Abstract:
A medical device for stenting within a patient&#39;s vascular system is a low profile fixed-wire balloon catheter. The balloon is not attached directly to the wire-like structure of the catheter, providing a degree of independent rotation therebetween.

Description:
FIELD OF THE INVENTION 
     The invention relates to intraluminal endovascular stenting, and in particular, to a low profile fixed wire delivery catheter. 
     BACKGROUND OF THE INVENTION 
     Endovascular stenting is particularly useful for arteries which are blocked or narrowed and is an alternative to surgical procedures that intend to bypass the occlusion. The procedure involves inserting a prosthesis into a body tube and expanding it to prevent collapse of a vessel wall. While stenting has most commonly been used adjunctively, following an intervention such as angioplasty or atherectomy, there is increasing interest in primary, or direct stent placement. 
     Percutaneous transluminal angioplasty (PTCA) is used to open coronary arteries which have been occluded by a build-up of cholesterol fats or atherosclerotic plaque. Typically, a guide catheter is inserted into a major artery in the groin and is passed to the heart, providing a conduit to the ostia of the coronary arteries from outside the body. A balloon catheter and guidewire are advanced through the guiding catheter and steered through the coronary vasculature to the site of therapy. The balloon at the distal end of the catheter is inflated, causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten re-closure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary. 
     A stent is typically a cylindrically shaped device formed from wire(s) or a tube and is intended to act as a permanent prosthesis. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during an angioplasty procedure by using a balloon catheter bearing a compressed stent which has been loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen thereby forming a supporting relationship with the vessel walls. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter. 
     A balloon of appropriate size and pressure is first used to open the lesion. The process can be repeated with a stent loaded onto a balloon. Direct stenting involves simultaneously performing angioplasty and stent implantation using a stent mounted on a dilatation balloon. The stent remains as a permanent scaffold after the balloon is withdrawn. A balloon capable of withstanding relatively high inflation pressures may be preferable for stent deployment because the stent must be forced against the artery&#39;s interior wall so that it will fully expand, thereby precluding the ends of the stent from hanging down into the channel, encouraging the formation of thrombus. 
     In adjunctive stenting, a stent delivery system with a small diameter profile is not required because the narrowing is already enlarged by the preceding device. However, in direct stenting, the stent and delivery balloon catheter need to be inserted into a stenosis that has not been previously dilated. Thus, for direct stenting to be applicable to many patients, the stent and delivery system must have a very low profile. The primary advantage of direct stenting is the procedural efficiency gained by eliminating a primary angioplasty step. The resulting procedure can be shorter and less expensive. 
     Primary angioplasty followed by stent placement typically requires a catheter exchange, which is usually performed over a guidewire. Given the prevalence of this staged procedure, the most commonly used balloon catheters have been over-the-wire types, having either a full length guidewire lumen or a short, distal guidewire lumen as found in rapid exchange catheters. Fixed wire, or “balloon-on-a-wire” type balloon catheters have been seldom used for primary angioplasty in stenting procedures, and these catheters have not been used to deliver stents at all. With their small size and wire-like trackability, fixed wire catheters are able to provide relatively quick and simple balloon placement and access to lesions that cannot be reached with other types of catheters. The small size of fixed wire catheters also permits their use through very small guiding catheters. However, these balloon catheters lack the ability to maintain guide wire position across a lesion and they may encounter problems re-crossing a dilated area. Thus, the present invention addresses these concerns to provide a fixed wire catheter suitable for direct stenting and accessing tortuous anatomy such as that found in the neurovascular. 
     SUMMARY OF THE INVENTION 
     The catheter of the present invention includes a wire-like metal shaft having a hollow portion defining a lumen extending therethrough. A core wire extends from a connection adjacent the distal end of the hollow portion. The connection includes multiple lateral crimps in the hollow portion, creating multiple lobes arranged around the core wire to provide communication with the lumen of the hollow portion. An elongate radiopaque tip spring is mounted to the distal tip of the core wire. A balloon is carried on the distal end of the shaft, but in a manner such that its distal end is unattached to the shaft thereby enabling the wire-like shaft to be rotated substantially independently of the balloon so that its rotation is not impaired. The proximal end of the balloon is attached to the distal end of an elongate outer tube, the proximal end of which is attached to the distal end of the hollow portion. The distal end of the balloon is attached adjacent the distal end of an inner tube, the proximal end of which is attached to and surrounds the core wire. The distal end of the inner tube extends distal to the balloon and surrounds the proximal end of the radiopaque tip spring. The balloon may be inflated and deflated through the lumen in the hollow portion, which communicates with the annular lumen defined between the outer and inner tubes. 
     In another embodiment of the invention, a compressed stent is mounted onto the deflated balloon of the fixed wire catheter. 
     An object of the invention is to provide an improved catheter and stent combination for low profile direct stenting. 
     Another object of the invention is to provide an improved catheter and stent combination for direct stenting in distal vascular anatomy. 
     Another object of the invention is to provide an improved catheter and stent combination for use through small diameter guiding catheters. 
     Another object of the invention is to provide an improved fixed-wire type balloon catheter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmented sectional illustration of one embodiment of the catheter; 
     FIG. 1A is a cross-sectional illustration of the catheter as seen along line  1 A— 1 A of FIG. 1; 
     FIG. 1B is a cross-sectional illustration of the catheter as seen along line  1 B— 1 B of FIG. 1; 
     FIG. 1C is a cross-sectional illustration of the catheter as seen along line  1 C— 1 C of FIG. 1; 
     FIG. 1D is a cross-sectional illustration of the catheter as seen along line  1 D— 1 D of FIG. 1; 
     FIG. 1E is a cross-sectional illustration of the catheter as seen along line  1 E— 1 E of FIG. 1; 
     FIG. 2 is a lateral view of the distal end of the catheter, with the balloon inflated and a stent mounted thereon. 
     FIG. 3 is a fragmented sectional illustration of the distal portion of another embodiment of the catheter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows one embodiment of the invention in which the catheter includes an elongate flexible metal shaft indicated generally by the reference character  10 , and which may be preferably formed from hypotubing of stainless steel, shape memory metal or other suitable material. The overall length of the catheter may be on the order of 150 cm. The shaft  10  includes an elongate hollow proximal portion  11 , about 100 cm long, and a core wire  20 , about 50 cm long. By way of example, the proximal portion of the shaft may be on the order of 0.025″ diameter having a wall thickness of the order of 0.0025″ and may be coated with a thin film of high lubricity material, such as Teflon primer paint or the like. The proximal portion  11  defines a lumen  12 , which communicates, as will be described, with the interior of the balloon  34  to inflated and deflate the balloon on the distal end of the shaft. A fitting  14  is mounted on the proximal end of the shaft  10  to facilitate connection with an inflation device, not shown, as appreciated by those of skill in the art. The shaft  10  has sufficient torsional rigidity so that it may transmit rotation effectively to the distal end of the catheter to control manipulation and steering of the distal end. 
     The core wire  20  is formed of stainless steel or other suitable metal wire and is attached, at its proximal end to the distal end of the proximal portion  11 . To facilitate the attachment between proximal portion  11  and core wire  20 , multiple lateral indentations, or crimps  16 , are formed adjacent the distal end of the proximal portion. The crimps  16  are spaced around portion  11  such that the interior surfaces of the crimps  16  contact and center core wire  20  within lumen  12 . The number, size and spacing of the crimps  16  provide therebetween lobes  44  in lumen  12 , arranged around core wire  20 . Preferably, four pairs of crimps  16  are used, as shown in FIGS. 1 and 1A, and at least one crimp is joined to core wire  20 , as by welding, brazing, soldering, adhesive or the like. The core wire  20  is tapered in a distal direction so that the device is of increasing flexibility toward the distal end. By way of example, the core wire  20  may be 50 cm long and may taper from a 0.017″ diameter at its proximal end to a 0.002″ diameter at its distal end. 
     A helical tip spring  22  is secured to the distal tip of the core wire  20  as by solder joint  24  with a portion of the tip spring extending distally beyond the distal tip of the core wire  20 . A stainless steel or tungsten or other material shaping ribbon  26  may be extended from solder joint  24  to a spring tip  28 . The tip  28  may be soldered or the like, and is rounded to present a smooth surface. The tip spring is preferably about 25 mm long and has an outer diameter of approximately 0.012″. It may be wound from 0.0025″ diameter wire, such as 92% platinum and 8% tungsten alloy wire. 
     As shown in FIG. 1, the catheter includes an outer tube  30  that is formed from an appropriate thin flexible plastic material such as polyether block amide. The outer tube  30  is attached at its proximal end to the shaft proximal portion  11 , as by heat lamination. The outer tube  30  may be of the order of 45 cm long and may have an outer diameter of about 0.037″, stepping down to a diameter of about 0.030″ for the distal 20 cm. The wall thickness of the outer tube  30  may be about 0.003″. The distal end of the outer tube  30  is attached, as by adhesive or melt bonding, to the proximal neck of the balloon  34 . 
     The balloon  34  may be formed by extrusion blow molding techniques that are conventional for balloons used in angioplasty or stent delivery. Some suitable materials for the balloon  34  are polyethylene terephthalate, polyether block amide, polyamide and polymer alloys or blends that may include these materials. By way of example, for use in delivering coronary stents, the body of the balloon may be from about 1 cm to 2.5 cm long, and have a diameter from about 2.0 mm to 3.5 mm. The double wall thickness of such balloons may range from approximately 0.0009″ to 0.0013″. 
     The distal end of the balloon  34  is attached, at its distal neck  36 , adjacent the distal end of an inner tube  38  that extends proximally about the tapered core wire  20  and is attached at its proximal end to the core wire  20  by adhesive, as illustrated at  40 . The inner tube  38  is thin walled and is preferably formed from thermoset polyimide. The wall thickness of the inner tube  38  is of the order of 0.001″ or less. The inner tube  38  should have an inside diameter just slightly greater than the diameter of the core wire  20 , and may be approximately 0.009″ inside diameter. Inner tube  38  extends distally beyond balloon distal neck  36  and surrounds the proximal end of tip spring  22 , as shown in FIG.  3 . Preferably, inner tube  38  is extended by use of an extension tube  50  which may be bonded between balloon neck  36  and the distal end of inner tube  38 , as shown in FIG.  1 . Alternatively, extension tube  50  may be omitted, and the distal end of inner tube  38  may be formed with a step-up in diameter to accept the mounting of balloon neck  36 , and to extend over the proximal end of tip spring  22 . The inner tube  38  may be about 45 cm long. The foregoing configuration results in an inner tube  38  which displays a substantial degree of column strength to resist axial buckling of the inner tube when it is subjected to an compressive load, such as when the catheter is advanced through a patient&#39;s blood vessel. The thin wall for the inner tube  38  permits a substantial amount of rotation to be absorbed by the inner tube, yet the inner tube will not buckle under axial loads because of the support of the core wire  20 . 
     As shown in FIG. 1, radiopaque marker bands  42  may be attached to the inner tube  38  within the balloon  34  to facilitate fluoroscopic determination of the position of the balloon in the patient&#39;s arteries. For the alternative embodiment shown in FIG. 3, radiopaque marker bands  42  may be attached to the core wire  20 , within inner tube  38 . 
     The lobes  44  communicate the inflation lumen  12  with the annular lumen  46  defined between the outer and inner tubes  30 ,  38 . Thus, it will be appreciated that the balloon can be inflated and deflated by an inflation medium through the lumens  12  and  46 , and lobes  44 . 
     FIG. 2 illustrates a fixed-wire catheter according to the invention with a stent  55  mounted on balloon  34 , which is shown in its expanded state. A distal extension of inner tube  38 , or preferably, extension tube  50  may be used as follows for wrapping the balloon  34  and for loading the stent  55 . The catheter may be constructed with a long extension tube  50  extending distal to the spring tip  28 . Tube  50  may then be gripped by a tool distal to and without damaging tip spring  22 . By pulling extension tube  50  with the tool, which is not shown, the balloon can be drawn by its distal neck  36  into a tubular fixture, not shown, to tightly wrap the balloon around the catheter shaft. A similar action may be used to draw the tightly wrapped balloon inside the stent  55 , which is preferably pre-compressed to a small diameter. By pulling the balloon  34 , the balloon wrapping and stent loading actions may utilize greater forces than the catheter could withstand if the balloon were being pushed instead. After the stent  55  has been loaded onto the balloon  34 , extension tube  50  can be trimmed to the length shown, for example using an excimer laser, which will not damage the underlying tip spring  22 . 
     Balloon  34  is preferably modified to retain the stent  55 , using the technique disclosed in U.S. Pat. No. 5,836,965 issued to Jendersee et al. As also disclosed in Jendersee, retainers  60  may be formed on one or both ends of the balloon  34 . A particular advantage of providing a proximal retainer  60  is that it will help prevent the proximal end of the stent  55  from catching on the tip of a guiding catheter, should the physician wish to remove the stent delivery catheter without deploying the stent. 
     Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are recognized as being within the scope of the present invention. Accordingly, the present invention is not limited to the particular embodiments which have been described in detail herein.