Systems, devices, and methods for synchronization of anti-tachyarrhythmia pacing in an extravascular implantable system

Abstract

The present disclosure relates to synchronization of anti-tachyarrhythmia pacing in an extravascular implantable system. An extravascular implantable cardioverter defibrillator (ICD) system receives cardiac electrical signals through an extravascular sensing electrode vector by an electrical sensing circuit and senses cardiac events from the cardiac electrical signals. The ICD system detects a tachyarrhythmia from the cardiac electrical signals and determines a tachyarrhythmia cycle length from the cardiac electrical signals. The ICD system determines an ATP interval based on the tachyarrhythmia cycle length and sets an extended ATP interval that is longer than the ATP interval. The ICD delivers ATP pulses to the patient's heart via an extravascular pacing electrode vector that is different from the sensing electrode vector. The ATP pulses include a lead ATP pulse delivered at the extended ATP interval after a cardiac event is sensed from the cardiac electrical signals and a second ATP pulse delivered at the ATP interval after the lead ATP pulse.

Description

[0001] This application is a divisional application of the invention patent application entitled "Synchronization of Anti-tachycardia Pacing in Extravascular Implantable Systems" with an international application date of 2017 / 03 / 02, international application number PCT / US2017 / 020413, and Chinese national phase application number 201780017223.0. Technical Field

[0002] This disclosure generally relates to implantable medical devices, and more specifically to a system, apparatus, and method for delivering anti-tachycardia pacing pulses using a cardiovascular external electrode. Background Technology

[0003] Various implantable medical devices (IMDs) for delivering treatment, monitoring a patient's physiological condition, or combinations thereof, have been clinically implanted or proposed for clinical implantation in patients. Some IMDs may employ one or more elongated electrical leads carrying stimulating electrodes, sensing electrodes, and / or other sensors. IMDs can deliver treatment to or monitor the condition of various organs, nerves, muscles, or tissues (such as the heart, brain, stomach, spinal cord, pelvic floor, etc.). Implantable medical leads can be configured to position electrodes or other sensors at desired locations to deliver electrical stimulation or sense physiological conditions. For example, electrodes or sensors may be carried along a distal portion of the lead, which may extend subcutaneously, submuscularly, or venously. The proximal portion of the lead may be coupled to an implantable medical device housing containing circuitry such as signal generation and / or sensing circuitry.

[0004] Some IMDs, such as pacemakers or implantable cardioverter-defibrillators (ICDs), deliver therapeutic electrical stimulation to a patient's heart via electrodes carried by one or more implantable leads and / or the pacemaker or ICD housing. The leads can be transvenous, for example, advanced into the heart through one or more veins to position the endocardial electrode in close contact with the cardiac tissue. Other leads can be non-venous leads implanted outside the heart (e.g., in the epicardium, pericardium, or subcutaneously). The electrode is used to deliver electrical pulses to the heart to resolve abnormal heart rhythms.

[0005] ICDs, capable of delivering electrical pulses to treat abnormal heart rhythms, typically sense signals representing the heart's inherent depolarization and analyze these signals to identify abnormal rhythms. Upon detecting an abnormal rhythm, the device can deliver appropriate electrical stimulation to restore a more normal rhythm. For example, when bradycardia or tachycardia is detected using endocardial or epicardial electrodes, a pacemaker or ICD can deliver pacing pulses to the heart. When rapid ventricular tachycardia or fibrillation is detected using electrodes carried by transvenous or non-transvenous leads, an ICD can deliver a high-voltage cardioversion or defibrillation shock to the heart. Summary of the Invention

[0006] In general, this disclosure relates to techniques for delivering extracardiac antitachycardia pacing (ATP) pulses via an implantable medical device. An ICD operating according to the techniques disclosed herein sets an extended leading ATP interval for controlling the timing of the leading pulse of the ATP pulse sequence relative to a cardiac event sensed from a sensing electrode vector. Extracardiac pacing electrode vectors are used to deliver the ATP pulses.

[0007] In one example, this disclosure provides a cardiovascular implantable cardioverter defibrillator system including a sensing circuit, a treatment delivery circuit, and a control circuit. The sensing circuit is configured to receive cardiac electrical signals via a cardiovascular sensing electrode vector and to sense cardiac events from the cardiac electrical signals. The treatment delivery circuit is configured to deliver antitachycardia pacing pulses to a patient's heart via a cardiovascular pacing electrode vector different from the cardiovascular sensing electrode vector. The control circuit is coupled to the sensing circuit and the treatment delivery circuit and is configured to detect tachycardia from the cardiac electrical signals, determine the tachycardia cycle length, determine an ATP interval based on the tachycardia cycle length, set an extended ATP interval longer than the ATP interval, and control the treatment delivery circuit to deliver a series of ATP pulses, the series of ATP pulses including a lead ATP pulse delivered with the extended ATP interval after the cardiac event is detected by the sensing circuit and a second ATP pulse delivered with the ATP interval after the lead ATP pulse.

[0008] In another example, this disclosure provides a method performed by an extracardiac ICD system, the method comprising receiving cardiac electrical signals via an extracardiac sensing electrode vector through an electrical sensing circuit, sensing a cardiac event from the cardiac electrical signals, and detecting tachycardia from the cardiac electrical signals. The method further comprises determining the tachycardia cycle length from the cardiac electrical signals, determining an ATP interval based on the tachycardia cycle length, setting an extended ATP interval longer than the ATP interval, and delivering an ATP pulse to the patient's heart via an extracardiac pacing electrode vector different from the extracardiac sensing electrode vector. The ATP pulse includes a lead ATP pulse delivered with an extended ATP interval after the cardiac event is sensed from the cardiac electrical signals by the sensing circuit, and a second ATP pulse delivered with an ATP interval after the lead ATP pulse.

[0009] In another example, this disclosure provides a non-transient computer-readable storage medium including a set of instructions that, when executed by control circuitry of an extra-cardiovascular implantable cardioverter defibrillator system, cause the system to receive cardiac electrical signals via extra-cardiovascular sensing electrode vectors through sensing circuitry, sense cardiac events from the cardiac electrical signals, detect tachycardia from the cardiac electrical signals, determine the tachycardia cycle length from the cardiac electrical signals, determine an ATP interval based on the tachycardia cycle length, set an extended ATP interval longer than the ATP interval, and deliver ATP pulses to the patient's heart via extra-cardiovascular pacing electrode vectors different from the extra-cardiovascular sensing electrode vectors. The ATP pulses include a lead ATP pulse delivered with an extended ATP interval after the sensing circuitry senses a cardiac event from the cardiac electrical signals, and a second ATP pulse delivered with an ATP interval after the lead ATP pulse.

[0010] The present invention is intended to provide an overview of the subject matter described herein. It is not intended to provide an exclusive or exhaustive interpretation of the apparatuses and methods described in detail in the following drawings and description. Further details of one or more examples are set forth in the following drawings and description. Attached Figure Description

[0011] Figure 1A and 1B This is a conceptual diagram based on an example of an extravascular ICD system.

[0012] Figure 2A-2C Therefore, with Figure 1A-1B The diagram shows a concept of a patient 12 with an ICD system 10 implanted, arranged in different implant configurations.

[0013] Figure 3 It is shown Figure 1A-2C A conceptual diagram of the distal portion of another example of a cardiovascular external lead.

[0014] Figure 4It is based on an example Figure 1A-2C A schematic diagram of the ICD.

[0015] Figure 5 It is a graph of ECG signals acquired using cardiovascular external sensing electrode vectors and ECG signals representing cardiac electrical signals occurring at effective capture sites of cardiovascular external pacing electrode vectors.

[0016] Figure 6 This is a flowchart of an example method for delivering ATP by an extravascular ICD system.

[0017] Figure 7 This is a flowchart of a method for delivering ATP by an extravascular ICD system, based on another example.

[0018] Figure 8 This is a flowchart of a method for controlling ATP delivery by an extra-cardiovascular ICD system, based on another example. Detailed Implementation

[0019] In general, this disclosure describes techniques for delivering ATP using implantable, extracardiac electrodes. As used herein, the term "extracardiac" refers to a location outside the blood vessels, heart, and pericardium surrounding a patient's heart. Implantable electrodes carried by extracardiac leads can be positioned extrathoracically (outside the thoracic cavity and sternum) or intrathoracically (below the thoracic cavity or sternum), but typically not in close contact with myocardial tissue. The techniques disclosed herein provide methods for controlling the timing of the leader pulses in an ATP sequence to facilitate a high probability of capturing myocardium outside the physiological refractory period at the site of effective stimulation.

[0020] Figure 1A and Figure 1B This is a conceptual diagram based on an example extravascular ICD system 10.

[0021] Figure 1A This is a front view of the ICD system 10 implanted in the patient 12. Figure 1B This is a side view of the ICD system 10 implanted in the patient 12. The ICD system 10 includes an ICD 14 connected to cardiovascular external electrical stimulation and sensing leads 16. The ICD system 10 is capable of providing defibrillation shocks and / or cardioversion shocks, as well as pacing pulses. Figure 1A and Figure 1B Describe it.

[0022] The ICD 14 includes a housing 15 that forms a hermetically sealed protective layer for the internal components of the ICD 14. The housing 15 of the ICD 14 may be formed of a conductive material, such as titanium or a titanium alloy. The housing 15 may serve as a housing electrode (sometimes referred to as a can electrode). In the examples described herein, the housing 15 may serve as an active can electrode used in delivering cardioversion / defibrillation (CV / DF) shocks or other high-voltage pulses delivered using a high-voltage therapeutic circuit. In other examples, the housing 15 may be used in conjunction with a lead-based cathode electrode for delivering unipolar, low-voltage cardiac pacing pulses. In other instances, the housing 15 of the ICD 14 may include multiple electrodes on an external portion of the housing. The external portion (multiple) of the housing 15 serving as electrodes may be coated with a material such as titanium nitride.

[0023] The ICD 14 includes a connector assembly 17 (also referred to as a connector block or head) that includes an electrical feedthrough through a housing 15 to provide an electrical connection between a conductor extending within the lead body 18 of the lead 16 and electronic components included within the housing 15 of the ICD 14. As will be described in further detail herein, the housing 15 may accommodate one or more processors, memories, transceivers, sensors, inductive circuitry, therapeutic delivery circuitry, a power supply, and other components for sensing cardiac electrical signals, detecting heart rhythm, and controlling and delivering electrical stimulation pulses to treat abnormal heart rhythms.

[0024] Lead 16 includes an elongated lead body 18 having a proximal end 27 and a distal portion 25, the proximal end 27 including a lead connector (not shown) configured to connect to an ICD connector assembly 17, and the distal portion 25 including one or more electrodes. Figure 1A and Figure 1B In the example shown, the distal portion 25 of lead 16 includes defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28, 30, and 31. In some cases, defibrillation electrodes 24 and 26 may form a defibrillation electrode together, as they can be configured to be activated simultaneously. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes, in which case each of electrodes 24 and 26 can be activated independently. In some instances, defibrillation electrodes 24 and 26 are coupled to an electrically isolating conductor, and ICD 14 may include a switching mechanism to allow electrodes 24 and 26 to be used as a single defibrillation electrode (e.g., activated simultaneously to form a common cathode or anode) or as separate defibrillation electrodes (e.g., activated individually, one as a cathode and one as an anode; or activated one at a time, one as an anode or cathode and the other remaining inactive, with housing 15 serving as the active electrode).

[0025] Electrodes 24 and 26 (and in some examples, housing 15) are referred to herein as defibrillation electrodes because they are used, individually or collectively, to deliver high-voltage stimulation therapy (e.g., cardioversion or defibrillation shock). Electrodes 24 and 26 may be elongated coil electrodes and generally have a relatively large surface area for delivering high-voltage electrical stimulation pulses compared to low-voltage pacing and sensing electrodes 28, 30, and 31. However, in addition to or in lieu of high-voltage stimulation therapy, electrodes 24 and 26, along with housing 15, may also be used to provide pacing, sensing, or both pacing and sensing functions. In this sense, the use of the term "defibrillation electrode" herein should not be construed as limiting electrodes 24 and 26 to applications of high-voltage cardioversion / defibrillation shock therapy only. As described herein, electrodes 24 and 26 may be used as pacing electrode vectors for delivering extracardiac pacing pulses (such as ATP pulses) and / or as sensing vectors for sensing cardiac electrical signals and detecting ventricular tachycardia (VT) and ventricular fibrillation (VF).

[0026] Electrodes 28, 30, and 31 are relatively small surface area electrodes used for delivering low-pressure pacing pulses and for sensing cardiac electrical signals. Electrodes 28, 30, and 31 are referred to as pacing / sensing electrodes because they are generally configured for low-pressure applications, for example, as cathodes or anodes for delivering pacing pulses and / or sensing cardiac electrical signals. In some instances, electrodes 28, 30, and 31 may provide pacing-only functionality, sensing-only functionality, or both.

[0027] exist Figure 1A and Figure 1B In the example shown, electrode 28 is positioned proximal to defibrillator electrode 24, and electrode 30 is positioned between defibrillator electrodes 24 and 26. A third pacing / sensing electrode 31 may be positioned distal to defibrillator electrode 26. In other examples, no, one or more pacing / sensing electrodes may be positioned proximal to defibrillator electrode 24; no, one or more pacing / sensing electrodes may be positioned between defibrillator electrodes 24 and 26; and / or no, one or more pacing / sensing electrodes may be positioned distal to defibrillator electrode 26.

[0028] exist Figure 1A and Figure 1B In the example, electrodes 28 and 30 are shown as ring electrodes, and electrode 31 is shown as a hemispherical tip electrode. However, electrodes 28, 30, and 31 can comprise any type of electrode from a variety of different types, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, segmented electrodes, etc., and can be positioned at any location along the distal portion 25 of lead 16. Furthermore, electrodes 28, 30, and 31 can have similar types, shapes, sizes, and materials, or they can differ from each other.

[0029] Lead 16 extends subcutaneously or submuscularly above the thoracic cavity 32 from connector assembly 27 of ICD 14 toward the center of the patient 12's trunk (e.g., toward the xiphoid process 20 of patient 12). Near the xiphoid process 20, lead 16 bends or turns and extends subcutaneously or submuscularly above the thoracic cavity and / or sternum, substantially parallel to the sternum 22. Although in Figure 1A and Figure 1B The lead 16 is shown to be laterally offset from and substantially parallel to the sternum 22. It can be implanted at other locations, such as above the sternum 22, offset to the right or left of the sternum 22, angled laterally to the left or right of the sternum 22, etc. Alternatively, the lead 16 can be placed along other subcutaneous or submuscular pathways. The path of the lead 16 can depend on the location of the ICD 14, the arrangement and location of the electrodes carried by the distal portion 25 of the lead, and / or other factors.

[0030] A conductor (not shown) extends from the lead connector at the proximal lead end 27 through one or more cavities of the elongated lead body 18 of the lead 16 to electrodes 24, 26, 28, 30, and 31 positioned along the distal portion 25 of the lead body 18. The lead body 18 may have a tubular or cylindrical shape. In other examples, the distal portion 25 (or all portions) of the elongated lead body 18 may have a flat, strip-like, or paddle-like shape. The lead body 18 of the lead 16 may be formed of a non-conductive material (including silicone, polyurethane, fluoropolymers, mixtures thereof, and other suitable materials) and shaped to form one or more cavities in which one or more conductors extend. However, the techniques disclosed herein are not limited to this construction or to any particular lead body design.

[0031] Each elongated conductor contained within lead body 18 is electrically coupled to a corresponding defibrillator electrode 24 and 26 and a pacing / sensing electrode 28, 30, and 31. Each of the pacing and sensing electrodes 28, 30, and 31 is coupled to a corresponding conductor, which may be a separate corresponding conductor within the lead body. This corresponding conductor electrically couples electrodes 24, 26, 28, 30, and 31 to the circuitry (such as treatment circuitry and / or sensing circuitry) of ICD 14 via a connection in connector assembly 17 (including an associated electrical feedthrough through housing 15). The conductors transmit treatment from the treatment circuitry within ICD 14 to one or more of the defibrillator electrodes 24 and 26 and / or the pacing / sensing electrodes 28, 30, and 31, and transmit sensed electrical signals from one or more of the defibrillator electrodes 24 and 26 and / or the pacing / sensing electrodes 28, 30, and 31 to the sensing circuitry within ICD 14.

[0032] The ICD 14 can acquire electrical signals corresponding to the electrical activity of the heart 26 via a combination of sensing vectors including combinations of electrodes 28, 30, and / or 31. In some examples, the housing 15 of the ICD 14 is used in combination with one or more electrodes from the sensing electrode vectors of electrodes 28, 30, and / or 31. The ICD 14 can even acquire cardiac electrical signals using sensing vectors including one or two defibrillation electrodes 24 and / or 26 (e.g., between electrodes 24 and 26) or by combining one of electrodes 24 or 26 with one or more electrodes from electrodes 28, 30, and 31 and / or the housing 15.

[0033] The ICD 14 analyzes cardiac electrical signals received from one or more sensing vectors to monitor abnormal rhythms, such as bradycardia, ventricular tachycardia (VT), or ventricular fibrillation (VF). The ICD 14 can perform morphological analysis of heart rate and / or cardiac electrical signals to monitor rapid arrhythmias according to any of a variety of rapid arrhythmia detection techniques. An example technique for detecting rapid arrhythmias is described in U.S. Patent No. 7,761,150 (Ghanem et al.).

[0034] ICD 14 generates and delivers electrical stimulation therapy in response to the detection of a rapid arrhythmia (e.g., VT or VF). ICD 14 may deliver ATP in response to VT detection, and in some cases, ATP may be delivered before or during the charging of the high-voltage capacitor in an attempt to avoid the need for a CV / DF shock. ATP may be delivered using an extracardiac pacing electrode vector selected from any of electrodes 24, 26, 28, 30, 31, and / or housing 15. The pacing electrode vector may differ from the sensing electrode vector. In one example, a cardiac electrical signal is sensed between pacing / sensing electrodes 28 and 30, and an ATP pulse is delivered between pacing / sensing electrode 30, which serves as the cathode, and defibrillation electrode 24, which serves as the return anode. In other examples, an ATP pulse may be delivered between pacing / sensing electrode 28 and either (or both) defibrillation electrodes 24 or 26, or between defibrillation electrodes 24 and 26. These examples are not intended to be limiting, and it is recognized that other sensing electrode vectors and ATP electrode vectors may be selected according to the individual patient's needs.

[0035] The myocardial site first captured by the ATP pulse delivered by the selected extracardiac pacing electrode vector is referred to herein as the "capture site." This capture site is spaced apart from the pacing cathode and pacing anode electrodes, which, in extracardiac ICD systems (such as System 10), do not directly contact the myocardium. A time difference may exist between the time it takes for the R wave to be sensed by the sensing electrode vector and the time it takes for the inherent propagating depolarization associated with the sensed R wave to actually reach the capture site. The distance between the extracardiac electrodes and between the extracardiac electrodes and the heart can result in a significant time difference between the time it takes for the R wave to be sensed by the extracardiac sensing electrode vector and the time for myocardial cell depolarization and repolarization at the capture site. If the tissue at the capture site is in its physiological refractory period when the ATP pulse is delivered, the pulse will not capture the heart.

[0036] To successfully terminate detected VT, all ATP pulses are expected to capture the myocardium, overdrive the heart back to a normal sinus rhythm. For overdrive pacing, each pacing pulse in the ATP sequence should arrive at the capture site after the physiological refractory period following the previous myocardial depolarization and before the next anticipated intrinsic ventricular depolarization. Therefore, ATP pulses can be delivered with a pacing interval shorter than the detected VT interval but longer than the anticipated physiological refractory period following the sensed R wave or the previous ATP pulse. By capturing the myocardium with a leading ATP pulse of a shorter interval than the detected VT interval, the remaining ATP pulses are more likely to capture the myocardium because they will also be properly timed relative to the myocardial refractory period, thus increasing the likelihood of successful VT termination.

[0037] However, a potential time difference between the sensing R wave used to control the timing of the leader ATP pulse and the time of depolarization at the capture site can cause leader ATP pulse capture failure if the capture site is still in the refractory period at the time of pulse delivery. The technique disclosed herein takes into account this potential time difference between the sensing R wave and the actual depolarization and repolarization times at the capture site. In transvenous ICD systems or any system capable of delivering ATP using endocardial or epicardial electrodes in direct or close contact with myocardial tissue, this time difference may be nonexistent or negligible.

[0038] If ATP fails to terminate VT or upon detection of VF, the ICD 14 can deliver one or more cardioversion or defibrillation (CV / DF) shocks via one or both of the defibrillation electrodes 24 and 26 and / or the housing 15. The ICD 14 can deliver CV / DF shocks using electrodes 24 and 26 alone, or by using electrodes 24 and 26 together as a cathode (or anode) and the housing 15 as an anode (or cathode). The ICD 14 can use a pacing electrode vector comprising one or more of electrodes 24, 26, 28, 30, and 31 and the housing 15 of the ICD 14 to generate and deliver other types of electrical stimulation pulses, such as post-shock pacing pulses or bradycardia pacing pulses.

[0039] Figure 1A and Figure 1B This is illustrative in nature and should not be considered as limiting the practice of the techniques disclosed herein. In other examples, lead 16 may include fewer than three pacing / sensing electrodes or more than three pacing / sensing electrodes and / or a single defibrillator electrode or more than two electrically isolated or electrically coupled defibrillator electrodes or electrode segments. Pacing / sensing electrodes 28, 30 and / or 31 may be located elsewhere along the length of lead 16. For example, lead 16 may include a single pacing / sensing electrode 30 between defibrillator electrodes 24 and 26 and may not include pacing / sensing electrodes distal to defibrillator electrode 26 or proximal to defibrillator electrode 24. Various example configurations of cardiovascular external leads and electrodes, as well as their sizes, that can be implemented in conjunction with the cardiovascular external pacing techniques disclosed herein are described in U.S. Publication No. 2015 / 0306375 (Marshall et al.) and U.S. Publication No. 2015 / 0306410 (Marshall et al.).

[0040] ICD 14 is shown subcutaneously implanted along the left side of patient 12 along thoracic cavity 32. In some instances, ICD 14 may be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. However, ICD 14 may be implanted in other subcutaneous or submuscular locations within patient 12. For example, ICD 14 may be implanted in a subcutaneous pouch in the pectoral muscle region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22, and bend or turn downward from the manubrium subcutaneously or submuscularly to the desired location. In yet another example, ICD 14 may be placed in the abdomen. Lead 16 may also be implanted in other extravascular locations. For example, as per [reference to...] Figure 2A-2C As described, the distal portion 25 of the lead 16 can be implanted under the sternum / pleural cavity in the substernal space.

[0041] External device 40 is shown as telemetry communicating with ICD 14 via communication link 42. External device 40 may include a processor, display, user interface, telemetry unit, and other components for communicating with ICD 14 to transmit and receive data via communication link 42. A radio frequency (RF) link (such as...) can be used. A communication link 42 is established between ICD 14 and external device 40 (using Wi-Fi or Medical Implantable Communication Service (MICS) or other RF or communication bands).

[0042] External device 40 can be implemented as a programmer for use in hospitals, clinics, or physicians' offices to retrieve data from ICD 14 and program operating parameters and algorithms into ICD 14 for controlling ICD 14 functions. External device 40 can be used to program cardiac rhythm detection parameters and therapeutic control parameters used by ICD 14. Control parameters for generating and delivering ATP according to the techniques disclosed herein can be programmed into ICD 14 using external device 40.

[0043] Data stored or acquired by the ICD 14 (including physiological signals or associated data derived therefrom, device diagnostic results, and a history of detected rhythmic events and delivered treatments) can be retrieved from the ICD 14 by an external device 40 upon request. The external device 40 may alternatively be implemented as a home monitor or a handheld device.

[0044] Figure 2A-2C Therefore, with Figure 1A-1B The diagram shows a concept of a patient 12 with an extra-cardiovascular ICD system 10 implanted, arranged in different implant configurations. Figure 2A This is a front view of a patient 12 with an ICD system 10 implanted. Figure 2B This is a side view of patient 12 with an implanted ICD system 10. Figure 2C This is a transverse view of a patient 12 with an ICD system 10 implanted. In this arrangement, the lead 16 of the system 10 is at least partially implanted under the sternum 22 of the patient 12. The lead 16 extends subcutaneously or submuscularly from the ICD 14 toward the xiphoid process 20, and bends or turns near the xiphoid process 20 and extends upward in a substernal position within the anterior mediastinum 36.

[0045] The anterior mediastinum 36 can be considered as being transversely defined by the pleura 39, posteriorly defined by the pericardium 38, and anteriorly defined by the sternum 22. In some instances, the anterior wall of the anterior mediastinum 36 may also be formed by the transverse thoracic muscle and one or more costal cartilages. The anterior mediastinum 36 includes a certain amount of loose connective tissue (such as celluloid), adipose tissue, some lymphatic vessels, lymph nodes, substernal muscle tissue, small lateral branches of the internal thoracic artery or vein, and the thymus. In one example, the distal portion 25 of the lead 16 extends substantially along the posterior side of the sternum 22 within the loose connective tissue and / or substernal muscle tissue of the anterior mediastinum 36.

[0046] A suture implanted such that the distal portion 25 is essentially within the anterior mediastinum 36 can be referred to as a "substernal suture." Figure 2A In the example shown in -C, lead 16 is substantially centered below sternum 22. However, in other instances, lead 16 may be implanted such that it is laterally offset from the center of sternum 22. In some instances, lead 16 may extend laterally such that the distal portion 25 of lead 16 is located below / below thoracic cavity 32, other than or in place of sternum 22. In other instances, the distal portion 25 of lead 16 may be implanted in other extracardiac intrathoracic locations (including pleural cavity) or around and near, but not typically within, the pericardial lining 38 of heart 26. Other implantation sites and lead and electrode arrangements that can be used in conjunction with the cardiac pacing techniques described herein are generally disclosed in the patent applications identified above.

[0047] Figure 3 It shows the curved distal portion 25' with a lead body 18'. Figure 1A-2C A conceptual diagram of the distal portion 25' of another example of the cardiovascular external lead 16. The lead body 18' can be formed to have a curved, bent, meandering, or serrated shape along the distal portion 25'. In the example shown, defibrillation electrodes 24' and 26' are carried along the curved portion of the lead body 18'. A pacing / sensing electrode 30' is carried between defibrillation electrodes 24' and 26'. A pacing / sensing electrode 28' is carried proximal to the proximal defibrillation electrode 24'. In this example, no electrode is provided distal to the defibrillation electrode 26'.

[0048] like Figure 3As shown, lead 18' can be formed with a curved distal portion 25' comprising two "C"-shaped curves, which together can resemble the Greek letter epsilon "ε". Defibrillation electrodes 24' and 26' are each carried by one of two corresponding C-shaped portions of the distal portion 25', which extend or curve in the same direction away from the central axis 31 of lead 18'. In the example shown, pacing / sensing electrode 28' is proximal to the C-shaped portion carrying electrode 24', and pacing / sensing electrode 30' is proximal to the C-shaped portion carrying electrode 26'. In some instances, pacing / sensing electrodes 28' and 30' can be approximately aligned with the central axis 31 of the straight proximal portion of lead 18', such that the midpoints of defibrillation electrodes 24' and 26' are laterally offset from electrodes 28' and 30'. Other examples of cardiovascular external leads that can be implemented using the pacing techniques described herein are generally disclosed in U.S. Patent Publication No. 14 / 963,303, which include one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by a curved, meandering, wavy, or serrated distal portion of the lead body.

[0049] Figure 4 This is a schematic diagram based on an example ICD 14. Enclosed in housing 15 (in...) Figure 4 The electronic circuitry system within the ICD (illustrated schematically as an electrode) includes software, firmware, and hardware that collaboratively monitors one or more cardiac electrical signals, determines when electrical stimulation therapy is needed, and delivers therapy as needed according to a programmed therapy delivery algorithm and control parameters. The software, firmware, and hardware are configured to detect and differentiate between VT and VF to determine when ATP or CV / DF shocks are required. The ICD 14 is coupled to a cardiovascular external lead, such as lead 16 carrying cardiovascular external electrodes 24, 26, 28, 30, and 31, for delivering electrical stimulation pulses to the patient's heart and for sensing cardiac electrical signals.

[0050] The ICD 14 includes control circuitry 80, memory 82, therapeutic delivery circuitry 84, sensing circuitry 86, and telemetry circuitry 88. A power supply 98 provides power to the circuitry of the ICD 14 (including each of components 80, 82, 84, 86, and 88) as needed. The power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between the power supply 98 and each of the other components 80, 82, 84, 86, and 88 will be made from... Figure 4The overall block diagram is for understanding purposes, but is not shown for clarity. For example, power supply 98 may be coupled to low-voltage and high-voltage charging circuits included in therapeutic delivery circuit 84 to charge low-voltage and high-voltage capacitors included in therapeutic delivery circuit 84, respectively, to generate corresponding low-voltage pacing pulses (such as bradycardia pacing, post-shock pacing, or ATP pulses), or to generate high-voltage pulses, such as CV / DF shock pulses. In some examples, the high-voltage capacitor is charged instead of the low-voltage capacitor and used for ATP delivery.

[0051] Figure 4 The functional blocks shown represent the functions included in ICD 14 and may include any discrete and / or integrated electronic circuitry components that implement analog and / or digital circuitry capable of producing the functions attributed to ICD 14 herein. Various components may include application-specific integrated circuits (ASICs), electronic circuitry, processors (shared, dedicated, or grouped) and memories executing one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components that provide the described functions. The specific form of the software, hardware, and / or firmware used to implement the functions disclosed herein will be determined primarily by the specific system architecture employed in the device and the specific detection and treatment delivery methods employed by ICD 14. In light of the disclosure herein, providing the software, hardware, and / or firmware to implement the described functions within the context of any modern ICD system is within the capabilities of those skilled in the art.

[0052] Memory 82 may include any volatile, non-volatile, magnetic, or electrically non-transient computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device. Furthermore, memory 82 may include a non-transient computer-readable medium storing instructions that, when executed by one or more processing circuits, cause control circuitry 80 or other ICD components to perform various functions belonging to ICD 14 or those ICD components. The non-transient computer-readable medium storing instructions may include any of the media listed above.

[0053] The functions attributed to ICD 14 in this document can be implemented as one or more integrated circuits. Describing different features as components (e.g., circuits) is intended to emphasize different functional aspects and does not necessarily imply that these components (e.g., circuits or modules) must be implemented by separate hardware or software components. Rather, the functions associated with one or more components can be performed by separate hardware, firmware, or software components, or integrated within common hardware, firmware, or software components. For example, ATP delivery operations can be performed by therapeutic delivery circuit 84 under the control of control circuit 80, and can include operations implemented in a processor executing instructions stored in memory 82, as well as control signals, such as timing and pacing pulse amplitude signals, sent from control circuit 80 to therapeutic delivery circuit 84.

[0054] Control circuit 80 communicates, for example, via a data bus with treatment delivery circuit 84 and sensing circuit 86 for sensing cardiac electrical activity, detecting heart rhythm, and controlling the delivery of cardiac electrical stimulation therapy in response to sensed cardiac signals. Treatment delivery circuit 84 and sensing circuit 86 are electrically coupled to electrodes 24, 26, 28, and 30 (and 31, if present) carried by leads 16 (e.g., as shown in the image). Figure 3 (as shown in the figure), and housing 15, which can be used as a common electrode or ground electrode or as an active can electrode for delivering CV / DF electric shock pulses or ATP pulses.

[0055] The sensing circuit 86 may be selectively coupled to electrodes 28, 30 and housing 15 to monitor the electrical activity of a patient's heart. The sensing circuit 86 may also be selectively coupled to defibrillation electrodes 24 and / or 26 for use in sensing electrode vectors. The sensing circuit 86 is enabled to selectively monitor one or more sensing vectors selected from available electrodes 24, 26, 28, 30 and housing 15 at a given time. For example, the sensing circuit 86 may include a switching circuitry system for selecting which of electrodes 24, 26, 28, 30 and housing 15 are coupled to a sensing amplifier or other cardiac event detection circuitry system included in the sensing circuit 86. The switching circuitry system may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable for selectively coupling components of the sensing circuit 86 to selected electrodes. In some cases, control circuitry 80 may control the switching circuitry system to selectively couple the sensing circuit 86 to one or more sensing electrode vectors. The cardiac event detection circuitry system within the sensing circuit 86 may include one or more sensing amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other analog or digital components.

[0056] In some examples, the electrical sensing circuit 86 includes multiple sensing channels for acquiring cardiac electrical signals from multiple sensing vectors selected from electrodes 24, 26, 28, 30, and housing 15. Each sensing channel can be configured to amplify, filter, and rectify the cardiac electrical signal received from selected electrodes coupled to the corresponding sensing channel to improve signal quality for sensing cardiac events (e.g., R waves). For example, each sensing channel may include a pre-filter and an amplifier for filtering and amplifying the signal received from a selected pair of electrodes. The resulting raw cardiac electrical signal can be passed from the pre-filter and amplifier to a cardiac event detection circuitry system for sensing cardiac events from the received cardiac electrical signal. The cardiac event detection circuitry system may include a rectifier, a post-filter and amplifier, a sensing amplifier, a comparator, and / or an analog-to-digital converter for detecting cardiac events when the cardiac electrical signal crosses a sensing threshold. The sensing threshold can be set by control circuitry 80 based on a value stored in memory 82, which can be programmed by a user and passed from control circuitry 80 to sensing circuitry 86 via a data bus. The sensing circuit 86 may include an automatically adjusting sensing amplifier that, in some examples, compares a cardiac signal that has decayed from an initial value to a minimum sensing floor with a sensing threshold.

[0057] Upon detecting a cardiac event, the sensing circuit 86 can generate a sensing event signal, such as an R-wave sensing event signal, which is transmitted to the control circuit 80. The control circuit 80 uses the sensing event signal to detect heart rhythm and determine the need for treatment. The sensing circuit 86 can also transmit a digital electrocardiogram (ECG) signal to the control circuit 80 for morphological analysis to be performed to detect and differentiate heart rhythms.

[0058] Signals from the selected sensing vector can be passed through a bandpass filter and amplifier, provided to a multiplexer, and subsequently converted into multi-bit digital signals by an analog-to-digital converter. All these signals are included in sensing circuitry 86 for storage in random access memory (RAM) included in memory 82 via a data / address bus under the control of direct memory access circuitry. Control circuitry 80 can be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in RAM 82, using any of the numerous signal processing methods available for analyzing cardiac signals and cardiac event waveforms (e.g., R waves) to identify and classify the patient's heart rhythm. A tachyarrhythmia detection system is described in U.S. Patent No. 5,545,186 (Olson et al.).

[0059] The treatment delivery circuit 84 includes a charging circuit system, one or more charge storage devices (such as one or more high-voltage capacitors and, in some examples, one or more low-voltage capacitors), and a switching circuit system for controlling when the capacitors(multiple) discharge at selected pacing electrode vectors or CV / DF shock vectors. The treatment delivery circuit 84 may, based on control signals received from the control circuit 80, perform actions such as charging the capacitors to a programmed pulse amplitude and discharging the capacitors to a programmed pulse width. The control circuit 80 may include various timers or counters for controlling when to deliver ATP pulses.

[0060] For example, control circuit 80 may include a pacemaker timing and control circuitry system having a programmable digital counter set by a microprocessor of control circuit 80 for controlling the basic time intervals associated with various pacing modes or anti-tachycardia pacing sequences delivered by ICD 14. The microprocessor of control circuit 80 may also set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses, based on programmed values ​​stored in memory 82.

[0061] During pacing, the escape interval counter within the pacemaker timing and control circuitry is reset upon sensing an R wave (as indicated by a signal from sensing circuitry 86). Depending on the selected pacing mode, a pacing pulse is generated by the pulse output circuitry of treatment delivery circuitry 84. The pacing output circuitry is coupled via a switch matrix to the desired electrode for discharging one or more capacitors across the pacing load. The escape interval counter is reset upon generating the pacing pulse, thereby controlling the basic timing of cardiac pacing functions, including antitachycardia pacing. The duration of the escape interval is determined by control circuitry 80 via a data / address bus. The count value presented in the escape interval counter, when reset by the sensed R wave, can be used to measure the RR interval for detecting the occurrence of various arrhythmias.

[0062] The memory 82 includes a read-only memory (ROM) in which the program controlling the operation of the control circuit 80 resides. The memory 82 may further include random access memory (RAM) configured as a plurality of recirculation buffers capable of storing a series of measured intervals for analysis by the control circuit 80 for the prediction or diagnosis of arrhythmias.

[0063] In response to the detection of ventricular tachycardia, antitachycardia pacing therapy can be delivered by loading a scheme from a microprocessor included in control circuitry 80 into pacemaker timing and control circuitry according to the type and rate of the detected tachycardia. As described below, according to the techniques disclosed herein, the microprocessor or other control circuitry system included in control circuitry 80 can be programmed or configured to determine a reference point between an R-wave sensed by sensing circuitry 86 using a first sensing electrode vector (e.g., between pacing / sensing electrodes 28 and 30 as shown in FIG. 1) and an R-wave signal obtained by sensing circuitry 86 using a second sensing electrode vector (e.g., between pacing / sensing electrode 30 and defibrillation electrode 24). The second sensing electrode vector may be an electrode vector for ATP delivery, or may include at least one electrode for ATP delivery, e.g., between pacing / sensing electrode 30, which serves as a cathode, and defibrillation electrode 24, which serves as a return anode.

[0064] In response to the detection of a VT, the microprocessor of control circuit 80 can determine the VT cycle length (e.g., using a counter for determining the time interval between consecutive R-wave sensing event signals). Based on the VT cycle length, control circuit 80 can calculate a desired ATP interval as a portion of the VT cycle length. However, the microprocessor of control circuit 80 can determine a longer leading ATP interval than the desired ATP interval to control the timing of the leading ATP pulse. The microprocessor can load the extended ATP interval and the desired ATP interval into the pacemaker timing and control circuitry system for controlling the timing of each pulse in the ATP sequence. For example, a timer or counter in the pacemaker timing and control circuitry can be set to the extended ATP interval to control the timing of the leading ATP pulse of the ATP sequence delivered by treatment delivery circuitry 84. Subsequently, one or more timers can be set to the desired ATP interval to control subsequent ATP pulses following the leading pulse of the ATP sequence. The leading extended ATP interval can be determined by the microprocessor to be a predetermined interval at least longer than the desired ATP interval. When an ATP sequence is delivered via a cardiovascular pacing electrode vector, and there is a time difference between the time when the R wave is sensed by the sensing circuit 86 and the time when the propagation depolarization associated with the sensed R wave reaches the capture site of the myocardium, this prolonged lead ATP interval promotes a high probability of myocardial capture.

[0065] In cases requiring higher voltage cardioversion or defibrillation pulses, the control circuit microprocessor activates the cardioversion and defibrillation control circuitry system included in control circuitry 80 to initiate charging of a high-voltage capacitor via a charging circuit, both of which are included in treatment delivery circuitry 84, under the control of a high-voltage charging control line. The voltage on the high-voltage capacitor is monitored via a voltage capacitor line (which passes through control circuitry 80). When the voltage reaches a predetermined value set by the microprocessor of control circuitry 80, a logic signal is generated on the full line of the capacitor transmitted to treatment delivery circuitry 84, terminating charging. Under the control of the pacemaker timing and control circuitry system, the output circuitry of treatment delivery circuitry 84 delivers defibrillation and cardioversion pulses to the heart via a control bus. The output circuitry determines the electrodes used for delivering the cardioversion and defibrillation pulses and the pulse waveform. The treatment delivery and control circuitry system disclosed in any of the patents identified above can typically be implemented in ICD 14.

[0066] Control parameters used by control circuit 80 to detect heart rhythm and control treatment delivery can be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes features for communication with external device 40 using RF communication as described above. Figure 1A The transceiver and antenna (shown in the diagram) communicate. Under the control of the control circuit 80, the telemetry circuit 88 can receive downlink telemetry from the external device 40 and send uplink telemetry to the external device 40. In some cases, the telemetry circuit 88 can be used to send communication signals to and receive communication signals from another medical device implanted in the patient 12.

[0067] Figure 5 Figure 100 shows an ECG signal 102 that can be acquired by sensing circuit 85 using an extra-cardiac sensing electrode vector, and an ECG signal 110 representing the cardiac electrical signal occurring at the effective capture site of the extra-cardiac pacing electrode vector. ECG signal 102 includes an R wave 104 sensed by sensing circuit 86 at time 105. The next intrinsic R wave 106 is shown occurring at VT interval 108. ATP interval 120 can be calculated by control circuit 80 based on VT interval 108 as, for example, 80% or other percentage of the VT interval.

[0068] The ECG signal 110, representing the cardiac electrical signal occurring at the capture site, includes an R wave 114 occurring at a time interval 112 after the sensing circuit 86 senses the R wave 104. The pacing pulse delivered from the R wave sensing event signal generated by the sensing circuit 86 to the calculated ATP interval 120 can occur during the myocardial refractory period at the capture site, which includes the repolarization phase represented by the T wave 115. If a leader ATP pulse is delivered during the myocardial refractory period, the ATP pulse may fail to capture the myocardium. When the VT cycle length remains relatively stable and the leader ATP pulse fails to capture, subsequent ATP pulses may also arrive during the refractory period of subsequent cardiac cycles, making it possible for all ATP pulses to fail to capture the heart and successfully terminate VT.

[0069] A leader pacing pulse 126 of the ATP sequence, delivered by an external cardiovascular electrode, is delivered from an R-wave sensing event signal corresponding to the sensed R-wave 104 with an extended ATP interval 124. In some examples, the extended ATP interval 124 may be set to the VT cycle length 108. The leader ATP pulse 126 may arrive just before or during local depolarization at the capture site, as indicated by the R-wave 116, and may or may not capture the heart. However, the next pacing pulse 128 of the ATP sequence is delivered after the leader pulse 126 with an ATP interval 120, and is expected outside the refractory period following the previous R-wave 116. The extended ATP interval 124 can alternatively be set to a predetermined short interval less than the VT cycle length 108 (e.g., 10 ms shorter than the VT cycle length), or set to a higher percentage of the VT cycle length (e.g., 90% to 95% of the VT cycle length) compared to a relatively low percentage (e.g., 80% to 85% of the VT cycle length) used to calculate the ATP interval 120. Subsequent ATP pulses following the leader pulse 126 are delivered according to a desired ATP protocol (e.g., burst, ramp, burst plus ramp, or other desired ATP sequences). Numerous patents describe ATP protocols that can be used to control subsequent pulses of an ATP sequence, including U.S. Patent No. 5,458,619 (Olson) and U.S. Patent No. 6,167,308 (DeGroot).

[0070] In other examples, in response to the detection of VT, control circuitry 80 may enable sensing circuitry 86 to acquire cardiac electrical signals using one or both of the electrodes (cathode and / or anode) included in the pacing electrode vector for ATP delivery. For example, the pacing electrode vector cathode may be used in conjunction with the pacing electrode vector anode or another selected electrode or ICD housing 15 to sense cardiac electrical signals 110 prior to the delivery of the lead ATP pulse 126. The time interval 112 (also referred to herein as the “time difference interval” or simply the “difference interval”) may be determined by control circuitry 80 as the interval from the time R wave 104 sensed by sensing circuitry 86 to the threshold crossover point of R wave 114 acquired using at least one electrode in the pacing electrode vector, the maximum dV / dt of R wave 114, the maximum rectified peak amplitude of R wave 114, or other reference points of R wave 114.

[0071] Control circuit 80 can determine an extended ATP interval 120 for controlling the timing of the leader ATP pulse 126 by adding a difference interval 112 to an ATP interval 120 determined based on the VT cycle length 108. Alternatively, an ATP extension interval 122 longer than the difference interval 112 can be determined by adding a predetermined fixed interval or percentage of the difference interval 112 to the difference interval 112. The ATP extension interval 122 can be added to the calculated ATP interval 120 for controlling the delivery of the leader ATP pulse 126 at the extended ATP interval 124. The next ATP pulse 128 can be delivered at the determined ATP interval 120. Subsequent ATP pulses of the ATP sequence are delivered at the ATP interval 120 or according to the desired ATP protocol. It is understood that... Figure 5 The various time intervals represented in the diagram (e.g., VT cycle length 108, calculated ATP interval 120, differential interval 112, extended interval 122, and extended ATP interval 124) can be determined by a microprocessor included in the control circuit 80 using cardiac event signals received from the sensing circuit 86 over multiple cardiac cycles.

[0072] Figure 6 This is a flowchart 200 illustrating an example method for delivering ATP using an extravascular ICD system. At box 202, ICD 14 detects VT according to an implemented rapid arrhythmia detection algorithm. This is achieved from one or more sensing electrode vectors (e.g., in...). Figure 1A-3 VT is detected in the cardiac electrical signal received between electrodes 28 and 30 shown, or any of the sensing electrode vectors described above. At block 204, control circuitry 80 determines the VT cycle length. The VT cycle length (e.g., Figure 5The VT cycle length 108 can be determined based on the interval between R-wave sensing event signals received from the electrical sensing circuit 86. The VT cycle length determined by the control circuit 80 is determined based on cardiac electrical signals (multiple) acquired using sensing electrode vectors (multiple).

[0073] At box 206, control circuitry 80 determines the desired ATP interval based on the VT cycle length. The desired ATP interval can be a predetermined percentage of the VT cycle length, such as 80%, 85%, or 90% of the VT cycle length. Alternatively, the desired ATP interval can be a predetermined amount of time less than the VT cycle length, for example, 20 ms to 50 ms shorter than the determined ATP interval. At box 208, control circuitry 80 enables therapeutic delivery circuitry 84 to deliver a lead ATP pulse with an extended ATP interval longer than the desired ATP interval. In one example, the lead ATP pulse is delivered at box 208 at the VT cycle length. In another example, the lead ATP pulse is delivered with an interval slightly shorter than the VT cycle length (e.g., 10 ms shorter, but longer than the desired ATP interval determined at box 206).

[0074] The leading ATP pulse is synchronized to the R wave sensed by the sensing electrode vector using the sensing electrode vector. For example... Figure 5 As shown, R-wave 104 can be sensed at time 105. Control circuit 80 can initiate a leading ATP interval 124, which is set to be equal to the VT cycle length 108 or equal to an interval slightly shorter than the VT cycle length but longer than the desired ATP interval 120. When the leading ATP interval 124 expires, a leading ATP pulse 126 is delivered.

[0075] Depending on its timing relative to the next inherent depolarization occurring at the capture site, the leader ATP pulse may or may not capture the heart at the capture site. (See again) Figure 5 If the difference in time 112 between the sensing of the R wave 104 and the sensing of the R wave 104 from the sensing electrode vector is negligible, such that the associated depolarization at the capture site occurs substantially at the same time as the sensing of the R wave, then the leading ATP pulse 126 may not capture at the capture site or may result in fusion beating. Fusion beating occurs when some cardiomyocytes are depolarized by the delivered pacing pulse while other cardiomyocytes are depolarized by the propagating intrinsic depolarization wavefront.

[0076] In response to the leader pulse 126 at the capture site, regardless of whether capture, fusion, or non-capture occurs, the next ATP pulse 128 is appropriately timed to capture myocardium at the capture site, outside the physiological refractory period, and before the next inherent depolarization at the capture site. In this example, where the difference interval 112 is negligible, the leader ATP pulse 126 can be delivered with the desired ATP interval 120, and myocardium can be successfully captured at the capture site outside the physiological refractory period. However, delivering the leader ATP pulse 126 with a prolonged ATP interval 124 promotes a high probability that all subsequent ATP pulses will be outside the physiological refractory period, even if it is unknown whether the difference interval 112 is negligible. In other words, in the method of flowchart 200, control circuit 80 is not required to determine the difference interval 112.

[0077] When the difference interval 112 between the time 105 when R wave 104 is sensed and the time when depolarization actually occurs at the capture site is clinically significant, the leader ATP pulse 126, set to the VT cycle length, will occur earlier than the next intrinsic depolarization at the capture site. As a result, the leader ATP pulse 126 will capture the myocardium at the capture site and may occur outside the refractory period of the preceding intrinsic depolarization at the capture site. The next ATP pulse 128, delivered at the desired ATP cycle length, is appropriately timed outside the refractory period following the pacing-induced depolarization at the capture site and at the expected desired ATP interval 120. By delivering the leader pulse 126 at the VT cycle length or a slightly shorter interval than the VT cycle length but extended from the desired ATP interval 120, regardless of the difference interval 112, the next ATP pulse 128 and all subsequent ATP pulses ( Figure 5 (Not shown in the image) will be appropriately timed to capture myocardium outside the physiological refractory period at the capture site.

[0078] Return to Figure 6 Flowchart 200, where further reference is made. Figure 5At box 210, the next ATP pulse 128 is delivered after the lead ATP pulse with a desired ATP interval 120. At box 212, all subsequent ATP pulses are delivered according to the programmed ATP sequence. In one example, a sequence of 8 to 12 pulses is delivered with a desired ATP interval 120, in addition to delivering the lead pulse with an extended interval. However, in other instances, the ATP sequence may include fewer than 8 pulses or more than 12 pulses. When the lead ATP pulse is delivered with an extended interval 124, the sequence may be extended by one pulse to ensure that the minimum desired number of ATP pulses capture the heart. For example, if the programmed ATP sequence is 8 pulses, the total number of pulses may be 9, including the lead pulse. Control circuitry 80 determines whether ATP treatment has successfully terminated VT and responds with additional treatment as needed if VT is re-detected or VF is detected after ATP completion.

[0079] Figure 7 This is a flowchart 300 of a method for delivering ATP by an extra-cardiac ICD system, according to another example. At block 302, ICD 14 detects VT according to an implemented detection algorithm. Control circuitry 80, as previously described, determines the VT cycle length, for example, from the RR interval between R-wave sensing event signals generated by sensing circuitry 86. The VT cycle length is determined from cardiac electrical signals acquired using sensing electrode vectors. At block 306, control circuitry 80 determines the desired ATP interval based on the VT cycle length, as described above. Figure 5 and Figure 6 As described.

[0080] In response to the detection of VT, control circuit 80 enables sensing circuit 86 to acquire a cardiac electrical signal at block 308 using a second sensing electrode vector, which is the same as the pacing electrode vector used for ATP delivery. In other examples, a second sensing electrode vector is used to acquire a second cardiac electrical signal acquired at block 308, which includes at least one electrode among the electrodes used in the pacing electrode vector, for example, at least a pacing cathode or at least a pacing anode. To determine a reliable estimate of the time interval between the R-wave sensing event signal from the first sensing electrode vector and depolarization at the capture site, in one example, at least a pacing cathode electrode may be used to acquire the second cardiac electrical signal acquired at block 308. The pacing electrode vector and the first sensing electrode vector are different vectors. The pacing electrode vector and the second sensing electrode vector may be the same vector or have at least one common electrode.

[0081] At box 310, control circuit 80 determines the difference interval 112 ( Figure 5The difference interval 112 can be determined by identifying a reference point of the R-wave of a second cardiac electrical signal received using a second sensing electrode vector included in one or both of the pacing electrode vectors. As described above, the reference point can be, but is not limited to, a threshold crossover point, the maximum peak amplitude of the rectified cardiac electrical signal, or the maximum dV / dt. The difference interval 112 can be determined as the time interval from the R-wave sensing event signal generated using the first sensing electrode vector to the reference point determined from the second sensing electrode vector. In other examples, a similar reference point of the R-wave of the first sensing electrode vector signal can be determined, and the difference interval 112 is determined between the reference point of the R-wave from the first sensing electrode vector signal and a similar reference point of the R-wave from the second sensing electrode vector signal, which can be a pacing vector or include at least one electrode in a pacing electrode vector for ATP delivery.

[0082] At block 312, control circuit 80 determines and sets an extended ATP interval. The extended ATP interval is determined based on the difference interval determined at block 310 and the VT cycle length determined at block 304 and / or the desired ATP interval determined at block 306. For example, the extended ATP interval can be set to the desired ATP interval determined at block 306 plus the determined difference interval. Upon sensing an R-wave from the first sensing electrode vector (e.g., upon receiving an R-wave sensing event signal from sensing circuit 86), the extended ATP interval is initiated by the pacemaker timing and control circuitry system of control circuit 80. The extended ATP interval can be set to at least the desired ATP interval plus the difference interval, up to the VT cycle length plus the difference interval. In this way, the lead ATP pulse has a high probability of being delivered outside the myocardial refractory period at the capture site.

[0083] At box 314, a lead ATP pulse is delivered by the treatment delivery circuit 84 upon the expiration of the extended ATP interval. At box 316, the actual lead ATP interval can be stored for use in ATP feedback and analysis algorithms. The actual lead ATP interval is based on the time of the most recent intrinsic depolarization at the myocardium, as estimated by the R-wave reference point of the second cardiac electrical signal acquired via the second sensing electrode vector used to determine the difference interval 112. The actual lead ATP interval is the time from the reference point to the lead ATP pulse, for example, Figure 5 The interval is 130. This actual leading ATP interval can be used when assessing the effectiveness of ATP therapy in terminating VT.

[0084] At box 318, a second ATP pulse (following the leader ATP pulse) is delivered at the desired ATP interval determined at box 306 based on the detected VT cycle length. According to the programmed ATP treatment protocol, all remaining ATP pulses are delivered at box 320. For example, a sequence of 8 to 12 pulses can be delivered at the ATP interval determined at box 306. In other examples, a ramp sequence of ATP pulses can be delivered, where the interval between each consecutive ATP pulse is shorter than the interval of the immediately preceding ATP pulse. It is recognized that numerous ATP sequences defining the number and interval of ATP pulses following the leader pulse can be used according to the ATP treatment implemented in ICD 14.

[0085] In some examples, if ATP fails to terminate the detected tachycardia, the stored actual leading ATP interval can be used to adjust the extended ATP interval for subsequent ATP sequences. For example... Figure 7 As shown, if VT is not re-detected at box 322, the ICD can return to box 302 to await the next VT detection. If VT is re-detected, the extended ATP interval is adjusted at box 324 so that it differs from the extended ATP interval used to deliver the first ATP sequence. The adjusted extended ATP interval can be set to be equal to or less than the VT cycle length, but greater than the VT cycle length minus the time difference interval determined at box 310. The adjusted extended ATP interval can be longer or shorter than the first extended ATP interval, depending on the actual leading ATP interval determined at box 316. For example, if the actual leading ATP interval is found to be shorter than the ATP interval determined at box 306 or shorter than the VT cycle length minus the time difference interval, the adjusted extended ATP interval can be increased. If the actual leading ATP interval is determined to be longer than the VT cycle length, the extended ATP interval can be shortened.

[0086] At block 326, control circuit 80 controls therapeutic delivery circuit 84 to deliver a second sequence of ATP pulses, the second sequence of ATP pulses having a leader pulse delivered after a cardiac event sensed by sensing electrode vector by sensing circuit 86 with an adjusted extended ATP interval, and a next ATP pulse delivered after the leader pulse with a desired ATP interval determined at block 306. Figure 7 The example shown involves delivering two ATP sequences in an attempt to terminate VT. It should be recognized that more than two ATP sequences may be delivered to terminate VT. It should be understood that if the maximum number of ATP sequences delivered fails to terminate VT, a cardioversion / defibrillation shock may be delivered by ICD 14.

[0087] Figure 8This is a flowchart 400 of a method for controlling ATP delivery by an extravascular ICD system, according to another example. At box 402, ICD 14 detects VT and delivers ATP at box 404, the ATP comprising a leader ATP pulse delivered with an extended ATP interval, the extended ATP interval being set based on determining the VT cycle length and the differential interval, as combined with... Figure 7 The flowchart 300 describes this. At box 406, the actual ATP interval of the leader pulse is determined as the difference between the differential interval and the prolonged ATP interval. For example, as... Figure 5 As shown, the actual leading ATP interval 130 is the extended ATP interval 124 minus the differential interval 112.

[0088] At box 408, the actual prematureity of the leader pulse is determined by control circuit 80. The prematureity of an individual ATP pulse is typically the difference between the ATP interval and the VT cycle length, used to control the timing of ATP pulse delivery. However, in the case of the extravascular ICD system 10, the actual prematureity of the leader pulse in a series of ATP pulses will depend on the difference interval 112 ( Figure 5 In this way, it can be Figure 5 The actual early onset of the leader pulse 126 shown is determined as the VT cycle length 108 minus the extended ATP interval 124 plus the differential interval 112.

[0089] If N pulses of ATP sequence are delivered, then the desired ATP interval is determined (e.g., Figure 5 The ATP interval 120 shown delivers all remaining ATP pulses. The individual premature onset of each of the remaining ATP pulses (i.e., the second to Nth pulses) is the VT cycle length 108 minus the ATP interval 120. The control circuit 80 can be configured at block 410 to determine the total premature onset of ATP treatment as the sum of the individual premature onsets of all pulses in the ATP sequence. In one example, if the VT cycle length is 380 ms, the ATP interval 120 can be determined to be 305 ms (approximately 80% of the VT cycle length). If a sequence of 8 pulses is delivered, the second to eighth pulses each have an individual premature onset of 75 ms. If the extended ATP interval 124 is set to the VT cycle length minus 10 ms or 370 ms, and the differential interval is determined to be 20 ms, the individual premature onset of the leader pulse is 10 ms (380 ms minus 370 ms plus 20 ms). The total premature occurrence of the 8 pulse sequences was approximately 535 ms (10 ms premature occurrence of the leader pulse plus 7 times the individual premature occurrence of the remaining 7 pulses, totaling 75 ms).

[0090] At box 412, the control circuitry can determine the return cycle length after the last ATP pulse as the time from the last ATP pulse to the earliest occurrence of the R wave after the last ATP pulse. If VT is not re-detected after ATP, as determined at box 414, the ATP sequence is successful, as indicated at box 416. However, if VT is re-detected at box 414, the control circuitry 80 can determine a new ATP sequence with adjusted total early activation based on the total early activation of delivered ATP and the return cycle length determined at box 412. It may be necessary to increase the total early activation to successfully terminate VT. Techniques for analyzing the response to ATP therapy and adjusting the total early activation in response to the re-detection of VT are generally disclosed in U.S. Patent No. 8,706,221 (Belk et al.).

[0091] At box 418, total early onset can be increased by increasing the individual early onset of one or more pulses in the ATP sequence and / or increasing the total number of pulses in the ATP sequence. In one example, the individual early onset of the leading ATP pulse is increased by shortening the extended ATP interval to a minimum leading ATP interval not less than the desired ATP interval 120 plus the difference interval 112. At box 420, the adjusted ATP sequence with increased total early onset is delivered. This process can be repeated by returning to box 406 to allow for multiple ATP attempts using the actual early onset of the leading ATP pulse to determine the total early onset of the ATP sequence, for feedback in making adjustments to the ATP therapy. While in Figure 8 While not explicitly shown, it is recognized that a maximum number of ATP attempts can be made before delivering electrical shock therapy to terminate a VT rhythm that was not successfully terminated by ATP therapy. For example, at box 418, the total premature onset can be adjusted after the first ATP attempt, and an adjusted ATP sequence with increased total premature onset can be delivered at box 418 without returning to box 406. If VT is detected again after a second ATP attempt, control circuit 80 can control treatment circuit 84 to deliver electrical shock therapy to terminate VT. It is further recognized that if VT accelerates to the point that VF is detected after any ATP attempt, electrical shock therapy can be delivered as needed to terminate the tachyarrhythmia.

[0092] Therefore, methods and apparatus for delivering anti-tachycardia pacing pulses using cardiovascular external electrodes have been presented in the foregoing description with reference to specific embodiments. In other examples, the various methods described herein may include steps performed in a different order or combination than those shown and described herein. It should be understood that various modifications may be made to the reference embodiments without departing from the scope of this disclosure and the appended claims.

Claims

1. A medical device comprising: sensing circuitry configured to: receive a first cardiac electrical signal; and sense, from the first cardiac electrical signal, first cardiac events each associated with a myocardial depolarization; control circuitry coupled to the sensing circuitry and configured to: detect tachycardia from the first cardiac electrical signal; set an ATP interval; and set a first prolonged ATP interval that is longer than the ATP interval; and therapy delivery circuitry coupled to the control circuitry and configured to deliver a first therapy after the control circuitry detects tachycardia by: delivering a first lead ATP pulse at the first prolonged ATP interval from a first one of the first cardiac events sensed by the sensing circuitry from the first cardiac electrical signal; and delivering a second ATP pulse at the ATP interval after the first lead ATP pulse. the control circuitry is further configured to set the ATP interval by:

2. The medical device of claim 1, wherein, determining a tachycardia cycle length from the first cardiac electrical signal; and setting the ATP interval to be less than the tachycardia cycle length. the control circuitry is further configured to set the first prolonged ATP interval to the determined tachycardia cycle length.

3. The medical device of claim 2, wherein, 4. The medical device of claim 1, wherein: the control circuitry is further configured to: redetect tachycardia from the first cardiac electrical signal after the therapy delivery circuitry delivers the first therapy; and in response to redetecting tachycardia, set a second prolonged ATP interval that is different than the first prolonged ATP interval; and the therapy delivery circuitry is further configured to deliver a second therapy after the control circuitry redetects tachycardia by: delivering a second lead ATP pulse delivered at the second prolonged ATP interval from a second one of the first cardiac events sensed by the sensing circuitry from the first cardiac electrical signal; and delivering a third ATP pulse at the ATP interval after the second lead ATP pulse. the control circuitry is further configured to set the second prolonged ATP interval based on at least the first prolonged ATP interval. the control circuitry is further configured to set the second prolonged ATP interval based on at least the first prolonged ATP interval by:

5. The medical device of claim 4, wherein, determining a tachycardia cycle length from the first cardiac electrical signal; and 6. The medical device of claim 5, wherein, setting the second prolonged ATP interval based on the determined tachycardia cycle length and the first prolonged ATP interval.

7. The medical device of claim 5, wherein: the sensing circuitry is further configured to: receive a second cardiac electrical signal different than the first cardiac electrical signal; and sense, from the second cardiac electrical signal, second cardiac events each associated with a myocardial depolarization; the control circuitry is further configured to: ​ ​ determining a time difference from a first cardiac event to a second cardiac event, the first cardiac event sensed by the sensing circuit from the first cardiac electrical signal, the second cardiac event sensed by the sensing circuit from the second cardiac electrical signal; and setting the second extended ATP interval based on the first extended ATP interval and the time difference.

8. The medical device of claim 7, wherein: the control circuit is further configured to: determine a tachycardia cycle length from the first cardiac electrical signal; determine an actual early onset of the first preceding ATP pulse as the tachycardia cycle length minus the first extended ATP interval plus the time difference; and determine a total early onset of the first therapy including the actual early onset of the first preceding ATP pulse; and the therapy delivery circuit is further configured to deliver the second therapy having a total early onset greater than the total early onset of the first therapy.

9. The medical device of claim 8, wherein, the therapy delivery circuit is further configured to: deliver the first therapy by delivering a first number of ATP pulses after the second ATP pulse; and deliver the second therapy having a total early onset greater than the total early onset of the first therapy by at least one of: delivering a second number of ATP pulses after the third ATP pulse, the second number of ATP pulses being more than the first number of ATP pulses; and reducing the ATP interval.

10. The medical device of claim 1, wherein, further comprising a housing configured to receive an extravascular lead.

11. An implantable medical device comprising: a memory; a control circuit configured to perform operations comprising: receiving a first cardiac electrical signal; sensing first cardiac events from the first cardiac electrical signal, each first cardiac event being associated with a myocardial depolarization; detecting tachycardia from the first cardiac electrical signal; setting an ATP interval; setting a first extended ATP interval that is longer than the ATP interval; and delivering a first therapy after detecting tachycardia by: delivering a first preceding ATP pulse at the first extended ATP interval from a first one of the first cardiac events sensed from the first cardiac electrical signal; and delivering a second ATP pulse at the ATP interval after the first preceding ATP pulse. setting the ATP interval comprises:

12. The implantable medical device of claim 11, wherein, determining a tachycardia cycle length from the first cardiac electrical signal; and setting the ATP interval to be less than the tachycardia cycle length. setting the first extended ATP interval comprises setting the first extended ATP interval to the determined tachycardia cycle length.

13. The implantable medical device of claim 12, wherein, the control circuit is further configured to perform operations comprising:

14. The implantable medical device of claim 11, wherein, after delivering the first therapy, redetecting tachycardia from the first cardiac electrical signal; in response to redetecting tachycardia, setting a second extended ATP interval that is different from the first extended ATP interval; and delivering a second therapy after redetecting tachycardia by: ​ ​ deliver a second pre-pulse ATP pulse delivered at the second extended ATP interval based on a second one of the first cardiac events sensed from the first cardiac electrical signal; and deliver a third ATP pulse after the second pre-pulse ATP pulse at the ATP interval.

15. The implantable medical device of claim 14, wherein, the control circuit is further configured to set the second extended ATP interval based on at least the first extended ATP interval.

16. The implantable medical device of claim 15, wherein, setting the second extended ATP interval based on at least the first extended ATP interval includes: determining a tachycardia cycle length from the first cardiac electrical signal; and setting the second extended ATP interval based on the determined tachycardia cycle length and the first extended ATP interval.

17. The implantable medical device of claim 15, wherein, the control circuit is further configured to: receive a second cardiac electrical signal different from the first cardiac electrical signal; sense second cardiac events from the second cardiac electrical signal each associated with a myocardial depolarization; determine a time difference from a first cardiac event sensed from the first cardiac electrical signal to a second cardiac event sensed from the second cardiac electrical signal; and set the second extended ATP interval based on the first extended ATP interval and the time difference.

18. The implantable medical device of claim 17, wherein, the control circuit is further configured to: determine a tachycardia cycle length from the first cardiac electrical signal; determine an actual early onset of the first pre-pulse ATP pulse as the tachycardia cycle length minus the first extended ATP interval plus the time difference; determine a total early onset of the first therapy including the actual early onset of the first pre-pulse ATP pulse; and deliver the second therapy having a total early onset greater than the total early onset of the first therapy.

19. The implantable medical device of claim 18, wherein, the control circuit is further configured to deliver the first therapy by delivering a first number of ATP pulses after the second ATP pulse; wherein delivering the second therapy having a total early onset greater than the total early onset of the first therapy includes at least one of: delivering a second number of ATP pulses after the third ATP pulse, the second number of ATP pulses more than the first number of ATP pulses; and reducing the ATP interval.

20. A non-transitory computer-readable storage medium storing a set of instructions that, when executed by a control circuit of a medical device, cause the device to: receive a cardiac electrical signal; sense cardiac events from the cardiac electrical signal each associated with a myocardial depolarization; detect a tachycardia from the cardiac electrical signal; set an ATP interval; set an extended ATP interval longer than the ATP interval; and deliver a therapy as a first therapy after detecting the tachycardia by: deliver a first pre-pulse ATP pulse at the extended ATP interval based on a first one of the cardiac events sensed from the cardiac electrical signal; and deliver a second ATP pulse after the first pre-pulse ATP pulse at the ATP interval. ​

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