Abstract:
An endo luminal support structure includes strut members interconnected by swivel joints to form a series of linked scissor mechanisms. The structure can be remotely actuated to compress or expand its shape by adjusting the scissor joints within a range of motion. In particular, the support structure can be repositioned within the body lumen or retrieved from the lumen. The support structure can be employed to introduce and support a prosthetic valve within a body lumen.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/055,441, which is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/US2009/051324, filed Jul. 21, 2009, which designated the United States and which claims the benefit of U.S. Provisional Application No. 61/082,489, filed on Jul. 21, 2008, all of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Endoluminal stents can be implanted in a vessel or tract of a patient to help maintain an open lumen. The stents can also be used as a frame to support a prosthetic device or to deliver a therapeutic agent. Stents can be implanted by either an open operative procedure or a closed operative procedure. When an option exists, the less invasive closed procedure is generally preferred because the stent can be guided through a body lumen, such as the femoral artery, to its desired location. Closed procedures typically use one of two techniques. 
         [0003]    One closed procedure employs balloon catheterization where an expandable stent encloses an inflatable balloon. In this procedure, the stent is implanted by inflating the balloon, which causes the stent to expand. The actual positioning of the stent cannot be determined until after the balloon is deflated and, if there is a misplacement of the stent, the process cannot be reversed to reposition the stent. 
         [0004]    The other closed procedure employs a compressed stent enclosed by a removable sheath. In this procedure, a stent made from a shape memory alloy, such as Nitinol, is held in a compressed state by a sheath. The stent is implanted by withdrawing the sheath, causing the stent to expand to its nominal shape. Again, if there is a misplacement of the stent, the process cannot be reversed to reposition the stent. 
         [0005]    Positioning errors are particularly dangerous when the stent is used to support a cardiac valve. Serious complications and patient deaths have occurred due to malpositioning of the valve at the implant site in the body, using the available stent-mounted valves. Malpositioning of the valve has resulted in massive paravalvular leakage, device migration, and coronary artery obstruction. The majority of these complications were unavoidable, but detected at the time of the procedure. However, due to inability to reposition or retrieve the device, these problems were impossible to reverse or mitigate during the procedure. 
       SUMMARY 
       [0006]    An endoluminal support structure or stent in accordance with certain embodiments of the invention solves certain deficiencies found in the prior art. In particular, the support structure can be repositioned within the body lumen or retrieved from the lumen. 
         [0007]    A particular embodiment of the invention includes a support apparatus implantable within a biological lumen. The support apparatus can include a plurality of elongated strut members interlinked by a plurality of swivel joints, wherein the swivel joints can cooperate with the stent members to adjustably define a shaped structure between a compressed orientation and an expanded orientation. 
         [0008]    More particularly, the shaped structure can be one of a cylindrical, a conical, or an hourglass shape. A swivel joint can form a scissor mechanism with a first strut member and a second strut member. Furthermore, the strut members can be arranged as a series of linked scissor mechanisms. The apparatus can further include an actuation mechanism to urge the swivel joints within a range of motion. 
         [0009]    The apparatus can also include a prosthetic valve coupled to the shaped structure. 
         [0010]    Another particular embodiment of the invention can include as medical stem implantable within a biological lumen. The medical stent can include a plurality of elongated strut members, including a first strut member and a second strut member, and a swivel joint connecting the first strut member and the second strut member. 
         [0011]    In particular, the swivel joint can form a scissor mechanism with the first strut member and the second strut member. The swivel joint can bisect the first strut member and the second strut member. The swivel joint can interconnect a first end of the first strut member with a first end of the second strut member. 
         [0012]    The plurality of strut members can be arranged as a series of linked scissor mechanisms. The strut members can also be non-linear. The strut members can be arranged to form one of a cylindrical, a conical, or an hourglass shape. 
         [0013]    The stent can further include an adjustment mechanism to exerting a force to urge the strut members about the swivel joint within a range of motion. 
         [0014]    The stent can include a prosthetic valve coupled to the strut members. 
         [0015]    Specific embodiments of the invention can include prosthetic valves that are rotatable or conventional. 
         [0016]    A rotatable prosthetic valve can include a first structural member coupled to the strut members, a second structural member rotatable relative to the first structural member, and a plurality of pliable valve members connecting the first structural member with the second structural member such that rotation of the second structural member relative to the first structural member can urge the valve members between an open and a closed state. In particular, the rotation of the second structural member can be responsive to the natural flow of a biological fluid. 
         [0017]    A conventional prosthetic, valve can include, a plurality of pliable valve leaflets having commissures at the intersection of two strut members. The prosthetic valve can further include a skirt material coupled to the strut members. 
         [0018]    A particular advantage of a support structure in accordance with embodiments of the invention is that it enables a prosthetic valve to be readily retrieved and repositioned in the body. If following deployment, the valve is mal positioned or deemed dysfunctional, the support structure allows the valve to be readily repositioned and re-deployed at a new implant site, or removed from the body entirely. This feature of the device can prevent serious complications and save lives by enabling the repair of mal-positioned devices in the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
           [0020]      FIG. 1  is a perspective view of a particular endoluminal support structure. 
           [0021]      FIG. 2  is a perspective view of a four strut section of the stent of  FIG. 1 . 
           [0022]      FIG. 3  is a perspective view of a compressed support structure of  FIG. 1 . 
           [0023]      FIG. 4  is a perspective view of the support structure of  FIG. 1  in a fully expanded state. 
           [0024]      FIG. 5  is a perspective view of the support structure of  FIG. 2  having a particular actuator mechanism. 
           [0025]      FIG. 6  is a perspective view of the support structure of  FIG. 2  having another particular actuator mechanism. 
           [0026]      FIG. 7  is a perspective view of a particular support structure and control catheter assembly usable with the actuator mechanisms of  FIGS. 5 and 6 . 
           [0027]      FIG. 8  is a perspective view of a particular rotating prosthetic valve assembly. 
           [0028]      FIG. 9  is a perspective view of the valve assembly of  FIG. 8  while being closed. 
           [0029]      FIG. 10  is a perspective view of the valve assembly of  FIG. 8  one completely closed. 
           [0030]      FIG. 11  is a perspective view of the valve of  FIGS. 8-10  in combination with the support structure of  FIG. 1 . 
           [0031]      FIG. 12  is a perspective view of the valve of  FIG. 11  in the open position. 
           [0032]      FIG. 13  is a perspective view of a traditional tissue valve mounted to the support structure of  FIG. 1 . 
           [0033]      FIG. 14  is a perspective view of the valve structure of  FIG. 13  having a hill inner skirt. 
           [0034]      FIG. 15  is a perspective view of the valve structure of  FIG. 13  having a full outer skirt. 
           [0035]      FIG. 16  is a perspective view of the arrangement of strut members in a conical-shaped support structure configuration. 
           [0036]      FIG. 17  is a perspective view of all hourglass-shaped support structure configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    Particular embodiments of the invention include endoluminal support structures (stents) and prosthetic valves. 
         [0038]      FIG. 1  is a perspective view of a particular endoluminal support structure. As shown, the support structure  10  is a medical stent that includes a plurality of longitudinal strut members  11  interconnected by a plurality of swivel joints  15 . In particular, the swivel joints  15  allow the interconnected strut members  11  to rotate relative to each other. As shown, there are eighteen struts  11 . 
         [0039]    The strut members  11  are fabricated from a rigid or semi-rigid biocompatible material, such as plastics or other polymers and metal alloys, including stainless steel, tantalum, titanium, nickel-titanium (e.g. Nitinol), and cobalt-chromium (e.g. ELGILOY). The dimensions of each strut can be chosen in accordance with its desired use. In a particular embodiment, each strut member is made from stainless steel, which is 0.005-0.020 inch thick. More particularly, each strut is 0.010 inch thick 300 series stainless steel. While all struts  11  are shown as being of uniform thickness, the thickness of a strut can vary across a strut, such as a gradual increase or decrease in thickness along the length of a strut. Furthermore, individual struts can differ in thickness from other individual struts in the same support structure. 
         [0040]    As shown, each strut member  11  is bar shaped and has a front surface  11   f  and a back surface  11   b . The strut members can however be of different geometries. For example, instead of a uniform width, the struts can vary in width along its length. Furthermore, an individual strut can have a different width than another strut in the same support structure. Similarly, the strut lengths can vary from strut to strut within the same support structure. The particular dimensions can be chosen based on the implant site. 
         [0041]    Furthermore, the struts can be non-flat structures. In particular, the struts can include a curvature, such as in a concave or convex manner in relationship to the inner diameter of the stent structure. The struts can also be twisted. The non-flatness or flatness of the struts can be a property of the material from which they are constructed. For example, the struts can exhibit shape-memory or heat-responsive changes in shape to the struts during various states. Such states can be defined by the stent in the compressed or expanded configuration. 
         [0042]    Furthermore, the strut members  11  can have a smooth or rough surface texture. In particular, a pitted surface can provide tensile strength to the struts. In addition, roughness or pitting can provide additional friction to help secure the support structure at the implant site and encourage irregular encapsulation of the support structure  10  by tissue growth to further stabilize the support structure  10  at the implant site over time. 
         [0043]    In certain instances, the stent could be comprised of struts that are multiple members stacked upon one another. Within the same stent, some struts could include elongated members stacked upon one another in a multi-ply configuration, and other struts could be one-ply, composed of single-thickness members. Within a single strut, there can be areas of one-ply and multi-ply layering of the members. 
         [0044]    Each strut member  11  also includes a plurality of orifices  13  spaced along the length of the strut member  11 . On the front surface  11   f , the orifices are countersunk  17  to receive the head of a fastener. In a particular embodiment, there arc thirteen equally spaced orifices  13  along the length of each strut member  11 , but more or less orifices can be used. The orifices  13  are shown as being of uniform diameter and uniform spacing along the strut member  11 , but neither is required. 
         [0045]    The strut members  11  are arranged as a chain of four-bar linkages. The strut members  11  are interconnected by swivelable pivot fasteners  25 , such as rivets, extending through aligned orifices  13 . It should be understood that other swivelable fasteners  25  can be employed such as screws, bolts, ball-in-socket structures, nails, or eyelets, and that the fasteners can be integrally formed in the struts  11  such as a peened semi-sphere interacting with an indentation or orifice, or a male-female coupling. In addition to receiving a fastener, the orifices  13  also provide an additional pathway for tissue growth-over to stabilize and encapsulate the support structure  10  over time. 
         [0046]      FIG. 2  is a perspective view of a four strut section of the stent of  FIG. 1 . As shown, two outer strut members  11 - 1 ,  11 - 3  overlap two inner strut members  11 - 2 ,  11 - 4 , with their back surfaces in communication with each other. 
         [0047]    In particular, the first strut member  11 - 1  is swivelably connected to the second strut member  11 - 1  by a middle swivel joint  15 - 1  using a rivet  25 - 1 , which utilizes orifices  13  that bisect the strut members  11 - 1 ,  11 - 2 . Similarly, the third strut member  11 - 3  is swivelably connected to bisect the fourth strut member  11 - 4  by a middle swivel joint  15 - 7  using a rivet  25 - 7 . It should be understood that the middle swivel joints  15 - 1 ,  15 - 7  function as a scissor joint in a scissor linkage or mechanism. As shown, the resulting scissor arms are of equal length. It should also be understood that the middle joint  15 - 1 ,  15 - 7  need not bisect the joined strut members, but can instead utilize orifices  13  offset from the longitudinal centers of the strut members resulting in unequal scissor arm lengths. 
         [0048]    In addition to the middle scissor joint  15 - 1 , the first strut member  11 - 1  is swivelably connected to the third strut member  11 - 3  by a distal anchor swivel joint  15 - 5 , located near the distal ends of the strut members  11 - 1 ,  11 - 3 . Similarly, the first strut member  11 - 1  is swivelably connected to the fourth strut member  11 - 4  by a proximal anchor swivel joint  15 - 3 , located near the proximal ends of the strut members  11 - 1 ,  11 - 4 . To reduce stresses on the anchor rivets  25 - 3 ,  25 - 5 , the distal and proximal ends of the struts  11  can be curved or twisted to provide a flush interface between the joined struts. 
         [0049]    As can be seen, the support structure  10  ( FIG. 1 ) is fabricated by linking together a serial chain of scissor mechanisms. The chain is then wrapped to join the last scissor mechanism with the first scissor mechanism in the chain. By actuating the linkage the links can be opened or closed, which results in expanding or compressing the stent  10  ( FIG. 1 ). 
         [0050]    Returning to  FIG. 1 , by utilizing the swivel joints  15 , the diameter of the stent can be compressed for insertion through a biological lumen, such as an artery, to a selected position. The stent can then be expanded to secure the stent at the selected location within the lumen. Furthermore, after being expanded, the stent can be recompressed for removal from the body or for repositioning within the lumen. 
         [0051]      FIG. 3  is a perspective view of a compressed support structure of  FIG. 1 . When compressed, the stent  10  is at its maximum length and minimum diameter. The maximum length is limited by the length of the strut members, which in a particular embodiment is 15 mm. The minimum diameter is limited by the width of the strut members, which in a particular embodiment is 0.052 inch. 
         [0052]      FIG. 4  is a perspective view of the support structure of  FIG. 1  in a fully expanded state. As shown, the fully expanded support structure  10  forms a ring, which can be used as an annuloplasty ring. 
         [0053]    In particular, if one end of the stent circumference is attached to tissue, the compression of the stent will enable the tissue to cinch. Because the stent has the ability to have an incremental and reversible compression or expansion, the device could be used to provide an individualized cinching of the tissue to increase the competency of a heart valve. This could be a useful treatment for mitral valve diseases, such as mitral regurgitation or mitral valve prolapse. 
         [0054]    While the support structure  10  can be implanted in a patient during an open operative procedure, a closed procedure will often be more desirable. As such, the support structure  10  can include an actuation mechanism to allow a surgeon to expand or compress the support structure from a location remote from the implant site. Due to the properties of a scissor linkage wrapped into a cylinder ( FIG. 1 ), actuation mechanisms can exert work to expand the stent diameter by either increasing the distance between neighboring scissor joints, and decreasing the distance between the anchor joints. 
         [0055]      FIG. 5  is a perspective view of the support structure of  FIG. 2  having a particular actuator mechanism. As shown, the actuator mechanism  30  includes a dual-threaded rod  32  positioned on the inside of the support structure  10  ( FIG. 1 ). It should be understood, however, that the actuator mechanism  30  can instead be positioned on the outside of the support structure  10 . Whether positioned on the inside or outside, the actuator mechanism  30  operates in the same way. 
         [0056]    The rod includes right-hand threads  34 R on its proximal end and left-hand threads  34 L on its distal end. The rod  32  is mounted the anchor points  15 - 3 ,  15 - 5  using a pair of threaded low-profile support mounts  35 - 3 ,  35 - 5 . Each end of the rod  32  is terminated by a hex head  37 - 3 ,  37 - 5  for receiving a hex driver (not shown). As should be understood, rotating the rod  32  in one direction will urge the anchor points  25 - 3 ,  25 - 5  outwardly to compress the linkages while rotating the rod  32  in the opposite direction will urge the anchor points  25 - 3 ,  25 - 5  inwardly to expand the linkages. 
         [0057]      FIG. 6  is a perspective view of the support structure of  FIG. 2  having another particular actuator mechanism. As shown, the actuator mechanism  30 ′ includes a single-threaded rod  32 ′ positioned on the inside of the support structure  10  ( FIG. 1 ). The rod  32 ′ includes threads  34 ′ on one of its ends. The rod  32 ′ is mounted to low-profile anchor points  15 - 3 ,  15 - 5  using a pair of support mounts  35 ′- 3 ,  35 ′- 5 , one of which is threaded to mate with the rod threads  34 ′. The unthreaded end of the rod  32 ′ includes a retaining stop  39 ′ that bears against the support mount  35 ′- 5  to compress the support structure. Each end of the rod  32 ′ is terminated by a hex head  37 ′- 3 ,  37 ′- 5  for receiving a hex driver (not shown). Again, rotating the rod  32 ′ in one direction will urge the anchor points  25 - 3 ,  25 - 5  outwardly to compress the linkages while rotating the rod  32 ′ in the opposite direction will urge the anchor points  25 - 3 ,  25 - 5  inwardly to expand the linkages. 
         [0058]    In addition, because the struts overlap, a ratcheting mechanism can be incorporated to be utilized during the sliding of one strut relative to the other. For example, the stent could lock at incremental diameters due to the interaction of features that are an integral part of each strut. An example of such features would be a male component (e.g. bumps) on one strut surface which mates with the female component (e.g. holes) on the surface of the neighboring strut surface, as the two struts slide pass one another. Such structures could be fabricated to have an orientation, such that they incrementally lock the stent in the expanded configuration as the stent is expanded. Such a stent could be expanded using a conventional balloon or other actuation mechanism described in this application. 
         [0059]    Because the support structure  10  of  FIGS. 5 and 6  are intended to be implanted during a closed surgical procedure, the actuator mechanism is controlled remotely by a surgeon. In a typical procedure, the support structure  10  is implanted through a body lumen, such as the femoral artery using a tethered endoluminal catheter. As such, the actuator mechanism  30  can be controlled via the catheter. 
         [0060]      FIG. 7  is a perspective view of a particular support structure and control catheter assembly usable with the actuator mechanisms of  FIGS. 5 and 6 . The control catheter  40  is dimensioned to be inserted with the support structure through a biological lumen, such as a human artery. As shown, the control catheter  40  includes a flexible drive cable  42  having a driver  44  on its distal end that removably mates with a hex head  37 ,  37 ′ of the actuator mechanism ( FIGS. 5 and 6 ). The proximal end of the cable  42  includes a hex head  46 . In operation, the proximal hex head  46  of the cable  42  is rotated by a surgeon, using a thumb wheel or other suitable manipulator (not shown). Rotation of the hex head  46  is transferred by the cable  42  to the driver head  44  to turn the actuator rod  30 ,  30 ′ ( FIGS. 5 and 6 ). 
         [0061]    The cable  42  is encased by a flexible outer sheath  48 . The distal end of the outer sheath  48  includes a lip or protuberance  49  shaped to interface with the support structure  10 . When the cable  42  is turned, the outer sheath lip  49  interacts with the support structure  10  to counteract the resulting torque. 
         [0062]    By employing threads, the rod is self-locking to maintain the support structure in the desired diameter. In a particular embodiment, the rod  32 ,  32 ′ has a diameter of 1.0 mm and a thread count of 240 turns/inch. While a threaded rod and drive mechanism are described, other techniques can be employed to actuate the linkages depending on the particular surgical application. For example, the actuator mechanism can be disposed within the thickness of the strut members, instead of inside or outside of the stent. For example, worm gears or a rack and pinion mechanism can be employed as known in the art. One of ordinary skill in the art should recognize other endoluminal actuation techniques. In other situations, the support structure can be implanted during an open procedure, which may not require an external actuation mechanism. 
         [0063]    Although there are other uses for the described support structure, such as drug delivery, a particular embodiment supports a prosthetic valve. In particular, the support structure is used in combination with a prosthetic valve, such as for an aortic valve replacement. 
         [0064]      FIG. 8  is a perspective view of a particular rotating prosthetic valve assembly. The prosthetic valve  100  comprises a three leaflet configuration shown in an open position. The leaflets are derived from a biocompatible material, such as animal pericardium (e.g. bovine, porcine, equine), human pericardium, chemically-treated pericardium, gluteraldehyde-treated pericardium, tissue engineered materials, a scaffold for tissue engineered materials, autologous pericardium, cadaveric pericardium, Nitinol, polymers, plastics, PTFE, or any other material known in the art. 
         [0065]    The leaflets  101   a ,  101   b ,  101   c  are attached to a stationary cylindrical member  105  and a non-stationary cylindrical member  107 . One side of each leaflet  101  is attached to the non-stationary cylindrical member  107 . The opposing side of each leaflet  101  is attached to the stationary cylindrical member  105 . The attachment of each leaflet  101  is in a direction generally perpendicular to the longitudinal axis of the cylindrical members  105 ,  107 . In this embodiment, each leaflet  101  is pliable, generally rectangular in shape, and has a 180 degree twist between its attachments to stationary member  105  and non-stationary member  107 . Each leaflet  101  has an inner edge  102  and an outer edge  103 , with the edges  102   c ,  103   c  of one leaflet  101   c  being referenced in the figure. As known in the art, the leaflets can be fabricated from either biological or non-biological materials, or a combination of both. 
         [0066]    One way to actuate the valve to close is by utilizing the forces exerted by the normal blood flow or pressure changes of the cardiac cycle. More specifically, the heart ejects blood through the fully open valve in the direction of the arrow shown in  FIG. 8 . Shortly thereafter, the distal or downstream blood pressure starts to rise relative to the proximal pressure across the valve, creating a backpressure on the valve. 
         [0067]      FIG. 9  is a perspective view of the valve assembly of  FIG. 8  while being closed. That backpressure along the direction of the arrow causes the axially displacement of the leaflets  101  and non-stationary member  107  towards the stationary cylindrical member  105 . As the leaflets  101  move from a vertical to horizontal plane relative to the longitudinal axis, a net counter-clockwise torque force is exerted on the non-stationary member  107  and leaflets  101 . The torque force exerts a centripetal force on the leaflets  101 . 
         [0068]      FIG. 10  is a perspective view of the valve assembly of  FIG. 8  once completely closed. Complete closure of the valve  100  occurs as the leaflets  101  displace to the center of the valve and the non-stationary cylindrical member  107  rests upon the stationary member  105 , as shown. 
         [0069]    The function of the valve  100  opening can be understood by observing the reverse of the steps of valve closing, namely following the sequence of drawings from  FIG. 10  to  FIG. 8 . 
         [0070]    In considering the valve  100  as an aortic valve replacement, it would remain closed as shown in  FIG. 10 , until the heart enters systole. During systole, as the myocardium forcefully contracts, the blood pressure exerted on the valve&#39;s proximal side (the side closest to the heart) is greater than the pressure on the distal side (downstream) of the closed valve. This pressure gradient causes the leaflets  101  and non-stationary cylindrical member  107  to displace away from the stationary member  105  along the axial plane. The valve  100  briefly assumes the half-closed transition state shown in  FIG. 9 . 
         [0071]    As the leaflets  101  elongate from a horizontal to vertical orientation along the axial plane, a net torque force is exerted on the leaflets  101  and non-stationary cylindrical member  107 . Since the valve  100  is opening, as opposed to closing, the torque force exerted to open the valve is opposite to that exerted to close the valve. Given the configuration of embodiment shown in  FIG. 9 , the torque force that opens the valve would be in clockwise direction. 
         [0072]    The torque forces cause the leaflets  101  to rotate with the non-stationary member  107  around the longitudinal axis of the valve  100 . This, in turn, exerts a centrifugal force on each leaflet  101 . The leaflets  101  undergo radial displacement away from the center, effectively opening the valve and allowing blood to flow away from the heart, in the direction shown by the arrow in  FIG. 8 . 
         [0073]    To summarize, the valve passively functions to provide unidirectional blood flow by linking three forces. Axial, torque, and radial forces are translated in a sequential and reversible manner, while encoding the directionality of prior motions. First, the axial force of blood flow and pressure causes the displacement of the leaflets  101  and non-stationary members  107  relative to the stationary member  105  along the axial plane. This is translated into a rotational force on the leaflets  101  and non-stationary member  107 . The torque force, in turn, displaces the leaflets  101  towards or away from the center of the valve, along the radial plane, which closes or opens the valve  100 . The valve  100  passively follows the pathway of opening or closing, depending on the direction of the axial force initially applied to the valve by the cardiac cycle. 
         [0074]    In the body, the stationary cylindrical member  105  can secured and fixed in position at the implant site, while the non-stationary member  107  and distal ends of Ieaflets  101  are free to displace along the axial plane. In using the prosthetic valve as an aortic valve replacement, the stationary member  105  would be secured in the aortic root. As the blood pressure or flow from the heart, increases, the valve  100  changes from its closed configuration to the open configuration, with blood ejecting through the valve  100 . 
         [0075]    Specific advantages of the rotating valve of  FIGS. 8-10 , along with further embodiments, are described in the above-incorporated parent provisional patent application. 
         [0076]      FIG. 11  is a perspective view of the valve of  FIGS. 8-10  in combination with the support structure of  FIG. 1 . As shown in the closed position, the valve&#39;s stationary member  105  is attached to the support structure  10 . The valve&#39;s non-stationary member  107  is not attached to the support structure  10 . This enables the non-stationary member  107  to displace along the axial plane along with the leaflets  101  during valve opening or closing. In this particular embodiment, the valve  100  occupies a position that is closer to one end of the support structure  10 , as shown. 
         [0077]      FIG. 12  is a perspective view of the valve of  FIG. 11  in the open position. As noted above, the non-stationary member  107  is not attached to support structure  10 , and is thus free to displace along the axial plane, along with the leaflets  101 . In this particular embodiment, during full opening, non-stationary member  107  and the leaflets  101  remain within the confines of the support structure  10 . 
         [0078]    The stented valve  110  can be implanted during a closed procedure as described above. However, because of the operation of the non-stationary member within the body of the stent, the actuator mechanism to compress and expand the stent would not be disposed within the stent. 
         [0079]    Further embodiments of the stented valve  110 , positioning of the valve in the body, and procedures for implantation are described in the above-incorporated parent provisional patent application. In addition, a tissue valve can be draped on the support structure. Additional embodiments should be apparent to those of ordinary skill in the art. 
         [0080]      FIG. 13  is a perspective view of a traditional tissue valve mounted to the support structure of  FIG. 1 . As shown, a stented valve  120  includes a prosthetic tissue valve  121  attached to a support structure  10 , such as that described above. 
         [0081]    The tissue valve  121  includes three pliable semi-circular leaflets  121   a ,  121   b ,  121   c , which can be derived from biocompatible materials as noted with reference to  FIG. 8 . Adjacent leaflets are attached in pairs to commissures  123   x ,  123   y ,  123   z  on the support structure  10 . In particular, the commissures  123   x ,  123   y ,  123   z  correspond with spaced-apart distal anchor points  13   x ,  13   y ,  13   z  on the support structure  10 . In an 18-strut stent, the commissures are attached the structure  10  via corresponding fasteners  25  at every third distal anchor point. 
         [0082]    From the commissures, the leaflet sides are connected to the adjacent diagonal struts. That is, the sides of the first leaflet  121   a  are sutured to the struts  11 -Xa and  11 -Za, respectively; the sides of the second leaflet  121   b  are sutured to the struts  11 -Xb and  11 -Yb, respectively; and the sides of the third leaflet  121   c  are sutured to the struts  11 -Yc and  11 -Zc, respectively. Those sutures end at the scissor pivot points on the diagonal struts. 
         [0083]    In the configuration shown, neighboring struts  11  are attached to one another in a manner that creates multiple arches  128  at the ends of the stent. Posts for leaflet attachment, or commissures, are formed by attaching neighboring leaflet to each of the struts that define a suitable arch  128   x ,  128   y ,  128   z . In the configuration shown, there are three leaflets  121   a ,  121   b ,  121   c , each of which is attached to a strut along two of its opposing borders. The commissures are formed by three equi-distance arches  128   x ,  128   y ,  128   z  in the stent. 
         [0084]    The angled orientation of a strut in relationship to its neighboring strut enables the leaflets  121   a ,  121   b ,  121   c  to be attached to the stent in an triangular configuration. This triangular configuration simulates the angled attachment of the native aortic leaflet. In the native valve this creates an anatomical structure between leaflets, known as the inter-leaflet trigone. Because the anatomical inter-leaflet trigone is believed to offer structural integrity and durability to the native aortic leaflets in humans, it is advantageous to simulate this structure in a prosthetic valve. 
         [0085]    One method of attachment of the leaflets to the struts is to sandwich the leaflet between a multi-ply strut. The multiple layers are then held together by sutures. Sandwiching the leaflets between the struts helps to dissipate the forces on leaflets and prevent the tearing of sutures through the leaflets. 
         [0086]    The remaining side of each leaflet  121   a ,  121   b ,  121   c  is sutured annularly across the intermediate strut members as shown by a leaflet seam. The remaining open spaces between the struts are draped by a biocompatible skirt  125  to help seal the valve against the implant site and thus limit paravalvular leakage. As shown, the skirt  125  is shaped to cover those portions of the stent below and between the valve leaflets. 
         [0087]    In more detail, the skirt  125  at the base of the valve is a thin layer of material that lines the stent wall. The skirt material can be pericardial tissue, polyester, PTFE, or other material or combinations of materials suitable for accepting tissue in growth, including chemically treated materials to promote tissue growth or inhibit infection. The skirt layer functions to reduce or eliminate leakage around the valve, or “paravalvular leak”. To that end, there are a number of ways to attach the skirt material layer to the stent, including:
       the skirt layer can be on the inside or the outside of the stent;   the skirt layer can occupy the lower portion of the stent;   the skirt layer can occupy the lower and upper portion of the stent;   the skirt layer can occupy only the upper portion of the stent;   the skirt layer can occupy the area between the struts that define the commissure posts;   the skirt layer can be continuous with the leaflet material;   the skirt layer can be sutured to the struts or a multitude of sites; or   the skirt layer can be secured to the lower portion of the stent, and pulled or pushed up to cover the outside of the stent during the deployment in the body.
 
The above list is not necessarily limiting as those of ordinary skill in the art may recognize alternative draping techniques for specific applications.
       
 
         [0096]      FIG. 14  is a perspective view of the valve structure of  FIG. 13  having a full inner skirt. A stented valve  120 ′ includes a prosthetic tissue valve  121 ′ having three leaflets  121   a ′,  121   b ′,  121   c ′ attached to a support structure  10 . A skirt layer  125 ′ covers the interior surface of the stent  10 . As such, the valve leaflets  121   a ′,  121   b ′,  121   c ′ are sutured to the skirt layer  125 ′. 
         [0097]      FIG. 15  is a perspective view of the valve structure of  FIG. 13  having a full outer skirt. A stented valve  120 ″ includes a prosthetic tissue valve  121 ″ having three leaflets  121   a ″,  121   b ″,  121   c ″ attached to a support structure  10 , such as that described in  FIG. 13 . A skirt layer  125 ″ covers the exterior surface of the stent  10 . 
         [0098]    The tissue valve structures  120 ,  120 ′,  120 ″ can also be implanted during a closed procedure as described above. However, the actuator mechanism to compress and expand the stent would be attached to avoid the commissure points and limit damage to the skirt layer  125 ,  125 ′,  125 ″, such as by mounting the actuator mechanism on the outer surface of the stent  10 . 
         [0099]    While the above-described embodiments have featured a support structure having linear strut bars and equal length scissor arms, other geometries can be employed. The resulting shape will be other than cylindrical and can have better performance in certain applications. 
         [0100]      FIG. 16  is a perspective view of the arrangement of strut members in a conical-shaped support structure configuration. In the conical structure  10 ′, the strut members  11  are arranged as shown in  FIG. 2 , except that the middle scissor pivots do not bisect the struts. In particular, the middle scissor pivots (e.g.  15 ′- 1 ,  15 ′- 7 ) divide the joined strut members (e.g.  11 ′- 1 ,  11 ′- 2  and  11 ′- 3 ,  11 ′ 4 ) into unequal segments of 5/12 and 7/12 lengths. When fully assembled, the resulting support structure thus conforms to a conical shape when expanded. For illustration purposes, the stent  10 ′ is shown with a single-threaded actuator rod  32 ′ ( FIG. 6 ), but it is not a required element for this stent embodiment. 
         [0101]    The stent  10 ′ can also assume a cone shape in its expanded configuration by imposing a convex or concave curvature to the individual strut members  11  that comprise the stent  10 ′. This could be achieved by using a material with memory, such as shape-memory or temperature sensitive Nitinol. 
         [0102]    A valve can be orientated in the cone-shaped stent  10 ′ such that the base of the valve was either in the narrower portion of the cone-shaped stent, with the non-base portion of the valve in the wider portion of the cone. Alternatively, the base of the valve can be located in the widest portion of the stent with the non-base portion of the valve in the less-wide portion of the stent. 
         [0103]    The orientation of a cone-shaped stent  10 ′ in the body can be either towards or away from the stream of blood flow. In other body lumens (e.g. respiratory tract or gastrointestinal tract), the stent could be orientated in either direction, in relationship to the axial plane. 
         [0104]      FIG. 17  is a perspective view of an hourglass-shaped support structure configuration. In this configuration, the circumference around the middle pivot points  15 ″- 1 ,  15 ″- 7 ,  15 ″- 9  (the waist) is less than the circumference at either end of the stent  10 ″. As shown, the hourglass shaped support structure  10 ″ is achieved by reducing the number of strut members  11 ″ to six and shortening the strut members  11 ″ in comparison to prior embodiments. As a result of the shortening, there are fewer orifices  13 ″ per strut member  11 ″. Because of the strut number and geometry, each strut member  11 ″ includes a twist at points  19 ″ along there longitudinal planes. The twists provide a flush interface between joined strut  15 ″- 3 . 
         [0105]    An hourglass stent configuration could also be achieved by imposing concave or convex curvatures in individual bars  11 ″. The curvature could be a property of the materials (e.g. shape-memory or heat-sensitive Nitinol). The curvature could be absent in the compressed stent state and appear when the stent is in its expanded state. 
         [0106]    It should be noted that any of the above-described support structures can be extended beyond the anchor joints at either of both ends of the stent. By coupling a series of stents in an end-to-end chain fashion, additional stent lengths and geometries can be fabricated. In particular, an hourglass-shaped stent could be achieved by joining two cone-shaped stents at their narrow ends. The hourglass shape can also be modified by assembling the middle scissor pivots off center as shown in  FIG. 14 . 
         [0107]    Particular embodiments of the invention offer distinct advantages over the prior art, including in their structure and applications. While certain advantages are summarized below, the summary is not necessarily a complete list as there may be additional advantages. 
         [0108]    The device allows the user to advert the serious complications that can occur during percutaneous heart valve implantation. Because the device is retrievable and re-positionable during implantation into the body, the surgeon can avoid serious complications due to valve mal-positioning or migration during implantation. Examples of these complications include occlusion of the coronary arteries, massive paravalvular leakage, or arrthymias. 
         [0109]    The device can also decrease vascular access complications because of the device&#39;s narrow insertion profile. The device&#39;s profile is low, in part, due to its unique geometry, which allows neighboring struts in the stent to overlap during stent compression. The device&#39;s low profile is further augmented by eliminating the necessity for a balloon or a sheath. The device&#39;s narrow profile offers the advantage of widening the vascular access route options in patients. For instance, the device can enable the delivery of the prosthetic valve through an artery in the leg in a patient whom would have previously been committed to a more invasive approach through the chest wall. The device therefore aims to decrease complications associated with the use of large profile devices in patients with poor vascular access. 
         [0110]    The tissue valve embodiments can offer improved durability by allowing for attachment of the leaflets to flexible commissural posts. The flexible posts allow dissipation of the stress and strain imposed on the leaflet by the cardiac cycle. The use of multi-ply struts enables the leaflets to be sandwiched in between the struts, which re-enforces the leaflet attachments and prevents tearing of sutures. The valve further assumes a desirable leaflet morphology, which further reduces the stress and strain on leaflets. Namely, the angled leaflet attachment to the stent is similar to the native human aortic valve&#39;s inter-leaflet trigone pattern. These properties significantly improve the longevity of percutaneous heart valve replacement therapies. 
         [0111]    The device could reduce or eliminate arrthymia complications due to the incremental expansion or compression of the stent. The stent can employ a screw mechanism for deployment, which enables the stent to self-lock or un-lock at all radii. This enables more controlled deployment and the potential for individualizing the expansion or compression of the device in each patient. Because the expansion or compression of the device is reversible at any stage during the procedure, the surgeon can easily reverse the expansion of the device to relieve an arrythmia. In addition, if an arrythmia is detected during implantation, the device can be re-positioned to further eliminate the problem. 
         [0112]    The device can reduce or eliminate paravalvular leak due to the device&#39;s ability to be accurately positioned, and re-positioned, if necessary. That can considerably decrease the occurance and severity of paravalvular leaks. 
         [0113]    The device eliminates balloon-related complications. The screw mechanism of deployment exploits the mechanical advantage of a screw. This provides for forceful dilation of the stent. The lever arms created by the pivoting of the struts in the scissor linkage of the stent, transmits a further expansion force to the stent. The stent is expanded without the need for a balloon. In addition, the ability of the device to be forcefully dilated reduces or eliminates the need for pre- or post-ballooning during the implantation procedure in patients. 
         [0114]    The device has more predictable and precise positioning in the body because the difference between the height of the stent in the compressed and expanded position is small. This “reduced foreshortening” helps the surgeon to position the device in the desirable location in the body. The ability to re-position the device in the body further confers the ability to precisely position the device in each individual. 
         [0115]    In addition to the mechanical advantages, the device enables a wider population of patients to be treated by a less invasive means for valve replacement. For example, the device enables patients with co-morbidites, whom are not candidates for open chest surgical valve replacement, to be offered a treatment option. The device&#39;s ability to assume a narrow profile also enables patients who were previously denied treatment due to poor vascular access (e.g. tortuous, calcified, or small arteries), to be offered a treatment option. The durability of the valve should expand the use of less-invasive procedures to the population of otherwise healthy patients, whom would otherwise be candidates for open chest surgical valve replacement. The device&#39;s ability to be forcefully expanded, or assume hourglass, or conical shapes, potentially expands the device application to the treatment of patients diagnosed with aortic insufficiency, as well as aortic stenosis. 
         [0116]    The device can also provide a less invasive treatment to patients with degenerative prosthesis from a prior implant, by providing for a “valve-in-valve” procedure. The device could be accurately positioned inside the failing valve, without removing the patient&#39;s degenerative prosthesis. It would help the patient by providing a functional valve replacement, without a “re-do” operation and its associated risks. 
         [0117]    While this invention has been particularly shown and described with references to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the embodiments without departing from the scope of the invention encompassed by the appended claims.