FIELD OF THE INVENTION 
       [0001]    The present invention relates to a medical device for use in the vessel of a patient for the purpose of diagnosing or treating the patient, such as mapping tissue and/or ablating tissue using radio frequency (RF) or other sources of energy. More particularly, the invention relates to a deflectable catheter having a center strut bonded into the deflecting portion of the catheter tip to define an inseparable composite tip structure that maximizes the open internal volume of the catheter tip and the torsional rigidity of the catheter tip while minimizing the outside diameter of the catheter tip and providing uniform on-plane tip deflection. The invention also covers a method for making the same. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many abnormal medical conditions in humans and other mammals have been associated with disease and other aberrations along the lining or walls that define several different body spaces. In order to treat such abnormal conditions of the body spaces, medical device technologies adapted for delivering various therapies to the body spaces using the least invasive means possible. 
         [0003]    As used herein, the term “body space,” including derivatives thereof, is intended to mean any cavity within the body which is defined at least in part by a tissue wall. For example, the cardiac chambers, the uterus, the regions of the gastrointestinal tract, and the arterial or venous vessels are all considered illustrative examples of body spaces within the intended meaning. 
         [0004]    The term “vessel,” including derivatives thereof, is herein intended to mean any body space which is circumscribed along a length by a tubular tissue wall and which terminates at each of two ends in at least one opening that communicates externally of the body space. For example, the large and small intestines, the vas deferens, the trachea, and the fallopian tubes are all illustrative examples of vessels within the intended meaning. Blood vessels are also herein considered vessels, including regions of the vascular tree between their branch points. More particularly, the pulmonary veins are vessels within the intended meaning, including the region of the pulmonary veins between the branched portions of their ostia along a left ventricle wall, although the wall tissue defining the ostia typically presents uniquely tapered lumenal shapes. 
         [0005]    One means of treating body spaces in a minimally invasive manner is through the use of catheters to reach internal organs and vessels within a body space. Electrode or electrophysiology (EP) catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., the femoral artery, and then guided into the chamber of the heart that is of concern in order to perform an ablation procedure. 
         [0006]    Steerable catheters are generally well-known. For example, U.S. Pat. No. RE 34,502 describes a catheter having a control handle comprising a housing having a piston chamber at its distal end. A piston is mounted in the piston chamber and is afforded lengthwise movement. The proximal end of the catheter body is attached to the piston. A puller wire is attached to the housing and extends through the piston and through the catheter body. The distal end of the puller wire is anchored in the tip section of the catheter to the side wall of the catheter shaft. In this arrangement, lengthwise movement of the piston relative to the housing results in deflection of the catheter tip section. The design described in U.S. Pat. No. RE 34,502 is generally limited to a catheter having a single puller wire. 
         [0007]    Bidirectional steerable catheters are also generally well known, as a variety of designs have been proposed. In many such designs, such as those described in U.S. Pat. Nos. 6,066,125, 6,123,699, 6,171,277, 6,183,463 and 6,198,974, a pair of puller wires extend through a lumen in the main portion of the catheter shaft and then into opposing off axis lumens in a deflectable tip section where the distal end of each puller wire is attached to the outer wall of the deflectable tip. Pulling one wire in a proximal direction causes the tip to deflect in the direction of the off axis lumen in which that wire is disposed. 
         [0008]    In other designs, such as those described in U.S. Pat. No. 5,531,686, the puller wires are attached to opposite sides of a rectangular plate that is fixedly mounted at its proximal end and extends distally within a lumen in the tip section. In this arrangement, pulling one of the wires proximally causes the rectangular plate to bend in the direction of the side to which the pulled puller wire is attached, thereby causing the entire tip section to deflect. 
         [0009]    In all of the designs for a steerable catheter, the method of manufacturing is generally complex, time-consuming and does not necessarily result in a catheter that accurately translates the longitudinal motion of the pull wire into uniform on-plane tip deflection. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention is directed to an improved steerable catheter, more particularly a bidirectional steerable catheter. The catheter comprises an elongated, tubular catheter body having at least one lumen extending therethrough and a deflectable tubular tip section having a center strut and two half-cylindrical lumens extending therethrough. The center strut is bonded, preferably thermally, to the interior of the tubular catheter substantially along the entire length of the center strut thereby creating an inseparable tip structure. 
         [0011]    The catheter further comprises first and second puller wires having proximal and distal ends. Each puller wire extends from a control handle at the proximal end of the catheter body through a lumen in the catheter body and into one of the lumens in the tip section. The puller wires may be disposed in a tubular sleeve dimensioned so as to maintain the puller wires in close adjacent relationship. The distal ends of the puller wires are fixedly attached either to opposite sides of the center strut, to the tip electrode or the tubular structure of the distal tip section of the catheter. 
         [0012]    The control handle includes a steering assembly having a lever arm carrying a pair of pulleys for drawing corresponding puller wires to deflect the tip section of the catheter. The pulleys are rotatably mounted on opposing portions of the lever arm such that one pulley is moved distally as the other pulley is moved proximally when the lever arm is rotated. Because each puller wire is trained on a respective pulley, rotation of the lever arm causes the pulley that is moved proximally to draw its puller wire to deflect the tip section in the direction of the off-axis lumen in which that puller wire extends. 
         [0013]    Specifically, the present invention is a composite catheter tip comprising an extruded thin walled elastomeric tube spirally wrapped with a reinforcing braid wherein the elastomeric tube that has a center strut comprised of a thin elongated rectangular metallic strip where both thin longitudinal sides (edges) of the said strip are bonded, preferably thermally, to the inside wall of the elastomeric tube thereby creating a composite structure with inseparable members. The term “inseparable” is used to denote the creation of a composite structure between the elastomeric tube and the metallic strip so that any attempt to separate the elastomeric tube and metallic strip would cause irreversible destruction of the composite structure. 
         [0014]    This composite tip structure provides two enclosed, large diametrically-opposed, half moon shaped lumens extending through the tip providing space for wiring, sensors, fluid carrying tubing and the like. The strut separating the half moon shaped lumens can be constructed from any of a number of superelastic (metallic) alloys such as nitinol, beta titanium or spring tempered stainless steel. This composite catheter tip design maximizes the cross-sectional area of the open lumens in the catheter tip and torsional rigidity of the catheter tip while minimizing the outer diameter of the catheter tip by providing a single uniform area moment of inertia at any cross section of the longitudinal_axis of the catheter tip because the bonded center strut and elastomeric tube are not allowed to move with respect to each other during tip deflection. This composite structure provides uniform on-plane tip deflection and uniform torque and deflection forces regardless of the tip deflection angle because the tip cross-sectional area moment of inertia remains constant along the entire tip length during tip deflection. All known prior art tip designs exhibit varying cross-sectional area moments of inertia during tip deflection because the inner strut and outer elastomeric tube are fixed to each other only at their proximal and distal end locations and the strut and outer tube move with respect to each (other) during tip deflection. In all prior art designs, the combined centroidal axis of the independently moving strut and outer tube is continuously variable during tip curvature since the absolute distance between the centroidal axis of the whole (strut and outer tube) and the centroidal axis of each of the parts is variable. This produces non-uniform torque and deflection forces that are dependent on the degree of tip curvature. 
         [0015]    The deflection curve profile of the catheter tip can be modified by varying the area moment of inertia of the strut cross section perpendicular to the struts longitudinal axis by utilizing cutting or coining operations that either remove material or change the material thickness in various portions of the center strut cross section. The composite deflecting tip with a bonded center strut has a large width to thickness ratio thus providing a first centroidal axis that has a large area moment of inertia and a second corresponding low area moment of inertia about a centroidal axis orthogonal to the first centroidal axis thereby providing exceptional on-plane deflection characteristics. 
         [0016]    The method of the present invention results in a single unified high-performance composite structure for the deflecting tip assembly of a deflectable catheter that combines the properties of elastomers and metals and eliminates extruded core lumens. The two half-cylindrical lumens created by the bonded strut provide a large volume in which to place wiring, tip force and location sensors and tip irrigation lumens. Alternatively, an intermediate portion between the deflectable tip section and the tip electrode can be provided in which there is no center strut and which provides even greater room for temperature and location sensors. Catheter tip diameters can be reduced since the working volume of the tip lumen is maximized with this design. 
         [0017]    In a preferred embodiment of the catheter an elongate tubular member having a proximal end and a distal end and having a lumen is thermally bonded to the longitudinal edges of a center strut that extends in the deflectable portion of the catheter. This bonding creates an inseparable composite structure from the elongate tubular member and the center strut. 
         [0018]    A tip electrode is disposed at the distal end of the tubular member. A molded coupling has a distal portion adapted to receive a portion of the proximal end of the tip electrode and a proximal portion having at least one slot adapted to receive at least one of the first or second longitudinal edges of the center strut. 
         [0019]    The distal end of the center strut comprises at least one snap-fit notch and the molded coupling further comprises at least one snap-fit wedge adapted to receive the snap-fit notch. This construction enables the rapid assembly of the tip electrode and the composite tubular member and center strut. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1A-C  are a planar views of a deflectable EP catheter with rocker type deflection control handle in accordance with the present invention. 
           [0021]      FIG. 1D  is a planar view of the friction control knob located on the rocker type deflection control handle. 
           [0022]      FIG. 2  is a longitudinal cross-sectional view of the deflectable distal tip section and a portion of the proximal section of the catheter of  FIG. 1 . 
           [0023]      FIG. 3  is a cross-sectional view of the tubular section of the EP catheter of  FIG. 2  through line A-A. 
           [0024]      FIG. 4  is an exploded perspective view of the distal tip of an embodiment of a deflectable catheter in accordance with the present invention. 
           [0025]      FIG. 5  is a perspective view of a tip electrode of the deflectable tip section of a catheter in accordance with the present invention. 
           [0026]      FIG. 6  is a cross-sectional perspective view of a molded coupling of the deflectable tip section of a catheter in accordance with the present invention. 
           [0027]      FIG. 7   a  is a planar view of a puller wire for use in the deflectable tip section of a catheter in accordance with the present invention. 
           [0028]      FIG. 7   b  is a perspective view of the distal section of a deflectable catheter in accordance with the present invention. 
           [0029]      FIG. 8  is an elevational view of a center strut in accordance with a further embodiment the deflectable tip section of a catheter in accordance with the present invention. 
           [0030]      FIG. 9  is a perspective view view of the device for manufacturing the deflectable tip section of a catheter in accordance with the present invention. 
           [0031]      FIG. 10  is a perspective view of the distal tip of a deflectable catheter in accordance with the present invention. 
           [0032]      FIG. 11  is a perspective view of the distal tip of a deflectable catheter in accordance with the present invention. 
           [0033]      FIG. 12  is a perspective view of a device for manufacturing the deflectable tip section of a catheter in accordance with the present invention. 
           [0034]      FIGS. 13A-D  depict various control signals and a schematic for the control circuitry for use in the manufacture of a deflectable catheter in accordance with the present invention. 
           [0035]      FIGS. 14A-D  depict various control signals and a schematic for an alternative embodiment of the control circuitry for use in the manufacture of a deflectable catheter in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]      FIGS. 1A-C  depict a planar view of an embodiment of a deflectable catheter in accordance with the present invention. As shown in  FIG. 1B , a preferred catheter  100  comprises an elongated tubular catheter body having a proximal section  32 , a distal tip section  34  and a control handle  36  at the proximal end of the proximal section  32 . Tip electrode  38  and optional ring electrode  40  are placed at or near deflectable distal tip section  34  so as to provide a source of ablation energy if the desired device is an RF ablation catheter or for receiving electrical signals if the catheter is a diagnostic EP mapping catheter. Control handle  36  may be one of many designs capable of placing a pulling force on puller wires used to deflect the deflectable tip section  34 . Preferably, control handle  36  is the handle used in the Biosense EZ-Steer bidirectional family of products which control handle is depicted in  FIGS. 1A-C . The “rocker” type lever  37  pulls one of two puller wires to deflect the catheter tip in one direction ( FIG. 1A ) then can alternatively select the second (opposite) puller wire to deflect the catheter tip in the other direction ( FIG. 1C ). The control handle  36  also had an adjustable friction control knob  37   a  shown in  FIG. 1D  that allows the operator to use the rocker lever  37  in a free state or to adjust the tension to lock the rocker level  37  and the deflected tip in place. The amount of friction in the movement of the rocker lever  37  increases as the friction control knob  37   a  is rotated clockwise until it reaches the fully locked position. 
         [0037]      FIG. 2  depicts a cross-sectional view of the transition from proximal section  32  and deflectable section  34  of catheter  100  taken perpendicular to the center strut  80  that forms a portion of the catheter and  FIG. 3  depicts the cross-section of the catheter of  FIG. 2  through line A-A. Catheter  100  comprises an elongated tubular construction having a central lumen  58  through the distal portion  32  and two half-cylindrical lumens  58   a  and  58   b  in the deflectable tip portion  34 . The proximal section  32  is flexible but substantially non-compressible along its length. Proximal section  32  can be made of any suitable construction and made of any suitable material. The preferred construction comprises an outer wall  30  made of Pellethane or PEBAX and an optional inner wall  18 . The outer wall  30  may also comprise an imbedded braided mesh of stainless steel or similar material to increase torsional stiffness so that when control handle  36  is rotated the distal send of proximal section  32  as well as the distal section  34  will rotate in a corresponding manner. 
         [0038]    The overall length of the length of the catheter will vary according to its application for use but a preferred length is between approximately 90 and 120 cm and more preferably between approximately 100 and 110 cm. The outer diameter of the proximal section  32  is also a design characteristic that varies according to the application of the catheter but is preferably less than approximately 8 French (Fr). Optional inner wall  18  comprises a polymeric tube which may optionally be spirally-sliced and is sized so that the outer diameter is about the same size or slightly smaller than the inner diameter of outer wall  30  thereby providing additional stiffness which can be controlled by the pitch angle of the spiral slice. 
         [0039]    In the embodiment shown, the distal section  34  and the proximal section  32  are separate structures that have been fixedly attached to each other. Proximal section  32  and distal section  34  may be attached using a polyurethane adhesive at the joint  35  between the two sections. Other means of attachment include joining the proximal and distal sections using heat to fuse the sections together. 
         [0040]    In the EP catheter of the present invention, tip electrode  38  and optional ring electrodes  40  shown in  FIGS. 1A-1C  are each electrically connected to one of the bundle of lead wires  70 . Each wire in the bundle of lead wire  70  extends from the control handle  36  through the lumen  58  in the proximal section  32  and through one of lumens  58   a  or  58   b  in distal section  34  to tip electrode  38  and optional ring electrode (or electrodes)  40 . The proximal end of each lead wire  70  is connected to an appropriate connector (not shown) in the control handle  36  which can be connected to a suitable source of RF energy or to an EP mapping or other diagnostic or therapeutic system. 
         [0041]    Irrigation lumen  90  provides a conduit for transporting fluid from the proximal end of the catheter to the distal tip portion  34 . Irrigation lumen  90  is in fluid communication with one or more fluid ports in the tip electrode  38 .  FIGS. 4 and 5  depict on possible arrangement of irrigation fluid ports  439  in a tip electrode. Irrigation lumen  90  is used to transport an irrigation fluid through the catheter and out through the fluid ports in the tip in order to reduce coagulation of bodily fluids such as blood at or near the tip electrode. 
         [0042]    In a bidirectional catheter a pair of puller wires  44   a  and  44   b  extend through the through lumen  58  in the proximal section  32  and each extend through one of lumens  58   a  and  58   b  in distal section  34 . The puller wires are made of any suitable material such as stainless steel or Nitinol wire or a non-metallic yarn such as Vectran® material. Preferably, each puller wire  44  is covered with a lubricious coating such as PTFE or a similar material. Each puller wire  44  extends from the control handle  36  to near the tip of distal section  34 . 
         [0043]    A sleeve or sleeves (not shown) may be used to house the puller wires proximally to the soft tip of the catheter. The sleeve is used to keep each puller wire on its respective sides of the center strut. For bi-directional deflection the opposing puller wires will always be placed in a separate lumen. With this design placing multiple puller wires in one lumen would be used for achieving different deflection curves in one deflection direction. Such a sleeve may be made of any suitable material, e.g., polyamide or polyimide. 
         [0044]    Examples of other suitable control handles  36  that can be used with the present invention are described in U.S. Pat. Nos. 6,123,699, 6,171,277, 6,183,463 and 6,198,974 the disclosures of which are hereby incorporated by reference. In such control handles proximal movement of the thumb control relative to the handle housing results in proximal movement of the first piston and first puller wire relative to the handle housing and catheter body, which results in deflection of the tip section in the direction of the lumen into which the first puller wire extends. Distal movement of the thumb control relative to the handle housing results in distal movement of the first piston, causing proximal movement of the second piston and puller wire relative to the handle housing and catheter body, which results in deflection of the tip section in the direction of the lumen into which the second puller wire extends. Additional configurations of puller wires  44  and gearing within the control handle may be used such as those disclosed in U.S. Pat. No. 7,077,823 which is also hereby incorporated by reference. 
         [0045]    The distal section  34  is comprised of an inner layer  62 , braid layer  64  and outer layer  66  of the distal tip section described in greater detail below with respect to the method of manufacturing the catheter of the present invention discussed below with reference to  FIG. 12 . 
         [0046]    Additionally, a safety wire  95  may be used to secure the tip electrode to the catheter shaft so as to prevent detachment of the tip electrode. The safety wire is preferably a 0.0065 inch diameter monel which is routed through the lumen  58  in the proximal portion  32  of the catheter as well as through one of the two lumens  58   a  or  58   b  in the distal tip portion  34 . The distal end of the safety wire is attached to the tip electrode  38  while the proximal portion is attached to an anchor point inside the control handle  36 . 
         [0047]      FIG. 4  depicts an exploded view of the distal tip of a deflectable catheter in accordance with the present invention.  FIG. 5  is a perspective view of tip electrode  438 . Tip electrode  438  depicted in  FIGS. 4 and 5  is a machined metallic electrode comprised of a metal that is non-reactive in bodily fluid such as of gold, platinum, palladium or an alloy thereof. Tip electrode  438  may also be made of a first metal such as copper, silver, gold, aluminum, beryllium, bronze, palladium or alloys thereof which is then plated either internally and/or externally with a non-reactive metal such as gold, platinum, palladium or an alloy thereof. Tip electrode  438  may include a plurality of irrigation ports  439  connected to a central irrigation lumen  440  although such ports and lumens are optional. The proximal end of tip electrode  438  comprises a base  437  having a smaller diameter than the remainder of the tip electrode and adapted to fit coupling  442 . Base  437  may include a plurality of serrations  437   a  that improve the bonding of tip electrode  438  into coupling  442 . Base  437  of the tip electrode  438  is heat bonded or ultrasonically welded to the coupling  442 . Tip dome  438   a  may be machined to provide a rounded atraumatic distal tip in order to reduce tissue damage during placement and/or use of the catheter. Lumen  495  provides a passageway for safety wire  95  and lumen  470  provides a passageway for lead wire  70  that provide energy to the tip electrode  438 . Lead wire  70  is attached to tip electrode  438  using an electrically conductive solder or epoxy. 
         [0048]    Injection molded coupling  442  depicted in  FIGS. 4 and 6  has a distal section  443  with an internal diameter at its distal end adapted to receive the base  437  of tip electrode  438  and has a proximal section  441  with a slot  441   a  adapted to receive the distal end  480  of the center strut  80 . Coupling  442  is injection molded from a medical grade polymer such as PEEK, ABS or Polycarbonate or other appropriate material known to one skilled in the art. Distal end  480  of center strut  80  also includes a snap-fit notch  481  adapted to lock over snap-fit wedge  441 b in the coupling  442  thereby providing a mechanism for the quick assembly of the distal section of the deflectable catheter which method is described in greater detail below. Puller wire anchor holes  444   a  and  444   b  are lumens that are adapted to receive puller wires  44   a  and  44   b.  Puller wires adapted for this use are shown in  FIG. 7A . Puller wires  44   a  and  44   b  for use in this embodiment are preferably made of Vectran® wire which has had a ball of epoxy  444   c  attached to its distal end. The Vectran® wire should be cleaned with alcohol and/or an ultrasonic bath before application of a ball of epoxy that is then cured under ultraviolet light. It is important that the epoxy be well fixed to the distal end of the puller wires  44   a  and  44   b.  Alternatively, the puller wire could be high strength stainless steel (304V) to which a ball is produced at one end using a high-speed laser melting process. 
         [0049]    A single puller wire  44 , made of a non-metallic yarn such as Vectran® material, may be attached to the distal end of the catheter by threading the puller wire through one or more anchor holes  82   a - e  in center strut  80  so that the opposing ends of the puller wire,  44   a  and  44   b,  reside on opposing sides of the center strut as depicted in  FIG. 8 . Such anchor holes  82   a - e  in center strut  80  preferably have a diameter of 0.015 inch and are spaced apart by approximately 0.078 inch. Such anchor holes may be placed in the center strut  80  by laser cutting, punching and drilling. The number of holes on the strut, and the placement of the puller wires in one or more anchor holes  82   a - e  will alter the curve shape and allow for both symmetric and asymmetric curve designs. For creating a symmetric curve the opposing ends of the puller wires would exit the same anchor hole towards opposing sides of the strut. Means for changing curve shape can be controlled by the distance between anchor holes used for the opposing ends of the puller wire. When the end of each of the pull wires  44   a  and  44   b  are attached to opposing sides of the center strut  80 , pulling pull wire  44   a  or  44   b  in the proximal direction will cause the distal end of the catheter  100  to deflect in-plane in the direction of the off-axis lumen in which the respective puller wire extends. 
         [0050]    An alternate embodiment (not shown) uses two puller wires with metallic ferrules or plastic slugs to constrain the puller wires in their respective anchor hole located in the center strut. The puller wire would be threaded through the center strut on one side using the ferrule as a constraint from pulling completely through the anchor hole. An additional method for anchoring the puller wires is soldering, welding or using an adhesive to attach them to the center strut. 
         [0051]    Alternatively, the puller wires do not need to be attached to the center strut. A puller wire or puller wires could be attached to the tip dome or the distal end of the catheter&#39;s soft deflectable tip section.  FIGS. 9-11  show multiple configurations of tip electrodes  38  that are adapted to receive a single puller wire  44 . The single puller wire  44  connected to the tip electrode  38  provides bi-directional control. To achieve this, a single puller wire is threaded through the dome electrode with the opposite sides of the puller wire residing on opposite sides of the center strut. Deflection direction will correspond with the path of least resistance. Moreover, individually manipulating a puller wire will result in in-plane deflection in the direction of the off-axis lumen in which the respective puller wire extends. Such embodiment directly supports symmetric curve designs. 
         [0052]      FIGS. 10 and 11  depict hollow tip electrodes  38  that are adapted to receive a plug  45  which is force fit into the hollow dome. Puller wire  44  is threaded through the plug. One or more puller wires may be anchored in this manner. The puller wire is constrained in place once the plug is appropriately placed in the tip electrode. 
         [0053]      FIG. 7B  depicts another embodiment of the distal tip section of the catheter  100  where the puller wires are attached to the side wall of the distal tip section  34  of catheter  100 . A small hole  71  is drilled through the inner layer  62 , braid layer  64  and outer layer  66  of the distal tip section. After the hole  71  is drilled, a grinder is used to lightly reduce the outer profile around the hole by removing approximately length=0.04″ depth=0.013″ of material. A stainless steel puller wire bar  72  is attached to the distal end of the puller wire  44  via crimping to a ferrule or other means of adhesion. When the puller wire  44  is brought through the anchor window the bar rests on the outer profile of the thermoplastic soft deflectable tip section. Polyurethane is used to pot over the puller wire bar  72  thereby rebuilding the original profile of the distal tip section  34 . In this manner each puller wire may be anchored to the outer periphery of the catheter  100  at any location along the longitudinal axis of the distal tip section  34 . It is possible to anchor multiple puller wires in this manner, each on opposing sides of the center strut. Changing the location of the anchoring location changes the deflection profile of the catheter. 
         [0054]    The proximal end of the center strut  80  extends out of the proximal end of the soft deflectable tip portion. The proximal end of the center strut may be tapered so it can be readily placed within the proximal section  32  of the catheter helping to support the transition area. A sleeve preferably composed of PTFE may be placed over the tapered portion of the center strut constraining the puller wires and thereby preventing them from crossing. The sleeve is form fitting so it is tight around the center strut and wires but not so tight as to prevent the puller wires from readily moving in the longitudinal direction. 
         [0055]      FIG. 12  depicts a device for manufacturing the distal tip section of the present invention. The inner layer  62  of the distal section  34  of a catheter in accordance with the present invention is produced by extruding a thin layer of a thermoplastic elastomeric material, preferably between 0.0025-0.0035 inch in thickness, over an acetyl polymer mandrel of the appropriate diameter. The inner layer  62  is then over-braided with a synthetic fiber braid layer  64  of approximately 0.002 to 0.003 inches in diameter. In a preferred embodiment the synthetic fiber is Pen monofilament from Biogeneral Advanced Fiber Technology. Next a second coat of elastomeric material is extruded over the braided inner layer to create the outer layer  66 . The inner layer  62  and the outer layer  66  may be made from elastomers having the same shore hardness or from materials having different shore hardnesses. Preferably, the elastomer is PEBAX or Pellethane due to processability and high heat deflection temperatures. 
         [0056]    After the outer layer  66  of elastomeric material is applied, the outside of the outer layer  66  is centerless ground to the desired finished outside diameter French size. The acetyl mandrel is removed and the center strut  80  is inserted through the center of the elastomeric tube  60 . A half-moon elongated spacer made from a high temperature polymer such as PEEK, Teflon or liquid crystal polymer may be inserted into both sides of the inner diameter of the elastomeric tube  60  to stabilize and center the center strut  80  with respect to the center of the longitudinal axis of the elastomeric tube. This interim assembly is placed in the device depicted in  FIG. 12 . 
         [0057]    Clamps  103   a  and  103   b  are used to clamp both longitudinal ends of the center strut  80 . The clamps  103   a  and  103   b  of the device of  FIG. 12  are constructed from an electrically conductive material such as copper. Clamp  103   b  retracts and puts the strut under controlled tension using a pneumatic push-pull cylinder  104  or alternate automatically controlled tensioning means. The interim assembly is then nested and constrained in two fixtures  102   a  and  102   b  having half-cylindrical indentations adapted to receive the assembly. Fixtures  102   a  and  102   b  when mated together by using fixture adjustment mechanism  106   a  and  106   b  place pressure on the interim assembly in order to limit localized heat distortion in the outside tip diameter. Fixtures  102   a  and  102   b  may be constructed from high heat transfer materials such as aluminum or copper. A proportional-integral-derivative (PID) temperature feedback loop controls electrical current introduced between the clamps  103   a  and  103   b  in order to heat the center strut  80  thereby causing the inner layer  62  inner diameter to thermally bond with both thin longitudinal sides of the center strut  80  to define a composite structure with inseparable members. The strut temperature is monitored using a temperature feedback sensor  105 , preferably a non-contact, fast response time thermopile based infrared sensor that senses the strut surface temperature. 
         [0058]    One method for heating the center strut using the device shown in  FIG. 12  uses the feedback controlled power circuit depicted in  FIG. 13D . An infrared temperature sensor  510  monitors the temperature of the heated center strut  80  and provides an input voltage to a programmable logic controller (PLC)  520  analog to digital converter module. The PLC  520  controls the analog switching solid state relay  530  with a built in synchronization circuit to control low-voltage, (5-28 VAC) 50-60 hertz alternating current by varying the phase-angle to rapidly heat the center strut  80 . The proportional, integral, and derivative (PID) loop temperature feedback control by the PLC enables the strut temperature to be monitored and the PLC adjusts the phase angle accordingly to achieve the correct temperature set point. The line voltage, AC load current and control input to the analog switching solid state relay  530  can be seen in  FIGS. 13A-C  respectively. The circuit is powered by 120V AC line voltage  501  controlled by switch  502  and protected by 10 amp fuse  503  which is stepped down using transformer  505  resulting in 12-24 V AC output. 
         [0059]    An alternate method for closed loop heating of the center strut is shown in  FIGS. 14A-D . In the schematic of  FIG. 14D  for the heating power control circuitry, line voltage (120V AC)  601  controlled by switch  602  and protected by 10 amp fuse  603  is stepped down and converted into 12-24 V DC using step down transformer  604  and bridge rectifier  605 . A direct current solid state relay  630  is used to rapidly switch (on-off) 5-24 volt direct current using a time proportioning control PID loop algorithm that controls the mosfet or transistor output of the programmable logic controller  620  to the solid state relay control side. The control output pulse width and duration is dependent on the analog temperature measurement feedback from the thermopile based infrared sensor  610  to the PLC. 
         [0060]    Once heating is completed, the tension is removed from the from the strut by translating clamp  103   a  using the pneumatic push pull cylinder and the two halves of fixture  102   a  and  102   b  are retracted away from the assembly using fixture adjustment mechanisms  106   a  and  106   b.    
         [0061]    The distal tip section  34  with bonded center strut can then be affixed to the proximal section  32  as discussed above. The tip electrode  34  is affixed to the distal end of the distal tip section  34  and one of the lead wires  70  is attached to the electrode. A puller wire  44  or puller wires  44   a  and  44   b  are attached to the distal end using one of the arrangements discussed above. If the tip electrode contains fluid ports  39  then an irrigation lumen  90  is attached to the tip electrode and is routed through one of the two lumens. 
         [0062]    One additional step in the manufacturing process is the roughening of side edges of the center strut  80  to create abrasions of approximately 250-500 micro inches to improve adhesion to the inner diameter of the elastomeric tube 
         [0063]    The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
         [0064]    Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.
A catheter for diagnosing or treating the vessels found within a body or body space includes a center strut that is bonded, preferably thermally, along its longitudinal axis with the thermoplastic tubular member within which it is housed. The tubular member preferably has three layers: an inner layer, a braided layer and an outer layer. The composite catheter is made using a process in which two half-cylinder shaped mandrels are placed on each side of the center strut while the strut is heated in order to cause the thermal bonding. The bonded center strut provides in-plane deflection and improved transfer of torque to the tip of the catheter.