Abstract:
A guidewire having a flexible coil with a tapered distal tip. Preferably, the flexible coil has a polymer coating at least at its tapered distal portion. The polymer coating may comprise polyurethanes or other suitable polymers. The guidewires of the invention provide desirable performance characteristics, particularly when used to cross relatively tight lesions such as chronic total occlusions.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the field of intravascular guiding members. In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced in the patient&#39;s vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is first advanced out of the distal end of the guiding catheter into the patient&#39;s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Conventional guidewires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient&#39;s vascular system. 
     A major requirement for guidewires and other guiding members is that they be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. However, they also must have sufficient column strength to be pushed through a patient&#39;s vascular system or other body lumen without kinking. These characteristics are especially difficult to achieve when designing guidewires capable of crossing relatively tight lesions, particularly with chronic total occlusions (CTO&#39;s). Conventional guidewires typically do not have distal tips capable of crossing such lesions. 
     Accordingly, there is a need for guidewire designs that facilitate the crossing of relatively tight lesions without sacrificing handling characteristics. The present invention satisfies these and other needs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a guidewire or other guiding member having a tapered distal coil. Generally, the guidewire comprises an elongated core member having a proximal section and a distal section and a coil disposed about and secured to the distal core section. The coil has a distal portion which tapers distally to the distal end thereof. At least part of the tapered distal portion of the coil is provided with a polymer coating which bridges or encapsulates individual turns of the coil. 
     The polymer coating covers the coil a distance of at least about 1.5 cm and may extend the entire length of the coil, e.g. up to a distance of about 40 cm from the distal end of the coil and preferably a distance of about 2 to about 12 cm from the distal end of the coil. The polymer coating has a thickness of about 0.0001 inch to 0.004 inch (0.0025 mm to 0.1 mm). 
     The outer diameter of the distal portion of the coil may taper from about 0.001 inch to 0.035 inch (0.0025 cm to 0.089 cm), to an outer diameter of about 0.006 inch to about 0.02 inch (0.15-0.51 mm), preferably about 0.008 inch to about 0.014 inch (0.2-0.36 mm). The tapered portion of the coil is about 1 cm to about 10 cm in length, preferably about 2 to about 5 cm in length. The entire coil length may range from about 3 to about 40 cm, preferably about 10 to about 30 cm. 
     The tapered coil, particularly with the polymer coating which bridges or encapsulates the turns of the coil, facilitates advancement through tight lesions such as CTO&#39;s. The polymer coating provides a smoother surface than the coil turns alone, and fixes the turns of the coil for a more damage tolerant distal tip. 
     These and other features of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic, elevational view of a guidewire embodying features of the invention. 
     FIG. 2 is a transverse cross sectional view of the guidewire shown in FIG. 1 taken along the lines  2 — 2 . 
     FIG. 3 is a longitudinal cross sectional view taken through the tapered portion of the coil illustrating the polymer bridge between the turns of the coil. 
     FIG. 4 is a schematic, elevational view of a core member which may be suitable for the guidewire shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-3 illustrate a guidewire  10  embodying features of the invention that is adapted to be inserted into a patient&#39;s body lumen, such as an artery or vein. The guidewire  10  comprises an elongated, core member  11 , having a proximal core section  12  and a distal core section  13  and a helical coil  14  which is disposed about and secured to the core member  11  at its distal end by welding or soldering which forms the rounded plug  15 . The coil  14  has a distal portion  16  which tapers distally to the distal end of the coil  14  secured to the rounded plug  15 . The proximal end  17  of the coil  14  is secured by suitable means such as soldering to the core member  11 . The coil  14  may also be secured at an intermediate location  18  at the junction between the tapered distal portion  16  and the constant diameter proximal coil portion  19  by suitable means such as soldering. 
     If desired, lengths of the coil can be stretched, for example from about 5 to about 50 percent, preferably about 10 to 30 percent of the length, to impart greater flexibility and also facilitate encapsulation by the polymeric layer. As known in the art, helical coil  14  can comprise a plurality separate coils, such as intermediate and tip coils, configured with screw stretches to facilitate securing them together. The ends of the coils may have the turns of the coil stacked together as desired. 
     At least the tapered distal portion  16  of the helical coil  14  and preferably the entire length of coil  14  has a polymer coating or layer  20 , which may be applied by spray coating, dip coating or other suitable means, to either encapsulate the tapered distal coil portion  16  or to at least bridge the turns of the tapered portion of the coils. The coating is preferably a urethane, but other polymers may be used. Presently preferred polymers include black and clear thermoset aliphatic polyurethanes. The polymer coating reduces the friction of the coil, imparting a more lubricious and effortless feel to the guidewire, improving its handling. The polymer coating also locks the intermediate and tip coils in place, creating a more damage tolerant coil. 
     The polymer layer  20  bridging the space between turns of the tapered portion  16  of coil  14  is best shown in FIG.  3 . The inner space defined by the interior of the tapered portion  16  of the coil  14  should not be filled with polymeric materials because the mass of polymer would prevent the necessary movement of the tapered coil portion  16  which is required to guide the tip through tight lesions. 
     FIG. 3 illustrates the bridging of the polymer between the turn of the tapered portion  16  of coil  14 . 
     FIG. 4 depicts the elongated core member  11  of the guidewire  10  shown in FIG.  1 . The distal section  13  of the elongated core member  11 , has distally tapered portions  21  and  22  that become smaller in the distal direction followed by cylindrical sections  23  and  24  of constant diameters. Preferably, there is a final manually shapeable flat section  25  at the distal end of core member  11 . 
     The core member can be formed from high strength materials such as stainless steel, or other high modulus materials, or can be formed from superelastic or shape memory materials, such as nickel titanium alloys. The core member  11  may have a coating (not shown) of lubricous material such as a fluoropolymer (sold under the trademark Teflon(r) by DuPont, de Nemours &amp; Co.) or other suitable lubricous coatings such as other fluoropolymers, hydrophilic coatings and polysiloxane coatings. The coil  14  may be formed of suitable materials such as those from which the core is made or radiopaque materials such as platinum, palladium, tungsten and alloys thereof. 
     Various dimensions are suitable for the practice of this invention and may be adapted as desired for particular applications. In one embodiment designed for coronary artery uses, the overall length of guidewire  10  may be about 150 cm to 300 cm, but typically is 190 cm. The proximal portion  12  of the core member has an outer diameter of about 0.008 inch to 0.035 inch (0.2-0.9 mm), preferably about 0.01 to about 0.014 inch (0.25-0.36 mm). The tapered sections  21  and  22  may have lengths of about 3.0 cm to 6.0 cm and cylindrical sections  23  and  24  may have lengths of about 3.0 cm to 20.0 cm. The distal cylindrical portion  24  has a diameter of about 0.0028 inch to 0.0037 inch (0.071 cm to 0.094 cm). The flattened portion  25  preferably has a thickness of about 0.0015 inch to about 0.0031 inch (0.038-0.079 mm) and a length of about 0.5 to about 1 cm. Helical coil  14  may generally be formed from round wire having a diameter of about 0.0015 inch to 0.006 inch (0.038-0.15 cm) or from ribbon wire having a rectangular cross section with dimensions of about 0.0005 inch by 0.0015 inch (0.013-0.038 cm) to 0.002 inch by 0.006 inch (0.051-0.15 mm). The length of the coil can range from about 0.5 cm to the entire length of the device, with a preferred range of 1.0 cm to about 30.0 cm. The distal tapered coil section may have a length of about 1 to about 40, preferably 5 about 2 to about 12, with 3 cm being one present embodiment. At the proximal end of the coil  14 , the outer diameter can range from about 0.01 inch to 0.30 inch (0.25-7.62 mm), preferably from about 0.010 inch to 0.018 inch (0.025 cm to 0.046 cm). At the distal end, the coil  14  can have a diameter ranging from about 0.006 to about 0.014 inch (0.15-0.35 mm), preferably about 0.008 inch to about 0.012 inch (0.20-0.3 mm), typically about 0.010 inch (0.025 cm). In particular, the use of ribbon wire, having a rectangular cross section, allows a reduced tip diameter such as about 0.008 inch (0.020 cm) when using wire with dimensions of 0.001 inch by 0.003 inch (0.025-0.076 mm). The polymer coating  20  may have a thickness from about 0.0001 inch to 0.004 inch (0.0025-0.10 mm). The polymer coating may cover just the tapered distal tip coils, or the tapered distal tip and the intermediate coils or the full length of the guidewire. The coating covers the coil a distance of about 1.5 cm to 40 cm from the distal end of the coil, preferably about 2 to about 12 cm, from the distal end of the coil. The coating  20  may be one or multiple polymer layers of the same or different polymeric materials. 
     It will be apparent from the foregoing that, while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Moreover, those skilled in the art will recognize that features shown in one embodiment may be utilized in other embodiments.