Abstract:
A stent delivery system for delivering a stent comprising, a stent disposed on the distal end of the catheter, and an inner core, wherein the inner core is resistant to appreciable compression or accordion. The catheter further comprising a first sheath covering a portion of the inner core, wherein at least a portion of the distal end of the inner core is left uncovered by the first sheath, a retractable sheath which covers at least a portion of the stent and a portion of the distal end of the inner core and a retracting means for retracting the distal sheath to release the stent.

Description:
The present application is a continuation application of U.S. application Ser. No. 09/129,458, filed: Aug. 4, 1998, now U.S. Pat. No. 6,096,054, which was a divisional application of U.S. application Ser. No. 08/484,006, filed Jun. 7, 1995, which issued on Aug. 4, 1998 as U.S. Pat. No. 5,788,707, both of which are incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a stent delivery catheter system, such as the kind used in percutaneous transluminal coronary angioplasty (PTCA) procedures. More particularly, it relates to a stent delivery catheter employing a novel retractable protective sheath and a compression resistant inner shaft, and to a method of making the retractable protective sheath. 
     BACKGROUND OF THE INVENTION 
     In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. An over the wire (OTW) balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The OTW catheter may have a guide wire lumen which is as long as the catheter or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter. Alternatively, a fixed wire balloon catheter could be used. This device features a guide wire which is affixed to the catheter and cannot be removed. 
     In certain known stent delivery catheters, a stent and an optional balloon are positioned at the distal end of the catheter, around a core lumen. The stent and balloon are held down and covered by a sheath or sleeve. When the distal portion is in its desired location of the targeted vessel the sheath or sleeve is pulled back to expose the stent. After the sheath is removed, the stent is free to expand or be expanded. Such stent delivery catheters have had problems with the integrity of the inner core and the outer sheath. In a normal pull back system the friction encountered when pulling the distal sheath off of the stent causes the innermost shaft to compress or accordion and the outermost sheath to elongate. This increases the likelihood of the inner core collapsing and the failure of the device to deploy the stent. 
     The present invention is directed toward remedying this collapsing or accordion type failure of the inner core. The invention is also directed toward an improved sheath and a method of making a low friction, strong, flexible sheath to be used in the stent delivery catheter. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved stent delivery catheter. The catheter includes a stent disposed on the distal end of the catheter, an inner core, which is flexible and resistant to appreciable compression or accordion, and an outer sheath covering a majority of the inner core, excluding at least a portion of the distal end of the inner core. The catheter further comprises a retractable distal sheath which covers at least a portion of the stent and a portion of the distal end of the inner core and a retracting means for retracting the distal sheath to release the stent. 
     The present invention further provides a retractable distal sheath and a method for making said retractable distal sheath. The inventive method comprises: placing a sheath comprising tetrafluoroethylene fluorocarbon polymers (TFEF) or fluorinated ethylene-propylene resins (FEP), such as Teflon™, on a mandrel, and winding a wire coil around the sheath. The sheath or tubing is then heated, allowing the tubing to soften and the wire coil to create grooves in the soft tubing. After a certain period of heating, the tubing is allowed to cool and the mandrel and wire coil are removed. The resulting sheath demonstrates increased flexibility, sufficient strength and a low coefficient of friction. 
     Other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of the structure, and the combination of parts and economics of manufacture, will become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this specification. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows a side view of a catheter according to the invention including a cross-sectional view of the distal portion thereof. 
     FIG. 2 shows a partial cut away view of a distal portion of a catheter according to the invention. 
     FIG. 3 shows a side view of the proximal end of a catheter according to the invention showing the manifold portion thereof. 
     FIGS. 4 a - 4   d  show side views of optional contour patterns for the retractable distal sheath of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 there is shown a cross-section of the distal portion of a specific embodiment of a stent delivery catheter generally designated as  10 . The device generally comprises an outer sheath  20  which covers the majority of the catheter excluding a portion of the distal end of the catheter. This sheath  20  is characterized by a low friction coefficient and high flexibility, and preferably is comprised of a polyolefinic ionomer material, such as a single layer Surlyn™ sheath. The outer sheath  20  surrounds an inner core  40  which extends to the distal tip  12  of the catheter. The inner core is preferably a spring coil  40 , the manufacture of which is well known in the art, and is fashioned to be both flexible when navigated through body lumens and rigid when being pulled back upon itself during stent release. The spring coil may be made from a variety of material, including stainless steel, elgiloy, Nitinol™, Kevlar™ or other metals and structural plastics. Preferably, it is made from stainless steel. The present invention further comprises a retractable distal sheath  14  covering a stent  18 , which is loaded around the distal end of the inner core  40 , and a retracting member  41 , which is connected to the retractable distal sheath  14  and allows the physician to retract the distal sheath  14  from the proximal end of the catheter. The retractable sheath  14  may be flexible or rigid, and is generally used to protect stent  18  and the vessel wall and/or to hold a self-expanding stent in the delivery configuration. The distal sheath  14  and the method for making it are discussed further below. The retracting member  41  may be a rod, a tube, a pull back wire or the like, but is preferably a wire. The retracting member  41  extends proximally through the outer sheath  20 , preferably through a retracting member lumen  80 , such as a tube preferably made from high density polyethylene (HDPE), but which could also be made from low density polyethylene (LDPE), polyimide, Teflon™ or other lubricious shaft material. In the preferred embodiment, the retracting member lumen  80  extends longitudinally under the outer sheath  20 , and houses the pull back wire  41 . The retracting member lumen  80  that houses the pull back wire  41  may also carry flushing fluid for purging and cleaning the catheter at the distal end. Retracting member  41  exits the retracting member lumen  80  at exit hole  90 , and continues distally to where it is attached to the distal sheath at point  21 . The invention additionally comprises a proximal sheath  16  which covers the exposed area between the outer sheath  20  and the distal sheath  14 , serving to protect the inner core  40  and the retracting member  41  in this area. The proximal sheath  16  is adhered to the proximal end of the distal sheath  14  and slidably overlaps the distal end of the outer sheath  20 . As the distal sheath  14  is retracted, the proximal sheath  16  is forced back, sliding over the outer sheath  20  giving the distal sheath room to retract. The distance between the proximal end of the distal sheath  14  and exit hole  90  should preferably be far enough apart to allow complete release of the stent. The distal sheath  14  and the proximal sheath  16  may be two separate sheaths adhered to one another, or they may be combined to form on continuous sheath. Finally, a stiffening wire  60 , preferably made from stainless steel, but which could also be made from Nitinol™ or Elgiloy, may also be incorporated longitudinally along the axis of the catheter  10  for extra stability and control. 
     FIG. 2 shows the layers of the catheter excluding the distal portion of the outer sheath  20 , the distal and proximal sheaths and the stent. As shown, the stiffening wire  60  and the retracting member lumen  80 , which are positioned longitudinally along the catheter, may be truncated prior to the flexible distal tip. The truncated portion  28  may be terminated at the end of the outer sheath  20  or extend into the gap between the distal end of the outer sheath  20  and the proximal end of the distal sheath  14 , as shown in FIG.  1 . The retracting member  41  extends out through the truncated lumen  28  connecting with the distal sheath  14 . 
     In the preferred embodiment, the distal sheath  14  is connected via a short section of hypotube  22 , configured as an annular ring, to the pull back wire  41 . The proximal end of the distal sheath  14  is adhered to the annular ring  22  and the pull back wire  10  is connected, preferably welded, to the inside of the annular ring  22 . Proximal to the placement of the stent  18  is a stopper  24 . The stopper  24  is usually a piece of tubing attached at position  23  to the inner core, and is used to prevent the stent  18  from moving proximally when the distal sheath  14  is pulled back over the stent  18 . 
     The proximal portion of the catheter, as shown in FIG. 3, comprises of a manifold system  27  which includes a sliding member  26  slidably integrated between the distal end of the manifold and the proximal Luer fitting  30 . It is connected to the pull back wire  41  by a weld, insert mold or other connection means. By sliding the sliding member  26  of the manifold  27 , distal to proximal, the distal sheath  14  is retracted exposing the stent  18 . The manifold  27  may further comprise a hydrating luer  32 , which is located on the distal end of the manifold  27  and is used to hydrate the distal tip  12 . 
     The inner core  40  is a non-compressible inner shaft that resists collapse or accordion type failure during the retraction of the distal sheath  14 . In the preferred embodiment, a spring coil, most preferably a  6 -fillar spring coil, is utilized for the inner core of the delivery device. A spring coil  40  such as used in the present invention provides both flexibility during placement and rigidity during distal sheath retraction. The spring coil  40  allows the delivery system to deploy the stent  18  despite the amount of friction encountered at the distal end resulting from the use of a self expanding stent  18 . As the wire  41  is pulled back to expose the self expanding stent  18 , the spring coil  40  will collapse slightly upon itself until the excess pitch has been taken up. Once this has happened, the spring coil  40  behaves as a rigid solid structure and therefore will not accordion, providing enough structural support for the distal sheath  14  to be pulled back and expose the self expanding stent  18 . 
     To prepare the stent delivery catheter  10  the stent  18  is compressed and loaded on the distal end of the inner core  40  inside of the distal sheath  14 . The stent  18  is surrounded by protective distal sheath  14 . The distal sheath remains covering the underlying stent during the placement of the stent  18  by the delivery catheter  10  through the patient&#39;s vasculature. During the placement of the stent, protective distal sheath  14  protects the patient&#39;s vasculature from the stent  18 . When it is time to expand the stent  18  into an enlarged diameter form and secure the stent in a patient&#39;s vasculature, the distal sheath  14  is retracted from over stent  18  by sliding the sliding member  26  proximally. As the sliding member is pulled back the distal sheath  14  starts to retract. Once the stent  18  is dragged slightly back by the retracting distal sheath and is butted up against the stopper  24 , the stent  18  expands fully as the distal sheath  14  continues to be pulled back. Preferably the stent is self expanding, such as a well known Nitinol™ stent, or it may be expanded by means of an optional internal balloon (not shown) positioned under the stent on the distal end of the inner core  40 , as is well known in the art. Once the sheath  14  is fully retracted the optional placement balloon would be inflated through its inflation lumen (not shown) to deploy the stent. After the stent is expanded and in place, the catheter is withdrawn. 
     The stent deployment catheter preferably incorporates a distal sheath material covering the stent with the following characteristics: low coefficient of friction to slide over the stent, which may comprise collagen material coating or bare metal, radial strength in order to hold down the self expanding stent and high flexibility to maneuver through torturous vasculature. Sheaths comprising tetrafluoroethylene fluorocarbon polymers (TFEF) or fluorinated ethylene-propylene resins (FEP), such as Teflon™, have been found by the inventor to have the least amount of friction when dragged against the stent and inner core, while providing adequate radial strength to hold the stent in place. However, the TFEF/FEP sheaths have thick walls and make the distal tip too stiff for use in the peripheral anatomy. The present invention contemplates using TFEF/FEP sheaths as the distal sheath, or both the distal sheath and the proximal sheath, of the stent deployment catheter and a new method of making the thick TFEF/FEP sheaths more flexible for use in a tortuous anatomy. 
     In making the desired distal sheath, a standard piece of Teflon™ tubing is placed on a mandrel just slightly smaller than the tubing&#39;s inner diameter. Using a coil winder, a wire coil is wound directly over the tubing advancing from one end to the other end, noting the pitch and tension of the wire as the coil is laid on top of the Teflon™ tubing. The wire chosen can be either a round cross section or a rectangular cross section, preferably round with a diameter between 0.005″-0.015″. Heat is applied circumferentially to the coil wound tubing, at about 375° C.-450° C., preferably 420° C. The tubing is then allowed to cool to approximately room temperature and the spring coil and the mandrel are removed from the tubing leaving a contoured tube. The coil winder used to create the contoured surface may be wound to produce a variety of contour patterns. FIGS. 4 a - 4   d  illustrate possible configurations. The amount of flexibility can be controlled by varying the amount of tension on the wire, the size of the wire, the wire profile, and the pitch of the wire. Preferably, a pitch of 0.010″-0.075″ is utilized. 
     This type of heat method provides a contoured surface on the Teflon™ sheath which results in a measurably improved retractable sheath having increased flexibility and sufficient strength. During heating, the tension from the hot wire leaves grooves in the softened tubing which allow the tubing to be more flexible. The resultant increase in flexibility is by approximately seven times when compared to the original piece of tubing, while still providing enough radial strength to hold down the stent as well as providing the needed lubricity to remove the sheath from the stent. While fluorinated polymers are preferred, any thermoformable polymer may be employed. 
     The contouring process may also be used to provide flexible shafts for other medical devices such as balloon catheters or infusion catheters, or for any other devices in which a flexible shaft is needed. In an infusion catheter, flexibility could be provided by contouring the distal end of the device. In a balloon catheter, the contouring could be used on either the inflation lumen or guidewire lumen as it would provide for fluid containment while providing flexibility. 
     The above disclosure is intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.