Patent Publication Number: US-2022226111-A1

Title: Prosthetic heart valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/516,089 filed Jul. 18, 2019, which is a continuation of U.S. patent application Ser. No. 15/194,375, filed Jun. 27, 2016, now U.S. Pat. No. 10,537,423, which is a continuation of U.S. patent application Ser. No. 13/253,689, filed Oct. 5, 2011, now U.S. Pat. No. 9,393,110, which claims the benefit of U.S. Provisional Application No. 61/390,107, filed Oct. 5, 2010, and U.S. Provisional Application No. 61/508,513, filed Jul. 15, 2011, all of which are herein incorporated by reference. 
    
    
     FIELD 
     The present disclosure concerns embodiments of prosthetic heart valves, and delivery systems for implanting heart valves. 
     BACKGROUND 
     The human heart can suffer from various valvular diseases. These valvular diseases can result in significant malfunctioning of the heart and ultimately require replacement of the native valve with an artificial valve. There are a number of known artificial valves and a number of known methods of implanting these artificial valves in humans. 
     Various surgical techniques may be used to replace or repair a diseased or damaged valve. Due to stenosis and other heart valve diseases, thousands of patients undergo surgery each year wherein the defective native heart valve is replaced by a prosthetic valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. The problem with surgical therapy is the significant risk it imposes on these chronically ill patients with high morbidity and mortality rates associated with surgical repair. 
     When the native valve is replaced, surgical implantation of the prosthetic valve typically requires an open-chest surgery during which the heart is stopped and patient placed on cardiopulmonary bypass (a so-called “heart-lung machine”). In one common surgical procedure, the diseased native valve leaflets are excised and a prosthetic valve is sutured to the surrounding tissue at the valve annulus. Because of the trauma associated with the procedure and the attendant duration of extracorporeal blood circulation, some patients do not survive the surgical procedure or die shortly thereafter. It is well known that the risk to the patient increases with the amount of time required on extracorporeal circulation. Due to these risks, a substantial number of patients with defective native valves are deemed inoperable because their condition is too frail to withstand the procedure. By some estimates, more than 50% of the subjects suffering from valve stenosis who are older than 80 years cannot be operated on for valve replacement. 
     Because of the drawbacks associated with conventional open-heart surgery, percutaneous and minimally-invasive surgical approaches are garnering intense attention. In one technique, a prosthetic valve is configured to be implanted in a much less invasive procedure by way of catheterization. For instance, U.S. Pat. Nos. 5,411,522 and 6,730,118, which are incorporated herein by reference, describe collapsible transcatheter heart valves that can be percutaneously introduced in a compressed state on a catheter and expanded in the desired position by balloon inflation or by utilization of a self-expanding frame or stent. 
     An important design parameter of a transcatheter heart valve is the diameter of the folded or crimped profile. The diameter of the crimped profile is important because it directly influences the physician&#39;s ability to advance the transcatheter heart valve through the femoral artery or vein. More particularly, a smaller profile allows for treatment of a wider population of patients, with enhanced safety. 
     SUMMARY 
     The present disclosure is directed toward methods and apparatuses relating to prosthetic valves, such as heart valves, delivery apparatuses, and assemblies of heart valves mounted on delivery apparatuses. 
     An exemplary embodiment of an assembly for implanting a prosthetic heart valve in a patient&#39;s body comprises a delivery apparatus comprising an elongated shaft and a radially expandable prosthetic heart valve mounted on the shaft in a radially collapsed configuration for delivery into the body. The prosthetic heart valve comprises an annular frame having an inflow end portion and an outflow end portion, and a leaflet structure positioned within the frame. The outer diameter of the inflow end portion of the frame is smaller than the outer diameter of the outflow end portion of the frame. The reduced diameter of the inflow end can be due to a reduce amount of materials positioned within the inflow end portion of the frame. The reduced diameter at the inflow end portion can make room for an outer skirt positioned around the inflow end portion. 
     In some embodiments, the heart valve can further comprise an outer skirt positioned around an outer surface of the inflow end portion of the frame such that an outer diameter of an inflow end portion of the prosthetic valve, inclusive of the outer skirt, is still less than or equal to an outer diameter of an outflow end portion of the prosthetic valve. 
     In some embodiments, the leaflet structure can comprise a plurality of leaflets that each comprises opposing side tabs on opposite sides of the leaflet. The side tabs can be secured to the outflow end portion of the frame. Each leaflet can further comprise a free outflow edge portion extending between the side tabs adjacent to the outflow end of the frame and an inflow edge portion extending between the side tabs adjacent to the inflow end of the frame. The inflow edge portion can comprise opposing axial edge portions that extend from the side tabs toward the inflow end in a generally axial direction and an intermediate edge portion that extends between the axial edge portions. The intermediate edge portion can comprise a curved apex portion adjacent to the inflow end of the frame and a pair of oblique portions that extend between the axial edge portions and the apex portion. The oblique portions can have a greater radius of curvature than the apex portion, forming a generally V-shaped leaflet. 
     In some embodiments, the frame comprises a plurality of angularly spaced commissure windows each comprising an enclosed opening between first and second axially oriented side struts. In these embodiments, the leaflet structure comprises a plurality of leaflets each comprising two opposing side tabs, each side tab being paired with an adjacent side tab of an adjacent leaflet to form commissures of the leaflet structure. Each commissure extends radially outwardly through a corresponding commissure window of the frame to a location outside of the frame and is sutured to the side struts of the commissure window. In some of these embodiments, the commissure windows of the frame are depressed radially inwardly relative to the portions of the frame extending between adjacent commissure windows when the prosthetic valve is in the collapsed configuration on the shaft. 
     In some embodiments, the frame comprises an inflow row of openings at the inflow end portion of the frame, an outflow row of openings at the outflow end portion of the frame, and at least one intermediate row of openings between the inflow row of openings and outflow row of openings. The openings of the inflow row of openings are larger than the openings of the at least one intermediate row of openings. 
     In some embodiments, portions of the leaflet structure protrude through openings in the frame while in the collapsed configuration on the shaft. 
     In some embodiments, the inflow end portion of the frame comprises a frame thickness that is less than a frame thickness of an intermediate portion of the frame between the inflow end portion and the outflow end portion. 
     Embodiments disclosed here can comprise an implantable prosthetic valve that is radially collapsible to a collapsed configuration and radially expandable to an expanded configuration. Such prosthetic valves can comprise an annular frame, a leaflet structure positioned within the frame, and an annular outer skirt positioned around an outer surface of the frame. The outer skirt can comprise an inflow edge secured to the frame at a first location, an outflow edge secured to the frame at a second location, and an intermediate portion between the inflow edge and the outflow edge. When the valve is in the expanded configuration, the intermediate portion of the outer skirt comprises slack in the axial direction between the inflow edge of the outer skirt and the outflow edge of the outer skirt, and when the valve is collapsed to the collapsed configuration, the axial distance between the inflow edge of the outer skirt and the outflow edge of the outer skirt increases, reducing the slack in the outer skirt in the axial direction. 
     In some of these embodiments, the outer skirt is not stretched in the axial direction when the valve is radially collapsed to the collapsed configuration and slack is removed from the intermediate portion of the outer skirt. 
     Some embodiments of an implantable prosthetic valve comprise an annular frame comprising a plurality of leaflet attachment portions, and a leaflet structure positioned within the frame and secured to the leaflet attachment portions of the frame. The leaflet structure comprises a plurality of leaflets, each leaflet comprising a body portion, two opposing primary side tabs extending from opposite sides of the body portion, and two opposing secondary tabs extending from the body adjacent to the primary side tabs. The secondary tabs are folded about a radially extending crease such that a first portion of the secondary tabs lies flat against the body portion of the respective leaflet, and the secondary tabs are folded about an axially extending crease such that a second portion of the secondary tabs extends in a different plane than the first portion. The second portion of each secondary tab is sutured to a respective primary tab and the secondary tabs are positioned inside of the frame. 
     In some of these embodiments, the first portion of each the secondary tab pivots about the axially extending crease and lays flat against the second portion of the secondary tab when the valve is collapsed to a radially collapsed configuration. The first portion of each secondary tab comprises an inner edge spaced radially from an inner surface of the frame, and the body portion of the leaflet articulates about the inner edges of the two secondary tabs of the leaflet in response to blood flowing through the valve when the valve is in operation within a patient&#39;s body. 
     Some embodiments disclosed herein comprise an implantable prosthetic valve that is radially collapsible to a collapsed configuration and radially expandable to an expanded configuration. The prosthetic valve comprises an annular frame having an inflow end portion and an outflow end portion, a leaflet structure positioned within the frame, and an annular inner skirt positioned within the frame. The inner skirt is secured to the inside of the frame and the inner skirt comprises a weave of a first set of strands with a second set of strands, both the first and second sets of strands being non-parallel with the axial direction of the valve. When the valve is collapsed from the expanded configuration to the collapsed configuration, the axial length of the frame increases and the both the first and second sets of strands rotate toward the axial direction of the valve, allowing the inner skirt to elongate in the axial direction along with the frame. 
     In some of these embodiments, the first set of strands are substantially perpendicular to the second set of strands when the valve is in the expanded configuration. In some embodiments, the first set of strands forms a first angle with the axial direction of the valve and the second set of strands forms a second angle with the axial direction of the valve, the first and second angles being substantially equal. In some of these embodiments, the first and second sets of strands comprise 20-denier yarn. 
     Some embodiments of an implantable prosthetic valve comprise a radially collapsible and expandable annular frame comprising a plurality of angularly spaced commissure windows each comprising an enclosed opening between first and second axially oriented side struts. The valve also comprises a leaflet structure positioned within the frame and comprising a plurality of leaflets each comprising two opposing side tabs. Each side tab is paired with an adjacent side tab of an adjacent leaflet to form commissures of the leaflet structure. Each pair of side tabs extends radially outwardly through a corresponding commissure window to a location outside of the frame, the portions of the tabs located outside of the frame extending circumferentially away from one another and along an exterior surface of the side struts. The valve further comprises a plurality of wedges, each wedge being positioned between the side struts of a commissure window and separating the pair of side tabs extending through the commissure window, the wedge being urged radially inwardly against the side tabs. 
     The wedges can be elongated in an axial direction and correspond in axial length with an axial length of the side struts of the commissure windows. The wedges can further restrict rotational movement of the pair of side tabs relative to the commissure window. Each wedge can be sutured to a flexible reinforcing sheet that is also sutured to each of the pair of side tabs, and each can be sutured to the pair of side tabs. The wedges can comprise a non-metallic material, such as suture material. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-3  show an exemplary embodiment of a prosthetic heart valve. 
         FIGS. 4-10  show an exemplary frame of the heart valve of  FIG. 1 . 
         FIGS. 11, 12, 13, 14, 15A, and 15B  show another exemplary frame for use in a prosthetic heart valve. 
         FIGS. 16A and 16B  show an exemplary inner skirt of the heart valve of  FIG. 1 . 
         FIG. 17  shows another embodiment of a prosthetic heart valve in a compressed (crimped) condition with a deformed frame. 
         FIG. 18  shows the heart valve of  FIG. 1  in a compressed state and mounted on an exemplary balloon catheter. 
         FIGS. 19A, 9B, and 20  show the assembly of the inner skirt of  FIG. 16A  with the frame of  FIG. 4 . 
         FIGS. 21-28  show the assembly of an exemplary leaflet structure. 
         FIGS. 29-35  show the assembly of commissure portions of the leaflet structure with window frame portions of the frame. 
         FIGS. 36-40  show the assembly of the leaflet structure with the inner skirt along a lower edge of the leaflets. 
         FIG. 41  shows an exemplary outer skirt laid out flat. 
         FIGS. 42 and 43  show the exemplary prosthetic heart valve of  FIG. 1 . 
         FIGS. 44-48  show an alternative embodiment of a prosthetic heart valve. 
         FIGS. 49-52  show portions of an alternative embodiment of a frame. 
         FIG. 53  shows a portion of the frame of  FIG. 4  in a radially compressed state. 
         FIG. 54  shows a cross-sectional profile of the frame of  FIG. 4 , showings a general tapering from the outflow end to the inflow end. 
         FIG. 55  shows the frame of  FIG. 4  in an unrolled, flat configuration. 
         FIG. 56  shows the heart valve of  FIG. 1  in a compressed state and mounted on an exemplary balloon catheter. 
         FIGS. 57 and 58  shows an embodiment of a leaflet have a generally V-shaped configuration. 
         FIG. 59  shows a cross-sectional view of an alternative embodiment of a prosthetic valve having a variable thickness frame. 
         FIG. 60  is a side view of an embodiment of a frame of a valve having commissure windows, prior to mounting a leaflet structure to the frame. 
         FIG. 60A  is an enlarged side view of one commissure window of  FIG. 60 . 
         FIG. 61  is a perspective view of an embodiment of a prosthetic valve comprising the frame of  FIG. 60  and a leaflet structure mounted to the valve. 
         FIG. 62  is an enlarged side view of one commissure of the valve of  FIG. 61 . 
         FIGS. 63-71  are cross-sectional views of a commissure of the valve of  FIG. 61  showing various techniques for suturing a pair of leaflet side tabs to a commissure window using a reinforcing sheet. 
         FIGS. 72-74  show balloon expansion of an alternative embodiment of a frame for a prosthetic valve having inflow and outflow end portions of reduced thickness. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3  show various views of a prosthetic heart valve  10 , according to one embodiment. The illustrated valve is adapted to be implanted in the native aortic annulus, although in other embodiments it can be adapted to be implanted in the other native annuluses of the heart. The valve  10  can have four main components: a stent, or frame,  12 , a valvular structure  14 , an inner skirt  16 , and an outer skirt  18 . 
     The valvular structure  14  can comprise three leaflets  40 , collectively forming a leaflet structure, which can be arranged to collapse in a tricuspid arrangement, as best shown in  FIG. 2 . The lower edge of leaflet structure  14  desirably has an undulating, curved scalloped shape (suture line  154  shown in  FIG. 1  tracks the scalloped shape of the leaflet structure). By forming the leaflets with this scalloped geometry, stresses on the leaflets are reduced, which in turn improves durability of the valve. Moreover, by virtue of the scalloped shape, folds and ripples at the belly of each leaflet (the central region of each leaflet), which can cause early calcification in those areas, can be eliminated or at least minimized. The scalloped geometry also reduces the amount of tissue material used to form leaflet structure, thereby allowing a smaller, more even crimped profile at the inflow end of the valve. The leaflets  40  can be formed of pericardial tissue (e.g., bovine pericardial tissue), biocompatible synthetic materials, or various other suitable natural or synthetic materials as known in the art and described in U.S. Pat. No. 6,730,118, which is incorporated by reference herein. 
     The bare frame  12  is shown in  FIG. 4 . The frame  12  can be formed with a plurality of circumferentially spaced slots, or commissure windows,  20  (three in the illustrated embodiment) that are adapted to mount the commissures of the valvular structure  14  to the frame, as described in greater detail below. The frame  12  can be made of any of various suitable plastically-expandable materials (e.g., stainless steel, etc.) or self-expanding materials (e.g., Nitinol) as known in the art. When constructed of a plastically-expandable material, the frame  12  (and thus the valve  10 ) can be crimped to a radially compressed state on a delivery catheter and then expanded inside a patient by an inflatable balloon or equivalent expansion mechanism. When constructed of a self-expandable material, the frame  12  (and thus the valve  10 ) can be crimped to a radially compressed state and restrained in the compressed state by insertion into a sheath or equivalent mechanism of a delivery catheter. Once inside the body, the valve can be advanced from the delivery sheath, which allows the valve to expand to its functional size. 
     Suitable plastically-expandable materials that can be used to form the frame  12  include, without limitation, stainless steel, a nickel based alloy (e.g., a cobalt-chromium or a nickel-cobalt-chromium alloy), polymers, or combinations thereof. In particular embodiments, frame  12  is made of a nickel-cobalt-chromium-molybdenum alloy, such as MP35N™ (tradename of SPS Technologies), which is equivalent to UNS R30035 (covered by ASTM F562-02). MP35N™/UNS R30035 comprises 35% nickel, 35% cobalt, 20% chromium, and 10% molybdenum, by weight. It has been found that the use of MP35N to form frame  12  provides superior structural results over stainless steel. In particular, when MP35N is used as the frame material, less material is needed to achieve the same or better performance in radial and crush force resistance, fatigue resistances, and corrosion resistance. Moreover, since less material is required, the crimped profile of the frame can be reduced, thereby providing a lower profile valve assembly for percutaneous delivery to the treatment location in the body. 
     Referring to  FIGS. 4 and 5 , the frame  12  in the illustrated embodiment comprises a first, lower row I of angled struts  22  arranged end-to-end and extending circumferentially at the inflow end of the frame; a second row II of circumferentially extending, angled struts  24 ; a third row III of circumferentially extending, angled struts  26 ; a fourth row IV of circumferentially extending, angled struts  28 ; and a fifth row V of circumferentially extending, angled struts  32  at the outflow end of the frame. A plurality of substantially straight axially extending struts  34  can be used to interconnect the struts  22  of the first row I with the struts  24  of the second row II. The fifth row V of angled struts  32  are connected to the fourth row IV of angled struts  28  by a plurality of axially extending window frame portions  30  (which define the commissure windows  20 ) and a plurality of axially extending struts  31 . Each axial strut  31  and each frame portion  30  extends from a location defined by the convergence of the lower ends of two angled struts  32  to another location defined by the convergence of the upper ends of two angled struts  28 .  FIGS. 6, 7, 8, 9 and 10  are enlarged views of the portions of the frame  12  identified by letters A, B, C, D and E, respectively, in  FIG. 4 . 
     Each commissure window frame portion  30  mounts a respective commissure of the leaflet structure  14 . As can be seen each frame portion  30  is secured at its upper and lower ends to the adjacent rows of struts to provide a robust configuration that enhances fatigue resistance under cyclic loading of the valve compared to known cantilevered struts for supporting the commissures of the leaflet structure. This configuration enables a reduction in the frame wall thickness to achieve a smaller crimped diameter of the valve. In particular embodiments, the thickness T of the frame  12  ( FIG. 4 ) measured between the inner diameter and outer diameter is about 0.48 mm or less. 
     The struts and frame portions of the frame collectively define a plurality of open cells of the frame. At the inflow end of the frame  12 , struts  22 , struts  24 , and struts  34  define a lower row of cells defining openings  36 . The second, third, and fourth rows of struts  24 ,  26 , and  28  define two intermediate rows of cells defining openings  38 . The fourth and fifth rows of struts  28  and  32 , along with frame portions  30  and struts  31 , define an upper row of cells defining openings  40 . The openings  40  are relatively large and are sized to allow portions of the leaflet structure  14  to protrude, or bulge, into and/or through the openings  40  when the frame  12  is crimped in order to minimize the crimping profile. 
     As best shown in  FIG. 7 , the lower end of the strut  31  is connected to two struts  28  at a node or junction  44 , and the upper end of the strut  31  is connected to two struts  32  at a node or junction  46 . The strut  31  can have a thickness S 1  that is less than the thicknesses S 2  of the junctions  44 ,  46 .  FIG. 53  shows a portion of the frame  12  in a crimped state. The junctions  44 ,  46 , along with junctions  64 , prevent full closure of openings  40 .  FIG. 18  shows the valve  10  crimped on a balloon catheter. As can be seen, the geometry of the struts  31 , and junctions  44 ,  46  and  64  assists in creating enough space in openings  40  in the crimped state to allow portions of the leaflets to protrude (i.e., bulge) outwardly through openings. This allows the valve to be crimped to a relatively smaller diameter than if all of the leaflet material is constrained within the crimped frame. 
     The frame  12  is configured to prevent or at least minimize possible over-expansion of the valve at a predetermined balloon pressure, especially at the outflow end portion of the frame, which supports the leaflet structure  14 . In one aspect, the frame is configured to have relatively larger angles  42   a,    42   b,    42   c,    42   d,    42   e  between struts. The larger the angle, the greater the force required to open (expand) the frame. This phenomenon is schematically illustrated in  FIGS. 15A and 15B .  FIG. 15A  shows a strut  32  when the frame  12  is in its compressed state (e.g., mounted on a balloon). The vertical distance d 1  between the ends of the struts is greatest when the frame is compressed, providing a relatively large moment between forces F 1  and F 2  acting on the ends of the strut in opposite directions upon application of an opening force from inflation of the balloon (or expansion of another expansion device). When the frame expands radially, the vertical distance between the ends of the strut decreases to a distance d 2 , as depicted in  FIG. 15B . As the vertical distance decreases, so does the moment between forces F 1  and F 2 . Hence, it can be seen that a relatively greater expansion force is required as the vertical distance and the moment between the ends of the strut decreases. Moreover, strain hardening (stiffening) at the ends of the strut increases as the frame expands, which increases the expansion force required to induce further plastic deformation at the ends of the strut. As such, the angles between the struts of the frame can be selected to limit radial expansion of the frame at a given opening pressure (e.g., inflation pressure of the balloon). In particular embodiments, these angles are at least 110 degrees or greater when the frame is expanded to its functional size, and even more particularly these angles are at least 120 degrees or greater when the frame is expanded to its functional size. 
     In addition, the inflow and outflow ends of a frame generally tend to over-expand more so than the middle portion of the frame due to the “dog boning” effect of the balloon used to expand the valve. To protect against over-expansion of the leaflet structure  14 , the leaflet structure desirably is secured to the frame  12  below the upper row of struts  32 , as best shown in  FIG. 1 .  FIG. 55  shows a flattened view of the frame  12  similar to  FIG. 5 , but showing a line  176  superimposed over the frame to indicate the position of the upper edges of the leaflets  40 . Thus, in the event that the outflow end of the frame is over-expanded, the leaflet structure is positioned at a level below where over-expansion is likely to occur, thereby protecting the leaflet structure from over-expansion. 
     In a known valve construction, the leaflets can protrude outwardly beyond the outflow end of the frame when the valve is crimped if the leaflets are mounted too close to the distal end of the frame. If the delivery catheter on which the crimped valve is mounted includes a pushing mechanism or stop member that pushes against or abuts the outflow end of the valve (for example, to maintain the position of the crimped valve on the delivery catheter), the pushing member or stop member can damage the exposed leaflets that extend beyond the outflow end of the frame. Another benefit of mounting the leaflets at a location spaced from the outflow end  178  of the frame is that when the valve is crimped on a delivery catheter, as shown in  FIG. 56 , the leaflets  40  do not protrude beyond the outflow end  178  of the frame in the axial direction. As such, if the delivery catheter includes a pushing mechanism or stop member that pushes against or abuts the outflow end of the valve, the pushing mechanism or stop member can contact the end  178  of the frame, and not leaflets  40 , so as to avoid damage to the leaflets. 
     Also, as can be seen in  FIG. 5 , the openings  36  of the lowermost row of openings in the frame are relatively larger than the openings  38  of the two intermediate rows of openings. As shown in  FIG. 54 , this allows the frame, when crimped, to assume an overall tapered shape that tapers from a maximum diameter D 1  at the outflow end of the valve to a minimum diameter D 2  at the inflow end of the valve. When crimped, the frame  12  has a reduced diameter region extending along a portion of the frame adjacent the inflow end of the frame, indicated by reference number  174 , that generally corresponds to the region of the frame covered by the outer skirt  18 . The diameter of region  174  is reduced compared to the diameter of the upper portion of the frame (which is not covered by the outer skirt) such that the outer skirt  18  does not increase the overall crimp profile of the valve. When the valve is deployed, the frame can expand to the cylindrical shape shown in  FIG. 4 . In one example, the frame of a 26-mm valve, when crimped, had a diameter D 1  of 14 French at the outflow end of the valve and a diameter D 2  of 12 French at the inflow end of the valve. 
       FIGS. 11 and 12  show an alternative frame  50  that can be incorporated in the valve  10 . The frame  50  comprises multiple rows of circumferentially extending, angled struts  52  that are connected to each other at nodes, or connecting portions,  54  and  56 . The uppermost row of struts  52  are connected to an adjacent row of struts by a plurality of axially extending struts  58  and commissure window frame portions  60 . Each commissure frame portion  60  defines a slot, or commissure window,  62  for mounting a respective commissure of the valvular structure, as described in greater detail below. In particular embodiments, the thickness T of the frame  50  is about 0.45 mm or less.  FIGS. 13 and 14  are enlarged views of the portions of the frame  50  identified by letters A and B, respectively, in  FIG. 12 . 
     The main functions of the inner skirt  16  are to assist in securing the valvular structure  14  to the frame  12  and to assist in forming a good seal between the valve and the native annulus by blocking the flow of blood through the open cells of the frame  12  below the lower edge of the leaflets. The inner skirt  16  desirably comprises a tough, tear resistant material such as polyethylene terephthalate (PET), although various other synthetic or natural materials can be used. The thickness of the skirt desirably is less than 6 mil, and desirably less than 4 mil, and even more desirably about 2 mil. In particular embodiments, the skirt  16  can have a variable thickness, for example, the skirt can be thicker at its edges than at its center. In one implementation, the skirt  16  can comprise a PET skirt having a thickness of about 0.07 mm at its edges and about 0.06 mm at its center. The thinner skirt can provide for better crimping performances while still providing good perivalvular sealing. 
     The skirt  16  can be secured to the inside of frame  12  via sutures  70 , as shown in  FIG. 39 . Valvular structure  14  can be attached to the skirt via one or more thin PET reinforcing strips  72  (which collectively can form a sleeve), discussed below, which enables a secure suturing and protects the pericardial tissue of the leaflet structure from tears. Valvular structure  14  can be sandwiched between skirt  16  and the thin PET strips  72  as shown in  FIG. 38 . Sutures  154 , which secure the PET strip and the leaflet structure  14  to skirt  16 , can be any suitable suture, such as an Ethibond suture. Sutures  154  desirably track the curvature of the bottom edge of leaflet structure  14 , as described in more detail below. 
     Known fabric skirts comprise a weave of warp and weft fibers that extend perpendicular to each other and with one set of fibers extending perpendicularly to the upper and lower edges of the skirt. When the metal frame, to which the fabric skirt is secured, is radially compressed, the overall axial length of the frame increases. Unfortunately, a fabric skirt, which inherently has limited elasticity, cannot elongate along with the frame and therefore tends to deform the struts of the frame and prevents uniform crimping. 
       FIG. 17  shows an example of a crimped valve where the struts have been deformed in several places, as indicated by reference number  100 , by a skirt having fibers that extend perpendicular to the upper and lower edges of the skirt. Moreover, the fabric tends to bunch or create bulges of excess material in certain locations, which limits the minimum crimping profile and prevents uniform crimping. 
     Referring to  FIG. 16B , in contrast to known fabric skirts, the skirt  16  desirably is woven from a first set of fibers, or yarns or strands,  78  and a second set of fibers, or yarns or strands,  80 , both of which are non-perpendicular to the upper edge  82  and the lower edge  84  of the skirt. In particular embodiments, the first set of fibers  78  and the second set of fibers  80  extend at angles of about 45 degrees relative to the upper and lower edges  82 ,  84 . The skirt  16  can be formed by weaving the fibers at 45 degree angles relative to the upper and lower edges of the fabric. Alternatively, the skirt can be diagonally cut from a vertically woven fabric (where the fibers extend perpendicular to the edges of the material) such that the fibers extend at 45 degree angles relative to the cut upper and lower edges of the skirt. As further shown in  FIG. 16B , the opposing short edges  86 ,  88  of the skirt desirably are non-perpendicular to the upper and lower edges  82 ,  84 . For example, the short edges  86 ,  88  desirably extend at angles of about 45 degrees relative to the upper and lower edges and therefore are aligned with the first set of fibers  78 . Therefore the overall shape of the skirt is that of a rhomboid. 
       FIGS. 19A and 19B  shows the skirt  16  after opposing edge portions  90 ,  92  have been sewn together to form the annular shape of the skirt. As shown, the edge portion  90  can be placed in an overlapping relationship relative to the opposite edge portion  92 , and the two edge portions can be sewn together with a diagonally extending suture line  94  that is parallel to edges  86 ,  88 . The upper edge portion of the skirt  16  can be formed with a plurality of projections  96  that define an undulated shape that generally follows the shape of the fourth row of struts  28  immediately adjacent the lower ends of axial struts  31 . In this manner, as best shown in  FIG. 20 , the upper edge of skirt  16  can be tightly secured to struts  28  with sutures  70 . Skirt  16  can also be formed with slits  98  to facilitate attachment of the skirt to the frame. Slits  98  are dimensioned so as to allow an upper edge portion of skirt to be partially wrapped around struts  28  and reduce stresses in the skirt during the attachment procedure. For example, in the illustrated embodiment, skirt  16  is placed on the inside of frame  12  and an upper edge portion of the skirt is wrapped around the upper surfaces of struts  28  and secured in place with sutures  70 . Wrapping the upper edge portion of the skirt around struts  28  in this manner provides for a stronger and more durable attachment of the skirt to the frame. The skirt  16  can also be secured to the first, second, and third rows of struts  22 ,  24 , and  26 , respectively, with sutures  70 . 
     Referring again to  FIG. 16B , due to the orientation of the fibers relative to the upper and lower edges, the skirt can undergo greater elongation in the axial direction (i.e., in a direction from the upper edge  82  to the lower edge  84 ). 
     Thus, when the metal frame  12  is crimped (as shown in  FIG. 18 ), the skirt  16  can elongate in the axial direction along with the frame and therefore provides a more uniform and predictable crimping profile. Each cell of the metal frame in the illustrated embodiment includes at least four angled struts that rotate towards the axial direction (i.e., the angled struts become more aligned with the length of the frame). The angled struts of each cell function as a mechanism for rotating the fibers of the skirt in the same direction of the struts, allowing the skirt to elongate along the length of the struts. This allows for greater elongation of the skirt and avoids undesirable deformation of the struts when the valve is crimped. 
     In addition, the spacing between the woven fibers or yarns can be increased to facilitate elongation of the skirt in the axial direction. For example, for a PET skirt  16  formed from 20-denier yarn, the yarn density can be about 15% to about 30% less than a conventional PET skirt. In some examples, the yarn spacing of the skirt  16  can be from about 155 yarns per inch to about 180 yarns per inch, such about 160 yarns per inch, whereas in a conventional PET skirt the yarn spacing can be from about 217 yarns per inch to about 247 yarns per inch. The oblique edges  86 ,  88  promote uniform and even distribution of the fabric material along inner circumference of the frame during crimping so as to minimize bunching of the fabric to facilitate uniform crimping to the smallest possible diameter. Additionally, cutting diagonal sutures in a vertical manner may leave loose fringes along the cut edges. The oblique edges  86 ,  88  help minimize this from occurring. As noted above,  FIG. 17  shows a crimped valve with a conventional skirt that has fibers that run perpendicular to the upper and lower edges of the skirt. Comparing  FIGS. 17 and 18 , it is apparent that the construction of skirt  16  avoids undesirable deformation of the frame struts and provides more uniform crimping of the frame. 
     In alternative embodiments, the skirt can be formed from woven elastic fibers that can stretch in the axial direction during crimping of the valve. The warp and weft fibers can run perpendicular and parallel to the upper and lower edges of the skirt, or alternatively, they can extend at angles between 0 and 90 degrees relative to the upper and lower edges of the skirt, as described above. 
     The inner skirt  16  can be sutured to the frame  12  at locations away from the suture line  154  so that the skirt can be more pliable in that area (see  FIG. 28 ). This can avoid stress concentrations at the suture line  154 , which attaches the lower edges of the leaflets to the skirt  16 . 
     As noted above, the leaflet structure  14  in the illustrated embodiment includes three flexible leaflets  40  (although a greater or fewer number of leaflets can be used). As best shown in  FIG. 21 , each leaflet  40  in the illustrated configuration has an upper (outflow) free edge  110  extending between opposing upper tabs  112  on opposite sides of the leaflet. Below each upper tab  112  there is a notch  114  separating the upper tab from a corresponding lower tab  116 . The lower (inflow) edge portion  108  of the leaflet extending between respective ends of the lower tabs  116  includes vertical, or axial, edge portions  118  on opposites of the leaflets extending downwardly from corresponding lower tabs  116  and a substantially V-shaped, intermediate edge portion  120  having a smooth, curved apex portion  119  at the lower end of the leaflet and a pair of oblique portions  121  that extend between the axial edge portions and the apex portion. The oblique portions can have a greater radius of curvature than the apex portion. Each leaflet  40  can have a reinforcing strip  72  secured (e.g., sewn) to the inner surface of the lower edge portion  108 , as shown in  FIG. 22 . 
     The leaflets  40  can be secured to one another at their adjacent sides to form commissures  122  of the leaflet structure. A plurality of flexible connectors  124  (one of which is shown in  FIG. 23 ) can be used to interconnect pairs of adjacent sides of the leaflets and to mount the leaflets to the commissure window frame portions  30 . The flexible connectors  124  can be made from a piece of woven PET fabric, although other synthetic and/or natural materials can be used. Each flexible connector  124  can include a wedge  126  extending from the lower edge to the upper edge at the center of the connector. The wedge  126  can comprise a non-metallic material, such as a rope or a piece of Ethibond 2-0 suture material, secured to the connector with a temporary suture  128 . The wedge  126  helps prevent rotational movement of the leaflet tabs once they are secured to the commissure window frame portions  30 . The connector  124  can have a series of inner notches  130  and outer notches  132  formed along its upper and lower edges. 
       FIG. 24  shows the adjacent sides of two leaflets  40  interconnected by a flexible connector  124 . The opposite end portions of the flexible connector  124  can be placed in an overlapping relationship with the lower tabs  116  with the inner notches  130  aligned with the vertical edges of the tabs  116 . Each tab  116  can be secured to a corresponding end portion of the flexible connector  124  by suturing along a line extending from an outer notch  132  on the lower edge to an outer notch  132  on the upper edge of the connector. Three leaflets  40  can be secured to each other side-to-side using three flexible connectors  124 , as shown in  FIG. 25 . 
     Referring now to  FIGS. 26 and 27 , the adjacent sub-commissure portions  118  of two leaflets can be sutured directly to each other. In the example shown, PTFE-6-0 suture material is used to form in-and-out stitches  133  and comb stitches  134  that extend through the sub-commissure portions  118  and the reinforcing strips  72  on both leaflets. The two remaining pairs of adjacent sub-commissure portions  118  can be sutured together in the same manner to form the assembled leaflet structure  14 , which can then be secured to the frame  12  in the following manner. 
     As noted above, the inner skirt  16  can be used to assist in suturing the leaflet structure  14  to the frame. As shown in  FIG. 28 , the skirt  16  can have an undulating temporary marking suture  136  to guide the attachment of the lower edges of each leaflet  40 . The skirt  16  itself can be sutured to the struts of the frame  12  using sutures  70 , as noted above, before securing the leaflet structure  14  to the skirt  16 . The struts that intersect the marking suture  136  desirably are not attached to the skirt  16 . This allows the skirt  16  to be more pliable in the areas not secured to the frame and minimizes stress concentrations along the suture line that secures the lower edges of the leaflets to the skirt. The portion of the skirt  16  demarcated by rectangle  140  initially is left unsecured to the frame  12 , and is later secured to the frame after the leaflet structure  14  is secured to the skirt, as further described below. As noted above, when the skirt is secured to the frame, the fibers  78 ,  80  of the skirt (see  FIG. 16B ) generally align with the angled struts of the frame to promote uniform crimping and expansion of the frame. 
       FIG. 29  is a cross-sectional view of a portion of the frame and leaflet structure showing the adjacent tab portions of two leaflets secured to a corresponding window frame portion  30 .  FIGS. 30-36  show one specific approach for securing the commissure portions  122  of the leaflet structure  14  to the commissure window frame portions  30  of the frame. First, as shown in  FIG. 30 , the flexible connector  124  securing two adjacent sides of two leaflets is folded widthwise and the upper tab portions  112  are folded downwardly against the flexible connector. As best shown in  FIGS. 30 and 31 , each upper tab portion  112  is creased lengthwise (vertically) to assume an L-shape having an inner portion  142  folded against the inner surface of the leaflet and an outer portion  144  folded against the connector  124 . The outer portion  144  can then be sutured to the connector  124  along a suture line  146 . Next, as shown in  FIG. 31 , the commissure tab assembly (comprised of a pair of lower tab portions  116  connected by connector  124 ) is inserted through the commissure window  20  of a corresponding window frame portion  30 .  FIG. 32  is a side view of the frame  12  showing the commissure tab assembly extending outwardly through the window frame portion  30 . 
     As best shown in  FIGS. 29 and 33 , the commissure tab assembly is pressed radially inwardly at the wedge  126  such that one of the lower tab portions  116  and a portion of the connector  124  is folded against the frame  12  on one side of the window frame portion  30  and the other lower tab portion  116  and a portion of the connector  124  is folded against the frame  12  on other side of the window frame portion  30 . A pair of suture lines  148  are formed to retain the lower tab portions  116  against the frame  12  in the manner shown in  FIG. 29 . Each suture line  148  extends through connector  124 , a lower tab portion  116 , the wedge  126 , and another portion of connector  124 . Then, as shown in  FIGS. 29 and 34 , each lower tab portion  116  is secured to a corresponding upper tab portion  112  with a primary suture line  150  that extends through one layer of connector  124 , the lower tab portion  116 , another layer of connector  124 , another layer of connector  124 , and the upper tab portion  112 . Finally, as shown in  FIGS. 29 and 35 , the suture material used to form the primary suture line  150  can be used to further form whip stitches  152  at the edges of the tab portions  112 ,  116  that extend through two layers of connector  124  sandwiched between tab portions  112 ,  116 . 
     As shown in  FIGS. 29 and 30 , the folded down upper tab portions  112  form a double layer of leaflet material at the commissures. The inner portions  142  of the upper tab portions  112  are positioned flat abutting layers of the two leaflets  40  forming the commissures, such that each commissure comprises four layers of leaflet material just inside of the window frames  30 . This four layered portion of the commissures can be more resistant to bending, or articulating, than the portion of the leaflets  40  just radially inward from the relatively more rigid four layered portion. This causes the leaflets  40  to articulate primarily at inner edges  143  of the folded-down inner portions  142  in response to blood flowing through the valve during operation within the body, as opposed to articulating about the axial struts of the window frames  30 . Because the leaflets articulate at a location spaced radially inwardly from the window frames  30 , the leaflets can avoid contact with and damage from the frame. However, under high forces, the four layered portion of the commissures can splay apart about a longitudinal axis  145  ( FIG. 29 ) adjacent to the window frame  30 , with each inner portion  142  folding out against the respective outer portion  144 . For example, this can occur when the valve  10  is compressed and mounted onto a delivery shaft, allowing for a smaller crimped diameter. The four layered portion of the commissures can also splay apart about axis  145  when the balloon catheter is inflated during expansion of the valve, which can relieve some of the pressure on the commissures caused by the balloon and so the commissures are not damaged during expansion. 
     After all three commissure tab assemblies are secured to respective window frame portions  30 , the lower edges of the leaflets  40  between the commissure tab assemblies can be sutured to the inner skirt  16 . For example, as shown in  FIGS. 36-38 , each leaflet  40  can be sutured to the skirt  16  along suture line  154  using, for example, Ethibond thread. The sutures can be in-and-out sutures extending through each leaflet  40 , the skirt  16  and each reinforcing strip  72 . Each leaflet  40  and respective reinforcing strip  72  can be sewn separately to the skirt  16 . In this manner, the lower edges of the leaflets are secured to the frame  12  via the skirt  16 . As shown in  FIG. 38 , the leaflets can be further secured to the skirt with blanket sutures  156  that extend through each reinforcing strip  72 , leaflet  40  and the skirt  16  while looping around the edges of the reinforcing strips  72  and leaflets  40 . The sutures  156  can be formed from PTFE suture material.  FIGS. 39 and 40  show the frame  12 , leaflet structure  14  and the skirt  16  after securing the leaflet structure and the skirt to the frame and the leaflet structure to the skirt. 
       FIG. 41  shows a flattened view of the outer skirt  18  prior to its attachment to the frame  12 . The outer skirt  18  can be laser cut or otherwise formed from a strong, durable piece of material, such as woven PET, although other synthetic or natural materials can be used. The outer skirt  18  can have a substantially straight lower edge  160  and an upper edge  162  defining a plurality of alternating projections  164  and notches  166 . As best shown in  FIG. 42 , the lower edge  160  of the skirt  18  can be sutured to the lower edge of the inner skirt  16  at the inflow end of the valve. As shown in  FIG. 43 , each projection  164  can be sutured to the second rung II of struts  24  of the frame  12 . The corners  162  of the projections  164  can be folded over respective struts of rung II and secured with sutures  168 . 
     As can be seen in  FIGS. 1, 3 and 43 , the outer skirt  18  is secured to the frame  12  such that when the frame is in its expanded state, there is excess material or slack between the outer skirt&#39;s lower and upper edges  160 ,  162  that does not lie flat against the outer surface of the frame  12 . In other words, the outer skirt is configured with excess material which causes the outer skirt to bulge outwardly as the frame foreshortens (i.e., shortens in length) during radial expansion. Accordingly, when the valve  10  is deployed within the body, the excess material of the outer skirt  18  can fill in gaps between the frame  12  and the surrounding native annulus to assist in forming a good fluid-tight seal between the valve and the native annulus. The outer skirt  18  therefore cooperates with the inner skirt  16  to avoid perivalvular leakage after implantation of the valve  10 . In another advantageous feature, the slack between the lower and upper edges of the outer skirt  18  allows the frame  12  to elongate axially during crimping without any resistance from the outer skirt and the outer skirt does not substantially affect the outer diameter of the prosthetic valve in the crimped condition. 
       FIG. 56  shows the valve  10  of  FIGS. 1-3 and 42-43  mounted on an elongated shaft  180  of a delivery apparatus, forming a delivery assembly for implanting the valve  10  in a patient&#39;s body. The valve  10  is mounted in a radially collapsed configuration for delivery into the body. The shaft  180  comprises an inflatable balloon  182  for expanding the balloon within the body, the crimped valve  10  being positioned over the deflated balloon. The frame  12  of the valve  10 , when in the radially compressed, mounted configuration, comprises an inflow end portion  174  (see  FIG. 54 ) that has an outer diameter D 2  that is smaller than the outer diameter D 1  of the outflow end portion of the frame. The tapering of the frame can be at least partially due to the V-shaped leaflets  40 , as the V-shaped leaflets have less leaflet material within the inflow end portion of the frame  12  compared to a more rounded, U-shaped leaflet. Due to the tapered shape of the frame  12  in the mounted state, even with the additional thickness of the outer skirt  18  positioned around the inflow end portion  174  of the frame  12  the overall outer diameter of the inflow end portion of the valve  10  can be about equal to, or less than, the overall outer diameter of the outflow end portion of the valve. 
     Furthermore, as shown in  FIG. 56 , the valve  10  comprises commissure portions of the leaflets extending radially outwardly through corresponding window frame portion  30  to locations outside of the frame and sutured to the side struts of the commissure window frame. To minimize the crimp profile of the valve, the window frame portions  30  can be depressed radially inwardly relative to the surrounding portions of the frame, such as the frame portions extending between adjacent commissure windows, when the valve is radially compressed to the collapsed configuration on the shaft. For example, the commissure windows  30  of the frame can be depressed inwardly a radial distance of between 0.2 mm and 1.0 mm relative to the portions of the frame extending between adjacent commissure windows when the valve is radially collapsed. In this way, the outer diameter of the outflow end portion the valve comprising the commissure portions can be generally consistent, as opposed to the commissure portions jutting outward from the surrounding portions of the valve, which could hinder delivery of the valve into the body. Even with the radially depressed commissure window frames  30 , the outer diameter of the inflow end portion of the frame can still be smaller than, or about equal to, the outer diameter of the outflow end portion of the frame when the valve is radially collapsed on the shaft, allowing for a minimal maximum overall diameter of the valve. By minimizing the diameter of the valve when mounted on the delivery shaft, the assembly can be contained within a smaller diameter catheter and thus can be passed through smaller vessels in the body and can be less invasive in general. 
       FIG. 44  illustrates a prosthetic heart valve  200 , according to another embodiment. The heart valve  200  includes a frame, or stent,  202  and a leaflet structure  204  mounted on the stent. The leaflet structure  204  can include a plurality of leaflets  218  (e.g., three, as depicted), which can be sutured to each other and to the frame  202  using suitable techniques and/or mechanisms. The frame  202  can be adapted to include commissure frame portions  30  (as shown in  FIG. 4 ) to assist in suturing the leaflets to the frame. 
     The frame  202  shares some design features of the frame  12  described above. In particular, like frame  12 , the frame  202  has relatively large frame openings  206  along the area of the frame that supports the leaflet structure, as shown in  FIG. 45 . The openings  206  are defined by a row of angled struts  208  at the outflow end of the frame, a plurality of axially extending, circumferentially spaced struts  210 , and an intermediate row of angled struts  212 . As shown, the axial struts  210  desirably are thinner than the junctions  214  connecting the opposite ends of the axial struts  210  to the convergence of two struts  212  and to the convergence of two struts  208 . By virtue of this configuration, the width of openings  206  remain large enough when the valve is radially compressed to a delivery configuration to allow portions of the leaflet structure  204  to protrude outwardly through the openings, as indicated at  216  in  FIGS. 46 and 47 . This allows the valve to be crimped to a relatively smaller diameter than if all of the leaflet material is constrained within the crimped frame. 
     For purposes of comparison,  FIG. 48  is a cross section of a known prosthetic valve  250  showing the valve in its crimped state. When the valve is radially compressed, the spacing between adjacent struts is relatively small and does not allow portions of the leaflet structure to protrude outwardly through the frame. Consequently, the presence of all of the leaflet material being constrained within the inside of the frame limits the crimping diameter of the valve. 
       FIGS. 49 and 50  show a flattened section of an alternative frame construction that can allow portions of the leaflets to protrude outwardly through the frame in the crimped state. This frame construction can be implemented in the valve  10  described above.  FIG. 49  shows the frame section in the radially compressed state while  FIG. 50  shows the frame section in the radially expanded state. The frame (only a portion of which is shown) includes a first, circumferentially extending row of angled struts  442  and at least a second, circumferentially extending row of angled struts  444 . Some openings in the frame are diamond shaped openings  446  formed by adjacent struts  442  connected to each other at their upper ends and adjacent struts  444  connected to each other at their lower ends. The frame also includes larger openings  448  that are formed by adjacent struts  442  connected at their upper ends to respective ends of a horizontal strut  450  and by adjacent struts  444  connected at their lower ends to respective ends of a horizontal strut  452 . When the frame is radially compressed, the horizontal struts  450 ,  452  maintains the width W of openings  448  large enough to permit portions of the valve&#39;s leaflets to protrude outwardly through the frame. Thus, the width of openings  448  is greater than the width of openings  446  when the frame is crimped. The frame can be formed with openings  446 ,  448  alternating around the circumference of the frame. Alternatively, openings  448  can be located at selected positions along the frame&#39;s length and circumference to correspond to areas where the leaflet material tend to bunch up within the frame, such as between the commissures. 
       FIGS. 51 and 52  show a flattened section of another frame construction that can allow portions of the leaflets to protrude outwardly through the frame in the crimped state. This frame construction can be implemented in the valve  10  described above.  FIG. 51  shows the frame section in the radially compressed state while  FIG. 52  shows the frame section in the radially expanded state. The frame (only a portion of which is shown) includes a first, circumferentially extending row of angled struts  402  and at least a second, circumferentially extending row of angled struts  404 . Some openings in the frame are diamond shaped openings  406  formed by adjacent struts  402  connected to each other at their upper ends and adjacent struts  404  connected to each other at their lower ends. The frame also includes openings  408  that are formed by adjacent struts  402  connected at their upper ends to an enlarged node or junction  410  and by adjacent struts  404  connected at their lower ends to an enlarged node or junction  412 . The junctions  410 ,  412  add rigidity to the frame at those locations such that when the frame is radially compressed, the width W of openings  408  remains large enough to permit portions of the valve&#39;s leaflets to protrude outwardly through the frame. Thus, the width of openings  408  is greater than the width of openings  406  when the frame is crimped. The frame can be formed with openings  406 ,  408  alternating around the circumference of the frame. Alternatively, openings  408  can be located at selected positions along the frame&#39;s length and circumference to correspond to areas where the leaflet material tend to bunch up within the frame, such as between the commissures. 
       FIG. 57  shows a leaflet  500  for a prosthetic valve (e.g., valve  10  or  200 ), according to another embodiment. The leaflet  500  has an overall V-shape, similar to leaflets  40  described above. The leaflet  500  has two tab portions  502  on opposite sides of the leaflets which are secured to adjacent tab portions of other leaflets to form the commissures of the leaflet structure. The sub-commissure portion of the leaflet  500  (the portion below the tabs  502 ) include two substantially straight edges  504  that extend from respective locations just below the tabs  502  to a curved lower edge  506 .  FIG. 58  shows the general shape of the leaflet  500  when the valve is crimped. The frame (not shown in  FIGS. 57-58 ) slightly elongates when crimped, causing the leaflet  500  to become slightly elongated. 
     The tapered profile of the sub-commissure portion of the leaflet reduces the amount of leaflet material in the lower half of the crimped valve to minimize the crimp diameter of that portion of the valve. Thus, if additional components are mounted to that portion of the valve, such as an outer skirt  18 , the reduced profile of that portion of the valve can help offset or minimize the increase in diameter caused by the additional component. Additionally, the commissure tabs  502  are relatively short and require less sutures for forming the commissures of the leaflet structure than known leaflet designs (such as T-shaped and scalloped leaflets), which better distributes and reduces the bulkiness of the leaflet material when the valve is crimped. 
       FIG. 59  shows a cross-sectional view of a valve  500 , according to another embodiment. The valve  500  comprises a frame  502 , leaflets  504 , and an outer skirt  18  mounted (e.g., by sutures) to the outer surface of the frame  502 . The frame  502  has a thickness that varies along its length to optimize strength where needed, yet minimize material (and therefore crimp profile) at selected regions of the frame. In the embodiment shown, the outflow end portion  506  of the frame has a maximum thickness T 1  (measured from the inside diameter to the outside diameter of that portion of the frame) and the inflow end portion  508  of the frame has a minimum thickness T 2  (measured from the inside diameter to the outside diameter of that portion of the frame). It should be noted that the struts of the frame  502  (which are not shown in  FIG. 59 ) that form the outflow end portion  506  have a thickness T 1  and the struts that form the inflow end portion  508  have a thickness T 2 . The frame  502  can have an identical construction to the frame  12  described above, except for the variable thickness of the frame. The areas of reduced thickness can be formed using a variety of manufacturing techniques, such as electro-polishing selected portions of the frame (the non-polished portions can be masked), grinding selected portions of the frame, wire cutting, or other suitable techniques. 
     The outflow end portion  502  generally corresponds to the region of the frame that supports the commissures of the leaflets  504  and typically experiences the greatest loading on the valve. Therefore the outflow end portion  502  of the frame has a greater thickness T 1  selected to provide the required strength under anticipated loads. The inflow end portion  508  supports an additional layer of material by virtue of the outer skirt  18 . The reduced thickness of the inflow end portion  508  allows the inflow end portion to be crimped to a smaller diameter than the outflow end portion. This offsets or minimizes the increase in the crimp diameter caused by the addition of the outer skirt  18 . 
       FIGS. 60-62  show an another embodiment of an implantable prosthetic valve  310  that comprises a leaflet structure  314  and a radially collapsible and expandable frame  312  (similar to the frame  50  shown in  FIG. 11 ) having a plurality of radially spaced commissure windows  318  that are used to secure the leaflet structure within the frame. The valve  310  also comprises a skirt  316  secured between the inner surface of the frame  312  and the curved lower edges  364  of the leaflet structure  314 . The valve  310  has a lower, inflow end  340  and an upper, outflow end  342 . 
     As shown in  FIG. 60A , each window  318  comprises an enclosed opening  334  between two axially extending side struts  320 , respectively. Each side strut comprises a generally rectangular, e.g. square, cross-sectional profile, as shown in  FIG. 63 . Each rectangular side strut  320  comprises four surfaces: an exterior surface  324  on a radially outward facing side, and interior surface  326  on a radially inward facing side, a medial surface  328  on a side facing the other side strut, and a lateral surface  330  on a side facing away from the other side strut. In other embodiments, side struts can comprise other cross-sectional shapes, such circular or hexagonal. 
     The leaflet structure comprises a plurality of leaflets  360 , each comprising a pair of side tabs  366  secured to the frame  312 , a curved lower edge  364  secured to the skirt  316 , and an articulation portion  372  between the side tabs and the lower edge. Each side tab  366  is paired with an adjacent side tab of another leaflet  360  to form commissures  376  of the leaflet structure  314 . Each pair of side tabs  366  extends radially outwardly through a corresponding commissure window  318  to a location outside of the frame  312  and is secured to the side struts  320  of the window, such as with sutures, as shown in  FIG. 62 . In some embodiments, each side tab  366  comprises an end portion  368  (see  FIG. 64 ) and the two side tab end portions  368  of each commissure  376  extend circumferentially away from one another and along the exterior surfaces  324  of respective side struts  320  of the window  318 . 
     In some embodiments, each commissure  376  further comprises at least one non-rigid reinforcing sheet  378  sutured to the side tabs  366  and to the side struts  320 . The sheets  378  can comprise a flexible, tear resistant material, including a variety of natural and/or synthetic biocompatible materials. Exemplary synthetic materials can include polymers such as nylon, silicone, and polyesters, including PET. In one example, the sheets  378  comprise a woven PET fabric. 
     Each reinforcing sheet  378  can be generally rectangular (when laid flat) and can comprise a middle portion  380  and opposing end portions  386 . In some embodiments, a first end portion  386  of the sheet is secured to a first side strut  320  and a second end portion  386  of the sheet is secured to the second side strut  320 , as shown in  FIG. 64 . The sheet  378  separates the side tabs  366  from the side struts  320  such that side tabs do not contact the side struts. For example, each end portion  386  of the sheet can be wrapped completely around a respective side strut  320 , as shown in  FIG. 64 . 
     The side tabs  366  and the reinforcing sheet  378  can be secured to the side struts  320  in multiple stages. For example,  FIG. 63  shows an exemplary first suturing stage wherein the sheet is positioned such that the middle portion  380  of the sheet extends circumferentially across outer surfaces of the end portions  368  of the side tabs  366  and each end portion  386  of the sheet extends between a respective side tab  366  and the exterior, medial and interior surfaces  324 ,  328 ,  326 , respectively, of a respective side strut  320 . The sheet  378  surrounds the side tabs  366  and protects the side tabs from edges of the side struts  320 . A pair of in-and-out sutures  390  can secure each side tab  366  and one end of the sheet  378  to a respective strut  320 . As shown in  FIG. 63 , each suture  390  can be oriented generally perpendicularly to the circumference of the frame  312  along the lateral surfaces  330  of the side struts  320  and can pass radially back and forth through the commissure  376  at a plurality of difference longitudinal positions. Each suture  390  can intersect a first layer of the sheet  378 , a side tab end portion  368 , a second layer of the sheet, and a third layer of the sheet, in that order moving radially inward. The sutures  390  secure the sheet  378  to the side tab end portions  368  and tighten the sheet end portions  386  around the side struts  320 , thereby securing the side tabs  366  to the side struts  320  and securing the leaflet structure  314  to the frame  312 . 
       FIG. 64  shows an exemplary second suturing stage wherein a second pair of sutures  392  are used to tie down loose portions of the reinforcing sheet  378 . For example, the second sutures  392  can intersect the portions of the middle portion  380  and the end portions  386  of the sheet that extend laterally beyond the first sutures  390 . The second sutures  392  can be helical whip stitches that intersect the commissures  376  at a plurality of different longitudinal positions, as shown in  FIG. 62 , and secure the loose portions of the sheet  378  tightly against the lateral surfaces  330  of the side struts. 
     Both the first sutures  390  and the second sutures  392  can be positioned adjacent to the lateral surfaces  330  of the struts  320  and spaced away from the window opening  334 . This placement of the sutures can reduce the stress on the sutures caused by movement of the articulation portions  372  of the leaflets. Instead, much of this stress is transferred from flex hinges  370  of the leaflets to the side struts  320  near interior-medial edges  332  of the struts. 
     The reinforcing sheet  378  protects the flex hinges  370  from damage caused by the interior-medial edges  332  of the struts  320  as the leaflets articulate between open and closed positions, as shown in  FIG. 64 . In addition, some embodiments can also include longitudinally extending cushion strips  374  positioned between the flex hinges  370  and the struts  320 , such as adjacent to the interior-medial edges  332 , as shown in  FIG. 64 , to further protect the flex hinges from damage caused by the struts. The cushion strips  374  can comprise a flexible, compressible material, such as PET fabric, pericardial tissue, or various other biocompatible materials. In some embodiments, the cushion strips can comprise a tube filled with a resilient material. For example, the cushion strip can comprise a PET tube filled with pericardial tissue. In other embodiments, the outer tubular covering of the cushion strips can be formed from sheet  378  and can be filled with a resilient material. The sheet can be secured around the resilient material with sutures to retain the cushioning strips properly located as shown in  FIG. 64 . In other embodiments, separate cushion strips  374  can be sutured to the reinforcing sheet  378 . The cushion strips  374  can have a thickness similar to the bars  62  to provide a radial clearance between the side struts  320  and the articulating portions  372  of the leaflets to prevent or minimize contact between the leaflets and the inner surface of the frame during the cardiac cycle. 
       FIG. 65  shows an embodiment similar to  FIGS. 63 and 64  but with a different suturing pattern. In  FIG. 65 , the sutures  390  are replaced with sutures  398  that secure the sheet  378  around the end portions  368  of the side tabs. Each suture  398  intersects the middle portion  380  of the sheet, one of the side tabs  366 , and a second layer of the sheet adjacent to the medial-exterior edge  324  of each side strut. The sutures  398  can comprise in-and-out stitches that intersect the commissures at a plurality of different longitudinal positions. Each end portion of the sheet  378  can comprise a folded portion  388  that is folded under to form a double layer of the sheet  378  along the surface of the respective side strut  320 . The sutures  392  secure the end portions  386  of the sheet and the end portions  368  of the side tabs tightly around the lateral surfaces  330  of the side struts. 
       FIGS. 66 and 67  show an alternative method for suturing the side tabs  366  and the sheet  378  to the side struts  320 .  FIG. 66  shows suture line  394  positioned along the exterior surfaces  324  of the side struts and generally perpendicular to the radius of the frame. The suture  394  intersects both side tabs  366  and both end portions  386  of the sheet  378 . The suture  394  secures each end portion  386  of the sheet tightly around the medial, interior, and lateral surfaces  328 ,  326 ,  330 , respectively, of the respective side strut  320 , and also secures the middle portion  380  of the sheet loosely around the end portions  368  of the side tabs  366 . In the embodiment shown in  FIG. 66 , the suture  394  intersects a first sheet layer A, a second sheet layer B, the two side tabs  366 , a third sheet layer C, and a fourth sheet layer D, in that order. 
     After the first suture  394  is in place, the end portions  368  of the side tabs are spread apart and positioned adjacent to the exterior surfaces  324  of the side struts  320 , as shown in  FIG. 67 . This tightens the loose middle portion  380  of the sheet around the end portions  368  of the side tabs. A pair of sutures  396  can then secure the middle portion  380  of the sheet tightly to the end portions  386  of the sheet to hold the end portions  368  of the side tabs in place, as shown in  FIG. 67 . The sutures  396  can be looping whip stitches that intersect the commissure  376  at a plurality of different longitudinal positions, similar to the sutures  392  in  FIG. 64 . 
       FIGS. 68 and 69  show another alternative method for suturing the side tabs  366  and the sheet  378  to the side struts  320 .  FIG. 68  shows a suture line  395  positioned along the exterior side of the window opening and oriented generally perpendicular to the radius of the frame. The suture  395  intersects both side tabs  366  and two portions of the sheet  378 . The suture  395  secures the middle portion  380  of the sheet which extends loosely around the end portions  368  of the side tabs  366 . In the embodiment shown in  FIG. 68 , the suture  395  intersects a first sheet layer A, a first side tab B, a second side tab C, and a second sheet layer D, in that order. 
     After the first suture  395  is in place, the end portions  368  of the side tabs are spread apart and positioned adjacent to the exterior surfaces  324  of the side struts  320 , as shown in  FIG. 69 . This tightens the loose middle portion  380  of the sheet around the end portions  368  of the side tabs. A pair of sutures  397  can then secure the middle portion  380  of the sheet tightly to the end portions  386  of the sheet to hold the end portions  368  of the side tabs in place, as shown in  FIG. 69 . The end portions  386  of the sheet can comprise a folded under portion  388 , creating a double layer of sheet material to reinforce the sutures  397 . The sutures  397  can be looping whip stitches that intersect the commissure  376  at a plurality of different longitudinal positions, similar to the sutures  392  in  FIG. 62 . 
       FIGS. 70 and 71  show yet another alternative method for suturing the side tabs  366  and the sheet  378  to the side struts  320 .  FIG. 70  shows the suture line  395  positioned along the exterior side of the window opening and oriented generally perpendicular to the radius of the frame. The suture  395  intersects both side tabs  366  and four portions or layers of the sheet  378 . Each end portion  386  of the sheet comprises a folded portion  388  that forms a double layer of sheet material between the side tabs  366  and the medial surfaces  328  of the side struts. The suture  395  secures the middle portion  380  of the sheet loosely around the end portions  368  of the side tabs  366 . As shown in  FIG. 70 , each stitch of the suture  395  intersects a first pair of sheet layers comprising layers A and B, a first side tab C, a second side tab D, and a second pair of sheet layers comprising layers E and F, in that order. 
     After the first suture  395  is in place, the end portions  368  of the side tabs are spread apart and positioned adjacent to the exterior surfaces  324  of the side struts  320 , as shown in  FIG. 71 . This tightens the middle portion  380  of the sheet around the end portions  368  of the side tabs. A pair of sutures  397  can then secure the middle portion  380  of the sheet tightly to the end portions  386  of the sheet to hold the end portions  368  of the side tabs in place, as shown in  FIG. 71 . The folded portions  388  of the sheet create a double layer of sheet material to reinforce the sutures  397 . The sutures  397  can be looping whip stitches that intersect the commissure  376  at a plurality of different longitudinal positions, similar to the sutures  392  in  FIG. 62 . 
     The commissure various configurations for attaching the leaflet structure  314  to the window frames  318  shown in  FIGS. 61-71  can also be used as alternative ways to attach the leaflet structure  14  of the valve  10  of  FIGS. 1-3  to the window frame portions  30  of frame  12 . 
       FIGS. 72-74  show a prosthetic heart valve assembly  600  comprising an embodiment of a frame  602  for a prosthetic valve mounted on a balloon  606  of a delivery shaft  604 . The frame  602  can be similar in shape to the frame  12  and can comprise in inflow end portion  610 , an outflow end portion  612  and an intermediate portion  614 . For clarity, the other components of the valve, such as the leaflets and the skirts, are not shown. The frame  602  can have a reduced thickness at the inflow end portion  610  and at the outflow end portion  612 , relative to the thickness of the intermediate portion  614 . Due to the thinner end portions, when the balloon  606  is inflated the end portions  610 ,  612  offer less resistance to expansion and expand faster than the intermediate portion  614 , as shown in  FIG. 73 . Because the end portions expand faster than the intermediate portion, the frame  602  becomes confined on the balloon  606 , inhibiting the frame from sliding towards either end of the balloon and reducing the risk of the frame sliding off the balloon prematurely. As shown in  FIG. 74 , further inflation of the balloon can cause the intermediate portion  614  of the frame to expand to the same final diameter as the end portions  610 ,  612  for implantation, after which the balloon can be deflated and removed. Controlling the position of the valve on the balloon can be important during delivery, especially with frames that foreshorten during expansion and move relative to the balloon. In the embodiment shown in  FIGS. 72-74 , the intermediate portion  614  of the frame can be held constant relative to the balloon while the two end portions foreshorten towards the intermediate portion due to the “dog-bone” effect of the balloon. Any conventional means can be used to produce the frame  602  with reduced thickness at the end portions  610 ,  612 , such as sanding down the end portions with sand paper or the like. In one embodiment, the end portions  610 ,  614  of the frame have a thickness of about 0.37 mm while the intermediate portion  614  has a thickness of about 0.45 mm. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope of these claims.