Abstract:
An articulating segment for a catheter includes a tube shaped member that is formed with a helical cut around the tube&#39;s axis. The cut extends through the member, between its outer and inner surfaces, and defines a pitch angle with the axis that can be varied according to the desired flexibility of the segment. A flexible coating is positioned on the outer surface of the tube to cover the helical cut and to provide a fluid-tight condition during articulation of the segment.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention pertains generally to catheters. More particularly, the present invention pertains to articulating segments that can be used to conform a catheter to the tortuous paths and configurations that are operationally necessary for the catheter to be positioned in, or to pass through the vasculature of a patient. The present invention is particularly, but not exclusively, useful as a fluid-tight articulating segment that can effectively serve as a cryo-chamber in the operation of a cryo-catheter.  
       BACKGROUND OF THE INVENTION  
       [0002]     In general, a catheter is any hollow, flexible tube that can be inserted into a body cavity, duct or vessel for any of a variety of purposes. In each case, to be effective, the catheter must be somehow controllable so that it can be properly positioned in the body. Additionally, a catheter must have the structural capability of performing its intended purpose once it has been properly positioned. Of the many different types of medical catheters that are presently being used, the so-called cryo-catheters are of particular interest for the present invention. As is well known, these catheters are used primarily for the purpose of cryo-ablating tissue in the vasculature of a patient.  
         [0003]     Unlike other types of catheters, a cryo-catheter is unique in that it has a cooling segment. Preferably, the cooling segment of a cryo-catheter is capable of being cooled to temperatures as low as approximately eighty-five Kelvin. With this requirement in mind, several competing structural characteristics for the cooling segment of a cryo-catheter become of particular importance. For one, the cooling segment of a cryo-catheter needs to be made of a thermally conductive material. Such materials without modification, however, do not typically have the flexibility that is required for maneuvering a catheter through the vasculature of a patient. Thus, if a thermally conductive material such as stainless steel is to be used, it needs to be somehow structurally modified to achieve the required flexibility. This however, in turn, leads to a consideration of other requirements such as fluid confinement in the cooling segment, and resistance to increases in fluid pressure.  
         [0004]     Whatever modifications may be required to construct an effective cryo-catheter, it is clear the resulting structure must be sufficiently strong to confine a pressurized fluid refrigerant in the cooling segment. With this in mind, appreciate that a cryo-catheter is essentially nothing more than a tube. Thus, to accomplish certain of the requirements mentioned above, it must have good “hoop strength” for confining the pressurized fluid. Further, because pressurized fluids are involved, the structure of the cooling segment must also be fluid-tight to prevent any leakage of the fluid refrigerant. At the same time, the cryo-catheter must remain sufficiently flexible so it can be maneuvered while being advanced through the vasculature of a patient. Finally, it must also be sufficiently strong to resist kinking.  
         [0005]     In light of the above, it is an object of the present invention to provide an articulating segment for a cryo-catheter that is made with a thermally conductive material which is structurally modified to provide the required flexibility for use in an invasive catheter. Another object of the present invention is to provide an articulating segment for a cryo-catheter which is thermally conductive, is flexible and is sufficiently strong to contain a pressurized refrigerant fluid. Still another object of the present invention is to provide an articulating segment for a cryo-catheter which is relatively simple to manufacture, is easy to use and is comparatively cost effective.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with the present invention, an articulating segment for use in the cooling chamber of a cryo-catheter includes a tube shaped member that has an outer surface and an inner surface. The tube shaped member defines an axis and it is formed with a helical cut that goes around the axis. Specifically, the cut extends through the wall of the tube shaped member between its outer surface and its inner surface. In addition to this tube shaped member, the articulating segment includes a flexible coating that is positioned on the outer surface of the tube shaped member. This flexible coating covers the helical cut and provides a fluid-tight condition for the lumen that is created in the articulating segment of the tube shaped member.  
         [0007]     Structurally, the helical cut in the articulating segment defines a pitch angle (α) that is measured between the cut and the axis of the tube shaped member. Preferably, this pitch angle (α) is in a range between forty-five and ninety degrees. Within this range, the pitch angle (α) can be varied during manufacture to achieve a predetermined flexibility for the segment. More specifically, an increase in the pitch angle (α) will provide increased flexibility for the segment. As a practical matter, this flexibility can be increased to a point where the predetermined flexibility for the articulating segment allows the tube shaped member to be bent with a radius of curvature of approximately fifteen mm.  
         [0008]     In line with the description given above, the articulating segment can be thought of as being formed by a flat, narrow, ribbon-like band that is wound into a spiral. Importantly, for enhanced strength, this band has a substantially rectangular-shaped cross-section that is bounded by the upper and lower surfaces, and by opposed first and second edges. In this structure, the helical cut is formed as a gap between the first and second edges of the band. For disclosure purposes, this gap has a depth between the outer and inner surfaces that is in a range of 0.1 mm to 0.2 mm, and it has a width substantially perpendicular to the depth that is formed in a range of 10 microns and 100 microns. As a practical matter, however, unless the articulating segment is being bent, the edges of the band will generally be in contact with each other and, consequently, there will be no effective gap width.  
         [0009]     Preferably, the tube shaped member is made of stainless steel or Nitinol and the flexible coating is made of nylon or of a polymer material.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:  
         [0011]      FIG. 1  is a perspective view of the distal extension of a cryo-catheter that includes an articulating segment in accordance with the present invention, wherein portions are removed for clarity; and  
         [0012]      FIG. 2  is an enlarged cross-sectional view of the articulating segment of the present invention as seen along the line  2 - 2  in  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring initially to  FIG. 1 , the distal extension of a cryo-catheter is shown and generally designated  10 . In this extension, the cryo-catheter  10  includes a shaft  12  and it has a distal segment  14 . As indicated, the shaft  12  of catheter  10  generally defines an axis  16  that extends along the length of the catheter  10 . For the specific case wherein the catheter  10  is a cryo-catheter, a cryo-tip  18  will be located at the extreme distal end of the catheter  10 . This cryo-tip  18  will then establish a cooling chamber for the cryo-catheter  10  that extends proximally from the cryo-tip  18  back through a predetermined distance along the shaft  12 . Insofar as the present invention is concerned, it is to be appreciated that the description of the catheter  10  as being a cryo-catheter is merely exemplary. Specifically, the present invention pertains to other type catheters as well.  
         [0014]     Still referring to  FIG. 1  it will be seen that, structurally, the shaft  12  and the distal segment  14  of cryo-catheter  10  include a tube shaped member  20  which is covered by a flexible coating  22 . Preferably, the tube shaped member  20  is a so-called hypotube that is made of a highly thermally conductive material such as stainless steel or Nitinol. On the other hand, the flexible coating  22  is preferably made from a material such as Pebax or nylon. Although it is preferred that the flexible coating  22  be somewhat thermally conductive, it is perhaps more important that the flexible coating  22  have the lubricity and bio-compatibility properties which are required for medical catheters. Further, the flexible coating  22  should be made of a material that can be securely positioned on the tube shaped member  20 . A more detailed structural description of the distal segment  14  is possible with reference to  FIG. 2 .  
         [0015]     With reference to  FIG. 2  it can be appreciated that the tube shaped member  20  is formed with a gap  24  which is helically shaped, and which is centered on the axis  16 . Specifically, the gap  24  is created by a helical cut that extends between the outer surface  26  and the inner surface  28  of the tube shaped member  20 . From a different aspect, the creation of gap  24 , in turn, creates a substantially flat, narrow, ribbon-like band which is configured into a spiral to form the tube shaped member  20 . Importantly, this band has a substantially rectangular cross-section that is bounded by the outer surface  26 , the inner surface  28  and opposed edges  30  and  32 .  
         [0016]     Several operational benefits result from the rectangular shaped cross-section of the tube shaped member  20  in distal segment  14 . For one, this configuration effectively maximizes the amount of material that is available to resist “hoop stress” in the distal segment  14 . Thus, the tube shaped member  20  is able to contain higher fluid pressures inside the lumen  34  of tube shaped member  20  than might otherwise be possible. Further, the surface area  36  of flexible coating  22  in gap  24  that may be directly exposed to fluid pressures in lumen  34  is minimized.  
         [0017]     As is also to be appreciated with reference to  FIG. 2 , the gap  24  can be geometrically varied during manufacture to obtain a predetermined flexibility for distal segment  14 . Along with considerations of other dimensions of the tube shaped member  20  (e.g. its diameter), a pitch angle (α) can be established for the helical cut of gap  24  that will directly affect flexibility. Specifically, for a tube shaped member  20  having a given diameter, flexibility of the distal segment  14  can be increased or decreased by, respectively, using a larger or smaller pitch angle (α). Preferably, the pitch angle (α) will be selected in a range between approximately forty-five and ninety degrees.  
         [0018]     Still referring to  FIG. 2  it will be seen that the gap  24  is characterized as having a width  38  and a depth  40 . In particular, the width  38  of the gap  24  will be determined by the amount of material that is removed during the manufacture of the distal segment  14 . On the other hand, the depth  40  of gap  24  will depend on the thickness of the tube shaped member  20  that is selected for use in the manufacture of the distal segment  14 . As intended for the present invention, the helical cut for gap  24  will be made by a laser beam using well known technology. Accordingly, the width  38  of gap  24  will preferably be manufactured to be in a range between approximately 10 microns and approximately 100 microns. The depth  40  of gap  24 , however, will generally be in a range between approximately 0.1 mm and 0.2 mm. In any event, it is envisioned that the cross-section will be rectangular.  
         [0019]     As disclosed above, a flexible coating  22  is positioned on the outer surface  26  of the tube shaped member  20  to cover the outer surface  26  and the gap  24 . This then effectively provides a fluid-tight condition for the lumen  34 . Additionally, as indicated above, the flexible coating  22  provides a degree of lubricity that will assist in the advancement of the catheter  10  into the vasculature of a patient.  
         [0020]     In operation, the distal segment  14  of catheter  10  needs to be articulated for several reasons. These reasons include, steerability for the catheter  10  as it is being advanced to position the distal segment  14  at a site in the vasculature of a patient. Also, if the catheter  10  is a cryo-catheter, the distal segment  14  must be able to confine pressurized fluid refrigerants and be configurable to conform with tissue that is to be cryo-ablated. As envisioned for the present invention, these objectives are met by the ability of the structure for distal segment  14  to be bent on a curve of radius “R” as shown in  FIG. 1 . For the purposes of the present invention, the radius of curvature “R”, as measured from a center of curvature at point  42 , may be as short as fifteen mm.  
         [0021]     While the particular Articulation Segment for a Catheter as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.