Abstract:
A stent/graft assembly includes a tubular graft having an upstream end, a downstream end and a tubular passage between the ends. The assembly also includes a tubular stent having an upstream end, a downstream end and a tubular passage. The upstream end of the tubular graft is affixed in substantially end-to-end relationship with the downstream end of the tubular stent. The affixation may employ sutures, bonding, hooks or the like. The end-to-end connection may also require a slight overlapping to ensure an adequate affixation. The end-to-end disposition of the tubular graft and tubular stent reduces the cross-sectional profile of the stent/graft assembly. One or more wires may extend from the tubular stent through the tubular graft for anchoring near the downstream end of the tubular graft. The wire prevents axial collapsing of the tubular graft and provide radial support for the tubular graft.

Description:
This application claims the benefit of provisional application No. 60/283,108 filed Apr. 11, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention relates to a stent and graft assembly for treating vascular anomalies, such as aneurysms. 
   2. Description of the Related Art 
   Vascular anomalies are considered to include blood vessels that are damaged, weakened or otherwise impaired. The anomaly may include a local change in the cross-sectional dimensions of the blood vessel. For example, aneurysms include a local area where a blood vessel expands to a larger cross-sectional area due to disease, weakening or other damage. 
   The abdominal aorta extends from the heart and through the abdomen. The abdominal aorta then feeds abdominal organs and the right and left iliac arteries that bring blood to the right and left legs respectively. The aorta is prone to aneurysms. Abdominal aortic aneurysms that are not treated in a timely manner can lead to rupture, detachable, infection or the production of emboli which can flow downstream and clot a smaller blood vessel. A ruptured abdominal aortic aneurysm typically is fatal due to a loss of the large volume of blood that flows through the abdominal aorta. 
   Aneurysms can be corrected by grafts. The typical graft is implanted surgically by accessing the site of the aneurysm, cutting open the aneurysm and then surgically forming an appropriate fabric into a tubular shape that spans the aneurysm. Thus, upstream and downstream ends of the prior art graft are sutured to healthier regions of the blood vessel. 
   The prior art also includes endovascular grafts. An endovascular graft comprises a flexible tubular member formed from a synthetic fabric. The graft is selected to have an outside cross-sectional dimension that approximates the inside cross-sectional dimensions of the blood vessel on either side of the aneurysm. The graft also is selected to have a length that exceeds the length of the damaged area of the blood vessel. An unsupported flexible tubular graft has a tendency to collapse in the presence of the flowing blood and could be transported downstream by the blood flow. As a result, endovascular grafts are used in combination with a stent. Stents take many forms, including balloon expandable stents and self-expanding stents, but typically are resilient cylindrical members that are inserted axially through the tubular graft prior to insertion into the blood vessel. The stent and the graft are sutured together prior to deployment so that the opposed ends of the stent align with the opposed ends of the graft. The endovascular graft assembly then is inserted through a healthy region of the blood vessel and is advanced through the circulatory system to the aneurysm or other damaged region of the blood vessel. More particularly, the endovascular graft assembly is advanced to a position where the endovascular graft assembly bridges the aneurysm or other damaged portion of the blood vessel. However, the opposed axial ends of the endovascular graft assembly extend beyond the aneurysm. The stent then is expanded to hold the graft in an expanded tubular condition with at least the opposed axial end regions of the graft being urged tightly against the interior of healthy regions of the blood vessel. The stent and the graft of the prior art endovascular graft assembly are coaxial, and longitudinally coextensive. 
   Prior art assemblies of stents and grafts typically perform well. However, the coaxially and longitudinally coextensive arrangement of the stent and graft has resulted in a cross-sectionally large assembly. A cross-sectionally large graft and stent assembly can be difficult to insert and deliver intravascularly to the damaged section of the blood vessel and may require surgery. 
   The inventor herein has developed low-profile stent/graft structures, as shown for example in U.S. Pat. No. 6,015,422, U.S. Pat. No. 6,102,918 and U.S. Pat. No. 6,168,620. 
   In view of the above, it is an object of the subject invention to provide improvements in vascular stent and graft assemblies that provide a small cross-section and low profile. 
   It is also an object of the invention to provide an endovascular stent and graft assembly that can be introduced easily into and through the damaged or diseased section of a blood vessel. 
   A further object of the subject invention is to provide a system of endovascular stents and grafts that can be assembled intravascularly through damaged regions of a blood vessel. 
   Another object of the invention is to provide an endovascular stent/graft assembly that prevents migration of the assembly after deployment. 
   An additional object of the invention is to provide an endovascular stent/graft assembly for treating patients with short and/or angulated vascular necks adjacent an aneurysm. 
   Yet another object of the invention is to provide a system of endovascular grafts and stents that will prevent an aneurysm from filling with blood that flows into the aneurysm from small side blood vessels. 
   SUMMARY OF THE INVENTION 
   The subject invention is directed to an endovascular graft assembly that comprises at least one tubular vascular graft and at least one fixation device. The tubular graft and the fixation device are connected substantially in end-to-end relationship with little or no longitudinal overlap. The tubular graft has a length that exceeds the length of a damaged section of a blood vessel that is being repaired by the endovascular graft assembly. The tubular graft also has a cross-sectional size that is about 10%–30% wider than the cross-sectional size of the blood vessel that is being repaired. The tubular graft preferably is formed from a synthetic material, such as a material formed from an ultra thin polyester fiber, or other vascular graft materials known to those skilled in this art. 
   The fixation device may comprise a generally tubular stent. One end of the tubular stent is securely affixed to one end of the tubular graft. The end-to-end fixation of the graft to the stent preferably is carried out with little or no telescoping between the tubular graft and the stent. However, a slight amount of telescoping (e.g. 0–20 mm) may be required to ensure a secure and substantially permanent interengagement. The connection between the tubular graft and the tubular stent may be achieved by hooking, stitching, fusing or other such secure connection techniques. The connection need not be continuous around the peripheries of the stent and the tubular graft. Thus, the stent and the tubular graft merely may be connected at one location on their respective ends or at plural spaced-apart locations. 
   The fixation device need not be a tubular stent. Rather, the fixation device may comprise a plurality of hooks that extend from at least one longitudinal end of the tubular graft. The hooks can be engaged with healthy sections of blood vessel on either side of an aneurysm. The fixation device may further include an annular ring affixed to an axial end of the tubular graft, and the hooks may project axially from the ring. The ring functions to keep the tubular graft open during insertion of the endovascular graft assembly into the blood vessel. 
   The endovascular graft assembly further comprises an internal stent to provide radial support for the tubular graft of the endovascular graft assembly. However, unlike prior art endovascular graft assemblies, the internal stent of the subject invention is deployed after the end-to-end assembly of the fixation device and tubular graft have been positioned properly across the aneurysm. The internal stent may be a balloon expandable stent or a self-expanding stent. However, the insertion of the internal stent after the insertion of the end-to-end assembly of the fixation device and tubular graft greatly facilitates the deployment of the entire endovascular stent/graft assembly to the proper location. 
   The endovascular graft assembly may further include at least one support that extends from the fixation device into the graft to prevent the graft from collapsing radially or axially during or after installation and/or to provide radially outward support for the graft. The support may comprise at least one longitudinally extending wire extending from the fixation device substantially entirely through the graft and then anchored at the axial end of the graft opposite the stent. The support may alternatively comprise a coil extending substantially from the fixation device, through the graft and to the end of the graft opposite the fixation device. The support may be connected to the fixation device or unitary with portions of the fixation device. 
   The endovascular graft assembly may comprise at least two fixation devices connected respectively to opposite ends of a tubular graft. The endovascular graft assembly may further comprise a plurality of tubular grafts connected respectively to opposite axial ends of fixation devices. The tubular graft and tubular fixation devices need not be all of identical cross-sectional sizes. Additionally, the assembly may comprise plural fixation devices connected axially to the legs or branches of a bifurcated or trifurcated graft, such as a graft having an inverted Y-shape. Furthermore, certain components of the assembly may be assembled intravascularly and intraoperatively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational, partly in section, view of an endovascular stent/graft assembly in accordance with a first embodiment of the invention. 
       FIG. 2  is an enlarged elevational view, partly in section, of a connection between the stent and graft of the assembly in either  FIG. 1 . 
       FIG. 3  is an enlarged elevational view partly in section, similar to  FIG. 2 , but showing an alternate connection between the stent and graft. 
       FIG. 4  is an elevational view of the graft with hooks for fixation to the stent or to a blood vessel. 
       FIG. 5  is an elevational view similar to  FIG. 4 , but showing hooks on the tubular stent. 
       FIG. 6  is an elevational view of an endovascular stent/graft assembly in accordance with a second embodiment of the invention. 
       FIG. 7  is a schematic illustration of the endovascular stent/graft assembly of  FIG. 1  inserted into a blood vessel. 
       FIG. 8  is a schematic illustration of an insertion of the endovascular stent/graft assembly of  FIG. 1  into the abdominal aorta. 
       FIG. 9  is a schematic illustration of the endovascular stent/graft assembly of  FIG. 1  deployed through the right iliac artery and then inserted into the left iliac artery. 
       FIG. 10  is an elevational view, partly in section of a third alternate endovascular stent/graft assembly. 
       FIG. 11  is a perspective view of a fourth embodiment of an endovascular stent/graft assembly in accordance with the subject invention. 
       FIG. 12  is a perspective view of an endovascular stent/graft assembly in accordance with a fifth embodiment of the subject invention. 
       FIG. 13  is a side elevational view of the endovascular stent/graft assembly of  FIG. 12  with a cross-sectional variation along the length of the graft to accommodate cross-sectional variations of the blood vessel. 
       FIG. 14  is a schematic view of a modular endovascular stent/graft assembly that represents a sixth embodiment of the invention intended primarily for deployment into the abdominal aorta and adjacent regions of the left and right iliac arteries. 
       FIG. 15  is a schematic view of a seventh embodiment of an endovascular stent/graft assembly in accordance with the invention. 
       FIG. 16  is a schematic view of an eighth embodiment of an endovascular stent/graft assembly in accordance with the invention. 
       FIG. 17  is a schematic view of a modular endovascular stent/graft assembly that represents a ninth embodiment of the invention intended primarily for deployment into the abdominal aorta and adjacent regions of the left and right iliac arteries. 
       FIG. 18  is a schematic view of a variation of the stent/graft assembly of  FIG. 17 . 
       FIG. 19  is a schematic view of a tenth embodiment of an endovascular stent/graft assembly in accordance with the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An endovascular stent/graft assembly in accordance with a first embodiment of the invention is identified generally by the numeral  10  in  FIG. 1 . The endovascular stent/graft assembly  10  includes a substantially tubular graft  12  having a flexible wall formed from a synthetic material, such as a polyester material that is substantially impervious to fluid transmission or that becomes substantially impervious after exposure to blood. The tubular graft  12  has an upstream end  14 , a downstream end  16  and a fluid passage  18  extending between the ends. The endovascular stent/graft assembly  10  further comprises a tubular stent  20  having an upstream end  22 , a downstream end  24  and a passage  26  extending between the ends. The tubular stent  20  may be of known construction and may be formed from materials that are known to those skilled in the art of treating vascular anomalies with endovascular stent/graft assemblies, such as polyethylene terepthalate and PTFE, including materials sold under the trademarks DACRON® and GORTEX®. 
   The terms upstream and downstream used to define the ends of the tubular graft  12  and the tubular stent  20  are employed with reference to the direction of blood flow existing during insertion of a stent graft assembly  10 . More particularly, the endovascular stent/graft assembly preferably will be inserted into a blood vessel such that the tubular stent  20  is upstream and facing into the flow of blood. The tubular graft  12  then will trail behind the stent relative to the direction of insertion of the endovascular stents/graft assembly  10  and relative to the direction of the blood flow. This preferred orientation of the endovascular stent/graft assembly  10  will enable the much more flexible tubular graft  12  to perform much in the nature of a wind-sock that is urged into an extended condition by forces exerted by the blood flow. A reversed insertion, of this first embodiment, on the other hand, could cause the flexible tubular graft  12  to collapse in response to the blood flow. 
   As shown generally in  FIG. 1  and more specifically in  FIGS. 2 and 3 , the tubular graft  12  and the tubular stent  20  are connected substantially in end-to-end axial relationship. More particularly, as shown in  FIG. 2 , the upstream end  14  of the tubular graft  12  is butted against the downstream end  24  of the tubular stent  20  to achieve a true end-to-end axial connection between the tubular graft  12  and the tubular stent  20 . This pure axial end-to-end abutment can be achieved by fusing, suturing or other known connection means that will be appreciated by persons skilled in this art. 
   The true end-to-end axial connection may be difficult to achieve with certain material employed for the tubular graft and the tubular stent. In these situations, a substantially end-to-end axial connection can be achieved with a slight telescoping overlap as shown schematically in  FIG. 3 . With this optional arrangement, the inner circumferential surface of the tubular graft  12  adjacent the upstream end  14  may be telescoped slightly over the outer circumferential surface of the tubular stent  20  adjacent the downstream end  24 . Sutures, fusing or other known connections then may be employed to permanently affix the slightly overlapped ends of the tubular graft  12  and the tubular stent  20 . 
     FIGS. 2 and 3  depict substantially continuous connection between the annular periphery at the upstream end of the tubular graft  12  and the annular periphery at the downstream end  24  of the tubular stent  20 . However, such a continuous connection may not be required in many situations. Rather, one or more points of contact and affixation may be sufficient between the upstream end  14  of the tubular graft  12  and the downstream end of the tubular stent  20 . 
   The endovascular stent/graft assembly  12  further comprises an internal stent  27  that is deployed after the end-to-end connected tubular graft  12  and tubular stent  20  are in place. The internal stent  27  may be a balloon expandable stent or a self-expanding stent and functions to maintain tubular graft  12  in an expanded non-occluded condition. Furthermore, the internal stent  27  maintains outer circumferential surface regions of the tubular graft  12  near the upstream and downstream ends  14  and  16  in face-to-face engagement with the inner surface of the blood vessel upstream and downstream from the aneurysm. The insertion of the internal stent  27  after positioning the tubular graft  12  and the tubular stent  20  is considerably easier than the prior art endovascular grafts that simultaneously attempt to advance a coaxial arrangement of graft and stent that are longitudinally coextensive with one another. 
   An alternate end-to-end connection between the tubular graft  12 , as shown in  FIG. 4 , includes a plurality of hooks  28  woven or otherwise incorporated into the tubular graft  12  to extend axially beyond at least the upstream end  14 . The hooks  28  on the upstream end  14  of the tubular graft  12  can be engaged into the circumferential surface of the blood vessel. Thus, the hooks  28  function as a fixation device that is an alternate to the tubular stent  20  shown in  FIGS. 1–3 . The hooks  28  can be mounted to an annular ring (not shown) that can be affixed to the upstream end  14  of the tubular graft  12 . Thus, the combination of the ring and the hooks  28  may function as the fixation device. A variation of the  FIG. 4  embodiment, the hooks  28  at the upstream end  14  of the tubular graft  12  can be engaged into portions of the tubular stent  20  adjacent the downstream end  24 . Alternatively, as shown in  FIG. 5 , hooks  30  may extend axially beyond the downstream end  24  of the tubular stent  20  for engagement with portions of the tubular graft  12  adjacent the upstream end  14 . 
     FIG. 6  shows an endovascular stent/graft assembly  32  in accordance with a second embodiment of the invention. The endovascular stent/graft assembly  32  includes a tubular graft  12  substantially identical to the tubular graft  12  in the embodiment of  FIG. 1 . The stent/graft assembly  32  further includes an upstream tubular stent  20  substantially identical to the tubular stent  20  in the embodiment of  FIG. 1 . However, the stent/graft assembly  32  further includes a downstream stent  34 . The downstream stent  34  has an upstream end  36 , a downstream end  38  and a tubular passage  40  extending between the ends. The upstream end  36  of the downstream stent  34  is connected in substantially end-to-end relationship with the downstream end  16  of the tubular graft  12  by any of the connection arrangements depicted respectively in  FIGS. 2–5 . The downstream stent  34  can be connected to the tubular graft prior to insertion of the stent/graft assembly  32  into the blood vessel. Alternatively, the sub-assembly of the tubular graft  12  and the upstream stent  20  can be inserted into the blood vessel substantially as shown in  FIG. 1 . The downstream stent  34  then can be inserted subsequently and connected intraoperatively to the downstream end  16  of the tubular graft  12 . 
   As noted above, and as illustrated generally in  FIG. 1 , the endovascular stent/graft assembly  10  is fixed into the blood vessel with the tubular graft  12  in a downstream position relative to the tubular stent  20 . This orientation, does not, however, imply a required direction of insertion. For example, as depicted in  FIG. 7 , a catheter C is employed to insert the endovascular stent/graft assembly  10  into a blood vessel V along the direction of flow and the tubular graft  12  leading the tubular stent  20 . Thus, despite the slow movement of the catheter C and the stent/graft assembly  10  through the blood vessel V in the direction of the blood flow, the tubular graft  12  will extend axially beyond the tubular stent  20  with a substantially wind-sock effect as described above and as shown in  FIG. 7 . Alternatively, the catheter C can be used to insert the endovascular stent/graft assembly  10  in opposition to the direction of blood flow, but with the tubular stent  20  in the upstream position and leading the endovascular stent/graft assembly  10  into the direction of blood flow. More specifically,  FIG. 8  schematically depicts the insertion of the endovascular stent/graft assembly  10  through the right iliac artery  40  and into the abdominal aorta  42 , with the tubular stent  20  in the upstream position relative to the tubular graft  12 , and with the tubular stent  20  leading the insertion against the direction of blood flow. 
   In certain procedures, the stent/graft assembly may start in a direction against the flow of blood but move into a different blood vessel to follow the flow of blood. More particularly,  FIG. 9  depicts the insertion of the stent/graft assembly  10  into the right iliac artery  40  for eventual insertion into the left iliac artery  44 . The initial part of this insertion will have the endovascular stent/graft assembly  10  inverted relative to the preferred and eventual orientation. Thus, the tubular graft  12  may initially be in an upstream position, and accordingly may collapse somewhat during the initial stages of the insertion. However, the tubular graft  12  of the stent/graft assembly will move into the downstream position relative to the tubular stent  20  as the stent/graft assembly  10  moves into the left iliac artery  44 . Thus, any collapsing of the more flexible graft  12  that may have occurred during initial insertion through the right iliac artery  40  will be offset by the above-described wind-sock effect as the stent/graft assembly  10  moves into the left iliac artery  44 . 
   In certain instances, it may be desirable to provide support for the tubular graft  12  of the stent/graft assembly  10 . For example, a third embodiment of the endovascular stent/graft assembly is identified generally by the numeral  46  in  FIG. 10 . The endovascular stent/graft assembly  46  includes a tubular graft  12  with an upstream end  14 , a downstream end  16  and a tubular passage therebetween, substantially as in the first and second embodiments. The stent/graft assembly  46  further includes a tubular stent  20  having an upstream end  22 , a downstream end  24  and a tubular passage  26  extending between the ends. As in the first embodiment, the upstream end  14  of the tubular graft  12  is affixed in substantially end-to-end relationship with the downstream end  24  of the tubular stent  20 . The endovascular stent/graft assembly  46  differs from the first embodiment by the inclusion of a single wire  48  extending from the tubular stent  20  axially along the tubular graft  12  and affixed to the tubular graft  12  in proximity to downstream end  16 . The wire  48  ensures that the tubular graft  12  will remain substantially in an extended condition and will prevent the downstream end  16  of the tubular graft  12  from collapsing toward the tubular stent  20 . The provision of the wire  48  may be helpful, for example, in instances depicted in  FIG. 9  where an endovascular stent/graft assembly may travel in counter flow direction with the tubular graft  12  in an upstream position relative to the tubular stent  20 . Thus, the wire  48  allows the assembly  46  to be deployed with the tubular stent  20  downstream of the tubular graft  12  when there is no upstream landing place for the tubular stent  20 . A second internal stent, such as the internal stent  27  of  FIG. 1 , then is deployed to open the tubular graft  12 . In this embodiment, the wind sock effect does not occur. 
   A fourth embodiment of the endovascular stent/graft assembly is identified by the numeral  50  in  FIG. 11 . The endovascular stent/graft assembly  50  is a variation of the stent/graft assembly  46  of  FIG. 10  in that a plurality of wires  52  extend axially from the stent  20  substantially to the downstream end  16  of the tubular graft  12  where the wires  52  are affixed to the tubular graft  12 . The stent/graft assembly  50  prevents axial collapsing of the tubular stent  20 , substantially as with the embodiment of  FIG. 10 . However, the wires  52  will further provide radially support for the tubular graft  12  and will resist radially collapsing of the graft  12 . 
   A fourth embodiment of the endovascular stent/graft assembly is identified by the numeral  54  in  FIGS. 12 and 13 . The stent/graft assembly  54  is similar to the stent/graft assemblies of  FIGS. 10 and 11 . However, the axially aligned wires of the previous embodiment are replaced with a coil  56 . The coil  56  may be anchored to the tubular stent  20  or to the upstream end  14  of the tubular graft  12  for affixation to the downstream end  16  of the tubular graft  12 . The coil  56  resists axially collapsing and will assist with axial extension in response to any axial collapse that does occur. Additionally, the coil  56  provides greater outwardly directed radially forces on the tubular graft  12  then either of the previous embodiments. 
   The endovascular stent/graft assembly  32  of  FIG. 6  shows that a plurality of stents  20 ,  34  can be assembled with a single tubular graft  12 . The principles embodied in  FIG. 6  can be employed further to develop more complex modular assemblies. For example,  FIG. 14  shows a modular assembly for repairing vascular anomalies in the region where the abdominal aorta  42  meets the right iliac artery  40  and the left iliac artery  44 . In particular, the modular endovascular stent/graft assembly  58  comprises a first modular subassembly  60  with a first tubular stent  62  with an upstream end  64  and an opposed downstream end  66 . The first modular subassembly  60  further comprises a first tubular graft  68  with an upstream end  70  connected substantially in end-to-end axial relationship with the downstream end  66  of the first stent  62 . The first tubular graft  68  further includes a downstream end  72 . The first modular component  60  is deployed from a right leg approach into the right iliac artery  40 . The first tubular stent  62  then is advanced sufficiently into the abdominal aorta  42  for the first tubular stent  62  to be upstream of the aneurysm or other vascular abnormality in the abdominal aorta  42 . 
   The modular assembly  60  further includes a second tubular stent  74  that is mounted unrestrained in the first tubular graft  68  at a location downstream from or within the aneurysm. The first tubular graft  68  further includes tubular exit  76  at a location between the second tubular stent  74  and the downstream end  72  of the first tubular graft. The second tubular stent  74  preferably is cross-sectionally larger than both the exit  76  and portions of the first tubular graft  68  in proximity to the exit  70 . Thus, the unrestrained second tubular stent  74  will not slip longitudinally into either the exit  76  or downstream portions of the first tubular graft  68 . 
   The assembly  58  further includes a second tubular graft  78  with an upstream end  80  and a downstream end  81 . The second tubular graft  78  is deployed from a left leg approach into the left iliac artery  44  and is advanced through the exit  76  of the first tubular graft  68 . The upstream end  80  of the second tubular graft  78  is connected substantially end-to-end with the second tubular stent  74 . Internal stents then may be inserted, such as the internal stent  27  described with respect to the first embodiment. 
   A seventh embodiment of the endovascular stent/graft assembly of the subject invention is identified generally by the numeral  82  in  FIG. 15 . The assembly  82  comprises first and second endovascular stent/graft subassemblies  83  and  84 . The first subassembly  83  comprises a first stent  85  and a first tubular graft  86 . Similarly, the second subassembly  84  comprises a second stent  87  and a second graft  88 . The assembly  82  further includes a generally disc-like drum secured in the abdominal aorta  42  at a location upstream of the aneurysm. The drum  90  has first and second mounting apertures  92  and  94  through which portions of the first and second tubular grafts  86  and  88  extend. The extreme upstream ends of the tubular grafts  86  and  88  are secured respectively in end-to-end relationship with the downstream end of the first and second tubular stents  85  and  87 , while the downstream ends of the tubular grafts  86  and  88  are disposed respectively in the right and left iliac arteries  40  and  44 . The drum or disc  90  prevents blood from flowing around the tubular grafts  86  and  88  and into the region of the aneurysm where blood pressure could cause a rupture of the aneurysm. The stents  85  and  87  provide a secure mounting of the endovascular stent/graft assembly  82  relative to the aneurysm, and prevent any parts of the assembly  82  from migrating downstream due to the pressure of the blood flow. The endovascular stent/graft assembly  82  of  FIG. 15  is used in combination with internal stents, such as the internal stent  27  in  FIG. 1 , that are introduced to the tubular grafts  86  and  88  after complete implantation of portions of the assembly  82  depicted in  FIG. 15 . Additionally, the assembly  82  may be used in combination with one or two downstream stents, or other fixation devices secured to downstream ends of the respective tubular grafts  86  and  88 . 
   An eighth embodiment of the endovascular stent/graft assembly of the subject invention is identified generally by the numeral  96  in  FIG. 16 . The stent/graft assembly  96  is designed in recognition of the fact that somewhat less than half of all patients have a neck defined in the abdominal aorta immediately upstream of the aneurysm. The neck is aligned to the aneurysm at an angle of less than 180°. Although endovascular grafts exhibit some flexibility, it can be cumbersome to advance an initially linear endovascular stent/graft assembly through the aneurysm and through the angularly aligned portions of the aneurysm and neck of the abdominal aorta  42 . To avoid this difficulty, the endovascular stent/graft assembly  96  of  FIG. 16  is preformed to exhibit a curve between the upstream and downstream ends. The curved endovascular stent/graft assembly  96  is better suited for deployment and fixation into regions of the abdominal aorta  42  that have the angulated neck of  FIG. 16 . 
     FIG. 17  shows an endovascular stent/graft assembly  98  with a stent  20 , substantially identical to the stents  20  described and illustrated above. More particularly, the stent  20  of the assembly  98  in  FIG. 17  has opposed upstream and downstream ends  22  and  24 . The assembly  98  includes a one piece bifurcated graft  100 . The graft  100  includes an upstream end  102  that is fixed in substantially end-to-end axial engagement with the downstream end  24  of the stent  20 . Additionally, the graft  100  includes two downstream legs  104  and  106  for disposition respectively in the right and left iliac arteries  40  and  44 . The one piece bifurcated graft  100  of  FIG. 17  eliminates some of the intraoperative assembly required with the modular system of  FIG. 14 . The bifurcated graft  100  is used with one or more internal stents that are deployed after insertion substantially as described with respect to the other embodiments. Additionally, downstream stents can be affixed to either of the downstream legs  104  and  106 . 
   Variations of the  FIG. 17  embodiment also may be provided. For example, more than two legs may be provided. Furthermore the stent  20  may have branches intermediate its length, and tubular grafts may be connected in substantially end-to-end relationship with the branches of the stent. 
   An example of a variation of the  FIG. 17  embodiment is illustrated in  FIG. 18 . In particular,  FIG. 18  shows an endovascular stent/graft assembly  198  with a stent  20  identical to the stent  20  described and illustrated above. The assembly  198  includes a graft  200  with a tubular upstream end  202  connected to the downstream end  24  of the stent  20 . The graft  200  also has a tubular downstream end  204  and three tubular branches  206 ,  208  and  210  extending transversely from intermediate positions along the graft  200 .  FIG. 18  shows the endovascular stent/graft assembly  198  deployed for treating an aneurysm of the thoracic aorta  212 . The tubular branches  206 ,  208  and  210  extend to arteries that branch from the thoracic aorta  212 , including the left subclavian artery  216 , the left carotid artery  218  and the brachiocephalic artery  220 . 
   In many instances, small blood vessels will communicate with portions of the abdominal aorta that have the aneurysm. Blood delivered by these blood vessels can increase pressure between the aneurysm and the graft. Such pressure can lead to a rupture of the aneurysm and/or damage to the graft. The endovascular graft assembly  108  of  FIG. 19  is specifically configured to occlude small side blood vessels that lead into the aneurysm. More particularly, the assembly  108  includes an outer stent/graft subassembly  110  that comprises an upstream tubular stent  112  and a downstream expandable graft  114 . The stent  112  and graft  114  are connected in substantially end-to-end axial alignment as described and illustrated with respect to the other embodiments herein. The downstream graft  114  of the outer stent/graft subassembly  110  differs from the tubular grafts described and illustrated above. More particularly, the outer graft  114  may be a synthetic fabric or a detachable balloon that has been used in the prior art. Specifically, the outer graft  114  can be expanded radially to conform substantially to the shape of the aneurysm and to thereby occlude the small blood vessels that lead into the aneurysm. The assembly  108  further includes an inner stent/graft subassembly  116  that has an upstream stent  118  and a downstream tubular graft  120 . The inner subassembly  116  may be substantially identical to the endovascular stent/graft assembly  10  described with respect to  FIG. 1  and other embodiments set forth above. Thus, the tubular graft  120  of the inner subassembly  116  is not expandable. An inner stent similar to the inner stent  27  described and illustrated above may extend through the tubular graft  120 . The space between the inner and outer graft  114  and  120  may be filled with blood, a contrast liquid, an adhesive or water. Variations of this embodiment may include a detachable balloon between the inner graft  120  and the expandable outer graft  114 . Alternatively, the detachable balloon may make the separate inner graft unnecessary. Still further, the detachable balloon may make a separate internal stent for the outer graft unnecessary. 
   While the invention has been described with respect to certain preferred embodiments, it is apparent that various changes can be made without departing from the scope of the invention as defined by the appended claims. For example, for each of the optional embodiments, and variations thereof, the substantially end-to-end stent-to-graft connections can be pure end-to-end abutment as depicted schematically in  FIG. 2  or a slightly overlapped telescoped arrangement, as shown in  FIG. 3 . In other options, there may be a greater telescoping between the graft and stent prior to deployment and/or during deployment. However, the graft and stent then may be extended intraoperatively into the slightly overlapped relationship depicted in  FIG. 3 .