Patent Publication Number: US-8979924-B2

Title: Apparatus and methods for repairing the function of a diseased valve and method for making same

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/436,521, filed May 18, 2006 now U.S. Pat. No. 7,799,072, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/682,939, filed on May 20, 2005, the subject matter of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to an apparatus and methods for repairing the function of a diseased valve, such as a cardiac or venous valve, via an endovascular technique, and is further directed to methods for making the apparatus. 
     BACKGROUND OF THE INVENTION 
     It is known to implant prosthetic valves in various body passages to replace native valves that are diseased or otherwise defective in some manner. Blood pressure, as provided by heart activity via the arteries, is normally sufficient to maintain the flow of blood in one direction through the vasculature. The blood pressure in the veins is much lower than in the arteries and venous valves function to limit the backflow of blood through the veins. Numerous such venous valves are located throughout the venous system and are particularly important to maintaining directional blood flow in the lower extremities. 
     Venous valves can become incompetent and lead to chronic venous insufficiency. Various surgical techniques have been developed for treating incompetent venous valves including valvuloplasty, transplantation, and replacement with a prosthetic valve. These known surgical techniques include both open and percutaneous approaches. As with any prosthetic, compatibility issues for prosthetic venous valves are important, along with the need to avoid thrombosis and platelet deposition. 
     Another common type of prosthetic valve is a prosthetic cardiac valve. Prosthetic cardiac valves have been used to replace all four of the native cardiac valves. Cardiac valve replacement has traditionally been done though an invasive open surgical procedure, although endovascular (or percutaneous) approaches are being developed. 
     The four native cardiac valves (mitral, aortic, tricuspid, and pulmonary) serve to direct the flow of blood through the two sides of the heart in a forward direction. On the left (systemic) side of the heart, the mitral valve is located between the left atrium and the left ventricle, while the aortic valve is located between the left ventricle and the aorta. These two valves direct oxygenated blood coming from the lungs, through the left side of the heart, into the aorta for distribution to the body. On the right (pulmonary) side of the heart, the tricuspid valve is located between the right atrium and the right ventricle, while the pulmonary valve is located between the right ventricle and the pulmonary artery. These two valves direct de-oxygenated blood coming from the body, through the right side of the heart, into the pulmonary artery for distribution to the lungs, where it again becomes re-oxygenated to begin the circuit anew. 
     All four of these native cardiac valves are passive structures that do not themselves expend any energy and do not perform any active contractile function. The valves consist of moveable leaflets that open and close in response to differential pressures on either side of the valve. The mitral and tricuspid valves are referred to as atrioventricular valves because they are situated between an atrium and a ventricle on each side of the heart. The mitral valve has two leaflets and the tricuspid valve has three leaflets. The aortic and pulmonary valves are referred to as semilunar valves because of the unique appearance of their leaflets, which are often termed “cusps” and which are shaped somewhat like a half-moon. The aortic and pulmonary valves each have three cusps. 
     Cardiac valves can exhibit abnormal anatomy and function as a result of congenital or acquired valve disease. Congenital valve abnormalities may be so severe that emergency surgery is required within the first few hours of life, or they may be well-tolerated for many years only to develop a life-threatening problem in an elderly patient. Acquired valve disease may result from causes such as rheumatic fever, degenerative disorders of the valve tissue, bacterial or fungal infections, and trauma. 
     The two major problems that can develop with cardiac valves are stenosis, in which a valve does not open properly, and insufficiency (also called regurgitation), in which a valve does not close properly. Stenosis and insufficiency may occur concomitantly in the same valve or in different valves. Both of these abnormalities increase the workload and stress placed on the heart. The severity of this increased stress on the heart, and the heart&#39;s ability to adapt to it, determine whether the abnormal valve will have to be surgically repaired or replaced. 
     In addition to stenosis and insufficiency of cardiac valves, surgery may also be required for certain types of bacterial or fungal infections in which the valve may continue to function normally, but nevertheless harbors an overgrowth of bacteria on the leaflets of the valve that may flake off (or embolize) and lodge downstream in a vital artery. If this occurs on the valves of the left side (i.e., the systemic circulation side) of the heart, embolization results in sudden loss of the blood supply to the affected body organ and immediate malfunction of that organ. The organ most commonly affected by such embolization is the brain, in which case the patient suffers a stroke. Thus, surgical replacement of either the mitral or the aortic valve may be necessary for this problem even though neither stenosis nor insufficiency of either valve is present. 
     If a cardiac valve must be replaced, there are currently several options available, and the choice of a particular type of prosthesis (i.e., artificial valve) depends on factors such as the location of the valve, the age and other specifics of the patient, and the surgeon&#39;s experiences and preferences. Available prostheses include mechanical valves, tissue valves, and homograft valves. 
     Mechanical valves include caged all valves, bi-leaflet valves, and tilting disk valves. The main advantage of mechanical valves is their long-term durability. Their main disadvantage is that they require the patient to take systemic anticoagulation drugs for the rest of his or her life, because of the propensity of mechanical valves to cause blood clots to form on them. 
     Tissue valves are typically constructed either by sewing the leaflets of porcine aortic valves to a stent (to hold the leaflets in proper position), or by constructing valve leaflets from porcine or bovine pericardial tissue and sewing them to a stent. The stents may be rigid or slightly flexible and are typically covered with a fabric, such as the material sold under the trademark DACRON™, and then attached to a sewing ring for fixation to the patient&#39;s native valve annulus. The porcine or bovine tissue is chemically treated to alleviate any antigenicity (i.e., to reduce the risk that the patient&#39;s body will reject the foreign tissue). Tissue valves may be used to replace any of the heart&#39;s four valves. The main advantage of tissue valves is that they do not cause blood clots to form as readily as do the mechanical valves, and therefore, they do not necessarily require systemic anticoagulation. 
     Homograft valves are harvested from human cadavers. Homograft valves are most commonly implanted in the aortic position, but are also occasionally implanted in the pulmonary position. Homograft valves are specially prepared and frozen in liquid nitrogen, where they are stored for later use. The advantage of aortic homograft valves is that they appear to be as durable as mechanical valves, but do not promote blood clot formation and therefore do not require anticoagulation. The main disadvantage of these valves is that they are not available in sufficient numbers to satisfy the needs of patients who need new aortic or pulmonary valves. Homograft valves are also extremely expensive and can be more difficult to implant than either mechanical valves or tissue valves. 
     Cardiac valve replacement using any of the aforementioned prostheses has traditionally been done via an open surgical technique in which the thoracic cavity is opened. This exacting operation requires use of a heart-lung machine for external circulation of the blood as the heart is stopped and opened during the surgical intervention and the artificial cardiac valve is implanted under direct vision. This operation exposes the patient to many risks especially in the elderly population. Hence, an apparatus for repairing the function of a diseased cardiac or venous valve via an endovascular (or percutaneous) procedure, rather than an open surgical procedure, could offer tremendous benefits for these patients, many of whom have no options today. 
     SUMMARY OF THE INVENTION 
     The present invention includes an apparatus for repairing the function of a diseased valve. The apparatus comprises an annular first support member expandable to a first diameter. An annular second support member is spaced axially apart from the first support member and is expandable to a second diameter that is independent of the first diameter. A tubular graft section interconnects the first and second support members. The graft section defines an annulus having a third diameter that is independent of each of the first and second diameters. A prosthetic valve is secured within the annulus of the graft section. The bioprosthetic valve has at least two valve leaflets that are coaptable to permit the unidirectional flow of blood. 
     In accordance with one aspect of the invention, an expandable ring encircles the annulus of the graft section and supports the prosthetic valve secured within the annulus. 
     In accordance with another aspect of the invention, the apparatus further comprises at least one tubular conduit having first and second ends. The second end is received in a passage in the graft section and the first end is for positioning in a branch blood vessel. 
     In accordance with another aspect of the invention, a method for making an apparatus to repair the function of a diseased valve is provided. According to the inventive method an annular first support member expandable to a first diameter and an annular second support member expandable to a second diameter that is independent of the first diameter are provided. A tubular graft section is also provided. The graft section defines an annulus having a third diameter that is independent of each of the first and second diameters. The first and second support members are interconnected with the graft section such that the support members are spaced axially apart by the graft section. A bioprosthetic valve having at least two valve leaflets that are coaptable to permit the unidirectional flow of blood is secured within the annulus of the graft section. 
     In accordance with another aspect of the invention, a minimally invasive method for repairing the function of a diseased valve is provided. According to the inventive method, an apparatus including annular first and second support members that are spaced axially apart and are expandable to independent first and second diameters, respectively, is provided. The apparatus further includes a prosthetic valve and a tubular graft section interconnecting the first and second support members. The graft section defines an annulus having a third diameter that is independent of the first and second diameters. The prosthetic valve is secured within the annulus of the graft section. The apparatus is collapsed and loaded into a sheath for intravascular delivery. The apparatus is inserted into the vasculature and advanced to a location with the vasculature adjacent the diseased valve. The sheath is retracted and the first and second support members expand into engagement with the vasculature at the respective first and second diameters to form a seal between at least one of the first and second support members and the vasculature. The suspension of the prosthetic valve inside the graft section at the third diameter and within the vasculature adjacent the diseased valve assumes the function of the diseased valve. 
     In accordance with another aspect of the present invention, an apparatus for repairing the function of a diseased valve comprises an annular support member having inner and outer surfaces. The support member is expandable to a first diameter. A tubular first graft section for sealing against a vessel wall adjacent the diseased valve is connected to the outer surface of the support member. A tubular second graft section is secured to the inner surface of the support member. The second graft section defines an annulus having a second diameter that is smaller than and independent of the first diameter of the support member. A prosthetic valve is secured within the annulus of the second graft section. The bioprosthetic valve has at least two valve leaflets that are coaptable to permit the unidirectional flow of blood. 
     In accordance with another aspect of the present invention, a method for making an apparatus to repair the function of a diseased valve is provided. According to the inventive method, an annular support member expandable to a first diameter is provided. The support member has inner and outer surfaces. A tubular first graft section is connected to the outer surface of the support member for sealing against a vessel wall adjacent the diseased valve. A tubular second graft section is connected to the inner surface of the support member. The second graft section defines an annulus having a second diameter that is smaller than and independent of the first diameter. A bioprosthetic valve having at least two valve leaflets that are coaptable to permit the unidirectional flow of blood is secured within the annulus of the second graft section. 
     In accordance with another aspect of the present invention, a minimally invasive method for repairing the function of a diseased valve is provided. According to the inventive method, an apparatus including an annular support member having inner and outer surfaces and which is expandable to a first diameter is provided. The apparatus further includes a prosthetic valve and first and second tubular graft sections. The first graft section is connected to the outer surface and the second graft section is connected to the outer surface. The second graft section defines an annulus having a second diameter that is smaller than and independent of the first diameter. The prosthetic valve is secured within the annulus of the second graft section. The apparatus is collapsed and loaded into a sheath for intravascular delivery. The apparatus is inserted into the vasculature and advanced to a location with the vasculature adjacent the diseased valve. The sheath is retracted and the support member is expanded into engagement with the vasculature, forming a seal between the first graft section and the vasculature. The suspension of the prosthetic valve inside the second graft section at the second diameter and within the vasculature adjacent the diseased valve assumes the function of the diseased valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view of an apparatus for repairing the function of a diseased valve in accordance with the present invention; 
         FIG. 2  is a schematic side view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a schematic sectional view of the apparatus of  FIG. 1 ; 
         FIG. 4  is a sectional view taken along  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a aide view similar to  FIG. 2  illustrating an optional construction for the present invention; 
         FIG. 6  is a schematic sectional view of a portion of a heart illustrating one option for placement of the apparatus of  FIG. 1  to repair the function of a diseased tricuspid valve; 
         FIG. 7  is a view similar  FIG. 6  illustrating another option for placement of the apparatus of  FIG. 1  to repair the function of a diseased tricuspid valve; 
         FIG. 8  is a view similar to  FIGS. 6 and 7  illustrating yet another option for placement of the apparatus of  FIG. 1  to repair the function of a diseased tricuspid valve; 
         FIG. 9  is a view similar to  FIGS. 6-8  illustrating still another option for placement of the apparatus of  FIG. 1  to repair the function of a diseased tricuspid valve; 
         FIG. 10  is a schematic sectional view of apparatus for repairing the function of a diseased valve in accordance with a second embodiment of the present invention; 
         FIG. 11  is a schematic side view of the apparatus of  FIG. 10 ; 
         FIG. 12  is a sectional view taken along  12 - 12  in  FIG. 10 ; 
         FIG. 13  is a schematic sectional view of a portion of a heart illustrating one option for placement of the apparatus of  FIG. 10  to repair the function of a diseased aortic valve; 
         FIG. 14  is a schematic sectional view of an apparatus for repairing the function of a diseased valve in accordance with a third embodiment of the present invention; 
         FIG. 15  is a schematic sectional view of an apparatus for repairing the function of a diseased valve in accordance with a fourth embodiment of the present invention; 
         FIG. 16  is a schematic perspectives view of an apparatus for repairing the function of a diseased valve in accordance with a fifth embodiment of the present invention; 
         FIG. 17  is a schematic side view of the apparatus of  FIG. 16 ; 
         FIG. 18  is a schematic perspective view of an apparatus for repairing the function of a diseased valve in accordance with a sixth embodiment of the present invention; 
         FIG. 19  is a schematic side view of the apparatus of  FIG. 18 ; 
         FIG. 20  is a sectional view of an apparatus for repairing the function of a diseased valve in accordance with a seventh embodiment of the present invention; and 
         FIG. 21  is a sectional view of an apparatus for repairing the function of a diseased valve in accordance with an eighth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention is directed to an apparatus and methods for repairing the function of a diseased valve, such as a cardiac or venous valve, via an endovascular technique, and is further directed to methods for making the apparatus. As representative of the present invention,  FIGS. 1-4  illustrate a first embodiment of an apparatus  10  for repairing the function of a diseased cardiac valve, such as a tricuspid valve  12  shown schematically in  FIGS. 6-8 . It should be apparent, however, to those skilled in the art that the apparatus  10  disclosed herein can also be used to repair the function of other cardiac valves as well as venous valves. The apparatus  10  includes annular first and second support members  14  and  16 , a tubular graft section  18  interconnecting the support members, and a prosthetic valve  20  secured within the graft section. 
     The first support member  14  comprises a self-expanding or balloon expandable stent made from stainless steel, but could alternatively be made from any suitable medical grade plastic or metal, including shape memory metals such as Nitinol. The first support member  14  has oppositely disposed proximal and distal ends  22  and  24  connected by axially extending beams  26  having a known “M” or “Z” shape. 
     The axially extending beams  26  define generally cylindrical inner and outer surfaces (not numbered) for the first support member  14 . In the expanded condition shown in  FIGS. 1-4 , the outer surface of the first support member  14  has a first diameter D 1  ( FIG. 2 ) that has been selected to exceed the largest potential venous diameter for a given patient. 
     Both the proximal and distal ends  22  and  24  of the first support member  14  include a plurality of eyelets  28  spaced circumferentially about the ends. The first support member further includes a plurality of hooks (or barbs)  30  located on the outer surface of the beams  26 . The hooks  30  extend radially outward and at an angle to prevent migration of the support member  14  upon implantation. It should be understood that the location, quantity, configuration, and orientation of the hooks  30  may be altered depending on specific needs of the apparatus  10 . 
     The second support member  16  resembles the first support member  14  and comprises two conjoined self-expanding stents made from stainless steel, but which could alternatively be made from any suitable medical grade plastic or metal, including shape memory metals such as Nitinol. The two stents of the second support member  16  together define oppositely disposed proximal and distal ends  32  and  34  connected by axially extending beams  36  having a known “M” or “Z” shape. 
     The axially extending beams  36  define generally cylindrical inner and outer surfaces.(not numbered) for the second support member  16 . In the expanded condition shown in  FIGS. 1-4 , the outer surface of the second support member  16  has a second diameter D 2  that has been selected to exceed the largest potential venous diameter for a given patient. It should be noted that, when implanted, the second support member  16  is free to expand to the second diameter D 2  ( FIG. 2 ) independent of the expansion of the first support member  14  to the first diameter D 1 . 
     Both the proximal and distal ends  32  and  34  include a plurality of eyelets  38  spaced circumferentially about the ends. The second support member further includes a plurality of hooks (or barbs)  40  located on the outer surface of the beams  36 . The hooks  40  extend radially outward and at an angle to prevent migration of the support member upon implantation. It should be understood that the location, quantity, and configuration of the hooks  40  may be altered depending on the specific needs of the apparatus  10 . 
     It should also be understood that that the invention is not limited to the particular configuration of the illustrated first and second support members  14  and  16 , and that the first and second support members need not be similarly configured. Further, it is contemplated that the lengths of the first and second support members  14  and  16  will be varied based on the needs of a particular implantation. In addition, it should be noted that radiopaque markers may be attached at various locations on the first and second support members  14  and  16  to aid with placement of the apparatus  10  under fluoroscopy. 
     To enhance the biocompatibility of the apparatus  10 , it is contemplated that at least a portion of the first and second support members  14  and  16  may be coated with a therapeutic agent such as, for example, an anti-coagulant, an anti-thrombogenic agent, an anti-proliferative agent, an anti-inflammatory agent, an antibiotic, an angiogenesis agent, a statin, a growth factor, or stem cells. The therapeutic agent may be loaded into a compound or polymer that is coated onto the support members  14  and  16  for a time-delayed release into surrounding tissue. 
     The apparatus  10  further includes the tubular graft section  18  interconnecting the first and second support members  14  and  16 . As shown in the Figures, the first and second support members  14  and  16  may be interconnected only by the graft section  18 , with no other structures interconnecting the first and second support members, in some embodiments of the present invention. In other words, the graft section  18 , in those embodiments of the present invention, is the only structure of the apparatus which is directly connected to both the first and second support members  14  and  16 . The graft section  18  comprises a biocompatible material such as Dacron®, woven velour, polyurethane, PTFE, or heparin-coated fabric. Alternatively, the graft section  18  may be a biological material such as bovine or equine pericardium, a homograft, an autograft, or cell-seeded tissue. 
     The graft section  18  has an hourglass shape defined by first and second end portions  50  and  52  ( FIG. 2 ) and a neck portion  54  located between the ends. The neck portion  54  of the graft section  18  is formed by a converging portion  56 , which extends inward from the first end  50  to an annulus  58 , and a diverging portion  60 , which extends outward from the annulus toward the second end  52 . The annulus  58  of the graft section  18  defines a third diameter D 3  that is less than and independent of the first and second diameters D 1  and D 2  of the first and second support members  14  and  16 , respectively. As may be seen in  FIG. 1 , one or more axial seams  61  in the graft section  18  are used to create a smaller diameter at the annulus  58  than at either of the end portions  50  and  52 . 
     The first end portion  50  of the graft section  18  is secured about the outer surface of the distal end  24  of the first support member  14 . As shown in  FIGS. 1-4 , the first end portion  50  may be Sutured to the eyelets  28  at the distal end  24  of the first support member  14 . Alternatively, it is contemplated that first end portion  50  may be sutured to other structure at the distal end  24  of the first support member  14  depending on the configuration of the stent used. It is further contemplated that the first end portion  50  may be woven to the distal end  24  of the first support member  14  or otherwise attached in another suitable manner. 
     The second end portion  52  of the graft section  18  is secured to the inner surface of the proximal end  32  of the second support member  16 . As shown in  FIGS. 1-4 , the second end portion  52  may be sutured to the eyelets  38  at the proximal end  32  of the second support member  16 ; Alternatively, it is contemplated that the second end portion  52  may be woven to the proximal end  32  of the second support member  16  or otherwise attached in another suitable manner. 
     The second end portion  52  of the graft section  18  further includes a plurality of extension flaps  62  that extend, axially toward the distal end  34  of the second support member  16 . The extension flaps  62  are connected, such as by sutures, to the beams  36  of the second support member  16 . The number and circumferential orientation of the extension flaps  62  correspond to the number and orientation of leaflets in the prosthetic valve  20 . 
     The bioprosthetic valve  20  may be a homograft, an autograft, or made from a harvested biological material including, but not limited to, bovine pericardial tissue, equine pericardial tissue or porcine pericardial tissue. Alternatively, the bioprosthetic valve  20  may be made from a biocompatible synthetic material including, but not limited to, polyurethane or expanded PTFE. 
     The bioprosthetic valve  20  is secured, by sutures or other suitable means, within the annulus  58  of the neck portion  54  of the graft section  18  so that the valve is suspended inside the graft section at the third diameter D 3 . In the illustrated embodiments, the bioprosthetic valve  20  has three leaflets  64  that are coaptable to permit the unidirectional flow of blood. However, it should be understood that the prosthetic valve  20  could have less than three or more than three leaflets. Each of the leaflets  64  of the prosthetic valve  20  may be sutured to a respective one of the extension flaps  62  of the graft section  18  to create a minor amount of valve insufficiency in the apparatus  10  if so desired. 
       FIG. 5  illustrates an optional construction for the apparatus  10  in which an expandable ring  66  encircles the annulus  58  of the graft section  18  to support the prosthetic valve  20 . The ring  66  may comprise a single wire or a small stent. The ring  66  may be made from a shape memory metal, such as Nitinol, or any other suitable medical grade plastic or metal. As shown in  FIG. 5 , the sutures that are used to secure the prosthetic valve  20  in the annulus  58  of the graft section  18  may extend around the ring  66  to strengthen the attachment of the valve  20  to the annulus of the graft section. Further, the ring  66  can be used to positively establish the third diameter D 3  at the annulus  58  of the graft section  18 . 
     One application for the present invention is to repair the function of the diseased tricuspid valve  12  ( FIG. 6 ). To enable delivery and deployment of the apparatus  10 , the apparatus is radially collapsed and loaded into a sheath (not shown) over a catheter (not shown). After de-airing of the assembly, the apparatus  10  is delivered via a venotomy into the femoral vein and may be assisted with access through an internal jugular vein to establish through-and-through access. In the application of the apparatus  10  illustrated in  FIG. 6 , the apparatus is delivered to a desired location in the inferior vena cava (IVC) just below the right atrium (RA), but above the hepatic veins, under fluoroscopic and/or transesophageal echocardiographic guidance. 
     Once the apparatus  10  is advanced to the desired location, the sheath is retracted to allow the first and second support members  14  and  16  to expand radially outward into engagement with the IVC wall as shown in  FIG. 6 . It should be noted that a balloon (not shown) may be used to assist with the expansion or stabilization of one or both of the support members  14  and  16 . As the support members  14  and  16  expand into the IVC wall, the hooks  30  and  40  on the beams  26  and  36  of the support members embed into the vessel wall to secure the apparatus  10  from migration in the IVC or right atrium. 
     Significantly, in the implanted condition shown in  FIG. 6 , the second support member  16  expands to the second diameter D 2 , which is the diameter of the IVC at that specific vascular location, and is able to independently expand and contract with the IVC in accordance with fluctuations in venous pressure or capacitance. Furthermore, the first support member  14  expands to the first diameter D 1 , which is the diameter of the IVC at that specific vascular location, and is able to independently expand and contract with the IVC in accordance with fluctuations in venous pressure or capacitance. In addition, the first end  50  of the graft section  18  that encircles the distal end  24  of the first support member  14  seals against the wall of the IVC to prevent any blood leakage around the apparatus  10 . 
     Notwithstanding the flexibility of the diameters of the first and second support members  14  and  16 , the diameter of the prosthetic valve  20  is predetermined by the third diameter D 3  of the annulus  58  of the graft section  18  and is functionally independent of the diameters of the first and second support members. This functional independence of the diameter of the prosthetic valve  20  suspended within the graft section  18  helps to prevent antegrade and retrograde blood leaks around the prosthetic valve and ensures proper valvular function. Further, the extra-cardiac location of the apparatus  10  reduces potentially detrimental effects of cardiac contraction and provides an anatomically favorable region for fixation and sealing. Finally in the location shown in  FIG. 6 , the apparatus  10  eliminates systolic flow through the hepatic veins and IVC. 
       FIG. 7  illustrates placement of the apparatus  10  for repairing the function of the tricuspid valve in the superior vena cava (SVC). The apparatus  10  is delivered to a desired location in the SVC just above the right atrial junction, but below the azygos vein, under fluoroscopic and/or transesophageal echocardiographic guidance. The apparatus  10  is then deployed in the same basic manner as described above with regard to placement in the IVC. 
     In the implanted condition shown in  FIG. 7 , the second support member  16  expands to the second diameter D 2 , which is the diameter of the SVC at that specific vascular location, and is able to independently expand and contract with the SVC in accordance with fluctuations in venous pressure or capacitance. Furthermore, the first support member  14  expands to the first diameter D 1 , which is the diameter of the SVC at that specific vascular location, and is able to independently expand and contract with the SVC in, accordance with fluctuations in venous pressure or capacitance, In addition, the first end  50  of the graft section  18  that encircles the distal end  24  of the first support member  14  seals against the wall of the SVC to prevent any blood leakage around the apparatus  10 . 
     Notwithstanding the flexibility of the diameters of the first and second support members  14  and  16 , the diameter of the prosthetic valve  20  is predetermined by the third diameter D 3  of the annulus  58  of the graft section  18  and is functionally independent of the diameters of the first and second support members. This functional independence of the diameter of the prosthetic valve  20  suspended within the graft section  18  helps to prevent antegrade and retrograde blood leaks around the prosthetic valve and ensures proper valvular function. 
       FIG. 8  illustrates repairing the function of the tricuspid valve by placing a first apparatus  10  in the IVC and a second apparatus  10  in the SVC. The first apparatus  10  is placed in the IVC just below the right atrium but above the hepatic veins, and the second apparatus  10  is placed in the SVC just above the right atrial junction but below the azygos vein. Alternatively, it is contemplated that the apparatus may be formed by a single second support member  16  that spans from the SVC to the IVC. 
     Both the first apparatus  10  and the second apparatus  10  are deployed and function in the same basic manner as previously described. In the implanted condition shown in  FIG. 8 , the second support member  16  of the first apparatus  10  expands to the second diameter D 2 , which is the diameter of the IVC at that specific vascular location, and is able to independently expand and contract with the IVC in accordance with fluctuations in venous pressure or capacitance. Furthermore, the first support member  14  of the first apparatus  10  expands to the first diameter D 1 , which is the diameter of the IVC at that specific vascular location, and is able to independently expand and contract with the IVC in accordance with fluctuations in venous pressure or capacitance. In addition, the first end  50  of the graft section  18  of the first apparatus  10  that encircles the distal end  24  of the first support member  14  seals against the wall of the IVC to prevent any blood leakage around the apparatus. 
     Similarly, the second support member  16  of the second apparatus  10  expands to the second diameter D 2 , which is the diameter of the SVC at that specific vascular location, and is able to independently expand and contract with the SVC in accordance with fluctuations in venous pressure or capacitance. Furthermore, the first support member  14  of the second apparatus  10  expands to the first diameter D 1 , which is the diameter of the SVC at that specific vascular location, and is able to independently expand and contract with the SVC in accordance with fluctuations in venous pressure or capacitance. In addition, the first end  50  of the graft section  18  of the second apparatus  10  that encircles the distal end  24  of the first support member  14  seals against the wall of the SVC to prevent any blood leakage around the apparatus. 
     Notwithstanding the flexibility of the diameters of the first and second support members  14  and  16  of each apparatus  10 , the diameter D 3  of each of the prosthetic valves  20  is predetermined by the third diameter D 3  of the annulus  58  of the respective graft section  18  and is functionally independent of the diameters of the first and second support members. This functional independence of the diameter of each of the prosthetic valves  20  helps to prevent antegrade and retrograde blood leaks around the prosthetic valves and ensures proper valvular function. 
       FIG. 9  illustrates another option for repairing the function of the diseased tricuspid valve  12  using a modified version of the apparatus. In  FIG. 9 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “a”. The apparatus  10   a  includes lower and upper support sections  14   a,  a valve section  80  suspended between the support sections, and a graft enclosure  82 . 
     The lower support section  14   a  of the apparatus  10   a  is placed in the IVC just below the right atrium but above the hepatic veins, and the upper support section  14   a  is placed in the SVC just above the right atrial junction but below the azygos vein. The valve section  80  includes a support member  16   a  and the bioprosthetic valve,  20  secured therein. The valve section  80  is deployed in the right atrium at a location adjacent the tricuspid valve  12 . The graft enclosure  82  extends over the valve section  80  and the majority of the lower and upper support sections  14   a  to form a lining in the right atrium between the valve section, the IVC, and the SVC. 
     In the implanted condition shown in  FIG. 9 , the lower support section  14   a  expands to the diameter of the IVC and is able to independently expand and contract with the IVC in accordance with fluctuations in venous pressure or capacitance. In addition, the portion of the graft enclosure  82  that covers the lower support section  14   a  seals, against the wall of the IVC to prevent any blood leakage around the apparatus  10   a.  Similarly, the upper support section  14   a  expands to the diameter of the SVC and is able to independently expand and contract with the SVC in accordance with fluctuations in venous pressure or capacitance. The portion of the graft enclosure  82  that covers the upper support section  14   a  seals against the wall of the SVC to prevent any blood leakage around the apparatus  10   a.    
     Notwithstanding the flexibility of the diameters of the lower and upper support sections  14   a,  the diameter of the prosthetic valve  20  is predetermined by the third diameter D 3  of the annulus  58  of the valve section  80  and is functionally independent of the diameters of the support sections. 
     The apparatus  10  and  10   a  and associated methods described above help to protect the lower and/or upper body from elevated venous pressures caused by a diseased tricuspid valve. Problems such as ascites, liver dysfunction; edema and cardiac cirrhosis that are often associated with severe tricuspid valve regurgitation can be treated using the apparatus and methods according to the present invention. Further, the apparatus  10  and  10   a  and methods of the present invention provide a minimally invasive, endovascular approach to treat severe valvular disease, which is particularly important for high risk patients. 
       FIGS. 10-12  illustrate an apparatus for repairing the function of a diseased valve in accordance with a second embodiment of the present invention. In the second embodiment of  FIGS. 10-12 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “b”. 
     The graft section  18   b  of the apparatus  10   b  includes first and second passages  90  and  92  extending axially through the neck portion  54   b.  Each of the first and second passages  90  and  92  terminates at openings in the converging portion  56   b  and the diverging portion  60   b,  respectively. As shown in  FIG. 12 , the passages  90  and  92  are spaced circumferentially apart and may have an elliptical shape in cross-section. It should be understood that the spacing and quantity of passages  90  and  92  may be varied based on the specific application for the apparatus  10   b.  The apparatus  10   b  of  FIGS. 10-12  is configured for repairing the function of a diseased aortic or other type of valve (not shown). 
     The apparatus  10   b  further includes first and second tubular conduits  94  and  96  that are receivable in the first and second passages  90  and  92 , respectively. The first and second conduits  94  and  96  are made of a biocompatible material such as Dacron®, woven velour, polyurethane, PTFE, or heparin-coated fabric. Alternatively, the conduits  94  and  96  may be made from a biological material such as bovine or equine pericardium, a homograft, an autograft, or cell-seeded tissue. It should be understood that the quantity of conduits  94  and  96  may be varied based on the specific application for the apparatus  10   b.    
     Each of the first and second conduits  94  and  96  has oppositely disposed first and second ends  98  and  100 . The first end  98  of each of the conduits  94  and  96  may have a cylindrical configuration supported by a stent  102  for securing the first end in a branch vessel. The second end  100  of each of the conduits  94  and  96  may have an elliptical configuration for mating with the elliptical passages  90  and  92 . The second end  100  of the conduits  94  and  96  will be larger in diameter than the first end  98  so that the conduits taper in diameter from the second end to the first end. This taper assists in inserting the conduits  94  and  96  into the passages  90  and  96  and in ensuring a sealed connection between the conduits and the graft section  18   b.  As shown in  FIG. 11 , it is contemplated that the Nitinol ring  66 , previously described with regard to  FIG. 5 , could also be used in the embodiment of  FIGS. 10-12 . 
       FIG. 13  illustrates placement of the apparatus  10   b  in accordance with the second embodiment to repair the function of a diseased aortic valve. It should be noted that it may be desirable to excise the native aortic leaflets prior to implantation of the apparatus  10   b.  To enable delivery and deployment of the apparatus, the apparatus  10   b  is radially collapsed and loaded into a sheath (not shown) over a catheter (not shown). Carotid or subclavian access may be used to cannulate the aorta (AO) and each of the two coronary arteries (CA). 
     After de-airing of the assembly, the apparatus  10   b  is introduced into the aorta. Under fluoroscopic and/or transesophageal echocardiographic guidance, the apparatus  10   b  is advanced to the desired location above the annulus of the, native aortic valve. Wires placed within the coronary arteries may be loaded through guides (not Shown) in the conduits  94  and  96  to ensure proper orientation. The sheath is retracted to allow the first and second support members  14  and  16  to expand radially outward into engagement with the aortic wall as shown in  FIG. 13 . It should be noted that a balloon (not shown) may be used to assist with the expansion of one or both of the support members  14  and  16 . As the support members  14  and  16  expand into the vessel wall, the hooks  30  and  40  on the beams  26  and  36  of the support members embed into the vessel wall to secure the apparatus  10   b  from migration in the aorta. 
     The first and second conduits  94  and  96  are then inserted into the passages  90  and  92  in the graft section  18   b  and the first end  98  of each of the conduits is placed into the coronary arteries. The placement of the conduits  94  and  96  into the coronary arteries bridges the prosthetic valve  20  with the conduits and allows the arteries to be perfused during diastole, or systole (depending on the valve structure). 
     In the implanted condition shown in  FIG. 13 , the second support member  16  expands to the second diameter D 2 , which is the diameter of the ascending aortic, and is able to independently expand and contract with the aorta in accordance with fluctuations in venous pressure or capacitance. Furthermore, the first support member  14  expands to the first diameter D 1 , which is the diameter of the aortic root, and is able to independently expand and contract with the aorta in accordance with fluctuations in venous pressure or capacitance. In addition, the first end  50  of the graft section  18   b  that encircles the distal end  24  of the first support member  14  seals against the wall of the aorta to prevent any blood leakage around the apparatus  10   b.    
     Notwithstanding the flexibility of the diameters of the first and second support members  14  and  16 , the diameter of the prosthetic valve  20  is predetermined by the third diameter D 3  of the annulus  58  of the graft section  18   b  and is functionally independent of the diameters of the first and second support members. This functional independence of the diameter of the prosthetic valve  20  suspended within the graft section  18   b  helps to prevent antegrade and retrograde blood leaks around the prosthetic valve and ensures proper valvular function. 
       FIG. 14  illustrates an apparatus for repairing the function of a diseased valve in accordance with a third embodiment of the present invention. In the third embodiment of  FIG. 14 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “c”. 
     The primary difference between the apparatus  10   c  of  FIG. 14  and the apparatus of  FIGS. 1-4  is the use of a single support member  110  that is expandable to a first diameter D 1 . A first graft section  120  is secured to the inner surface of the support member  110 . The prosthetic valve  20  is suspended within the annulus  58  of the neck portion  54  of the graft section  120  at a second diameter D 2  that is smaller than and independent of the first diameter D 1  of the support member. A second graft section  122  extends from the first graft section  120  and wraps around a first end  112  of the support member  110 , although it should be understood that the first and second graft sections could be made of separate pieces of material. It is contemplated that the Nitinol ring  66 , previously described with regard to  FIG. 5 , could also be used in the embodiment of  FIG. 14 . 
     The apparatus  10   c  may be deployed in the same basic manner as described above with regard to the other embodiments to repair the function of a diseased tricuspid valve. Once implanted in either the SCV or the IVC, the support member  110  expands to the first diameter D 1 , which is the diameter of the vasculature at that specific location, and is able to independently expand and contract with the vasculature in accordance with fluctuations in venous pressure or capacitance. In addition, the second graft section  122  that encircles the first end  112  of the support member  110  seals against the wall of the vasculature to prevent any blood leakage around the apparatus  10   c.    
     Notwithstanding the flexibility of the first diameter D 1  of the support member  110 , the diameter of the prosthetic valve  20  is predetermined by the second diameter D 2  of the annulus  58  of the graft section  120  and is functionally independent of the diameter of the support member. This functional independence of the diameter of the prosthetic valve  20  suspended within the graft section  120  helps to prevent antegrade and retrograde blood leaks around the prosthetic valve and ensures proper valvular function. 
       FIG. 15  illustrates an apparatus for repairing the function of a diseased valve in, accordance with a fourth embodiment of the present invention. In the fourth embodiment of  FIG. 15 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “d”. The apparatus  10   d  of  FIG. 15  is similar to the apparatus of  FIG. 14 , but includes the first and second passages  90  and  92  and corresponding first and second tubular conduits  94  and  96  of  FIGS. 10-12  so that the apparatus can be used to repair the function of a diseased aortic valve. The first and second conduits  94  and  96  are inserted into the passages  90  and  92  in the graft section  120  following placement of the apparatus  10   d  above the native aortic valve, and the first end  98  of each of the conduits is placed into the coronary arteries. The placement of the conduits  94  and  96  into the coronary arteries allows the arteries to be perfused during diastole. 
     When implanted, the support member  110  expands to the first diameter D 1 , which is the diameter of the aorta at that specific location, and is able to independently expand and contract with the aorta in accordance with fluctuations in venous pressure or capacitance. In addition, the second graft section  122  that encircles the first end  112  of the support member  110  seals against the wall of the aorta to prevent any blood leakage around the apparatus. 
     Notwithstanding the flexibility of the first diameter D 1  of the support member  110 , the diameter of the prosthetic valve  20  is predetermined by the second diameter of the annulus  58  of the graft section  120  and is functionally independent of the diameter of the support member. This functional independence of the diameter of the prosthetic valve  20  suspended within the graft section  120  helps to prevent antegrade and retrograde blood leaks around the prosthetic valve and ensures proper valvular function. 
       FIGS. 16-17  illustrate an apparatus  10   e  for repairing the function of a diseased valve in accordance with a fifth embodiment of the present invention. In the fifth embodiment of  FIGS. 16-17 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “e”. Description of common elements and operation similar to those in the previously described embodiments will not be repeated with respect to the fifth embodiment. 
     The primary difference between the apparatus  10   e  of  FIGS. 16-17  and the apparatus  10  of  FIGS. 1-4  is that the second end portion  52  of the graft section  18  further includes a plurality of extension struts  62   e  that extend axially toward the distal end  34  of the second support member  16 , in lieu of the extension flaps  62  of the previously described apparatus  10 . The extension struts  62   e  are each connected, such as by sutures, to one of the leaflets  64  of the bioprosthetic valve  20  and may act to support the leaflets  64  in a desired manner. The number and circumferential orientation of the extension struts  62   e  should correspond to the number and orientation of leaflets  64  in the bioprosthetic valve  20 . It is contemplated that the Nitinol ring  66 , previously described with regard to  FIG. 5 , could also be used in the fifth embodiment of  FIGS. 16-17  to anchor the extension struts  62   e.  Conversely, the extension struts  62   e  could be directly anchored, via sutures or the like, to the second end portion  52  of the graft section  18 , as shown in  FIGS. 16-17 . 
       FIGS. 18-19  illustrate an apparatus for repairing the function of a diseased valve in accordance with a sixth embodiment of the present invention. In the sixth embodiment of  FIGS. 18-19 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “f”. Description of common elements and operation similar to those in the previously described embodiments will not be repeated with respect to the sixth embodiment. 
     The primary difference between the apparatus  10   f  of  FIGS. 18-19  and the apparatus  10   e  of  FIGS. 16-17  is that the plurality of extension struts  62   f,  extending axially toward the distal end  34  of the second support member  16 , are connected together at a distal end (not numbered) thereof by a strut ring  124 . The extension struts  62   f  are each connected, such as by sutures, to one of the leaflets  64  of the bioprosthetic valve  20  and to the strut ring  124 . The extension struts  62   f  may act to support the leaflets  64  in a desired manner in cooperation with the strut ring  124 . As in the aforementioned embodiments, the number and circumferential orientation of the extension struts  62   f  of the sixth embodiment should correspond to the number and orientation of leaflets  64  in the bioprosthetic valve  20 . 
       FIG. 20  illustrates an apparatus for repairing the function of a diseased valve in accordance with a seventh embodiment of the present invention. In the seventh embodiment of  FIG. 20 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “g”. Description of common elements and operation similar to those in the previously described embodiments will not be repeated with respect to the seventh embodiment. 
     The primary difference between the apparatus  10   g  of  FIG. 20  and the apparatus  10  of  FIGS. 1-4  is that the bioprosthetic valve  20   g  is secured, by sutures or other suitable means, in an off-center orientation within a cross-section of the graft section  18 , as shown in  FIG. 20 . One or more biasing sutures  126  is placed to draw the annulus  58   g  of the neck portion  54   g  of the graft section  18 , to which the bioprosthetic valve  20   g  is secured, toward a chosen side of the annular first or second support member  14  or  16 . This off-center placement of the bioprosthetic valve  20   g  with respect to the graft section  18 , as seen in cross-section, allows the apparatus  10   g  to have a desired directionality. The directionality, or radial orientation, of the off-center bioprosthetic valve  20   g  of the apparatus  10   g  according to the seventh embodiment may be readily selected by one of ordinary skill in the art for a particular application of the present invention. 
       FIG. 21  illustrates an apparatus for repairing the function of a diseased valve in accordance with an eighth embodiment of the present invention. In the eighth embodiment of  FIG. 21 , components of the apparatus that are similar, but not identical, to previously described components carry the suffix “h”. Description of common elements and operation similar to those in the previously described embodiments will not be repeated with respect to the eighth embodiment. 
     The primary difference between the apparatus  10   h  of  FIG. 21  and the apparatus  10   b  of  FIGS. 10-12  is that the bioprosthetic valve  20   h  is secured, by sutures or other suitable means, in an off-center orientation within a cross-section of the graft section  18 , as shown in  FIG. 21  and in a similar manner to the apparatus  10   g  of the seventh embodiment. One or more biasing sutures  126  is placed to draw the annulus  58   h  of the neck portion  54  of the graft section  18 , to which the bioprosthetic valve  20   h  is secured, toward a chosen side of the annular first or second support member  14  or  16 . This, off-center placement of the bioprosthetic valve  20   h  with respect to the graft section  18 , as seen in cross-section, allows the apparatus  10   h  to have a desired directionality. The directionality, or radial orientation, of the off-center bioprosthetic valve  20   h  of the apparatus  10   h  according to the eighth embodiment may be readily selected by one of ordinary skill in the art for a particular application of the present invention. For example, the directionality of the off-center bioprosthetic valve  20   h  may be chosen to bias the bioprosthetic valve  20   h  away from the first and second conduits  94  and  96 , as shown in  FIG. 21 , and thereby avoid crushing or other fluid obstruction of the first and second conduits. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. As mentioned previously, it should be understood by those skilled in the art that the apparatus and methods disclosed above could be adapted for repairing the function of a venous valve. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.