Map and ablate open irrigated hybrid catheter

An embodiment of an open-irrigated catheter system comprises a tip section, a distal insert, and mapping electrodes. The tip section has an exterior wall that defines an open interior region within the tip section. The exterior wall includes mapping electrode openings and irrigation ports. The exterior wall is conductive for delivering radio frequency (RF) energy for an RF ablation procedure. The irrigation ports are in fluid communication with the open interior region to allow fluid to flow from the open interior region through the irrigation ports. The distal insert is positioned within the tip section to separate the open region into a distal fluid reservoir and a proximal fluid reservoir. The mapping electrodes are positioned in the mapping electrode openings in the tip section.

TECHNICAL FIELD

This application relates generally to medical devices and, more particularly, to systems, devices and methods related to open-irrigated hybrid catheters used to perform mapping and ablation functions.

BACKGROUND

Aberrant conductive pathways disrupt the normal path of the heart's electrical impulses. For example, conduction blocks can cause the electrical impulse to degenerate into several circular wavelets that disrupt the normal activation of the atria or ventricles. The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms called arrhythmias. Ablation is one way of treating arrhythmias and restoring normal contraction. The sources of the aberrant pathways (called focal arrhythmia substrates) are located or mapped using mapping electrodes situated in a desired location. After mapping, the physician may ablate the aberrant tissue. In radio frequency (RF) ablation, RF energy is directed from the ablation electrode through tissue to an electrode to ablate the tissue and form a lesion.

SUMMARY

An embodiment of an open-irrigated catheter system comprises a tip section, a distal insert, and mapping electrodes. The tip section has an exterior wall that defines an open interior region within the tip section. The exterior wall includes mapping electrode openings and irrigation ports. The exterior wall is conductive for delivering radio frequency (RF) energy for an RF ablation procedure. The irrigation ports are in fluid communication with the open interior region to allow fluid to flow from the open interior region through the irrigation ports. The distal insert is positioned within the tip section to separate the open region into a distal fluid reservoir and a proximal fluid reservoir. The mapping electrodes are positioned in the mapping electrode openings in the tip section.

A catheter system embodiment comprises a conductive exterior wall with mapping electrode openings, wherein the conductive exterior wall is configured for use in delivering RF energy for ablation functions. The catheter system embodiment may, but need not, be an open-irrigated catheter. The catheter system embodiment includes mapping electrodes positioned in the mapping electrode openings, and noise artifact isolators positioned in the mapping electrode openings. The mapping electrodes are electrically insulated from the exterior wall by the noise artifact isolators.

An electrode assembly embodiment comprises an electrode, an electrode shaft, and a noise artifact isolator. The electrode has a circumference defining sides of the electrode, a first surface, and a second surface opposite the first surface. The electrode shaft extends from the second surface of the electrode, and is in electrical conduction with the electrode. The noise artifact isolator is in contact with the sides of the electrode and surrounds the circumference of the electrode.

A method of forming an open-irrigated catheter tip includes inserting a distal insert into a distal tip section and connecting the distal tip section to a proximally adjacent structure. Inserting the distal insert includes moving the distal insert into the distal tip section until a distal extension of the insert contacts a distal end of the distal tip section to self-position the distal insert proximate to irrigation ports.

DETAILED DESCRIPTION

This present subject matter generally relates to a radiofrequency (RF) ablation catheter system. The catheter is referred to as a hybrid catheter herein as it can be used simultaneously for both localized mapping and ablation functions. The hybrid catheter is configured to provide localized, high resolution ECG signals during ablation. The localized mapping enables the mapping to be more precise than that which can be achieved with conventional ablation catheters. The hybrid catheter has an open-irrigated catheter design. A cooling fluid, such as a saline, is delivered through the catheter to the catheter tip, where the fluid exits through irrigation ports to cool the electrode and surrounding tissue. Clinical benefits of such a catheter include, but are not limited to, controlling the temperature and reducing coagulum formation on the tip of the catheter, preventing impedance rise of tissue in contact with the catheter tip, and maximizing potential energy transfer to the tissue. Additionally, the localized intra cardiac electrical activity can be recorded in real time or near-real time right at the point of energy delivery.

FIGS. 1A-1Dillustrate an embodiment of a hybrid catheter with distal irrigation ports and three microelectrodes used to perform the mapping function. The illustrated catheter100includes a catheter tip body101, an open-irrigated tip section102used to perform mapping and ablation functions, and mapping electrodes103. With reference toFIG. 1B, the illustrated embodiment includes a generally hollow tip body and a distal insert104disposed therein and configured to separate a proximal fluid reservoir105and distal fluid reservoir106. The hollow tip body has an open interior region defined by an exterior wall of the tip section. Fluid flow through these reservoirs is used to provide targeted cooling of portions of the tip electrode. In the illustrated embodiment, the hollow tip body has a generally cylindrical shape. By way of an example and not limitation, an embodiment of tip body has a diameter on the order of about 0.08-0.1 inches, has a length on the order of about 0.2-0.3 inches, and has an exterior wall with a thickness on the order of 0.003-0.004 inches.

The illustrated distal insert104includes openings or apertures107sized to receive a microelectrode and its corresponding noise artifact isolator108. These microelectrodes used in the mapping function to image localized intra cardiac activity. The device may be used to record high resolution, precise localized electrical activity, to prevent excessive heating of the ablation electrode, to allow greater delivery of power, to prevent the formation of coagulum and to provide the ability to diagnose complex ECG activity. The illustrated distal insert104also includes a fluid conduit or passage109to permit fluid to flow for the proximal fluid reservoir105to the distal fluid reservoir106, a thermocouple opening110sized to receive a thermocouple111, and openings112sized to receive electrical conductors113used to provide electrical connections to the microelectrodes103. Also illustrated is a thermocouple wire114connected to the thermocouple111. By way of example and not limitation, an embodiment of the distal insert is fabricated from stainless steel.

The tip section102is formed from a conductive material. For example, some embodiments use a platinum-iridium alloy. Some embodiments use an alloy with approximately 90% platinum and 10% iridium. This conductive material is used to conduct RF energy used to form legions during the ablation procedure. A plurality of irrigation ports115or exit ports are shown near the distal end of the tip section102. By way of example and not limitation, an embodiment has irrigation ports with a diameter approximately within a range of 0.01 to 0.02 inches. Fluid, such as a saline solution, flows from the distal fluid reservoir106, through these ports115, to the exterior of the catheter. This fluid is used to cool the ablation electrode tip and the tissue near the electrode. This temperature control reduces coagulum formation on the tip of the catheter, prevents impedance rise of tissue in contact with the catheter tip, and increases energy transfer to the tissue because of the lower tissue impedance.

FIGS. 1A-1Dillustrate a three microelectrode embodiment in which the three microelectrodes are used to perform mapping functions. However, the hybrid catheter may include other numbers of microelectrodes. For example,FIGS. 2A-2Dillustrate an embodiment of a hybrid catheter with distal irrigation ports and four microelectrodes used to perform the mapping function.

The illustrated catheter200includes a catheter tip body201, an open-irrigated tip section202used to perform mapping and ablation functions, and microelectrodes203. With reference toFIG. 1B, the illustrated embodiment includes a generally hollow tip body and a distal insert204disposed therein and configured to separate a proximal fluid reservoir205and distal fluid reservoir206. The illustrated distal insert204includes openings or apertures207sized to receive a microelectrode and its corresponding noise artifact isolator208. The illustrated distal insert204also includes a fluid conduit or passage209to permit fluid to flow from the proximal fluid reservoir205to the distal fluid reservoir206, a thermocouple opening210sized to receive a thermocouple211, and openings212sized to receive electrical conductors213used to provide electrical connections to the microelectrodes203. Also illustrated is a thermocouple wire214connected to the thermocouple211.

FIGS. 3A-3Dillustrate a microelectrode with a noise artifact isolator, according to various embodiments. The illustrated microelectrode303is surrounded by the noise artifact isolator308. An electrode shaft315is connected to the electrode303, and provides an electrical connection between the electrode and the electrical conductors. The microelectrodes are small, independent diagnostic sensing electrodes embedded within the walls of the ablation tip of the RF ablation catheter. The noise artifact isolator electrically isolates the small electrodes from the conductive walls of the ablation tip. According to various embodiments, the noise artifact isolator is a polymer-based material sleeve and/or adhesive that encapsulates the microelectrodes. The isolator has a lip316over the outside edge of the microelectrode circumference that blocks the RF pathway into the surface of the microelectrodes. According to various embodiments, the lip extends a distance within a range of approximately 0.002 to 0.020 inches past the surface of the electrode. According to various embodiments, the lip extends a distance of approximately 0.003 inches around the circumference of the microelectrode. The isolator isolates the noise entrance creating a much cleaner electrogram during an RF ablation mode. An in-vitro test result provides evidence that the illustrated isolator significantly reduce the noise artifact during RF. These electrically-isolated microelectrodes are able to sense highly localized electrical activity, avoid a far field component, and simultaneously achieve the ability to ablate tissue without noise artifact during RF mode.

FIGS. 4A-4Cillustrate an embodiment of a hybrid catheter in which the tip body includes separate distal and proximal portions, and where both the distal and proximal portions of the tip body are configured to connect to the distal insert that separates the distal and proximal portions. The embodiment illustrated inFIGS. 4A-4Cprovides a design to simplify manufacturing of the open-irrigated, mapping and ablation catheter. The illustrated device has a distal and proximal chamber separated into proximal417and distal tip sections418. These sections are separated by the distal insert419, which accommodates microelectrodes420, a cooling flow channel421, and a thermocouple slot422. The illustrated distal insert419includes openings or apertures424sized to receive a microelectrode and its corresponding noise artifact isolator423, and openings424sized to receive electrical conductors425used to provide electrical connections to the microelectrodes420. The distal tip has distal holes or irrigations ports415around the proximal edge of the domed section of the tip.

The illustrated distal insert has ends with distal and proximal lip edges470D an470P. Both the distal and proximal tip sections418and417are designed to fit over the lip edges of the distal insert ends. Specifically, a proximal side471of the distal tip section fits over the distal lip470D and a distal side472of the proximal section fits over the proximal lip470P. A middle portion of the distal insert, between the proximal and distal lips470P and470D, has an outer surface473substantially flush with an outer surface474of the distal and proximal tip sections. In some embodiments, the distal and proximal tips sections are bonded to the distal insert. The bonding process may involve a swaging/mechanical locking method, precise laser welding, force press fit, soldering and other means of chemical/mechanical bonding. The separate tip design provides a simple assembly process to bond the thermocouple and simplifies cleaning of the device.FIG. 4Balso illustrates a thermocouple. Thus, according to a method for forming an open-irrigated catheter tip, a distal lip of a distal insert is inserted in a proximal end of the distal tip section. Mapping electrodes are seated in mapping openings around a circumference of the distal insert. A distal end of a proximal tip section is inserted over a proximal lip of the distal insert. A bonding process is performed to bond the distal and proximal tip sections to the distal insert.

FIGS. 5A-5Cillustrate an embodiment of a map and ablate catheter with distal and proximal irrigation ports. The illustrated embodiment provides an open-irrigation RF ablation catheter with mapping and ablation functions in a Blazer tip platform. The Blazer tip is a tip developed by Boston Scientific. The relatively large surface area of the Blazer tip allows more power to be delivered, which hallows a larger lesion to be made. The larger surface area also promotes increased passive cooling by blood over the electrode.

The illustrated catheter has a tip section526with distal fluid ports527, and proximal fluid ports528. The distal insert529is made of plastic components such as Ultem inside the tip which is designed to separate a proximal reservoir530and a distal reservoir531for targeted cooling portions of the tip electrode, provide openings for the cooling fluid and the thermocouple, and provide housing for the microelectrodes532to image real time localized intra cardiac activity. The ends of this distal insert are encapsulated with adhesives to completely isolate distal tip chamber from proximal tip chamber.

The cooling lumen533is designed to cool the proximal/distal chamber while insulating the microelectrode lead wire junction from cooling fluid. The cooling lumen533includes several micro holes534in the proximal area of the tip to allow fluid to pass through these micro holes534and through the distal end of the cooling lumen, cooling the proximal tip and ultimately exiting through the proximal tip holes528. The cooling lumen and tip ports can be configured in different modes to optimize cooling efficiency for both distal and proximal chamber. For example, different diameter sizes and orientations can be implemented to adjust cooling.

Some embodiments include a three microelectrode configuration and some embodiments include a four microelectrode configuration.FIG. 5Cillustrates a distal insert529for a four microelectrode configuration. The illustrated insert529has openings536through which an electrical connection can be made with the microelectrodes532. The tip size is within a range of approximately 4-10 mm, for example. Some embodiments do not include a proximal cooling chamber. The microelectrodes532, which are used in the mapping function, are isolated from the conductive tip used to perform the ablation using a noise artifact isolator535.

FIG. 5Dillustrates an embodiment of the present subject matter incorporated into a Blazer tip. The illustrated embodiment includes a catheter body537and a tip section526, and includes a plurality of ring electrodes538, the microelectrodes532, distal fluid ports527and proximal fluid ports528.

FIGS. 6A-6Billustrate an embodiment of a map and ablate catheter with distal irrigation ports627. The cooling lumen633includes micro holes634to pass fluid in a proximal reservoir to cool the proximal portion of the tip. This fluid passes into the distal reservoir out through the distal fluid ports627.

Some embodiments shorten the cooling lumen up to the proximal end of the distal insert, allowing the fluid to cool the proximal end of the chamber before passing the distal tip chamber and ultimately passing thru the distal tip holes.FIGS. 7A-7Billustrate an example of a map and ablate catheter with distal irrigation ports727and a proximal fluid chamber, where fluid exits a cooling lumen into a proximal reservoir730before passing into the distal reservoir731and exiting the distal irrigation ports727.

Electrical signals, such as electrocardiograms (ECGs), are used during a cardiac ablation procedure to distinguish viable tissue from not viable tissue. If ECG amplitudes are seen to attenuate during the delivery of RF energy into the tissue, the delivery of RF energy into that specific tissue may be stopped. However, noise on the ECG signals makes it difficult to view attenuation. It is currently believed that internal cooling fluid circulation, cooling fluid circulating externally in contact with other electrodes, and/or fluid seepage in between the electrodes and their housing may cause the noise on this type of ablation catheter.

Various embodiments, as described below, isolate the microelectrode signal wires from the cooling fluid circulating in the proximal chamber of the hollow ablation electrode, and thus are expected to reduce the noise that is contributed from the internal cooling fluid circulation. The fluid seal can be provided without bonding or adhesive. The electrical components within the tip are isolated from the cooling flow of irrigation fluid while the irrigation fluid maintains internal cooling of the proximal and distal portions of the tip electrode. Further, as provided in more detail below, these designs have the potential of increasing the accuracy of the temperature readings from the thermocouple.

Various distal insert embodiments include design elements configured for self-positioning the distal insert during manufacturing. These embodiments reduce the number of processing steps to join the distal insert to the tip electrode.

FIGS. 8A-8Cillustrate various distal insert embodiments configured for self-alignment and configured to isolate electrical components from the irrigation fluid. Some embodiments are configured for self-alignment, some embodiments are configured to isolate electrical components from the irrigation fluid, and some embodiments as illustrated are configured for both self-alignment and for isolating electrical components from the irrigation fluid.FIG. 8Aillustrates a distal insert embodiment with fluid channels formed in a peripheral surface of the insert,FIG. 8Billustrates a distal insert embodiment with fluid lumens formed through the distal insert, andFIG. 8Cillustrates a section view of the distal insert embodiment ofFIG. 8A.

The illustrated distal inserts832A and832B include a distally-extending member833. The distal insert includes a main body portion834A and834B and a channel835extending from a proximal channel end836through the main body portion to a distal channel end837. The main body portion834A and834B has a circumference or outer diameter generally complementary to an inside diameter of the exterior wall of the tip section, and has a peripheral surface with openings838therein sized to receive the electrodes. The exterior wall of the tip section also has mapping electrode apertures. During assembly, the apertures in the exterior wall and the apertures in the distal insert are aligned, and the mapping electrodes are positioned and potted within the apertures. The channel has an interior passage that is isolated from the proximal fluid reservoir. Mapping electrode wires extend through the interior passage of the channel into smaller channels839in the main body portion of the distal insert to the mapping electrodes.

The distal insert embodiments illustrated inFIGS. 8A-8Cinclude a circumferential groove840, on which an o-ring is seated to form a seal between the distal insert and the exterior wall of the hollow electrode to prevent fluid from seeping around the side of the distal insert. This seal, generally illustrated inFIG. 8Cas a seal area, prevents fluid from seeping between the distal insert and the exterior wall of the tip section, and between the electrodes and their housing.

FIGS. 9A-9Cillustrate various embodiments for realizing a seal area between the distal inserts and the exterior wall of the electrode tip.FIG. 9Agenerally illustrates the groove940and o-ring941, such as was generally illustrated inFIGS. 8A-8C. Other embodiments include annular or circumferential detents942formed as part of the main body and configured to extend away from the peripheral surface of the main body, as generally illustrated inFIG. 9B. These detents engage the interior surface of the exterior wall of the tip section, thus securing the distal insert within the tip section. Some embodiments, as generally illustrated inFIG. 9C, form the peripheral surface with a circumferential gasket943configured to provide a seal between the distal insert and the exterior wall. The gasket943may be formed from a flexible material such as a polymer. These embodiments for realizing a seal are not intended to be an exclusive list, as other seals may be used to seal the fluid from the mapping electrodes.

FIG. 10illustrates a section view of a tip electrode assembly embodiment1044that includes an embodiment of a distal insert1032. The distal insert partitions a hollow ablation electrode into a proximal chamber1045and a distal chamber1046, thus allowing cooling of the proximal chamber1045. The cooling of the proximal chamber1045mitigates heating known as “edge effect” before the fluid is directed into the distal chamber1046and discharged through irrigation ports into the vasculature. The distal insert houses multiple, smaller electrodes in apertures1038in the tip electrode to provide localized electrical information.

The illustrated embodiment simplifies and improves the consistency of the method for positioning the insert into the hollow tip electrode. The distal insert1032is inserted into the hollow tip electrode1044and is automatically located within the electrode due to the distally-extending member1033of the isolation channel. The outer diameter of the insert and the o-ring are designed such that no additional adhesive is necessary to form a seal between the tip and the distal insert. The proximal section1047of the isolation channel terminates in a slot of the adjacent component1048that is potted with adhesive.

The exterior wall of the tip section has a distal end1049separated from the irrigation ports1050of the electrode by a predetermined distance1051, and the distally-extending member is configured with a predetermined length1052to position the distal insert in the tip section on a proximal side of the irrigation ports1050when the distal channel end abuts the distal end of the exterior wall of the electrode.

When the apparatus is inserted into a hollow tip electrode in the direction illustrated by arrow1053, the distal section of the isolated channel has a length that positions the distal edge of the insert above or proximal to the irrigation ports, allowing the irrigation ports provide fluid communication between the distal chamber and the exterior of the ablation electrode.

The overall diameter of the apparatus is similar enough to the inside diameter of the tip electrode that an o-ring placed in the circumferential groove provides an adequate seal forcing cooling fluid to flow through the fluid channels1054, also illustrated inFIG. 8Aat854. Because of the design characteristics, manufacturing processes are reduced.

The channel houses the thermocouple and signal wires from the microelectrodes. The proximal end of the insulated channel terminates in the adjacent structure within the tip, which is potted with epoxy and isolated from the cooling fluid. The thermocouple is in contact with the distal end of the electrode tip. Some embodiments provide slots1055at the distal channel end of the channel allowing cooling fluid to circulate into contact with the thermocouple. Some embodiments do not include slots, but rather provide a fluid-tight seal between the channel and the distal end of the electrode tip, such that the fluid does not circulate into contact with the thermocouple.

RF generators are configured with a cut-off temperature, where the RF ablation energy is cut off if the temperature reaches a particular level. However, some RF generators are configured with a relatively low cut-off temperature that reflects a less-than-accurate temperature measurement. The slots1055are believed to allow the embodiments of the present subject matter to operate with such devices. Various embodiments provide four slots. Other embodiments include other numbers of slots. Embodiments that include a slotted channel seal the channel at a more proximate position to prevent fluid from traveling through the channel toward the wiring. Some embodiments do not include slots, but rather seal the distal channel end to the distal wall of the electrode to prevent fluid from contacting the thermocouple. Such embodiments that isolate the thermocouple are believed to provide more accurate temperature measurements.

The distal insert includes fluid paths from the proximal chamber to the distal chamber to create a back pressure as fluid enters the proximal chamber, causing the fluid to circulate before being forced through the channels into the distal chamber. According to various embodiments, the fluid paths have an equal cross-sectional area and equally positioned around the center of the distal insert. Various embodiments include three equally-spaced fluid paths. In some embodiments, the fluid paths are fluid channels856formed in a peripheral surface857of the main body of the distal insert. The fluid channels provide the fluid pathways toward the exterior of the distal insert, thus allowing the insert to seat more electrodes around its circumference. In some embodiments, the fluid paths are lumens858formed through the main body of the distal insert. The lumens858provide further isolation of the mapping electrodes from the fluid, as the fluid flowing through the lumens is not in contact with the interface between the peripheral surface of the insert and the inner surface of the exterior wall of the electrode.

Wire channel branches, illustrated at839inFIG. 8Cand at1039inFIG. 10, allow the signal wires from the microelectrodes to enter the isolated channel. The illustrated embodiment is designed with three equally-spaced microelectrodes. Thus, the distal electrode embodiment includes three wire channels extending from an electrode aperture in the distal insert to the wire channel. According to various embodiments, these channel branches are angled (e.g. 15 to 60 degrees) to aid wire threading. This entire section is potted with adhesive to isolate this section from any potential cooling fluid.

FIG. 10also generally illustrates a method for forming an open-irrigated catheter tip. A distal insert1032is inserted into a distal tip section or hollow electrode1044. The distal insert includes a distal extension and the distal tip section includes a distal end and irrigation ports separated from the distal end by a predetermined distance. Inserting the distal insert includes moving the distal insert into the distal tip section until the distal extension contacts the distal end of the distal tip section to self-position the distal insert proximate to the irrigation portions. The distal tip section is connected to a proximally adjacent structure. For example, some embodiments swage the distal tip section to join the distal tip section against the proximally adjacent structure1044. The distal insert partitions the distal tip section into a distal fluid reservoir between the distal insert and the distal end, and a proximal fluid reservoir between the distal insert and the proximally adjacent structure. The distal insert provides fluid communication between the distal and proximal fluid reservoirs. In various embodiments, inserting the distal insert into the distal tip section includes aligning mapping electrode apertures in the distal insert with mapping electrode apertures in the distal tip section. The mapping electrodes are seated into the mapping electrode apertures. Wires connected to the mapping electrodes run through the channel of the distal insert.

FIG. 11illustrates an embodiment of a mapping and ablation system1156that includes an open-irrigated catheter. The illustrated catheter includes an ablation tip1157with mapping microelectrodes1158and with irrigation ports1159. The catheter can be functionally divided into four regions: the operative distal probe assembly region (e.g. the distal portion of catheter body1160), a main catheter region1161, a deflectable catheter region1162, and a proximal catheter handle region where a handle assembly1163including a handle is attached. A body of the catheter includes a cooling fluid lumen and may include other tubular element(s) to provide the desired functionality to the catheter. The addition of metal in the form of a braided mesh layer sandwiched in between layers of plastic tubing may be used to increase the rotational stiffness of the catheter.

The deflectable catheter region1162allows the catheter to be steered through the vasculature of the patient and allows the probe assembly to be accurately placed adjacent the targeted tissue region. A steering wire (not shown) may be slidably disposed within the catheter body. The handle assembly may include a steering member such as a rotating steering knob that is rotatably mounted to the handle. Rotational movement of the steering knob relative to the handle in a first direction may cause a steering wire to move proximally relative to the catheter body which, in turn, tensions the steering wire, thus pulling and bending the catheter deflectable region into an arc; and rotational movement of the steering knob relative to the handle in a second direction may cause the steering wire to move distally relative to the catheter body which, in turn, relaxes the steering wire, thus allowing the catheter to return toward its form. To assist in the deflection of the catheter, the deflectable catheter region may be made of a lower durometer plastic than the main catheter region.

The illustrated system1156includes an RF generator1164used to generate the energy for the ablation procedure. The RF generator1164includes a source1165for the RF energy and a controller1166for controlling the timing and the level of the RF energy delivered through the tip1157. The illustrated system1156also includes a fluid reservoir and pump1167for pumping cooling fluid, such as a saline, through the catheter and out through the irrigation ports1159. A mapping signal processor1168is connected to the electrodes1158, also referred to herein as microelectrodes. The mapping signal processor1168and electrodes1158detect electrical activity of the heart. This electrical activity is evaluated to analyze an arrhythmia and to determine where to deliver the ablation energy as a therapy for the arrhythmia. 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/or firmware. Various disclosed methods may be implemented as a set of instructions contained on a computer-accessible medium capable of directing a processor to perform the respective method.