Abstract:
A catheter assembly is provided having an inner member and an outer member extending along a longitudinal axis, the inner member and the outer member having a coaxial configuration and dimensioned for relative axial movement. The outer member has a wall defining a longitudinal slot; a leaf spring is connected to the inner member, the leaf spring being adapted to engage with the longitudinal slot so as to maintain rotational alignment between inner member and outer member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to stent delivery systems, which are used to implant a stent into a patient&#39;s body lumen to maintain the patency thereof. The stent delivery system is useful in the treatment and repair of body lumens, including coronary arteries, renal arteries, carotid arteries, and other body lumens.  
           [0002]    Stents are generally cylindrically-shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other body lumen. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway therethrough. Stents also are useful in maintaining the patency of a body lumen, such as a coronary artery, after a percutaneous transluminal coronary angioplasty (PTCA) procedure or an atherectomy procedure to open a stenosed area of the artery.  
           [0003]    Typically, a stent is delivered intraluminally through a percutaneous incision through the femoral or renal arteries. The stent is mounted on the distal end of an elongated catheter and the catheter and stent are advanced intraluminally to the site where the stent is to be implanted. A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally. Three different approaches for expanding stents have been developed in the art, namely, balloon expanded stents, elastically self-expanding stents, and heat expanded stents. Balloon expanded stents are placed over a deflated balloon mounted on the catheter. The balloon is then inflated to expand the stent radially outwardly into contact with the arterial wall, whereupon the stent undergoes plastic deformation and remains in an expanded state to hold open and support the artery. Elastically self-expanding stents are adapted to be delivered in an elastically compressed state while confined within an outer restraining sheath, but to elastically expand when the sheath is removed and to provide support to the vessel within which it is implanted. Heat expanded stents are made from heat-sensitive materials such as nickel-titanium, are cooled in a compressed shape before insertion into the patient, but assume a pre-existing expanded shape when exposed to the body temperature of a patient.  
           [0004]    With respect to self-expanding stents, typically a retractable sheath is positioned over the self-expanding stent which is mounted on the distal end of the catheter. Once the catheter has been advanced intraluminally to the site where the stent is to be implanted, the sheath is withdrawn thereby allowing the self-expanding stent to expand radially outwardly into contact with the arterial wall, thereby holding open and supporting the artery. Both balloon expanded stents and heat sensitive self-expanding stents may also be delivered within a retractable sheath, similar to that used with a self-expanding stent. In such cases the sheath may function to secure the stent on the catheter during insertion or to prevent sharp edges of the stent from tearing at the wall of the lumen during insertion.  
           [0005]    One embodiment of a catheter delivery system is the so-called “over-the-wire” delivery system, in which a catheter is introduced into the patient over a guide wire which has been previously introduced. In this embodiment, the guide wire runs within a lumen extending the entire length of the catheter. Another embodiment of the catheter delivery system is the so-called “rapid exchange” delivery system, in which the guide wire runs within a lumen in the catheter extending from the distal tip of the catheter to a point just proximal of where the stent is positioned on the catheter, at which point the lumen terminates on the outside of the catheter and the guide wire emerges from the catheter to extend proximally, outside of the catheter. This “rapid exchange” configuration allows the surgeon to rapidly and single-handedly place the delivery system over the guide wire or to exchange one delivery system for another, because the length of the guide wire lumen in the catheter is much shorter than used in an over-the-wire delivery system.  
           [0006]    One of the problems associated with the prior art catheter-delivery systems which use a retractable outer sheath is that the addition of a retractable sheath tends to reduce the overall flexibility of the delivery system. Another problem is that, in the case of the rapid exchange delivery system, the addition of a retractable sheath to surround the catheter introduces a problem of rotational alignment between the sheath and the catheter. Upon commencement of installing the delivery system over the guide wire, the surgeon must introduce the proximal tip of the guide wire into the catheter lumen at the distal tip of the catheter. The surgeon then advances the guide wire proximally through the catheter lumen until the proximal tip of the guide wire emerges from the catheter and protrudes through an opening in the wall of the sheath. If, during the foregoing process, the sheath rotates relative to the catheter, the surgeon may have difficulty in aligning the opening with the guide wire tip, so as to get the guide wire tip to protrude from the opening. This complication can be a major problem for the surgeon to resolve under the pressure of surgery.  
           [0007]    Thus, there has been found in the art a need for a reliable rapid-exchange stent delivery system for a self expanding stent, in which rotational alignment between the outer sheath and the catheter may be maintained prior to and during the process of positioning the delivery system over the guide wire. Further, the art has found a need for a delivery system for a self expanding stent which has improved flexibility characteristics. The present invention addresses these and other needs.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a catheter delivery system having improved flexibility characteristics. In a further aspect, the invention is directed to a rapid-exchange catheter delivery system having an outer sheath, in which the sheath is held in rotational alignment with the catheter prior to and during the process of positioning the delivery system over a guide wire.  
           [0009]    A catheter assembly for removably attaching an intravascular stent is provided in which an elongated catheter has an inner member and an outer member extending along a longitudinal axis wherein the inner member and the outer member have a coaxial configuration and are dimensioned for relative axial movement. A self-expanding stent, having an open lattice structure, and being adapted to be expandable to an open configuration, is mounted on the inner member, within the outer member.  
           [0010]    The present invention includes a leaf spring, attached to the inner member, which engages with a slot on the outer member so as to maintain the inner member and the outer member in rotational alignment. The leaf spring is adapted to deflect radially inwardly and to disengage from the slot in the outer member, either after the distal tip of a guide wire is extended from within the outer member over the leaf-spring outwardly through the slot in the outer member, or when the outer member is proximally withdrawn relative to the inner member.  
           [0011]    In a further aspect of the invention, the distal end of the inner member is configured as a helical coil to enhance the overall flexibility of the delivery assembly.  
           [0012]    The invention also includes a method of implanting a self-expanding stent utilizing the catheter-delivery system described above. Using the catheter-delivery system, a guide wire is proximally advanced through a lumen of the delivery system from the distal end until it encounters the leaf-spring, whereupon the guide wire is deflected outwards through the slot. The leaf spring is deflected radially inwardly and disengages from the slot in the outer member when the outer member is proximally withdrawn relative to the inner member.  
           [0013]    The invention also relates to a method of assembling the delivery system described above. The method includes inserting the ends of the leaf spring through the wall of a tubular sleeve so that the ends are positioned within the lumen and the center portion of the leaf-spring is positioned outside the lumen of the sleeve. The sleeve is then slid over the inner member to a desired position on the inner member. The sleeve may be attached by friction fit, adhesive, or laser welding.  
           [0014]    Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a sectional view of a stent delivery system embodying features of the present invention.  
         [0016]    [0016]FIG. 1 a  is a detail view of an aspect of FIG. 1, showing an embodiment of how the leaf-spring mechanism may be positioned relative to the inner member.  
         [0017]    [0017]FIGS. 2 a ,  2   b  and  2   c  are sectional views exemplifying embodiments of the leaf-spring mechanism embodying features of the present invention.  
         [0018]    [0018]FIG. 3 is a perspective view of an aspect of the stent delivery system of FIG. 1.  
         [0019]    [0019]FIGS. 4 through 6 exemplify the stages of deploying a stent within a body lumen using a delivery system made in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    The present invention relates to a rapid exchange delivery catheter system in which a stent is delivered intraluminally into a human patient&#39;s body lumen, such as a coronary artery, carotid artery, renal artery, peripheral artery and veins, and the like. The invention provides for a stent delivery catheter assembly, a method of assembly, and a method of use in which a stent is implanted in a patient.  
         [0021]    There are numerous prior art stent delivery systems which may be used in conjunction with the present invention. The stent delivery systems suitable for use with the present invention are “rapid exchange” delivery systems which have an outer sheath adapted to slide over an inner sheath so as to cover a stent. The invention described in detail herein is described in the context of an elastically self-expanding stent delivery system. However, the invention is not limited to such use, and may equally be used with a delivery system for a balloon expanded stent or heat expanded stent.  
         [0022]    In one embodiment of the invention, as exemplified in FIG. 1, a rapid exchange catheter assembly  20  is provided to deliver and implant a stent. Rapid-exchange catheters are known in the art and details of the construction and examples of use are set forth in U.S. Pat. Nos. 5,458,613; 5,346,505; and 5,300,085. Rapid exchange catheter assembly  20  incorporates an inner member  22  and an outer member  24  arranged in coaxial alignment. Inner member  22  is slidably positioned within outer member  24  and relative axial movement between the two members is provided by inner member control handle  26  and outer member control handle  28 . The control handles  26 ,  28  can take numerous forms, but are depicted schematically for ease of illustration. As an example, however, control handles  26 ,  28  can take the form of a thumb-switch arrangement, a rotating-screw-type arrangement, or a ratcheting arrangement. Such control handle means are well known in prior art catheter-delivery systems.  
         [0023]    Inner member  22  has a proximal end  30  and a distal end  32 . Inner member comprises a catheter  34  which has proximal end  36  and distal end  38 . The catheter  34  may be surrounded by a firstjacket  35 , adapted to lend lubricity to the inner member. Inner member further comprises a guide wire lumen  40 , having proximal end  42  and distal end  44 . As exemplified in FIG. 1, guide wire lumen  40  is configured to extend distally, from its proximal end  42  which is positioned adjacent to catheter  34  and just proximal of the distal end  38  thereof, to its distal end  44  which is located at the distal end  32  of the inner member. The profile of the guide wire lumen  40  extends distally along and adjacent the catheter  34 , and then deflects from being adjacent to the catheter so as to extend coaxially therewith.  
         [0024]    Inner member  22  further includes a helical coil  46  having a proximal end  48  and a distal end  50 . The helical coil may be positioned surrounding the guide wire lumen  40  at a location on the guide wire lumen where it extends coaxially with the catheter  34 . As exemplified in FIG. 3, the helical coil  46  may be connected to the catheter  34  by means of flexible arms  52  which extend from the coil to a ring  54  surrounding the catheter  34  and crimped onto the catheter. Preferably, the helical coil, arms, and rings may be laser cut from a single tubular metallic structure. The arms are adapted to transfer axial force from the catheter  34  to the helical coil  46 . It will be appreciated that the helical coil  46  provides a degree of stiffness to the inner member at a position where there is no catheter, while at the same time providing adequate flexibility.  
         [0025]    With continued reference to FIG. 1, inner member  22  further comprises a distal tip  56  which surrounds the guide wire lumen  40  at the distal end  32  of the inner member, and is shaped to provide a low profile a traumatic end so as to facilitate movement of the delivery system through the patient&#39;s vasculature. A flexible protective layer  58  may cover the distal tip. A self expanding stent  60  in compressed state may be positioned about the distal tip  52 , held in place by outer member  24 . A blocking element  62  adapted to prevent proximal movement of the stent  60  relative to inner member  22  may be positioned between the distal tip  56  and the helical coil  46 , and may also be adapted to act as a radio-opaque marker. In an alternative embodiment, the helical coil may extend all the way to the distal end  32  of the inner member, with the distal tip  56  adapted to accommodate the coil. A second protective jacket  63  may surround the coil  46 , the guide wire lumen  40 , and portion of the catheter  34 , as exemplified in FIG. 1.  
         [0026]    The outer member  24  is configured to surround the inner member  22 , and may have a diameter at its distal end larger than at its proximal end in order to accommodate all the elements of the inner member. The self-expanding stent  60  in its compressed state is positioned around the distal tip  56  of the inner member  22  and is held in compressed state by the outer member  24 . As exemplified in FIGS.  4 - 6 , when the outer member is withdrawn proximally relative to the inner member, the stent  60  is permitted to assume its expanded state so as to support the body lumen within which it is implanted.  
         [0027]    A further component of the inner member  22  is a leaf spring  64 . In one embodiment the leaf-spring may be attached to the catheter  34  via a cylindrical sleeve  66  adapted to fit onto the catheter at a position proximal of the proximal end  42  of the guide wire lumen  40 . For purposes of assembly, the leaf-spring may be first attached to the cylindrical sleeve  66  by inserting the ends of the leaf-spring through the wall of the sleeve so that the central portion of the leaf-spring is positioned on the outside of the sleeve lumen while the ends of the leaf-spring are positioned within the sleeve lumen, as exemplified in FIG. 1 a . The resulting combination may then be slid longitudinally over the catheter  34  to the desired position, as exemplified in FIG. 1. The sleeve may be fixed to the inner member either by adhesive, by heat welding, or by laser welding. Alternatively, the sleeve may be heated prior to sliding it over the inner member, so that, when cooled, a friction fit to the inner member is achieved. Once the leaf-spring  64  is fixed to the inner member, it is adapted to protrude into a slot  68  formed in the wall of the outer member  24 . In a further aspect, the leaf spring may also protrude beyond the slot so that a substantial portion of the leaf spring is positioned outside the outer member. It will be appreciated that when the leaf-spring protrudes into the slot it provides rotational alignment between the outer member and the inner member. By maintaining such rotational alignment, the ease with which a guide wire may be threaded through the delivery system  20  is greatly enhanced, as is explained more fully below. In one particular embodiment, the leaf-spring may be made of a material having highly elastic properties such as a nickel-titanium alloy including Nitinol, or a chromium-cobalt-nickel alloy including Elgiloy™ (manufactured and sold by Elgiloy of Elgin, Ill.), which will not readily lose its shape through plastic deformation should it be subjected to large strain. This quality is useful in that it has been found that, during assembly or storage of the delivery catheter  20 , the leaf-spring  64  may be accidentally subjected to strains which might plastically deform or fracture a leaf-spring of similar proportions made of stainless steel.  
         [0028]    In one embodiment, outer member  24  may be modified in that the perimeter of the slot  68  in the outer member may be reinforced by adding thereto a collar  69  formed of the same material as the outer member, so that the thickness of the outer member along the longitudinal edges of the slot is greater than the overall average thickness of the outer member. The collar may be connected to the outer member by adhesive or known heat or laser welding techniques. It will be appreciated that the ability of the outside catheter to resist bending is reduced in the vicinity of the slot, and thus accidental excessive bending at the location of the slot may cause the outer member to plastically deform and form a permanent kink along a longitudinal edge of the slot, which may render the delivery assembly unusable. Thus, reinforcement of the outer member in the vicinity of the slot as described above may reduce accidental damage of such kind. The slot itself may be cut into the outer member and the collar with a sharp edge, or, alternatively, by known means using laser.  
         [0029]    With reference to FIGS.  4 - 6 , preparation for deploying a stent within a patient (not shown) using the delivery assembly of the present invention may commence using procedures which are well-known in the art, with the positioning of a guide wire  70  in the vasculature of the patient, after which the proximal tip (not shown) of the guide wire is left protruding from the patient. The proximal tip is then inserted in the distal end  44  of the guide wire lumen  40  and threaded through the guide wire lumen until the proximal tip emerges from the proximal end  42  of the lumen. When the proximal tip of the guide wire is further advanced proximally from the proximal end  42  of the guide wire lumen, it may first contact the leaf-spring  64  and then deflect outwardly to emerge from the slot  68  in the outer member  24 . While the short cross section of the leaf-spring may be generally rectangular (FIG. 2 a ), in order to facilitate outward deflection of the guide wire the short cross sectional profile of the leaf-spring may depart from a rectangular shape, and may either have a generally “U” shape or a generally “V” shape as exemplified in FIGS. 2 b  and  2   c . The leaf-spring may be adapted to remain engaged within the slot after the guide wire is advanced through the slot, as exemplified in FIG. 4, but to disengage at a later stage, as set forth below. The delivery system  20  is then advanced over the guide wire and its distal portion is inserted into the patient as required. In order to implant the self-expanding stent  60 , the guide wire  70  is positioned in a patient&#39;s body lumen, at vessel wall  72 , and typically guide wire  70  extends past a stenosed region  74 . The catheter  20  is advanced along the guide wire until the stent  60  is positioned within stenosed region  74 .  
         [0030]    As exemplified in FIGS. 5 and 6, self-expanding stent  60  is implanted in stenosed region  74  by moving outer member  24  in a proximal direction, either while simultaneously moving inner member  22  in a distal direction or while holding it stationary relative to the patient. The leaf-spring  64  may be adapted to disengage from the slot when the outer member is moved proximally over the inner member, in that the outer member may depress the leaf-spring and, also, the outer member itself may slightly deform so as to pass over the leaf-spring. As portions of self-expanding stent  60  are no longer contained by outer member  24 , the stent will expand radially outwardly into contact with the vessel wall  72  in the area of stenosed region  74 . When fully deployed and implanted, as shown in FIG. 6, the stent  60  will support and hold open the stenosed region  74  so that blood flow is not restricted. It will be appreciated that, after the leaf-spring is disengaged from the slot and during proximal movement of the outer member  24  relative to inner member  22 , the leaf-spring  64  represents no appreciable resistance to the movement of the outer member  24 , as the leaf-spring is no longer engaged in the slot  68  of the outer member but may slide against the inner wall of the outer member. After stent  60  is implanted and contacts stenosed region  74 , the catheter  20  and guide wire  70  are withdrawn from the patient&#39;s vascular system.  
         [0031]    The stent as described herein can be formed from any number of materials, including metals, metal alloys and polymeric materials. Preferably, the stent may be formed from metal alloys such as stainless steel, tantalum, or the so-called heat sensitive metal alloys such as nickel titanium (NiTi). Stents formed from stainless steel or similar alloys typically are designed, such as in a helical coil or the like, so that they are spring biased outwardly.  
         [0032]    With respect to all of the embodiments disclosed above, inner member  22  and outer member  24  can be formed from polymeric materials including polyurethanes, polyethylenes, polyethylterpthalate, and nylons. Similarly, sleeve  66  can be formed from polyurethane, elastomeric polyesters and the like. Generally speaking, the more proximal portions of inner member  22  and outer member  24  will be formed of a polymeric material that is stiffer than the distal section so that the proximal section has sufficient pushability to advance through the patient&#39;s vascular system. On the other hand, the more distal portion of inner member  22  and outer member  24  can be formed of a more flexible material so that the distal portion of the catheter will remain flexible and track more easily over the guide wire.  
         [0033]    Other modifications and improvements may be made without departing from the scope of the invention. For example, the leaf spring is not limited to the shape exemplified in the drawings, but may be any expanding member and may assume any shape which expands to protrude through an opening or slot in the outer member. Accordingly, it is not intended that the invention be limited, except as by the appended claims.