Patent Publication Number: US-2007112412-A1

Title: Endoluminal vascular prosthesis

Description:
This application is a continuation of U.S. application Ser. No. 09/034,689 filed on Mar. 4, 1998. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to endoluminal vascular prostheses, and, in one application, to self-expanding endoluminal vascular prostheses for use in the treatment of abdominal aortic aneurysms.  
      An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta, a major artery of the body, as it passes through the abdomen. The abdomen is that portion of the body which lies between the thorax and the pelvis. It contains a cavity, known as the abdominal cavity, separated by the diaphragm from the thoracic cavity and lined with a serous membrane, the peritoneum. The aorta is the main trunk, or artery, from which the systemic arterial system proceeds. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries.  
      The aneurysm usually arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. When left untreated, the aneurysm may eventually cause rupture of the sac with ensuing fatal hemorrhaging in a very short time. High mortality associated with the rupture led initially to transabdominal surgical repair of abdominal aortic aneurysms. Surgery involving the abdominal wall, however, is a major undertaking with associated high risks. There is considerable mortality and morbidity associated with this magnitude of surgical intervention, which in essence involves replacing the diseased and aneurysmal segment of blood vessel with a prosthetic device which typically is a synthetic tube, or graft, usually fabricated of Polyester, Urethane, P, DACRON®, TEFLON®, or other suitable material.  
      To perform the surgical procedure requires exposure of the aorta through an abdominal incision which can extend from the rib cage to the pubis. The aorta must be closed both above and below the aneurysm, so that the aneurysm can then be opened and the thrombus, or blood clot, and arteriosclerotic debris removed. Small arterial branches from the back wall of the aorta are tied off, The DACRON® tube, or graft, of approximately the same size of the normal aorta is sutured in place, thereby replacing the aneurysm. Blood flow is then reestablished through the graft. It is necessary to move the intestines in order to get to the back wall of the abdomen prior to clamping off the aorta  
      If the surgery is performed prior to rupturing of the abdominal aortic aneurysm, the survival rate of treated patients is markedly higher than if the surgery is performed after the aneurysm ruptures, although the mortality rate is still quite high. If the surgery is performed prior to the aneurysm rupturing, the mortality rate is typically slightly less than 10%. Conventional surgery performed after the rupture of the aneurysm is significantly higher, one study reporting a mortality rate of 66.5%. Although abdominal aortic aneurysms can be detected from routine examinations, the patient does not experience any pain from the condition. Thus, if the patient is not receiving routine examinations, it is possible that the aneurysm will progress to the rupture stage, wherein the mortality rates are significantly higher.  
      Disadvantages associated with the conventional, prior art surgery, in addition to the high mortality rate include the extended recovery period associated with such surgery; difficulties in suturing the graft, or tube, to the aorta; the loss of the existing aorta wall and thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients having abdominal aortic aneurysms; and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. A patient can expect to spend from one to two weeks in the hospital after the surgery, a major portion of which is spent in the intensive care unit, and a convalescence period at home from two to three months; particularly if the patient has other illnesses such as heart, lung, liver, and for kidney disease, in which case the hospital stay is also lengthened. Since the graft must be secured, or sutured, to the remaining portion of the aorta, it is many times difficult to perform the suturing step because the thrombosis present on the remaining portion of the aorta, and that remaining portion of the aorta wall may many times be friable, or easily crumbled.  
      Since many patients having abdominal aortic aneurysms have other chronic illnesses, such as heart, lung, liver, and/or kidney disease, coupled with the fact that many of these patients are older, the average age being approximately 67 years old, these patients are not ideal candidates for such major surgery.  
      More recently, a significantly less invasive clinical approach to aneurysm repair, known as endovascular grafting, has been developed. Parodi, et al. provide one of the first clinical descriptions of this therapy. Parodi, J. C., et al., “Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,” 5 Annals of Vascular Surgery 491 (1991). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft in the endolurninal position (within the lumen of the artery). By this method, the graft is attached to the internal surface of an arterial wall by means of attachment devices (expandable stents), typically one above the aneurysm and a second stent below the aneurysm.  
      Stents permit fixation of a graft to the internal surface of an arterial wall without sewing or an open surgical procedure. Expansion of radially expandable stents is conventionally accomplished by dilating a balloon at the distal end of a balloon catheter. In U.S. Pat. No. 4,776,337, for example, Palmaz describes a balloon-expandable stent for endovascular treatments. Also known are self-expanding stents, such as described in U.S. Pat. No. 4,655,771 to Wallsten.  
      Notwithstanding the foregoing, there remains a need for a transluminally implantable endovascular prosthesis, such as for spanning an abdominal aortic aneurysm. Preferably, the tubular prosthesis can be self expanded at the site to treat the abdominal aortic aneurysm.  
     SUMMARY OF THE INVENTION  
      There is provided in accordance with one aspect of the present invention an endoluminal prosthesis. The endoluminal prosthesis comprises a tubular wire support having a proximal end, a distal end and central lumen extending therethrough. The wire support comprises at least a first and a second axially adjacent tubular segments, joined by a connector extending therebetween. The first and second segments and the connector are formed from a single length of wire.  
      In one embodiment, the wire in each segment comprises a series of proximal bends, a series of distal bends, and a series of wall (strut) segments connecting the proximal bends and distal bends to form a tubular segment wall. Preferably, at least one proximal bend on a first segment is connected to at least one corresponding distal bend on a second segment. The connection may be provided by a metal link, a suture, or other connection means known in the art.  
      Preferably, the endoluminal prosthesis further comprises a polymeric layer such as a tubular PTFE sleeve, on the support.  
      In accordance with another aspect of the present invention, there is provided a method of making an endoluminal prosthesis. The method comprises the steps of providing a length of wire, and forming the wire into two or more zig zag sections, each zig zag section connected by a link. The formed wire is thereafter rolled about an axis to produce a series of tubular elements positioned along the axis such that each tubular element is connected to the adjacent tubular element by a link. Preferably, the method further comprises the step of positioning a tubular polymeric sleeve concentrically on at least a portion of the endoluminal prosthesis.  
      In accordance with another aspect of the present invention, there is provided a multizone endoluminal prosthesis. The multizone prosthesis comprises a tubular wire support having a proximal end, a distal end and a central lumen extending therethrough. The wire support comprises at least a first and a second axially adjacent tubular segments, joined by a connector extending therebetween. The first tubular segment has a different radial strength than the second tubular segment. In one embodiment, the prosthesis further comprises a third tubular segment. At least one of the tubular segments has a different radial strength than the other two tubular segments. In another embodiment, a proximal end of the prosthesis is self expandable to a greater diameter than a central region of the prosthesis.  
      In accordance with another aspect of the present invention, there is provided an endoluminal prosthesis. The prosthesis comprises an elongate flexible wire, formed into a plurality of axially adjacent tubular segments spaced along an axis. Each tubular segment comprises a zig zag section of wire, having a plurality of proximal bends and distal bends, with the wire continuing between each adjacent tubular segment creating an integral structural support system throughout the longitudinal length of the device. The prothesis is radially collapsible into a first, reduced cross sectional configuration for implantation into a body lumen, and self expandable to a second, enlarged cross sectional configuration at a treatment site in a body lumen.  
      Preferably, the prosthesis further comprises an outer tubular sleeve surrounding at least a portion of the prosthesis. One or more lateral perfusion ports may be provided through the tubular sleeve.  
      In one embodiment, the prosthesis has an expansion ratio of at least about 1:5, and, preferably at least about 1:6. The prosthesis in another embodiment has an expanded diameter of at least about 20 mm in an unconstrained expansion, and the prosthesis is implantable using a catheter no greater than about 16 French. Preferably, the prosthesis has an expanded diameter of at least about 25 mm, and is implantable on a delivery device having a diameter of no more than about 16 French.  
      In accordance with a further aspect of the present invention, there is provided a method of implanting an endoluminal vascular prosthesis. The method comprises the steps of providing a self expandable endoluminal vascular prosthesis, having a proximal end, a distal end, and a central lumen extending therethrough. The prosthesis is expandable from a first, reduced diameter to a second, enlarged diameter. The prosthesis is mounted on a catheter, such that when the prosthesis is in the reduced diameter configuration on the catheter, the catheter diameter through the prosthesis is no more than about 16 French. The catheter is thereafter introduced into the body lumen and positioned such that the prosthesis is at a treatment site in the body lumen. The prosthesis is released at the treatment site, such that it expands from the first diameter to the second diameter, wherein the second diameter is at least about 20 mm.  
      Further features and advantages of the present invention will become apparent to those of ordinary skill in the art in view of the disclosure herein, when considered together with the attached drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic representation of an endoluminal vascular prosthesis in accordance with the present invention, positioned within a symmetric abdominal aortic aneurysm.  
       FIG. 2  is an exploded view of an endoluminal vascular prosthesis in accordance with the present invention, showing a self expandable wire support structure separated from an outer tubular sleeve.  
       FIG. 3  is a plan view of a formed wire useful for rolling about an axis into a multi-segment support structure in accordance with the present invention.  
       FIG. 4  is an enlarged detail view of a portion of the formed wire illustrated in  FIG. 3 .  
       FIG. 5  is a cross sectional view taken along the lines  5 - 5  of  FIG. 4 .  
       FIG. 6  is an alternate cross sectional view taken along the lines  5 - 5  of  FIG. 4 .  
       FIG. 7  is a fragmentary view of an alternate wire layout in accordance with a further aspect of the present invention.  
       FIG. 8  is an elevational view of a crosslinked wire layout in accordance with the present invention.  
       FIG. 8A  is a plan view of a formed wire layout useful for forming the crosslinked embodiment of  FIG. 8 .  
       FIG. 9  is a fragmentary view of an alternate wire layout in accordance with a further aspect of the present invention.  
       FIG. 10  is a fragmentary view of an alternate wire layout in accordance with a further aspect of the present invention.  
       FIG. 11  is a fragmentary view of an apex in accordance with one aspect of the present invention.  
       FIG. 12  is a fragmentary view of an alternate embodiment of an apex in accordance with the present invention.  
       FIG. 13  is a further embodiment of an apex in accordance with the present invention.  
       FIG. 14  is a fragmentary view of a further wire layout in accordance with the present invention.  
       FIG. 15  is a fragmentary view of a further wire layout in accordance with the present invention.  
       FIG. 16  is a fragmentary view of a further wire layout in accordance with the present invention.  
       FIG. 17  is a schematic illustration of a delivery catheter in accordance with the present invention, positioned within an abdominal aortic aneurysm.  
       FIG. 18  is an illustration as in  FIG. 17 , with the endoluminal prosthesis partially deployed from the delivery catheter.  
       FIG. 19  is a cross sectional view taken along the lines  19 - 19  of  FIG. 17 .  
       FIG. 20  is a detailed fragmentary view of a tapered wire embodiment in accordance with a further aspect of the present invention.  
       FIG. 21  is a schematic representation of the abdominal aortic anatomy, with an endoluminal vascular prosthesis of the present invention positioned within each of the right renal artery and the right common iliac. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 1 , there is disclosed a schematic representation of the abdominal part of the aorta and its principal branches. In particular, the abdominal aorta  30  is characterized by a right renal artery  32  and left renal artery  34 . The large terminal branches of the aorta are the right and left common iliac arteries  36  and  38 . Additional vessels (e.g., second lumbar, testicular, inferior mesenteric, middle sacral) have been omitted for simplification. A generally symmetrical aneurysm  40  is illustrated in the infrarenal portion of the diseased aorta An expanded endoluminal vascular prosthesis  42 , in accordance with the present invention, is illustrated spanning the aneurysm  40 . Although features of the endoluminal vascular prosthesis of the present invention can be modified for use in a bifurcation aneurysm, such as the common iliac bifurcation, the endolurninal prosthesis of the present invention will be described herein primarily in terms of its application in the straight segment of the abdominal aorta, or Thoracic or iliac arteries.  
      The endoluminal vascular prosthesis  42  includes a polymeric sleeve  44  and a tubular wire support  46 , which are illustrated in situ in  FIG. 1 . The sleeve  44  and wire support  46  are more readily visualized in the exploded view shown in  FIG. 2 . The endoluminal prosthesis  42  illustrated and described herein depicts an embodiment in which the polymeric sleeve  44  is situated concentrically outside of the tubular wire support  46 . However, other embodiments may include a sleeve situated instead concentrically inside the wire support or on both of the inside and the outside of the wire support. Alternatively, the wire support may be embedded within a polymeric matrix which makes up the sleeve. Regardless of whether the sleeve  44  is inside or outside the wire support  46 , the sleeve may be attached to the wire support by any of a variety of means, including laser bonding, adhesives, clips, sutures, dipping or spraying or others, depending upon the composition of the sleeve  44  and overall graft design.  
      The polymeric sleeve  44  may be formed from any of a variety of synthetic polymeric materials, or combinations thereof, including PTFE, PE, PET, Urethane, Dacron, nylon, polyester or woven textiles. Preferably, the sleeve material exhibits relatively low inherent elasticity, or low elasticity out to the intended enlarged diameter of the wire cage  46 . The sleeve material preferably has a thin profile, such as no larger than about 0.002 inches to about 0.005 inches.  
      In a preferred embodiment of the invention, the material of sleeve  44  is sufficiently porous to permit ingrowth of endothelial cells, thereby providing more secure anchorage of the prosthesis and potentially reducing flow resistance, sheer forces, and leakage of blood around the prosthesis. Porosity in polymeric sleeve materials may be estimated by measuring water permeability as a function of hydrostatic pressure, which will preferably range from about 3 to 6 psi.  
      The porosity characteristics of the polymeric sleeve  44  may be either homogeneous throughout the axial length of the prosthesis  42 , or may vary according to the axial position along the prosthesis  42 . For example, referring to  FIGS. 1 and 2 , different physical properties will be called upon at different axial positions along the prosthesis  42  in use. At least a proximal portion  55  and a distal portion  59  of the prosthesis  42  will seat against the native vessel wall, proximally and distally of the aneurysm. In these proximal and distal portions, the prosthesis preferably encourages endothelial growth, or, at least, permits endothelial growth to infiltrate portions of the prosthesis in order to enhance anchoring and minimize leakage. A central portion  57  of the prosthesis spans the aneurysm, and anchoring is less of an issue. Instead, minimizing blood flow through the prosthesis wall becomes a primary objective. Thus, in a central zone  57  of the prosthesis  42 , the polymeric sleeve  44  may either be nonporous, or provided with pores of no greater than about 60% to 80%.  
      A multi-zoned prosthesis  42  may also be provided in accordance with the present invention by positioning a tubular sleeve  44  on a central portion  57  of the prosthesis, such that it spans the aneurysm to be treated, but leaving a proximal attachment zone  55  and a distal attachment zone  59  of the prosthesis  42  having exposed wires from the wire support  46 . In this embodiment, the exposed wires  46  are positioned in contact with the vessel wall both proximally and distally of the aneurysm, such that the wire, over time, becomes embedded in cell growth on the interior surface of the vessel wall.  
      In one embodiment of the prosthesis  42 , the sleeve  44  and/or the wire support  46  is tapered, having a relatively larger expanded diameter at the proximal end  50  compared to the distal end  52 . The tapered design may allow the prosthesis to conform better to the natural decreasing distal cross section of the vessel, to reduce the risk of graft migration and potentially create better flow dynamics.  
      The tubular wire support  46  is preferably formed from a continuous single length of round (shown in  FIG. 5 ) or flattened (shown in  FIG. 6 ) wire. The wire support  46  is preferably formed in a plurality of discrete segments  54 , connected together and oriented about a common axis. Each pair of adjacent segments  54  is connected by a connector  66  as will be discussed. The connectors  66  collectively produce a generally axially extending backbone which adds axial strength to the prosthesis  42 . Adjacent segments can be connected both by the backbone, as well as by other structures, including circumferentially extending sutures  56  (illustrated in  FIGS. 1 and 2 ), solder joints, wire loops and any of a variety of interlocking relationships. The suture can be made from any of a variety of biocompatible polymeric materials or alloys, such as nylon, polypropylene, or stainless steel. Other means of securing the segments  54  to one another are discussed below (see  FIG. 8 ).  
      The segmented configuration of the tubular wire support  46  facilitates a great deal of flexibility. Each segment  54 , though joined to adjacent segments, may be independently engineered to yield desired parameters. Each segment may range in axial length from about 0.3 to about 5 cm. Generally, the shorter their length the greater the radial strength. An endoluminal prosthesis may include from about 1 to about 50 segments, preferably from about 3 to about 10 segments. For example, while a short graft patch, in accordance with the invention, may comprise only 2 segments and span a total of 2 to 3 cm, a complete graft may comprise 4 or more segments and span the entire aortic aneurysm. In addition to the flexibility and other functional benefits available through employment of different length segments, further flexibility can be achieved through adjustments in the number, angle, or configuration of the wire bends associated with the tubular support Potential bend configurations are discussed in greater detail below (see  FIGS. 4-16 ).  
      A variety of additional advantages can be achieved through the multi-segment configuration of the present invention. For example, referring to  FIG. 2 , the wire cage  46  is dividable into a proximal zone.  55 , a central zone  57  and a distal zone  59 . As has been discussed, the wire cage  46  can be configured to taper from a relatively larger diameter in the proximal zone  55  to a relatively smaller diameter in the distal zone  59 . In addition, the wire cage  46  can have a transitional tapered and or stepped diameter within a given zone.  
      The cage  46  can also be provided with a proximal zone  55  and distal zone  59  that have a larger relative expanded diameter than the central zone  57 , as illustrated in  FIG. 2 . This configuration may desirably resist migration of the prosthesis within the vessel. The proximal zone  55  and/or distal zone  59  can be left without an outer covering  44 , with the outer sleeve  44  covering only the central zone  57 . This permits the proximal and distal zones  55 ,  59  to be in direct contact with tissue proximally and distal to the lesion, which may facilitate endothelial cell growth.  
      In addition to having differing expanded diameters in different zones of the prosthesis  42 , different zones can be provided with a different radial expansion force, such as ranging from about 0.2 lbs to about 0.8 lbs. In one embodiment, the proximal zone  55  is provided with a greater radial force than the central zone  57  and/or distal zone  59 . The greater radial force can be provided in any of a variety of manners discussed elsewhere herein, such as through the use of an additional one or two or three or more proximal bends  60 , distal bends  62  and wall sections  64  compared to a reference segment  54  in the central zone  57  or distal zone  59 . Alternatively, additional spring force can be achieved in the proximal zone  55  through the use of the same number of proximal bends  60  as in the rest of the prosthesis, but with a heavier gauge wire. Radial force beyond the expanded diameter limit of the central zone  57  can be achieved by tightening the suture  56  as illustrated in  FIG. 2  such that the central zone  57  is retained under compression even in the expanded configuration. By omitting a suture at the proximal end and/or distal end of the prosthesis, the proximal end and distal end will flair radially outwardly to a fully expanded configuration as illustrated in  FIG. 2 .  
      The wire may be made from any of a variety of different alloys, such as elgiloy, nitinol or MP35N, or other alloys which include nickel, titanium, tantalum, or stainless steel, high Co—Cr alloys or other temperature sensitive materials. For example, an alloy comprising Ni 15%, Co 40%, Cr 20%, Mo 7% and balance Fe may be used. The tensile strength of suitable wire is generally above about 300 K psi and often between about 300 and about 340 K psi for many embodiments. In one embodiment, a Chromium-Nickel-Molybdenum alloy such as that marketed under the name Conichrom (Fort Wayne Metals, Indiana) has a tensile strength ranging from 300 to 320 K psi, elongation of 3.5-4.0% and breaking load at approximately 80 lbs to 70 lbs. The wire may be treated with a plasma coating and be provided with/without coating such as: PTFE, Teflon, Perlyne and Drugs.  
      In addition to segment length and bend configuration, discussed above, another determinant of radial strength is wire gauge. The radial strength, measured at 50% of the collapsed profile, preferably ranges from about 0.2 lb to 0.8 lb, and generally from about 0.4 lb to about 0.5 lb. or more. Preferred wire diameters in accordance with the present invention, range from about 0.004 inches to about 0.020 inches. More preferably, the wire diameters range from about 0.006 inches to about 0.018 inches. In general, the greater the wire diameter, the greater the radial strength for a given wire layout. Thus, the wire gauge can be varied depending upon the application of the finished graft, in combination with/or separate from variation in other design parameters (such as the number of struts, or proximal bends  60  and distal bends  62  per segment), as will be discussed. A wire diameter of approximately 0.018 inches may be useful in a graft having four segments each having 2.5 cm length per segment, each segment having six struts intended for use in the aorta, while a smaller diameter such as 0.006 inches might be useful for a 0.5 cm segment graft having 5 struts per segment intended for the iliac artery. The length of cage  42  could be as long as about 28 cm.  
      In one embodiment of the present invention, the wire diameter is tapered from the proximal to distal ends. Alternatively, the wire diameter may be tapered incrementally or stepped down, or stepped up, depending on the radial strength requirements of each particular clinical application. In one embodiment, intended for the abdominal aortic artery, the wire has a cross section of about 0.018 inches in the proximal zone  55  and the wire tapers down to a diameter of about 0.006 inches in the distal zone  59  of the graft  42 . End point dimensions and rates of taper can be varied widely, within the spirit of the present invention, depending upon the desired clinical performance.  
      Referring to  FIG. 3 , there is illustrated a plan view of the single formed wire used for rolling about a longitudinal axis to produce a four segment tubular wire support The formed wire exhibits distinct segments, each corresponding to an individual tubular segment  54  in the tubular support (see  FIGS. 1 and 2 ).  
      Each segment has a repeating pattern of proximal bends  60  connected to corresponding distal bends  62  by wall sections  64  which extend in a generally zig zag configuration when the segment  54  is radially expanded. Each segment  54  is connected to the adjacent segment  54  through a connector  66 , except at the terminal ends of the graft. The connector  66  in the illustrated embodiment comprises two wall sections  64  which connect a proximal bend  60  on a first segment  54  with a distal bend  62  on a second, adjacent segment  54 . The connector  66  may additionally be provided with a connector bend  68 , which may be used to impart increased radial strength to the graft and/or provide a tie site for a circumferentially extending suture.  
      Referring to  FIG. 4 , there is shown an enlarged view of the wire support illustrating a connector  66  portion between adjacent segments  54 . In the embodiment shown in  FIG. 4 , a proximal bend  60  comprises about a 180 degree arc, having a radial diameter of (w) (Ranging from 0.070 to 0.009 inches), depending on wire diameter followed by a relatively short length of parallel wire spanning an axial distance of d 1 . The parallel wires thereafter diverge outwardly from one another and form the strut sections  64 , or the proximal half of a connector  66 . At the distal end of the strut sections  64 , the wire forms a distal bend  62 , preferably having identical characteristics as the proximal bend  60 , except being concave in the opposite direction. The axial direction component of the distance between the apices of the corresponding proximal and distal bends  60 ,  62  is referred to as (d) and represents the axial length of that segment. The total expanded angle defined by the bend  60  and the divergent strut sections  64  is represented by α. Upon compression to a collapsed state, such as when the graft is within the deployment catheter, the angle α is reduced to α′. In the expanded configuration, α is generally within the range of from about 35° to about 45°. The expanded circumferential distance between any two adjacent distal bends  62  (or proximal bends  60 ) is defined as (s).  
      In general, the diameter W of each proximal bend  60  or distal bend  62  is within the range of from about 0.009 inches to about 0.070 inches depending upon the wire diameter. Diameter W is preferably as small as possible for a given wire diameter and wire characteristics. As will be appreciated by those of skill in the art, as the distance W is reduced to approach two times the cross section of the wire, the bend  60  or  62  will exceed the elastic limit of the wire, and radial strength of the finished segment will be lost Determination of a minimum value for W, in the context of a particular wire diameter and wire material, can be readily determined through routine experimentation by those of skill in the art. Similarly, although at least some distance of d 1  is desired, from the apex to the first bend in the wall section  64 , the distance d 1  is preferably minimized within the desired radial strength performance requirements. As d 1  increases, it may disadvantageously increase the collapsed profile of the graft.  
      As will be appreciated from  FIGS. 3 and 4 , the sum of the distances (s) in a plane transverse to the longitudinal axis of the finished graft will correspond to the circumference of the finished graft in that plane. For a given circumference, the number of proximal bends  60  or distal bends  62  is directly related to the distance (s) in the corresponding plane. Preferably, the finished graft in any single transverse plane will have from about 3 to about 10 (s) dimensions, preferably from about 4 to about 8 (s) dimensions and, more preferably, about 5 or 6 (s) dimensions for an aortic application Each (s) dimension corresponds to the distance between any two adjacent bends  60 - 60  or  62 - 62  as will be apparent from the discussion herein. Each segment  54  can thus be visualized as a series of triangles extending circumferentially around the axis of the graft, defined by a proximal bend  60  and two distal bends  62  or the reverse.  
      By modifying wire support parameters (such as d, d 1 , s, alpha and alpha′), the manufacturer enjoys tremendous design control with respect to the total axial length, axial and radial flexibility, radial force and expansion ratios, and consequently prosthesis performance. For example, an increase in the dimension (w) translates directly into an increased collapsed profile since the circumference of the collapsed profile can be no smaller than the sum of the distances (w) in a given transverse plane. Similarly, an increase in the number of proximal bends  60  in a given segment may increase radial strength, but will similarly increase the collapsed profile. Since the primary radial force comes from the proximal bends  60  and distal bends  62 , the wall sections  64  act as a lever arm for translating that force into radial strength. As a consequence, decreasing the length of strut sections  64  for a given number of proximal bends  60  will increase the radial strength of the segment but call for additional segments to maintain overall graft length. Where a minimal entry profile is desired, radial strength is best accomplished by decreasing the length of wall sections  64  rather than increasing the number of proximal bends  60 . On the other hand, increasing the number of (shorter) segments  54  in a given overall length graft will increase the degree of axial shortening upon radial expansion of the graft. Thus, in an embodiment where axial shortening is to be avoided, increased radial strength may be optimized through selection of wire material or wire gauge and other parameters, while minimizing the number of total segments in the graft. Other geometry consequences of the present invention will be apparent to those of skill in the art in view of the disclosure herein.  
      In one embodiment of the type illustrated in  FIG. 8A , w is about 2.0 mm ±1 mm for a 0.018 inch wire diameter. D 1  is about 3 mm ±1 mm, d is about 20 mm ±1 mm, c is about 23 mm ±1 mm, g is about 17 mm, ±1 mm, a is about 3 mm ±1 and b is about 3 mm ±1 mm. Specific dimensions for all of the foregoing variables can be varied considerably, depending upon the desired wire configuration, in view of the disclosure herein.  
      Referring to  FIG. 7 , there is shown an alternative wire layout having a plurality of radiussed bends  70  in one or more sections of strut  64  which may be included to provide additional flex points to provide enhanced fluid dynamic characteristics and maintain the tubular shape.  
      In another embodiment of the wire support, illustrated in  FIG. 8 , each pair of adjacent proximal and distal segments,  76  and  78 , may be joined by crosslinking of the corresponding proximal and distal bends. Thus, a proximal bend  60  from a distal segment  78  is connected to the corresponding distal bend  62  of a proximal segment  76 , thereby coupling the proximal segment  76  and distal segment  78 . The connection between corresponding proximal bends  60  and distal bends  62  can be accomplished in any of a variety of ways as will be apparent to those of skill in the art in view of the disclosure herein. In the illustrated embodiment, the connection is accomplished through the use of a link  72 . Link  72  may be a loop of metal such as stainless steel, a suture, a welded joint or other type of connection. Preferably, link  72  comprises a metal loop or ring which permits pivotable movement of a proximal segment  76  with respect to a distal segment  78 .  
      In one example of an endoluminal vascular prosthesis in accordance with the present invention, the proximal segment  76  is provided with six distal bends  62 . The corresponding distal segment  78  is provided with six proximal bends  60  such that a one to one correspondence exists. A link  72  may be provided at each pair of corresponding bends  60 ,  62 , such that six links  72  exist in a plane transverse to the longitudinal axis of the graft at the interface between the proximal segment  76  and the distal segment  78 . Alternatively, links  72  can be provided at less than all of the corresponding bends, such as at every other bend, every third bend, or only on opposing sides of the graft. The distribution of the links  72  in any given embodiment can be selected to optimize the desired flexibility characteristics and other performance criteria in a given design.  
      The use of connectors such as cross link  72  enables improved tracking of the graft around curved sections of the vessel. In particular, the wire cage  46  as illustrated in  FIG. 8  can be bent around a gentle curve, such that it will both retain the curved configuration and retain patency of the central lumen extending axially therethrough. The embodiment illustrated in  FIG. 2  may be more difficult to track curved anatomy while maintaining full patency of the central lumen. The ability to maintain full patency while extending around a curve may be desirable in certain anatomies, such as where the aorta fails to follow the linear infrarenal path illustrated in  FIG. 1 .  
      Referring to  FIG. 8   a , there is illustrated a plan view of a formed wire useful for rolling about an axis to produce a multi-segmented support structure of the type illustrated in  FIG. 8 . In general, the formed wire of  FIG. 8   a  is similar to that illustrated in  FIG. 3 . However, whereas any given pair of corresponding distal bends  62  and proximal bends  60  of the embodiment of  FIG. 3  overlap in the axial direction to facilitate threading a circumferential suture therethrough, the corresponding distal bend  62  and proximal bend  60  of the embodiment illustrated in  FIG. 8   a  may abut end to end against each other or near each other as illustrated in  FIG. 8  to receive a connector  72  thereon.  
      The appropriate axial positioning of a distal bend  62  with respect to a corresponding proximal bend  60  can be accomplished in a variety of ways, most conveniently by appropriate formation of the connector bend  68  between adjacent segments of the wire cage.  
       FIGS. 9-16  illustrate alternative bend configurations in accordance with the present invention.  FIG. 9  shows one embodiment having the proximal and distal bends as eyelets, but the connector bend  68 , remaining in the usual configuration. The embodiment illustrated in  FIG. 10  has the proximal and distal bends as well as the connector bend in the eyelet configuration. Various eyelet designs in accordance with the present invention are shown in greater detail in  FIGS. 11-13 , including a double-looped circular eyelet ( FIG. 11 ), a double-looped triangular eyelet ( FIG. 12 ), and a single-looped triangular eyelet ( FIG. 13 ). The eyelets can be used to receive a circumferentially extending suture or wire as has been described.  
      Additional embodiments of the wire configuration are illustrated in  FIGS. 14-16 .  FIG. 14  shows an embodiment of the proximal  60  and distal  62  bends in which double bends are employed to increase the flexion. Alternatively,  FIG. 15  shows triangular bends having a more pronounced length (d 1 ) of parallel wire, and accordingly shorter wall sections  64 . Another embodiment of the proximal and distal bends is shown in  FIG. 16 , wherein the triangular bends include additional flexion points in the form of wall segment bends  70 .  
      Referring to  FIGS. 17 and 18 , a deployment device and method in accordance with a preferred embodiment of the present invention are illustrated. A delivery catheter  80 , having a dilator tip  82 , is advanced along guidewire  84  until the (anatomically) proximal end  50  of the collapsed endoluminal vascular prosthesis  86  is positioned between the renal arteries  32  and  34  and the aneurysm  40 . The collapsed prosthesis in accordance with the present invention has a diameter in the range of about 2 to about 10 mm. Preferably, the diameter of the collapsed prosthesis is in the range of about 3 to 6 mm (12 to 18 French). More preferably, the delivery catheter including the prosthesis will be 16 F, or 15 F or 14 F or smaller.  
      The prosthesis  86  is maintained in its collapsed configuration by the restraining walls of the tubular delivery catheter  80 , such that removal of this restraint would allow the prosthesis to self expand. Radiopaque marker material may be incorporated into the delivery catheter  80 , and/or the prosthesis  86 , at least at both the proximal and distal ends, to facilitate monitoring of prosthesis position. The dilator tip  82  is bonded to an internal catheter core  92 , as illustrated in  FIG. 18 , wherein the internal catheter core  92  and the partially expanded prosthesis  88  are revealed as the outer sheath of the delivery catheter  80  is retracted. The internal catheter core  92  is also depicted in the cross-sectional view in  FIG. 19 .  
      As the outer sheath is retracted, the collapsed prosthesis  86  remains substantially fixed axially relative to the internal catheter core  92  and consequently, self-expands at a predetermined vascular site as illustrated in  FIG. 18 . Continued retraction of the outer sheath results in complete deployment of the graft. After deployment, the expanded endoluminal vascular prosthesis has radially self-expanded to a diameter anywhere in the range of about 20 to 40 mm, corresponding to expansion ratios of about 1:2 to 1:20. In a preferred embodiment, the expansion ratios range from about 1:4 to 1:8, more preferably from about 1:4 to 1:6.  
      In addition to, or in place of, the outer sheath described above, the prosthesis  86  may be maintained in its collapsed configuration by a restraining lace, which may be woven through the prosthesis or wrapped around the outside of the prosthesis in the collapsed reduced diameter. Following placement of the prosthesis at the treatment site, the lace can be proximally retracted from the prosthesis thereby releasing it to self expand at the treatment site. The lace may comprise any of a variety of materials, such as sutures, strips of PTFE, FEP, polyester fiber, and others as will be apparent to those of skill in the art in view of the disclosure herein. The restraining lace may extend proximally through a lumen in the delivery catheter or outside of the catheter to a proximal control. The control may be a pull tab or ring, rotatable reel, slider switch or other structure for permitting proximal retraction of the lace. The lace may extend continuously throughout the length of the catheter, or may be joined to another axially moveable element such as a pull wire.  
      In general, the expanded diameter of the graft in accordance with the present invention can be any diameter useful for the intended lumen or hollow organ in which the graft is to be deployed. For most arterial vascular applications, the expanded size will be within the range of from about 10 to about 40 mm. Abdominal aortic applications will generally require a graft having an expanded diameter within the range of from about 20 to about 28 mm, and, for example, a graft on the order of about 45 mm may be useful in the thoracic artery. The foregoing dimensions refer to the expanded size of the graft in an unconstrained configuration, such as on the table. In general, the graft will be positioned within an artery having a slightly smaller interior cross section than the expanded size of the graft. This enables the graft to maintain a slight positive pressure against the wall of the artery, to assist in retention of the graft during the period of time prior to endothelialization of the polymeric sleeve  44 .  
      The radial force exerted by the proximal segment  94  of the prosthesis against the walls of the aorta  30  provides a seal against the leakage of blood around the vascular prosthesis and tends to prevent axial migration of the deployed prosthesis. As discussed above, this radial force can be modified as required through manipulation of various design parameters, including the axial length of the segment and the bend configurations. In another embodiment of the present invention, radial tension can be enhanced at the proximal, upstream end by changes in the wire gauge as illustrated in  FIG. 20 . Note that the wire gauge increases progressively along the wall segments  64  from T 1  at the proximal bends  60  to T 2  at the distal bends  62 . Consequently, the radial flex exerted by the distal bends  62  is greater than that exerted by the proximal bends  60  and the radial tension is thereby increased at the proximal end  50  of the prosthesis. T 1  may range from about 0.001 to 0.01 inches whereas T 2  may range from about 0.01 to 0.03 inches.  
      An alternative embodiment of the wire layout which would cause the radial tension to progressively decrease from the proximal segments to the distal segments, involves a progressive or step-wise decrease in the wire gauge throughout the entire wire support, from about 0.01 to 0.03 inches at the proximal end to about 0.002 to 0.01 inches at the distal end. Such an embodiment, may be used to create a tapered prosthesis. Alternatively, the wire gauge may be thicker at both the proximal and distal ends, in order to insure greater radial tension and thus, sealing capacity. Thus, for instance, the wire gauge in the proximal and distal segments may about 0.01 to 0.03 inches, whereas the intervening segments may be constructed of thinner wire, in the range of about 0.001 to 0.01 inches.  
      Referring to  FIG. 21 , there is illustrated two alternative deployment sites for the endoluminal vascular prosthesis  42  of the present invention For example, a symmetrical aneurysm  33  is illustrated in the right renal artery  32 . An expanded endoluminal vascular prosthesis  42 , in accordance with the present invention, is illustrated spanning that aneurysm  33 . Similarly, an aneurysm of the right common iliac  37  is shown, with a prosthesis  42  deployed to span the iliac aneurysm  37 .  
      Referring to  FIG. 22 , there is illustrated a modified embodiment of the endovascular prosthesis  96  in accordance with the present invention. In the embodiment illustrated in  FIG. 22 , the endovascular prosthesis  96  is provided with a wire cage  46  having six axially aligned segments  54 . As with the previous embodiments, however, the endovascular prosthesis  96  may be provided with anywhere from about 2 to about 10 or more axially spaced or adjacent segments  54 , depending upon the clinical performance objectives of the particular embodiment.  
      The wire support  46  is provided with a tubular polymeric sleeve  44  as has been discussed. In the present embodiment, however, one or more lateral perfusion ports or openings are provided in the polymeric sleeve  44 , such as a right renal artery perfusion port  98  and a left renal artery perfusion port  100  as illustrated.  
      Perfusion ports in the polymeric sleeve  44  may be desirable in embodiments of the endovascular prosthesis  96  in a variety of clinical contexts. For example, although  FIGS. 1 and 22  illustrate a generally symmetrical aneurysm  40  positioned within a linear infrarenal portion of the abdominal aorta, spaced axially apart both from bilaterally symmetrical right and left renal arteries and bilaterally symmetrical right and left common iliacs, both the position and symmetry of the aneurysm  40  as well as the layout of the abdominal aortic architecture may differ significantly from patient to patient. As a consequence, the endovascular prosthesis  96  may need to extend across one or both of the renal arteries in order to adequately anchor the endovascular prosthesis  96  and/or span the aneurysm  40 . The provision of one or more lateral perfusion ports enables the endovascular prosthesis  96  to span the renal arteries while permitting perfusion therethrough, thereby preventing “stent jailing” of the renals. Lateral perfusion through the endovascular prosthesis  96  may also be provided, if desired, for a variety of other arteries including the second lumbar, testicular, inferior mesenteric, middle sacral, and alike as will be well understood to those of skill in the art.  
      The endovascular prosthesis  96  is preferably provided with at least one, and preferably two or more radiopaque markers, to facilitate proper positioning of the prosthesis  96  within the artery. In an embodiment having perfusion ports  98  and  100  such as in the illustrated design, the prosthesis  96  should be properly aligned both axially and rotationally, thereby requiring the ability to visualize both the axial and rotational position of the device. Alternatively, provided that the delivery catheter design exhibits sufficient torque transmission, the rotational orientation of the graft maybe coordinated with an indexed marker on the proximal end of the catheter, so that the catheter may be rotated and determined by an external indicium of rotational orientation to be appropriately aligned with the right and left renal arteries.  
      In an alternative embodiment, the polymeric sleeve  44  extends across the aneurysm  40 , but terminates in the infrarenal zone. In this embodiment, a proximal zone  55  on the prosthesis  96  comprises a wire cage  46  but no polymeric sleeve  44 . In this embodiment, the prosthesis  96  still accomplishes the anchoring function across the renal arteries, yet does not materially interfere with renal perfusion. Thus, the polymeric sleeve  44  may cover anywhere from about 50% to about 100% of the axial length of the prosthesis  96  depending upon the desired length of uncovered wire cage  46  such as for anchoring and/or lateral perfusion purposes. In particular embodiments, the polymeric sleeve  44  may cover within the range of from about 70% to about 80%, and, in one four segment embodiment having a single exposed segment, 75%, of the overall length of the prosthesis  96 . The uncovered wire cage  46  may reside at only a single end of the prosthesis  96 , such as for traversing the renal arteries. Alternatively, exposed portions of the wire cage  46  may be provided at both ends of the prosthesis such as for anchoring purposes.  
      In a further alternative, a two part polymeric sleeve  44  is provided. A first distal part spans the aneurysm  40 , and has a proximal end which terminates distally of the renal arteries. A second, proximal part of the polymeric sleeve  44  is carried by the proximal portion of the wire cage  46  which is positioned superiorly of the renal arteries. This leaves an annular lateral flow path through the side wall of the vascular prosthesis  96 , which can be axially aligned with the renal arteries, without regard to rotational orientation.  
      The axial length of the gap between the proximal and distal segments of polymeric sleeve  44  can be adjusted, depending upon the anticipated cross sectional size of the ostium of the renal artery, as well as the potential axial misalignment between the right and left renal arteries. Although the right renal artery  32  and left renal artery  34  are illustrated in  FIG. 22  as being concentrically disposed on opposite sides of the abdominal aorta, the take off point for the right or left renal arteries from the abdominal aorta may be spaced apart along the abdominal aorta as will be familiar to those of skill in the art. In general, the diameter of the ostium of the renal artery measured in the axial direction along the abdominal aorta falls within the range of from about 7 cm to about 20 cm for a typical adult patient.  
      Clinical and design challenges, which are satisfied by the present invention, include providing a sufficient seal between the upstream end of the vascular prosthesis and the arterial wall, providing a sufficient length to span the abdominal aortic aneurysm, providing sufficient wall strength or support across the span of the aneurysm, and providing a sufficient expansion ratio, such that a minimal percutaneous axis diameter may be utilized for introduction of the vascular prosthesis in its collapsed configuration.  
      Prior art procedures presently use a 7 mm introducer (18 French) which involves a surgical procedure for introduction of the graft delivery device. In accordance with the present invention, the introduction profile is significantly reduced. Embodiments of the present invention can be constructed having a 16 French or 15 French or 14 French or smaller profile (e.g. 3-4 mm) thereby enabling placement of the endoluminal vascular prosthesis of the present invention by way of a percutaneous procedure. In addition, the endoluminal vascular prosthesis of the present invention does not require a post implantation balloon dilatation, can be constructed to have minimal axial shrinkage upon radial expansion, and avoids the disadvantages associated with nitinol grafs.  
      While a number of preferred embodiments of the invention and variations thereof have been described in detail, other modifications and methods of using and medical applications for the same will be apparent to those of skill in the art. Accordingly, it should be understood that various applications, modifications, and substitutions may be made of equivalents without departing from the spirit of the invention or the scope of the claims.