Abstract:
Implantable electrode lead for stimulation in or on the heart, comprising a body having an insulating and sealing outer surface, at least one electrical connection between an outwardly electrically active region having a connecting unit for the electrical connection to a cardiac pacemaker, cardioverter/defibrillator or other suitable electrically active implantable device, and an active or passive fixation. To reduce the electrical resistance while, at the same time, providing for a long life, the outwardly electrically active regions are manufactured with a component of high bioresistance, biocompatibility and non-toxicity, and a component with low electrical resistance.

Description:
FIELD OF THE INVENTION 
   The invention relates to an implantable electrode lead, in particular a defibrillation electrode lead, comprising at least one electrical conductor having a proximal connection region for an electrotherapeutic implantable device as well as at least one electrically active outer surface that is connectable via the conductor to the electrotherapeutic implantable device. 
   BACKGROUND OF THE INVENTION 
   Electrode leads of the generic type are well known from the prior art. They serve as an electrical connection between an electrotherapeutic implantable device, which may be a neurostimulator, pacemaker, defibrillator or other suitable electrotherapeutic implantable device, and the location being treated in the body. These may be whole variety of locations in the body. One example given here is a cardiac electrode lead. The electrode leads not only serve to transmit therapeutic pulses, but they also serve to transmit body and measurement signals to the implant, so that an appropriate treatment can take place specifically in response to the body signals. This treatment may represent a stimulation pulse that is suitable for replacing the missing stimulus generation. The treatment may also be a high-energy defibrillation pulse. 
   In medical technology the term electrode lead is referred to in short, as “electrode”. It refers in this definition not only to the point of transition of the electric energy according to the physical definition, but it also refers to the line consisting of the electrical conductor including its enveloping insulation, as well as to all other functional elements that are permanently connected to the line. For reasons of clarity, the section of the electrode that actually functions within the physical meaning, which includes the point of transition of the electric energy, will be referred to below as “electrically active region”. 
   Measures must be taken to ensure that a long-term implantation in the body—i.e., in a highly corrosive environment—occurs without significant degradation processes and does not result in an undesirable immunological reaction. 
   For the region of the long stretched-out feed line, which must, of course, be electrically insulated toward the outside, biocompatible synthetic materials present themselves. The most important synthetic material in this context is silicone rubber. 
   For the region of the electrically active region it is important to take into consideration electrophysical effects. An electrically active region of an implantable electrode must have a low electrical resistance. This is decisive for a successful emittance of stimulation pulses, since an implantable medical device is dependent upon an independent power supply. This power supply is ensured by means of a battery, which, obviously, has a limited size. 
   To be avoided is the formation of a corrosion layer, which causes the electrical resistance to increase, with the consequence that endogenous signals can not be transmitted correctly to the implantable medical device. Also, the energy output increases as well. 
   Regarded as commonly used material with high bioresistance, but also with high electrical resistance, are cobalt-chrome alloys (e.g. MP35N). Platinum, iridium, or an alloy of these two metals are also regarded as bioresistant materials. The platinum-iridium alloys, in particular, are known for having a high electrical resistance. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to make available an implantable electrode lead that incorporates least one electrically active region for the electrical stimulation of cardiac tissue and avoids the above-mentioned shortcomings. This object is met according to the invention with the outwardly electrically active region being composed of at least one element of “Drawn Filled Tube” (DFT) having
         a component of high bioresistance, biocompatibility and non-toxicity, and   a component with low electrical resistance.       

   The inventive electrode has a long stretched-out body having a proximal and a distal end. Provided at the proximal end is a connection to an electrotherapeutic implantable device. This device may be a pacemaker, cardioverter/defibrillator or other suitable heart rhythm device. Disposed at the distal end is a fastening means for the secure fastening of the electrode to the cardiac tissue. This may be a so-called passive fixation on one hand, which is designed anchor-shaped and in this manner can interlock with the trabecules of the ventricular heart muscle. One example for an electrode of this type can be seen in U.S. Pat. No. 6,236,893 B1. On the other hand, it may be an active fixation that can be actively screwed into the cardiac tissue by means of a screwable helix-shaped screw. This screw electrode may be electrically conductive as well, and thus act as an additional electrically active region. An active fixation of this type is described, for example, in EP 0 680 771. The medial region of the electrode, which is located between the proximal and distal end, is sealed against the environment and insulated. The outer surface is coated in this case with silicone or similar synthetic material. In the distal region of this electrode, the sealed and insulated outer surface is interrupted by at least one electrically active region. These electrically active regions are additional electrodes that may, for example, permit a stimulation of the above type in the atrium of the heart. Said areas may also be designed floating, i.e., the electrically active regions are not located at the wall but “swim” along in the bloodstream. 
   All electrically active regions have at least one element made of DFT (Drawn Filled Tube) consisting of two components, namely a bioresistant, biocompatible and non-toxic component, and a component made of a material with low electrical resistance. The one component is usually designed such as to protect the other component. A bioresistant, biocompatible and non-toxic component protects another component made of a material with low electrical resistance. Preferred are platinum, iridium, or an alloy of these two materials. 
   According to the invention, the special electrophysical properties of an electrically active region are:
         Low electrical resistance and   High bioresistance to corrosion.       

   These two properties do not exist in any known material up to now. Materials with low electrical resistance usually have a low bioresistance, and vice versa. According to the invention, this problem is solved with a thin layer of bioresistant material and high electrical resistance on a core of a material with low electrical resistance. If the material with the high electrical resistance is appropriately dimensioned, the total resistance of the system of both components is altered only insignificantly. 
   In one embodiment the core with the low electrical resistance is composed of a material from the vanadium group (5 th  subgroup of the classification of elements) or copper group (1 st  subgroup of the classification of elements). The core of the DFT wire is preferably composed of tantalum (Ta), niobium (Nb) or gold (Au). 
   The invention will be explained below based on a defibrillation electrode. The electrode may also be a cardiac electrode of a different type, such as an intracardial or epicardial pacemaker electrode. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  shows a partial view of the proximal region of the electrode, 
       FIG. 1   b  shows a partial view of the distal region of the electrode, 
       FIG. 2  shows a detail view of a shock coil of a defibrillation electrode, 
       FIG. 3  shows a detail view of a shock coil of a defibrillation electrode with an electrical feed line, 
       FIG. 4  shows a partial section through the distal region of the defibrillation electrode, 
       FIG. 5  shows a section through an element of the shock coil. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1   a  shows the proximal region of a defibrillation electrode lead  1  having an electrode body  3  that is electrically insulated and sealed toward the outside, various proximal connectors  4   a ,  4   b , and  4   c  for the electrical contact with an electrotherapeutic implantable device not visible here, and a partially visible guide wire  7 , which ensures a reliable feeding of the electrode into the region of the heart being treated. The guide wire  7  is removed after the electrode has been successfully implanted. 
     FIG. 1   b  additionally shows the distal region of the defibrillation electrode lead  1  with an outwardly insulated and sealed electrode body  3  representing the electrically and therapeutically active region of the electrode. Shown are the different electrically active regions embedded in the electrode body  3 , like under  5   a  and  5   b  two independent shock coils for delivering a therapeutic high-energy pulse to the cardiac tissue, and the two measuring electrodes  6   a  and  6   b , which permit an intracardial measurement of biosignals. The measured signals permitting a targeted treatment by means of the two shock coils  5   a  and  5   b.    
   In  FIG. 1   b  the distal region of a so-called actively fixable electrode is shown. This means that the electrode must be connected to the cardiac tissue by means of an element that is actuated by the user. This is accomplished with a type of screw that is situated at the distal end. One advantage of this design is the utilization as an electrically active region. The measuring electrode  6   b  is, at the same time, the active fixation. The mechanism is shown more clearly in  FIG. 4 . It depicts the distal end of the defibrillation electrode  1  with a portion of the electrically insulated and sealed electrode body  3  and portions of the electrically active regions embedded therein, which are the shock coil  5   b  and the measuring electrodes  6   a  and  6   b . Clearly visible is the helix-shaped active fixation, which is rotatable relative to the electrode body  3  and can, therefore, be screwed into the heart. 
   In an additional embodiment of this invention a passive fixation will be described which—as can be inferred from the name—does not need to be actively attached to the cardiac tissue by the user. The passive interlocking connection is designed anchor-shaped in such a way that the electrode automatically interlocks itself with the trabecules of the cardiac tissue. 
   The proximal region ( FIG. 1   a ) and the distal region ( FIG. 1   b ) are connected to one another at the respective ends  2   a  and  2   b . Between  2   a  in  FIG. 1   a  and  2   b  in  FIG. 1   b  there may be length that is not defined in detail, which is design-related. 
     FIG. 2  is a detail view of the shock coil  4   a  or  4   b  of a defibrillation electrode  1  having a proximal end  11  and a distal end  12 . Between the two ends  11  and  12  the shock coil is wound helically. In order to attain a better flexibility and better embedding in the electrically insulating and sealing electrode body  3 , the coil is wound in such a way that a clearance  14  is provided between two windings  13   a  and  13   b . If the coil is wound transversal to the axis  15 , the clearance  14  is reduced on the inside of the winding, on the outside the clearance  14  increases. 
   In a preferred embodiment the coil is implemented as a ribbon whose dimension is longer in the axial than in the radial direction. The larger contact area of the electrically active helixes with the cardiac tissue that is obtained in this manner offers advantages in the transmission of the high-energy pulse to the cardiac tissue. 
   In another embodiment the shock coil is formed of a round wire. 
     FIG. 3  shows the above described shock coils  4   a  or  4   b  of a defibrillation electrode  1  having a proximal end  11  and a distal end  13  with an electrically conductive connection  16  extending inside the outwardly electrically insulating and sealing electrode body  12 , and an electrical connection to one of the connecting units  4   a ,  4   b  or  4   c  that are provided for the connection to an electrically active implantable device. The electrically conductive connection is permanently connected to the shock coil  10  at the proximal and distal ends  11  and  12  by means of thermal connecting methods, such as welding or soldering, in order to thus create a reliable electrical connection. The electrically conductive connection is preferably a DFT cable, as described in EP 0 927 561 B1. In additional, different embodiments it may also be a wire, a DFT wire, an electrically conductive ribbon, an electrically conductive DFT ribbon, or an electrically conductive synthetic material. 
     FIG. 4  shows a partial section through the distal region of the defibrillation electrode with an outwardly electrically insulating and sealing electrode body  3 , the electrically active regions  6   a  and  6   b  as measuring electrodes—the latter also used as active fixation in an actively fixable defibrillation electrode—and shock electrode  5   b  for delivering high-energy pulses to the cardiac tissue. The electrode body is composed of an outer synthetic-material layer  17  and an additional synthetic-material layer  18  radially inwardly adjoining the outer synthetic-material layer. 
   Additionally located in the electrode body  3  are one or multiple electrically conductive connections  16  and a lumen  19  for receiving the guide wire during implantation of the electrode in the heart. 
   The outer synthetic-material layer  17  ensures the electrical insulation and fluid seal. Additionally, the material of the layer is selected such that it reduces the friction between the vessel wall and electrode so as to permit an easy insertion of the electrode through the vessel system to the heart. The outer synthetic-material layer  17  is formed of a biostable synthetic material. This is preferably a silicone rubber. The inner synthetic-material layer mainly serves to hold the shape of the electrode and to absorb influences in the form of inwardly directed forces. This layer is also formed of a biocompatible synthetic material. This is preferably a polyurethane. Additionally, biocompatible synthetic materials on the basis of polycarbonates, epoxysilane, polysulfone, polyethylene, and polyester also present themselves for both layers  17  and  18 . 
   Also visible in  FIG. 4  is that the electrically active region  5   b —like the electrically active region  5   a  and  6   a —is embedded in the outer synthetic-material layer  17 . This ensures a friction-free implantation of the electrode. At the distal end  12  the electrically active region  5   b  is permanently connected to an electrically conductive connection  16 . 
     FIG. 5  shows a section through a winding  13   a  or  13   b  of the electrically active region  5   a  or  5   b . Visible is a DFT ribbon of an additional embodiment. It consists of an enveloping component  30  and a core component  31 . An additional embodiment of the invention is a DFT wire with a concentric design of the enveloping component  30  and core component  31 . 
   The enveloping component  30  of a material with high bioresistance and high electrical resistance is composed of platinum, iridium, or an alloy of the two materials. The core component  31  of a material with low electrical resistance but relatively low bioresistance is preferably from the vanadium group (5 th  subgroup of the classification of elements) or copper group (1 st  subgroup of the classification of elements). The core component  31  preferably consists of tantalum, niobium or gold. The thickness ratio between the enveloping component  30  and core component  31  is 1:3 to 1:40. If the electrically active region has a coil from a ribbon, then the thickness ratio between the enveloping component  30  and core component  31  is between 1:20 and 1:40 in the x-direction, and between 1:2 and 1:10 in the y-direction, particularly advantageous is a ratio in the x-direction between 1:25 and 1:30 and in the y-direction between 1:3 and 1:8. Particularly suitable, however, is a ratio in the x-direction between 1:27 and 1:29 and in the y-direction between 1:4 and 1:7. 
   The outer contour of the enveloping component  30  of the shown section through a helix  13   a  or  13   b  is designed in an advantageous manner and consists of three components:
         a base  33  essentially facing in the inwardly oriented side of the electrode body  3 ,   two opposed sides  34   a  and  34   b , facing in the direction of the distal or proximal end of the electrically active regions  5   a ,  5   b , or  6   a , and   a half-round configuration  32  consisting of the segment of a circle facing in the outwardly oriented side of the electrode body.       

   The base  33  lies on the inside outer layer  18  of the electrode body  3  and is constructed of a straight section in the x-direction. The two sides  34   a  and  34   b  are completely embedded in the outer layer  17 . They extend away in the xy-coordinate system from the base  33  with a comparatively larger y-component than x-component. The side  34   a  faces, with an identical y-component having an opposed identical x-component, toward side  34   b , away from the base  33 . The half-round configuration  32  has a radius about a virtual center point that is many times longer than half the diameter of the electrode body  3 . The summit of the half-round configuration  32  therefore projects out from the electrode body  3 . This advantageous design has advantages in the transmission of a pulse to the cardiac tissue especially at the boundary areas between the electrically active regions and the electrically insulating and sealing electrode body  3 . 
   The core component  31  in drawing  5   a  adapts to the outer contour of the enveloping component  30 , however, it has rounded edges. The radius of the roundings of the core component  31  at the edges of the enveloping component  30  increases, the sharper the angle between the sides of the outer contour of the enveloping component  30 .