Patent Publication Number: US-7901449-B2

Title: Bifurcated endoluminal prosthesis

Description:
This application is a continuation application of application Ser. No. 10/692,886 filed Oct. 24, 2003, which is a continuation of Ser. No. 08/463,987, filed Jun. 5, 1995, now pending, which is a divisional of Ser. No. 08/317,763, filed Oct. 4, 1994, now U.S. Pat. No. 5,609,627, which is a continuation-in-part of Ser. No. 08/312,881, filed Sep. 27, 1994, now pending. The present application is also a continuation-in-part of Ser. No. 08/312,881. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention related to a bifurcated endoluminal prosthesis for use in a bifurcated blood vessel such, for example, as the infrarenal portion of a mammalian aortic artery where it bifurcates to the common iliac arteries. The present invention also embraces a stent connecting means for connecting a stent (e.g. a stent which forms part of an endoluminal prosthesis) to another stent, as well as apparatus and method for introducing prostheses to the vasculature and methods of treating angeological diseases. 
     A stent is used to provide a prosthetic intraluminal wall e.g. in the case of a stenosis to provide an unobstructed conduit for blood in the area of the stenosis. An endoluminal prosthesis comprises a stent which carries a prosthetic graft layer of fabric and is used e.g. to treat an aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of embolism, or of the natural artery wall bursting. Typically, a stent or endoluminal prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm by so-called “minimally invasive techniques” in which the stent is compressed radially inwards and is delivered by a catheter to the site where it is required through the patient&#39;s skin or by a “cut down” technique in which the blood vessel concerned is exposed by minor surgical means. When the stent is positioned at the correct location, the catheter is withdrawn and the stent is caused or allowed to re-expand to a predetermined diameter in the vessel. 
     U.S. Pat. No. 4,886,062 discloses a vascular stent which comprises a length of sinuous or “zig-zag” wire formed into a helix; the helix defines a generally cylindrical wall which, in use, constitutes a prosthetic intraluminal wall. The sinuous configuration of the wire permits radial expansion and compression of the stent; U.S. Pat. No. 4,886,062 discloses that the stent can be delivered percutaneously and expanded in situ using a balloon catheter. 
     U.S. Pat. No. 4,733,665 discloses an expandable intraluminal graft which is constituted by a tubular member formed from a plurality of intersecting elongate members which permit radial expansion and compression of the stent. 
     EP-A-0556850 discloses an intraluminal stent which is constituted by a sinuous wire formed into a helix; juxtaposed apices of the wire are secured to one another so that each hoop of the helix is supported by its neighboring hoops to increase the overall strength of the stent and to minimize the risk of plaque herniation; in some embodiments the stent of EP-A-0556850 further comprises a tubular graft member to form an endoluminal prosthesis. 
     The prior art stents and prostheses mentioned above are generally satisfactory for the treatment of aneurysms, stenoses and other angeological diseases at sites in continuous unbifurcated portions of arteries or veins. 
     However, the prior art stents and prostheses are not wholly satisfactory for use where the site of desired application of the stent or prosthesis is juxtaposed or extends across a bifurcation in an artery or vein such, for example, as the bifurcation in the mammalian aortic artery into the common iliac arteries. For example, in the case of an abdominal aortic aneurysm (“AAA”) in the infrarenal portion of the aorta which extends into one of the common iliac arteries, the use of one of the prior art prosthesis referred to above across the bifurcation into the one iliac artery will result in obstruction of the proximal end of the other common iliac artery; by-pass surgery is therefore required to connect the one iliac artery in juxtaposition with the distal end of the prosthesis to the other blocked iliac artery. It will be appreciated by a person skilled in the art that it is desirable to avoid surgery wherever possible; the requirement for by-pass surgery associated with the use of the prior art prosthesis in juxtaposition with a bifurcation in an artery therefore constitutes a significant disadvantage. 
     SUMMARY OF THE INVENTION 
     Throughout this specification, the term “proximal” shall mean “nearest to the heart,” and the term “distal” shall mean “furthest from the heart.” 
     According to one aspect of the present invention there is provided a stent connecting means for connecting two intraluminal stents one to the other to define a continuous lumen through the two stents, the stent connecting means including a first stent including a male engaging portion which can be compressed radially inwardly, and a second stent including a female cooperating portion. The male engaging portion may be entered into the female cooperating portion in a radially compressed state and thereafter caused or allowed to expand in the female cooperating portion; the arrangement being such that in service the interengagement of the male engaging portion and the female cooperating portion serves to resist longitudinal separation of the two stents one from the other. 
     Typically, the first stent may include a proximal male engaging portion; the second stent may include a distal female cooperation portion. The male engaging portion may be flared radially outwardly towards its extremity, and the female cooperating portion may be tapered radially inwardly towards its extremity. In some embodiments, the male engaging portion may comprise a frustoconical wall which flares outwardly towards its longitudinal extremity; the female engaging portion may comprise a frustoconical wall which tapers radially inwardly towards its longitudinal extremity. 
     Alternatively, said male engaging and female cooperating portions may be substantially untapered; they may be substantially cylindrical. 
     The male engaging portion of the first stent may be resiliently compressible in a radially inwards direction such that in the radially compressed state it is capable of self-reexpansion to engage in the female cooperating portion. Typically, each of said first and second stents may be resiliently compressible. 
     In use therefore the second stent may be delivered in a radially compressed state by using a catheter; when the second stent is located at the site of use, the catheter may be withdrawn thereby allowing the second stent to re-expand to engage the endoluminal surface of the blood vessel. 
     The first stent may then be delivered percutaneously or by a “cut down” technique to a site distal of the second stent such that the male engaging portion of the first stent in the radially compressed state is entered into the expanded female cooperating portion of the second stent; the catheter may then be withdrawn allowing the first stent to re-expand such that the male engaging portion engages in the female cooperating portion of the second stent. 
     In some embodiments of the present invention the second stent may have two transversely spaced distal female cooperating portions; the second stent may therefore constitute a bifurcated stent for use in juxtaposition with a bifurcation in a blood vessel. 
     Each of the two transversely spaced distal female cooperating portions may be adapted for connection to a first male stent which, in use, extends across the bifurcation into a respective one of the branched blood vessels. 
     In a particular aspect of the present invention there is provided a bifurcated intraluminal stent for use in juxtaposition with an angeological bifurcation; the bifurcated intraluminal stent comprising a proximal portion adapted to be positioned in service in a blood vessel in juxtaposition with a bifurcation, a first distal stent portion adapted to extend across the bifurcation into one of the branched blood vessels and a second distal stent portion adapted to allow blood to flow from the proximal portion into the other branched vessel. The first distal stent portion may be formed integrally with the proximal portion. 
     In some embodiments the second distal stent portion may comprise a female cooperating portion which is adapted to engage a male engaging portion of a another stent adapted to extend in the other branched blood vessel such that, in use, the bifurcated stent can be connected in situ to the other stent. The bifurcated intraluminal stent may therefore constitute a second stent in accordance with the present invention comprising a distal female cooperating portion disposed intermediate the proximal and distal extremities of the stent; the other stent may constitute a first stent in accordance with the present invention. 
     Typically, the proximal end of said second stent may be flared radially outwardly towards its extremity to engage the endoluminal surface of the artery thereby to resist longitudinal movement of the second stent in service. 
     Each of the first and second stents may comprise a sinuous wire formed into a tubular configuration. The sinuous and tubular configurations may be imparted to the wire by winding it on a mandrel. Typically, each stent may be made from a shape memory nitinol (nickel-titanium) wire which may be wound on to the mandrel to form the stent in a tubular configuration of slightly greater diameter than the diameter of the blood vessel in which the stent is intended to be used. The stent may be annealed at an elevated temperature and then allowed to cool in air so that the nitinol wire “remembers” the configuration in which it was wound on the mandrel. 
     Said nitinol wire may be type “M” nitinol wire which is martensitic at temperatures below about 13° C. and is austenitic at temperatures above about 25° C.; it will be appreciated therefore that the type “M” wire will be austenitic at body temperature of 37° C. Typically, the annealing may be conducted at about 500° C. or more for at least about 60 minutes; after cooling the wire may be immersed in cold water to facilitate removal of the wire from the mandrel with the wire in its maleable martensitic form. Typically, the cold water may have temperature of less than about 10° C.; the wire may be immersed for about 5 minutes or more. An advantage of using nitinol wire to form the stent in accordance with the present invention is that the nitinol wire is “super elastic” in its austenitic state; the radial outward force exerted by the stent on the wall of the blood vessel in use is therefore substantially constant irrespective of the diameter of the vessel and the expanded stent. 
     In some embodiments the wire may have a helical configuration as disclosed in EP-A-0556850. Alternatively, the wire may be of an entirely novel configuration, namely one in which the wire forms a plurality of hoops such that the plane of the circumference of each hoop is substantially perpendicular to the longitudinal axis of the stent. Each hoop may comprise a substantially complete turn of the wire having a sinuous configuration; optionally, as each hoop is completed, the point of winding the wire may be displaced longitudinally with respect to the winding axis to form the next hoop. When the next hoop is complete, the point of winding is moved further longitudinally with respect to the winding axis to the form the next succeeding hoop and so on. 
     It will appreciated that an advantage of this novel arrangement is that the planes of the hoops are not skewed with respect to the longitudinal axis of the stent; the longitudinal ends of the stent are “square” to said longitudinal axis, so that when the stent is caused or allowed to expand in situ there is substantially no twisting of the stent as it shortens in length. It will be appreciated that this represents a significant advantage, as in areas of stenosis or aneurysm it is desirable to minimize the movement of the stent within the blood vessel so as to reduce the potential trauma to the patient. A stent of this configuration may be used, apart from the bifurcated embodiment otherwise taught herein, in any application which in stents generally have heretofor been used. 
     Typically, the stents of this invention whether of the helical or perpendicular variety, also comprise a securing means for securing an apex of the sinuous wire in one hoop to a juxtaposed apex of a neighboring hoop so that each hoop is supported by its neighbors. The securing means may comprise a loop element of a suture material, for example, to tie the juxtaposed apices together; the loop element may also comprise a loop formed of a thermoplastics material such, for example, as polypropylene. Alternatively, the securing means may be a bead formed of a thermoplastic material around juxtaposed apices. Also alternatively, the securing means may be a loop, ring, or staple formed of wire such as nitinol. 
     The male engaging portion and female cooperating portion, of the first and second interengaging stents of this invention, may be formed separately from the remainder of the respective non-engaging portions of these stents and then the engaging and non-engaging portions secured to one another by securing means. 
     In one embodiment of the present invention, the proximal and distal stent portions of the bifurcated stent in accordance with the present invention may be formed separately; the distal end of the proximal stent portion may be secured to the wider proximal end of a first intermediate frustoconical stent portion; the narrower distal end of the first intermediate frustoconical stent portion may be secured to the proximal end of the distal stent portion. The female cooperating portion of the bifurcated stent may be constituted by a second frustoconical stent portion which is secured to the distal end of the proximal stent portion in juxtaposition with the first frustoconical portion. 
     Alternatively the first and second frustoconical portions may be omitted; the proximal and distal stent portions may be secured directly one to the other. 
     The female cooperating portion may be constituted by a generally cylindrical stent portion secured to said proximal stent portion in transversely spaced relation to the distal portion. 
     Each of the first and second stents of the bifurcated form of the present invention may carry a tubular graft layer formed from a biocompatible fabric in juxtaposition with the stent; the combined stent and graft layer constituting an endoluminal prosthesis. Typically the graft layer may be disposed externally of the stent; it will be appreciated however that in some embodiments the graft layer may be disposed internally of the stent. In some embodiments the graft layer may be secured to the stent by loop elements such, for example, as loops of polypropylene. The biocompatible fabric may be a polyester fabric or a polytetrafluoroethylene fabric; typically said fabric may be woven or a warp knitted polyester fabric. In some embodiments the woven or a warp knitted fabric may be formed in a seam-free bifurcated configuration as a sleeve for a bifurcated stent. 
     In some embodiments the male engaging portion of the first stent and the female cooperating portion of the second stent may be left uncovered. Alternatively, the fabric graft layer may extend to the proximal extremity on the external surface of the male engaging portion, and may be folded over the distal extremity of the female engaging portion to form an inner sleeve; in use the external fabric of the male engaging portion may butt against the folded over portion of the fabric internally of the female cooperating portion to form a substantially blood tight seal. 
     The present invention in one aspect therefore includes a bifurcated endoluminal prosthesis comprising a bifurcated stent in accordance with the invention and a tubular graft layer. 
     The first stent having the male engaging portion may also have a tubular graft layer. If required the first prosthesis may be introduced in a radially compressed state such that the male engaging portion of the first prosthesis is engaged in the intermediate female cooperating portion of the bifurcated prosthesis; the first prosthesis is then caused to be allowed to re-expand in situ such that the male engaging portion engages in the female cooperating portion to resist longitudinal separation of the two prosthesis in service. 
     The bifurcated prosthesis may be adapted for use in the infrarenal portion of a mammalian aorta in juxtaposition with the bifurcation of the common iliac arteries for the treatment of abdominal aortic aneurysms. In use the bifurcated endoluminal prosthesis may be introduced into the infrarenal portion of the aorta using a catheter such that the first distal stent portion extends into one of the branched iliac arteries; the catheter may then be withdrawn allowing the prosthesis to re-expand in situ. 
     It will be appreciated by a person skilled in the art that the prostheses may be introduced to the site of use percutaneously or by “cut down” techniques. 
     Any of the stents according to this invention may be provided on its external surface with circumferentially spaced wire barbs or hooks adapted to engage in the endoluminal surface of the host artery to resist longitudinal movement or slippage of the stent in use. Typically the barbs or hooks may be disposed on part of the stent which is provided with a fabric graft layer such that in use the points of the artery which are engaged by the barbs or hooks are covered by the fabric graft. It will be appreciated by a person skilled in the art that the trauma to the artery wall caused by the hooks or barbs may cause emboli; the provision of the fabric graft over the barbs or hooks in use will therefore help to prevent the introduction of such emboli into the blood stream. 
     The male engaging portion for the first stent may be provided with circumferentially spaced hooks or barbs on its external surface to engage the internal surface of said female cooperating means, thereby to reinforce the connecting means against longitudinal separation of the stents one from the other in the service. 
     The present invention therefore provides a connecting means for connecting two stents longitudinally one to the other. It will be appreciated that this represents a significant step forward in the art as it allows the provision of a bifurcated endoluminal prosthesis for use in juxtaposition e.g. with arterial bifurcations without requiring by-pass surgery to connect one of the branched arteries to the other branched artery. 
     In particular, the invention provides a bifurcated endoluminal prosthesis which can be positioned in an artery in juxtaposition with a bifurcation to extend into one of the branched arteries; the bifurcated prosthesis can be connected to another prosthesis which extends into the other branched artery. The prosthesis can be delivered percutaneously or by “cut down” methods and connected together in situ thereby to provide effective treatment of an angeological disease such, for example, as an aneurysm or a stenosis which extends across a bifurcation in a blood vessel without the need for by-pass surgery. 
     In another aspect, this invention provides an introducer for delivering, into the vasculature at an angeological bifurcation where a blood vessel branches into two branched vessels, a bifurcated endoluminal stent or prosthesis having a proximal portion adapted to be disposed in the blood vessel and a distal portion adapted to be disposed at least partially in one of the two branched vessels. The introducer comprises a tubular outer sheath, a proximal portion pusher disposed at least partially within the outer sheath, and a distal portion pusher disposed at least partially within the proximal portion pusher. 
     The present invention further provides an introducer for delivering into the vasculature at an angeological bifurcation where a blood vessel branches into two branched vessels, an endoluminal prosthesis having a proximal stent portion and a distal stent portion. The introducer comprises a tubular outer sheath, a proximal portion pusher disposed at least partially within the outer sheath and having a proximal end adapted to contact the proximal stent portion, a distal portion pusher disposed at least partially within the proximal portion pusher and having a proximal end adapted to contact the distal stent portion; and a balloon catheter, having a balloon attached thereto, disposed at least partially within the distal portion pusher. 
     This invention in another aspect provides a method for delivering a bifurcated endoluminal stent or prosthesis having a proximal portion and a first distal portion into the vasculature at an angeological bifurcation where a blood vessel branches into a first branched vessel and a second branched vessel. The method comprises inserting a first introducer containing the stent or prosthesis into the vasculature to a predetermined delivery location, the first introducer comprising an outer sheath, a proximal portion pusher, and a distal portion pusher; withdrawing the outer sheath of the first introducer while maintaining the proximal portion pusher in a fixed position until the proximal portion of the stent or prosthesis is deployed from the first introducer into the blood vessel; withdrawing the outer sheath and the proximal portion pusher while maintaining the distal portion pusher in a fixed position until the first distal portion of the stent or prosthesis is deployed from the first introducer at least partially into the first branched vessel; and withdrawing the first introducer from the vasculature. 
     This invention further provides a method for delivering, into the vasculature at an angeological bifurcation where a blood vessel branches into two branched vessels, an endoluminal prosthesis having a proximal stent portion, and a distal stent portion. The method comprises the steps of inserting an introducer containing the prosthesis into the vasculature to a predetermined delivery location, the introducer comprising an outer sheath, a proximal stent portion pusher, a distal stent portion pusher, and a balloon catheter having a balloon attached thereto; inflating the balloon to at least partially block blood flow in the blood vessel; withdrawing the outer sheath of the introducer while maintaining the proximal stent portion pusher in a fixed position until the proximal stent portion of the prosthesis is deployed from the introducer into the blood vessel; withdrawing the outer sheath and the proximal stent portion pusher while maintaining the distal stent portion pusher in a fixed position until the distal stent portion of the prosthesis is deployed from the introducer into the blood vessel; and withdrawing the introducer from the vasculature. 
     In general, this invention provides a method of treating an angeological disease at a bifurcation site where a blood vessel branches into a first branched vessel and a second branched vessel comprising the steps of disposing in the blood vessel a proximal portion of an endoluminal stent; directing blood flow from the blood vessel into the first branched vessel through a first distal portion of the endoluminal stent, the first distal portion being connected to the proximal portion and extending into the first branched vessel; and directing blood flow from the blood vessel into the second branched vessel through a second distal portion of the endoluminal stent, the second distal portion being connected to the proximal portion and extending into the second branched vessel. This method may be applied to aneurysms, occlusions, or stenosis. 
     Following is a description by way of example only and with reference to the accompanying drawings of the present invention, including novel stent constructions and methods of manufacture and use thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aspects, features and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1   a  is a front view of a bifurcated intraluminal stent in accordance with the present invention constituting part of an endoluminal prosthesis. 
         FIG. 1   b  is a front view of another stent which is adapted to be connected to the bifurcated stent of  FIG. 1   a.    
         FIG. 2(   a ) is a side view of part of the bifurcated stent of  FIG. 1   a  opened up to show its construction. 
         FIG. 2(   b ) is a side view of an exemplary mandrel used to form the part of the bifurcated stent shown in  FIG. 2(   a ). 
         FIG. 3  is a side view of another part of the bifurcated stent of  FIG. 1   a  opened up to show its construction. 
         FIG. 4(   a ) is a side view of yet another part of the bifurcated stent of  FIG. 1   a  opened up to show its construction. 
         FIGS. 4(   b )- 4 ( f ) are partial exploded views of the exemplary stent of  FIG. 4(   a ) illustrating alternative means for securing juxtaposed apices according to the present invention. 
         FIG. 5  is a schematic perspective view of a bifurcated endoluminal prosthesis in accordance with the present invention. 
         FIG. 6  is a schematic view of another bifurcated endoluminal prosthesis in accordance with the present invention. 
         FIG. 7  is a schematic view of yet another bifurcated endoluminal prosthesis in accordance with the present invention. 
         FIG. 8(   a ) is a cross-sectional view of an exemplary assembled introducer according to the present invention. 
         FIGS. 8(   b )- 8 ( e ) are side views of the component parts of the introducer of  FIG. 8(   a ). 
         FIG. 8(   f ) is a partial cross-sectional view of the introducer of  FIG. 8(   a ). 
         FIG. 8(   g ) is a cross-sectional view of part of the introducer of  FIG. 8(   f ) taken along the line A-A. 
         FIG. 9  is a side cross-sectional view of a portion an alternative embodiment of an introducer according to the present invention. 
         FIGS. 10(   a ) and  10 ( b ) are side views of other alternative embodiments of an introducer according to the present invention. 
         FIGS. 11 through 20  are sequential cross-sectional views of the bifurcation of the abdominal aortic artery during introduction of an exemplary prosthesis according to the present invention. 
         FIGS. 21(   a )- 21 ( c ) are cross-sectional views of alternative insertion apparatus according to the present invention. 
         FIGS. 22 and 23  are side views of alternative stents according to the present invention. 
         FIGS. 24(   a ),  24 ( b ),  25 ,  26  and  27  are sequential cross-sectional views of the bifurcation of the abdominal aortic artery during introduction of an exemplary prosthesis according to the present invention. 
         FIGS. 28 and 29  are cross-sectional side views of alternative delivery apparatus according to the present invention. 
         FIGS. 30-34  are sequential cross-sectional views of the bifurcation of the abdominal aortic artery during introduction of an exemplary prosthesis according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The entire disclosure of U.S. patent application Ser. No. 08/463,987, filed Jun. 5, 1995 is expressly incorporated by reference herein. 
     The present invention includes apparatus and method for treating angeological diseases in any bifurcated blood vessel. One example of such a bifurcated blood vessel is the infrarenal portion of a mammalian aortic artery where it bifurcates to the common iliac arteries. Examples of diseases that can be treated using the apparatus and method of the present invention include aneurysm, stenosis, and occlusion. 
     A bifurcated stent in accordance with the present invention which is indicated at  10  in  FIG. 1   a  comprises a wire skeleton which is constructed in four separate parts, namely a proximal part  12 , a first frustoconical part  14 , a first distal part  16  and a second frustoconical part  18 . Said bifurcated stent  10  carries a fabric graft layer ( FIGS. 5 ,  6 , and  7 ) for use as an endoluminal prosthesis e.g. in the infrarenal portion of a mammalian aorta in juxtaposition with the bifurcation of the common iliac arteries. It will be appreciated, however, that bifurcated stents (with or without fabric graft layers) for use in different parts of the angeological system and for different mammals can be constructed in accordance with the invention by varying the dimensions of the stent accordingly. 
     Each of the four parts of the bifurcated stent  10  is made in substantially the same way by winding a shape memory nitinol wire, typically nitinol type M wire, onto a mandrel  46 . 
     The construction of the exemplary proximal part  12  of the bifurcated stent  10  is shown in  FIGS. 2(   a ) and  2 ( b ); nitinol wire type M wire typically having a diameter of 0.46 mm (0.018″) is wound around mandrel  46  to form a plurality of hoops  20 . The winding surface of mandrel  46  is provided with a plurality of upstanding pins  47  disposed in a zig-zag pattern for each of the hoops  20  so that in each hoop  20  the nitinol wire follows a sinuous path to define a plurality of circumferentially spaced apices  22 . Each hoop  20  is wound onto mandrel  46  such that the plane of the circumference of each hoop  20  is substantially perpendicular to the longitudinal axis of the mandrel. 
     When one hoop  20  e.g. the hoop indicated at  20   a  has been formed, the point of winding of the nitinol wire is displaced longitudinally with respect to the axis of mandrel  46  to form the next successive hoop  20   b . The stent shown in  FIG. 2(   a ) is the stent formed on mandrel  46  shown in  FIG. 2(   b ) after cutting the stent longitudinally and rotating it 45 degrees to show the construction of the stent. 
     The proximal part of the exemplary bifurcated stent of  FIG. 1   a  is formed on the mandrel with a diameter of about 24 mm and a length in the longitudinal direction of about 55 mm. From  FIGS. 1(   a ),  2 ( a ), and  2 ( b ) it will be noted that the proximal part  12  is constituted by three hoops  20  of unit width at the proximal end  24  of the proximal part  12 , two intermediate hoops  25  of twice unit width and, at its distal end  26 , by a single hoop  20  of unit width. In the illustrated embodiment, intermediate hoops  25  have a plurality of offsets  25   a . Offsets  25   a  are formed when the wire is passed around pins  47  on mandrel  46 . Offsets  25   a  add stability to the stent. When the nitinol wire has been wound onto mandrel  46 , the nitinol wire is annealed at an elevated temperature and then allowed to cool. 
     In this embodiment of the invention the wire is annealed at a temperature of about 500° C. for 60 minutes and is then allowed to cool in air. The purpose of the annealing is so that the nitinol wire in its austenitic form “remembers” its configuration as wound on mandrel  46 ; it will be appreciated therefore that other temperatures and durations for the annealing are included within the present invention provided the nitinol wire “remembers” its wound configuration. 
     After annealing and cooling, the wire is immersed in cold water at less than 10° C. for about 5 minutes; the wire is then removed from the mandrel, and juxtaposed apices  22  of neighboring hoops  20  are secured together by securing means  99  (see  FIG. 4(   a )), which are, in this example, 0.003″ polypropylene filaments. Each apex  22  of each hoop  20  which has a juxtaposed apex of a neighboring hoop  20  is tied to the juxtaposed apex  22 . It will be appreciated, however, that in other embodiments of the invention only some of the juxtaposed apices  22  may be secured in this way. 
     In addition to polypropylene filaments, the securing means may comprise a loop element  99   a  of a suture material, for example, to tie the juxtaposed apices together, as shown in  FIG. 4(   b ). The securing means may also comprise bead  99   b  formed of a thermoplastic material around juxtaposed apices, as shown in  FIG. 4(   c ). Also alternatively, the securing means may be a loop  99   c , ring  99   d , or staple  99   e  formed of wire such as nitinol, as shown in  FIGS. 4(   d ),  4 ( e ), and  4 ( f ) respectively. 
     The exemplary first and second frustoconical parts  14 ,  18  of the skeleton shown in the figures are formed in substantially the same way as the proximal part  12  by winding nitinol wire onto a mandrel and then annealing the wire before removing it from the mandrel. As shown in  FIG. 3 , the first and second frustoconical parts  14 ,  18  are each constituted by three hoops  20  of unit width. The mandrel is tapered such that the proximal end of each of the exemplary frustoconical parts  14 ,  18  is formed with a diameter of about 12 mm and the distal end  32  of each is formed with a diameter of about 9 mm. The overall length of each of the exemplary frustoconical parts  14 ,  18  is about 18 mm. The wire used for the frustoconical parts  14 ,  18  is nitinol type M wire having a diameter of 0.28 mm (0.011″). Juxtaposed apices  22  of each of the exemplary frustoconical parts  14 ,  18  are tied together using 0.03″ polypropylene filaments as described above. The first and second frustoconical parts  14 ,  18  are secured to the distal end  26  of the proximal part  12  of the stent  10  in transversely spaced relation as shown in  FIG. 1   a  by securing the apices  22  of the hoop  20  forming the wider proximal end  30  of each of the frustoconical parts  14 ,  18  to juxtaposed apices  22  of the hoop  20  on the distal end  26  of the proximal part  12 . 
     The exemplary first distal part  16  of the bifurcated stent  10  is formed by winding nitinol type M wire typically having a diameter of 0.28 mm (0.011″) onto a mandrel to form twelve longitudinally spaced hoops  20  as shown in  FIG. 4 ; the exemplary first distal part has an overall length of about 66 mm and a uniform diameter of about 9 mm. The proximal end  34  of the distal part  16  is secured to the narrower distal end  32  of the first frustoconical part  14  by tying each apex  22  on the proximal end  34  of the first distal part  16  to a juxtaposed apex on the distal end  32  of the first frustoconical part  14  using, in this embodiment, 0.003″ polypropylene filaments. 
     The proximal part  12 , the first and second frustoconical parts  14 ,  18 , and the first distal part  16  are each covered with a tubular graft layer of a biocompatible woven fabric ( FIGS. 5 ,  6 , and  7 ) such, for example, as a plain woven fabric made from 30 or 40 denier polyester. The tubular fabric layers may be attached to the proximal and distal parts  12 ,  16  of the stent  10  by stitching with, for example, 0.003″ polypropylene filaments around the apices  22  of the underlying skeleton. The fabric covered stent constitutes one form of an endoluminal prosthesis. 
     The proximal part  12  of the wire skeleton may be provided with a plurality of circumferentially spaced hooks or barbs  43  which project through the tubular fabric layer to engage in the endoluminal surface of a host artery in service. 
     The sinuous configuration of each turn  20  of the wire skeleton of the stent  10  allows the prosthesis to be compressed resiliently radially inwards so that it can be received in a catheter e.g. a 16 or 18 French catheter for percutaneous or cut down delivery, e.g. to an intraluminal site in the infrarenal section of the aortic artery. Larger diameter catheters up to, e.g., 20 French, may be used to deliver the prosthesis using “cut down” procedures. 
     An x-ray opaque marker may be attached to one or more ends of a stent so that the delivery of the stent can be monitored using x-rays. As shown in  FIG. 4(   a ), such a radiopaque marker may typically comprise a gold or platinum wire  17  crimped onto an end of stent  16 . Alternatively, the radiopaque marker may be a tube  17   a  disposed around a length of wire on the stent, also as shown in  FIG. 4(   a ). Typically, in the bifurcated stent the marker is secured to the stent in line with the distal stent portion so that the distal stent portion can be aligned with and inserted into one of the branched arteries in situ. 
     The bifurcated endoprosthesis is positioned in the infrarenal section of the aortic artery in juxtaposition with the bifurcation of the common iliac arteries such that the first distal part  16  of the prosthesis extends into one of the common iliac arteries. The catheter is then withdrawn allowing the stent  10  to re-expand towards its configuration as wound on the mandrel in which it was annealed until the stent engages the endoluminal surface of the host artery. The barbs or hooks engage the endoluminal surface of the host artery to resist longitudinal displacement or slipping of the prosthesis in use. 
     It will be appreciated that when the bifurcated prosthesis is positioned and re-expanded in the fitted position, blood can flow from the aortic artery into the proximal part  12  of the prosthesis from where it can flow into the one common iliac artery through the frustoconical part  14  and the first distal part  16  and also into the other common iliac artery through the second frustoconical part  18 . 
     In cases where it is required to implant a prosthesis in the other common iliac artery a second prosthesis comprising a second stent  40  as shown in  FIG. 1   b  can be used. The second stent  40  includes a wire skeleton comprising a proximal frustoconical part  42  and a distal part  44 . The distal part  44  of the second stent  40  also may be covered with a tubular graft layer of a biocompatible fabric such, for example, as polyester or polytetrafluoroethylene fabric ( FIGS. 5 ,  6 , and  7 ). 
     The frustoconical proximal part  42  is constructed in the same way as the frustoconical parts  14 ,  18  of the bifurcated stent  10 ; the distal part  44  is constructed in the same way as the distal part  16  of the bifurcated stent  10 . The distal end of the frustoconical proximal part  42  is secured to the proximal end of the distal part  44  by securing juxtaposed apices using polypropylene filaments as described above. 
     In use, the second prosthesis is compressed radially inwards and is received in a catheter for percutaneous or “cut down” delivery to the other common iliac artery. The frustoconical proximal part  42  is guided, in the radially compressed state, into the second frustoconical part  18  of the bifurcated stent  10 . The catheter is then withdrawn allowing the second stent  40  to re-expand towards its remembered configuration, until the distal part  14  engages the endoluminal surface of the other common iliac artery, and the outer surface of the frustoconical proximal part  42  engages the interior surface of the second frustoconical part  18  of the bifurcated stent  10 . 
     As with other stents described herein, the frustoconical proximal part  42  may be formed with circumferentially spaced barbs or hooks  43 , as shown in  FIG. 1   b , which engage in the wire skeleton of the second frustoconical part  18  of the bifurcated stent  10 . When barbs  43  are on proximal portion  12 , they engage the inner wall of the artery. 
     The tapered configurations of the second frustoconical part  18  of the bifurcated stent  10  and of the proximal frustoconical part  42  of the second stent  40  are such that in the fitted position as described, the prosthesis are locked together to resist longitudinal separation in service. Barbs or hooks on the second stent  40  and/or an frustoconical proximal part  42  help to resist such longitudinal separation. 
     In another example of the present invention a bifurcated endoluminal prosthesis  50  as shown in  FIG. 5  includes a bifurcated stent comprising a proximal portion  52  which tapers radially inwardly from its proximal end  54  to its distal end  56 , and first and second transversely spaced frustoconical distal portions  58 ,  60  which are secured to the distal end  56  of the proximal portion  52 ; the proximal portion  52  is covered with a tubular graft layer of a biocompatible fabric  62 . 
     In use the prosthesis is delivered percutaneously or by “cut down” methods to an artery in juxtaposition with an arterial bifurcation; blood can flow through the frustoconical proximal portion  52  into each of the branched arteries through the first and second distal frustoconical portions  58 ,  60 . If a prosthesis is required in one or both of the branched arteries, a separate prosthesis comprising a stent of the type shown in  FIG. 1   b  referred to above covered with fabric can be connected to the bifurcated prosthesis  50  by inserting and re-expanding the proximal end of such a separate prosthesis in one or both of the distal frustoconical portions  58 ,  60  of the prosthesis  50  for engagement therein. 
     Another variant of the present invention is shown in  FIG. 6  which shows a bifurcated endoluminal prosthesis  70  having a proximal portion  72  which is secured at its distal end  74  to two transversely spaced frustoconical intermediate portions  76 ,  78 . 
     One of said frustoconical intermediate portions  76  is secured at its distal end to an elongate distal portion  80 . The proximal end  82  of the proximal portion  72  is flared radially outwards towards its proximal end  82  to engage the intraluminal surface of the host blood vessel in service. Save for this flared portion, the entire endoprosthesis is covered with a fabric graft layer as shown in  FIG. 6 ; said graft layer is carried externally of the wire skeleton and is folded over the distal extremity  84  of the other frustoconical intermediate portion  78  to form an internal lining in said other frustoconical immediate portion  78 . 
     Said other frustoconical intermediate portion  78  constitutes a female cooperating portion in accordance with the present invention which is adapted to receive a male engaging portion of another prosthesis as indicated at  86  in  FIG. 6 . Said other prosthesis  86  includes a frustoconical proximal portion  88  which constitutes the male engaging portion and an elongate distal portion  90 . The whole of the other prosthesis  86  is covered with a fabric graft layer as shown in  FIG. 6 . In service, the male engaging portion  88  of the other prosthesis  86  is entered into and engaged with the female cooperating portion  78  of the bifurcated prosthesis  70  in situ in the manner herein before described. The fabric layer on the male engaging portion  88  butts face-to-face on the folded over portion of the fabric layer disposed internally of the female cooperating portion  78  to form a substantially blood-tight seal therewith. 
     Yet another example of the present invention is shown in  FIG. 7  in which a bifurcated endoluminal prosthesis  91  has a generally cylindrical proximal portion  92 ; said proximal portion  92  is connected at its distal end  93  to an elongate, generally cylindrical distal portion  94 . Said proximal portion  92  is also connected at its distal end  93  to a generally cylindrical intermediate portion  95  which is secured in transversely spaced relation to the elongate distal portion  94 . Said cylindrical intermediate portion  95  constitutes a female engaging portion which is adapted to receive a generally cylindrical male-engaging portion of a second elongate prosthesis (not shown). The male engaging portion is equipped with circumferentially spaced external barbs to engage in the female cooperating portion in service. As shown in  FIG. 7 , the whole of the bifurcated prosthesis  91  is covered with an external fabric graft layer save for a flared portion  96  towards the proximal end  97  of the proximal portion  92 . 
     Referring to  FIGS. 8(   a )- 8 ( f ), an exemplary embodiment of a delivery system according to the present invention will be described. This system is used to deploy the bifurcated stent  10  when it is covered with a fabric graft layer to create an endoluminal prosthesis. Introducer  100  includes outer sheath  101 . Outer sheath  101  is a cylindrical tube adapted to be inserted either percutaneously or by “cut-down” procedures into the vasculature from an entry point to the bifurcation site where the prosthesis is to be deployed. 
     Housed within outer sheath  101  is proximal portion pusher  102 . Proximal portion pusher  102  is a cylindrical tube having an outside diameter smaller than the inside diameter of outer sheath  101 . Proximal portion pusher  102  is preferably slidable throughout the length of outer sheath  101 . 
     Disposed within proximal portion pusher  102  is distal portion pusher  103 . Distal portion pusher  103  is a cylindrical tube slidably contained within distal portion pusher  102 . Distal portion pusher  103  is preferably adapted to slide throughout the entire length of proximal portion pusher  102 . 
     Disposed within distal portion  103  is balloon catheter  104 . Balloon catheter  104  is adapted to slide within distal portion pusher  103 . At the leading end  105  of balloon catheter  104  is nose cone  106 . Balloon  107  is attached to balloon catheter  104  between nose cone  106  and proximal end  115  of proximal portion pusher  102 . 
     As shown in  FIG. 8(   g ), which is a cross-sectional view of balloon catheter  104  in the direction A-A of  FIG. 8(   f ), balloon catheter  104  has a guide wire conduit  104   a . Guide wire conduit  104   a  extends throughout the length of balloon catheter  104  for passing a guide wire (not shown) through introducer  100 . In the illustrated embodiment, balloon catheter  104  also includes injection orifice  109  and an injection conduit  109   a . Injection conduit  109   a  connects injection orifice  109  to an injection site  108  at or near the distal end of balloon catheter  104  as shown in  FIG. 8(   e ). Radiopaque liquid may be injected into injection site  108 , through injection conduit  109   a , out injection orifice  109 , and into the vasculature to monitor deployment of the prosthesis. 
     Also in the illustrated embodiment of  FIGS. 8(   f ) and  8 ( g ), balloon catheter  104  has an inflation orifice  110  located at a point where balloon  107  is attached to balloon catheter  104 . A balloon inflation conduit  110   a  connects balloon inflation orifice  110  to balloon inflation site  111  ( FIG. 8(   e )). Balloon  107  may be inflated and deflated from balloon inflation site  111  during delivery of the prosthesis. 
     In an alternative embodiment illustrated in  FIG. 9 , seals  150 ,  151  may be disposed around the distal ends  160 ,  161  of outer sheath  10  and proximal portion pusher  102 . Seals  150 ,  151  may be formed of silicone tubes. 
       FIG. 10(   a ) shows an alternative embodiment of introducer  100 . As shown in  FIG. 10(   a ), wings  112  and  113  are provided at the distal end of introducer  100 . Wing  112  is connected to proximal portion pusher  102 , and wing  113  is connected to outer sheath  101 . Wings  112  and  113  indicate the rotational orientation of proximal portion pusher  102  and outer sheath  101 , respectively. This in turn indicates the orientation of proximal portion  12  within outer sheath  101  and distal portion  16  within proximal portion pusher  102 . Wings  112  and  113  in the illustrated embodiment are also provided with holes  112   a  and  113   a.    
     As shown in  FIG. 10(   b ), a rod  128  or other fixation device may be attached to wings  112  and  113  using e.g. bolts through holes  112   a  and  113   a  secured by wing nuts  129  or other securing means. Rod  128  prevents relative movement of proximal portion pusher  102  and outer sheath  101 . Wings may also be provided on distal portion pusher  103  and used to secure distal portion pusher  103  to either proximal portion pusher  102  or outer sheath  101  using a fixation device as described above. 
     Also shown in  FIG. 10(   a ) as part of introducer  100  is hemostasis valve  114 . Hemostasis valve  114  is connected to distal portion pusher  103  and acts as a simple seal around balloon catheter  104 . Although it prevents fluid loss, hemostasis valve  114  allows balloon catheter  104  to slide within distal portion pusher  103 . Alternatively, a Touhy-Borst valve (not shown) may be used instead of hemostasis valve  114 . The Touhy-Borst valve is a device that may be manually tightened over balloon catheter  104 . Lightly tightening such a valve permits balloon catheter  104  to slide; firmly tightening such a valve clamps balloon catheter  104  in place. 
     In use, the prosthesis must first be loaded into introducer  100 . Outer sheath  101  is first removed from introducer  100 . Balloon catheter  104  is then threaded through distal portion  16  and proximal portion  12  of the prosthesis. The prosthesis is then cooled to a temperature of approximately 10° C. or below and radially compressed. For this purpose, the prosthesis may be immersed in cold water. The prosthesis should preferrably remain in the water during the loading operation. 
     As supporting stent  10  is compressed beneath the fabric covering of the prosthesis, excess fabric is produced. This excess fabric may simply be pinched together and laid over the compressed prosthesis in longitudinal folds. 
     Distal portion  16  of the prosthesis in the radially compressed state is then inserted into proximal portion pusher  102 . Outer sheath  101  is then pulled over proximal portion  12  of the prosthesis and over proximal portion pusher  102 . A thread (not shown) may be attached to the proximal end of proximal portion  12  of the prosthesis and threaded through outer sheath  101 . This thread may then be used to pull proximal portion  12  through outer sheath  101 . During the loading process, it is important to keep proximal portion  12  and distal portion  16  of the prosthesis properly aligned with outer sheath  101  and proximal portion pusher  102 . Marks may be placed on the outside of outer sheath  101  and proximal portion pusher  102  to ensure proper alignment. 
     Referring again to  FIG. 8(   f ), the prosthesis is inserted such that the outer surface of proximal portion  12  contacts and is radially restrained by outer sheath  101 , and the outer surface of distal portion  16  contacts and is radially restrained by proximal portion pusher  102 . End  115  of proximal portion pusher  102  longitudinally engages proximal portion  12  of the prosthesis as shown in  FIG. 8(   f ). 
     Balloon catheter  104  is positioned such that nose cone  106  just clears proximal end  117  of outer sheath  101 . The introducer is now in condition for insertion into the patient. 
     Referring to  FIG. 11 , introducer  100  is passed through an entry point (not shown) either in the patient&#39;s skin (percutaneous operation) or into the vasculature itself which has been surgically exposed (“cut-down” operation). Introducer  100  is inserted over a guide wire  170  into the vasculature from the entry point to the desired delivery location at an angeological bifurcation. 
     In the aorta, introducer  100  is positioned such that end  117  of outer sheath  101  is approximately level with renal arteries  180  as shown in  FIG. 11 . Balloon catheter  104  is then extended while maintaining outer sheath  101  in a fixed position. Balloon catheter  104  in this embodiment is extended until distal end  105  of nose cone  106  is approximately 35 mm above the proximal tip  117  of outer sheath  101 . Then, while maintaining proximal portion pusher  102  in a fixed position, outer sheath  101  is withdrawn until the proximal tip of the prosthesis is level with proximal tip  117  of outer sheath  101 . It will be noted that balloon catheter  104  does not move while outer sheath  101  is so withdrawn. 
     Introducer  100  is then repositioned to place the prosthesis in the desired deployment location. Proper placement may be facilitated with the use of radiopaque markers as described above. Balloon catheter  104  is then extended such that balloon  107  is above renal arteries  180 . Balloon  107  is then inflated to occlude the aorta as shown in  FIG. 12 . 
     While maintaining proximal portion pusher  102  in a fixed position, outer sheath  101  is withdrawn until the proximal end of the prosthesis emerges from outer sheath  101  as shown in  FIG. 13 . Using a radiopaque marker  120  disposed on proximal end of the prosthesis, the introducer is rotated until proper alignment of the prosthesis is obtained. In the illustrated embodiment, radiopaque marker  120  is a platinum wire twisted around an apex of the prosthesis in a “V” shape. To ensure proper alignment, the stent should be rotated until only the profile of the V is seen and shows up as a straight line rather than a “V”. 
     Outer sheath  101  is further withdrawn while maintaining proximal portion pusher  102  fixed until proximal portion  12  is fully deployed from the end of outer sheath  101 , and the frustoconical portion  18  of the prosthesis just clears end  117 , as shown in  FIG. 14 . 
     Balloon  107  is then deflated to allow blood to flow through proximal portion  12  and out frustoconical portion  18  of the prosthesis. Balloon  107  is withdrawn into the prosthesis until the distal end  118  of nose cone  106  is just above the proximal end of the prosthesis. Balloon  107  is then inflated to seat the prosthesis, which may be provided with barbs (not shown) at its proximal end, against the wall of the aorta, as shown in  FIG. 15 . 
     Distal portion pusher  103  is then maintained in a fixed position while outer sheath  101  is withdrawn. Once outer sheath  101  has been withdrawn to the point at which proximal end  117  of outer sheath  101  is flush with proximal end  115  of proximal portion pusher  102 , both outer sheath  101  and proximal portion pusher  102  are withdrawn, still maintaining distal portion pusher  103  in a fixed position. Outer sheath  101  and proximal portion pusher  102  are withdrawn until distal portion  16  of the prosthesis is deployed clear of proximal end  116  of distal portion pusher  103  as shown in  FIG. 16 . Balloon  107  is slowly deflated to allow blood flow to be established through the proximal portion  12  of the prosthesis and out through frustoconical portion  18 . Balloon  107  may be used to model distal portion  16  of the prosthesis as necessary by inflating balloon  107  where needed to expand distal portion  16 . Balloon  107  is then deflated, and introducer  100  is withdrawn from the vasculature, leaving the guide wire  170  in place, as shown in  FIG. 17 . 
       FIG. 21(   a ) illustrates an exemplary second introducer  300  used for deploying second distal part  44 . Second introducer  300  of the illustrated embodiment comprises cylindrical outer sheath  301  and female Luer lock assembly  310 . Second introducer  300  also has hemostasis valve  361  contained within a hub  362  thereof. Cartridge  311  shown in  FIG. 21(   b ) is adapted to be attached to second introducer  300 . Cartridge  311  has threaded male Luer lock assembly  312  provided on its proximal end. Cartridge  311  has outer tube  313  which houses inner tube  314 . 
     In use, a thin-walled tube (not shown) is first threaded through distal portion  44 . This tube serves as a guide wire guide, allowing a guide wire to be threaded straight through distal portion  44  as discussed below. Distal portion  44  containing the thin-walled tube is then cooled, radially compressed, and inserted into inner tube  314  of cartridge  311  in a manner similar to that described for inserting the bifurcated prosthesis into proximal portion pusher  102  and outer sheath  101 . When distal portion  44  has been loaded into inner tube  314  of cartridge  311 , the thin-walled tube serving as a guide wire guide extends out both ends of cartridge  311 . 
     A guide wire  171  is then inserted into the vasculature to the bifurcation site and through distal stent portion  12  as shown in  FIG. 18 . A dialator  359  ( FIG. 21(   c )) having an outer diameter slightly less than the inner diameter of second introducer  300  is then inserted into second introducer  300  such that tapered end  360  extends out end  320  of second introducer  300 . End  360  of dialator  359  has a hole therein that is just slightly larger than guide wire  171  and tapers gradually outward from the hole to the outer diameter of dialator  359 . 
     Second introducer  300  is then inserted into the vasculature over guide wire  171  by passing guide wire  171  into and through dialator  359 . Dialator  359  with tapered end  360  provides a smooth transition within the blood vessel from the diameter of guide wire  171  to the diameter of second introducer  300 . Second introducer  300  is maneuvered such that outer sheath  301  is inside frustoconical portion  18  of proximal portion  12  by at least 20 mm in this embodiment, as shown in  FIG. 19 . Dialator  359  is then removed from second introducer  300  and from the vasculature and is discarded. 
     Cartridge  311  is then passed over guide wire  171  by passing guide wire  171  through the thin-walled guide wire guide within distal portion  44  contained in cartridge  311 . The guide wire guide is then removed and discarded. 
     Cartridge  311  is then lockingly engaged with introducer  300  by mating male Luer lock assembly  310  with female Luer lock assembly  312 . Such locking engagement prevents relative movement of cartridge  311  and introducer  300 . Preventing relative movement lends stability and reliability to the insertion process that has not heretofore been achieved. 
     A pusher  315  is then inserted into inner tube  314  of cartridge  311  such that proximal end  317  of pusher  315  longitudinally contacts a distal end of distal portion  44  within inner tube  314 . Pusher  315  pushes distal portion  44  through cartridge  311  and into outer sheath  301  of introducer  300 . Distal portion  44  is pushed through outer sheath  301 , which remains in a fixed position, until distal portion  44  is at proximal end  320  of outer sheath  301  (see  FIG. 19 ). Again, radiopaque markers  120  may be used to align distal portion  44  properly with proximal portion  12 . 
     Pusher  302  is held firmly in place, and outer sheath  301  is withdrawn approximately 2 cm. This deploys frustoconical part  42  of distal part  44  inside the frustoconical part  18  as shown in  FIG. 19 . The outer surface of frustoconical part  42  engages the inner surface of frustoconical part  18  such that distal portion  44  is connected to proximal portion  12  to resist longitudinal separation. 
     Outer sheath  301  may then be withdrawn while maintaining pusher  302  in a fixed position to fully deploy distal portion  44 , as shown in  FIG. 20 . If necessary, balloon catheter  104  may be inserted through sheath  301  in order to model distal portion  44 . Introducer  301  and guide wires  170 ,  171  are then removed from the vasculature and the entry points are closed. 
     The delivery apparatus and method described above are particularly useful in treating an abdominal aortic aneurysm with a bifurcated prosthesis according to the present invention. Other diseases and alternative embodiments of the prosthesis and delivery method will now be described. 
     In the case of an abdominal aortic aneurysm confined to the aorta and not extending far enough to affect the iliac arteries, a straight (i.e. non-bifurcated) stent may be used. Preferably, for such applications, the straight stent comprises a composite of at least two axially aligned stent segments. Two embodiments of such straight stents are described herein, each comprising axially aligned stent requests, each of the requests comprising one or more adjacent hoops, perpendicular to a common axis, and each hoop being formed of wire in a sinuous or zigzag configuration with some or all of the juxtaposed apices in adjacent hoops secured to one another. 
     First, referring to  FIG. 22 , straight stent  400  comprises proximal stent portion (or segment)  401 , distal stent portion  402 , and an intermediate portion  403 . 
     Proximal portion  401  is a ring formed of a number of longitudinally spaced hoops  20  as described in connection with the formation of stent  10  above. In the illustrated embodiment, two hoops  20  are used, each hoop  20  having a unit width. 
     Distal portion  402  is also a ring formed of longitudinally displaced hoops  20  in the manner described above. Distal ring  402  has two hoops  20  of unit width in the illustrated embodiment. 
     Intermediate portion  403  of straight stent  400  is formed of biocompatible woven fabric such as, for example, a plain woven fabric made from 30 or 40 denier polyester. In this embodiment, intermediate fabric section  403  does not cover a stent. Fabric portion  403  is attached at its proximal and distal ends to the proximal and distal stent portions, respectively, by stitching, for example, with 0.003 inch polypropylene filaments around apices  22  of the stent portions. Other than such connections at its longitudinal ends, intermediate fabric section  403  is unsupported by any stent. 
     The second embodiment of a straight stent that may be used according to this invention is illustrated in  FIG. 23 . Straight stent  450  includes stent portion  451 , constructed of wire loops as described above with reference to stent portions  401  and  402 . Stent portion  451  is partially covered by fabric  452 . In this embodiment, fabric portion  451  covers and is supported by stent  451 , whereas with stent  400 , the fabric portion  403  is not supported by a stent. 
     To treat an abdominal aortic aneurysm that does not extend down over the walls of the iliac arteries, as shown in  FIG. 24(   a ), straight stent  400  (or  450 ) is disposed as illustrated in  FIG. 26 . Proximal stent portion  401  engages the inner walls of the aorta above the aneurysm. Distal stent portion  402  engages the inner wall of the aorta below the aneurysm. Intermediate fabric portion  403  extends across the aneurysm, providing a strong, stable lumen for blood flow through the aorta. 
       FIG. 28  illustrates the delivery apparatus used to implant straight stent  400  in the vasculature. This apparatus is very similar to that described above for the delivery system to be used with the bifurcated stent or prosthesis. Accordingly, like reference numerals refer to the same components. 
     In the introducer  410  shown in  FIG. 28 , proximal portion pusher  102  engages proximal stent portion  401 . Distal portion pusher  103  engages distal stent portion  402 . 
     In use, straight stent  400  is first charged into the introducer by cooling it to temperatures below 10° C., radially compressing it, and inserting it within outer sheath  101 , as described above in connection with the bifurcated stent or prosthesis. The remainder of introducer  410  is also assembled as described in connection with introducer  100 . 
     Introducer  410  is passed through an entry point (not shown) over guide wire  411  as shown in  FIG. 24(   a ). This insertion may be accomplished using percutaneous or cut-down techniques. Introducer  410  is then inserted to the desired delivery location. 
     In the aorta, introducer  410  is positioned and balloon  107  is inflated above the renal arteries in the same manner as described above in connection with the bifurcated stent and as illustrated in  FIG. 24(   a ). 
     While maintaining proximal portion pusher  102  in a fixed position, outer sheath  101  is withdrawn until proximal portion  401  of stent  400  emerges from outer sheath  101  as shown in  FIG. 24(   b ). Using a radiopaque marker  420  disposed on the proximal end of the proximal portion  401 , stent  400  is optimally aligned within the aorta. Outer sheath  101  is further withdrawn until proximal portion  401  emerges therefrom, as shown in  FIG. 25 . Outer sheath  101  is then further withdrawn until it is flush with proximal portion pusher  102 . Then both outer sheath  101  and proximal portion pusher  102  are withdrawn while maintaining distal portion pusher  103  in a fixed position. Distal portion  402  is thus deployed from the end of outer sheath  101 , as shown in  FIG. 26 . 
     Balloon  107  is then deflated and withdrawn inside proximal portion  401  where balloon  107  is re-inflated to seat the stent  400 , as shown in  FIG. 27 . Balloon  107  is then withdrawn, along with the introducer  410  as described above, and the entry point is closed. 
       FIG. 29  illustrates the apparatus used to deploy straight stent  450 , shown in  FIG. 23 , of the present invention. This apparatus is very similar to that described above for the delivery system to be used with the bifurcated stent or prosthesis. Accordingly, like reference numerals refer to the same components. 
     Proximal portion pusher  102  in this embodiment is glued to distal portion pusher  103  such that ends  115  and  116  are flush. These flush ends are adapted to engage stent  450  within outer sheath  101 . 
     In use, straight stent  450  is first charged into introducer  490  by cooling it to temperatures below 10° C., radially compressing it, and inserting it within outer sheath  101 , as described above in connection with the bifurcated stent or prosthesis. The remainder of introducer  490  is also assembled as described in connection with introducer  100 . 
     Introducer  490  is passed through an entry point (not shown) over a guide wire  411  as shown in  FIG. 30 . This insertion may be accomplished using percutaneous or cut-down techniques. Introducer  490  is then inserted to the desired delivery location. 
     In the aorta, introducer  490  is positioned and balloon  107  is inflated above the renal arteries in the same manner as described above in connection with the bifurcated stent and as illustrated in  FIG. 31 . 
     While maintaining attached proximal portion pusher  102  and distal portion pusher  103  in a fixed position, outer sheath  101  is withdrawn until proximal portion  451  of stent  450  emerges from outer sheath  101  as shown in  FIG. 32 . Using a radiopaque marker  420  disposed on the proximal end of the proximal portion  451 , stent  450  is optimally aligned within the aorta. Outer sheath  101  is then completely withdrawn until stent  450  is deployed into the aorta as shown in  FIG. 33 . 
     Balloon  107  is then deflated and withdrawn inside proximal portion  451  where balloon  107  is re-inflated to seat the stent  450 , as shown in  FIG. 34 . Balloon  107  is then withdrawn, along with the introducer  490  as described above, and the entry point is closed. 
     The angeological disease of occlusion is the blockage of an artery resulting from a buildup or clot of soft thrombus. There are two types of occlusions that can occur at the aorta-iliac bifurcation. The first is infrarenal occlusion. In this case, the blockage extends in the aorta from just below the renal arteries into the iliac arteries. The second type is an occlusion that is limited to the immediate area of the bifurcation. 
     To treat an infrarenal occlusion, a canalization is first made through the thrombus by methods known in the art. A bifurcated endoluminal prosthesis according to the present invention is then implanted at the bifurcation site to provide an unobstructed lumen extending from the aorta into each of the iliac arteries. Blood can thus flow freely from the aorta to the iliac arteries. 
     The bifurcated endoluminal prosthesis according to the present invention that is used to treat an occlusion must be fabric covered. This is necessary to prevent embolization from the thrombus remaining on the wall of the recanalized artery. 
     An occlusion at the bifurcation is treated by recanalizing the artery as above. A bifurcated endoluminal prosthesis according to the present invention may be implanted at the bifurcation. Because the occlusion is limited to the immediate bifurcation site, however, the proximal portion of the prosthesis may be shorter than that discussed above. 
     To implant the bifurcated endoluminal prosthesis to treat both types of occlusion, the delivery system comprising introducer  100  discussed above for delivering the bifurcated endoluminal prosthesis to treat an abdominal aortic aneurysm is used. The same delivery method discussed above for implanting the bifurcated endoluminal prosthesis to treat abdominal aortic aneurysms is used to implant the device to treat the occlusion. 
     Using the method and apparatus of this invention to treat occlusion provides an unobstructed lumen through which blood can flow from the aorta to the iliac arteries. 
     The angeological disease of stenosis is a narrowing of an artery caused by a buildup of hard calcified plaque. This is usually caused by a buildup of cholesterol. To treat such an angeological disease, angioplasty is performed on the plaque according to methods well known in the art. The bifurcated endoluminal stent according to the present invention is then implanted at the bifurcation site. This stent is the same as that described above for treatment of an abdominal aortic aneurysm. To treat the stenosis, however, it is not necessary to cover the stent with a fabric, thus creating a prosthesis. Because restenosis is rare at the bifurcation site, there is no need to isolate the blood flowing in the lumen from the walls of the arteries. 
     The delivery system used to implant the bifurcated endoluminal stent used to treat stenosis is the same as that illustrated in  FIG. 8  except that balloon  107  is not required. Because there is no fabric around the stent to be affected by blood flow in the arteries and cause migration of the bifurcated stent, it is not necessary to block the blood flow with the balloon. Otherwise, the delivery system for implanting the bifurcated stent to treat stenosis is the same as that for implanting the bifurcated prosthesis to treat abdominal aortic aneurysm. 
     Similarly, with the exception of the steps involving inflation of balloon  107  to block blood flow, the method of delivering the bifurcated endoluminal stent to treat stenosis is the same as that described above for delivering the bifurcated endoluminal prosthesis to treat abdominal aortic aneurysm.