Abstract:
An intravascular catheter including a proximal stiff metallic tube and a distal flexible tube. A distal portion of the metallic tube has a portion removed to define a void (e.g., spiral slot) which decreases the stiffness of the metallic tube. A proximal portion of the distal flexible tube is disposed in the void to provide a secure connection and to blend the stiffness of the metallic proximal tube and the flexible distal tube without significantly increasing profile.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to catheters. More specifically, the present invention relates to intravascular microcatheters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Intravascular catheters are used to diagnose and treat a wide variety of vascular diseases in various parts of the human vasculature. To access the cerebral vasculature, as well as other remote and tortuous vascular sites, it is desirable to have a catheter that has good navigational capabilities.  
         SUMMARY OF THE INVENTION  
         [0003]    To address this need, the present invention provides, in one example, an intravascular microcatheter having a relatively stiff proximal shaft (e.g., super elastic hypotube) for pushability and torqueability. The microcatheter also includes a relatively flexible distal shaft portion (e.g., coil reinforced multi-layered gradient polymer tube) for trackability. To provide a smooth transition between the relatively stiff proximal shaft and the relatively flexible distal shaft, a transition region is provided by integrating portions of the proximal shaft and portions of the distal shaft in a manner that provides a secure connection and that minimizes profile increase. The result is a low profile microcatheter having superior response and control to navigate through tortuous vasculature to remote vascular sites.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a schematic plan view of an intravascular microcatheter in accordance with an embodiment of the present invention;  
         [0005]    [0005]FIG. 2 is a longitudinal sectional view taken along line  2 - 2  in FIG. 1;  
         [0006]    [0006]FIG. 3 is a cross-sectional view taken along line  3 - 3  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 catheter  10  in accordance with an embodiment of the present invention. For purposes of illustration only, the catheter  10  is shown in the form of an intravascular microcatheter, but the catheter  10  may comprise virtually any catheter used for intravascular applications. By way of example, the length, profile, pushability, trackability, and other performance characteristics of the microcatheter  10  may be selected to enable intravascular insertion and navigation to the cerebral vasculature.  
         [0010]    In the embodiment illustrated, the microcatheter  10  may include a relatively stiff proximal portion  12  for pushability and torqueability. The microcatheter  10  may also include a relatively flexible distal portion  14  for trackability. The proximal shaft portion  12  may comprise a super elastic alloy (e.g., nitinol) hypotube  20 , and the distal shaft portion  14  may comprise a coil reinforced multi-layer tube  30 . To facilitate a smooth transition between the relatively stiff proximal shaft portion  12  and the relatively flexible distal shaft portion  14 , a transition section  16  may be utilized as described in more detail hereinafter.  
         [0011]    The microcatheter  10  may include a lumen  40  (as best seen in FIGS.  2 - 4 ) extending therethrough to facilitate the delivery of fluids (e.g., thrombolytic agents, radiopaque dye, saline, drugs, etc.) therethrough, and/or to facilitate the insertion of other medical devices (e.g., occlusive coils, guide wires, balloon catheters, etc.) therethrough. To provide access to the lumen  40  and to facilitate connection to ancillary devices, the microcatheter  10  may include a hub or manifold  18  connected to the proximal end of the proximal shaft portion  12 . The lumen  40  may extend through the entire length of the microcatheter  10  (i.e., through hub  18 , proximal shaft portion  12 , mid-shaft transition portion  16 , and distal shaft portion  14 ) to establish a path from a point outside the patient&#39;s body to a remote site within the patient&#39;s vascular system.  
         [0012]    With reference to FIGS.  2 - 4 , the proximal  12 , distal  14 , and transition  16  sections of the shaft will be discussed in more detail.  
         [0013]    As mentioned above, the proximal shaft section  12  may include a metallic hypotube  20  formed of a super elastic material such as a nickel titanium alloy, or other suitable material such as stainless steel. For example, the hypotube  20  may comprise nitinol having a length of about 120-150 cm and a wall thickness of about 0.0015-0.004 inches. A portion of the distal end of the hypotube  20  may be removed to define one or more voids  22 . In the example shown, the voids  22  comprise a helical or spiral slot cut into the wall of the hypotube  20  utilizing a suitable process such as laser cutting. The helical slot  22  may have a width of about 0.0002 inches or more, and may have a pitch which varies linearly from proximal to distal to gradually reduce the stiffness of the hypotube  20 . For example, the distal 60 cm may be laser cut to define a helical slot  22 , with the proximal segment having a pitch that gradually reduces from about 0.10 inches to about 0.001 inches, with the remaining distal segment having a constant/continuous pitch of about 0.001 inches. Alternatively, the pitch may gradually reduce through the distal segment as well.  
         [0014]    Those skilled in the art will recognize that the voids  22  may comprise a variety of geometries, including without limitation, a continuous slot as shown, a series of slots or holes distributed around the circumference and length of the hypotube  20 , etc. In addition, the voids  22  may extend completely through the wall of the hypotube  20  or may simply form a recess therein.  
         [0015]    The distal shaft section  14  may include an inner liner  32  formed of a lubricious polymer such as PTFE or HDPE. An inner layer  34  comprising a polymer such as polyether block amide (e.g., PEBAX) may be placed over the inner liner  32 . The outside diameter of the inner layer  34  may be approximately 0.001 inches smaller than the inside diameter of the hypotube  20  to allow the inner liner  32  and the inner layer  34  to be disposed therein. The inner liner  32  and the inner layer  34  may extend through the transition region  16  of the hypotube  20 , or through the entire length of the hypotube  20  including the transition region  16  and the proximal shaft portion  12 .  
         [0016]    For example, the inner liner  32  and the inner layer  34  may extend through the entire length of the hypotube  20 , with  30  cm extending beyond the distal end of the hypotube  20 . With the assistance of a support mandrel disposed in the lumen of the combined inner liner  32  and inner layer  34 , the same  32 / 34  may be inserted into the proximal end of the hypotube  20  and advanced until the distal end thereof extends 30 cm beyond the distal end of the hypotube  20 . As it is being advanced, a suitable adhesive such as cyanoacrylate may be applied to the outer surface of the proximal  10  cm of the inner layer  34  for securement to the inside surface of the proximal end of the hypotube  20 . At this time, the hub  18  may be connected to the proximal end of the hypotube shaft  20 .  
         [0017]    Optionally, a reinforcement layer  36  such as a single coil, multiple coils, or multiple interwoven coils (i.e., a braid) may be disposed over the combined inner liner  32  and inner layer  34  extending beyond the distal end of the hypotube  20 . The reinforcement layer may comprise round wire or rectangular ribbon wire, for example. A proximal portion of the reinforcement layer  36  may be disposed in the voids  22  to provide a secure, low profile connection to the distal end of the hypotube  20 , and to prevent migration of the reinforcement layer  36 . For example, if the reinforcement layer  36  comprises a single coil and the voids  22  define a helical slot, the coil  36  may be wound into one or more of the distal slots.  
         [0018]    Other portions of the distal composite shaft section  30  may be disposed in the voids  22  in addition to or in place of the coils  36 . For example, a portion of the inner layer  34  and/or outer layer  38  may be disposed in the voids  22  to modify or enhance the connection between the distal composite shaft  30  and the proximal hypotube shaft  20 .  
         [0019]    An outer layer  38  formed of a suitable polymeric material may then be placed over the transition region  16  and the distal shaft section  14 , and optionally over the proximal shaft section  12  as well. In particular, the outer layer  38  may extend from a point  24  on the hypotube  20  proximal of the spiral cut  22  to the terminal end of the combined inner liner  32 , inner layer  34 , and coil reinforcement layer  36 . The outer layer may be formed of a flexible polymer such as polyether block amide (e.g., PEBAX), and may have a gradual transition in flexibility as provided by the gradient extrusion process described in co-pending patent application Ser. No. 09/430,327, entitled METHOD AND APPARATUS FOR EXTRUDING CATHETER TUBING, the entire disclosure of which is hereby incorporated by reference. By way of example, not limitation, the outer layer  38  may comprise a polyether block amide (e.g., PEBAX) polymer tube formed by gradient extrusion, with a durometer transitioning from  55 D to  25 D from proximal to distal. The gradient transition in the outer layer  38  provides superior flexibility, response, and control, while contributing to the smooth transition  16  from the relatively stiff proximal section  12  to the relatively flexible distal section  14 . Alternatively, the outer layer  38  may comprise a polymer tube having a continuous durometer, or a series of connected polymer tubes having different durometers.  
         [0020]    From the foregoing, it will be apparent to those skilled in the art that the present invention, in one exemplary embodiment, provides an intravascular microcatheter  10  having a relatively stiff proximal hypotube shaft  20  for pushability and torqueability, and a relatively flexible distal composite shaft  30  for trackability. To provide a smooth transition between the relatively stiff proximal shaft  12  and the relatively flexible distal shaft  14 , a transition region  16  is provided by integrating portions of the proximal shaft (e.g., spiral cut  22  portion of the hypotube  20 ) and portions of the distal shaft (e.g., coil reinforcement  36 ) in a manner that provides a secure connection and that minimizes profile increase.  
         [0021]    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.