Abstract:
An apparatus for manufacture and method manufacturing of implantable, coiled electrodes that are integral with their associated conductor. Electrodes of differing selected sizes may be manufactured by the method described herein and mounted on a single catheter. The size of the electrodes may be selected to optimize electrode performance for sensing, stimulation or other purposes. The apparatus comprises a motor-driven winding mandrel. A tensioning device, mounted generally perpendicularly to the axis of rotation of the mandrel, controls tension in a wire being formed into a coiled electrode. A holding apparatus clamps a portion of the wire along the mandrel. In one embodiment, the holding apparatus comprises a sheath surrounding the mandrel. The mandrel fits into a hole in the sheath. By controlling the diameter of the hole with respect to the diameter of the mandrel, the radius of curvature of a bend between the coiled electrode and a straight part of the wire can be controlled. The coiled electrodes may be coated with materials such as titanium nitride, iridium oxide, or other materials to provide a fine surface structure or improved biocompatibility for the electrode.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of Invention  
           [0002]    This invention relates to catheters or to electrodes adapted to be inserted into a body cavity. More specifically, the invention involves a method for making an electrode having a controlled surface area and an integral conductor. The invention further involves assembling such manufactured electrodes on a catheter containing a large number of such electrodes.  
           [0003]    2. Background Art  
           [0004]    Cardiovascular disease is the leading cause of death in the United States, Europe and Japan, claiming more lives each year than all other diseases combined. The prevalence of this disease has prompted the development of numerous methods and devices to diagnose and treat various cardiac problems. One such device that aids in the diagnosis and treatment of heart disease is the electrode catheter. In general, various types of catheters containing electrodes have been used to perform endocardial procedures for treatment and diagnosis of cardiac related problems.  
           [0005]    Examples of these devices include the stimulation catheter of Berkovits U.S. Pat. No. 3,825,015, the flow directed catheter of Blake et. al. U.S. Pat. No. 3,995,623, the multi-contact plunge electrode of Kline U.S. Pat. No. 4,172,451, the defibrillating catheter of Schulte et al. U.S. Pat. No. 5,545,205, the implantation catheter of Obino et al. U.S. Pat. No. 5,800,498 and the pacing lead delivery catheter of Bonner U.S. Pat. No. 6,055,457.  
           [0006]    More specifically, in the diagnosis of cardiac conditions, electrode catheters have been used to map cardiac electrical activity. This mapping procedure is useful for the detection and treatment of conduction abnormalities and heart tissue deficiencies. Some cardiac mapping procedures are described in the article entitled: “Techniques of Intraoperative Electrophysiologic Mapping” in the American Journal of Cardiology, by John J. Gallagher, et al. which appeared in Volume 49 pages 221-240 January of 1982.  
           [0007]    During a typical mapping procedure, a cardiac map is generated by recording the electric signals from the heart and depicting them spatially as a function of time. In an endocardial procedure, an electrode catheter is inserted into a chamber of the heart to measure signals directly by contact with the inside walls of the chamber. Accordingly, the number and placement of electrodes on or within the catheter is an important design consideration for maximizing effectiveness and efficiency for this internal procedure.  
           [0008]    Several prior art electrode catheters have been used to generate cardiac maps. Hess U.S. Pat. No. 4,573,473 teaches a catheter with four electrode contacts on a flat planar surface. Gelinas et al. U.S. Pat. No. 4,522,212 teaches a catheter with three or more separated flexible leg electrodes. Chilson U.S. Pat. No. 4,699,147 and Edwards U.S. Pat. No. 5,471,982 define catheters with flexible electrodes that form a basket when extended. Giba et al. U.S. Pat. No. 5,997,526 discloses a shape memory catheter having electrode plates or bands. Unfortunately, such prior art devices are hard to deploy and complicated to manipulate. These difficulties often result in numerous unsuccessful treatment attempts as well as time-consuming procedures.  
           [0009]    It is known that the effectiveness of an implantable electrode is related to the surface area of the electrode. For different functions, however, the relationship between electrode size and electrode effectiveness is different. For example, stimulation thresholds (the electrical energy necessary to cause a muscular contraction in the heart) are generally lower for smaller electrodes. On the other hand, larger electrodes are usually better for sensing intrinsic electrical activity in the heart or other part of the body. Modern pacemaker leads often utilize a stimulation tip or a ring electrode for both pacing and sensing. Current lead tips are composed of solid metal, cut and shaped into a variety of geometries. In general, the surface area of the lead tip is usually approximated as a hemisphere, regardless of the actual shape of the tip. Manufacture of such electrodes can be difficult and time consuming. For example, a solid blank of metal may be machined to form a shank at one end. The opposite end may be rounded to form a hemisphere that is then bisected by a plurality of slots. The intersection of the slots may then be hollowed out. Extremely fine machining tools or electron beam machining may be necessary.  
           [0010]    The completed electrode is usually coupled to a conductor by crimping or welding two metal components together. Because of the small size of the parts, expensive laser techniques are often employed. If the metals are different, as they often are, new alloys appear at the union. There may be reduced strength, reduced fatigue resistance, or changes in electromotive force resulting in corrosion. All of these changes are unpredictable.  
           [0011]    Many of the problems of the art are addressed in U.S. patent application Ser. No. 09/761,333, the disclosure of which is incorporated herein by reference. In application Ser. No. 09/761,333, a catheter is described comprising a collection of wire leads disposed in a flexible tube. Each wire lead has a terminal end, an insulated portion and a non-insulated coiled electrode. The continuous coiled electrode preferably has at least one but no more than twenty-five turns. To prevent the coils from unraveling, the coils of each electrode may be knitted, glued or fused together, for example. Starting at the distal end of the tube, the coiled electrode of each wire lead protrudes from the tube at predetermined longitudinal positions and coils around the exterior of the tube. The ends of the collection of wire leads protrude from the proximal end of the tube and are coupled to a suitable connector for connection to an apparatus which may be used to map the cardiac tissues, to monitor the condition of the heart, or to apply appropriate therapy.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    The apparatus for manufacture and method described herein provides for the manufacture of coiled sensing and stimulation electrodes that are integral with their associated conductor. The stimulation electrodes are continuous with a conductor so that no attachment mechanism, such as a weld, is necessary to connect the conductor to the electrode. A catheter with such electrodes can be inserted into a patient&#39;s heart to stimulate the heart, map cardiac electrical activity, heart wall position, heart wall motion and tissue viability for purposes of medical diagnosis and treatment of congestive heart failure, bradycardia or tachyarrhythmias, as well as other purposes. Electrodes of differing selected sizes may be manufactured by the method described herein and mounted on a single catheter. The size of the electrodes may be selected to optimize electrode performance for sensing, stimulation or other purposes.  
           [0013]    The apparatus comprises a motor-driven winding mandrel. Reduction gears may substantially reduce the rotation speed of the mandrel. A control unit may detect the number of turns of the mandrel and can halt the apparatus at a selected number of turns. A tensioning device, mounted generally perpendicularly to the axis of rotation of the mandrel, controls tension in a wire being formed into a coiled electrode. A holding apparatus clamps a portion of the wire along the mandrel. In one embodiment, the holding apparatus comprises a sheath surrounding the mandrel and capturing the wire between the mandrel and the sheath. The mandrel fits into a hole in the sheath. By controlling the diameter of the hole with respect to the diameter of the mandrel, the radius of curvature of a bend between the coiled electrode and a straight part of the wire can be controlled.  
           [0014]    The apparatus winds individual small coils of any selected diameter and any selected number of turns. The surface area of the electrode can be readily determined and specified. Electrodes of different sizes can be placed at selected locations along a lead or catheter, allowing the electrodes to be optimized for sensing, stimulation, or other functions. The coiled electrode portions may be coated with materials such as titanium nitride, iridium oxide, or other materials. The coating may provide a fine surface structure or improved biocompatibility for the electrode.  
           [0015]    It is an object of the invention, therefore, to provide an apparatus and method for manufacturing implantable electrodes having controllable surface areas.  
           [0016]    It is a further object of the invention to provide an apparatus and method for manufacturing coiled electrodes having an integral conductor.  
           [0017]    Another object of the invention is to provide for the manufacture of coil electrodes with integral conductors having transitional bends between the electrode and the conductor or wire.  
           [0018]    Yet another object of the invention is to control the radius of curvature of the transitional bend.  
           [0019]    Still another object of the invention is to provide an apparatus that can plastically deform a wire into a coiled electrode having a specified number of turns. These and other objects and features of the invention will be apparent from the following detailed description, taken with respect of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0020]    [0020]FIG. 1 shows a catheter with multiple coil electrodes implanted in a heart.  
         [0021]    [0021]FIG. 2 shows a catheter with multiple coil electrodes.  
         [0022]    [0022]FIG. 3 shows an enlarged view of a coiled electrode on a portion of a catheter.  
         [0023]    [0023]FIG. 4 shows a cross section of the catheter of FIG. 2.  
         [0024]    [0024]FIG. 5 shows an apparatus for manufacturing coiled electrodes for the catheter of FIG. 2.  
         [0025]    [0025]FIG. 6 a portion of the apparatus of FIG. 5.  
         [0026]    [0026]FIG. 7 shows a cross section of the portion of the catheter of FIG. 3.  
         [0027]    [0027]FIG. 8 shows a flow chart depicting the steps in manufacturing the catheter using the apparatus of FIG. 5.  
         [0028]    [0028]FIG. 9 shows a flow chart depicting alternative steps in manufacturing the catheter using the apparatus of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    A multi-electrode lead or catheter  10  using coil electrodes made according to the apparatus and method of this invention is shown in FIG. 1. The catheter or lead may be implanted in the heart  12  or other body cavity of a patient. Implantation in the right atrium of the heart is illustrated, but implantation in any other chamber of the heart, blood vessel or body cavity is possible. The lead  10  includes an external biocompatible polymer tube  14  having a straight portion  16  and a shaped portion  18 . The tube may be made of polyurethane or other similar materials that may be thermally shaped so that the shaped portion  18  retains any desired configuration. In FIG. 1 the shaped portion  18  is shown as having a spiral shape, but many other shapes may be selected as well. The spiral or coil shaped lead of FIG. 1 places electrodes around the entire atrial chamber of the heart. This embodiment allows complete sensing and stimulating control around the entire chamber.  
         [0030]    It will be apparent that numerous shapes could be selected to address the clinical needs of a particular patient. Moreover, because the position of the electrodes in the heart or other body cavity is determined as much by physiology and implantation technique as by the characteristics of the lead, the effectiveness of the electrodes is best determined after implantation and is substantially independent from the location of a given electrode along the lead. For this reason, the availability of multiple redundant electrodes along a lead can be advantageous. The apparatus and method of this invention allow such electrodes to be manufactured efficiently.  
         [0031]    Attached to tube  14  of the lead  10  of any configuration, there are provided a plurality of electrodes E 1 , E 2 , E 3 , E 4 , E 5 , . . . En. The electrodes E 1  . . . En are formed of coils of exposed wire or cable wound about the tube  14 , as shown in FIG. 2 and FIG. 3. The catheter  10  includes a collection of wire leads  20  each having opposed terminal ends  22  and coiled electrodes E 1  . . . En. The collection of wire leads  20  is encased in a tube  14 . The tube  14  also has a tip member  24 . The wire leads  20  are made from an electrical conductor  26 . In the preferred embodiment, the electrical conductor is a MP35N, platinum, nitinol or stainless steel wire with a 0.003 inch (0.076 mm) diameter. The conductor may also be a cable such as a 1×7 cable made from seven 0.001 inch (0.025 mm) strands, with an overall diameter of 0.003 (0.076 mm). The wire lead has an insulated portion  28 . The insulating material in the preferred embodiment has a thickness of 0.001 inch (0.024 mm) or less. Such insulating materials may include ETFE, PEA, polyimide, parylene, or polyurethane. Generally, the length of the wire lead must be coordinated with the length of the tube  14 . The wire lead has a terminal end  22 . The terminal end  22  of each wire is attached to a connector  30  for coupling electrically to a device for sensing or stimulating the heart or other body organ.  
         [0032]    The wire  20  also has a coiled electrode En at the opposite end from the terminal end  22 . The coiled electrode En is formed of several helical spirals or coils of the conductor  26 . The diameter of each coil is sufficiently large to wrap around the exterior surface of the tube  14  of the catheter  10 . In the preferred embodiment, the coiled electrode has between one and ten coils.  
         [0033]    The wire  20  passes through a predrilled hole  32  in the tube  14 . The predrilled hole  32  determines the exact location of the electrode. By changing the position and spacing of the hole, leads may be designed to cluster more electrodes along a selected segment of the lead. Preferably the coil En and wire  20  are formed of one continuous wire, as described below. The loops of the coil En are welded  34  or otherwise connected together to provide additional structural stability. Each electrode is connected to corresponding wires which extend through the length of tube  14  and which are shown exiting through end  38  for the sake of clarity. Wires  26  are insulated by insulators  28 , so that they are not shorted to each other within the tube  14 . Further details of the electrode En are disclosed in co-pending commonly assigned application Ser. No. 09/761,333, incorporated herein by reference.  
         [0034]    The tube  14  can be formed with a longitudinal cavity  40 , as shown in the cross sectional view of FIG. 4, taken along line  4 - 4  of FIG. 2. The cavity  40  holds the wires  20 . The lead  10  can be straightened by inserting a substantially straight stylet  42  into a separate cavity  44 . The stylet  42  is also flexible but is less flexible than the lead  10  so that as it is inserted into the cavity  44 , it forces the tube  14  to straighten. The lead  10  is then inserted into the heart, blood vessel or other body cavity. After implantation of the lead  10 , the stylet  42  is withdrawn and the lead  10  flexes back and takes a predetermined configuration, for example, the configuration shown in FIG. 1.  
         [0035]    An apparatus  50  for forming coil electrodes having a well-defined surface area is illustrated in FIG. 5. The apparatus  50  comprises a drive mechanism  52  with an electric motor  54  coupled by a gear train  56  to a chuck  58 . The chuck  58  supports a cylindrical mandrel  60 . A spool  62  of wire is mounted to feed a wire  64  substantially parallel to a longitudinal axis of the mandrel  60 . The mandrel  60  is rotated about the longitudinal axis to produce the coil. To produce a coiled electrode on a wire, the wire  64  is fed through an external sheath  66  and extended along the mandrel  60 . The sheath has a through bore  68  large enough to receive both the mandrel  60  and the wire  64 . Clearly, the diameter of the bore in the mandrel is chosen with reference to the desired size of the tube  14  of the catheter  10 . The sheath  66  has a proximal end  67  that is usually mounted proximal to the spool  62  of wire. A flange  69  at the proximal end  67  of the sheath makes manipulation of the sheath easier. Preferably the resulting coil electrode, which forms near a distal end  71  of the sheath, will have an inside diameter the same size as the outside diameter of the tube. When the electrode and tube are assembled, a slight interference fit will then tend to hold the electrode in a desired place along the tube.  
         [0036]    The diameter of the bore  68  of the external sheath  66  will be slightly larger than the diameter of the mandrel  60  to accept the wire  64 . The tightness of the fit between the sheath, wire and mandrel will affect the sharpness of a bend  70  between the coil electrode and the wire lead  20 , that is, the straight portion of the wire  64  that will be inserted into the tube  14 . This bend  70  can best be seen in FIG. 3. A portion  73  of the bore may be enlarged to allow a larger bend  70  to form as the mandrel is rotated. With the wire  64  extending through the bore  68  of the sheath and along the mandrel, the sheath  66  is pushed onto the mandrel, capturing the wire  64  between the mandrel and the sheath. The wire  64  is then extended generally perpendicular to the axis of the mandrel, that is, between plus or minus 30 degrees from true perpendicular, more preferably between plus or minus 15 degrees from true perpendicular. An end  72  of the wire  64  is attached to a tensioning device  74 . The tensioning device may comprise, for example, a pulley  76  and suspended weight  78  or ball slide. Other tensioning devices, such as a spring or pneumatics, can also be used. The amount of tension is set to plastically deform the wire  64 . This tension is therefore dependent on such factors as the composition and diameter of the wire and the diameter of the mandrel.  
         [0037]    A controller  80  in electrical communication with the drive mechanism  52  controls the action of the apparatus  50 . Preferably, the controller comprises a programmable counter  82  such that a specified number of turns or partial turns may be specified. A sensor  84  detects the rotation of the electric motor or of the chuck or mandrel, so that the number of turns can be counted at the controller  80 . Alternatively, of course, displacement of the wire  64  or of the tensioning device, particularly movement of the weight  78 , could be used to control the operation of the apparatus.  
         [0038]    Responsive to the controller  80 , the electric motor  54  turns the chuck  58  and mandrel  60 . Preferably the mandrel  60  turns at slow speed, for example 1 revolution per second, for better control of the formation of the coil electrode. The gear train  56  reduces the speed to the electric motor  54  to the speed desired for the chuck. When the mandrel has been turned the selected amount, and a coil electrode formed in the wire  64 , a free end  86  of the wire  64  may be trimmed away. The sheath and wire can be removed from the mandrel. A desired length wire lead  20  can be extracted from the spool  62  and the coil electrode and wire lead can be severed from the wire. The apparatus is then ready to make another electrode and wire lead combination. The wire lead  20  slides into an insulator  28 , such as a polyimide tube or can be coated with a deposition process such as parylene. FIG. 7 depicts the installation of a wire lead  20  into a tube  14  with holes  32 . The terminal end  22  of the wire lead  20  is inserted from the exterior surface  88  through the hole  32  into the central cavity  40  away from the distal end  90  of the tube.  
         [0039]    [0039]FIG. 3 shows a coiled electrode En extending out through a hole  32  with the insulated portion  28  of the wire lead within the tube  14 . In the completed assembly of the catheter  10 , the coils of the coiled electrode En are wrapped around the exterior surface  88  of the tube  14 . The coils  98  of the coiled electrode En are knit together or otherwise connected by a cross-bar  34  to keep the coils from separating from the tube and to keep the coils wrapped tightly together. In one embodiment, the coils are knit to each other or fused with a heat source such as an eximer laser. Thus, the cross-bar  34  between the coils  98  is formed by welds or a fusing of the coils  54 . In an alternative embodiment, the coils  54  are joined with an adhesive.  
         [0040]    The steps in the assembly of the catheter are summarized in FIG. 8. The assembly process starts with extending a wire or cable along a rotatable mandrel, step  100 . The wire is secured along the mandrel, step  102 . A free end of the wire or cable is placed under tension at an angle generally perpendicular to the axis of rotation of the mandrel, step  104 . The tension is sufficient to cause plastic deformation of the wire. The mandrel is revolved, step  106 , forming a coil electrode around the mandrel. Because the rotations can be precisely selected and because the size of the wire and the size of the mandrel are known, the size and surface area of the electrode can be determined. Consequently, different sizes of electrodes may be specified for different functions on the same or different catheters. Re-tooling for production of different size electrodes is unnecessary. The electrode windings or loops may then be knit together, step  108 . This may comprise welding or adhesive or other processes. The wire and electrode are then removed from the mandrel, step  110 . After the electrode and wire are removed from the mandrel, the wire is insulated, step  112 . This may comprise inserting the wire into an insulating polyimide tube, or coating with an insulating material.  
         [0041]    At the same time, a biocompatible, flexible tube is prepared, step  114 . In a drilling step  116 , angled holes for each wire lead are drilled into the tube. In an insertion step  118 , each wire lead is entrained into the tube by inserting one terminal end  22  of a wire lead into each hole  32  and forcing the wire lead  20  down the length of the tube  14  until only the coiled electrode En extends from the hole  32 . After each wire lead  20  is separately inserted, the tip member is installed, step  120 , and then the electrode catheter is given its shape, step  122 , by heating the catheter in a jig.  
         [0042]    An alternative procedure is illustrated in FIG. 9. In this procedure, the steps  100  through  106  and  112  through  122  are as described above in connection with FIG. 8. Steps  108  and  110 , however, have been reversed and are labeled  108   a  and  110   a . In the process of FIG. 8, the electrode windings are knit together at step  108  while the coil electrode is still on the mandrel. Thereafter, the electrode and wire are removed from the mandrel, step  110 . In the process of FIG. 9, the electrode and wire are first removed from the mandrel, step  110   a . With the electrode free from the mandrel, the windings or loops can be joined as described above by welding, adhesive or other process.  
         [0043]    The exemplary apparatus and method provide for production of coiled electrodes whose surface area can be specified and varied without extensive re-tooling or re-design. Electrodes on implantable catheters can be optimized for function and multiple electrodes can be provided at low cost. The electrodes and wires communicating to devices are formed of a single integral wire or cable, eliminating stress points at the junction between electrodes and communicating wires.  
         [0044]    Those skilled in the art will recognize that changes may be made to the described embodiments of the invention without departing from the teachings thereof. The foregoing description is intended to be illustrative and not restrictive, and the scope of the invention is intended to be set forth in the following claims.