Abstract:
An intravascular catheter having an elongate shaft that is entirely non-magnetically responsive and at least partially radiopaque, including a reinforcement layer. The reinforcement layer may comprise a non-magnetically responsive radiopaque metal, such as a multi-strand Tungsten braid. The improved shaft of the present invention is compatible with x-ray and MRI visualization techniques, and may be incorporated into a wide variety of intravascular catheters such as guide catheters, diagnostic catheters, balloon catheters, etc.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to catheter shafts. More specifically, the present invention relates to reinforced catheter shafts for intravascular devices such as guide catheters, diagnostic catheters, balloon catheters, and the like.  
         BACKGROUND OF THE INVENTION  
         [0002]    Diagnostic catheters and guide catheters are commonly used to facilitate the diagnosis and treatment of vascular diseases such as coronary artery disease and peripheral vascular disease. Such catheters commonly include a braid reinforcement layer disposed between an inner layer and an outer layer. The braid reinforcement provides torsional rigidity, column strength, kink resistance, as well as radiopacity. However, conventional braid reinforcement materials such as stainless steel are not MRI (magnetic resonance imaging) compatible due to ferro-magnetic properties. Because different visualization techniques may be employed to facilitate intravascular navigation, it is desirable to have a catheter shaft that is both radiopaque for x-ray visualization and non-magnetically responsive for MRI compatibility.  
         SUMMARY OF THE INVENTION  
         [0003]    To address these desirable features, the present invention provides, for example, an intravascular catheter comprising a reinforced shaft that is entirely non-magnetically responsive and at least partially radiopaque. In one specific example and without limitation, the present invention provides an elongate catheter shaft that is entirely non-magnetically responsive and at least partially radiopaque, wherein the shaft includes an inner layer, an outer layer, a reinforcement layer disposed between the inner and outer layers, and a soft distal tip. The reinforcement layer may comprise a braid of non-magnetically responsive radiopaque metal wires, the outer layer may comprise a non-radiopaque flexible polymer, the inner layer may comprise a non-radiopaque lubricious polymer, and the soft distal tip may comprise a polymer loaded with a radiopaque non-magnetically responsive filler. The inner layer, the outer layer and the reinforcement layer may extend from the proximal end of the shaft to the proximal end of the distal tip, leaving the tip flexible and atraumatic. 
       
    
    
     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, shown as a guide or diagnostic catheter;  
         [0005]    [0005]FIG. 2 is a cross-sectional view taken along line  2 - 2  in FIG. 1;  
         [0006]    [0006]FIG. 3 is a longitudinal sectional view taken along line  3 - 3  in FIG. 1;  
         [0007]    FIGS.  4 A- 4 C are fragmentary views of various braid options; and  
         [0008]    [0008]FIG. 5 is a partially sectioned fragmentary view of the catheter shaft shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    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.  
         [0010]    Refer now to FIG. 1 which illustrates an intravascular catheter in accordance with an embodiment of the present invention. For purposes of illustration and discussion only, the intravascular catheter shown in FIG. 1 is in the form of a guide or diagnostic catheter  10 , but may comprise virtually any catheter used for intravascular applications. For example, the intravascular catheter may comprise a balloon catheter, an atherectomy catheter, a drug delivery catheter, a stent delivery catheter, etc.  
         [0011]    As used herein, magnetically non-responsive materials refer to materials that are compatible with magnetic resonance imaging techniques. By way of example, not limitation, non-magnetically responsive materials include materials with a magnetic susceptibility (absolute value) less than 1×10 −4 , preferably less than 1×10 −5  and ideally near zero (0). By contrast, magnetically responsive materials include materials with a magnetic susceptibility (absolute value) greater than or equal to 1×10 −4  Generally speaking, polymers and some metals such as Titanium are magnetically non-responsive, and metals such as stainless steel and other ferrous containing metals are magnetically responsive.  
         [0012]    The guide or diagnostic catheter  10  may have a length and an outside diameter sufficient to enable intravascular insertion and navigation. For example, the catheter  10  may have a length of approximately 100 cm-150 cm and an outside diameter of approximately 4F-9F. The guide or diagnostic catheter  10  may be substantially conventional except as described herein and shown in the drawings.  
         [0013]    The catheter  10  includes an elongate shaft  12  having a proximal end and distal end. A distal tip  16  is connected to the distal end of the elongate shaft  12 . The distal tip  16  and a distal portion of the elongate shaft  12  may be curved depending on the particular clinical application. The elongate shaft  12  and the distal tip  16  include a lumen  18  extending therethrough to facilitate insertion of other medical devices (e.g., guide wires, balloon catheters, etc.) therethrough, and/or to facilitate injection of fluids (e.g., radiopaque dye, saline, drugs, etc.) therethrough. A conventional manifold  14  is connected to the proximal end of the elongate shaft  12  to facilitate connection to other medical devices (e.g., syringe, Y-adapter, etc.) and to provide access to the lumen  18 .  
         [0014]    As best seen in FIGS. 2 and 3, the elongate shaft  12  may be multi-layered. In this embodiment, the elongate shaft  12  may include an outer layer  30 , a reinforcement layer  32 , and an inner layer  34 . The distal tip  16  may comprise the outer layer  30  extending beyond the inner layer  34  and the reinforcement layer  32  to define a soft atraumatic tip.  
         [0015]    The inner layer  34  may comprise a lubricious polymer such as HDPE or PTFE, for example. In one particular embodiment, the inner layer  34  may comprise PTFE having a wall thickness of 0.001 in., and an inside diameter of 0.058 inches. In this example, the inner layer  34  is non-magnetically responsive and non-radiopaque, but may be made radiopaque by utilizing known filler materials such as bismuth subcarbonate.  
         [0016]    The outer layer  30  may comprise, at least in part, a polyether-ester elastomer sold under the trade name ARNITEL. The outer layer  30  may be formed, for example, by extrusion, co-extrusion, interrupted layer co-extrusion (ILC), or fusing several segments end-to-end. The outer layer may have a uniform stiffness or a gradual reduction in stiffness from the proximal end to the distal end thereof. The gradual reduction in stiffness may be continuous as by ILC or may be stepped as by fusing together separate extruded tubular segments end-to-end. The outer layer may be impregnated with a reinforcing material such as liquid crystal polymer (LCP) fibrils. For example, a proximal portion of the outer layer  30  may comprise 74D ARNITEL with 6% LCP, a mid portion may comprise 63D ARNITEL, and a distal portion may comprise 55D ARNITEL. The distal tip  16  may comprise 40D ARNITEL loaded with 46% bismuth subcarbonate to render it radiopaque. The proximal portion, mid portion, distal portion and distal tip may have lengths of 34 in., 3 in., 1.5 in., and 0.15 in., respectively. The proximal, mid and distal portions may have a wall thickness of 0.005 in., and the distal tip may have a wall thickness of 0.005 in. In this example, the outer layer  30  is non-radiopaque and non-magnetically responsive, while the distal tip  16  is radiopaque and non-magnetically responsive.  
         [0017]    The reinforcement layer  32  may comprise a metal wire braid, for example. The metal wire braid may comprise a non-magnetically responsive (i.e., non-ferrous) radiopaque metal such as Tungsten, Gold, Titanium, Silver, Copper, Platinum, Iridium, other non-ferrous dense metals, or alloys thereof. Tungsten exhibits tensile properties (strength and rigidity) similar to or higher than those of stainless steel, which is a conventional reinforcement material that exhibits magnetic responsiveness due to some ferrous content and is therefore not MRI compatible. Tungsten is also relatively dense and therefore relatively radiopaque. Tungsten is also relatively inexpensive compared to other more precious metals and alloys.  
         [0018]    Alternatively, the reinforcement layer  32  may be formed of a non-metal material such as poly-para-phenylene terephthalamide (KEVLAR) fibers, LCP fibers, other polymeric filaments, or glass fibers, including monofilament and multi-filament structures of each.  
         [0019]    As seen in FIGS.  4 A- 4 C, the braid reinforcement layer  32  may comprise one or more strands  36  of non-magnetically responsive (i.e., non-ferrous) radiopaque material. Each strand  36  may be flat (ribbon), round, and/or hollow. By way of example, not limitation, the braid  32  may include triple strands  36  braided in a three-over-three pattern as seen in FIG. 4A, quadruple strands  36  braided in a four-over-four pattern as seen in FIG. 4B, or quintuple strands  36  braided in a five-over-five pattern as shown in FIG. 4C. As seen in FIG. 5, a triple strand (three-over-three) reinforcement braid  32  utilizing 0.001 inch diameter Tungsten wire strands  36  with a pic count (pic count refers to the number intersections between strand sets per lineal unit) of 66+/−5 pics/inch has been found to provide good radiopacity without requiring loading of the outer layer  30 , and good shaft  12  performance in terms of kink resistance, torque transmission, pushability, and shape retention.  
         [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 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.