Abstract:
Apparatus for enhancing pushability and minimizing kinking of a balloon catheter is provided, wherein a catheter comprises inner and outer tubes, and a balloon that is proximally affixed to the outer tube and distally affixed to the inner tube. The outer tube extends distal to the proximal affixation point and at least partially into the balloon segment to provide additional stiffness and pushability. The outer tube may taper and connect to the inner tube or to radiopaque markers disposed thereon. The outer tube further may be selectively reinforced, as by using multipart construction or using different tube textures, to selectively provide added stiffness in areas susceptible to kinking.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of application Ser. No. 09/999,493 filed Nov. 30, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a surgical catheter, and more particularly, a balloon catheter having a reinforced distal segment to facilitate catheter pushability and minimize kinking.  
       BACKGROUND OF THE INVENTION  
       [0003]     Angioplasty and stenting are widely used techniques for treating vascular disease. In balloon angioplasty, a catheter having an inflatable balloon affixed to its distal end is guided through a patient=s vasculature with the balloon in a deflated state, and the balloon is positioned within a vascular lesion. The balloon then is inflated to compress the atherosclerotic plaque against the vessel wall to restore adequate blood flow in the vessel. Stenting involves the deployment of small tubular prostheses, either balloon expanded or self-expanding, that radially expand to maintain vessel patency, and are commonly used in conjunction with balloon angioplasty.  
         [0004]     One problem associated with the use of balloon catheters is that kinks may develop along the catheter. Because the catheter must be relatively flexible to be advanced through tortuous vasculature, a flexible catheter is prone to kink when pushed from its proximal end by the physician. This is especially so when the distal end encounters resistance from a tight stenosis. The term “pushability” describes the ability of a catheter to transmit longitudinal forces from the proximal to the distal end, without creating kinks, and this is an integral characteristic of a successful catheter design.  
         [0005]     Previously-known balloon catheters have attempted to enhance pushability primarily by reinforcing a proximal segment of the catheter. U.S. Pat. No. 5,626,600 to Horzewski et al. (Horzewski) describes a balloon dilatation catheter comprising proximal and distal extremities, an inflation lumen extending therethrough, a balloon disposed on the distal extremity that communicates with the inflation lumen, and a separate guidewire lumen. A small plug may be disposed within the guidewire lumen to separate the guidewire lumen into a proximal stiffening section and distal guidewire section. A stiffening mandrel may be inserted into the proximal stiffening section of the guidewire lumen, proximal to the plug, to influence proximal stiffness and to enhance pushability of the catheter. According to the patent, the apparatus strives to enhance catheter pushability by proving a catheter having a stiff proximal portion, a soft distal portion and a very soft low profile tip portion.  
         [0006]     One drawback associated with the catheter described in the Horzewski patent is the potential for kinks to develop at the distal end of the catheter, i.e., near the balloon. The stiff proximal section may be readily advanced, but the location where the soft distal portion joins the stiff proximal section may be particularly susceptible to kinking. This adverse event is especially likely to occur when the very soft distal section is attempted to be pushed through a tight stenosis because there is no distal reinforcement.  
         [0007]     Furthermore, the distal end of the above-described balloon catheter would be particularly susceptible to kink when used during a stenting procedure. This is because mounting a stent over the balloon increases the rigidity of the soft distal section, and the joint between the soft and rigid segments is susceptible to kink when the catheter is pushed forcefully.  
         [0008]     Other catheter designs have provided an outer tube that extends through the balloon segment to the distalmost end of the catheter. U.S. Pat. No. 5,085,636 to Burns (Burns) describes a catheter comprising an elongated flexible tube having an inflatable balloon at its distal end. There is one single lumen for both the guidewire and inflation/deflation functions, as a pair of distal valves provide a fluid tight seal around the guidewire during inflation and deflation of the balloon. The patent suggests that the elongated flexible tube that extends to the distalmost end of the catheter may be of an integral or multipart construction.  
         [0009]     The Burns patent specifically recommends manufacturing the proximal section from “hypotube” (stainless steel hypodermic needle tube), while the distal segment comprises a flexible polymer tube. Like the Horzewski device, Burns strives to increase overall pushability by providing a primarily reinforced proximal segment. However, like the device described in the Horzewski patent, the flexible distal end of the device in the Burns patent still will be susceptible to kinking, when it encounters a tight stenosis. In particular, kinking may occur at the proximal balloon connection because at this location a flexible polymer tube section is disposed between the stiff hypotube section and the relatively stiff balloon section.  
         [0010]     In view of these drawbacks of previously known balloon catheters, it would be desirable to provide apparatus that increases the push force transmitted from the outer tube to the distal end of the catheter, e.g., to facilitate pushability of the distal end through a tight stenosis.  
         [0011]     It still further would be desirable to provide apparatus having a substantially continuous stiffness transition between the outer tube of a coaxial catheter and the stent section of the catheter.  
         [0012]     It still further would be desirable to provide apparatus that minimizes the formation of kinks near the distal end of a balloon catheter.  
       SUMMARY OF THE INVENTION  
       [0013]     In view of the foregoing, it is an object of the present invention to provide apparatus that increases the push force transmitted from the outer tube to the distal end of the catheter, e.g., to facilitate pushability of the distal end through a tight stenosis.  
         [0014]     It is another object of the present invention to provide apparatus having a substantially continuous stiffness transition between the outer tube of a coaxial catheter and the balloon section of the catheter.  
         [0015]     It is another object of the present invention to provide apparatus that minimizes the formation of kinks near the distal end of a balloon catheter.  
         [0016]     These and other objects of the present invention are accomplished by providing apparatus suitable for enhancing distal pushability of a balloon catheter. The apparatus preferably comprises a catheter having an outer tube, an inner guidewire tube that extends coaxially within the outer tube, and a balloon disposed near the distal end of the catheter. The balloon is affixed at a proximal affixation point to the outer tube, and affixed at a distal affixation point to the inner tube. Unlike previously-known catheter designs, the outer tube extends at least partially through the balloon segment, i.e., distal to the proximal balloon affixation point, and the outer tube may be reinforced to increase stiffness and pushability along this segment of the catheter.  
         [0017]     In a preferred embodiment, the outer tube gradually tapers just distal to the proximal affixation point. The taper extends at least partially through the balloon segment to a smaller diameter, such that it does not substantially increase the overall distal profile of the catheter. An inflation aperture is provided in the outer tube at a location just distal to the proximal affixation point.  
         [0018]     The apparatus further preferably comprises at least one radiopaque marker affixed to the inner tube and disposed within the balloon segment. The distal end of the outer tube may be affixed to the radiopaque marker to enhance stiffness within the balloon segment and increase pushability of the catheter through a tight stenosis. Alternatively, the outer tube may taper distal to the proximal balloon affixation point and connect directly to the inner tube, such that the outer tube and inner tube become a single reinforced tube. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which:  
         [0020]      FIG. 1  is an illustration of the distal end of a previously-known coaxial catheter design;  
         [0021]      FIGS. 2A-2C  are a schematic of the distal end of a reinforced catheter in accordance with the present invention, and a helical stiffening coil having constant and varying pitches, respectively;  
         [0022]      FIGS. 3A-3C  describe an alternative embodiment of the present invention having a separate connecting tube, and means for affixing the connecting tube to the outer tube using a butt-weld and lap-weld, respectively; and  
         [0023]      FIG. 4  describes an alternative embodiment of the present invention having an outer tube that tapers to connect to the inner guidewire tube. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring to  FIG. 1 , a previously-known balloon catheter from U.S. Pat. No. 5,492,532 to Ryan et al. (Ryan) is described. Catheter  20  comprises outer tube  22 , inner tube  24 , and balloon  26  having proximal and distal ends, the proximal end of balloon  26  being affixed to outer tube  22  at proximal affixation point  27  and distally affixed to inner tube  24  at point  29 . Outer tube  22  and inner tube  24  are provided in a coaxial alignment, such that inflation lumen  23  communicates with balloon  26  while guidewire lumen  25  allows catheter  20  to be advanced over a guidewire.  
         [0025]     One drawback associated with this previously-known design is that outer tube  22  terminates at proximal affixation point  27 . Consequently, the segment distal to outer tube  22  will be susceptible to kinking when the distal end of catheter  20  is advanced into a tight stenosis. The push force provided at the proximal end of catheter  20  may not be fully transmitted to the distalmost end of catheter  20 , in part because outer tube  22  terminates at point  27 .  
         [0026]     The previously-known catheter design in  FIG. 1  further is susceptible to kinking when used in a stenting procedure. For example, if a stent is mounted on balloon  26 , it may span section S and form a relatively rigid segment along this portion of catheter  20 . Because outer tube  22  also provides a relatively rigid segment, the flexible segment K may be formed between outer tube  22  and proximal end of stent section S will be susceptible to kinking when the distal end of catheter  20  encounters a tight stenosis.  
         [0027]     Referring to  FIG. 2A , catheter  40  constructed in accordance with principles of the present invention is described. Catheter  40  comprises proximal and distal ends, of which the distal end is depicted in  FIG. 2 . The proximal end of catheter  40  communicates with a traditional proximal hub assembly (not shown) that comprises a proximal guidewire entry port and an inflation/deflation port.  
         [0028]     The distal end of catheter  40  comprises outer tube  42 , inner tube  44  and balloon  46 , each having proximal and distal ends. Inner tube  44  extends coaxially within outer tube  42  and extends beyond the distal end of balloon  46 . Inflation/deflation lumen  43  and guidewire lumen  45  communicate with the proximal inflation/deflation port and guidewire entry port, respectively. Guidewire lumen  45  of inner tube  44  is configured to permit the advancement of catheter  40  over guidewire  50 .  
         [0029]     The proximal end of balloon  46  is affixed to outer tube  42  at proximal affixation point  47 , e.g., using a solder, weld or biocompatible adhesive, while the distal end of balloon  46  is affixed to inner tube  44  at distal affixation point  53 , as shown in  FIG. 2A . The area extending between proximal and distal affixation points  47  and  53  defines balloon segment  55 . The apparatus preferably further comprises radiopaque markers  48  affixed to inner tube  44  and disposed within balloon segment  55 .  
         [0030]     In accordance with principles of the present invention, outer tube  42  extends distally beyond proximal affixation point  47  to enhance stiffness within balloon segment  55 . Outer tube  42  preferably comprises taper  49  that reduces the diameter of outer tube  42  within balloon segment  55  to reduce the overall distal profile. Alternatively, taper  49  may be omitted and tube  42  may continue at its original diameter throughout balloon segment  55 .  
         [0031]     In a preferred embodiment, outer tube  42  tapers inward just distal to proximal affixation point  47 , and the distal end of outer tube  42  is affixed to one or more radiopaque marker bands  48 , as shown in  FIG. 2A . The reduced diameter distal section of tube  42  may extend the entire length of balloon segment  55  and may be affixed to inner tube  44  and the distal end of balloon  46  at distal affixation point  53 .  
         [0032]     In the embodiment described in  FIG. 2A , outer tube  42  comprises at least one inflation aperture  52  disposed in a lateral surface at a location distal to point  47  and proximal to the most proximal radiopaque marker  48 . Inflation aperture  52  permits fluid communication between the proximal inflation/deflation port and balloon  46  via lumen  43 . In an alternative embodiment, outer tube  42  may terminate proximal to the most proximal radiopaque marker within balloon segment  55 , in which case the distalmost tip of tube  42  would communicate directly with balloon  48  via lumen  43 .  
         [0033]     The characteristics of outer tube  42  may vary along its length to influence stiffness at selected locations, particularly to provide increased stiffness along balloon segment  55 . The characteristics of outer tube  42  may be varied regionally by providing a rigid section, braided or spiral-shaped section, or by providing bores or slits at selected locations.  FIGS. 2B and 2C  illustrate embodiments wherein helical coils  65  and  67 , having constant and varying pitches, respectively, may be used to selectively enhance stiffness of outer tube  42 . Helical coils  65  and  67  may enhance stiffness of outer tube  42  proximal to or within balloon segment  55 . Optionally, outer tube  42  may be affixed to inner tube  44  at selected locations along catheter  40 , e.g., using a solder or weld, to enhance stiffness and pushability so long as inflation lumen  43  is not completely blocked.  
         [0034]     Outer tube  42  may be manufactured using a single-wall tubing, or may be provided as co-extruded tubing to allow for different surface properties inside and outside the tubing. The characteristics of catheter  40  further may be altered by manufacturing outer tube  42  using at least one material along its length, e.g., a combination of stainless steel and polymeric materials using adhesives or advanced extrusion techniques. It should be appreciated that providing different materials and/or varying the textures of outer sheath  42  at any combination of locations is intended to fall within the scope of the present invention.  
         [0035]     Referring to  FIG. 3 , an alternative embodiment of catheter  40  is described wherein the distal end of outer tube  42  communicates with a separate connecting tube  57  having proximal and distal ends. Connecting tube  57  is disposed within balloon segment  55  and preferably is affixed to at least one radiopaque marker  48 , as shown. The distal end of outer tube  42  may be affixed to the proximal end of connecting tube  57 , e.g., using biocompatible adhesive.  FIGS. 3B-3C , corresponding to inset  3  of  FIG. 3A , illustrate outer tube  42  being affixed to connecting tube  57  via butt-weld  58  and lap-weld  60 , respectively. Lap-weld  60  is preferred to butt-weld  58  because lap-weld  60  may be less susceptible to kink as push forces are transmitted from outer tube  42  to connecting tube  57 . The embodiments described in FIGS.  3  provide reinforced tube segments of differing characteristics without having to manufacture one relatively complicated piece for outer tube  42 . Furthermore, connecting tube  57  prevents kinks from developing between radiopaque markers  48 , an otherwise common location for the formation of kinks.  
         [0036]     Referring to  FIG. 4 , an alternative embodiment of catheter  40  in accordance with the present invention is described. Outer tube  42  is affixed to the proximal end of balloon  46  at proximal affixation point  47 , then tapers via taper  49  to connect to inner tube  44 . In this embodiment, outer tube  42  and inner tube  44  become a single, reinforced tube  59  when connected. As described hereinabove, the properties of outer tube  42  and reinforced tube  59  may be tailored to provide varying stiffness at selected locations along the length of catheter  40 .  
         [0037]     While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.