Abstract:
A prosthetic heart valve includes annularly spaced commissure portions, each of which includes a tip. The stent is formed from a polymeric material, and is specifically configured to perform similarly to conventional metal stents. A first fabric covers each of the tips, and a second fabric covers the first fabric and remaining exposed portions of the stent. A first layer of tissue covers the second fabric, and a second layer of tissue overlies the second fabric. The second layer of tissue includes leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to prosthetic heart valve replacement, and more particularly to aortic valve replacement using a biological prosthetic heart valve that has a monolithic polymeric stent. 
       BACKGROUND OF THE INVENTION 
       [0002]    The heart is the core muscle responsible for pumping life-sustaining blood through the body via an intricate network of vessels. It works ceaselessly and beats 100,000 times a day and 40 million times a year. 
         [0003]    In its simplest form, the human heart can be described as a four-chamber structure, each chamber filling with a new round of blood with every beat. The chambers are called the right atrium, left atrium, right ventricle and left ventricle. Each chamber is connected with a valve. These valves operate similarly to check valves and ensure blood flows in the proper direction through the heart. The right chambers receive blood that is low in oxygen and then pump the blood through the pulmonary artery and into the lungs. The left side of the heart receives the now oxygen-rich blood from the lungs and the left ventricle pumps the blood out to the body, through the aorta. 
         [0004]    When the valves of the human heart cease to work properly, leakage can occur between the chambers of the heart, resulting in a lower blood pressure or high resistance for the blood to pass through. One solution is to replace malfunctioning valves with either a mechanical or a biological valve. 
         [0005]    A stented tissue heart valve is a replacement prosthetic heart valve composed of a stent covered in biological tissue. The stented tissue heart valve replaces the diseased, damaged or malfunctioning valve, such as the aortic valve between the left ventricle and the aorta. It is designed for supra-annular placement. Its functional purpose is to maintain structural integrity with a high-strength fatigue-resistant stent at the core. 
         [0006]    Through cardiac surgery, the malfunctioning heart valve can be removed and then replaced by the stented tissue valve. Selection of the appropriate size replacement valve is of great importance. Prosthetic heart valves typically have a diameter between about 19 mm and about 29 mm. The valve size selection is determined through a sizer-replica of the 19-29 mm diameter valve. Once an appropriate size is selected to fit a patient, sutures are sewn into the aortic tissue. The sewing cuff of the prosthetic valve is then threaded over these sutures, and the valve is transferred down to the aortic opening where it is firmly attached. 
         [0007]    Numerous replacement prosthetic heart valves have been designed. Conventional prosthetic heart valves are manufactured from a metallic stent assembly and bovine pericardium tissue. The stent assembly consists of a core (called a stent) formed from metal, such as titanium alloy, a polyester fabric forming the sewing cuff and porcine tissue covering all edges of the stent. The bovine pericardium tissue is attached to the stent assembly to form three leaflets which cooperate to permit blood to flow in one direction, but not the other. 
         [0008]    An example of a stent  10  for use in a conventional prosthetic heart valve is shown in  FIG. 1 , and is discussed more fully in U.S. Patent Application Publication No. 2008/0147179, the disclosure of which is hereby incorporated herein by reference. Stent  10  is an annular structure formed from metal, such as titanium. In a typical process, stent  10  may be formed by laser cutting a titanium tube to the desired shape, followed by electro-polishing the resultant structure. The stent structure includes a base  4 , commissure posts  60 A- 60 C extending from the base, a blood inflow edge  12 , and a blood outflow edge  14 . Stent  10  can have a diameter ranging from about 19 mm to about 29 mm and a wall thickness PA T  ranging from about 0.25 mm to about 0.33 mm, depending on the selected size of the stent. The width W of each commissure post typically ranges from about 1.45 mm to about 1.51 mm. 
         [0009]    Numerous geometrically-shaped openings are provided within metallic stent  10 . Elongated openings  22 A,  22 B, and  22 C extend along the lengths of posts  60 A- 60 C. The portions of elongated openings  22  closer to inflow edge  12  are generally rectangular in shape, whereas the portions of elongated openings  22  closer to outflow edge  14  are more triangular in shape. Each elongated opening  22  includes five distinct edges  24 A, 24 B, 24 C, 24 D, and  24 E that generally form the shape of an elongated bottle. 
         [0010]    Openings  18 A- 18 F extend around the circumference of base  4 . Each opening  18  includes three distinct edges  20 A,  20 B, and  20 C that generally form the shape of a right triangle, and more specifically a 30-60-90 right triangle. Edge  20 C is directly adjacent an edge  24 A or  24 D of an opening  22  in a commissure post. As shown, openings  18 ,  22  are positioned a predetermined distance away from the inflow and outflow edges of stent  10 . As a result, inflow edge portion  28  has a width PA 1  between inflow edge  12  and edges  20 A of openings  18 , and a width PA 3  between inflow edge  12  and edges  24 E of openings  22 . Similarly, outflow edge portion  30  has a width PA 2  between outflow edge  14  and edges  20 B of openings  18 , and a width PA 4  between outflow edge  14  and edges  24 B,  24 C of openings  22 . The widths PA 1  and PA 3  of inflow edge portion  28  are substantially similar to the widths PA 2  and PA 4  of the outflow edge portion  30 . Such dimensional uniformity in stent  10  is believed to provide a stable structure that can minimize deformation of the stent, especially during handling of the stent by surgeons. 
         [0011]    Despite the improved design of the stent shown in  FIG. 1 , there is still room for further improvements. For example, because of the plastic behavior of metals, metallic stents are subject to deformation during handling and implantation in a patient. A need therefore exists for prosthetic valves having improved stent designs that are less prone to deformation, but that are capable of reliable production. 
       SUMMARY OF THE INVENTION 
       [0012]    One aspect of the present invention provides prosthetic heart valves having an annular stent comprised of a polymeric material. In one embodiment of the heart valve, the stent may have a base and annularly spaced commissure portions projecting from the base, each commissure portion including a tip. The stent may have a wall thickness between about 0.50 mm and about 1.15 mm. The heart valve may further include a fabric covering the stent; a first layer of tissue covering the fabric; and a second layer of tissue overlying the first layer of tissue and including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. The heart valve may further include a sewing cuff structure adjacent the base of the stent. 
         [0013]    Preferably, the polymeric material is polyetheretherketone. Alternatively, the polymeric material may be selected from the group consisting of polysulfone, polyphenylsulfone, liquid crystal polymer, polyoxymethylene, and polypropylene. 
         [0014]    At least one of the tips may have a tip deflection less than about 3 mm when the heart valve is in use in a patient. Preferably, the tip deflection is greater than about 0 mm and less than about 3 mm. 
         [0015]    The stent may include an inflow edge adjacent the base, an outflow edge adjacent the tips, and a plurality of openings between the inflow edge and the outflow edge. Each opening may have a first edge at a first spaced distance from the inflow edge and a second opening at a second spaced distance from the outflow edge, the second spaced distance being greater than the first spaced distance. The first spaced distance may be between about 0.4 mm and 1.2 mm. The second spaced distance may be between about 0.6 mm and 2.2 mm. 
         [0016]    The first layer of tissue of the prosthetic heart valve may comprise mammalian pericardium tissue, in particular porcine pericardium tissue. The second layer of tissue may also comprise mammalian pericardium tissue, in particular bovine pericardium tissue. 
         [0017]    Another embodiment of the prosthetic heart valve includes an annular stent having annularly spaced commissure portions, each commissure portion including a tip. The stent may be comprised of a polymeric material having a thickness of between about 0.50 mm and about 1.15 mm. The heart valve may further include a first fabric covering each of the tips; a second fabric covering the first fabric and remaining exposed portions of the stent; a first layer of tissue covering the second fabric; and a second layer of tissue overlying the first layer of tissue and including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. 
         [0018]    At least one of the tips may have a tip deflection less than about 3 mm when the heart valve is in use in a patient. Preferably, the tip deflection is greater than about 0 mm and less than about 3 mm when the heart valve is in use in a patient. 
         [0019]    The first layer of tissue of the prosthetic heart valve may comprise mammalian pericardium tissue, particularly porcine pericardium tissue. The second layer of tissue may also comprise mammalian pericardium tissue, particularly bovine pericardium tissue. 
         [0020]    The stent may include a base, an inflow edge adjacent the base, an outflow edge adjacent the tips and a sewing cuff structure adjacent the inflow edge. 
         [0021]    In yet another embodiment, the prosthetic heart valve may include an annular stent comprised of a polymeric material. The stent may have annularly spaced commissure portions, each commissure portion having a tip. The heart valve may further include a fabric covering the stent; a first tissue layer covering the fabric; and a second tissue layer overlying the first tissue layer and including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. 
         [0022]    Another aspect of the present invention provides a method of making a prosthetic heart valve. The method includes providing an annular stent comprised of a polymeric material. The stent has a base and annularly spaced commissure portions projecting from the base, each commissure portion including a tip. The method further includes covering the stent with a fabric; covering the fabric with a first layer of tissue; and arranging a second layer of tissue over the first layer of tissue, the second layer of tissue including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. The step of providing the stent may include molding the polymeric material using an injection molding process. 
         [0023]    In another method according to this aspect of the invention, a method of making a prosthetic heart valve includes providing an annular stent comprised of a polymeric material having a thickness between about 0.50 mm and about 1.15 mm. The stent has a base and annularly spaced commissure portions projecting from the base, each commissure portion including a tip. The method further includes covering each of the tips with a first fabric; covering the first fabric and remaining exposed portions of the stent with a second fabric; covering the second fabric with a first layer of tissue; and arranging a second layer of tissue over the first layer of tissue, the second layer of tissue including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. The step of providing the stent may include molding the polymeric material using an injection molding process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view of a stent of a prosthetic heart valve according to the prior art; 
           [0025]      FIG. 2  is a perspective view of a stent of a prosthetic heart valve in accordance with one embodiment of the invention; 
           [0026]      FIG. 3  is a top plan view of the stent in  FIG. 2 ; 
           [0027]      FIG. 4  is a ⅓ sectional front elevation of the stent shown in  FIG. 2 ; 
           [0028]      FIG. 5  is a ⅓ side perspective view showing the deflection of the stent post tip upon the application of external forces; 
           [0029]      FIG. 6  is a perspective view of a portion of the stent of  FIG. 2  with a covering thereover; 
           [0030]      FIG. 7  is a perspective view of another component prior to assembly to the stent shown in  FIG. 2 ; 
           [0031]      FIG. 8  is an elevational view of another component prior to assembly to the stent shown in  FIG. 2 ; 
           [0032]      FIG. 9  is a perspective view of an assembly of the components of FIGS.  2  and  6 - 8  in accordance with the present invention; 
           [0033]      FIGS. 10 and 11 , respectively, are perspective top and bottom views of the assembly of  FIG. 9  with another component added in accordance with the invention; 
           [0034]      FIG. 12  is a perspective view of tissue prior to assembly with the stent assembly shown in  FIG. 9 ; 
           [0035]      FIG. 13  is a perspective view of a tool that is useful in the manufacture of heart valves in accordance with the invention; 
           [0036]      FIG. 14  is an enlarged schematic view of a representative portion of an assembly of components in accordance with the invention; 
           [0037]      FIG. 15  is a top perspective view of an assembly in accordance with the present invention provided on the tool shown in  FIG. 13 ; and 
           [0038]      FIG. 16  is a perspective view of a completed prosthetic heart valve in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Referring now to  FIG. 2 , an illustrative embodiment of a stent  100  of a prosthetic heart valve ( FIG. 14 ) in accordance with one embodiment of the invention is shown. Stent  100  is a hollow annular structure for use as a component of a tricuspid valve for aortic valve replacement. The outer diameter D ( FIG. 3 ) of the valve stent may range from about 18 mm to about 24 mm, depending on the size of the native valve annulus into which the prosthetic valve is to be implanted. Stent  100  has a continuous and curved stent base  104  and three commissure posts  160 A- 160 C that surround an annular opening  102 . An inflow edge  112  and outflow edge  110  define the longitudinal ends of stent  100 . Stent base  104  has a nonuniform height H B  that extends from inflow edge  112  to the portions of outflow edge  110  that extend between commissure posts  160 A,  160 B and  160 C. 
         [0040]    The three commissure posts  160 A,  160 B and  160 C may be evenly spaced around stent base  104 . Commissure posts  160 A- 160 C extend generally upwardly from base  104  to post tips  180 A- 180 C positioned at the free ends of the respective commissure posts, with the commissure tips terminating at respective apexes  181 A- 181 C that lie on the outflow edge  110 . Each commissure post  160  may have a height H C  that extends from the inflow edge  112  to a respective apex  181  and an overall triangular shape. The height H C  may be between about 10.0 mm and about 15.0 mm, with the overall height of stent  100 , taking into consideration the scalloped profile of inflow edge  112  (described below), being between about 11 mm and about 17 mm. The post tips  180 A- 180 C each may have the same predetermined width W 1 , which preferably is greater than the width of conventional metal stents. The width W 1  may range from about 2.0 mm to about 3.7 mm, depending on the selected size of stent  100 . 
         [0041]    Outflow edge  110  extends continuously along the outermost top portion of stent  100 . As shown, outflow edge  110  extends between and around each commissure post  160 . The contour of outflow edge  110  is scalloped, extending downwardly from the apex  181  of one post tip  180  and upwardly toward the apex of the next adjacent post tip. For example, outflow edge  110  extends downwardly from the apex  181 B of post tip  180 B towards base  104 , and then upwardly along post tip  180 C to the apex  181 C thereof. The inflow edge  112  may also be slightly curved or scalloped. In that regard, inflow edge  112  may rise in the regions longitudinally below each commissure post  160 A- 160 C and fall in the regions therebetween. 
         [0042]    Geometric openings are provided within stent  100  in order to increase the flexibility of the stent and withstand fatigue, particularly as the valve leaflets open and close during use. Turning first to base  104 , base openings  118 A,  118 B,  118 C,  118 D,  118 E and  118 F may extend around the base  104 . Two of these base openings may be provided between each pair of adjacent commissure posts  160 . For example, two base openings  118 C, 118 D may be provided between commissure posts  160 B and  160 C. Each base opening  118  has a top edge  116 A and a bottom edge  116 B joined together by a first rounded end  116 C farther from a commissure post and a second rounded end  116 D closer to the commissure post. Bottom edge  116 B may extend generally parallel to inflow edge  112 , while top edge  116 A extends generally parallel to outflow edge  110 . Accordingly, edges  116 A and  116 B may diverge from one another as they approach each commissure post  160 , with the second rounded end  116 D having a larger radius of curvature R 2  than the radius of curvature R 3  of the first rounded end  116 C. The radius of curvature R 2  may be between about 0.4 mm and about 0.90 mm and the radius of curvature R 3  may be between about 0.25 mm and about 0.50 mm. Geometric openings may also be present within each commissure post  160 . Thus, commissure posts  160 A- 160 C may have respective post openings  122 A- 122 C that extend along the height H C  of the commissure post. For example, post opening  122 B may have a first rounded edge  124 A, a second rounded edge  124 B and a third rounded edge  124 C which collectively are joined in a generally triangular shape. The first and second rounded edges  124 A, 124 B may generally follow the contour of outflow edge  110 , whereas the third rounded edge  124 C may generally follow the contour of inflow edge  112 . First rounded edge  124 A and third rounded edge  124 C join at a corner  126 A having a radius of curvature R 1  between about 0.70 mm and about 1.60 mm. Similarly, third rounded edge  124 C and second rounded edge  124 B join at a corner  126 B having a radius of curvature R 5  that is substantially the same as the radius of curvature R 1 , i.e., between about 0.70 mm and about 1.60 mm. Finally, first rounded edge  124 A and second rounded edge  124 B join at a corner  126 C having a radius of curvature R 4  between about 0.45 mm and about 0.60 mm. Additional round openings  132 A- 132 C may be provided in respective post tips  180 A- 180 C above post openings  122 . 
         [0043]    The geometry of stent  100  will be described in more detail with reference to  FIG. 4 . Base openings  118 , post openings  122 , and round openings  132  may be spaced a predefined distance away from outflow edge  110  and inflow edge  112 . An inflow edge portion  128  and an outflow edge portion  130  are defined between the edges of the respective openings and the respective outflow and inflow edges  110 , 112 . Outflow edge portion  130  has a width T 1  between outflow edge  110  and edge  116 A of base opening  118 ; widths T 2  and T 4  between respective edges  124 A, 124 B of post opening  122  and outflow edge  110 ; and width T 3  between opening  132  and post apex  181 . Similarly, inflow edge portion  128  has a width T 5  between edge  116 B of base opening  118  and inflow edge  112 ; and a width T 6  between edge  124 C of post opening  122  and inflow edge  112 . Generally, the width (T 1 - 14 ) of outflow edge portion  130  is greater than the width (T 5 ,T 6 ) of inflow edge portion  128 . More particularly, outflow edge portion  130  may have a width between about 0.6 mm and about 2.2 mm, whereas inflow edge portion  128  may have a width between about 0.4 mm and about 1.2 mm. It will be appreciated from  FIG. 4  that widths T 2  and T 4  may not be constant along their entire lengths. That is, in order to have corner  126 C as close as possible to the apex  181  of the commissure post  160 , and to have a large enough radius R 4  at the corner to minimize stresses thereat, the width of outflow edge portion  130  may taper downwardly as it approaches corner  126 C. Similarly, the other widths, namely, T 1 , T 3 , T 5  and T 6 , may not be constant along their entire lengths, but may vary slightly to accommodate the radii of openings  118  and  122 . 
         [0044]    Stent  100  is formed from a polymeric material, and may be formed from an injection molded monolithic polymer. As used herein, the term “monolithic” refers to a structure that is formed entirely from a polymeric material, rather than to structures that may have a non-polymeric core and a polymeric coating, or a polymeric core and a non-polymeric coating. The term “monolithic” is not intended to be limited to structures formed from a single polymeric material. Thus, “monolithic” polymer structures include those that may be formed from a mixture of different polymeric materials, as well as those that may include layers or regions formed from the same or different polymeric materials. Moreover, although injection molding is a preferred manufacturing method for stent  100 , it is contemplated that the stent may be formed by other techniques known in the art. For example, stent  100  may be formed by laser cutting a tube of polymeric material in a manner similar to the manner in which the prior art metal stents are made. 
         [0045]    The use of a polymer to form stent  100  allows for greater durability of the stent and prosthetic heart valve during both handling and implantation of the prosthetic valve as compared to prior art stents comprised of metal. In particular, polymers generally have an elastic deformation curve that extends over a large range of stresses, whereas metals may exhibit elastic deformation under low stresses, but may deform plastically under higher stresses. Thus, the use of polymers rather than metals reduces the possibility of plastically deforming the overall diameter or circumference of the stent. Additionally, once the completed valve is surgically implanted within the body, coaptation of the leaflets will cause the post tips to deflect. For example,  FIG. 5  illustrates the deflection of post tip  180 C inwardly by an amount ΔD. The polymer stents  100  of the present invention minimize the amount of post tip deflection ΔD to no greater than about 3 mm. However, some small amount of deflection may be desirable. Therefore, the amount of post tip deflection is preferably greater than 0 mm and less than 3 mm. 
         [0046]    Providing an injection molded monolithic polymeric stent further allows for design modifications to the geometry of the stent that are unavailable or unfeasible when designing metal stents. For example, as previously discussed in the background section, conventional metal stents have an inflow edge region with a width that is substantially similar to the width of the outflow edge region. This uniform design provides for a stable stent structure that allows surgeons to easily grasp the valve assembly with minimal deformations to the stent. However, in contrast, the polymer stents of the present invention have an outflow edge portion  130  with a greater width than the inflow edge portion  128 . Despite this difference, deflection of no greater than about 3 mm at the tips of the commissure posts  160  can be achieved. This amount of deflection resembles the strength and minimal degree of deflection of conventional metallic stents. 
         [0047]    In order to achieve the same structural and mechanical properties as metallic stents, it is desirable to form polymeric stents with a greater overall thickness. The thickness T of polymeric stents can be substantially greater than the thickness of typical metal stents, lending to greater durability of the stent before and after implantation, while exhibiting at least the same strength and deflection properties as a metal stent. In that regard, polymeric stents according to the present invention may have a thickness T ( FIGS. 2-3 ) from about 0.50 mm to about 1.15 mm, depending on the size of the stent and the polymeric material forming the stent. Furthermore, the thickness may be substantially constant throughout the stent. Alternatively, the thickness may be greater at the outflow edge portion  130  of the stent than at the inflow edge portion  128 , such as where it is desirable to minimize the cross-section of the stent confronting blood flow. Moreover, the thickness of the stent may be less along a central longitudinal section of the commissure portions  160  (i.e., in the areas immediately adjacent openings  122  and  132 ), such as to minimize stress concentrations that could potentially lead to stent failure under stress. 
         [0048]    A particularly preferred polymer for forming stent  100  is PolyEtherEtherKetone (“PEEK”). PEEK is a high-performance, semi-crystalline thermoplastic. Its ability to retain mechanical and chemical resistance properties at high temperatures makes it a good candidate for stent  100 . The Young&#39;s modulus of PEEK is 3.6 GPa and its tensile strength ranges from 90 to 100 Mpa. PEEK has a glass transition temperature at around 143° C. (289° F.) and it melts at around 343° C. (662° F.). It is highly resistant to attack by both organic and aqueous environments. These characteristics of PEEK make it biologically compatible and enable it to be implanted within the human body. Although many grades of PEEK may be employed for forming the stents  100  of the present invention, PEEK-816-00 Victrex® 151G, available from Victrex PLC of Lancashire, United Kingdom, is preferred. In addition to PEEK, stent  100  may be formed from other types of polymers, including without limitation polysulfone (e.g., PES-1024-00 Radel® AG320 NT-760, available from Solvay Specialty Polymers); polyphenylsulfone (e.g., PPSU-2804-00 Radel® R-5800 NT, available from Solvay Specialty Polymers); liquid crystal polymer (e.g., LCP-001 Vectra® A1115 natur, available from Ticona, United States); polyoxymethylene (e.g., POM-1748-00 Hostaform® C27021, available from Ticona, United States); and polypropylene (e.g., PP-1851-00 Bormed™ HD850M0, available from Borealis Nucleation Technology). 
         [0049]    The polymeric stent configurations that can be constructed and arranged in accordance with the present embodiments are numerous. Examples of such configurations are provided in Table A below. Dimensions T 1 -T 6 , R 1 -R 4 , post height (H C ), and total stent height (H T ) referred to in Table A are shown in  FIG. 4 ; and inner diameter (“ID”), outer diameter (“OD”), minimum wall thickness (“WT MIN ”) and maximum wall thickness (“WT MAX ”) are shown in  FIG. 3 . The dimensions in Table A are merely exemplary, and various modifications thereof may be made within the scope of the present invention. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE A 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Nom 
                 Wall 
                   
                   
                 Nom 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Inner 
                 thickness 
                   
                   
                 Outer 
               
               
                 Stent 
                   
                   
                   
                   
                   
                   
                 R1/ 
                   
                   
                   
                   
                 Diam 
                 WT MIN-   
                 Post 
                 Total 
                 Diam 
               
               
                 Size 
                 T1 
                 T2 
                 T3 
                 T4 
                 T5 
                 T6 
                 R5 
                 R2 
                 R3 
                 R4 
                 W1 
                 “ID” 
                 WT MAX   
                 Hgt H c   
                 Hgt H T   
                 “OD” 
               
               
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 Mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
                 mm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 19 
                 0.8 
                 1 
                 0.8 
                 1 
                 0.6 
                 0.9 
                 0.73 
                 0.472 
                 0.365 
                 0.55 
                 2.4 
                 16.821 
                 0.65-0.865 
                 10.17 
                 11.59 
                 17.9 
               
               
                 21 
                 1 
                 1.4 
                 0.8 
                 1.4 
                 0.8 
                 0.9 
                 0.77 
                 0.55 
                 0.3 
                 0.5 
                 2.2 
                 18.79 
                 0.65-0.87 
                 11.88 
                 12.7 
                 19.88 
               
               
                 23 
                 1 
                 1.4 
                 1 
                 1.4 
                 0.6 
                 1 
                 0.77 
                 0.54 
                 0.45 
                 0.5 
                 3 
                 20.768 
                 0.65-0.856 
                 11.88 
                 13.6 
                 21.83 
               
               
                 25 
                 1.2 
                 1.8 
                 1.25 
                 1.8 
                 0.65 
                 1 
                 0.95 
                 0.61 
                 0.44 
                 0.5 
                 3.5 
                 22.928 
                 0.65-0.786 
                 12.9 
                 14.8 
                 23.85 
               
               
                 27 
                 1.5 
                 2 
                 1.25 
                 2 
                 0.7 
                 1 
                 1.55 
                 0.86 
                 0.46 
                 0.5 
                 3.5 
                 26.289 
                 0.65-1.056 
                 14.68 
                 16.9 
                 27.75 
               
               
                 29 
                 1.5 
                 2 
                 1.25 
                 2 
                 0.7 
                 1 
                 1.55 
                 0.86 
                 0.46 
                 0.5 
                 3.5 
                 26.43 
                 0.65-0.985 
                 14.68 
                 16.9 
                 28.645 
               
               
                   
               
             
          
         
       
     
         [0050]    With reference now to  FIGS. 6-16 , once the size of the prosthetic heart valve to be implanted has been determined and the appropriate size stent  100  has been selected, the fabric and tissue may be assembled onto the stent to provide a completed prosthetic heart valve assembly  1200  ( FIG. 16 ). Turning first to  FIG. 6 , a sleeve-like fabric cover  200  can be provided over each commissure post  160 . As shown, fabric commissure tip cover  200  extends over the apex  181  of the respective commissure post  160 . Tip covers  200  help prevent post tips  180  from poking through the additional fabric and tissue that will be mounted on the stent. One example of a suitable fabric for use in making covers  200  is reemay fabric, which is a spun form of polyester, although other types of fabric may be used. Fabric covers  200  can be secured in place by suturing to the associated post tip  180 . 
         [0051]    An illustrative embodiment of a cuff filler ring  400  is shown in  FIG. 7 . Ring  400  has an annular shape with scalloped edges extending around an opening  404 .  FIG. 8  illustrates an embodiment of a polyester fabric tube  300  for use in assembling prosthetic valve  1200 . Tube  300  is essentially an elongated piece of fabric in a tubular configuration. Stent  100  (with coverings  200 ) and ring  400  ( FIG. 6 ) may be placed coaxially around the outside surface  306  of a lower portion  302  of fabric tube  300 . Ring  400  may be placed around stent  100  so that the inner edge  402  of the ring is adjacent to and around the inflow edge portion  128  of the stent. In a preferred arrangement, ring  400  will be positioned around stent  100  so that the scalloped edges of the ring are aligned with the scalloped contour of the inflow edge portion  128  of the stent. 
         [0052]    With the components properly positioned, the upper portion  304  of tube  300  may be inverted and pulled down over the exposed outer surface of stent  100  and ring  400  and pulled tightly enough to conform to outflow edge portion  130 . Sutures may be used to hold all of these components together as an assembly  500  shown in  FIG. 9 , so that stent  100 , fabric covers  200 , and ring  400  are completely encased within fabric  300 . Upper portion  304  of fabric  300  conforms closely to stent  100  above ring  400 , and in particular, follows the scalloped contour of outflow edge portion  130  around the circumference of assembly  500 . 
         [0053]    Once the fabric covering  300  is in place, tissue may be mounted onto the assembly  500 . Referring to  FIG. 10 , tissue  600 , such as porcine pericardium, may be mounted onto the exposed inner surface  370  and outer surface  380  ( FIG. 9 ) of assembly  500  so that each surface of the assembly is covered in tissue. Sutures may be used to secure tissue  600  to assembly  500 . Once completed, the assembly  700  shown in  FIGS. 10-11  results. The addition of tissue  600  can help to enhance the durability and reduce the thrombogenicity of the finished valve. Apart from somewhat thickening the overall structure of the predecessor assembly  500 , the addition of tissue  600  does not significantly change the shape of any portion of the assembly  700 . 
         [0054]    Although porcine pericardium is mentioned above for tissue  600 , other types of tissue may be used to cover assembly  500  if desired. Examples of such other possible tissue include any mammalian pericardium (e.g., equine or bovine pericardium). 
         [0055]    With tissue  600  in place, leaflets can be added to the assembly  700  using a pre-formed sheet  800  of tissue, such as a sheet of bovine pericardium tissue. Referring to  FIG. 12 , sheet  800  has been die cut to a shape that can be used to form all three leaflets of a finished valve. Note that lower edge  804  of sheet  800  (as viewed in  FIG. 12 ) is scalloped to conform to the blood-inflow edge of the stent  100  and the overall scalloped shape of the finished valve assembly  700 . Upper portion  806  of sheet  800  forms the three leaflets of the valve. Shallow downward cuts  802  are positioned between the individual leaflet portions adjacent the upper edge  810  of sheet  800 , but sheet  800  preferably remains a unitary sheet so that it can be used to form all three leaflets in the finished valve. Although bovine pericardium is mentioned above as the tissue forming sheet  800 , it is to be appreciated that other types of tissue may be used in its place. Examples of such other possible tissue for sheet  800  include any mammalian pericardium (e.g., equine or porcine pericardium). 
         [0056]      FIG. 13  illustrates a tool  900  that can be used in the manufacture of valve  1200 . Tool  900  may be a mounting mandrel that can be inserted coaxially into assembly  700  so that each of the commissure portions  910   a - 910   c  of the mandrel is angularly or rotationally aligned with a respective one of the commissure portions  710   a - 710   c  ( FIG. 10 ) of assembly  700 . In addition, each of the scalloped edge portions  930  of mandrel  900  may be positioned adjacent a corresponding scalloped outflow edge portion  730  of assembly  700 . 
         [0057]    With mandrel  900  positioned inside of assembly  700 , as described in the preceding paragraph, sheet  800  may be wrapped around the outside of assembly  700  above the sewing cuff portion of the assembly. The sewing cuff portion is the portion that includes ring  400  in its interior. This wrapping may be done with the scalloped lower edge  804  of tissue  800  just above and conformed to the scalloped sewing cuff of assembly  700 . In addition, each of cuts  802  may be adjacent a respective one of two of commissures  710 , and the extreme left and right edges of tissue  800  may come together adjacent the third commissure  710 . The portion of tissue  800  above each outflow edge portion  730 , 930  may then be pressed radially inwardly so that it resets on the adjacent concave surface  940  of mandrel  900 . Tissue  800  may be stitched to assembly  700  (but not to mandrel  900 ) in this condition. For example,  FIG. 14  shows stitching  1002  that may be used to hold the initially free, left and right edges of tissue  800  together adjacent one of the commissures  710  of assembly  700 . Other stitching  1004  in  FIG. 14  is used to stitch tissue  800  to assembly  700  all the way around the assembly just above the sewing ring portion of the assembly. The resulting valve structure shown in  FIG. 15  may be referred to as assembly  1000 . 
         [0058]      FIG. 15  shows assembly  1000  still mounted on mandrel  900  as described in the immediately preceding paragraphs. Note in particular that the portion of tissue  800  above each of outflow edge portions  730  remains pressed in against the adjacent concave surface  940  of mandrel  900 . With assembly  1000  in this condition on mandrel  900 , the assembly may be subjected to fixation of the tissue. Such fixation of the tissue may be accomplished using any conventional and suitable means, including cross-linking of the tissue by exposing it to cross-linking agents such as glutaraldehyde or epoxides such as TGA (triglycidyl amine). Such fixation of the tissue stabilizes the tissue and renders it substantially biologically inert and bio-compatible. The fixation of the tissue in contact with shaped surfaces  940  also gives the tissue a bias to return to that shape when it is not subjected to external forces. On the other hand, the fixation still leaves the tissue sufficiently flexible that the leaflet portions of tissue  800  above outflow edge portions  730  can deflect outwardly to open the valve and let blood flow out when a ventricular contraction pressurizes the blood in the ventricle below the valve. When that ventricular pressure ceases, however, the leaflet portions above outflow edge portions  730  come together again (coapt) and close the valve. 
         [0059]    After the tissue of assembly  1000  has been subjected to fixation as described above, assembly  1000  can be removed from mandrel  900 . The result is a completed prosthetic heart valve  1200  as shown in  FIG. 16 . In use, valve  1200  has the operating characteristics described in the preceding paragraphs. 
         [0060]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. 
         [0061]    It will be appreciated that the various dependent claims and the features set forth therein can be combined in different ways than presented in the initial claims. It will also be appreciated that the features described in connection with individual embodiments may be shared with others of the described embodiments.