Abstract:
A flexible cryosurgical catheter having a deflectable segment adjacent its distal end, a pull wire through said catheter connected to the deflectable segment, and a deflection mechanism in its handle for pulling on the pull wire to establish a desired curvature in the deflectable segment.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of application Ser. No. 09/935,296, filed Aug. 21, 2001, which is currently pending. The contents of application Ser. No. 09/935,296 are incorporated herein by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention is in the field of cryosurgical catheters.  
           [0005]    2. Background Art  
           [0006]    In the treatment of various medical conditions, it is sometimes beneficial to apply an extremely cold temperature at one or more selected, isolated locations in or near a selected organ in the patient&#39;s body. As an example, it can be beneficial in the treatment of cardiac arrhythmia to apply cryosurgical temperatures at selected locations in the patient&#39;s heart, to create localized areas of necrotic tissue. Similarly, it can be beneficial to apply extremely cold temperatures at selected locations in other organs, or in a vascular system of the patient. The application of extremely cold temperatures can be achieved by inserting a flexible cryosurgical catheter through a vascular system to the desired location. The flexible catheter can have a heat transfer element at or near its distal end. The heat transfer element can be cooled to a cryosurgical temperature and placed in contact with a selected area of biological tissue.  
           [0007]    It would be desirable to facilitate the application of cold temperatures by devising an apparatus with the ability to flex the tip of the cryosurgical catheter in a desired direction, to assist in guiding the catheter through a tortuous path to the selected location in or near a selected organ, or in a vascular system.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    According to certain embodiments of the invention, a surgical device is provided for applying cold temperatures at locations within the human body, via minimally invasive techniques. More specifically, the device may comprise a deflectable catheter, passable through the larger blood vessels and cavities of the heart, having a distal tip which can be deflected by remotely located means. The apparatus has conduits for the delivery and removal of refrigerant fluids within the catheter, and conductors for the monitoring of temperature and electrical impulse. A proximally located handle has a mechanism for activating the deflection of a distal catheter tip in a single plane. In certain embodiments, a flexible multiple conduit tubular vessel attached to the handle terminates in a dual channel quick connect plug for interfacing the catheter with a cryogenic fluid supply unit.  
           [0009]    The catheter may have a torque transmitting tubular member extending from the handle to a distally located flexible tubular segment which, in turn, terminates in a high thermal conductivity tip. A deflection mechanism in the handle may manipulate the curvature of the distal flexible tubular segment of the catheter, and a braking or locking mechanism in the handle may be used to maintain a set curvature of the tip, with the tip deflection being in a predefined plane. A portion of the deflection mechanism in the handle insures that the axial tension imposed to effect deflection of the catheter tip is not transferred to the catheter shaft, thereby preventing transmission of force to the shaft. A mechanism is also incorporated into the handle to aid in the straightening of the distal tip section of the catheter, once deflection is released. A tensioning mechanism maintains a user adjustable, relatively constant tip deflection force throughout the range of motion.  
           [0010]    Another feature that may be provided in the catheter is a device for monitoring interior catheter pressure near the catheter tip region. The conduits for refrigerant fluid delivery and removal, and the conduit for pressure monitoring are separated from the deflection mechanism in the handle, thereby relieving the need to hermetically seal the handle.  
           [0011]    The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of the apparatus according to an embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a partial longitudinal section view of the apparatus shown in FIG. 1;  
         [0014]    [0014]FIG. 3 is an elevation view of the proximal end of the apparatus shown in FIG. 2;  
         [0015]    [0015]FIG. 4 is an elevation view of a portion of the apparatus shown in FIG. 2;  
         [0016]    [0016]FIG. 5 is a longitudinal section view of the portion of the apparatus shown in FIG. 4;  
         [0017]    [0017]FIGS. 6 and 7 are transverse section views of the apparatus shown in FIG. 2;  
         [0018]    [0018]FIG. 8 is an elevation view of the distal portion of the apparatus shown in FIG. 1;  
         [0019]    [0019]FIGS. 9 through 15 are transverse section views of the apparatus shown in FIG. 8;  
         [0020]    [0020]FIG. 16 is a longitudinal section view of the portion of the apparatus shown in FIG. 8;  
         [0021]    [0021]FIG. 17 is a longitudinal section view of the distal end of the portion of the apparatus shown in FIG. 16;  
         [0022]    [0022]FIG. 18 is a longitudinal section view of an intermediate part of the portion of the apparatus shown in FIG. 16;  
         [0023]    [0023]FIGS. 19 and 20 are longitudinal section views of an alternate embodiment of the distal portion of the apparatus shown in FIG. 1; and  
         [0024]    [0024]FIG. 21 is a partially exploded view of the apparatus of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    As shown in FIG. 1, the apparatus  100  includes a flexible catheter  16  attached to a handle  20 , which is attached by a flexible tube  25  to a cryogenic fluid unit (not shown). As seen in FIGS. 16, 17, and  18 , a spring wire  4  and a pull wire  5  are incorporated into the catheter  16 , to facilitate a controlled deflection of the distal portion of the catheter  16 .  
         [0026]    As shown in FIGS. 8, 16,  17 , and  18 , the distal tip  1  of the catheter  16  is a closed end hollow tube which can be machined, formed, cast or molded from a highly conductive metal, preferably copper. The copper can be gold plated to insure biocompatibility. Proximal to the catheter tip  1 , there can be a tip union  3  formed from a weldable metal, preferably stainless steel. The tip union  3  and the catheter tip  1  can be attached and hermetically sealed together by soldering or brazing. The tip union  3  can in turn be attached to a particularly flexible segment at the distal end of the catheter  16 .  
         [0027]    Within the chamber  2  of the catheter tip  1 , a plurality of electrical conductors  7   a , 7   b , 7   c , 7   d  can be attached, for the transmission of electrical signals. The electrical conductors  7   a , 7   b , 7   c , 7   d  can be seen best in FIGS. 7 and 9 through  13 . Two of the attached conductors can form a thermocouple, preferably a T type with one wire material being copper and the second being thermocouple grade constantan. A third conductor, preferably formed of nickel, can be attached to the interior of the catheter tip  1 , for monitoring of electro-physiological signals. The electrical conductors can be coated with an insulating material, such as polyimide. A capillary tube  6  can terminate, at a distal end, in the chamber  2  of the catheter tip  1 . The capillary tube  6  preferably has inner and outer diameters of 0.010 inches and 0.016 inches, respectively. The distal orifice of the capillary tube  6  can be located approximately 0.05 to 0.07 inches proximal to the distal end of the catheter tip  1 . The capillary tube  6  is the distal extension of a high-pressure refrigerant fluid line  29  which extends proximally through the catheter  16 , the handle  20 , and the flexible tubular connection  25  to the cryogenic unit. The distal portion of the capillary tube  6  and its distal orifice comprise a Joule Thomson expansion element.  
         [0028]    Welded to the interior surface of the tubular tip union  3  are two metal components, a spring wire component  4  and a pull wire component  5 , both preferably stainless steel, which are located diametrically opposed to each other. The spring wire component  4  is composed of multiple flat wires, each of which is essentially rectangular in cross section, with each rectangular wire having one cross-sectional dimension significantly greater than the cross-sectional dimension perpendicular thereto. This spring wire component  4  extends proximally from the tip union  3  through, and just proximal to, the flexible segment of the catheter  16 .  
         [0029]    The flat wires are stacked and attached to each other in the spring wire component  4  to essentially form a leaf spring. More specifically, the spring wire component  4  consists of a base flat wire with a length slightly longer than the length of the distal flexible segment of the catheter  16 . Near the proximal end of this base flat wire are stacked additional flat wires of progressively shorter lengths, with each having a proximal end terminating preferably a short distance distal to the proximal end of the base wire. In the preferred embodiment, there are at least three of these additional flat wires, with at least some of these having progressively shorter lengths than the base flat wire. All of the stacked flat wires preferably have similar rectangular cross-sectional dimensions.  
         [0030]    The distal end of the base wire of the spring wire component  4  is firmly bonded or welded to the tip union  3  distal to the flexible catheter segment, and the proximal end of the base wire is firmly bonded or welded to a shaft union  15  proximal to the flexible catheter segment. The essentially rectangular leaf spring  4  functions as a spine through the flexible segment of the catheter  16 , with the smaller cross-sectional dimension of the spine  4  defining a direction in which deflection of the flexible segment of the catheter  16  will occur. The spine  4  also resists deflection of the flexible catheter segment in a direction perpendicular to the defined direction of deflection.  
         [0031]    The second metal component attached to the tip union  3  is a pull or tendon wire component  5  which, when axially tensioned, imposes a bending moment on the flexible segment of the catheter  16 , with a resulting deflection in the direction defined by the spine component  4 . The tendon wire  5  extends proximally from the tip union  3  to a deflection mechanism in the handle  20 .  
         [0032]    Located proximally from the catheter tip  1  is a multi-lumen core tube  9 , which extends proximally, from a point approximately two catheter diameters proximal to the catheter tip  1 , through the flexible segment of the catheter  16 . The core tube  9  can be extruded from a polymer material having a balance between its structural properties and its elastomeric properties. A preferred material for the core tube extrusion  9  is Pebax. The core tube  9  may consist of a continuous segment, or several axially arranged segments of Pebax. For a continuous core tube  9 , the hardness and the elastic modulus are constant throughout its length. For the multiple segment embodiment, each segment of core tube  9  can have a hardness and an elastic modulus less than the hardness and elastic modulus of the adjacent segment, progressing proximally to distally. This results in a core tube  9  which is softer and more flexible near its distal end than near its proximal end.  
         [0033]    As shown in FIG. 14, the core tube  9  has multiple lumens, which can be geometrically shaped and positioned to give the flexible segment of the catheter  16  a mass moment of inertia lower in the defined direction of deflection than in the direction perpendicular to the direction of deflection. The preferred embodiment of the core tube  9  contains five lumens  10   a , 10   b , 10   c , 10   d , 10   e . The core tube  9  has a central lumen  10   d  for passage of the tendon wire  5 , and a rectangular lumen  10   e  positioned outwardly from the central lumen  10   d . The rectangular lumen  10   e  is for passage of the spine wire  4 . Diametrically opposite the rectangular lumen  10   e , on the other side of the central lumen  10   d , is located a half-annular shaped lumen  10   a , through which the capillary tube  6  passes. This half-annular lumen  10   a  also provides a return path for low pressure refrigerant gas. Two additional lumens  10   b , 10   c  located outwardly from the central lumen  10   d  carry the aforementioned electrical conductors  7   a , 7   b , 7   c , 7   d.    
         [0034]    Located at the distal and proximal ends of the core tube  9  are two rigid multi-lumen coupler elements  8 , 11 , preferably fabricated from a metal such as stainless steel. As shown in FIGS. 17 and 18, each coupler  8 , 11  is a multi-lumen tubular structure with an outer diameter equivalent in size to the outer diameter of the core tube  9 . The preferred embodiment of the coupler  8 , 11  is a tubular structure with at least three lumens  12   a , 12   b , 12   c , as shown in FIG. 15. These are a center circular lumen  12   c , an essentially oval lumen  12   b  located outwardly from the center lumen  12   c , and a partial annular lumen  12   a  that essentially encircles about ¾ of the circumference of the center lumen  12   c . In the catheter assembly, the center lumen  12   c  of each coupler  8 , 11 , through which the tendon wire  5  passes, axially aligns with the center lumen  10   d  of the core tube  9 . The oval lumen  12   b  of each coupler  8 , 11 , through which the spine wire  4  passes, aligns axially with the rectangular lumen  10   e  of the core tube  9 .  
         [0035]    The distal coupler  8  is encased in the tip union  3 , and the proximal coupler  11  is encased or captured in the shaft union  15 , which is also a stainless steel tube. In the preferred embodiment, the shaft union  15  is thin-walled, preferably having a wall thickness less than about 0.003 inch, and it has a length at least five times longer than the proximal coupler  11 . The proximal coupler  11  is rigidly held within the shaft union  15  by mechanical means, such as a swage or bezel, or by soldering means, brazing means, welding means, or a combination of the cited means.  
         [0036]    In another embodiment shown in FIGS. 19 and 20, instead of the core tube  9 , a tubular compression spring  62  extends proximally through the flexible segment of the catheter  16 . The tubular spring  62  is located proximally from the tip union  3  and firmly attached thereto, by being bonded, welded, soldered, or brazed. The tubular spring  62  is composed of a flat wire having a rectangular cross section, with the smaller of the rectangular dimensions directed radially from the center of the tubular shape, and with the greater of the rectangular dimensions directed substantially axially along the tubular shape. The pitch between coils of the tubular spring  62  is designed to enable bending of the tubular spring  62  perpendicular to the axis of the catheter  16 . The pitch may be fixed or variable. In the preferred embodiment, the proximal portion of the tubular spring  62  has a smaller gap between coils than the distal portion of the tubular spring  62 , causing the tubular spring  62  to be more flexible near its distal end. The tubular spring embodiment also has a multi-lumen proximal coupler  11  and a shaft union  15 .  
         [0037]    Inserted into, and rigidly fixed to, the center lumen  12   c  of the proximal coupler  11  is a sheath union  17 . The sheath union  17  is a single lumen formed metal tube. In the preferred embodiment, the sheath union  17  is firmly held to the proximal coupler  11  by mechanical means, or by being soldered, brazed or welded to the center lumen  12   c  of the proximal coupler  11 . Inserted into, and rigidly fixed to, the center lumen  12   c  of the distal coupler  8  is a distal coupler union  19 . The distal coupler union  19  is a single lumen formed metal tube with a flared distal end. In the preferred embodiment, the distal coupler union  19  is firmly held to the distal coupler  8  by mechanical means, or by being soldered, brazed, or welded to the center lumen  12   c  of the distal coupler  8 .  
         [0038]    The pull or tendon wire  5  passes from the tip union  3  through the distal coupler union  19 , then through the center lumen  10   d  of the core tube  9  or through the spring tube  62 , then into and through the sheath union  17 . The essentially rectangular spine  4  passes through the oval lumens  12   b  of the couplers  8 , 11  and into the catheter shaft union  15 . The spine  4  may be firmly attached to the shaft union  15  by welding means. The sensor wires  7   a , 7   b , 7   c , 7   d  passing through the core tube  9  or the spring tube  62  freely pass unobstructed through the partial annular lumens  12   a  of the couplers  8 , 11 . Also passing through the partial annular lumens  12   a  of the couplers  8 , 11  is the capillary tube  6  on the distal end of the high pressure fluid line  29 . The portions of the lumens  12   a , 12   b , 12   c  of the couplers  8 , 11  not taken up by wires and tubes make up the low pressure refrigerant gas return.  
         [0039]    A flexible jacket  14  covers all of the catheter elements from the shaft union  15  to the tip union  3 , encasing the core tube  9  or the spring tube  62 , and all other internal elements. The flexible jacket  14  is a tube extruded from an elastomeric polymer with a hardness and modulus of elasticity less than or equal to the material of the core tube  9 . The jacket  14  has sufficient wall thickness to maintain circularity without buckling, during the bending of the jacket  14  around a one inch radius, through a 180 degree angle. In the preferred embodiment, the jacket  14  has a length of about 5 centimeters, a diameter of about 0.130 inch and wall thickness of about 0.020 inch. The flexible tubular jacket  14  can be firmly attached to the distal portion of the outer diameter of the shaft union  15  and to the proximal portion of the outer diameter of the tip union  3 , by a combination of adhesive bonding and thermal fusion. The jacket tube  14  can also be thermally fused to the core tube  9  or the spring tube  62 . In the embodiment using the spring tube  62 , the spring tube  62  can impart additional hoop strength to the jacket tube  14 , thereby preventing buckling during bending. The adhesive bonding and thermal fusing of the jacket tube  14  to the tip union  3  and the shaft union  15  creates a hermetically sealed cavity extending from the catheter tip  1  to the shaft union  15 .  
         [0040]    Two millimeters proximal to the catheter tip  1 , a sensor band  13 , preferably formed from platinum, is swaged, fitted or bonded around the flexible jacket tube  14 . Conductively attached to the platinum sensor band  13  is a nickel wire, which is passed through the wall of the jacket tube  14 , and either into and through one of the conductor lumens  10   b , 10   c  of the core tube  9  or between the inner diameter of the jacket tube  14  and the outer diameter of the spring tube  62 , passing proximally past the shaft union  15 . The sensor band  13  and the nickel wire comprise a means for sensing ECG electrical impulses.  
         [0041]    A tightly wound wire coil sheath  18  encases the pull or tendon wire  5 . The sheath  18  terminates on its distal end within the proximal portion of the sheath union  17  and is attached thereto. The sheath  18  extends proximally through the catheter  16  into the handle  20 . The sheath  18  preferably has an outer diameter of about 0.021 inch, and is fabricated of tightly wound 0.003 inch diameter wire. During deflection of the tip, axial displacement and tensile force are imposed upon the pull or tendon wire  5 . The sheath  18  prevents axial compression of the catheter body  16 . While preventing axial compression of the catheter body  16 , the coils of the sheath  18  pack together, and the sheath  18  behaves as an incompressible body, thereby allowing efficient transmission of tensile force and axial displacement to the flexible portion of the catheter  16 , which results in the deflection of the flexible portion of the catheter  16 .  
         [0042]    Connected, bonded and thermally fused to the shaft union  15  and the flexible jacket tube  14  is the main catheter shaft  63 . The catheter shaft  63  is a tubular element with an outer diameter comparable in size to the outer diameter of the flexible jacket  14 , and with an inner diameter comparable to the outer diameter of the shaft union  15 . The catheter shaft  63  is a composite structure designed to transmit torque to the catheter tip  1  and the flexible portion of the catheter  16  during manipulation of the catheter  16 .  
         [0043]    In one embodiment, the catheter shaft  63  includes a relatively stiff thin walled inner tube of thermoplastic, such as polyimide. A stainless steel wire braid is placed over the polyimide tube, and a more flexible polymer covers the wire braid. In this embodiment, the inner polyimide tube has a thickness of about 0.0015 to about 0.002 inch, the braid is woven from 0.001 inch wire, and the outer layer is a flexible polymer such as Pebax. The flexible outer layer thickness is significantly greater than the inner polyimide tube, preferably about 0.010 to about 0.015 inch. The catheter shaft  63  terminates on its distal end at the shaft union  15  and the flexible segment of the catheter  16 . The catheter shaft  63  extends proximally through the handle  20 , terminating proximal to the handle  20 .  
         [0044]    In another embodiment, the catheter shaft  63  is comprised of a thermoplastic extrusion with an embedded stainless steel braid. The hardness and elastic properties of the extrusion, and the pitch and number of wires in the braid are chosen to give the desired torque transfer properties to the catheter shaft  63 , as is well known in the art.  
         [0045]    The sensor conductors  7   a , 7   b , 7   c , 7   d , the sheath-encased pull wire  5 , and the capillary tube  6  exit the proximal coupler  11 , enter into and pass through the catheter shaft  63 , and exit the catheter shaft  63  within the interior of the handle  20 . An additional small diameter tube, the gauge tube  22 , is contained within the catheter shaft  63  for monitoring of the return fluid pressure. The gauge tube  22  has a preferable outer diameter of about 0.029 inches and inner diameter of about 0.024 inches. The gauge tube  22  terminates on its distal end adjacent to the proximal coupler  11  and extends proximally through the catheter shaft  63 , exiting the catheter shaft  63  within the interior of the handle  20 .  
         [0046]    As shown in FIG. 7, a sheath tube  34  is employed about the sheath  18 . The sheath tube  34  has a preferable inner diameter of about 0.024 inch, thereby allowing free movement of the sheath  18  within the sheath tube  34 . During catheter usage, the pressure at the distal end of the sheath tube  34  is below atmospheric. The sheath tube  34  terminates proximally within the interior of the handle  20 , where pressure is essentially atmospheric. The length and dimensions of the sheath tube  34  are designed to provide a high resistance to fluid movement between the interior of the catheter  16  and the interior of the handle  20 . With the sheath  18  and the tendon  5  passing through the sheath tube  34 , the available space for fluid movement between the sheath tube  34  and the sheath  18 , and between the sheath  18  and the tendon  5 , is minimal. Utilization of a sheath tube  34  thusly configured allows the sheath  18  and the tendon  5  components of the deflection apparatus to exit the fluid filled interior of the catheter  16  with no subsequent leakage of fluid, thereby eliminating the need to hermetically seal the handle  20 .  
         [0047]    The high pressure capillary tube  6  extends from the catheter tip  1  to a point about 10 inches proximal to the catheter tip  1 , where it transitions into a larger high pressure tube  29 . The transition site is hermetically sealed and can withstand pressures in excess of 1000 psi, without compromise. The high pressure tube  29  then extends proximally through the catheter shaft  63  and exits the catheter shaft  63  within the interior of the handle  20 .  
         [0048]    As shown in FIG. 2, the handle  20  incorporates a means for securing the catheter shaft  63 , the articulation mechanism, an electrical connector or receptacle  31 , and a pathway for the catheter shaft  63 , the high pressure tube  29 , and the gauge tube  22  to pass through. As the catheter shaft  63  enters the handle  20 , it is firmly captured and bonded into the catheter support  33 . The catheter support  33  is a hollow tubular structure with features on its proximal end that allow for securing to slots within the handle  20 .  
         [0049]    The catheter shaft  63  enters the handle  20  on the distal end of the handle  20 , passes through the handle  20 , and exits the handle  20  through an exit port on the proximal end of the handle  20 . Four exit site holes are made in the wall of the catheter shaft  63  within the handle  20 . The exit site holes are drilled or cut preferably at an angle of about 10 to 15 degrees off the axis of the catheter shaft  63 , thereby allowing tubes within the catheter shaft lumen to exit without deformation or buckling. One exit site hole (not shown) is provided to allow the high pressure tube  29  to exit the catheter shaft  63 . Another exit site hole (not shown) is provided to allow the gauge tube  22  to exit the catheter shaft  63 . A third exit site hole  46  is provided to allow the sensor wires  7   a , 7   b , 7   c , 7   d  to exit the catheter shaft  63 . A fourth exit site hole is provided to allow the sheath tube  34 , the sheath  18  and the tendon wire  5  to exit the catheter shaft  63 .  
         [0050]    In the preferred embodiment, the high pressure tube  29  exits the catheter shaft  63  within the handle  20  at the most proximal location, extends essentially parallel to the catheter shaft  63 , and exits the handle  20  through the exit port on the proximal end of the handle  20 . A hermetic seal is placed about the juncture where the high pressure tube  29  exits the catheter shaft  63 . Just distal to the high pressure tube exit site hole, is the gauge tube exit site hole. In the preferred embodiment, the gauge tube  22  exits the catheter shaft  63  within the handle  20 , extends essentially parallel to the catheter shaft  63 , and exits the handle  20  through the exit port on the proximal end of the handle  20 . A hermetic seal is placed about the juncture where the gauge tube  22  exits the catheter shaft  63 . At a site slightly distal to the gauge tube exit site hole, the sensor wires  7   a , 7   b , 7   c , 7   d  exit the shaft  63 , pass across the handle  20  and are conductively connected, soldered, or crimped to an electrical receptacle  31 . Hermetic seals are placed about the connection of the wires to the receptacle  31  and about the wire exit site hole  46  on the shaft  63 .  
         [0051]    At a site just proximal to the point where the catheter shaft  63  enters the handle  20 , the sheath tube  34 , the sheath  18  and the tendon wire  5  exit the catheter shaft  63 . A hermetic seal is place about the sheath tube  34  exiting the catheter shaft  63 . The tightly wound coil spring which makes up the sheath  18  exits the sheath tube  34 , is looped slightly, and then transitions into a larger tightly wound coil spring, the sheath extension  35 , 36 . The loop  37  in the sheath  18  as it exits the catheter shaft  63  is a service loop which allows the sheath  18  to move independently of the catheter shaft  63 , thereby preventing the imposition of tensile or compressive forces on the catheter shaft  63 .  
         [0052]    The sheath extension  35 , 36  passes through, and is firmly bonded, welded, soldered, or brazed to an adjustment screw  44  with an attached adjustment nut  45 . The adjustment screw  44  and nut  45  are securely positioned within the handle  20 . Rotation of the adjustment nut  45  on the screw  44  moves the screw  44  and the attached sheath extension  35 , 36  distally or proximally, depending on the direction of rotation of the nut  45 . Use of the adjustment screw  44  and nut  45  allows for fine adjustment of the service loop  37  of the sheath  18 . The adjustment screw  44  also divides the sheath extension  35 , 36  into a compressive segment  35  distal to the screw  44 , and a tensile segment  36  proximal to the screw  44 . The purpose of this division will become apparent later.  
         [0053]    The sheath extension  35 , 36  and the enclosed tendon wire  5  exit the proximal side of the adjustment screw  44  and pass around a pulley  38 , to a point where they are both firmly connected, preferably swaged or crimped, to a swivel connector  39 . In this connector  39 , the proximal end of the tightly wound coil spring of the sheath extension  36  and the proximal end of the tendon wire  5  are joined together. The swivel connector  39  is fastened to a lever arm  41  and allowed to swivel about the connection point. The lever arm  41 , an axle  42 , and an activation lever  23  make up the deflection lever mechanism.  
         [0054]    Movement of the activation lever  23  in one direction rotates the axle  42 , which in turn moves the lever arm  41  to pull on the tendon wire  5  and the sheath extension  36 . Movement of the lever arm  41  in this direction imparts a proximally directed displacement to both the tendon wire  5  and the proximal portion of the sheath extension  35 . This proximal displacement is transmitted down the tendon wire  5  to the distal end of the distal flexible segment of the catheter  16 . The initial portion of the proximal displacement works to compress the tightly wound coil of the sheath  18 . The sheath  18  stiffens and prevents any further proximal displacement, and prevents compressive force from being transmitted to the catheter shaft  63 , thereby allowing all remaining displacement to be used to effect a bending of the distal bendable segment of the catheter  18 . During activation of tip deflection, the sheath  18  and the sheath extension  35  extending from the shaft union  15  in the catheter  16  to the adjustment screw  44  in the handle  20  are under compression. The sheath extension  36  extending from the proximal side of the adjustment screw  44  to the lever arm  41  is under tension.  
         [0055]    Release of the activation lever  23  will cause the portion of the sheath extension  36  which is extending from the proximal side of the adjustment screw  44  to recoil and bring the lever mechanism back to its initial position. This forces the tendon wire  5  toward the catheter tip  1 , and along with the assistance of the spine wire  4  and the elastic properties of the distal jacket tube  14 , this results in a straightening of the distal deflection segment of the catheter  16 . During activation of the deflection mechanism, the service loop  37  in the sheath  18  inside the handle  20  allows the catheter  16  to be bent without affecting tip deflection.  
         [0056]    A locking or braking mechanism is employed on the deflection lever mechanism to allow the user to set a desired level of tension in the articulation mechanism to restrain the recoil action of the sheath extension  36 , and this level of tension will then be held throughout the articulation of the tip. Also, by tightening the brake knob  24 , the tension level can even be set high enough to lock the movement of the articulation mechanism to hold deflection of the distal portion of the catheter  16  in any desired position from 0 to 270 degrees. Tightening of the brake knob  24  imparts an axial force to the tension shaft  64  by means of a metal threaded insert (not shown) that is pressed into the brake knob  24 . The two tabs of the tension shaft  64  in turn apply compression to drag washers (not shown). Reactive force generated by the drag washers forces the lever shaft  42  against the side of the handle  20 , resisting rotation of the lever shaft  42 .  
         [0057]    Extending proximally from the handle  20  is a larger flexible tube  25 , the flex line, which houses the proximal portion of the catheter shaft  63 , the high pressure fluid line  29 , and the gauge line  22 , as shown in FIGS. 2 and 6. In the preferred embodiment, the flex line  25  is a corrugated tube constructed from a polymer such as polyethylene. The distal end of the flex line  25  is connected to the handle  20 , and its proximal end is connected to a gas line connector  27 . Running essentially parallel within the flex line  25  are the high pressure fluid line  29 , the gauge line  22 , and a continuation of the catheter shaft  63 , which is the low pressure fluid line  47 . The gauge line  22  exits the flex line  25  just distal to the gas line connector  27  and terminates in a standard luer fitting  30 .  
         [0058]    As shown in FIGS. 3, 4, and  5 , the high pressure fluid line  29  and the low pressure fluid line  47  enter into and pass through the gas line connector  27 , with the low pressure line  47  terminating at the distal portion of a dual gas line fitting  28 , and with the high pressure fluid line  29  passing all the way through the dual gas line fitting  28 . The tubes of the low and high pressure fluid lines  47 , 29  are potted to the gas line connector  27  to prevent fluid leakage. Where the low pressure fluid line  47  terminates, there are orifices  51  for the passage of fluid into a mating receptacle (not shown). Just distal to these low pressure orifices  51  is a quad o-ring  49  which prevents low pressure fluid leakage when the dual gas line fitting  28  is inserted into a mating receptacle (not shown). The high pressure fluid line  29  passes through the cavity of the gas line connector  27  and through the dual gas line fitting  28 . At the proximal extremity is a check valve actuator  53  which is actually a proximal extension of the high pressure fluid line  29 . High pressure orifices  52  are provided in the proximal extension of the high pressure fluid line  29 , to allow for the passage of high pressure fluid into the high pressure fluid line  29 . A second quad o-ring  50  is located about the dual gas line fitting  28  just distal to the high pressure orifices  52 , to prevent leakage of high pressure fluid when the dual gas line fitting  28  is inserted into the mating receptacle (not shown).  
         [0059]    The dual gas line fitting  28  has a mating and locking means  48  which allows the dual gas line fitting  28  to be securely connected to the mating receptacle (not shown). The check valve actuator  53  located most proximally on the dual gas line fitting  28  acts to open a check valve in the precooler assembly (not shown) when the dual gas line fitting  28  is connected to the mating receptacle (not shown). Conversely, disconnecting the dual gas line fitting  28  from the mating receptacle (not shown) breaks contact between the check valve actuator  53  and the check valve (not shown), thus closing the check valve, minimizing gas escape from, or pressure change within, the cryo refrigerant system.  
         [0060]    While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.