Abstract:
Intravascular catheters having a curved portion subjected to heat at or above the melt temperature thereof to reduce residual stress and eliminate heat history.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to catheters for performing medical procedures. More particularly, the present invention relates to intravascular catheters having a curved portion.  
         BACKGROUND OF THE INVENTION  
         [0002]    A wide variety of intravascular catheters have been developed to diagnose and treat vascular diseases. Some types of catheters include a curved or shaped distal portion in order to facilitate navigation of the catheter through the vasculature. Formation of the curved portion usually comprises shaping and heat treating the distal end of the catheter below the melting point of the polymers contained therein, which may result in undesirable physical properties.  
         SUMMARY OF THE INVENTION  
         [0003]    To reduce or eliminate such undesirable physical properties, the present invention provides design and manufacturing alternatives for catheters having a shaped or curved portion as described in more detail hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a plan view of a catheter including a shaped distal portion according to an embodiment of the invention, together with a retention sleeve; and  
         [0005]    [0005]FIG. 2 is an enlarged view of the shaped distal portion of the catheter shown in FIG. 1, together with a retention sleeve and a forming mandrel.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0006]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings illustrate embodiments by way of example, not limitation.  
         [0007]    [0007]FIG. 1 is a plan view of a catheter  10  comprising an elongate shaft  12  having a proximal end  14 , a distal end  16 , and a shaped distal portion  20 . Shaped distal portion  20  includes at least one polymeric segment and/or layer which allows the distal portion  20  to be formed by shaping and heat treating it to a temperature above the melting point of one or more of the polymeric segment(s) and/or layer(s). It is believed that heat treating to temperatures above the melting point of the polymeric segment(s) or layer(s) of the distal portion  20  may eliminate heat history, residual stress, and morphological orientation and may restore the original physical properties of catheter  10 . Such heat treating is not limited to the distal portion  20 , but may be equally applicable to any portion of catheter  10 , including shaped and straight portions, to eliminate heat history, residual stress, and morphological orientation.  
         [0008]    As used herein, heat treating is understood to be mean a thermal process of exposing or generating heat in the polymeric segment(s) or layer(s). Heat treating may be accomplished by a number of methods and techniques. For example, heat treating may include exposure of the polymeric segment(s) or layer(s) of the distal portion  20  to infrared energy, radio frequency electromagnetic energy, radiant heating, laser energy, etc. Alternatively, the polymeric segment(s) or layer(s) of the distal portion  20  may be placed into an oven or a die that is coupled to a heat source. A person of ordinary skill in the art will be familiar with heat treating techniques appropriate for multiple embodiments of the invention.  
         [0009]    Catheter  10  may comprise any one of multiple different catheter types. These catheter types include, but are not limited to, a guide catheter, a diagnostic catheter, a balloon catheter, an atherectomy catheter, etc. A person of ordinary skill in the art will be familiar with different types of catheters appropriate for multiple embodiments of the present invention. For purposes of illustration only, catheter  10  is depicted in FIG. 1 as a guide catheter.  
         [0010]    A manifold  18  may be disposed at proximal end  14  of elongate shaft  12 . Manifold  18  may comprise a single-port adapter (as shown) for a guide catheter, or a double-port adapter, a multi-port adapter, a connector, etc., depending on the type of catheter selected. A therapeutic or diagnostic device (not shown) such as an inflatable balloon or a rotating burr may be connected to distal end  16  of elongate shaft  12 , depending on the type of catheter selected. The elongate shaft  12  may also incorporate one or more lumens and/or mechanisms necessary to operate such therapeutic and diagnostic devices.  
         [0011]    Elongate shaft  12  may be generally tubular and may be manufactured from a number of materials including, but not limited to, polymers such as polyoxymethylene (POM), polybutylene terephthalate (PBT), polyether block ester available under the trade name ARNITEL, polyether block amide (PEBA), fluorinated ethylene propylene (FEP), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyurethane, polytetrafluoroethylene (PTFE), polyether-ether ketone (PEEK), polyimide, polyamide, polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polysufone, nylon, and perfluoro(propyl vinyl ether) (PFA); polymer/metal composites including any of the polymers described above in combination with a metallic reinforcement such as a coil or braid formed of stainless steel, nickel alloy, or nickel-titanium alloy; and combinations thereof. Elongate shaft  12  may be manufactured so as to maintain a level of flexibility and torquability appropriate for maneuvering catheter  10  through the vasculature. For example, shaped portion  20  may comprise a polymer/metal composite having an inner lubricious polymer layer (e.g., PTFE), an intermediate reinforcement layer (e.g., SST braid), and an outer polymeric layer (e.g., PEBA) to facilitate thermal processing as described in more detail below.  
         [0012]    The shaped distal portion  20  is conventionally included to aid in the advancement of catheter  10  through the vasculature. For example, the shaped distal portion  20  may aid navigation of the catheter  10  over the aortic arch to access a coronary artery. The shaped distal portion  20  is typically formed by shaping and holding the catheter  10  in a configuration having a curve near distal end  16  and then heat treating catheter  10  to a temperature below the melting point of all polymers contained in the shaft  12 .  
         [0013]    Such shaping and heat treating of the catheter  10 , followed by cooling thereof, imparts and maintains the shape or curve of the distal portion  20 . However, such shaping and heat treating catheters may also lead to changes in the physical properties of catheter  10 . For example, shaping and heating may increase the residual stress, alter the morphological orientation of particles within elongate shaft  12 , and/or alter stiffness of elongate shaft  12 . Changes in these and other physical properties may compromise the intended physical characteristics contemplated during the design of catheter  10 .  
         [0014]    It is therefore desirable, in some cases, to restore the virgin or original characteristics of the polymeric materials contained within the shaped distal portion  20  or other portions of the elongate shaft  12 . Although annealing, tempering, or other similar thermal processing techniques may be utilized to alleviate a limited amount of residual stress and restore to a limited degree the original morphological orientation, such techniques only heat the polymeric materials to a temperature below the melting point thereof, which may not completely accomplish the objective. Thus, heat treating the distal portion  20  or any other portion of the shaft  12  to a temperature below the melting point of the polymers contained therein may be sub-optimal and may compromise the intended performance of the catheter  10 .  
         [0015]    To avoid such a compromise, the present invention provides design and manufacturing alternatives for constructing catheter  10  having a distal shaped portion  20  that is formed by thermal processing above or equal to the melting temperature of the polymers contained therein.  
         [0016]    For example, if the polymer(s) of the distal portion  20  comprise a blend of 10% ARNITEL brand polyether block ester and 90% PBT, the distal portion  20  may be heated to a temperature of 480 F for 2 minutes to have the desired effect. Also by way of example, if the polymer(s) of the distal portion  20  comprise DELRINE brand POM, the distal portion  20  may be heated to a temperature of 400 F for 4 minutes to have the desired effect.  
         [0017]    Because heat treating the shaped distal portion  20  involves raising the temperature of the polymers contained therein to a point greater than or equal to the melting point thereof, it may be desirable to utilize a retention sleeve  22  during the thermal processing. The retention sleeve functions to maintain the outer shape and structure of the distal portion  20  and to prevent the molten polymers from flowing. The sleeve  22  may extend over all or a portion of the elongate shaft  12 , depending on the length of the shaft  12  exposed to the heat. After thermal processing and cooling, the sleeve  22  may be removed or left thereon to reduce polymeric creep (i.e., to retain the shape of the distal portion  20 ).  
         [0018]    As mentioned above, one of the purposes for including sleeve  22  is to maintain the shape and structure of elongate shaft  12  during heating. Because the temperature of elongate shaft  12  may equal or exceed the melting point of the polymers contained therein, molten polymeric portions of elongate shaft  12  may flow and cause unwanted deformation. The sleeve  22 , thus, provides a physical barrier for preventing molten or partially molten portions of elongate shaft  12  from flowing away from their intended position and thus preserves the shape and structure of the outside surface of catheter  10 . To better serve this function, the sleeve  22  may have a melting temperature that is greater than that of the polymeric materials of elongate shaft  12  being heat treated. The sleeve  22  may comprise, for example, a heat shrink tube made of fluorinated ethylene propylene.  
         [0019]    [0019]FIG. 2 is an enlarged view of the shaped distal portion  20 , together with the sleeve  22  and a mandrel  28 . The mandrel  28  may be disposed within the elongate shaft  12  (e.g., within a lumen of elongate shaft  12 ) to extend through the distal portion  20  and/or other portions of the shaft  12  subject to heat treatment. As with the sleeve  22 , the mandrel  28  provides a physical barrier to prevent molten or partially molten portions of elongate shaft  12  from flowing away from their intended position and thus preserves the shape and structure of the inside surface of catheter  10 . The combination of the sleeve  22  and the mandrel  28  provide barriers for both the inside surface and the outside surface of the portion(s) of the elongate shaft  12  subject to heat treatment.  
         [0020]    As mentioned previously, the entire shaft  12  may be subject to heat treatment, or the heat treating process may be localized to a portion of elongate shaft  12 . For example, heat exposure or generation may occur only along portions of elongate shaft  12  where the sleeve  22  is disposed thereon. In other words, the heat treatment zone may be limited to the region between the proximal  24  and distal  26  ends of the sleeve  22 . When utilizing localized heat treatment, the unheated portions of the shaft  12  serve to limit molten polymer flow at the respective ends of the heat treatment zone.  
         [0021]    For example, the heat treatment zone may be limited to a region between the proximal end  24  and distal end  26  of the sleeve  22 . In this scenario, the length of the elongate shaft  12  not covered by the sleeve  22  would not be subject to heat treating, and thus would not be molten. These non-molten sections of elongate shaft  12  serve as a barrier for preserving the shape and structure of elongate shaft  12  at the ends of the heat treatment zone. When the sleeve  22  and the mandrel  28  are used in this scenario, essentially all sides of elongate shaft  12  subject to heat would have structural support during heat treatment.  
         [0022]    If the entire length of the shaft  12  were exposed to heat, or if localized heat were applied to the distal end  16  of the shaft  12 , there would not be a non-molten portion of the shaft  12  at the distal end of the heat treatment zone. In this scenario, a cap  30  coupled to a distal end  32  of the mandrel  28  may be used to prevent the flow of molten polymeric material at the distal extremity  16 . In this embodiment, the cap  30  may abut the distal end  16  of elongate shaft  12  and the distal end  26  of the sleeve  22  to provide structural support. Alternatively, the sleeve  22  may incorporate an inward facing flange at the distal end  26  thereof to serve the same function. Those skilled in the art will recognize alternative designs and arrangements to accomplish the same function.  
         [0023]    It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, arrangement of parts and order of steps without departing from the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.