Abstract:
Endovascular prostheses are disclosed that are configured to repair a native venous valve having improper or non-existent valve leaflet coaptation caused by vessel weakness and/or distention. The prostheses are configured to be implanted in the venous system immediately downstream of the malfunctioning valve and act as repair devices to restore proper function to the venous valve by reconfiguring and supporting the valve leaflets and thereby improving their coaptation.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to endovascular prostheses for treatment of chronic venous insufficiency and more particularly to venous valve repair prostheses for restoring apposition to valve leaflets of a malfunctioning venous valve. 
       BACKGROUND OF THE INVENTION 
       [0002]    Venous valves are self-closing, one-way valves found within native veins and are used to assist in returning blood back to the heart in an antegrade blood flow direction from all parts of the body. The venous system of the leg for example includes the deep venous system and the superficial venous system, both of which are provided with venous valves that are intended to prevent retrograde flow, which can lead to blood pooling or stasis in the leg. Incompetent valves can also lead to reflux of blood from the deep venous system to the superficial venous system and the formation of varicose veins. Superficial veins which include the greater and lesser saphenous veins have perforating branches in the femoral and popliteal regions of the leg that direct blood flow toward the deep venous system and generally have a venous valve located near the junction with the deep venous system. Deep veins of the leg include the anterior and posterior tibial veins, popliteal veins, and femoral veins. Deep veins are surrounded in part by muscular tissues that assist in generating flow by muscle contraction during normal walking or exercising. 
         [0003]    Blood pressure in the veins of the lower leg of a healthy person may range from 0 mm Hg to over 200 mm Hg, depending on factors such as the activity of the body (i.e., stationary or exercising), the position of the body (i.e., supine or standing), and the location of the vein (i.e., ankle or thigh). For example, venous pressure may be approximately 80-90 mm Hg while standing and may be reduced to 60-70 mm Hg during exercise. Despite exposure to such pressures, the valves of the leg are very flexible and can close with a pressure differential of less than one mm Hg. 
         [0004]    Veins typically in the leg can become distended from prolonged exposure to excessive blood pressure and due to weaknesses found in the vessel wall. Distension of veins can cause the natural valves therein to become incompetent leading to retrograde blood flow in the veins. Such veins no longer function to help pump or direct the blood back to the heart during normal walking or use of the leg muscles. As a result, blood tends to pool in the lower leg and can lead to leg swelling and the formation of deep venous thrombosis and phlebitis. The formation of thrombus in the veins can further impair venous valvular function by causing valvular adherence to the venous wall with possible irreversible loss of venous function. Continued exposure of the venous system to blood pooling and swelling of the surrounding tissue can lead to post phlebitic syndrome with a propensity for open sores, infection, and may lead to limb amputation. 
         [0005]    Chronic venous insufficiency (CVI) occurs in patients that have deep and superficial venous valves of their lower extremities (distal to their pelvis) that have failed or become incompetent due to the aforementioned vessel weakness as well as, for e.g., valve prolapse, congenital valvular abnormalities, such as missing valves, and/or vascular disease that results in valve damage. As a result, such patients may suffer from varicose veins, swelling and pain of the lower extremities, edema, hyper pigmentation, lipodermatosclerosis, and/or deep vein thrombosis (DVT). Such patients are at increased risk for development of soft tissue necrosis, ulcerations, pulmonary embolism, stroke, heart attack, and amputations. 
         [0006]    Repair and replacement of venous valves presents a formidable challenge due to the low blood flow rate found in native veins, the very thin and distensible wall structure of the venous wall and the venous valve, and the ease and frequency with which venous blood flow can be impeded or totally blocked for a period of time. Surgical reconstruction techniques used to address venous valve incompetence include venous valve bypass using a segment of vein with a competent valve, venous transposition to bypass venous blood flow through a neighboring competent valve, and valvuloplasty to repair the valve cusps. These surgical approaches may involve placement of synthetic, allograft and/or xenograft prostheses inside of or around the vein. However, such prostheses have not been devoid of problems, such as thrombus formation and valve failure due to the implanted prostheses causing non-physiologic flow conditions and/or excessive dilation of the vessels with a subsequent decrease in blood flow rates. 
         [0007]    Percutaneous endoluminal methods for treatment of venous insufficiency are being studied, some of which include placement of synthetic, allograft and/or xenograft valve prosthesis that suffer from similar problems as the surgically implanted ones discussed above. In light thereof, there is still a need in the art for an improved device that may be percutaneously placed within a vein having an existing insufficient, malfunctioning venous valve to re-establish apposition between the valve leaflets to thereby restore proper flow through the vein segment. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Embodiments hereof are directed to an implant or prosthesis configured to repair a venous valve that has improper or non-existent valve leaflet coaptation caused by vessel weakness and/or distention. The implant is configured to be implanted in the venous system immediately downstream, i.e., closer to the heart in the direction of blood flow, of the malfunctioning valve and acts as a repair device to restore proper function to the venous valve by reconfiguring and supporting the valve leaflets to thereby improve their coaptation. 
         [0009]    In an embodiment, the prosthesis has a tubular body that defines a blood flow lumen along a longitudinal axis of the prosthesis, wherein the tubular body includes an anchor portion for securing a longitudinal position of the prosthesis within the vessel, and a plurality of valve apposition portions longitudinally separated from the anchor portion by respective connector portions. The valve apposition portions are disposed toward each other relative to the longitudinal axis of the prosthesis from respective connector portions and are spaced apart a distance for receiving the native valve leaflets therebetween. 
         [0010]    In an embodiment, a wire of a superelastic or resilient material is formed into a first helix from a distal end to a proximal end of the prosthesis and a second overlaying helix from the proximal end to the distal end of the prosthesis to define the tubular body of the prosthesis. Free ends of the wire at a distal end of the prosthesis define respective valve apposition portions with distal lengths of the first and second helix forming respective connector portions of the prosthesis and proximal lengths of the first and second helix forming an anchor portion of the prosthesis. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    The foregoing and other features and advantages of the invention will be apparent from the following description of embodiments thereof as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
           [0012]      FIGS. 1A-1B  are schematic representations of open and closed configurations of a healthy valve within a vein. 
           [0013]      FIG. 2  is a schematic representation of retrograde blood flow through an incompetent or malfunctioning valve within a vein. 
           [0014]      FIG. 3  is a side view of a venous valve repair prosthesis in accordance with an embodiment hereof. 
           [0015]      FIG. 3A  is an end view of the prosthesis of  FIG. 3  taken in the direction of line A-A thereof. 
           [0016]      FIG. 3B  is a modified side view of the prosthesis of  FIG. 3  depicting first and second helix of a wire wrapped to form the prosthesis. 
           [0017]      FIG. 4  depicts a sectional view of the prosthesis of  FIG. 3  implanted within a vein to repair a malfunctioning valve within a vein. 
           [0018]      FIG. 5  is a side view of a delivery system in accordance with an embodiment hereof. 
           [0019]      FIG. 5A  is a sectional view of the delivery system of  FIG. 5  taken along line A-A thereof. 
           [0020]      FIG. 6  is a side view of a catheter component of the delivery system shown in  FIG. 5  in accordance with an embodiment hereof. 
           [0021]      FIG. 6A  is a cross-sectional view of the catheter component of  FIG. 6  taken along line A-A thereof. 
           [0022]      FIG. 7  is a side view of a sheath component of the delivery system shown in  FIG. 5  in accordance with an embodiment hereof. 
           [0023]      FIG. 8  is a side view of a delivery system in accordance with another embodiment hereof. 
           [0024]      FIG. 9  is a side view of a venous valve repair prosthesis in accordance with another embodiment hereof. 
           [0025]      FIG. 10  is a side view of a venous valve repair prosthesis in accordance with another embodiment hereof. 
           [0026]      FIG. 11  is a side view of a venous valve repair prosthesis in accordance with another embodiment hereof. 
           [0027]      FIG. 12  is a perspective view of a venous valve repair prosthesis in accordance with another embodiment hereof. 
           [0028]      FIG. 13  is a side view of the prosthesis of  FIG. 12 . 
           [0029]      FIG. 13A  is an end view of the prosthesis of  FIG. 13  taken in the direction of line A-A thereof. 
           [0030]      FIG. 14  is a perspective view of a venous valve repair prosthesis in accordance with another embodiment hereof. 
           [0031]      FIG. 15  is a side view of the prosthesis of  FIG. 14 . 
           [0032]      FIG. 15A  is an end view of the prosthesis of  FIG. 15  taken in the direction of line A-A thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Specific embodiments of the present invention are described below with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician. In addition, the term “self-expanding” is used in the following description with reference to the prostheses hereof and is intended to convey that the structures are shaped or formed from a material that can be provided with a mechanical memory to return the structure from a compressed or constricted delivery configuration to an expanded deployed configuration. Non-exhaustive exemplary materials that are suitable for forming self-expanding prosthesis in accordance with embodiments hereof include stainless steel, a pseudo-elastic metal such as a nickel titanium alloy or nitinol, or a so-called super alloy, which may have a base metal of nickel, cobalt, chromium, or other metal. Mechanical memory may be imparted to a wire or other structure by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy, such as nitinol. Various polymers that can be made to have shape memory characteristics may also be suitable for use in embodiments hereof to include polymers such as polynorborene, trans-polyisoprene, styrene-butadiene, and polyurethane. As well poly L-D lactic copolymer, oligo caprolactone copolymer and poly cyclo-octine can be used separately or in conjunction with other shape memory polymers. 
         [0034]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of embodiments hereof are in the context of treatment of blood vessels such as the superficial leg veins, the invention may also be used in any other body vessels and passageways where it is deemed useful. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
         [0035]      FIGS. 1A-1B  are schematic representations of the function of a healthy native valve N V  within a vein V. Valves within the venous system are configured in a variety of shapes that depend on anatomical location, vessel size, and function. For example, the typical shape of the venous valve in man includes two flaps, a.k.a. cusps or leaflets having free edges that sealingly meet, when closed, to form a commissure. Venous valves are typically associated with a broadened area of the vein forming a sinus pocket behind each leaflet. The natural venous valve leaflet configuration referenced herein is for clarity of function and is not limiting in the application of the referenced embodiments. Venous valve N V  controls blood flow through the lumen defined by vein V via leaflets L. More particularly, venous valve N V  opens to allow antegrade blood flow A BF  through leaflets L and toward the heart as shown in  FIG. 1A . Venous valve N V  closes to prevent backflow or retrograde blood flow R BF  through leaflets L as shown in  FIG. 1B . 
         [0036]      FIG. 2  is a schematic representation of retrograde blood flow through an incompetent venous valve due to vessel weakness. Backflow or retrograde blood flow R BF  leaks through venous valve N V  creating blood build-up that eventually may destroy the venous valve and cause a venous wall bulge V WB . More specifically, the wall of vein V may expand into a pouch or bulge, such that the vessel has a knotted external appearance when the pouch is filled with blood. The distended vessel wall area may occur on the outflow or downstream side of the valve above leaflets L as shown in  FIG. 2 , and/or on the inflow or upstream side of the valve below leaflets L. After a venous valve segment becomes incompetent, the vessel wall dilates and fluid velocity therethrough decreases, which may lead to flow stasis and thrombus formation in the proximity of the venous valve. 
         [0037]      FIG. 3  is a side view of a venous valve repair prosthesis  100  in a deployed or expanded configuration in accordance with an embodiment hereof with  FIG. 3A  being an end view of prosthesis  100  taken in the direction of line A-A of  FIG. 3  and with  FIG. 3B  being a modified side view of prosthesis  100  that depicts first and second helix  103 ,  105  of a wire  101  wrapped to form prosthesis  100 . In accordance with embodiments hereof, wire  101  may be a single wire or ribbon of a material noted above, or one or more joined wires or ribbons of the same or different materials noted above without departing from the scope hereof. Prosthesis  100  is a self-expanding endovascular prosthesis that is deformable or compressible into a reduced diameter delivery configuration (as shown in  FIG. 5A ) to be percutaneously deliverable to a treatment site within the vasculature via a delivery catheter, wherein prosthesis  100  returns to an expanded or deployed configuration as shown in  FIG. 3  upon release from the delivery catheter during implantation. In an embodiment, self-expanding prosthesis  100  is formed from wire  101  of a shape memory material, such as nitinol or one of the other materials noted above, that has been wrapped around a suitable mandrel and heat treated to define a tubular body  102  having a blood flow lumen  104  extending along a longitudinal axis L A  thereof. Generally as depicted in  FIG. 3B , wire  101  is wrapped in a first direction such that a first helix  103  (shown as a dashed line) is formed to extend from a first or distal end  106  of prosthesis  100  to a second or proximal end  108  of prosthesis  100  and is then wrapped back over itself in a second direction opposite of the first direction such that a second helix  105  (shown as a solid line) is formed to extend from the second or proximal end  108  of prosthesis  100  to the first or distal end  106  of prosthesis  100  to thereby define tubular body  102 . As such, respective windings of the second helix  105  are wound on top of the windings of the first helix  103  and the first and second helix  103 ,  105  may be considered to be wound in opposite directions, such that one helix is right-handed and the other is left-handed. With wire  101  wrapped or wound to form tubular body  102  as noted above, first and second ends  107 ,  109  of wire  101 , which are also referred to herein as the free ends  107 ,  109  of wire  101 , are each disposed at distal end  106  of prosthesis  100  and are each shaped into a closed loop to define a pair of first and second valve apposition portions  110 ,  112  of prosthesis  100 , as discussed in detail below. 
         [0038]    Tubular body  102  of wire  101  is formed to include an anchor portion  114 , a pair of first and second connector portions  116 ,  118  and the pair of first and second valve apposition portions  110 ,  112 , wherein the pair of valve apposition portions  110 ,  112  are longitudinally displaced from anchor portion  114  by respective connector portions  116 ,  118 . Anchor portion  114  is configured to secure a longitudinal position of prosthesis  100  within a healthy portion of the vein downstream of the native valve to be repaired, with connector portions  116 ,  118  configured to extend through the weakened area of the vessel to position the valve apposition portions  110 ,  112  at the valve leaflets, as discussed in more detail below. First or distal lengths L 1  of first and second helix  103 ,  105  form respective connector portions  116 ,  118  and second or proximal lengths L 2  of overlaying first and second helix  103 ,  105  form anchor portion  114 , wherein a first pitch P 1  between respective windings of the first and second helix  103 ,  105  that form respective connector portions  116 ,  118  is greater than a second pitch P 2  between respective windings of the overlaying first and second helix  103 ,  105  that form anchor portion  114 . In the configuration shown in  FIG. 3 , anchor portion  114  with windings that are closer together than the windings in the connector portions  116 ,  118  is less flexible and provides firm support of the prosthesis within the vessel, with connector portions  116 ,  118  providing a more flexible attachment for first and second valve apposition portions  110 ,  112 . In another embodiment, the density or pitch between, and/or angle of consecutive windings may be varied along the length L 2  of anchor portion  114  to provide additional longitudinal flexibility thereto. In another embodiment for certain applications, an inverse relationship of the pitch or distance between windings of the anchor portion versus the pitch or distance between windings of the connector portions may be desired, i.e., with the anchor portion having a greater pitch between windings than the pitch between windings of the connector portions, such that the anchor portion is made more flexible than the connector portions. 
         [0039]    Valve apposition portions  110 ,  112  extend toward each other from their respective connector portions  116 ,  118  to be substantially transverse or at a right angle with respect to longitudinal axis L A  of prosthesis  100 , as depicted by transverse axis T A  in  FIGS. 3 and 3B . Valve apposition portions  110 ,  112  are aligned with each other along transverse axis T A  such that respective valve contacting segments  120 ,  122  thereof are spaced apart a suitable distance D for receiving leaflets of a native valve therebetween when prosthesis  100  is implanted. In the embodiment of  FIGS. 3 ,  3 A and  3 B, valve apposition portions  110 ,  112  define substantially parallel valve contacting segments  120 ,  122  that are configured for supporting the native valve leaflets therebetween. By substantially parallel it is meant that the valve contacting segments  120 ,  122  extend along the same transverse plane or parallel transverse planes of the prosthesis or one or the other may deviate therefrom by plus or minus 5 degrees. In embodiments hereof, distance D between valve contacting segments  120 ,  122  of valve apposition portions  110 ,  112  is within the range of less than 1 mm to 24 mm to be suitable for use in repairing venous valves of the superficial and deep leg veins, such as for placement within the common femoral vein. In another embodiment, distance D may be sized to be equal to substantially one third of a diameter of the vessel in which it is to be implanted. 
         [0040]      FIGS. 9-11  are side views of venous valve repair prosthesis  900 ,  1000 ,  1100 , respectively, in a deployed or expanded configuration that illustrate variations of connector portions and valve apposition portions in accordance with various embodiments hereof. With reference to  FIG. 9 , prosthesis  900  includes an anchor portion  914 , first and second connector portions  916 ,  918  and first and second valve apposition portions  910 ,  912 . Valve apposition portions  910 ,  912  are angled outward or distally of a transverse axis T A  at distal end  906  of the prosthesis to be at other than a right angle with respect to longitudinal axis L A  of prosthesis  900  and are longitudinally displaced from anchor portion  914  by respective connector portions  916 ,  918 , each of has a swag or curved shape. With reference to  FIG. 10 , prosthesis  1000  includes an anchor portion  1014 , first and second connector portions  1016 ,  1018  and first and second valve apposition portions  1010 ,  1012 . Valve apposition portions  1010 ,  1012  extend toward each other from distal end  1006  of the prosthesis to be at right angles with respect to longitudinal axis L A  of prosthesis  1000  and are longitudinally displaced from anchor portion  1014  by respective connector portions  1016 ,  1018 , each of which has a sinusoidal or wave-like shape. With reference to  FIG. 11 , prosthesis  1100  includes an anchor portion  1114 , first and second connector portions  1116 ,  1118  and first and second valve apposition portions  1110 ,  1112 . Valve apposition portions  1110 ,  1112  are angled inward or proximally of a transverse axis T A  at distal end  1106  of the prosthesis to be at other than a right angle with respect to longitudinal axis L A  of prosthesis  1100  and are longitudinally displaced from anchor portion  1114  by respective connector portions  1116 ,  1118 , each of which is substantially straight with a swag or inwardly curved section therein. The connector portions of prosthesis  900 ,  1000 ,  1100  are configured to be radially apposed to a wall of the vessel in the same orientation as the respective anchor portions thereof. With reference to the various angles at which valve apposition portions of prosthesis  900 ,  1000 ,  1100  may be disposed relative the longitudinal axis of the prosthesis, each orientation permits a different level of support to be provided to the valve leaflets, with the outwardly extending valve apposition portions  910 ,  912  of prosthesis  900  considered to provide the least support to the valve leaflets and valve apposition portions  1110 ,  1112  of prosthesis  1100  considered to provide the most support to the valve leaflets. 
         [0041]    In accordance with embodiments hereof, prosthesis  900 ,  1000 ,  1100  may be formed from a single wire or one or more joined wires of a material noted above with overlaying helices as described above with reference to the embodiment of  FIG. 3 , or interlaying helices with windings of one helix alternately crossing over and then under windings of the other helix. In accordance with other embodiments hereof, prosthesis  900 ,  1000 ,  1100  may be formed from a plurality of wires of a material noted above having the windings aligned such that parallel right-handed or left-handed helices are formed, as described below with reference to the embodiment of  FIGS. 12 ,  13  and  13 A. 
         [0042]      FIG. 12  is a perspective and  FIG. 13  is a side view of a venous valve repair prosthesis  1200  in a deployed or expanded configuration in accordance with another embodiment hereof, with  FIG. 13A  depicting an end view of the prosthesis taken in the direction of line A-A of  FIG. 13 . Prosthesis  1200  includes an anchor portion  1214 , first and second connector portions  1216 ,  1218  and first and second valve apposition portions  1210 ,  1212 . Anchor portion  1214  is configured to secure a longitudinal position of prosthesis  1200  within a healthy portion of the vein downstream of the native valve to be repaired and may include a greater or lesser portion of prosthesis  1200  than is shown in  FIG. 13 , with connector portions  1216 ,  1218  being the remainder of prosthesis  1200  that are configured to extend through the weakened area of the vessel to position the valve apposition portions  1210 ,  1212  at the valve leaflets, as discussed in more detail below with reference to the embodiment of  FIG. 3 . Valve apposition portions  1210 ,  1212  extend toward each other from distal end  1206  of the prosthesis  1200  to be at right angles with respect to longitudinal axis L A  of prosthesis  1200  but in alternate embodiments may be angled outward or inward as previously discussed above with reference to the embodiment of  FIGS. 9 and 11  for certain applications. 
         [0043]    In the embodiment of  FIGS. 12 ,  13  and  13 A, prosthesis  1200  is formed by winding at least two wires of a material noted above in parallel such that the windings of the subsequently formed helices are aligned with each other and therefore both run in the same direction. As shown in  FIGS. 12 and 13 , the dual helix that form prosthesis  1200  run in a counterclockwise direction as viewed from a proximal end  1208  of the prosthesis such that each helix is a left-handed helix. It would be understood by one of skill in the art that the dual helix of prosthesis  1200  may run in a clockwise direction such that each helix is a right-handed helix without departing from the scope hereof. The dual windings that form anchor portion  1214  have the same pitch or distance between consecutive windings as the respective windings that form connector portions  1216 ,  1218 . In contrast to the embodiments of FIGS.  3  and  9 - 11 , aligned or parallel windings as shown in anchor portion  1214  may provide more longitudinal flexibility to that portion of prosthesis  1200  than the overlapping or interlaid windings of anchor portions  314 ,  914 ,  1014 ,  1114  as shown and described above, which may be considered as providing relatively more radial rigidity to that portion of prosthesis  100 ,  900 ,  1000 ,  1100 , respectively. In another embodiment, the pitch between the dual windings of the anchor portion of prosthesis  1200  and the pitch between the respective windings that form the connector portions may be varied, i.e., greater or lesser with respect to each other, depending on whether more or less flexibility or radial strength is desired in one or both of those regions of the prosthesis. 
         [0044]      FIG. 14  is a perspective and  FIG. 15  is a side view of a venous valve repair prosthesis  1400  in a deployed or expanded configuration in accordance with another embodiment hereof, with  FIG. 15A  depicting an end view of the prosthesis taken in the direction of line A-A of  FIG. 15 . Prosthesis  1400  includes an anchor portion  1414 , a connector portion  1416  and first and second valve apposition portions  1410 ,  1412 . Anchor portion  1414  is configured to secure a longitudinal position of prosthesis  1400  within a healthy portion of the vein downstream of the native valve to be repaired and may include a greater or lesser portion of prosthesis  1400  than is shown in  FIG. 15 , with connector portion  1416  being the remainder of prosthesis  1400  that is configured to extend through the weakened area of the vessel to position the valve apposition portions  1410 ,  1412  at the valve leaflets, as discussed in more detail below with reference to the embodiment of  FIG. 3 . Valve apposition portions  1410 ,  1412  extend toward each other from distal end  1406  of the prosthesis  1400  to be at right angles with respect to longitudinal axis L A  of prosthesis  1400  but in alternate embodiments may be angled outward or inward as previously discussed above with reference to the embodiment of  FIGS. 9 and 11  for certain applications. 
         [0045]    In the embodiment of  FIGS. 14 ,  15  and  15 A, prosthesis  1400  is formed in an expanded or deployed configuration by laser cutting a tube of a shape memory material into the pattern shown in the figures and heat setting the cut tube, as would be known to one of ordinary skill in the art. Accordingly, prosthesis  1400  would act differently as it returns to the expanded configuration from a compressed delivery configuration from the wire-formed prosthesis described above due to the solid nature of the “connections” of prosthesis  1400 , as relative movement that is permitted between the overlaying or interlaying wires of the prior embodiments is eliminated. Valve apposition portions  1410 ,  1412  may be integral portions of the cut tube that are bent into the position shown in the figures prior to shape setting the cut tube, or may be separately formed components that are subsequently joined thereto by any suitable method known in the art. In embodiments hereof, a suitable shape memory material for such a tube includes but is not limited to nitinol. In an embodiment, a density or pitch P 1  of the cut pattern in connector portion  1416  may be increased relative to a density or pitch P 2  of the cut pattern in anchor portion  1414  to provide additional longitudinal flexibility to connector portion  1416 . 
         [0046]      FIG. 4  depicts a sectional view of prosthesis  100  of  FIG. 3  implanted within a vein V to repair venous valve Nv, which had previously separated valve leaflets L 1  (as depicted by dashed lines in  FIG. 4 ) due to venous wall bulge V WB . Prosthesis  100  is shown repairing or restoring apposition between valve leaflets L of venous valve Nv by supporting valve leaflets L between valve apposition portions  110 ,  112 . With apposition of valve leaflets L restored by prosthesis  100 , retrograde blood flow R BF  is prevented from leaking or back flowing through venous valve N V . Anchor portion  114  is configured to secure a longitudinal position of prosthesis  100  within vein V and has an expanded or deployed diameter that is larger than the diameter of a healthy portion of vein V downstream of venous valve N V  in the direction of antegrade blood flow A BF . Due to the high dispensability of some veins, in accordance with embodiments hereof, the expanded or deployed diameter of the anchor portion may be made significantly larger than the diameter of a healthy portion of the vein V in which it is to be deployed to maintain fixation. 
         [0047]    In an embodiment, spikes or other anchoring structure (not shown) may be used along anchor portion  114  to aid in securing the longitudinal position of prosthesis  100 . The respective windings of connector portions  116 ,  118  have an expanded or deployed diameter that is substantially equal to the expanded or deployed diameter of the windings of anchor portion  114  so as to prevent interference with the function of the venous valve Nv, and particularly the valve leaflets L that are surrounded thereby. By substantially equal deployed diameters it is meant that each of the connector portions and the anchor portion are formed to have the same diameter or to have diameters that differ no more than 10%. In an embodiment, a length of prosthesis  100  is twice the diameter of the vessel in which it is implanted in order to assure self-centering and proper hold of the prosthesis within the patient&#39;s vein. 
         [0048]    Prosthesis  100  may be delivered through the vasculature to a target site of a malfunctioning venous valve in a minimally invasive endovascular/endoluminal approach. The endovascular approach generally involves opening a vein with a needle, inserting a guidewire into the vein through the lumen of the needle, withdrawing the needle, inserting over the guidewire a dilator located inside an associated sheath introducer having a hemostasis valve, removing the dilator and inserting a delivery catheter through the hemostasis valve and sheath introducer into the blood vessel. The delivery catheter with prosthesis  100  secured therein may then be tracked through the vasculature to the target site. Alternatively, the delivery catheter with prosthesis  100  may be routed through the vasculature over a guidewire without use of an associated sheath introducer. For example, a delivery catheter loaded with prosthesis  100  can be percutaneously introduced into the vasculature, for e.g., into a greater saphenous vein, and prosthesis  100  may then be delivered endovascularly to the treatment site where it is then deployed. 
         [0049]    In embodiments hereof one of endovascular prosthesis delivery system  530  shown in  FIGS. 5-7  and endovascular prosthesis delivery system  830  shown in  FIG. 8  may be used to deliver and deploy prosthesis  100  at the treatment site for repair of a malfunctioning venous valve. With reference to  FIGS. 5-7 , delivery system  530  includes a catheter component  532  and a sheath component  540 . Catheter component  532  includes an elongate catheter inner shaft  534  defining a guidewire lumen  533  therethrough that has an atraumatic tapered tip  536  attached to a distal end thereof and a hub  538  for accepting a guidewire attached at a proximal end thereof. Catheter component  532  also includes a handle  542  attached to the proximal end of catheter shaft  534  that has a stepped outer diameter such that handle  542  includes a smaller diameter distal section  541  for receipt within a proximal portion of sheath component  540 , as described below, and a larger diameter proximal section  543  for manipulation by the clinician. A stopper  548  is attached to an outer surface of catheter shaft  534  to radially extend therefrom and is disposed proximal of distal tip  536  at a position to permit loading of anchor portion  114  of prosthesis  100  on a proximal side of stopper  548  while first and second valve apposition portions  110 ,  112  of prosthesis  100  are loaded on a distal side of stopper  548 , as described in more detail below. In an embodiment, stopper  548  has an oval shape to extend in opposite radial directions from catheter shaft  534  as shown in  FIG. 6A , which permits connector portions  116 ,  118  of prosthesis  100  to freely extend on either side thereof between anchor portion  114  and a respective first and second valve apposition portion  110 ,  112  when prosthesis  100  is loaded as noted above. 
         [0050]    Sheath component  540  includes an elongate tubular sheath  544  defining a delivery lumen  545  therethrough that has a tapered tip  550  at a distal end thereof and a sheath handle  552  attached to a proximal end thereof for manipulation by a clinician. In an embodiment, sheath handle  552  includes a hemostasis valve (not shown) that serves as one-way valve to prevent blood loss from between catheter shaft  534  and tubular sheath  544 . As shown in  FIG. 5A , delivery lumen  545  of tubular sheath  544  is sized to have a sliding relationship with stopper  548  and thus is sized to receive catheter shaft  534  therein so as to hold prosthesis  100  in the delivery configuration described above. Stopper  548  functions to restrict longitudinal movement of prosthesis  100  relative to catheter shaft  534  when sheath  544  is proximally retracted during deployment of prosthesis  100 , as described below. In addition, stopper  548  permits staged deployment of prosthesis  100  by allowing first and second valve apposition portions  110 ,  112  of prosthesis  100  to be released to return to their expanded configuration while anchor portion  114  of prosthesis  100  remains compressed within delivery system  530 , to thereby facilitate during deployment the adjustment of a position of first and second valve apposition portions  110 ,  112  with respect to the valve leaflets of the malfunctioning venous valve. 
         [0051]    In an embodiment, tapered tip  550  includes a marker band  551  there around to permit visualization of a position of the distal opening of tubular sheath  544  and stopper  548  includes a marker band  549  there around to permit visualization of a position of tapered tip  550  in relation to stopper  548  during deployment. In an alternate embodiment instead of stopper  548  including marker band  549 , a print marker (not shown) may be made on catheter shaft  534  that represents how far tubular sheath  544  may be retracted in order to only release first and second valve apposition portions  110 ,  112  of prosthesis  100  therefrom. 
         [0052]    When tubular sheath  544  is fully advanced over catheter shaft  534  as shown in  FIG. 5 , the tapered distal tip  536  of catheter component  532  mates with the tapered tip  550  of tubular sheath  544  to create a smooth transition for tracking delivery system  530  to the treatment site within the vasculature. In addition, smaller diameter distal section  541  of catheter handle  542  is sized to be received within delivery lumen  545  of tubular sheath  544  to permit catheter component  532  and sheath component  540  to be secured together by a clamping device  546  during introduction and tracking of delivery system  530  to the treatment site within the vasculature. Clamping device  546  is configured to temporarily lock the catheter and tubular sheath components of the delivery system together to prevent relative longitudinal movement therebetween. 
         [0053]    In an embodiment, prosthesis  100  is loaded within a distal section of delivery system  100  by first threading prosthesis  100  over distal tip  536  of catheter component  532  so that the prosthesis partly sits distal of and partly sits proximal of stopper  548 , as described above and shown in  FIG. 5A . Prosthesis  100  is then compressed toward catheter shaft  534  into a reduced diameter delivery configuration and tubular sheath  544  is distally advanced there over until tapered tip  550  of sheath component  540  abuts with distal tip  536  of catheter component  532 . Thereafter catheter component  532  and sheath component are fixed to one and other by securing clamping device  546 . 
         [0054]    Prosthesis  100  is intended to be implanted downstream of a malfunctioning venous valve in order to exert pressure on the valve leaflets of the venous valve. In an embodiment hereof, delivery system  530  with prosthesis  100  loaded therein as described in the preceding paragraph is introduced into the vasculature above the Saphenous Junction according to standard percutaneous entry techniques to permit advancement of delivery system  530  through the vasculature to the affected venous valve in a retrograde venous approach. Initially a guidewire may be introduced to cross the treatment site such that delivery system  530  may be tracked over the guidewire and advanced to the treatment site. Once delivery system  530  is tracked to the treatment site, clamping device  546  is opened to permit movement between catheter component  532  and sheath component  540 . Sheath component  540  is then proximally retracted until tapered tip  550  is aligned with stopper  548 , such that first and second valve apposition portions  110 ,  112  of prosthesis  100  are released to return to their expanded configurations downstream of the malfunctioning venous valve. Clamping device  546  is then used to secure catheter component  532  and sheath component  540  together to fix the new position of tubular sheath  544  relative to catheter shaft  534 . Thereafter rotation and advancement of delivery system  530  permits first and second valve apposition portions  110 ,  112  of prosthesis  100  to be properly aligned with the valve leaflets so that delivery system  530  may then be distally advanced until the valve leaflets are positioned between and contacted by first and second valve apposition portions  110 ,  112 . In an embodiment, correct positioning of the first and second valve apposition portions  110 ,  112  would be verified with the use of fluoroscopy and/or ultrasound at this stage of the procedure. Clamping device  546  is opened again so that sheath component  540  may be proximally retracted a sufficient distance to permit anchor portion  114  to return to its expanded configuration and thereby fully release or deploy prosthesis  100  from the delivery system. Delivery system  530  is then removed from the vasculature. 
         [0055]    With reference to  FIG. 8 , delivery system  830  includes a catheter component  832 , a sheath component  840  and a tubular stopper component  860 . Catheter component  832  includes an elongate catheter shaft  834  defining a guidewire lumen  833  therethrough that has a tapered tip  836  attached to a distal end thereof and a hub  838  for accepting a guidewire attached at a proximal end thereof. A stopper  848  is attached to an outer surface of catheter shaft  834  to radially extend therefrom and is disposed proximal of distal tip  836  at a position to permit loading of anchor portion  114  of prosthesis  100  on a proximal side of stopper  848  while first and second valve apposition portions  110 ,  112  of prosthesis  100  are loaded on a distal side of stopper  848  to function as similarly described with reference to stopper  548  of delivery system  530 . 
         [0056]    Tubular stopper component  860  includes an elongate tubular stopper shaft  862  that defines a lumen  863  through which catheter component  832  extends. A handle  864  is attached to a proximal end of stopper shaft  862  for manipulation by a clinician. In an embodiment, handle  864  includes a hemostasis valve (not shown) that serves as a one-way valve to prevent blood loss between catheter shaft  834  and stopper shaft  862  and/or includes a locking mechanism (not shown) with which stopper component  860  may be fastened to catheter shaft  834  by screwing. 
         [0057]    Sheath component  840  includes an elongate tubular sheath  844  defining a delivery lumen  845  therethrough that has a tapered tip  850  at a distal end thereof and a sheath handle  852  attached to a proximal end thereof for manipulation by a clinician. In an embodiment, sheath handle  852  includes a hemostasis valve (not shown) that serves as a one-way valve which prevents blood loss between tubular sheath  844  and stopper shaft  862 . Tubular sheath  844  includes an internal ridge  866  that protrudes into delivery lumen  845  distal of stopper shaft  862 . Other than at ridge  866 , delivery lumen  845  is sized to have a sliding relationship with stopper  848  and stopper shaft  862 . 
         [0058]    As similarly described with reference to delivery system  530 , prosthesis  100  is held in a radially compressed delivery configuration within a distal section of delivery system  830  between tubular sheath  844  and catheter shaft  834  with stopper  848  being positioned between first and second valve apposition portions  110 ,  112  and anchor portion  114  as described above. Stopper  848  functions to restrict longitudinal movement of prosthesis  100  relative to catheter shaft  834  when sheath  844  is proximally retracted during deployment of prosthesis  100 , as described below. 
         [0059]    Stopper component  860  is slidable relative to each of catheter component  832  and sheath component  840 . Stopper component  860  is configured to be selectively fixed and positioned with respect to catheter component  832  via the locking mechanism of stopper handle  864  to permit proximal retraction of sheath  844  until ridge  866  of sheath  844  contacts a distal end  865  of stopper shaft  862 . For example, in  FIG. 8  delivery system  830  is shown secured by clamping device  846  in a first delivery configuration that permits the staged release of prosthesis  100 . In the first delivery configuration, stopper component  860  is fixed to catheter component  832  such that distal end  865  of stopper shaft  862  is proximally spaced from ridge  866  a distance D 1 , which is the same distance D 1  between distal tip  850  of tubular sheath  844  and stopper  848 . Accordingly, after delivery system  830  has been introduced and tracked through the vasculature to a treatment site and clamping device  846  has been released, as similarly described with reference to delivery system  532 , tubular sheath  844  may be proximally retracted the distance D 1  until ridge  866  abuts distal end  865  of stopper shaft  862 , which corresponds to distal tip  850  of sheath  844  being retracted and positioned at or over stopper  848 . In such a partially deployed configuration, first and second valve apposition portions  110 ,  112  of prosthesis  100  are released to return to their expanded configurations. Clamping device  846  is then used to secure delivery system  830  in the new position, which may be considered a second delivery configuration with tubular sheath  844  retracted to stopper  848 . Thereafter, first and second valve apposition portions  110 ,  112  may be maneuvered to align with the venous valve leaflets, wherein once alignment is confirmed then delivery system  830  may be distally advanced until the valve leaflets are positioned between and contacted by first and second valve apposition portions  110 ,  112 . In order to deploy anchor portion  114  of prosthesis  100 , stopper handle  864  is unlocked from catheter shaft  834  so that stopper component  860  may be proximally withdrawn a sufficient distance, such as approximately 2 to 5 cm, to release anchor portion  114  from tubular sheath  844  so that anchor portion  114  returns to its expanded configuration. Delivery system  830  is then removed from the vasculature. 
         [0060]    In accordance with embodiments hereof, catheter shafts  532 ,  832 , tubular sheaths  544 ,  844  and stopper shaft  862  are generally thin-walled, flexible tubular structures of a polymeric material, such as polyether block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, or polyimide, and may be formed from one or more tubular components. Optionally, catheter shafts  532 ,  832 , tubular sheaths  544 ,  844  and stopper shaft  862  or some portion thereof may be formed as a composite having a reinforcement material incorporated within a polymeric body in order to enhance strength and/or flexibility. Suitable reinforcement layers include braiding, wire mesh layers, embedded axial wires, embedded helical or circumferential wires, and the like of a suitable biocompatible metal or metal alloy. In an embodiment, distal sections of tubular sheaths  544 ,  844  that cover and compress prosthesis  100  may be composite tubular structures of a polymeric material that is reinforced with a braided or webbed layer of a suitable biocompatible metal or metal alloy. In embodiments hereof, distal tips  536 ,  836  are soft atraumatic structures that may be formed from a suitable polymer, such as polyether block amide, polyurethane, or silicone elastomer. In embodiments hereof, hubs  538 ,  838  and handles  552 ,  852 ,  864  are molded polymeric structures of polycarbonate, acetal or polyamide or similar injection molded polymer that may include fittings, one-way valves and/or locking mechanisms as would be understood by one of ordinary skill in the art. Components may be joined using a number of techniques including heat bonding using hot air or lasers or adhesives, such as cyanoacrolate. 
         [0061]    While various embodiments have been described above, it should be understood that they have been presented only as illustrations and examples of the present invention, and not by way of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.