Abstract:
A catheter to be used without a guidewire which includes a support wire shaft formed of metal, a balloon mounted on a distal portion of the catheter, and an inflation shaft for inflating the balloon, wherein a core wire may be interchangeably inserted into the support wire shaft when the catheter is within a human body to change the stiffness and improve control thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to catheters, and more particularly to catheters with variable stiffness that may be used with an interchangeable core wire.  
           [0003]    2. Background of the Invention  
           [0004]    Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.  
           [0005]    One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. Radial expansion of the coronary artery occurs in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen. The wall of the artery itself is also stretched when the balloon is inflated.  
           [0006]    One or multiple dilations may be necessary to effectively dilate the artery. In many instances, multiple dilations using multiple “over-the-wire” balloon catheters having balloons with increasingly larger diameters may be required. An over-the-wire catheter is one where a guidewire lumen is provided so that the catheter can be guided to the stenosis site by running the entire catheter length along the guidewire.  
           [0007]    Conventional angioplasty guidewire typically include a proximal shaft, an intermediate section and a flexible distal tip. The proximal shaft comprises a solid wire or a solid wall tube. The proximal shaft primarily functions to guide and support a catheter, and to smoothly transmit rotation from the proximal end to an intermediate section.  
           [0008]    The intermediate section extends axially from the proximal shaft and generally comprises a tapered core wire surrounded by a coiled spring and typically has more flexibility than the proximal shaft. Like the proximal shaft, the intermediate section must assist in guiding the catheter and smoothly transmitting rotation. However, some degree of flexibility in the intermediate section is desirable to conform the catheter to the curvature of the aortic arch and the coronary arteries.  
           [0009]    In a typical procedure, a physician will first insert and advance a guidewire to the stenosis site. An initial over-the-wire balloon dilation catheter having a fairly small diameter balloon is then passed over the guidewire to the site and the balloon is inflated to partially dilate the vessel. The balloon is then deflated and the catheter withdrawn. Balloon catheters having progressively larger balloons are then advanced to the stenosis along the guidewire, inflated, deflated, and then withdrawn in succession to sufficiently enlarge the lumen of the artery.  
           [0010]    All balloon catheters include an inflation lumen through which a fluid can be forced to pressurize the balloon. As such, balloon catheters having a full-length guidewire lumen, must have at least two lumens. Catheters having more than one lumen are commonly referred to as “dual-lumen” or “multi-lumen” catheters.  
           [0011]    Multi-lumen catheters have cross-sections in a variety of shapes. FIGS. 1 and 2 are examples of prior art dual lumen catheter cross-sections. FIG. 1 is a cross-section of coaxial catheter  100 . Coaxial catheter  100  includes inner tube  102  and outer tube  104 . Inner tube  102  defines an inner lumen or guidewire lumen  108  adapted to receive guidewire  106 . Annular inflation lumen  110  is defined between inner tube  102  and outer tube  104 , and is in fluid communication with an interior of a dilatation balloon (not shown).  
           [0012]    In use, a guidewire is introduced into a coronary artery and is steered by manipulation of its proximal end, while being observed under a fluoroscope, until the guidewire passes through a stenosis in the artery. Once the guidewire is in place, a balloon dilatation catheter is advanced over the guidewire, being thus guided directly to the stenosis so as to place the balloon within the stenosis. Once so placed, the balloon is inflated under substantial pressure to dilate the stenosis.  
           [0013]    The anatomy of coronary arteries varies widely from patient to patient. Often a patient&#39;s coronary arteries are irregularly shaped and highly tortuous. The tortuous configuration of the arteries may present difficulties to the physician in proper placement of the guidewire, and advancement of the catheter to the site of the stenosis. A highly tortuous coronary anatomy typically will present considerable resistance to advancement of the catheter over the guidewire.  
           [0014]    With some types of catheter construction, the increased resistance may cause a tendency for portions of the catheter to collapse or buckle axially. For example, in a catheter having a shaft formed from inner and outer coaxial tubes, such as is shown in FIG. 1, and a balloon mounted to the distal ends of the tubes, there may be a tendency for the tubes to “telescope” when presented with an increase in resistance. The telescoping of the tubes tends to draw the ends of the balloon together slightly, but sufficiently to permit the balloon to become bunched-up as it is forced through the stenosis. The bunching-up of the balloon makes it more difficult for the balloon to cross the stenosis.  
           [0015]    Additionally, it is sometimes necessary for the physician to place a torque load on the guidewire in an effort to overcome resistance encountered in a vessel. Torque is also used to steer the guidewire through separate passages and bifurcation of the anatomy. A torque load applied to a coaxial catheter can cause the outer tube to twist, while the inner tube remains stationary, causing a rotation of the tubes relative to one another.  
           [0016]    [0016]FIG. 2 shows a cross-sectional view of a non-coaxial dual-lumen catheter  200 . An inflation lumen  202  is in fluid communication with an interior of a dilatation balloon (not shown). A guidewire lumen  204  is defined at least in part by an inner tubular member  206  which extends the entire length of the catheter body. A guidewire  208  is shown within guidewire lumen  204 . As explained above, catheter  200  is slid over guidewire  208  through a tortuous blood vessel.  
           [0017]    However, once a catheter is selected and tracked over a guidewire inserted in a patient&#39;s vasculature, the physician may discover that the catheter has insufficient stiffness at its distal end to cross a lesion. This limits the use of such catheters in many procedures. Accordingly, a need exists for a physician to be able to change (for example, to increase) the stiffness of a catheter being used to traverse a particularly difficult lesion without removing the catheter from the patient&#39;s vasculature.  
         BRIEF SUMMARY OF THE INVENTION  
         [0018]    The present invention is directed to a catheter that substantially obviates one or more of the problems and disadvantages of the related art.  
           [0019]    There is provided a dilatation catheter including a hollow support wire shaft formed of metal or plastic, such that a core wire may be interchangeably inserted into the support wire shaft when the catheter is within a body lumen. A balloon is mounted on a distal portion of the catheter and an inflation shaft is coupled to the balloon.  
           [0020]    A proximal portion of the support wire shaft is arranged side-by-side with a proximal portion of the inflation shaft. However, a transition area is provided wherein a distal portion of the support wire shaft proximal of the balloon becomes coaxial with a distal portion of the inflation shaft where the inflation shaft is in fluid communication with the balloon.  
           [0021]    In one embodiment of the invention, the support wire shaft is bonded to the inflation shaft over a substantial portion of their proximal length. In another embodiment, a jacket encapsulates and secures a substantial portion of the proximal length of the support wire shaft and the inflation shaft.  
           [0022]    A distal portion of the support wire shaft that extends distally of the balloon is constructed to be more flexible than a portion of the support wire shaft proximal of the balloon. In one embodiment, a metal coil forms a distalmost portion of the support wire shaft distal of the balloon and imparts additional flexibility and maneuverability to the catheter. In another embodiment, a portion of the support wire shaft includes a helical slit to gradually decrease stiffness of the support wire shaft as it extends just proximal of, through and distal of the balloon. A metal coil may then be utilized at a distalmost end of the helical slit portion of the support wire shaft to further increase the flexibility and maneuverability of the catheter thereof.  
           [0023]    A dilatation catheter according to the present invention also includes a core wire locking mechanism that is used to secure a core wire relative to the support wire shaft in which it is inserted. However, a catheter in accordance with the present invention is constructed to be sufficiently stiff to traverse a tortuous path within a patient&#39;s vasculature without a core wire inserted within the support wire shaft.  
           [0024]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0025]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:  
         [0027]    [0027]FIG. 1 is a cross-sectional view of a prior art coaxial catheter;  
         [0028]    [0028]FIG. 2 is a cross-sectional view of a prior art dual lumen non-coaxial catheter;  
         [0029]    [0029]FIG. 3 is a schematic view of a balloon catheter assembly according to the present invention;  
         [0030]    [0030]FIG. 4 is a cross-section of an embodiment of a proximal catheter shaft according to the present invention across line C-C of FIG. 3;  
         [0031]    [0031]FIG. 5 is a cross-section across line B-B of FIG. 3;  
         [0032]    [0032]FIG. 6 is a cross-section across line A-A of FIG. 3;  
         [0033]    [0033]FIG. 7 is an expanded view of a distal portion of the catheter of the present invention;  
         [0034]    [0034]FIG. 8 is an expanded view of a transition area proximal of a balloon of the catheter of the present invention;  
         [0035]    [0035]FIG. 9 is an expanded view of a coil tip of the catheter of the present invention;  
         [0036]    [0036]FIG. 10 is an expanded view of a balloon portion of the catheter of the present invention;  
         [0037]    [0037]FIG. 11 is an expanded view of an intermediate bond area of the catheter of the present invention;  
         [0038]    [0038]FIG. 12 is an expanded area of a skive portion area of the catheter of the present invention;  
         [0039]    [0039]FIG. 13 illustrates a cross-section of another embodiment of a proximal catheter shaft of the present invention across line C-C of FIG. 3 with an overjacket shown;  
         [0040]    [0040]FIG. 14 illustrates a cross-section of another embodiment of a proximal catheter shaft according to the present invention across line C-C of FIG. 3 illustrating an alternative inflation shaft shape;  
         [0041]    [0041]FIG. 15 illustrates a cross-section of another embodiment of a proximal catheter shaft according to the present invention across line C-C of FIG. 3 illustrating integrally formed shafts;  
         [0042]    [0042]FIG. 16 is a view of FIG. 7 with a core wire inserted;  
         [0043]    [0043]FIG. 17 shows a screw and nut type wire lock mechanism of the present invention;  
         [0044]    FIGS.  18 A- 18 B show a lever type wire lock mechanism of the present invention;  
         [0045]    [0045]FIG. 19 shows a chuck (or bushing) type wire lock mechanism of the present invention;  
         [0046]    [0046]FIG. 20 shows a cross-section of a coil tip and hypotube joint of the present invention; and  
         [0047]    [0047]FIG. 21 shows a cross-section of a butt joint of the hypotube and coil tip of the present invention.  
         [0048]    [0048]FIG. 22 shows an embodiment of the catheter of the present invention using a coaxial arrangement of inflation shaft and support wire shaft. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]    The embodiments of the present invention are now described with reference to the figures where like reference numbers indicate identical or functionally similar elements. While specific materials and method steps are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other materials or method steps can be used.  
         [0050]    Referring first to FIG. 3, an embodiment of a dilatation catheter  301  is shown. Dilatation catheter or balloon catheter  301  includes a proximal portion  330  and a distal portion  331 . Proximal portion  330  of catheter  301  includes a luer hub (“inflation luer”)  320 . Distal portion  331  of catheter  301  includes a dilatation balloon  308 . An interior of balloon  308  is in fluid communication with an external source of inflation fluid through an inflation shaft  304 . As may be further seen from FIG. 3, distal portion  331  of catheter  301  includes a flexible coil tip  311  and a hemispheric end cap  312 .  
         [0051]    Catheter  301  includes two shafts (tubular members), a support wire shaft  303  and inflation shaft  304 , which are arranged side-by-side substantially along the length of proximal portion  330  and transition to a coaxial arrangement in distal portion  331 . The structure of catheter  301  of the present invention may therefore be referred to as a multi-lumen structure. Support wire shaft  303  is hollow and extends distal of balloon  308  to flexible coil tip  311 . Support wire shaft  303  is flexible enough to function as a catheter, but stiff enough to act as a guide wire with or without an additional core wire. Support wire shaft  303  includes a variable pitch spiral cut (helical cut) portion  310  (a hollow inner member) that preferably begins proximal of balloon  308  and ends at flexible coil tip  311 . Note that spiral cut portion  310  distal of balloon  308  is where having changing stiffness characteristics of catheter  301  (e.g., to make catheter  301  more flexible) is particularly advantageous.  
         [0052]    Inflation shaft  304  includes a skive portion  314 , where inflation shaft  304  transitions to a distal tubing portion  307 , which is coaxial with support wire shaft  303 . Skive portion  314  is positioned approximately 25-30 cm proximal of balloon  308 , and is about 5-7 cm long. Skive portion  314  provides a transition in stiffness from higher stiffness to lower stiffness moving from proximal to distal direction. Distal tubing portion  307  is coupled to a proximal end of balloon  308 .  
         [0053]    Further, as shown in FIG. 3, inflation luer  320  includes a wire lock  321 . Wire lock  321  is used to lock an inserted core wire in place (not shown in FIG. 3, but see FIG. 16, which shows a core wire (support wire)  1616  inserted in catheter  301 ) such that the core wire moves with catheter  301 , i.e., in tandem with catheter  301 .  
         [0054]    Support wire shaft  303  is preferably ahypotube throughout its length, thus being sufficiently stiff to act as a guidewire. Accordingly, catheter  301  of the present invention is usable without core wire  1616 , since it possesses both the necessary flexibility to navigate tortuous arteries, and yet has necessary stiffness and trackability to cross lesions therein. Additionally, support wire shaft  303  is hollow and adapted to have core wire  1616  inserted into it, such that a distal end of core wire  1616  extends through balloon  308  to flexible coil tip  311 , thereby traversing an interior of balloon  308  through support wire shaft  303 . In addition, core wire  1616  is insertable through support wire shaft  303  to reach and be inserted into a length of flexible coil tip  311 .  
         [0055]    Flexible coil tip  311  is typically hollow, and is welded to a distal portion of support wire shaft  303  so that core wire  1616  may be advanced therethrough to end cap  312  (see also FIGS.  20 - 21  and corresponding discussion below). An optional recess may be provided in a distal portion of support wire shaft  303 , to facilitate the welding of coil tip  311  to support wire shaft  303 . End cap  312  is typically roughly hemispherical in shape.  
         [0056]    Both support wire shaft  303  and inflation shaft  304  may be hypotubes, made of surgical grade stainless steel, such as No. 304 or No. 316. Alternatively, both or either may be made of polymeric materials, such as polyamide or Grilamide. Alternatively still, both or either may be made of a composite metal-polymer material. Generally, the selection of the material will depend on the degree of stiffness desired and the dimensions and wall thickness needed, particularly from support wire shaft  303 . Both support wire shaft  303  and inflation shaft  304  can be manufactured using a metal extrusion process or a polymer extrusion process. Inflation shaft  304  can also be made from such materials as AESN, and polymeric materials including silicone rubber, polypropylene, polyethylene, polyvinylchloride, fluoropolymers and the like or other dielectric materials, as would be apparent to one skilled in the relevant art.  
         [0057]    Inflation shaft  304  is in fluid communication with balloon  308 , and is used to inflate and deflate balloon  308 . After balloon catheter  301  is properly positioned in a blood vessel, an inflation fluid is forced through inflation shaft  304  to inflate balloon  308 , forcing balloon  308  to expand against the interior of the blood vessel. After expansion, balloon  308  is deflated through the same inflation shaft  304  used for inflation, and catheter  301  is withdrawn.  
         [0058]    Balloon  308  is formed of a thin pliable material capable of expanding from a compact, collapsed state to an expanded diameter. Balloon  308  may be formed from polyethylene teraphthalate (PET) using a drawing and blow molding process so as to provide biaxial orientation to the material. PET balloons exhibit the desirable properties of high burst strength and relatively low radial expansion when inflated to high pressures. Alternatively, balloon  308  may be formed from polyethylene, polypropylene, polyvinyl chloride or other material, as would be apparent to one skilled in the relevant art. Balloon  308  is approximately 2-4 cm long and is attachable to distal portion  331  of catheter  301  by methods known in the art, including gluing, melting or welding.  
         [0059]    [0059]FIG. 4 illustrates a cross-section across line C-C of FIG. 3. As shown in FIG. 4, catheter  301  of the present invention includes the two shafts side-by-side, support wire shaft  303  and inflation shaft  304 . It will be appreciated that although inflation shaft  304  is shown as being smaller in diameter then support wire shaft  303 , this need not be the case. Generally, inflation shaft  304  needs to have a diameter such that balloon  308  can be deflated in approximately 10-15 seconds. At the same time, there is market demand for catheters with low profiles. Similarly, the dimensions of support wire shaft  303  are sufficient for core wire  1616  to fit within and slide through support wire shaft  303 . Core wire  1616  does not need to be as big in diameter as conventional guide wires. Support wire shaft  303  should be slightly larger in diameter than core wire  1616 , for example, by about 0.001 to 0.005 inches.  
         [0060]    [0060]FIG. 5 shows a cross-section across line B-B of FIG. 3. As may be seen from FIG. 5, and also in FIGS. 7 and 8, support wire shaft  303  in distal portion  331  just proximal of, within and distal of balloon  308  includes spiral cut portion  310  that acts to increase the flexibility of support wire shaft  303 .  
         [0061]    [0061]FIG. 6 shows a cross-section of FIG. 3 across line A-A, which illustrates flexible coil tip  311  of catheter  301  of the present invention. An outer diameter of flexible coil tip  311  is generally comparable to an outer diameter of spiral cut portion  310  of support wire shaft  303 . Flexible coil tip  311  is typically made from a small diameter steel wire, such as no. 304 or 316 grade stainless steel wire, and is wrapped around a mandril into the shape shown in FIGS. 7 and 9. Other possible materials for flexible coil tip  311  include Nitinol, and MP35N. Flexible coil tip  311  is the most flexible part of catheter  301 . Coil tip  311  terminates with the (roughly) hemispheric end cap  312 .  
         [0062]    [0062]FIGS. 7 and 8 show an enlarged view of distal portion  331  of catheter  301  of the present invention. As may be seen from FIGS. 7 and 8, moving from a proximal position to a distal position, catheter  301  of the present invention includes inflation shaft  304  and support wire shaft  303 , which are positioned substantially side-by-side (generally adjacent to each other). In skive portion  314 , inflation shaft  304  gradually transitions to a transition tube  805 , in an intermediate transition bond area  800  of catheter  301 . Transition tube  805  is typically more flexible than inflation shaft  304 . Transition tube  805  is bonded to distal tubing portion  307  with a transition bond (joint)  804 . Distal tubing portion  307  is typically made of a polymeric material, such as PEBAX or polyester.  
         [0063]    Transition bond  804  joins transition tube  805  to distal tubing portion  307 . (See also FIG. 12 illustrating the conversion bond area in greater detail.) Distal tubing portion  307  is in fluid communication with balloon  308  for inflation. Support wire shaft  303  extends through and distal of balloon  308  to coil tip  311 . In FIG. 7, a stent  712  is shown mounted on balloon  308 . An overjacket  709  covers support wire shaft  303  distal of balloon  308  (and optionally covers the entire spiral cut portion  310  of support wire shaft  303 ). Overjacket  709  may be made of a polymer, such as Nylon-based polymers (e.g., PEBAX), or polyester-based polymers. An optional radiopaque marker  713  is also shown in FIGS. 7 and 10.  
         [0064]    As discussed above, support wire shaft  303  includes spiral cut portion  310 , such that the spiral cut begins approximately around skive portion  314  (see also FIG. 8), and ends at coil tip  311 . The pitch of the spiral cut gradually decreases as one moves in direction from proximal to distal. For example, in one embodiment, the pitch of the spiral cut is approximately 1 mm where the spiral cut begins near skive portion  314 , and reduces to approximately 0.25 mm at the spiral coil tip  311 , ie., a factor of 4. The gradual decrease in the pitch of the spiral cut allows for a gradual (i.e., continuous) transition in flexibility in direction from proximal to distal.  
         [0065]    [0065]FIG. 9 further illustrates distal portion  331  of catheter  301  of the present invention. As shown in FIG. 9, spiral cut portion  310  is coupled to flexible coil tip  311 , for example, by welding. As noted above, a recess may be formed in the distal portion of spiral cut portion  310  of support wire shaft  303  to enable better coupling between the distal portion of spiral cut portion  310  and flexible coil tip  311 .  
         [0066]    [0066]FIG. 20 shows a cross-section of one way to couple coil tip  311  and spiral cut portion  310  of support wire shaft  303 . Coil tip  311  is typically made from a wire 0.002 to 0.004 inches in diameter. Spiral cut portion  310  may have a wall thickness from about 0.006 inches to 0.007 inches. To couple coil tip  311  to spiral cut portion  310 , a recess  2001  is provided in support wire shaft  303 . Note that a reverse of this approach may also be utilized to insure a constant outer diameter between spiral cut portion  310  of support wire shaft  303  and coil tip  311 .  
         [0067]    [0067]FIG. 21 illustrates a cross-section of how a simple butt joint  2101  can be used to couple spiral cut portion  310  and coil tip  311 .  
         [0068]    [0068]FIG. 10 illustrates additional detail of the balloon portion of catheter  301 . As shown in FIG. 10, the balloon portion includes distal tubing portion  307 , which is fluidly coupled to balloon  308 . Spiral cut portion  310  is shown as passing through the interior of balloon  308 , and, as noted above, is hollow to enable core wire  1616 , inserted into support wire shaft  303 , to reach coil tip  311 . FIG. 10 also shows PEBAX overjacket  709  on spiral cut portion  310 .  
         [0069]    [0069]FIG. 11 is an expanded view of intermediate bond area  800  of catheter  301  of the present invention as shown in FIG. 8. As may be seen from FIG. 11, intermediate bond area  800  includes transition tube  805 , distal tubing portion  307 , transition bond  804 , and spiral cut portion  310  that includes overjacket  709  (not shown in FIG. 11). Note that overjacket  709  may be placed around the entire spiral cut portion  310  in order to seal it, so as to maintain inflation pressure and prevent leaks. Furthermore, balloon  308  may be thermally bonded to overjacket  709 .  
         [0070]    [0070]FIG. 12 illustrates a conversion bond area of catheter  301  in greater detail. As shown in FIG. 12, support wire shaft  303  is side-by-side with inflation shaft  304  proximal of skive portion  314 . Transition tube  805  provides fluid communication between skive portion  314  of inflation shaft  304  and distal tubing portion  307  (as shown in FIG. 11). Spiral cut portion  310  of support wire shaft  303  begins just distal of skive portion  314  and is coaxial with transition tube  805 .  
         [0071]    [0071]FIG. 13 illustrates a cross-section of another embodiment of a proximal catheter shaft according to the present invention across line C-C of FIG. 3. Specifically, FIG. 13 illustrates a jacket  1301  surrounding support wire shaft  303  and inflation shaft  304 . Jacket  1301  may be used to couple (bond) support wire shaft  303  and inflation shaft  304  together, throughout proximal portion  330  of catheter  301  For example, for an approximately 100-135 cm long catheter  301 , jacket  1301  preferably extends for approximately 70-80% of its proximal length. It is anticipated that even if the coupling were to extend for a much smaller portion, for example, 5-10 cm, the coupling effect provided is still beneficial to the user in terms of added torquability and steerability.  
         [0072]    Other methods of bonding support wire shaft  303  and inflation shaft  304  may be used. For example, the two shafts  303 ,  304  may be welded together throughout a substantial portion of their lengths. Alternatively, they may be welded together only in selected portions, for example, the proximal 5-10 cm. Shafts  303 ,  304  may be epoxied or glued together. Shafts  303 ,  304  may also be coupled together using a plurality of “ties.” 
         [0073]    Another embodiment of a proximal catheter shaft according to the present invention includes extruding shafts  303 ,  304  together as an integrated unit, as shown in FIG. 15. Yet another option includes extruding shafts  303 ,  304  separately, bringing them in contact, and laser fusing (or laser welding) them together.  
         [0074]    [0074]FIG. 14 illustrates a cross-section of another embodiment of a proximal catheter shaft according to the present invention across line C-C of FIG. 3 illustrating an alternative shape of inflation shaft  304 . As noted above, the market continues to demand ever lower catheter profiles. Accordingly, inflation shaft  304  is formed to correspond to an outer surface of support wire shaft  303 , so as to create a “crescent” shape. Other cross-sectional shapes of inflation shaft  304  may include a substantially D-shape, such that an overall profile of catheter  301  is reduced.  
         [0075]    Although in the embodiment described above, the conversion bond area shown in FIG. 12 includes transition tube  805  between inflation shaft  304  and distal tubing portion  307 , with the distal tubing portion  307  fluidly coupled to balloon  308 , alternatively, inflation shaft  304  may extend to balloon  308  and be in direct fluid communication with balloon  308  such that transition tube  805  and distal tubing portion  307  are eliminated. Thus, one piece of tubing would extend from the proximal end of the balloon  308  to the inflation luer  320  and wire lock  321 . This one piece of tubing may be formed from alternating polymers such that the distal end is pure PEBAX, the proximal end is pure Grilamide, and a midsection contains layers or a mixture of PEBAX and Grilamide.  
         [0076]    The variable pitch spiral cut of portion  310  of support wire shaft  303  may be accomplished by laser cutting. Portion  310  is positioned in a jig, and advanced forward while the laser forms a thin cut. By varying the speed of the advance, the pitch of the spiral cut portion  310  can gradually transition from a large pitch (more stiff) to a small pitch (more flexible). Alternatively, a blade may be used to form the spiral cut on portion  310 . The hypotube may be held in a jig, while a blade, oriented at the required angle, is brought in contact with portion  310  of support wire shaft  303 . While portion  310  is rotated and advanced, the blade cuts a spiral slit in portion  310 . The use of a blade, rather than a laser, may be more desirable when portion  310  is formed of a polymer, such as Grilamide or polyamide.  
         [0077]    As shown in FIG. 3, catheter  301  includes wire lock  321  that is similar to a syringe locking port. Core wire  1616  includes a mating surface, such that it can be screwed on and locked onto luer  320 . The mating surface may be nut-like, as discussed below. Other options for holding core wire  1616  fixed relative to catheter  301  include the use of a crimping mechanism on inflation luer  320 , or, for example, mechanical jaws that grip core wire  1616 .  
         [0078]    [0078]FIG. 17 shows an example of a screw-and-nut type wire lock mechanism  321  of the present invention. As shown in FIG. 17, support wire shaft  303  terminates in a molded plastic end  1703  having a thread  1704 . Note core wire  1616  inserted into support wire shaft  303 . A proximal end of core wire  1616  terminates in a nut  1705  that includes a locking cap  1701 . Thread  1704  is preferably a standard luer thread commonly used on domestic and international catheter luers. Thread  1704  allows a syringe to be attached to a support wire shaft  303  for flushing it with a saline solution (not shown). Thread  1704  also allows locking cap  1701  to be screwed in place. By engaging locking cap  1701  with thread  1704 , the operator secures core wire  1616  to catheter  301 , making it an integral part thereof.  
         [0079]    FIGS.  18 A- 18 B show a lever lock type mechanism used as wire lock mechanism  321 . As shown in FIGS.  18 A- 18 B, wire lock mechanism  321  includes a locking portion  1801 , which is “hinged” at a pivot portion  1803 . To lock core wire  1616  in place, locking portion  1801  is pressed down against core wire  1616  until it is secured by a thumb portion  1802 . To release core wire  1616 , thumb portion  1802  is pushed back. This design allows core wire  1616  to be fixed in place at any point along its length, without necessarily advancing it fully within catheter  301 .  
         [0080]    [0080]FIG. 19 shows a chuck/bushing type wire lock mechanism  321 . As shown in FIG. 19, wire lock mechanism  321  includes a female portion  1901 , which includes threads  1902 , that are coupled to a male portion  1903 . Male portion  1903  is in turn coupled to support wire shaft  303 . The space  1904  between female portion  1901  and male portion  1903  may include a number of mechanisms, such as a 3-jawed chuck, or a rubber (or polymer) bushing where upon the wire is held in place when the female portion  1901  is tightened over the male portion  1903 . Both a 3-jawed chuck mechanism and the rubber or polymer bushing will transfer an axial force into a circumferential force.  
         [0081]    Catheter  301  of the present invention allows for greater control of its distal portion  331 , and greater steerability. The ability to add core wire  1616  after tracking catheter  301  through a patient&#39;s vasculature allows for greater control of the stiffness and other characteristics of catheter  301 , such that an operator has greater flexibility during the procedure.  
         [0082]    The use of catheter  301  of the present invention in most applications eliminates the extra step of inserting a guide wire, due to the use of a “hollow guide wire”, i.e., support wire shaft  303 . Further, the present invention allows for interchangeability (replaceability) of a core wire within support wire shaft  303 . Catheter  301  of the present invention may be used in coronary, peripheral, and cranial applications.  
         [0083]    [0083]FIG. 22 shows an embodiment of the catheter of the present invention using a coaxial arrangement of inflation shaft  304  and support wire shaft  303 . Other corresponding elements have been numbered with the same reference numerals as in FIG. 3.  
         [0084]    It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.