Catheter having enhanced distal pushability

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.

FIELD OF THE INVENTION

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

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.

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.

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.”

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a previously-known balloon catheter from U.S. Pat. No. 5,492,532 to Ryan et al. (Ryan) is described. Catheter20comprises outer tube22, inner tube24, and balloon26having proximal and distal ends, the proximal end of balloon26being affixed to outer tube22at proximal affixation point27and distally affixed to inner tube24at point29. Outer tube22and inner tube24are provided in a coaxial alignment, such that inflation lumen23communicates with balloon26while guidewire lumen25allows catheter20to be advanced over a guidewire.

One drawback associated with this previously-known design is that outer tube22terminates at proximal affixation point27. Consequently, the segment distal to outer tube22will be susceptible to kinking when the distal end of catheter20is advanced into a tight stenosis. The push force provided at the proximal end of catheter20may not be fully transmitted to the distalmost end of catheter20, in part because outer tube22terminates at point27.

The previously-known catheter design inFIG. 1further is susceptible to kinking when used in a stenting procedure. For example, if a stent is mounted on balloon26, it may span section ‘S’ and form a relatively rigid segment along this portion of catheter20. Because outer tube22also provides a relatively rigid segment, the flexible segment ‘K’ may be formed between outer tube22and proximal end of stent section ‘S’ will be susceptible to kinking when the distal end of catheter20encounters a tight stenosis.

Referring toFIG. 2A, catheter40constructed in accordance with principles of the present invention is described. Catheter40comprises proximal and distal ends, of which the distal end is depicted inFIG. 2. The proximal end of catheter40communicates with a traditional proximal hub assembly (not shown) that comprises a proximal guidewire entry port and an inflation/deflation port.

The distal end of catheter40comprises outer tube42, inner tube44and balloon46, each having proximal and distal ends. Inner tube44extends coaxially within outer tube42and extends beyond the distal end of balloon46. Inflation/deflation lumen43and guidewire lumen45communicate with the proximal inflation/deflation port and guidewire entry port, respectively. Guidewire lumen45of inner tube44is configured to permit the advancement of catheter40over guidewire50.

The proximal end of balloon46is affixed to outer tube42at proximal affixation point47, e.g., using a solder, weld or biocompatible adhesive, while the distal end of balloon46is affixed to inner tube44at distal affixation point53, as shown inFIG. 2A. The area extending between proximal and distal affixation points47and53defines balloon segment55. The apparatus preferably further comprises radiopaque markers48affixed to inner tube44and disposed within balloon segment55.

In accordance with principles of the present invention, outer tube42extends distally beyond proximal affixation point47to enhance stiffness within balloon segment55. Outer tube42preferably comprises taper49that reduces the diameter of outer tube42within balloon segment55to reduce the overall distal profile. Alternatively, taper49may be omitted and tube42may continue at its original diameter throughout balloon segment55.

In a preferred embodiment, outer tube42tapers inward just distal to proximal affixation point47, and the distal end of outer tube42is affixed to one or more radiopaque marker bands48, as shown inFIG. 2A. The reduced diameter distal section of tube42may extend the entire length of balloon segment55and may be affixed to inner tube44and the distal end of balloon46at distal affixation point53.

In the embodiment described inFIG. 2A, outer tube42comprises at least one inflation aperture52disposed in a lateral surface at a location distal to point47and proximal to the most proximal radiopaque marker48. Inflation aperture52permits fluid communication between the proximal inflation/deflation port and balloon46via lumen43. In an alternative embodiment, outer tube42may terminate proximal to the most proximal radiopaque marker within balloon segment55, in which case the distalmost tip of tube42would communicate directly with balloon48via lumen43.

The characteristics of outer tube42may vary along its length to influence stiffness at selected locations, particularly to provide increased stiffness along balloon segment55. The characteristics of outer tube42may 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 2Cillustrate embodiments wherein helical coils65and67, having constant and varying pitches, respectively, may be used to selectively enhance stiffness of outer tube42. Helical coils65and67may enhance stiffness of outer tube42proximal to or within balloon segment55. Optionally, outer tube42may be affixed to inner tube44at selected locations along catheter40, e.g., using a solder or weld, to enhance stiffness and pushability so long as inflation lumen43is not completely blocked.

Outer tube42may 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 catheter40further may be altered by manufacturing outer tube42using 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 sheath42at any combination of locations is intended to fall within the scope of the present invention.

Referring toFIG. 3, an alternative embodiment of catheter40is described wherein the distal end of outer tube42communicates with a separate connecting tube57having proximal and distal ends. Connecting tube57is disposed within balloon segment55and preferably is affixed to at least one radiopaque marker48, as shown. The distal end of outer tube42may be affixed to the proximal end of connecting tube57, e.g., using biocompatible adhesive.FIGS. 3B–3C, corresponding to inset3ofFIG. 3A, illustrate outer tube42being affixed to connecting tube57via butt-weld58and lap-weld60, respectively. Lap-weld60is preferred to butt-weld58because lap-weld60may be less susceptible to kink as push forces are transmitted from outer tube42to connecting tube57. The embodiments described inFIG. 3provide reinforced tube segments of differing characteristics without having to manufacture one relatively complicated piece for outer tube42. Furthermore, connecting tube57prevents kinks from developing between radiopaque markers48, an otherwise common location for the formation of kinks.

Referring toFIG. 4, an alternative embodiment of catheter40in accordance with the present invention is described. Outer tube42is affixed to the proximal end of balloon46at proximal affixation point47, then tapers via taper49to connect to inner tube44. In this embodiment, outer tube42and inner tube44become a single, reinforced tube59when connected. As described hereinabove, the properties of outer tube42and reinforced tube59may be tailored to provide varying stiffness at selected locations along the length of catheter40.