Patent Publication Number: US-9895223-B2

Title: Cardiac valve prosthesis

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/548,013, filed on Nov. 19, 2014, which is a continuation of U.S. patent application Ser. No. 13/972,022, filed on Aug. 21, 2013, now U.S. Pat. No. 8,920,492, which is a continuation of U.S. patent application Ser. No. 13/341,336, filed on Dec. 30, 2011, now U.S. Pat. No. 8,540,768, which is a continuation of Ser. No. 12/139,686, filed on Jun. 16, 2008, now U.S. Pat. No. 8,539,662, which is a continuation of U.S. patent application Ser. No. 11/352,021 filed on Feb. 10, 2006, now U.S. Pat. No. 7,857,845, which claims priority under 35 U.S.C. §119 from Italian patent application number TO2005/A000074, filed on Feb. 10, 2005. Each of the above-identified applications is hereby incorporated by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present invention relates to cardiac-valve prostheses. More specifically, the present invention is directed to a prosthesis that is amenable to a minimally-invasive implantation. 
     BACKGROUND 
     Recently, there has been increasing consideration given to the possibility of using, as an alternative to traditional cardiac-valve prostheses, valves designed to be implanted using minimally-invasive surgical techniques or endovascular delivery (the so-called “percutaneous valves”). Implantation of a percutaneous valve (or implantation using thoracic-microsurgery techniques) is a far less invasive act than the surgical operation required for implanting traditional cardiac-valve prostheses. Further details of exemplary percutaneous implantation techniques are provided in U.S. Publication 2002/0042651, U.S. Pat. No. 3,671,979, and U.S. Pat. No. 5,954,766, which are hereby incorporated by reference. 
     These prosthetic valves typically include an anchoring structure, which is able to support and fix the valve prosthesis in the implantation position, and prosthetic valve elements, generally in the form of leaflets or flaps, which are stably connected to the anchoring structure and are able to regulate blood flow. 
     Furthermore, the methods of implantation of valves via a percutaneous route or by means of thoracic microsurgery are very frequently irrespective of the effective removal of the natural valve leaflets. Instead, the cardiac valve may be introduced in a position corresponding to the natural annulus and deployed in situ by simply divaricating definitively the natural valve leaflets. 
     There is a need for a percutaneous valve that does not run the risk of being displaced (dislodged) with respect to the implantation position, as a result of the hydraulic thrust exerted by the blood flow. There is a further need for a percutaneous valve that secures tightly to the flow duct generally defined by the natural valve annulus, such that it resists blood flow around the outside of the percutaneous valve structure. 
     SUMMARY 
     In an exemplary embodiment, a cardiac valve prosthesis according to the invention is made so that the entire armature of the valve, or at least the anchorage parts, adhere to the native walls of the implantation site, without interfering with the blood flow, which thus remains practically free. In a preferred way, the anchorage portions moreover have appropriate slits that prevent their interference with the coronary ostia. The anchorage portions and the portions of functional support of the armature can constitute either different parts of a single structure or parts that are structurally distinct from one another. Super-elastic materials can be used in order to obtain a structure that is able to be collapsed for advancement to its implantation site, and to self-recover its expanded geometry once the prosthesis is deployed in the implantation position. The entire armature of the valve, or at least the anchorage parts, can be made even of re-absorbable material, whereas the valve leaflets can be made of biological and/or synthetic tissues, in part colonizable or re-absorbable. In this way, it is possible to obtain anchorage of the device during the period necessary for integration of the valve prosthesis with the physiological tissues of the anatomical site of implantation. Subsequently, there is dissolution of the artificial structure that enables initial anchorage. Amongst the various advantages linked to this solution to be emphasized is the creation of the ideal conditions for a possible prosthetic re-implantation. The armature can include anchorage formations or portions of the supporting structure of the valve flaps made at least partially of shape-memory material (e.g., Nitinol) that enable creation or regulation of the anchorage, i.e., regulation of the modalities and the magnitude of splaying-out of the valve leaflets through control of the memory of the shape-memory material (e.g., by controlling its temperature), according to a mechanism similar to what is described in the document No. EP-A-1 088 529. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, purely by way of non-limiting example, with reference to the annexed plate of drawings, in which: 
         FIG. 1  is a general perspective view of a cardiac-valve prosthesis according to one embodiment of the present invention; 
         FIGS. 2 to 7  illustrate different embodiments of an armature portion of the cardiac valve prosthesis according to the present invention; 
         FIGS. 8 and 9  illustrate plan and cross-sectional views, respectively, of the cardiac valve prosthesis implanted at an implantation site in a patient, according to an embodiment of the present invention; and 
         FIG. 10  is a schematic cross-sectional view of an implantation site for the cardiac valve prosthesis according to one embodiment of the present invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     In the figures of the annexed plate of drawings, the reference number  1  designates as a whole a cardiac-valve prosthesis, which can be implanted percutaneously or resorting to techniques of thoracic microsurgery, or else of implantation of a “sutureless” type. Essentially, the prosthesis  1  represented in  FIG. 1  includes an armature  2 , having the characteristics that emerge more clearly from the representation of  FIGS. 2 to 7 , and a valve sleeve  3  coupled to the armature  2  and including three valve leaflets  3   a ,  3   b ,  3   c.    
     As illustrated in  FIG. 2 , the armature  2  of the prosthesis  1  can have a general cage-like structure, with a general symmetry of a cylindrical type about a principal axis X 1 . In percutaneous valves the axis X 1  is designed to correspond usually to the principal axis of the distal part of the catheter used for implantation of the prosthesis  1 . For the present purpose, the axis X 1  can be viewed basically as an entity of a purely geometrical nature. As shown, the armature  2  defines a lumen which operates as a flow tube or duct to accommodate the flow of blood there through. As will be readily apparent to those skilled in the art, a major characteristic of the present invention is the absence of structural elements that can extend in the lumen through which blood flows. 
     The valve sleeve  3  may be constructed according to various techniques known in the art. For example, techniques for the formation of the valve leaflets, assembly of the valve sleeve and installation thereof on an armature that can be used in the context of the present invention are described in EP-A-0 133 420, EP-A-0 155 245 and EP-A-0 515 324 (all of which are hereby incorporated by reference), the latter document referring to the construction of a cardiac-valve prosthesis of biological tissue of the type commonly referred to as “stentless.” 
     As further illustrated, the valve sleeve  3  includes a base portion  30  with an overall annular pattern, designed to extend from the lower portion of the prosthesis  1 , which, in the implantation site, is in a position proximal with respect to the direction of flow of the blood through the prosthesis (from below upwards, as viewed in  FIG. 1 ). Starting from the base portion  30 , there extend in an axial direction towards the inside of the structure of the prosthesis  1  three pleat formations  32 . The valve leaflets  3   a ,  3   b  and  3   c  extend like a festoon, with a general claw-like conformation, between pairs of pleat formations  32  adjacent to one another. 
     As illustrated in  FIG. 1 , each valve leaflet  3   a ,  3   b  and  3   c  has a fluidodynamically proximal edge with an arched pattern, which extends from the base formation  30  and along two adjacent pleat formations  32 , and a fluidodynamically distal edge, which extends towards the central orifice of the prosthesis so as to be able to co-operate with the homologous edges of the other valve leaflets. The terms “fluidodynamically proximal” and “fluidodynamically distal” refer to the direction of free flow of the blood through the prosthesis, a direction that is from below upwards, as viewed in the figures of the annexed plate of drawings. 
     As will be understood by those of ordinary skill in the art, in operation, the valve leaflets  3   a ,  3   b ,  3   c  are able to undergo deformation, divaricating and moving up against the armature  2  so as to enable free flow of the blood through the prosthesis. When the pressure gradient, and hence the direction of flow, of the blood through the prosthesis tends to be reversed, the valve leaflets  3   a ,  3   b ,  3   c  then move into the position represented in  FIG. 1 , in which they substantially prevent the flow of the blood through the prosthesis. Usually, the valve leaflets  3   a ,  3   b ,  3   c  are made in such a way as to assume spontaneously, in the absence of external stresses, the closed configuration represented in  FIG. 1 . 
       FIGS. 2 through 7  depict the armature  2  according to various embodiments of the present invention. Referring first to  FIG. 2 , it is shown that the armature  2  (which may be made of metal material, such as for example the material commonly referred to as Nitinol) includes two annular elements  20   a ,  20   b , which generally occupy respective end positions within the armature  2 . In one embodiment, in the site of implantation of the prosthesis  1 , the annular elements  20   a  and  20   b  are designed to be located, respectively, upstream and downstream of the sinuses of Valsalva. 
     During implantation, the prosthesis  1  is advanced towards the implantation site in a radially contracted configuration, with the annular elements  20   a  and  20   b  in a radially collapsed configuration. In one embodiment, when so collapsed, the annular elements  20   a ,  20   b  have a minimum diameter of about 5 to about 15 mm, according to the technique of implantation for which the prosthesis is designed. Once the prosthesis  1  has reached the implantation site, the annular elements  20   a ,  20   b  are made/allowed to expand until they reach their normal expanded configuration, with a diameter that ranges, in one embodiment, from about 18 to about 30 mm. 
     In order to enable the movement of expansion, the annular elements  20   a  and  20   b  are made, according to the illustrated embodiment, with a mesh structure substantially resembling the mesh structure of a stent for angioplasty. It will be appreciated in fact that the annular elements  20   a  and  20   b  are designed to perform a movement of radial expansion (with subsequent maintenance of the radially expanded configuration) substantially resembling the movement of expansion in situ of an angioplasty stent. 
     In the example of embodiment illustrated herein, the annular elements  20   a  and  20   b  have a rhomboidal-mesh structure. In other embodiments, the parts  20   a ,  20   b  can be made with any structure that is able to ensure the necessary functionality. 
     In one embodiment, as shown in  FIG. 2 , the annular element  20   a  designed to be located in a position proximal with respect to the flow of the blood through the prosthesis  1  (i.e., on the inflow side of the blood in the prosthesis  1  in the conditions of free flow) may have a proximal end that is at least slightly flared outward like an enlarged opening of the flow duct of the blood. This configuration functions to promote a more positive anchorage of the annular element  20   a , and in turn, the prosthesis  1 , to the valve annulus, thus promoting the perivalvar tightness, improving the haemodynamics, and adapting (i.e., radiusing) the lines of blood flow in the ventricular chamber to the flow tube constituted by the valve sleeve. 
     As shown, the annular elements  20   a ,  20   b  are connected to one another by anchor members  22 , which in the illustrated embodiment, are generally arched, projecting towards the outside of the prosthesis  1 . In one embodiment, the anchor members  22  are designed such that when the prosthesis  1  is positioned at the implantation site, the anchor members  22  can extend on the outside of the sinuses of Valsalva so as to ensure firm anchorage in situ of the prosthesis  1 . 
     With the prosthesis  1  in the radially contracted configuration adopted for implantation, the anchor members  22  are normally maintained in a position (not shown) recalled towards the central axis X 1  of the prosthesis  1 . This can occur, for example, via a retention means such as a tubular sheath of an implantation catheter through which the radially contracted prosthesis is advanced. Subsequently, once disengaged from the retention means, the anchor members  22  may assume the arched pattern represented in the figures so as to be able to project (protrude), in one embodiment, within the sinuses of Valsalva. 
     As will be appreciated by those skilled in the art, the sinuses of Valsalva are, in a normal heart, three in number, and are distributed in an approximately angularly uniform way around the root of the artery distal to the semilunar valve (i.e., the aortic or pulmonary valve). Accordingly, as illustrated, the prosthesis  1  may include three anchor members  22  (or three groups of anchor members) set at an angular distance apart of about 120° with respect to the central axis X 1  of the prosthesis. 
     In the exemplary embodiment illustrated, the anchor members  22  are made in the form of ribbon-like elements that extend in a generally sinusoidal or serpentine path, with bends or open loops situated on either side with respect to an ideal line extending approximately in the direction of the generatrices of the overall cylindrical shape of the prosthesis. In another embodiment of the invention, the sinusoidal pattern can be obtained with bends or open loops that extend from one side and from the other with respect to a line that extends in a circumferential direction with respect to the prosthesis. In yet another embodiment, the anchor members  22  may have a mesh structure, for example closed rhomboidal meshes of the same type as the one represented with reference to the annular elements  20   a ,  20   b , or to simple segments of curve lying in roughly radial planes. Additionally, as discussed above, each anchor member  22  can consist either of a single element or of a plurality of elements (e.g., pairs of anchor members  22  as shown in  FIGS. 2-7 ) that extend in a direction in which they are generally set alongside one another. 
     The annular elements  20   a  and  20   b  and the respective anchor members  22  substantially form the basic structure of the armature  2  of the prosthesis  1 , which is designed to ensure positioning and anchorage in situ of the prosthesis  1  itself. 
     Associated then to the annular elements  20   a  and  20   b  are further support members, generically designated by  24  in all of  FIGS. 2 to 7 , which operate to support the valve sleeve  3  on the armature  2  of the prosthesis  1 . In the embodiment represented in  FIG. 2 , the support members  24  are simply represented by three generally flat bars extending between and connecting the annular members  20   a ,  20   b . As further illustrated, the support members  24  are set at an angular distance apart of about 120°, with each generally located at a position that is approximately centrally intermediate the anchor members  22 . 
     As may be appreciated from a comparative examination of  FIGS. 1 and 2 , the support members  24  are designed to enable the installation of the valve sleeve  3  in a condition such that the base portion  30  thereof is arranged in general in a position around the annular element  20   a  of the armature  2 , while each of the pleat formations or folds  32  in turn embraces one of the elements or support members  24 , while the valve leaflets  3   a ,  3   b  and  3   c  extend in a festoon, each between two adjacent support members  24 . The general apertured structure both of the annular element  20   a  and of the support members  24  (note the particular holes designated by  26 ) enables fixing of the valve sleeve  3  on the armature  2  by, for example, suturing stitches according to known techniques. In the case where flaps of polymeric materials are used, the flaps can be formed directly on the structure, using techniques such as, for example, dip casting. 
     In this regard, both the armature  2  and the aforesaid suturing stitches can be advantageously provided with a coating of biocompatible carbon material, which may be applied according to the solutions described in U.S. Pat. No. 4,624,822, U.S. Pat. No. 4,758,151, U.S. Pat. No. 5,084,151, U.S. Pat. No. 5,133,845, U.S. Pat. No. 5,370,684, U.S. Pat. No. 5,387,247, and U.S. Pat. No. 5,423,886, the contents of which are hereby incorporated by reference. 
     The apertured structure of the supporting formations  24 , and of the armature  2  in general, means that the armature  2  does not exert any substantial obtrusive effect, preventing, for example, interference in regard to the coronary ostia. 
       FIG. 3  depicts an alternative embodiment of the armature  2  of the present invention. The variant embodiment represented in  FIG. 3  as a whole resembles the embodiment represented in  FIG. 2 , with the exception that (in the embodiment of  FIG. 3 ) the support members  24  provided for anchorage of the valve sleeve  3  do not extend completely in bridge-like fashion between the two annular parts  20   a  and  20   b . Rather, in the embodiment illustrated in  FIG. 3 , the support members  24  are projecting elements that extend in cantilever fashion starting from the annular element  20   a , and do not reach the annular element  20   b . In particular, the lengths of the aforesaid cantilevered support members  24  are determined in such a way as to extend for a length sufficient to enable anchorage of the valve sleeve  3  to the support members  24  at the pleat formations  32 . Thus, in one embodiment, the support members  24  do not include any portions other than those portions which operate to support the valve sleeve  3 . 
       FIG. 4  illustrates another embodiment of the armature  2  according to the present invention. As shown, in the embodiment of  FIG. 4 , like that shown in  FIG. 3 , the support members  24  project in cantilever fashion from the annular element  20   a . As further shown in  FIG. 4 , in this embodiment, the support members  24  have associated thereto fork-like structures  28 . Each fork-like structure  28  has a root portion connected to the annular element  20   b  and two prongs that extend on either side of the respective support member  24  and then connect up to the annular element  20   a  on opposite sides with respect to the area in which the support member  24  projects in cantilever fashion from the formation  20   a.    
     As further shown in  FIG. 4 , in one embodiment, the support members  24  are generally tapered, such that they have widths that decrease gradually moving away from the annular element  20   a , that is, in the proximal-to-distal direction with reference to the direction of free flow of the blood through the prosthesis. As will be apparent to those skilled in the art, tapering of the support members  24  may be employed in any of the embodiments illustrated in  FIGS. 2 to 4 . Similarly, any of the other characteristics of the support members  24  or the anchor members  22 , which albeit herein represented are identical to one another in each of the embodiments illustrated, could in actual fact be different from one another. That is, in any embodiment of the valve prosthesis  1 , there could coexist, in a single prosthesis, anchor members  22  or support members  24  different from one another, with characteristics drawn from different embodiments amongst the plurality of embodiments illustrated herein. 
     The solution represented in  FIG. 4  generally provides a more rigid anchorage structure as compared to the embodiment of  FIG. 3 . In the embodiment illustrated in  FIG. 4 , the fork-like formations  24  effectively fix the axial dimension of the prosthesis  1 , which promotes the expansion of the anchor members  22  in the sinuses of Valsalva. At the same time, in the illustrated embodiment of  FIG. 4 , the support members  24 , which operate to facilitate attachment of the valve sleeve  3  to the armature  2 , are maintained flexible and of modulatable stiffness. 
     In the embodiment represented in  FIG. 5 , the support members  24  are provided in positions corresponding to both of the annular elements  20   a ,  20   b . In this case, however, the support members  24  provided for anchorage of the valve sleeve  3  are reduced to small hooking cantilevers, each provided with an eyelet  26 . The eyelets  26  can be used directly for passing and tying the wires that extend from the valve sleeve  30 . 
     Yet another embodiment is shown in  FIG. 6 , in which the support members  24  are arranged in opposed pairs, with each of the support members  24  within a pair extending in cantilever fashion from one of the annular elements  20   a ,  20   b  and being connected by a connecting element  34 . In one embodiment, the connecting elements  34  may have a generally filiform (i.e., relatively long and thin) shape, whereby the connecting elements  34  may be made relatively flexible and thus may provide a flexible connection between the support members  24 . In one embodiment, the connecting elements  34  may be made from biocompatible metal alloys (e.g., Nitinol) or polymeric materials suitable for applications in the field of implantations (e.g., acetal resins). 
     As shown, the overall configuration of the embodiment of  FIG. 6  generally resembles, from a geometrical standpoint, the embodiment represented in  FIG. 2 . The difference lies in the fact that, whereas the support members  24  represented in  FIG. 2  are as a whole generally stiff (taking into account the intrinsic flexibility of the material that constitutes them), the connecting elements  34  shown in  FIG. 6  may have a filiform shape with a relatively high flexibility. The embodiment illustrated in  FIG. 6  thus enables the configuration for hooking of the valve sleeve  3  to the armature  2  of the prosthesis to be rendered elastic/flexible and renders the extent of the anchor members  22  independent of that of the support members  24 , thus enabling a greater elasticity of design. 
       FIG. 7  depicts yet another embodiment of the armature  2 , which is otherwise similar to the embodiment illustrated in  FIG. 6 , except that in the embodiment of  FIG. 7 , the mutually facing pairs of support members  24  are not connected to each other (as by the connecting members  34  in  FIG. 6 ). Instead, in the embodiment represented in  FIG. 7 , a supporting element  36  extends between and connects each of the support members  24  extending in cantilever fashion from the annular element  20   b . As shown, the supporting elements  36  may extend in a generally festoon-like or catenary path between each of the support members  24  attached to the annular part  20   b . The supporting elements  36  are configured such that each can support one of the valve leaflets  3   a ,  3   b , or  3   c  of the valve sleeve  3 . The supporting elements  36  may be made of substantially rigid or flexible materials. 
     In another embodiment (not shown), the supporting elements  36  may be configured to extend from the support members  24  extending in cantilever fashion from the annular element  20   a.    
     As will be readily understood by those skilled in the art, festoon-like or catenary pattern of the supporting elements  36  may be generally configured to match the homologous pattern of the proximal edges of the valve leaflets  3   a ,  3   b  and  3   c  (see  FIG. 1 ), defining the profile of the edge for anchorage of the functional flaps and, possibly, enabling connection by suture of the aforesaid proximal edges of the valve leaflets to the festoon-like supporting elements  36 . This enables the use of relatively simple valve sleeves  3 , assigning the formation of the profile of the functional flaps of the valves to the supporting elements  36 . 
     The embodiments of the present invention described herein enables, in the final position of implantation, the entire armature  2  of the prosthesis  1 , or at least the anchorage parts, to adhere to the native walls of the implantation site, without interfering with the blood flow, which thus remains practically free. Additionally, the armature  2  and anchor members  22  moreover have a generally apertured structure (for example, appropriate slits), which prevents interference with the coronary ostia. 
     The anchorage portions and the portions of functional support of the armature  2  can constitute either different parts of a single structure or parts that are structurally distinct from one another. The entire armature  2 , or at least the anchorage parts (e.g., the anchor members  22 ), may be made of re-absorbable material, whereas the valve sleeve  3  can be constituted by biological and/or synthetic tissues, which are in part colonizable or re-absorbable. 
     Alternatively, as discussed above, the armature  2  can contain anchorage formations (e.g., anchor members  22 ) made at least partially of shape-memory material (e.g., Nitinol), which enable creation or regulation of the anchorage through the control of the memory of the shape-memory material (e.g., controlling its temperature). 
       FIGS. 8 and 9  illustrate plan and cross-sectional views, respectively, of the prosthesis  1  in its implanted state in an aortic valve replacement, according to an embodiment of the invention. As shown, and as discussed in detail above, the prosthesis  1  can be implanted such that the annular elements  20   a  and  20   b  occupy positions proximal and distal, respectively, of the Valsalva sinuses VS, with the flared proximal end of the annular member  20   a  forming the proximal entrance of the lumen defined by the armature  2  of the prosthesis  1 . In the illustrated embodiment, the anchor members  22  can be arranged in three pairs positioned relative to the sinuses of Valsalva such that the radially projecting portion of each of the anchor members  22  projects into the respective sinus of Valsalva and engages the aortic wall therein. As further shown, the anchor members  22  of each pair can be positioned on opposite sides of the coronary ostia CO in the respective sinuses of Valsalva. Additionally, as discussed above and shown in  FIGS. 8 and 9 , the serpentine or otherwise generally apertured structure of the anchor members  22  substantially avoids interference with the coronary ostia CO. Finally, as can be seen from  FIGS. 8 and 9 , the valve leaflets  3   a ,  3   b ,  3   c  can be positioned within the lumen for blood flow formed by the annular elements  20   a ,  20   b , with the support members  24  extending into the lumen by a minimal amount. 
     The armature  2  of the prosthesis  1 , according to one embodiment, is manufactured by first cutting a blank part from a tube of a biocompatible metal (e.g., Nitinol, or a cobaltum-chromium alloy) having an outer diameter which is at an intermediate size between the fully radially contracted and the fully expanded device dimensions. For example, the tube may have an outer diameter of between about 8 mm to about 14 mm. In one embodiment, the tube has a diameter of about 10 mm. In one embodiment, the tube wall may vary between about 0.3 mm to about 0.5 mm, depending on the required stiffness required and the size of the prosthesis  1 . 
     In one embodiment, the final dimension and shape of the framework is achieved by a sequence of expansion cycles. A specific heat treatment is applied after each expansion cycle to homogenize and stress relieve the material, which allows the shape and properties of the structure of the armature  2  to be set. Although the number of forming steps may vary among devices, for the geometries described above with respect to the present invention, and using Nitinol for the tube blank, an exemplary number of forming steps is around three. Among these steps, the first two provide the final diameter of the annular elements  20   a ,  20   b . For example, if the fully-expanded diameter for implantation is 23 mm, the final cylindrical shape of the armature  2  can be achieved using a tube blank of about 10 mm in diameter, a first expansion from about 10 mm to about 18 mm, and a second expansion from about 18 mm to about 23 mm. Optionally, the final diameter can be made slightly larger (e.g. about 25 mm in the previous example) in order to oversize the armature  2  with respect to the physiological annulus, thus imparting a radial force to the wall of the annulus at the nominal implant diameter. 
     The third forming step is aimed to impart the radially extending shape of the anchor members  22  such that they will fit and anchor within the Valsalva sinuses. The corresponding heat treatment, according to one embodiment, includes exposing the deformed armature  2  to a temperature from about 480° C. to about 550° C., for a time ranging from about 5 minutes to about 30 minutes, depending on the desired final transformation temperature. For example, in order to obtain a super-elastic behavior at 37° C. (the normal working condition in human body) the heat treatments subsequent to the two initial expansion steps may be performed at about 480° C. for a time of about 9 minutes, and the final heat treatment (after the third expansion) is performed at about 500° C. for a time of about 9 minutes. 
     After the forming process is complete, the armature  2  may undergo one or more surface treatments, for example, sandblasting and electropolishing, to provide a sufficiently smooth surface and to remove the shallow defects. The armature  2  may thereafter be finally exposed to a carbon coating process in order to improve its hemocompatibility. 
     As shown in  FIGS. 8-9 , for an aortic valve replacement, the final geometrical shape of the armature  2  will generally approximate the physiological shape and dimension of the aortic root, such that the anchor members  22  generally conform to the walls of the respective Valsalva sinuses VS. 
       FIG. 10  shows a schematic cross sectional view of an implantation site for an aortic valve replacement. Referring to  FIG. 10 , exemplary proportions of the relevant features at the implantation site for an aortic valve replacement are as follows (assuming the annulus diameter D imp  (implanting diameter) equal to 1): 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Approximate 
                 Approximate 
               
               
                   
                   
                 Minimum 
                 Maximum 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Height of Valsalva 
                 0.8 
                 1 
               
               
                   
                 sinuses (H): 
                   
                   
               
               
                   
                 Max. diameter of 
                 1.3 
                 1.7 
               
               
                   
                 Valsalva sinuses 
                   
                   
               
               
                   
                 (Dmax): 
                   
                   
               
               
                   
                 Distance between 
                 0.3 
                 0.5 
               
               
                   
                 Valsalva max. 
                   
                   
               
               
                   
                 diameter and 
                   
                   
               
               
                   
                 basic annulus 
                   
                   
               
               
                   
                 plane (Hmax): 
                   
                   
               
               
                   
                 Diameter at the 
                 0.8 
                 1.4 
               
               
                   
                 sino-tubular 
                   
                   
               
               
                   
                 junction (Dstj): 
               
               
                   
                   
               
            
           
         
       
     
     According to one exemplary embodiment, H is about 0.9, Dmax is about 1.5, Hmax is about 0.35, and Dstj is about 1.2. 
     The commissural points of the elastic collapsible valve  3  are mounted to the armature  2  (e.g., by attachment to the support members  24 ) such that the valve leaflets  3   a ,  3   b , and  3   c  can fold and expand together. The valve  3 , including the valve leaflets  3   a ,  3   b ,  3   c , can be, for example, a glutaraldehyde fixed pericardium valve which has three cusps that open distally to permit unidirectional blood flow. 
     In one embodiment, the valve member may use two pericardium sheets. The first sheet forms the three moving cusps, the second sheet coats part of the armature  2  surface so that there is no contact between the armature  2  and the valve leaflets avoiding the risk of abrasion due to repeated impact against the metallic material of the armature  2 . In addition, this second sheet redistributes the stress applied by blood pressure on the prosthetic leaflets, avoiding the risk of stress concentration. 
     The two sheets of pericardium may be stitched together flat using suture thread coated with a film of biocompatible material, and then close in a cylindrical shape. The type of stitch used may be varied to accommodate the directional differences in the forces exerted at each point of the suture, to ensure that the stitches themselves don&#39;t become the origin of fatigue fracture lines. The two sheets may be stitched together in a flat position so when the leaflets open they recover their original cylindrical configuration, forming a cylindrical duct. 
     The elastically collapsible valve sleeve  3  can be mounted on the armature  2  by means of a number of suture stitches. Both of the sheets are useful for attaching the valve sleeve  3  to the armature  2  by stitching. 
     The valve member can use a tissue fixation and shaping of the leaflets  3   a ,  3   b ,  3   c  by means of a fluidic, atraumatic system with chemicals useful for cross-linking and then may be exposed to a detoxification post treatment to increase long-term performance. An additional pericardium sheet corresponding to base portion  30  of the valve sleeve  3  can be positioned in a generally cylindrical fashion around the annular element  20   a  so as to improve the sealing capability of the prosthesis  1  to the valve annulus. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.