US20080086175A1

US20080086175A1 - Method and apparatus for reducing defibrillation threshold

Info

Publication number: US20080086175A1
Application number: US11/760,987
Authority: US
Inventors: Imad Libbus; Avram Scheiner; Stephen J. Hahn
Original assignee: Cardiac Pacemakers Inc
Current assignee: Cardiac Pacemakers Inc
Priority date: 2006-10-04
Filing date: 2007-06-11
Publication date: 2008-04-10
Also published as: EP2510973A3; EP2510973A2; WO2008042468A2; EP2081643B1; JP5308338B2; WO2008042468A3; JP2010505527A; US8983598B2; US20080086174A1; EP2081643A2

Abstract

An antitachyarrhythmia system uses vagal nerve stimulation in combination with one or more additional techniques to lower the defibrillation threshold (DFT). Examples of such additional techniques include using electrical shock waveforms each including a plurality of pulses and using defibrillation electrode configurations each including an electrode placed in the coronary sinus or coronary vein.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending, commonly assigned, U.S. patent application Ser. No. 11/538,488, filed on Oct. 4, 2006 and is related to co-pending, commonly assigned, U.S. patent application Ser. No. 11/275,943, filed on Feb. 6, 2006, which is a continuation of U.S. patent Ser. No. 10/629,343, filed on Jul. 28, 2003, now abandoned, which is a continuation of U.S. patent Ser. No. 10/118,603, filed on Apr. 8, 2002, now abandoned, which is a division of U.S. patent application Ser. No. 09/448,648, now abandoned, which are hereby incorporated by reference in their entirety.

FIELD

This application relates generally to medical devices and, more particularly, to systems, devices and methods for providing neurally-mediated anti-arrhythmic therapy.

BACKGROUND

The heart is the center of a person's circulatory system. The left portions of the heart draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart draw deoxygenated blood from the body organs and pump it to the lungs where the blood gets oxygenated. Contractions of the myocardium provide these pumping functions. In a normal heart, the sinoatrial node, the heart's natural pacemaker, generates electrical impulses that propagate through an electrical conduction system to various regions of the heart to excite the myocardial tissues of these regions. Coordinated delays in the propagations of the electrical impulses in a normal electrical conduction system cause the various portions of the heart to contract in synchrony, which efficiently pumps the blood. Blocked or abnormal electrical conduction or deteriorated myocardial tissue causes dysynchronous contraction of the heart, resulting in poor hemodynamic performance, including a diminished blood supply to the heart and the rest of the body. Heart failure occurs when the heart fails to pump enough blood to meet the body's metabolic needs.
Tachyarrhythmias are abnormal heart rhythms characterized by a rapid heart rate. Examples of tachyarrhythmias include supraventricular tachycardias (SVT's) such as atrial tachycardia (AT), and atrial fibrillation (AF), and the more dangerous ventricular tachyarrhythmias which include ventricular tachycardia (VT) and ventricular fibrillation (VF). Abnormal ventricular rhythms occur when re-entry of a depolarizing wavefront in areas of the ventricular myocardium with different conduction characteristics becomes self-sustaining or when an excitatory focus in the ventricle usurps control of the heart rate from the sinoatrial node. The result is rapid and ineffective contraction of the ventricles out of electromechanical synchrony with the atria. Many abnormal ventricular rhythms exhibit an abnormal QRS complex in an electrocardiogram because the depolarization spreads from the excitatory focus or point of re-entry directly into the myocardium rather than through the normal ventricular conduction system. Ventricular tachycardia is typically characterized by distorted QRS complexes that occur at a rapid rate, while ventricular fibrillation is diagnosed when the ventricle depolarizes in a chaotic fashion with no identifiable QRS complexes. Both ventricular tachycardia and ventricular fibrillation are hemodynamically compromising, and both can be life-threatening. Ventricular fibrillation, however, causes circulatory arrest within seconds and is the most common cause of sudden cardiac death.
Cardioversion, an electrical shock delivered to the heart synchronously with the QRS complex, and defibrillation, an electrical shock delivered without synchronization to the QRS complex, can be used to terminate most tachyarrhythmias. Cardioversion and defibrillation are referred generally herein as antitachycardia shocks. The electric shock terminates the tachyarrhythmia by simultaneously depolarizing the myocardium and rendering it refractory. A class of cardiac rhythm management (CRM) devices known as an implantable cardioverter defibrillator (ICD) provides this kind of therapy by delivering a shock pulse to the heart when the device detects tachyarrhythmias. One type of ICD is a subcutaneous ICD. However, the defibrillation threshold (DFT) for a subcutaneous ICD is significantly elevated as compared to an intracardiac ICD. Because the energy required for each electrical shock is a significant factor determining battery life, and hence the longevity, of the ICD, reduction of DFT is generally desired.

SUMMARY

An antitachyarrhythmia system uses vagal nerve stimulation in combination with one or more additional techniques to lower the defibrillation threshold (DFT). Examples of such additional techniques include using electrical shock waveforms each including a plurality of pulses and using defibrillation electrode configurations each including an electrode placed in the coronary sinus or coronary vein.
In one embodiment, an antitachyarrhythmia system includes a sensor, a vagal nerve stimulator, defibrillation electrodes, and a defibrillator. The sensor detects a cardiac activity indicated for a defibrillation shock. The vagal nerve stimulator delivers vagal nerve stimulation to lower a defibrillation threshold in preparation for delivering the defibrillation shock. The defibrillator delivers the defibrillation shock to the heart through the defibrillation electrodes, which include at least one left ventricular (LV) electrode configured to be placed in a coronary sinus or coronary vein.
In one embodiment, a method for defibrillating a heart is provided. A cardiac activity indicated for a defibrillation shock is detected. Neural stimulation is applied to lower a defibrillation threshold in preparation for the defibrillation shock. The defibrillation shock is delivered using defibrillation electrodes including at least one LV electrode placed in the coronary sinus or coronary vein.
This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which are not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method according to various embodiments.

FIG. 2 illustrates a timing diagram for an example of the method illustrated in FIG. 1.

FIG. 3 illustrates an embodiment of implantable medical device (IMD) having a neural stimulation (NS) component and an implantable cardioverter defibrillator (ICD) component.

FIG. 4 illustrates an embodiment of a microprocessor-based implantable device.

FIG. 5 illustrates a system embodiment including an implantable medical device (IMD) and an external system or device.

FIG. 6 illustrates a system embodiment including an external device, an implantable neural stimulator (NS) device and an ICD device.

FIG. 7 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation.

FIG. 8 illustrates an embodiment of a system, including a subcutaneous ICD and an implantable vagal nerve stimulator.

FIG. 9 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation.

FIG. 10 illustrates an embodiment of a system, including a subcutaneous ICD and an implantable vagal nerve stimulator.

FIG. 11 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation.

FIG. 12 is a block diagram illustrating an embodiment of an external system.

FIG. 13 illustrates an embodiment of an implantable medical device with an intracardiac lead system for delivering anti-arrhythmic therapy.

FIG. 14 illustrates an embodiment of an antitachycardia shock waveform.

FIG. 15 illustrates another embodiment of an antitachycardia shock waveform.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refers to the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present subject matter. References to “an”, “one”, or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more than one embodiment. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined only by the appended claims, along with the full scope of legal equivalents to which such claims are entitled.
An embodiment includes an implantable device adapted to provide subcutaneous anti-arrhythmic therapy, and to provide vagal stimulation to suppress and prevent tachyarrhythmias such as ventricular tachycardia (VT) or ventricular fibrillation (VF). The vagal stimulation can be delivered intermittently or in response to sensed cardiac activity. An embodiment of the device is adapted to respond to the detection of a potentially lethal tachyarrhythmia by delivering a subcutaneous antitachycardia shock, using synchronous vagal stimulation to lower the defibrillation threshold (DFT) and enhance the efficacy of the shock therapy. In various embodiments, the vagal stimulation significantly decreases the DFT. The illustrated embodiment of the device includes an implantable pulse generator connected to a neural stimulation lead for vagal nerve stimulation. Vagal nerve stimulation is applied intermittently, or in response to sensed cardiac activity predetermined to be an indicator of potentially lethal tachyarrhythmias. An example of such cardiac activity includes ST-segment elevation detected by wireless ECG. The subcutaneous device includes cardiac sensing and defibrillation capabilities, and is adapted to detect tachyarrhythmias (such as VT/VF) and deliver an antitachycardia shock. In various embodiments, the device is adapted to deliver vagal nerve stimulation for a short period of time (e.g. 5-7 seconds) before applying the shock to lower the DFT and counteract the inefficient shock delivery. Without the application of vagal nerve stimulation, the DFT for a subcutaneous ICD is significantly elevated as compared to an intracardiac ICD.
Various embodiments provide two implantable units that communicate wirelessly. One unit is placed in the pectoral region, and connected to a neural stimulation lead for vagal nerve stimulation. The other unit is placed abdominally, and is responsible for cardiac sensing and cardioversion/defibrillation. In yet another embodiment, both units are involved in the cardiac sensing and/or cardioversion/defibrillation.
In an embodiment, vagal nerve stimulation is applied intermittently, such as ten seconds per minute, to prevent or abate progression of cardiac disease development. Abating disease progression includes preventing the disease progression, or slowing down or reducing the intensity of the disease progression. In this case, the portion of the device responsible for cardiac sensing and cardioversion/defibrillation monitors heart rate, and ensures that the heart rate does not fall below unacceptable levels during vagal nerve stimulation. Other parameters such as blood pressure or minute ventilation can be used to assess the appropriateness of the neural stimulation. If heart rate falls below a programmable threshold, the device adjusts the stimulation (e.g. reducing the amount or turning off the vagal nerve stimulation).
A subcutaneous ICD with vagal stimulation capability can be used by any patient at elevated risk for cardiac arrhythmias, and is believed to be particularly beneficial for patients with moderately-elevated risk who likely would not receive an ICD with intracardiac leads.
FIG. 1 illustrates a method according to various embodiments. The illustrated method includes, at 101, detecting a predetermined cardiac activity that has been indicated for an antitachycardia shock. Various embodiments use the lead(s) of a subcutaneous ICD to detect the predetermined cardiac activity. Various embodiments use electrodes on a housing of a subcutaneously implanted device to detect the predetermined cardiac activity. Various embodiments detect the predetermined cardiac activity using a wireless EEG, which uses only electrodes on the subcutaneously implanted device to detect the cardiac activity. An example of cardiac activity that has been indicated for an antitachycardia shock includes an elevated ST-segment. When it is determined that a shock should be applied, the process proceeds to 102 to deliver vagal nerve stimulation in response to predetermined cardiac activity to lower a defibrillation threshold (DFT) in preparation for the antitachycardia shock. The vagal nerve stimulation can be delivered through a lead to a vagus nerve in the cervical region. Various embodiments use a lead with a nerve cuff electrode. Various embodiments use a transvascular lead fed into the internal jugular vein, or other vessel, to place at least one electrode proximate to a vagus nerve. Various embodiments use satellite electrodes in wireless communication with the subcutaneous defibrillator. The satellite electrodes can be self powered or can receive power wirelessly (e.g. through ultrasound transducers that recharge batteries or deliver power as needed for the stimulation). The shock is subcutaneously delivered, as illustrated at 103.
Various embodiments apply prophylactic vagal nerve stimulation, as illustrated at 104. The prophylactic vagal nerve stimulation can be provided as a therapy in addition to the nerve stimulation therapy to lower DFT, or can be provided as a therapy without the nerve stimulation therapy to lower DFT. Modulation of the sympathetic and parasympathetic nervous system with neural stimulation has been shown to have positive clinical benefits, such as protecting the myocardium from further remodeling and predisposition to fatal arrhythmias following a myocardial infarction. One example of a prophylactic vagal nerve stimulation includes stimulation delivered to prevent ventricular fibrillation, such as may be applied after a myocardial infarction. Although the mechanisms are not completely understood at present, various studies have indicated that sympathetic hyperactivity often triggers life-threatening ventricular arrhythmias in the setting of acute myocardial ischemia. Another example of a prophylactic vagal nerve stimulation includes stimulation to prevent development of a cardiac disease, such as anti-remodeling therapy.
FIG. 2 illustrates a timing diagram for an example of the method illustrated in FIG. 1. As illustrated at 204, vagal nerve stimulation is delivered intermittently as part of a prophylactic therapy. For example, the prophylactic therapy can be delivered on a schedule, such as 5 minutes every hour. Arrow 201 illustrates a time when it is determined that it is appropriate or desirable to provide an antitachycardia shock. As illustrated at 202 vagal nerve stimulation is delivered to lower a defibrillation threshold (DFT) in anticipation of the shock. Various embodiments deliver the neural stimulation to lower the DFT for less than one minute, various embodiments deliver the neural stimulation to lower the DFT for less than 15 seconds, and various embodiments deliver the neural stimulation for a duration between approximately 5 seconds to approximately 7 seconds. At 203, a subcutaneous defibrillator delivers a defibrillation shock after the DFT has been lowered. According to various embodiments, for example, the shock is delivered within one minute after initiating the neural stimulation to lower the DFT. Various embodiments deliver the shock within 20 seconds after initiating the neural stimulation to lower the DFT. Various embodiments deliver the shock within 10 seconds after initiating the neural stimulation to lower the DFT. The DFT will not be lowered if the neural stimulation is delivered for too long of a duration before the defibrillation shock is delivered. Various embodiments terminate the neural stimulation delivered to lower DFT at or approximately when the shock is delivered.
FIG. 3 illustrates an IMD 305 having a neural stimulation (NS) component 306 and ICD component 307, according to various embodiments of the present subject matter. The illustrated device includes a controller 308 and memory 309. According to various embodiments, the controller includes hardware, software, or a combination of hardware and software to perform the neural stimulation and ICD functions. For example, the programmed therapy applications discussed in this disclosure are capable of being stored as computer-readable instructions embodied in memory and executed by a processor. According to various embodiments, the controller includes a processor to execute instructions embedded in memory to perform the neural stimulation and ICD functions. An example of an ICD function includes antitachycardia shock therapy 310 such as may include cardioversion or defibrillation, and examples of NS functions include parasympathetic stimulation and/or sympathetic inhibition to lower DFT 311, and parasympathetic stimulation and/or sympathetic inhibition as part of a prophylactic therapy 312 such as a therapy to prevent or diminish cardiac remodeling and/or a therapy applied after a myocardial infarction to prevent ventricular fibrillation. The controller also executes instructions to detect a tachyarrhythmia. The illustrated device further includes a transceiver 313 and associated circuitry for use to communicate with a programmer or another external or internal device. Various embodiments include a telemetry coil.
The ICD therapy section 307 includes components, under the control of the controller, to stimulate a heart and/or sense cardiac signals using one or more electrodes. The illustrated ICD therapy section includes a pulse generator 314 for use to provide an electrical signal through electrodes to stimulate a heart, and further includes sense circuitry 315 to detect and process sensed cardiac signals. An interface 316 is generally illustrated for use to communicate between the controller 308 and the pulse generator 314 and sense circuitry 315. The present subject matter is not limited to a particular number of electrode sites.
The NS therapy section 306 includes components, under the control of the controller, to stimulate a neural stimulation target, and in some embodiments sense parameters associated with nerve activity or surrogates of nerve activity such as blood pressure and respiration. Three interfaces 317 are illustrated in the NS therapy section 306. However, the present subject matter is not limited to a particular number interfaces, or to any particular stimulating or sensing functions. Pulse generators 318 are used to provide electrical pulses to electrode(s) or transducers for use to stimulate a neural stimulation target. According to various embodiments, the pulse generator includes circuitry to set, and in some embodiments change, the amplitude of the stimulation pulse, the frequency of the stimulation pulse, the burst frequency of the pulse, and the morphology of the pulse such as a square wave, triangle wave, sinusoidal wave, and waves with desired harmonic components to mimic white noise or other signals. The controller can control the initiation and termination of neural stimulation pulse trains. Sense circuits 319 are used to detect and process signals from a sensor, such as a sensor of nerve activity, blood pressure, respiration, and the like. The interfaces 317 are generally illustrated for use to communicate between the controller 308 and the pulse generator 318 and sense circuitry 319. Each interface, for example, may be used to control a separate lead. Various embodiments of the NS therapy section only include a pulse generator to stimulate or inhibit a neural target such as a vagus nerve.
FIG. 4 shows a system diagram of an embodiment of a microprocessor-based implantable device, according to various embodiments. The controller of the device is a microprocessor 420 which communicates with a memory 421 via a bidirectional data bus. The controller could be implemented by other types of logic circuitry (e.g., discrete components or programmable logic arrays) using a state machine type of design, but a microprocessor-based system is preferable. As used herein, the term “circuitry” should be taken to refer to either discrete logic circuitry or to the programming of a microprocessor.
The illustrated device includes an ICD channel that includes electrodes 422A, 422B and 422C, a sensing amplifier 423 for use in detecting cardiac activity using at least some of electrodes 422A, 422B and 422C, a shock pulse generator 424 for use in delivering an antitachycardia shock using at least some of electrodes 422A, 422B and 422C, and a channel interface 425 adapted to communicate bidirectionally with microprocessor 420. Although three electrodes are illustrated, the ICD channel can use more or fewer electrodes, including at least one can electrode 426. Wireless EEG, for example, can be detected using can electrodes. The interface may include analog-to-digital converters for digitizing sensing signal inputs from the sensing amplifiers and registers that can be written to by the microprocessor in order to output pacing pulses, change the pacing pulse amplitude, and adjust the gain and threshold values for the sensing amplifiers. The sensing circuitry detects a chamber sense, either an atrial sense or ventricular sense, when an electrogram signal (i.e., a voltage sensed by an electrode representing cardiac electrical activity) generated by a particular channel exceeds a specified detection threshold. Such senses can be used to detect a cardiac rhythm that is indicated for a defibrillation shock. The intrinsic atrial and/or ventricular rates can be measured by measuring the time intervals between atrial and ventricular senses, respectively, and used to detect atrial and ventricular tachyarrhythmias.
The illustrated electrodes are connected via conductors within the lead to a switching network 427 controlled by the microprocessor. The switching network is used to switch the electrodes to the input of a sense amplifier in order to detect intrinsic cardiac activity and to the output of a pulse generator in order to deliver an antitachycardia shock. The switching network also enables the device to sense or shock either in a bipolar mode using lead electrodes or in a unipolar mode using a lead electrode and the device housing (can) 426 or an electrode on another lead serving as a ground electrode.
Neural stimulation channels, identified as channels A and B, are incorporated into the device for delivering parasympathetic stimulation and/or sympathetic inhibition, where one channel includes a bipolar lead with a first electrode 428A and a second electrode 429A, a pulse generator 430A, and a channel interface 431A, and the other channel includes a bipolar lead with a first electrode 428B and a second electrode 429B, a pulse generator 430B, and a channel interface 431B. Other embodiments may use unipolar leads in which case the neural stimulation pulses are referenced to the can or another electrode. The pulse generator for each channel outputs a train of neural stimulation pulses which may be varied by the controller as to amplitude, frequency, duty-cycle, and the like. In this embodiment, each of the neural stimulation channels uses a lead which can be subcutaneously tunneled or intravascularly disposed near an appropriate stimulation site. Other types of leads and/or electrodes may also be employed. A nerve cuff electrode may be used around the cervical vagus nerve bundle to provide parasympathetic stimulation or around the aortic or carotid sinus nerve to provide sympathetic inhibition. In an embodiment, the leads of the neural stimulation electrodes are replaced by wireless links, and the electrodes for providing parasympathetic stimulation and/or sympathetic inhibition are incorporated into satellite units.
The figure illustrates a telemetry interface 432 connected to the microprocessor, which can be used to communicate with an external device. The illustrated microprocessor 420 is capable of performing neural stimulation therapy routines and myocardial stimulation routines. Examples of NS therapy routines include an NS therapy to lower DFT, and an NS prophylactic therapy to prevent ventricular fibrillation after a myocardial infarction, or to prevent progression of cardiac disease. Examples of myocardial therapy routines include an antitachycardia shock therapy such as cardioversion/defibrillation.
FIG. 5 illustrates a system 533 including an IMD 534 and an external system or device 535, according to various embodiments of the present subject matter. Various embodiments of the IMD 534 include a combination of NS and ICD functions. The external system 535 and the IMD 534 are capable of wirelessly communicating data and instructions. In various embodiments, for example, the external system and IMD use telemetry coils to wirelessly communicate data and instructions. Thus, the programmer can be used to adjust the programmed therapy provided by the IMD, and the IMD can report device data (such as battery and lead resistance) and therapy data (such as sense and stimulation data) to the programmer using radio telemetry, for example. According to various embodiments, the IMD stimulates a neural target to lower DFT in preparation for a shock, and subcutaneously delivers the shock. Various embodiments of the IMD also deliver a programmed neural stimulation therapy as part of a prophylactic treatment for ventricular fibrillation or venticular remodeling.
The external system allows a user such as a physician or other caregiver or a patient to control the operation of IMD and obtain information acquired by the IMD. In one embodiment, external system includes a programmer communicating with the IMD bi-directionally via a telemetry link. In another embodiment, the external system is a patient management system including an external device communicating with a remote device through a telecommunication network. The external device is within the vicinity of the IMD and communicates with the IMD bi-directionally via a telemetry link. The remote device allows the user to monitor and treat a patient from a distant location. The patient monitoring system is further discussed below.
The telemetry link provides for data transmission from implantable medical device to external system. This includes, for example, transmitting real-time physiological data acquired by the IMD, extracting physiological data acquired by and stored in IMD, extracting therapy history data stored in implantable medical device, and extracting data indicating an operational status of the IMD (e.g., battery status and lead impedance). Telemetry link also provides for data transmission from external system to the IMD. This includes, for example, programming the IMD to acquire physiological data, programming the IMD to perform at least one self-diagnostic test (such as for a device operational status), and programming the IMD to deliver at least one therapy.
FIG. 6 illustrates a system 633 including an external device 635, an implantable neural stimulator (NS) device 636 and a subcutaneous ICD 637, according to various embodiments of the present subject matter. Various aspects involve a method for communicating between an NS device and the ICD. The illustrated NS device and the ICD are capable of wirelessly communicating with each other, and the external system is capable of wirelessly communicating with at least one of the NS and the CRM devices. For example, various embodiments use telemetry coils to wirelessly communicate data and instructions to each other. In other embodiments, communication of data and/or energy is by ultrasonic means. Rather than providing wireless communication between the NS and ICD devices, various embodiments provide a communication cable or wire, such as an intravenously-fed lead, for use to communicate between the NS device and the ICD device. In some embodiments, the external system functions as a communication bridge between the NS and ICD devices.
FIG. 7 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation. The location of the device 734 is in a subcutaneous space that is developed during the implantation process, and the heart 738 is not exposed during this process. The subcutaneous space is below the patient's skin and over muscle tissue and the rib cage. The lead 739 of the subcutaneous electrode traverses in a subcutaneous path around the thorax terminating with its distal electrode lateral to the left scapula to deliver current between the can and electrode to the majority of the ventricular myocardium. A distal electrode on the lead is a coil electrode that is used for delivering the cardioversion/defibrillation energy across the heart. The lead can also include sense electrodes spaced a distance to provide good QRS detection. The sensing of QRS waves can be carried out using sense electrodes on the housing of the device 734 or using a combination of lead electrodes and housing electrodes. The sensing vectors between electrodes can be adjusted to provide the best detection of cardiac activity. When a shock is to be applied, the sensing electrodes can be turned off and isolated from damage caused by the shock. A neural stimulation lead 740 extends from the device 734 to a vagal target. The neural stimulation lead 740 can be tunneled subcutaneously to the vagus nerve, or can be transvascularly fed to the internal jugular vein adjacent to the vagus nerve. Satellite electrodes may be used to deliver neural stimulation.
FIG. 8 illustrates an embodiment of a system, including a subcutaneous ICD 837 and an implantable vagal nerve stimulator 836. The ICD 837 has a subcutaneous lead 839 similar to the lead 739 described with respect to FIG. 7. A separate vagal nerve stimulator 836 includes a neural stimulation lead 840, which can be tunneled subcutaneously to the vagus nerve, or can be transvascularly fed to the internal jugular vein adjacent to the vagus nerve. The ICD and nerve stimulator are adapted to communicate with each other. The illustrated system illustrates wireless communication between the devices, such as may be achieved using ultrasound or radiofrequency signals. A subcutaneously tunneled tether can connect the two implanted devices, and communication and/or power can be provided through the tether. Thus, the neural stimulation to lower the DFT can be coordinated with the delivery of the subcutaneous defibrillation.
FIG. 9 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation. In the illustrated embodiment, there are two subcutaneous leads 939A and 939B connected to the ICD 934. The cardioversion/defibrillation energy can be delivered between the active surface of the device housing and electrodes on each lead. The desired electrodes for sensing and/or shocking can be selected by the device. A neural stimulation lead 940 extends from the device 934 to a vagal target. The neural stimulation lead 940 can be tunneled subcutaneously to the vagus nerve, or can be transvascularly fed to the internal jugular vein adjacent to the vagus nerve. Satellite electrodes may be used to deliver neural stimulation.
FIG. 10 illustrates an embodiment of a system, including a subcutaneous ICD 1037 and an implantable vagal nerve stimulator 1036. The ICD 1037 has subcutaneous leads 1039A and 1039B similar to the leads 939A and 939B described with respect to FIG. 9. A separate vagal nerve stimulator 1036 includes a neural stimulation lead 1040, which can be tunneled subcutaneously to the vagus nerve, or can be transvascularly fed to the internal jugular vein adjacent to the vagus nerve. The ICD and nerve stimulator are adapted to communicate with each other. The illustrated system illustrates wireless communication between the devices, such as may be achieved using ultrasound or radiofrequency signals. A subcutaneously tunneled tether can connect the two implanted devices, and communication and/or power can be provided through the tether. Thus, the neural stimulation to lower the DFT can be coordinated with the delivery of the subcutaneous defibrillation.
FIG. 11 illustrates an embodiment of a subcutaneous ICD with vagal nerve stimulation. The illustrated ICD 1134 provides vagal nerve stimulation using satellite electrodes 1141. The satellite electrode can include its own power, and can wirelessly communicate with the ICD. The satellite electrodes can include nerve cuff electrodes, transvascular electrodes, and subcutaneous electrodes. The subcutaneous ICD 1134 may be used in adults where chronic transvenous/epicardial ICD lead systems pose excessive risk or have already resulted in difficulty such as sepsis or lead fractures, and may be used for use in children whose growth poses problems with transvenous ICDs. FIG. 11 also illustrates the placement of the subcutaneous lead 1139, which is fed in a serpentine fashion rather than a taught configuration. As the child grows, the bends in the lead straighten allowing the proper electrode placement to be maintained. An anchor can be used to fix the distal end of the lead.
FIG. 12 is a block diagram illustrating an embodiment of an external system 1242. The external system includes a programmer, in some embodiments. In the embodiment illustrated in FIG. 12, the external system includes a patient management system. As illustrated, external system 1242 is a patient management system including an external device 1243, a telecommunication network 1244, and a remote device 1245. The external device 1243 is placed within the vicinity of an IMD and includes external telemetry system 1246 to communicate with the IMD. Remote device(s) 1245 is in one or more remote locations and communicates with the external device 1243 through the network 1244, thus allowing a physician or other caregiver to monitor and treat a patient from a distant location and/or allowing access to various treatment resources from the one or more remote locations. The illustrated remote device 1245 includes a user interface 1247.
In various embodiments, the vagal nerve stimulation is applied to reduce the DFT for an antitachycardia shock delivering through subcutaneous and/or intracardiac electrodes. In various embodiments, in addition to delivering neural stimulation in preparation for an antitachycardia shock as discussed above, one or more other techniques are used to further lower the DFT. For illustrative purposes, embodiments of such other techniques are discussed below with reference to FIGS. 13-15. In these embodiments, various configurations of intracardiac electrodes are discussed as specific examples. However, the present subject matter applies to delivery of an antitachycardia shock through intracardiac, subcutaneous, or external electrodes, or various combinations of these electrodes. In general, any two or more of the methods and devices for the vagal nerve stimulation and for other techniques for lowering the DFT may be combined to reduce or minimize the energy required to terminate a tachyarrhythmic episode.
FIG. 13 illustrates an embodiment of an IMD 1348 with an intracardiac lead system for delivering an anti-arrhythmic therapy. In various embodiments, IMD 1348 represents any IMD that includes ICD functions or a combination of NS and ICD functions, where the NS functions provide for lowering of the DFT. Examples of IMD 1348 include devices 534, 637, 734, 837,934, 1037, and 1134 discussed above. The lead system includes implantable intracardiac leads 1350, 1355, and 1365.
IMD 1348 includes a hermetically sealed can housing an electronic circuit that senses physiological signals and delivers therapeutic electrical pulses. The hermetically sealed can also functions as a can electrode 1349 for sensing and/or pulse delivery purposes. In various embodiments, in addition to the NS and ICD functions, IMD 1348 performs one or more other monitoring and/or therapeutic functions such as drug delivery and biologic therapy delivery functions. In one embodiment, a drug therapy or biologic therapy is delivered to further reduce the DFT.
Lead 1350 is a right atrial (RA) pacing lead that includes an elongate lead body having a proximal end 1351 and a distal end 1353. Proximal end 1351is coupled to a connector for connecting to IMD 1348. Distal end 1353 is configured for placement in the RA in or near the atrial septum. Lead 1350 includes an RA tip electrode 1354A, and an RA ring electrode 1354B. RA electrodes 1354A and 1354B are incorporated into the lead body at distal end 1353 for placement in or near the atrial septum, and are each electrically coupled to IMD 1348 through a conductor extending within the lead body. RA tip electrode 1354A, RA ring electrode 1354B, and/or can electrode 1349 allow for sensing an RA electrogram indicative of RA depolarizations and delivering RA pacing pulses.
Lead 1355 is a right ventricular (RV) pacing-defibrillation lead that includes an elongate lead body having a proximal end 1357 and a distal end 1359. Proximal end 1357 is coupled to a connector for connecting to IMD 1348. Distal end 1359 is configured for placement in the RV. Lead 1355 includes a supraventricular defibrillation electrode such as a superior vena cava (SVC) defibrillation electrode 1356, an RV defibrillation electrode 1358, an RV tip electrode 1360A, and an RV ring electrode 1360B. SVC defibrillation electrode 1356 is incorporated into the lead body in a location suitable for supraventricular placement in the SVC and/or the RA. RV defibrillation electrode 1358 is incorporated into the lead body near distal end 1359 for placement in the RV. RV electrodes 1360A and 1360B are incorporated into the lead body at distal end 1359. Electrodes 1356, 1358, 1360A, and 1360B are each electrically coupled to IMD 1348 through a conductor extending within the lead body. SVC defibrillation electrode 1356, RV defibrillation electrode 1358, and/or can electrode 1349 allow for delivery of cardioversion/defibrillation pulses to the heart. RV tip electrode 1360A, RV ring electrode 1360B, and/or can electrode 1349 allow for sensing an RV electrogram indicative of RV depolarizations and delivering RV pacing pulses.
Lead 1365 is a left ventricular (LV) coronary pacing-defibrillation lead that includes an elongate lead body having a proximal end 1361 and a distal end 1363. Proximal end 1361 is coupled to a connector for connecting to IMD 1348. Distal end 1363 is configured for placement in the coronary vein (as illustrated) or the coronary sinus. Lead 1365 includes one or more LV pacing and/or defibrillation electrodes for placement along the coronary sinus and/or the coronary vein over the LV. Examples of such LV electrodes as illustrated in FIG. 13 include a coronary sinus (CS) electrode 1369 and a coronary vein (CV) electrode 1368. CS electrode 1369 and CV electrode 1368 are each electrically coupled to IMD 1348 through a conductor extending within the lead body. In various embodiments, CS electrode 1369, CV electrode 1368 and/or the can electrode 1349 allow for sensing an LV electrogram indicative of LV depolarizations and delivering LV pacing pulses. In various embodiments, electrodes selected from CS electrode 1369, CV electrode 1368, SVC defibrillation electrode 1356, RV defibrillation electrode 1358, and/or can electrode 1349 allow for delivery of antitachycardia shocks to the heart.
CS electrode 1369, CV electrode 1368, SVC defibrillation electrode 1356, and RV defibrillation electrode 1358 are specific examples of electrodes 422A, 422B, and 422C, and can electrode 1349 is a specific example of can electrode 426. The leads and electrodes in FIG. 13 are for illustrative purposes only. Other lead configurations may be used, depending on monitoring and therapeutic requirements. For example, additional leads may be used to provide access to additional cardiac regions, and leads 1350, 1355, and 1365 may each include more or fewer electrodes along the lead body at, near, and/or distant from the distal end, depending on specified monitoring and therapeutic needs.
FIG. 14 illustrates an embodiment of an antitachycardia shock waveform that includes a biphasic pulse. One electrode system for delivering an antitachycardia shock with such a waveform includes SVC defibrillation electrode 1356, RV defibrillation electrode 1358, and can electrode 1349. For example, RV defibrillation electrode 1358 is used as the cathode, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be used as the anode, for the shock delivery. The addition of at least one of the LV electrodes (CS electrode 1369 and CV electrode 1368) to this electrode system will lower the DFT. In one embodiment, RV defibrillation electrode 1358 is used as the cathode, and SVC defibrillation electrode 1356, at least one of the CS electrode 1369 and CV electrode 1368, and can electrode 1349 are electrically wired to be used as the anode, for delivering a ventricular defibrillation shock. In another embodiment, RV defibrillation electrode 1358 and at least one of the CS electrode 1369 and CV electrode 1368 are electrically wired to be used as the cathode, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be sued as the anode, for delivering a ventricular defibrillation shock. In another embodiment, CS defibrillation electrode 1369 is used as the cathode, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be used as the anode, for delivering an atrial defibrillation shock. In each of these embodiments, the polarity may be reversed.
FIG. 15 illustrates another embodiment of an antitachycardia shock waveform that includes multiple pulses for each single shock. Using a shock waveform including multiple pulses will lower the DFT. In the illustrated embodiment, the antitachycardia shock waveform includes a monophasic auxiliary pulse followed by a biphasic primary pulse. The primary pulse is delivered through a primary electrode set along a current pathway in a portion of the heart. The auxiliary pulse is delivered through an auxiliary electrode set to another portion of the heart where the current intensity resulting from the primary pulse is at or near a minimum. In various embodiments, the primary electrode set differs from the auxiliary electrode set by at least one electrode.
In one embodiment, the primary electrode set and the auxiliary electrode set each include electrodes selected from SVC defibrillation electrode 1356, RV defibrillation electrode 1358, the LV electrodes (CS electrode 1369 and CV electrode 1368), and can electrode 1349.
In one embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, can electrode 1349 is used as the anode for delivering the auxiliary pulse, SVC defibrillation electrode 1356 is used as the cathode for delivering the primary pulse, and RV defibrillation electrode 1358 is used as the anode for delivering the primary pulse.
In another embodiment, SVC defibrillation electrode 1356 is used as the cathode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is used as the anode for delivering the auxiliary pulse, CS electrode 1369 is used as the cathode for delivering the primary pulse, and can electrode 1349 is used as the anode for delivering the primary pulse.
In another embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, SVC defibrillation electrode 1356 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is used as the cathode for delivering the primary pulse, and CS electrode 1369 is also used as the anode for delivering the primary pulse.
In another embodiment, RV defibrillation electrode 1358 is used as the cathode for delivering the auxiliary pulse, can electrode 1349 is used as the anode for delivering the auxiliary pulse, CS electrode 1369 is used as the cathode for delivering the primary pulse, and SVC defibrillation electrode 1356 is used as the anode for delivering the primary pulse.
In another embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, can electrode 1349 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is used as the cathode for delivering the primary pulse, and can electrode 1349 is used as the anode for delivering the primary pulse.
In another embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is also used as the cathode for delivering the primary pulse, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be used as the anode for delivering the primary pulse.
In another embodiment, RV defibrillation electrode 1358 is used as the cathode for delivering the auxiliary pulse, CS electrode 1369 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 and CS electrode 1369 are electrically wired to be used as the cathode for delivering the primary pulse, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be used as the anode for delivering the primary pulse.
In another embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, can electrode 1349 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 and CS electrode 1369 are electrically wired to be used as the cathode for delivering the primary pulse, and SVC defibrillation electrode 1356 and can electrode 1349 are electrically wired to be used as the anode for delivering the primary pulse.
In another embodiment, CS electrode 1369 is used as the cathode for delivering the auxiliary pulse, can electrode 1349 is used as the anode for delivering the auxiliary pulse, RV defibrillation electrode 1358 is used as the cathode for delivering the primary pulse, and CS electrode 1369, SVC defibrillation electrode 1356, and can electrode 1349 are electrically wired to be used as the anode for delivering the primary pulse.
In one embodiment, the primary pulse has a primary pulse width in the range of 0.5 to 20 milliseconds, the auxiliary pulse has an auxiliary pulse width in the range of 0.5 to 10 milliseconds, and the primary pulse and the auxiliary pulse are separated by an interpulse delay in the range of 0 to 20 milliseconds. In one embodiment, one or more of the primary pulse width, the auxiliary pulse width, and the interpulse delay are programmable.
The electrode configurations and waveforms for the antitachycardia shock discussed in this document are specific examples. In various embodiments, the electrode system for delivering the antitachycardia shock may include intracardiac electrodes, epicardial electrodes, subcutaneous electrodes, and any combination thereof; and the waveform of the antitachycardia shock may include one or more pulses and/or phases. Examples of such electrode configurations and waveforms are also discussed in U.S. Pat. No. 5,107,834, entitled “LOW ENERGY MULTIPLE SHOCK DEFIBRILLATION/CARDIOVERSION DISCHARGE TECHNIQUE AND ELECTRODE CONFIGURATION”, assigned to Cardiac Pacemakers, Inc., U.S. Pat. No. 5,540,723, entitled “METHOD AND APPARATUS FOR DELIVERING AN OPTIMUM SHOCK DURATION IN TREATING CARDIAC ARRHYTHMIAS”, assigned to Duke University and Cardiac Pacemakers, Inc., U.S. Pat. No. 5,603,732, entitled “SUBCUTANEOUS DEFIBRILLATION ELECTRODES”, assigned to Cardiac Pacemakers, Inc., U.S. Pat. No. 5,978,705, entitled “METHOD AND APPARATUS FOR TREATING CARDIAC ARRHYTHMIA USING AUXILIARY PULSE,” assigned to UAB Research Foundation, U.S. Pat. No. 6,002,962, entitled “IMPLANTABLE TRIPHASIC WAVEFORM DEFIBRILLATOR”, assigned to UAB Research Foundation, and U.S. patent application Ser. No. 11/275,943, entitled “METHOD AND APPARATUS FOR TERMINATION OF CARDIAC TACHYARRHYTHMIAS”, assigned to Cardiac Pacemakers, Inc., filed on Feb. 6, 2006, which are incorporated herein by reference in their entirety. Other waveforms and electrode configurations are possible as determined by those of ordinary skill in the art upon reading and understanding this document. In various embodiments, microprocessor 420 controls the electrode configuration and the waveform for each delivery of the antitachycardia shock. In one embodiment, either of both of the electrode configuration and the waveform for the antitachycardia shock is programmable by a user through external system 1242.
In various embodiments, in response to the detection of a specified cardiac activity indicated for an antitachycardia shock, vagal nerve stimulation is delivered for a neurostimulation period before the antitachycardia shock is delivered. In one embodiment, the neurostimulation period is between 1 second and 20 seconds. In one embodiment, the neurostimulation period is programmable, such as by a user through external system 1242. In various embodiments, the antitachycardia shock that follows the vagal nerve stimulation has a waveform as illustrated in FIG. 14 or FIG. 15 or any other known cardioversion/defibrillation waveform. In one embodiment, microprocessor 420 initiates and times the neurostimulation period and initiates the delivery of the antitachycardia shock upon expiration of the neurostimulation period. In one embodiment, microprocessor 420 initiates the delivery of the antitachycardia shock upon expiration of the neurostimulation period only if the specified cardiac activity sustains at the end of the neurostimulation period.
The methods illustrated in this disclosure are not intended to be exclusive of other methods within the scope of the present subject matter. Those of ordinary skill in the art will understand, upon reading and comprehending this disclosure, other methods within the scope of the present subject matter. The above-identified embodiments, and portions of the illustrated embodiments, are not necessarily mutually exclusive. These embodiments, or portions thereof, can be combined. In various embodiments, the methods provided above are implemented as a computer data signal embodied in a carrier wave or propagated signal, that represents a sequence of instructions which, when executed by a processor cause the processor to perform the respective method. In various embodiments, methods provided above are implemented as a set of instructions contained on a computer-accessible medium capable of directing a processor to perform the respective method. In various embodiments, the medium is a magnetic medium, an electronic medium, or an optical medium. One of ordinary skill in the art will understand that the modules and other circuitry shown and described herein can be implemented using software, hardware, and combinations of software and hardware.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments as well as combinations of portions of the above embodiments in other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. A system configured to be coupled to a heart including a right atrium (RA) connected to a superior vena cava (SVC), a right ventricle (RV), a left ventricle (LV), a coronary sinus, and a coronary vein, the system comprising:

a sensor configured to detect a cardiac activity indicated for a defibrillation shock;

a vagal nerve stimulator configured to deliver vagal nerve stimulation to lower a defibrillation threshold in preparation for delivering the defibrillation shock;

a plurality of defibrillation electrodes including at least one LV electrode configured to be placed in the coronary sinus or coronary vein; and

a defibrillator configured to deliver the defibrillation shock to the heart through the plurality of defibrillation electrodes.

2. The system of claim 1, comprising an implantable housing configured to house both the vagal nerve stimulator and the defibrillator.

3. The system of claim 1, comprising a first implantable housing configured to house the vagal nerve stimulator and a second implantable housing configured to house the defibrillator.

4. The system of claim 1, comprising a controller configured to initiate and time a neurostimulation period in response to the detection of the cardiac activity, and wherein the vagal nerve stimulator is configured to deliver the vagal nerve stimulation during the neurostimulation period.

5. The system of claim 4, wherein the controller is configured to initiate the delivery of the defibrillation shock in response to an expiration of the neurostimulation period.

6. The system of claim 5, wherein the controller is configured to initiate the delivery of the defibrillation shock if the cardiac activity remains detected at the end of the neurostimulation period.

7. The system of claim 4, wherein the controller is configured to control a waveform of the defibrillation shock, the waveform including a plurality of pulses.

8. The system of claim 7, wherein the controller is configured to control a waveform of the defibrillation shock, the waveform including an auxiliary pulse followed by a primary pulse.

9. The system of claim 8, wherein the controller is configured to time an interpulse interval between the auxiliary pulse and the primary pulse.

10. The system of claim 8, comprising a plurality of electrodes coupled to the defibrillator, the plurality of electrodes including:

an auxiliary electrode set through which the auxiliary pulse is delivered; and

a primary electrode set through which the primary pulse is delivered,

wherein the auxiliary electrode set is different from the primary electrode set by at least one electrode.

11. The system of claim 1, comprising an implantable housing and a plurality of electrodes, the implantable housing configured to house at least the defibrillator, the plurality of electrodes coupled to the defibrillator and including:

the at least one LV electrode;

a supraventricular defibrillation electrode configured to be placed in one or more of the SVC and the RA;

an RV defibrillation electrode configured to be placed in the RV; and

a can electrode including at least a portion of the implantable housing.

12. The system of claim 11, wherein the plurality of electrodes are connected to the defibrillator such that the RV defibrillation electrode is used as a cathode for delivering the defibrillation shock, and the at least one LV electrode, the SVC defibrillation electrode, and the can electrode are electrically wired to be used as an anode for delivering the defibrillation shock.

13. The system of claim 11, comprising a lead including a primary end, a distal end, and an elongate body coupled between the primary end and the distal end, the primary end configured to be coupled to the defibrillator, the distal end including the at least one LV electrode, the lead configured to allow the distal end to be placed in the coronary sinus.

14. The system of claim 11, comprising a lead including a primary end, a distal end, and an elongate body coupled between the primary end and the distal end, the primary end configured to be coupled to the defibrillator, the distal end including the at least one LV electrode, the lead configured to allow the distal end to be placed in the coronary vein.

15. A method for defibrillating a heart including a right atrium (RA) connected to a superior vena cava (SVC), a right ventricle (RV), a left ventricle (LV), a coronary sinus, and a coronary vein, comprising:

detecting a cardiac activity indicated for a defibrillation shock;

applying neural stimulation to lower a defibrillation threshold in preparation for the defibrillation shock; and

delivering the defibrillation shock using a plurality of defibrillation electrodes including at least one LV electrode placed in the coronary sinus or coronary vein.

16. The method of claim 15, comprising:

initiating and timing a neurostimulation period in response to the detection of the cardiac activity; and

delivering a vagal nerve stimulation during the neurostimulation period.

17. The method of claim 16, comprising establishing the neurostimulation period to a period between 1 second and 20 seconds.

18. The method of claim 16, comprising initiating the delivery of the defibrillation shock in response to an expiration of the neurostimulation period.

19. The method of claim 18, comprising initiating the delivery of the defibrillation shock if the cardiac activity sustains at the end of the neurostimulation period.

20. The method of claim 15, wherein delivering the defibrillation shock comprises delivering a defibrillation shock having a waveform including a plurality of pulses.

21. The method of claim 20, wherein delivering the defibrillation shock having the waveform including the plurality of pulses comprises delivering a defibrillation shock having a waveform including an auxiliary pulse followed by a primary pulse, and wherein delivering the defibrillation shock using the plurality of defibrillation electrodes comprises delivering the auxiliary pulse using an auxiliary electrode set and delivering the primary pulse using a primary electrode set, the auxiliary electrode set different from the primary electrode set by at least one electrode.

22. The method of claim 21, comprising controlling an interpulse interval between the auxiliary pulse and the primary pulse.

23. The method of claim 22, comprising setting the interpulse interval to a time interval between 0 and 20 milliseconds.

24. The method of claim 15, wherein delivering the defibrillation shock using the plurality of defibrillation electrodes comprises using the at least one LV electrode, a supraventricular defibrillation electrode placed in one or more of the SVC and the RA, an RV defibrillation electrode placed in the RV, and a can electrode including at least a portion of an implantable housing configured to house at least a defibrillator from which the defibrillation is delivered.

25. The method of claim 24, wherein delivering the defibrillation shock using the plurality of defibrillation electrodes comprises:

using the RV defibrillation electrode as a cathode; and

using the at least one LV electrode, the SVC defibrillation electrode, and the can electrode as an anode, the at least one LV electrode, the SVC defibrillation electrode, and the can electrode electrically wired to each other.

26. The method of claim 24, wherein using the at least one LV electrode comprises using an electrode placed in the coronary sinus.

27. The method of claim 24, wherein using the at least one LV electrode comprises using an electrode placed in the coronary vein.

28. A system coupled to a heart including a right atrium (RA) connected to a superior vena cava (SVC), a right ventricle (RV), a left ventricle (LV), a coronary sinus, and a coronary vein, the system comprising:

means for detecting a cardiac activity indicated for a defibrillation shock;

means for applying neural stimulation to lower a defibrillation threshold in preparation for the defibrillation shock; and

means for subcutaneously delivering the defibrillation shock using a plurality of defibrillation electrodes including at least one LV electrode placed in the coronary sinus or coronary vein.