Abstract:
A thin-walled reinforced catheter shaft having polymers that are reinforced with a variable wire size radiopaque braid which maintains the thin-wall of the shaft while providing improved properties in terms of radiopacity, kink resistance, tortional rigidity, column strength and burst strength.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to intravascular medical devices. More specifically, the present invention relates to intravascular catheters such as guide and diagnostic catheters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Intravascular catheter shafts commonly incorporate a reinforcement layer such as a stainless steel wire braid to enhance the strength of the shaft. Generally speaking, however, stainless steel wire braid is not highly radiopaque, and therefore is not highly visible using conventional x-ray radiographic visualization techniques.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention addresses this problem by providing, for example, an intravascular catheter having a reinforced elongate shaft which combines high strength (e.g., stainless steel) wires and highly radiopaque (e.g., tungsten) wires in an interwoven braid. The high strength wires provide torque, column strength and burst strength to the shaft, while the highly radiopaque wires provide enhanced radiopacity. The radiopaque wires have a diameter which is preferably less than the diameter of the high strength wires to avoid compromising the thin walls of the shaft.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a plan view of an intravascular catheter in accordance with an embodiment of the present invention;  
         [0005]    [0005]FIG. 2 is a cross-sectional view taken along line  2 - 2  in FIG. 1;  
         [0006]    [0006]FIG. 3 is a schematic illustration of the braid reinforcement pattern used in the intravascular catheter shown in FIG. 1; and  
         [0007]    [0007]FIG. 4 is a cross-sectional view taken along line  4 - 4  in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.  
         [0009]    Refer now to FIG. 1 which illustrates a plan view of an intravascular catheter  10  in accordance with an embodiment of the present invention. Intravascular catheter  10  may comprise a wide variety of intravascular catheters such as a coronary guide or diagnostic catheter as shown. However, those skilled in the art will recognize that the principles and concepts described herein may be applied to virtually any intravascular catheter including balloon catheters, atherectomy catheters, etc. Except as described herein, the catheter  10  may be manufactured using conventional techniques and may be used in accordance with the intended clinical application.  
         [0010]    In this particular example, the intravascular catheter  10  includes an elongate shaft  30  having a proximal end and a distal end. A hub and strain relief assembly  20  is connected to the proximal end of the elongate shaft  30 . A proximal flared portion  42  of the elongate shaft  30  mechanically enhances the bond to the hub and strain relief assembly  20 . The hub and strain relief assembly  20  includes a main body portion  22 , a pair of flanges  24  to facilitate gripping and manipulation of the catheter  10 , and a strain relief  26  to reduce the likelihood of kinking between the relatively stiff body portion  22  and the relatively flexible shaft  30 . The hub and strain relief assembly  20  may be of conventional design and may be connected to the proximal end of the elongate shaft  30  utilizing conventional techniques.  
         [0011]    The elongate shaft  30  includes a series of shaft segments which generally increase in flexibility toward the distal end of the elongate shaft  30 . In this particular embodiment, the elongate shaft  30  includes a first shaft segment  32 , a second shaft  34 , a third shaft segment  36 , and a forth shaft segment  38 . The elongate shaft  30  also includes a distal atraumatic tip  40  and a proximal flared portion  42 . The various shaft segments  32 / 34 / 36 / 38  are described in more detail with reference to FIG. 2, and the distal tip portion is described in more detail with reference to FIGS. 2 and 4.  
         [0012]    Refer now to FIG. 2 which illustrates a cross-sectional view of the elongate shaft  30  taken along line  2 - 2  in FIG. 1. The cross-sectional view of the elongate shaft  30  shown in FIG. 2 is representative of the construction of each of the shaft segments  32 / 34 / 36 / 38  in addition to the proximal portion of distal tip  40 . The distal portion of the distal tip  40  is represented by the cross-sectional view illustrated in FIG. 4 taken along line  4 - 4  in FIG. 1.  
         [0013]    With continued reference to FIG. 2, the elongate shaft  30  includes an outer layer  52 , an inner layer  54 , and a reinforcement layer  50  disposed therebetween. The inner layer  54  defines a lumen  44  which extends through the entire length of the elongate shaft  30  and is in fluid communication with a lumen (not shown) extending through the hub assembly  20 .  
         [0014]    The inner layer  54  may comprise a lubricous polymeric material such as PTFE having an inside diameter of approximately 0.070 inches and a wall thickness of approximately 0.001 inches. The outer layer  52  may comprise a thermoplastic polymer such as a co-polyester thermoplastic elastomer (TPE) available under the tradename Arnitel. The outer layer  52  may have an inside diameter roughly corresponding to the outside diameter of the inner layer  54  and a wall thickness of approximately 0.005 inches. The reinforcement layer  50  is described in more detail with reference to FIG. 3.  
         [0015]    The hub and strain relief  20  may have a length of approximately 2.10 inches and the elongate shaft  30  may have an overall length of approximately 39.1 inches. The distal tip segment  40  may have a length of approximately 0.130 inches, with the proximal 0.080 inches having a cross-section as shown in FIG. 2, and the distal 0.050 inches having a cross-section as shown in FIG. 4. The first shaft segment  32  may have a length of approximately 0.60 inches, the second shaft segment  34  may have a length of approximately 0.40 inches, the third shaft segment may have a length of approximately 0.030 inches, and the fourth shaft segment  38  may have a length of approximately 16.0 inches.  
         [0016]    As mentioned previously, the various shaft segments  32 / 34 / 36 / 38  gradually decrease in stiffness toward the distal end of the elongate shaft  30 . The decrease in stiffness may be provided by varying the hardness of the outer layer  52  corresponding to each shaft segment  32 / 34 / 36 / 38 . For example, the distal unreinforced portion of the tip  40  may comprise a soft thermoplastic elastomer (TPE) sold under the name Hytrel having a hardness of  30 D. To facilitate radiographic visualization, the unreinforced portion of the distal tip  40  may be loaded with 50% bismuth subcarbinate.  
         [0017]    The outer layer  52  of the first shaft segment  32  and the proximal reinforced portion of the distal tip  40  may be formed of a TPE polymer sold under the tradename Arnitel having a hardness of  46 D. The outer layer  52  of the second shaft segment  34  may be formed of a TPE polymer available under the tradename Arnitel having a hardness of  55 D. The outer layer  52  of the third shaft segment  36  may be formed of a TPE polymer available under the tradename Arnitel having a hardness of  68 D. The outer layer  52  of the fourth shaft segment  38  may be formed of a TPE polymer available under the tradename Arnitel having a hardness of  74 D mixed with 6% liquid crystal polymer (LCP).  
         [0018]    With reference to FIG. 3, the reinforcement layer  50  comprises an interwoven metal braid comprising a first wire or pair of wires  56  wound in a first helical direction and a second wire or pair of wires  58  wound in a second helical direction different from the first helical direction. The first wire or pair of wires  56  may comprise a highly radiopaque metal such as a tungsten having a relatively small diameter, and the second wire or pair of wires  58  may be formed of a high strength metal such as stainless steel having a relatively large diameter. The highly radiopaque wire or wires  56  provide clear visualization of substantially the entire length of the elongate shaft  30  during x-ray visualization. The high strength wire or wires  58  provide tortional rigidity, column strength and burst strength to the elongate shaft  30 .  
         [0019]    The highly radiopaque wire or wires  56  preferably have a diameter which is less than the diameter of the high strength wire or wires  58  such that the radiopaque wire or wires  56  do not significantly contribute to the overall wall thickness of the elongate shaft  30 . Also preferably, the radiopaque wire or wires  56  and the high strength wire or wires  58  are wound in a two-over-two pattern as shown in FIG. 3 with an intersection  60  count or pic count of about 60 intersections per inch. The braid reinforcement  50  may comprise, for example, 16 strands of tungsten wire having a diameter approximately 0.0015 inches interwoven in a two-over-two pattern with 16 strands of stainless steel wire  58  having a diameter of approximately 0.0020 inches.  
         [0020]    Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.