Patent Publication Number: US-2007106357-A1

Title: Intravascular Electronics Carrier Electrode for a Transvascular Tissue Stimulation System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims benefit of U.S. Provisional Patent Application No. 60/734,019 filed Nov. 4, 2005. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      Not Applicable  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates implantable electronic medical devices, such as cardiac pacemakers and defibrillators for example, for stimulating tissue of animal for therapeutic purposes; and more particularly to electrode assemblies for such devices.  
      2. Description of the Related Art  
      A remedy for a patient with certain physiological ailments is to implant a stimulation device that applies an electrical pulse to an organ or part of an organ which is affiliated with the ailment. The stimulation device includes an electronic pulse generator from which electrical leads extend to electrodes in contact with parts of the organ, which when electrically stimulated provide therapy to the patient.  
      U.S. Pat. No. 6,907,285 discloses an improved apparatus, that is implanted in the blood vascular of an animal for physiological stimulation of cardiac tissue. That apparatus is formed by a transvascular platform which includes at least one intravascular electronics-electrode carrier on which is mounted a wireless radio frequency (RF) receiver and an electronic capsule containing stimulation circuitry. The stimulation circuitry receives a radio frequency signal from an extracorporeal power supply and derives an electrical voltage from the energy of that signal. The voltage is applied in the form of suitable electrical waveforms to electrodes, thereby stimulating the tissue.  
      A tubular, mesh stent is commonly used to enlarge a constricted blood vessel. The stent has a collapsed state in which its diameter is minimized to enable insertion on a catheter through the blood vessels to the region of constriction. At that location, the stent is released and enlarges diametrically so that is outer circumference expands the blood vessel. The mesh stents are formed of stainless steel, Nitinol or similar shape-memory material. Similar stents have been proposed for securing stimulation electrodes in blood vessels.  
      A challenge in designing an intravascular electronics-electrode carrier is to provide a means for reliably connecting an electrode to a carrier, such as a stent. A common technique connected the electrode by a material/mechanical transition, such as a helical spring coil or a welded joint. This type of transition provided a point of potential failure of the apparatus due to mechanical fatigue and posed a limitation on the flexibility of the electrode/carrier assembly.  
     SUMMARY OF THE INVENTION  
      In an implanted medical device for stimulation of body tissue, a material and mechanical transition between an electrical lead and an electrode carrier is avoided by incorporating the conductor of the lead into the carrier.  
      An electrode assembly, for implantation into an animal to stimulate tissue inside the animal, comprises an electrode carrier and first electrode lead. The electrode carrier of a mesh material is adapted to contact the tissue. The first electrode lead for a stimulation signal has a first conductor encased in electrical insulation. A portion of the first electrode lead is woven through the mesh of the electrode carrier and a section of the first conductor in that first portion is devoid of the first electrical insulation, thereby forming an electrode.  
      The mesh material of the electrode carrier can be electrically conductive so that the entire carrier functions as the electrode. Alternatively the mesh material may either be non-conductive or have an outer non-conductive sheath, in which cases only the exposed section of the first conductor acts as an electrode.  
      In another aspect of the invention, a second electrode lead also is woven through the mesh of the electrode carrier. The second electrode includes a second conductor with a section that is devoid of electrical insulation, thereby forming another electrode. In this version the exterior surfaces of the electrode carrier are electrically non-conductive and the exposed sections of the first and second conductors are electrically separated from each other.  
      Several arrangements of one or two electrode carriers of this type are utilized in implanted medical devices described herein for stimulating the tissue of an animal. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  depicts intracorporeal and extracorporeal components of a wireless transvascular platform for tissue stimulation;  
       FIG. 2  is a schematic diagram of a first embodiment of an intravascular electrode carrier that is an intracorporeal component of the transvascular platform;  
       FIG. 3  is an isometric view of a portion of an electrical lead for the intravascular electrode carrier;  
       FIG. 4  is a schematic diagram of a second embodiment of an intravascular electrode carrier to which a pair of electrical lead connect;  
       FIG. 5  is a schematic diagram of a third embodiment of an intravascular electrode carrier connected to a single electrical lead connect having two conductors;  
       FIG. 6  shows an electrode configuration of the medical apparatus for left atrial/ventricular pacing and sensing;  
       FIG. 7  illustrates a electrode configuration for defibrillation and left atrial and ventricular pacing and sensing; and  
       FIG. 8  is an electrode carrier configuration for atrial fibrillation treatment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      With initial reference to  FIG. 1 , a wireless transvascular platform  10  for tissue stimulation includes a medical device  12  implanted inside the body  11  of an animal and an external power supply  14 . The medical device stores energy received via radio frequency signal from the external power supply  14  and used that energy to power an electronic circuit  30  mounted on an electronic carrier  31 .  
      The external power supply  14  includes a battery  15 , a radio frequency (RF) power transmitter  16 , a power feedback module  18 , an RF communication receiver  20 , and an implant monitor  22 . In addition, an optional communication module  24  may be provided to exchange data and commands via communication link  23  with other apparatus (not shown), such as a programming computer or patient monitor. The communication link  23  may be a wireless link such as a radio frequency signal or a cellular telephone call.  
      The battery  15  is rechargeable allowing for patient mobility with periodic recharge cycles. Depending upon the type and size of the battery, the time between recharge cycles may be days, months or years. Power transmitter  16  and a first antenna  25  periodically transmit a first radio frequency signal  26  that is pulse width modulated (PWM) to convey varying amounts of energy to the medical device  12 . The medical device  12  uses that energy to charge an electrical storage device in the electronic circuit  30 . The charge of the storage device is monitored and the electronic circuit  30  sends data indicating its power needs via a second radio frequency signal  28 . The second radio frequency signal is received at the external power supply  14  by a second antenna  29  and the RF communication receiver  20 . The power feedback module  18  is part of closed loop system that receives the medical device&#39;s power needs data and responds by controlling the duty cycle of the first radio frequency signal  26  to ensure that the medical device  12  has a sufficient amount of electrical power.  
      The implant monitor  22  receives other data, such as physiological conditions of the animal, status of the medical device and trending logs, for example, that have been collected by the implanted electronic circuit  30  and sent via the second radio frequency signal  28 . This data is provided to the communication module  24  so that medical personnel can review the data or be alerted when a particular condition exists.  
      Referring still to  FIG. 1 , the implanted medical device  12  includes the electronic circuit  30  mentioned above which includes an RF transceiver and a tissue stimulation circuit, similar to that used in conventional pacemakers and defibrillators. That electronic circuit  30  is located in a large blood vessel  32 , such as the inferior vena cava (IVC), for example. One or more, electrical leads  33  and  34  extend from the electronic circuit through the animal&#39;s blood vasculature to locations in the heart  36  where pacing and sensing are desired. Each lead has an electrical conductor enclosed in an electrically insulating outer layer. The electrical leads  33  and  34  terminate at electrode assemblies  38  at those locations.  
       FIG. 2  illustrates the details of a first embodiment of the electrode assembly  38  comprising an electrode carrier  40  to which an electrode lead  33  from the electronic circuit  30  connects. A mesh-type electrode carrier  40  can be employed which is similar to stents commonly used to enlarge constricted blood vessels. That type of carrier comprises a plurality of wires formed to have a memory defining a tubular shape or envelope. Those wires may be heat-treated platinum, Nitinol, a Nitinol alloy wire, stainless steel, plastic wires or other materials. Plastic or substantially nonmetallic wires may be loaded with a radiopaque substance which provides visibility with conventional fluoroscopy. A catheter assembly is used to implant the components of the medical device  12  in the animal&#39;s circulatory system. The electrode carrier  40  has a shape memory so that it normally assumes an expanded tubular configuration when unconfined, but is capable of assuming a collapsed configuration when disposed and confined within a catheter assembly. In that collapsed state, the electrode carrier  40  has a relatively small diameter enabling it to pass freely through the vasculature of an animal. After being properly positioned in the desired blood vessel, the electrode carrier is released from the catheter assembly and expands to engage the blood vessel wall thereby becoming anchored in place.  
      The electrode lead  33  from the electronic circuit  30  extends to the electrode carrier  40  where a bare conductor  46  of the lead engages the electrode carrier. A conduction path  42  through tissue of the animal completes an electrical circuit back to the electronic circuit  30 . One form of a mesh-type electrode carrier  40  has a plurality of helical, metal strands  44  that are interwoven to form a tube. In one embodiment, the strands  44  are electrically conductive and contact the bare conductor  46  portion of the electrode lead  33  which is helically woven with the strands of the carrier. Thus, the entire electrode carrier  40  functions as the electrode. Alternatively, the strands  44  are formed of non-conductive material or are insulated by a non-conductive surface coating, in which cases only the bare conductor  46  portions of the electrode lead functions as the electrode.  
      As a further variation, the conductor  46  can be exposed only at remote tip of the electrode lead, thereby creating a focused point of electrical contact with tissue of the animal. Another variation is shown in  FIG. 3 , in which a portion of the outer insulating layer  45  facing outward from the carrier is removed from the electrode lead  33  to expose a small section of the inner electrical conductor  46 , thus forming an electrode at that region of the lead. Additional portions of the outer insulating layer  45  can be removed to form more electrodes along the lead  33 . In all those alternative, the bare conductor  46  does not have to extend the full length of the electrode carrier.  
      The materials that form the inner electrical conductor  46 , and the electrode carrier  40  must possess certain characteristics, such as fatigue resistance to flexing (especially for components to be implanted in or near the apex of heart or the ventricles) and high electrical conductivity. The components such as the outer insulating layer  45  of the electrode lead  33 , and the electrode carrier  40  must be compatible with the tissue in which they will be implanted. Those components must exhibit resistance to adverse biological reactions and to formation of insulating oxides. Examples of suitable materials include stainless steel and alloys containing silver, nickel and chromium.  
      In a second embodiment of the electrode assembly  38  shown in  FIG. 4 , a pair of electrode leads  51  and  52  extend from the stimulator electronic circuit  30  to an electrode carrier  50  that has the same structure as electrode carrier  40  previously described. However, the stands  53  of the electrode carrier  50  do not have electrically conductive surfaces, i.e. the strands either are formed of non-conductive material or have a non-conductive surface coating. Bare conductors  54  and  55  portions of the two electrode leads  51  and  52 , respectively, are interwoven into the stands of the electrode carrier  50 . The bare conductors  54  and  55  are arranged so that they do not contact each other. Alternatively, only a small section of each electrode leads  51  and  52  in the electrode carrier  50  have an exposed conductor with those portions being spaced apart longitudinally along the electrode carrier  50 . An electrical circuit is completed between the bare conductors  54  and  55  by the adjacent animal tissue, thereby providing localized stimulation or sensing.  
      With reference to  FIG. 5 , a third embodiment of the electrode assembly  38  comprises an mesh-type electrode carrier  56  that has electrically non-conducting exterior surfaces similar the electrode carrier  50 . A single electrode lead  57  extends from the stimulator electronic circuit  30  and has two electrically insulated conductors  58  and  59  encased in an insulating outer sheath. The two electrically insulated conductors  58  and  59  emerge from the outer sheath at the electrode carrier  50  and have their individual outer insulations removed from portions that are woven through the mesh of the electrode carrier  56 . The exposed portions of each conductor are electrically separated from each other.  
      The design of a medical device that provides a reliable connection of an electrode to the conductor of the lead and to the electrode carrier requires configurations that are customized to the specific application of that device in the animal&#39;s body.  FIGS. 6-8  show three exemplary configurations for such specific applications. For ease of illustration the electrodes in these figures are shown as being ring-shaped.  
       FIG. 6  shows an implanted medical device  60  using the new transvascular framework for cardiac pacing. An electronics carrier  62 , having an expandable stent-like mesh structure, is deployed in the inferior vena cava  64  and holds the RF receiving coil  68  and an electronic capsule  66  containing the electronic circuit  30 . For pacing the left atrium  70 , a first pair of positive and negative electrodes  72  are mounted on a first electrode carrier  73  placed at the proximal end of coronary sinus  74 . To pace the left ventricle  76 , a second pair of positive and negative electrodes  78  are mounted on a second electrode carrier  77  that is placed at the distal end of coronary sinus  74 . Each electrode in pairs  72  and  78  is connected to the electronic capsule  66  by a separate conductor in an electrical lead.  
      Both the positive and negative pacing electrodes are on the same electrode carrier  73  and  77  spaced approximately one centimeter apart, for example. Therefore, the carrier cannot have any conductive material bridging the two electrodes. Alternatively, separate electrode carriers could be used for each electrode.  FIG. 6  illustrates a configuration for bipolar pacing, in which a pair of ring-shaped electrodes are provided for each heart chamber, with each ring having a small (e.g. 1.0 mm) diameter. For other forms of pacing, a single ring or a curved plate may be placed adjacent the left ventricle  76  and another similar electrode near the left atrium  70 .  
       FIG. 7  depicts an intravascular electronics-electrode carrier configuration  80  for defibrillation and pacing. An electronics carrier  82 , similar to the one in  FIG. 6 , holds an electronics capsule  84  and a receiving coil  86 . A first pair of electrodes  88  are mounted on an electrode carrier  90  placed at the proximal end of coronary sinus  74 . This electrode carrier  90  is a continuous elongated wire strand that extends through the coronary sinus  74  for a distance of 10.0 cm, for example, to a distal end at a point adjacent the left ventricle  76 . The first pair of electrodes  88  at the proximate end of the carrier sense cardiac activity adjacent the left atrium  70 , and a second pair of electrodes  92  at the distal end sense cardiac activity adjacent the left ventricle  76 . During defibrillation, the entire electrode carrier  90  becomes an anode and a metallic housing of the electronics capsule  84  or the receiving coil  86  functions as a cathode. The electrode-carrier  90  in this situation is similar to coils on leads of a traditional implanted cardiac defibrillator (ICD). Alternatively the polarity of the defibrillation pulses applied to the capsule  84  and the electrode carrier  90  can be reversed, as well as being biphasic.  
       FIG. 8  illustrates an electronics-electrode carrier configuration  100  for treatment of atrial fibrillation. Here, a combined electronics-electrode carrier  102  is expanded to become embedded in the wall of the inferior vena cava  64  adjacent to the vagal nerve. The electronics-electrode carrier  102  holds an RF receiver coil  104  and an electronic capsule  106 , that is connected to two stimulation electrodes  108  extending circumferentially around the carrier in contact with the wall of the blood vessel. Electrical pulses are applied across those electrodes  108  to stimulate the vagal nerve. Electrical leads run from the electronic capsule  106  to a remote pair of electrodes  110  located in the coronary sinus  74  to sense cardiac activity at that site. While the vagal nerve is being stimulated by the stimulation electrodes  108  and activity of the left ventricle can be sensed using the remote pair of electrodes  110 . Alternatively, the vagal nerve stimulation can be performed at the site in the coronary sinus  74  or other cardiac vasculature sites.  
      It should be noted that in preferred configurations in  FIGS. 6-8 , each electrode can be formed by a single helical strand of the mesh stent that forms the respective electrode carrier with an electrical effect very similar to that of a ring-shaped electrode extending around the carrier. In this case, a remaining part of the electrode carrier is insulated. Using a carrier strand in this manner eliminates potential problems associated with welded joints at the electrode to electrode carrier interface. In another version, a plurality of contact electrodes are mounted on, but insulated from a metal carrier. Here, the circuitry in the electronic circuit is able to select different electrodes to act as the anode and cathode for stimulation. This redundancy provides improved reliability of the stimulation delivery system as it allows selection of another electrode, if poor conductivity is detected at a particular electrode. Alternatively, several combinations of positive and negative electrode pairs can be sequentially tested by the electronic circuit and the pair that provides the best response can be chosen for the stimulation. In yet another embodiment, each electrode is mounted on a separate electrode carrier. Further, each electrode may be chosen by the electronic circuit to be negative or positive with respect to the metal housing of the electronic capsule.  
      It should be further noted that one of the electrodes or the electronic capsule may be located in any other suitable vessel, such as a basilic vein for example, instead of being located at inferior vena cava.  
      The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.