Abstract:
A Balloon dilation catheter comprising an elongated tubular shaft and an inner tube defining inflation and guide wire lumens. A dilation balloon is mounted on the distal end of the tubular shaft and communicates with the inflation lumen. The guide wire lumen extends through the balloon. A stiffening wire is positioned within the tubular shaft and has a proximal end secured in the proximal portion of the catheter. The distal end of the stiffening wire is anchored within the inner tube in an area adjacent the guide wire entrance port. The stiffening wire maximizes strength to the proximal portion of the catheter while maintaining flexibility in the distal end of the catheter as well as the balloon.

Description:
This is a continuation of U.S. patent application Ser. No. 08/387,906, filed Jun. 29, 1995, now U.S. Pat. No. 5,823,995, which is Section 371 of PCT/US93/07943, filed Aug. 24, 1993, which is a continuation-in-part of U.S. patent application Ser. No. 07/934,948 filed Aug. 25, 1992 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a dilatation catheter and more particularly to a monorail type dilation catheter having a stiffening wire. 
     BACKGROUND OF THE INVENTION 
     Monorail dilatation catheters are commonly used in angioplasty procedures because the unique construction of such catheters enables the rapid exchange of the catheter once it is inserted into the patient. For example, U.S. Pat. No. 4,762,129 to Bonzel discloses a monorail catheter having a short tube defining a guide wire lumen at the distal end of the catheter. The tube extends through the balloon from the distal end to a point proximal of the proximal end of the balloon. This tube terminates at an aperture opening to the exterior of the catheter such that most of the length of the guide wire from the balloon to the proximal end of the catheter is exterior of the catheter. Rapid exchange and manipulation of the dilatation catheter is facilitated because the catheter segment contacting the surface of the guide wire is only as long as the balloon. 
     Although the monorail catheter provides rapid catheter exchange, it tends to lack stiffness and, therefore, is difficult to push through a patient&#39;s blood vessels. In the Bonzel construction, a stiffening wire extends through the catheter imparting stiffness to the catheter. However, the stiffening wire may impart stiffness in areas of the catheter where flexibility is desired, for example in the balloon. 
     Due to the construction of the catheter, heretofore it has not been feasible to terminate a stiffening wire in a dilatation catheter proximal of the section of the catheter in which flexibility is desired. To provide enhanced flexibility in situations where a stiffening wire is used, tapered stiffening wires have been proposed. Schneider (Europe) AG sells a dilatation balloon catheter in which a tapered stiffening wire “floats” within the catheter, i.e., the stiffening wire is not anchored at its distal and proximal ends. While this construction, in the ideal situation, may provide the requisite stiffness and maintain distal flexibility, the floating stiffening wire is prone to movement which can lead to problems in manipulating the catheter. 
     OBJECTS OF THE INVENTION 
     The object of the invention is to provide a dilatation catheter in which a stiffening wire terminates proximal of the distal end of the catheter and is securely anchored in place at both its distal and proximal ends. 
     A more specific object of the invention is to provide a catheter of the monorail type in which a stiffening wire is anchored at the proximal end of the catheter and wherein the distal end of the stiffening wire terminates at and is secured in place within the catheter in the region of the entrance port for the guide wire. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a balloon dilation catheter of the monorail type includes a stiffening wire secured at both its ends in a selected position such that maximum strength is imparted in the proximal portion of the catheter while flexibility is maintained in the distal portion of the catheter and the balloon. In the preferred embodiment, the catheter comprises an elongated tubular shaft with a dilatation balloon mounted on its distal end. An inner tube extends distally from a position proximal of the guide wire port and is adapted to receive the guide wire which is inserted through the port. The space between the tubular shaft and the inner tube provides an inflation lumen for the balloon. In accordance with the invention, a stiffening wire is anchored at its proximal end within the catheter and the distal end of the stiffening wire is retained within the inner tube in the vicinity of the guide wire port. 
    
    
     THE DRAWINGS 
     FIG. 1 is a schematic plan view of a monorail catheter in accordance with the invention; 
     FIG. 2 is a plan view partially in section showing one way in which the stiffening wire may be anchored in the luer fitting; 
     FIG. 3 is a sectional view along the line  3 — 3  of FIG. 2; 
     FIG. 4 is a plan view partially in section showing how the dilatation balloon is secured to the distal end of the catheter; 
     FIG. 5 is a detailed cross-sectional view of a catheter manufactured in accordance with the preferred embodiment of the invention showing the fused laminate in the region of the guide wire port; 
     FIG. 6 is a sectional view along the line  6 — 6  of FIG. 5; 
     FIG. 7 is a sectional view along the line  7 — 7  of FIG. 5; 
     FIG. 8 is a detailed sectional view showing the inner tube with the retained stiffening wire inserted into the catheter shaft prior to the final assembly step in which the fused laminate is formed; 
     FIG. 9 is a sectional view along the line  9 — 9  of FIG. 8; 
     FIG. 10 is a sectional view along the line  10 — 10  of FIG. 8; and 
     FIG. 11 is a plan view partially in section showing an alternative method for anchoring the proximal end of the stiffening wire within a luer fitting. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, a dilation catheter in accordance with the invention comprises an elongated tubular shaft  16  which consists of a proximal shaft  32  and a distal shaft  34 . The distal shaft overlaps the proximal shaft in such a way as to form a guide wire port  30  through which a guide wire  12  can be introduced in conventional fashion. The lumen for the guide wire is formed by an inner tube  14  which may be made of the same material as distal shaft  34 , i.e., a flexible heat shrinkable material such as high density polyethylene. Inner tube  14  extends from a point just proximal of the guide wire port  30  to the distal end of the balloon. The proximal end of shaft  32  is connected to a luer fitting  18 . A dilatation balloon  26 , which may be of convention design, is secured at the distal end of the shaft  34 . Fluid introduced through a connector  20  of luer  18  causes balloon  26  to expand in conventional fashion. 
     In the preferred embodiment, the annular space  24  between the distal shaft  34  and inner tube  14  forms an inflation lumen. The shaft  34  terminates proximal to the distal end of the inner tube  14  (FIG.  4 ). As shown in FIG. 4, the proximal end of balloon  26  is connected and sealed to the distal end of the distal shaft  34 . The inner tube  14  extends through the balloon  26  and is sealed at its distal end to the distal end of the balloon. Adhesive  29  provides a rounded end at the distal end of the balloon. 
     The balloon  26  is formed from either a noncompliant polyethylene terephthalate (PET) or a more compliant material such as urethane. It is preferred that the balloon is coated with a highly lubricous, abrasion resistant coating. An example of a preferred coating is that disclosed in U.S. Pat. No. 5,077,352 to Elton, and assigned to the assignee of the present invention, C. R. Bard of Murray Hill, N.J., the disclosure of which is incorporated herein by reference. As disclosed in that patent, a flexible, lubricous organic polymeric coating is formed by applying a mixture of an isocyanate, a polyol, poly(ethylene oxide), and a carrier liquid to the surface to be coated. The carrier liquid is removed and the mixture reacted to form a polyurethane coating with associated poly (ethylene oxide) giving a highly lubricous, abrasion resistant, flexible coating. 
     A radiopaque coil spring  72  is positioned within the  10  balloon  26  around the inner tube  14  (FIG.  4 ). The coil spring  72  ensures flexibility of the balloon, the distal portion of the catheter, and the tip. The radiopaque coil spring enables the balloon  26  to be identified under X-ray. In one embodiment, the coil was formed from 0.0025 inch spring coil material such as a gold-platinum combination. The formed coil may be about 4.5 mm long. The chosen coil parameters depend on the desired flexibility characteristics to be imparted to the distal end of the catheter. 
     In accordance with the invention, a stiffening wire  50 , tapered at its distal end, extends from the luer  18  axially through proximal shaft  32  to the vicinity of the guide wire port  30  where it is positioned within the inner tube  14 . The tapered end of the stiffening wire  50  includes five adhesive beads  27  and is anchored within the proximal end of inner tube  14  by heat shrinking the inner tube to the stiffening wire as explained further below. Slots  40  and  36  are cut in inner tube  14  and proximal shaft  32 , respectively, so that the guide wire  12  can be inserted through the port  30  and into the lumen within inner tube  14  distal of port  30 . As shown in FIG. 5, the inner tube  14  may be bonded to a distal portion of the proximal shaft  32  and the distal shaft  34  to form a tubular laminate. Since fluid must be introduced into the balloon in the passageway  24  between the inner tube  14  and the distal shaft  34 , a fluid passageway  35  is provided from the proximal shaft  32  through the thermally bonded section of the catheter into the region where the distal shaft  34  and inner tube  14  are coaxial. This region starts at the left-hand side of FIG.  5  and extends into the balloon where the distal shaft  34  terminates. 
     FIG. 2 shows one way in which the proximal end of the stiffening wire  50  may be anchored within the luer fitting  18 . The luer fitting  18  includes a cylindrical balloon leg  54 , its distal end abutting against the proximal end of the proximal shaft  32 . The stiffening wire  50  includes a crimp  52  at its proximal end which passes through the wall of balloon leg  54  so that the crimped portion lies against the exterior surface of the balloon leg  54 . Wire  50  is positioned within the balloon leg during the molding process. A strain relief tube  56  envelops the proximal shaft  32  distal of its junction with the balloon leg  54 . A shrink tube  58  is placed over the crimped portion of wire  50  and a proximal section of strain relief tube  56  and serves to secure the assembly when heat is applied. The luer may also include a conically shaped cover  60  which is secured to the luer by conventional adhesives and serves partly as a strain relief member. 
     An alternative structure for anchoring the proximal end of the stiffening wire within the luer fitting is shown in FIG.  11 . In this case, the proximal end of the stiffening wire  50  includes a hook  62  which is embedded in a molded insert  64  of the luer during the molding process. The proximal end of the proximal shaft  32  is also embedded within the insert  64  during the molding process. During the molding process, a core pin (not shown) is positioned within the mold to form a lumen  65  to enable the introduction of air into the shaft  32  to inflate the balloon. After the insert  64  is molded, the assembly is over-molded with material  66  to form the finished luer fitting. The over-mold material  66  provides strain relief and is shaped to facilitate manipulation when a source of air is to be connected to the luer. 
     In the preferred embodiment, the proximal shaft  32  is an extruded polymer tube (for example, high molecular weight high density polyethylene). However, all or part of the proximal shaft  32  may comprise a hypotube in which case the proximal end of the stiffening wire is joined to the distal end of the hypotube rather than to the luer. If the proximal shaft were to consist of a hypotube and extruded polymer tube, the two would be joined together by conventional means. 
     The precise point at which the stiffening wire so terminates is not critical but it is preferred that the stiffening wire terminate in the vicinity of the guide wire port  30 . The point of termination will depend on the desired flexibility of the distal section of the catheter. 
     Assembly of the preferred embodiment of the catheter according to the invention is as follows. First, the adhesive beads  27  are applied to the distal end of the stiffening wire  50  and cured. Stiffening wire  50  is then inserted into the inner tube  14  with a patency mandrel between the wire and tube in the area where the tube and wire are not to be bonded together. A shrink tube is then placed over the assembly and the inner tube  14  heat welded to the stiffening wire  50 . The shrink tube and patency mandrel are removed. 
     As shown in FIG. 8, the stiffening wire assembly thus formed is then placed in the proximal shaft  32 . The proximal end of wire  50  is attached to luer  18  as described above and heat welded into position. 
     Next, a flat mandrel  37  is positioned between inner tube  14  and proximal shaft  32  to provide for the fluid passageway  35  through the fused laminate after heat welding. Similarly, a patency mandrel (not shown) is positioned in the inner tube  14  to maintain an opening for the guide wire  12 . A shrink tube is positioned over this assembly and heat applied to weld the inner tube  14  to proximal shaft  32 . The shrink tube and patency mandrel are then removed. 
     Slots  36  and  40  are then cut through the proximal shaft  32  and inner tube  14  to provide an opening for the guide wire into the lumen within the inner tube  14 . A patency mandrel is then placed within the inner tube extending through the slots. The flared distal shaft  32  is inserted over the distal end of the proximal shaft  34  and up over the slots and patency mandrel with the proximal end of the distal shaft  32  overlapping the stiffening wire  50 . The shrink tube is applied over the joint area and heat applied to weld the entire assembly to form the fused laminate. The shrink tube is removed and then the patency mandrel and flat mandrel  37  are removed leaving the fused laminate with a guide wire port into the inner tube  14  and the fluid passageway  35  through the fused laminate. 
     During the welding process, the portion of proximal shaft  32  just proximal of slot  36  is “folded down” into contact with the wire retention section of inner tube  14  to form a sloped wall  38  (FIG.  5 ). The close positional relation among the guide wire opening  40  of the inner tube  14 , the guide wire entrance port  30 , and the sloped wall  38  of the proximal shaft  32  forms a smooth transition and passageway for the guide wire into the inner tube  14 . The smooth transition and passageway not only aids in initial guide wire placement into the catheter, but also facilitates catheter exchange. 
     The stiffening wire  50  may be formed from different materials. A 302 or 304 stainless steel has been found satisfactory. Plastics, composite metals, and other materials also can be used as long as the selected material imparts the desired stiffness to the proximal portion of the catheter. 
     With a catheter that is about 150 cm long, and with a conventional length dilatation balloon, the stiffening wire  50  is about 121 cm long. In one embodiment, the wire is about 0.016 +/−0.0003 inches diameter and tapers down to about a 0.003+/−0.0003 inch diameter cylindrical portion. The tapered portion may be approximately 10+/−0.5 cm long, and the cylindrical portion about 10 mm+/−2 mm. When the wire is formed of a metallic material such as stainless steel, the distal 9 cm may be stress relieved. 
     The monorail catheter of the present invention offers several benefits over prior art monorail catheters. The use of a stiffening wire anchored proximally at the luer and distally adjacent to the guide wire entrance port enhances pushability, kink resistance at the guide wire entrance port, and the flexibility transition from the proximal portion to the distal portion of the catheter. The use of a single lumen shaft at the proximal portion of the catheter maximizes the inflation/deflation lumen and reduces deflation times to a minimum. The different coaxial inner and outer shaft materials are chosen from materials to enhance performance characteristics. The coaxial distal section minimizes tip distension during balloon inflation.