Abstract:
The present invention is a stent delivery system that uses short section of guidewire fixedly attached to the distal section of a balloon angioplasty catheter onto which a stent is co-axially mounted. By not having a guidewire that slides through the balloon of the balloon angioplasty catheter, the deflated balloon on which the stent is mounted can have a reduced diameter. Therefore, the outer diameter of the pre-deployed stent mounted onto that balloon is also minimized. This provides a smaller profile, i.e., a smaller outer diameter, for the stent. The time to perform a stent delivery procedure is reduced; a separate guidewire does not have to be placed prior to using the stent delivery system to place the stent at the site of a stenosis. Another embodiment of the present invention has a core wire that extends for nearly the entire length of the stent delivery system, the guidewire having different levels of stiffness for different portions of the core wire&#39;s length.

Description:
REFERENCE TO PRIOR APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/444,104 filed on Nov. 22, 1999 now U.S. Pat. No. 6,375,660, and Ser. No. 10/107,221, filed Mar. 26, 2002, pending. 
    
    
     FIELD OF USE 
     This invention is in the field of devices for percutaneous insertion into a vessel of the human body to place a stent at the site of an obstruction. 
     BACKGROUND OF THE INVENTION 
     Stents are well known devices for placement in vessels of the human body to obtain and maintain patency of that vessel. The greatest use for stents has been for placement within a stenosis in a coronary artery. When a stent is used for treating a coronary artery stenosis, it has always been necessary to first place a guidewire through the stenosis. The next step in the stenting procedure may be to pre-dilate the stenosis with a balloon angioplasty catheter that is advanced over that guidewire. The catheter may be of the over-the-wire or rapid exchange variety. The balloon angioplasty catheter is then removed and a stent delivery system which includes the stent is advanced over the guidewire, and the stent is then deployed at the site of the dilated stenosis. 
     Recent improvements in the design of stent delivery systems have made it possible to eliminate the step of pre-dilatation for the treatment of many classes of stenoses. The delivery of a stent to the site of a stenosis without pre-dilatation has been commonly referred to as “direct stenting”. However, even with direct stenting, a guidewire is still required as a precursor to advancing the stent delivery system over that guidewire to place the stent at the site of a stenosis. Placing the guidewire requires additional procedure time. 
     SUMMARY OF THE INVENTION 
     The present invention is a stent delivery system that uses short section of guidewire fixedly attached to the distal section of a balloon angioplasty catheter onto which a stent is co-axially mounted. By not having a guidewire that slides through the balloon of the balloon angioplasty catheter, the deflated balloon on which the stent is mounted can have a reduced diameter. Therefore, the outer diameter of the pre-deployed stent mounted onto that balloon is also minimized. This provides a smaller profile, i.e., a smaller outer diameter, for the stent. A minimum profile at the distal section of the stent delivery system is highly advantageous for improving the percentage of cases that can be treated by means of direct stenting; i.e., without requiring pre-dilation of a stenosis. An advantage of the present invention is that a separate guidewire is eliminated, thus saving any costs associated with such a guidewire. Additionally, the time to perform a stent delivery procedure is reduced; a separate guidewire does not have to be placed prior to using the stent delivery system to place the stent at the site of a stenosis. 
     One embodiment of the present invention uses a core wire that extends for the entire length of the stent delivery system. This core wire is also centrally located in the fixed guidewire that extends from the distal end of the balloon onto which the stent is mounted. Although this core wire can be made from a conventional metal such as stainless steel, the use of shape memory metal alloys (such as the nickel titanium alloy known as Nitinol) is ideal for such a core wire. 
     Furthermore, in a preferred embodiment of this invention , the Nitinol used for the fixed guidewire portion of the stent delivery system should have a transition temperature that is greater than body temperature. Therefore, prior to insertion, the interventional cardiologist who inserts the stent delivery system can make an appropriate bend into the end of the guidewire in order to maneuver the end of the guidewire into a specific artery. If the guidewire becomes damaged in passing through some difficult vasculature, the present invention describes the use of a special heater that can then be used to heat the guidewire to a temperature above its transition temperature, so that the guidewire would have its pre-damaged shape restored. Typically, the pre-damaged state would be a substantially straight wire or a wire with a slight, pre-set bend. After the guidewire cools below body temperature, the guidewire could then be reshaped again by the interventional cardiologist, to once again try to navigate through some tortuous part of the vasculature. 
     In a Nitinol implementation of the core wire of the stent delivery system, most of the core wire that lies proximal to the proximal end of the guidewire should have a transition temperature below body temperature. Therefore, the superelastic properties of the Nitinol core wire proximal section will greatly reduce the probability of any kinking of the core wire that might occur if the metal were stainless steel. 
     Another embodiment of the present invention has a core wire that extends for nearly the entire length of the stent delivery system, the guidewire having different levels of stiffness for different portions of the core wire&#39;s length. For example, the proximal section should be extremely “pushable” would be the most stiff. The portion that lies within the balloon expandable stent should be very flexible, since the stent would be able to provide the needed “pushability”. The present invention envisions that the variations in stiffness may be accomplished by changing the diameter of the core wire or by using different materials for different sections of the core wire. 
     Thus an object of the present invention is to provide a means for placing a stent within a vessel of the human body without requiring a separate guidewire, thus saving the cost of the guidewire and also saving the time required to place a separate guidewire through an obstruction such as an arterial stenosis. 
     Another object of the present invention is to reduce the outside diameter (i.e., the profile) of the distal section of the stent delivery system so as to optimize the capability of the stent delivery system for direct stenting. 
     Still another object of the present invention is to have a guidewire fixed at the end of a balloon angioplasty catheter with a stent co-axially mounted onto the catheter&#39;s inflatable balloon, and further that the length of the cylindrical portion of the inflated balloon that extends beyond each end of the stent (the “balloon overhang”) is less than 1.0 mm, preferably less than 0.5 mm and optimally nearly 0 mm; the minimum balloon overhang being advantageous for reducing any likelihood of arterial wall dissection beyond the edges of the stent when the balloon is inflated. 
     Still another object of this invention is to have a core wire extending through most of the length of the fixed wire stent delivery system, the core wire being made from a shape memory alloy such as Nitinol with a transition temperature for the fixed guidewire region of the core wire being higher than body temperature, and most of the proximal portion of the core wire having a transition temperature below body temperature. 
     Still another object of this invention is to have a core wire extending through most of the length of fixed wire stent delivery system, the core wire having different portions each with different cross sectional areas thereby providing different levels of stiffness. 
     Yet another object of this invention is to have the proximal section of the core wire be the stiffest part of the core wire, in order to enhance system pushability. 
     Yet another object of this invention is to have the section of the core wire that lies within the balloon expandable stent be significantly less stiff than portions of the core wire that lie proximal to the balloon. These and other important objects and advantages of this invention will become apparent from the detailed description of the invention and the associated drawings provided herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a side view of a stent delivery system having a balloon angioplasty catheter and having a fixed guidewire extending beyond the distal end of the balloon angioplasty catheter. 
         FIG. 2  is a longitudinal cross section of the distal section of the stent delivery system that is shown in FIG.  1 . 
         FIG. 3  is an enlarged transverse cross section of the distal section of the stent delivery system at section  3 — 3  of FIG.  2 . 
         FIG. 4  is a longitudinal cross section of another embodiment of the present invention that utilizes an elongated core wire. 
         FIG. 5  is an enlarged transverse cross section of the stent delivery system at section  5 — 5  of  FIG. 4  showing the connection between elongated core wire and the proximal tube of the stent delivery system. 
         FIG. 6  is a longitudinal cross section of the distal portion of another embodiment of the present invention that has an elongated core wire extending to the proximal end of the stent delivery system. 
         FIG. 7  is a longitudinal cross section of the proximal portion of the embodiment of the present invention of  FIG. 6  showing the elongated core wire extending to near the proximal end of the stent delivery system. 
         FIG. 8  is a transverse cross section of the stent delivery system at section  8 — 8  of FIG.  7 . 
         FIG. 9  is a cross section of a heating unit for raising the temperature of the distal portion of the core wire of the stent delivery system (i.e., the fixed guidewire). 
         FIG. 10  is a longitudinal cross section of the distal portion of another embodiment of the present invention that has an elongated core wire extending to the proximal end of the stent delivery system where the section of the core wire within the balloon expandable stent is significantly less stiff than more proximal portions of the core wire. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  illustrate a stent delivery system  10  having a fixed guidewire  11  that is fixedly attached to the distal end of a balloon angioplasty catheter that has a minimum profile for the distal section of the balloon angioplasty catheter. The distal section of the stent delivery system  10  includes a guidewire  11 , a proximal elastic band  18 , a stent-on-balloon section  30  and a distal elastic band  16 . The stent-on-balloon section  30  includes an inflatable balloon  34  onto which a balloon expandable stent  32  is co-axially mounted. A cylindrically shaped distal section of the balloon  34  is fixedly attached to a proximal section of the guidewire  11  that includes a plastic cylinder  14  that is fixedly attached to a central core wire  13  of the guidewire  11 . 
     A helical wire coil  15  is wrapped around the core wire  13  for most of the length of the core wire  13 . The outside diameter of the guidewire  11  would typically be 0.014 inches. However, outside diameters between 0.008 and 0.035 inches could be used. The diameter of the core wire  13  would typically be between 0.002 and 0.014 inches. However, it should be understood that the core wire  13  could have a tapered section and could also have a flattened or square cross section situated within the wire coil  15 . The flattened section of the core wire  13  is ideally suited for retaining a bend that is created by the doctor just before placing the stent delivery system  10  into a vessel of a human subject. 
     The material of the guidewire  11  would typically be stainless steel, tantalum, Nitinol or a combination of such metals. A distal section of the guidewire  11  could be substantially straight or it could be substantially curved as generally indicated in  FIGS. 1 and 2 . The curve could be as supplied by the manufacturer or it could be made or adjusted by the person (typically an interventional cardiologist) placing the stent delivery system  10  into the patient. The length of the guidewire  11  that lies distal to the distal end of the balloon  34  should be approximately 1.0 to 2.0 cm and certainly less than 5 cm. Furthermore, a plastic layer with a lubricious outer surface could be substituted for the helical wire coil  15 . It is also envisioned that the coil  15  could be coated with Teflon® or another lubricious material. 
     A proximal section of the balloon  34  is fixedly attached to a distal section of a central cylindrical tube  20 . The central cylindrical tube  20  would typically be formed from a plastic material such as polyurethane, polyethylene, nylon, Teflon®, or any of the many similar polymeric materials used for balloon angioplasty catheters. The outside diameter of the tube  20  would typically be between 0.5 and 2.0 mm. The length of the tube  20  would typically be between 10 and 40 cm. 
     The central tube  20  can be joined at its proximal end to the distal end of a proximal cylindrical tube  21 . It is envisioned that the proximal tube  21  would extend for most of the length of the stent delivery system  10 . A Luer fitting  22  located at the proximal end of the proximal tube  21  would be used for fluid connection by means of the attachment thread  23  to a stop-cock (not shown) to which a syringe can be attached that provides a source of inflation fluid for the balloon  34 . The syringe or a fluid pumping device that includes a pressure gauge can be used to inflate the balloon  34  with contrast medium to deploy the stent  32  into a stenosis. The syringe or pumping device would also be used to deflate the balloon  34  after the stent  32  has been deployed. 
       FIG. 2  shows three layers of the balloon  34 , which layers would typically be formed by rolling the balloon  34  in a spiral manner (like a “jellyroll”) as seen in FIG.  3 . For the sake of clarity, only three layers are shown in  FIG. 2  on each side of the balloon  34 . [To be technically correct, six layers should be shown in  FIG. 2  on each side of the balloon  34 .] Although  FIG. 3  shows a rolled balloon  34 , it should be understood that a conventional balloon made with a multiplicity of folded wings could also be used. 
     It should be understood that a conventional guidewire must be able to be rotated in order to place it into a specific artery that has the stenosis that is to be treated. To be effective as a stent delivery system for direct stenting, the stent delivery system  10  must have the capability to apply torque to the guidewire  11  so that the guidewire&#39;s distal tip  12  can be selectively advanced at an arterial bifurcation into the branch artery that is to be stented. 
     When the stent delivery system is percutaneously placed into a vessel of a human body, the Luer fitting  22  remains exterior to that body, where it can be held and rotated by the physician in order to apply a torque to rotate the distal end  12  of the guidewire  11 . When a twist is applied to the Luer fitting  22 , the spiral-shaped balloon  34  would tend to form a tightened spiral or would loosen depending upon the direction of the twist that is applied. By having the proximal elastic band  18  and distal elastic band  16  shrunk onto the portions of the balloon  34  that have the shape of a frustum of a cone when the balloon  34  is inflated, loosening of the spiral shape of the folded balloon  34  is prevented even if the direction of twist applied to the Luer fitting  22  would otherwise have unwound that spiral. In this manner, the structure shown in  FIGS. 1 and 2  is capable of using the Luer fitting  22  to apply the twist that is required for positioning the guidewire  11  into virtually any arterial stenosis selected for direct stenting. 
     It should be noted that the elastic bands  16  and  18  should be made from an elastomer such as silicone rubber. The portion of the band that lies over the balloon  34  can expand radially when the balloon  34  is inflated to deploy the stent  32 . The elastic bands  16  and  18  could be solvent swelled and then placed in position or heat shrinking could be used for their placement. In either case, after placement they would snugly fit onto the balloon  34  as shown in  FIGS. 1 and 2 . Furthermore, the band  16  could be adhesively bonded to the guidewire  11  and/or the balloon  34 . The band  18  can be adhesively bonded to the central tube  20 . 
     Another embodiment of the present invention is shown in  FIGS. 4 and 5 . This embodiment differs from the embodiment of  FIGS. 1 and 2  in that the core wire  13  of  FIG. 1 and 2  is considerably lengthened. The elongated core wire  43  of  FIGS. 4 and 5  extends through the balloon  34 , into, and through the central tube  20 . Although the elongated core wire  43  could have its proximal end terminate within the central tube  20 , it would more advantageously extend into the proximal tube  21 . The core wire  43  could even extend to the Luer fitting  22 . The proximal end of the core wire  43  can be fixedly attached to a cylindrical, multi-lumen connector  44  that has lumens  46  through which fluid can be passed to inflate and deflate the balloon  34 . The arrows  45  indicate the direction of fluid flow for inflating the balloon  34 . The purpose of the elongated core wire  43  is to provide additional pushability and also to enhance the transmission of torque to the guidewire  11 . Another purpose of the core wire  43  is to prevent inadvertent separation of the guidewire  11  from the stent delivery system  10 . 
     An important feature of the stent delivery system  10  would be to minimize the length of the cylindrical portion of the balloon  34  that extends beyond each end of the stent  32  when the balloon is inflated. This length is called “balloon overhang”. Because the guidewire  11  cannot remain in the treated stenosis after the stent delivery system  10  is taken out of the patient, it is important that edge dissections of the arterial wall that occur more frequently with longer lengths of balloon overhang be avoided. To accomplish a reduced occurrence of stent edge dissections, balloon overhang of the balloon  34  at each end of the stent  32  should be less than 1.0 mm and preferably less than 0.5 mm. Ideally, the balloon overhang should be 0±0.5 mm. How to achieve reduced balloon overhang is explained in detail in the U.S. patent application Ser. No. 09/373,552, entitled “Stent Delivery Catheter with Enhanced Balloon Shape”, incorporated herein by reference. 
     In  FIGS. 2 ,  3  and  4 , the balloon  34  is shown to bulge outwardly between the struts of the stent  32 . This method for holding the stent  32  more securely onto the balloon  34 , is called “nesting”. It is understood that the stent  32  could either be mechanically crimped onto the balloon  34  or it could be nested. 
     It should be understood that the proximal tube  21  could extend from the proximal end of the balloon  34  to the Luer fitting  22  that is situated at the proximal end of the stent delivery system  10 . That is, this invention will function satisfactorily without having a central tube  20 . Furthermore, wire reinforcing in the wall of either or both the tube  20  or the tube  21  is envisioned for improving the pushability of the stent delivery system  10 . 
       FIGS. 6 ,  7  and  8  illustrate an additional embodiment of the present invention. Specifically,  FIGS. 6 and 7  are longitudinal cross-sections of a stent delivery system  50  that has an improved metal core wire. Although they are not shown in  FIG. 6 , it is clearly envisioned that elastic bands such as the elastic bands  16  and  18  of  FIGS. 1 and 2  could also be used with the stent delivery system  50  of FIG.  6 . The stent delivery system  50  has a fixed guidewire  52  with a centrally located distal core wire portion  51 D to which a conically shaped plastic piece  53  is attached. The inflatable balloon  55  is joined at its distal end to the plastic piece  53  and joined at its proximal end to a central tube  56 . A pre-deployed stent  54  is co-axially mounted onto the balloon  55 . Preferably, the stent  54  would be coated with a drug eluting coating such as the drug sirolimus. 
     The central tube  56  connects at its proximal end to the distal end of the proximal tube  58 . The proximal end of the proximal tube  58  is fixedly joined to a Luer fitting  61  and also connected to a multi-lumen connector  59  having pass-through lumens  60 . The transverse cross section of the multi-lumen connector  59  is shown in FIG.  8 . The proximal end of the proximal core wire portion  51 P can have a reduced diameter at its proximal end where it is fixedly attached to the multi-lumen connector  59 . Fluid can be injected through the Luer fitting  61  to inflate the balloon  55  and deploy the stent  54 . This fluid would pass through the lumens  60  and the passageway  57  and into the balloon  55 . The balloon  55  would be deflated by pulling the fluid out through the Luer fitting  61 . 
     The core wire of the stent delivery system  50  is formed in three parts, namely a distal core wire portion  51 D, a central core wire portion  51 C and a proximal core wire portion  51 P. The distal core wire portion  51 D is centrally located with the fixed guidewire  52  located at the distal end of the stent delivery system  50 . As with the embodiment of  FIGS. 1-4 , the cross section of the of the core wire portion  51 D of the fixed guidewire could be flat, square or round. The fixed guidewire  52  has a distal region R 1  and a proximal region R 2 . The central core wire portion  51 C extends in the region R 3  with an essentially uniform diameter from the proximal end of distal region R 2  to where the core wire diameter increases to become the proximal core wire portion  51 P. 
     Although the core wire could be formed from a conventional metal such as stainless steel, optimally the core wire would be fabricated from a shape memory alloy such as Nitinol. An optimum design for a Nitinol core wire would have the distal region R 1  having a transition temperature that is higher than the temperature of the human body. For example, the transition temperature for the region R 1  would be greater than 105° F. and optimally approximately 115° F. Thus, if the guidewire  52  is bent by the interventional cardiologist as might be needed for entering a particular branch of the coronary arteries, that bend would be maintained even at body temperature. 
     The region R 3  would have a transition temperature that is below body temperature so that any kinking of the core wire that is proximal to the proximal end of the region R 2  would be automatically straightened when the stent delivery system  50  is placed into a human subject. A typical transition temperature for the region R 3  could be approximately 80° F. to 90° F. from its martensitic crystalline state to its austenitic crystalline state. 
     The region R 2  would be designed such that the transition temperature at its distal end would be the same as the transition temperature of the region R 1 , and the transition temperature at its proximal end would be the same as for the region R 3 . Thus, there would be a change in the transition temperature from somewhat above body temperature at the distal end of the region R 2  to a transition temperature somewhat below body temperature at the proximal end of the region R 2 . Thus, any kinking of the core wire proximal to region R 2  would automatically be straightened when the stent delivery system  50  was placed into the human subject. Furthermore, the interventional cardiologist could put whatever bend he wished into the region R 1  without that bend changing shape when the stent delivery system  50  is placed into the human subject. 
     The fixed guidewire  52  has, for most of its length, a helical metal coil that surrounds the core wire  51 D. Although this coil is typically formed from stainless steel, it could also be formed from Nitinol or more optimally from a highly radiopaque metal such as the alloy L605 or MP35N, or the element tantalum. In any case, the outer surface of the coil should be coated with a lubricious plastic such as Teflon®. 
     Because the outer surfaces of the central tube  56  and the proximal tube  58  each will make contact with the inner surface of a guiding catheter or the inner surface of curved coronary arteries, there can be a considerable degree of fiction between those tubes  56  and  58  and their surroundings. To provide the best control of the angular position of the fixed guidewire  52 , it is desirable to exert the torque to control the angular position of the guidewire  52  by means of the core wire that extends from the proximal end of the guidewire  52  to the proximal end of the stent delivery system  50 . By coating the entire outer surface of the core wire including the sections  51 C and  51 P and/or coating the inner surfaces of the central tube  56  and proximal tube  58  with a lubricious coating, any frictional resistance between the core wire and the tubes  56  and  58  would be greatly reduced. By applying such lubricious coating(s), the core wire could more readily transfer a torque from the core wire&#39;s proximal end to the fixed guidewire  52  and therefore, the angular placement of the guidewire  52  could be more readily controlled. 
     It would be highly undesirable to have to discard the stent delivery system  50  with its stent  54 , if the guidewire  52  became bent or kinked when pushed through a tortuous coronary artery prior to delivering the stent  54  into an arterial stenosis. 
     In the case where the guidewire  52  is made of Nitinol, if such damage to the guidewire  52  were to occur, the heater  70  of  FIG. 9  could be used to restore the shape of the guidewire  52 . By exposing the guidewire  52  to a temperature that exceeds the transition temperature of the Nitinol in the region R 1  the guidewire  52  would return to a straightened, pre-formed state. 
     The heater  70  would be used only if there was some significant kinking of the guidewire  52 . The heater  70  has a generally cylindrical body  72 , generally cylindrical, thermostatically controlled heating elements  74  and a sterile cover  76  having a hole  76 H into which the guidewire  52  could be placed if it became damaged. For more rapid heat transfer into the guidewire  52 , the hole  76 H could be filled with a sterile saline solution that is readily available in a catheterization laboratory. Exposing the guidewire  52  to a temperature above the transition temperature of the distal core wire portion  51 D in the region R 1  would restore the guidewire  52  to its original shape prior to the interventional cardiologist having placed the stent delivery system  50  into the human subject. After the guidewire  52  is removed from the heater  70  and returns to a temperature below body temperature, the interventional cardiologist would be able once again to reshape the guidewire  52  to allow the distal end of the stent delivery system  50  to be maneuvered to a specific location in the coronary vasculature. 
     One of the goals of the present invention is to have a minimum outside diameter for the stent mounted onto the balloon to allow for easy delivery into even small or highly curved coronary arteries. Therefore, it is important that the wall thickness of the stent be as small as possible within the constraint of achieving adequate radial rigidity for dilating an arterial stenosis. Although stainless steel could be used for this purpose, improved radiopacity for such a thin-walled stent could be better achieved by using a metal having a higher density, such as the materials previously noted. 
       FIG. 10  illustrates still another embodiment of the present invention. Specifically,  FIG. 10  is a longitudinal cross section of a stent delivery system  100  that has an improved metal core wire. Though they are not shown in 
       FIG. 10 , it is clearly envisioned that elastic bands such as the elastic bands  16  and  18  of  FIGS. 1 and 2  could also be used with but are not required for the stent delivery system  100  of FIG.  10 . The stent delivery system  100  has a fixed guidewire  152  with a centrally located distal core wire portion  151 D to which a cylindrical shaped plastic piece  153  is attached. The inflatable balloon  155  is joined at its distal end to the plastic piece  153  and joins at its proximal end to a central tube  156 . (Folds in the inflatable balloon are not shown in this figure.) A pre-deployment stent  154  is co-axially mounted onto the balloon  155 . Ideally, the stent  154  would be coated with a drug coating such as the drug sirolimus. The central tube  156  connects at its proximal end to the distal end of the proximal tube  158 . The proximal end of the proximal tube  158  may be similar in structure to the proximal end of the stent delivery system  50  shown in FIG.  7 . 
     The core wire of the stent delivery system  100  is formed in four parts, namely a distal core wire portion  151 D, a central core wire portion  51 C lying within the balloon  155 , a mid-section  151 B that extends from the proximal end of the balloon  155  to the proximal end of the tube  156 , and a proximal section  151 A that extends from the distal end of the tube  158  to the proximal end of the tube  158 . The distal core wire portion  151 D is centrally located within the fixed guidewire  152  and is located at the distal end of the stent delivery system  100 . The distal and central portions of the core wire  151 D and  151 C are similar in diameter and both are thinner than the sections  151 A and  151 B. As with the other embodiments, the wire  151 D could have a cross section that is flat, square or round. Sections  151 A and  151 B have a greater cross sectional area to improve pushability and torquability of the system  100  through the coronary anatomy. 
     The mid-section  151 B of the core wire has a decreased cross sectional area as compared to the proximal portion  151 A to facilitate bending of the section of the system  100  between the balloon  155  and the proximal tube  158 . The length of the mid-section  151 B and the tube  156  should be between 5 and 15 cm for best application to the coronary vasculature. As the proximal section including the proximal tube  158  and proximal core wire  151 A are intended to lie proximal to the coronary vasculature, they may be less flexible than the sections of the catheter  100  that are more distal. The use of Nitinol shape memory core wires described for the embodiment  50  of  FIGS. 5 and 6  is also applicable to the system  100  of FIG.  10 . 
     Various other modifications, adaptations, and alternative designs are of course possible in light of the above teachings. Therefore, it should be understood at this time that within the scope of the appended claims, the invention might be practiced otherwise than as specifically described herein.