Abstract:
A bifurcated endoluminal prosthesis is provided that includes a valve or gate in one of the bifurcated branches. The valve or gate prevents flow of blood through the branch when it is closed and permits the flow of blood when it is open. In one variation, the valve comprises a spring member attached to a graft material substantially impermeable to the flow of blood. The spring member holds the graft material over the opening that forms a lumen in the bifurcated portion. The spring member may be flipped from a closed position in which it is initially deployed, to an open position whereby the graft material forms an opening continuous with lumen in the bifurcated portion permitting the flow of blood therethrough. The invention may be used in bifurcated or branched tubular grafts for endoluminal placement within a body lumen, including blood vessels, and for the treatment of abdominal and other aneurysms.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to tubular prostheses such as grafts and endoluminal prostheses including, for example, stent-grafts and aneurysm exclusion devices, and methods for placement of such grafts and endoluminal structures. Further, the present invention relates to a stent graft and deployment method.  
         BACKGROUND OF THE INVENTION  
         [0002]    A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries such as those located within coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.  
           [0003]    A number of vascular devices have been developed for replacing, supplementing or excluding portions of blood vessels. These vascular grafts may include but are not limited to endoluminal vascular prostheses and stent grafts, for example, aneurysm exclusion devices such as abdominal aortic aneurysm (“AAA”) devices that are used to exclude aneurysms and provide a prosthetic lumen for the flow of blood.  
           [0004]    One very significant use for endoluminal or vascular prostheses is in treating aneurysms. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease or a genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. Typically an abdominal aneurysm will begin below the renal arteries and may extend into one or both of the iliac arteries.  
           [0005]    Aneurysms, especially abdominal aortic aneurysms, have been treated in open surgery procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique in view of the alternative of a fatal ruptured abdominal aortic aneurysm, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex and requires long hospital stays due to serious complications and long recovery times and has high mortality rates. In order to reduce the mortality rates, complications and duration of hospital stays, less invasive devices and techniques have been developed. The improved devices include tubular prostheses that provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site. They are introduced into the blood vessel using a catheter in a less or minimally invasive technique. Although frequently referred to as stent-grafts, these devices differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen in a sealing engagement with the vessel wall without further opening the natural blood vessel that is already abnormally dilated.  
           [0006]    Typically these endoluminal prostheses or stent grafts are constructed of graft materials such as woven polymer materials (e.g., Dacron,) or polytetrafluoroethylene (“PTFE”) and a support structure. The stent-grafts typically have graft material secured onto the inner diameter or outer diameter of a support structure that supports the graft material and/or holds it in place against a luminal wall. The prostheses are typically secured to a vessel wall above and below the aneurysm site with at least one attached expandable annular spring member that provides sufficient radial force so that the prosthesis engages the inner lumen wall of the body lumen to seal the prosthetic lumen from the aneurysm  
           [0007]    Abdominal Aortic Aneurysms are frequently treated with bifurcated devices that provide an artificial lumen for flow of blood past the aneurysm and into the iliac vessels that branch off from the aorta. One such commonly used device comprises a bifurcated device having one branch portion longer than the other branch portion. This enables deployment of the main body through one of the iliac arteries where the longer branch is deployed. An extension leg is then deployed through the second iliac artery and is connected with the shorter branch portion.  
           [0008]    Iliac vessels associated with abdominal aneurysms frequently have tortuous and twisted anatomies and other structural abnormalities that can prevent effect introduction of an extension leg through an iliac vessel. Often it must be decided prior to deployment whether to use a single lumen prosthesis through one iliac vessel and join the vessels with a shunt further down in the anatomy, or to use a bifurcated prosthesis with an extension. Often a surgeon may not be able to determine the appropriate course of action until the prosthesis is in place or after attempts have been made to deploy an extension graft through a tortuous iliac artery. It would be desirable to provide a device that would enable the decision to be made during the deployment procedure. Devices have been proposed in U.S. Pat. No. 6,102,938, incorporated herein by reference, that provide for sealing off a bifurcated portion of a bifurcated AAA device before or after deployment. Such device is designed for situations where a determination is made during a procedure that it would not be possible to introduce an extension leg into the shorter bifurcated portion to provide blood flow through one of the iliac vessels. It would be desirable to provide an improved or alternative device for accomplishing such task.  
           [0009]    Frequently, the AAA procedures are performed in emergency situations where the aorta has ruptured or is extremely fragile and about to rupture. In these situations, frequently a single leg device is deployed through the aorta and one of the iliac vessels occluding the second iliac vessel. This may be done because of the importance of reestablishing blood flow through the aorta and iliac vessel and stopping the loss of blood through the ruptured or rupturing vessel. Such situations may not permit deployment of the second (extension) leg. During this crucial time, in using an existing bifurcated device, blood would be able to flow through the shorter bifurcated portion of the prosthesis into the area of the aneurysm. Accordingly it would be desirable to provide an improved or alternative device that allows for deployment of a bifurcated device in emergency situations that would prevent further blood flow into the area of the aneurysm.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly one embodiment according to the present invention provides a novel device and method that include providing a bifurcated device with one leg initially in an occluded position preventing flow of blood through that portion into the aorta. Once the implant is in place and blood is excluded from the aneurysm site, an extension may be introduced and the occluded side opened to blood flow through the extension.  
           [0011]    An embodiment of the endoluminal prosthesis comprises a bifurcated tubular member constructed of a graft material and at least one annular support member. The tubular graft is formed of a woven fiber for conducting fluid. The tubular member includes, a proximal opening and distal openings though the bifurcated portions providing a lumen or lumens through which body fluids may flow. When deployed, annular support members support the tubular graft and/or maintain the lumen in a conformed, sealing arrangement with the inner wall of a body lumen. One of the bifurcated portions is provided with a valve that can open or close to permit or prevent the flow of blood through the bifurcated portion. Various embodiments of the valve includes a member that move a section of graft or other material over or away from the opening into the short iliac leg of the bifurcated prosthesis to close or open the short leg to the flow of blood.  
           [0012]    The annular support members of an embodiment of the prosthesis each comprise an annular expandable member formed by a series of connected compressible diamond structures. Alternatively, the expandable member may be formed of an undulating or sinusoidal patterned wire ring or other compressible spring member. Preferably the annular support members are radially compressible springs biased in a radially outward direction, which when released, bias the prosthesis into conforming fixed engagement with an interior surface of the vessel. Annular support members are used to create a seal between the prosthesis and the inner wall of a body lumen as well as to support the tubular graft structure. The annular springs are preferably constructed of Nitinol. Examples of such annular support structures are described, for example, in U.S. Pat. Nos. 5,713,917 and 5,824,041 incorporated herein by reference. When used in an aneurysm exclusion device, the support structures have sufficient radial spring force and flexibility to conformingly engage the prosthesis with the body lumen inner wall, to avoid excessive leakage, and prevent pressurization of the aneurysm, i.e., to provide a leak resistant seal. Although some leakage of blood or other body fluid may occur into the aneurysm isolated by the prosthesis, an optimal seal will reduce the chances of aneurysm pressurization and resulting rupture.  
           [0013]    The annular support members are attached or mechanically coupled to the graft material along the tubular graft by various means, such as, for example, by stitching onto either the inside or outside of the tubular graft.  
           [0014]    An embodiment according to the present invention provides such a tubular graft for endoluminal placement within a blood vessel for the treatment of abdominal and other aneurysms. In this embodiment, the endoluminal prosthesis is an aneurysm exclusion device forming a lumen for the flow of body fluids excluding the flow at the aneurysm site. The aneurysm exclusion device may be used for example, to exclude an aneurysm in the aorta (Abdominal Aortic Aneurysm (“AAA”) device) in which the prosthesis is bifurcated.  
           [0015]    The generally Y-shaped bifurcated tubular prosthesis has a trunk joining at a graft junction with a pair of lateral limbs, namely an ipsilateral limb and a contralateral limb. In a bifurcated prosthesis, the proximal portion of the prosthesis comprises a trunk with a proximal opening and the distal portion is branched into at least two branches with distal openings. Preferably the ipsilateral limb is longer so that when deployed, it extends into the common iliac. The contralateral limb includes a valve located therein that is initially in a closed position in which body fluids flow from the proximal opening through the distal opening of the ipsalateral limb while the flow of body fluid through the contralateral limb is prevented by the valve. A single limb extension member is provided having a mating portion for coupling with a lateral limb of a bifurcated member and an adjustable length portion extending along an axis from a distal end of the mating portion. The insertion of the limb extension into the contralateral portion of the main prosthesis opens the valve which is then in part maintained open by the extension limb, permitting blood flow from the proximal opening in the main prosthesis through the distal opening in the contralateral and extension limbs.  
           [0016]    The valve in one embodiment comprises a plurality of support members coupled to a section of graft material. One of the support members is an annular member forming an opening for the flow of body fluids. A proximal support member is a semicircular member which has an closed position in which the section of graft material forms a cover over the opening formed by the annular member, and an open position in which the section of graft material is held is a position against the wall of the prosthesis so that the opening formed by the annular member is in fluid communication with the flow of body fluid through the prosthesis.  
           [0017]    In another embodiment the valve comprises a plurality of annular support members coupled to a section of graft material where at least one of the annular support members is configured to be folded to form a semicircular member engaged to an inner circumference of the bifurcated prosthesis. When the valve is in an open position, the support members are in an open configuration whereby the annular members and a section of graft material form a lumen through which blood may flow. When the valve is in a closed position, one of the annular support members is folded to that the graft material attached to the folded annular member is drawn across the opening through the short leg in which the valve is located.  
           [0018]    In another embodiment the valve comprises a graft material sewn in part on an inner circumference of the bifurcated prosthesis and forming a pocket when the valve is closed. A portion of an annular member is sewn on to at least a portion of the section of graft material not sewn on to the prosthesis. When the valve is in a closed position, the annular member holds section of the graft material in a position over the opening in the short leg of the prosthesis. The annular member in this position is across from the location where the opposite side of the section of graft material is sewn on to the prosthesis. When the valve is in a closed position, the annular member holds the pocket formed by the section of graft material closed. The annular member in this position is against the location where the section of graft material is sewn on to the prosthesis so that the opening in the short leg provides a lumen through which blood may flow from the proximal end of the prosthesis to the distal end of the short leg.  
           [0019]    The compressed profile of the prosthesis, including the valve, is sufficiently low to allow the endoluminal graft to be placed into the vasculature using a low profile delivery catheter. The prosthesis can be placed within a diseased vessel via deployment means at the location of an aneurysm. Various means for deliver of the device through the vasculature to the site for deployment, are well known in the art and may be found for example is U.S. Pat. Nos. 5,713,917 and 5,824,041. In general, the endoluminal prosthesis is radially compressed and loaded in a catheter for delivery to the deployment site. The aneurysm site is located using an imaging technique such as fluoroscopy and is guided through a femoral iliac artery with the use of a guide wire to the aneurysm site. Once appropriately located, a sheath restraining the tubular graft may be retracted to release the annular springs to expand and attach or engage the tubular member to the inner wall of the body lumen. The iliac extension is also loaded into a catheter and is then located into the main body of the stent graft and within the iliac vessel and is placed through an opened valve where it is deployed. According to an embodiment, when deployed, the iliac has proximal annular springs which when located within the inner lumen of the main body hold or maintain the valve open. The distal portion of the extension extends into one of the iliac vessels. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a side elevational view of an endoluminal prosthesis of the prior art.  
         [0021]    [0021]FIG. 2A is a side view of a valve in a closed position as positioned in a prosthesis according to an embodiment of the invention.  
         [0022]    [0022]FIG. 2B is a top cross sectional of a proximal most support member of the valve of FIG. 2A.  
         [0023]    [0023]FIG. 2C is a top cross sectional of a middle support member of the valve of FIG. 2A.  
         [0024]    [0024]FIG. 2D is a top cross sectional of a distal most support member of the valve of FIG. 2A.  
         [0025]    [0025]FIG. 2E is a front cut away view of the valve of FIG. 2A in a closed position.  
         [0026]    [0026]FIG. 2F is a back cut away view of the valve of FIG. 2A in a closed position.  
         [0027]    [0027]FIG. 3 is a top view of the prosthesis and valve of FIG. 2A.  
         [0028]    [0028]FIG. 4A is a side view of a valve of the prosthesis of FIG. 2A in an open position.  
         [0029]    [0029]FIG. 4B is a side view of the valve of FIG. 4A in an open position.  
         [0030]    [0030]FIG. 5 is a top view of the prosthesis and valve of FIGS.  4 A- 4 B.  
         [0031]    [0031]FIG. 6 is a perspective partial cutaway view of the prosthesis of FIG. 2A.  
         [0032]    [0032]FIG. 7 is perspective partial cutaway view of the prosthesis of FIG. 4A with an extension in place and the valve in an open position.  
         [0033]    [0033]FIG. 8 is a side view of another embodiment of a valve in a closed position according to the invention.  
         [0034]    [0034]FIG. 9A is a top view of the prosthesis and valve of FIG. 8.  
         [0035]    [0035]FIG. 9B is a front cut away view of the valve of FIG. 9A in an open position.  
         [0036]    [0036]FIG. 9C is a back cut away view of the valve of FIG. 9A in an open position.  
         [0037]    [0037]FIG. 10 is a side view of a valve of the prosthesis of FIG. 8 in an open position.  
         [0038]    [0038]FIG. 11A is a top view of the prosthesis and valve of FIG. 10.  
         [0039]    [0039]FIG. 11B is a side view of the valve of FIG. 11A in an open position.  
         [0040]    [0040]FIG. 12 is a side view of another embodiment of a valve in a closed position according to the invention.  
         [0041]    [0041]FIG. 13 is a perspective partial cutaway view of the prosthesis of FIG. 12.  
         [0042]    [0042]FIG. 14 is a side view of a valve of the prosthesis of FIG. 12 in an open position.  
         [0043]    [0043]FIG. 15 is perspective partial cutaway view of the prosthesis of FIG. 14. 
     
    
     DETAILED DESCRIPTION  
       [0044]    [0044]FIG. 1 illustrates a bifurcated prosthesis of the prior art. The prosthesis  210  is shown in place in an abdominal aorta  20 . The aorta  20  is joined by renal arteries  22  and  24  at the aorto-renal junction  26 . Just below the aorta-renal junction  26  is an aneurysm  28 , a diseased region where the vessel wall is weakened and expanded. Below the aneurysm  28 , the aorta  20  bifurcates into right and left iliac vessels  21 ,  23 , respectively. The elongated bifurcated tubular prosthesis  210  is deployed at the region of aneurysm  28  for the purpose of relieving blood pressure against the weakened vessel wall, by acting as a fluid conduit through the region of the aneurysm  28 . In its deployed condition, a main body portion  216  of the prosthesis  210  defines a conduit for blood flow through the aorta  20  and into the iliac vessel  21 . Before deploying an iliac extension (not shown), blood unobstructedly flows through the short iliac portion  219  into the aorta  20  as illustrated.  
         [0045]    Annular support members (rings)  212  attached to a tubular graft  25 , are designed to exert a radially outward force, sufficient to bias the tubular graft  215  of the endoluminal prosthesis  210  into conforming fixed engagement with the interior surface of aorta  20  above aneurysm  28 . The tubular graft  215  provides a leak resistant seal between the prosthesis and the inner wall of the aorta  20 . The proximal aortic portion  217  of the prosthesis  210  is located within aorta  20 , and the long ipsalateral iliac portion limb  218  is located within the right iliac vessel  21 . The short iliac portion  219  is located within the aorta  20 . The flow of blood after the main body portion  216  has been deployed is illustrated in FIG. 1.  
         [0046]    After deployment of the main body portion  216 , a contralateral iliac extension limb (not shown) may be located within left iliac vessel  23 , and near the graft junction  221  within the short iliac portion  219 . The contralateral iliac extension limb (not shown) may include a proximal support member biasing the extension into conforming fixed engagement with the interior surface of the short iliac portion  219 .  
         [0047]    To deploy the prosthesis  210 , the main body portion  216  of the prosthesis is loaded into a catheter (not shown). The main body is placed in a constrained position within a sheath or cover (not shown) of the catheter and maintains main body  216  in a compressed configuration as it is delivered to the aneurysm site. The main body portion  216  is delivered in a compressed state via catheter through a surgically accessed femoral artery, to the desired deployment site. The cover is retracted when the distal end of the catheter (not shown) is located at the deployment site, releasing the annular members  212  from the compressed position to expand into the deployed position illustrated in FIG. 1.  
         [0048]    Using a second catheter (not shown), the contralateral iliac extension limb (not shown) may be separately deployed through a surgically accessed femoral artery and into the short iliac portion  219  after placement of the main body portion  216 .  
         [0049]    FIGS.  2 A- 15  illustrate embodiments of the endoluminal prosthesis, delivery systems and methods according to the present invention. The arrows in these figures indicate the flow of blood when deployed in the corresponding configuration, within an aorta of a patient. Although an endoluminal prosthesis, delivery system and method according to the invention may be used in any bifurcated or branched body lumen that conducts body fluid, they are described herein with reference to a bifurcated device used in the treatment of an aortic aneurysm, in particular in the abdomen of a patient.  
         [0050]    FIGS.  2 A- 7  illustrate an embodiment of the invention in which a bifurcated prosthesis  50  includes a main aortic portion  52 , which splits into a long iliac portion  53  and a short iliac portion  54 . The main aortic portion  52  and the iliac portions  53 ,  54  define a conduit splitting into two conduits through which blood may flow to bypass an aortic aneurysm. The prosthesis  50  comprises a tubular graft  55  and a series of radially compressible annular support members (not shown but similar to support members  212  described above with reference to FIG. 1) attached to tubular graft  55 . The annular support members support the graft and/or bias the prosthesis  50  into conforming fixed engagement with an interior surface of an aorta  20 . The annular support members are preferably spring members having predetermined radii and are preferably constructed of a material such as Nitinol in a superelastic, shape set annealed condition. The tubular graft  55  is preferably formed of a biocompatible, low-porosity woven fabric, such as a woven polyester. The graft material is thin-walled so that it may be compressed into a small space, yet capable of acting as a strong, leak-resistant, fluid conduit when in tubular form. In this embodiment, the annular support members are sewn to the outside of the tubular graft  55  material by sutures. Alternative mechanisms of attachment may be used (such as embedding or winding within material, adhesives, staples or other mechanical connectors) and the annular support members may be attached to the inside of the tubular graft  55 .  
         [0051]    A valve  60  is located adjacent or within the conduit corresponding to the short iliac portion  54 . The valve  60  has an open position (FIGS.  4 A- 4 B,  5  and  7 ) and a closed position (FIGS. 2A, 2E,  2 F,  3  and  6 ). The valve  60  includes three support members  61 ,  62 ,  63  generally formed of attached diamond-like structures. The distal most support member  61  (FIG. 2D) comprises an annular member in which the diamond-like structures are attached in a ring. The support members  62  (FIG. 2C) and  63  (FIG. 2B) comprise cylindrical-wall-like partial rings or semicircular members. The valve  60  may be a separate insert that is held in position within the short iliac portion  54  by the radial force of the support member  61  which may be a spring member formed e.g., of Nitinol against the inside of the short iliac portion  54 . Alternatively or in addition, the valve  60  may be attached to the inner wall of the short iliac portion  54  by suturing or other attachment means.  
         [0052]    The support members  62 ,  63  may be flipped (elastically everted) from a first position forming a semicircle with an inner and outer circumference, to a second position in which the side forming the inner circumference in the first position becomes the outer circumference in the second position and the side forming the outer circumference in the first position becomes the inner circumference in the second position (the ends approximately maintaining their position to the inner wall of the short iliac leg). The support members  62 ,  63  are in the first and closed position in FIGS. 2A, 2E,  2 F,  3  and  6  and are in the second and open position in FIGS.  4 A- 4 B,  5  and  7 .  
         [0053]    The support members  61 ,  62 ,  63  are sewn onto a section of graft material  65 . The section of graft material  65  is configured to extend around the inner circumference of the annular support member  61  forming a tube around the annular support member  61 . The section of graft material  65  is shaped or cut so that it is generally semicircular in shape where it is sewn around the support members  62 ,  63  to match the shape of those members  62 ,  63 . The section of graft material  65  is located on the inner circumference of the support members  62 ,  63  when they are in the first, closed position, and, on the outer circumference of the support members  62 ,  63  when they are in the second, open position.  
         [0054]    When in the first and closed position as illustrated in FIGS. 2A, 2E,  2 F,  3 , and  6 , the support member  61  holds the section of graft material  65  in place around the circumference of the lumen in the short iliac portion  54  of the prosthesis  50  where it forms a lumen  66 . The support members  62  and  63  hold the section of graft material  65  in a position over the lumen  66  forming a cover  67  (FIG. 3) that prevents the flow of blood through the lumen  66  or the short iliac portion  54 . The proximal most support member  63  holds a portion  65   a  of a section of the graft material  65  against a first portion  55   a  of an inner circumference of the tubular graft  55 . (FIGS. 2E, 2F) The support member  62  located between support members  61  and  63  provides a transition for the section of the graft material  65  across the lumen  66  to provide the cover  67  (FIGS. 2E, 2F).  
         [0055]    The support members  62  and  63  are flipped (elastically everted) over into the second, open position as illustrated in FIGS.  4 A- 4 B,  5  and  7 . In this position, the graft material  65  surrounding the support members  62 ,  63  that in the first position formed the cover  67 , is held in position against the inner wall (i.e., a second portion  55   b  of an inner circumference of the tubular graft  55  opposite from the first portion  55   a  of the inner circumference) of the short iliac portion  54  of the prosthesis  50  so that it does not interfere with the flow of blood through the lumen  66 .  
         [0056]    In one embodiment the prosthesis  50  is deployed as follows. The valve  60  is initially in a closed position and the prosthesis  50  is loaded into a catheter  80 . The prosthesis  50  along with the valve  60  may be radially compressed within a delivery catheter  80 . The catheter  80  is located in position to deploy the prosthesis in the abdominal aorta of a patient with an aneurysm in the aorta (not shown) below the aortarenal junction (not shown). The prosthesis is deployed by retracting a sheath that is holding the prosthesis  50  in its radially compressed position.  
         [0057]    Surgical methods and apparatus for accessing the surgical site are generally known in the art and may be used to place the catheter within the vasculature and deliver the prosthesis to the deployment site. Additionally, various actuation mechanisms for retracting sheaths of catheters are known in the art. The prosthesis  50  may be delivered to the deployment site by one of several ways. A surgical cut down may be made to access a femoral iliac artery. The catheter  80  is then inserted into the artery and guided to the aneurysm site using fluoroscopic imaging where the prosthesis  50  is then deployed. The members  51  supporting the graft  55 , biased in a radially outward direction, are released to expand and engage the prosthesis  50  in the vessel against the vessel wall to provide an artificial lumen for the flow of blood. Another technique includes percutaneously accessing the blood vessel for catheter delivery, i.e., without a surgical cutdown. An example of such a technique is set forth in U.S. Pat. No. 5,713,917, incorporated herein by reference.  
         [0058]    When deployed, the prosthesis  50  is in position with the aortic portion  52  engaging the neck region just below the renal arteries  22 ,  24 . The long iliac portion  53  is located within the iliac vessel  21  while the short iliac portion  54  is within the aorta  20  just proximal of the iliac vessel  23  as illustrated in FIG. 2A, 3 and  6 .  
         [0059]    Referring to FIG. 7, a catheter  80  has been inserted through the iliac vessel  23  in a manner that is typically used to deploy an extension graft, and the extension member  68  has been deployed. In inserting the catheter  80 , the tip  81  of the catheter  80  is first inserted by guiding it between the inner wall of the short iliac portion  54  and the outer circumference of the support members  62 ,  63  in their closed position. The tip  81  of the catheter  80  is tapered so that as it is inserted, it flips the support members  62 ,  63  into the second position, opening the valve  60 . The support members  62 ,  63  demonstrate an over center spring action whereby they are stable in both the closed and open valve positions illustrated in FIGS.  2 A- 7 . Once the support members  62 ,  63  are moved over a center, they will move to the opposite position.  
         [0060]    Once the support member  62 ,  63  are moved from the closed valve position to the open valve position, the extension member  68  that is loaded in the catheter  80  is released from the catheter  80  in a position in which at least a portion of the extension member  68  is located within the lumen  66  in the open valve  60  and maintains the valve  60  in an open position with the radial force exerted by support members  69  on the extension member  68  (as shown in FIG. 7). The extension member  68  extends into the iliac artery and forms a lumen for the flow of blood therethrough. The support members are constructed of a Nitinol that is preset to maintain a closed configuration so in the absence of an opening force, the valve will close  
         [0061]    According to this embodiment, the valve  60  is initially in a closed position when the prosthesis  50  is deployed. Thus, flow of blood into the aneurysm through the short iliac portion or leg  54  is prevented until an extension member  68  is placed the second iliac artery  23  and into the short iliac portion  54 . The valve  60  thus will remain closed if the surgeon determines that it is not feasible or desirable to deploy an extension member through the iliac vessel  23 .  
         [0062]    FIGS.  8 - 11 B illustrate another embodiment according to the invention in which a bifurcated prosthesis  110  includes a main aortic portion  112 , which splits into a long iliac portion  113  and a short iliac portion  114 . The main aortic portion  112  and the iliac portions  113 ,  114  define a conduit splitting into two conduits through which blood may flow to bypass an aortic aneurysm. The prosthesis  110  comprises a tubular graft  115  and a series of radially compressible annular support members (not shown but similar to support members  212  described above with reference to FIG. 1) attached to tubular graft  115 . The annular members support the graft and/or bias the prosthesis  110  into conforming fixed engagement with an interior surface of an aorta (not shown). The annular support members are preferably spring members having predetermined radii and are preferably constructed of a material such as Nitinol in a superelastic, shape set annealed condition. The tubular graft  115  is preferably formed of a biocompatible, low-porosity woven fabric, such as a woven polyester. The graft material is thin-walled so that it may be compressed into a small diameter, yet capable of acting as a strong, leak-resistant, fluid conduit when in tubular form. In this embodiment, the annular support members are sewn on to the outside of the tubular graft  115  material by sutures. Alternative mechanisms of attachment may be used (such as embedding or winding within material, adhesives, staples or other mechanical connectors) and the annular support members may be attached to the inside of the tubular graft  115 .  
         [0063]    A valve  120  is located adjacent or within the conduit corresponding to the short iliac portion  114 . The valve  120  has an open position (FIGS. 10, 11A and  11 B) and a closed position (FIGS. 8 and 9A- 9 C). The valve  120  includes three support members  121 ,  122  and  123  comprising attached diamond-like structures formed into rings. The valve  120  may be held in position within the short iliac portion  114  by the radial force of the distal most support member  121  which may be a spring member formed e.g., of Nitinol. Alternatively or in addition, the valve  120  may be attached in part to the inner wall of the short iliac portion  114 , for example, by suturing or other mechanical means.  
         [0064]    The support members  121 ,  122 ,  123  are sewn onto section of a graft material  125 . The graft material  125  extends around the inner circumference of the annular support members  121 ,  122 ,  123  forming at tube around the inner circumference of the annular support members  121 ,  122 ,  123 .  
         [0065]    The support members  122 ,  123  may be flipped (elastically everted) from a first position in which the support members are folded into semicircular configurations (wherein each ring forming a support member ( 122 , or  123 ) are folded into two folded halves), to a second position in which the support members  122 ,  123  are opened into ring configurations. The support members  122 ,  123  are in the first and closed position in FIGS. 8 and 9A- 9 C and are in the second and open position in FIGS. 10, 11A and  11 B.  
         [0066]    When in the first and closed position as illustrated in FIGS.  8 , and  9 A- 9 C, the support member  121  holds the section of the graft material  125  in place around the circumference of the lumen in the short iliac portion  114  of the prosthesis  110  where it forms a lumen  126 . The support members  122  and  123  are folded so that the outer side of a portion  125   b  of the section of the graft material  125  is held in a position over the lumen  126 , thus forming a cover  127  that prevents the flow of blood through the lumen  126  or the short iliac portion  114 . The proximal most support member  123  holds a portion  125   a  of a section of the graft material  125  against an inner circumference of a portion of the valve  120  that is held against a first portion  115  a of the inner circumference of the short iliac portion  114  of the tubular graft  115  (FIGS. 9B, 9C). The support member  122  located between support members  121  and  123  provides a transition for the section of the graft material  125  across the lumen  126  to provide the cover  127  (FIGS. 9B, 9C).  
         [0067]    The support members  122  and  123  are flipped over into the second, open position as illustrated in FIGS. 10, 11A and  11 B. In this position, the portion  125   a  of the section of the graft material  125  surrounding the support members  122 ,  123  that in the first position formed the cover  127 , is in tubular configuration, in which the section of the graft material  125  is held against the inner wall of the short iliac portion  114  of the prosthesis  110  so that it does not interfere with the flow of blood through the lumen  126 . The prosthesis  120  in the open position, as illustrated in FIG. 11B, extends partially proximally of the inner wall of the graft junction  121  within the short iliac portion  119  that divides the short iliac portion  119  from the long iliac portion  118 .  
         [0068]    The prosthesis  110  is deployed in a manner similar to the prosthesis  50  described above with reference to FIGS.  2 A- 7 . The valve  120  is initially in a closed position and the prosthesis  110  is loaded into a catheter (not shown). The prosthesis  110  along with the valve  120  may be radially compressed within a delivery catheter and is positioned and deployed in the abdominal aorta of a patient. According to this embodiment, the valve  120  is initially in a closed position when the prosthesis  110  is deployed. Thus, flow of blood into the aneurysm through the short iliac portion or leg  114  is prevented until an extension member (not shown) is placed through the second iliac artery (not shown) and into the short iliac portion  114 . The valve  120  thus will remain closed if the surgeon determines that it is not feasible or desirable to deploy an extension member through the iliac vessel.  
         [0069]    An extension graft (not shown) is deployed in a manner similar to the deployment of the extension member  68  described above with reference to FIG. 7. Accordingly, the tip of a catheter into onto which the prosthesis  110  is loaded (not shown) is guided between the folded portions  122   a ,  122   b  of the support member  122  in its closed configuration, and the folded portions  123   a ,  123   b  of the support member  123  in its closed configuration. The tip of the catheter is tapered so that as it is inserted, it opens the support members  122 ,  123  into the second positions, opening the valve  120 . The extension member that is loaded in the catheter is then released from the catheter in a position in which at least a portion of the extension member is located within the lumen  126  in the open valve  120  and maintains the valve  120  in an open position with the radial force exerted by the extension member. The extension member extends into the iliac artery and forms a lumen for the flow of blood therethrough. The support members  122 ,  123  are constructed of a similar material as support members  61 ,  62 , and  63 , described above with reference to FIGS.  2 A- 7 .  
         [0070]    FIGS.  12 - 15  illustrate an embodiment of the invention in which a bifurcated prosthesis  150  includes a main aortic portion  152 , which splits into a long iliac portion  153  and a short iliac portion  154 . The main aortic portion  152  and the iliac portions  153 ,  154  define a conduit splitting into two conduits or lumens through which blood may flow to bypass an aortic aneurysm including lumen  156  through the short iliac portion  154 . The prosthesis  150  comprises a tubular graft  155  and a series of radially compressible annular support members (not shown, but similar to support members  212  described herein with reference to FIG. 1) attached to tubular graft  155 . The annular members  151  support the graft and/or bias the prosthesis  150  into conforming fixed engagement with an interior surface of an aorta. The annular support members are preferably spring members having predetermined radii and are preferably constructed of a material such as Nitinol in a superelastic, shape set annealed condition. The tubular graft  155  is preferably formed of a biocompatible, low-porosity woven fabric, such as a woven polyester. The graft material is thin-walled so that it may be compressed into a small diameter, yet capable of acting as a strong, leak-resistant, fluid conduit when in tubular form. In this embodiment, the annular support members are sewn on to the outside of the tubular graft  155  material by sutures. Alternative mechanisms of attachment may be used (such as embedding or winding within material, adhesives, staples or other mechanical connectors) and the annular support members may be attached to the inside of the tubular graft  155 .  
         [0071]    A valve  160  is located adjacent or within the lumen  156  of the short iliac portion  154 . The valve  160  has an open position (FIGS. 14 and 15) and a closed position (FIGS. 12 and 13). The valve  160  comprises a support member  161  sewn onto a section of graft material  165  shaped in the form of a pocket. The support member  161  comprises attached diamond-like structures formed into a semicircular member and is sewn onto the top edge of the pocket-shaped section of graft material  165 . The support member  161  is constructed of a similar material as support members  61 ,  62 , and  63 , described above with reference to FIGS.  2 A- 7 . The support member  161  has a first position corresponding to the first and closed position of the valve in which the support member is in sealing engagement with a portion of the inner circumference of the tubular graft  155  of the prosthesis  150 . The support member  161  has a second position corresponding to the second and open position of the valve  160  where the support member  161  is in sealing engagement with a second portion of an inner circumference of the tubular graft  155 , the second portion being on a opposite side of the tubular graft from the first portion. A portion of the section of graft material  165  is secured, e.g., sewn, onto the inner wall of the short iliac portion  154  that forms the lumen  156 , i.e. to the second portion of the inner circumference of the tubular graft  155 , so that the portion of the section of graft material provides a leak resistant seal with the inner wall of the tubular graft  155 . The graft material  165 , when the valve  160  is in the first and closed position as illustrated in FIGS.  12 , and  13 , forms a cover  167  over the lumen  156  in the short iliac portion  154  of the prosthesis  150  that prevents the flow of blood through the lumen  156 . The graft material  165  extends around the inner circumference of the annular support members  161  so that graft material  165  and the support structure  161  when in the closed position, form a leak resistant seal with the inner wall of the short iliac portion  154 . In addition to attaching the graft  165  to the inner wall of the short iliac portion  154 , the valve  160  is held in position within the short iliac portion  154  by the radial force of the support member  161  which may be a spring member formed e.g., of Nitinol. The support member  161  holds the valve  160  in the first and closed position in FIGS. 12 and 13 and in the second and open position in FIGS. 14 and 15.  
         [0072]    The support member  161  may be flipped from a first position in which the valve  160  is closed, to a second position in which the valve  160  is open. In the first position, the support member forms a semicircle with an inner and outer circumference. When it is in its second position, the side forming the inner circumference in the first position becomes the outer circumference in the second position and the side forming the outer circumference in the first position becomes the inner circumference in the second position. When the support member  161  is flipped over into the second, open position as illustrated in FIGS. 14 and 15 the graft material  165  surrounding the support member  161  that in the first position formed the cover  167 , and the graft material  165  that is attached to the inner wall of the short iliac portion  154 , is held by the support member  161  against the inner wall of the short iliac portion  154  of the prosthesis  150  so that it does not interfere with the flow of blood through the lumen  156 . The graft material  165  is located on the inner circumference of the support member  161  when it is in the first, closed position, and, on the outer circumference of the support member  161  when it is in the second, open position.  
         [0073]    The prosthesis  150  is deployed in a manner similar to the prosthesis  50  described above with reference to FIGS.  2 A- 7 . The valve  160  is initially in a closed position and the prosthesis  150  is loaded into a catheter (not shown). The prosthesis  150  along with the valve  160  may be radially compressed within a delivery catheter and is positioned and deployed in the abdominal aorta of a patient. Thus, flow of blood into the aneurysm through the short iliac portion or leg  154  is prevented until an extension member (not shown) is placed through the second iliac artery (not shown) and into the short iliac portion  154 . The valve  160  thus will remain closed if the surgeon determines that it is not feasible or desirable to deploy an extension member through the iliac artery.  
         [0074]    An extension graft (not shown) is deployed in a manner similar to the deployment of the extension member  68  described above with reference to FIG. 7. Accordingly, the tip of a catheter into onto which the prosthesis  150  is loaded (not shown) is guided between the inner wall of the short iliac portion  154  and the outer circumference of the support member  161  in its closed position. The tip of the catheter is tapered so that as it is inserted, it flips the support member  161  into the second position whereby the support member  161  holds the graft material  165  in a position against the inner wall of the short iliac portion so that the valve  160  is open and the graft material  165  does not obstruct the flow of blood through the short iliac portion  154 . The extension member that is loaded in the catheter is then released from the catheter in a position in which at least a portion of the extension member is located adjacent the support member  161  and maintains the valve  160  in an open position with the radial force exerted by the extension member. The extension member extends into the iliac artery and forms a lumen for the flow of blood therethrough.  
         [0075]    While the invention has been described with reference to particular embodiments, it will be understood to one skilled in the art that variations and modifications may be made in form and detail without departing from the spirit and scope of the invention.