Abstract:
A stent-carrying balloon catheter in which a balloon is positioned within a stent for expanding the stent upon dilation of the balloon. The balloon includes a circumferential fold over a portion of the balloon itself, the fold encompassing a circumferential end portion of the stent for securing it in place until dilation of the balloon.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to improved apparatus suitable for stent delivery and implantation. 
     Stents are implantable devices which are placed within body lumens and the like, such as blood vessels. Stents are typically tubular in form, the diameter of which can be increased for implantation. They maybe made of plastic or metal. Stents are usually introduced for implantation percutaneously by means of a catheter and the diameter of the stent is increased by inflation of a balloon on the catheter. 
     In one aspect, this invention relates to an improvement in the stent delivery system described in U.S. Pat. No. 4,950,227 to Savin et al., entitled “Stent Delivery System” and issued on Aug. 21, 1990. This patent is incorporated herein in its entirety by reference. 
     That patent discloses a stent delivery system in which a catheter carries, on its distal end portion, a stent which is held in place around the catheter prior to and during percutaneous delivery by means of one and preferably two sleeves. The sleeves are positioned around the catheter with one end portion attached thereto and overlap an end portion(s) of the stent to hold it in place on the catheter in a contracted condition. Each sleeve is elastomeric in nature so as to stretch and release the stent when it expands for implantation. The stent is expandable by means of the expandable balloon on the catheter. 
     SUMMARY OF THE INVENTION 
     In a first aspect, this invention provides securement of a stent on a balloon by means of a folded or rolled end portion of the balloon itself. 
     In another aspect of this invention the balloon configured as described above is used in combination with the elastic sleeves of the Savin et al. patent. 
     Additionally, the balloon shape may be modified, as by enlarged cone portions, to facilitate the above improvements. 
     Moreover, these features may be used alone or in combination and may be applied to one or both ends of the stent to secure it for delivery. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     FIG. 1 is an axial cross-section view of one embodiment of a balloon catheter of the present invention, showing the catheter operatively disposed in a body conduit. 
     FIG. 2 is an axial cross-section view of a balloon catheter, the balloon being rolled or folded onto the catheter cannula to encompass the ends of the stent carried by the balloon; 
     FIG. 3 is an enlarged cross-section view of one end of the balloon of FIG. 2; 
     FIG. 4 is a schematic plane view of the distal end portion of a balloon catheter having a stent fixed to the catheter by means of folds in the balloon and retractable sleeves; 
     FIGS. 5,  6 ,  7  and  8  are schematic views showing simultaneous expansion of a catheter balloon and stent and the resultant release of the stent from the balloon and retaining sleeves; 
     FIG. 9 is a schematic showing of a balloon of modified construction according to the invention; 
     FIG. 10 is an axial cross-section similar to FIG. 1 showing the balloon of FIG. 9 on a catheter with retractable sleeves, and 
     FIG. 11 is a schematic view in fragment of another embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A stent-carrying balloon catheter is illustrated generally in FIG.  1  and designated by the reference numeral  10 . The catheter  10  is operatively disposed in a body conduit defined by walls  11  and includes an elongate cannula  12  having a distal end  14  and a proximal end (not shown). 
     Catheter  10  includes a balloon  16  (inflated) having a distal end wall  18  and a proximal end wall  21 . A central wall  27  is disposed between end wall  18  and  21  in a central region  30  of balloon  16 . 
     In this embodiment the end walls  18  and  21  are relatively thick and relatively small in diameter. This is in comparison to central wall  27  of balloon  16  which is relatively thin and relatively large in diameter. 
     A pair of transition walls or cones  32  and  34  are of particular interest to the preferred embodiment of this invention. A stent  36  is shown on balloon  16  being expanded by the dilated balloon. 
     Referring to FIGS. 2 and 3, the cones  32  and  34  of particular interest are discussed in more detail. As can be seen in the Figures, cone portions  32  and  34  are rolled or folded as at  32   a  and  32   b  under or over themselves and the catheter cannula  12  to encompass the ends  36   a  and  36   b  respectively of the stent thus securing it to the catheter. 
     Upon inflation of balloon  16 , folds  32   a  and  32   b  open to a configuration similar to that shown in FIG. 1 to release the stent for expansion by the balloon. 
     Referring to FIG. 4, a stent delivery system  10  includes a balloon catheter  12  having a balloon  16  fixed to the catheter for remote inflation as is known in the art. The catheter includes an elongate cannula  46  and may include marker bands  44 . Balloon  16  is shown in a somewhat contracted state. A stent  36  is positioned about balloon  16  on catheter  12  and held by two overlying retaining sleeves, a proximal one  40  and a distal one  42 . 
     Stent  36  may be of any known type. In this instance for example it may be a balloon expandable stent of stainless steel, such as the known types which are cut or etched from hypotubes. 
     Sleeves  40  and  42  may be axially fixed along catheter  12  as by an adhesive (not shown). The sleeves overlap stent  36  at each of the stent ends or margin  36   a  and  36   b  as shown. Additionally, further securement of stent  36  is provided by balloon folds  32   a  and  32   b  similar to those shown in FIGS. 2 and 3. 
     Sleeves  40  and  42  are comprised of elastomeric polymeric material such as rubber, urethane, styrenes, silicone, polyurethane, polyethylene, PET, ABS and polyimides. A lubricant additive such as silicone may be included in or on the sleeves. Additionally, further securement of stent  16  is provided by balloon folds  32   a  and  32   b  similar to those shown in FIGS. 2 and 3. 
     Referring to FIGS. 5,  6 ,  7  and  8 , the stent delivery system  10  of FIG. 4 is inserted percutaneously by known technique into a body lumen or the like. As the stent is positioned (FIG.  2 ), balloon  16  is expanded (FIGS.  6  and  7 ). During balloon expansion, stent  36  is also expanded and sleeves  40  and  42  deform elastically while balloon folds  32   a  and  32   b  open to release the stent. The balloon is then deflated by standard technique and catheter  12  with sleeves  40  and  42  is axially removed leaving stent  36  implanted (FIG.  8 ). 
     In some instances, only one sleeve may be provided at one end in the system. Also, only one fold may be provided in the balloon at one end. Preferably, the fold(s) are in the end regions of the balloon but could be located anywhere to accommodate the size stent used relative to the balloon length used. 
     Referring now to FIG. 9, a balloon  16  of modified construction according to the invention is shown. Balloon  16  includes a central body portion  30  of a nominal size, distal catheter attachment ends  18  and  21 , and cone portions  32  and  34 , also in end regions of the balloon. Cone portions  32  and  34  are larger in diameter, at least adjacent to their attachment to body  30 , than the nominal body  30  size. 
     A purpose of this construction modification in the balloon is to facilitate sleeve retraction as is shown in FIG.  10 . As can be seen from the Figure, when balloon  30  begins to inflate, the enlarged cones  32  and  34  increase in size to aid in sleeve  40  and  42  retraction to expose the stent  36  for expansion upon further inflation of the balloon. 
     It is contemplated within the purview of this invention that the balloon, particularly in the region of the cones, may be physically modified so as to change the mechanical characteristics of the balloon in order to facilitate folding of the balloon. For example, this may be accomplished by forming slits or other apertures in those regions of the balloon. Sealing would be accomplished by the balloon fold or by covering by the sleeves. Such apertures might be formed in the balloon as made or formed in it later. For example, when the stent is crimped to the balloon, the stent ends maybe utilized to form apertures in the balloon material. 
     Referring now to FIG. 11, which is a fragment schematic of a catheter system similar to those of the preceding Figures, a modified balloon construction is shown in which the stent  36  is positioned within a raised end  16   a  and  16   b  of balloon  16 . Optionally, a dam  50  may be included as is known in the art. The balloon will preferably include raised end portions at both ends as shown. However, only one end, preferably the distal end  16   a,  could be raised. The raised relationship may be slitted by forming it in the balloon similar to the construction shown in FIG.  9 . Rotating sleeves may be optionally used in this embodiment. 
     The above Examples and disclosure are 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.