US20070135883A1 - Cardiac Stimulation system - Google Patents

Abstract

Some embodiments of pacing systems employ wireless electrode assemblies to provide pacing therapy. The wireless electrode assemblies may wirelessly receive energy via an inductive coupling so as to provide electrical stimulation to the surrounding heart tissue. In certain embodiments, the wireless electrode assembly may include one or more biased tines that shift from a first position to a second position to secure the wireless electrode assembly into the inner wall of the heart chamber.

Description

CROSS REFERENCE TO RELATED APPLICATION
• This application claims priority to U.S. Provisional Application Ser. No. 60/748,964 filed on Dec. 9, 2005 and entitled “CARDIAC STIMULATION SYSTEM,” the contents of which are incorporated herein by reference.
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 a heart condition, 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. Some pacing instruments (e.g., a pacemaker) may be implanted in a patient's body so that pacing electrodes in contact with the heart tissue provide electrical stimulation to regulate electrical conduction in the heart tissue. Such regulated electrical stimulation may cause the heart to contract and hence pump blood.
• Conventionally, pacemakers 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 tissue 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 in the left side of the heart. One reason is that the high pumping pressure on the left side of the heart may cause a thrombus or clot that forms on a 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 to a site (external to the left heart chambers) in a cardiac vein over the left side of the heart. While a single lead may occlude a cardiac vein over the left heart locally, this is overcome by the fact that other cardiac veins may compensate for the occlusion and deliver more blood to the heart. Nevertheless, multiple wired leads positioned in cardiac veins can cause significant occlusion, thereby limiting the number of heart tissue sites at which electrical energy may be delivered to the left side of the heart.
• Some pacing systems may use wireless electrodes that are attached to the epicardial surface of the heart (external to the heart chambers) to stimulate heart tissue. In these systems, the wireless electrodes are screwed into the outside surface of the heart wall, which can reduce the effectiveness of the electrical stimulation in some circumstances.
SUMMARY
• Some embodiments of pacing systems employ wireless electrode assemblies to provide pacing therapy. The wireless electrode assemblies may receive energy via an inductive coupling so as to provide electrical stimulation to the surrounding heart tissue. In certain embodiments, a wireless electrode assembly may be directed through a guide catheter in a heart chamber to deliver at least a portion of the wireless electrode assembly through the endocardium. For example, the electrode assembly may include first and second fixation devices to secure the electrode assembly to the heart chamber wall. In such circumstances, the first fixation device may oppose rearward migration of the electrode assembly out of the heart chamber wall, and the second fixation device may oppose forward migration into the heart chamber wall. Accordingly, the wireless electrode assembly can be readily secured to the heart chamber wall and incorporated into the surrounding heart tissue over a period of time.
• In some embodiments, a wireless electrode assembly may include a body portion that at least partially contains a circuit to electrically stimulate an electrode. The wireless electrode assembly may also include first and second biased tines to shift from a loaded condition to an outwardly extended condition to secure the body portion to a heart chamber wall. The first and second biased tines may be generally opposed to one another.
• Particular embodiments may include an electrode delivery system for delivering a wireless electrode assembly into a heart chamber. The system may include a wireless electrode assembly including a body portion and first and second biased tines to shift from a loaded condition to an outwardly extended condition to secure the body portion to a heart chamber wall. The first and second biased tines may oppose one another. The system may also include a delivery catheter to direct the wireless electrode assembly through a heart chamber and toward a heart chamber wall. The delivery catheter may include an opening in a distal end such that, when the wireless electrode assembly is separated from the opening in the distal end of the catheter, the first and second biased tines shift from the loaded condition to the outwardly extended condition.
• Some embodiments may include a method of inserting a wireless electrode assembly into a heart chamber wall. The method may include inserting a first biased tine of a wireless electrode assembly through a portion of endocardium and into a heart chamber wall. The first biased tine may shift from a loaded condition to an outwardly extended condition to secure the body portion to a heart chamber wall. The method may also include causing a second biased tine of the wireless electrode assembly to shift from the loaded condition to the outwardly extended condition to secure the body portion to a heart chamber wall. The first and second biased tines may be generally opposed to one another when in their respective outwardly extended conditions.
• These and other embodiments described herein may provide one or more of the following advantages. First, the wireless electrode assemblies may eliminate or otherwise limit the need for wired pacing leads, thereby reducing the risk of stroke or other embolic injury from a thrombus or clot and reducing the risk of occluding cardiac veins (external to the heart chambers). Second, the wireless electrode assemblies may be secured to the inner wall of one more heart chambers, which may provide more efficient transfer of electrical stimulation. Third, the wireless electrode assemblies may be secured to a heart chamber wall in a manner that opposes both forward migration and rearward migration of the electrode assembly. In such circumstances, the secure attachment of the wireless electrode assembly with the heart wall may increase the likelihood of incorporating the electrode assembly into surrounding tissue, thereby further reducing the likelihood of forming a thrombus or clot in the heart chamber.
• The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
• FIG. 1 is a perspective view of a stimulation system and at least a portion of an electrode delivery system, in accordance with some embodiments of the invention.
• FIG. 2 is a diagram of at least a portion of a device of the stimulation system ofFIG. 1.
• FIG. 3 is a diagram of at least a portion of a wireless electrode assembly of the stimulation system ofFIG. 1.
• FIG. 4 is a section view of a heart and at least a portion of the electrode delivery system ofFIG. 1.
• FIG. 5 is a perspective view of a wireless electrode assembly, in accordance with some embodiments of the invention.
• FIG. 6 is a perspective view of a wireless electrode assembly, in accordance with some embodiments of the invention.
• FIGS.7A-D are partial cross-sectional views of the delivery of the wireless electrode assembly ofFIG. 5.
• FIG. 8 is a partial cross-sectional view of the delivery of the wireless electrode assembly ofFIG. 6.
• Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
• Referring toFIG. 1, anelectrical stimulation system10 may include one or morewireless electrode assemblies120. Thewireless electrode assemblies120 are implanted within chambers of theheart30. In this example, there are two implanted in theleft ventricle34 and two implanted in theright ventricle38, but the wireless electrode assemblies may be implanted in theleft atrium32, theright atrium36, or both. As described below in connection withFIGS. 4-8, thewireless electrode assemblies120 may be delivered to one or more chambers of theheart30 using anelectrode delivery system100. The electrode delivery system may include aguide catheter110 that is directed through one or more veins or arteries to the targeted chamber of the heart30 (e.g., theleft ventricle34 is the targeted chamber in the embodiment shown inFIG. 1). After theguide catheter110 is deployed into the targeted heart chamber thewireless electrode assemblies120 may be consecutively delivered through theguide catheter110 using at least onedelivery catheter115, which may include a steering mechanism (e.g., steering wires, a shape memory device, or the like) to delivery thewireless electrode assembly120 to the targeted site on the heart chamber wall.
• The distal end of eachwireless electrode assembly120 may include one or more fixation devices, such as tines As described in more detail below in connection withFIGS. 5 and 6, thetines132 and134 can secure thewireless electrode assembly120 to the heart chamber wall. In some embodiments, each of thewireless electrode assemblies120 may include a circuit comprising an internal coil and an electrical charge storage device (not shown inFIG. 1). As described in more detail below in connection withFIG. 3, the internal coil can be inductively coupled with an external power source coil so as to charge the electrical charge storage device (e.g., a battery, capacitor, or the like) contained within thewireless electrode assembly120. Also in some embodiments, each of thewireless electrode assemblies120 has a triggering mechanism in the circuit to deliver stored electrical charge to adjacent heart tissue (some examples are described in more detail below in connection withFIG. 3). In alternative embodiments, one or more of thewireless electrode assemblies120 may have no energy storage device. In such circumstances, each wireless electrode assembly may be comprised, for example, of a ferrite core having caps at each end with ring electrodes encircling the caps. A number of turns of fine insulated wire may be wrapped around the central portion of the core so as to receive energy from a magnetic field produced by a shaped driving signal and designed to activate the electrodes.
• Referring still toFIG. 1, thesystem10 may also include a pacingcontroller40 and atransmitter50 that drives anantenna60 for communication with thewireless electrode assemblies120. The pacingcontroller40 includes circuitry to sense and analyze the heart's electrical activity, and to determine if and when a pacing electrical pulse needs to be delivered and by which of thewireless electrode assemblies120. The sensing capability may be made possible by having sense electrodes included within the physical assembly of the pacingcontroller40. Alternatively, a conventional single or dual lead pacemaker may sense the local cardiac electrocardiogram (ECG) and transmit this information toantenna60 for use bycontroller40 in determination of the timing of wireless electrode assembly firing. In either case, thewireless electrode assembly120 need not be provided with sensing capability, and also thewireless electrode assemblies120 need not be equipped with the capability of communicating to the pacing controller40 (for example, to communicate information about sensed electrical events). In alternative embodiments, the wireless electrode assemblies may communicate sensed information to each other and/or to thecontroller40.
• Thetransmitter50—which is in communication with, and is controlled by, the pacingcontroller40—may drive an RF signal onto theantenna60. In one embodiment, thetransmitter50 provides both (1) a charging signal to charge the electrical charge storage devices contained within thewireless electrode assemblies120 by inductive coupling, and (2) an information signal, such as a pacing trigger signal, that is communicated to a selected one or more of thewireless electrode assemblies120, commanding thatwireless electrode assembly120 deliver its stored charge to the adjacent heart tissue.
• One parameter of thewireless electrode assembly120 that may affect the system design is the maximum energy required to pace theventricle34,38 or other chamber of theheart30. This energy requirement can include a typical value needed to pace ventricular myocardium, but also can include a margin to account for degradation of contact between the electrodes and tissue over time. In certain embodiments, eachwireless electrode assembly120 may require the maximum pacing threshold energy. This threshold energy is supplied to the wireless electrode assemblies between heartbeats by an external radio frequency generator (which may also be implanted), or other suitable energy source that may be implanted within the body. Parameter values for some embodiments may be:
• • Threshold pacing voltage=2.5 Volts
  • Typical lead impedance=600 Ohms
  • Typical pulse duration=0.4 mSec
  • Derived threshold energy=4 micro-Joules
• Because RF fields at frequencies higher than about 200 kHz may be attenuated by the body's electrical conductivity, and because electric fields of any frequency may be attenuated within the body, energy transmission through the body may be accomplished in some embodiments via a magnetic field at about 20-200 kHz (or by a magnetic field pulse that contains major frequency components in this range), and preferably by transmission of magnetic fields in the range of 100-200 kHz when transmission is through relatively conductive blood and heart muscle.
• Still referring toFIG. 1, the pacingcontroller40 and thetransmitter50 may be housed in a single enclosure that is implantable within a patient. In such a configuration, the single enclosure device may have a single energy source (battery) that may be either rechargeable or non-rechargeable. In another configuration, the pacingcontroller40 and thetransmitter50 may be physically separate components. As an example of such a configuration, the pacingcontroller50 may be implantable, for example in the conventional pacemaker configuration, whereas the transmitter50 (along with the antenna60) may be adapted to be worn externally, such as in a harness that is worn by the patient. In the latter example, the pacingcontroller40 would have its own energy source (battery), and that energy would not be rechargeable given the relatively small energy requirements of the pacingcontroller40 as compared to the energy requirements of thetransmitter50 to be able to electrically charge thewireless electrode assemblies120. In this case, the pacingcontroller40 would sense the local cardiac ECG signal through a conventional pacing lead, and transmit the sensed information to the external controller. Again, transmission of information, as opposed to pacing energy, has a relatively low power requirement, so a conventional pacemaker enclosure and battery would suffice.
• The external programmer70 is used to communicate with the pacingcontroller40, including after the pacingcontroller40 has been implanted. The external programmer70 may be used to program such parameters as the timing of stimulation pulses in relation to certain sensed electrical activity of the heart, the energy level of stimulation pulses, the duration of stimulation pulse (that is, pulse width), etc. The programmer70 includes anantenna75 to communicate with the pacingcontroller40, using, for example, RF signals. Theimplantable pacing controller40 is accordingly equipped to communicate with the external programmer70, using, for example, RF signals. Theantenna60 may be used to provide such communications, or alternatively, the pacingcontroller40 may have an additional antenna (not shown inFIG. 1) for external communications with the programmer70, and in an embodiment where thetransmitter50 andantenna60 are housed separately from thecontroller40, for communications with thetransmitter50.
• Still referring toFIG. 1, at least a portion of thesystem10 is shown as having been implanted in a patient, and in addition, the programmer70 is also shown that is external to the patient. Thecontroller40 andtransmitter50 may be housed in a device that is shaped generally elongate and slightly curved so that it may be anchored between two ribs of the patient, or possibly around two or more ribs. In one example, the housing for thecontroller40 andtransmitter50 is about 2 to 20 cm long and about 1 to 10 centimeters cm in diameter, may be about 5 to 10 cm long and about 3 to 6 cm in diameter. Such a shape of the housing for thecontroller40 andtransmitter50, which allows the device to be anchored on the ribs, may provide an enclosure that is larger and heavier than conventional pacemakers, and may provide a larger battery having more stored energy. In addition, thecontroller40 may comprise a defibrillator that discharges energy to theheart30 through electrodes on the body ofcontroller40 when fibrillation is sensed. Other sizes and configurations may also be employed as is practical.
• In some embodiments, theantenna60 may be a loop antenna comprised of a long wire that is electrically connected across an electronic circuit contained within the controller/transmitter housing, which circuit delivers pulses of RF current to theantenna60, generating a magnetic field in the space around theantenna60 to charge thewireless electrode assemblies120, as well as RF control magnetic field signals to command thewireless electrode assemblies120 to discharge. In such embodiments, theantenna60 may comprise a flexible conductive material so that it may be manipulated by a physician during implantation into a configuration that achieves improved inductive coupling between theantenna60 and the coils within the implantedwireless electrode assemblies120. In one example, theloop antenna60 may be about 2 to 22 cm long, and about 1 to 11 cm wide, and may be about 5 to 11 cm long, and about 3 to 7 cm wide. Placement of theantenna60 over the ribs may provide a relatively large antenna to be constructed that has improved efficiency in coupling RF energy to the pacingwireless electrode assemblies120.
• As shown inFIG. 1, some embodiments of thesystem10 may also include a pulse generator device90 (or pacemaker device) and associated wired leads95 which extend from the pulse generator device90 and into one or more chambers of the heart30 (e.g., into the right atrium36). For example, thesystem10 may include wired leads95 from the pulse generator device90 that extend into theright atrium36 and theright ventricle38 while wireless electrode assemblies are disposed in theleft atrium32 and theleft ventricle34. The pulse generator device90 may be used to sense the internal ECG, and may also communicate with thecontroller40 and/ortransmitter50 as previously described.
• As previously described, in some embodiments, each of thewireless electrode assemblies120 includes a rechargeable battery or other charge storage device. This battery may provide power for delivering pacing energy to the tissue, and for operating communications, logic, and memory circuitry contained within the assembly. In some alternative embodiments, a transmitter and an antenna may be external to the patient (as opposed to theimplantable transmitter50 andantenna60 depicted inFIG. 1), and may serve to recharge the batteries within the electrode assemblies. 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). Daily recharging for predetermined to periods (e.g., about 30 minutes) may be required in some cases. In these circumstances, thewireless electrode assemblies120 may be autonomous pacemaker-like devices, which can sense the local electrogram and only pace when the local tissue is not refractory. Such electrodes may communicate with the programming unit70 to receive pacing instructions and transmit data stored in local memory. In these embodiments, eachwireless electrode assembly120 may also communicate with other implantedwireless electrode assemblies120. For example, oneelectrode assembly120 in the right atrium may be designated as the “master,” and all other implanted electrodes are “slaves,” that pace with pre-programmed delays relative to the “master.” As such, a master electrode in the right atrium may only sense the heart's sinus rhythm, and trigger pacing of the slaves with programmed delays.
• Referring toFIG. 2, an embodiment of adevice80 including thecontroller40,transmitter50, associatedantenna60 is shown in block diagram form. Included within thedevice80 is: abattery82, which may be recharged by receiving RF energy from a source outside the body viaantenna60;ECG sensing electrodes84 and associatedsensing circuitry86;circuitry87 for transmitting firing commands to the implanted wireless electrode assemblies, transmitting status information to the external programmer, receiving control instructions from the external programmer and receiving power to recharge the battery; and a controller orcomputer88 that is programmed to control the overall functioning of the pacing control implant. In alternative embodiments,antenna60 may receive signals from the individualwireless electrode assemblies120 containing information regarding the local ECG at the site of each wireless electrode assembly, and/or theantenna60 may receive signals from a more conventional implanted pacemaker regarding the ECG signal at the sites of one or more conventional leads implanted on the right side of the heart.
• Referring toFIG. 3, some embodiments of awireless electrode assembly120 may include areceiver coil122 that is capable of being inductively coupled to a magnetic field source generating a time-varying magnetic field at the location ofcoil122, such as would be generated by thetransmitter50 and theantenna60 depicted inFIG. 1. The RF current in the external antenna may be a pulsed alternating current (AC) or a pulsed DC current, and thus the current induced through thereceiver coil122 would likewise be an AC or pulsed DC current. The current induced incoil122 may be proportional to the time rate of change of the magnetic field generated at the site ofcoil122 by the external RF current source. In some embodiments, a four-diode bridge rectifier123 may connected across thereceiver coil122 to rectify the AC or pulsed DC current that is induced in thereceiver coil122. A three-position switch device124 may be connected so that when theswitch device124 is in a first position, therectifier123 produces a rectified output that is imposed across acapacitor125. As such, when theswitch device124 is in the position1 (as is the case inFIG. 4), thecapacitor125 stores the induced electrical energy.
• Theswitch device124, in this example, is a voltage-controlled device and is connected to sense a voltage across thecapacitor125 to determine when thecapacitor125 has been sufficiently charged to a specified pacing threshold voltage level. When thecapacitor125 is sensed to have reached the specified pacing threshold level, the voltage-controlledswitch device124 moves to aposition2, which disconnects thecapacitor125 from thecoil122. With theswitch device124 in theposition2, thecapacitor125 is electrically isolated and remains charged, and thus is ready to be discharged. The voltage controlledswitch device124 may comprise a solid state switch, such as a field effect transistor, with its gate connected to the output of a voltage comparator that compares the voltage oncapacitor125 to a reference voltage. The reference voltage may be set at the factory, or adjusted remotely (e.g., after being implanted) via signals sent from the physician programmer unit70 (FIG. 1), received bycoil122 and processed by circuitry not shown inFIG. 3. Any electronic circuitry contained within thewireless electrode assembly120, including the voltage controlled switch, can be constructed with components that consume very little power, for example CMOS. Power for such circuitry is either taken from a micro-battery contained within the wireless electrode assembly, or supplied by draining a small amount of charge fromcapacitor125.
• Still referring toFIG. 3, a narrow bandpass filter device126 may also be connected across thereceiver coil122, as well as being connected to the three-position switch device124. The bandpass filter device126 passes only a single frequency of communication signal that is induced in thecoil122. The single frequency of the communication signal that is passed by thefilter device126 may be unique for the particularwireless electrode assembly120 as compared to other implanted wireless electrode assemblies. When thereceiver coil122 receives a short magnetic field burst at this particular frequency, thefilter device126 passes the voltage to theswitch device124, which in turn moves to aposition3.
• With theswitch device124 in theposition3, thecapacitor125 may be connected in series through twobipolar electrodes121 and129, to the tissue to be stimulated. As such, at least some of the charge that is stored on thecapacitor125 is discharged through the tissue. When this happens, the tissue becomes electrically depolarized. In one example embodiment described in more detail below, thebipolar electrodes121 and129 across which stimulation pulses are provided are physically located at opposite ends (e.g., a proximal end and a distal end) of thewireless electrode assembly120. After a predetermined, or programmed, period of time, the switch returns to position1 so thecapacitor125 may be charged back up to the selected threshold level.
• It should be noted that, for sake of clarity, the schematic diagram ofFIG. 3 shows only the electrical components for energy storage and switching for particular embodiments of thewireless electrode assembly120. Not necessarily shown are electronics to condition the pacing pulse delivered to the tissues, which circuitry should be understood from the description herein. Some aspects of the pulse, for example pulse width and amplitude, may be remotely programmable via encoded signals received through thefilter device126 of thewireless electrode assembly120. In this regard,filter126 may be a simple band pass filter with a frequency unique to a particular wireless electrode assembly, and the incoming signal may be modulated with programming information. Alternatively, filter126 may consist of any type of demodulator or decoder that receives analog or digital information induced by the external source incoil122. The received information may contain a code unique to each wireless electrode assembly to command discharge ofcapacitor125, along with more elaborate instructions controlling discharge parameters such as threshold voltage for firing, duration and shape of the discharge pulse, etc.
• Using wireless electrode assemblies of the type shown inFIG. 3, all of the implantedwireless electrode assemblies120 may be charged simultaneously by a single burst of an RF charging field from atransmitter antenna60. Because back reaction of thewireless electrode assemblies120 on theantenna60 may be small, transmitter50 (FIG. 1) losses may be primarily due to Ohmic heating of the transmitantenna60 during the transmit burst, Ohmic heating of the receivecoil122, and Ohmic heating of conductive body tissues by eddy currents induced in these tissues by the applied RF magnetic field. By way of comparison, if eightwireless electrode assemblies120 are implanted and each is addressed independently for charging, thetransmitter50 may be turned ON eight times as long, which may require almost eight times more transmit energy, the additional energy being primarily lost in heating of the transmitantenna60 and conductive body tissues. With thewireless electrode assembly120 ofFIG. 3, however, all implanted wireless electrode assemblies can be charged simultaneously with a burst of RF current inantenna60, and antenna and body tissue heating occurs only during the time required for this single short burst. Each wireless electrode assembly is addressed independently through itsfilter device126 to trigger pacing. The transmitted trigger fields can be of much smaller amplitude, and therefore lose much less energy to Ohmic heating, than the transmitted charging pulse.
• Pending U.S. patent application Ser. No. 10/971,550 (filed on Oct. 20, 2004), Ser. No. 11/075,375 (filed on Mar. 7, 2005), and Ser. No. 11/075,376 (filed on Mar. 7, 2005), all owned by the assignee of this application, describe various features of wireless electrode assemblies, systems to deliver the wireless electrode assemblies to the heart, and electronic components to activate the wireless electrode assemblies to deliver electrical stimulation. It should be understood from the description herein that some of the features described in these three patent applications (Ser. Nos. 10/971,550, 11/075,375, and 11/075,376) may be applicable to particular embodiments described herein.
• Referring now toFIG. 4, some embodiments of anelectrode delivery system100 may include aguide catheter110 and adelivery catheter115. Thecatheters110 and115 may comprise an elongate body that extends from a proximal end (outside the patient's body, not shown inFIG. 4) to a distal end (depicted inFIG. 4 as extending into the patient's heart30). Thedelivery catheter115 fits within a lumen of theguide catheter110, and can be advanced through theguide catheter110 so that a distal end of thedelivery catheter115 extends out of a distal opening of theguide catheter110. Theguide catheter110 may be directed through one or more veins or arteries to the targeted chamber of the heart30 (e.g., theleft ventricle34 is the targeted chamber in the embodiment shown inFIG. 4). Theguide catheter110 may comprise a steering mechanism (e.g., steering wires, shape memory device, or the like) to shift the distal end and may include at least onemarker band112 to permit viewability of the distal end of theguide catheter110 using medical imaging techniques. Such amarker band112 may aid a physician when steering theguide catheter110 to the targeted heart chamber.
• After theguide catheter110 is deployed into the targeted heart chamber, thewireless electrode assemblies120 may be advanced into the heart tissue through theguide catheter110 using at least onedelivery catheter115. Thewireless electrode assemblies120 may be consecutively delivered through theguide catheter110 using at least onedelivery catheter115. In some embodiments, thedelivery catheter115 may include at least onemarker band116 to permit viewability of the distal end of thedelivery catheter115 using medical imaging techniques. Thedelivery catheter115 may include a steering mechanism (e.g., steering wires, shape memory device, or the like) to shift the distal end. For example, thedelivery catheter115 may comprise a shape memory device (e.g., one or more wires comprising Nitinol or another shape memory material) to provide a predetermined curvature near the distal end of thedelivery catheter115. The shape memory device may be activated by a change in electrical charge or by a change in temperature. In one example, thedelivery catheter115 may include a shape memory device near the distal end that is capable of providing a 90-degree deflection curve near the distal end immediately before a longitudinally straight section at the distal end of thecatheter115.
• In some approaches to the targeted tissue, the steering mechanism (e.g., steering wires, shape memory device, or the like) of thedelivery catheter115 can be manipulated so that a deflected portion near the distal end of the delivery catheter abuts against the septum wall of the targeted heart chamber. For example, the deflected portion of the delivery catheter may abut against theseptum wall39 between theleft ventricle34 and theright ventricle38 while a longitudinally straight section of thecatheter115 extends the distal end against the targeted heart chamber wall to receive the wireless electrode assembly120 (refer to the dotted-line example depicted inFIG. 4). Accordingly, the deflected portion of thedelivery catheter115 can abut against the septum wall to support the position of the distal end of thedelivery catheter115 during the deployment of thewireless electrode assembly120 into the targeted heart tissue35 (refer, for example, to FIGS.7A-D and8). Such an approach may provide leverage and stability during the insertion process for theelectrode assembly120.
• Thedelivery catheter115 includes an opening at the distal end in which an associatedwireless electrode assembly120 is retained in a loaded position. Thewireless electrode assembly120 may include a body portion that has a length and a radius configured to be retained with thedelivery catheter115. As described in more detail below, some embodiments of the body portion of thewireless electrode assembly120 may have a radius, for example, of about 1.25 mm or less and may have a length, for example, of about 10 mm or less. Wireless electrode assemblies configured for insertion into an atrial wall may be smaller than those configured for insertion into the ventricle walls.
• In the exemplary embodiment shown inFIG. 4, thewireless electrode assemblies120 comprise a pointed-tip cylindrical body having a forward portion embedded within the heart wall tissue and a rearward portion that is inside the heart chamber but not fully embedded in the heart wall tissue. The pointeddistal tip130 of theelectrode assembly120 facilitates penetration into the heart wall tissue, and the proximal end of the electrode assembly is configured to remain outside of the heart wall. However, in some embodiments, both thedistal tip130 and the proximal end of theelectrode assembly120 can be embedded within theheart wall tissue30. As described in more detail below, theelectrode assembly120 may include twofixation devices132 and134 that generally oppose one another, such as a set of distal tines and a set of proximal tines. The distal tines can be coupled to and extend from a periphery of a forward portion of the body of theelectrode assembly120, and the proximal tines can be coupled to and extend from a periphery of a rearward portion of the body. As described in more detail below, the set of distal tines extend somewhat outwardly from the body of theelectrode assembly120 but also rearwardly so as to prevent the electrode from becoming dislodged from the heart wall once theelectrode assembly120 is implanted. Also as described in more detail below, the set of proximal tines extend somewhat outwardly from the body of theelectrode assembly120 but also forwardly so as to prevent theelectrode assembly120 from penetrating entirely through the heart wall.
• As thewireless electrode assembly120 is deployed fromdelivery catheter115,tines132 and134 located externally on thewireless electrode assembly120 may adjust to a deployed position (e.g., an outwardly extended condition). Such an adjustment to the deployed position may be caused, for example, due to spring bias of thetines132 and134 (described in more detail below). When thetines132 and134 are in the deployed position, thetines132 and134 are capable of securing thewireless electrode assembly120 to the targeted tissue site (e.g., described in more detail below, for example, in connection withFIGS. 7-8). In some embodiments, the opening at the distal end of thedelivery catheter115 may be part of conduit that extends through the elongated body of thecatheter115. In other embodiments, the opening at the distal end of thedelivery catheter115 may extend only a partial length into the delivery catheter115 (e.g., with a narrower channel extending fully to the proximal end of thedelivery catheter115 to provide space for the plunger mechanism140).
• Referring toFIGS. 5 and 6, thetines132 and134 of thewireless electrode assembly120 may be configured in a number of orientations. For example, thetines132 and134 can be arranged in a configuration (refer toFIG. 5) that permits theelectrode assembly120 to penetrate a substantial length into the heart wall tissue (described in more detail below in connection withFIGS. 7A-7D). In another example, thetines132 and134 can be arranged in a configuration (refer toFIG. 6) that permits theelectrode assembly120 to penetrate a lesser amount into the heart wall tissue (described in more detail below in connection withFIG. 8). In some embodiments,wireless electrode assembly120 may include aproximal electrode121 at or near a proximal end and adistal electrode129 at or near a distal end. Theproximal electrode121 anddistal electrode129 may provide bipolar electrode capabilities for thewireless electrode assembly120, thereby permitting theassembly120 to supply an electrical charge between the proximal anddistal electrodes121 and129 (and across the nearby heart tissue).
• As previously described, thefixation device132 may include a set of biased tines arranged near the distal end of thewireless electrode assembly120 so as to secure thewireless electrode assembly120 to the heart chamber wall. Thefixation device134 may include a first set of biased tines arranged near the proximal end of thewireless electrode assembly120 which can also serve to secure theassembly120 to the heart chamber wall. In some embodiments, thetines134 arranged near the proximal end may have a different configuration and orientation from the opposingtines132 arranged near the distal end. For example, as shown in the embodiments depicted inFIGS. 5-6, thedistal tines132 may generally oppose theproximal tines134. In these circumstances, at least some of thetines132 and134 are biased to adjust from a loaded condition to a deployed condition. For example, when in the loaded condition, thetines132 and134 may be arranged generally along thebody128 of thewireless electrode assembly120 so as to fit within the cavity at the distal end of the delivery catheter115 (refer, for example, to FIG.7A). Thetines132 and134 may be biased to adjust to the deployed condition while advancing from thedelivery catheter115. When in the deployed condition, thedistal tines132 may be disposed in an outwardly extended orientation that opposes the outwardly extended orientation of theproximal tines134. In one example, thedistal tip130 may penetrate into the heart chamber wall when a force is applied to the wireless electrode assembly120 (e.g., penetrate the endocardium and possibly into the myocardium). During penetration, thetines132 and134 are biased to transition from the loaded condition (described in more detail below in connection with FIGS.7A-D) to the deployed condition as illustrated bytines132aand134a(inFIG. 5) andtines132band134b(inFIG. 6). Such a configuration permits thewireless electrode assembly120 to be readily secured to the heart chamber wall after advancing from thedelivery catheter115.
• As previously described, thewireless electrode assembly120 may be arranged in the delivery catheter115 (FIG. 4) so that thetines132 and134 are in a loaded condition. Thus, when theelectrode assembly120 is advanced out of the distal end of thedelivery catheter115, thetines132 and134 transition into their respective deployed conditions. In some embodiments, thetines132 and134 may comprise biocompatible material that is capable of flexing from the loaded condition to the deployed condition. For example, one ore more of thetines132 and134 may comprise a shape memory alloy (e.g., Nitinol or the like), stainless steel, titanium, metal alloys (e.g., nickel-cobalt base alloys such as MP35N), composite materials, or the like.
• In the embodiment depicted inFIG. 5, thedistal tines132aandproximal tines134acan be arranged so that a substantial length of the electrode assemble120 penetrates into the heart wall tissue. In these circumstances, thedistal tines132amay penetrate in the heart wall tissue to hinder rearward migration of theelectrode assembly120 back into the hear chamber, and theproximal tines134aare configured to abut or partially penetrate into the wall surface to hinder forward migration of theassembly120 toward the outside of the heart. Thus, when in the deployed condition, thedistal tines132aoppose migration of thewireless electrode assembly120 in the generally proximal direction and theproximal tines134aoppose migration in the generally distal direction. Accordingly, the opposing orientation of thetines132aand134asecures thewireless electrode assembly120 to the heart tissue in a manner so that a portion of the proximal end of thewireless electrode assembly120 is not embedded in the heart tissue. Becausetines132aand134acan retain theelectrode assembly120 in the heart tissue without substantial migration, the proximal end of theelectrode assembly body128 can be incorporated into the surrounding heart tissue over a period of days or weeks. In these embodiments, thewireless electrode assembly120 may be immobilized by the surrounding tissue to prevent future dislodgement. In such circumstances, the patient may receive anti-coagulants, Aspirin, or other drugs (e.g., PLAVIX, CUMODIN, etc.) for several months after the operation or until incorporation of thewireless electrode assembly120 into the surrounding tissue has occurred.
• In this embodiment depicted inFIG. 5, thedistal tines132aand theproximal tines134aare slightly curved and are oriented in an opposing manner when in the deployed condition. The curvature of theproximal tines132 is such that thetines134acontact the surface of the heart tissue near the proximal tines' extremities. In addition, theproximal tines134acan be positioned along thebody128 and curved in a manner so that thefree end135aof eachproximal tine134aabuts or partially penetrates into the heart wall tissue after a portion of theelectrode assembly120 has penetrated therein. Thewireless electrode assembly120 can be advanced into theheart wall tissue35 so that theproximal tines134acause a slight spring-back action after abutting or partially penetrating into the heart wall tissue. For example, theproximal tines134amay flex outwardly when forced into engagement with the heart wall tissue, and such an outward flexing action can cause a slight spring back motion to thewireless electrode assembly120. Thedistal tines132amay flex outwardly in response to this slight spring-back motion in the proximal direction, thereby enhancing the engagement of the heart tissue between thedistal tines132aand theproximal tines134a.
• Still referring toFIG. 5, theproximal tines134acan be positioned along thebody128 and curved in a manner so that thefree end135aof eachproximal tine134aabuts or partially penetrates into the heart wall tissue after a substantial portion of theelectrode assembly120 has penetrated therein. For example, in this embodiment, theproximal tines134aare configured such that thefree end135aof eachtine134a(when in the deployed condition) is disposed a longitudinal distance D₁rearward of thedistal tip130. In this embodiment, the longitudinal distance D₁is greater than half the overall length L of theelectrode assembly120. In such circumstances, a majority of the length of theelectrode assembly120 can penetrate into the heart wall tissue before theproximal tines134aengage the heart wall to oppose forward migration. This example of substantial penetration of theelectrode assembly120 into the heart wall tissue may be effective when advancing theelectrode assembly120 into portions of the heart having thicker myocardial walls (e.g., some heart walls around the left and right ventricles). In addition, when a substantial portion of theelectrode assembly120 penetrates into the heart tissue, the non-penetrating proximal portion of theelectrode assembly120 is reduced, thereby promoting efficient healing and incorporation into the surrounding heart tissue.
• In the embodiment depicted inFIG. 6, thedistal tines132bandproximal tines134bcan be arranged so that a lesser length of theelectrode assembly120 penetrates into the heart wall tissue. For example, thedistal tines132bmay be substantially different in length than theproximal tines134b. Also, theproximal tines134bmay have a greater curvature than theproximal tines134apreviously described in connection withFIG. 5 so that the contact between the surface of the heart tissue and the proximal tines is near the apex of the curvature. In these embodiments, theproximal tines134bcan be positioned along thebody128 and curved in a manner so that thecurvature apex135bof eachproximal tine134babuts the heart wall tissue after a partial length of theelectrode assembly120 has penetrated therein. For example, theproximal tines134bare configured such that the apex135b(when in the deployed condition) is disposed at a longitudinal distance D₂rearward of thedistal tip130. In this embodiment, the longitudinal distance D₂is about half the overall length L of theelectrode assembly120. Accordingly, about half of theelectrode assembly120 can penetrate into the tissue before theproximal tines134boppose forward migration. Such penetration to a limited length of theelectrode assembly120 may be effective when advancing theelectrode assembly120 into portions of the heart wall having a reduced wall thickness (e.g., some heart walls around the right atrium).
• As previously described, thetines132band134bare oriented in an opposing fashion to secure thewireless electrode assembly120 to the heart tissue in a manner that opposes reward migration and forward migration, thereby permitting incorporation into the surrounding tissue. For example, theproximal tines134bmay flex outwardly when forced against the heart wall tissue, and such an outward flexing action can cause a slight spring back motion to thewireless electrode assembly120. Thedistal tines132bmay flex outwardly in response to this slight spring-back motion in the proximal direction, thereby enhancing the engagement of the heart tissue between thedistal tines132band theproximal tines134b.
• In some embodiments, theproximal tines134bof the electrode assembly may be nonaligned with thedistal tines132balong the body of theelectrode assembly128. For example, as shown inFIG. 6, thedistal tines132bmay be tangentially shifted about 45° along the body circumference as compared to theproximal tines134bso that theproximal tines134banddistal tines132bare nonaligned. As described in more detail below in connection withFIG. 8, such nonalignment between theproximal tines134band thedistal tines132bcan permit one set of tines (e.g., theproximal tines134b) to partially deploy before fully exiting the distal opening of thedelivery catheter115. In these circumstances, the partial deployment of theproximal tines134bbefore fully exiting thedelivery catheter115 can facilitate the abutting engagement between theproximal tines134band the heart chamber wall.
• It should be understood that in some embodiments of thewireless electrode assembly120, thedistal tines132 may also serve as at least a portion of thedistal electrode129. Also, in some embodiments,proximal tines134 may also serve as at least a portion of theproximal electrode121. For example, thetines132 and134 may comprise an electrically conductive material (e.g., stainless steel or another metallic material) and may be electrically connected to the distal and proximal electrode circuitry (respectively).
• Referring now to FIGS.7A-D, some embodiments of thewireless electrode assemblies120 may be press fit into the conduit of thedelivery catheter115 so that aplunger mechanism144 may be used to separate thewireless electrode assembly120 from thedelivery catheter115. As shown inFIG. 7A, thedelivery catheter115 may be steered and directed toward a targeted site at the surface of heart tissue35 (e.g., a heart chamber wall). Thedelivery catheter115 may contain at least a distal portion of atube portion142 that is coupled to anactuation rod140. As previously described, in some approaches to the targeted tissue, the steering mechanism (e.g., steering wires, shape memory device, or the like) of thedelivery catheter115 can be manipulated so that a deflected portion near the distal end of thedelivery catheter115 abuts against the septum wall of the targeted heart chamber. For example, the portion117 (FIG. 7A) of thedelivery catheter115 may be deflected to abut against the septum wall while a longitudinally straight section of thecatheter115 extends toward the targetedheart tissue35. As such, some portion (e.g., portion117) thedelivery catheter115 can abut against the septum wall to support the position of the distal end of thedelivery catheter115.
• Thewireless electrode assembly120 may be releasably engaged with thetube portion142. For example, thewireless electrode assembly120 may be press-fit into thetube portion142. In another example, thetube portion142 may have a square cross-sectional shape, a hexagonal cross-sectional shape, a keyed cross-sectional shape, or other noncircular cross-sectional shape to engage the complementary shaped body of thewireless electrode assembly120. Thetube portion140 may be substantially rigid so as to retain thefixation devices132 and134 of thewireless electrode assembly120 in a loaded condition (as shown, for example, inFIG. 7A). In some embodiments, one or both of theactuation rod140 and theplunger mechanism144 may extend to an actuation device (e.g., a hand-operated trigger mechanism) at the proximal end of thedelivery catheter115 outside the patient's body. In some embodiments, thetube portion142 and theactuation rod140 may be fixedly arranged in thedelivery catheter115 so as to deliver one electrode assembly at a time. Alternatively, thetube portion142 and theactuation rod140 may be movable through lumen of thedelivery catheter115 so that a number of electrode assemblies can be consecutively passed through thedelivery catheter115.
• As shown inFIG. 7B, the distal end of thedelivery catheter115 may abut the surface of theheart tissue35 to prepare thewireless electrode assembly120 for fixation to thetissue35. In this embodiment, the distal end of thedelivery catheter115 includes amarker band116 to facilitate the steering and guidance of the delivery catheter (e.g., a physician may employ medical imaging techniques to view themarker band116 while thedelivery catheter115 is in the heart30).
• Referring toFIG. 7C, theelectrode assembly120 can be advanced through the distal opening of the delivery catheter115 (and the tube portion142) and into thetissue35. This operation may be performed by advancing theplunger mechanism144 against the proximal end of thewireless electrode assembly120 to thereby force thedistal tip130 of thewireless electrode assembly120 to penetrate through the endocardium and possibly into the myocardium. For example, the force may be applied by manipulating the actuation device (e.g., the hand-operated trigger mechanism connected to the proximal end of the plunger mechanism144) to force theplunger mechanism144 in the distal direction relative to the actuation rod140 (and the tube portion142). As such, thedistal tip130 of theelectrode assembly120 pierces the tissue surface and advances into thetissue35.
• Referring toFIG. 7D, when thedelivery catheter115 is fully separated from thewireless electrode assembly120, thefixation devices132 and134 can transition from a loaded condition to a deployed condition. In this embodiment, thefixation devices132 and134 comprise tines that are biased to the deployed condition (refer, for example, toFIGS. 5-6) after being released from thetube portion142 of thedelivery catheter115. As previously described in connection withFIG. 5, thetines132 and134 can be configured so that a substantial portion of theelectrode assembly120 penetrates into thetissue35 before the forward migration is hindered by theproximal tines134. For example, theelectrode assembly120 can penetrate the longitudinal length D₁into theheart tissue35 so that a majority of the overall length of theelectrode assembly120 is advanced into thetissue35. In these embodiments, thedistal tines132acan transition to the deployed condition in which eachtine132ais outwardly extended in a generally proximal direction when thedistal tip130 penetrates into theheart tissue35. Also in these embodiments, theproximal tines134acan transition to the deployed condition in which eachtine134ais extended outwardly in a generally distal direction when thedelivery catheter115 is separated from the proximal end of thewireless electrode assembly120.
• As previously described, in some circumstances, theproximal tines134amay flex outwardly when forced against the heart wall tissue, and such an outward flexing action can cause a slight spring back motion to thewireless electrode assembly120. Thedistal tines132amay flex outwardly in response to this slight spring-back motion in the proximal direction, thereby enhancing the engagement of theheart tissue35 between thedistal tines132aand theproximal tines134a. Such an opposed orientation of thetines132aand134ahinders rearward migration and forward migration of theelectrode assembly120. As previously described, thetissue35 may grow and eventually incorporate thewireless electrode assembly120 therein, thereby preventing thewireless electrode assembly120 from dislodgement from thetissue35. In the example depicted inFIG. 7D, theproximal tines134aare illustrated as abutting against theheart tissue35. It should be understood that, in some embodiments, theproximal tines134amay at least partially penetrate into theheart tissue35 when theelectrode assembly120 is advanced therein.
• Referring toFIG. 8, other embodiments of thewireless electrode assembly120 includefixation devices132 and134 that transition into different configurations. For example, thefixation devices132band134bmay include tines that are biased to transition into a deployed condition (after being released from the delivery catheter115) as described in connection withFIG. 6. In such embodiments thetines132band134bmay deploy to outwardly extended orientations that generally oppose one another. Thetines132 and134 can be configured so that a limited length of theelectrode assembly120 penetrates thetissue35 before the forward migration is opposed by theproximal tines134b(e.g., before thecurvature apex135babuts the tissue35). For example, theelectrode assembly120 can penetrate the longitudinal length D₂into theheart tissue35 so that about half of the overall length of theelectrode assembly120 is advanced into thetissue35. As previously described, in some circumstances, theproximal tines134bmay flex outwardly when forced against theheart wall tissue35, and such an outward flexing action can cause a slight spring back motion to thewireless electrode assembly120. Thedistal tines132bmay flex outwardly in response to this slight spring-back motion in the proximal direction, thereby enhancing the engagement of theheart tissue35 between thedistal tines132band theproximal tines134b. Such opposed orientations of thetines132band134bhinders rearward and forward migration of theelectrode assembly120. Also, as previously described, thetissue35 may grow and eventually incorporate thewireless electrode assembly120 therein, thereby preventing thewireless electrode assembly120 from dislodgement from thetissue35.
• Still referring toFIG. 8, theproximal tines134bmay be configured to at least partially deploy before exiting the distal opening of thedelivery catheter115. As such, theproximal tines134bmay at least partially curve outwardly from thebody128 of the electrode assembly before contacting theheart wall tissue35. In these circumstances, theproximal tines134bmay curve so as to abut against theheart wall tissue134bwithout the extremities of theproximal tines134bpenetrating into thetissue35. Because theproximal tines134bcan at least partially deploy before exiting the distal opening of thedelivery catheter115, theproximal tines134bcan achieve the greater curvature previously described in connection withFIG. 6 so that the contact between theheart tissue35 and theproximal tines134bis near thecurvature apex135b(FIG. 6).
• For example, in some embodiments,electrode assembly120 can be arranged in thetube portion142 so that theproximal tines134bare aligned with deployment slots146 (FIG. 8) formed in thetube portion142. Accordingly, when the electrode assembly is advanced into theheart tissue35, theproximal tines134bat least partially extend outwardly into thedeployment slots146, thereby permitting theproximal tines134bto partially deploy before exiting the distal opening of thedelivery catheter115. As previously described in connection withFIG. 6, theproximal tines134bmay be nonaligned with thedistal tines132balong the body of theelectrode assembly128. Such nonalignment between theproximal tines134band thedistal tines132bcan permit theproximal tines134bto partially deploy in thedeployment slots146 while thedistal tines132bare retained against theelectrode body128 in thetube portion142. Alternatively, thedistal tines132bcan be generally aligned with theproximal tines134bso that both thedistal tines132band theproximal tines134bpass through thedeployment slots146 during advancement of theelectrode assembly120 from thedelivery catheter115. It should be understood that, in some embodiments, thedeployment slots146 may extend through the distal circumferential end of thedelivery catheter115 so that theproximal tines134bcan at least partially deploy through the distal circumferential end of thedelivery catheter115 before exiting the distal opening of thedelivery catheter115.
• In some embodiments of thedelivery catheter115 described herein, thedelivery catheter115 may be wholly separate from theactuation rod140 so that theactuation rod140 slides through a conduit passing through thedelivery catheter115. In such circumstances, theactuation rod140 may be completely retracted from the delivery catheter so that a second wireless electrode assembly may be detachably coupled to the actuation rod140 (or to an unused, different actuation rod140) and then directed through thedelivery catheter115 already disposed in the patient's body. In other embodiments, thedelivery catheter115 and theactuation rod140 may be coupled to one another. In such circumstances, thedelivery catheter115 andactuation rod140 may be removed from the guide catheter110 (FIG. 4) so that a second wireless electrode assembly may be detachably coupled to the actuation rod140 (or to a previously unused delivery catheter/actuation rod having a similar construction) and then directed through theguide catheter110 already disposed in the patient's body.
• In some embodiments, thedelivery catheter115 may include a tube portion that is configured to retain a plurality of wireless electrode assemblies120 (e.g., similar totube portion142 but having a greater length to receive a multitude of assemblies120). For example, the delivery catheter may be configured to carry two, three, four, five, ten, twelve, ormore electrode assemblies120 in a serial (end to end) arrangement. As such, theplunger mechanism144 can be used to force eachelectrode assembly120 into different tissue sites without retracting the delivery catheter out of the heart. As described previously, the actuation mechanism may force theplunger144 in a generally distal direction. In the serially arranged embodiment, theplunger144 applies the force to the mostrearward assembly120 in the serial arrangement, which in turn applies a force from thedistal tip130 of the mostrearward assembly120 to the proximal end of thenext assembly120 in the serial arrangement. In this fashion, the application of force can propagate through the serial arrangement until theassembly120 nearest theheart tissue35 is delivered to the target site (as described previously, for example, in connection withFIG. 7D). It should be understood that the serial arrangement may compriseelectrode assemblies120 as described in connection withFIG. 5, as described in connection withFIG. 6, or some combination thereof.
• Some of the embodiments described herein permit a plurality of pacing electrodes to be deployed at multiple pacing sites. The pacing sites may be located in theleft atrium32, theleft ventricle34, theright atrium36, the right ventricle, or a combination thereof. Furthermore, the pacing electrodes may comprise wired pacing leads95 (FIG. 1), wireless electrode assemblies, or a combination thereof. Providing electrical stimulation at multiple pacing sites and in multiple heart chambers may be used to treat a number of conditions. One such condition is congestive heart failure (CHF). It has been found that CHF patients have benefited from bi-ventricular pacing, that is, pacing of both theleft ventricle34 and theright ventricle38 in a timed relationship. It is believed that many more patients could benefit if multiple sites in the left andright ventricles34 and36 could be synchronously paced. In addition, pacing at multiple sites may be beneficial where heart tissue through which electrical energy must propagate is scarred or dysfunctional, which condition halts or alters the propagation of an electrical signal through that heart tissue. In these cases multiple-site pacing may be useful to restart the propagation of the electrical signal immediately downstream of the dead or sick tissue area. Synchronized pacing at multiple sites on the heart may inhibit the onset of fibrillation resulting from slow or aberrant conduction, thus reducing the need for implanted or external cardiac defibrillators. Arrhythmias may result from slow conduction or enlargement of the heart chamber. In these diseases, a depolarization wave that has taken a long and/or slow path around a heart chamber may return to its starting point after that tissue has had time to re-polarize. In this way, a never ending “race-track” or “circus” wave may exist in one or more chambers that is not synchronized with normal sinus rhythm. Atrial fibrillation, a common and life threatening condition, may often be associated with such conduction abnormalities. Pacing at a sufficient number of sites in one or more heart chambers, for example in the atria, may force all tissue to depolarize in a synchronous manner to prevent the race-track and circus rhythms that lead to fibrillation.
• A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims (22)

1. A wireless electrode assembly for electrical stimulation of heart tissue, comprising:

a body portion at least partially containing a circuit to deliver electrical energy to an electrode to electrically stimulate heart wall tissue;

a first fixation structure extending from the body portion in a generally forward orientation and being biased to shift from a retained condition to an outwardly extended condition to engage heart wall tissue; and

a second fixation structure extending from the body portion in a generally rearward orientation and being to shift from a retained condition to an outwardly extended condition to engage heart wall tissue.

2. The wireless electrode assembly ofclaim 1, wherein the first fixation structure comprises at least one tine that opposes forward migration of the body portion through the heart wall tissue when in the outwardly extended condition.

3. The wireless electrode assembly ofclaim 2, wherein the second fixation structure comprises at least one tine that opposes rearward migration of the body portion through the heart wall tissue when in the outwardly extended condition.

4. The wireless electrode assembly ofclaim 1, wherein at least the electrode of the body portion is insertable through endocardium and into myocardium of the heart wall tissue.

5. The wireless electrode assembly ofclaim 4, wherein the body portion has a radius of about 1.25 mm or less, and wherein the body portion has a length of about 10 mm or less.

6. The wireless electrode assembly ofclaim 1, wherein the first and second fixation structures comprise a material selected from the group consisting of Nitinol, stainless steel, and a nickel-cobalt alloy.

7. The wireless electrode assembly ofclaim 1, wherein the circuit comprises an internal coil to inductively couple with an external power source coil and comprises an electrical charge storage device that is recharged from current inductively generated by the internal coil.

8. A wireless electrode assembly at least partially implantable through an interior surface of a heart chamber wall, the electrode assembly comprising:

a body portion having an electrode for electrically stimulating cardiac tissue;

a first set of tines biased outwardly and extending forwardly from a rearward radial periphery of the body portion, the first set of tines opposing a rearward portion, but not a forward portion, of the body portion from being advanced into the heart chamber wall when the electrode assembly is longitudinally advanced in a forward direction toward the interior surface of the heart chamber wall; and

a second set of tines extending rearwardly and biased outwardly from a forward radial periphery of the body portion, the second set of tines opposing the forward portion of the body portion from becoming dislodged from heart wall tissue after the longitudinal advancement of the forward body portion into the heart chamber wall.

9. The wireless electrode assembly ofclaim 8, wherein at least the forward portion of the body portion is insertable through endocardium and into myocardium of the heart wall tissue.

10. The wireless electrode assembly ofclaim 9, wherein the body portion has a radius of about 1.25 mm or less, and wherein the body portion has a length of about 10 mm or less.

11. The wireless electrode assembly ofclaim 8, wherein the first set of tines and the second set of tines comprise a material selected from the group consisting of Nitinol, stainless steel, and a nickel-cobalt alloy.

12. The wireless electrode assembly ofclaim 8, wherein the body portion comprises a circuit that includes an internal coil to inductively couple with an external power source coil and an electrical charge storage device that is recharged from current inductively generated by the internal coil.

13. An electrode delivery system, the system comprising:

a wireless electrode assembly including a body portion and first and second tines that are biased to shift from a loaded condition to an outwardly extended condition to secure the body portion to a heart chamber wall, the first and second biased tines generally opposing one another; and

a delivery catheter to direct the wireless electrode assembly through a heart chamber and toward an interior surface of a heart chamber wall, the delivery catheter including an opening in a distal end such that, when the wireless electrode assembly is separated from the opening in the distal end of the catheter, the first and second tines shift from the loaded condition to the outwardly extended condition.

14. The electrode delivery system ofclaim 13, wherein when the first and second tines shift to the outwardly extended condition, the first tines are outwardly extended in a generally distal orientation and the second biased tines are outwardly extended in a generally proximal orientation.

15. The electrode delivery system ofclaim 13, further comprising a guide catheter to direct the distal end of the delivery catheter into the heart chamber.

16. The electrode delivery system ofclaim 15, further comprising an actuation member that includes a push rod device to separate the wireless electrode assembly from the opening in the distal end of the delivery catheter.

17. The electrode delivery system ofclaim 13, wherein the wireless electrode assembly is releasably retained in the delivery catheter by a tubular wall, the tubular wall comprising one or more deployment slots generally aligned with at least one of the first and second tines.

18. A method of inserting a wireless electrode assembly into a heart chamber wall, comprising:

inserting a set of distal tines of a wireless electrode assembly through a portion of endocardium and into a heart chamber wall, the set of distal tines being biased to shift from a retained condition to an outwardly extended condition to secure the wireless electrode assembly to a heart chamber wall; and

causing a set of proximal tines of the wireless electrode assembly to shift from a retained condition to an outwardly extended condition to secure the wireless electrode assembly to the heart chamber wall,

the set of distal tines extending in a generally rearward orientation when in the outwardly extended condition and the set of proximal tines extending in a generally forward orientation when in the outwardly extended condition.

19. The method ofclaim 18, wherein a portion of the wireless electrode assembly is secured to the heart chamber so as to be at least partially incorporated into the endocardium of the heart chamber wall over a period of time.

20. The method ofclaim 18, further comprising delivering the wireless electrode assembly in a delivery catheter to a targeted heart chamber.

21. The method ofclaim 20, when the set of distal tines and the set of proximal tines are shifted to their respective outwardly extended conditions when the wireless electrode assembly is separated from a distal opening of the delivery catheter.

22. The method ofclaim 18, further comprising implanting a wireless power source coil proximal to the heart so that the wireless power source coil is arrange for inductive coupling with an internal coil of the wireless electrode assembly.

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