Abstract:
A flexible prosthetic tissue-type heart valve having commissures that are substantially decoupled from a cusp support structure. The valve includes three leaflets having arcuate cusp edges and opposed concave shaped free edges, with outwardly-directed attachment tabs therebetween. A cusp support structure in either one or more pieces attaches to the leaflet cusp edges. Three commissures are each formed partly with an axially-extending insert member to which two adjacent leaflet tabs attach. An inverted V-shaped clip maintains close contact between the adjacent leaflet tabs and provides a stress-relieving clamping action in conjunction with the insert member. The insert member attaches about its lower end to base sections of the cusp support structure, or to an intermediate sewing ring, so that the commissures may pivot about the cusp support structure. The sewing band is scalloped and enables attachment of the valve along the scalloped aortic root so as to couple the valve to the natural motion of the aorta. Increased vibrational damping results from this biomechanical coupling.

Description:
RELATED APPLICATION  
       [0001]    The present application is a divisional of application Ser. No. 09/668,660, filed on Sep. 22, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to medical devices and particularly to flexible tissue-type heart valve prostheses designed to attach along the valve annulus and adjacent anatomical wall structure.  
         BACKGROUND OF THE INVENTION  
         [0003]    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, although repair or replacement of the aortic or mitral valves is most common because they reside in the left side of the heart where pressures are the greatest.  
           [0004]    Where replacement of a heart valve is indicated, the dysfunctional valve is typically cut out and replaced with either a mechanical valve, or a tissue valve. Tissue valves are often preferred over mechanical valves because they typically do not require long-term treatment with anticoagulants. The most common tissue valves are constructed with whole porcine (pig) valves, or with separate leaflets cut from bovine (cow) pericardium. Although so-called stentless valves, comprising a section of porcine aorta along with the valve, are available, the most widely used valves include some form of stent or synthetic leaflet support. Typically, a wireform having alternating arcuate cusps and upstanding commissures supports the leaflets within the valve, in combination with an annular stent and a sewing ring. The alternating cusps and commissures mimic the natural contour of leaflet attachment. Importantly, the wireform provides continuous support for each leaflet along the cusp region so as to better simulate the natural support structure. However, the tissue material tends to calcify after the long term implantation. That is, calcium compound accumulates in the tissue leaflets, eventually making them stiff. The tissue leaflet area along the wireform is especially susceptible to the calcification because of the high bending stresses imposed at that interface.  
           [0005]    Many prior art stented valves are relatively rigid, typically containing an annular metal or plastic stent ring that provides internal support for an outer sewing ring and the wireform-mounted valve cusps and commissures. This design also provides a basic structure to facilitate valve assembly, which is hand made by highly skilled workers. Although this type of valve has been proven effective, some researchers assert that it excessively occludes the natural orifice area, and thus reduces potential blood flow therethrough. Although stentless valves generally provide greater orifice area, they do not have the advantage of the reliable leaflet support structure of stented valves. Moreover, a stentless valve is more difficult to make, and the implantation of such a device requires much more skill and experience of the cardiac surgeon. Only a few heart centers in the United States are able to perform such a procedure and thus the use of stentless valves is restricted.  
           [0006]    More flexible stented valves have been proposed, including U.S. Pat. No. 5,549,665 to Vesely, et al. In the Vesely patent, the valve stent commissures may attach to the ascending aorta and may pivot outward for the purpose of reducing localized stresses in the leaflets: The stent commissures are prevented by stops from inward pivoting to ensure proper valve functioning. However, the stent structure appears to be relatively complex, with numerous interior surfaces, thus raising concerns of thromboembolisms and even component failure.  
           [0007]    In view of the foregoing, it is evident that an improved flexible valve that addresses the apparent deficiencies in existing heart valves is necessary and desired. In particular, there is a need for a bioprosthetic valve that provides a large orifice opening and has a dimensionally stable stent to facilitate the valve assembly and implantation.  
         SUMMARY OF THE INVENTION  
         [0008]    This invention details a partially stented valve design. The stent is to be completed by the natural aortic root when the valve is implanted. The final valve conforms to the movement of the natural aortic root and therefore provides a larger orifice area like a stentless valve. The valve, however, includes a stent structure that will facilitate the valve assembly and implantation procedures. The movement of the stent structure and leaflet shape also helps to reduce stress concentration in the valve leaflet.  
           [0009]    In one embodiment, the present invention provides a heart valve for implantation in an annulus of a heart having commissures on an outflow end adapted to move in conformity with an anatomical wall structure adjacent the annulus. The heart valve comprises three leaflets made of a biocompatible and compliant material, each leaflet having a rounded cusp edge opposite a free edge, and a pair of generally oppositely-directed tabs separating the cusp edge and free edge. A cusp support structure generally defines a ring and a valve axis and has three rounded sections each adapted to conform to the cusp edge of the leaflets. The cusp edge of each leaflet is attached to a different rounded section of the cusp support structure so that the three leaflets are arranged generally evenly about the valve axis, the attached leaflet cusp edges and rounded sections together defining valve cusps curving toward an inflow end of the valve. Three valve commissure posts disposed between the valve cusps project generally axially toward an outflow end of the valve. The commissure posts are defined by two adjacent leaflet tabs, a generally axially extending insert member, and an inverted V-shaped clip positioned radially inward from the insert member. The adjacent leaflet tabs are juxtaposed to extend radially outward with respect to the axis through the inverted V-shaped clip and are wrapped around and secured to the insert member, an inflow end of each commissure post is generally pivotally coupled with respect to the cusp support structure so as to permit both radially inward and outward movement thereof, the valve commissure posts being attachable to the anatomical wall structure. Finally, a sewing band shaped to follow the valve cusps and being attached therealong provides a platform for implanting the heart valve such that the valve cusps are attachable adjacent the annulus or in the supraannular position (i.e., just above the annulus).  
           [0010]    In another aspect of the invention, an aortic heart valve adapted to have reduced vibration-related strain is provided, comprising three leaflets each having arcuate cusp edges on their inflow ends, free edges on the outflow ends, and two side tabs. Three cusp supports each attach to the cusp edge of one of the leaflets to define valve cusps, the cusps being disposed generally in a circle about a valve axis at an inflow end of the valve. Three generally axially extending commissure posts are disposed in between the valve cusps around the circle and extend toward an outflow end of the valve. The commissure posts are defined by a relatively rigid insert and adjacent tabs of two leaflets attached thereto. The inserts are structurally separate from the three cusp supports but coupled thereto at an end closest to the cusp supports to enable radial pivoting of the outflow end of the commissure posts. Finally, a sewing band shaped to follow the valve cusps and attached therealong is provided. The sewing band and inserts providing a platform for implanting the aortic heart valve such that the valve cusps are attachable adjacent the annulus, and the inserts are attachable to the ascending aorta. In this manner, the commissure posts are freely moveable with respect to the valve cusps so as to generally pivot radially in and out in conjunction with movement of the ascending aorta during the repetitive cycles of systole and diastole such that the heart valve is dynamically coupled to the damping characteristics of the ascending aorta.  
           [0011]    In a further aspect of the invention, a tissue-type heart valve adapted to have reduced stress risers in the leaflets, comprises three leaflets each having arcuate cusp edges on their inflow ends, free edges on the outflow ends, and two side tabs, the free edges extending between the side tabs in a concave fashion. The valve may include commissure posts to which adjacent leaflet tabs attach, each post including an insert around which the leaflet tabs wrap. The valve further may include a cusp support structure attached to the cusps of each leaflet, wherein the insert is pivotally coupled to the cusp support structure. Desirably, a sewing band for attachment to a valve annulus that surrounds the cusp support structure and is truncated in the region of the inserts to permit direct attachment of the commissure posts to an anatomical wall structure adjacent the annulus. Each leaflet free edge further may include a region that is above a line extending between the middle of the free edge and the side tabs so that the region is not placed in direct tension during closure of the valve. The region is preferably generally triangular and culminates in an apex, and a concave filet may exist between the apex and the side tab.  
           [0012]    A further understanding of the nature advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an assembled perspective view of the flexible heart valve of the present invention;  
         [0014]    [0014]FIG. 2 is an exploded perspective view of the heart valve of FIG. 1;  
         [0015]    [0015]FIG. 2A is a sectional view through a cusp support structure of the heart valve of FIG. 1, taken through line  2 A- 2 A of FIG. 2;  
         [0016]    [0016]FIG. 3 is a perspective view of components of the three commissures of the heart valve of FIG. 1 positioned with respect to the cusp support structure shown in phantom;  
         [0017]    [0017]FIG. 4A is an elevational view of an inverted V-shaped clip forming a portion of each of the valve commissures;  
         [0018]    [0018]FIG. 4B is a perspective view of the inverted V-shaped clip of FIG. 4A showing a fabric-covering thereon;  
         [0019]    [0019]FIGS. 5A and 5B are front and side elevational views, respectively, of an insert member that forms another portion of each of the valve commissures;  
         [0020]    [0020]FIG. 6 is a vertical sectional view through a valve cusp taken along line  6 - 6  of FIG. 1;  
         [0021]    [0021]FIG. 7 is a vertical sectional view through a valve commissure taken along line  7 - 7  of FIG. 1;  
         [0022]    [0022]FIG. 8 is a horizontal sectional view through a valve commissure taken along line  8 - 8  of FIG. 1;  
         [0023]    [0023]FIG. 9 is a perspective view of an alternative three-piece cusp support structure for the flexible valve of the present invention, also showing the positioning of valve commissure components;  
         [0024]    [0024]FIG. 10 is an elevational view of the alternative cusp support structure and valve commissure components of FIG. 9, further illustrating a sewing band in phantom;  
         [0025]    [0025]FIG. 11 is a top plan view of the alternative three-piece cusp support structure of FIG. 9;  
         [0026]    [0026]FIG. 12 is a plan view of a valve leaflet of the prior art;  
         [0027]    [0027]FIG. 13A is a plan view of a first embodiment of a valve leaflet for use in the flexible valve of the present invention;  
         [0028]    [0028]FIG. 13B is a plan view of a second embodiment of a valve leaflet for use in the flexible valve of the present invention;  
         [0029]    [0029]FIG. 14 is a perspective view of a cusp support structure as seen in FIG. 2, and alternative commissure components for use in a flexible valve of the present invention;  
         [0030]    [0030]FIG. 15 is an elevational view of the assembly of FIG. 14, further illustrating a sewing band in phantom; and  
         [0031]    [0031]FIGS. 16A and 16B are front and side elevational views, respectively, of an insert member of the valve of FIG. 14 coupled to a cusp support structure.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    The following detailed description, and the figures to which it refers, are provided for the purpose of describing examples and specific embodiments of the invention only and are not intended to exhaustively describe all possible examples and embodiments of the invention. Identical elements and features are given the same reference number as appropriate for purposes of describing the various embodiments of the present invention.  
         [0033]    Referring now to FIGS. 1 and 2, a replacement tissue type heart valve  21  of the present invention for implantation in an annulus of a heart is constructed about a valve axis  25  that defines an outflow end  27  and an inflow end  29 . The valve includes commissures  23  directed to the outflow end and adapted to move in conformity with an anatomical wall structure adjacent the annulus of the heart. Although the valve  21  of the present invention is particularly suitable for implantation at the aortic valve position, it may also function adequately in other valve positions. The valve has three leaflets  31  made of a biocompatible compliant material, each of which has a rounded cusp edge  33  opposite a free edge  35  and a pair of generally oppositely-directed tabs  37  separating the cusp edge and the free edge. The specific shapes of alternative embodiments of the leaflets  31  of the present invention are shown in FIGS. 13A and 13B, and will be described in more detail below.  
         [0034]    A valve cusp support structure  39  is provided, generally defining a ring comprised of three rounded sections  41  connected by commissure base sections  43 . The entire support structure  39 , including the rounded sections  41  and base sections  43 , is covered with a fabric sleeve  44 . Each of the rounded sections  41  conforms and attaches to a rounded cusp edge  33  of a leaflet via the fabric sleeve  44 . As seen in the cross-section of FIG. 2A, the fabric sleeve  44  exhibits a flap  47  formed by juxtaposed free ends of the fabric material to which the cusp edge  33  of each leaflet  31  attaches, such as with sutures (not shown). The cusp edge  33  of each leaflet  31  is attached to a different rounded section  41  of the cusp support structure  39  so that the three leaflets  31  are arranged generally evenly distributed 120° apart about the valve axis  25 . The attached leaflet cusp edges  33  and rounded sections  41  together define valve cusps  45  concavely curved toward the inflow end  29  of the valve.  
         [0035]    The three valve commissure posts  23  are disposed between the valve cusps  45  and project generally axially toward the outflow end  27  of the valve. The commissure posts  23  include a generally axially extending insert member  51  attached to two adjoining leaflet tabs  37 , here shown sutured together at butt joint  49 . Alternatively, as will be described below with respect to FIG. 8, the leaflet tabs  37  may overlap and can be mutually attached via stitching through holes in the insert member  51 . The leaflet free edges  35  coapt in the middle of the valve and the free edges of each two adjacent leaflets are juxtaposed so that the tabs  37  extend radially outwardly from the valve axis  25  through an inverted V-shaped clip  53  positioned radially inward from the insert member  51 . Each insert member  51  is sutured to the cover fabric of the commissure base section  43  so as to permit both radially inward and outward movement of the outflow end of the commissure posts. This generally pivoting attachment (shown by arrow  54  in FIG. 7) may be accomplished in a number of ways, several of which are disclosed herein, and to some extent decouples the radial movement of the valve commissures  23  from its cusps  45 .  
         [0036]    A sewing band  55  shaped to follow the valve cusps  45  and to an extent the valve commissures  23  provides a platform for attaching the heart valve to vestigial heart tissue, such as the aortic annulus or aortic root tissue. As partially seen in FIG. 1, the sewing band  55  is encompassed within a fabric cover  61  (shown partially cutaway). The valve cusps  45  are attachable adjacent the annulus with the valve commissures  23  attachable to the adjacent anatomical wall structure itself. Consequently, when implanted, structural support for each valve commissure  23  is provided by the native aorta, through the V-shaped clip  53  and insert member  51 . In the preferred embodiment, the valve  21  is attached to the root tissue that comprised part of the native aortic heart valve. Attachment in this manner allows the replacement valve to more freely move and thus exhibit greater flexibility to match the blood flow capacity of the native aortic heart valve. Moreover, this biomechanical coupling provides natural tissue damping to help suppress excessive vibrations within the valve  21  during its rapid closing.  
         [0037]    Referring to the exploded view of FIG. 2, the component parts of the invention will be described in more detail. As mentioned, the three tissue leaflets  31  have a tab section  37 , a rounded cusp edge  33  and a free edge  35 . The insert members  51  rest on the relatively rigid fabric-covered commissure base sections  43  (in this embodiment a rod-like element), and are attached thereto. For instance, sutures are passed through each insert member  51  and around the associated commissure base section to allow the insert member to move both radially inwardly and radially outwardly. This allows the finished commissure posts (FIGS. 7 and 8) to move both radially inwardly and radially outwardly. V-clips  53  and sewing band  55  are shown in their relative orientation in FIG. 2 without connecting structure, to be described below.  
         [0038]    [0038]FIG. 3 shows the relative orientation of the V-shaped clip  53  (shown isolated in FIGS. 4A and 4B), and the insert member  51  on the cusp support structure  39  (shown in phantom) when they are assembled. The cusp support structure  39  may be formed in a generally annular or ring like shape. The V-shaped clips  53 , seen in FIGS. 4A and 4B, cinch the tissue leaflet free edges  35  to the commissure posts, as indicated in FIG. 8. In a preferred embodiment, a shroud-like fabric cover  56  is provided around each V-shaped clip  53  to facilitate attachment to the adjacent valve components. FIGS. 5A and 5B show front and side views of the insert member  51  having a series of through holes  52 .  
         [0039]    [0039]FIG. 6 is a sectional view taken along the  6 - 6  line of FIG. 1, showing the attachment of the rounded cusp edge  33  of the tissue leaflet, the rounded section  41  of the cusp support structure  39  and the sewing band  55 . The three pieces are sutured or otherwise attached together in this manner at least along the valve cusps  45  shown in FIG. 1.  
         [0040]    [0040]FIG. 7 illustrates one embodiment of the attachment of the insert member  51  to the commissure base section  43  of the cusp support structure utilizing a suture  59  looped through holes  52  in the insert member and then around the base section. The insert  51  is thereby freely attached to the commissure base section  43  to allow its outflow end to move radially inwardly and outwardly, as indicated by arrow  54 . The sewing band  55  is not connected to the insert member  51  but instead receives each commissure base section  43  in a groove portion  60 . An outflow flange  62  stops short of the insert members  51  and the V-shaped clip  53 . That is, the flange  62  of the sewing band  55  is axially truncated so as not to extend fully up each commissure  23 . In this arrangement, the valve commissures  23  are exposed to the aortic wall so that they can be sutured directly thereto.  
         [0041]    In an alternative embodiment, the commissure base sections  43  of the cusp support structure  39  are omitted to result in three separate cusp supports that attach to the sewing ring  55 , such as seen in FIG. 6. In such an alternative, each insert member  51  will rest directly on the sewing ring, and its inflow end may be sutured to the sewing ring.  
         [0042]    1. FIGS. 7 and 8 illustrate the complete structure of the commissures  23  wherein adjacent leaflet tabs  37  wrapped around the insert member  51  and are sutured together on the radially outward side of the insert member. Fabric-covered V-shaped clip  53  is placed over adjoining leaflet tabs  37  and the fabric cover  56  includes a shroud long enough to wrap around the insert member  51 . After the V-shaped clip  53  is placed over the leaflets at the commissure  23 , the shroud of the fabric cover  56  is pulled down to cover the outward side of the insert member  51  and the leaflet tabs  37 , and the free ends thereof are wrapped around the insert member  51  and sutured together (using sutures, not shown). Also, the fabric cover  56  may be sutured to the insert member  51  and leaflet tabs  37  through the aligned holes at the insert member  51  for additional support, such as by using a stitch  57 . The V-shaped clips  53  are desirably formed of a flexible material that flexes apart during an opening cycle of the valve wherein fluid flow through the valve causes the free edges  35  of adjacent leaflet tabs  37  to separate.  
         [0043]    In this manner the leaflet tabs  37  are anchored to the commissures  23  by the clamping action between the insert  51  and the V-shaped clip  53 . That is, each leaflet  31  experiences radially inward forces upon closing of the valve  21 , which also tends to pull the insert member  51  inwardly. Because the fabric cover  56  attaches to the surrounding native aorta, and thus the V-shaped clip  53  is retained thereby, this radially inward movement of the insert member  51  clamps the leaflet tabs  37  between the insert member and the clip. This anchoring prevents the sutures, such as suture  57 , from being directly stressed and pulled apart through the leaflet material when the valve closes by blood flow during diastole. Further, this anchoring prevents any tissue stitches from being exposing to direct hemodynamic loading and thus prevent stress concentration.  
         [0044]    FIGS.  9 - 11  show an alternative embodiment of the invention wherein a cusp support structure  39 ′ comprises three separate rounded sections  65  each respectively supporting the rounded cusp edge  33  of a leaflet. Adjacent rounded sections maybe interconnected with separate connector sections  67  and intermediate V-shaped clips  53 . The connector sections  67  may be made of a highly compliant material, for example a fabric, silicone or other elastomer to allow the rounded sections to move with respect to one another and more flexibly accommodate static or dynamic distortions in the shape of the native heart tissue. As before, insert  51  and V-shaped clips  53  are shown in the relative orientation as before to form the valve commissures to which the leaflet tabs (not shown) attach.  
         [0045]    The three separate rounded sections  65  may be relatively rigid rod-like elements made of biocompatible metals or polymers. Alternatively, the rounded sections  65  may be made of a preformed biocompatible fabric having a radially outward tab to which the cusp edge of a leaflet attaches. In the latter case, the rounded sections  65  are less rigid than a metal or polymer material, but provide sufficient stiffness to facilitate fabrication and implantation.  
         [0046]    [0046]FIG. 10 shows the use of the scalloped-shaped cusp support structure of FIG. 9 with a corresponding scalloped shaped sewing band  55 . As is known, this scalloped shape more readily accommodates use of the sewing band as a platform to suture the sewing band to aortic root tissue, which is likewise scalloped. In this embodiment the sewing band is sutured directly to the valve annulus, with the commissure posts attached to the aortic wall to allow the leaflets to fluctuate radially inwardly and outwardly in a more natural manner. The inserts  51  are desirably directly sutured to the sewing band  55 , and thus there is no direct connection between the inserts  51  and the cusp support structure  39 ′, and the valve commissures remain free to move inwardly and outwardly.  
         [0047]    [0047]FIG. 12 shows a leaflet of prior art tissue-type replacement heart valves. The free edge  71  of prior art leaflets generally extends straight across between the opposed tabs  73 .  
         [0048]    For the present invention, the tissue leaflets should be configured as shown in either FIG. 13A or  13 B for reduced stress in the highly flexible valves. Leaflet free edge  35  between the tabs  37  is concave with either one or more curvatures (i.e., simple or complex curves). The outline of the free edge  71  of a prior art leaflet is shown in phantom superimposed over the new leaflets. As can be seen, extra material  75  is provided at the leaflet tabs  37  to accommodate the additional stresses imposed upon the leaflets from the increased radially inward and outward movement of the valve commissures. That is, the leaflet tabs  37  are axially higher than the middle portions of the free edges. In the embodiment of FIGS.  13 A, the leaflet tabs  37  continue outward a straight edge  77  from the concave free edge  35 . In the embodiment of FIG. 13B, a concave transition filet  79  is provided from an apex  81  of the free edge  35  to reduce the height of the tabs at the valve commissures from that shown in FIG. 13A. The triangular region near the apex  81  is not placed in direct tension from valve closure forces, and helps reduce stress concentrations in the integrally connected regions that are in direct tension.  
         [0049]    Referring now to FIG. 14, in an alternative embodiment, the lower end of each insert member  51 ′ bifurcates to straddle the commissure base section  43 . The lower end of the insert member  51  thus straddles the base section  43  to facilitate radially inward and outward pivoting and reduces the tendency to slip off of the commissure base section. The bifurcation ends  83  seen in FIGS. 16A and 16B are disposed on either side of the commissure base section  43  and are secured thereto using a suture  85 .  
         [0050]    [0050]FIG. 14 shows the relative orientation of the three valve commissure posts, each including a V-shaped clip  53 , an insert member  51 ′ and the cusp support structure  39 , when they are assembled. FIG. 15 shows the embodiment of FIG. 14 further including the sewing band  55  in phantom.  
         [0051]    In the various valves of the present invention, structural support from the cusp supports is provided to facilitate fabrication and implantation. The commissures remain flexibly coupled to the rest of the valve to enable aortic wall mounting, and dynamic coupling with the natural tissue. A concave free edge of the leaflet, preferably with an apex region that is not placed in direct tension, further prevents stress risers in the leaflets, and contributes to durability.  
         [0052]    While the foregoing is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Moreover, it will be obvious that certain other modifications may be practiced within the scope of the appended claims.