Patent Abstract:
Improved, adaptable tissue-type heart valves and methods for their manufacture are disclosed wherein a dimensionally stable, pre-aligned tissue leaflet subassembly is formed and its peripheral edge clamped between and attached to an upper shaped wireform and a lower support stent. A variety of adaptable structural interfaces including suture rings, flanges, and conduits may be attached to the support stent with or without an outlet conduit disposed about the wireform to provide a tissue-type heart valve adaptable for use in either a natural heart or in mechanical pumping devices. The methods include forming individual leaflets with a template and using the template to attach the leaflets together to form a tissue leaflet subassembly. The template and leaflets include a straight edge terminating in oppositely directed tabs, and a curvilinear cusp edge extending opposite the straight edge. The template may include a guide slot in its straight edge and the assembly includes aligning two leaflet tabs with the template and passing sutures through the guide slot and through the leaflet tabs. The leaflet subassembly is mated to a wireform with the tabs extending through commissure posts of the wireform. A support stent having an upper surface matching the lower surface of the wireform sandwiches the edges of the leaflet subassembly therebetween. Separated tabs on the leaflet subassembly are passed through the wireform commissures and attached to adjacent stent commissures so as to induce clamping of the leaflet tabs between the stent commissures and wireform commissures upon a radially inward force being applied to the leaflets.

Full Description:
RELATED APPLICATIONS 
     The present application is a division of U.S. application Ser. No. 09/264,801, filed Mar. 9, 1999, entitled “Methods of Tissue Heart Assembly,” now U.S. Pat. No. 6,102,944, which is a continuation of U.S. application Ser. No. 08/826,408, filed Mar. 27, 1997, entitled “Tissue Heart Valves with Subassemblies,” now issued as U.S. Pat. No. 5,928,281. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to tissue-type prosthetic heart valves and in particular to stents used in the fabrication of such valves. 
     BACKGROUND OF THE INVENTION 
     Prosthetic heart valves are used to replace damaged or diseased heart valves. In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary valves. Prosthetic heart valves can be used to replace any of these naturally occurring valves. Two primary types of heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a pivoting mechanical closure to provide unidirectional blood flow. The other is a tissue-type or “bioprosthetic” valve which is constructed with natural-tissue valve leaflets which function much like a natural human heart valve, imitating the natural action of the flexible heart valve leaflets which seal against each other or coapt between adjacent tissue junctions known as commissures. Each type of prosthetic valve has its own attendant advantages and drawbacks. 
     Operating much like a rigid mechanical check valve, mechanical heart valves are robust and long lived but require that valve implant patients utilize blood thinners for the rest of their lives to prevent clotting. They also generate a clicking noise when the mechanical closure seats against the associated valve structure at each beat of the heart. In contrast, tissue-type valve leaflets are flexible, silent, and do not require the use of blood thinners. However, naturally occurring processes within the human body may attack and stiffen or “calcify” the tissue leaflets of the valve over time, particularly at high-stress areas of the valve such as at the commissure junctions between the valve leaflets and at the peripheral leaflet attachment points or “cusps” at the outer edge of each leaflet. Further, the valves are subject to stresses from constant mechanical operation within the body. Accordingly, the valves wear out over time and need to be replaced. Tissue-type heart valves are also considerably more difficult and time consuming to manufacture. 
     Though both mechanical-type and tissue-type heart valves must be manufactured to exacting standards and tolerances in order to function for years within the dynamic environment of a living patient&#39;s heart, mechanical-type replacement valves can be mass produced by utilizing mechanized processes and standardized parts. In contrast, highly trained and skilled assembly workers make tissue-type prosthetic valves by hand. Typically, tissue-type prosthetic valves are constructed by sewing two or three flexible natural tissue-leaflets to a generally circular supporting wire frame or stent. The wire frame or stent is constructed to provide a dimensionally stable support structure for the valve leaflets which imparts a certain degree of controlled flexibility to reduce stress on the leaflet tissue during valve closure. A biocompatible cloth covering on the wire frame or stent provides sewing attachment points for the leaflet commissures and cusps. Similarly, a cloth covered suture ring can be attached to the wire frame or stent to provide an attachment site for sewing the valve structure in position within the patient&#39;s heart during a surgical valve replacement procedure. 
     With over fifteen years of clinical experience supporting their utilization, tissue-type prosthetic heart valves have proven to be an unqualified success. Recently their use has been proposed in conjunction with mechanical artificial hearts and mechanical left ventricular assist devices (LVADs) in order to reduce damage to blood cells and the associated risk of clotting without using blood thinners. Accordingly, a need is developing for a tissue-type prosthetic heart valve that can be adapted for use in conjunction with such mechanical pumping systems. This developing need for adaptability has highlighted one of the drawbacks associated with tissue-type valves—namely, the time consuming and laborious hand-made assembly process. In order to provide consistent, high-quality tissue-type heart valves having stable, functional valve leaflets, highly skilled and highly experienced assembly personnel must meticulously wrap and sew each leaflet, and valve component into an approved, dimensionally appropriate valve assembly. Because of variations in tissue thickness, compliance and stitching, each completed valve assembly must be fine tuned using additional hand-crafted techniques to ensure proper coaptation and functional longevity of the valve leaflets. As a result, new challenges are being placed upon the manufacturers of tissue-type prosthetic valves in order to meet the increasing demand and the increasing range of uses for these invaluable devices. 
     Accordingly, consistent with the developing practice of the medical profession, there is a continuing need for improved tissue-type prosthetic heart valves which incorporate the lessons learned in clinical experience, particularly the reduction of stress on the valve leaflets while maintaining desirable structural and functional features. Additionally, there is a growing need for improved tissue-type prosthetic heart valves which can be adapted for use in a variety of positions within the natural heart or in mechanical pumps, such as artificial hearts or ventricular assist devices, as well as alternative locations in the circulatory system. Further, in order to address growing demand for these devices, there is a need for tissue-type heart valves that are simpler and easier to manufacture in a more consistent manner than are existing valves. 
     SUMMARY OF THE INVENTION 
     Directed to achieving the foregoing objective and to remedying the problems in the prior art, disclosed herein are novel tissue heart valve constructions and components thereof, and simplified methods of fabricating the same. The improved tissue heart valves of the present invention are fabricated to include standardized leaflet structure subassemblies that can be modified readily to adapt to different intended applications. Of equal importance, the leaflet structure subassemblies uniformly distribute tensile loads along the entire peripheral leaflet cusp, reducing stress points and significantly improving the long-term functionality of the valve assembly. As an added benefit of the present invention, the stability and adaptability of the tissue valve subassembly is achieved through simplified manufacturing processes utilizing fewer steps and subassemblies. This manufacturing protocol can be incorporated into branched, adaptable manufacturing techniques for the production of tissue heart valves having a variety of end uses. Further, these improved construction techniques expedite the overall manufacturing process and improve the consistency of the tissue valves so produced while simultaneously reducing the need for post-assembly fine tuning and quality-control procedures. 
     According to one aspect of the present invention, a tissue-type heart valve includes a dimensionally stable, pre-aligned tissue leaflet subassembly, a generally circular wireform, and a generally circular support stent. The wireform has a bottom surface dimensioned to receive the pre-aligned tissue leaflet subassembly in fixed, mating engagement. The support stent has an upper surface dimensioned to seat and fix in meeting engagement with the pre-aligned tissue leaflet subassembly which is fixedly disposed in mating engagement with the bottom surface of the wireform. 
     Pursuant to this construction, an exemplary tissue valve includes a plurality of tissue leaflets that are templated and attached together at their tips to form a dimensionally stable and dimensionally consistent coapting leaflet subassembly. Then, in what is essentially a single process, each of the leaflets of the subassembly is aligned with and individually sewn to a cloth-covered wireform, from the tip of one wireform commissure uniformly, around the leaflet cusp perimeter, to the tip of an adjacent wireform commissure. As a result, the sewed sutures act like similarly aligned staples, all of which equally take the loading force acting along the entire cusp of each of the pre-aligned, coapting leaflets. The resulting tissue-wireform structural assembly thereby formed reduces stress and potential fatigue at the leaflet suture interface by distributing stress evenly over the entire leaflet cusp from commissure to commissure. This improved, dimensionally stable, reduced-stress assembly is operatively attached to the top of a previously prepared cloth-covered stent to clamp the tissue leaflet cusps on a load-distributing cloth seat formed by the top of the cloth-covered stent without distorting the leaflets or disturbing their relative alignment and the resultant coaptation of their mating edges. 
     The stent is secured to the assembly with the commissures of the stent extending up into the corresponding commissures of the leaflet, wireform assembly. The stent itself can be formed of an inner polyester film support secured to a surgically acceptable metal ring such as an Elgiloy™ metal stiffener having a cloth cover cut, folded and sewn around the support and stiffener combination. Alternatively, instead of having an Elgiloy outer band and a laminated polyester film support, the two stent layers can both be polyester layers or a single piece stent having appropriately flexible commissure posts. Either stent construction provides support and dimensional stability for the valve structure extending from commissure to commissure and being evenly distributed around each leaflet. This assembly methodology allows the evenly sutured tissue of the leaflet cusps to be sandwiched between the wireform and the stent and to thereby further distribute the loading forces more evenly around the attachment site. Because the tissue leaflets experience lower, more evenly distributed stresses during operation, they are less likely to experience distortion in use. Thus, a more stable, long lived, functional closure or coaptation of the leaflets is provided by this even distribution of attachment forces. 
     A number of additional advantages result from the present invention and the stent construction utilized therein. For example, for each key area of the stent, the flexibility can be optimized or customized. If desired, the coapting tissue leaflet commissures can be made more or less flexible to allow for more or less deflection to relieve stresses on the tissue at closing or to fine tune the operation of the valve. Similarly, the base radial stiffness of the overall valve structure can be increased or decreased to preserve the roundness and shape of the valve. 
     Unlike a rigid mechanical valve, the stent does not act as a rigid heart valve structure but as a radially stable, yet axially flexible support. A rigid structure is unnecessary by utilizing the teachings of the present invention because the valve leaflets are dimensionally pre-aligned along their mutually coapting mating or sealing edges prior to being directly attached to the base of the cloth-covered wireform. As a result, the entire sealing aspect of the valve can be aligned in three dimensions at once without the variability previously experienced in the construction of prior art tissue-type valves. In addition to eliminating the need for post-assembly adjustment, this pre-alignment provides for consistency and simplicity in the manufacture of the valve structure. Further, the wire form functions as a template for suturing the leaflet cusps to the valve subassembly with uniform stitching from commissure tip to commissure tip. This produces a dimensionally consistent structure that can interface with the stent in a previously unobtainable uniform manner. The consistent dimensional integrity of the leaflet wireform subassembly enables the stent to function as a stress relieving support clamp which further secures the leaflet cusps in the valve structure to provide an added degree of stability and stress distribution. If desired, providing the top of the stent with a single or double fold of covering cloth provides the stent lip with a deformable cloth seat that assists in the distribution of load around the leaflet cusps and simplifies sewing the stent to the tissue leaflet wireform subassembly. Those skilled in the art will appreciate that attaching the stent to the tissue leaflet wireform functions to stabilize the projecting commissure posts of the valve subassembly without stiffening their desirable axial flexibility. This novel construction technique eliminates the need for separate commissure posts at the tissue leaflet commissures and also eliminates multiple tissue and cloth layers at the wireform commissure posts which adds to uniformity and consistency in valve production and eliminates assembly steps. As a result, valve manufacture is not only improved, but also simplified and expedited as well. 
     The stent also functions as an adaptable structural interface, allowing the tissue-wireform-stent structural subassembly to be attached to a variety of additional structures dependent upon intended valve placement and operating environments. For example, with the supporting stent secured to the tissue-wireform structural assembly, the resulting valve assembly can be attached to, for example, a suture ring, a flange or a conduit depending on the desired valve application. To form a conduit valve, the suture ring can be attached directly to the inflow or base of the stent to enable the implanting surgeon to sew the valve in place within the heart. Alternatively, when the valve is to be used for artificial hearts or for left ventricular assist devices (LVADs), a more rigid flange can be attached to the stent inflow to function as a mechanical mount. In some circumstances it may be desirable to form a conduit valve wherein flexible or rigid conduits are required to replace a missing portion of a patient&#39;s aorta or to interface with an artificial blood pumping device. In such circumstances, an inlet conduit may be attached to the stent inflow and, if desired, a corresponding outflow conduit can be attached inside or outside of the valve wireform. Unlike prior art tissue heart valves, the present invention provides this flexibility and adaptability of use because key valve components can be standardized for different types of valves or valve applications. This manufacturing and structural consistency also improves quality control and provides repeatability and consistency in the formation of the valves. It also simplifies final assembly that in turn provides for increased production rates without sacrificing consistent product quality. 
     More specifically, as part of the flexibility of the present invention, the stent is designed to be adaptable so that different ways of attaching the valve to its various intended applications can be accommodated. The novel construction that allows for this universal application results from the stent providing a complete uniform support to the dimensionally stable, pre-aligned wireform/leaflet subassembly. Because of this adaptability, the valve of the present invention can function in a variety of applications, including that of a temporary heart valve prosthesis within a circulatory support system using a relatively rigid flange or a conduit assembly rather than a standard soft sewing ring. Alternatively, the present invention can function as a prosthetic valve having a soft, scallop-shaped sewing ring for aortic positioning or a soft flat sewing ring for mitral positioning, or as a conduit valve by incorporating proximal and distal conduits attached on both the inflow and outflow valve ends. The outflow conduit can have a sinus shape to improve blood flow if desired. Within an artificial heart system, the valve of the present invention mimics the hemodynamic pumping action of the heart while sustaining the patient until a donor heart is located and successfully transplanted. In this application, both blood inflow and outflow functions can be accommodated by the present invention. 
     Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an exemplary heart valve of the present invention illustrating the assembly relationship of the standardized components and alternative valve attachment application structures; 
     FIG. 2 is a perspective view illustrating the step of templating and trimming exemplary leaflets used in making a tissue heart valve of the present invention; 
     FIG. 3 illustrates the initial steps of templating and pre-aligning the leaflets of the valve subassembly; 
     FIG. 4 shows additional steps in the pre-alignment of the valve leaflet subassembly; 
     FIG. 5 is an enlarged view illustrating an exemplary attachment step of the pre-aligned leaflets to a wireform commissure tip; 
     FIG. 6 is a perspective view illustrating the subsequent preliminary attachment of the exemplary leaflet cusps to the wireform of FIG. 5; 
     FIG. 7 is a perspective view illustrating the. uniform attachment of the perimeter cusps of leaflets to the cloth covered wireform; 
     FIG. 8 is an enlarged view of one of the pairs of attached leaflet tabs of FIG. 7 illustrating the uniform attachment of the cusps to the wireform commissure tip; 
     FIG. 9 is a perspective view illustrating the attachment of the exemplary tissue leaflet-wireform structural subassembly to an exemplary stent of the present invention; 
     FIG. 10 is an enlarged view of one of the pairs of leaflet tabs of FIG. 9 illustrating a further attachment step of the stent to the wireform at the commissure tip, clamping the leaflet cusps therebetween; 
     FIG. 11 is an enlarged view of one of the commissure tips of the tissue-wireform structural assembly of FIG. 10 illustrating the clamping of the leaflets by the stent; 
     FIG. 12 is a perspective view illustrating a final attachment step of the exemplary tissue-wireform structural assembly to the stent; 
     FIG. 13 is an enlarged view taken on circle  13  of FIG. 12 illustrating additional exemplary attachment techniques; 
     FIG. 14 is an enlarged view taken on circle  14  of FIG. 12 illustrating additional exemplary attachment techniques; 
     FIG. 15 is a perspective view illustrating an exemplary attachment step of the tissue leaflet tabs at the commissure tip; 
     FIG. 16 is a view similar to FIG. 15 illustrating an alternative attachment step; 
     FIG. 17 is an exploded perspective view illustrating an exemplary multi-piece stent formed of a flexible support and an associated stiffener of the present invention; 
     FIG. 18 is a perspective view illustrating the attachment of the support to the stiffener of FIG. 17; 
     FIG. 19 is a perspective view illustrating an initial step in the covering of the stent components of FIG. 18 with cloth; 
     FIG. 20 is an enlarged view of the top of FIG. 19 illustrating additional steps in the attachment of the cloth to the stent components; 
     FIG. 21 is a perspective view illustrating additional steps of fabricating sewing tabs for attaching the cloth to the stent components; 
     FIG. 22 is an enlarged view of a portion of FIG. 20 illustrating subsequent fabrication steps; 
     FIG. 23 is an enlarged cross-sectional view taken on line  23 — 23  of FIG. 22; 
     FIG. 24 is a view similar to FIG. 22 illustrating additional fabrication steps; 
     FIG. 25 is a perspective view of the cloth-covered stent of FIG. 18 illustrating the cloth seating lip; 
     FIG. 26 is an enlarged cross-sectional view on line  26 — 26  of FIG. 25 illustrating additional aspects of the fabrication of the exemplary stent assembly; 
     FIG. 27 is a perspective view illustrating initial components of an exemplary suture ring of the present invention; 
     FIG. 28 is an enlarged cross-sectional view illustrating aspects of the fabrication of the exemplary suture ring; 
     FIG. 29 is a perspective view illustrating additional features of the exemplary suture ring assembly; 
     FIG. 30 is an enlarged sectional view of a portion of FIG. 29 illustrating additional aspects of the fabrication of the suture ring assembly; 
     FIG. 31 is an enlarged sectional view illustrating additional aspects of the finished exemplary suture ring assembly; 
     FIG. 32 is an exploded perspective view illustrating positioning and assembly of a suture ring and leaflet subassembly configuration; 
     FIG. 33 is a top perspective view illustrating additional suture ring leaflet subassembly attachment steps; 
     FIG. 34 is a bottom perspective view illustrating further exemplary suture ring attachment steps; 
     FIG. 35 is a cutaway perspective view illustrating an exemplary attachment of an outflow conduit to an exemplary valve of the present invention; 
     FIG. 36 is an enlarged cross-sectional view illustrating additional aspects of the conduit attachment; 
     FIG. 37 is a cross sectional view similar to FIG. 36 illustrating alternative conduit attachment features; and 
     FIG. 38 is an exploded perspective view illustrating additional valve attachment alternatives of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring more particularly to the drawings, FIG. 1 is an exploded assembly view, illustrating exemplary alternative embodiments of an improved, adaptable tissue valve  50 , its individual components and its alternative configurations produced in accordance with the teachings of the present invention. Valve  50  includes a pre-aligned, standardized leaflet subassembly  52 , a cloth-covered wireform  54  and a support stent  56 . As will be discussed in detail below, during assembly of valve  50 , the pre-aligned leaflet subassembly  52  and the cloth-covered wireform  54  are first assembled in accordance with the present invention to form a tissue-wireform structural assembly  58  (see FIGS. 2 to  9 ). Then, the structural assembly  58  is secured to stent  56  to form the assembled valve  50 . 
     As illustrated FIG. 1, valve  50  is uniquely configured to enable production of several useful alternative valves for a variety of end-use applications. For example, if the desired application is the replacement of a native heart valve, valve  50  can be attached to a relatively soft suture ring  60  for subsequent sewing into place within a heart (not shown). Alternatively, if it is desired to use valve  50  in a left ventricular assist device (LVAD) or in a mechanical heart pump, valve  50  can be mounted to an appropriately rigid mechanical flange  62 . Further, in both natural and mechanical applications where it is desirable to incorporate a conduit, valve  50  may be attached to either an inflow conduit  64  and/or an outflow conduit  66 . 
     Production of the Tissue-Wireform Structural Assembly 
     In the present disclosure, exemplary valve  50  is illustrated as a three-leaflet or tricuspid valve. However, it will be appreciated by those skilled in the art that valve  50  may be configured to have two leaflets or any other desired leaflet configuration depending on the intended application. 
     A first step in the assembly of tissue valve  50  is the attachment of tissue leaflets  68  to one another to form a consistently dimensioned, standardized leaflet subassembly. Tissue leaflets are typically formed from pericardial, porcine or similar tissue obtained from donor organs, which tissue is preserved or “fixed” prior to use in assembling a valve. Those skilled in the art will appreciate that the dimensions of leaflet subassembly  52  will vary depending upon the intended end use and associated positioning and dimensional requirements of the finished valve. However, pre-alignment and stitching in accordance with the teachings of the present invention not only simplifies the manufacture of valve  50  but also functions to align the entire valve mating or seating surfaces at once. This eliminates variations in leaflet alignment and dimensional relationships and significantly minimizes the need to adjust the tissue leaflets after final assembly of the valve in order to ensure proper coaptation at the mating edges of the leaflets. 
     Referring now to FIG. 2, the desired number of tissue leaflets  68  (in this example, three leaflets) are obtained from natural tissue as known in the art, and each leaflet  68  is trimmed to the appropriate desired shape and size for the intended valve use using template  69 , defining a generally straight or linear coapting mating edge  70  having opposing ends  71 ,  72  and a generally arcuate peripheral cusp  73  extending therebetween. More particularly, each leaflet  68  is placed on a cutting board  74  and the selected template  69  is then placed over the leaflet  68 . Tissue  75  extending beyond the boundaries of template  69  is then cut away using a sharp razor blade  76  or similar cutting tool. 
     A characteristic of pericardial tissue is that one surface is smoother than the opposite surface. Accordingly, it is desirable that the less smooth surface be identified to serve as the mating surface at edge  70  with an adjacent leaflet edge  70 . After the leaflets  68  are trimmed and the mating surfaces identified, two of the leaflets  68   a ,  68   b  are pre-aligned or mated together along with template  69  as shown in FIG.  3 . The two leaflets  68   a ,  68   b  are then attached or stitched together at one end  71  to define the first in a plurality of pairs of aligned, mating leaflet ends. For example, a needle that has been “double-threaded,” that is, needle  78  that has been threaded with a looped (or “folded”) segment of thread  80  is inserted and pushed through the leaflets  68   a ,  68   b  at the location dictated by guide slot  82  at one end of template  69 . Template  69  may then be removed, with needle  78  being brought over the top of leaflets  68   a ,  68   b  and passed back through the loop and pulled tightly. Naturally, alternative attachment methods or stitches may be utilized within the scope and teaching of the present invention. The opposite ends  72  of the first two leaflets  68   a ,  68   b  of the exemplary three leaflet valve are not sewn together at this time. 
     Referring now to FIG. 4, a third leaflet  68   c  is pre-aligned and attached to the other two leaflets  68   a ,  68   b  in a tricuspid format, again using template  69 . In particular, third leaflet  68   c  is mated with template  69 , and the respective unsewn ends  72  of the first two leaflets  68   a ,  68   b  are spread out and then aligned with the respective opposite ends  71 ,  72  of templated third leaflet  68   c . Again using guide slot  82  of the template  69  as a guide, a double-threaded needle with thread  80  is inserted through each of the unsewn pairs of the three leaflets  68   a ,  68   b ,  68   c  to secure the leaflet ends together in pairs as shown. The template may then be removed, and, for each stitch, needle  78  may be brought over the top of leaflets  68   a ,  68   b ,  68   c  and passed back through the loop and pulled tightly to produce leaflet subassembly  52  having three leaflet mating ends. 
     Referring now to FIGS. 5 and 6, it is preferred to attach leaflet subassembly  52  to the underside or bottom  83  of wireform  54 . Exemplary wireform  54  is a wire reinforced cloth having a cloth edge  84  and is shaped in a manner substantially conforming to the shape of the leaflet subassembly structure  52 . In the embodiment shown, wireform  54  is generally circular in shape and has a sinusoidal undulation defining a plurality of commissure tips  86  corresponding to the pairs of leaflet mating ends. The cloth of wireform  54  includes the circumferential cloth edge  84  that serves as a sewing or attachment surface for the leaflet subassembly  52 . Exemplary wireform  54  includes the three raised commissure tips  86  which receive the three respective pairs of attached mating ends of leaflets  68   a, b , and  c  of the pre-aligned leaflet subassembly  52 . 
     An exemplary technique for attaching the leaflet pairs at an end of the leaflet subassembly  52  to one of the commissure tips  86  of wireform  54  is shown in FIG.  5 . Needle  78  (not shown) with looped thread  80 , which was used to sew the leaflet ends together, is inserted up from leaflets  68  (as shown in dashed lines), through an inner edge of cloth edge  84  as indicated at  87 , so that the top surfaces of mating leaflets  68  are secured into contact with wireform  54 . The needle is then re-inserted through an outer edge of and from underneath cloth edge  84  as indicated at  88 ′, and a first lock  89 , preferably a single lock stitch, is made with thread  80 . The locking process can be repeated as indicated at  88 ″ with a second lock  90 , preferably a double lock stitch. Finally, the needle can be inserted into the middle of and from underneath cloth edge  84  as indicated at  91  and the thread pulled so that first and second locks  89 ,  90  are pulled underneath cloth edge  84  and thereby hidden and protected during the remaining fabrication process. The excess thread is then trimmed and discarded. This method is repeated for securing each of the respective pairs of attached, aligned mating leaflet ends of mated leaflets  68   a ,  68   b ,  68   c  of subassembly  52  to the respective commissure tips  86  of wireform  54 . Thus, wireform  54  functions as an additional, permanent template for positioning the leaflet commissures in their final position relative to one another. As an added benefit of the present invention, this manufacturing technique further stabilizes the position of the coapting valve leaflets relative to one another prior to attachment of the leaflet cusps to the wireform. Thus, it is possible to attach the entire peripheral leaflet cusp uniformly from the tip of one commissure to the next in order to produce consistent attachment stress along the leaflet edge. 
     Referring now to FIGS. 6 and 7, the next exemplary step for securing the exemplary leaflet subassembly  52  to wireform  54  is to attach peripheral cusps  92  of each of the leaflets  68  to cloth edge  84 . In that connection, slip knots  94  (i.e., knots that may be undone) are spaced periodically along wireform  54  to temporarily fit leaflet cusps  92  in position on wireform  54 . Three of the slip knots  94  may be made for each leaflet cusp  92 , with one at the center of the cusp and two at points of inflection with the commissures, as this helps to uniformly stabilize the cusp in position during attachment to wireform  54 . 
     As shown in FIGS. 7 and 8, temporarily secured leaflet cusps  92  then are attached to wireform cloth edge  84 , preferably using double-threaded “in-and-out” sutures  96 , starting from a center position  98  of each leaflet cusp  92  and running to the tips of each commissure  86 . At about one millimeter from the commissure tips  86 , the threads are locked, buried and trimmed, preferably as described previously. Thus, unlike prior art tissue valves wherein leaflets are attached individually and the peripheral stitching of the cusps terminates before the tips of the commissures, producing a potential stress point, the method of the present invention produces a novel tissue valve assembly having uniform stitching from commissure tip to commissure tip and consistently aligned coapting leaflet mating edges. 
     Attachment of the Tissue-Wireform Structural Assembly to a Support Stent 
     For purposes of further explanation, once the assembled tissue-wireform structural assembly, which is identified by reference numeral  58 , is produced as discussed above, the assembly  58  is then attached to a support or stent  56 . Referring to FIGS. 9,  10 , and  11 , the tissue-wireform structural assembly  58  is first fitted onto the correspondingly configured stent  56  in a manner that will uniformly clamp the peripheral cusp edges of the leaflets  68  between an upper surface  99  (see FIG. 1) of stent  56  and the lower surface of wireform  54 . This assembly technique further distributes stresses and loads of the leaflets  68  and contributes to their functional longevity. Moreover, pre-alignment of the leaflets  68  and attachment to the wireform  54  enables the dimensions of the entire valve  50  to be aligned at once and eliminates the dimensional variation that could occur in prior art valves due to the utilization of separate commissure posts. In particular, stent  56  is dimensioned to mate or seat with the configuration of assembly  58 , and assembly  58  is mated to stent  56  such that the lower surface of each commissure tip  86  of wireform  54  mates with the top surface of a corresponding and complementary stent commissure tip  100 . Care is taken to ensure that central opening  102  formed by coapting mating leaflets  68  is not distorted while mating tissue-wireform structural assembly  58  to stent  56 . Similarly, care is taken to ensure that leaflets  68  are uniformly clamped and remain evenly tensioned throughout this process. 
     Once wireform assembly  58  is mated to stent  56 , a temporary pin  104  can be inserted at the bottom curve of each leaflet cusp  92  to temporarily secure wireform assembly  58  to stent  56 . Stent  56  and assembly  58  then are sutured together as shown in FIGS. 10 and 11. Suturing of assembly  58  to stent  56  begins at the tops of the commissure tips  86 . In particular, a double-threaded needle (not shown) is inserted through stent commissure tip  100  as indicated at  105 ′, between free tab ends  106 ,  108  of adjacent pairs of leaflets  68 , and through cloth edge  84  of wireform assembly  58  as indicated at  109 ″. The needle is then inserted through the looped thread to form a single lock  110 . A double lock  112  is then formed, with the needle being inserted through stent commissure tip at  105 ″ and through cloth edge  84  at  109 ″, substantially in the manner previously discussed so that double lock  112  is able to be pulled underneath cloth edge  84 . Excess thread exiting from cloth edge  84  as indicated at  113  may then be trimmed and discarded. The identical procedure may be performed for the remaining commissure tips  86  of the wireform assembly  58 . As a result, wireform commissure tips  86  evenly match with stent commissure tips  100 . 
     With reference to FIGS.  9  and  12 - 14 , the exemplary attachment procedure can be completed by inserting a double-threaded needle as previously described through stent  56  near the top of stent commissure tip  100  as indicated at  114 ′, through tissue leaflet  68  and through cloth edge  84  of wireform  54  as indicated at  115 ′. The needle is then re-inserted in a reverse manner through cloth edge at  115 ″, through stent commissure tip  100  at  114 ″ and passed through loop  115  of the double thread. With reference to FIG. 14, the suture is then tightened so that loop  115  is positioned securely and firmly against stent commissure tip  100 . In-and-out suturing  116  (see also FIGS. 15 and 16) is then performed along the mating edges of stent  56  and wireform assembly  58  up to the next wire form assembly and stent commissure tips  86 ,  100 . With reference to FIG. 13, at a position near the top of the commissure tip  86 , a single lock  118  and a double lock  120  can be formed, and the thread can be buried beneath cloth edge  84  of wireform assembly  58  as described previously. It will be appreciated that the suturing just described may be initiated at any of the stent commissure tips  100  and that the in-and-out suturing  116  may be performed in either a clockwise or a counter-clockwise manner around the periphery of stent  56 . 
     Upon completion of the in-and-out suturing  116  around the periphery of stent  56 , the free tab ends  106 ,  108  of each pair of tissue leaflets  68  need to be secured to the respective stent commissure tip  100 . Referring to FIGS. 15 and 16, two exemplary alternatives are provided to perform this task. 
     Referring to FIG. 15, a first exemplary alternative is to configure tab ends  106 ,  108  to form a butt joint  122 . In particular, tab ends  106 ,  108  are trimmed such that, when folded towards each other, the respective end edges of each tab end  106 ,  108  mate evenly to form, preferably, a straight center line descending vertically from the top of commissure tip  100 . The two leaflet tab ends  106 ,  108  are then stitched together with stitching  124 . 
     Referring to FIG. 16, a second exemplary alternative for securing leaflet tab ends  106 ,  108  is to configure tab ends  106 ,  108  to mate evenly to form a flush junction  126  with cloth edge  84  of wireform  54  on either side of commissure tip  100 . In particular, leaflet tab ends  106 ,  108  can be trimmed so that the end edges of each tab  106 ,  108  are sized to fit flush with cloth edge  84  of the wireform. Leaflet tab ends  106 ,  108  are then stitched to cloth edge  84  of wireform  54  with stitching  128  as shown. The alternative flush junction  126  so formed provides a somewhat flatter commissure than butt junction  122  of the first alternative does, and, therefore, flush junction  126  may be more desirable when a more compact valve is needed. Both exemplary methods, however, allow even and reliable distribution of the load on the tissue leaflets at the commissures. 
     Assembly of an Exemplary Stent 
     From the foregoing description, it will be appreciated that stent  56  is configured to have a structure suitable for mating and supporting wireform assembly  58 . In that connection, an exemplary structure of stent  56  will now be described with reference to FIG.  17 . Those skilled in the art will appreciate that the exemplary stent described herein is a multi-piece construction. However, it is contemplated as being within the scope of the present invention to provide a single-piece stent. However, the multi-piece stent assembly illustrated may make it easier to engineer or fine tune the radial stability of the stent while maintaining desirable axial flexibility of the commissure posts. The first step in the assembly of exemplary stent  56  is to fabricate an inner support member  130  and an outer support member  132 , which, when mated together, generally form the shape of stent  56  which ultimately conforms to the configuration of wireform assembly  58 . In the exemplary embodiments inner support member  130  is configured with three upstanding posts  134  that serve as the support structures for the stent commissure tips  100 . Outer support member  132  also may include posts  136  that correspond to the posts  134  of the inner support member  130 . However, posts  136  are truncated and therefore do not match the height of posts  134  on inner member  130 . The inner and outer support members  130 ,  132  may be fabricated from a metal or plastic material depending on the desired characteristics of valve  50 . 
     Disposed on inner support member  130  are a plurality of sewing holes  138  along the periphery of member  130  and on the posts  134 . The outer support member  132  includes at least one sewing hole  139  on each of its truncated posts  136  that correspond with respective ones of the sewing holes  138  on each post  134  of the inner member  130 . The inner diameter of outer support member  132  is sized to form a slip fit with the outer diameter of inner support member  130 . 
     Inner support member  130  is placed within outer support member  132  such that sewing holes  139  of outer support member  132  align with sewing holes  138  on the respective posts  134  of inner member  130 . The two members are then sewn together by inserting a double-threaded needle as described previously through the aligned holes  138 ,  139 . As shown in FIG. 18, thread  140  inserted through each of the aligned holes  138 ,  139  is then passed through end loop  142  and tightened. The thread may then be locked using, for example, a slip knot (not shown), which is a knot that may slide along the thread to abut the support members. Accordingly, posts  134  of inner support member  130  flex to a greater extent from base portions thereof to tops thereof, and outer support member  132  augments the radial stability of inner support member  130 , with the truncated posts  136  providing rigidity to base portions of posts  134  of inner support member  130 . 
     Referring now to FIG. 19, once the inner and outer support members  130 ,  132  are sewn together, a covering cloth  144 , preferably made from woven polyester, is cut and formed into a cylindrical tube for covering the combined support members  130 ,  132 . Those skilled in the art will appreciate that the covering cloth is equally applicable to single-piece stent assemblies. Covering cloth  144  includes two crease lines  146 ,  148 , the first of which,  146 , is formed from folding an edge of cloth  144  to form a fold which receives posts  134  of inner support member  130 . There is approximately 1 mm to 1.5 mm between first crease line  146  and a top edge  149  (see FIGS. 17 and 18) of each post  134  in the exemplary embodiment. Second crease line  148  is located such that it corresponds to a lower edge  150  (see FIG. 18) of combined support members  130 ,  132 . 
     Referring now to FIG. 20, to secure covering cloth  144  to support members  130 ,  132 , a threaded needle may be inserted through cloth  144 , through a hole  151  of one of inner member posts  134 , through the second layer of cloth  144  and then back through cloth  144  through the same hole  151  and through cloth  144 . The needle then can be passed through a loop to form a first lock  152 . This threading step may be performed up to two more times. The excess thread is then trimmed and discarded. The same procedure can be followed for each of the three posts  134  on inner support member  130 . 
     Then, as shown in FIG. 21, the next exemplary step involves stitching covering cloth  144  to inner and outer support members  130 ,  132  along an upper edge  137  of inner support member  130 . First, lower edge  154  of cloth  144  can be folded into the interior of support members  130 ,  132  along crease line  148  such that second crease line  148  defines the lower end or bottom of the support member structure. This fold results in dual-layered cloth  144  (including outer and inner cloth layers  156 ,  158 ) enveloping support members  130 ,  132 . Then, using a single threaded needle, the layered cloth is stitched together at  155  along the curvature of the upper edge  153  of support members  130 ,  132 . The stitching  155  is preferably backstitching, which is accomplished by inserting the needle a stitch length, for example, to the right and bringing it up an equal distance to the left. However, the stitching  155  does not extend to the tops . 149  of posts  134 , leaving a space of approximately 1 mm between the top  149  of post  134  and the stitching  155 . After stitching the upper edge  153  of support members  130 ,  132 , the cloth  144  then can be stitched in a similar manner at  156  along the lower edge  150  of support members  130 ,  132 . The last stitch is then locked by tying a slip knot, which may be performed up to three times to lock the stitching securely in place. 
     Referring now to FIGS. 21-26, cloth  144  as now attached to support members  130 ,  132  is trimmed to conform to the shape of support members  130 ,  132  and, if desired, to provide a gasket-like sewing edge. To accomplish this, outer cloth layer  157  can be sliced downwardly from a top edge thereof to a distance approximately 5 mm to 6 mm above the top edge  153  of inner support member  130 . In a similar manner, inner cloth layer  158  can be sliced downwardly from a top edge thereof to a distance approximately 2 mm to 3 mm above the bottom of the slice in outer cloth layer  157 . The slices are made at a location midway between adjacent posts  134  of inner member  130  and are intended to align with one another in the downward direction, as indicated at  160 . 
     Next, outer cloth layer  157  can be trimmed along the upper edge  153  of inner support member  130 , starting at the bottom of the slice formed in outer cloth layer  157 . In this exemplary embodiment of the present invention the trimming is performed in a manner such that the contour of the cloth  144  extends a distance of approximately 4 mm to 5 mm above the lower curved portions of the upper edge  153  of support member  130 , a distance of approximately 2 mm to 3 mm above portions of support member  130  in the areas at or near the base of posts  134  of support member  130  and a distance of about 0.5 mm to 2 mm above the tops  149  of posts  134  of support member  130 . 
     As shown in FIG. 22, inner cloth layer  158  is then folded over the tops  149  of posts  134  of inner member  130  and is anchored to posts  134  with a threaded needle stitched through sewing hole  151  in posts  134  in the manner previously described with respect to the upper folded section of cloth  144 . However, after these locking stitches are executed, the needle is passed under the cloth so as to exit from the top of post  134 . 
     Next, a series of trimming operations can be performed. Referring to FIGS. 22 and 23, a folded portion  162  of inner cloth layer  158  is trimmed around the entire circumference of the cloth so that lower edge  164  of folded portion  162  is approximately 1 mm to 1.5 mm from the stitch in hole  151  of post  134 . A folded portion  168  of outer cloth layer  157  is folded over the tops  149  of post  134  of inner support member  130 . Folded portion  162  of the inner cloth layer  158  is further trimmed so that its remaining edges are flush with the edges of the previously trimmed inner cloth layer  158 . With regard to the non-folded portion of inner cloth layer  158 , this layer is trimmed in a manner such that its edges extend approximately 2 mm beyond the edges of the previously trimmed outer cloth layer  157 . The 2 mm extension of the inner cloth layer  158  beyond the outer cloth layer  157  provides the material desired to form a seating and attachment or sewing surface on the stent. 
     Each of the trimming operations is performed starting from the central area between posts  134  of inner support member  130  to the tops  149  of posts  134 . The arrangements of inner cloth layer  158 , outer cloth fold  168 , outer cloth layer  157  and inner cloth fold  162  are shown in the enlarged cross-section of FIG.  23 . 
     The remaining exemplary step to complete the assembly of the stent  56  is to fold and suture the cloth layers to form a sewing edge  169  around the stent  56 . Referring to FIG. 24, inner cloth layer  158  is folded around post  134  and stitched so as to enclose post  134 . More specifically, the thread previously inserted through the top of post  134  when connecting folded outer cloth layer  157  through sewing hole  151  is now used to create first and second locks  172  on the top of post  134  so as to hold inner cloth layer  158  in place on the top of post  134 . A wipstitch  174  may then be utilized to further secure exemplary inner cloth layer  158  downwardly around post  134  approximately 8 mm from the top of post  134 . When the bottom of the post  134  is reached, first and second locks are formed, and the thread is trimmed and discarded. The above-described stitching operation is performed for each of the three posts  134 . However, for the last of the posts  134  to be stitched, instead of trimming the thread after forming the first and second locks  172 , untrimmed thread  176  can be used for performing the stitching of the cloth along the remaining edges of support members  130 ,  132  between posts  134 . 
     In that connection, with reference to FIGS. 25 and 26, inner cloth layer  158  is folded over the outer cloth layer  157 , and an alternating stitching is applied to hold the folded layers in place on the support members and thereby to form the sewing edge  169  on the stent. After completing the stitching around the remaining portions of the support members  130 ,  132 , a first and second lock stitch can be formed with the thread, and the excess thread is trimmed and discarded to complete the assembled stent  56 . 
     Assembly of an Exemplary Suture Ring 
     Where valve  50  is intended for use in the replacement of a native heart valve, a soft suture ring  60  is contemplated for use in completing the valve structure. For example, referring to FIG. 27, an exemplary ring washer  180  is provided which is preferably made from non-woven polyester, such as a material sold under the trade name REMAY manufactured by Remay, Inc., Old Hickory, Tenn. Also provided is a silicone sponge waffle annulus  182  for mating with washer  180 . In that connection, annulus  182  is configured to have a walled lip  184  configured to be disposed along the inner circumference  185  of washer  180 . Lip  184  is contoured to include three depressions  186  that correspond with the lower curved surfaces between each commissure on valve  50 . Washer  180  mounts on waffle annulus  182  such that washer  180  surrounds the walled lip  184 . This produces a soft, relatively flexible, yet stable suture ring internal structure which, when covered with cloth as discussed below, functions as a compliant, stitchable interface between the natural tissues of the heart and the prosthetic tissue valve  50 . 
     As shown in FIG. 28, before mounting washer  180  on waffle annulus  182 , a cloth  188  is positioned around washer  180  to extend from the inner circumference  185  to the outer circumference  189 . Washer  180  is then mounted on waffle annulus  182  such that cloth  188  is sandwiched between waffle annulus  182  and washer  180 . Cloth  188  is placed to extend a distance  190  of approximately 3 mm to 5 mm beyond the outer circumferential edge  189  of washer  180 , as shown in FIG.  28 . Washer  180 , cloth  188  and waffle annulus  182  are then sewn together using, for example, in-and-out suturing  192  around the circumference of washer  180 . The exemplary suturing is preferably placed a distance  194  of approximately 1 mm from the outer circumferential edge  189  of washer  180 . If desired, a second suture line (not shown) may be added at the same location as the first suture line, with each stitch of the second suture line placed between the stitches of the first suture line. The resulting suture  192  then appears as a continuous line of stitching. Additionally, as shown in FIG. 29, to further secure cloth  188  and waffle annulus  182  together, back stitching  195  may be applied in the space between the walled lip  184  of annulus  182  and washer  180 , which space is indicated at  196  in FIG.  28 . 
     Referring now to FIG. 30, cloth  188  can be attached to depressions  186  of the structural assembly of washer  180  and waffle annulus  182  with, for example, a single-threaded needle inserted at one corner  198  of depression  186  (through cloth  188  and annulus  182 ) and then with a double slip knot to secure the thread at corner  198 . In-and-out stitching  200  can be then used to secure cloth  188  to the contour of depression  186 . The same method can be followed for each depression  186 . The excess cloth is then trimmed to the outer edge of washer  180  as indicated at  201 . 
     With additional reference to FIG. 31, an outer portion  202  of cloth  188  then can be folded around the external surfaces of washer  180  and tucked under washer  180  between washer  180  and waffle annulus  182 . Because of annulus  182  is pliant, annulus  182  deforms and accommodates the outer portion  202  of cloth  188 . Using a single-threaded needle, an alternating stitch  204  can be used to secure folded cloth  188  underneath washer  180 . After completing the stitching of the entire circumference of washer  180 , a double knot can be formed to secure the stitching, yielding a finished suture ring. 
     Attachment of the Suture Ring to the Exemplary Valve 
     Referring to FIGS. 32 and 33, to attach suture ring  60  or an alternative structure such as flange  62  (see FIG. 1) to valve  50 , depressions  186  of suture ring  60  are aligned with the descending peripheral cusps  206  of valve  50  and then mated together. More specifically, valve  50  is placed on suture ring  60  such that cloth edge  84  of the wireform  58  on the lower-most portion of each cusp on valve  50  is substantially flush with a top surface of suture ring  60  at corresponding depressions  186 . Care is taken with the placement such that kinking or wrinkling of tissue leaflets  68  is avoided. Valve  50  can be temporarily pinned in place on suture ring  60  with needles  208  to facilitate this procedure. 
     As shown in FIG. 34, the assembly of pinned valve  50  and suture ring  60  can be flipped over, and suture ring  60  can be stitched to valve  50  along mating edges  209  of ring  60  and valve  50 . More specifically, in the exemplary embodiment a single threaded needle can be used to sew suture ring  60  to the cloth of the stent structure. To facilitate the stitching step, the pieces are held temporarily, yet securely in place with additional needles  208 . The opposite side of ring  60  and valve  50  can be sewn together in a similar manner. 
     Attachment of Valve to Outflow Conduit 
     Referring now to FIGS. 35-37, in certain applications, it may be desirable to attach valve  50  to an outflow conduit such as that shown at  66 . For example, in some patients requiring replacement of the aortic valve, a portion of the aorta itself may be damaged or diseased such that it needs replacement as well. Accordingly, consistent with the teachings of the present invention, the adaptable tissue valve structure can be modified to include an outflow conduit  66  that will function to replace the damaged aorta. Alternatively, in some intended mechanical pumping applications the adaptable tissue valve of the present invention may be provided with an outflow conduit to facilitate interfacing with the mechanical pumping structure. In either alternative, this can be accomplished as shown in FIGS. 35 and 36 where an outflow conduit  66  may be attached to wireform  54  at the time that the tissue leaflets  68  are being secured. In particular, referring to FIG. 36, conduit  66  may be secured on a side of wireform  54  opposite to tissue leaflets  68  by, for example, stitching. Alternatively, as shown in FIG. 37, conduit  66  may be stitched and secured to wireform  54  on the same side as tissue leaflets  68 , or sandwiched therebetween. A third option is to simply secure conduit  66  to the periphery of the finished valve (not shown) as a subsequent sewing step. The valve  50  may be attached to an outflow conduit either with or without a sinus. 
     Alternative Configurations for Inflow Side of Valve 
     FIG. 38 illustrates additional exemplary alternative options available for modification and attachment of valve  50 . For example, as discussed above, when it is desired to use valve  50  as a conduit valve, suture ring  60  may be attached to valve  50  as previously described. Alternatively, in applications such as artificial hearts or left ventricular assist devices (LVADs), suture ring  60  is not necessarily required; hence, the lower end of stent  56  may be attached to flange  62  for use in mounting the valve in the artificial heart or LVAD. 
     Yet a further alternative adaptation involves those applications where an inflow conduit  64  is desired. In such applications, inflow conduit  64  may be attached directly to stent  56  of valve  50 . More specifically, inflow conduit  64  may be configured to have a stepped circumference  210  that snugly mates with the outer periphery (or, alternatively, the inner periphery) of stent  56  and which can be sewn thereto. In this configuration, for example, in an artificial heart or an LVAD application, suture ring  60  could be attached to inflow conduit  64  rather than to valve  50 . 
     Conclusion 
     In view of the foregoing description of exemplary embodiments of valve  50  and the components thereof, the present invention satisfies the need for improved tissue-type prosthetic heart valves in which stress is reduced on valve leaflets  68  while desirable structural and functional features are maintained. Additionally, valve  50  is adaptable for use in a variety of positions within the natural heart or in mechanical pumps. Further, valve  50  is simpler and easier to manufacture in a more consistent manner than existing valves. The standardized leaflet structure subassembly  52  of the present invention can be modified readily to adapt to different intended applications. Of equal importance, leaflet subassembly  52  uniformly distributes tensile loads along the entire periphery of leaflet cusps  92 , reducing stress points and significantly improving the long-term functionality of valve  50 . As an added benefit of the present invention, the stability and adaptability of the tissue valve subassembly is achieved through simplified manufacturing processes utilizing fewer steps and subassemblies. This manufacturing protocol can be incorporated into branched, adaptable manufacturing techniques for the production of tissue heart valves having a variety of end uses. Further, these improved construction techniques expedite the overall manufacturing process and improve the consistency of valve  50  while simultaneously reducing the need for post-assembly fine tuning and quality-control procedures. 
     The plurality of tissue leaflets  68  being attached together as described form the dimensionally stable and dimensionally consistent coapting leaflet subassembly  52 . Further, sutures  96  used to attach cusps  92  to wireform  54  act like similarly aligned staples, all of which equally take the loading force acting along the entire periphery of cusp  92  of each pre-aligned, coapting leaflet  68 . The resulting tissue-wireform structural assembly  58  reduces stress and potential fatigue at the leaflet suture interface by distributing stress evenly over the entire leaflet cusp  92  from commissure to commissure. Further, tissue-wireform structural assembly  58  may be attached to cloth-covered stent  56  without disturbing leaflets  68  or disturbing their relative alignment and the resultant coaptation of their mating edges. 
     Stent  56  as fabricated according to the present invention provides evenly distributed support and dimensional stability for each leaflet  68  of the valve structure  50  from commissure to commissure. This assembly methodology allows the evenly sutured tissue of leaflet cusps  92  to be sandwiched between wireform  54  and stent  56  and to thereby further distribute the loading forces more evenly around the attachment site. Because leaflets  68  experience lower, more evenly distributed stresses during operation, leaflets  68  are less likely to experience distortion in use. Thus, a more stable, long lived, functional closure or coaptation of leaflets  68  is provided by this even distribution of attachment forces. 
     Furthermore, for each key area of stent  56 , the flexibility can be optimized or customized. If desired, the coapting tissue leaflet commissures  86  can be made more or less flexible to allow for more or less deflection to relieve stresses on the tissue at closing or to fine tune the operation of valve  50 . Similarly, the base radial stiffness of the overall valve structure can be increased or decreased to preserve the roundness and shape of valve  50 . Unlike a rigid mechanical valve, stent  56  does not act as a rigid heart valve structure but as a radially stable, yet axially flexible support. A rigid structure is unnecessary by utilizing the teachings of the present invention because leaflets  68  are dimensionally pre-aligned along their mutually coapting mating or sealing edges  70  prior to being directly attached to cloth-covered wireform  54 . As a result, the entire sealing aspect of valve  50  can be aligned in three dimensions at once without the variability previously experienced in the construction of prior art tissue-type valves. In addition to eliminating the need for post-assembly adjustment, this pre-alignment provides for consistency and simplicity in the manufacture of valve  50 . Further, wireform  54  functions as a template for suturing leaflet cusps  92  to the valve subassembly with uniform stitching from commissure tip  86  to commissure tip  86 . This produces a dimensionally consistent structure that can interface with stent  56  in a previously unobtainable uniform manner. The consistent dimensional integrity of leaflet wireform subassembly  58  enables stent  56  to function as a stress relieving support clamp which further secures leaflet cusps  92  in valve  50  to provide an added degree of stability and stress distribution. If desired, providing the top  99  of the stent  56  with a single, or double fold of covering cloth  144  provides the stent lip with a deformable cloth seat that assists in the distribution of load around leaflet cusps  92  and simplifies sewing stent  56  to tissue-wireform structural subassembly  58 . Those skilled in the art will appreciate that attaching stent  56  to tissue-wireform structural subassembly  58  functions to stabilize the projecting commissure posts of the valve subassembly without stiffening their desirable axial flexibility. This novel construction technique eliminates the need for separate commissure posts at the tissue leaflet commissures and also eliminates multiple tissue and cloth layers at wireform commissures  86  which adds to uniformity and consistency in valve production and eliminates assembly steps. As a result, valve manufacture is not only improved, but simplified and expedited as well. 
     Stent  56  also functions as an adaptable structural interface, allowing the tissue-wireform-stent structural subassembly to be attached to a variety of additional structures dependent upon intended valve placement and operating environments, including soft suture ring  60 , mechanical flange  62 , inflow conduit  64 , and outflow conduit  66 . Unlike prior art tissue heart valves, the present invention provides this flexibility and adaptability of use because key valve components can be standardized for different types of valves or valve applications. This manufacturing and structural consistency also improves quality control and provides repeatability and consistency in the formation of the valves. It also simplifies final assembly that in turn provides for increased production rates without sacrificing consistent product quality. 
     As part of the flexibility of the present invention, stent  56  may be designed to be adaptable so that different ways of attaching valve  50  to various intended applications can be accommodated. The novel construction that allows for this universal application results from stent  56  providing a complete uniform support to the dimensionally stable, pre-aligned wireform/leaflet subassembly  58 . Because of this adaptability, valve  50  can function in a variety of applications, including that of a temporary heart valve prosthesis within a circulatory support system using a relatively rigid flange or a conduit assembly rather than a standard soft sewing ring. Alternatively, valve  50  can function as a prosthetic valve having a soft, scallop-shaped sewing ring for aortic positioning or a soft flat sewing ring for mitral positioning, or as a conduit valve by incorporating proximal and distal conduits attached on both the inflow and outflow valve ends. The outflow conduit can have a sinus shape to improve blood flow if desired. Within an artificial heart system, valve  50  mimics the hemodynamic pumping action of the heart while sustaining the patient until a donor heart is located and successfully transplanted. In this application, both blood inflow and outflow functions can be accommodated by valve  50 . 
     From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those skilled in the art. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the claims appended hereto.

Technology Classification (CPC): 0