one helical screw in electrode and two ring electrodes as shown here. Examples of various pacing electrode arrangements for providing cardiac pacing along the native conduction system of the heart and / or ventricular myocardium are generally disclosed in U.S. Patent No. 11,426,578 (Yang, et al.), and U.S. Patent No. 11,007,369 (Sheldon, et al.), both of which are incorporated herein by reference in their entirety.

[0056] Housing 115 is formed from a biocompatible material, such as a stainless steel or titanium alloy. In some examples, the housing 115 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide, among others. The entirety of the housing 115 may be insulated, but only electrodes 162, 164 and165 are uninsulated. Tip electrode 164 may serve as a cathode electrode and can be coupled to internal circuitry, e.g., a pacing pulse generator and cardiac electrical signal sensing circuitry, enclosed by housing 115 via an electrical feedthrough crossing housing 115. Electrodes 162 and 165 may be formed as a conductive portion of housing 115 defining respective ring electrodes that are electrically isolated from each other and from the other portions of the housing 115 as generally shown in FIG. 3.

[0057] Pacemaker 114 may include features for facilitating deployment to and fixation at an implant site. For example, pacemaker 114 may optionally include a delivery tool interface 171 at the proximal end 172 of pacemaker 114 that is configured to connect to a delivery device, such as a catheter, used to position pacemaker 114 at an implant location during an implantation procedure. The delivery tool interface 171 may enable a clinician to advance, retract and steer pacemaker 114 to an implant site and rotate pacemaker 114 to advance the helical tip electrode 164 into the cardiac tissue. Helical tip electrode 164 in this example provides fixation of pacemaker 114 at the implant site. In other examples, however, pacemaker 114 may include a set of fixation tines or other fixation members to secure pacemaker 114 to cardiac tissue. Numerous types of active and / or passive fixation members may be employed for anchoring or stabilizing pacemaker 114 in an implant position. Pacemaker 114 may be capable of bidirectional wireless communication with anexternal device 40 for programming sensing and pacing control parameters, e.g., as generally described above in conjunction with FIG. 1A.

[0058] Using the cardiac event signal sensing techniques disclosed herein for sensing atrial P-waves and ventricular R-waves, pacemaker 114 may be configured to operate in one or more pacing modes, such as atrial synchronous ventricular pacing, dual chamber pacing, atrial single chamber pacing and / or atrial asynchronous ventricular single chamber pacing. Using the cardiac event signal sensing techniques disclosed herein for sensing atrial P-waves and ventricular R-waves, pacemaker 114 may be configured to detect one or more types of tachyarrhythmia, such as atrial fibrillation (AF), atrial flutter, sinus tachycardia and / or other SVT rhythms. Pacemaker 114 may track an atrial tachyarrhythmia burden. For example, the cumulative AF episode time duration over 24 hours or other time periods may be tracked and stored in the pacemaker memory for transmitting to external device 40. Pacemaker 114 may use the cardiac event signal sensing techniques for detecting and discriminating SVT and VT / VF. When a detected tachyarrhythmia is determined to be an SVT, pacemaker 114 may deliver atrial ATP - to terminate the SVT in some examples. When VT / VF is detected based on an analysis of the rate of sensed P-waves, sensed R-waves and patterns of sensed P-waves and sensed R- waves, for example as generally described below in conjunction with FIG. 11, pacemaker 114 may be configured to withhold ATP delivery. In other examples, pacemaker 114 may be configured to deliver ATP to the ventricular chambers (e.g., using tip electrode 164 paired with ring electrode 162), e.g., when ICD 14 is co-implanted with pacemaker 114 so that CV / DF shock capabilities are available if ATP does not terminate or the VT / VF.

[0059] FIG. 4 is a conceptual diagram of a medical device configured to sense cardiac electrical signals and deliver cardiac electrical stimulation according to some examples. The electronic circuitry enclosed within housing 15 (shown conceptually as an electrode in FIG. 4) may include software, firmware and / or hardware that cooperatively monitor cardiac electrical signals, determine when an electrical stimulation therapy is necessary, and deliver therapy as needed according to programmed therapy delivery algorithms and control parameters. FIG. 4 is described with reference to ICD 14 of FIGs. 1 A-2C for the sake of illustration. It is to be understood that the circuitry and functionality generally described in conjunction with FIG. 4 and other flow charts and diagrams presented hereinwith reference to ICD 14 may be adapted as needed for implementation in the pacemaker 114 shown in FIG. 3.

[0060] ICD 14 may be coupled to a lead, such as lead 16 carrying electrodes 24, 26, 28, 30 and 31, for delivering electrical stimulation pulses to the patient’s heart and for sensing cardiac electrical signals. ICD 14 includes a control circuit 80, memory 82, therapy delivery circuit 84, cardiac electrical signal sensing circuit 86, and telemetry circuit 88. A power source 98 provides power to the circuitry of ICD 14, including each of the components 80, 82, 84, 86, and 88 as needed. Power source 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between power source 98 and each of the other components 80, 82, 84, 86 and 88 are to be understood from the general block diagram of FIG. 4 but are not shown for the sake of clarity. For example, power source 98 may be coupled to one or more charging circuits included in therapy delivery circuit 84 for charging holding capacitors included in therapy delivery circuit 84 that are discharged at appropriate times under the control of control circuit 80 for producing electrical pulses according to a therapy protocol. Power source 98 is also coupled to components of cardiac electrical signal sensing circuit 86, such as sense amplifiers, analog-to-digital converters, switching circuitry, etc. as needed.

[0061] The circuits shown in FIG. 4 represent functionality included in ICD 14 and may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions attributed to ICD 14 herein. Functionality associated with one or more circuits may be performed by separate hardware, firmware and / or software components, or integrated within common hardware, firmware and / or software components. For example, cardiac electrical signal sensing and analysis for detecting arrhythmia may be performed cooperatively by sensing circuit 86 and control circuit 80 and may include operations implemented in a processor or other signal processing circuitry included in sensing circuit 86 and / or control circuit 80 executing instructions stored in memory 82 and control signals such as blanking and timing intervals and sensing threshold amplitude signals sent from control circuit 80 to sensing circuit 86.

[0062] Control circuit 80 and sensing circuit 86 may include hardware configured to perform subroutines of signal processing and analysis techniques disclosed herein toreduce the processing burden associated with firmware and / or software execution of processing routines. For example hardware subroutines (HSRs) may be implemented in sensing circuit 86 and control circuit 80 to perform specific processing functions such as dedicated math operations, which may include any of sum, absolute value, difference, ratio, product, extrema, histogram counts, signal filtering (e.g., biquad filter, difference filter or other filters), etc. These HSRs could be called by control circuit firmware when processing and analyzing a cardiac signal for sensing cardiac event signals and detecting arrhythmia. These HSRs can unload the processing burden associated with firmware and / or software processing to reduce current drain of power source 98 and thereby extend the useful life of ICD 14. For example, as further described below, mathematical operations performed on pairs of sample points (operands) of two different cardiac electrical signals sensed by ICD 14 for determining one or more cardiac sensing signals from which cardiac event signals are detected may be executed by an HSR included in sensing circuit 86 or control circuit 80.

[0063] The various circuits of ICD 14 may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, state machine, HSR, or other suitable components or combinations of components that provide the described functionality. The particular form of software, hardware and / or firmware employed to implement the functionality disclosed herein will be determined primarily by the particular system architecture employed in the ICD and by the particular sensing, detection and therapy delivery methodologies employed by the ICD. Providing software, hardware, and / or firmware to accomplish the described functionality in the context of any modem medical device system, given the disclosure herein, is within the abilities of one of skill in the art.

[0064] Memory 82 may include any volatile, non-volatile, magnetic, or electrical non- transitory computer readable storage media, such as random access memory (RAM), readonly memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other memory device. Furthermore, memory 82 may include non-transitory computer readable media storing instructions that, when executed by one or more processing circuits, cause control circuit 80, sensing circuit 86 and / or other ICD components to perform various functions attributed to ICD 14 or thoseICD components. The non-transitory computer-readable media storing the instructions may include any of the media listed above.

[0065] Control circuit 80 communicates, e.g., via a data bus, with therapy delivery circuit 84 and sensing circuit 86 for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling delivery of cardiac electrical stimulation therapies in response to sensed cardiac signals. Therapy delivery circuit 84 and sensing circuit 86 may be electrically coupled to electrodes 24, 26, 28, 30 and 31 carried by lead 16 and / or the housing 15, which may function as a common or ground electrode or as an active can electrode for delivering CV / DF shock pulses or cardiac pacing pulses.

[0066] Cardiac electrical signal sensing circuit 86 (also referred to herein as “sensing circuit” 86) may be selectively coupled to electrodes 28, 30 and 31 and / or housing 15 in order to monitor electrical activity of the patient’s heart. Sensing circuit 86 may additionally be selectively coupled to defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector together or in combination with one or more of electrodes 28, 30 and 31 and / or housing 15. Sensing circuit 86 may be enabled to receive cardiac electrical signals from at least two sensing electrode vectors selected from the available electrodes 24, 26, 28, 30, 31 and housing 15 in some examples. At least two, three or more cardiac electrical signals from two, three or more different sensing electrode vectors may be received simultaneously by sensing circuit 86 in some examples. Sensing circuit 86 may monitor one or more cardiac electrical signals for sensing cardiac event signals, e.g., P- waves attendant to intrinsic atrial myocardial depolarizations and R-waves attendant to intrinsic ventricular myocardial depolarizations.

[0067] In some examples, sensing circuit 86 may include multiple sensing channels 81, 83, 85 and 87 for receiving multiple cardiac electrical signals simultaneously for sensing cardiac event signals and performing cardiac electrical signal morphology analysis. Sensing circuit 86 may include switching circuitry for selecting which of electrodes 24, 26, 28, 30, 31 and housing 15 are coupled to each sensing channel 81, 83, 85 and 87. In this example, sensing circuit 86 includes an atrial (A) sensing channel 81, a first ventricular (V) sensing channel 83, a second V sensing channel 85 and a morphology signal channel 87.

[0068] Each sensing channel 81, 83, 85 and 87 may be configured to amplify, filter and digitize the cardiac electrical signal received from a respective sensing electrode vector toimprove the quality of the received signal for sensing cardiac event signals and / or for signal morphology analysis. The cardiac event detection circuitry within sensing circuit 86 may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers or other analog and / or digital components as described further in conjunction with FIG. 5. A cardiac event sensing threshold may be automatically adjusted by each sensing channel 81, 83 and 85 under the control of control circuit 80, based on sensing threshold control parameters, such as various timing intervals and sensing threshold amplitude values that may be determined by control circuit 80, stored in memory 82, and / or controlled by hardware, firmware and / or software of control circuit 80 and / or sensing circuit 86. For example, atrial (A) sensing channel 81 may apply a P-wave sensing threshold to an incoming cardiac electrical signal for sensing atrial P-waves. Each of V sensing channels 83 and 85 may apply an R-wave sensing threshold to a respective incoming cardiac electrical signal for sensing ventricular R-waves. Techniques for sensing cardiac event signals are described below in greater detail.

[0069] Upon sensing a cardiac event signal based on a sensing threshold crossing, sensing circuit 86 may pass a cardiac sensed event signal, e.g., an atrial sensed event (Asense) signal or a ventricular sensed event (Vsense) signal to control circuit 80. Asense and Vsense signals received from sensing circuit 86 by control circuit 80 can be used by control circuit 80 for determining sensed event intervals, e.g., PP intervals (PPIs) and RR intervals (RRIs) and in some cases PR intervals (PRIs) and / or RP intervals (RPIs). A PPI is the time interval between two consecutively received Asense signals received by control circuit 80 from A sensing channel 81. An RRI is the time interval between two consecutively Vsense signals received by control circuit 80 from the same V sensing channel 83 or 85, which may also be referred to as an “in-channel” sensed event interval. In some instances, when a Vsense signal is received following a delivered pacing pulse, the RRI is determined from the pacing pulse to the Vsense signal. As such, cardiac event intervals may include time intervals from a pacing pulse delivered by therapy delivery circuit 84 to a cardiac sensed event signal received from sensing circuit 86. A PRI is the time interval from an atrial event (sensed or paced) to the next Vsense signal. An RPI is the time interval from a ventricular event (sensed or paced) to the next Asense signal. Control circuit 80 may include a timing circuit 90 for determining cardiac event intervalssuch as PPIs and RRIs. Based on determined PPIs and / or RRIs (and in some examples RPIs and / or PRIs), control circuit 80 may detect atrial and / or ventricular arrhythmias, e.g., bradycardia, asystole, SVT, VT, and / or VF.

[0070] Illustrative techniques disclosed herein are described in conjunction with sensing circuit 86 including at least one A sensing channel 81 and at least one V sensing channel 83. As described below in conjunction with FIG. 5, an A sensing channel may receive a cardiac electrical signal, also referred to as an “atrial signal,” from an atrial sensing electrode vector. The A sensing channel 81 may additionally receive a ventricular signal from a V sensing channel 83 or 85 for determining an atrial sensing signal. The “atrial sensing signal” can be determined as a combination of the received atrial signal and the received ventricular signal. The atrial sensing signal can be a signal determined from at least two received signals that are combined, e.g., according to one or more mathematical operations, to produce the atrial sensing signal from which atrial event signals are detected. The A sensing channel 81 may apply a P-wave sensing threshold to the atrial sensing signal for detecting the atrial event signals. In some examples, two (or more) A sensing channels may be included for enabling control circuit 80 to validate Asense signals received from two different A sensing channels.

[0071] As described below in conjunction with FIG. 5, a V sensing channel 83 or 85 may receive a cardiac electrical signal, also referred to as an “ventricular signal,” from a ventricular sensing electrode vector. The V sensing channel 83 or 85 may additionally receive an atrial signal from the A sensing channel 81 for determining a ventricular sensing signal. The “ventricular sensing signal” can be determined as a combination of the received atrial signal and the received ventricular signal. The ventricular sensing signal can be a signal determined from at least two received signals that are combined, e.g., according to one or more mathematical operations, to produce the ventricular sensing signal from which ventricular event signals are detected. The V sensing channel 83 or 85 may apply an R-wave sensing threshold to the ventricular sensing signal for sensing ventricular event signals. In some examples, a second V sensing channel 85 may be included in sensing circuit 86. Control circuit 80 may be configured to validate Vsense signals received from one V sensing channel based on Vsense signals received from the second V sensing channel. For example, a Vsense signal received from a first V sensing channel 83 or 85 may be identified as a true or valid Vsense signal when a Vsense isreceived from the second V sensing channel 85 or 83 within a validation time window from the first V sensing channel. Examples of techniques for two-channel sensing of ventricular event signals that may be performed by control circuit 80 for validating Vsense signals received from two V sensing channels are generally disclosed in U.S. Patent Application Publication No. 2023 / 0100431 Al (Liu et al., filed August 29, 2022), the content of which is incorporated herein by reference in its entirety.

[0072] As shown in FIG. 4, sensing circuit 86 may include a morphology signal channel 87 for passing a digitized electrocardiogram (ECG) signal to control circuit 80 for performing morphology analysis. Control circuit 80 may be configured to enable or power on morphology signal channel 87 to sense a cardiac electrical signal that can be passed to control circuit 80 for processing and analysis. Time segments of the morphology signal received from morphology signal channel 87 may be buffered in memory 82. In various examples, a relatively short time segment, e.g., 150 to 600 ms or about 180 to 500 ms in duration, may be buffered in response to a Vsense signal received from at least one of V sensing channels 83 or 85. A morphology analysis, e.g., R-wave morphology matching, may be performed for verifying a Vsense signal as being a true R-wave or, in some instances, identifying a likely VT / VF waveform (e.g., a non-sinus QRS waveform based on a low R-wave morphology matching score, e.g., when compared to an R-wave template representative of an R-wave conducted from the atria during normal sinus rhythm).

[0073] In other examples, control circuit 80 may be configured to enable morphology signal channel 87 to sense and pass a morphology signal for buffering, processing and analyzing relatively longer cardiac signal segments, e.g., 0.5 to 5 second segments or 0.5 to 3 second segments as examples. The relatively longer cardiac signal segments may be obtained independent of the relative timing of Vsense or Asense signals received from sensing circuit 85. The relatively longer cardiac signal segments may be analyzed for detecting asystole, for example, when no Asense or Vsense signals are being received. The relatively longer cardiac signal segments may be analyzed for detecting evidence of VT / VF, e.g., when fibrillation waves or low amplitude R-waves may be undersensed by V sensing channels 83 and 85. Examples of methods for obtaining a time segment of a morphology signal and performing morphology analysis for detecting arrhythmia that may be implemented in conjunction with the techniques disclosed herein are generally disclosed in U.S. Patent Application Publication No. 2023 / 0148939A1 (Aranda Hernandezet al., filed October 7, 2022), the content of which is incorporated herein by reference in its entirety.

[0074] The four cardiac electrical signals received by sensing channels 81, 83, 85 and morphology signal channel 87 may be received from four different sensing electrode vectors selected from the available electrodes 24, 26, 28, 30 and 31 and housing 15. In other examples, two cardiac electrical signals may be received by sensing circuit 86 from two different sensing electrode vectors, with one signal passed to the first V sensing channel 83 and another signal passed to A sensing channel 81. Either or both of the two signals may be passed to control circuit 80 as a multi-bit digital ECG signal used by control circuit 80 for morphology analysis for analysis of a predetermined time segment of the ECG signal for detecting arrhythmias. A third cardiac electrical signal may be received by the second V sensing channel 85 if included. Examples of sensing electrode vectors that may be switchably connected to multiple sensing channels of sensing circuit 86 are described below in conjunction with FIG. 5.

[0075] Control circuit 80 may include a timing circuit 90 and an arrhythmia detection circuit 92. Timing circuit 90 may be configured to control various timers and / or counters used in setting various time intervals and windows used in sensing cardiac event signals, determining time intervals between received Asense signals and Vsense signals, performing morphology analysis and controlling the timing of cardiac pacing pulses and CV / DF shocks generated by therapy delivery circuit 84. Timing circuit 90 may start various timers in response to receiving Asense signals and Vsense signals from sensing circuit 86 for timing cardiac event intervals, e.g., PPIs and RRIs, between consecutively received cardiac event signals. Timing circuit 90 may pass the cardiac event intervals to arrhythmia detection circuit 92 for detecting and counting tachyarrhythmia intervals.

[0076] Arrhythmia detection circuit 92 may be configured to analyze cardiac event intervals received from timing circuit 90 and, in some examples, a cardiac electrical signal (also referred to herein as the “morphology signal”) received from morphology signal channel 87 for detecting arrhythmia. Arrhythmia detection circuit 92 may be configured to detect a long ventricular pause, asystole, SVT, and / or VT / VF based on sensed cardiac electrical signals meeting respective detection criteria. For example, when a threshold number of Vsense signals from one sensing channel 83 or 85 each occur at a sensed event interval (RRI) that is less than a tachyarrhythmia detection interval, control circuit 80 maydetect VT / VF. An RRI that is less than the tachyarrhythmia detection interval can be counted as a tachyarrhythmia interval. In some examples, a tachyarrhythmia detection based on the threshold number of tachyarrhythmia intervals being reached may be confirmed or rejected based on an atrial rate analysis using received Asense signals, AV interval pattern analysis using both Asense and Vsense signals, and / or morphology analysis of the morphology signal received from morphology channel 87. Arrhythmia detection circuit 92 may be implemented in control circuit 80 as hardware, software and / or firmware that processes and analyzes signals received from sensing circuit 86 for detecting arrhythmia according to a variety of arrhythmia detection algorithms.

[0077] In some examples, arrhythmia detection circuit 92 may include comparators and counters for counting PPIs and RRIs determined by timing circuit 90 that fall into various rate detection zones for determining an atrial rate and a ventricular rate or performing other rate- or interval-based assessment of Asense signals and Vsense signals for detecting and discriminating SVT and VT / VF. For example, arrhythmia detection circuit 92 may compare the RRIs determined by timing circuit 90 to one or more tachyarrhythmia detection interval zones, such as a tachycardia detection interval zone and a fibrillation detection interval zone. RRIs falling into a detection interval zone are counted by a respective VT interval (VTI) counter or VF interval (VFI) counter and in some cases in a combined VT / VF interval counter. The VF detection interval threshold may be set to 300 to 350 milliseconds (ms), as an example. For instance, if the VF detection interval is set to 320 ms, RRIs that are less than 320 ms are counted by the VFI counter. When VT detection is enabled, the VT detection interval may be programmed to be in the range of 350 to 420 ms, or 400 ms as an example. RRIs that are less than the VT detection interval but greater than or equal to the VF detection interval may be counted by a VTI counter. VT or VF may be detected when the respective VT or VFI counter (or a combined VT / VF interval counter) reaches a threshold number of intervals to detect (NID).

[0078] As an example, the NID to detect VT may require that the VTI counter reaches 18 VTIs, 24 VTIs, 32 VTIs or other selected NID. In some examples, the VTIs may be required to be consecutive intervals, e.g., 18 out of 18, 24 out of 24, or 32 out of 32 or 100 out of the most recent 100 consecutive RRIs. The NID required to detect VF may be programmed to a threshold number of X VFIs out of Y consecutive RRIs. For instance, the NID required to detect VF may be 18 VFIs out of the most recent 24 consecutive RRIs, 30VFIs out 40 consecutive RRIs, or as high as 120 VFIs out of 160 consecutive RRIs as examples (or other percentage of a specified number of RRIs). When a VTI or VFI counter reaches a respective NID, a ventricular tachyarrhythmia may be detected by arrhythmia detection circuit 92. The NID may be programmable and range from as low as 12 to as high as 120, with no limitation intended. A VTI counter or VFI counter may reach a respective NID when VTIs or VFIs are detected consecutively or non-consecutively out of a specified number of most recent RRIs. In some cases, a combined VT / VF interval counter may count both VTIs and VFIs and detect a tachyarrhythmia episode based on the fastest intervals detected when a specified NID is reached.

[0079] Arrhythmia detection circuit 92 may be further configured to detect atrial tachyarrhythmia (AT) intervals from PPIs received from timing circuit 90 and count AT intervals for detecting an SVT. In some examples, an SVT, such as atrial fibrillation, may be detected by arrhythmia detection circuit 92 based on an analysis of RRI variability, PRIs, RPIs, ratio of atrial rate to ventricular rate or other rate or interval-based analysis. Detection of SVT by arrhythmia detection circuit 92 may enable control circuit 80 to discriminate between SVT and VT / VF for appropriate control of CV / DF shock delivery for treating potentially life-threatening tachyarrhythmias.

[0080] Arrhythmia detection circuit 92 may be configured to perform other signal analysis for determining if other detection criteria are satisfied before detecting an SVT or VT / VF based on an NID being reached, such as P-wave morphology criteria and / or R-wave morphology criteria, onset criteria, stability criteria and noise and oversensing rejection criteria. To support these additional analyses, sensing circuit 86 may pass a digitized morphology signal to control circuit 80 from morphology signal channel 87, for morphology analysis performed by arrhythmia detection circuit 92 for detecting and discriminating heart rhythms. A cardiac electrical signal received by the morphology signal channel 87 (and / or any of sensing channels 83, 85 or 87) may be passed through a filter and amplifier, provided to a multiplexer and thereafter converted to a multi-bit digital signal by an analog-to-digital converter, all included in sensing circuit 86, for storage in memory 82. Memory 82 may include one or more circulating buffers to temporarily store digital cardiac signal segments for analysis performed by control circuit 80. Control circuit 80 may be a microprocessor-based controller, which may include HSRs, that employs digital signal analysis techniques to characterize the digitized signalsstored in memory 82 to recognize and classify the patient’s heart rhythm employing any of numerous signal processing methodologies for analyzing cardiac signals and cardiac event waveforms, e.g., P-waves and sinus or non-sinus R-waves.

[0081] Therapy delivery circuit 84 includes at least one charging circuit 94, including one or more charge storage devices such as one or more high voltage capacitors for generating high voltage shock pulses for treating VT / VF. Charging circuit 94 may include one or more low voltage capacitors for generating relatively lower voltage pulses, e.g., for cardiac pacing therapies. Therapy delivery circuit 84 may include switching circuitry 95 that controls when the charge storage device(s) are discharged through an output circuit 96 across a selected pacing electrode vector or CV / DF shock vector.

[0082] In response to detecting VT / VF, control circuit 80 may schedule a therapy and control therapy delivery circuit 84 to generate and deliver the therapy, such as ATP and / or CV / DF shock(s). Therapy can be generated by initiating charging of high voltage capacitors of charging circuit 94. Charging is controlled by control circuit 80 which monitors the voltage on the high voltage capacitors, which is passed to control circuit 80 via a charging control line. When the voltage reaches a predetermined value set by control circuit 80, a logic signal is generated on a capacitor full line and passed to therapy delivery circuit 84, terminating charging. A CV / DF shock pulse is delivered to the heart under the control of the timing circuit 90 by an output circuit 96 of therapy delivery circuit 84 via a control bus. The output circuit 96 may include an output capacitor or other output circuitry through which the charged high voltage capacitor is discharged via switching circuitry, e.g., an H-bridge, which determines the electrodes used for delivering the cardioversion or defibrillation pulse and the pulse wave shape. Therapy delivery circuit 84 may be configured to deliver electrical stimulation pulses for inducing tachyarrhythmia, e.g., T- wave shocks or trains of induction pulses, upon receiving a programming command from external device 40 (FIG. 1A) during ICD implant or follow-up testing procedures.

[0083] In some examples, the high voltage therapy circuit configured to deliver CV / DF shock pulses can be controlled by control circuit 80 to deliver pacing pulses, e.g., for delivering ATP, post shock pacing pulses, bradycardia pacing pulses, atrial synchronous ventricular pacing pulses, or asystole pacing pulses. Therapy delivery circuit 84 may be configured to generate and deliver cardiac pacing pulses using the high voltage capacitor(s) that are chargeable to a shock voltage amplitude by charging the high voltagecapacitor(s) to a relatively lower voltage corresponding to a cardiac pacing pulse amplitude for capturing and pacing the ventricular myocardium. Therapy delivery circuit 84 may include a low voltage therapy circuit including one or more separate or shared charging circuits, switch circuits and output circuits for generating and delivering relatively lower voltage pacing pulses for a variety of pacing needs. Charging of capacitors to a programmed pulse amplitude and discharging of the capacitors for a programmed pulse width may be performed by therapy delivery circuit 84 according to control signals received from control circuit 80 for delivering cardiac pacing pulses. Timing circuit 90 may include various timers or counters that control when cardiac pacing pulses are delivered, e.g., by timing out various pacing escape intervals. The microprocessor of control circuit 80 may set the amplitude, pulse width, polarity or other characteristics of cardiac pacing pulses, which may be based on programmed values stored in memory 82. Circuitry included in a therapy delivery circuit 84 for generating and delivering electrical stimulation pulses according to a therapy delivery protocol can vary between devices and is not limited to any particular therapy delivery circuitry configuration for use in conjunction with the cardiac signal sensing and arrhythmia detection methods disclosed herein.

[0084] Control parameters utilized by control circuit 80 for sensing cardiac event signals, detecting arrhythmias, and controlling therapy delivery may be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes a transceiver and antenna for communicating with external device 40 (shown in FIG. 1A) using RF communication or other communication protocols as described above. Under the control of control circuit 80, telemetry circuit 88 may receive downlink telemetry from and send uplink telemetry to external device 40.

[0085] FIG. 5 is a conceptual diagram of circuitry that may be included in sensing circuit 86 shown in FIG. 4 according to some examples. Sensing circuit 86 may include A sensing channel 81, at least one V sensing channel 83, optionally a second V sensing channel 85, and, in some examples, morphology signal channel 87. For the sake of illustration, sensing circuit 86 is described as being included in ICD 14 and capable of receiving multiple cardiac electrical signals by four different sensing channels in the example shown (though fewer or more sensing channels could be provided). When sensing circuit 86 is included in the leadless pacemaker 114 shown in FIG. 3, sensing circuit 86 may include only the Asensing channel 81 (e.g., coupled to electrodes 164 and 165) and the V sensing channel 83 (e.g., coupled to electrodes 162 and 164) for receiving two different cardiac electrical signals via an atrial sensing electrode vector and a ventricular sensing electrode vector.

[0086] The A sensing channel 81 may receive a cardiac electrical signal, referred to as an “atrial signal,” via an atrial sensing electrode vector. The A sensing channel 81 may be selectively coupled via switching circuitry included in sensing circuit 86 to an atrial sensing electrode vector including at least one electrode carried by lead 16 (e.g., shown in FIG. 1A). In the implant position shown in FIGs. 1A-2C, the distal electrode 31 located at or adjacent to the distal end 29 of lead 16 (see FIG. 1A), may be in operative proximity to the atrial chambers for sensing P- waves. For example, the cardiac electrical signal received via electrode 31 and electrode 30 may include P-waves having a signal strength that promotes reliable P-wave sensing by A sensing channel 81. In the example shown, A sensing channel 81 receives a cardiac electrical signal from electrodes 31 and 30. In other examples, A sensing channel 81 may receive a cardiac electrical signal from electrode 31 paired with one of defibrillation electrodes 24 or 26 or housing 15. Depending on the position and orientation of lead 16 relative to the patient’s heart, electrode 30 or electrode 28 may be in operative proximity to the atrial chambers and may be used in an atrial sensing electrode vector. In some examples, the atrial sensing electrode vector selected for receiving an atrial signal by A sensing channel 81 includes at least one electrode carried by lead 16 that is in closest physical proximity to the atria of the patient’s heart. In some examples, the atrial sensing electrode vector selected for receiving an atrial signal by A sensing channel 81 includes two pacing / sensing electrodes carried by lead 16 that are in closest physical proximity to the atria of the patient’s heart.

[0087] The V sensing channels 83 and 85 may each receive a cardiac electrical signal for use in sensing ventricular event signals. First V sensing channel 83 and second V sensing channel 85 may each be selectively coupled via switching circuitry 89 included in sensing circuit 86 to a respective ventricular sensing electrode vector including at least one electrode carried by lead 16. First V sensing channel 83 may be coupled to a first ventricular sensing electrode vector for receiving a first ventricular signal, and second V sensing channel 85 may be coupled to a second ventricular sensing electrode vector, different than the first ventricular sensing electrode vector for receiving a second ventricular signal, different than the first ventricular signal. In some examples, first Vsensing channel 83 may be coupled to a ventricular sensing electrode vector that is a short bipole, having a relatively shorter inter-electrode distance than the ventricular sensing electrode vector coupled to the second V sensing channel 85 or to morphology signal channel 87. In the example shown, the first V sensing channel 83 is coupled to pace / sense electrodes 28 and 30 carried by lead 16. In some examples, first V sensing channel 83 may be coupled to a sensing electrode vector that is approximately vertical (when the patient is in an upright position) or approximately aligned with the cardiac axis to increase the likelihood of a relatively high R-wave signal amplitude relative to the P-wave signal amplitude. A relatively short inter-electrode distance, e.g., between electrodes 28 and 30 carried by lead 16, may be relatively less likely to be contaminated by skeletal muscle myopotential noise, EMI or other non-cardiac noise compared to a relatively longer interelectrode distance but may have greater variability in R-wave signal strength compared to a relatively longer inter-electrode distance.

[0088] The second V sensing channel 85 can be optional in some examples and may be coupled to a second ventricular sensing electrode vector that is a short bipole or a relatively longer bipole compared to the first ventricular sensing electrode vector. The second ventricular sensing electrode vector may also be generally vertical or aligned with the cardiac axis. However, the second ventricular sensing electrode vector may be orthogonal or transverse relative to the first ventricular sensing electrode vector in other examples. In the example shown, the second V sensing channel 85 is coupled to pace / sense electrode 30 and housing 15 such that it is a relatively longer bipole that is substantially transverse to the ventricular sensing electrode vector coupled to the first V sensing channel 83. In other examples, the first or second V sensing channels may be coupled to either of pace / sense electrodes 28 or 30 paired with housing 15, either of pace / sense electrodes 28 or 30 paired with coil electrode 24, or either of pace sense electrodes 28 or 30 paired with coil electrode 26, as long as at least one electrode is different between the two V sensing electrode vectors. In further examples, either or both of first or second V sensing channels 83 or 85 may be coupled to a sensing electrode vector that does not necessarily include one of pace / sense electrodes 28 or 30. For example, a sensing electrode vector may be coupled to sensing channel 83 or sensing channel 85 that includes one or both of coil electrodes 24 or 26 and / or housing 15.

[0089] In the examples shown in FIGs. 1A-2C, the distal portion 25 of lead 16 extends superiorly from a location inferior to the heart such that the more proximal electrodes 28 and 30 are in operative proximity to the ventricles for use in receiving ventricular signals. In other examples, the distal portion 25 of lead 16 may extend inferiorly from a location superior to the heart such that the most distal electrode 31 (and the middle electrode 30) may be in operative proximity to the ventricles for receiving a ventricular signal, and the most proximal electrode 28 may be in operative proximity to the atria for receiving an atrial signal. It is to be understood, therefore, that the example atrial sensing electrode vectors and ventricular sensing electrode vectors are illustrative in nature and may vary between lead and electrode configurations and lead and electrode implant positions and orientations relative to the patient’s heart.

[0090] Sensing circuit 86 may include a morphology signal channel 87 for sensing a cardiac electrical signal passed to control circuit 80, e.g., as a multi-bit digital ECG signal, for performing morphology analysis as generally described above. Morphology signal channel 87 may receive a raw cardiac electrical signal from a sensing electrode vector that may be different than the sensing electrode vectors coupled to sensing channels 81, 83 and 85. In the example shown, the morphology signal sensing electrode vector includes electrode 24 and housing 15. In other examples, the morphology signal sensing electrode vector may include any one of electrodes 24, 26, 28, 30 or 31 carried by lead 16 paired with housing 15. Morphology signal channel 87 may be selectively coupled to a relatively long bipole having an inter-electrode distance or spacing that is relatively greater than the sensing electrode vector coupled to A sensing channel 81, first V sensing channel 83 and / or second V sensing channel 85 in some examples. The morphology sensing electrode vector coupled to morphology signal channel 87 may provide a relatively far-field or more global cardiac signal compared to a relatively shorter bipole that may be coupled to one of the other sensing channels 81, 83 or 85.

[0091] The sensing electrode vectors coupled to sensing channels 81, 83, 85 and 87 may each be different sensing electrode vectors. In other examples, however, the sensing electrode vector coupled to one of sensing channels 81, 83 or 85 may be the same sensing electrode vector coupled to the morphology signal channel 87. In this case, circuitry of a sensing channel 81, 83 or 85 and the morphology signal channel 87 may be combined orinclude shared components such that a morphology signal and A sense or V sense signals may be output to control circuit 80 from one sensing channel.

[0092] In the illustrative example shown in FIG. 5, the signals received by each sensing channel 81, 83, 85 and 87 are provided as differential input signals to a pre-filter and preamplifier 102, 62a, 62b, and 72, respectively. Non-physiological high frequency and DC signals may be filtered by a low pass or bandpass filter included in each of pre-filter and pre-amplifiers and high voltage signals may be removed by protection diodes included in pre-filter and pre-amplifiers. The pre-filter and pre-amplifiers 62a, 62b, 72 and 102 may amplify the pre-filtered signal by a gain of between 10 and 100, and in one example a gain of 17, though each channel 81, 83, 85 and 87 may have a different gain and filter bandwidth. Pre-filter and pre-amplifiers 62a, 62b, 72 and 102 may convert the differential input signal to a single-ended output signal passed to a respective analog-to-digital converter (ADC) 63a, 63b, 73, and 103. Pre-filter and pre-amplifiers 62a, 62b, 72 and 102 may provide anti-alias filtering and noise reduction prior to digitization.

[0093] ADC 63a, ADC 63b, ADC 73, and ADC 103 convert the respective first ventricular electrical signal, second ventricular electrical signal, morphology signal and atrial electrical signal from an analog signal to a digital bit stream, which may be sampled at 128 or 256 Hz, as examples. The ADCs of sensing circuit 86 may be sigma-delta converters (SDC), but other types of ADCs may be used. In some examples, the outputs of each ADC 63a, 63b, 73 and 103 may be provided to decimators (not shown), which function as digital low-pass filters that increase the resolution and reduce the sampling rate of the respective cardiac electrical signals.

[0094] The digital outputs of ADCs 63a, 63b, 73 and 103 may each be passed to respective filters 64a, 64b, 74 and 104, which may be digital bandpass filters. The bandpass filters of the respective sensing channels 81, 83, 85 and morphology signal channel 87 may have the same or different bandpass frequencies. For example, filters 64a and 64b may have a bandpass of approximately 10 Hz to 50 Hz, or approximately 13 Hz to 39 Hz, for passing R-waves typically occurring in this frequency range. The filter 104 of the A sensing channel 81 may have a bandpass the same or similar to the V sensing channels 83 and 85. In other examples, the A sensing channel 81 may have a somewhat lower bandpass, e.g., 8 to 32 Hz for passing P-waves which may have a slightly lowerfrequency content than R-waves. Filter 74 of the morphology signal channel 87 may have a relatively wider bandpass of approximately 2.5 to 100 Hz.

[0095] In some examples, each sensing channel 81, 83, 85 and morphology signal channel 87 may further include a notch filter 107, 67a, 67b, and 76, respectively, to filter 50 Hz and 60 Hz noise signals. Each notch filter 107, 67a, 67b, and 76 may be individually turned on or off in some examples. The narrow bandpass and notch-filtered signal (if notch filter is turned on) in each of the two V sensing channels 83 and 85 and the A sensing channel 81 is passed from the respective filter 67a, 67b or 107 to a rectifier 65a, 65b or 105 to produce a bandpass filtered, rectified signal output.

[0096] In the example shown, A sensing channel 81 may include a low pass filter 110 for receiving the bandpass filtered, rectified signal from rectifier 105. After rectification, low pass filter 110 may output a smoothed, rectified atrial signal 109. V sensing channel 83 may include a low pass filter 112 for receiving the bandpass filtered, rectified ventricular signal from rectifier 65a. Low pass filter 112 may output a smoothed, rectified ventricular signal 69. Low pass filter 110 and low pass filter 112 may be 2 Hz, 3 Hz, 4 Hz or 5 Hz low pass filters, as examples. Low pass filter 110 and low pass filter 112 may be infinite impulse response (IIR) filters, which may be designed to introduce minimal delay in the processing of the received raw atrial and ventricular signals for determining an atrial sensing signal and / or ventricular sensing signal to facilitate real time sensing of atrial event signals and ventricular event signals. In other examples, low pass filters 110 and / or 112 may be a finite impulse response (FIR) filters.

[0097] The smoothed, rectified ventricular signal 69 can be passed from V sensing channel 83 to the A sensing channel 81. The A sensing channel 81 may be configured to determine an atrial sensing signal 120 as a combination of the atrial signal 109 and the ventricular signal 69. The atrial sensing signal 120 may be determined by A sensing channel 81 by performing a mathematical operation on pairs of sample points from the atrial signal 109 and ventricular signal 69 as operands. In the example shown, a summation block 119 receives the atrial signal 109 and the ventricular signal 69 and outputs the atrial sensing signal 120 by summing the atrial signal 109 with the inverse of the ventricular signal 69 to obtain the atrial sensing signal 120 as a non-rectified difference signal between the rectified atrial signal 109 and the rectified ventricular signal 69.

[0098] The atrial sensing signal 120 can be a non-rectified signal that may be passed to a low pass filter 111 to provide a smoothed, non-rectified atrial sensing signal to P-wave detector 106. Low pass filter 111 may be a 3 to 4 Hz IIR filter or FIR filter, as examples. The P-wave detector 106 is configured to apply a P-wave sensing threshold to the atrial sensing signal 120 determined from a combination of the atrial signal 109 received, filtered and rectified by A sensing channel 81 and the ventricular signal 69 received, filtered and rectified by V sensing channel 83. In response to a P-wave sensing threshold crossing, the A sensing channel 81 produces an A sense signal 108 that is passed to control circuit 80.

[0099] The atrial sensing signal 120 may be determined by determining a sum, difference, ratio or product of paired sample points including one sample point from the atrial signal 102 and one sample point form the ventricular signal 69. In other examples, the paired sample points may be combined according to a non-linear function, e.g., a logarithmic or exponential function. The paired sample points may be time aligned sample points. In other examples, each pair of the paired sample points may include one sample point from the atrial signal 102 and a second sample point from the ventricular signal 69 that is shifted in time relative to the atrial signal sample point (e.g., one, two or more sample points earlier or later than the atrial signal sample point).

[0100] In some examples, the atrial signal 109 from the A sensing channel 81 may be passed to the V sensing channel 83. The V sensing channel 83 may sum the rectified ventricular signal 69 with the inverse of the atrial signal 109 to obtain a ventricular sensing signal 122 that may be passed to a low pass filter 124 (e.g., a 3 to 4 Hz low pass IIR filter or FIR filter) and on to R-wave detector 66a. R-wave detector 66a may apply an R-wave sensing threshold to the ventricular sensing signal 122 received from low pass filter 124. In response to an R-wave sensing threshold crossing, the V sensing channel 83 produces a Vsense signal 68a that is passed to control circuit 80.

[0101] In various examples, ventricular sensing signal 122 may be determined by sensing circuit 86 by determining a sum, difference, ratio or product of paired sample points including one sample point from the atrial signal 102 and one sample point form the ventricular signal 69. The paired sample points may be time aligned sample points. In other examples, each pair of paired sample points may include one sample point from the atrial signal 102 and a second sample point from the ventricular signal 69 that is shifted intime relative to the atrial signal sample point (e.g., one, two or more sample points earlier or later than the atrial signal sample point).

[0102] The ventricular sensing signal 122 and the atrial sensing signal 120 may each be determined by sensing circuit 86 by performing a different operation on pairs of sample points obtained from the ventricular signal 69 and the atrial signal 102. In the example shown, the atrial sensing signal 120 can be determined by subtracting the ventricular signal 69 from the atrial signal 102. The ventricular sensing signal 122 can be determined by subtracting the atrial signal 102 from the ventricular signal 69. In other examples, the atrial sensing signal 120 can be determined as the ratio of the atrial signal 102 to the ventricular signal 69, and the ventricular sensing signal 122 can be determined as the ratio of the ventricular signal 69 to the atrial signal 102. In other examples, the atrial sensing signal 120 could be determined using a first operation, e.g., addition, performed on the operands (sample points) obtained from the atrial signal 102 and ventricular signal 69, and the ventricular sensing signal 122 could be determined using a different, second operation (e.g., subtraction, division or multiplication) of the operands obtained from the atrial signal 102 and the ventricular signal 69).

[0103] In the example shown in FIG. 5, the second V sensing channel 85 may pass the rectified ventricular signal output from rectifier 65b to an R-wave detector 66b. The second V sensing channel 85 may apply an R-wave sensing threshold to the received, rectified ventricular signal. The R-wave sensing threshold may be controlled separately from the R-wave sensing threshold controlled by R-wave detector 66a in some examples. In response to an R-wave sensing threshold crossing by the rectified ventricular signal, the second V sensing channel 85 may produce a Vsense signal 68b that can be passed to control circuit 80. In other examples, when a second V sensing channel 85 is included, V sensing channel 85 may receive the rectified atrial signal 109 for determining a second ventricular sensing signal in any of the manners described above for determining a first ventricular sensing signal 122. The second ventricular sensing signal determined using the atrial signal 109 may be passed to R-wave detector 66b for sensing R-waves.

[0104] The P-wave detector 106 and the R-wave detectors 66a and 66b may each include an auto-adjusting sense amplifier, comparator and / or other detection circuitry that compares the incoming signal to a sensing threshold and produces a sensed cardiac event signal (e.g., Asense signal 108, Vsense signal 68a or Vsense signal 68b) when therespective signal crosses the respective sensing threshold, which may be outside any blanking periods applied by the sensing circuitry, e.g. a post-pace blanking period, a postsense blanking period, a post-atrial ventricular blanking period applied by R-wave detectors 66a and 66b or a post- ventricular atrial blanking period applied by P-wave detector 106.

[0105] The P-wave sensing threshold applied to the incoming atrial sensing signal by P- wave detector 106 may be a fixed threshold, e.g., a programmed value or determined by control circuit 80 based on an average or median maximum peak amplitude of previously sensed P-waves. In other examples, the P-wave sensing threshold may be a multi-level or decreasing threshold that may decrease from a starting value to a sensing floor. The starting value may be set to a percentage of the maximum peak amplitude of one or more most recently sensed P-waves. The sensing floor or minimum value may correspond to a programmed atrial sensitivity. The P-wave sensing threshold may decrease from the starting value to the sensing floor according to one or more step decrements and / or decay rates.

[0106] The R-wave sensing thresholds applied to the incoming ventricular sensing signal or ventricular signal by R-wave detectors 66a and 66b may be a fixed threshold, e.g., a programmed value or determined by control circuit 80 based on an average or median maximum peak amplitude of previously sensed R-waves by each respective V sensing channel 83 and 85. In other examples, the R-wave sensing thresholds may be multi-level or decreasing thresholds that may each decrease from a starting value to a sensing floor. The starting value may be set to a percentage of the maximum peak amplitude of one or more most recently sensed R-waves. The sensing floor or minimum value may correspond to a programmed ventricular sensitivity. The R-wave sensing threshold may decrease from the starting value to the sensing floor according to one or more step decrements (which may occur at specified drop time intervals) and / or decay rates (over one or more decay intervals). The R-wave sensing thresholds used by R-wave detectors 66a and 66b may be controlled separately according to different R-wave sensing threshold control parameters.

[0107] The wideband-filtered, digital cardiac electrical signal 78 output from morphology signal channel 87 may be passed to control circuit 80 for performing morphology analysis when needed for arrhythmia detection by control circuit 80. In some examples, the digital cardiac electrical signal 78 is passed to rectifier 75 and a rectified wideband filtered signal79 is passed to control circuit 80 for processing and analysis. In some cases, both the filtered, non-rectified signal 78 and the rectified signal 79 are passed to control circuit 80 from morphology signal channel 87 for use in determining morphology features of the ECG signal.

[0108] The configuration of sensing channels 81, 83 and 85 and morphology signal channel 87 as shown in FIG. 5 is illustrative in nature. Sensing circuit 86 may include more or fewer components than illustrated in FIG. 5 and some components may be shared between sensing channels 81, 83 and 85 and morphology signal channel 87. For example, a common cardiac electrical signal from a selected sensing electrode vector may be received by a prefilter and preamplifier circuit and ADC and subsequently be passed to a narrowband filter in one of sensing channels 83 or 85 and to a wideband filter in morphology signal channel 87. In other examples, sensing circuit 86 may include two sensing channels 81 and 83 and a wideband filtered morphology signal may be passed from one of sensing channels 81 or 83 to control circuit 80. Furthermore, the components for filtering, amplifying, digitizing, rectifying, etc. may be arranged in a different order or combination than shown in FIG. 5 and some components may be shared between sensing channels 81, 83, 85 and morphology signal channel 87.

[0109] FIG. 6 is a conceptual diagram 200 of an atrial sensing signal 206 and a ventricular sensing signal 216 that may be determined by the A sensing channel 81 and V sensing channel 83, respectively, of FIG. 5 according to some examples. Signal 202 may be the signal received by A sensing channel 81 after bandpass filtering and amplifying. Signal 202 may be passed to rectifier 105 and low pass filtered to produce the rectified, smoothed atrial signal 204. The atrial signal 204 and the ventricular signal 214 (described below) may be combined according to one or more operations performed on paired sample points of the atrial signal 204 and ventricular signal 214 to determine the atrial sensing signal 206 by sensing circuit 86. In the example shown, the atrial sensing signal 206 represents the difference signal obtained by the A sensing channel 81 by subtracting the smoothed, rectified ventricular signal 214 received from V sensing channel 83 from the smoothed, rectified atrial signal 204. P-wave detector 106 may apply a P-wave sensing threshold 208 to the non-rectified atrial sensing signal 206. An Asense signal 210 may be produced by the A sensing channel 81 in response to a P-wave sensing threshold crossing by the atrial sensing signal 206.

[0110] Signal 212 may be received by the V sensing channel 83. Signal 212 represents the bandpass filtered and amplified signal that may be passed to rectifier 65a and low pass filtered to produce the smoothed, rectified ventricular signal 214. Ventricular signal 214 may be combined with atrial signal 204 according to one or more operations performed on paired sample points of the ventricular signal 214 and atrial signal 204 to determine the ventricular sensing signal 216. Ventricular sensing signal 216 may be obtained by the V sensing channel 83 by subtracting the rectified atrial signal 204 received from A sensing channel 83 from the rectified ventricular signal 214 and passing the resulting non-rectified difference signal through a low pass filter. R-wave detector 66a may apply an R-wave sensing threshold 218 to the non-rectified ventricular sensing signal 216. A Vsense signal220 may be produced by the V sensing channel 83 in response to an R-wave sensing threshold crossing by the non-rectified ventricular sensing signal 216.

[0111] In various examples, control circuit 80 may optionally verify a received Asense signal 210 based on the Vsense signal 220 being received within an expected atrioventricular (AV) time interval 222. The expected AV time interval 222 may extend between a minimum expected AV conduction time to a maximum expected AV conduction time after the Asense signal 210. The expected AV time interval 222 may be programmable and patient- specific and may begin 100 to 140 ms after the Asense signal 210 and extend 200 to 250 ms after the Asense signal 210. Control circuit 80 may verify a received Vsense signal 220 when the Vsense signal 220 is received during the expected AV time interval 222 following an Asense signal 210.

[0112] Additionally or alternatively, control circuit 80 may optionally verify a received Asense signal 210 based on a crossing 223 of a negative threshold 209 by the non-rectified atrial sensing signal 206 within the expected AV time interval 222 from the Asense signal 210. Additionally or alternatively, control circuit 80 may verify the Asense signal 210 when a crossing 227 of the negative threshold 219 by ventricular sensing signal 216 occurs within an atrial event confirmation time interval 221of Asense signal 210. Because the negative portion of ventricular sensing signal 216 corresponds to the P-wave of the atrial signal 204 that is subtracted from the ventricular signal 214, a negative threshold crossing by ventricular sensing signal 216 is expected to occur within a short time interval221 (e.g., within 10 to 30 ms) from Asense signal 210.

[0113] Control circuit 80 may optionally verify a received Vsense signal 220 when the Vsense signal 220 is received within an expected AV time interval 222 relative to a crossing 227 of a negative threshold 219 by the ventricular sensing signal 216.Additionally or alternatively, control circuit 80 may verify the Vsense signal 220 when the crossing of the negative threshold 219 by ventricular sensing signal 216 that occurs prior to the Vsense signal 220 also occurs within an atrial event confirmation time interval of Asense signal 210. Because the negative portion of ventricular sensing signal 216 corresponds to the P-wave of atrial signal 204 that is subtracted from ventricular signal 214 in this example, a negative threshold crossing 227 by ventricular sensing signal 216 is expected to occur within a short time interval 221, e.g., 50 ms or less, from Asense signal 210. Additionally or alternatively, control circuit 80 may verify a received Vsense signal 220 when a crossing 223 of a negative threshold 209 by atrial sensing signal 206 occurs within a confirmation time interval 226 of the Vsense signal 220. It is recognized that various timing relationships of positive and / or negative threshold crossings of the nonrectified atrial sensing signal and non-rectified ventricular sensing signal 216 may be performed for confirming an Asense signal 210 and / or a Vsense signal 220.

[0114] FIG. 7 is a flow chart 300 of a method that may be performed by a medical device for sensing cardiac event signals and controlling cardiac electrical stimulation therapies according to some examples. FIG. 7 and other flow charts and diagrams presented herein are described with reference to the ICD 14 shown conceptually in FIG. 5. However, it is to be understood that other implantable medical devices, e.g., pacemaker 114 of FIG. 3, configured to sense cardiac electrical signals and control cardiac electrical stimulation therapies may be configured to perform the techniques disclosed herein for detecting atrial event signals and / or ventricular event signals.

[0115] With continued reference to FIGs. 4 and 5, at block 302 of FIG. 6, sensing circuit 86 senses a first cardiac electrical signal. The first cardiac signal is referred to here as an “atrial signal” because the first cardiac signal may be received by the A sensing channel 81. The first cardiac electrical signal may be received by the A sensing channel 81 via a sensing electrode vector that is in operative proximity to the atria for promoting relatively high amplitude P- waves and / or relatively low amplitude R-waves (e.g., see signal 202 of FIG. 6) compared to the cardiac electrical signals received via other available sensing electrode vectors (e.g., see signal 212 of FIG. 6). The first cardiac electrical signal sensedat block 302 may be sensed using an atrial sensing electrode vector including extra-cardiac electrodes that are located relative to the patient’s heart so that one or both atrial chambers are relatively more proximate to one or both electrodes of the atrial sensing electrode vector, and one or both ventricular chambers of the patient’ s heart are relatively more distant from the one or both electrodes of the atrial sensing electrode vector. For example, as shown in FIG. 5, the most distal pace / sense electrodes 30 and 31 (e.g., as shown in FIG. 1A) may be selected as the atrial sensing electrode vector for sensing the first cardiac electrical signal received as an atrial signal by A sensing channel 81 at block 302.

[0116] At block 304, sensing circuit 86 receives a second cardiac electrical signal. The second cardiac signal is referred to here as a “ventricular signal” because the second cardiac signal may be received by the V sensing channel 83 shown in FIG. 5. The second cardiac electrical signal may be sensed using a ventricular sensing electrode vector that is in operative proximity to the ventricles for promoting relatively high amplitude R- waves and / or relatively low amplitude P-waves (e.g., see signal 212 of FIG. 6) compared to cardiac electrical signals that may be received by other available sensing electrode vectors (e.g., see signal 202 of FIG. 6). The second cardiac electrical signal received at block 304 may be sensed via a ventricular sensing electrode vector including extra-cardiac electrodes that are located relative to the patient’s heart so that one or both ventricles are relatively more proximate to one or both of the electrodes of the ventricular sensing electrode vector and one or both atria of the patient’ s heart are relatively more distant from the one or both electrodes of the ventricular sensing electrode vector. For example, as shown in FIG. 5, the most proximal pace / sense electrodes 28 and 30 (shown in FIG. 1 A) may be selected as the ventricular sensing electrode vector used for receiving the second cardiac electrical signal as a ventricular signal by the V sensing channel 83 at block 304.

[0117] The particular electrode locations and sensing electrode vectors used for receiving the first cardiac electrical signal at block 302 as an atrial signal by A sensing channel 81 and the second cardiac electrical signal received at block 304 as a ventricular signal by V sensing channel 83 may vary between examples depending on the particular medical device and electrode system being used, lead implant location and orientation relative to the patient’s heart, individual patient need (e.g., inter-patient differences in the amplitude and other characteristics of the P-waves and R-waves) and / or other factors. In some examples, the relative amplitude of P-waves is not necessarily greater than the amplitudeof R-waves in the atrial signal. The relative amplitude of R-waves may not necessarily be greater than the amplitude of P-waves in the ventricular signal. By receiving an atrial signal and a ventricular signal and determining an atrial sensing signal from paired sample points of the atrial signal and the ventricular signal, P-wave detection from the atrial sensing signal may be improved and more reliable than P-wave detection from the atrial signal that is not modified by the ventricular signal. By determining a ventricular sensing signal from paired sample points of the atrial signal and the ventricular signal, R-wave detection from the ventricular sensing signal may be improved and more reliable than R- wave detection from the ventricular signal that is not modified by the atrial signal. Reliable detection of both P-waves and R-waves by an ICD or pacemaker promotes improved cardiac rhythm detection and the benefit of appropriate and timely cardiac electrical stimulation therapy delivery.

[0118] Accordingly, at block 306, sensing circuit 86 may determine atrial sensing signal sample points by determining a mathematical combination of paired sample points where each pair of sample points includes a sample point of the atrial signal and a sample point of the ventricular signal. In some examples, an atrial sensing signal is determined by performing a mathematical operation on time-aligned pairs of sample points obtained from the atrial signal and the ventricular signal. As shown in FIG. 5, the atrial sensing signal may be determined by subtracting (or adding the inverse of) the ventricular signal from (to) the atrial signal. In other examples, sensing circuit 81 may determine the atrial sensing signal by multiplying, dividing, or adding time-aligned paired samples points of the atrial signal and the ventricular signal. The atrial signal may be passed to a P-wave detector 106 (see FIG. 5) for sensing atrial event signals (e.g., detecting atrial P-waves) from the atrial sensing signal.

[0119] In other examples, combinations of pairs of non-time aligned sample points may be determined for producing sample points of an atrial sensing signal at block 306. For instance, sample points of the atrial signal and sample points of the ventricular signal may be aligned using a fiducial point of each of the atrial signal and the ventricular signal. For example, a sensing window may be defined relative to a P-wave or R-wave sensing threshold crossing by a respective atrial signal or ventricular signal, relative to a preceding Asense signal, Vsense signal, pacing pulse or other reference point. The maximum peak amplitude of the atrial signal during the sensing window may be identified. The maximumpeak amplitude of the ventricular signal during the sensing window may be identified. The sample points of one of the atrial signal or the ventricular signal may be shifted in time to align the two identified maximum peak amplitudes. A difference, sum, product or ratio of paired sample points aligned based on the maximum peak amplitudes of the atrial signal and ventricular signal may be determined for determining the atrial sensing signal at block 306.

[0120] At block 308, sensing circuit 86 may determine a ventricular sensing signal by determining a second, different combination of paired sample points of the atrial signal and the ventricular signal. In some examples, a ventricular sensing signal is determined by determining a mathematical combination of pairs of time aligned sample points of the atrial signal and the ventricular signal. As shown in FIG. 5, the second combination of the atrial signal and the ventricular signal may be determined by subtracting (or adding the inverse of) the atrial signal from (to) the ventricular signal. In other examples, the second combination of the atrial signal sample points and the ventricular signal sample points may be determined by multiplying, dividing, or adding time-aligned samples points of the atrial and ventricular signals for producing a ventricular sensing signal at block 308.

[0121] In other examples, sensing circuit 86 may perform operations on non-time aligned sample points at block 308 for producing sample points of a ventricular sensing signal. For instance, as described above, sample points of the atrial signal and sample points of the ventricular signal may be aligned using a fiducial point, such as a maximum peak amplitude identified during a sensing window, of each of the atrial signal and the ventricular signal. Sensing circuit 86 may determine the ventricular sensing signal at block 308 to be different than the atrial sensing signal received at block 306 by performing a different operation of time-aligned sample points, performing a different operation of nontime aligned sample points, or performing a different temporal alignment of the sample points of the atrial signal and the ventricular signal for pairing sample points as operands used in determining the ventricular sensing signal.

[0122] At block 310, sensing circuit 86 may apply a P-wave sensing threshold to the atrial sensing signal for detecting atrial event signals. An Asense signal may be produced by sensing circuit 86 and passed to control circuit 80 in response to the atrial sensing signal crossing (or meeting) the P-wave sensing threshold. For example, as shown in FIG. 5, the non-rectified low pass filtered atrial sensing signal determined at block 306 may be passedto a P-wave detector 106. The incoming atrial sensing signal sample points may be compared to a P-wave sensing threshold by P-wave detector 106 for detecting atrial P- waves and generating Asense signals. As described above, in some examples, when a positive P-wave sensing threshold crossing is detected and followed by a negative confirmation sensing threshold crossing (e.g., within an expected AV conduction time interval), sensing circuit 86 may generate (or confirm) the Asense signal.

[0123] At block 312, sensing circuit 86 detects ventricular event signals from the ventricular sensing signal. The ventricular sensing signal determined at block 308 may be passed to an R-wave detector 66a (see FIG. 5) for detecting R-waves. The incoming ventricular sensing signal sample points may be compared to an R-wave sensing threshold. In response to the ventricular sensing signal meeting (e.g., equal to or greater than) the R- wave sensing threshold, the sensing circuit 86 may produce a Vsense signal that can be passed to control circuit 80. As described above, in some examples, when a positive R- wave sensing threshold crossing is detected and preceded by a negative confirmation sensing threshold crossing (e.g., within an expected AV conduction time window), sensing circuit 86 may generate or confirm the Vsense signal.

[0124] At block 314, control circuit 80 controls therapy delivery circuit 84 to deliver electrical stimulation pulses based on the received Asense signals and Vsense signals. Control circuit 80 may perform various timing related functions in response to receiving the Asense signals and the Vsense signals. For example, control circuit 80 may determine the value of one or more timers or counters for determining PPIs, PRIs, RPIs and / or RRIs for use by arrhythmia detection circuit 92. The determined PPIs, PRIs, RPIs and / or RRIs may be used by arrhythmia detection circuit 92 in detecting an arrhythmia, e.g., for detecting asystole, bradycardia, atrial flutter, AF, and / or detecting VT / VF and discriminating between VT / VF and SVT. A variety of arrhythmia detection algorithms may be executed by control circuit 80 using the received Asense signals and / or Vsense signals for detecting the cardiac rhythm.

[0125] In response to detecting a ventricular tachyarrhythmia, e.g., VT or VF, control circuit 80 may control therapy delivery circuit 84 to deliver one or more therapies, e.g., one or more ATP therapies and / or one or more CV / DF shock therapies. In response to detecting an SVT based at least in part on Asense signals, control circuit 80 may determine an atrial tachyarrhythmia burden. For example, control circuit 80 maydetermine the duration of a detected atrial tachyarrhythmia episode and determine the cumulative duration of all atrial tachyarrhythmia episodes detected over a specified time period, e.g., 24 hours. Control circuit 80 may determine an average 24-hour atrial tachyarrhythmia burden in some examples. Control circuit 80 may generate an output that is stored in memory 82 for transmission by telemetry circuit 88 relating to detected SVTs, e.g., data relating to the determined atrial tachyarrhythmia burden, the number of SVT episodes detected, the duration of each SVT episode, or the like.

[0126] Control of a therapy based on Asense signals and Vsense signals at block 314 may include controlling therapy delivery circuit 84 to deliver a pacing pulse and starting (or restarting) one or more pacing escape intervals by control circuit 80 for scheduling pending pacing pulses for delivery by therapy delivery circuit 84. Timing circuit 90, for example, may start a ventricular pacing interval in response to receiving a Vsense signal and cancel any pending ventricular pacing pulse. The ventricular pacing interval may be a lower rate interval, a hysteresis pacing interval, or a rate response interval, as examples, for avoiding asystole, a long ventricular pause, bradycardia or generally controlling a minimum ventricular rate according to patient need. Timing circuit 90 may start an AV pacing interval in response to receiving an Asense signal for controlling atrial synchronous ventricular pacing pulses. In other examples, if no Vsense signal is received for a threshold time interval, control circuit 80 may detect a long pause or asystole and control therapy delivery circuit to generate a pacing pulse.

[0127] FIG. 8 is a flow chart 400 of a method for sensing cardiac event signals by a medical device according to another example. In some examples, an atrial sensing signal may be determined using an atrial signal and a ventricular signal as described according to any of the examples given above. The ventricular sensing signal, however, may be the rectified ventricular signal that is not combined in any manner with the atrial signal. With reference to FIG. 5, for example, the smoothed, rectified ventricular signal 69 may be passed to R-wave detector 66a without performing any operation on paired sample points of the atrial signal and the ventricular signal 69. In other examples, the second V sensing channel 85 may be enabled to sense ventricular event signals from the output of rectifier 65b to produce Vsense signals 68b that are passed to control circuit 80 for use in controlling cardiac electrical stimulation therapies.

[0128] As shown in FIG. 8, sensing circuit 86 may receive a first cardiac electrical signal at block 402 as an atrial signal received via an atrial sensing electrode vector by the A sensing channel 81. At block 404, sensing circuit 86 may receive a second cardiac electrical signal as a ventricular signal received via a ventricular sensing electrode vector by V sensing channel 83. In some examples, a second V sensing channel 85 may be included in sensing circuit 86 for receiving a second ventricular signal via a second ventricular sensing electrode vector. At block 406, sensing circuit 86 may determine an atrial sensing signal using paired sample points of the atrial signal and the ventricular signal received from V sensing channel 83 (or from V sensing channel 85). The atrial sensing signal may be determined according to any of the example methods described herein.

[0129] At block 410, sensing circuit 86 senses atrial event signals, e.g., based on a P-wave sensing threshold being met by the atrial sensing signal. At block 412, sensing circuit 86 senses ventricular event signals, e.g., based on an R-wave sensing threshold being met by the ventricular signal received by V sensing channel 83 or V sensing channel 85. Referring again to FIGs. 4 and 5, the ventricular signal 69 may be passed to R-wave detector 66a without determining a ventricular sensing signal using the atrial signal 109. A Vsense signal 68a may be produced by R-wave detector 66a in response to the R-wave sensing threshold being met. In FIG. 6, the smoothed rectified signal 214 may correspond to ventricular signal 69, for example. V sensing channel 83 may apply the R-wave sensing threshold 218 to the ventricular signal 214 for sensing R-waves. Sensing circuit 86 may produce Vsense signal 226 in response to the ventricular signal 214 crossing the R-wave sensing threshold 218.

[0130] When a ventricular event signal is sensed (based on an R-wave sensing threshold crossing) within a suspected oversense window from the sensed atrial event signal (“yes” branch of block 414), sensing circuit 86 may analyze one or more features of the atrial sensing signal and / or ventricular signal for confirming the sensed atrial event signal at block 416. The process of confirming a sensed atrial event signal at block 414 may be performed by sensing circuit 86 when an R-wave sensing threshold crossing by the ventricular signal is detected within the suspected oversense window of the P-wave sensing threshold crossing by the atrial sensing signal. The suspected oversense window may be 20 ms to 100 ms and may be 30 to 50 ms as non-limiting examples. When the P-wave sensing threshold crossing and the R-wave sensing threshold crossing are received within the suspected oversense window, the P-wave sensing threshold crossing could be an oversensed R-wave or the R-wave sensing threshold crossing could be an oversensed P- wave.

[0131] When an R-wave sensing threshold crossing does not occur within the suspected oversense window of the P-wave sensing threshold crossing (“no” branch of block 414), the sensed atrial event signal and the sensed ventricular event signal (separated in time by more than the suspected oversense window) may be deemed valid sensed event signals without performing additional signal analysis. Sensing circuit 86 may produce an Asense signal and a Vsense signal that are passed to control circuit 80. If the atrial sensed event signal is confirmed, sensing circuit 86 may apply a post-atrial blanking period, a post- atrial refractory period and / or a post-atrial ventricular blanking period at block 414. At block 418, control circuit 80 controls therapy delivery circuit 84 to generate and deliver (or withhold) cardiac electrical stimulation pulses as needed according to a programmed therapy (e.g., pacing mode, ATP, CV / DF shocks etc.) based on the Asense signal and the Vsense signal.

[0132] When the atrial event signal is sensed based on a P-wave sensing threshold crossing by the atrial sensing signal and a ventricular event signal is sensed based on an R- wave sensing threshold crossing within the suspected oversense window from each other (“yes” branch of block 414), sensing circuit 86 may perform signal analysis at block 416 to confirm the atrial event signal as likely being a valid P-wave.

[0133] Sensing circuit 86 may confirm the sensed atrial event signal according to any of the methods described above, e.g., in conjunction with FIG. 6. In other examples, the sensed atrial event signal may be confirmed by determining a maximum peak amplitude of the sensed atrial event and by determining a maximum peak amplitude of the sensed ventricular event. With reference to FIG. 6, following a P-wave sensing threshold crossing, sensing circuit 86 may determine the maximum peak amplitude 230, e.g., during a peak tracking window or atrial blanking period applied in response to the P-wave sensing threshold crossing (coinciding with Asense signal 210). P-wave detector 106 may include a peak track and hold circuit or other circuitry configured to determine the amplitude of the maximum peak 230 of the sensed waveform.

[0134] In this example where ventricular event signals are sensed from the ventricular signal 214 shown in FIG. 6, sensing circuit 86 may determine the maximum peak amplitude 232 of the sensed waveform following the R-wave sensing threshold crossing. R-wave detector 66a may include a peak track and hold circuit or other circuitry configured to determine the amplitude of the maximum peak of the ventricular signal during a peak tracking window or ventricular blanking period following the R-wave sensing threshold crossing.

[0135] Sensing circuit 86 may confirm the atrial sensed event signal based on a quantitative relationship of the maximum peak amplitudes of the atrial sensing signal and the ventricular signal used to sense atrial events and ventricular events, respectively. For example, a difference or ratio of the atrial maximum peak amplitude 230 (FIG. 6) and the ventricular maximum peak amplitude 232 (FIG. 6) may be compared to a discrimination threshold. To illustrate, if the ventricular maximum peak amplitude 232 less the atrial maximum peak amplitude 230 or the ratio of the ventricular maximum peak amplitude 232 to the atrial maximum peak amplitude 230 is less than a P-wave confirmation threshold, the sensed atrial event signal may be confirmed and the Asense signal 210 may be passed to control circuit 80 and used, e.g., by arrhythmia detection circuit 92 and / or timing circuit 90, for determining if a cardiac electrical stimulation pulse is needed according to a programmed therapy.

[0136] In other examples, the ventricular maximum peak amplitude 232 and the atrial maximum peak amplitude 230 may be added together or multiplied together and compared to a P-wave confirmation threshold. When the sum or product of the atrial maximum peak amplitude 230 and ventricular maximum peak amplitude 232 is less than a P-wave confirmation threshold, sensing circuit 86 may confirm the sensed atrial event signal and pass the Asense signal 210 to control circuit 80 for use in determining a need for a cardiac electrical stimulation pulse. The sensed ventricular event signal may be deemed invalid as likely being an oversensed P-wave on the V sensing channel 83. The Vsense signal 226 may not be generated by sensing circuit 86 (or may be ignored by control circuit 80) when the sensed atrial event signal is confirmed.

[0137] At block 418, control circuit 80 may control therapy delivery based on the confirmed Asense signal but ignore the sensed ventricular event signal in determining cardiac event intervals, starting post-ventricular blanking and refractory periods, and / orstarting pacing escape intervals. An AV pacing interval may be started in response to the Asense signal. If a ventricular pacing interval expires without a valid Vsense signal received from sensing circuit 86, a pacing pulse may be delivered to pace the ventricles.

[0138] When the P-wave confirmation threshold is not met (e.g., the quantitative relationship determined between the atrial maximum peak amplitude and the ventricular maximum peak amplitude is greater than or equal to the P-wave confirmation threshold), the sensed ventricular event signal may be confirmed. Sensing circuit 86 may pass a Vsense signal to control circuit 80. The sensed atrial event signal may be determined invalid as likely being an oversensed R-wave on the A sensing channel 81. In this case, any post-atrial blanking and refractory periods are not applied in response to the sensed atrial event signal determined to be invalid. The process of FIG. 8 may advance to block 418 (“no” branch of block 416) to control therapy delivery based on the confirmed Vsense signal but ignore the Asense signal in this case. A pending ventricular pacing pulse may be inhibited in response to the Vsense signal. Post-ventricular blanking and refractory periods may be started. A ventricular pacing interval may be started. An RRI and PRI may be determined that ends with the Vsense signal for use in detecting tachyarrhythmia.

[0139] FIG. 9 is a flow chart 500 of a method for sensing cardiac event signals by a medical device according to another example. In the example of FIG. 8, an atrial sensing signal is determined using a received atrial signal and a received ventricular signal. Events sensed from the atrial sensing signal within a suspected oversensing confirmation window from a Vsense signal can be confirmed as an atrial sensed event signal by performing additional signal analysis, such as comparing a quantitative relationship of the maximum peak amplitudes of the atrial sensing signal and the ventricular signal. In the example of FIG. 9, an atrial sensing signal and a ventricular sensing signal are each determined from a received atrial signal and from a received ventricular signal. Events sensed from either the atrial sensing signal or the ventricular sensing signal within a suspected oversensing confirmation window from each other may be confirmed as either a sensed atrial event or a sensed ventricular event based on additional signal analysis, e.g., by a comparison of a confirmation threshold to a quantitative relationship of the atrial maximum peak amplitude and the ventricular maximum peak amplitude.

[0140] As shown in FIG. 9, sensing circuit 86 may receive a first cardiac electrical signal at block 502 as an atrial signal received via an atrial sensing electrode vector by the Asensing channel 81. At block 504, sensing circuit 86 may receive a second cardiac electrical signal as a ventricular signal received via a ventricular sensing electrode vector by V sensing channel 83. At block 506, sensing circuit 86 may determine an atrial sensing signal using paired sample points of the atrial signal and the ventricular signal according to any of the example methods described herein. At block 510 sensing circuit 86 may determine a ventricular sensing signal using paired sample points of the atrial signal and the ventricular signal according to any of the example methods described herein. The atrial sensing signal and the ventricular sensing signal can be determined according to a different operation, different time alignment of sample points and / or different order of operands (e.g., atrial sample point minus ventricular sample point or vice versa) in various examples.

[0141] At block 512, sensing circuit 86 monitors the atrial sensing signal for a P-wave sensing threshold crossing. If an atrial event signal is sensed based on a P-wave sensing threshold crossing, sensing circuit 86 may determine if a ventricular event signal is sensed from the ventricular sensing signal within the suspected oversense window at block 514. If not (“no” branch of block 514), the atrial event signal is deemed a valid sensed atrial event. An Asense signal may be produced and post-atrial sense blanking and refractory periods can be started at block 518. The post-atrial sense blanking and refractory periods can be started having an effective starting time of the P-wave sensing threshold crossing time.

[0142] If a ventricular event is sensed within the suspected oversense window (“yes” branch of block 514), sensing circuit 86 and / or control circuit 80 may perform signal analysis at block 516 for confirming either the sensed atrial event or the sensed ventricular event. As generally described in conjunction with FIG. 8, in some examples sensing circuit 86 may determine an atrial maximum peak amplitude and a ventricular maximum peak amplitude. Sensing circuit 86 (or control circuit 80) may determine a quantitative relationship of the atrial maximum peak amplitude and the ventricular maximum peak amplitude (e.g., the difference, ratio, sum or product) and compare the quantitative relationship to a confirmation threshold at block 516. The confirmation threshold may be selected to discriminate between the quantitative relationship value expected when the sensed event is a true P-wave versus when the sensed event is a true R-wave. In some examples, when the quantitative relationship is less than the confirmation threshold, thesensed atrial event is confirmed (“yes” branch of block 516). Post-atrial sense blanking and refractory periods may be applied at block 518.

[0143] The confirmation threshold may be satisfied for confirming the sensed atrial event when the quantitative relationship is less than (and in some examples less than or equal to) the confirmation threshold. The sensed ventricular event may be confirmed at block 524 when the quantitative relationship is greater than (and in some examples greater than or equal to) the confirmation threshold. It is recognized, however, that depending on how the quantitative relationship is determined, the confirmation threshold for confirming sensed atrial events could be met when the quantitative relationship is greater than the confirmation threshold rather than less than.

[0144] When the sensed ventricular event signal is confirmed at block 524 (“no” branch of block 516), sensing circuit 86 may apply post- ventricular sense blanking and refractory periods at block 530. The post-ventricular sense blanking and refractory periods may have an effective starting time corresponding to the time of the R-wave sensing threshold crossing. After confirming the sensed atrial or ventricular event, control circuit 80 may control therapy delivery circuit in accordance with the confirmed sensed cardiac event signal at block 532. For example, cardiac pacing escape interval(s) may be started or allowed to continue to run depending on the type of cardiac event, atrial or ventricular, that is confirmed. For example, an AV pacing interval may be started in response to a confirmed sensed atrial event signal and a ventricular pacing interval that is running at the time of the confirmed sensed atrial event signal may continue running without being restarted. If a sensed ventricular event is confirmed, a pending ventricular pacing pulse may be cancelled and a ventricular pacing interval may be restarted. Various timers or counters used to time out cardiac event intervals, e.g., PPIs, RRIs, PRIs and / or RPIs, may be restarted as appropriate based on which type of cardiac event, atrial or ventricular, is confirmed. Tachyarrhythmia detection algorithms may receive a cardiac event interval determined in response to the confirmed sensed cardiac event, e.g., a PPI and / or RPI when the confirmed event is an atrial event or an RRI or PRI when the confirmed event is a ventricular event. Therapy delivery circuit 84 may be controlled to deliver, delay, or cancel a scheduled cardiac electrical stimulation pulse based on at least the most recently confirmed sensed cardiac event signal. In some examples, if the confirmed sensed cardiacevent signal results in tachyarrhythmia detection criteria being met, therapy delivery circuit 84 may begin charging high voltage capacitors used to deliver a CV / DF shock.

[0145] Referring again to block 512, when an atrial event signal is not sensed (no P-wave sensing threshold crossing by the atrial sensing signal) but a ventricular event signal is sensed at block 520, sensing circuit 86 may determine if an atrial event is sensed within the suspected oversense window from the R-wave threshold crossing by the ventricular sensing signal at block 522. If not (“no” branch of block 522), the ventricular event signal may be confirmed. A Vsense signal may be passed to control circuit 80. Sensing circuit 86 may apply post- ventricular sense blanking and refractory periods at block 530. Control circuit 80 may control therapy delivery circuit 84 based on at least the Vsense signal in accordance with programmed therapies.

[0146] When an atrial event signal is sensed within the suspected oversense window from the sensed ventricular event signal, sensing circuit 86 (and / or control circuit 80) may perform signal analysis at block 526 for confirming one or the other of the sensed atrial event signal or the sensed ventricular event signal. For example, when the ventricular sensing signal crosses the R-wave sensing threshold and the atrial sensing signal crosses the P-wave sensing threshold within the suspected oversense window from the R-wave sensing threshold crossing, sensing circuit 86 may perform an analysis at block 526 for confirming the sensed ventricular event signal. As described above, in some examples, sensing circuit 86 may determine a quantitative relationship of the atrial maximum peak amplitude and the ventricular maximum peak amplitude. The quantitative relationship may be compared to a confirmation threshold that discriminates between a true R-wave and a true P-wave. If the quantitative relationship meets the confirmation threshold requirement for confirming the sensed ventricular event signal (“yes” branch of block 526), sensing circuit 86 may apply post- ventricular sense blanking and refractory periods at block 530. At block 532, control circuit 80 may control therapy delivery circuit 84 in generating, delivering, withholding, canceling or scheduling one or more electrical stimulation pulses in accordance with programmed therapy algorithms based on at least the confirmed sensed ventricular event signal.

[0147] If, however, the quantitative relationship meets the confirmation threshold requirement for confirming the sensed atrial event signal at block 526 (“no” branch), sensing circuit 86 may confirm the sensed atrial event signal at block 528 and apply post-atrial sense blanking and refractory periods at block 518. Control circuit 80 may control therapy delivery circuit 84 at block 530 in generating, delivering, delaying, canceling or scheduling one or more electrical stimulation pulses in accordance with programmed therapy algorithms based on at least the confirmed sensed atrial event signal.

[0148] FIG. 10 is a flow chart 600 of a method for detecting ventricular tachyarrhythmia by an IMD according to some examples. With reference to the ICD shown in FIG. 4, sensing circuit 86 receives a ventricular signal at block 602 and an atrial signal at block 604. Sensing circuit 86 may perform atrial sensing at block 608 by determining an atrial sensing signal from the ventricular signal and the atrial signal according to any of the examples described above and applying a P-wave sensing threshold to the atrial sensing signal for sensing atrial event signals. Atrial event signals sensed based on a P-wave sensing threshold crossings may optionally be confirmed in some instances, e.g., using the techniques described in conjunction with FIG. 6 or FIG. 8.

[0149] Sensing circuit 86 may perform ventricular sensing at block 606 by applying an R- wave sensing threshold to the received ventricular signal, e.g., after filtering and rectifying the received ventricular signal. In other examples, sensing circuit 86 may determine a ventricular sensing signal from the received ventricular signal and the received atrial signal and apply an R-wave sensing threshold to the ventricular sensing signal. Sensed ventricular events may be confirmed in some instances, e.g., using the techniques described in conjunction with FIG. 6 or FIG. 9.

[0150] When a ventricular event is sensed by sensing circuit 86 (“yes” branch of block 606), control circuit 80 may determine an RRI at block 610. The RRI is the time interval from a most recent preceding sensed ventricular event to the currently sensed ventricular event. When an atrial event is sensed by sensing circuit 86 (“yes” branch of block 608), control circuit 80 may determine a PPI at block 612. The PPI is the time interval from a most recent preceding sensed atrial event to the currently sensed atrial event.

[0151] At block 614, control circuit 80 may determine if an NID is reached for detecting VT / VF. If an NID is reached for detecting VT / VF, control circuit 80 may evaluate PPIs that may be buffered in memory for determining if an SVT, e.g., atrial fibrillation or atrial flutter, is detected at block 616. PPIs shorter than an atrial tachyarrhythmia interval threshold may be counted for detecting an SVT when the number of atrial tachyarrhythmia intervals reaches a threshold number of intervals. When a threshold number of atrialtachyarrhythmia intervals is detected, the NID is likely reached due to the SVT. Control circuit 80 may advance to block 625 and withhold detecting VT / VF based on the NID being reached when evidence of an SVT is detected based on P-wave sensing. A VT / VF therapy is withheld by withholding the VT / VF detection when the NID is reached and an SVT is detected based on P-wave sensing.

[0152] As described above in conjunction with FIG. 7, in response to detecting an SVT based at least in part on Asense signals, control circuit 80 may determine data related to detected SVT episodes, such as determining the duration of the SVT episode, determining an atrial tachyarrhythmia burden, updating the total number of SVT episodes detected since implant or last ICD interrogation, or the like. ICD 14 may transmit SVT related data for receipt by another medical device, such as external device 40 of FIG. 1 A.

[0153] If the PPIs do not meet SVT detection criteria at block 616, e.g., less than a threshold number of the PPIs are shorter than an atrial tachyarrhythmia interval threshold, control circuit 80 may determine one or more noise metrics at block 618. Skeletal muscle myopotentials or environmental noise such as electromagnetic interference may cause non-cardiac noise signals in the received ventricular signal to be sensed as R-waves.Control circuit 80 may determine one or more noise metrics at block 618 for determining if the received ventricular signal is noise contaminated. For example, signal pulses may be counted and / or signal pulse amplitudes may be analyzed for determining if noise pulses are likely present in the received ventricular signal. In some examples, noise metrics may be determined from a morphology signal segment received from the morphology signal channel 87 shown in FIG. 4. Example techniques that may be used for determining noise metrics and when a noise rejection rule is satisfied are generally described in U.S. Patent No. 10,470,681 (Greenhut, et al.) and in U.S. Patent No. 10,561,332 (Zhang, et al.), both of which patents are incorporated herein by reference in their entirety.

[0154] In some instances, T- waves in the received ventricular signal may be oversensed by sensing circuit 86 as false R-waves. In some examples, control circuit 80 may determine T-wave oversensing (TWOS) metrics at block 620. Determining TWOS metrics may include determining an alternating pattern of short and long RRIs, alternating ventricular maximum peak amplitudes, and / or alternating morphology matching scores determined between unknown sensed event signals and a known R-wave template stored in memory 82. Numerous methods for determining TWOS metrics for use in detectingTWOS may be used in conjunction with the techniques disclosed herein. Example methods of detecting TWOS and determining when a TWOS rejection rule is met are generally disclosed in U.S. Patent No. 10, 850,113 (Cao, et al.), incorporated herein by reference in its entirety, and in the above-incorporated U.S. Patent No. 10,470,681 (Greenhut, et al.).

[0155] Control circuit 80 determines when a VT / VF rejection rule is satisfied at block 622. A VT / VF rejection rule may be satisfied when control circuit 80 detects noise corruption based on the noise metrics determined at block 618. A VT / VF rejection rule may be satisfied when control circuit 80 detects TWOS based on the TWOS metrics determined at block 620. If a VT / VF rejection rule is met based on noise metrics or TWOS metrics, control circuit 80 may, at block 625, withhold a VT / VF detection based on the NID being reached. Control circuit 80 may control therapy delivery circuit 84 to withhold a VT / VF therapy by withholding the VT / VF detection even though the NID is reached.

[0156] If no VT / VF rejection rule is satisfied at block 622, control circuit 80 may detect VT / VF at block 624 when the NID is reached and an SVT is not detected based on sensed P-waves. At block 626, control circuit 80 may control therapy delivery circuit 84 to deliver one or more therapies according to a programmed menu of therapies for terminating the detected VT / VF. The therapies may include one or more ATP therapies and / or one or more CV / DF shocks.

[0157] FIG. 11 is a flow chart 700 of a method for detecting tachyarrhythmia and controlling VT / VF therapies by an IMD according to another example. With reference to the ICD shown in FIG. 4 and sensing circuitry of FIG. 5, sensing circuit 86 receives a ventricular signal via a ventricular sensing electrode vector at block 702 and an atrial signal via an atrial sensing electrode vector at block 704. Sensing circuit 86 may perform atrial event signal sensing at block 708 by determining an atrial sensing signal from the ventricular signal and the atrial signal according to any of the examples described above and applying a P-wave sensing threshold to the atrial sensing signal for sensing atrial event signals. Sensed atrial event signals may be confirmed in some instances, e.g., using the techniques described in conjunction with FIG. 6 or FIG. 8.

[0158] Sensing circuit 86 may perform ventricular sensing at block 706 by applying an R- wave sensing threshold to the received ventricular signal, e.g., after filtering and rectifying the received ventricular signal. In other examples, sensing circuit 86 may determine aventricular sensing signal from the received ventricular signal and the received atrial signal and apply an R-wave sensing threshold to the ventricular sensing signal. Sensed ventricular events may be confirmed in some instances, e.g., using the techniques described in conjunction with FIG. 6 or FIG. 9.

[0159] When a ventricular event signal is sensed by sensing circuit 86 (“yes” branch of block 706), control circuit 80 may determine an RRI at block 610. The RRI is the time interval from a most recent preceding sensed ventricular event signal to the currently sensed ventricular event signal (e.g., at the time of the R-wave sensing threshold crossing). When an atrial event signal is sensed by sensing circuit 86 (“yes” branch of block 708), control circuit 80 may determine a PPI at block 712. The PPI is the time interval from a most recent preceding sensed atrial event signal to the currently sensed atrial event signal (e.g., the time of the P-wave sensing threshold crossing). In some examples, the time of an Asense signal may be used for determining a PRI and / or RPI at block 712 relative to the next subsequent Vsense signal or most recent preceding Vsense signal, respectively. The time of sensed atrial events and sensed ventricular events and / or the RRIs and PPIs (and PRIs and RPIs) may be buffered in memory 82 for comparing to tachyarrhythmia interval thresholds, counting tachyarrhythmia intervals, comparing atrial and ventricular rates to each other, and analyzing patterns of Asense signals and Vsense signals for discriminating between SVTs and VT / VF as further described below.

[0160] At block 714, control circuit 80 may determine if an NID is reached for detecting VT / VF. If an NID is reached for detecting VT / VF, control circuit 80 may verify that noise detection criteria are not met at block 716. If noise is detected in the ventricular signal and / or the morphology signal (from morphology sensing channel 87), for example, control circuit 80 may withhold a VT / VF detection and VT / VF therapy delivery at block 735 even though the NID is reached. The NID may be reached due to noise contamination of the ventricular signal resulting in oversensing of noise as false R-waves. Various noise metrics may be determined at block 716 to determine if a noise rejection rule is satisfied as generally described above in conjunction with FIG. 9 and in the above-incorporated U.S. Patent No. 10,470,681 (Greenhut, et al.) and U.S. Patent No. 10,561,332 (Zhang, et al.).

[0161] When noise is not detected at block 716, e.g., when a noise rejection rule is not satisfied, control circuit 80 may determine if a representative value of the RRIs, e.g., a median RRI, is shorter than an SVT limit. The SVT limit may be the shortest RRIexpected when an SVT is being conducted to the ventricles. The SVT limit may be programmable to 250 to 300 ms as examples. If the representative value of RRIs contributing to the NID being met is less than the SVT limit, analysis of PPIs, PRIs, and / or R-wave morphology for discriminating between an SVT and VT / VF may be skipped. The fast ventricular rate may be evidence of a true fast VT or VF. Control circuit 80 may advance to block 728 to evaluate the sensed cardiac electrical signals for possible TWOS in some examples. In other examples, control circuit 80 may advance directly to block 732 and detect VT / VF based on the fast ventricular rate without noise being detected.

[0162] If the representative RRI is not less than SVT limit at block 718, control circuit 80 may perform an interval analysis at block 720 for discriminating between a conducted SVT, VT / VF and, in some examples, a double tachyarrhythmia (SVT and VT / VF occurring simultaneously). The times of Asense and Vsense signals, which may be buffered in memory 82 as timing markers and / or recent PPIs, PRIs, RPIs and RRIs may be analyzed for classifying the heart rhythm. This interval-based analysis may evaluate PPIs, RRIs, PRIs and RPIs for comparing the relationship between the rate of Asense and Vsense signals and patterns of AV conduction to various rhythm classification criteria.

[0163] For example, control circuit 80 may classify the rhythm as AF when the atrial rate determined from PPIs is faster than the ventricular rate determined from RRIs and the RRIs are irregular. Control circuit 80 may classify the rhythm as atrial flutter when the atrial rate is faster than the ventricular rate and occurs at a 2: 1 or 3:2 rate ratio indicating the regular pattern of AV conduction that can occur during atrial flutter.

[0164] Control circuit 80 may classify the rhythm as sinus tachycardia when the atrial rate and the ventricular rate are equal with 1 : 1 AV conduction and a gradual increase in the ventricular rate has occurred with PRIs in a normal AV conduction range. In some examples, other SVTs such as junctional rhythms, e.g., AV nodal reentrant tachycardia, can be classified by control circuit 80 when the PRIs are very short (near simultaneous Asense and Vsense signals) and the rate of Vsense signals are 1: 1 with Asense signals. In some instances, an SVT and a VT / VF can occur at the same time. In this case, control circuit 80 may detect a double tachycardia when the PPIs meet a rate or an NID for detecting atrial tachycardia, the RRIs meet a rate or an NID for detecting VT / VF and the PRIs are variable such that the timing of Vsense signals are dissociated with the timing of Asense signals. Some examples of interval and pattern based analysis for detecting anddiscriminating heart rhythms according to a set of hierarchical rules that may be combined with the cardiac event signal sensing methods disclosed herein are generally described in U.S. Patent No. 6,487,443 (Olson, et al.), incorporated herein by reference in its entirety.

[0165] In an illustrative example, control circuit 80 may buffer a specified number of PPIs and RRIs in memory 82, for example the most recent 8 to 20 PPIs and RRIs or most recent 12 PPIs and RRIs. Control circuit 80 may determine a median PPI and median RRI (or other representative value of the most recent PPIs and RRIs) from the buffered intervals. When the median RRI is longer than the SVT limit (“no branch of block 718), control circuit 80 performs the interval analysis at block 720. Control circuit 80 may determine various cardiac event interval metrics based on Asense and Vsense signals received from sensing circuit 86 and buffered in memory 82 for classifying the heart rhythm, e.g., as AF, atrial flutter, sinus tachycardia, other SVT, VT / VF or double tachycardia, based on the atrial rate, ventricular rate and patterns of Asense and Vsense signals, which may be referred to as an “AV interval pattern.” To determine the AV interval pattern, control circuit 80 may determine PRIs, RPIs and the ratio of Asense signals to Vsense signals (or Vsense signals to Asense signals) for example. For instance, control circuit 80 may determine if the ratio of Asense to Vsense signals occur in a 1: 1 relationship (each Asense signal is followed by only one Vsense signal), 2: 1 relationship (two Asense signals occur for every one Vsense signal), or 3:2 relationship (three Asense signals for every two Vsense signals). Control circuit 80 may determine the PRIs for determining if the PRIs fall into a normal AV conduction time range (indicating normal sinus tachycardia), if the PRIs indicate near simultaneous Asense and Vsense signals (indicating other 1: 1 SVTs such as junctional rhythms) or if the PRIs are irregular indicating dissociation between Asense and Vsense signals (indicating VT / VF or double tachyarrhythmia). Dissociation between Asense and Vsense signals may be detected by control circuit 80 when at least X out of Y (e.g., 4 out of 8 or 6 out of 12) RRIs occur with no Asense during the RRI. Additionally or alternatively, dissociation between Asense and Vsense signals may be detected by control circuit 80 when at least one PRI occurring during the most recent Y Vsense signals is more than a threshold difference from an average, median or other representative measure of PRIs. The threshold difference may be 30 to 80 ms or 40 ms as examples.

[0166] As indicated above, the interval analysis performed at block 720 may evaluate the regularity of the RRIs for classifying the rhythm. Control circuit 80 may identify the mostcommonly occurring RRIs out of the RRIs counted toward the NID being reached. For example, the one, two or three most commonly occurring RRIs out of the RRIs counted toward the NID being reached may be determined. The percentage of RRIs occurring at the most commonly occurring interval(s) may be compared to one or more regularity thresholds for use in classifying the heart rhythm. For instance, when the percentage of most common RRIs is at least 75% of the buffered RRIs and other SVT criteria are met (e.g., atrial rate criteria and PRI dissociation), a double tachyarrhythmia may be detected by control circuit 80. When the percentage of most common RRIs of the buffered RRIs is less than 50% and other criteria for detecting AF are met (e.g., an AF evidence count reaches a threshold value as described below), control circuit 80 may classify the rhythm as AF. When the Asense signal to Vsense signal ratio is 1: 1, the percentage of the most common RRIs may be required to be at least 25% in order to classify the rhythm as a 1: 1 SVT such as a junctional rhythm.

[0167] Control circuit 80 may count the number of RRIs in which two or more Asense signals occur as evidence of AF. When the AF evidence count reaches a threshold value, e.g., 6 out of the most recent 8 RRIs as a non-limiting example, AF evidence criteria may be met for classifying the rhythm as AF. The AF evidence criteria for classifying the rhythm may include other requirements such as irregular RRIs based on the percentage of RRIs that are the most commonly occurring RRI(s) as described above.

[0168] In some examples, control circuit 80 may identify far field R-wave (FFRW) oversensing by the A sensing channel 81 to avoid a mis-classification of the rhythm as an SVT. For example, FFRW oversensing may be detected by control circuit 80 when exactly two Asense signals occur during an RRI, the PRIs or RPIs are regular, and the PPIs ending with the two Asense signals occur in a short-long or long- short pattern. Additionally or alternatively, at least one PRI associated with the two Asense signals may be required to be less than a short PRI threshold, e.g., less than 50 to 80 ms or less than 60 ms. Additionally or alternatively, at least one RPI associated with the two Asense signals may be required to be less than a short RPI threshold, e.g., less than 140 to 180 ms or less than 160 ms as examples. If FFRW oversensing is occurring on the A sensing channel 81, e.g., when FFRW oversensing is identified for at least one-third of the most recent RRIs, and other SVT criteria are met, the rhythm may be classified as sinus tachyarrhythmia by control circuit 80 at block 722.

[0169] If the rhythm classification based on the interval analysis is an SVT at block 722, e.g., AF, atrial flutter, sinus tachycardia or other 1: 1 SVT (“yes” branch of block 722), control circuit 80 may withhold VT / VF detection and therapy at block 735. If the rhythm classification based on the interval analysis is VT / VF, double tachycardia, or is indeterminate or unclassified (“no” branch of block 722), control circuit 80 may advance to block 724 to perform additional analysis for confirming the VT / VF before detecting VT / VF and delivering a therapy (at blocks 732 and 734). In some instances, an SVT may be causing the VT / VF NID to be reached even when the interval analysis performed at block 720 does not result in an SVT classification. A morphology analysis may be performed to discriminate between SVT and VT / VF when the interval analysis does not yield a rhythm classification and / or when the rhythm classification is VT / VF but the ventricular rate is not faster than the atrial rate. In other instances, TWOS may be occurring on the V sensing channel 83 (and sometimes both the A sensing channel 81 and the V sensing channel 83) causing the NID for detecting VT / VF to be reached. Additional analysis may be performed by control circuit 80 after performing the interval-based analysis at block 720 when an SVT classification is not made to avoid delivery of ATP and / or a CV / DF shock in the presence of an SVT or TWOS.

[0170] At block 724, control circuit 80 may verify that the ventricular rate is faster than the atrial rate based on a comparison of the RRIs to the PPIs, e.g., based on a median RRI being shorter than a median PPI. If the ventricular rate is faster than the atrial rate (“no” branch of block 724), control circuit 80 may advance to block 728 to perform a TWOS analysis. If the ventricular rate is not faster than the atrial rate, an SVT may be present that was not detected based on the interval-based analysis performed at block 720. If the ventricular rate is equal to or slower than the atrial rate (“yes” branch of block 724), control circuit 80 may advance to block 726 to perform a morphology-based analysis for detecting an SVT.

[0171] A cardiac signal segment from V sensing channel 81, V sensing channel 83 and / or morphology signal channel 87 may be obtained and buffered in memory 82 in response to a Vsense signal to obtain a signal waveform corresponding to one sensed ventricular event signal (e.g., including exactly one R-wave sensing threshold crossing). One or more cardiac signal segments including exactly one R-wave sensing threshold crossing may be obtained for performing the morphology analysis at block 726. The unknown signalwaveform sensed as a ventricular event signal may be compared to a normal sinus rhythm R-wave template stored in memory 82. The R-wave template may be acquired by control circuit 80 during normal sinus rhythm by determining an ensemble average of multiple R- wave signal waveforms each associated with an R-wave sensing threshold crossing. A morphology analysis may be performed by control circuit 80 using wavelet transform techniques for determining a morphology matching score between the unknown signal waveform and the R-wave template. Other waveform correlation techniques may be used for determining how closely an unknown sensed signal waveform matches a known R- wave template. If a threshold number of Vsense signals are associated with a signal waveform having a morphology matching score that is greater than a match threshold, control circuit 80 may determine that the rhythm is an SVT at block 726. Control circuit 80 may withhold VT / VF detection and ventricular tachyarrhythmia therapy at block 735. Other morphology-based analysis may be performed at block 726 to discriminate between an SVT and VT / VF, e.g., as disclosed in U.S. Patent No. 10,555,684 (Zhang et al.), incorporated herein by reference in its entirety.

[0172] When the morphology-based analysis does not yield an SVT classification of the heart rhythm at block 726, control circuit 80 may determine TWOS metrics at block 728 for determining if TWOS is occurring on the V sensing channel 83 (or V sensing channel 85) that reached the NID. TWOS metrics may be determined at block 728 according to any of the methods described above in conjunction with FIG. 10 or the above-incorporated references, U.S. Patent No. 10, 850,113 (Cao, et al.) and U.S. Patent No. 10,470,681 (Greenhut, et al.).

[0173] When TWOS is detected or a TWOS rejection rule is met based on the determined TWOS metrics, control circuit 80 may withhold the VT / VF detection based on the NID being reached and control therapy delivery circuit 84 to not deliver ATP or CV / DF shocks (block 735 following “yes” branch of block 730). For instance, TWOS may be detected or a TWOS rejection rule may be satisfied for rejecting the VT / VF detection based on the NID being reached when alternating short and long RRIs, alternating maximum peak amplitudes, and / or alternating sensed waveform signal morphology (e.g., alternating morphology matching scores), or other alternating behavior of the sensed ventricular event signals is detected for a threshold number of Vsense signals.

[0174] When TWOS is not detected or a TWOS rejection rule is not met (“no” branch of block 730), control circuit 80 may detect VT / VF at block 732. In response to the VT / VF detection, control circuit 80 may control therapy delivery circuit 84 to deliver one or more sequences of ATP and / or one or more CV / DF shocks at block 734, e.g., according to a programmed menu of therapies, to terminate the detected VT / VF. In this way, control circuit 80 may use the Asense signals received from A sensing channel 81 in combination with the Vsense signals received from V sensing channel 83 (and / or V sensing channel 85) for detecting and discriminating tachyarrhythmias and controlling ventricular tachyarrhythmia therapy delivered by therapy delivery circuit 84.

[0175] Further disclosed herein is the subject matter of the following examples:

[0176] Example 1. A medical device including a therapy delivery circuit configured to deliver a cardiac electrical stimulation therapy by generating one or more cardiac electrical stimulation pulses and a sensing circuit configured to receive a first cardiac electrical signal as an atrial signal and receive a second cardiac electrical signal as a ventricular signal. The sensing circuit may determine an atrial sensing signal from the atrial signal and the ventricular signal, compare the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals and sense an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The medical device may further include a control circuit in communication with the sensing circuit and the therapy delivery circuit. The control circuit may be configured to determine if a cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal and control the therapy delivery circuit to either generate or not generate the cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

[0177] Example 2. The medical device of example 1 wherein the sensing circuit is further configured to determine a ventricular sensing signal from the atrial signal and the ventricular signal, where the ventricular sensing signal is different than the atrial sensing signal. The sensing circuit may compare the ventricular sensing signal to an R-wave sensing threshold for sensing ventricular event signals and sense a ventricular event signal in response to the ventricular sensing signal meeting the R-wave sensing threshold. The control circuit may be further configured to determine if the cardiac electrical stimulationpulse is needed according to the cardiac electrical stimulation therapy based on the sensed atrial event signal and the sensed ventricular event signal.

[0178] Example 3. The medical device of any one of examples 1 or 2 wherein the sensing circuit is further configured to determine the atrial sensing signal by determining a first combination of paired sample points of the atrial signal and the ventricular signal, where each pair of the paired sample points includes one sample point from the atrial signal and one sample point from the ventricular signal that is time aligned with the one sample point from the atrial signal.

[0179] Example 4. The medical device of any one of examples 1 — 3 wherein the sensing circuit is further configured to rectify the atrial signal, rectify the ventricular signal, and determine the atrial sensing signal by determining a non-rectified first difference signal between paired sample points of the rectified atrial signal and the rectified ventricular signal.

[0180] Example 5. The medical device of any one of examples 1 — 4 wherein the sensing circuit is further configured to compare the atrial sensing signal to the P-wave sensing threshold by comparing the atrial sensing signal to the P-wave sensing threshold having a first polarity, compare the atrial sensing signal to a second threshold having a second polarity opposite the first polarity and verify the sensed atrial event signal in response to the atrial sensing signal meeting the second threshold and meeting the P-wave sensing threshold.

[0181] Example 6. The medical device of any one of examples 2 — 5 wherein the sensing circuit is further configured to determine the atrial sensing signal by determining each sample point of the atrial sensing signal as a first combination of a pair of sample points of the atrial signal and the ventricular signal and determine the ventricular sensing signal by determining each sample point of the ventricular sensing signal as a second combination of a pair of sample points of the atrial signal and the ventricular signal, the second combination being different than the first combination.

[0182] Example 7. The medical device of any one of examples 1 — 6 wherein the therapy delivery circuit is further configured to generate the one or more cardiac electrical stimulation pulses for delivering a shock therapy. The control circuit may be further configured to detect a ventricular tachyarrhythmia using at least the sensed atrial eventsignal and control the therapy delivery circuit to deliver the shock therapy in response to detecting the ventricular tachyarrhythmia.

[0183] Example 8. The medical device of any one of examples 1 — 6 wherein the control circuit is further configured to control the therapy delivery circuit to deliver a ventricular pacing pulse in response to the sensed atrial event signal.

[0184] Example 9. The medical device of any one of examples 1 — 8 wherein the control circuit is further configured to detect a tachyarrhythmia based on at least the ventricular signal, determine that the detected tachyarrhythmia is a supraventricular tachyarrhythmia based on at least the sensed atrial event signal; and determine if the cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal by determining that a shock pulse is not needed in response to determining that the detected tachyarrhythmia is a supraventricular tachyarrhythmia. The control circuit may control the therapy delivery circuit to not deliver the shock pulse in response to detecting the tachyarrhythmia when the detected tachyarrhythmia is determined to be the supraventricular tachyarrhythmia.

[0185] Example 10. The medical device of any one of examples 1 — 10 wherein the control circuit is further configured to detect an atrial tachyarrhythmia based on at least the sensed atrial event signal and withhold a ventricular tachyarrhythmia detection in response to detecting the atrial tachyarrhythmia. The control circuit may control the therapy delivery circuit to withhold a ventricular tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

[0186] Example 11. The medical device of example 10 further comprising a telemetry circuit, wherein the control circuit is further configured to determine an atrial tachyarrhythmia burden in response to detecting the atrial tachyarrhythmia and generate an output based on the determined atrial tachyarrhythmia burden. The telemetry circuit may be configured to transmit a signal based on the generated output.

[0187] Example 12. The medical device of any one of examples 10 — 11 wherein the control circuit is further configured to control the therapy delivery circuit to deliver an atrial tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

[0188] Example 13. The medical device of any one of examples 1 — 12 wherein the sensing circuit is further configured to, in response to sensing the atrial event signal, determine a sensed atrial event signal feature from the atrial sensing signal, determine aventricular signal feature using at least the ventricular signal, determine a quantitative relationship between the atrial event signal feature and the ventricular signal feature, compare the quantitative relationship to a confirmation threshold and confirm the sensed atrial event signal in response to the quantitative relationship meeting the confirmation threshold.

[0189] Example 14. The medical device of example 13 wherein the sensing circuit is further configured to determine the sensed atrial event signal feature by determining an atrial maximum peak amplitude, determine the ventricular signal feature by determining a ventricular maximum peak amplitude and determine the quantitative relationship by determining at least one of a ratio, difference, sum or product of the atrial maximum peak amplitude and the ventricular maximum peak amplitude.

[0190] Example 15. The medical device of any one of examples 13-14 wherein the sensing circuit is further configured to start a suspected oversense window in response to sensing the atrial sensing signal meeting the P-wave sensing threshold, sense a ventricular event signal based on at least the ventricular signal and determine the quantitative relationship between the atrial event signal feature and the ventricular signal feature in response to the ventricular event signal being sensed during the suspected oversense window.

[0191] Example 16. The medical device of any one of examples 13-15 wherein the sensing circuit is further configured to detect a ventricular event signal when the quantitative relationship does not meet the confirmation threshold.

[0192] Example 17. The medical device of any one of examples 1-16 wherein the control circuit is further configured to determine if a cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal by: determining that a threshold number of ventricular tachyarrhythmia intervals are detected based on at least the ventricular signal, determining that a supraventricular tachyarrhythmia is not detected based on at least the sensed atrial event signal, determining at least one of a noise metric or a T-wave oversensing metric using at least the ventricular signal, determining that a ventricular tachyarrhythmia rejection rule is not met based on the at least one of the noise metric or the T-wave oversensing metric, detecting a ventricular tachyarrhythmia in response to the ventricular tachyarrhythmia rejection rule not being met and the supraventricular tachyarrhythmia not being detectedwhen the threshold number of ventricular tachyarrhythmia intervals are detected, and determining that the cardiac electrical stimulation pulse is needed in response to detecting the ventricular tachyarrhythmia. The therapy delivery circuit is configured to generate the cardiac electrical stimulation pulse in response to the control circuit detecting the ventricular tachyarrhythmia.

[0193] Example 18. A method comprising receiving a first cardiac electrical signal as an atrial signal, receiving a second cardiac electrical signal as a ventricular signal, determining an atrial sensing signal from the atrial signal and the ventricular signal, comparing the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals, and sensing an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The method may further include determining if a cardiac electrical stimulation pulse is needed according to a cardiac electrical stimulation therapy based on at least the sensed atrial event signal and either generating or not generating the cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

[0194] Example 19. The method of example 18 further comprising determining a ventricular sensing signal from the atrial signal and the ventricular signal where the ventricular sensing signal is different than the atrial sensing signal. The method further comprising comparing the ventricular sensing signal to an R-wave sensing threshold for sensing ventricular event signals, sensing a ventricular event signal in response to the ventricular sensing signal meeting the R-wave sensing threshold and determining if the cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on the sensed atrial event signal and the sensed ventricular event signal.

[0195] Example 20. The method of any one of examples 18 or 19 further comprising determining the atrial sensing signal by determining a first combination of paired sample points of the atrial signal and the ventricular signal, where each pair of the paired sample points includes one sample point from the atrial signal and one sample point from the ventricular signal that is time aligned with the one sample point from the atrial signal.

[0196] Example 21. The method of any one of examples 18 — 20 further comprising rectifying the atrial signal, rectifying the ventricular signal and determining the atrial sensing signal by determining a non-rectified first difference signal between paired sample points of the rectified atrial signal and the rectified ventricular signal.

[0197] Example 22. The method of any one of examples 18 — 21 further comprising comparing the atrial sensing signal to the P-wave sensing threshold by comparing the atrial sensing signal to a P-wave sensing threshold having a first polarity, comparing the atrial sensing signal to a second threshold having a second polarity opposite the first polarity and verifying the sensed atrial event signal in response to the atrial sensing signal meeting the second threshold and meeting the P-wave sensing threshold.

[0198] Example 23. The method of any one of examples 19 — 22 further comprising determining the atrial sensing signal by determining each sample point of the atrial sensing signal as a first combination of a pair of sample points of the atrial signal and the ventricular signal and determining the ventricular sensing signal by determining each sample point of the ventricular sensing signal as a second combination of a pair of sample points of the atrial signal and the ventricular signal, where the second combination is different than the first combination.

[0199] Example 24. The method of any one of examples 18 — 23 further comprising detecting a ventricular tachyarrhythmia using at least the sensed atrial event signal and delivering a shock therapy in response to detecting the tachyarrhythmia.

[0200] Example 25. The method of any one of examples 18 — 24 further comprising delivering a ventricular pacing pulse in response to the sensed atrial event signal.

[0201] Example 26. The method of any one of examples 18 — 25 further comprising detecting a tachyarrhythmia based on at least the ventricular signal, determining that the detected tachyarrhythmia is a supraventricular tachyarrhythmia based on at least the sensed atrial event signal, and determining if the cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal by determining that a shock pulse is not needed in response to determining that the detected tachyarrhythmia is a supraventricular tachyarrhythmia.

[0202] Example 27. The method of any one of examples 18 — 26 further comprising detecting an atrial tachyarrhythmia based on at least the sensed atrial event signal, withholding a ventricular tachyarrhythmia detection in response to detecting the atrial tachyarrhythmia and withholding a ventricular tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

[0203] Example 28. The method of example 27 further comprising determining an atrial tachyarrhythmia burden in response to detecting the atrial tachyarrhythmia, generating anoutput based on the determined atrial tachyarrhythmia burden and transmitting a signal based on the generated output.

[0204] Example 29. The method of any one of claims 27 — 18 further comprising delivering an atrial tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

[0205] Example 30. The method of any one of examples 18 — 29 further comprising, in response to sensing the atrial event signal, determining a sensed atrial event signal feature from the atrial sensing signal, determining a ventricular signal feature using at least the ventricular signal, determining a quantitative relationship between the atrial event signal feature and the ventricular signal feature, comparing the quantitative relationship to a confirmation threshold and confirming the sensed atrial event signal in response to the quantitative relationship meeting the confirmation threshold.

[0206] Example 31. The method of example 30 further comprising determining the sensed atrial event signal feature by determining an atrial maximum peak amplitude, determining the ventricular signal feature by determining a ventricular maximum peak amplitude, and determining the quantitative relationship by determining at least one of a ratio, difference, sum or product of the atrial maximum peak amplitude and the ventricular maximum peak amplitude.

[0207] Example 32. The method of any one of examples 30 — 31 further comprising starting a suspected oversense window in response to sensing the atrial sensing signal meeting the P-wave sensing threshold, sensing a ventricular event signal based on at least the ventricular signal, and determining the quantitative relationship between the atrial event signal feature and the ventricular signal feature in response to the ventricular event signal being sensed during the suspected oversense window.

[0208] Example 33. The method of any one of examples 30-32 further comprising detecting a ventricular event signal when the quantitative relationship does not meet the confirmation threshold.

[0209] Example 34. The method of any one of examples 18-33 further comprising determining if a cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal by determining that a threshold number of ventricular tachyarrhythmia intervals are detected based on at least the ventricular signal, determining that a supraventriculartachyarrhythmia is not detected based on at least the sensed atrial event signal, determining at least one of a noise metric or a T-wave oversensing metric using at least the ventricular signal, determining that a ventricular tachyarrhythmia rejection rule is not met based on the at least one of the noise metric or the T-wave oversensing metric and detecting a ventricular tachyarrhythmia in response to the ventricular tachyarrhythmia rejection rule not being met and the supraventricular tachyarrhythmia not being detected when the threshold number of ventricular tachyarrhythmia intervals are detected. The method may further include determining that the cardiac electrical stimulation pulse is needed in response to detecting the ventricular tachyarrhythmia and generating the cardiac electrical stimulation pulse in response to detecting the ventricular tachyarrhythmia.

[0210] Example 35. A non-transitory, computer readable medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to receive a first cardiac electrical signal as an atrial signal, receive a second cardiac electrical signal as a ventricular signal, determine an atrial sensing signal from the atrial signal and the ventricular signal, compare the atrial sensing signal to a P- wave sensing threshold for sensing atrial event signals and sense an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold. The instructions may further cause the medical device to determine if a cardiac electrical stimulation pulse is needed according to a cardiac electrical stimulation therapy based on at least the sensed atrial event signal and either generate or not generate a cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

[0211] It should be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are described as being performed by a single circuit or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0212] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware -based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0213] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPLAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0214] Thus, a medical device has been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.

Claims

WHAT IS CLAIMED IS:

1. A medical device comprising: a therapy delivery circuit configured to deliver a cardiac electrical stimulation therapy by generating one or more cardiac electrical stimulation pulses; a sensing circuit configured to: receive a first cardiac electrical signal as an atrial signal; receive a second cardiac electrical signal as a ventricular signal; determine an atrial sensing signal from the atrial signal and the ventricular signal; compare the atrial sensing signal to a P-wave sensing threshold for sensing atrial event signals; and sense an atrial event signal in response to the atrial sensing signal meeting the P-wave sensing threshold; and a control circuit in communication with the sensing circuit and the therapy delivery circuit and configured to: determine if a cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal; and control the therapy delivery circuit to either generate or not generate the cardiac electrical stimulation pulse according to the determined need for the cardiac electrical stimulation pulse.

2. The medical device of claim 1 wherein: the sensing circuit is further configured to: determine a ventricular sensing signal from the atrial signal and the ventricular signal, the ventricular sensing signal being different than the atrial sensing signal; compare the ventricular sensing signal to an R-wave sensing threshold for sensing ventricular event signals; and sense a ventricular event signal in response to the ventricular sensing signal meeting the R-wave sensing threshold; andthe control circuit is further configured to: determine if the cardiac electrical stimulation pulse is needed according to the cardiac electrical stimulation therapy based on the sensed atrial event signal and the sensed ventricular event signal.

3. The medical device of any one of claims 1 — 2 wherein the sensing circuit is further configured to determine the atrial sensing signal by determining a first combination of paired sample points of the atrial signal and the ventricular signal, where each pair of the paired sample points includes one sample point from the atrial signal and one sample point from the ventricular signal that is time aligned with the one sample point from the atrial signal.

4. The medical device of any one of claims 1 — 3 wherein the sensing circuit is further configured to: rectify the atrial signal; rectify the ventricular signal; and determine the atrial sensing signal by determining a non-rectified first difference signal between paired sample points of the rectified atrial signal and the rectified ventricular signal.

5. The medical device of any one of claims 1 — 4 wherein the sensing circuit is further configured to: compare the atrial sensing signal to the P-wave sensing threshold by comparing the atrial sensing signal to the P-wave sensing threshold having a first polarity; compare the atrial sensing signal to a second threshold having a second polarity opposite the first polarity; and verify the sensed atrial event signal in response to the atrial sensing signal meeting the second threshold and meeting the P-wave sensing threshold.

6. The medical device of any one of claims 1 — 5 wherein the sensing circuit is further configured to:determine the atrial sensing signal by determining each sample point of the atrial sensing signal as a first combination of a pair of sample points of the atrial signal and the ventricular signal; determine a ventricular sensing signal from the atrial signal and the ventricular signal by determining each sample point of the ventricular sensing signal as a second combination of a pair of sample points of the atrial signal and the ventricular signal, the second combination being different than the first combination.

7. The medical device of any one of claims 1 — 6 wherein: the therapy delivery circuit is further configured to generate the one or more cardiac electrical stimulation pulses for delivering a shock therapy; and the control circuit is further configured to: that the cardiac electrical stimulation pulse is needed by detecting a ventricular tachyarrhythmia using at least the sensed atrial event signal; and control the therapy delivery circuit to generate the shock therapy in response to detecting the ventricular tachyarrhythmia.

8. The medical device of any one of claims 1 — 6 wherein the control circuit is further configured to control the therapy delivery circuit to deliver a ventricular pacing pulse in response to the sensed atrial event signal.

9. The medical device of any one of claims 1 — 8 wherein the control circuit is further configured to: detect a tachyarrhythmia based on at least the ventricular signal; determine that the detected tachyarrhythmia is a supraventricular tachyarrhythmia based on at least the sensed atrial event signal; and determine that the cardiac electrical stimulation pulse is not needed according to the cardiac electrical stimulation therapy based on at least the sensed atrial event signal by determining that a shock pulse is not needed in response to determining that the detected tachyarrhythmia is a supraventricular tachyarrhythmia; andcontrol the therapy delivery circuit to not generate the shock pulse in response to detecting the tachyarrhythmia when the detected tachyarrhythmia is determined to be the supraventricular tachyarrhythmia.

10. The medical device of any one of claims 1 — 9 wherein the control circuit is further configured to: detect an atrial tachyarrhythmia based on at least the sensed atrial event signal; withhold a ventricular tachyarrhythmia detection in response to detecting the atrial tachyarrhythmia; and control the therapy delivery circuit to not generate a ventricular tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

11. The medical device of claim 10 further comprising a telemetry circuit, wherein: the control circuit is further configured to: determine an atrial tachyarrhythmia burden in response to detecting the atrial tachyarrhythmia; and generate an output based on the determined atrial tachyarrhythmia burden; and the telemetry circuit is configured to transmit a signal based on the generated output.

12. The medical device of any one of claims 10 — 11 wherein the control circuit is further configured to control the therapy delivery circuit to deliver an atrial tachyarrhythmia therapy in response to detecting the atrial tachyarrhythmia.

13. The medical device of any one of claims 1 — 12 wherein the sensing circuit is further configured to: in response to sensing the atrial event signal, determine a sensed atrial event signal feature from the atrial sensing signal; determine a ventricular signal feature using at least the ventricular signal; determine a quantitative relationship between the atrial event signal feature and the ventricular signal feature;compare the quantitative relationship to a confirmation threshold; and confirm the sensed atrial event signal in response to the quantitative relationship meeting the confirmation threshold.

14. The medical device of claim 13 wherein the sensing circuit is further configured to: determine the sensed atrial event signal feature by determining an atrial maximum peak amplitude; determine the ventricular signal feature by determining a ventricular maximum peak amplitude; and determine the quantitative relationship by determining at least one of a ratio, difference, sum or product of the atrial maximum peak amplitude and the ventricular maximum peak amplitude.

15. The medical device of any one of claims 13-14 wherein the sensing circuit is further configured to: start a suspected oversense window in response to sensing the atrial sensing signal meeting the P-wave sensing threshold; sense a ventricular event signal based on at least the ventricular signal; and determine the quantitative relationship between the atrial event signal feature and the ventricular signal feature in response to the ventricular event signal being sensed during the suspected oversense window.

16. The medical device of any one of claims 13-15 wherein the sensing circuit is further configured to detect a ventricular event signal when the quantitative relationship does not meet the confirmation threshold.

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