Patent Publication Number: US-2020276447-A1

Title: Temporary electrode connection for wireless pacing systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is a continuation of U.S. patent application Ser. No. 15/043,210 (Attorney Docket No. 41567-724.401), filed Feb. 12, 2016, now U.S. Pat. No. ______, which is a divisional of U.S. patent application Ser. No. 12/890,308 (Attorney Docket No. 41567-724.301, now U.S. Pat. No. 9,283,392), filed Sep. 24, 2010, which is a continuation of International Patent Application No. PCT/US2009/037978 (Attorney Docket No. 41567-724.601), filed Mar. 23, 2009, which claims the benefit of provisional U.S. Application No. 61/039,335 (Attorney Docket No. 41567-724.101), filed Mar. 25, 2008, the full disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The field of the present invention relates generally to implanted devices for tissue stimulation, monitoring, and other therapeutic or diagnostic functions, and specifically to implantable devices for the stimulation of cardiac tissue, for example pacemakers or implantable cardioverter-defibrillators (ICDs). More specifically, it pertains to such devices utilizing wireless energy transfer, for example using ultrasound energy. 
     BACKGROUND 
     Pacemakers provide electrical stimulus to heart tissue to cause the heart to contract and hence pump blood. Conventionally, pacemakers include a pulse generator, typically implantable in a patient&#39;s pectoral region, with one or more leads (wires) extending from the pulse generator into a heart chamber. The lead terminates at an electrode, which is implanted in the heart. 
     While pacemakers using leads are widely used, they have several drawbacks. For example, the gradual intertwining of leads with heart tissue over time secures the lead in place but also hinders lead removal or repositioning. Another drawback to using leads is the limit placed on the number of heart sites that may be stimulated. While pacing at multiple sites may be beneficial for treating different heart conditions such as congestive heart failure, arrhythmia and atrial fibrillation, using multiple leads may block a clinically significant fraction of the cross section of the veins and cavities through which the leads are routed. 
     Pacing systems using wireless electrodes have been suggested as a way of overcoming the limitations of conventional systems with leads, with wireless receiver-stimulator electrodes implanted into the heart wall and in wireless communication with transmitter(s) for energy delivery or for communication of control or feedback signals. The inventors of this patent application have proposed systems using implantable wireless electrodes that receive acoustic energy and convert it into electrical energy for electrically stimulating the heart. Such methods and systems have been disclosed in co-pending U.S. Patent Application Nos. (Publication No.) 20060136004, 20060136005, 20070027508, 20070055184, 20070078490 and 20070060961 and Ser. No. 11/752,775, which are herein incorporated by reference in their entirety. As another example, U.S. Patent Application No. (Publication No.) 2006/0085039 discloses a system using implantable wireless electrodes that receive energy via inductive coupling of a coil in the electrode to a radio frequency antenna attached to a central pacing controller. 
     When implanting a wireless receiver-stimulator, the choice of the implantation location is important for at least two reasons. First, it is desirable that the tissue in electrical contact with the stimulation electrodes of the receiver-stimulator be sufficiently excitable to allow efficient pacing stimulation by the receiver-stimulator. Secondly, it is desirable that the wireless receiver-stimulator be positioned relative to the wireless transmitter to allow efficient wireless communication between the two, particularly with respect to energy transmission and reception. 
     While the determination of the location in conventional systems with leads involves fairly straightforward techniques, such techniques do not translate directly for wireless pacing systems. In a conventional pacing system, determination of an excitable tissue location is customarily practiced by monitoring electrogram (EGM) signals at the implantation site and additionally by stimulating or pacing through the electrodes, before permanently implanting them in the patient. The user simply connects the proximal end of the pacing lead into a pacemaker programmer or other electrophysiology instrumentation that allows the user to monitor EGM signals from the electrodes on the lead and to stimulate through the electrodes on the lead to confirm that the implant location is appropriate. 
     In contrast, in a wireless system one obstacle is the lack of a direct connection to one or more of the electrodes for the monitoring of EGM signals. Additionally, stimulating through the wireless electrodes involves transmission of energy from a transmitter to a receiver-stimulator through a wireless process, whether for charging the receiver-stimulator or for transduction from wirelessly delivered energy to stimulation energy. This lumps two effects together: the efficiency of the wireless transfer of energy (by whatever means the system employs, such as acoustic energy, radio frequency (RF), or other means) and the properties and excitability of the tissue that the pacing electrodes are placed over. This could result in user confusion and potentially inaccurate determination of pacing thresholds and energy conversion efficiencies. 
     For example, in a conventional pacing system with leads, a high pacing threshold implies a poor location for placing the pacing electrodes. This may indicate, for example, that the electrodes are not in close proximity to the tissue or are placed over non-excitable tissue. A straightforward resolution of this problem is moving the electrode until an appropriate location is found. In contrast, in a wireless system a high energy level that is required to pace could be the result of inefficient or poor wireless transfer of energy from the transmitter to the receiver-stimulator, or, similar to the conventional pacing system, the result of a poor location of the receiver-stimulator not in close proximity to the tissue or over non-excitable tissue. 
     An extension of the above lead-based techniques to wireless stimulation systems comprises establishing electrical contact between one or more of the electrodes of an implantable wireless receiver-stimulator, a delivery system (such as a catheter or the like), and the tissue. Alternatively, surrogate electrodes on the delivery system, i.e., not the electrodes of the wireless receiver-stimulator, may be used for assessing whether the tissue is excitable. However, it requires the use of one or more of the electrodes of the implantable wireless receiver-stimulator to fully assess the efficient and effective transfer of energy to the receiver-stimulator from the transmitter. The desirable approach is to use one or more of the electrodes of the implantable wireless receiver-stimulator to sense local tissue EGMs in order to (1) determine a suitable implant location, as well as (2) determine efficiency of energy conversion by the wireless implant. For example, such a technique is partially suggested in the above referenced U.S. Patent Application (Publication No.) 2006/0085039. Another approach to determine the appropriate location for implantation of the electrodes is to observe the hemodynamic parameters of the heart upon stimulating a location. Such an approach is described in the Applicants&#39; co-pending U.S. Patent Application (Publication No.) 2007/0060961. While this desirable approach may be constructed, it does give rise to a number of challenges. 
     First, once the wireless electrode is implanted, disconnected from the delivery system, and the delivery system is removed, any conductive material at the severed connection on the wireless implant, remaining exposed after disconnecting the delivery system from the electrode(s), presents a potential alternate electrical path between the implant electrodes and the exposed remains, allowing some or all of the stimulation current to bypass the desired stimulation path and thereby reduce or entirely undermine stimulation effectiveness. 
     Second, it is also desirable to be able to assess conversion efficiency in-situ, perhaps over a variety of energy transmission conditions. It would be desirable to perform this assessment while directly connected to one or more of the electrodes without requiring that the wireless implant deliver electrical output (stimulation energy) at sufficient strength to capture tissue. By monitoring the electrical energy output, the efficiency of transmission can be assessed and the likelihood of pacing capture can be correlated with the efficiency. 
     Therefore, it is desirable to have a wireless pacing system that allows the user to determine a suitable implant location and assess the efficiency of energy conversion prior to permanent implantation by using the pacing electrodes of the receiver-stimulator, and further eliminate exposed residual conductive material after removal of the delivery system. 
     SUMMARY 
     Embodiments of the present invention are directed to wireless receiver-stimulator devices for cardiac stimulation. An implantable wireless receiver-stimulator is implanted into a location in the heart using a delivery system, which typically comprises a delivery catheter but may take other forms as well. The receiver-stimulator comprises a cathode and an anode, and is configured to receive energy delivered by a controller-transmitter. The receiver-stimulator converts the energy to electrical energy and delivers the electrical energy as pacing pulse (stimulation) energy, through the cathode and anode stimulation electrodes, which stimulates the heart. By practice, the cathode is typically the P- and the anode is typically the P+ for the stimulation electrodes. 
     The delivery system comprises conductive wires routed through the catheter which temporarily connect one or more of the electrodes of the receiver-stimulator to an external monitor and pacing controller. A first temporary electrical connection connects the delivery system with the receiver-stimulator&#39;s cathode, and a second temporary electrical connection connects the delivery system with the receiver-stimulator&#39;s anode. The system may be operated with a single temporary connection, preferably to the cathode, and an indifferent electrode, which may be a separate electrode acting as the anode (apart from the anode of the receiver-stimulator) that is integrated into the delivery system or on a separate device, or still further a body surface electrode. Temporary electrical connections allow the user to monitor the heart&#39;s electrical activity at a location in the heart as sensed by the receiver-stimulator&#39;s cathode and anode and determine whether the location indicates excitable heart tissue. Alternatively, combination of the temporary electrical connection between the receiver-stimulator&#39;s cathode and a monitoring system and a permanent electrical connection between the indifferent electrode and the monitoring system can also be used to determine whether the location indicates excitable heart tissue. 
     Once a receiver-stimulator is positioned at a heart location intended as the implant location, the heart tissue is stimulated using electrical stimulation energy from an external pacing controller delivered to the tissue through the receiver-stimulator&#39;s cathode and an anode via the temporary electrical connection(s), thereby allowing determination of an acceptable electrical pacing threshold at the location of the cathode prior to permanent attachment of the wireless receiver-stimulator to the heart wall. 
     The temporary electrical connection can also be used to determine the efficiency of conversion of energy to electrical stimulation energy by the receiver-stimulator at a given location in the heart. In one embodiment, this is accomplished by delivering acoustic energy from a wireless controller-transmitter or similar implantable or externally-applied acoustic transmitter to the wireless receiver-stimulator, converting the acoustic energy to electrical energy, and delivering electrical energy to the heart tissue through the receiver-stimulator&#39;s cathode and an anode, while monitoring the electrical energy using an external monitor connected to the electrodes via the temporary electrical connections through the delivery system. The electrical energy in this embodiment need not be at pacing strength, since conversion efficiency can be gauged even at lower energy levels. In an alternative embodiment, the heart is stimulated at pacing strength using the electrical energy that was converted from the acoustic energy, and the EGM generated by the stimulation of heart tissue is monitored using the temporary electrode connections on the receiver-stimulator or other electrodes, e.g., surface EKG electrodes or other electrodes mounted on the delivery system. 
     When a suitable implantation location is determined, the wireless receiver-stimulator is attached to the heart wall and the temporary electrical connections are disconnected using a disconnect mechanism. The disconnect mechanism is configured to prevent the creation of an unwanted secondary set of conductive areas on the receiver-stimulator. 
     In one embodiment, the disconnect mechanism seals an electrical contact point of the cathode temporary electrical connection on the receiver-stimulator from patient fluid or tissue. In another embodiment, the disconnect mechanism comprises a magnetically operated switch which opens when the delivery system is detached from the receiver-stimulator, thereby internally disconnecting the cathode temporary electrical connection contact point on the receiver-stimulator from the active electrodes of the receiver-stimulator. In other embodiments, the disconnect mechanism comprises bellows configured to stretch and disconnect the cathode temporary electrical connection when the delivery system is disconnected, or a conductive dome structure configured to pop out and disconnect the cathode temporary electrical connection when the delivery system is pulled away and disconnected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A-1C  are diagrammatic views of a wireless cardiac stimulation device and a delivery system. 
         FIG. 2A  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a retracted state. 
         FIG. 2B  is a diagrammatic view of a needle assembly. 
         FIG. 2C  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in an injected state. 
         FIG. 2D  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a triggered state. 
         FIG. 2E  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a released state. 
         FIG. 2F  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a tethered state. 
         FIG. 2G  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a tether broken state. 
         FIG. 2H  is a cross sectional view of a wireless cardiac stimulation device and a delivery system in a delivered state. 
         FIG. 3  is a diagrammatic view of a delivery system. 
         FIG. 4  is a flow diagram illustrating the steps for implantation of a receiver-stimulator into the heart. 
         FIG. 5A  is a diagrammatic view of a sealed disconnect mechanism of a wireless receiver-stimulator. 
         FIG. 5B  is a diagrammatic view of a conductive wire passing through a hole or slit of the sealed disconnect mechanism of  FIG. 2A  and connecting with the cathode. 
         FIG. 5C  is a diagrammatic view of a magnetically operated disconnect mechanism. 
         FIG. 5D  is a diagrammatic view of a magnetically operated disconnect mechanism. 
         FIGS. 5E-5F  are diagrammatic views of a disconnect mechanism using a bellows. 
         FIGS. 5G-5H  are diagrammatic views of a disconnect mechanism using a conductive dome structure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. 
     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. In general, features described in one embodiment might be suitable for use in other embodiments as would be apparent to those skilled in the art. 
     A wireless cardiac stimulation system is disclosed that allows the user to assess tissue viability for excitation at a location in the heart, determine an acceptable electrical pacing threshold at the location, and determine operational efficiency of a wireless cardiac stimulation system at the location, prior to permanent implantation of the wireless pacing device. 
       FIGS. 1A-1C  are diagrammatic views of a wireless cardiac stimulation system  101 , in accordance with an embodiment of the present invention. A delivery system  102  with a wireless receiver-stimulator (hereinafter also abbreviated as “R-S”)  103  attached to the delivery system&#39;s distal tip  104  is inserted into the body of a patient. Typically, this would be through vascular access through the groin. Other entry sites sometimes chosen are found in the neck and are in general well known by physicians who practice such medical procedures. 
     The delivery system  102  is positioned so that the R-S  103  at the distal tip  104  of the delivery system  102  is appropriately situated on a part of the heart wall  105  where the R-S  103  is to be attached/implanted. The insertion of the delivery system  102  may be facilitated by the use of a guidewire and/or a guiding catheter, as is known in the art. In addition, the movement of the delivery system  102  may be monitored fluoroscopically. 
     The wireless R-S  103  comprises a cathode  106  and an anode  110  for stimulating patient tissue, with the cathode  106  located at the distal tip of the R-S  103 . The cathode is intentionally designed with a smaller surface area relative to the anode. This leads to higher current densities at the cathode, resulting in tissue stimulation at the cathode. Hence, the term cathode and stimulation electrode are interchangeably used. Additionally, the delivery system  102  comprises two temporary electrical connections between the R-S  103  and the delivery system  102 : a first temporary electrical connection for establishing electrical contact with the cathode  106  and a second temporary electrical connection for establishing electrical contact with the anode  110 . Alternatively, this may take the form of a single temporary electrical connection for establishing contact with the cathode  106  and the second electrical connection provided by an indifferent electrode  110 C configured onto the delivery system (see  FIG. 1B ) or an indifferent electrode  110 P that is configured to be in electrical contact with the patient&#39;s body that is remote from the delivery system (see  FIG. 1C ), wherein this second electrical connection is not temporary electrical connection. The temporary electrical connections comprise electrical contact points between the proximal end of the R-S  103  and the distal end of the delivery system  102 . Specifically, the first temporary electrical connection (for the cathode) is between a first electrical contact point on the proximal end of the R-S  103  and a first electrical contact point on the distal end of the delivery system  102 . Similarly, the second temporary electrical connection (for the anode) is between a second electrical contact point on the proximal end of the R-S  103  and a second electrical contact point on the distal end of the delivery system  102 . The temporary electrical connections provide conductive paths from the cathode  106  and anode  110  of the R-S  103  to an external monitor and pacing controller via conductive wires  107  routed through the delivery system  102 , allowing externally controlled monitoring and pacing. Once the R-S  103  is permanently attached to patient tissue, the R-S  103  detaches from the delivery system  102  and the temporary electrical connections are disconnected. 
     It is noted that on the R-S  103 , any metal or conductive material on the cathode&#39;s temporary electrical connection contact point that remains exposed after the R-S  103  detaches from the delivery system  102  presents a potential for an alternate electrical path between the remaining conductive material and the anode. This could allow some or all of the stimulation current to bypass the desired path between the cathode  106  at the distal tip of the R-S  103  and the anode  110 , at best reducing the efficiency of the wireless R-S  103  and at worst shunting energy away from the tissue and rendering the wireless R-S  103  ineffective. Therefore, various disconnect mechanisms for the cathode&#39;s temporary electrical connection are disclosed herein which isolate one or more electrical contact points of the cathode&#39;s temporary electrical connection on the wireless R-S  103 . One particular embodiment comprises using a non-hermetically sealed enclosure around the cathode&#39;s temporary electrical connection contact point on the R-S  103 . Another embodiment comprises using magnetic and/or mechanical switches internal to the R-S  103  for electrically isolating the cathode&#39;s temporary electrical connection contact point from the cathode itself. These and other embodiments are described in more detail below. The R-S  103  and the delivery system  102  will now be described in more detail. 
       FIG. 2A  shows a cross sectional view of a wireless R-S  103  attached to a delivery system  102 , in accordance with an exemplary embodiment of the present invention. The wireless R-S  103  comprises a needle assembly  115  (also called an axle assembly), also shown in  FIG. 2B . The needle assembly  115  has a cathode  106  at its distal tip for stimulating the heart tissue. The needle assembly  115  is coated with an insulating layer, such as a thin ceramic layer, except at the cathode  106 , at a segment  118   a  (shown in  FIG. 2B ) to allow for an electrical path from the internals of the R-S  103  to the cathode  106  via the needle assembly  115 , and at a proximal segment  118   b  (shown in  FIG. 2B ) to allow for an electrical path from the delivery system  102  to the cathode  106  via the needle assembly  115 . The needle assembly  115  further comprises a neck  119  configured to snap and disconnect as the delivery system  102  disengages from the R-S  103 . 
       FIG. 2A  shows the needle assembly  115  in a retracted state, with the cathode  106  fully within the R-S  103 . The needle assembly  115  comprises one or more barbs  116  coupled proximal to the cathode  106 . The barbs  116  are released when the needle assembly  115  is pushed sufficiently distally outward from the R-S  103  towards the heart wall  105 . The distal portion of the delivery system  102  is shown in an enlarged view in the bottom panel of  FIG. 2A . A conductive wire  123  in the delivery system  102  is coupled to a proximal segment  126  of the needle assembly  115  by a connecting collar  124 . 
     The outside of the wireless R-S  103  housing serves as an anode  110  for stimulating the heart tissue. The anode  110  may comprise only a portion of the R-S  103  housing, or it may comprise the entire outer surface of the R-S  103  housing. The R-S  103  preferably comprises an endothelial growth promoting covering  132  which does not insulate the surface of the anode  110 . For example, in one embodiment the covering  132  may comprise a polyester mesh. 
     The delivery system  102  comprises a flexible outer sheath  133  connected to a rigid collar  125  with flexible extensions or fingers  114 . The fingers  114  are held by tubular extension  121  radially outwards into place around an indentation  120  of the R-S  103 , thereby detachably attaching the delivery system  102  to the R-S  103 . In one embodiment, the fingers  114  are made of a superelastic material, such as Nitinol, and configured to collapse radially inwards in the absence of a restrictive force and thereby release the R-S  103 . Alternatively, the fingers  114  may comprise stainless steel, since it is contemplated that the strains experienced by such fingers  114  are small. A tubular extension  121  attached to the distal end of a retractable flexible wire coil  122  inside the sheath  133  provides such a restrictive force and holds the fingers  114  radially extended, preventing them from collapsing. To release the delivery system  102  from the R-S  103 , the wire coil  122  and its tubular extension  121  are retracted, thereby allowing the fingers  114  to collapse and release the R-S  103 . 
     Once the delivery system  102  has been maneuvered into place within the heart chamber, the wireless R-S  103 , being disposed at the distal end of the delivery system  102 , comes close to or contacts the heart wall  105  such that the cathode  106  is in electrical contact with the heart wall  105 . The anode  110  may be in contact with the heart wall  105  or it may remain within the chamber of the heart. Alternatively, any other indifferent electrode ( 110 C or  110 P), e.g., one positioned on the outer sheath of the delivery system  102  or placed on the patient&#39;s body remote from the delivery system, respectively, may be used as an anode. The wireless R-S  103  can thus be repositioned by the delivery system  102  to assess electrical activity at various locations of the heart wall  105  using the cathode  106  and the anode  110  or indifferent electrode  110 C or  110 P. 
     During the implantation of the wireless R-S  103 , temporary electrical connections from the delivery system  102  to the wireless R-S  103  electrodes are provided, one for the cathode  106  and one for the anode  110 . The exploded view in the bottom panel in  FIG. 2A  shows one or more electrical contact points  112   a  at the distal end of the delivery system  102  and one or more electrical contact points  112   b  at the proximal end of the R-S  103 , where the anode  110  of the R-S  103  comes into electrical contact with one or more fingers  114  of the delivery system  102  to form a temporary electrical connection for the anode  110 . Note that the contact points  112   a  and  112   b  are shown apart in the enlarged view of  FIG. 2A  for illustration purposes only, as they are actually in contact in the particular configuration of the R-S  103  shown in  FIG. 2A . One or more conductive wires coupled to the fingers  114 , provide a conductive path from the anode  110  to an external monitor or controller via the delivery system  102 . Optionally, these wires may also serve as articulation control wires. Alternatively, the rigid collar  125  makes electrical contact with the tubular extension  121  of flexible coil  122  which in turn provides a conductive path from anode  110  to an external monitor or controller via the delivery system  102 . In one embodiment, the R-S  103  and the fingers  114  are gold plated at the temporary electrical contact points  112  in order to provide increased electrical conductivity. 
     While a direct temporary electrical connection is provided from the delivery system  102  to the anode  110  as described above, it is contemplated that a direct connection from the delivery system  102  to the cathode  106  located at the distal tip of the wireless R-S  103  may provide alternative current paths, or may impose complications in manufacturing, cost or reliability. Thus, a temporary electrical connection between the distal end of the delivery system  102  and the proximal end of the wireless R-S  103  housing is disclosed herein that provides a conductive path from the distal tip of the delivery system  102  via the needle assembly  115  to the cathode  106 . 
     In one embodiment, this temporary electrical connection to the cathode  106  comprises an enclosure  117  configured around the neck segment  119  of the needle assembly  115 . At its distal end, the enclosure  117  is tightly coupled to the needle assembly  115 . Internally, the enclosure  117  comprises a seal  127  around the proximal segment  126  of the needle assembly  115 . The seal  127  may be made of silicone, rubber or other flexible insulating material. The seal  127  need not necessarily be hermetic, but it is configured to provide high enough electrical resistance, for example in excess of 10,000 ohms, between the detached temporary electrical connection and the heart wall  105  or the fluid within the heart chamber to allow substantially any electrical current applied to the needle  115  to flow through the electrical path of the cathode  106  to the anode  110 . 
     When the R-S  103  is permanently attached to the heart wall  105  and the delivery system  102  is to detach from the R-S  103 , the conductive wire  123  is retracted into the delivery system  102 , breaking the needle assembly  115  at the neck  119  and removing the proximal segment  126  of the needle assembly  115  from the enclosure  117 . In such an embodiment, the two end points of the broken neck represent the two temporary electrical contact points for the temporary electrical connection between the catheter and the cathode. Upon removal of the proximal segment  126  from the enclosure  117 , the seal  127  closes in around the hole left by the removed proximal segment  126 , electrically isolating the remaining part of the needle assembly  115  (which includes the cathode temporary electrical connection contact point on the R-S  103 ) inside the sealed enclosure  117  from patient fluid and tissue. 
     We now turn to describing a sequence of states for the R-S  103  as it goes from introduction into the patient to final attachment to the heart wall  105 . This sequence is shown in  FIGS. 2A-2H . In  FIG. 2A  (“retracted state”), the R-S  103  is initially introduced into the patient. The R-S  103  is attached to the delivery system  102  and the needle assembly  115  is in a retracted state. In  FIG. 2C  (“injected state”), a wire coil  131  and its extension  130  have pushed the needle assembly  115  distally with respect to the body of the R-S  103 , injecting the cathode  106  into the patient&#39;s heart wall  105  but without releasing the barbs  116 . The distal mechanism of the catheter is such that the extension  130  is limited in its travel so that movement of the wire coil  131  cannot move the needle assembly  115  into its triggered state, thereby obviating requirements for precise motion in the handle of the delivery system  102 . In  FIG. 2D  (“triggered state”), a wire coil  129  and its extension  128  have pushed the needle assembly  115  further out, releasing the barbs  116  and allowing the R-S  103  to securely attach itself to the heart wall  105 . 
     In  FIG. 2E  (“released state”), the wire coil  122  and its extension  121  are retracted into the delivery system  102 , thereby allowing the fingers  114  to radially collapse inwards and release the R-S  103 . At this point, the temporary electrical connection for the anode  110  is disconnected, as the contact points  112   a  on the one or more fingers  114  of the delivery system  102  disconnect from their corresponding contact points  112   b  on the R-S  103 . 
     In  FIG. 2F  (“tethered state”), the catheter sheath  133  and wire coils  122  and  131  are retracted and/or the wire coil  129  and wire  123  are extended, leaving the R-S  103  tethered to the wire  123  and in contact or in proximity with the tubular extension  128  of the wire coil  129 . The tethered state allows the R-S  103  to remain attached to the delivery system  102  and retrievable, while being only connected by a very flexible coupling. This flexibility allows the R-S  103  to move with the heart wall independently of the delivery system  102 , demonstrating under flouroscopic visualization that the R-S  103  is reliably attached to the heart wall  105 . Additionally, the delivery system  102  and the tethering mechanism can be moved by small amounts, changing the degree of slack without eliminating slack. Such movement may demonstrate that the attachment point of the R-S  103  to the heart wall remains fixed while the orientation of the R-S  103  with respect to the heart wall varies, further indicating reliable attachment. In  FIG. 2G  (“tether broken state”), the wire  123  is retracted while the wire coil  129  and its extension  128  exert a resistance against the R-S  103  and prevent it from being pulled along. This causes the needle assembly  115  to break at the neck  119 . The two end points of the broken neck  119  represent the two temporary electrical contact points for the temporary electrical connection between the delivery system  102  and the cathode  106 , with contact point  134   a  representing the electrical contact point at the distal end of the delivery system  102  and contact point  134   b  representing the electrical contact point at the proximal end of the R-S  103 . As the wire  123  continues to retract, it removes with it the broken proximal piece  126  of the needle assembly  115  from the enclosure  117 . Seal  127  closes following the removal of proximal piece  126 , forming an electrical isolation between needle  115  and the fluid surrounding the proximal end of the R-S  103 . In  FIG. 2H  (“delivered state”), the wire coil  129  and its extension  128  are retracted into the delivery system  102  along with the wire  123 , leaving the R-S  103  delivered in the heart wall  105 . 
       FIG. 3  is a diagrammatic view of a delivery system  102  and its handle  141 , in accordance with an embodiment of the present invention. 
     The delivery system  102  is configured for use in the cardiovascular system of a patient and configured to be compatible with standard transvascular tools, such as introducers and guiding sheaths, and conventional techniques related to the operation of such tools. 
     The delivery system  102  comprises one or more safety mechanisms, interlocks, or indicators configured to prevent inadvertent attachment or release of the R-S  103 . 
     As mentioned above, the delivery system  102  provides signal interconnect with an external monitor and pacing controller to facilitate location selection during an implant procedure by collecting local EGM signals, performing direct electrical pacing of the heart via electrical connections to one or more of the electrodes of the implantable R-S  103  device, and evaluating operational efficiency of the R-S  103 . 
     In one embodiment, the delivery system shaft  140  is formed from polymer tubing. Conductive wires  143 , deflection wires  147  and safety release interlock wires  146  are routed within the shaft  140 . A proximal handle assembly  141  comprises a deflection control mechanism  142 , a safety interlock release mechanism  145 , and shrouded electrical connectors  144  that terminate the conductive wires  143  and permit driving the R-S  103  electrodes directly with an externally-generated electrical pacing pulse, as well as monitoring of cardiac EGM signals at the R-S  103  electrodes. 
     In one embodiment, the delivery system  102  is configured to attach the R-S in the left ventricle (LV) by prolapsing the shaft  140  in the aortic arch and advancing through the aortic valve of the heart atraumatically, thereby allowing access to targeted endocardial locations within the LV. The distal portion of the delivery system  102  is deflectable in one plane in at least one direction, through the handle-mounted deflection control system. The deflection control system holds a desired deflection angle. Similarly, in other embodiments the delivery system can be configured to attach the R-S in any heart chamber or on the epicardial surface of the heart or within the vasculature of the heart. 
     The delivery system  102  and/or R-S  103  may comprise one or more radiopaque markers at the distal end to allow fluoroscopic confirmation of the state of R-S  103  deployment. In one embodiment, the markers are configured to clearly differentiate between various stages of deployment, possibly including but not limited to: a) cathode retracted, b) cathode extended, c) attachment tines deployed, d) R-S  103  released, e) tether advanced, f) tether broken, and g) tether retracted. 
     In one embodiment, the delivery system  102  comprises a control mechanism to extend and retract the needle assembly  115  of the R-S  103 . The control mechanism includes a safety mechanism to prevent accidental extension or retraction of the needle assembly  115 . The control mechanism and/or the R-S  103  allows for locking the needle assembly  115  into the desired position (retracted or injected as shown in exemplary  FIGS. 2A and 2C ). 
     The delivery system  102  comprises a control mechanism to activate the attachment mechanism of the R-S  103 , as shown in exemplary  FIG. 2D . This control mechanism and/or the R-S  103  design includes an interlock to prevent deployment of the R-S  103  attachment mechanism unless the cathode  106  is extended. The control mechanism to activate the attachment mechanism comprises multiple or multi-stage safety mechanisms to prevent inadvertent activation. 
     The delivery system  102  also comprises a control mechanism to release the R-S  103 , as shown in exemplary  FIGS. 2E-2H . The control mechanism and/or the R-S  103  design include an interlock to prevent release of the R-S  103  unless the attachment mechanism has been deployed. 
     The control mechanism to release the R-S  103  incorporates multiple or multi-stage safety mechanisms to prevent inadvertent activation. The delivery system  102  and/or R-S  103  comprise reliable means to verify a secure implantation prior to permanent release. 
     The delivery system  102  also comprises a control mechanism to tether out (extend) the R-S  103  away from the main body of the delivery system  102 , as shown in exemplary  FIG. 2F . The control mechanism and/or the R-S  103  design include an interlock to prevent tethering out of the R-S  103  unless the release mechanism has been deployed. The control mechanism to tether the R-S  103  incorporates multiple or multi-stage safety mechanisms to prevent inadvertent tether extension. The delivery system  102  and/or R-S  103  comprise reliable means to verify a secure implantation prior to detaching the tether. The delivery system  102  and the R-S  103  are removable from the vasculature with the tether extended or with the tether retracted. 
     The delivery system  102  also comprises a control mechanism to detach the tether and disconnect the temporary electrical connection from the R-S  103 , as shown in exemplary  FIG. 2G . In one embodiment the control mechanism detaches and disconnects, in alternative embodiments separate mechanisms may be applied to disconnect and detach. The control mechanism and/or the R-S  103  designs include an interlock to prevent disconnecting and detaching the tether of the delivery system  102  unless the release mechanism has been deployed. The control mechanism to disconnect the temporary electrical connection and detach the tether from the R-S  103  incorporates multiple or multi-stage safety mechanisms to prevent inadvertent detachment. The delivery system  102  and/or R-S  103  comprise reliable means to verify a secure implantation prior to disconnecting the temporary electrical connection and detaching the tether. The delivery system  102  is removable from the vasculature with the tether extended or with the tether retracted. 
     The delivery system  102  is removable from the vasculature by manual withdrawal through an introducer. Any enlargement or protrusion from the delivery system  102  as part of the R-S  103  release mechanism is retractable and/or reversible to allow removal. The delivery system  102  comprises conventional means to protect against accidental release of air into the vasculature or heart chamber before and after release of the R-S  103 . 
     In one embodiment, the delivery system  102  is mated with an R-S  103  prior to packaging. The delivery system  102  and R-S  103  are mated and packaged with the cathode  106  locked in a retracted state. In one embodiment, a delivery system  102  with a pre-mated R-S  103  are packaged in a single-use sterile pouch or tray, and a catheter extension cable is packaged in the same single-use sterile pouch or tray with the delivery system  102  and R-S  103 . 
       FIG. 4  is a flow diagram illustrating a method for implantation of a receiver-stimulator into the heart, in accordance with an embodiment of the present invention. At step  450 , an implantable wireless R-S  103  in retracted state is delivered into the heart at a candidate pacing location using a delivery system  102 . At step  452  the heart&#39;s electrical activity is monitored at the location in the heart as sensed by the cathode  106  in an injected state and an indifferent electrode, possibly anode  110  of the R-S  103 . At step  454  it is determined whether the location indicates excitable heart tissue, and if necessary the R-S  103  is repositioned until it is in contact with excitable heart tissue. 
     Once a location is determined to be excitable, the heart tissue is stimulated at step  456  using electrical stimulation energy from an external pacing controller delivered to the tissue through the cathode  106  in an injected state and an anode, possibly anode  110  of the R-S  103 , thereby allowing determination of an acceptable electrical pacing threshold at the location prior to permanent attachment of the R-S  103  to the heart wall. If the pacing threshold is not acceptable, the R-S  103  is repositioned and the above steps are repeated until an acceptable pacing threshold is found. 
     At step  460 , a wireless controller-transmitter (not shown) delivers acoustic energy to the wireless R-S  103 , which in turn delivers electrical energy converted by the R-S  103  from the acoustic energy to the heart tissue through the cathode  106  in an injected state and necessarily the anode  110 . At the same time, an external monitor, connected at least to the R-S  103  cathode  106  via the temporary electrical connection and to an indifferent electrode, possibly the anode  110  via its temporary electrical connections or alternatively an indifferent electrode  110 C on the delivery system  102  or the indifferent electrode  110 P, monitors and quantifies the delivered electrical energy at step  462  to determine the efficiency of conversion of acoustic energy to electrical energy by the R-S  103  at the current location and position in the heart. 
     As can be understood, electromagnetic energy (e.g., RF), could also be delivered wirelessly to the receiver-stimulator and the rest of the features and functionalities of the delivery system disclosed here could be used to identify the optimal location for the implant to efficiently stimulate heart tissue. 
     In one embodiment, the delivered electrical energy is at pacing strength to stimulate the tissue and the EGM generated by the stimulation of heart tissue is monitored using the temporary electrical connections to the cathode  106  and anode  110  to determine acoustic to electrical conversion efficiency. In an alternative embodiment, the delivered electrical energy is not at pacing/stimulation strength, but instead is at a level below the stimulation threshold; hence conversion efficiency can be gauged even at lower energy levels. In such an alternative embodiment, electrical monitoring via the temporary electrical connections to the cathode  106  and an anode, possibly the anode  110  via its temporary electrical connections or alternatively an indifferent electrode  110 C on the delivery system  102  or indifferent electrode  110 P that is remote from the delivery system, indicates the level of electrical energy generated by the R-S  103 . A comparison of this level of generated electrical energy against the amount of acoustic energy transmitted to the R-S  103  indicates the conversion efficiency of the R-S  103 . 
     When a suitable implantation location is determined, at step  466  the R-S  103  is attached to the heart wall in the triggered state, and at step  468  the temporary electrical connections to the cathode  106  and anode  110  are disconnected using a disconnect mechanism as the R-S  103  goes through the sequence of released state, tethered state, tether broken state, and delivered state, as described above in  FIGS. 2E-2H . 
     While the above exemplary embodiments of the R-S  103  shown in  FIGS. 2A-2G  use a particular disconnect mechanism for the temporary electrical connection to the cathode  106 , comprising a sealed enclosure  117  around a breakable neck  119  segment of the needle assembly  115 , there are a variety of other disconnect mechanisms for the cathode  106  temporary electrical connection that are contemplated herein. We now turn to describing such further embodiments. 
       FIG. 5A  is a diagrammatic view of a sealed disconnect mechanism  108  of a wireless R-S  103 , in accordance with an embodiment of the present invention, providing a temporary electrical connection between an electrical contact at a proximal position of the R-S  103  and an electrical contact at a distal position of the catheter assembly  102 . In this embodiment, the proximal end of the wireless R-S  103  comprises a connector receptacle  203  as part of a needle assembly  115 . The proximal tip of the connector receptacle  203  represents the electrical contact at a proximal position of the R-S  103 . The needle assembly  115  is insulated from the anode  110  by an insulator  205 . The insulator  205  may comprise ceramic, glass, or other insulating material, and additionally creates a hermetic seal between the body of the R-S  103  and the connector  203 . 
     The connector receptacle  203  is at the proximal end of the needle assembly  115  and is electrically connected to the cathode  106  via the needle assembly  115 . A seal  206  covers the connector receptacle  203  and comprises a hole or slit  207  to allow the conductive wire  123  of the delivery system  102  to pass through and electrically connect to the cathode  106  (via the connection to the connector receptacle  203 ). The distal tip of the conductive wire  123  represents the electrical contact at a distal position of the catheter assembly  102 . This is shown in  FIG. 5B . The seal  206  may comprise silicone, rubber or other flexible insulating material. 
     In one embodiment, the seal  206  is compressed so that the hole or slit  207  is forced closed when the wire  123  is withdrawn, thereby isolating the connector receptacle  203  and the needle assembly  115  from patient fluid or tissue. The seal  206  need not necessarily be hermetic, but it is configured to provide high enough electrical resistance through the temporary electrical path to the connector receptacle  203  to allow substantially any electrical current to flow through the electrical path of the cathode  106  to the anode  110 . 
     Instead of a seal, a magnetically operated switch internal to the wireless R-S  103  can be used to electrically connect the wire  123  to the cathode  106 .  FIG. 5C  is a diagrammatic view of a magnetically operated disconnect mechanism, in accordance with a first such embodiment of the present invention. This embodiment comprises a magnetically operated switch  211  internal to the R-S  103 . The delivery system  102  comprises a magnet  210  at its distal tip, and a magnetic metal disk  212  is attracted to the feed-through  204  by the catheter magnet  210 . The magnet  210  on the distal end of the delivery system  102  holds the switch  211  closed when the wireless R-S  103  is attached to the delivery system  102 , bringing the magnetic metal disk  212 , which is in contact with the cathode  106 , into contact with a feed-through  204 . 
     One or more springs  213  push the disk  212  away and hold the switch  211  open when the catheter magnet  210  detaches from R-S  103  and is withdrawn, at which point the switch  211  opens and the temporary electrical connection from the cathode  106  to the feed-through  204  is disconnected.  FIG. 5C  shows the delivery system  102  removed and the switch  211  open. 
       FIG. 5D  is a diagrammatic view of a magnetically operated disconnect mechanism, in accordance with a second such embodiment of the present invention. In this embodiment, the magnetically operated switch  220  is a “reed” switch. The reed switch  220  comprises a magnet  221  on the end of the reed lever  222 . Alternately, the reed lever  222  could be made of a magnetic metal, eliminating the need for magnet  221 . The magnet  221  is attracted to the feed-through  204  by a catheter magnet  210  and closes the switch  220  when the delivery system  102  is attached to the wireless R-S  103 . The reed switch  220  springs back when the catheter magnet  210  is detached from R-S  103  and is withdrawn, thereby causing electrical disconnection. 
       FIGS. 5E-5F  are diagrammatic views of a disconnect mechanism using bellows, in accordance with an embodiment of the present invention. The disconnect mechanism comprises bellows  301  comprising an inside lead  304  on the distal end of the bellows  301  and an outside lead  305  on the proximal end of the bellows  301 . The inside lead  304  is electrically connected to the cathode  106  via the needle assembly. The outside lead  305  may comprise a proximal segment for connecting with the conductive wire  123  of the catheter via a connecting collar, similar to the embodiment described in  FIGS. 2A-2G , and a mechanism for mechanical disconnection. The proximal segment, needle assembly, and connecting collar are not shown in  FIGS. 5E-5F , but they are analogous to those described above with reference to  FIGS. 2A-2G . 
     The bellows  301  is initially configured such that the outside lead  305  is in electrical contact with the inside lead  304  at the electrical contact point  302  as shown in  FIG. 5E , thereby providing a temporary electrical connection between the conductive wire  123  of the delivery system  102  and the cathode  106 . The bellows  301  stretches when the delivery system  102  is retracted and pulled away from the wireless R-S  103 , thereby disconnecting the temporary electrical connection to the cathode  106 , as shown in  FIG. 5F . When the delivery system  102  is retracted, it also detaches the delivery system  102  from the R-S  103 . Note that while this leaves the outside lead  305  physically connected to the bellows  301  and hence to the R-S  103 , the outside lead  305  is electrically isolated from the cathode  106 . In one embodiment, the insulator  205  is hermetically connected to the enclosure of the wireless R-S  103 . 
       FIGS. 5G-5H  are diagrammatic views of a disconnect mechanism using a conductive dome structure, in accordance with an embodiment of the present invention. The disconnect mechanism comprises an inside lead  313  on the distal end of the disconnect mechanism and a conductive dome structure  310  with a feature  314  on the proximal end of the disconnect mechanism. The inside lead  313  is electrically connected to the cathode  106  via the needle assembly. The conductive dome structure  310  is housed within an insulating cup  311 . The insulating cup  311  comprises ceramic or other insulating material. The feature  314  may comprise a proximal segment for connecting with the conductive wire  123  of the catheter via a detachable connecting collar, similar to the embodiment described in  FIGS. 2A-2G . The proximal segment, needle assembly, and connecting collar are not shown in  FIGS. 5E-5F , but they are analogous to those described above with reference to  FIGS. 2A-2G . 
     The conductive dome structure  310  is initially configured such that it is in electrical contact with the inside lead  313  at the electrical contact point  312  as shown in  FIG. 5G , thereby providing an electrical path between the conductive wire  123  of the delivery system  102  and the cathode  106 . The conductive dome structure  310  pops out when the delivery system  102  is retracted and pulled away from the wireless R-S  103 , thereby disconnecting the temporary electrical connection to the cathode  106 , as shown in  FIG. 5H . When the delivery system  102  is retracted, it detaches the delivery system  102  from the R-S  103 . Note that while this leaves the conductive dome structure  310  physically connected to the R-S  103 , the conductive dome structure  310  is electrically isolated from the cathode  106 . In one embodiment, the insulating cup  311  is hermetically connected to the enclosure of the wireless R-S  103 , the inside lead  313 , and the conductive dome structure  310 , as shown in  FIG. 5H . 
     In an alternative embodiment, the disconnect mechanism comprises a fuse internal to the R-S  103 . Once a suitable implant location has been determined and the R-S  103  has been attached to the heart, the fuse is opened (blown) by delivering sufficient current through the conductive wire  123  of the delivery system  102 . The opened fuse disconnects the temporary electrical connection to the cathode  106 . Alternatively, the disconnect mechanism may comprise an electronic switch internal to the R-S  103  which when activated disconnects the temporary electrical connection to the cathode  106 . 
     Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus of the present invention disclosed herein without departing from the spirit and scope of the invention as described here.