Abstract:
A catheter for use with a guidewire, the catheter having a distal tip that centers the guidewire even when the catheter is severely bent, thereby avoiding protrusion of the distal tip of the catheter at the outer meridian of the catheter bend and reducing the risk of the catheter tip catching on the luminal surface of the adjacent vasculature. The distal tip of the catheter incorporates at least one guidewire bearing, preferably multiple bearings in the form of longitudinally oriented ribs, which provide the centering characteristic with minimal friction between the inner surface of the catheter distal tip and the outer surface of the guidewire. Preferably, at least four guidewire bearings are provided.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of catheters intended for use with guidewires, and more particularly to the distal tip of such catheters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Catheters intended for use with guidewires have a distal tip with an inner diameter that is slightly larger than the outside diameter of the intended guidewire. The difference in diameter is necessary to provide the guidewire with operating clearance. When navigating tortuous anatomy or crossing a previously deployed stent, the guidewire is not concentric with the distal tip of the catheter due to this required clearance. Because of this required clearance, the distal tip of the catheter protrudes along the outer meridian of a severely bent catheter/guidewire assembly, with the result that it is at risk of catching on the vessel wall and consequently impede trackability of the catheter over the guidewire. This can result in an increase in the time of the procedure as the medical practitioner may be forced to withdraw the catheter and again attempt to maneuver the assembly through the tortuous anatomy responsible for the severe bend. Likewise, if the catheter tip catches on the luminal surface of the vessel wall, damage to the luminal surface may result, requiring surgical intervention. Similarly, the catheter tip is also at risk of catching on the struts at the end of a previously deployed stent, thereby impeding crossability.  
           [0003]    There have been various catheter designs in the art that describe centering concepts that relate to the tip of the catheter. U.S. Pat. No. 5,122,125 to Deuss teaches a guiding catheter having a tip portion with external ribs intended to center the catheter within the vessel it is being moved through. U.S. Pat. No. 6,228,110 to Munsinger describes a catheter with a tip portion including a series of bristles affixed to the luminal surface of the tip. The bristles are intended to serve as an axial brake designed to inhibit unintended axial motion between the catheter and a guidewire within the catheter. The concentric design of the bristles serves to center the guidewire within the catheter tip. However, the group of bristles are located some distance proximally from the distal end of the catheter, with the result that while an effective axial braking means is provided between the catheter and guidewire, the guidewire is not centered as it exits the distal end of the catheter.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to centering means provided to the distal tip of a catheter to assure that a guidewire or other device exiting the distal tip is substantially centered with respect to the distal tip, thereby reducing any risk of the edge of the catheter tip catching on the luminal surface of a vessel when the tip region of the catheter is severely bent, as is often the case when traversing tortuous vessels with the catheter.  
           [0005]    The centering means comprises at least one and preferably multiple bearing surfaces located on the luminal surface of the catheter tip. These bearing surfaces preferably take the form of ribs that project inwardly from the luminal surface of the catheter tip, the ribs preferably being oriented substantially parallel to the longitudinal axis of the catheter. They are preferably integrally formed on the luminal surface of the catheter tip and consequently are from the same material that comprises the catheter tip. Preferably, at least three, and more preferably at least four, such ribs are provided, equally spaced around the luminal surface of the catheter tip.  
           [0006]    To ensure optimal centering, these “bearings” can be formed to provide a slight interference with a guidewire or other device intended to be passed through the lumen of the catheter. The interference is of such a minimal amount that no perceptible increase in friction between the guidewire and catheter occurs.  
           [0007]    The bearings, particularly when they take the form of longitudinally-oriented ribs, are preferably of a relatively short length, extending back into the catheter from the distal tip for a length of, for example, about 6 mm or less, and may be as short as 3 mm or less. The proximal ends of the bearings preferably transition smoothly rather than abruptly into the luminal surface of the catheter. In transverse cross section, the ribs preferably have a semi-circular shape.  
           [0008]    The catheter tip of the present invention can be used with any catheter that is placed with a guidewire of any size. Possible applications include, but are not limited to, cardiology catheters (which are typically placed over guidewires of about 0.36 mm diameter), urology catheters (typically placed over guidewires of about 0.89 mm diameter) and radiology catheters (typically placed over guidewires of about 0.97 mm diameter).  
           [0009]    While it is preferred that the bearings take the form of ribs, other forms may be used such as hemispherical bumps or an annular ring placed at the luminal surface of the catheter tip.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a transverse cross section of a catheter distal tip and guidewire of the prior art.  
         [0011]    [0011]FIG. 2 is a side view of a catheter and guidewire of FIG. 1, showing the catheter in a bent state and showing the resulting “ledge” at the catheter tip where the guidewire exits.  
         [0012]    [0012]FIG. 3 is a transverse cross section of a catheter tip of the present invention showing bearings projecting from the luminal surface of the catheter tip.  
         [0013]    [0013]FIG. 3A is a transverse cross section of the catheter tip of FIG. 3 further showing a device such as a guidewire centered within the catheter tip.  
         [0014]    [0014]FIGS. 4 and 4A are longitudinal cross sections of catheter tips of the present invention, showing the bearings in the form of ribs oriented parallel to the longitudinal axis of the catheter.  
         [0015]    [0015]FIG. 5 is a longitudinal cross section of a catheter tip of the present invention, showing the bearings in the form of ribs oriented helically with respect to the longitudinal axis of the catheter.  
         [0016]    [0016]FIG. 6 is a longitudinal cross section of a catheter tip of the present invention, showing the bearings in the form of hemispheres located at the tip of the catheter.  
         [0017]    [0017]FIG. 7 is a transverse cross section of an alternative embodiment of the catheter tip.  
         [0018]    [0018]FIG. 8 is a transverse cross section of another alternative embodiment in the form of a variation of the tip described in FIG. 3.  
         [0019]    [0019]FIG. 9 is a transverse cross section of an alternative embodiment wherein wires are embedded in the material of the catheter tip and bearing.  
         [0020]    [0020]FIGS. 10 and 11 are longitudinal and transverse cross sections respectively of an alternative embodiment wherein a single bearing surface in the form of a circumferentially oriented raised ring-shaped bearing surface, located at the luminal surface of the distal tip of the catheter.  
         [0021]    [0021]FIGS. 12A and 12B describe sequential side views of the catheter tip, with the tip shown in cross section, as used to capture and collapse an embolic filter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 1 is a typical transverse cross section of the tip portion  11  of a catheter  10  of the prior art. A device such as a guidewire  12  is contained within the lumen of the catheter  10 . There is provided clearance, shown as dimension  13 , between the inside diameter of the tip portion  11  and the outside diameter of the guidewire  12 . As further described by the side view of FIG. 2, when the catheter  10  is severely bent as is often the case when traversing tortuous vessels with the catheter  10  and guidewire  12 , the guidewire will offset to the inner meridian of the bent catheter  10 . The result is that a ledge  14  is created by the wall thickness of the tip portion  11  of the catheter  10  in combination with the operating clearance  13  between the guidewire  12  and inside diameter of the tip portion  11 . It is this ledge  14  that poses a risk of catching on the luminal surface of the vasculature.  
         [0023]    [0023]FIG. 3 describes a transverse cross section of a tip portion  11  of a catheter  10  of the present invention. Projecting from the luminal surface of the tip portion  11  are multiple bearings  30 , serving as centering means for any device, such as a guidewire  12 , exiting the tip portion  11 . These bearings  30  are preferably located only in the region of the tip portion  11 , with result that the operating clearance between the device and the luminal surface of the catheter  10  is maintained over the remainder of the length of the catheter  10 .  
         [0024]    Bearings  30  can be formed to provide a slight interference with a guidewire or other device intended to be passed through the lumen of the catheter. For example, an inside diameter of the catheter tip as measured between two opposing bearings, shown as inside diameter  16 , may interfere in an amount of about 0.025 to 0.050 mm with the outside diameter of the intended guidewire. The interference is of such a minimal amount that no perceptible increase in friction between the guidewire and catheter occurs.  
         [0025]    [0025]FIG. 3A is a transverse cross section of the catheter tip  11  of FIG. 3 further showing a device such as guidewire  12  centered within catheter tip  11 .  
         [0026]    While four bearings  30  are shown, it is apparent that at least three are required. At least four are preferred, and more than four may be used, such as five, six, seven, eight, nine, ten, etc.  
         [0027]    The transverse cross section of FIG. 3A includes a device such as guidewire  12  shown centered with bearings  30 . In a preferred embodiment, there is a slight interference fit between opposing bearings  30  and guidewire  12 . Typically, the inside diameter of the catheter tip portion  11  as measured between opposing bearings  30  will be slightly less than the outside diameter of guidewire  12 . For example, for a guidewire having an outside diameter of about 0.36 mm (a typical cardiology catheter), the inside diameter of tip portion  11  as measured between opposing bearings  30  will preferably be about 0.31 mm.  
         [0028]    The longitudinal cross section of FIG. 4 shows a preferred embodiment wherein bearings  30  take the form of longitudinally-oriented ribs  31 , substantially parallel to the longitudinal axis  20  of catheter  10 . The distal end of the catheter  10  is indicated by arrow  41  and the proximal end is indicated by arrow  42 . These ribs  31  are preferably of a length that limits them to the tip portion  11  of the catheter  10 . A typical length for ribs extending for the full length of the tip portion  11  would be about 3 mm. While their height (as measured perpendicularly from the luminal surface) is maximized at the very distal end of the tip portion  11 , they preferably merge into the luminal surface of the catheter  10  at their proximal end.  
         [0029]    Alternatively, as shown by the longitudinal cross section of FIG. 4A, the height of the bearings  30  may be kept substantially constant along the full length of each bearing, so that each bearing  30  exerts a relatively uniform force along its entire length against a guidewire or other device inserted through the catheter tip  11 .  
         [0030]    While the distal end of tip portion  11  is shown to be square, that is, cut off so as to be perpendicular to the longitudinal axis  20  of the catheter  10 , it may be made with various shapes. It is believed that the end should most preferably be round in longitudinal cross section.  
         [0031]    In another embodiment shown in the longitudinal cross section of FIG. 5, the bearings may take the form of ribs oriented other than longitudinally, such as helically-oriented ribs  33 . The longitudinal cross section of FIG. 6 shows still another alternative wherein bearings are in the form of small protrusions  35  of hemispherical or substantially hemispherical shape, located at the very distal end of tip portion  11 . It is apparent that various shapes may be used for the protruding bearing surfaces.  
         [0032]    [0032]FIG. 7 describes a transverse cross section of an alternative embodiment of the catheter tip  11  wherein the bearings  30  are not of rounded cross section. Rather, the bearings  30  in this instance are of a shape that provides a larger contact area against the surface of the centered device.  
         [0033]    [0033]FIG. 8 shows a transverse cross section of the catheter tip  11  representing a variation of the embodiment described by the transverse cross section of FIG. 3. FIG. 8 describes relieved areas  81  on the exterior surface of the catheter tip that are directly opposite the bearings  30  on the luminal surface. These relieved areas  81  reduce the resistance of the bearings and allow for a more flexible and less rigid catheter tip  11 .  
         [0034]    The bearings are preferably integral to the luminal surface of the catheter tip, being molded as a part of that surface during the manufacture of the catheter tip. The catheter including the tip with bearings can be fabricated of various materials and combinations of materials known to those of skill in the art of catheters, using methods known in this art. These materials include polymers such as amide-based thermoplastic elastomers, silicones, polyurethanes, polyamides and various fluorinated polymers including polytetrafluoroethylene and fluorinated ethylene propylene. Materials of particular durometer may be selected according to the degree of flexibility or rigidity desired. The catheter tubing may be reinforced with materials such as braided wires embedded in the catheter wall.  
         [0035]    Alternatively, the bearings may be separately affixed if desired, by, for example, the use of adhesives suitable for the materials involved and for the medical use. This offers the possibility of providing bearings that have a different degree of flexibility (or rigidity) from the material of the remainder of the catheter tip. For example, bearings may be made of individual, relatively short pieces of metal wire for additional tip rigidity and/or radiopacity. The wire can be exposed as the actual bearing surface. Alternatively, as shown in the transverse cross section of FIG. 9, wires  91  may be embedded in the material of the catheter tip if it is preferred that the exposed bearing surface is the same material as that of the catheter tip.  
         [0036]    [0036]FIGS. 10 and 11 describe longitudinal and transverse cross sections respectively of an alternative embodiment wherein a single bearing surface in the form of a circumferentially oriented raised ring-shaped bearing surface  101 , located at the luminal surface of the distal tip of the catheter. While the longitudinal cross section shows a semi-circular profile for the bearing surface, it is apparent that other shapes may also be used. While the ring may be continuous around the entire circumference of the luminal surface, it is apparent that the ring may be interrupted as with notches to render it into two or more circumferentially oriented bearing surfaces.  
         [0037]    [0037]FIGS. 12A and 12B describe sequential side views of the catheter tip (with the catheter  10  and tip  11  shown in cross section) as used to capture and collapse an embolic filter  121 . For this application, the catheter tip  11  is made from an elastomeric material such as silicone, which allows the catheter tip portion  11  to slightly increase in diameter by stretching to accommodate the capture and collapse of the embolic filter  121  as shown. The tip aids in collapsing the filter  121  to a smaller size for removal from the vasculature and ensures that material captured in filter  121  is also withdrawn via the catheter  10 . Bearings  30  are preferably of a more rigid material than the catheter tip  11 , providing column strength that prevents the tip  11  from rolling inward and buckling.  
         [0038]    While the principles of the invention have been made clear in the illustrative embodiments set forth herein, it will be obvious to those skilled in the art to make various modifications to the structure, arrangement, proportion, elements, materials and components used in the practice of the invention. To the extent that these various modifications do not depart from the spirit and scope of the appended claims, they are intended to be encompassed therein.