Medical lead migration detection

Abstract

A medical device is configured to sense one or more electrophysiological signals including a distal vector signal sensed using a distal electrode of a medical electrical lead when the medical electrical lead is connected to the medical device. Based on at least the distal vector signal, the medical device may detect migration of the medical electrical lead carrying the distal electrode and generate an output in response to detecting the migration of the medical electrical lead.

Description

MEDICAL LEAD MIGRATION DETECTION

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 585,946, filed September 27, 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 detecting migration of an implantable medical electrical lead.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. The medical device may deliver therapeutic electrical stimulation to the heart, brain, nerve, muscle or other tissue via one or more electrodes on the medical device and / or on one or more medical electrical leads coupled to the medical device. For instance, the medical device may be a neurostimulator configured to sense neurological signals and deliver electrical stimulation pulses based on neurological signals sensed by the neurostimulator. In other examples, implantable or external cardiac pacemakers, cardioverter defibrillators, cardiac monitors and the like, may 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 using electrodes carried by a medical electrical lead operatively positioned for delivering the therapies to the patient’s heart.

[0004] For example, a cardiac pacemaker or cardioverter defibrillator may deliver therapeutic electrical stimulation to the heart via electrodes carried by one or more medical electrical leads. 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. Upon detection of an abnormal rhythm, such as bradycardia,tachycardia or fibrillation, an appropriate electrical stimulation pulse or pulses may be delivered to restore or maintain a more normal rhythm of the heart. For example, an implantable cardioverter defibrillator (ICD) may deliver pacing pulses to the heart of the patient upon detecting bradycardia or tachycardia or deliver high voltage cardioversion or defibrillation (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 electrical signals and detecting migration of a medical, electrical lead connected to the medical device based on the sensed electrical signals. A medical device operating according to the techniques disclosed herein can be configured to sense at least one electrophysiological signal (e.g., cardiac electrical signal, neurological signal or other electrophysiological signal) that is a distal vector signal sensed using a sensing electrode vector that includes at least one electrode carried by the medical electrical lead. The at least one electrode may be carried at or proximate to a distal end of the medical electrical lead connected by a proximal lead connector to the medical device. Based on processing and analysis of at least the distal vector signal, the medical device may detect migration of the distal end of the lead.

[0006] In some examples, the medical device is configured to sense the distal vector signal and a proximal vector signal. The proximal vector signal may be sensed using a proximal sensing electrode vector that includes an electrode carried by the medical electrical lead proximal to the more distal electrode (e.g., carried at or nearer to the distal end of the medical electrical lead). The proximal sensing electrode vector does not include the relatively more distal electrode used for sensing the distal vector signal. The medical device may be configured to perform an analysis of the distal vector signal and the proximal vector signal to detect migration of the medical electrical lead. The analysis may include detecting a threshold change in the distal vector signal when the proximal vector signal remains relatively unchanged compared to a previous timepoint. The analysis may include detecting a threshold change in a difference signal determined as a difference between the distal vector signal and the proximal vector signal. In the case of a cardiac medical device, the analysis may include detecting a change in cardiac electrical event signals, e.g., P-waves and / or R-waves, which may be sensed as electrical event signals inthe distal vector signal and / or in the proximal vector signal. Various examples of analyses performed using at least a distal vector signal for detecting migration of a medical electrical lead are further described herein.

[0007] In one example, the disclosure provides a medical device system including a housing having a connector block configured to receive at least one medical electrical lead having a distal end and carrying at least a distal electrode. The medical device system may further include a therapy delivery circuit configured to deliver an electrical stimulation therapy and a sensing circuit configured to receive one or more electrophysiological signals including a distal vector signal received via a distal sensing electrode vector including the distal electrode. The medical device system may further include a control circuit in communication with the sensing circuit and the therapy delivery circuit. The control circuit may be configured to, based on the one or more electrophysiological signals received by the sensing circuit, control the therapy delivery circuit to deliver the electrical stimulation therapy. The control circuit may be further configured to, based on at least the distal vector signal, detect migration of the medical electrical lead carrying the distal electrode and generate an output in response to detecting the migration of the medical electrical lead. The medical device system may further include a memory configured to store data corresponding to the generated output.

[0008] In another example, the disclosure provides a method including delivering a cardiac electrical stimulation therapy and sensing one or more cardiac electrical signals including a distal vector signal sensed via a distal sensing electrode vector including a distal electrode of a medical electrical lead. The method may further include, based on at least the distal vector signal, detecting migration of the medical electrical lead carrying the distal electrode and generating an output in response to detecting the migration of the medical electrical lead. The method may further include storing data corresponding to the output in a medical device memory.

[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 medical device, cause the medical device to sense a distal vector signal via a distal sensing electrode vector including a distal electrode of a medical electrical lead and sense a proximal vector signal via a proximal sensing electrode vector including a proximal electrode and not including the distal electrode. The proximal electrode is located moreproximally, i.e., further from the distal end of the medical electrical lead, than the distal electrode. The instructions may further cause the medical device to, based on the distal vector signal and the proximal vector signal, detect migration of the medical electrical lead, generate an output in response to detecting the migration of the medical electrical lead and store data corresponding to the output in a medical device memory.

[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 an ICD system that may be configured to detect lead migration according to the techniques disclosed herein.

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

[0013] FIG. 3 is a conceptual diagram of an ICD according to one example.

[0014] FIG. 4 is a conceptual diagram of circuitry that may be included in a sensing circuit of the ICD shown in FIG. 3 according to one example.

[0015] FIG. 5 is a conceptual diagram of electrophysiological signals that may be sensed and analyzed to detect lead migration by a medical device according to some examples.

[0016] FIG. 6 is a flow chart of a method that may be performed by a medical device for detecting lead migration according to some examples.

[0017] FIG. 7 is a flow chart of a method that may be performed by a medical device for detecting lead migration according to another example.

[0018] FIGs. 8A — 8C are diagrams illustrating changes in a distal vector signal that may occur due to lead migration.

[0019] FIG. 9 is a diagram illustrating changes that may occur in a proximal vector signal due to lead migration.DETAILED DESCRIPTION

[0020] In general, this disclosure describes a medical device and techniques for analyzing an electrophysiological signal sensed using electrodes carried by an implantable, medical electrical lead for detecting migration of the medical electrical lead. The medical electrical lead may be used for monitoring an electrophysiological signal and / or delivering electrical stimulation therapies. In various examples, the medical device connected to the medical electrical lead may be a pacemaker, ICD, cardiac monitor, electroencephalogram monitor or other neurological monitor, neurostimulator configured to deliver stimulation to the brain, spinal cord or other nervous system tissue, or any other medical device that utilizes electrodes carried by a medical electrical lead for sensing electrophysiological signals and / or delivering electrical stimulation therapies.

[0021] The examples presented herein relate to cardiac medical devices, e.g., an ICD or pacemaker, for the sake of illustration. However, it is to be understood that the techniques disclosed herein, may be implemented in other medical devices, e.g., any of the examples listed herein, configured to monitor an electrophysiological signal and / or deliver electrical stimulation therapies. A medical device operating according to the techniques disclosed herein senses and analyzes an electrophysiological signal for detecting migration of a distal end of a medical electrical lead coupled to the medical device. The medical device may determine one or more features of the electrophysiological signal sensed at a baseline timepoint via a distal sensing electrode vector that includes at least one electrode carried along a distal portion of the medical electrical lead. The medical device may determine the one or more features from the electrophysiological signal sensed at a later timepoint and detect migration of the distal end of the medical electrical lead based on a comparative analysis of the signal features determined at the baseline time point and the later timepoint.

[0022] In the context of a cardiac medical device, the medical device can be configured to sense cardiac electrical signals and detect migration of a medical electrical lead connected to the medical device based on the sensed cardiac electrical signals. In some 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.

[0023] 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 (e.g., outside the ribcage and sternum) or intra-thoracically (e.g., beneath the ribcage or sternum) but generally not in intimate contact with myocardial tissue, e.g., not within the heart or 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.

[0024] FIGs. 1A and IB are conceptual diagrams of one example of an ICD system 10 including an ICD 14 connected to a medical electrical lead 16. ICD 14 is configured to sense cardiac electrical signals and detect migration of lead 16 based on an analysis of sensed cardiac electrical signals. ICD 14 may generally 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 detecting lead migration as disclosed herein, however, may be implemented in a cardiac monitoring device or a cardiac pacemaker that does not necessarily include CV / DF shock delivery capabilities in some examples. Furthermore, the techniques disclosed herein for sensing cardiac electrical signals and detecting lead migration may be implemented in a variety of medical devices including external or implantable cardiac monitors, pacemakers, and ICDs.

[0025] 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 sensingcardiac 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 an electrode(s) may be coated with a material, such as titanium nitride, e.g., for reducing post- stimulation polarization artifact.

[0026] 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.

[0027] 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, 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.

[0028] 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 theelectrodes 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 sensing electrode vector for sensing cardiac electrical signals and determining a need for an electrical stimulation therapy. Either of electrodes 24 or 26 may be used as a sensing electrode in a sensing electrode vector that is used for receiving a cardiac electrical signal that is analyzed for detecting migration of lead 16.

[0029] 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.

[0030] 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 sensed 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 electrical event signals, in this case 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, or for determining a need for tachyarrhythmia therapies, e.g., anti-tachycardia pacing (ATP) or CV / DF shocks. In some examples, the sensed cardiac event signals may be analyzed for detecting lead migration according to the techniques disclosed herein.

[0031] 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.

[0032] 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 for detecting migration of lead 16 are not necessarily limited to a particular path of lead 16 or final locations of electrodes 24, 26, 28, 30 and 31.

[0033] 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 a therapy 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.

[0034] 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.

[0035] 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.

[0036] 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 disclosedherein 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.

[0037] 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 heart rate and / or morphology of the cardiac electrical signals to monitor for a long pause, bradycardia, atrial tachyarrhythmia and ventricular tachyarrhythmia, as examples. ICD 14 may generate and delivers 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.

[0038] 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 cardiac pacing pulse, such as a post-shock pacing pulse or bradycardia pacing pulse. The cardiac 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.

[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 andIB 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.

[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.

[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 bidirectionalcommunication 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. ICD 14 may transmit a notification or an alert to external device 40 subsequent to detecting migration of lead 16.

[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, detecting arrhythmias, detecting lead migration, and controlling 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. Lead 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 distalportion 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 “substernal 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 16 may 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] The distal portion 25 carrying electrodes 24, 26, 28 30 and 31 may be advanced to an implant location by tunneling distal end 29 of lead 16 through and / or between tissue layers, e.g., along a subcutaneous, submuscular and / or substernal pathway. Distal end 29 of lead 16 can remain a free terminal end that is not fixed at its final location by sutures or any other fixation member or mechanism. When implanted transvenously, distal end 29 may migrate, e.g., advance or retract, but generally remains bounded within a vessel lumen. When implanted in a non-transvenous location, distal end 29 may migrate laterally, e.g., relatively rightward or leftward directions, may advance (e.g., generally superiorly or cranially) or retract (e.g., generally inferiorly or caudally) and in some instances shift more anteriorly or posteriorly. In some examples, lead 16 may be provided with a fixation member at its distal end 29, such as a helical screw, hook, one or more tines or other fixation member to stabilize distal end 29 at the implant location. However, whether anchored by a fixation member (e.g. a suture or a fixation member that is provided as part of lead 16) or not, distal end 29 may migrate over time such that a cardiac electrical signal sensed using electrodes carried by its distal portion 25 may change over time. Because the greatest migration may occur at the free distal end 29 (relative to proximal end 27 attached to ICD 14), a cardiac electrical signal sensed using the distal-most electrode 31, at or nearest distal end 29, may change over time to a greater degree than an electrical signal sensed using a more proximal sensing electrode vector, e.g., a sensing electrode vector that does not include distal electrode 31.

[0050] Changes in the cardiac electrical signals sensed using lead 16 over time may alter the reliability of cardiac event signal sensing (e.g., sensing of R-waves attendant to ventricular depolarizations and / or P-waves attendant to atrial depolarizations).Undersensing and / or oversensing of cardiac event signals may lead to undersensing or oversensing of cardiac arrhythmias by ICD 14, which can result in either delivering an electrical stimulation therapy when not needed or not delivering an electrical stimulation when needed. As such, techniques disclosed herein may be used for detecting migration of a medical electrical lead, which may be implanted in an extra-cardiac location, to enable the patient and / or a caregiver to be notified of the lead migration and / or changes to be made by ICD 14 in one or more control parameters used in cardiac electrical signal sensing, detection of cardiac event signals (e.g., P-waves and R-waves), arrhythmia detection and / or therapy delivery.

[0051] FIG. 3 is a conceptual diagram of ICD 14 according to one example. The electronic circuitry enclosed within housing 15 (shown conceptually as an electrode in FIG. 3) 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. 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.

[0052] 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. 3 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 98is also coupled to components of cardiac electrical signal sensing circuit 86, such as sense amplifiers, analog-to-digital converters, switching circuitry, etc. as needed.

[0053] The circuits shown in FIG. 3 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 or lead migration as disclosed herein 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 Control signals such as blanking and timing intervals and sensing threshold amplitudes may be stored in memory 82 and retrieved from memory 82 by control circuit 80 for use by sensing circuit 86. The sensing threshold amplitudes may be applied to a sensed electrophysiological signal for sensing electrical event signals.

[0054] Control circuit 80 and sensing circuit 86 may include hardware configured to perform subroutines of signal processing and analysis techniques disclosed herein to reduce 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, detecting lead migration and / or 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.

[0055] 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.

[0056] 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 those ICD components. The non-transitory computer-readable media storing the instructions may include any of the media listed above.

[0057] 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.

[0058] 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, 30and 31 and / or housing 15. Sensing circuit 86 may be enabled to receive cardiac electrical signals from at least one sensing electrode vector 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.

[0059] 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 89 for selecting which 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. In some cases, switching circuit 89 may be controlled by control circuit 80 to select a different sensing electrode vector for electrically coupling to a given sensing channel 81, 83, 85 or 87 for sensing a cardiac signal that is used in detecting lead migration than when sensing circuit 86 is operating to perform cardiac event signal sensing for the purposes of monitoring the heart rhythm. As such, one or more sensing electrode vectors used for sensing cardiac electrical signals for monitoring the heart rhythm may be different than one or more sensing electrode vectors used for detecting lead migration.

[0060] 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 to improve the quality of the received signal for sensing cardiac event signals and 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. 4. 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 intervalsand 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, 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. P-waves and R-waves are examples of electrical event signals that may be sensed from an electrophysiological signal, in this case a cardiac electrical signal, based on an electrical event sensing threshold crossing.

[0061] 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 event 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. 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. 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.Control circuit 80 may include a timing circuit 90 for determining cardiac event intervals such 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.

[0062] 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. 4, an A sensing channel may receive acardiac 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 sensing P-waves (as atrial event signals). In some examples, two (or more) A sensing channels may be included for enabling control circuit 80 to validate Asense event signals received from two different A sensing channels.

[0063] As described below in conjunction with FIG. 4, 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. In some examples, 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 R-waves (sensed as ventricular event signals).

[0064] 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 is received 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 ApplicationPublication No. 2023 / 0100431 Al (Liu et al., filed August 29, 2022), the content of which is incorporated herein by reference in its entirety.

[0065] As shown in FIG. 3, 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). 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 event 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.

[0066] 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 of a predetermined time segment of the ECG signal for detecting arrhythmias. A third cardiac electrical signal may be received by thesecond 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. 4.

[0067] 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 event 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 event 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.

[0068] 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 may detect 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 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. 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 ventricularrate or performing other rate- or interval-based assessment of Asense event signals and Vsense signals for detecting and discriminating SVT and VT / VF.

[0069] 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).

[0070] 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, 30 VFIs 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.

[0071] Arrhythmia detection circuit 92 may be further configured to detect atrial tachyarrhythmia (AT) intervals from PPIs received from timing circuit 90 and count ATintervals 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. 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.

[0072] 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 signals stored 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.

[0073] 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.

[0074] 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 / orCV / 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 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.

[0075] 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 for pacing and capture the ventricles. 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 voltage capacitor(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 to capture and pace the ventricles 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 that capture the ventricles. 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 medical devices and is not limited to any particular therapy delivery circuitry configuration for use in conjunction with the cardiac signal sensing and lead migration detection methods disclosed herein.

[0076] 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.

[0077] FIG. 4 is a conceptual diagram of circuitry that may be included in sensing circuit 86 shown in FIG. 3 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.

[0078] 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 the or adjacent to the distal end 29 of lead 16 (e.g., 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 oneelectrode 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. The atrial signal received by A sensing channel 81 via the atrial sensing electrode vector that includes at least the distal most electrode 31 may be the distal vector signal analyzed by control circuit 80 for detecting lead migration in some examples.

[0079] 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 V sensing 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. The term “cardiac axis” as used herein refers to the electrical axis of the heart that represents the overall average direction of the ventricular depolarization (QRS complex). The cardiac axis may be between -30 degrees and + 60 degrees in normal patients but can deviate from this range, where the angle of measurement is positive in a clockwise direction beginning from a transverse plane or axis with zero degrees pointing to the patient’s left side. 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 relativelylonger inter-electrode distance but may have greater variability in R-wave signal strength compared to a relatively longer inter-electrode distance.

[0080] 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, 30 or 31. 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.

[0081] 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 closest operative proximity to the ventricles for receiving a ventricular signal. In this case, the most proximal electrode 28 may be in closest operative proximity to the atria for receiving the 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.

[0082] 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.

[0083] 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 or include 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.

[0084] The example sensing electrode vectors coupled to each sensing channel 81, 83, 85 and 87 may be changed by switching circuit 89 shown in FIG. 3. The sensing electrode vector coupled to a given sensing channel may depend in part on the relative position of lead 16 (see FIG. 1A) to the heart chambers and may be programmable by a user. In some examples, a sensing electrode vector selected by switching circuit 89 that is coupled to a given sensing channel 81, 83, 85 or 87 can be controlled by control circuit 80 for obtaining a cardiac signal, e.g., at least a distal vector signal, that is used by ICD 14 in an analysis for detecting lead migration. A cardiac signal sensed for detecting lead migration by a given sensing channel 81, 83, 85 or 87 may be the same or different than the sensingelectrode vector selectively coupled to the same sensing channel for cardiac event signal sensing and arrhythmia detection.

[0085] For example, electrodes 31 and 30 or electrodes 31 and 28 may be connected to A sensing channel 81 to sense a cardiac electrical signal that is relatively sensitive to changes in the position of the distal most electrode 31 relative to the patient’s heart due to lead migration. A cardiac electrical signal sensed using distal electrode 31, for example, may be more sensitive to changes due to lead migration than cardiac electrical signals sensed using other available sensing electrodes. For instance, when migration of lead distal end29 occurs, the cardiac electrical signal received using a sensing electrode vector that includes proximal electrode 28 and housing 15 may remain relatively unchanged due to greater stability of the position of the proximal portion of lead 16 and / or ICD 14. The cardiac electrical signal received using a sensing electrode vector including distal electrode 31 paired with any other available electrode (carried by lead 16 or ICD housing 15), however, may be significantly changed relative to a baseline signal recorded using the same sensing electrode vector prior to lead migration.

[0086] As described herein, in some examples control circuit 80 may detect migration of lead 16 by performing a comparative analysis of a first cardiac electrical signal (e.g., a distal vector signal) sensed using a first sensing electrode vector (e.g., a distal sensing electrode vector that includes most distal electrode 31) expected to be relatively sensitive to positional changes of the distal end 29 of lead 16 and a baseline signal sensed using the same sensing electrode vector at an earlier timepoint, prior to lead migration. Additionally or alternatively, control circuit 80 may detect migration of lead 16 by performing a comparative analysis of a first cardiac electrical signal (e.g., a distal vector signal) sensed using a first sensing electrode vector (e.g., a distal sensing electrode vector that includes a relatively distal electrode such as most distal electrode 31) expected to be relatively sensitive to positional changes of the distal end 29 of lead 16 and a second cardiac electrical signal (e.g., a proximal vector signal) sensed using a second sensing electrode vector (e.g., a proximal sensing electrode vector that includes a more proximal electrode30 or most proximal electrode 28) expected to be relatively insensitive (or less sensitive) to positional changes of the distal end 29 of lead 16.

[0087] In the illustrative example shown in FIG. 4, the signals received by each sensing channel 81, 83, 85 and 87 are provided as differential input signals to a pre-filter and pre-amplifier 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.

[0088] ADC 63a, ADC 63b, ADC 73, and ADC 103 may 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.

[0089] 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 lower frequency content than R-waves. Filter 74 of the morphology signal channel 87 may have a relatively wider bandpass of approximately 0.5 to 100 Hz, 1 to 100 Hz or 2.5 to 100 Hz as examples.

[0090] 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 Hzand 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 can be passed from the respective filter 67a, 67b or 107 to a rectifier 65a, 65b or 105 to produce a band pass filtered, rectified signal output.

[0091] In the example shown, A sensing channel 81 may include a low pass filter 110 for receiving the band pass filtered, rectified signal. 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 band pass 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.

[0092] 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 rectified ventricular signal 69.

[0093] The atrial sensing signal 120 can be a non-rectified signal that may be passed to a low pass filter 111 (e.g., a 3 to 4 Hz low pass filter) 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 theatrial signal 109 filtered and rectified by atrial sensing channel 81 and the ventricular signal 69 received from ventricular 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.

[0094] The atrial sensing signal 120 may be determined by determining a sum, difference, ratio or product of paired sample points, where each pair of sample points includes one sample point from the atrial signal 102 and one sample point from the ventricular signal 69. In other examples, the paired sample points may be combined according to a nonlinear 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 a first 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).

[0095] 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.

[0096] 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 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).

[0097] 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 exampleshown, 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).

[0098] In the example shown in FIG. 4, 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, which may be controlled separately from the R-wave sensing threshold controlled by R-wave detector 66a, to the received, rectified ventricular signal. 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 combining an atrial signal and a ventricular signal. The second ventricular sensing signal determined using the atrial signal 109 may be passed to R-wave detector 66b for sensing R-waves.

[0099] 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 event signal 108, Vsense signal 68a or Vsense signal 68b) when the respective 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.

[0100] 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.

[0101] 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 generally 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 of the 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 controlling separately according to different R-wave sensing threshold control parameters.

[0102] 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 signal 79 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.

[0103] In some examples, the non-rectified, wideband filtered signal 78 or the rectified signal 79 from morphology signal channel 87 may be analyzed by control circuit 80 for detecting lead migration. In some examples, a change in P- waves sensed by sensing channel 81 (e.g., change in P-wave amplitude or morphology, suspected P-wave undersensing, or suspected P-wave oversensing) may trigger analysis of the wideband filtered signal 78 by control circuit 80. For example, the non-rectified wideband filtered signal 78 may be analyzed for a change in the polarity and / or amplitude of cardiac event signals, e.g., P-waves, QRS waveforms and / or T-waves, in the signal 78. In order to detect a change in the polarity and / or amplitude of the QRS waveform that may be due to lead migration, switching circuit 89 may be configured to couple a distal sensing electrode vector to morphology sensing channel 87. The distal sensing electrode vector may include the most distal electrode 31 in combination with another electrode, e.g., the most proximal electrode 28, though other electrodes or housing 15 could be paired with distal electrode 31. The distal vector signal that includes the most distal electrode 31 may be most sensitive to changes due to lead migration. It is contemplated, however, that the distal vector signal may not necessarily include the most distal electrode of a medical electrical lead. Depending on the lead and electrode configuration, the sensing electrode vector used to sense a distal vector signal used in detecting lead migration may include an electrode that is generally positioned along a distal portion of a medical electrical lead and may be relatively closer to the distal end of the lead than the proximal end of the lead.

[0104] Some example changes in polarity and / or amplitude of the cardiac event signal waveforms that may occur with lead migration and be detectable by control circuit 80 as evidence of lead migration are described in conjunction with FIGs. 8 and 9. As mentioned previously, the electrodes selected to be coupled to one or more of the sensing channels 81 83, 85, and / or 87 for obtaining signals used for detecting lead migration may be different than the electrodes coupled to one or more of the sensing channels 81 83, 85, and / or 87 for obtaining signals for sensing cardiac event signals and performing morphology analysis for detecting arrhythmias.

[0105] The configuration of sensing channels 81, 83 and 85 and morphology signal channel 87 as shown in FIG. 4 is illustrative in nature. Sensing circuit 86 may include more or fewer components than illustrated in FIG. 4 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. 4 and some components may be shared between sensing channels 81, 83, 85 and morphology signal channel 87.

[0106] FIG. 5 is a conceptual diagram 200 of electrophysiological signals that may be used to detect lead migration. In the example of FIG. 5, the electrophysiological signals include 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. 4 according to some examples. Signal 202 may be the signal received by atrial sensing channel 202 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 event 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.

[0107] 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 sensingchannel 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 signal 220 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.

[0108] As described below in conjunction with the flow charts of FIGs. 6 and 7, control circuit 80 may analyze one or more of the non-rectified atrial signal 202, the smoothed rectified atrial signal 204, the atrial sensing signal 206 obtained by sensing circuit 86 using the distal electrode 31 of lead 16 paired with another available electrode in a distal sensing electrode vector. Control circuit 80 may detect migration of the distal end 29 of lead 16 based on an analysis of one or more of signals 202, 204 and / or 206 obtained at a baseline timepoint and a later timepoint for detecting changes in the signal obtained using the distal electrode 31 that may be indicative of lead migration.

[0109] In some examples, control circuit 80 may analyze one or more of the non-rectified ventricular signal 212, the smoothed rectified ventricular signal 214, and / or the ventricular sensing signal 216 obtained by sensing circuit 86 using a proximal sensing electrode vector that does not include the distal electrode 31 of lead 16. Control circuit 80 may detect migration of the distal end 29 of lead 16 based on an analysis of one or more of signals 212, 214 and / or 216 in combination with one of signals 202, 204 and / or 206 obtained at a baseline timepoint and a later timepoint for detecting changes in the signals obtained using the distal electrode 31 that may be indicative of lead migration when signals 212 and / or 214 remain relatively unchanged. For instance, a threshold change (e.g., at least + 20% or more) in the maximum peak amplitude 230 of signal 204 obtained during a lead migration check relative to a baseline maximum peak amplitude of the smoothed, rectified atrial signal 204 may be an indication of migration of the distal end 29 of lead 16. A threshold change in the maximum peak amplitude 234 of the atrial sensing signal 234 relative to the maximum peak amplitude of the atrial sensing signal obtained at a baseline timepoint may be evidence of migration of the distal end 29 of lead 16.

[0110] A threshold change in the maximum peak amplitude 230 of the atrial signal 204 in combination with less than a threshold change in the maximum peak amplitude 232 of the ventricular signal 214 may be evidence of lead distal end migration. A threshold change in the difference between maximum peak amplitude 230 and maximum peak amplitude 232determined during a lead migration check relative to the difference between the maximum peak amplitudes of the atrial signal 204 and the ventricular signal 214 determined at a baseline timepoint may be evidence of a lead distal end migration.

[0111] In some examples, a change in the atrial signal 204 that occurs when the ventricular signal 214 is relatively unchanged may be detected by comparing one or more features of the atrial sensing signal 206 and / or the ventricular sensing signal 216 determined during a lead migration check timepoint to the analogous features determined at a baseline timepoint. For instance, a threshold change in the maximum peak amplitude 234 or the maximum peak amplitude 236 compared to a respective baseline maximum peak amplitude may be determined as evidence of lead distal end migration. In some examples, a threshold change in the maximum peak amplitude 234 of P-waves, the maximum peak amplitude 236 of R-waves, and / or a quantitative relationship between maximum peak amplitudes 234 and 236 may be detected by control circuit 80 as a trigger for performing cardiac signal analysis for detecting lead migration.

[0112] FIG. 6 is a flow chart 300 of a method that may be performed by a medical device for detecting lead migration according to some examples. FIG. 6 and other flow charts and diagrams presented herein are described with reference to the ICD 14 shown conceptually in FIGs. 1A- 4. However, it is to be understood that other IMDs configured to sense electrophysiological signals via a medical electrical lead extending from the medical device may be configured to perform the techniques disclosed herein for detecting migration of the medical electrical lead based on features determined from the electrophysiological signals, which may include detecting electrical event signals from the sensed electrophysiological signals. Furthermore, it is contemplated that cardiac electrical signals sensed by an IMD such as ICD 14 may be transmitted to an external device, e.g., external device 40, for processing and analysis by the external device processor 52 for detection of lead migration. As such, it is to be understood that control circuitry performing the techniques disclosed herein for detecting lead migration and generating an output in response to the detected lead migration may be included in an external medical device configured to receive cardiac electrical signals sensed by an IMD. In some examples, the processing and analysis for detecting lead migration may be performed cooperatively by processing circuitry included in an IMD and an external device 40according to computer-readable instructions stored in memories of the IMD and external device 40.

[0113] At block 301, control circuit 80 may determine and store one or more baseline features of a cardiac electrical signal sensed using a distal sensing electrode vector. The cardiac electrical signal sensed using a distal sensing electrode vector is referred to herein as a “distal vector signal.” The distal sensing electrode vector may include the most distal electrode 31 carried by lead 16 connected to ICD 14. The distal sensing electrode vector may include distal electrode 31 and ring electrode 30 (the next most distal electrode along the distal portion 25 of lead 16) in one example. In other examples, the distal sensing electrode vector may include the distal electrode 31 paired with coil electrode 26, coil electrode 24, ring electrode 28 or housing 15.

[0114] A cardiac electrical signal sensed using the most distal electrode 31, nearest the free distal end 29 of lead 16, can be the most susceptible to changes due to migration of the distal end 29 of lead 16. The migration may be toward or away from the heart, e.g., closer to the atrial chambers or further from the atrial chambers. Accordingly, starting from a baseline timepoint, control circuit 80 may monitor changes in the distal vector signal sensed using distal electrode 31 over time to detect lead migration. In some instances, the two most distal electrodes, e.g., electrode 30 and 31 shown in FIG. 1A, may both shift in position relative to the patient’s heart when the free distal end 29 migrates such that the angle of the sensing vector along which the cardiac electrical signal is sensed relative to the cardiac axis may not change significantly even though the distal end 29 of lead 16 has migrated. The angle of the sensing vector along which the cardiac electrical signal is sensed, e.g., relative to the cardiac axis, may change more significantly when the distal sensing electrode vector includes the most distal electrode 31 and a most proximal electrode 28 or the ICD housing 15, which may remain in a relatively more stable position during lead migration. As such, a change in the cardiac electrical signal due to lead migration may be more readily detected from a distal vector signal sensed using the most distal electrode 31 and a most proximal electrode 28 or ICD housing 15 in some instances.

[0115] At block 302, control circuit 80 may determine baseline features of the distal vector signal at a baseline timepoint. The baseline timepoint may be the time of implantation of the lead 16. It is contemplated, however, that the baseline features of a distal vector signal may be determined (or redetermined) at any selected baselinetimepoint at or after implantation for use in detecting migration of lead 16 relative to the position of lead 16 at that selected baseline timepoint. With reference to FIG. 4, control circuit 80 may receive the smoothed rectified atrial signal 109 (e.g., shown as signal 204 in FIG. 5) as the distal vector signal sensed by A sensing channel 81 using distal electrode 31. Control circuit 80 may determine one or more features of the smoothed rectified atrial signal 109 as baseline features at block 302. In other examples, control circuit 80 may receive the atrial sensing signal 120 (before or after low pass filtering by filter 111) as the distal vector signal, which can be determined as a combination of the atrial signal 109 and the ventricular signal 69. Control circuit 80 may determine one or more baseline features of the atrial sensing signal 120 (shown as signal 206 in FIG. 4) as features of a distal vector signal at block 302.

[0116] In an illustrative example, the P-wave detector 106 of A sensing channel 81 may receive the non-rectified atrial sensing signal, e.g., signal 206 shown in FIG. 5. P-wave detector 106 may determine the maximum peak amplitude 230 following each P-wave sensing threshold crossing and pass the maximum peak amplitude 230 to control circuit 80. Control circuit 80 may determine the baseline distal vector signal feature as an average, median or other representative value of a specified number of received maximum peak amplitudes, e.g., 5 to 100 maximum peak amplitudes, of sensed atrial event signals. Furthermore, it is contemplated that a baseline distal vector signal feature may be a representative value of the signal feature determined from the distal vector signal at multiple timepoints spanning one hour, one day, one week or other relatively long time period (as opposed to a feature determined from one or a few heart beats) to remove physiological variability that may be inherent in the distal vector signal. For example, control circuit 80 may log the distal vector signal feature values in a histogram in memory 82 to enable a statistical analysis of the histogram values sampled over a relatively long time period, such as one hour, twelve hours, one day or one week. Accordingly, a baseline timepoint may be a timepoint that spans a period of time over which baseline features of at least one distal vector signal may be determined for establishing baseline feature representative value(s). The baseline timepoint may span several minutes, one hour, several hours, one day, one week or other selected period of time over which cardiac signal data is collected for establishing the baseline feature values. It is recognized that numerous signal features could be determined for characterizing the baseline distal vectorsignal such as but not limited to a slope, area, peak amplitude, peak polarity, mean amplitude of all sample points spanning a segment of the distal vector signal, normalized rectified amplitude of all sample points spanning a segment of the distal vector signal, or other signal feature that is representative or characteristic of the distal vector signal at a baseline timepoint. In some examples, the ratio, difference or other quantitative relationship of the maximum positive peak amplitude and the maximum negative peak amplitude may be determined (e.g., as described below in conjunction with FIGs. 8A-8C).

[0117] In other examples, the distal vector signal may be sensed using any of the example distal sensing electrode vectors listed herein, e.g., most distal electrode 31 paired with electrode 24, electrode 26, electrode 28, electrode 30 or housing 15 (see FIG. 1A). In some examples, the distal vector signal is a rectified or non-rectified wideband filtered signal and may be acquired by morphology signal channel 87, e.g., using electrodes 31 and 28. FIG. 6 is described, for the sake of convenience, as a process for analyzing one distal vector signal. In some examples, multiple distal vector signals may be analyzed for detecting changes in the distal vector signals that are indicative of lead migration. For example, one distal vector signal may be sensed using the most distal electrode 31 and the most proximal electrode 28, and a second distal vector signal may be sensed using the most distal electrode 31 and the housing 15. The two distal vector signals may be analyzed for detecting a change due to lead migration, which may be caused by a change in the direction or angle of at least one of the distal sensing electrode vectors relative to the patient’s heart due to lead migration. As discussed below in conjunction with FIGs. 8 and 9, relative changes in a distal vector signal between a baseline timepoint and a later timepoint may depend on the direction of migration of the free distal end 29 of lead 16 and / or the change in an angle between the distal sensing electrode vector and the cardiac axis from the baseline timepoint to the later timepoint. In some instances, one distal vector signal may change to a greater degree than a second distal vector signal (or a proximal vector signal as discussed below).

[0118] At block 304, control circuit 80 may determine that it is time for a lead migration check. A lead migration check may be performed on a daily, weekly, monthly or other scheduled basis. Additionally or alternatively a lead migration check may be performed on a triggered basis in response to determining a change in a pacing capture threshold, a change in a lead impedance measurement, detection of likely undersensing of P-wavesand / or R-waves, detection of oversensing of P-waves and / or R-waves, or following delivery of a high-voltage CV / DF shock. P-wave undersensing or oversensing or R-wave undersensing or oversensing may be suspected if P-waves and R-waves are not being sensed in a 1: 1 ratio. P-wave undersensing or oversensing may be suspected if the maximum peak amplitudes of sensed signals are near the P-wave sensing threshold amplitude at the time of the atrial sensed event signals. For example, low amplitude P- waves may be undersensed when some are being sensed having a peak amplitude just greater than the P-wave sensing threshold. In other instances, relatively high amplitude noise pulses, e.g., due to skeletal muscle myopotentials, having an amplitude near the programmed atrial sensitivity may be oversensed as P-waves. R-wave undersensing or oversensing may be suspected if the maximum peak amplitudes of sensed ventricular event signals are near the R-wave sensing threshold amplitude at the time of the ventricular sensed event signals. For example, low amplitude R-waves may be undersensed when some are being sensed having a peak amplitude just greater than the R- wave sensing threshold. In other instances, relatively high amplitude noise pulses, e.g., due to skeletal muscle myopotentials, having an amplitude near the programmed ventricular sensitivity may be oversensed as R-waves.

[0119] Oversensing of P-waves as false R-waves, oversensing of T-waves as false R- waves, or oversensing of R-waves as false P-waves may be suspected when the amplitudes, cardiac event intervals such as PPIs or RRIs, or other features of consecutively sensed cardiac event signals present an alternating pattern. PWOS can be detected on a V sensing channel 83 or 85 based on alternating peak amplitudes following R-wave sensing threshold crossings with alternating low amplitude peaks corresponding in time to P-wave sensing threshold crossings in the A sensing channel 81. R-wave oversensing can be detected on an A sensing channel 81 by detecting alternating peak amplitudes following P- wave sensing threshold crossings with every other P-wave sensing threshold crossing corresponding in time to R-wave sensing threshold crossings in a V sensing channel 81 or 83.

[0120] Additionally or alternatively, suspected oversensing on A sensing channel 81 and / or V sensing channel 83 may be detected by control circuit 80 when one or more pairs of Asense and Vsense signals are received near simultaneously or within a suspected oversense time interval from each other. Additionally or alternatively, suspected P-waveoversensing by V sensing channel 83 or 85 may be detected by control circuit 80 when a VT / VF interval counter reaches a threshold value for one or both of V sensing channels 83 and / or 85. Additionally or alternatively, suspected R-wave oversensing by A sensing channel 81 may be detected by control circuit 80 when an atrial tachyarrhythmia interval counter reaches a threshold value. Other analyses may be performed by control circuit 80 for detecting suspected undersensing or oversensing of cardiac event signals from a sensed cardiac electrical signal for triggering a lead migration check. Other analyses may include, for example, an analysis of the slope content (e.g., low slope content), peak amplitude analysis, pulse width analysis, and / or other methods for detecting suspected oversensing and / or undersensing may be used for triggering a lead migration check. Various methods for detecting oversensing of cardiac event signals may be implemented in a medical device configured to detect lead migration according to the techniques disclosed herein and may be used for triggering a lead migration check. Some example methods for detecting cardiac event oversensing that may be used in conjunction with the lead migration detection techniques disclosed herein are generally disclosed in U.S. Patent No. 9,597,525 (Cao, et al., filed May 6, 2015) and in U.S. Patent No. 11,135,441 (Zhang et al., filed June 24, 2019), the entire content of both incorporated herein by reference.

[0121] When control circuit 80 determines that it is time for a lead migration check at block 304, control circuit 80 may re-determine the distal vector signal feature(s) at block 306 that were previously determined from the distal vector signal at the baseline timepoint. At block 308, control circuit 80 may perform a comparative analysis of the new distal vector signal feature(s) and the baseline feature(s). For example, control circuit 80 may determine if a difference between a given baseline feature and the respective new feature is greater than a threshold. Depending on the direction of the migration of lead 16, a threshold change may be a negative change or a positive change. Therefore, control circuit 80 may compare an absolute value of the difference between a baseline feature value and a new feature value to a threshold value. In other examples, control circuit 80 may compare the new feature value to a threshold range that extends greater than and less than the baseline feature value. The threshold value or range used by control circuit 80 may depend on the particular feature being determined, the starting baseline value of the feature, and / or other factors. The threshold value or range can be selected to promote detection of lead migration that could result in improper sensing of cardiac electricalsignals and / or a change in a pacing capture threshold, for example. The threshold value or range can be determined by control circuit 80 as a percentage of the baseline feature value.

[0122] In some examples, distal vector signal features may be buffered in a histogram, e.g., on an hourly or daily basis so that when the lead migration check is performed, statistical analysis of the histogram values can be performed to compare to the baseline histogram analysis. For instance, the median or mode of the histogram values buffered in memory 82 during a baseline time period may be compared to the median or mode of the histogram values buffered in memory 82 over a later, lead migration check time period.

[0123] If the new feature of the distal vector signal does not represent a threshold change from the baseline feature value, control circuit 80 may return to block 304 to wait for the next time a lead migration check is scheduled or triggered. When the new feature value of the distal vector signal represents a threshold change from the baseline feature value, control circuit 80 may detect lead migration or suspected lead migration and perform a lead migration detection response at block 310.

[0124] The lead migration detection response may include storing data in memory 82 that can be transmitted by telemetry circuit 88. The stored data may include a lead migration detection alert, the new feature value(s) of the distal vector signal determined during the lead migration check, and / or an episode of the distal vector signal recorded contemporaneously with the lead migration check. In some examples, the stored data may include cardiac signal episodes and / or features determined from other cardiac electrical signals sensed by sensing circuit 86 using other sensing electrode vectors to provide a comparison between different sensing electrode vectors available for sensing cardiac event signals by sensing circuit 86.

[0125] Control circuit 80 may control telemetry circuit 88 to transmit data stored in memory 82 as part of the response performed at block 310. The transmitted data may include the baseline feature values (previously stored in memory 82), feature values determined during previous lead migration checks (previously stored in memory 82), and / or the new feature values of the distal vector signal determined during the current lead migration check. The transmitted data may include an episode of the distal vector signal stored at the baseline timepoint, during the current lead migration check and may include a distal vector signal episode stored during one or more intervening lead migration checks. In some examples, transmitted data may include an episode of one or more cardiacelectrical signals sensed by sensing circuit 86 using one or more other sensing electrode vectors.

[0126] External device 40 (FIG. 1A) may receive the transmitted distal vector signal episodes recorded at the baseline timepoint and the current lead migration check timepoint, which may be displayed on display unit 54 for review by a clinician. In some examples, distal vector signal episodes recorded at timepoints of one or more intervening lead migration checks (after the baseline timepoint but before the suspected lead migration detection) may be received by external device 40 and displayed for review by a clinician. Any other cardiac electrical signal episodes recorded and transmitted by ICD 14 in response to the suspected lead migration detection may be received and displayed by external device 40. Other cardiac electrical signal episodes may be reviewed by a clinician for providing information useful in reprogramming a sensing electrode vector, e.g., based on P-wave amplitude, R-wave amplitude, baseline noise amplitude etc. In some examples, in addition to or alternatively to transmitting and displaying cardiac signal episodes, cardiac signal features can be determined by control circuit 80 from the distal vector signal and / or one or more other cardiac signals sensed using other available atrial signal sensing electrode vectors and / or ventricular signal sensing electrode vectors, stored in memory 82 and transmitted by telemetry circuit 88 for receipt and display by external device 40.

[0127] A response to the lead migration detection that is performed at block 310 by control circuit 80 may include adjusting a cardiac event sensing control parameter used by sensing circuit 86 in sensing cardiac signals and detecting cardiac event signals. In some examples, adjusting a cardiac event sensing control parameter may include selecting a different sensing electrode vector (e.g., by switching circuit 89) for coupling to the A sensing channel 81, one or both of the V sensing channels 83 and 85, and / or the morphology signal sensing channel 87. A different sensing electrode vector may be selected for connection to one or more of the sensing channels 81, 83, 85 and 87 to promote a higher signal strength of desired cardiac event signals (e.g., higher R-wave amplitude in ventricular signals or higher P-wave amplitude in the atrial signal). A different sensing electrode vector may be selected for connection to one or more of the sensing channels 81, 83, 85 and 87 to promote improved signal quality with lower noise amplitude, e.g., when lead migration results in increased skeletal muscle noise pulseamplitudes that lead to P-wave or R-wave oversensing in a given sensing electrode vector signal.

[0128] A different sensing electrode vector may be selected for connection to A sensing channel 81 to reduce the likelihood of R-wave oversensing, T-wave oversensing and / or skeletal muscle noise oversensing by the A sensing channel 81. For example, if R-wave and / or T-wave peak amplitudes have increased in the distal sensing vector signal due to lead migration, the electrodes of the atrial sensing electrode vector may have migrated closer to the ventricular chambers or in an area of higher skeletal muscle myopotential activity. A new atrial sensing electrode vector may be selected that is now in closer operative proximity to the atrial chambers (or now further away from the ventricular chambers and / or skeletal muscle) than the original atrial sensing electrode vector, which may have migrated away from the atrial chambers. In some cases, e.g., if the distal end 29 has migrated too far from the atrial chambers to sense an atrial signal for reliable P-wave sensing and another atrial sensing electrode vector is not identified or available for reliable P-wave sensing, the A sensing channel 81 may be powered down or disabled. Control circuit 80 may switch to single chamber ventricular sensing for sensing R-waves, detecting ventricular arrhythmias, and controlling the delivery of cardiac electrical stimulation pulses generated by therapy delivery circuit 84.

[0129] In some examples, the response performed at block 310 may include selecting a different sensing electrode vector for connection to one or both of the V sensing channels 83 and 85 to reduce the likelihood of P-wave oversensing in the respective V sensing channel 83 or 85. For example, if P-wave peak amplitudes have decreased in the distal sensing vector signal due to lead migration, P-wave amplitude in a ventricular sensing electrode vector may have increased due to closer proximity of the ventricular sensing electrode vector to the atrial chambers resulting in P-wave oversensing. A new ventricular sensing electrode vector may be selected that is now in closer operative proximity to the ventricular chambers (or now further away from the atrial chambers) than the original ventricular sensing electrode vector, which may have migrated closer to the atrial chambers (or more generally further away from the ventricular chambers).

[0130] A process of selecting a new sensing electrode vector for connection to one or more of the sensing channels 81, 83, 85 or 87 of sensing circuit 86 may be performed at block 310 by control circuit 80 and may include an analysis of one or more cardiacelectrical signals sensed using different available sensing electrode vectors. A ratio between sensed ventricular event peak amplitudes and sensed atrial event peak amplitudes may be determined and used in selecting a ventricular sensing electrode vector and an atrial sensing electrode vector. A ratio between sensed cardiac event peak amplitudes (atrial or ventricular) and signal noise pulse peak amplitudes may be determined as a signal quality metric in some examples. Signal noise pulse peak amplitudes can be determined by control circuit 80 during a cardiac electrical signal segment extending before and after the sensed cardiac events as a signal to noise metric, for example. Control circuit 80 may select a new sensing electrode vector having a high signal to noise metric (e.g., relatively high cardiac event signal amplitude to low signal noise pulse amplitude ratio). Methods for determining muscle noise pulse counts in a cardiac signal segment that may be implemented in conjunction with the methods disclosed herein are generally disclosed in U.S. Patent. No. 10,750,970, filed December 17, 2018 (Stadler, et al.), incorporated herein by reference in its entirety. Muscle noise pulse counts may be determined by control circuit 80 as a signal quality metric. A sensing electrode vector that results in lower muscle noise pulse counts when the current atrial or ventricular sensing electrode vector results in relatively higher muscle noise pulse counts may be identified and selected by control circuit 80 as a new sensing electrode vector. One or more signal strength or signal quality metrics may be determined at block 310 by control circuit 80 for use in selecting a new atrial sensing electrode vector and / or a new ventricular sensing electrode vector in response to detecting lead migration. Examples of signal quality metrics that may be determined for use in selecting a new sensing electrode vector in response to detecting lead migration are generally disclosed in U.S. Patent No. 7,496,409 (Greenhut et al., filed February 24, 2009) and in U.S. Patent No. 7,904,153 (Greenhut, et al., filed March 8, 2011), the entire content of both incorporated herein by reference.

[0131] Adjustment of a sensing control parameter in response to lead migration detection that is performed at block 310 by control circuit 80 may include adjusting a cardiac event sensing control parameter. When a cardiac event amplitude increases or decreases in a given sensing channel due to lead migration, control circuit 80 may adjust a sensing control parameter accordingly. Control circuit 80 may adjust a sensing control parameter to effectively increase or decrease the cardiac event sensing threshold, e.g., the P-wave sensing threshold or the R-wave sensing threshold. Various control parameters that may beincreased or decreased may include an atrial sensitivity, a ventricular sensitivity, a percentage of the maximum peak amplitude of a sensed event signal used to set a starting sensing threshold amplitude, a percentage of the maximum peak amplitude of a sensed event signal used to set an intermediate sensing threshold amplitude, a decay rate of the sensing threshold amplitude, a decay time of the sensing threshold amplitude, a drop time interval at which the sensing threshold is decreased by a step decrement, and / or a step decrement applied to the sensing threshold amplitude upon expiration of a drop time interval.

[0132] A response to the lead migration detection that is performed at block 310 by control circuit 80 may include adjusting an arrhythmia detection control parameter. An arrhythmia detection control parameter may be used by a tachyarrhythmia detection algorithm performed by arrhythmia detection circuit 92 for example. An arrhythmia detection control parameter may be adjusted to effectively prolong the time required to detect VT / VF in some examples. When lead migration is detected, oversensing may cause a false detection of VT / VF. Control circuit 80 may increase an NID required for detecting VT / VF to reduce the likelihood of a false VT / VF detection due to oversensed signals. In some arrhythmia detection algorithms, a threshold number of tachyarrhythmia intervals may cause control circuit 80 to enable the morphology sensing channel 87 to begin receiving the morphology signal for buffering morphology signal segments in memory 82. Various signal morphology analysis methods may be performed by arrhythmia detection circuit 92 for confirming or rejecting a VT / VF detection when an NID is reached. Control circuit 80 may delay enabling the morphology sensing channel 87 and / or performing morphology analysis, which may require significant processing power, when lead migration is detected to avoid increasing current drain from power source 98 when some oversensing may be occurring. For example, control circuit 80 may increase the threshold number of VT / VF intervals required to power on the morphology sensing channel 87 for buffering cardiac signal segments in memory 82. Control circuit 80 may increase the threshold number of VT / VF intervals required to start cardiac signal segment morphology analysis performed by control circuit 80 for detecting an arrhythmia.

[0133] A response to the lead migration detection performed at block 310 may include a therapy delivery adjustment. A therapy delivery adjustment may include performing a pacing capture test for verifying ventricular capture by a pacing pulse delivered by aventricular pacing electrode vector. The pacing capture test may include delivering one or more pacing pulses at a current pacing pulse output (e.g., pulse amplitude, pulse width, and number of stacked pulses when a composite pacing pulse of two or more individual pulses is delivered to capture the ventricles). If loss of capture is determined (e.g., based on no evoked response signal sensed after the pacing pulse), control circuit 80 may control therapy delivery circuit 84 to perform a capture threshold test to determine the pacing pulse output required to capture the ventricles. The therapy delivery adjustment could include adjusting the pacing pulse output to promote capture of the ventricles during a pacing therapy (e.g., atrial synchronous ventricular pacing, bradycardia or asystole pacing, ATP, post-shock pacing, etc.). The therapy delivery adjustment could include adjusting a therapy delivery vector, e.g., a pacing electrode vector and / or a CV / DF shock delivery vector. The therapy delivery adjustment could include adjusting, e.g., increasing, a CV / DF shock energy to promote successful termination of a detected ventricular tachyarrhythmia when lead migration has occurred.

[0134] A therapy delivery adjustment could include disabling a pacing therapy. A pacing therapy that may be disabled may be one or more of atrial synchronous ventricular pacing, bradycardia pacing, and / or ATP, as non-limiting examples. A pacing therapy may be disabled when lead migration is detected because the lead migration may result in unreliable sensing for controlling pacing pulse delivery and / or unreliable capture by delivered pacing pulses and / or extraneous stimulation of skeletal muscle caused by cardiac pacing pulses.

[0135] FIG. 7 is a flow chart 400 of a method that may be performed by a medical device for detecting lead migration according to another example. In the example method described in conjunction with FIG. 6, control circuit 80 may detect lead migration based on a comparative analysis of at least one distal vector signal obtained at a lead migration check timepoint and the corresponding distal vector signal(s) obtained at a baseline timepoint. In the example of FIG. 7, differences between a distal vector signal relative to a proximal vector signal may be determined at a baseline timepoint and at a subsequent lead migration check timepoint. Control circuit 80 may detect lead migration (or suspected lead migration) based on a change in a difference between the distal vector signal and the proximal vector signal at a lead migration check timepoint relative to the difference between the two signals at the baseline timepoint. A proximal portion of the lead 16 maymigrate less than the distal end 29 of the lead 16 (see FIG. 1A). As such, changes in a cardiac electrical signal due to lead migration can be expected to be greater in a cardiac electrical signal sensed using a distal sensing electrode than a cardiac electrical signal sensed using a proximal sensing electrode in a sensing electrode vector that excludes the most distal electrode 31. Lead migration may be detected by control circuit 80 based on a threshold change in at least one distal vector signal when little or no change occurs in a proximal vector signal in some instances. In other instances, however, as discussed in conjunction with FIG. 9, a change in a proximal vector signal when little or no change occurs in a distal vector signal could be indicative of lead migration in a particular direction, e.g., retraction of lead 16 in an inferior or generally caudal direction relative to the patient’ s heart.

[0136] In some instances, a proximal vector signal may change less than or more than the distal vector signal due to lead migration. By analyzing changes in the relative difference between a feature of the distal vector signal and the analogous feature of the proximal vector signal, false lead migration detection due to changes in the distal vector signal and / or proximal vector signal due to causes other than lead migration can be avoided. For example, changes in patient posture, patient physical activity, environmental noise or other factors could cause a change in the distal vector signal at the time of the lead migration check that are unrelated to lead migration. Such changes may be expected to influence or alter both the distal vector signal and the proximal vector signal.

[0137] At block 402, control circuit 80 may determine and store baseline signal features and or signal differences determined from a distal vector signal and a proximal vector signal. Control circuit 80 may obtain the distal vector signal and determine one or more baseline features of the distal vector signal at the baseline timepoint according to any of the examples described above in conjunction with FIG. 6. An episode of the distal vector signal at the baseline timepoint may be stored in memory 82. The distal vector signal may be any signal sensed using the most distal electrode 31 paired with any other available electrode. The distal vector signal may be the atrial signal 109 sensed by A sensing channel 81 as described in conjunction with FIG. 4. The distal vector signal may be a wideband filtered signal sensed by morphology sensing channel 87 using the distal electrode 31 paired with proximal electrode 28 or housing 15. In some examples, two or more distal vector signals, each sensed using a sensing electrode vector that includes themost distal electrode 31, may be obtained and analyzed for determining respective baseline signal data at block 402.

[0138] Control circuit 80 may obtain a proximal vector signal and determine one or more baseline features of the proximal vector signal at the baseline timepoint at block 402. An episode of the proximal vector signal at the baseline timepoint may be recorded in memory 82. The proximal vector signal may be a signal sensed by sensing circuit 86 using a relatively more proximal sensing electrode vector than the distal sensing electrode vector used for sensing the distal vector signal. For example, the proximal vector signal may be any signal sensed using a sensing electrode vector that does not include the most distal electrode 31. The proximal vector signal may be sensed using a proximal sensing electrode vector that includes the most proximal electrode 28 paired with housing 15, pace sense electrode 30, or one of defibrillation electrodes 24 or 26. The proximal vector signal may be the ventricular signal 69 sensed by V sensing channel 83 or the ventricular sensing signal 122 (before or after low pass filtering by filter 124) determined as a combination of the atrial signal and the ventricular signal as described in conjunction with FIG. 4. In other examples, the proximal vector signal may be obtained by morphology signal channel 87 as a wideband filtered signal sensed using proximal electrode 28 paired with housing 15, electrode 30 paired with housing 15 or proximal electrode 28 paired with electrode 30.

[0139] The baseline feature(s) of the proximal vector signal can be analogous to the feature(s) determined from the distal vector signal. However, in some examples, the baseline feature(s) of the proximal vector signal may be different than the baseline features of the distal vector signal. For example, control circuit 80 may determine a representative P-wave amplitude from the distal vector signal based on maximum peak amplitudes received from A sensing channel 81 (e.g., see peak amplitude 230 in FIG. 6) or determined from the distal vector signal received by control circuit 80. Control circuit 80 may determine a representative R-wave amplitude from the proximal vector signal based on maximum peak amplitudes received from V sensing channel 83 (e.g., see peak amplitude 232 in FIG. 6) or determined from the proximal vector signal received by control circuit 80.

[0140] In some examples, control circuit 80 may combine the distal vector signal and the proximal vector signal at block 402 for storing baseline features and / or a baseline signal episode. For example, a distal vector signal may be sensed using distal electrode 31 incombination with proximal ring electrode 28. A proximal vector signal may be sensed using proximal ring electrode 28 in combination with housing 15. The distal vector signal and the proximal vector signal may be combined, e.g., by determining a sum or difference signal by adding or subtracting the distal vector signal and the proximal vector signal. For example, the combined vector signal may be the atrial sensing signal 120 (before or after low pass filtering by filter 111) determined by sensing circuit 86 as a combination of the atrial signal 109 and the ventricular signal 69 in some examples.

[0141] In some examples, a P-wave signal segment may be stored from the distal vector signal, the proximal vector signal and / or a combination of the distal vector signal and the proximal vector signal. The P-wave signal segment may be stored so that it extends a specified number of sample points earlier and later than a P-wave sensing threshold crossing by the atrial sensing signal received by P-wave detector 106. The P-wave signal segment may encompass exactly one sensed P-wave. In other examples, the P-wave signal segment may include multiple sensed P-waves based on the timing of P-wave sensing threshold crossings detected by A sensing channel 81.

[0142] Additionally or alternatively, an R-wave signal segment may be stored from the distal vector signal, the proximal vector signal and / or a combination of the distal vector signal and the proximal vector signal. The R-wave signal segment may be stored so that it extends a specified number of sample points earlier and later than an R-wave sensing threshold crossing by the ventricular sensing signal received by R-wave detector 66a, for example. The R-wave signal segment may encompass exactly one sensed R-wave. In other examples, an R-wave signal segment may include multiple sensed R-waves based on the timing of R-wave sensing threshold crossings detected by one of V sensing channel 83 or V sensing channel 85.

[0143] In other examples, control circuit 80 obtains a cardiac signal segment that includes a T-wave. A cardiac signal segment may include a P-wave, QRS waveform and / or T-wave to enable changes in the amplitude, shape, peak polarities, or other features of the atrial depolarization waveform, ventricular depolarization waveform and / or ventricular repolarization waveform to be analyzed.

[0144] After obtaining and storing baseline signal data at block 402, control circuit 80 may wait for a scheduled or triggered time for a lead migration check at block 406. When control circuit 80 determines that it is time for a lead migration check at block 406, e.g.,according to any of the examples described above in conjunction with FIG. 6, control circuit 80 may determine distal vector signal feature(s) at block 408 analogous to the distal vector signal feature(s) previously determined at the baseline timepoint. At block 410, control circuit 80 may determine proximal vector signal feature(s) that were previously determined from the proximal vector signal at the baseline timepoint.

[0145] At block 412, control circuit 80 may determine signal differences for detecting changes in the distal vector signal and / or changes in differences between the distal vector signal and the proximal vector signal that have occurred since the baseline timepoint. Control circuit 80 may determine the difference between distal vector signal features determined at the baseline timepoint and the distal vector signal features determined at the current lead migration check timepoint as generally described above in conjunction with FIG. 6. Control circuit 80 may determine the difference between proximal vector signal features determined at the baseline timepoint and the proximal vector signal features determined at the current lead migration check timepoint. Control circuit 80 may determine a difference between the combined signal determined from the distal vector signal and the proximal vector signal determined at the baseline timepoint and the combined signal determined at the current lead migration check timepoint.

[0146] At block 414, control circuit 80 may apply lead migration detection criteria to the signal differences determined at block 412. The lead migration detection criteria may include one or more thresholds or ranges applied to respective signal features or signal feature differences for detecting evidence of migration of the distal end 29 of lead 16. In some examples, control circuit 80 determines a change in the difference between a feature of the distal vector signal and a feature of the proximal vector signal from the baseline timepoint to the current timepoint. If the change in the difference between the distal vector signal and the proximal vector signal features is greater than a threshold change, lead migration may be detected by control circuit 80 at block 414. For example, control circuit 80 may determine a ratio or difference between the maximum peak amplitude of the distal vector signal (e.g., peak amplitude 230 shown in FIG. 6) and the maximum peak amplitude of the proximal vector signal (e.g., peak amplitude 232 shown in FIG. 6) at baseline and at the lead migration check timepoint. Control circuit 80 may compare to the baseline ratio or baseline difference to the analogous ratio or difference determined at the lead migration check timepoint. If the ratio or difference between peak amplitudes 230 and232 has changed by a threshold percentage, control circuit 80 may detect suspected lead migration.

[0147] In some examples, the distal vector signal and the proximal vector signal may be combined (e.g., in a difference signal) and compared to the baseline combined signal for determining a change relative to baseline of the difference between the distal and proximal vector signals. For example, a baseline feature may be determined from a difference signal determined by subtracting time-aligned sample points of a distal vector signal and a proximal vector signal. At the lead migration check timepoint, the feature may be determined from the difference signal determined by subtracting time- aligned sample points of the distal vector signal and the proximal vector signal. The difference between the baseline feature and the feature at the time of the lead migration check timepoint may be compared to a lead migration detection threshold. In some examples, a baseline feature of the atrial sensing signal may be compared to the analogous feature determined from the atrial sensing signal at the time of the lead migration check. The atrial sensing signal can be determined by sensing circuit 86 as the difference signal between the atrial signal and the ventricular signal. If a difference between the baseline feature of the atrial sensing signal and the new feature of the atrial sensing signal at the time of the lead migration check meets a threshold, lead migration may be detected.

[0148] In some examples, the lead migration detection criteria applied at block 414 may require that a change in the distal vector signal at the current timepoint relative to the baseline timepoint is greater than a threshold change. Control circuit 80 may detect lead migration at block 414 when the currently determined feature of the distal vector signal is greater than a threshold change from the baseline feature value of the distal vector signal and the change in the difference between the distal vector signal and the proximal vector signal features is greater than a threshold change.

[0149] Additionally or alternatively, the lead migration detection criteria applied at block 414 may require that a change in the proximal vector signal at the current timepoint relative to the baseline timepoint is less than a threshold change. Control circuit 80 may detect lead migration at block 414 when the currently determined feature of the proximal vector signal is less than a threshold change from the baseline feature value of the proximal vector signal and the change in the differences between the distal vector signal and the proximal vector signal features represents greater than a threshold change.

[0150] In some examples, the lead migration detection criteria may include a required threshold change in the distal vector signal relative to the baseline distal vector signal, a threshold change in a difference between the distal vector signal and the proximal vector signal relative to a baseline difference, and less than a threshold change in the proximal vector signal relative to the baseline proximal vector signal. A change in the distal vector signal or the proximal vector signal may be a change in peak amplitude, maximum or minimum slope, peak polarity, signal width, signal area, electrical event signal waveform morphology (e.g., P-wave morphology, R-wave morphology or T-wave morphology) or other selected feature of the respective signal determined as representative of a change in the signal that can occur with lead migration.

[0151] The difference between the combined distal and proximal vector signal relative to the combined distal and proximal vector signal at baseline can be determined as an amplitude difference, slope difference, morphology matching score or correlation of the baseline morphology and current morphology of the combined proximal and distal vector signals. It is contemplated that a variety of signal features or signal feature differences may be determined from the distal vector signal, proximal vector signal, and / or a combined signal determined from the distal vector signal and the proximal vector signal (e.g., a difference signal, summed signal, etc.) to detect a threshold change relative to the baseline signals indicative of a cardiac electrical signal change due to lead migration. A threshold change or range may be expressed as a percentage of the baseline value and may be + 10 %, + 20%, + 30%, + 40% or + 50% as examples.

[0152] If lead migration detection criteria are not met at block 414, control circuit 80 may return to block 406 to wait for the next time a lead migration check is scheduled or triggered. When the lead migration detection criteria are met at block 414, control circuit 80 may perform a lead migration detection response at block 416. Any of the example lead migration detection responses described above in conjunction with FIG. 6 may be performed at block 416.

[0153] FIGs. 8A — 8C are diagrams illustrating changes in a distal vector signal and a proximal vector signal that may occur due to lead migration. FIG. 8A is a diagram 500 of a lead 16 located in a baseline position relative to heart 8 and coupled to ICD 14. FIG. 8A includes an illustration of a distal vector signal 510 and a proximal vector signal 520 thatmay be sensed by sensing circuit 86 and analyzed by control circuitry of ICD 14 for establishing baseline timepoint features stored in memory 82.

[0154] The distal vector signal 510 may be sensed using a distal sensing electrode vector 504 including most distal electrode 31 in combination with the most proximal electrode 28. The proximal vector signal 520 may be sensed using a proximal sensing electrode vector 506 including the most proximal electrode 28 and the ICD housing 15. Each of the distal sensing electrode vector 504 and the proximal sensing electrode vector 506 are positioned at an angle relative to the cardiac axis 502 at the baseline timepoint. Distal sensing electrode vector 504 is shown at an angle 521 relative to the cardiac axis 502. Proximal sensing electrode vector 506 is shown at an angle 525 relative to the cardiac axis 502. When the free distal end 29 of lead 16 migrates, the angle of one or both of the distal sensing electrode vector 504 and the proximal sensing electrode vector 506 relative to the cardiac axis 502 may change, resulting in changes in the respective signals 510 and 520, e.g., changes in the peak amplitude and / or peak polarity or other morphological changes.

[0155] In the diagram 500, a QRS waveform of each of the distal vector signal 510 and the proximal vector signal 520 is shown. In the examples described below, features of the QRS waveform are described as being determined as baseline features for the sake of illustration. It is to be understood however, that one or more features of the P-wave, QRS waveform, and / or T-wave of the distal vector signal 510 and / or the proximal vector signal 520 may be determined for establishing baseline features and for comparing baseline features to lead migration check timepoint features for detecting lead migration.

[0156] One or more features of the distal vector signal 510, one or more features of the proximal vector signal 520, and / or one or more quantitative relationships between a feature of the distal vector signal 510 and a feature of the proximal vector signal 520 may be determined by control circuit 80 and stored in memory 82 as baseline features. As described above, the baseline features may be determined as statistically representative values determined from signal feature values stored in a histogram allocated in memory 82 sampled over a data gathering time period, e.g., one hour, one day, one week, etc.

[0157] In an illustrative example, the maximum positive peak amplitude 512 and the maximum (in absolute value) negative peak amplitude 514 of the distal vector signal 510 may be determined. The ratio, difference, sum or other quantitative relationship of the maximum positive peak amplitude 512 and the maximum negative peak amplitude 514may be determined and stored in memory 82. The maximum positive peak amplitude 522 and the maximum (in absolute value) negative peak amplitude 524 of the proximal vector signal 520 may be determined. The ratio, difference, sum or other quantitative relationship of the maximum positive peak amplitude 522 and the maximum negative peak amplitude 524 may be determined by control circuit 80 and stored in memory 82. In some examples, the ratio, difference or other quantitative relationship of the maximum positive peak amplitude 512 of distal vector signal 510 and the maximum positive peak amplitude 522 of the proximal vector signal 520 may be determined and stored as a baseline feature in memory 82. The ratio, difference or other quantitative relationship of the maximum negative peak amplitude 514 of distal vector signal 510 and the maximum negative peak amplitude 524 of the proximal vector signal 520 may be determined and stored as a baseline feature in memory 82.

[0158] It is recognized that numerous features of the distal vector signal and / or the proximal vector signal may be determined to characterize the baseline signals in various examples. Furthermore, a template of the distal vector signal 510 and / or a template of the proximal vector signal 520 may be established at the baseline timepoint and stored in memory 82 for comparison to the respective signal waveform obtained at a lead migration check time point.

[0159] FIG. 8B is a diagram 550 of lead 16 when free distal end 29 has migrated to the patient’s right as shown by directional arrow 551. In this illustrative example, the distal electrode vector 504 shifts into greater alignment with cardiac axis 502 compared to the baseline position of the distal electrode vector 504 shown in FIG. 8 A. The angle 541 between the distal sensing electrode vector 504 and the cardiac axis 502 is smaller than the baseline angle 521. Control circuit 80 may perform a lead migration check including sensing the distal vector signal 560 via the distal sensing electrode vector 504 between the most distal electrode 31 and the most proximal electrode 28. In other examples, the distal vector signal may be sensed using an electrode generally carried along a distal portion of lead 16, which may be positioned relatively closer to the distal end 29 than the proximal end of lead 16 in some examples, without necessarily requiring the distal vector signal to be sensed using the most distal electrode 31. Features of the distal vector signal 560, e.g., the maximum positive peak amplitude 562, the maximum negative peak amplitude 564, a quantitative relationship of the maximum peak amplitude 562 and the maximum negativepeak amplitude 564 may be determined by control circuit 80 for comparison to respective baseline feature values.

[0160] Changes in the distal vector signal 560 compared to the baseline distal vector signal 510 may occur due to the change in angle of the distal sensing electrode vector 504 relative to the cardiac axis 502. These changes may be detected based on a comparative analysis of features of the distal vector signal 560 sensed during a lead migration check timepoint and the features of the baseline distal vector signal 510 (in FIG. 8). For example, the maximum negative peak amplitude 564 may be decreased (in absolute value) Compared to the baseline negative peak amplitude 514. The maximum positive peak amplitude 562 may increase compared to the baseline positive peak amplitude 512. The changes in the relative values of the positive and negative peak amplitudes may occur, for example, when lead migration causes the distal sensing electrode vector 504 to become relatively more aligned with the cardiac axis 502 (e.g., smaller angle 541 compared to baseline angle 521). Control circuit 80 may detect lead migration based on at least a change in the maximum negative peak amplitude and / or a change in a quantitative relationship between the maximum positive peak amplitude 562 and the maximum negative peak amplitude 564 compared to the baseline quantitative relationship of the maximum positive peak amplitude 512 and the maximum negative peak amplitude 514.

[0161] In this example, the proximal vector signal 540 may remain substantially the same as the baseline proximal vector signal 520 because the proximal sensing electrode vector 506 remains relatively unchanged, e.g., relative to the cardiac axis 502 and heart 8. The peak positive amplitude 542 and peak negative amplitude 544 may be approximately equal to (or within a threshold range of) the baseline peak positive amplitude 522 and peak negative amplitude 524, respectively. In some examples, control circuit 80 detects migration of lead distal end 29 based on the changes in the distal vector signal 560 relative to the baseline distal vector signal 510. For example, control circuit 80 may detect lead migration based on at least the decreased (absolute value) maximum negative peak amplitude 514 and / or the increased maximum positive peak amplitude 562 relative to the baseline signal 510. While a decrease in the maximum negative peak amplitude 564 and an increase in the maximum positive peak amplitude 562 are illustrated in FIG. 8B, it is understood that other changes in the distal vector signal 560 could occur when the distal lead end 29 migrates to the patient’s right, depending on the relative locations of the distalsensing electrode vector 504 and heart 8 and cardiac axis 502. In some examples, control circuit 80 may detect lead migration when a threshold change in at least one feature of distal vector signal 560 relative to the baseline distal vector signal 510 is detected and the proximal vector signal 540 is relatively unchanged compared to the baseline proximal vector signal 520.

[0162] FIG. 8C is a diagram 570 of lead 16 when free distal end 29 has migrated to the patient’s left as shown by directional arrow 571. In this example, the proximal vector signal 590 may remain substantially the same as the baseline proximal vector signal 520 because the position of the proximal sensing electrode vector 506 remains relatively unchanged, e.g., relative to the cardiac axis 502 and heart 8. The maximum positive peak amplitude 592 and the maximum negative peak amplitude 594 may be relatively unchanged compared to the respective baseline maximum positive peak amplitude 522 and the baseline maximum negative peak amplitude 524. In some examples, control circuit 80 detects migration of lead distal end 29 based on the changes in the distal vector signal 580 relative to the baseline distal vector signal 510.

[0163] For example, control circuit 80 may detect lead migration based on at least the increased (absolute value) of the maximum negative peak amplitude 584. Additionally or alternatively, control circuit 80 may detect lead migration based on the decreased value of the maximum peak amplitude 582 relative to the baseline maximum peak amplitude 512. The increased maximum negative peak amplitude 584 and decreased maximum positive peak amplitude 582 may occur when the distal sensing electrode vector 504 shifts more out of alignment with the cardiac axis 502. The angle 591 between the distal sensing electrode vector 504 and the cardiac axis 502 has increased relative to the baseline angle 521 in this case. While an increase in the maximum negative peak amplitude 584 and decrease in the maximum positive peak amplitude 582 is illustrated in FIG. 8C, it is understood that other changes in the distal vector signal 580 could occur when the distal lead end 29 migrates to the patient’s left, depending on the relative locations of the distal sensing electrode vector 504 and heart 8 and cardiac axis 502. In some examples, control circuit 80 may detect lead migration when a threshold change in at least one feature of distal vector signal 580 relative to the baseline distal vector signal 510 is detected and the proximal vector signal 590 is relatively unchanged compared to the baseline proximal vector signal 520.

[0164] FIG. 9 is a diagram 600 of lead 16 coupled to ICD 14 illustrating migration of the distal end 29 in an inferior or caudal direction as shown by directional arrow 601, e.g., relative to the baseline position shown in FIG. 8A. In this example, the proximal vector signal 620 may change relative to the baseline proximal vector signal 520 (see FIG. 8A) because the angle 625 between the proximal sensing electrode vector 606 relative to the cardiac axis 602 and heart 8 changes (in this case increases) due to lead migration compared to the alignment of the baseline proximal sensing electrode vector 506 with the cardiac axis 502 shown in FIG. 8A (see angle 525). In some examples, control circuit 80 detects migration of lead distal end 29 based on the changes in the proximal vector signal 620 relative to the baseline proximal vector signal 520. For example, control circuit 80 may detect lead migration based on at least the increased (absolute value) of the maximum negative peak amplitude 624 compared to the maximum negative peak amplitude 524 of baseline proximal vector signal 520. Additionally or alternatively, control circuit 80 may detect the lead migration based on at least the decreased maximum peak amplitude 622 of the proximal vector signal 620 compared to the baseline proximal vector signal 520. While a decrease in the maximum positive peak amplitude 622 and an increase in the maximum negative peak amplitude 624 of the proximal vector signal 620 is illustrated in FIG. 9 relative to the baseline proximal vector signal 520 of FIG. 8A, it is understood that other changes in the proximal vector signal 620 could occur when the distal lead end 29 migrates in a caudal direction 601, depending on the relative locations of the proximal sensing electrode vector 606 and heart 8 and cardiac axis 602.

[0165] In this example, the QRS waveform of the distal vector signal 610 may be relatively unchanged compared to the baseline distal vector signal 510 because the angle of the distal sensing electrode vector 604 relative to the cardiac axis 602 may be relatively unchanged compared to the baseline angle 521 (shown in FIG. 8 A). However the P-wave peak amplitude (not shown) may be decreased, change polarity, and / or the QRS positive peak amplitude 612 and / or negative peak amplitude 614 may be changed relative to baseline because of the change in location of the distal electrode 31 and the proximal electrode 28. The diagrams of FIGs. 8A-9 are intended to illustrate some changes that could occur in a distal vector signal and a proximal vector signal due to migration of the distal end 29 of lead 16, with no limitation intended. These examples are intended to illustrate how various combinations of features of a distal vector signal and a proximalvector signal determined at a baseline timepoint and a later lead migration check timepoint can be used for detecting lead migration.

[0166] FIGs. 8A-9 are described in the context of an electrophysiological signal being sensed as a cardiac electrical signal and electrical event signal features being determined as cardiac event signal features (e.g., peak amplitudes and / or polarities of P-waves, QRS waveforms and / or T-waves). It is to be understood that the techniques disclosed herein for detecting lead migration may include determining electrical event signal features attendant to electrical activity detected from other types of sensed electrophysiological signals, e.g., electrical event signal features determined from electrophysiological signals sensed from the brain, spinal cord, nerve, muscle or other organs of the body. Such electrical event signals may correspond to the electrical depolarization and / or repolarization of electrically excitable tissue, such as tissues of the nervous system, skeletal muscle, smooth muscle or cardiac muscle.

[0167] Further disclosed herein is the subject matter of the following examples:

[0168] Example 1. A medical device system including a therapy delivery circuit configured to deliver an electrical stimulation therapy. The medical device system includes a sensing circuit configured to receive one or more electrophysiological signals via a medical electrical lead having a distal end and carrying at least a distal electrode. The one or more electrophysiological signals includes a distal vector signal received via a distal sensing electrode vector including the distal electrode. The medical device system includes a control circuit in communication with the sensing circuit and the therapy delivery circuit. The control circuit is configured to, based on the one or more electrophysiological signals received by the sensing circuit, control the therapy delivery circuit to deliver the electrical stimulation therapy and, based on at least the distal vector signal, detect migration of the medical electrical lead carrying the distal electrode. The control circuit may be configured to generate an output in response to detecting the migration of the medical electrical lead. The medical device system may include a memory configured to store data corresponding to the generated output.

[0169] Example 2. The medical device system of example 1 wherein the control circuit is further configured to determine a first feature of the distal vector signal at a first timepoint, determine a second feature of the distal vector signal at a second timepoint, and detectmigration of the medical electrical lead based on at least a difference between the first feature and the second feature.

[0170] Example 3. The medical device system of example 2 wherein the control circuit is further configured to determine the first feature and the second feature by determining at least one of a peak amplitude, a peak polarity, a waveform morphology template, a slope, a signal width, or a signal area.

[0171] Example 4. The medical device system of any one of examples 1 — 3 wherein the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead. The proximal electrode is spaced proximally from the distal electrode on the medical electrical lead. The proximal sensing electrode vector does not include the distal electrode. The control circuit is further configured to determine a difference between the distal vector signal and the proximal vector signal and detect migration of the medical electrical lead based on at least the difference between the distal vector signal and the proximal vector signal and a difference between the first feature and the second feature of the distal vector signal.

[0172] Example 5. The medical device system of any one of examples 2 — 4 wherein the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead. The proximal electrode is spaced proximally from the distal electrode on the medical electrical lead. The proximal sensing electrode vector does not include the distal electrode. The control circuit is further configured to determine a third feature of the proximal vector signal at the first timepoint, determine a fourth feature of the proximal vector signal at the second timepoint and detect migration of the medical electrical lead based on at least the difference between the first feature and the second feature meeting a first threshold and a difference between the third feature and the fourth feature meeting a second threshold.

[0173] Example 6. The medical device system of example 5 wherein the control circuit is further configured to determine that the difference between the third feature and the fourth feature meet the second threshold when the difference between the third feature and the fourth feature is less than the second threshold.

[0174] Example 7. The medical device system of any one of examples 1 — 6 wherein the sensing circuit is further configured to receive a proximal vector signal via a proximalsensing electrode vector including a proximal electrode carried by the medical electrical lead. The proximal electrode is spaced proximally from the distal electrode on the medical electrical lead. The proximal sensing electrode vector does not include the distal electrode. The control circuit is further configured to detect the migration of the medical electrical lead based on at least the distal vector signal by determining a combined signal from the distal vector signal and the proximal vector signal at a first timepoint, determining the combined signal from the distal vector signal and the proximal vector signal at a second timepoint, detecting a change in the combined signal determined at the second timepoint relative to the combined signal determined at the first timepoint and detecting migration of the medical electrical lead carrying the distal electrode based on the detected change in the combined signal.

[0175] Example 8. The medical device system of any one of examples 1 — 7 wherein the control circuit is further configured to generate the output by generating a lead migration detection notification. The medical device system further includes a telemetry circuit configured to transmit the lead migration detection notification.

[0176] Example 9. The medical device system of any one of examples 1 — 8 wherein the control circuit is further configured to generate the output by adjusting a sensing control parameter in response to detecting the migration of the medical electrical lead.

[0177] Example 10. The medical device system of example 9 wherein the control circuit is further configured to adjust the sensing control parameter by adjusting at least one of a sensing electrode vector used by the sensing circuit for sensing the one or more electrophysiological signals or an electrical event sensing threshold amplitude.

[0178] Example 11. The medical device system of any one of examples 1-10 wherein the control circuit is further configured to generate the output by adjusting an arrhythmia detection control parameter in response to detecting the migration of the medical electrical lead and detect an arrhythmia based on the adjusted arrhythmia detection control parameter. The control circuit is further configured to control the therapy delivery circuit to deliver the electrical stimulation therapy in response to detecting the arrhythmia.

[0179] Example 12. The medical device system of example 11 wherein the control circuit is further configured to adjust the arrhythmia detection control parameter by at least one of adjusting a first threshold number of tachyarrhythmia intervals required to detect a tachyarrhythmia or adjusting a second threshold number of tachyarrhythmia intervalsrequired to trigger a morphology analysis of the one or more electrophysiological signals received by the sensing circuit.

[0180] Example 13. The medical device system of any one of examples 1 — 12 wherein the control circuit is further configured to generate the output by performing a pacing capture test in response to detecting the migration of the medical electrical lead.

[0181] Example 14. The medical device system of any one of examples 1 — 13 wherein the control circuit is further configured to generate the output by adjusting a therapy control parameter used by the therapy delivery circuit to deliver the electrical stimulation therapy.

[0182] Example 15. The medical device system of example 14 wherein the control circuit is further configured to adjust the therapy control parameter by adjusting at least one of a therapy delivery electrode vector or a therapy delivery pulse output.

[0183] Example 16. The medical device system of any one of examples 1-15 wherein the control circuit is further configured to generate the output by disabling the electrical stimulation therapy in response to detecting the migration of the medical electrical lead.

[0184] Example 17. The medical device system of any one of examples 1-16 wherein the sensing circuit is further configured to sense the one or more electrophysiological signals by sensing an atrial signal and a ventricular signal, sense P-waves from the atrial signal and sense R-waves from the ventricular signal. The control circuit is further configured to detect one of suspected cardiac event signal oversensing or suspected cardiac event signal undersensing by the sensing circuit based on at least one of the sensed atrial signal, the sensed P-waves, the sensed ventricular signal or the sensed R-waves. The control circuit is configured to, responsive to detecting one of the suspected cardiac event signal oversensing or the suspected cardiac event signal undersensing, perform a lead migration check for detecting the migration of the medical electrical lead based on at least the distal vector signal.

[0185] Example 18. The medical device system of any one of examples 1 — 17 wherein the therapy delivery circuit is configured to deliver the electrical stimulation therapy by delivering a high voltage cardioversion / defibrillation shock. The control circuit is further configured to perform a lead migration check for detecting the migration of the medical electrical lead in response to the therapy delivery circuit delivering the high voltage cardioversion / defibrillation shock.

[0186] Example 19. The medical device system of any one of examples 1 — 18 wherein the control circuit is further configured to determine at a first time point, from the distal vector signal, a first quantitative relationship between a distal vector signal first positive peak amplitude and a distal vector signal first negative peak amplitude. The control circuit is further configured to determine at a second time point later than the first time point, from the distal vector signal, a second quantitative relationship between a distal vector signal second positive peak amplitude and a distal vector signal second negative peak amplitude. The control circuit is further configured to detect the migration of the medical electrical lead based on at least the distal vector signal by detecting the migration of the medical electrical lead based on at least the first quantitative relationship and the second quantitative relationship.

[0187] Example 20. The medical device system of example 19 wherein the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead. The proximal electrode spaced proximally from the distal electrode on the medical electrical lead. The proximal sensing electrode vector does not include the distal electrode. The control circuit is further configured to determine at the first time point a third quantitative relationship between a proximal vector signal first positive peak amplitude and a proximal vector signal first negative peak amplitude, determine at the second time point a fourth quantitative relationship between a proximal vector signal second positive peak amplitude and a proximal vector signal second negative peak amplitude and detect migration of the medical electrical lead based on at least the first quantitative relationship, second quantitative relationship, third quantitative relationship and fourth quantitative relationship.

[0188] Example 21. The medical device system of any one of examples 1 — 20 further comprising the at least one medical electrical lead. The medical electrical lead being an extra-cardiac lead. The control circuit being further configured to detect migration of the medical electrical lead after implantation of the medical electrical lead in an extra-cardiac location.

[0189] Example 22. The medical device system of any one of examples 1-21 wherein the therapy delivery circuit is further configured to deliver the electrical stimulation therapy by delivering a cardiac electrical stimulation therapy and the sensing circuit isfurther configured to receive the one or more electrophysiological signals by sensing at least one cardiac electrical signal.

[0190] Example 23. A method including sensing one or more electrophysiological signals including a distal vector signal sensed via a distal sensing electrode vector that includes a distal electrode of a medical electrical lead. The method includes, based on at least the distal vector signal, detecting migration of the medical electrical lead carrying the distal electrode. The method can include generating an output in response to detecting the migration of the medical electrical lead; and storing data corresponding to the output in a medical device memory.

[0191] Example 24. The method of example 23 further comprising determining a first feature of the distal vector signal at a first timepoint, determining a second feature of the distal vector signal at a second timepoint and detecting migration of the medical electrical lead based on at least a difference between the first feature and the second feature.

[0192] Example 25. The method of example 24 further comprising determining the first feature and the second feature by determining at least one of a peak amplitude, a peak polarity, a waveform morphology template, a slope, a signal width or a signal area.

[0193] Example 26. The method of any one of examples 23 — 25 further comprising sensing a proximal vector signal via a proximal sensing electrode vector that includes a proximal electrode and does not include the distal electrode. The proximal electrode being spaced proximally from the distal electrode on the medical electrical lead. The method further including determining a difference between the distal vector signal and the proximal vector signal and detecting migration of the medical electrical lead based on at least the difference between the distal vector signal and the proximal vector signal and a difference between the first feature and the second feature of the distal vector signal.

[0194] Example 27. The method of any one of examples 24 — 26 further comprising sensing a proximal vector signal via a proximal sensing electrode vector that includes a proximal electrode and does not include the distal electrode. The proximal electrode being spaced proximally from the distal electrode on the medical electrical lead. The method further including determining a third feature of the proximal vector signal at the first timepoint, determining a fourth feature of the proximal vector signal at the second timepoint and detecting migration of the medical electrical lead based on at least thedifference between the first feature and the second feature meeting a first threshold and a difference between the third feature and the fourth feature meeting a second threshold.

[0195] Example 28. The method of example 27 further comprising determining that the difference between the third feature and the fourth feature meet the second threshold when the difference between the third feature and the forth feature is less than the second threshold.

[0196] Example 29. The method of any one of examples 23 — 28 further comprising sensing a proximal vector signal via a proximal sensing electrode vector that includes a proximal electrode and does not include the distal electrode. The proximal electrode being spaced proximally from the distal electrode on the medical electrical lead. The method further including detecting the migration of the medical electrical lead based on at least the distal vector signal by determining a combined signal from the distal vector signal and the proximal vector signal at a first timepoint, determining the combined signal from the distal vector signal and the proximal vector signal at a second timepoint, detecting a change in the combined signal determined at the second timepoint relative to the combined signal determined at the first timepoint and detecting migration of the medical electrical lead carrying the distal electrode based on the detected change in the combined signal.

[0197] Example 30. The method of any one of examples 23 — 29 wherein generating the output comprises generating a lead migration detection notification and transmitting the lead migration detection notification.

[0198] Example 31. The method of any one of examples 22 — 29 wherein generating the output comprises adjusting a sensing control parameter in response to detecting the migration of the medical electrical lead.

[0199] Example 32. The method of example 31 wherein adjusting the sensing control parameter comprises adjusting at least one of a sensing electrode vector used for sensing the one or more electrophysiological signals or an electrical event sensing threshold amplitude.

[0200] Example 33. The method of any one of examples 23-32 further comprising generating the output by adjusting an arrhythmia detection control parameter in response to detecting the migration of the medical electrical lead, detecting an arrhythmia based on the adjusted arrhythmia detection control parameter and delivering an electrical stimulation therapy in response to detecting the arrhythmia.

[0201] Example 34. The method of example 33 wherein adjusting the arrhythmia detection control parameter comprises at least one of: adjusting a first threshold number of tachyarrhythmia intervals required to detect a tachyarrhythmia or adjusting a second threshold number of tachyarrhythmia intervals required to trigger a morphology analysis of the one or more electrophysiological signals received by the sensing circuit.

[0202] Example 35. The method of any one of examples 23 — 34 further comprising generating the output by performing a pacing capture test in response to detecting the migration of the medical electrical lead.

[0203] Example 36. The method of any one of examples 23 — 35 further comprising delivering an electrical stimulation therapy and wherein generating the output comprises adjusting a therapy control parameter used to deliver the electrical stimulation therapy.

[0204] Example 37. The method of example 36 wherein adjusting the therapy control parameter comprises adjusting at least one of a therapy delivery electrode vector or a therapy delivery pulse output.

[0205] Example 38. The method of any one of examples 23 — 37 wherein generating the output comprises disabling an electrical stimulation therapy in response to detecting the migration of the medical electrical lead.

[0206] Example 39. The method of any one of examples 23-38 further comprising sensing the one or more electrophysiological signals by sensing an atrial signal and a ventricular signal, sensing P-waves from the atrial signal, sensing R-waves from the ventricular signal, and detecting one of suspected cardiac event signal oversensing or suspected cardiac event signal undersensing based on at least one of the sensed atrial signal, the sensed P-waves, the sensed ventricular signal or the sensed R-waves. The method further including, responsive to detecting one of the suspected cardiac event signal oversensing or the suspected cardiac event signal undersensing, performing a lead migration check for detecting the migration of the medical electrical lead based on at least the distal vector signal.

[0207] Example 40. The method of any one of examples 23 — 39 further comprising delivering an electrical stimulation therapy by delivering a high voltage cardioversion / defibrillation shock and performing a lead migration check for detecting the migration of the medical electrical lead in response to the delivery of the high voltage cardioversion / defibrillation shock.

[0208] Example 41. The method of any one of examples 23-40 further comprising determining at a first time point, from the distal vector signal, a first quantitative relationship between a distal vector signal first positive peak amplitude and a distal vector signal first negative peak amplitude and determining at a second time point later than the first time point, from the distal vector signal, a second quantitative relationship between a distal vector signal second positive peak amplitude and a distal vector signal second negative peak amplitude. The method may further include detecting the migration of the medical electrical lead based on at least the distal vector signal by detecting the migration of the medical electrical lead based on at least the first quantitative relationship and the second quantitative relationship.

[0209] Example 42. The method of example 41 further comprising sensing a proximal vector signal via a proximal sensing electrode vector that includes a proximal electrode and does not include the distal electrode where the proximal electrode is spaced proximally from the distal electrode on the medical electrical lead. The method further including determining at the first time point a third quantitative relationship between a proximal vector signal first positive peak amplitude and a proximal vector signal first negative peak amplitude, determining at the second time point a fourth quantitative relationship between a proximal vector signal second positive peak amplitude and a proximal vector signal second negative peak amplitude and detecting the migration of the medical electrical based on at least the distal vector signal by detecting the lead migration based on at least the first quantitative relationship, second quantitative relationship, third quantitative relationship and fourth quantitative relationship.

[0210] Example 43. The method of any one of examples 23 — 42 further comprising detecting the migration of the medical electrical lead after implantation of the medical electrical lead in an extra-cardiac location.

[0211] Exaample 44. The method of any one of examples 23 — 43 further comprising, based on the one or more electrophysiological signals, controlling delivery of an electrical stimulation therapy.

[0212] Example 45. 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 sense a distal vector signal via a distal sensing electrode vector including a distal electrode of a medical electrical lead and sense a proximal vector signalvia a proximal sensing electrode vector including a proximal electrode and not including the distal electrode. The proximal electrode being located further from the distal end of the medical electrical lead than the distal electrode. The set of instructions further causing the medical device to, based on the distal vector signal and the proximal vector signal, detect migration of the medical electrical lead, generate an output in response to detecting the migration of the medical electrical lead and store data corresponding to the output in a medical device memory.

[0213] 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.

[0214] 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).

[0215] 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.

[0216] 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 system comprising: a therapy delivery circuit configured to deliver an electrical stimulation therapy; a sensing circuit configured to receive one or more electrophysiological signals via a medical electrical lead having a distal end and carrying at least a distal electrode, the one or more electrophysiological signals including a distal vector signal received via a distal sensing electrode vector that includes the distal electrode; a control circuit in communication with the sensing circuit and the therapy delivery circuit, the control circuit configured to: based on the one or more electrophysiological signals received by the sensing circuit, control the therapy delivery circuit to deliver the electrical stimulation therapy; based on at least the distal vector signal, detect migration of the medical electrical lead carrying the distal electrode; and generate an output in response to detecting the migration of the medical electrical lead; and a memory configured to store data corresponding to the generated output.

2. The medical device system of claim 1 wherein the control circuit is further configured to: determine a first feature of the distal vector signal at a first timepoint; determine a second feature of the distal vector signal at a second timepoint; and detect migration of the medical electrical lead based on at least a difference between the first feature and the second feature.

3. The medical device system of claim 2 wherein the control circuit is further configured to determine the first feature and the second feature by determining at least one of: a peak amplitude; a peak polarity; a waveform morphology template; a slope;a signal width; or a signal area.

4. The medical device system of any one of claims 2 — 3 wherein: the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead, the proximal electrode spaced proximally from the distal electrode on the medical electrical lead, the proximal sensing electrode vector not including the distal electrode; and the control circuit is further configured to: determine a difference between the distal vector signal and the proximal vector signal; and detect migration of the medical electrical lead based on at least the difference between the distal vector signal and the proximal vector signal and a difference between the first feature and the second feature of the distal vector signal.

5. The medical device system of any one of claims 2 — 4 wherein: the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead, the proximal electrode spaced proximally from the distal electrode on the medical electrical lead, the proximal sensing electrode vector not including the distal electrode; and the control circuit is further configured to: determine a third feature of the proximal vector signal at the first timepoint; determine a fourth feature of the proximal vector signal at the second timepoint; and detect migration of the medical electrical lead based on at least the difference between the first feature and the second feature meeting a first threshold and a difference between the third feature and the fourth feature meeting a second threshold.

6. The medical device system of claim 5 wherein the control circuit is further configured to determine that the difference between the third feature and the fourth feature meet the second threshold when the difference between the third feature and the fourth feature is less than the second threshold.

7. The medical device system of any one of claims 1 — 6 wherein: the sensing circuit is further configured to receive a proximal vector signal via a proximal sensing electrode vector including a proximal electrode carried by the medical electrical lead, the proximal electrode spaced proximally from the distal electrode on the medical electrical lead, the proximal sensing electrode vector not including the distal electrode; and the control circuit is further configured to detect the migration of the medical electrical lead based on at least the distal vector signal by: determining a combined signal from the distal vector signal and the proximal vector signal at a first timepoint; determining the combined signal from the distal vector signal and the proximal vector signal at a second timepoint; detecting a change in the combined signal determined at the second timepoint relative to the combined signal determined at the first timepoint; and detecting migration of the medical electrical lead carrying the distal electrode based on the detected change in the combined signal.

8. The medical device system of any one of claims 1 — 7 wherein the control circuit is configured to generate the output by generating a lead migration detection notification; and the medical device system further comprises a telemetry circuit configured to transmit the lead migration detection notification.

9. The medical device system of any one of claims 1 — 8 wherein the control circuit is further configured to generate the output by at least one of: adjusting a sensing control parameter in response to detecting the migration of the medical electrical lead;adjusting an arrhythmia detection control parameter in response to detecting the migration of the medical electrical lead; performing a capture test in response to detecting the migration of the medical electrical lead; or adjusting a therapy control parameter used by the therapy delivery circuit to deliver the electrical stimulation therapy.

10. The medical device system of any one of claims 1 — 9 wherein the control circuit is further configured to generate the output by disabling the electrical stimulation therapy in response to detecting the migration of the medical electrical lead.

11. The medical device system of any one of claims 1 — 10 wherein: the sensing circuit is further configured to: sense the one or more electrophysiological signals by sensing an atrial signal and a ventricular signal; sense P-waves from the atrial signal; and sense R-waves from the ventricular signal; and the control circuit is further configured to: detect one of suspected cardiac event signal oversensing or suspected cardiac event signal undersensing by the sensing circuit based on at least one of the sensed atrial signal, the sensed P-waves, the sensed ventricular signal or the sensed R-waves; and responsive to detecting one of the suspected cardiac event signal oversensing or the suspected cardiac event signal undersensing, perform a lead migration check for detecting the migration of the medical electrical lead based on at least the distal vector signal.

12. The medical device system of any one of claims 1 — 11 wherein: the therapy delivery circuit is configured to deliver the electrical stimulation therapy by delivering a high voltage cardioversion / defibrillation shock; andthe control circuit is further configured to perform a lead migration check for detecting the migration of the medical electrical lead in response to the therapy delivery circuit delivering the high voltage cardioversion / defibrillation shock.

13. The medical device system of any one of claims 1 — 12 wherein the control circuit is further configured to: determine at a first time point, from the distal vector signal, a first quantitative relationship between a distal vector signal first positive peak amplitude and a distal vector signal first negative peak amplitude; determine at a second time point later than the first time point, from the distal vector signal, a second quantitative relationship between a distal vector signal second positive peak amplitude and a distal vector signal second negative peak amplitude; and detect the migration of the medical electrical lead based on at least the distal vector signal by detecting the migration of the medical electrical lead based on at least the first quantitative relationship and the second quantitative relationship.

14. The medical device system of any one of claims 1 — 13 further comprising the medical electrical lead, wherein the medical electrical lead is an extra-cardiac lead, wherein the control circuit being further configured to detect migration of the medical electrical lead after implantation of the medical electrical lead in an extra-cardiac location.

15. The medical device system of any one of claims 1-14 wherein: the therapy delivery circuit is further configured to deliver the electrical stimulation therapy by delivering a cardiac electrical stimulation therapy; and the sensing circuit is further configured to receive the one or more electrophysiological signals by sensing at least one cardiac electrical signal.

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