Patent Description:
Heart failure (HF) is a debilitating, end-stage disease in which abnormal function of the heart leads to inadequate blood flow to fulfill the needs of the body's tissues. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately fill with blood between heartbeats, and the valves regulating blood flow may develop leaks, allowing regurgitation or backflow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness, and inability to carry out daily tasks may result. Not all HF patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive. As HF progresses, it tends to become increasingly difficult to manage.

Heart failure may result in patients experiencing ventricular arrhythmias, such as ventricular tachycardia (VT). VT may be treated by ablation and/or pacing.

Subcutaneous implantable cardioverter-defibrillators (SICDs) are a type of implantable cardiac device (ICD) generally used in patients who do not require cardiac pacing. This pacing limitation, however, prevents a potentially large pool of patients from getting an SICD. Although it has been suggested that leadless pacemakers may be used in conjunction with SICDs to support the needs of patients who require pacing, leadless pacemakers require an additional implantation procedure and may be relatively expensive.

Accordingly, it would be desirable to provide an SICD capable of treating VT by applying pacing.

<CIT> discloses implantable medical electrical leads having electrodes arranged such that a defibrillation coil electrode and a pace/sense electrode are concurrently positioned substantially over the ventricle when implanted. The leads include an elongated lead body having a distal portion and a proximal end, a connector at the proximal end of the lead body, a defibrillation electrode located along the distal portion of the lead body. The defibrillation electrode includes a first electrode segment and a second electrode segment proximal to the first electrode segment by a distance. The leads may include at least one pace/sense electrode located between the first defibrillation electrode segment and the second defibrillation electrode segment.

<CIT> discloses devices and methods for single therapy pulse (STP) therapy for tacharrythmia. The STP therapy can be delivered from a far-field position to allow a "global" capture approach to pacing. Due to the global capture in STP, a series of pulses, which is indicative of conventional anti-tachycardia pacing (ATP) delivered by transvenous systems, becomes unnecessary. One to four pulses at most are needed for STP, and after delivery of the one to four pulses, therapy delivery can be interrupted to determine whether the previously delivered therapy has been successful.

In one embodiment, the present disclosure is directed to a subcutaneous implantable cardioverter-defibrillator (SICD) implantable in a subject. The SICD includes a case including a controller, and at least one conductive lead extending from the case, the at least one conductive lead including a plurality of coil electrodes, wherein the SICD is configured, via the controller, to apply anti-tachycardia pacing (ATP) to the subject using the at least one conductive lead.

In another embodiment, the present disclosure is directed to a method of assembling a subcutaneous implantable cardioverter-defibrillator (SICD). The method includes coupling at least one conductive lead to a case, the at least one conductive lead including a plurality of coil electrodes. The method further includes installing a controller in the case, the controller configured to cause the SICD to apply anti-tachycardia pacing (ATP) to the subject using the at least one conductive lead.

The foregoing and other aspects, features, details, utilities and advantages of the present disclosure will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

The systems and methods described herein facilitate treating ventricular tachycardia (VT) by applying anti-tachycardia pacing (ATP) using a subcutaneous implantable cardioverter-defibrillator (SICD). That is, as described herein, the electrodes of an SICD may be used to treat patients that experience occasional VT. In some embodiments, the electrodes of the SICD may also be used to apply high voltage (HV) therapy.

<FIG> are schematic diagrams of different embodiments of an exemplary subcutaneous implantable cardioverter defibrillator (SICD) system that may be used to apply ATP to facilitate treating VT. The embodiments shown in <FIG> have been demonstrated, using computer modeling, to have relatively low defibrillation thresholds (DFTs) (i.e., the minimum amount of energy needed to return the heart to normal rhythm from cardiac dysrhythmia). For example, the embodiments shown in <FIG> may have DFTs from approximately <NUM> to <NUM> Joules (J). As described herein, the defibrillation electrodes in these SICD systems may be adapted to perform subcutaneous ATP. In some embodiments, linear defibrillation coils are divided into two portions (e.g., halves) to perform ATP from each partial coil or to perform combined ATP. The delivery of the ATP (and sensing of the subsequent evoked response, etc.) is controlled by a controller (e.g., a microprocessor) installed in the case of these SICD systems.

In the embodiments described herein, ATP may be performed using pulses having an amplitude corresponding to a relatively small supra-threshold margin (e.g., approximately <NUM> times the DFT) at relatively large pulse widths (e.g., from approximately <NUM> to <NUM> milliseconds (ms)). These pulses may be minimized to reduce skeletal muscle stimulation in the subject. For example, pulses in the <NUM> to <NUM> milliamp (mA) range may be driven into a <NUM> ohm (Ω) load using only approximately <NUM> to <NUM> volts (V).

In some embodiments, larger pacing pulses may be used to capture more of the subject's heart, which may increase the probability of a single ATP pulse (or relatively few ATP pulses) terminating VT. This facilitates treating VT without using high voltage defibrillation pulses.

In the following description, with respect to the embodiments shown in <FIG>, several possible vectors (i.e., electrode combinations) for subcutaneous ATP are recommended, along with non-pacing electrode combinations that may be used for detecting the evoked response. However, those of skill in the art will appreciate that the pacing and evoked response electrode combinations identified herein are merely examples, and that other vectors and combinations may be used within the spirit and scope of the disclosure.

<FIG> is a schematic diagram of one embodiment of an exemplary SICD system <NUM> that may be used to terminate VT in a heart <NUM> of a subject <NUM>. SICD system <NUM> includes a case <NUM>, a first conductive lead <NUM>, and a second conductive lead <NUM> extending from case <NUM>. First conductive lead <NUM> includes a first coil electrode <NUM> and a second coil electrode <NUM>. Further, second conductive lead <NUM> includes a third coil electrode <NUM> and a fourth coil electrode <NUM>. First coil electrode <NUM> and second coil electrode <NUM> may be, for example, portions (e.g., halves) of a single linear defibrillation coil on first conductive lead <NUM>. Third coil electrode <NUM> and fourth coil electrode <NUM> may similarly be portions (e.g., halves) of a single linear defibrillation coil on second conductive lead <NUM>.

In this embodiment, first coil electrode <NUM> and second coil electrode <NUM> are anterior of heart <NUM>, and second conductive lead <NUM> wraps around a side of the patient such that fourth coil electrode <NUM> is posterior of heart <NUM>. Further, first coil electrode <NUM> and second coil electrode <NUM> are oriented generally orthogonally to fourth coil electrode <NUM>. Alternatively, the case and coils of SICD system <NUM> may have any suitable position and orientation. For example, in some embodiments, first coil electrode <NUM> is positioned closer to case <NUM>, and second coil electrode <NUM> is positioned approximately where first coil electrode is shown in <FIG>. In yet another embodiment, first coil electrode <NUM>, second coil electrode <NUM>, third coil electrode <NUM>, and fourth coil electrode <NUM> are all included on a single lead that beings at case <NUM>, runs along the sternum, turns when proximate the xiphoid process, and wraps around to the side and back to place the coil electrodes in positions similar to those shown in <FIG>.

In this embodiment, ATP may be achieved using first coil electrode <NUM>, second coil electrode <NUM>, or a combination of first coil electrode <NUM> and second coil electrode <NUM>. Further, an evoked response may be detected using other combinations of the coils of SICD system <NUM>. For example, the following Table <NUM> lists several example pacing vectors and paced evoked response sensing electrode combinations. The numbers listed in Table <NUM> correspond to the part numbers of the components.

In some embodiments, the electrode combination that provides a smallest accelerometer signal (e.g., detected using an accelerometer in case <NUM>) is used for ATP (i.e., that combination is automatically selected by the controller). This facilitates reducing unnecessary skeletal muscle stimulation. Further, in some embodiments, SICD system <NUM> may automatically analyze (using the controller) which electrode combination detects the largest evoked response and automatically use this combination for evoked response detection. Further, if no evoked response is detected, the amplitude of the ATP pulses may be increased.

The following Table <NUM> lists several example electrode configurations for biphasic defibrillation pulse delivery with low DFT. Further, Table <NUM> lists corresponding electrode combinations for dual vector sensing.

Because myopotentials may be generated by skeletal muscle contraction on one vector and not the other, a cross-correlation is performed between the two sensing vectors to increase the signal to noise ratio in such situations. See, for example, <CIT>, and <CIT>. Further, in some embodiments, sensing vectors that provide a largest R-wave and/or a largest R-wave to T-wave ratio may be automatically selected to reduce the probability of under-sensing R-waves and over-sensing T-waves.

<FIG> is a schematic diagram of another embodiment of an exemplary SICD system <NUM> that may be used to terminate VT in heart <NUM> of subject <NUM>. SICD system <NUM> includes a case <NUM>, a first conductive lead <NUM>, and a second conductive lead <NUM> extending from case <NUM>. First conductive lead <NUM> includes a first coil electrode <NUM> and a second coil electrode <NUM>. Further, second conductive lead <NUM> includes a third coil electrode <NUM> and a fourth coil electrode <NUM>. First coil electrode <NUM> and second coil electrode <NUM> may be, for example, portions (e.g., halves) of a single linear defibrillation coil on first conductive lead <NUM>. Third coil electrode <NUM> and fourth coil electrode <NUM> may similarly be portions (e.g., halves) of a single linear defibrillation coil on second conductive lead <NUM>.

In this embodiment, first coil electrode <NUM> and second coil electrode <NUM> are anterior of heart <NUM>, and second conductive lead <NUM> wraps around a side of the patient such that fourth coil electrode <NUM> is posterior of heart <NUM>. Further, first coil electrode <NUM> and second coil electrode <NUM> are oriented generally parallel to fourth coil electrode <NUM>. Alternatively, the case and coils of SICD system <NUM> may have any suitable position and orientation. For example, in some embodiments, case <NUM> may be located in a mid-axillary position, on the left side of the subject, similar to the position of case <NUM> (shown in <FIG>).

In this embodiment, ATP may be achieved using first coil electrode <NUM>, second coil electrode <NUM>, or a combination of first coil electrode <NUM> and second coil electrode <NUM>. Further, evoked response may be detected using other combinations of the coils of SICD system <NUM>. For example, the following Table <NUM> lists several example pacing vectors and paced evoked response sensing electrode combinations. The numbers listed in Table <NUM> correspond to the part numbers of the components.

As with SICD system <NUM>, in some embodiments, the electrode combination that provides a smallest accelerometer signal (e.g., detected using an accelerometer in case <NUM>) is used for ATP. This facilitates reducing unnecessary skeletal muscle stimulation. Further, in some embodiments, SICD system <NUM> may automatically analyze which electrode combination detects the largest evoked response and automatically use this combination for evoked response detection. Further, if no evoked response is detected, the amplitude of the ATP pulses may be increased.

<FIG> is a schematic diagram of another embodiment of an exemplary SICD system <NUM> that may be used to terminate VT in heart <NUM> of subject <NUM>. SICD system <NUM> includes a case <NUM> and a first conductive lead <NUM> extending from case <NUM>. First conductive lead <NUM> includes a first coil electrode <NUM>, a second coil electrode <NUM>, and a third coil electrode <NUM>. First coil electrode <NUM>, second coil electrode <NUM>, and third coil electrode <NUM> may be, for example, portions (e.g., thirds) of a single linear defibrillation coil on first conductive lead <NUM>.

In this embodiment, first coil electrode <NUM>, second coil electrode <NUM>, and third coil electrode <NUM> are anterior of heart <NUM>. Further, first coil electrode <NUM> is oriented generally parallel to second coil electrode <NUM> and third coil electrode <NUM>. Alternatively, the case and coils of SICD system <NUM> may have any suitable position and orientation. For example, in some embodiments, first coil electrode <NUM> may be segmented into two separate coils.

In this embodiment, ATP may be achieved using first coil electrode <NUM>, second coil electrode <NUM>, third coil electrode <NUM>, or a combination of at least two of first coil electrode <NUM>, second coil electrode <NUM>, third coil electrode <NUM>. Further, evoked response may be detected using other combinations of the coils of SICD system <NUM>. For example, the following Table <NUM> lists several example pacing vectors and paced evoked response sensing electrode combinations. The numbers listed in Table <NUM> correspond to the part numbers of the components.

When applying ATP using a SICD system (such as SICD systems <NUM>, <NUM>, and <NUM>), to prevent sensing relatively large pacing pulse artifacts, a sense amplifier is blanked (i.e., prevented from sensing) just before delivery of pacing pulses. For example, <FIG> is a circuit diagram of one embodiment of signal processing circuitry <NUM> including a sense amplifier <NUM>. Signal processing circuitry <NUM> may be included within a case, such as cases <NUM>, <NUM>, and <NUM> (shown in <FIG>).

As shown in <FIG>, sense amplifier <NUM> includes a first input <NUM> connected to a sensing electrode <NUM> and a second input <NUM> connected to a reference electrode <NUM>. Further, a first input switch <NUM> is connected between first input <NUM> and sensing electrode <NUM>, and a second input switch <NUM> is connected between second input <NUM> and reference electrode <NUM>. In this embodiment, sensing electrode <NUM> and reference electrode <NUM> are different from a pacing electrode to prevent a pacing polarization artifact from obscuring the sensed evoked response. An output <NUM> of sense amplifier <NUM> is coupled to an analog to digital converter <NUM> via a resistor <NUM>, an output switch <NUM>, and a capacitor <NUM>.

Just prior to delivering an ATP pulse (e.g., <NUM> before delivering an ATP pulse), first input switch <NUM>, second input switch <NUM>, and output switch <NUM> are opened (e.g., using the controller). Capacitor <NUM> acts as a sample and hold element, retaining the measured EKG level just prior to pacing. After the pacing pulse is delivered (e.g., approximately <NUM> to <NUM> later), first input switch <NUM>, second input switch <NUM>, and output switch <NUM> are closed (e.g., using the controller), and sensing resumes. In this embodiment, the digitized output signal is analyzed for an evoked response by determining if the derivative of the signal exceeds a negative or positive threshold (e.g., ± <NUM> mV/ms) in a predetermined time period (e.g., <NUM> after the pacing pulse).

<FIG> is a trace of an example EKG <NUM> captured using signal processing circuitry <NUM> (shown in <FIG>). EKG <NUM> includes paced QRS complexes <NUM> and <NUM>. Pacing pulses <NUM> and <NUM> mark the onset of blanking, resulting in flat segments <NUM> and <NUM> following pacing pulses <NUM> and <NUM>. Sudden sharp downward transitions <NUM> and <NUM> mark the end of the blanking, and occur during a mid-region of paced QRS complexes <NUM> and <NUM>. The derivative of subsequent rapid upward deflections <NUM> and <NUM> can be processed to verify capture.

As shown in <FIG>, EKG <NUM> further includes native QRS complexes <NUM> and <NUM> that were detected and thus inhibited pacing. Further, EKG <NUM> includes a pacing pulse <NUM> that is not followed by an evoked response. Thus, EKG <NUM> subsequently includes a native QRS <NUM> that emerges as a result of the loss of capture of pacing pulse <NUM>.

<FIG> is a flowchart of an algorithm <NUM> for providing ATP therapy to extinguish VT with a minimal number of pacing pulses. Algorithm <NUM> may be implemented, for example, using SICD systems <NUM>, <NUM>, and <NUM>. Specifically, algorithm may be performed by the controller (e.g., a microprocessor) included in cases <NUM>, <NUM>, and <NUM>. Algorithm <NUM> starts at block <NUM>. Initially, in this embodiment, a percentage, Z, of a cycle length, CL, is set at <NUM>%. The cycle length is defined as the time interval between subsequent R waves. Alternatively, Z may be set to any suitable value.

At block <NUM>, is determined whether at least <NUM> of <NUM> VT events satisfy certain criteria. Alternatively, other ratios may be used (e.g., <NUM> of <NUM> events). If the cycle length is greater than <NUM> (indicating a sinus rhythm) for at least <NUM> of <NUM> events, flow proceeds to block <NUM>, and no action is taken. If the cycle length is less than <NUM> (indicating ventricular fibrillation (VF)) for at least <NUM> of <NUM> events, flow proceeds to block <NUM>, and a defibrillating shock is delivered. If, however, the cycle length is greater than or equal to <NUM> and less than or equal to <NUM> (indicating VT) for at least <NUM> of <NUM> events, flow proceeds to block <NUM>, and a single ATP pulse is delivered at Z (i.e., <NUM>%) of the cycle length following the last event.

Subsequently, at block <NUM>, it is determined whether capture is achieved based on the evoked response and/or extension of the cycle length. If capture is achieved, flow proceeds to block <NUM> and subsequently to block <NUM>, where it is determined whether Z is less than <NUM>%. If Z is not less than <NUM>%, flow proceeds to block <NUM>, at which point the amplitude of subsequent ATP pulses is increased (e.g., by <NUM>%), and Z is reduced by <NUM>%, before flow returns to block <NUM>. If Z is less than <NUM>%, flow proceeds to block <NUM>, and i) a predetermined number of ATP pulses (e.g., <NUM> to <NUM> pulses) are applied over the next cycle length at equally spaced intervals or, alternatively, ii) a predetermined number of ATP pulses (e.g., <NUM> to <NUM> pulses) are delivered at <NUM>% of the cycle length.

At block <NUM>, if capture is not achieved, flow proceeds to block <NUM> and subsequently to block <NUM>, where it is determined whether Z is less than <NUM>%. If Z is less than <NUM>%, flow proceeds to block <NUM>, at which point the amplitude of subsequent ATP pulses is increased (e.g., by <NUM>%), and Z is increased by <NUM>% (although keeping Z below <NUM>%), before flow returns to block <NUM>. If Z is not less than <NUM>%, flow proceeds to block <NUM>, and i) a predetermined number of ATP pulses (e.g., <NUM> to <NUM> pulses) are applied over the next cycle length at equally spaced intervals or, alternatively, ii) a predetermined number of ATP pulses (e.g., <NUM> to <NUM> pulses) are delivered at <NUM>% of the cycle length in an attempt to achieve capture.

In the systems and methods described herein, discomfort from the applied ATP may be reduced using several techniques.

For example, in some embodiments, the amplitude of the ATP pulses can be minimized by performing capture verification using the evoked response. For example, the paced evoked response may be analyzed to perform capture verification and to determine the capture threshold (which may be, e.g., approximately <NUM> to <NUM> mA). Further, the coil electrodes may be coated with a non-polarizable coating to reduce polarization, so that immediate sensing after pacing is possible.

Further, as described above, the sense amplifier can be blanked during pacing, and a sample and hold circuit (e.g., a capacitor) can be used to hold the ECG voltage during pacing to facilitate detecting the evoked response. If the evoked response is not detected, the ATP pulse amplitude may be increased on subsequent pulses until capture is achieved and verified from the evoked response.

Further, in some embodiments, monophasic cathodic pulses are delivered instead of biphasic pulses. Monophasic cathode pulses have lower thresholds, and may be less noxious to the subject.

In addition, in some embodiments, a learning mode is implemented that is capable of recognizing a pulse regiment that is effective in achieving VT termination, and using that pulse regiment in terminate subsequent future arrhythmias. For example, if the VT has a cycle length of <NUM>, and is terminated by a <NUM> mA pulse at <NUM>% of the cycle length, then the next time arrhythmia occurs, a <NUM> mA pulse is applied at <NUM>% of the cycle length. Similarly, if the VT has a cycle length of <NUM>, and is terminated by a <NUM> mA pulse at <NUM>% of the cycle length, then the next time arrhythmia occurs, a <NUM> mA pulse is applied at <NUM>% of the cycle length.

In some embodiments, a predetermined (and programmable) number of ATP pulses are applied to attempt VT termination before shocking is implemented. Alternatively, an algorithm may be used to provide cardioversion with a predetermined number of ATP attempts.

Further, in some embodiments, an in-line pacing electrode coil may be positioned over a point of maximum impulse (e.g., a V3 lead location) or in a parasternal location. The anode that does not provide the pacing may be the case or a larger electrode than the pacing electrode. In some embodiments, the entire shocking electrode may be used to perform ATP, allowing for multisite pacing that may improve ATP efficacy in many patients. Alternatively, the shocking electrode may be divided into multiple segments, as described above. In such cases, pacing may be achieved using either segment individually or both segments combined. Further, the electrode combination that provides the lowest pacing threshold may be automatically selected using a capture verification algorithm that measures the pacing threshold. For defibrillation, the segmented pacing electrode acts as one shocking electrode. Optimizing the pacing electrode size (i.e., length) may facilitate minimizing skeletal muscle stimulation while achieving adequate length for capture. For example, each segment may have a length from approximately <NUM> to <NUM> centimeters (cm).

In addition, in some embodiments, a short coil segment is utilized for a first one or more rounds of ATP, allowing for adjustment of cycle length and/or pacing output in each consecutive ATP round. In case of failure in the first one or more rounds to terminate the VT, two or more coil segments are electrically coupled for delivering a second one or more rounds of ATP. In this scheme, the first one or more rounds elicit less skeletal muscle and/or diaphragmatic contraction, while the second one or more rounds more aggressively attempt to capture ventricular myocardium to penetrate into the VT circuit, with less regard for skeletal muscle and/or diaphragmatic contraction.

In some embodiments, a time optimization of ATP pulse delivery is controlled to coincide with spatial optimization. Spatial optimization may be controlled largely by selection of one or more stimulating electrodes. Specifically, the smaller the electrode and the closer to the myocardium, the more the electrode behaves like a point stimulator. In contrast, the larger the electrode and the further from the myocardium, the more the electrode behaves like a field stimulator. Field stimulation, at a tissue level, may result in multiple coordinated yet spatially distributed stimulation capture locations.

For example, suppose a first ATP attempt uses a single short coil segment at a low-to-moderate stimulation amplitude. This would be expected to result in a virtual point stimulation. If the first ATP attempt fails to terminate the VT, modulation of timing with regard to cycle length can be performed (e.g., as described in associated with <FIG>). In some embodiments, subsequent ATP use one or more coil segments with larger dimensions than the coil segment of the first ATP attempt. Because of the larger size, the excitation at the same total energy will achieve stimulation that is more like field stimulation, which is more spatially diverse. Thus, when switching to a larger electrode, the Z value may be increased. Similarly, when switching to a larger coil length to reduce energy delivered (e.g., to avoid excessive stimulation of skeletal muscle), the Z value may be decreased accordingly.

For example, <FIG> is a flowchart of an algorithm <NUM> for providing ATP therapy to extinguish VT that incorporates a learning mode. Algorithm <NUM> may be implemented, for example, using SICD systems <NUM>, <NUM>, and <NUM>. Specifically, algorithm may be performed by the controller (e.g., a microprocessor) included in cases <NUM>, <NUM>, and <NUM>. Further algorithm <NUM> may be implemented in combination with algorithm <NUM> (shown in <FIG>).

At block <NUM>, after ATP is applied using a particular vector and stimulation parameters, it is determined whether the ATP was successful in terminating VT. If the ATP was successful, flow proceeds to block <NUM>, and the vector and stimulation parameters that were used in the ATP are recorded (i.e., stored) with an indication that the vector and stimulation parameters successfully terminated VT. Then, for future episodes, the recorded vector and stimulation parameters that previously resulted in terminating VT can be retrieved, and ATP is again applied using that same vector and stimulation parameters.

If, however, at block <NUM>, the ATP was not successful, flow proceeds to block <NUM>, and the vector and stimulation parameters are recorded with an indication that they were unsuccessful. Then, at block <NUM>, at least one of the vector and the stimulation parameters are modified and ATP is applied again. Flow then returns to block <NUM> to determine whether this ATP was successful.

Accordingly, the systems and methods described herein facilitate applying anti-tachycardia pacing ATP to treat VT using subcutaneous implantable cardioverter-defibrillators SICDs. An SICD implantable in a subject includes a case including a controller, and at least one conductive lead extending from the case. The at least one conductive lead includes a plurality of coil electrodes, wherein the SICD is configured, via the controller, to apply anti-tachycardia pacing (ATP) to the subject using the at least one conductive lead. Further, those of skill in the art will appreciate that, in some embodiments, the electrodes of the SICD (and the electrode configurations described herein) may also be used to apply high voltage (HV) therapy.

All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the disclosure. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting.

Claim 1:
A subcutaneous implantable cardioverter-defibrillator (SICD) (<NUM>; <NUM>; <NUM>) implantable in a subject (<NUM>) comprising:
a case (<NUM>; <NUM>; <NUM>) comprising a controller; and
at least one conductive lead (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>) extending from the case (<NUM>; <NUM>; <NUM>), the at least one conductive lead (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>) comprising a plurality of coil electrodes (<NUM>, <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>), wherein the SICD (<NUM>; <NUM>; <NUM>) is configured, via the controller, to apply anti-tachycardia pacing (ATP) to the subject (<NUM>) using the at least one conductive lead (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>), characterized in that the controller is configured to select an electrode combination for applying the ATP based on at least one of i) an accelerometer signal and ii) a previously detected evoked response.