Electrical stimulation of body tissue using interconnected electrode assemblies

Some embodiments of a cardiac stimulation system may include a plurality of electrode assemblies that are interconnected by one or more wires while at least one of the electrode assemblies (e.g., a control electrode) wirelessly receives energy through inductive coupling with a power communication unit external to the heart (e.g., a device implanted along one or more ribs). These embodiments may provide an arrangement for efficient inductive coupling from the power communication unit to the control electrode. Also, in some circumstances, the cardiac stimulation system may eliminate the need for wired leads that extend to a location outside the heart, thereby reducing the likelihood of infection that passes along the wire and into the heart.

TECHNICAL FIELD

This document relates to systems that electrically stimulate cardiac or other tissue.

BACKGROUND

Pacing instruments can be used to treat patients suffering from any of a number of heart conditions, such as a reduced ability to deliver sufficient amounts of blood from the heart. For example, some heart conditions may cause or be caused by conduction defects in the heart. These conduction defects may lead to irregular or ineffective heart contractions. Cardiac pacing systems (e.g., a pacemaker or an implantable defibrillator with pacing capability) may be implanted in a patient's body so that wire electrodes in contact with the heart tissue provide electrical stimulation to regulate electrical conduction in the heart tissue. Such regulated electrical stimulation is done to cause the heart to contract and hence pump blood.

The wired pacing systems in current use include a pulse generator that is implanted, typically in a patient's pectoral region just under the skin. One or more wired leads extend from the pulse generator so as to contact various portions of the heart. An electrode at a distal end of a lead may provide the electrical contact to the heart for delivery of the electrical pulses generated by the pulse generator and delivered to the electrode through the lead.

The use of wired leads may limit the number of sites of heart tissue at which electrical energy may be delivered. For example, most commercially available pacing leads are not indicated for use inside the left chambers of the heart. One reason is that the high pumping pressure in the left chambers of the heart may cause a thrombus or clot that forms on the bulky wired lead to eject into distal arteries, thereby causing stroke or other embolic injury. Thus, in order to pace the left side of the heart with a wired lead, most wired leads are directed through the cardiac venous system (outside the left chambers of the heart) to a site in a cardiac vein along the exterior of the left side of the heart.

In one example of a pacing therapy that includes pacing of a left heart chamber, a treatment known as biventricular pacing may be performed when the left ventricle does not contract in synchrony with the right ventricle. In order to perform such pacing therapy, typically a first wired lead is implanted through a vein into the right atrium, a second wired lead is implanted through a vein into the right ventricle, and a third wired lead is implanted through a vein and into the coronary sinus vein (to pace the left ventricle wall from outside the left ventricle). These three wired leads may be connected to a pacemaker device (e.g., implanted in the pectoral region) in an attempt to regulate the contractions of the right and left ventricles.

In addition to conventional wired pacing systems, a new class of pacing system is being developed that includes wireless operation. In such systems, a control module wirelessly communicates with electrode assemblies that are implanted along the outside of the heart tissue or embedded in a cardiac vein. The wireless communication from the control module can provide a source of power through inductive coupling to the implanted electrode assembly. One design issue for such wireless pacing systems is the efficiency of the inductive coupling between the control module and the implanted electrode assemblies, which can impact the battery life of the control module. For example, the further an implanted electrode assembly is away from the control module, the greater the power requirement for the control module to communicate with the implanted electrode. The power draw from the control module battery can be significant when inductively coupling with an implanted electrode assembly disposed on a distant portion of the heart.

SUMMARY

In some embodiments, a system for electrically stimulating heart tissue may include at least one wirelessly powered control assembly that is implantable at least partially in heart tissue. The control assembly may comprise, for example, a conductive coil to wirelessly receive energy from a magnetic field. The system may also include a plurality of stimulation electrode assemblies implantable at least partially into myocardial heart tissue. The system may further include a conductive wire assembly to connect the plurality of stimulation electrode assemblies with the control assembly when the control assembly and the stimulation electrode assemblies are implanted in the heart tissue so that the stimulation electrode assemblies receive electrical energy from the control assembly and deliver electrical stimulation to the heart.

In particular embodiments, a system for electrically stimulating heart tissue may include a wirelessly powered control assembly implantable in heart tissue proximate a heart apex. The control assembly may comprise, for example, an conductive coil to wirelessly receive RF (radio frequency) energy from a RF magnetic field. The system may also include a plurality of stimulation electrode assemblies implantable at least partially into heart tissue. Each stimulation electrode assembly may comprise at least one electrode pole to contact myocardial heart tissue. The system may further include a conductive wire assembly to connect the plurality of stimulation electrode assemblies with the control assembly when the control assembly and the stimulation electrode assemblies are implanted in the heart tissue so that the stimulation electrode assemblies receive electrical energy via the conductive wire assembly and deliver electrical stimulation to the heart. The system may also include a transmitter device implantable in implantable at an implantation site adjacent to one or more ribs and proximate the heart apex, the transmitter device comprising a power source and a RF antenna device to generate the RF magnetic field that wirelessly powers the control assembly.

In some embodiments, a system for electrically stimulating heart tissue may include an implantable stimulation pulse generator component attachable to heart tissue. The stimulation pulse generator component may have a receiver coil to wirelessly receive energy by inductive coupling. The system may also include multiple implantable electrode assemblies to be affixed to heart tissue. Further, the system may include a conductive wire assembly that connects the implantable stimulation pulse generator component with each of the multiple implantable electrode assemblies.

Some or all of the embodiments described herein may have one or more of the following advantages. First, some embodiments of the electrical stimulation system can provide effective cardiac pacing therapy or defibrillation therapy. Second, the stimulation system can provide efficient wireless transmission of power to the components implanted in the heart tissue. Third, such efficient wireless transmission of power to heart-implanted components may reduce the battery requirements, thereby increasing the battery life and possibly providing longer intervals between recharge appointments with a physician (e.g., in those embodiments in which the battery is rechargeable). Fourth, the stimulation electrode assemblies may receive electrical energy via a wire interconnection, but the wire assembly may not extend outside the heart, thereby reducing the likelihood of wire breakage. Fifth, because the wire assembly does not extend to a location outside the heart, the likelihood of an infection migrating into the heart can be reduced.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring toFIG. 1, a cardiac stimulation system100includes a number of implantable components that can be arranged, for example, within a patient. In this embodiment, the implantable components include a power communication unit122that wirelessly transmits radio-frequency (RF) energy or the like, a control electrode assembly104that receives the RF energy wirelessly transmitted by the power communication unit122(as indicated by the arrows), and a plurality (e.g., seventeen in this example) of stimulation electrode assemblies102that are each interconnected with the control electrode assembly104by a conductive wire assembly. The wired connection may permit the control electrode assembly104to efficiently distribute electrical energy to the stimulation electrode assemblies102that are implanted into the heart tissue. As shown inFIG. 1, the system100may also include an external device132(disposed outside the patient's body) that is capable of communicating wirelessly with the implanted components, for example, with the power communication unit122.

In the embodiment depicted inFIG. 1, the power communication unit122is implanted at a location proximate to the heart106, for example, between two ribs. This implant location along the ribs, while not used in all embodiments, may be selected due to the close proximity of this location to the control electrode assembly104to which the power communication unit122wirelessly transmits energy. In these circumstances, maintaining a relatively close distance between the power communication unit122and the control electrode assembly104helps to reduce battery power requirements for the power communication unit122(e.g., the energy draw required to generate a magnetic field may be reduced, thereby providing a longer battery life between recharge appointments, as described in more detail below). It should be understood that, in some embodiments, the power communication unit122may be an externally worn device (e.g., worn externally at a location along the one or more ribs).

In some alternative embodiments, the power communication unit122may be external to the patient, and may serve to recharge the batteries within the control electrode assembly104, to deliver physician programming to the software within control electrode assembly104, or a combination thereof. Such an external power communication unit may reside within a physician's office for patient recharging during routine visits. Alternatively the recharge transmitter and antenna may be incorporated into furniture, incorporated into the patient's bed, or worn by the patient (e.g. in a vest-type garment). In these circumstances, daily recharging for predetermined periods (e.g. 30 minutes) may be preferred to maintain a substantially full charge in the power storage source123(e.g., a rechargeable battery or the like) of the control electrode assembly104.

Referring toFIGS. 1-2A, the control electrode assembly104can include a fixation device133(described in more detail below) that allows the assembly104to be implanted into heart tissue. In the exemplary implant configuration ofFIGS. 1-2A, the control electrode assembly104is implanted into an external surface of the heart106and proximate to the heart's apex127. This implant location for the control electrode assembly104, while again not used in all embodiments, may facilitate the relatively close distance between the power communication unit122and the control electrode assembly104, and thus helps to reduce battery power requirements, as previously described. While only one control electrode assembly104is implanted in the configuration depicted inFIGS. 1-2A, some embodiments of the system100may employ a plurality of control electrode assemblies104, as described in more detail below.

Each stimulation electrode assembly102may also include a fixation device134(described in more detail below) that allows the electrode assembly102to be implanted into heart tissue. In the embodiment depicted inFIGS. 1-2A, each of the stimulation electrode assemblies102is implanted into an external surface of the heart106, adjacent to one of the four internal heart chambers110,112,114, and116. In particular, five stimulation electrode assemblies102are implanted in the heart wall adjacent to the right ventricle116, six electrode assemblies102are implanted in the heart wall adjacent to the left ventricle112, and three electrode assemblies102are implanted in the heart wall in each of the right and left atria114and110. It should be understood that, in alternative embodiments (described in more detail below in connection withFIG. 10), some or all of the electrode assemblies102and104can be implanted inside one or more heart chambers110,112,114, and116(e.g., implanted through the inner surface of the heart chamber walls).

When electrically activated, the electrode assemblies102stimulate the adjacent heart muscle tissue and cause the stimulated heart tissue to contract. In this embodiment, the control electrode assembly104is connected to all of the other seventeen electrode assemblies102by a conductive wire assembly118that extends from the control electrode assembly104to each of the seventeen electrode assemblies102. As previously described, the wired connection may permit the control electrode assembly104to efficiently distribute electrical energy to the stimulation electrode assemblies102that are implanted adjacent to the heart chambers.

Briefly, in operation, the transmission of RF energy by the power communication unit122wirelessly couples (through a shared electromagnetic field) a coil120in the unit122with a coil119in the control electrode assembly104. The inductive coupling causes an electrical current to be generated within the control electrode assembly104that can, for example, charge an internal battery, capacitor, or other rechargeable power source. At an appropriate point in time, the built-up electrical charge may then be selectively delivered, over the conductive wire assembly118, from the control electrode assembly104to any or all of the connected stimulation electrode assemblies102. The timing of the energy delivery may be controlled, for example, by either the power communication unit122, the control electrode assembly104, or the two components in combination, as will be described in more detail below. In some embodiments, the control electrode assembly104may itself include a unipolar electrode pole or bipolar electrode poles to stimulate tissue, although such a construction may not used in all embodiments.

The cardiac stimulation system100illustrated inFIGS. 1-2A, in some embodiments, can have advantages over other wireless stimulation system designs. For example, the embodiment of the cardiac stimulation system100shown inFIGS. 1-2Adoes not require the wireless transmission of RF energy to each and every stimulation electrode assembly102(including a distant electrode assembly102implanted adjacent to one of the atria). Instead, in this embodiment, the stimulation electrode assemblies102may receive electrical energy from a wired interconnection with a control electrode assembly104that is disposed in close proximity to the power communication unit122. Also, in some embodiments, the stimulation electrode assemblies102may have a less complex construction in that each electrode assembly102need not have an internal battery or capacitor. Instead, the energy may be stored in the battery, capacitor, or other power source in the control electrode assembly104, and the charge for a stimulation pulse may be generated only in the control electrode assembly104(which selectively delivers the stimulation pulses to the stimulation electrodes102).

Referring toFIG. 2A, the electrode assemblies102and104are interconnected to one another by the conductive wire assembly118(FIG. 2A). As such, at least one wire may extend along the heart wall between two or more of the electrode assemblies102or104. In the illustrative example shown inFIGS. 1-2A, the wire extends to each stimulation electrode102along the outside of the heart106(e.g., the dash lines represent the wire extending along the backside of the heart106). In this embodiment, the conductive wire assembly118does not extend outward to another portion of the body (e.g., to a pectoral region for connection with a pacemaker device or the like). Such a configuration can reduce the likelihood of an infection migrating along the wire from another body region and into the heart106and may can the likelihood of wire fatigue and breakage. Such beneficial results may be especially enhanced after at least a portion of the wire assembly118has been incorporated into the adjacent heart tissue. For example, the wire assembly118in this embodiment may be disposed against the epicardial surface126of the heart106after implantation of the electrode assemblies102and104. In these circumstances, at least a portion of the wire assembly118may embed into the adjacent heart tissue126over time and may therefore undergo less mechanical stress compared to wire leads that extend to a location outside the heart106(e.g., may not be subjected to a substantial number of stress cycles and may therefore be less prone to breakage as a result of the stress cycles).

The wire assembly118may comprise at least one wire having a conductive metallic material insulated with a substantially nonconductive material. In some embodiments, the wire may have a fine width, which may further enhance the likelihood of embedding into adjacent heart tissue. For example, the wire may have an outside diameter of less than about 0.010 inches and may be about 0.007 inches in diameter, and the diameter of the conductive metallic material may be less than about 0.008 inches and may be about 0.005 inches in diameter. It is believed that the substantially fine width of the wire118facilitates the process over time of the wires118incorporating into the heart tissue136along the epicardial surface126of the heart106. For example, after the stimulation electrode assembly102has been implanted, the wire118may be rested against the epicardial surface126where the heart tissue may grow over a substantial portion of the wire118over a period of time in which the patient heals. When the wire embeds into the adjacent heart tissue, the likelihood of the wire breaking or becoming dislodged is greatly reduced. In some embodiments, the outer surface of the wire may be textured or porous so as to facilitate the embedding process.

Still referring toFIG. 2A, the wire assembly118can be used to deliver electrical energy from the control electrode assembly104to the stimulation electrode assemblies102. The electrical energy delivery through the wire assembly118may be in the form of electrical stimulation pulses or in the form of a charging current (e.g., to power a charge storage capacitor in each stimulation electrode assembly102). For example, in the embodiment shown inFIG. 2A, the control electrode assembly104includes a power storage source123(e.g., a rechargeable battery device, a capacitor, or the like), control circuitry124, and pulse generator circuitry125. The electrical stimulation pulses generated by the pulse generator circuitry125in the control electrode assembly104may be selectively delivered through the wire assembly118to the stimulation electrode assemblies102for stimulation of the heart chamber walls. In an alternative example, the control electrode assembly104may include the power storage source123to supply a charging current through the wire assembly118to a charge storage capacitor in each stimulation electrode assembly102. The charging current from the control electrode assembly104can be supplied over any time interval in the cardiac cycle, and the control circuitry124in the control electrode assembly104would selectively signal the stimulation electrode assemblies102to activate their charge storage capacitors to provide a local stimulation pulse. Accordingly, in these embodiments, the implanted control electrode assembly104may wirelessly receive energy from outside the heart106(e.g., from the power communication unit122) and may deliver electrical energy to other implanted electrode assemblies102through the wire assembly118for electrical stimulation to the heart106.

As previously described, the control electrode assembly104may include power storage source123, such as a rechargeable battery, a capacitor, or the like. The power storage source123may be wirelessly recharged by the energy received from the inductive coupling between the coil119of the control electrode assembly104and the coil120of the power communication unit122. For example, a rechargeable battery in the control electrode assembly104may be recharged when an RF magnetic field is generated by the power communication unit122to wirelessly transmit energy to the coil119of the control electrode assembly104, which is connected to a recharging circuit to deliver a charging current to the battery. In a further example, one or more charge storage capacitors in the control electrode assembly104may be recharged when the RF magnetic field is generated by the power communication unit122. The recharge interval for the power storage source123may be affected by the charge volume of the power storage source123. Additionally, the recharging interval may be affected by the frequency and duration of the stimulation pulses delivered from the stimulation electrode assemblies102as required by the patient's heart to maintain a normal rhythm.

Referring toFIG. 2A, in some embodiments, the electrode assemblies102and104may be implanted through the epicardial tissue126of the heart106and into the myocardium108. In some circumstances, the conductive wire assembly118and the electrode assemblies102and104may be disposed fully inside the pericardial space (e.g., the internal space of the pericardium, which is a membranous sac that surrounds the heart106). The stimulation electrode assemblies102and the control electrode assembly104may include one or more fixation devices133and134(e.g., a helical tine, an adjustable hook, or the like) to secure the stimulation electrode assembly102to the walls of the heart chambers110,112,114, and116. In some embodiments, the control electrode assembly104may be secured by a fixation device133(e.g., retractable tines) proximate the apex127of the heart106—a position that may facilitate efficient inductive coupling with the power communication unit122. For example, the apex127of the heart106is generally near the superior surface of the chest and may experience relatively little change in orientation as the heart106beats. As such, the control electrode assembly104(and the coil119therein) does not substantially change orientation relative to the nearby ribs, even when the heart106contracts.

The power communication unit122may be implanted relatively near the control electrode assembly104, and in a substantially fixed orientation relative to the control electrode assembly104. For example, the power communication unit122(FIG. 1) may be implanted on, between, or under one or more ribs so as to be located relatively near to the control electrode assembly104. For example, the coil120of the power communication unit122may be disposed near the coil119of the control electrode assembly at a distance of about 5 mm to about 35 mm, about 5 mm to about 25 mm, and in some embodiments less than about 15 mm. Accordingly, such a substantially stable orientation of the control electrode assembly104, combined with the generally close proximity between the control electrode assembly104and the power communication unit122, may provide an arrangement for efficient inductive coupling from the power communication unit122to the control electrode assembly104. In such circumstances the power communication unit122may readily transmit energy to the power storage device123of the control electrode assembly104via wireless transmission between the coils119and120.

In the embodiment depicted inFIG. 2A, the power communication unit122may comprise a single housing configured to be implanted in proximity to the central electrode assembly104. The power communication unit122may include a power source130(e.g., an extended-life battery, a rechargeable battery, one or more capacitors, or the like), the antenna device121, and the induction coil120. In those embodiments in which the power source130is rechargeable, the energy to recharge the power source130may be wireless transmitted (e.g., via an inductive coupling) from an external device132located outside the patient's body, such as a recharge unit controlled by a computer device. Because the power communication unit122is implanted in a location external to the heart106(e.g., along one or more ribs), the power communications unit122may include a housing of sufficient size to retain a large-capacity battery. In addition, the efficient inductive coupling between the power communication unit122and the control electrode104(previously described) may reduce the energy draw from the power source130that is used to generate the RF magnetic field. As such, in those embodiments in which the power source130comprises a non-rechargeable extended-life battery, the power source may have a lifetime, for example, of more than two years, more than three years, more than four years, and preferably more than six years. Also, in those embodiments in which the power source comprises a rechargeable battery, the power source130may have a lifetime after a full charge, for example, of more than one month, more than three months, more than six months, and preferably a year or more. As a result, the recharging of the power source130may need only to occur when the patient visits his physician on a monthly, quarterly, or yearly basis.

As previously described, such an extended lifetime of the power source130in the power communication unit122may be facilitated by the efficient inductive coupling with the control electrode assembly104. For example, if the power communication unit122was required to generate a magnetic field sufficient to individually charge each of the stimulation electrode assemblies102(e.g., via an induction coil in each stimulation electrode assembly102), the energy draw from the power source130would be substantial. However, in this embodiment, the power communication unit122need only generate a magnetic field to transmit energy to the nearby control electrode assembly104, which thereafter distributes power to the stimulation electrode assemblies102via wire assembly118. In these circumstances, energy stored in the power source130of the power communication unit122is drained in a substantially conservative manner, thereby providing a longer lifetime to the power source130between recharge appointments.

Referring again toFIGS. 1-2A, the cardiac stimulation system100may be used to provide one or more of a number of treatments, such as pacing therapy to regulate the contractions of the heart106or defibrillation therapy of the heart106. During electrical stimulation, a wave of depolarization energy supplied by the stimulation electrode assembly102may propagate outwardly from the stimulation electrode assembly102to the stimulated volume of cells, thereby causing the heart106to contract. Each stimulation electrode assembly102may directly capture a certain volume of heart tissue to electrically stimulate, for example, about ten cubic centimeters. Thus implanting a plurality of stimulation electrode assemblies102in the heart106may provide the stimulation system100with the ability to capture a substantial portion of the myocardial tissue around the one or more targeted heart chambers110,112,114, and116. In theses circumstances, the likelihood of the heart106fibrillating or developing an arrhythmia may be substantially reduced.

In one example, consider a left ventricle112having an average diameter of about eight centimeters and an average wall thickness of about one centimeter. The total tissue volume of the left ventricle112could be estimated at about 200 cubic centimeters. Implanting approximately twenty stimulation electrode assemblies102(200 cubic centimeters/10 cubic centimeters/electrode assembly=20 electrode assemblies) that are generally uniformly spaced throughout the left ventricle wall may capture a substantial portion of the myocardial tissue around the left ventricle112. It should be understood that the estimated number of stimulation electrode assemblies102that may be implanted to provide substantially efficient pacing therapy may be dependent upon the size and health of the heart chambers110,112,114, and116that will be treated with pacing therapy. In some circumstances, large portions of the heart106may be healthy enough so as to provide substantially normal conduction of the depolarization energy wave that may be supplied by the stimulation electrode assembly102. As a result, fewer stimulation electrode assemblies102may be implanted for a given volume of heart tissue while maintaining the complete propagation of the imposed stimulation rhythm. Some patients that will be treated with pacing therapy may receive fewer stimulation electrode assemblies102, for example, between three and ten stimulation electrode assemblies102per heart chamber110,112,114, or116.

In the embodiments in which the stimulation electrode assemblies102can provide pacing therapy, the control electrode assembly104(e.g., the control circuitry124, pulse generator circuitry125, or a combination thereof) may activate the stimulation electrode assemblies102in at least one of a number of different patterns. For example, the control electrode assembly104may signal all of the stimulation electrode assemblies102disposed in a particular heart chamber to contemporaneously activate, thereby causing that heart chamber to contract (e.g., contemporaneously activate all six of the stimulation electrode assemblies102implanted in the myocardial tissue surrounding the left ventricle112). In these circumstances, all four of the heart chambers110,112,114, and116may be contemporaneously contracted (e.g., contemporaneously activating all of the stimulation electrodes102), or the left and right atria110and114may be contracted shortly before the left and right ventricles112and116are contracted. In a second example, the control electrode assembly104may signal all of the stimulation electrode assemblies102in a particular heart chamber, but the activation of these stimulation electrodes102may be offset depending on their location in the tissue around the hearth chamber. In the circumstances in which the stimulation electrode assemblies102are positioned around or within an infarct (dead or partially dead) tissue area through which electrical current does not travel or travels relatively slowly, the time differences between activation of the stimulation electrode assemblies102may account for the position of the stimulation electrode assemblies102and the infarct area. Also, in some circumstances, the stimulation electrode assemblies102may be positioned along the propagation path of electrical travel through the heart chamber walls, so the activation of these stimulation electrode assemblies102can be offset to mimic the natural electrical travel. In a third example, the control electrode assembly104may signal some (or one) but not all of the stimulation electrode assemblies102to activate. In some circumstances, not all the of the stimulation electrode assemblies102would be needed for effective pacing therapy, so activating only one or a few of the of the stimulation electrode assemblies102can conserve the battery power. The other of the stimulation electrode assemblies102that are not used for pacing therapy may be implanted for use in other types of therapies, for example, providing pacing therapy in response to a detected premature ventricular contraction (PVC) that indicates the onset of fibrillation or tachycardia.

In some embodiments in which the stimulation electrode assemblies102can provide “on-demand” pacing therapy, the control electrode assembly104(e.g., the control circuitry124, pulse generator circuitry125, or a combination thereof) may activate the stimulation electrode assemblies102in response to a irregular heart rhythm. For example, the plurality of stimulation electrode assemblies102, the control electrode assembly104, or a combination thereof may be configured to sense and react to an irregular heart rhythm. In such configurations, one or more of the electrode assemblies102and104may include sensor circuitry (e.g., electrogram sensor circuitry) that detects irregular heart rhythm. If the stimulation electrode assemblies102, the control electrode assembly104, or a combination thereof senses or anticipates an irregular rhythm, the control circuitry124in the control electrode104may include a programmed response to activate the stimulation electrode assemblies102in a pattern that may substantially restore a regular rhythm.

Additionally, if the control circuitry124in the control electrode104(or sensor circuitry located elsewhere in the cardiac stimulation system100) determines that defibrillation therapy should be implemented, the use of multiple electrode assemblies (e.g., electrode assemblies102and104) implanted in the heart chamber walls may reduce the total energy required to defibrillate the heart106. Such a reduction in the total electrical energy may be achieved because the electric fields fall off rapidly with distance away from the site of stimulation. For example, to capture the entire heart, some conventional defibrillators must use large input energy to capture tissue far removed from the stimulating electrode. As previously described, in some embodiments, about twenty electrode assemblies102could therefore capture a substantial portion of the myocardial tissue around the left ventricle112—a location where ventricle fibrillation can arise. It is believed that delivery of approximately 100 times the pacing threshold energy to each of the twenty electrode assemblies102would require less than one milli-joule of input energy, a small fraction of the total electrical energy delivered by conventional defibrillators. In addition, multi-site defibrillation energy could be delivered to the multiple electrode assemblies102in a timed sequence that optimizes the probability of defibrillation. Such a sequence may be determined by analysis of the local ECG signals measured from each electrode assembly102during a defibrillation episode. Furthermore, the electrode assemblies102may be employed to repress premature electrical stimulations arising in the myocardium that can precipitate fibrillation events. These “hot spots” can be repressed by rapid stimulation with a local electrode assembly102to keep such tissue refractory.

Referring briefly toFIG. 2B, in an alternative embodiment of the power communication unit122′ may comprise two housings interconnected by a wire. A first housing is implanted along one or more ribs in proximity to the apex127of the heart106, and a second housing can be implanted in a location (e.g., the abdomen) that is convenient for periodic recharging by the external device132(e.g., during a physician appointment). In these embodiments, the first housing may include the antenna device121and the coil120(e.g. to wirelessly communicate with and transmit energy to the control electrode104as previously described). Also, the second housing may include the power source130, control circuitry128, and a second coil129(e.g., to wirelessly receive energy from an external device for periodic recharging of the power source). A wire may be used to deliver electrical current from the power source130(in the second housing) to the antenna device121and induction coil120.

Referring now toFIGS. 3A-B, the stimulation electrode assemblies102may be connected to the control electrode assembly104by one of a number of wire assemblies. In this embodiment, each stimulation electrode assembly302a-d(e.g., constructed similar to stimulation electrode assemblies102shown inFIG. 2A) may be individually connected to the control electrode assembly104by a dedicated wire318a-dof the wire assembly318. For example, a stripline of wires318a-dmay extend from the control electrode assembly104, and the wires318a-dmay be partially separated from the stripline as each wire318a-dextends toward its respective stimulation electrode assembly302a-d. The separately attached wires318a-din the stripline may allow the control electrode assembly104to individually address the stimulation electrode assemblies302a-d. As previously described, the stimulation electrode assemblies302a-dand the control electrode assembly104may be implanted on the heart106, for example, through the epicardial surface126and within the pericardial space. The stimulation electrode assemblies302a-dmay include one or more fixation devices334(e.g., helical tines) to secure the stimulation electrode assemblies302a-dto the heart tissue. Also, as previously described, the control electrode assembly104may include one or more fixation devices133(e.g., retractable tines) to secure the control electrode assembly104into the heart tissue. For example, the fixation devices334and133may penetrate through the epicardium126and into the myocardium108.

The wire assembly318shown inFIGS. 3A-Bmay be employed when the stimulation electrode assemblies302a-doperate as unipolar electrodes. For example, each wire318a-dmay deliver a power signal from the control electrode104to its attached stimulation electrode assembly302a-dso that stimulation energy can be transmitted from unipolar electrode pole306of the stimulation electrode assembly302a-dto a second pole (e.g., on the control electrode assembly104). For example, the electrode pole306of the stimulation electrode assembly302amay be disposed along an exposed distal end of the helical tine334so that the electrode pole306is embedded into the heart tissue108. As shown inFIG. 3B, the wires318a-dmay comprise a conductive metallic material312that may be insulated with a substantially nonconductive material314. Each of the wires318a-dmay join with a mating jack, a crimp mechanism, or the like on the stimulation electrode assemblies302a-d. Additionally, the stripline of wires318a-dmay be releasably connected to the control electrode assembly104by a mating socket or a mating connector. Optionally, the stripline of wires318a-dmay be integrally constructed with the control electrode assembly104. In this embodiment, the body308of the stimulation electrode assembly302a-dmay include a generally non-curved surface that abuts against the tissue surface when the helical tine334penetrates into the tissue108. Thus, the stimulation electrode assemblies302a-dis delivered into the myocardium tissue108using the helical tine or other fixation device334while some portion of the body308rests against the tissue surface.

Referring now toFIGS. 4A-B, the stimulation electrode assemblies402a-cmay operate as bipolar electrodes and may be connected to the control electrode assembly104by a common ground line. In this embodiment a stripline wire assembly418having a number of power lines412a-cand at least one ground line413(FIG. 4A) may extend from the control electrode assembly104. The individual power lines412a-cmay partially separate from the stripline to connect with its associated stimulation electrode assembly402a-d(e.g., constructed similar to stimulation electrode assemblies102shown inFIG. 2A). The ground line413in the stripline wire418may extend to and connect with all of the stimulation electrode assemblies402a-d. As shown inFIG. 4B, the lines412a-cand413may comprise a conductive metallic material that is insulated with a substantially nonconductive material414.

As shown inFIG. 4A, each of the stimulation electrode assemblies402a-cmay contain both a first electrode pole404and a second electrode pole406that operate as bipolar electrodes. The first electrode pole404may be disposed along the portion of the electrode body408that presses against or otherwise contacts the heart tissue after implantation, and the second electrode pole406may be disposed along an exposed distal end of the helical tine434so that the second electrode pole406is embedded into the heart tissue108. As such, stimulation energy can be transmitted between the first and second electrode poles404and406so as to electrically stimulate the nearby heart tissue (e.g., the myocardial tissue108proximate to the electrode assembly402a-c).

In this embodiment, the control electrode assembly104controls the activation of the stimulation electrode assemblies402a-cin a high side drive mode. That is, the ground line413may provide a ground connection from the control electrode assembly104to all of the stimulation electrode assemblies402a-cand the control electrode assembly104may individually activate the stimulation electrode assemblies402a-cby controlling the delivery of electrical energy through each of the separate power line412a-c, respectively. Because the control electrode104is capable of individually transmitting stimulation pulses to selected stimulation electrodes402a-c, the control electrode104may include pulse generator circuitry125that generates the stimulation pulses, and the stimulation electrodes402a-cmay have a less complex construction (e.g., no local charge storage capacitors) so as to directly pass the stimulation pulses to the tissue. In an alternate embodiment, the control electrode assembly104can control the activation of the stimulation electrode assemblies402a-cin a low side drive mode. In these circumstances, the electrical line413may provide power to all of the stimulation electrode assemblies402a-cand the control electrode assembly104may individually activate the stimulation electrode assemblies402a-cby controlling the ground connection through the separately connected electrical lines412a-c.

Referring now toFIGS. 5A-B, some embodiments of the stimulation electrode assemblies may be connected to the control electrode assembly104by a wire assembly518having a shared power line and a shared ground line. In this embodiment the wire assembly518may extend from the control electrode assembly104and sequentially connect to a number of stimulation electrode assemblies502a-c(e.g., constructed similar to stimulation electrode assemblies102shown inFIG. 2A). For example, the wire assembly518may include a power line512that is connected to each of the stimulation electrode assemblies502a-cand may include a ground line513that is connected to each of the stimulation electrode assemblies502a-c. As shown inFIG. 5B, the wire assembly518may comprise a conductive metallic material (to separately form the lines512and513) that may be insulated with a substantially nonconductive material514. Similar to the embodiments described in connection withFIG. 4A, each of the stimulation electrode assemblies502a-cmay contain both a first electrode pole504and a second electrode pole506that operate as bipolar electrodes, and the first electrode pole504can be disposed along a portion of the electrode body508. As such, stimulation energy can be transmitted between the first and second electrode poles504and506so as to electrically stimulate the nearby heart tissue (e.g., the myocardial tissue108proximate to the electrode assembly502a-c). In some circumstances, the one of the electrical lines (e.g., line513) of the wire assembly518may deliver a control signal or other information that causes one of the stimulation electrode assemblies502a,502b, or502c(or a subset of the electrode assemblies502a-c) to activate and thereby stimulate the nearby heart tissue. In these embodiments, the control electrode104may deliver a charging current to charge storage capacitors in the stimulation electrode502a-c, and the stimulation electrodes502a-cmay have circuitry to detect the activation signal (from the control electrode) and then activate the charge storage capacitor to stimulate the heart tissue.

Referring toFIG. 6, in some embodiments, the power line612of the wire assembly618may be connected to one or more stimulation electrode assemblies602a-b(e.g., constructed similar to stimulation electrode assemblies102shown inFIG. 2A) in a manner that inductively transfers the power to the stimulation electrode assemblies602a-b. In this embodiment, the stimulation electrode assemblies602a-bmay have an attachment post603to receive a power line612of the wire assembly618. The power line612may be coiled around the attachment post603in an orientation to inductively couple with an internal coil620of the stimulation electrode assembly602a-b. Such a connection to the attachment post603may facilitate connection of the power line612to the electrode body608. Power may be supplied through the power line612at a substantially constant rate or over a particular time interval in the cardiac cycle to charge a power storage device (e.g., rechargeable battery, capacitor, or the like) in each stimulation electrode assembly602a-b. Optionally, the wire assembly618may include a ground line613that contacts a ground connection on the electrode assemblies602a-b. In those embodiments in which the stimulation electrode assemblies602a-bprovide unipolar functionality, the wire assembly618may not include the ground line613.

Referring toFIG. 7, the each of stimulation electrode assemblies102(or stimulation electrode assemblies302a-d,402a-c,502a-c, or602a-b) may include electrical circuitry700contained within the body of the stimulation electrode assembly102. As previously mentioned above, the stimulation electrode assemblies102may receive power signals, control signals, or both from the control electrode assembly104. At least a power line702and optionally a ground line704(e.g., in bipolar embodiments) may electrically connect the control electrode assembly104(not shown inFIG. 7) with at least a portion of the circuitry700(e.g., a microprocessor706) of the stimulation electrode assembly102. In some embodiments, communications circuitry708(e.g., sense amplifier, address decoder, or the like) may be in electrical communication with the power line702(or a separate communication line). In some embodiments, the communications circuitry708may be in electrical communication with the microprocessor706and may receive a modulated control signal from the control electrode assembly104, which is demodulated or decoded by the communication circuitry708before delivering signal to the microprocessor706for subsequent actions. A portion of a modulated signal may comprise coded signals (for example, frequency modulation, amplitude modulation, phase modulation, delta-sigma modulation, or the like). When a given stimulation electrode assembly102is activated, a gate (e.g., MOSFET) in the microprocessor706may open and the gate may connect the power line702to the heart tissue108for a pre-determined interval. In an alternative embodiment, the communication circuitry708may deliver the modulated control signal to the microprocessor706, and the microprocessor706may perform the demodulation or decoding.

Still referring toFIG. 7, the microprocessor706may be in electrical communication with stimulation circuitry710(e.g., a charge storage capacitor or the like that can be switched for activation), which is in electrical communication with the heart tissue108(e.g., via an electrode pole implanted in or near the myocardial tissue108). In some embodiments, the microprocessor706may provide a gate that permits the stimulation circuitry710to receive a charging current. When a control signal from the control electrode assembly104is received and interpreted by the microprocessor706, the microprocessor706may switch the stimulation circuitry710to an activate mode, and the stimulation circuitry710may deliver an electrical stimulation pulse to the heart tissue108. In other embodiments, the stimulation electrode assemblies102may have a less complex configuration that does not include a charge storage capacitor in the stimulation circuitry710that is recharged by a charging current transmitted from the control electrode104. Rather, the control electrode assembly104may include pulse generator circuitry125and may be connected to the stimulation electrode assemblies102in a manner to selectively deliver the stimulation pulses generated within the control electrode104(as previously described). In these embodiments, the stimulation circuitry710may receive the electrical pulses (e.g., via a dedicated power line) and pass the pulses directly to the heart tissue108.

In some embodiments, the microprocessor706may be in electrical communication with sensor circuitry712, which is in electrical communication with the heart tissue108. The sensor circuitry712may sense, for example, ECG signals in the heart tissue108and deliver signals to the microprocessor706. In this way, the microprocessor706can monitor the heart rhythm on a substantially regular basis. For example, the signal sensed by the sensor circuit712may be used by the microprocessor706to suspend pacing therapy at that location if a stimulation pulse (e.g., from a heart contraction) has already been sensed, thereby providing on-demand pacing. In another example, the sensed heart rhythm may indicate a fibrillation event, thereby causing the stimulation system100to respond with defibrillation therapy. In should be understood, that in some embodiments, the sensed signal information may be communicated back to the control electrode assembly104by the power/signal line or a separate communications line (not shown inFIG. 7).

Referring toFIG. 8, the control electrode assembly104may include electrical circuitry800that includes the power storage source123(e.g., rechargeable battery, a capacitor, or the like) as previously described in connection withFIGS. 1-2. The power storage source123may be in electrical communication with recharge circuitry804and power conditioner circuitry806. As previously described in connection withFIG. 2, the inductive coil119may wirelessly receive energy (via inductive coupling with the power communication unit122) and deliver the energy to the recharge circuitry804, which uses the energy to recharge the power storage source123. The coil119may also receive information, for example, concerning pulse waveforms, the timing of firing at each stimulation electrode assembly, or the like. In some embodiments, the coil119may be used to transmit information related to, for example, the pacing or stimulation thresholds, the sensed electrograms, or the like to the power communication unit122or the external device132.

A microprocessor810may be in electrical communication with the power conditioner circuitry806so as to coordinate the delivery of the power signal, control signals, ground line, or a combination thereof to the stimulation electrode assemblies102. For example, as previously described in connection withFIG. 7, the control electrode assembly104may provide power signals, control signals, or a combination thereof via a power line702while a ground line704extends to the stimulation electrode assemblies102. In some embodiments, the microprocessor810may receive, for example, a heart rhythm signal from one or more of the stimulation electrode assemblies102, thereby permitting the control electrode assembly104to monitor the heart rhythms on a substantially regular basis and respond, for example, when irregular heart rhythms are detected.

Referring toFIG. 9, some embodiments of a cardiac stimulation system may use the wire assembly918to contemporaneously serve as an induction coil (e.g., a larger form of the coil119described in connection withFIG. 2A). Similar to the previously described embodiments, the cardiac stimulation system900may include a plurality of stimulation electrode assemblies902and at least one control electrode assembly904that are interconnected by a wire assembly918. The plurality of interconnected electrode assemblies902and904may be implanted on an outside wall surface of one or more heart chambers110,112,114, and116. For example, as shown inFIG. 9, one or more stimulation electrode assemblies902may be implanted along the outer wall surfaces (e.g., epicardial surfaces) of the left atrium110, the left ventricle112, the right atrium114, and the right ventricle116, and the control electrode assembly904may be implanted along the outer surface of the heart106proximate to the apex127of the heart106.

In the embodiment depicted inFIG. 9, the wire assembly918may form a closed loop that is coiled around at least a portion of the heart106as the wire passes from one stimulation electrode902to the next. In such circumstances, the closed-loop wire assembly918may serve as a large area inductive coil (e.g., a larger form of the coil119described in connection withFIG. 2A) that can be inductively coupled to the power communication unit122. Similar to previously described embodiments, the power communication unit122may be implanted or attached to one or more ribs and may include a coil120that generates a magnetic field to wirelessly communicate power to the control electrode assembly904implanted on the heart106. Alternatively, the closed-loop wire assembly918may serve as a large area inductive coil that can be inductively coupled to an power communication unit external to the patient's body. For example, the recharge transmitter and antenna may be worn by the patient (e.g. in a vest-type garment) so that the antenna coil is wound around the patient's torso and is inductively coupled to the closed-loop wire assembly918implanted along the heart wall.

Similar to previously described embodiments, the wire assembly918can be used to deliver electrical energy from the control electrode assembly904to the stimulation electrode assemblies902. The electrical energy delivery through the wire assembly918may be in the form of electrical stimulation pulses or in the form of a charging current (e.g., to power a charge storage capacitor in each stimulation electrode assembly902). For example, in the embodiment shown inFIG. 9, the control electrode assembly904includes a power storage source923(e.g., a rechargeable battery device, a capacitor, or the like), control circuitry924, and pulse generator circuitry925. The electrical stimulation pulses generated by the pulse generator circuitry925in the control electrode assembly904may be selectively delivered through the wire assembly918to the stimulation electrode assemblies102for stimulation of the heart chamber walls. In an alternative example, the control electrode assembly904may include the power storage source923to supply a charging current through the wire assembly918to a charge storage capacitor in each stimulation electrode assembly902. The charging current from the control electrode assembly904can be supplied over any time interval in the cardiac cycle, and the control circuitry924in the control electrode assembly904would selectively signal the stimulation electrode assemblies902to activate their charge storage capacitors to provide a local stimulation pulse.

Referring toFIG. 10, some embodiments of a cardiac stimulation system1000may include stimulation electrode assemblies1002(e.g., constructed similar to stimulation electrode assemblies102shown inFIG. 2A) and at least one control electrode assembly1004(e.g., constructed similar to control electrode assembly104shown inFIG. 2A) that are implantable inside one or more heart chambers110,112,114, and116. For example, in this embodiment one control electrode assembly1004is implanted inside the left ventricle112, and another control electrode assembly1004is implanted inside the right ventricle116. Similar to the embodiments previously described in connection withFIGS. 1-2A, each control electrode assembly1004may include a coil that is inductively coupled to the power communication unit122so as to receive energy, data, or both, from the power communication unit122. The two control electrode assemblies1004can be disposed proximate to the apex127of the heart106to provide efficient inductive coupling with the power communication unit122. A separate wire assembly1018may be in electrical communication with each control electrode assembly1004and the associated stimulation electrode assemblies1002(e.g., those stimulation electrode assemblies1002implanted within the same heart chamber). Accordingly, the control electrode assemblies1004may wirelessly receive energy from the power communication unit122and may transmit energy via a wire assembly to the stimulation electrode assemblies1002to thereby stimulate the heart tissue (e.g., myocardial tissue108).

In this embodiment, the control electrode assemblies1004are anchored to the inner wall surface of the left ventricle112and the right ventricle1016by fixation devices1035(e.g., retractable tines or the like). For example, the fixation devices1035may penetrate through the endocardium109and into the myocardium tissue108. Also in this embodiment, the stimulation electrode assemblies1002are anchored to the inner wall surface of the left ventricle112and the right ventricle116by fixation devices1034(e.g., one or more biased tines near the proximal electrode and one or more opposing biased tines near the distal electrode). For example, the fixation devices1034may include biased distal tines that extend outwardly from the body of each electrode assembly1002after the distal portion of the body has penetrated through the endocardium109and into the myocardium tissue108. The fixation devices1034may also comprise an opposing set of biased proximal tines that extend outwardly from the body of the each electrode assembly1002. When the opposing biased tines are arranged in such an operative position, the stimulation electrode assembly1002remains embedded in the heart chamber wall. Following implantation and a healing period, at least a portion of the stimulation electrode assemblies1002, the control electrode assembly1004, and the wire assemblies1018may be incorporated into the adjacent heart tissue. In these embodiments, the wire assemblies1018do not exit the heart106, which can reduce the likelihood of an infection migrating from a location outside the heart along a wire and into the heart chambers110,112,114, and116.

Referring now toFIGS. 11A-B, some embodiments of an electrode assembly delivery system1100may be used to implant the stimulation electrode assemblies1002(FIG. 10) into the target heart chambers. The sheath system1100may include a delivery catheter1120that is guided to the targeted heart chamber (e.g., left ventricle112) via the arterial or venous systems. For example, a steerable guide sheath can be directed through one or more veins to the targeted chamber of the heart30. After the guide sheath is deployed into the targeted heart chamber, the delivery catheter1120, which may include a steering mechanism (e.g., steering wires, a shape  memory device, or the like) can be advanced through a lumen in the guide sheath to the targeted site on the heart chamber wall. In some circumstances, the guide sheath, the delivery catheter1120or both may be directed to the left ventricle112by passing through one or more veins, through the right atrium114, through the atrial septum, through the left atrium110, and into the left ventricle112. Preferably, the guide sheath is capable of maintaining a stable valve crossing (e.g., between the left atrium110and the left ventricle112), which can reduce trauma to the valve and facilitate the implantation of multiple stimulation electrode assemblies1002ainto the wall of the targeted heart chamber. In some embodiments, an endoscope or other surgical imaging device may be advanced through the guide sheath of the delivery catheter1120to provide the surgeon with images of the surgical site inside the heart chamber. AlthoughFIGS. 11A-Bshow the delivery of stimulation electrode assemblies1002a-b, it should be understood from the description herein that, in some embodiments, the delivery catheter1120may also be used to deliver the control electrode1004(FIG. 10) to the targeted heart chamber.

As shown inFIG. 11A, the stimulation electrode assembly1002ais shown within a distal portion of the delivery catheter1120. The stimulation electrode assembly1002ahas a main body1008that, in this example, is cylindrically shaped with a conical distal tip portion. The stimulation electrode assembly1002amay include two bipolar electrodes1006and1009that are capable of providing an electrical stimulation pulse to nearby heart tissue (e.g., myocardial tissue108). The distal electrode1006is located along the distal end of the stimulation electrode assembly1002a, and the proximal electrode1009is located along a proximal end. As previously described, the stimulation electrode assembly1002amay include a fixation device in the form of opposing biased tines that are configured to extended outwardly away from the body1008when released from the delivery catheter1120.

In some embodiments, an actuation member1122may advance the stimulation electrode assembly1002athrough a first lumen1126in the delivery catheter1120. The actuation member1122may releasably engage the stimulation electrode assembly1002aand may be used to implant the stimulation electrode assembly1102ainto the myocardium108. For example, the actuation member1122may be forced toward the distal end of the delivery catheter1020so as to drive the distal electrode1006and the biased tines1034into the tissue108. When the biased tines1034are separated from the opening at the distal end of the delivery catheter1020, the biased tines1034may shift outwardly away from the electrode body1008. The actuation member1122may continue to be forced toward the distal end of the delivery catheter1020so as to drive the proximal electrode1009toward the tissue108. When the biased tines near the proximal electrode1009are separated from the opening at the distal end of the delivery catheter1020, the biased tines may shift outwardly away from the body1008. In such circumstances, the biased tines1034near the distal electrode1006may prevent retraction of the wireless electrode assembly1002aout from the surface of the heart tissue108. Also, the biased tines near the proximal electrode1009may prevent migration of the wireless electrode assembly1002athrough the outside surface of the heart tissue108. In some embodiments, the opposing biased tines may retain the position of the wireless electrode assembly1002aso that the tissue108may grow and eventually incorporate the wireless electrode assembly1002atherein, thereby preventing the wireless electrode assembly1002afrom unintentional dislodgement from the tissue108.

Still referring toFIG. 11A, an wire attachment instrument1124may be advanced through a second lumen1128of the delivery catheter1120to connect the wire1018(FIG. 10) to the stimulation electrode1002aafter it is secured to the heart tissue. In this embodiment, the wire attachment instrument1124includes an adjustable crimping head125at its distal end that is configured to grasp a portion of the wire1018extending through the second lumen1128. The wire1018may extend through the second lumen1128adjacent to at least a portion of the wire attachment instrument1124, and a portion of the wire1018may extend distally out from the opening1132of the second lumen1128toward a previously implanted electrode assembly (not shown inFIGS. 11A-B). As described in more detail below, the crimping head1125may also direct a portion of the wire1018to an implanted electrode assembly1002aso as to attach that portion of the wire1018to the proximal portion of the electrode assembly1002a. Accordingly, the delivery catheter1120may provide access for the implantation of the electrode assemblies1002a-band the attachment of the wire interconnections1018therebetween.

Referring now toFIG. 11B, after the previously described electrode assembly1002ahas been secured to the heart wall, the delivery catheter may be shifted so that the wire attachment instrument can access the implanted assembly1002a. The wire attachment instrument1124may grasp the wire1018, for example, at point “a” (shown in bothFIGS. 11A and 11B) and direct that portion of the wire1018to the connection mechanism1040of the electrode assembly1002a. As previously described, the connection mechanism1040may comprising a mating jack, a crimp connector, or the like. The crimping head1125of the wire attachment instrument1124may crimp or otherwise attach the wire1018to the second stimulation electrode assembly1102aso that the electrode assembly1002ais connected by the wire1118to a previously implanted electrode assembly (not shown inFIGS. 11A-B). After the wire1018has been electrically connected to the electrode assembly1002a, the delivery catheter1120may be moved to a subsequent surgical site along the heart chamber wall. As shown, inFIG. 11B, another electrode assembly1002bmay be advanced through the first lumen1126of the delivery catheter1120in preparation for implantation at the subsequent surgical site. The subsequent electrode assembly1002bmay be implanted into the heart chamber wall using the actuation member1122as previously described in connection withFIG. 11A. Thereafter, the wire attachment instrument may grasp another portion of the wire1018(e.g., point “b” as shown inFIG. 11B) for connection to the electrode assembly1002b. Such a delivery procedure may be repeated until the desired number of stimulation electrode assemblies1002a-bare implanted in the heart chamber and are interconnected by one or more wires1018to the control electrode1004(FIG. 10). In these circumstances, the power communication unit122(FIG. 10) need only generate a magnetic field to transmit energy to the nearby control electrode assemblies1004(FIG. 10), which thereafter distributes power to the stimulation electrode assemblies1002a-bvia the wire interconnections1018.