Abstract:
A stent delivery system for medical treatment of a patient and for performing primary or direct stenting includes a balloon catheter, a stent, a sheath, and a flexible tapered introducer tip. The balloon catheter has a hub, shaft, and inflatable balloon, as well as a tubular stent mounted about the deflated balloon and crimped to an initial diameter. The introducer tip is affixed to the distal end of the balloon catheter and tapers to a maximum outer diameter equal to the crimped stent outer diameter plus the sheath wall thickness. The composite sheath has a multiple diameter design with a distal portion adapted to retractably cover the crimped stent, and a proximal portion having a smaller diameter. This smaller diameter enables greater flow of a radiopaque contrast fluid around the outside of the proximal sheath and through the inside of a guiding catheter, thus providing the system with a high visibility capability. The introducer tip defines a shoulder against which the sheath can push in a distal direction, assisting the stent delivery system to perform primary stent delivery without a preliminary angioplasty procedure.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     1. Technical Background 
     The present invention relates generally to medical devices, and more particularly to a stent delivery catheter system. 
     2. Discussion 
     Catheter systems are used in a variety of therapeutic applications, including many vascular treatments. Various types of catheters are available, such as balloon catheters for procedures such as angioplasty. Angioplasty can be used to treat vascular disease, in which blood vessels are partially or totally or partially blocked or narrowed by a lesion or stenosis. By way of example, the present invention will be described in relation to coronary and peripheral angioplasty and other vascular treatments. The coronary procedure is often referred to as PTCA, which stands for “percutaneous transluminal coronary angioplasty”. However, it should be understood that the present invention relates to any stent delivery system having the features of the present invention, and is not limited to angioplasty. 
     Most balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and an inflatable balloon attached near one end of the shaft. This end of the catheter where the balloon is located is customarily referred to as the “distal” end, while the other end is called the “proximal” end. The balloon is connected to one of the lumens extending through the shaft for the purpose of selectively inflating and deflating the balloon. The other end of this inflation lumen leads to a hub coupling at the other end for connecting the shaft lumens to various equipment. Examples of this type of balloon catheter are shown in U.S. Pat. No. 5,304,197, entitled “Balloons For Medical Devices And Fabrication Thereof,” issued to Pinchuk et al. on Apr. 19, 1994; and also in U.S. Pat. No. 5,370,615, entitled “Balloon Catheter For Angioplasty,” issued to Johnson on Dec. 6, 1994. 
     A common treatment method for using such a balloon catheter is to advance the catheter into the body of a patient, by directing the catheter distal end percutaneously through an incision and along a body passage until the balloon is located within the desired site. The term “desired site” refers to the location in the patient&#39;s body currently selected for treatment by a health care professional. After the balloon is disposed within the desired site, it can be selectively inflated to press outward on the body passage at a relatively high pressure to a relatively constant diameter, in the case of an inelastic or non-compliant balloon material. 
     This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to partially or completely re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. The narrowing of the body passageway lumen is called a lesion or stenosis, and may be formed of hard plaque or viscous thrombus. In the case of a blood vessel, this procedure is referred to as angioplasty. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel. 
     In some cases, a flexible cylinder or scaffold made of metal or polymers, which is called a stent, may be permanently implanted into the vessel following an angioplasty procedure. The stent tends to hold the lumen open longer, to reinforce the vessel wall and improve blood flow. 
     To improve efficiency and reduce time required for the vascular procedure, it is desirable to combine these two procedures, angioplasty and stent deployment. This combined procedure may be referred to as “primary stenting” or “direct stenting.” Several benefits may be realized by employing such a combined procedure, including reduced time of the procedure, less intervention, and fewer medical devices inserted into the patient&#39;s body. 
     During a primary stenting procedure, an initial angioplasty is not performed. Rather, a modified stent delivery system is used to cross or traverse a lesion or stenosis, expand the desired site in a fashion similar to angioplasty and deploy a stent, all in a single, unified procedure. In this direct stenting procedure, the stent delivery system is first advanced within the patient&#39;s body until the stent is located within the desired site, where the lesion or stenosis is present. 
     Of course, the operating environment for the stent delivery system may be more difficult when the initial broadening angioplasty or “pre-dilatation” is absent. In other words, the vessel may be narrowed or blocked, and the lesion or stenosis may even be calcified or hardened. The stent delivery system should preferably have a mechanism for more successfully traversing a more difficult environment. After crossing the lesion, the stent delivery system balloon is inflated to expand the stent, followed by deflation of the balloon and withdrawal of the stent delivery system. 
     Previously known stent delivery systems may have been merely a balloon catheter having a stent mounted and crimped onto the deflated balloon. Such elegantly simple devices have been sufficient for many applications, but a more sophisticated system may be desirable in more challenging cases and environments. 
     Friction forces may tend to cause a crimped stent to slip in a proximal direction while the catheter system is advanced, or to slip in a distal direction if the physician decides to withdraw the stent without deploying it. It is of course desirable to retain the stent securely in the proper position. 
     The stent delivery system should also preferably protect the stent from damage or deformation during this period. It is further desirable that the stent delivery system should be able to push through and traverse as many different anatomical arrangements and stenosis configurations as possible. Moreover, the stent delivery system should preferably have a positive mechanism for holding and then releasing, expanding, and deploying the stent at the desired site. 
     Accordingly, the stent delivery system also desirably includes a mechanism for securing the stent in the form of a sheath, capable of completely covering the crimped stent during insertion. This sheath is permanently mounted about the balloon catheter, yet able to slide in a proximal direction from the stent-covering position, to uncover the stent during inflation of the balloon and expansion of the stent. 
     Prior stent delivery systems were often designed for the smallest possible outer diameter or profile at the distal end. The small profile was preferred for access into small vessels following angioplasty. In addition, prior stent delivery systems generally provided distal tips which were as short as possible, sometime extending only a few millimeters beyond the distal balloon leg. 
     However, the present direct stent delivery system preferably contradicts these prior design ideas by providing an enlarged and lengthened, flexible tapering tip. This distal tip tapers gradually up to an outer diameter preferably equal to the largest outer diameter of the entire system, and tends to gently widen any particularly narrow stenoses. 
     In addition, the sheath should have sufficient wall thickness to push distally against a portion of the flexible tip, to increase the column strength of the stent delivery system. This enhanced “pushability” better enables the stent delivery system to traverse and cross a lesion or stenosis. 
     In addition, the stent delivery system should provide for high visibility under fluoroscopy. Often the stent delivery system will be used in conjunction with an outer guiding catheter, which surrounds and guides the stent delivery system into a position near the desired site. The visibility of the stent delivery system may be affected by the size of the lumen through which radiopaque contrast fluid is injected. This fluid shows up on a fluoroscope, and is generally injected through the annular space between the inner wall of the guiding catheter and the outer surface of the stent delivery system. The visibility of the stent delivery system under fluoroscopy can therefore preferably be increased by reducing the outer diameter of the stent delivery system along a major portion of all of its length. 
     Accordingly, the present invention preferably provides a direct stent delivery system for delivering and deploying a stent. This stent delivery system preferably also provides enhanced stent position retention, as well as stent protection, during longitudinal movement of the catheter. 
     The stent delivery system also is preferably capable of traversing total vessel occlusions, preferably having enhanced pushability and a positive stent release mechanism. 
     The stent delivery system also preferably has a high visibility arrangement for the injection of radiopaque contrast medium. 
     These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an external perspective view of a stent delivery system, arranged according to the principles of the present invention; 
     FIG. 2 is a longitudinal cross-section view of the stent delivery system of FIG. 1, shown in an initial configuration; 
     FIG. 3 is a partial longitudinal cross-section view of the stent delivery system of FIG. 2, wherein the sheath is partially retracted; 
     FIG. 4 is a partial longitudinal cross-section view of the stent delivery system of FIG. 3, wherein the balloon is inflated to expand the stent; 
     FIG. 5 is a partial side elevational view of a stent delivery system arranged according to the principles of the present invention, inserted to a location near a representative example of a desired treatment site; 
     FIG. 6 is a partial side elevational view of the stent delivery system of FIG. 5, advanced to a desired position; 
     FIG. 7 is a partial side elevational view of the stent delivery system of FIG. 6, in which the sheath is partially retracted to uncover the stent; 
     FIG. 8 is a partial side elevational view of the stent delivery system of FIG. 7, in which the balloon is inflated to expand the stent; 
     FIG. 9 is a partial side elevational view of a deployed stent, after removal of the stent delivery system; and 
     FIGS. 10 and 11 are partial cross-sectional views of alternative embodiments of the balloon catheter according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiments of the present invention is merely illustrative in nature, and as such it does not limit in any way the present invention, its application, or uses. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention. 
     Referring to the drawings, a stent delivery system is depicted, with one of the preferred embodiments of the present invention being shown generally at  10 . The stent delivery system  10  illustrated in FIG. 1 includes a balloon catheter  12 , a stent  14  crimped around a deflated balloon  16 , a flexible tapered introducer tip  18 , and a sheath  20 . The balloon catheter  12  has an inflatable balloon  16  and a balloon catheter hub  22 , each affixed near opposite ends of a flexible balloon catheter shaft  24 . The inflatable balloon  16  is located near the distal end of the balloon catheter shaft  24 , and the balloon catheter hub  22  is near the proximal end. 
     The balloon catheter hub  22  provides a maneuvering handle for the health care professional, as well as an inflation port  26  and a guidewire port  28 . Either or both the inflation port  26  or the guidewire port  28  may have a coupling, accompanied by a luer-lock fitting for connecting an inflation lumen  30  to a source of pressurized inflation fluid (not shown) in the conventional manner. 
     The balloon catheter shaft  24  defines one or more passages or lumens  30  and  32  extending through the shaft, one of which is an inflation lumen  30  connected to the balloon  16  to selectively inflate and deflate it. The inflation lumen  30  provides fluid communication between the interior of the balloon  16  at the distal end of the inflation lumen  30  and the hub inflation port  26 . 
     In the illustrated embodiment, at least a portion of the balloon catheter shaft  24  is constructed of an inner and outer tubular body  34  and  36 . The inner body  34  defines a guidewire lumen  32 , while the inflation lumen  30  is defined by the annular space between the inner and outer tubular bodies  34  and  36 . The guidewire lumen  32  is adapted to receive an elongated flexible guidewire  38  in a sliding fashion through a proximal guidewire port  28  in the balloon catheter hub  22 , and may ultimately extend out through a distal guidewire port  28  defined at a distal end of the inner body  34 . The guidewire  38  and balloon catheter  12  may thus be advanced or withdrawn independently, or the balloon catheter  12  may be guided along a path selected with the guidewire  38 . 
     The balloon catheter shaft  24  may of course have various configurations instead of this coaxial design shown in the drawings, including a single extruded multi-lumen tube defining any suitable number of parallel side-by-side lumens, a rapid-exchange configuration having a single lumen proximal shaft and a guidewire port at some location along the shaft, or a fixed-wire configuration having a short flexible and non-moveable guidewire section affixed to the tip, and others. Also, the balloon catheter shaft  24  may preferably have a proximal shaft portion formed of a metal hypotube, as is explained below. 
     The sheath  20  is permanently mounted about the balloon catheter  12 , yet able to slide a short distance longitudinally back and forth. The balloon catheter hub  22  provides fluid communication between the guidewire lumen  32  and guidewire coupling, as well as between the annular inflation lumen  30  and the inflation coupling. Of course, if the balloon catheter  12  has a fixed wire or rapid-exchange configuration, the balloon catheter hub  22  may not have a guidewire port  28  at all, but may rather have only an inflation port  26 . The inner and outer tubular bodies  34  and  36  are securely received within the balloon catheter hub  22 , and are surrounded by a tubular strain relief  40 . 
     When fully inflated as shown in FIG. 4, the balloon  16  has an inflated profile shape with a cylindrical working portion  42  having an inflated diameter located between a pair of conical end portions, and a pair of proximal and distal legs  44  and  46  affixed to the balloon catheter shaft  24 . The balloon  16  in its deflated profile shape as shown in FIG. 1 preferably has several pleats wrapped around the balloon catheter shaft  24 . The balloon material is preferably substantially inelastic, and stretches a relatively small amount under pressures of 15 atmospheres or more. Various different materials may be used, which preferably should be substantially inelastic. Some examples include Nylon, PEEK, Pebax, or a block copolymer thereof. 
     As shown in the drawings, the balloon  16  is preferably connected to the balloon catheter shaft  24  by affixing its distal end to the shaft inner tube  34 , and its proximal end to the shaft outer tube  36 . The balloon  16  thereby communicates with the annular inflation lumen  30  between the inner and outer shaft tubes  34  and  36 . The balloon  16  may alternatively be attached to the balloon catheter shaft  24  in any way that allows it to be inflated with fluid from the inflation lumen  30 . 
     The stent delivery system  10  of the present invention further has a flexible tapering introducer tip  18 , adapted to help cross and traverse lesions or stenoses. Prior balloon catheter designs tend toward very small profiles at their distal tips, with the understanding that a small profile might assist in crossing a narrow lesion. This profile is simply defined by the outer diameter of the inner tube at its distal end, which may even be drawn down to an even smaller diameter. For example, in a coronary PTCA balloon catheter, the profile of the inner tube distal tip may range from about 0.040 to as small as 0.024. All dimension in this application are expressed in inches, except where indicated otherwise. 
     However, the stent delivery system  10  of the present invention instead tapers up to a much larger profile diameter, equal to the largest outer diameter of the sheath  20 , which is slightly greater than the outer diameter of the crimped stent  14  itself. In the case of coronary direct stenting this preferred outer introducer tip  18  profile may range from about 0.047 to as much as 0.063, which is much greater than the diameter of the inner tube  34  distal profile. Indeed, the maximum diameter of the present introducer tip  18  may be more than twice that of the inner tube  34 . 
     The introducer tip  18  may be affixed to the distal end of the inner tube  34  by any appropriate method that provides secure attachment, including an adhesive or by heat welding. The material selection of the introducer tip  18  should be selected such that it is more flexible than the distal end of the inner tube  34 , even though the inner tube  34  is much smaller in diameter. This enhanced flexibility of the introducer tip  18  should preferably cooperate with the gently tapering slope to accurately follow the desired vascular path while minimizing the occurrence of any vascular trauma or complication, and tend to gently widen a stenosis or push aside thrombus. 
     Structurally, the introducer tip  18  as shown in the drawings preferably has a tapering conical main surface at its distal-most end, and a short cylindrical transition surface. The introducer tip  18  also has a short collar  48  with a slightly smaller outer diameter of preferably about 0.047-0.063, which defines a shoulder  50 . The introducer tip  18  further defines a tip guidewire lumen  32  and a larger opening for receiving the distal end of the balloon catheter shaft inner body  34 . The selection of material for the introducer tip  18  should be selected carefully, especially as far as its flexibility, preferably about 40-55D. The flexibility of the introducer tip  18  should be optimized to enable the stent delivery system  10  to accurately follow the guidewire  38  without causing prolapse. 
     The sheath  20  includes a composite diameter sheath tube and a sheath hub  52  and  54 . The sheath  20  is permanently mounted about the balloon catheter  12 , but they are the generally free to slide longitudinally a short distance. To accomplish this feature, the sheath hub  54  allows the balloon catheter shaft  24  to slidably advance and withdraw through the sheath  20 , and also preferably has a threaded screw-down locking device  56  for advancing the stent delivery system  10  as a single unit. As an alternative embodiment, a proximal portion of the balloon catheter shaft  24  may be formed or jacketed by a metal hypotube  58  or  60 , as illustrated in FIGS. 10 and 11. This improvement allows the locking device  56  to clamp down on the balloon catheter shaft  24  without crushing it or blocking one of the lumens. 
     The sheath hub  54  preferably also has an injection port  62  for allowing radiopaque contrast fluid to be injected through the sheath tube  52  and around the balloon catheter shaft  24 , thus illuminating the stent delivery system  10  on a fluoroscope. Rather than injecting through a guiding catheter (not shown), injecting radiopaque contrast through the sheath enables it to become visible when it extends distally beyond the guiding catheter. 
     The composite diameter sheath tube  52  includes at least a proximal and distal sheath tube  64  and  66 . The proximal sheath tube  64  has a smaller diameter than the distal sheath tube  66 . The minimum inner diameter of the distal sheath tube  66  is established by the crimped stent diameter, but the proximal sheath tube  64  may be smaller. The smaller proximal sheath  64  allows a higher volume and greater flow rate for injection of radiopaque contrast fluid through the guiding catheter and around the outside of the stent delivery system  10 . This high-visibility feature enables the physician to selectively see the position of the stent delivery system  10  within the patient&#39;s body more easily. 
     A stent of any suitable type or configuration is preferably provided with the stent delivery system of the present invention, such as the well-known Palmaz-Schatz balloon expandable stent. Various kinds and types of stents are available in the market, and many different currently available stents are acceptable for use in the present invention, as well as new stents which may be developed in the future. The stent depicted in the drawings is a cylindrical metal stent having an initial crimped outer diameter, which may be forcibly expanded by the balloon to a deployed diameter. When deployed in a body passageway of a patient, the stent is preferably designed to press radially outward to hold the passageway open. 
     The distal end  68  of the sheath  20  fits snugly around the cylindrical collar  48  of the introducer tip  18  and abuts the shoulder  50 . This distal end  68  of the sheath  20  thus can push against the shoulder  50  and assist in “pushability,” which is an ability to push through or cross complicated vascular anatomy. The wall thickness of the sheath tube  52  should be selected to be thick enough to add acceptable pushability. 
     The operation of the stent delivery system is depicted in FIGS. 5-9, may be inserted percutaneously along a guidewire and within an outer guiding catheter (not shown), until the guiding catheter distal end reaches the vicinity of the desired site. The stent delivery system is then advanced wherein the stent delivery system as shown in FIG. 6 until the stent covered by the sheath is positioned within the lesion  74 . 
     The sheath is then partially retracted to uncover the stent as in FIG.  7 . The balloon is inflated as in FIG. 8 to expand the stent, and the stent delivery system is removed from the patient&#39;s body as in FIG. 9, leaving the stent implanted at the desired site. 
     The balloon catheter system of the present invention may be made using any of the following methods, as well as various modifications that will be apparent to those skilled in the art. 
     Catheter manufacturing techniques are generally known in the art, including extrusion and co-extrusion, coating, adhesives, and molding. In particular for the present invention, the balloon catheter  12  may be made generally in a conventional manner. At some point before the introducer tip  18  is affixed to the distal end of the balloon catheter inner body, the sheath  20  is assembled onto the balloon catheter shaft  24 . Then the stent  14  is crimped onto the balloon  16 . After the introducer tip  18  is attached, the sheath  20  is advanced to cover the stent  14 , and the finished assembly is packaged and sterilized. 
     Of course, the components of the present stent delivery system  10  invention may be constructed of various materials and have a range of acceptable dimensions. 
     The scope of the present invention encompasses the full extent of the claims, regardless of specific numbers, materials, or other details present in this description of the preferred embodiment. 
     Preferably, the balloon catheter hub  22  and the sheath hub  54  are injection molded of any suitable material. The inner and outer balloon catheter shaft tubes  34  and  36  are preferably made of a polymer such as Nylon, the material stiffness of which may be selected as appropriate. 
     One of the advantages of the present invention is the relatively small profile diameter that is possible along most of the length of the stent delivery system  10 . Unless otherwise indicated, all dimensions are in inches. For example, the minimum crimped outer diameter of a stent may range from about 0.045-0.055. Each particular stent design of a particular expanded diameter will exhibit a minimum crimped diameter for several reasons, including that the stent struts or legs may overlap below that diameter. 
     In the case of a stent having a crimped outer diameter of 0.055, the sheath has a wall thickness of approximately 0.005 to as thin as 0.002, so the outer diameter of the distal sheath section is at most 0.060. On the tapered tip, the outer diameter and shoulder diameter match the outer and inner diameters of the distal sheath segment. 
     Because the diameter of the balloon catheter outer body is much less than that of the crimped stent, for example 0.033, the proximal sheath can also be smaller in diameter. For example, the proximal sheath segment might have a diameter of 0.045-0.050. 
     It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion describes merely exemplary embodiments illustrating the principles of the present invention, the scope of which is recited in the following claims. Those skilled in the art will readily recognize from the description, claims, and drawings that numerous changes and modifications can be made without departing from the spirit and scope of the invention.