Abstract:
A prosthetic heart valve includes a collapsible and expandable support frame extending between an inflow end and an outflow end and a plurality of commissures, wherein each commis sure is formed with an elongate opening. A plurality of leaflets are supported inside the support structure and operative for allowing flow in a first direction from the inflow end to the outflow end and to substantially block flow in an opposite direction from the outflow end to the inflow end. Each of the plurality of leaflets includes tabs. The prosthetic heart valve includes at least a first panel of fabric covering the opening of a first commissure. The first panel of fabric is attached to a first tab of a first leaflet via a suture extending orthogonal to the first panel of fabric, wherein the first panel of fabric is positioned radially outwardly of the first tab.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. application Ser. No. 15/138,115, filed Apr. 25, 2016, which is a continuation of U.S. application Ser. No. 13/648,119, filed Oct. 9, 2012, now U.S. Pat. No. 9,320,598, which is a continuation of U.S. application Ser. No. 12/170,341, filed Jul. 9, 2008, now U.S. Pat. No. 8,778,018, which is a divisional of U.S. application Ser. No. 10/390,951, filed Mar. 18, 2003, now U.S. Pat. No. 7,399,315, all of which are incorporated by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to medical implants, and more particularly to minimally-invasive or collapsible/expandable heart valves and methods of delivering and implanting such valves. 
       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 or bioprosthetic-type valve. Bioprosthetic-type valves are often preferred over mechanical valves because they typically do not require long-term treatment with anticoagulants. The most common bioprosthetic-type valves are constructed with whole porcine (pig) valves, or with separate leaflets cut from bovine (cow) pericardium. 
         [0005]    Although so-called stentless valves, comprising a section of xenograft (e.g., porcine) aorta and valve, are available, the most widely used valves include some form of artificial leaflet support. One such support is an elastic “support frame,” sometimes called a “wireform” or “stent,” which has a plurality (typically three) of large radius U-shaped cusps supporting the cusp region of the leaflets of the bioprosthetic tissue (i.e., either a whole valve or three separate leaflets). The free ends of each two adjacent cusps converge somewhat asymptotically to form upstanding commissures that terminate in U-shaped tips, each being curved in the opposite direction as the cusps, and having a relatively smaller radius. The support frame typically describes a conical tube with the commissure tips at the small diameter end. This provides an undulating reference shape to which a fixed edge of each leaflet attaches (via components such as fabric and sutures) much like the natural fibrous skeleton in the aortic annulus. Therefore, 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. 
         [0006]    The support frame is typically a non-ferromagnetic metal such as ELGILOY (a Co—Cr alloy) that possesses substantial elasticity. A common method of forming metallic support frames is to bend a wire into a flat (two-dimensional) undulating pattern of the alternating cusps and commissures, and then roll the flat pattern into a tube using a cylindrical roller. The free ends of the resulting three-dimensional shape, typically in the asymptotic region of the cusps, are then fastened together using a tubular splice that is plastically crimped around the ends. See FIGS. 3 and 4 of U.S. Pat. No. 6,296,662 for a support frame that is crimped together at a cusp midpoint. 
         [0007]    Some valves include polymeric “support frames” rather than metallic, for various reasons. For example, U.S. Pat. No. 5,895,420 discloses a plastic support frame that degrades in the body over time. Despite some favorable attributes of polymeric support frames, for example the ability to mold the complex support frame shape, conventional metallic support frames are generally preferred for their elastic properties, and have a proven track record in highly successfully heart valves. For example, the CARPENTIER-EDWARDS Porcine Heart Valve and PERIMOUNT Pericardial Heart Valve available from Edwards Lifesciences LLC both have ELGILOY support frames and have together enjoyed the leading worldwide market position since 1976. 
         [0008]    A conventional heart valve replacement surgery involves accessing the heart in the patient&#39;s thoracic cavity through a longitudinal incision in the chest. For example, a median sternotomy requires cutting through the sternum and forcing the two opposing halves of the rib cage to be spread apart, allowing access to the thoracic cavity and heart within. The patient is then placed on cardiopulmonary bypass which involves stopping the heart to permit access to the internal chambers. Such open heart surgery is particularly invasive and involves a lengthy and difficult recovery period. 
         [0009]    Some attempts have been made to enable less traumatic delivery and implantation of prosthetic heart valves. For instance, U.S. Pat. No. 4,056,854 to Boretos discloses a radially collapsible heart valve secured to a circular spring stent that can be compressed for delivery and expanded for securing in a valve position. Also, U.S. Pat. No. 4,994,077 to Dobbin describes a disk-shaped heart valve that is connected to a radially collapsible stent for minimally invasive implantation. 
         [0010]    Recently, a great amount of research has been done to reduce the trauma and risk associated with conventional open heart valve replacement surgery. In particular, the field of minimally invasive surgery (MIS) has exploded since the early to mid-1990s, with devices now being available to enable valve replacements without opening the chest cavity. MIS heart valve replacement surgery still typically requires bypass, but the excision of the native valve and implantation of the prosthetic valve are accomplished via elongated tubes or cannulas, with the help of endoscopes and other such visualization techniques. 
         [0011]    Some examples of more recent MIS heart valves are shown in U.S. Pat. No. 5,411,552 to Anderson, et al., U.S. Pat. No. 5,980,570 to Simpson, U.S. Pat. No. 5,984,959 to Robertson, et al., U.S. Pat. No. 6,425,916 to Garrison, et al., and PCT Publication No. WO 99/334142 to Vesely. 
         [0012]    Although these and other such devices provide various ways for collapsing, delivering, and then expanding a “heart valve” per se, none of them disclose much structural detail of the valve itself. For instance, the publication to Vesely shows a tissue leaflet structure of the prior art in  FIG. 1 , and an expandable inner frame of the invention having stent posts in  FIGS. 3A-3C . The leaflets are “mounted to the stent posts  22  in a manner similar to that shown in  FIG. 1 .” Likewise, Anderson describes mounting a porcine valve inside of an expandable stent “by means of a suitable number of sutures to form the cardiac valve prosthesis  9  shown in  FIG. 2 .” Such general disclosures stop short of explaining how to construct a valve in a manner that maximizes long-term efficacy. In particular, the particular means of attaching the leaflets to the MIS stent is critical to ensure the integrity and durability of the valve once implanted. All of the prior art MIS valves are inadequate in this regard. Furthermore, use of conventional support stents or wireforms is difficult in MIS valves because of the need to compress the valve into a relatively small diameter delivery package, which creates material challenges. 
         [0013]    Some MIS valves of the prior art are intended to be used without removing the natural valve leaflets. Sometimes the natural leaflets are heavily calcified, and their removal entails some risk of plaque particles being released into the bloodstream. Therefore, some of the MIS valves are designed to expand outward within the annulus and native leaflets, and compress the leaflets against the annulus. The relatively uneven surface of the calcified annulus and leaflets creates sizing problems and may complicate the delivery and placement steps. Prior art MIS valves are essentially tubular stents embellished with a native xenograft valve. The implant methodology is simply the conventional balloon expansion technique or pushing a self-expanding version from the end of a catheter. Minimal control over the placement of the valve is provided or contemplated. 
         [0014]    Despite some advances in MIS valve design, there remains a need for an MIS valve that is durable and which has a more flexible delivery and implantation methodology. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention provides improved prosthetic heart valves that can be implanted in a minimally-invasive manner, but which also has aspects that make it useful for conventional surgeries. The valves and implant tools and methods described herein provide a highly adaptive and simple to use endovascular delivery option for cardiac surgeons or cardiologists because of features that facilitate implantation. The valve is designed to be expelled from a delivery tube in an implant area and then expanded and/or positioned to contact the surrounding tissue without additional anchoring structures. Further, the valve and implant tools permit repositioning and even recollapse of the valve if needed. 
         [0016]    In accordance with a first aspect of the invention, a prosthetic heart valve support frame comprises a leaflet frame and three cusp positioners. The leaflet frame has a continuous, undulating shape that mimics the natural fibrous structure of an aortic valve. The leaflet frame has three cusp regions alternating with and intermediate three commissure regions, the three cusp regions being positioned at an inflow end of the support frame and circumferentially about a flow axis defined within the support frame. The three commissure regions are positioned at an outflow end of the support frame and circumferentially about the flow axis. The three cusp positioners are rigidly fixed with respect to the leaflet frame and are disposed circumferentially about the flow axis. Each cusp positioner is located at the outflow end of the support frame and intermediate two of the commis sure regions of the leaflet frame. 
         [0017]    The leaflet frame and the cusp positioners may be formed integrally as a single piece. Desirably, the support frame is formed by a process comprising providing a two-dimensional blank of the support frame, and forming the two-dimensional blank into the three-dimensional heart valve support frame. The leaflet frame and the cusp positioners may be made of Nitinol, preferably with a martensitic transition temperature of less than about 5° C. and an austenitic transition temperature of more than about 20° C. 
         [0018]    Each cusp positioner of the heart valve support frame desirably has a U-shape with an apex of the U-shape pointing toward the outflow end of the support frame and two legs of the U-shape pointing toward the inflow end. Each of the two legs of each U-shaped cusp positioner may be rigidly fixed to the continuous leaflet frame at a location approximately midway between a cusp region and a commissure region thereof. An anti-migration member such as an elongated section terminating in an enlarged and rounded head can be rigidly fixed to each cusp positioner to project therefrom. The cusp positioners may flare outwardly from the rest of the support frame to better contact surrounding tissue. 
         [0019]    The support frame further may include three cusp connectors rigidly fixed with respect to the leaflet frame and disposed circumferentially about the flow axis. Each cusp connector is located at the inflow end of the support frame and intermediate two of the cusp regions of the leaflet frame. Each cusp connector desirably has a U-shape with an apex of the U-shape pointing toward the inflow end of the support frame and two legs of the U-shape pointing toward the outflow end. In a preferred embodiment, the leaflet frame, cusp positioners, and cusp connectors are formed integrally as a single piece, and the three cusp positioners and three cusp connectors define a continuous, undulating shape that generally mimics the shape of the leaflet frame but is rotated 60° about the flow axis therefrom. 
         [0020]    Another aspect of the invention is a collapsible prosthetic heart valve that has a collapsible leaflet frame, three separate, flexible leaflets attached to the leaflet frame, and three cusp positioners rigidly fixed with respect to the leaflet frame. The leaflet frame has three cusp regions intermediate three commissure regions, the three cusp regions being positioned at an inflow end of the leaflet frame and circumferentially about a flow axis defined within the support frame. The three commissure regions are positioned at an outflow end of the leaflet frame and circumferentially about the flow axis. Each flexible leaflet has an arcuate cusp edge opposite a free edge and a pair of commissure edges therebetween. The leaflets attach around the leaflet frame with the cusp edge of each leaflet extending along one of the cusp regions, and a commissure edge of each leaflet meeting a commissure edge of an adjacent leaflet at one of the commissure regions. The three cusp positioners are rigidly fixed with respect to the leaflet frame and are disposed circumferentially about the flow axis, each cusp positioner being located at the outflow end of the leaflet frame and intermediate two of the commissure regions of the leaflet frame. 
         [0021]    The heart valve may incorporate the aforementioned features of the support frame, for example a leaflet frame with a continuous, undulating shape that mimics the natural fibrous structure of an aortic valve, cusp connectors, and anti-migration members on each cusp positoiner. Desirably, an inflow periphery of the heart valve is defined along alternating and rigidly fixed cusp regions and cusp connectors. The inflow periphery may have an external fabric covering, and the heart valve may further includes a fabric panel defining an exterior surface of the heart valve between each pair of cusp positioner and cusp connector. Preferably, the leaflet frame has a fabric covering along substantially its entire length, the fabric covering defining a flange, and wherein the arcuate cusp edges of the flexible leaflets attach to the fabric covering flange. The fabric covering flange may project generally outward from the leaflet frame such that the cusp edges of the flexible leaflets extend radially outward past and underneath the leaflet frame to be sewn to the fabric covering flange. Each flexible leaflet may have a pair of tabs extending on either side of its free edge, wherein two tabs of adjacent flexible leaflets meet and pass together to the outside of the adjacent commissure region of the leaflet frame and are attached thereto using sutures through the tabs. 
         [0022]    In accordance with a still further aspect of the invention, a collapsible prosthetic heart valve comprises:
       a continuous, collapsible leaflet frame having three U-shaped cusp regions intermediate three U-shaped commissure regions, the three cusp regions being positioned at an inflow end of the leaflet frame and circumferentially about a flow axis defined within the leaflet frame, the three commissure regions being positioned at an outflow end of the leaflet frame and circumferentially about the flow axis;   a cloth covering extending around the leaflet frame; and   three separate, flexible leaflets attached to the leaflet frame, each leaflet having an arcuate cusp edge opposite a free edge and a pair of commissure edges therebetween, the leaflets being attached around the leaflet frame with the cusp edge of each leaflet extending along one of the cusp regions, and a commissure edge of each leaflet meeting a commis sure edge of an adjacent leaflet at one of the commissure regions, the commissure edges of each leaflet further including a tab, wherein the tabs of two adjacent leaflets extend through the U-shape commissure region, diverge on the outside of commissure region, and are attached to the leaflet frame on the outside of the commis sure region.       
 
         [0026]    The present invention also encompasses a method of implanting a prosthetic aortic heart valve with a first step of providing a collapsible prosthetic heart valve having a collapsible leaflet frame defined by three cusp regions on an inflow end of the valve intermediate three commissure regions on an outflow end of the valve. The valve includes three cusp positioners on the outflow end and intermediate the three commissure regions. The method includes collapsing the prosthetic heart valve within a delivery tube, advancing the prosthetic heart valve within the delivery tube to an aortic annulus, expelling the prosthetic heart valve from the delivery tube by relative movement therebetween, expanding the prosthetic heart valve, and positioning the prosthetic heart valve such that the cusp positioners contact the two coronary and one non-coronary sinuses of the ascending aorta without blocking the coronary ostia. 
         [0027]    The method preferably includes the step of connecting a holder having flexible members to the commissure regions of the prosthetic heart valve and utilizing the flexible members to perform the step of positioning the prosthetic heart valve. Flexible members of the holder may also be connected to the cusp positioners and utilized to perform the step of positioning the prosthetic heart valve, or to rotate the prosthetic heart valve during the step of positioning. Advantageously, the flexible members may be used to re-collapse the prosthetic heart valve after the step of expanding. The prosthetic heart valve is desirably expanded in a location that is inferior to a final implant position such that the cusp positioners contact the surrounding aortic annulus, and the step of positioning comprises displacing the valve in a superior direction to a final implant position. The cusp positioners may be flared outward to define a circle about a flow axis of the valve greater than a circle about the flow axis defined by the three commissure regions, such that the step of displacing the valve in a superior direction causes the outwardly flared cusp positioners to be channeled into perspective coronary sinuses. 
         [0028]    In accordance with a preferred method, the collapsible leaflet frame is formed of a shape memory alloy having a martensitic transition temperature less than room temperature and an austenitic transition temperature less than body temperature, and the step of collapsing is done with the material of the leaflet frame at a temperature less than its martensitic transition temperature. For example, the step of collapsing may be done in conjunction with immersing the prosthetic heart valve in an ice bath to reduce the temperature of the material of leaflet frame to below its martensitic transition temperature. In another aspect, the collapsible leaflet frame may be formed of a shape memory alloy having a memory condition in its expanded state, and wherein the step of expanding the prosthetic heart valve comprises both permitting self-expansion of the valve to an intermediate diameter and then using a physical expander to increase the diameter of the valve to the memory condition of the leaflet frame. 
         [0029]    A further method of implanting a collapsible prosthetic heart valve provided by the present invention comprises first providing a self-expanding valve comprised of a material displaying hysteresis in the elastic or superelastic region. The valve is permitted to self-expand to a first diameter, and then the valve is assisted with a physical expander such as a balloon to further expand to a second diameter. 
         [0030]    The prosthetic heart valve may includes a collapsible leaflet frame formed of a shape memory alloy having a martensitic transition temperature less than room temperature and an austenitic transition temperature less than body temperature, and the method may further include a step of collapsing the valve with the material of the leaflet frame at a temperature less than its martensitic transition temperature. Fir example, the step of collapsing may be done in conjunction with immersing the prosthetic heart valve in an ice bath to reduce the temperature of the material of leaflet frame to below its martensitic transition temperature. 
         [0031]    The prosthetic heart valve may have a collapsible leaflet frame defined by three cusp regions on an inflow end of the valve intermediate three commissure regions on an outflow end of the valve, and three cusp positioners on the outflow end and intermediate the three commissure regions. In this case, the method may further include:
       collapsing the prosthetic heart valve within a delivery tube;   advancing the prosthetic heart valve within the delivery tube to an aortic annulus;   expelling the prosthetic heart valve from the delivery tube by relative movement therebetween;   expanding the prosthetic heart valve by the steps of permitting self-expansion and assisting further expansion; and   positioning the prosthetic heart valve such that the cusp positioners contact the two coronary and one non-coronary sinuses of the ascending aorta without blocking the coronary ostia.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a partial view of a patient&#39;s heart generally vertically section through the left ventricle and associated heart valves, and illustrating the implantation approach of a catheter-based prosthetic valve of the present invention; 
           [0038]      FIG. 2A  is a vertical sectional view through an aortic annulus and an exemplary prosthetic heart valve of the present invention implanted therein; 
           [0039]      FIG. 2B  is a top plan view of the implanted prosthetic heart valve of  FIG. 2A ; 
           [0040]      FIGS. 3A-3C  are perspective, top plan, and bottom plan views, respectively, of the prosthetic heart valve of  FIG. 2A ; 
           [0041]      FIG. 4  is a plan view of a prosthetic heart valve support frame of the present invention in a two-dimensional blank form prior to conversion to three-dimensional final form; 
           [0042]      FIG. 5  is a perspective view of the prosthetic heart valve support frame of  FIG. 4  in its three-dimensional final form with a leaflet frame and cusp positioners; 
           [0043]      FIGS. 5A and 5B  are views of a portion of the three-dimensional heart valve support frame of  FIG. 5  showing alternative cusp positioner configurations; 
           [0044]      FIG. 6A  is an elevational view of a partially assembled prosthetic heart valve as in  FIGS. 3A-3C ; 
           [0045]      FIG. 6B  is an elevational view of the prosthetic heart valve of  FIG. 6A  fully assembled; 
           [0046]      FIG. 7  is a plan view of an exemplary leaflet used in the prosthetic heart valves of the present invention; 
           [0047]      FIG. 8  is a partial sectional view of a commis sure region of the exemplary prosthetic heart valve taken along line  8 - 8  of  FIG. 3B ; 
           [0048]      FIG. 9  is a sectional view through a portion of the support frame of the exemplary prosthetic heart valve, taken along line  9 - 9  of  FIG. 8 ; 
           [0049]      FIG. 10  is a sectional view through a commissure tip region of the exemplary prosthetic heart valve, taken along line  10 - 10  of  FIG. 8 ; 
           [0050]      FIG. 11  is a schematic perspective view of a prosthetic heart valve support frame of the present invention being loaded into a delivery catheter; 
           [0051]      FIG. 12  is a perspective view of the support frame after having been loaded into a delivery catheter; 
           [0052]      FIGS. 13A-13B  are perspective and elevational views of an exemplary compressible/expandable heart valve holder attached to a prosthetic heart valve of the present invention; 
           [0053]      FIG. 14  is a perspective view of the expulsion of an assembled prosthetic heart valve and holder as in  FIGS. 13A and 13B  from the distal end of a delivery catheter; 
           [0054]      FIG. 15  is a bottom plan view of an exemplary compressible/expandable heart valve holder of the present invention; 
           [0055]      FIG. 16  is a plan view of a multi-armed flexible portion of the holder of  FIG. 15 ; and 
           [0056]      FIGS. 17A-17B  are two views of a rigid portion of the holder of  FIG. 15 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0057]    The present invention provides an improved minimally invasive (MIS) valve support frame, MIS valve, and methods of construction and delivery as described herein and shown in the accompanying drawings. 
         [0058]    The invention pertains primarily to flexible leaflet heart valves and internal support frames, which are also referred to in the art as stents or wireforms. As mentioned above, the flexible leaflets can be formed from biological (e.g., bovine pericardium) or synthetic material. In this context, a “support frame” for a flexible leaflet heart valve provides the primary internal structural support for the leaflets, and substantially mimics the natural fibrous skeleton of the respective valve annulus. More specifically, each of the leaflets has an outer edge that is coupled to a portion of the support frame such that its inner edge is free to move within the orifice area of the valve, thus providing the opening and closing surfaces thereof. A biological xenograft valve can be used to provide the flexible leaflets in the valves of the present invention, though the internal support frame is particularly suited to receive individual leaflets. 
         [0059]    The leaflet frames of the present invention have a continuous, undulating shape with three arcuate or U-shaped cusp regions on the inflow end separated by three upstanding and generally axially-oriented arcuate or U-shaped commissure regions on the outflow end. Around the circumference of the leaflet frame, the shape has an alternating structure of cusp-commissure-cusp-commissure-cusp-commissure, and generally describes a conical surface of revolution with the three commissures on the outflow end of the valve being closer together than the three cusps. Some support frames may alternatively describe a tubular surface of revolution about an axis. The cusp regions and commissure regions are evenly distributed about a flow axis through the support frame, and therefore the three cusp regions are 120° apart from each other, and each of the three commissure regions is 120° apart from the next and 60° from the adjacent cusp regions. 
         [0060]    The term “continuous” to describe the heart valve leaflet frame means that a single continuous and closed-shape line (i.e., loop) can be drawn following the sequential cusp and commissure regions, and “undulating” refers to the serpentine or alternating sinusoidal character of the line. More generally, a continuous, undulating heart valve leaflet frame approximates the shape of the natural fibrous tissue around the aortic valve annulus so as to mimic that natural support structure for optimum functionality of the prosthetic leaflets. 
         [0061]    The present invention primarily pertains to prosthetic heart valves suitable for minimally invasive delivery and implantation. Such minimally invasive valves are capable of being compressed or collapsed into a small profile and delivered through a catheter or cannula (a tube) to the site of implantation for remote expansion and anchoring thereto. It should be understood, however, that certain aspects of the invention described herein are beneficial for prosthetic heart valves in general, and thus not all of the claims should be construed to require a minimally invasive valve. 
         [0062]      FIG. 1  depicts a portion of a heart of a patient with the left ventricle LV, aortic valve AV, mitral valve MV, and ascending aorta AA shown in section. A delivery catheter or tube  20  is seen in position just prior to complete expulsion and expansion of a prosthetic heart valve  22  from a distal end thereof for implant at the aortic valve AV annulus. The aortic valve AV leaflets L may first be excised prior to implant of the valve  22 , or more preferably the leaflets L remain in place and are expanded outward and compressed against the lumen of the aortic valve AV annulus upon expansion of the valve. The distal end of the delivery tube  20  may optionally be stabilized by a balloon  24  (shown in phantom) inflated against the lumen of the ascending aorta AA, or through other means. The delivery tube  20  is preferably inserted in the vasculature of the patient using a larger diameter introducer  26  through a peripheral vessel such as the femoral artery or femoral vein. Alternatively, the peripheral vessel may be the internal jugular vein, the subclavian artery, the axillary artery, the abdominal aorta, the descending aorta, or any other suitable blood vessel. The introducer  26  may be inserted by surgical cut down or percutaneously using the Seldinger technique. 
         [0063]      FIGS. 2A and 2B  illustrate the prosthetic heart valve  22  implanted at the aortic valve AV annulus. The heart valve  22  includes three cusps  30  on an inflow end (one of which is not visible) and three commissures  32  on an outflow end. The direction of blood flow BF is indicated with an arrow in the ascending aorta AA. The natural leaflets are desirably compressed against the lumen of the aortic valve annulus by the prosthetic heart valve  22 , as seen in  FIG. 2B . The valve  22  is oriented about a flow axis such that the commissures  32  are generally aligned with the native commissures C, while the cusps (not shown but intermediate the commissures  32 ) are generally aligned with the natural cusps/leaflets L. The heart valve  22  contacts the lumen wall of the aortic valve AV annulus and desirably retains its position due to friction therebetween. In this regard, the heart valve  22  expands from its delivery configuration shown in  FIG. 1  to the expanded configuration in  FIGS. 2A and 2B . 
         [0064]    The valve  32  contacts the lumen wall around the entire periphery of the inflow end thereof and in certain areas adjacent to the inflow periphery, as will be explained below. The inflow periphery is defined by the lower ends of the cusps  30  as well as by the lower ends of three cusps connectors  40  that extend between and fill the gaps between the cusps  30 . Additionally, the heart valve  22  includes three cusp positioners  42 , two of which are visible in  FIG. 2A , that are rigidly fixed with respect to an internal valve support frame and are each located generally at the outflow end of the valve intermediate two of the commissures  32 . With reference to  FIG. 2B , the cusp positioners  42  are evenly distributed about a central flow axis  44 , and when implanted align with the native leaflets L. The cusp positioners  42  preferably extend radially farther outward than the commissures  32  and compress the leaflets L against the natural sinus cavities formed just above the aortic valve AV annulus. Coronary ostia CO open from two of the three sinus cavities, as seen in  FIG. 2A , and the cusp positioners  42  are sized and placed by the operator to avoid occluding flow through the coronary ostia CO. The advantageous structure and function of these cusp positioners  42  will be more fully explained below. 
         [0065]    With reference now to  FIGS. 3A-3C , the exemplary prosthetic heart valve  22  will be more fully described. The shape of an internal support frame  50  seen in  FIG. 5  generally governs the shape of the valve  22 . As mentioned, the valve  22  includes the aforementioned cusps  30  and commissures  32  evenly distributed about a flow axis  44 . The cusps  30  and cusp connectors  40  define a scalloped inflow periphery of the valve  22 , while the outflow periphery is defined by the three commissures  32  and the three cusp positioners  42 . The entire internal support frame  50  except for the cusp positioners  42  is covered over with one or more layers of material, the exterior layer of which is typically a fabric as shown (but not numbered). The use of a fabric such as polyethylene terephthalate provides a matrix into which surrounding tissue can grow to help anchor the valve in place. 
         [0066]    Three flexible leaflets  52  mount to the valve  22  in a trifoil configuration with free edges  53  thereof arranged to meet or coapt in the middle of the valve and provide one-way occlusion. An outer edge of each leaflet  52  attaches to the valve  22  between two of the commissures  32  and around one of the cusps  30 . An exemplary structural attachment of the leaflets  52  to the internal support frame  50  will be described below. 
         [0067]    As mentioned, each cusp connector  40  extends between two of the cusps  30 . A panel of fabric or other material  54  covers an area between the inflow or lower edge of each cusp connector  40  and the corresponding commissures  32 . Some of this panel of fabric  54  desirably contacts the lumen wall of the aortic valve AV annulus to help prevent leakage around the valve. 
         [0068]    The exemplary cusp positioners  42  each have an inverted U-shape with an apex pointed toward the outflow end of the valve  22  and two legs extending generally toward the inflow end and connecting with the remainder of the valve. The term “U-shape” is intended to cover all configurations that have two legs and an apex therebetween. Other figurative descriptions such as V-shaped, bell-shaped, sinusoidal, arcuate, or the like are therefore encompassed by the term “U-shape”. It is contemplated, however, that the cusp positioners  42  could assume other forms, such as a generally linear, cantilevered arm extending upward from the midpoint of each cusp  30 . In whatever form, the cusp positioners  42  provide the valve  22  with three points of contact with the surrounding tissue that is midway between the three commissures  32  so as to help stabilize and anchor the valve in its implant position. Moreover, the cusp positioners  42  desirably perform the function of compressing the native leaflets L outward against the sinus cavities, at least in those procedures where the leaflets L are not excised. 
         [0069]    The leaflets L in a diseased valve may be less than flexible, and indeed may be highly calcified. It is often considered preferable to avoid removing the leaflets L so as to avoid disturbing the calcification or other stenotic material that has built up around the leaflets. Therefore, the present invention desirably provides structure to compress the native leaflets L outward against the aortic wall sinus cavities and hold the leaflets in that position so as to avoid flapping and potentially interfering with blood flow through the prosthetic valve. The inverted U-shape of the cusp positioners  42  is believed to provide effective structure to both anchor the valve in the aortic valve AV annulus and also control, or corral, if you will, the obsolete native leaflets L. At the same time, the cusp positioners  42  are relatively minimal in total area so as to avoid unduly interfering with back flow of blood on the outflow side of each of the leaflets  52 , or to the coronary ostia CO. Therefore, the cusp positioners  42  are desirably defined by relatively thin members, as shown, as opposed to walls or panels, or the like. Multiple cusp positioners  42  per valve cusp  30  are conceivable, though the total solid volume taken up by the cusp positioners should be kept to a minimum so as to minimize the risk of occluding the coronary ostia CO. 
         [0070]    The axial height of the cusp positioners  42  relative to the commissures  32  is seen best in  FIG. 2A  (and in  FIG. 6B ). Preferably, the commissures  32  are slightly taller than the cusp positioners  42 , although such an arrangement is not considered mandatory. The main consideration in the size of the cusp positioners  42  is to avoid occluding the coronary ostia CO. Therefore, as seen in  FIG. 2A , the cusp positioners  42  contact the surrounding aortic valve AV lumen wall just below the coronary ostia CO. Of course, the anatomy of each patient differs slightly from the next, and the precise position of the coronary ostia CO cannot be predicted with absolute certainty. Furthermore, the final location of the cusp positioners  42  is dependent on the skill of the cardiac surgeon or cardiologist. In the ideal situation, however, the cusp positioners  42  are positioned just below and aligned circumferentially with the coronary ostia CO as seen in  FIGS. 2A and 2B . 
         [0071]      FIGS. 2B and 3B-3C  illustrate the relative outward radial position of the cusp positioners  42  with respect to the commissures  32  therebetween, and with respect to the cusp connectors  40 . As seen in the isolated view of the heart valve support frame  50  in  FIG. 5 , the cusp positioners  42  are angled or flared outward from the remainder of the support frame. This outward flaring helps ensure good contact between the apex of the cusp positioners  42  and the surrounding walls of the aortic valve AV sinus cavities. In this regard, the outer configuration of the heart valve  22  is designed to maximize contact with the aortic valve AV lumen wall both in the annulus and for a short distance into each sinus cavity. This extensive surface contact between the prosthetic valve  22  and the surrounding tissue may obviate the need for sutures, staples, sharp barbs or other such anchoring structure, although such structure could be used in conjunction with the valve. The valve  22  is merely expelled from the end of the delivery tube  20  ( FIG. 1 ), expanded with or without assistance of a balloon, and held in place by frictional contact between the inflow periphery against the annulus, and between the cusp positioners  42  and the sinus cavities (or intervening native leaflets). 
         [0072]    Each cusp positioner  42  further includes at least one anti-migration member  56  rigidly fixed thereto and designed to help anchor the support frame  50  to the surrounding tissue. In the illustrated embodiment, the anti-migration members  56  each preferably includes an elongated section  58  terminating in an enlarged and rounded head  60 , the configuration thus somewhat resembling a spoon. The anti-migration member  56  desirably projects out of the plane defined by the associated cusp positioner  42 , and may extend generally axially in the inflow direction from the apex thereof, as seen in  FIG. 3A . When the valve  22  is implanted, the anti-migration members  56  are designed to contact and become somewhat entrapped in the native leaflets. Therefore, the anti-migration members  56  act as a rounded barb of sorts to maintain the valve  22  in its implant position. The members  56  also may help prevent flapping of the native leaflets in the swirling blood flow. Numerous other configurations are contemplated, the general idea being that the anti-migration member  56  enhances the ability of the associated cusp positioner  42  to anchor to the surrounding tissue. In this regard, the term “anti-migration member” is meant to include any structure that enhances such anchoring, including both blunt and sharp structures (i.e., barbs). 
         [0073]    Various procedures and apparatuses for converting a two-dimensional blank such as shown in  FIG. 4  to the three-dimensional form of  FIG. 5  are described in more detail in co-pending U.S. patent application Ser. No. 10/251,651, filed Sep. 20, 2002, and entitled continuous heart valve support frame and method of manufacture. In short, the process involves bending the two-dimensional blank  70  around a cylindrical or conical mandrel and altering the material so as to retain its three-dimensional shape. For example, various nickel-titanium alloys (Nitinol) may be easily bent around a mandrel and then set into that shape using heat treatments. 
         [0074]    In an exemplary embodiment of the present invention, the internal support frame  50  of the valve  22  is made of a material that is highly flexible so as to permit maximum relative movement between the valve cusps and commissures, and in some cases to permit constriction into a small profile diameter for minimally invasive delivery to an implantation site. At the same time the support frame must possess a minimum amount of stiffness to provide the desired support to the leaflets. Therefore, there is a balance obtained between the requisite flexibility and stiffness. 
         [0075]    The material for the internal support frame is desirably “elastic,” which means that it has the capacity to rebound from imposed strain. Various NITINOL alloys are especially suitable for making the internal support frame of the present invention as in certain circumstances they are considered to be “superelastic.” Other materials that may be used include ELGILOY, titanium, stainless-steel, even polymers, and similar expedients. These latter materials do not display superelasticity but are still elastic. Other materials may fit within this definition but they must be suitable for long-term implantation in the body. 
         [0076]    The term “superelastic” (sometimes “pseudoelastic”) refers to that property of some materials to undergo extreme strains (up to 8%) without reaching their failure stress limit. Some so-called shape memory alloys (SMAs) are known to display a superelastic phenomena or rubber-like behavior in which a strain attained beyond the elastic limit of the SMA material during loading is recovered during unloading. This superelastic phenomenon occurs when load is applied to an austenitic SMA article which first deforms elastically up to the yield point of the SMA material (sometimes referred to as the critical stress). Upon the further imposition of load, the SMA material begins to transform into stress-induced martensite or “SIM.” This transformation takes place at essentially constant stress, up to the point where the SMA material is completely transformed into martensite. When the stress is removed, the SMA material will revert back into austenite and the article will return to its original, pre-programmed programmed or memorized shape. 
         [0077]    The support frame  50  is desirably constructed of a material that exhibits hysteresis in the elastic and/or superelastic region. “Hysteresis” indicates that when the material is strained beyond the “memory condition” (defined as unconstrained geometry) it produces a stress-strain curve that is different and higher than the stress-strain curve produced as the material attempts to return to its memory condition. An example of a material that exhibits such a hysteresis is NITINOL. The presence of this hysteresis implies that it requires a greater force to displace the material form its memory condition than the material exerts as it recovers to its memory condition. 
         [0078]    When using NITINOL the shape set is done at a particular temperature for a period of time designed to ensure certain properties in the material. Namely, the martensitic transition temperature is desirably less than room temperature and the austenitic transition temperature is desirably less than body temperature. For instance, the temperature below which the material is in martensitic form is around 0-5° C., while the temperature above which the material is in austenitic form is around 20-25° C. When the material is shape set in this way, the heart valve  22  can be cooled, such as in an ice bath, just prior to implant to change the crystalline structure of the support frame  50  to martensite and create high flexibility so as to enable compaction thereof into a small diameter delivery profile. After implant and expansion, the temperature rises from body heat above the austenitic transition temperature and thus the support frame  50  possesses the desired degree of stiffness to properly support the leaflets. 
         [0079]    The support frame  50  (and blank  70 ) includes a leaflet frame  72  defined by three cusp regions  74  intermediate three commissure regions  76 . In  FIG. 4  the leaflet frame  72  in the blank  70  exhibits a three-leaf clover shape, while in  FIG. 5  the leaflet frame  72  has a continuous, undulating shape as described above. A second three-leaf clover shape can be seen in  FIG. 4  formed by the three cusp connectors  40  and three cusp positioners  42 . When bent into the three-dimensional configuration of  FIG. 5 , two continuous, undulating shapes can be seen oriented 60° with respect to one another about the central flow axis. Each cusp connector  40  includes an apex  80  and a pair of legs  82  that rigidly attach to the leaflet frame  72  at junction points  84 . Likewise, each cusp positioner  42  includes an apex  90  and a pair of legs  92  that rigidly attach to the leaflet frame  72  at junction points  94 . In the preferred and illustrated embodiment, the junction points  84  and  94  are coincident. 
         [0080]      FIGS. 5A and 5B  show alternative cusp positioner configurations for the three-dimensional heart valve support frame  50  of  FIG. 5 . As mentioned above, the anti-migration members facilitate anchoring of the support frame  50  to the surrounding anatomy, and prevent axial and rotational movement of the valve  22 . The anti-migration members  56  shown in  FIG. 5  project generally axially in the inflow direction from the apex  90  of each cusp positioner  42 . In  FIG. 5A , a second anti-migration member  57  projects generally axially in the outflow direction from the apex  90  of each cusp positioner  42 . In  FIG. 5B , there are multiple anti-migration members  56  extending generally axially in the inflow direction. Various combinations, placements and orientations of these examples are contemplated, and the examples should not be considered limiting. 
         [0081]      FIG. 6A  shows the valve  22  almost completely assembled, but without the aforementioned cloth covers  54  that are seen in the fully assembled valve of  FIG. 6B . The covers  54  help prevent leakage of blood around the implanted valve  22 , and specifically in the areas between the each pair of cusps  30 . 
         [0082]      FIG. 7  illustrates an exemplary leaflet  52  in plan view. The free edge  50  is shown as linear, but may also be arcuate, angled, trapezoidal, or other configuration. Each leaflet includes a pair of opposed generally rectangular tabs  100  at either end of the free edge  53 . An arcuate cusp edge  102  extends between the tabs  100  and opposite the free edge  53 . The tabs  100  and arcuate cusp edge  102  are secured to the valve  22 , and specifically along the contours of the leaflet frame  72  seen in  FIG. 5 . 
         [0083]      FIG. 8  is an enlarged cutaway view of one of the commissures  32  of the valve  22  taken along line  8 - 8  of  FIG. 3B  and showing the internal construction thereof. The commissure region  76  of the leaflet frame  72  tapers down in the outflow direction to a closed tip  104 . Attachment flanges  106  are formed adjacent the tip  104  and desirably include a plurality of assembly holes  108  sized to permit passage of sutures therethrough. The adjacent leaflets  52  come together in the commissure regions  76  and the tabs  100  thereof are folded away from each other on the exterior of the flanges  106 . 
         [0084]    As seen in  FIG. 9 , the cusp edge  102  of each leaflet  52  attaches with sutures  110  to a cloth flange  112  of a tubular fabric cover  114  around the leaflet frame  72 . This configuration causes tensile forces imparted by the leaflets  52  to be transferred as much as possible to the frame  72  rather than being primarily borne by the attachment sutures  110 . 
         [0085]      FIG. 10  shows the attachment structure at the commissure tip  104 , and specifically illustrates sutures  120  passing through the fabric cover  114 , through the assembly holes  108 , and through the folded leaflet tabs  100 . A second suture  122  passes through the cloth flange  112 , the leaflet tab  100 , and cloth covers  54  (also shown in  FIG. 6B ). Because each of the leaflets  52  includes the tab  100  that extends to the outside of the leaflet frame  72 , high forces that are seen with closing of the valve are less likely to pull the sutures  120  through the tabs. That is, the construction shown in  FIG. 10  causes tensile forces imparted by the leaflets  52  to be transferred as much as possible from the sutures  120 ,  122  to the frame  72 , thus helping to prevent tearing of the flexible leaflets and rendering the valve  22  more durable. 
         [0086]      FIGS. 11 and 12  schematically illustrate a technique for loading a prosthetic heart valve of the present invention into a delivery tube. For the sake of clarity, only the support frame  50  is shown being loaded into the delivery tube  20 . A plurality of sutures or other such flexible members or filaments  130  are shown looped through each of the commissure regions  76  of the support frame  50 . These filaments  130  extend into the distal end of the delivery tube  20  and through its lumen to a proximal end (not shown) where they are connected to a tensioning device. In actual use, the filaments  130  would be threaded through the commissures  32  of the valve  22 , avoiding the flexible leaflets. A loading adapter  132  couples to the distal end of the delivery tube  20 . The adapter  132  includes an inner funnel-shaped opening  134 . Tension on the filaments  130  pulls the commissures  32  of the valve into the funnel-shaped opening  134  which gradually compresses the valve into a diameter smaller than the lumen of the delivery tube  20 . Once the valve  22  is positioned fully within the delivery tube  20 , as seen in  FIG. 12 , the filaments  130  and adapter  132  are removed. 
         [0087]      FIGS. 13-17  illustrate a minimally invasive holder for use with the prosthetic heart valves of the present invention.  FIGS. 13A and 13B  show the holder  150  attach to the heart valve  22  as described above. The holder  150  includes a multi-armed flexible portion  152  and a rigid portion  154  (seen in  FIGS. 17A-17B ). The flexible portion  152  includes a plurality, at least three, but preferably six flexible members or arms  156  extending outward from a central circular disk  158 . Each of the arms  156  terminates in a rounded end having an attachment aperture  160 . The arms  156  are distributed evenly about the circumference of the circular disk  158 , and are arrayed to attach to each of the commissures  32  and cusp positioners  42  of the valve  22 . Releasable sutures  162  or other such attachment structure are used for this purpose. 
         [0088]      FIG. 14  shows the assembled holder  150  and valve  22  emerging from the distal end of a delivery tube  20 . Prior to this stage, the flexible members or arms  156  are oriented generally axially within the tube  20  with the valve  22  also collapsed and having its outflow prongs coupled to the distal ends of the arms  156 . The arms  156  of the holder  150  are sufficiently flexible to be compressed into the small profile required for delivery through the delivery tube  20 . In this regard, the flexible portion  152  is desirably made of Nitinol. A handle  170  which may be flexible or rigid attaches to the holder  150  for manipulation thereof. Displacing the handle  170  in a distal direction with respect to the tube  20  therefore expels the valve/holder combination and the resiliency of the valve  22  and holder arms  156  causes them to spring outward. It should be understood that other designs of the holder  150  may be utilized, such as replacing the spring-like arms  156  with rigid members that are hinged and spring-biased. 
         [0089]      FIGS. 15-17  illustrate specifics of the exemplary flexible portion  152  and rigid portion  154 . In a relaxed configuration, the flexible portion  152  is planar, and may be cut from a sheet of Nitinol. The rigid portion  154  includes a proximal face  180  that is sized approximately the same as the circular disk  158 , and small enough to fit within the delivery tube  20 . A central threaded bore  182  opens to the proximal face  180  for receiving the handle  170 .  FIG. 15  illustrates a number of sutures  162  threaded through the holder  150  and used to couple the holder to the six outflow prongs of the prosthetic heart valve  22 . Desirably, these sutures  162  are anchored with respect to the holder and each one passes over a cutting guide in the holder such that the suture may be severed along its midpoint resulting in two free ends that can be pulled free of the valve. 
         [0090]    The holder  150  is sufficiently flexible to be compressed into a small profile and passed through the delivery tube  20 . At the same time, the flexible portion  152  and multiple flexible arms  156  have a sufficient degree of torsional strength to permit the operator to rotate the valve  22  during the implant procedure. Furthermore, the arms  156  are shaped to contact the distal mouth of the delivery tube  20  when the assembly is pulled toward the tube which, due to their radial stiffness, causes the arms to bend back toward their axial orientation within the tube. Since the distal ends of the arms are coupled to at least three of the outflow prongs of the prosthetic heart valve  22 , the valve constricts accordingly. Constriction of the valve  22  after having been fully expelled from the end of the delivery tube and expanded permits repositioning of the valve  22 . That is, the cusp positioners  42  are designed to contact the sinuses cavities or aortic wall after the valve  22  expands, and the retraction/constriction option afforded by the holder  150  may be necessary to disengage the cusp positioners from the surrounding tissue to reposition or re-orient the valve. Furthermore, the valve  22  can be completely collapsed and retracted back into the delivery tube to permit removal in case the surgeon or cardiologist deems the valve unsuitable for whatever reason. 
       Method of Use 
       [0091]    Prior to implant, the cardiac surgeon or cardiologist measures the aortic valve AV annulus using appropriate sizers, minimally invasive or not as the case may be, a number of which are available and which will not be further described herein. The correctly sized valve is then selected and compressed into the delivery catheter or tube  20 , such as with the use of the loading adapter  132  having the inner funnel-shaped opening  134  as seen in  FIG. 11 . To facilitate this loading step, the inner support frame  50  of the valve  20  must be able to withstand high stresses without failure. One method is to form the support frame  50  from a material that has superelastic properties, for instance a Nitinol that has a martensitic transition temperature of less than about 5° C. can be immersed in an ice bath to change its crystalline structure to martensite, which is a superelastic phase. Once loaded into the delivery tube  20 , the support frame  50  will not revert back to its original shape upon a temperature rise and thus does not exert undue outward force on the tube. The heart valve  22  may be loaded around an inflation balloon, but for the sake of a small profile the balloon is used after expulsion of the valve from the tube at the implantation site. 
         [0092]    With reference again to  FIG. 1 , the delivery tube  20  is seen in position just prior to complete expulsion and expansion of the prosthetic heart valve  22  from a distal end thereof for implant at the aortic valve AV annulus. The distal end of the delivery tube  20  may optionally be stabilized by a balloon  24  (shown in phantom) inflated against the lumen of the ascending aorta AA, or through other means. The delivery tube  20  is preferably inserted in the vasculature of the patient using a larger diameter introducer  26  through a peripheral vessel such as the femoral artery or femoral vein. Alternatively, the peripheral vessel may be the internal jugular vein, the subclavian artery, the axillary artery, the abdominal aorta, the descending aorta, or any other suitable blood vessel. The introducer  26  may be inserted by surgical cut down or percutaneously using the Seldinger technique. 
         [0093]    The prosthetic heart valve  22  is expelled from the delivery tube  20  by relative movement therebetween—i.e., by pushing the valve from the tube or by retracting the tube from around the valve. The valve  22  desirably self-expands into contact with the surrounding lumen wall, but may also be assisted with an inflation balloon or other such physical expander. 
         [0094]    With reference to  FIGS. 2A and 2B , the cusps positioners  42  help guide the prosthetic heart valve  22  into position in the aortic valve AV annulus. As mentioned above, the cusp positioners  42  desirably flare outward from the rest of the valve structure and are thus configured to contact the sinuses of the aortic valve AV while the cusps  30  are sized to fit within the annulus. In accordance with one method of implantation, the surgeon or cardiologist expels the heart valve  22  below (i.e., toward the left ventricle) its optimum implant position, and then axially displaces the valve upward into the desired position. Stated another way, the heart valve  22  is expanded in a location that is inferior to a final implant position such that the cusp positioners  42  contact the surrounding aortic annulus, and the valve is then repositioned by displacing the valve in a superior direction to a final implant position. As the valve  22  ascends, the cusp positioners  42  spring outward into the three valve sinuses and help rotationally orient the valve. That is, the sinuses channel the cusp positioners  42  and correct any rotational misalignment. Finally, the valve  22  is implanted with the cusp positioners  42  in the sinus cavities (preferably below the coronary ostia CO) and the cusps  30  and cusp connectors  40  forming a scalloped yet continuous contact wall against the aortic valve AV annulus or root. 
         [0095]    As mentioned, a physical expander (e.g., balloon) may be used to radially outwardly expand the valve  22  (including the internal support frame  50 ) beyond its self-expanded diameter so that it is firmly anchored in place. A prosthetic valve possessing hysteresis that is held in a reduced (first or constrained) diameter will exert an outward radial force that is less than the force at which it will resist an inward radial force. Therefore, if deployed in-situ, the device is not expected to exert enough force on the vessel wall to expand to the desired diameter. However, if the expansion is assisted by means of a balloon or other physical expander, the hysteresis of the material will allow it to better maintain its diameter once that diameter is achieved. This is unlike a self-expanding device that relies solely on the outward radial force of the device to achieve its desired diameter. It is also unlike balloon expanded devices that rely on a balloon to plastically deform the device into the desired diameter. Although it is conceivable that a balloon or other physical expander could be used in a self-expanding device made of a material that does not display a hysteresis, the benefits would not be as great. 
         [0096]    It will be appreciated that the invention has been described hereabove with reference to certain examples or preferred embodiments as shown in the drawings. Various additions, deletions, changes and alterations may be made to the above-described embodiments and examples, and it is intended that all such additions, deletions, changes and alterations be included within the scope of the following claims.