Patent Publication Number: US-2023149162-A1

Title: Prosthetic heart valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of PCT patent application no. PCT/US2021/043112, filed on Jul. 26, 2021, entitled PROSTHETIC HEART VALVE, which application claims the benefit of U.S. Provisional Application No. 63/056,868, filed on Jul. 27, 2020, entitled SMALL DIAMETER PROSTHETIC VALVE, each of which application is incorporated herein in its entirety by this specific reference. 
    
    
     FIELD 
     The present disclosure relates to prosthetic heart valves, and to methods and assemblies for forming leaflet assemblies and attaching the leaflet assemblies to the frame of such prosthetic 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 repair of the native valve or replacement of the native valve with an artificial valve. There are a number of known repair devices (e.g., stents) and artificial valves, as well as a number of known methods of implanting these devices and valves in humans. Percutaneous and minimally-invasive surgical approaches are used in various procedures to deliver prosthetic medical devices to locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. In one specific example, a prosthetic heart valve can be mounted in a crimped state on the distal end of a delivery apparatus and advanced through the patient&#39;s vasculature (e.g., through a femoral artery and the aorta) until the prosthetic heart valve reaches the implantation site in the heart. The prosthetic heart valve is then expanded to its functional size, for example, by inflating a balloon on which the prosthetic valve is mounted, actuating a mechanical actuator that applies an expansion force to the prosthetic heart valve, or by deploying the prosthetic heart valve from a sheath of the delivery apparatus so that the prosthetic heart valve can self-expand to its functional size. 
     Most expandable, transcatheter heart valves are used for mid to high expansion diameters, for example diameters ranging from 23 to 29 mm. While smaller prosthetic valves available, such as those with diameters of about 20 mm or less, smaller diameter valves are rarely used due to a variety of challenges. For example, smaller diameter prosthetic valves generally cause higher pressure gradients along the prosthetic valve, which can lead to various clinical risks, such as cavitation. Also, smaller prosthetic valves typically have shorter paravalvular sealing elements, which makes it more challenging for the clinician to align the prosthetic valve at the native annulus. Smaller prosthetic valves also can have relatively shorter frames, which can result in leaflet overhang, in which the native valve leaflets overhang the outflow end of the prosthetic valve, thereby disturbing blood flow and/or inhibiting full opening of the prosthetic leaflets. Further, smaller prosthetic valves have relatively smaller frame openings, which can inhibit coronary access through the frame with a catheter in a subsequent procedure. Finally, valve-in-valve procedures involving implantation of a second prosthetic valve in a previously implanted prosthetic valve is more challenging with relatively smaller prosthetic valves because it is more difficult to properly align and orient the second prosthetic valve within the previously implanted prosthetic valve while maintaining access to the coronary ostia. 
     Accordingly, a need exists for improved prosthetic heart valve leaflet assemblies and methods for assembling the leaflet assemblies to a frame of the prosthetic heart valve. 
     SUMMARY 
     In a representative embodiment, an implantable prosthetic device can comprise a frame movable between a radially compressed configuration and a radially expanded configuration, the frame having an inflow orifice, an outflow orifice, and comprising one or more commissure windows, and a valvular structure comprising a plurality of leaflets. Each leaflet comprising a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet to form a commissure tab assembly, each commissure tab assembly being coupled to a respective commissure window. Wherein each tab extends from the main body at an angle such that a radially outer edge of the tab corresponds to a draft angle of the frame. 
     In another representative embodiment, an implantable prosthetic device can comprise a cylindrical frame movable between a radially compressed configuration and a radially expanded configuration, and a valvular structure comprising a plurality of leaflets, each leaflet comprising a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body. Each tab can extend from the main body such that an outflow edge of the tab is disposed at a 90-degree angle relative to a longitudinal axis of the leaflet. 
     In another representative embodiment, an implantable prosthetic device can comprise a cylindrical frame movable between a radially compressed configuration and a radially expanded configuration, the frame comprising an inflow orifice and an outflow orifice and a valvular structure comprising a plurality of leaflets. Each leaflet can comprise a main body having an inflow edge and an outflow edge, a pair of opposing lower tabs extending from opposite sides of the main body, and a pair of opposing upper tabs extending from and coupled to the outflow edge of the leaflet via respective neck portions. Each lower tab can extend from the main body such that an outflow edge of the leaflet tab is disposed at a 90-degree angle relative to a longitudinal axis of the leaflet, and each lower tab can be paired with an adjacent upper tab of an adjacent leaflet to form a plurality of commissures, and each upper tab can be folded toward the inflow orifice of the frame such that the neck portion forms a rigid portion extending radially inwardly toward a longitudinal axis of the frame such that the outflow edge of the leaflet defines a selected geometric orifice area (GOA) within the outflow orifice. 
     In still another representative embodiment, an implantable prosthetic device can comprise a non-cylindrical frame having an inflow orifice and an outflow orifice, the frame movable between a radially compressed configuration and a radially expanded configuration, the frame having a shape in the radially expanded configuration that tapers from a first diameter at the outflow orifice to a second diameter at the inflow orifice, the second diameter being larger than the first diameter, and a valvular structure comprising a plurality of leaflets. Each leaflet can comprise a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, and each tab extends from the main body at an angle such that a radially outer edge of the tab corresponds to a draft angle of the frame. 
     In a representative embodiment, an implantable prosthetic device can include an annular frame that is movable between a radially compressed configuration and a radially expanded configuration, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame and a valvular structure comprising a plurality of leaflets, each leaflet having a main body including an inflow edge and an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet and secured to the frame to form a commissure assembly. The valvular structure is secured to the frame such that a gap is defined between the outflow edges of the leaflets and the outflow end of the frame, and each cell of the first row of cells is configured to be at least twice as wide as a selected coronary catheter. 
     A representative method can include inserting a distal end of a delivery apparatus into the vasculature of a patient, the delivery apparatus releasably coupled to a guest prosthetic valve movable between a radially compressed and a radially expanded configuration, the prosthetic valve including a frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame and configured to be at least twice as wide as a selected coronary catheter, and a valvular structure disposed within the frame and coupled to the frame such that a gap is defined between the outflow edges of the valvular structure and an outflow end of the frame. The method can further include advancing the guest prosthetic valve to a selected implantation site comprising a previously implanted host prosthetic valve, the host prosthetic valve comprising a host frame and a host valvular structure disposed within the host frame, positioning the guest prosthetic valve within the host prosthetic valve, and radially expanding the guest prosthetic valve within the previously implanted host prosthetic valve. 
     In some embodiments, the host frame comprises first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the host frame and configured to be at least twice as wide as a selected coronary catheter, and the host valvular structure is coupled to the host frame such that a gap is defined between the outflow edges of the host valvular structure and an outflow end of the host frame. In such embodiments, the method can further comprise inserting the selected coronary catheter through the gap of the guest prosthetic valve and the gap of the host prosthetic valve. 
     A representative method of assembling a prosthetic heart valve can comprise forming a valvular structure from a plurality of leaflets, each leaflet comprising an inflow edge, an outflow edge, and two opposing tabs, wherein the valvular structure is formed by coupling adjacent tabs of adjacent leaflets to one another to form respective commissures, positioning the valvular structure within a radially expandable and compressible frame, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame and configured to be at least twice as wide as a selected coronary catheter, and coupling the valvular structure to the frame such that a gap is defined between the outflow edges of each leaflet and an outflow edge of the frame when the valvular structure is in an open configuration. 
     In another representative embodiment, an assembly can comprise a first implantable prosthetic device and a second implantable prosthetic device. Each implantable prosthetic device can comprise an annular frame that is movable between a radially compressed configuration and a radially expanded configuration, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame, and a valvular structure comprising a plurality of leaflets. Each leaflet can have a main body including an inflow edge and an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet and secured to the frame to form a commissure assembly, the valvular structure can be secured to the frame such that a gap is defined between the outflow edges of the leaflets and the outflow end of the frame. Each cell of the first row of cells can be configured to be at least twice as wide as a selected coronary catheter, and the first implantable prosthetic device can be disposed withing the annular frame of the second implantable prosthetic device. 
     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 
         FIG.  1    is a perspective view of a prosthetic heart valve, according to one embodiment. 
         FIG.  2    is a perspective view of the prosthetic heart valve of  FIG.  1   , shown with the outer skirt removed and one of the leaflets transparent for purposes of illustration. 
         FIG.  3 A  is a perspective view of the frame of the prosthetic heart valve of  FIG.  1   . 
         FIG.  3 B  is a side elevation view of a portion of the frame of the prosthetic heart valve of  FIG.  1   . 
         FIG.  4    is a perspective view of a valve-in-valve configuration including the prosthetic heart valve of  FIG.  1    as the guest valve, according to one embodiment. 
         FIG.  5    is a perspective view of a valve-in-valve configuration, according to another embodiment. 
         FIG.  6    is a perspective view of an extreme valve-in-valve configuration, according to still another embodiment. 
         FIG.  7    is a side elevation view of a prosthetic heart valve, according to one embodiment. 
         FIG.  8    is a side elevation view of the frame of the prosthetic heart valve of  FIG.  7   . 
         FIG.  9    is a side elevation view of a prosthetic heart valve, according to another embodiment. 
         FIG.  10    is a side elevation view of a portion of the frame of the prosthetic heart valve of  FIG.  9   . 
         FIG.  11    is a perspective view of an embodiment of a prosthetic heart valve, according to one embodiment. 
         FIG.  12    is a side elevational view of a leaflet of the prosthetic heart valve of  FIG.  11   . 
         FIG.  13    is a top plan view of the prosthetic heart valve of  FIG.  11   , with the valvular structure shown in the open configuration. 
         FIG.  14    is a perspective view of a commissure portion of the prosthetic heart valve of  FIG.  11   . 
         FIG.  15    is a perspective view of a prosthetic heart valve, according to another embodiment. 
         FIG.  16    is a side elevational view of a leaflet of the prosthetic heart valve of  FIG.  15   . 
         FIG.  17    is a cross-sectional view of a commissure portion of the prosthetic heart valve of  FIG.  15   . 
         FIG.  18    is a top plan view of the prosthetic heart valve of  FIG.  18   , with the valvular structure shown in the open configuration. 
         FIG.  19    is a top plan view of a prosthetic heart valve with the valvular structure shown in the open configuration, according to another embodiment. 
         FIG.  20    is a side elevational view of a leaflet of the prosthetic heart valve of  FIG.  19   . 
         FIG.  21    is a side view of an embodiment of a prosthetic valve being implanted within a native aortic valve of a heart, which is partially shown. 
         FIG.  22    is a side view of an embodiment of a frame of a prosthetic valve implanted within a native aortic valve of a heart, which is partially shown. 
         FIG.  23    is a side view of an embodiment of an exemplary valve-in-valve configuration implanted within a native aortic valve of a heart, which is partially shown. 
     
    
    
     DETAILED DESCRIPTION 
     General Considerations 
     For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, apparatus, and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods, apparatus, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved. 
     Although the operations of some of the disclosed embodiments are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art. 
     All features described herein are independent of one another and, except where structurally impossible, can be used in combination with any other feature described herein. 
     As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the terms “coupled” and “associated” generally mean electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language. 
     In the context of the present application, the terms “lower” and “upper” are used interchangeably with the terms “inflow” and “outflow”, respectively. Thus, for example, the lower end of the valve is its inflow end and the upper end of the valve is its outflow end. 
     As used herein, the term “proximal” refers to a position, direction, or portion of a device that is closer to the user and further away from the implantation site. As used herein, the term “distal” refers to a position, direction, or portion of a device that is further away from the user and closer to the implantation site. Thus, for example, proximal motion of a device is motion of the device toward the user, while distal motion of the device is motion of the device away from the user. The terms “longitudinal” and “axial” refer to an axis extending in the proximal and distal directions, unless otherwise expressly defined. 
     Examples of the Disclosed Technology 
     Described herein are examples of prosthetic implants, such as prosthetic valves, that can be implanted within any of the native valves of the heart (e.g., the aortic, mitral, tricuspid and pulmonary valves). The present disclosure also provides frames for use with such prosthetic implants. The frames can comprise struts having different shapes and/or sizes to avoid coronary blockage and native leaflet overhang. The prosthetic heart valves may also include a plurality of leaflets attached to the frame. 
     The present disclosure also may include leaflet assemblies for prosthetic heart valves, leaflet commissure tab assemblies of a leaflet assembly, and methods for assembling leaflet commissure tab assemblies. The leaflet commissure tab assemblies may include a plurality of leaflet commissure support members. Each leaflet commissure tab assembly can include a pair of adjacent leaflet tabs coupled to one another by the commissure support member. Each leaflet commissure assembly can be formed by folding and securing a tab of each of the leaflets around a corresponding commissure support member. The adjacently arranged valve leaflets can then be coupled to one another, prior to being attached to the frame of the prosthetic heart valve. As a result, a leaflet assembly for a prosthetic heart valve may be more easily assembled off the frame of the prosthetic heart valve and the time and effort for securing the leaflet assembly to the frame of the prosthetic heart valve may be reduced. 
     Also disclosed herein are various small diameter prosthetic valves (e.g., 20 mm) that can address one or more of the drawbacks associated with known small diameter prosthetic valves. In particular, disclosed embodiments can be configured to reduce pressure gradients, avoid native leaflet overhang, and/or maintain access and blood flow to the coronary arteries, all issues commonly associated with smaller diameter valves. Disclosed embodiments can comprise a plurality of commissure tab assemblies of the leaflet assembly being coupled to the outside surface of the frame. The disclosed commissure tab assemblies can, for example, allow the valve leaflets to open wider than generally allowed in conventional valves, which increases the overall blood flow through the prosthetic valve to reduce high-pressure gradients. 
     Prosthetic valves disclosed herein can be radially compressible and expandable between a radially compressed state and a radially expanded state. Thus, the prosthetic valves can be crimped on or retained by an implant delivery apparatus in the radially compressed state during delivery, and then expanded to the radially expanded state once the prosthetic valve reaches the implantation site. It is understood that the valves disclosed herein may be used with a variety of implant delivery apparatuses. Though the prosthetic valves shown herein are described as plastically-deformable or balloon-expandable prosthetic valves, it should be noted that the frame shapes and leaflet configurations disclosed herein can be used with any type of prosthetic valve. For example, the frame shapes and leaflet configurations disclosed herein can be used with mechanically-expandable prosthetic heart valves in which the frame is radially expandable via one or more mechanical actuators (such as the prosthetic valves described in U.S. Pat. No. 10,603,165 and U.S. Provisional Application No. 63/085,947, filed Sep. 30, 2020, each of which is incorporated herein by reference in its entirety). The frames of some mechanical valves can comprise pivotable junctions between the struts of the frame, while others can comprise a unitary lattice frame expandable and/or compressible via mechanical means. The frame shapes and leaflet configurations described herein can additionally be used with other types of transcatheter prosthetic valves, including self-expandable prosthetic heart valves in which the frame is made from a shape memory material (e.g., Nitinol), such as disclosed in U.S. Pat. No. 10,098,734, which is incorporated herein by reference in its entirety. 
       FIGS.  1 - 2    illustrate an exemplary embodiment of a prosthetic heart valve  100 . The prosthetic heart valve  100  can be radially compressible and expandable between a radially compressed configuration and a radially expanded configuration. In particular embodiments, the prosthetic heart valve  100  can be implanted within the native aortic annulus, although it also can be implanted at other locations in the heart, including within the native mitral valve, the native pulmonary valve, and the native tricuspid valve. The prosthetic heart valve  100  can comprise an annular stent or frame  102  having a first or inflow end  104 , a second or outflow end  106 , a radially inner surface  108 , and a radially outer surface  110 . A valvular structure  122  comprising a plurality of leaflets  124 , can be disposed within the frame  102 , as described in more detail below. The valvular structure  122  can be configured to regulate the flow of blood through the prosthetic valve  100  from the inflow end  104  to the outflow end  106 . For purposes of illustration, the rearmost leaflet in  FIG.  2    is shown transparently. 
     The outflow end  106  can be coupled to a delivery apparatus for delivering and implanting the prosthetic heart valve within the native aortic valve is a transfemoral, retrograde delivery approach. Thus, in the delivery configuration of the prosthetic heart valve, the outflow end  106  is the proximal-most end of the prosthetic valve. In other embodiments, the inflow end  104  can be coupled to the delivery apparatus, depending on the particular native valve being replaced and the delivery technique that is used (e.g., trans-septal, transapical, etc.). For example, the inflow end  104  can be coupled to the delivery apparatus (and therefore is the proximal-most end of the prosthetic heart valve in the delivery configuration) when delivering the prosthetic heart valve to the native mitral valve via a trans-septal delivery approach. 
     As shown in  FIGS.  1  and  2   , the frame  102  can include a plurality of interconnected lattice struts  112  arranged in a lattice-type pattern and forming a plurality of apices  114  at the outflow end  106  of the prosthetic valve  100 . The struts  112  can also form similar apices  116  ( FIG.  2   ) at the inflow end  104  of the prosthetic valve  100 . The frame  102  can be made of any of various suitable plastically expandable materials, such as stainless steel or a cobalt chromium alloy, and/or self-expanding materials, such as a nickel titanium alloy (“NiTi”), for example Nitinol. When constructed of a plastically expandable material, the frame  102  (and thus the prosthetic valve  100 ) can be crimped to a radially compressed state on a delivery catheter and then expanded inside a patient by an inflatable balloon or any suitable expansion mechanism, such as the mechanical expansion mechanisms described in U.S. Provisional Application No. 63/085,947, filed Sep. 30, 2020 or U.S. Provisional Application No. 63/179,766 filed Apr. 26, 2021, which is incorporated herein by reference in its entirety. When constructed of a self-expandable material, the frame  102  (and thus the prosthetic valve  100 ) 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 prosthetic valve  100  can be advanced from the delivery sheath, which allows the valve to expand to its functional size. 
     In the illustrated embodiment, the struts  112  are pivotable or bendable relative to each other to permit radial expansion and contraction of the frame  102 . For example, the frame  102  can be formed (e.g., via laser cutting, electroforming or physical vapor deposition) from a single piece of material (e.g., a metal tube). As such, the inflow end  104  and the outflow end  106  of the frame  102  can move axially parallel to the longitudinal axis  118  ( FIG.  3 B ) of the prosthetic valve  100  as it is radially expanded or compressed, such as during assembly, preparation, or implantation of the prosthetic valve  100 . 
     In other embodiments, the frame  102  can be constructed by forming individual components (e.g., the struts and fasteners of the frame) and then mechanically assembling and connecting the individual components together. For example, the struts  112  can be pivotably coupled to one another at one or more pivot joints or pivot junctions along the length of each strut. Each of the pivot joints or pivot junctions (e.g., hinges) can allow the struts  112  to pivot relative to one another as the frame  102  is radially expanded or compressed. Further details regarding the construction of the frame and the prosthetic valve are described in U.S. Patent Publication No. 2018/0028310, which is incorporated herein by reference in its entirety. Other frames that can be implemented in the prosthetic valve are disclosed in U.S. Pat. Nos. 9,393,110 and 9,155,619, and 10,603,165, which are incorporated herein by reference in their entireties. 
     As shown in  FIG.  1   , the prosthetic valve  100  can also include an outer skirt  120  mounted on the outer surface  110  of the frame  102 . The outer skirt  120  can function as a sealing member for the prosthetic valve  100  by sealing against the tissue of the native valve annulus and helping reduce paravalvular leakage past the prosthetic valve. The outer skirt  120  can be formed from any of various suitable biocompatible materials, including any of various synthetic materials (e.g., PET) or natural tissue (e.g., pericardial tissue). The outer skirt  120  can be mounted to the frame  102  using sutures, an adhesive, welding, and/or other means for attaching the outer skirt  120  to the frame  102 . 
     Selection of the height of the frame of a prosthetic valve is an important consideration, especially for smaller diameter prosthetic valves (e.g., 20 mm or smaller). Generally speaking, the frame of a prosthetic valve desirably should be short enough to avoid extending beyond the sinotubular junction (STJ) line and avoid tilting of the prosthetic valve from its intended implanted orientation, yet long enough to avoid native leaflet overhang. It has been found that for patients needing a relatively smaller prosthetic valve (20 mm or smaller), a prosthetic valve having a height of about 14 mm or shorter can increase the risk of leaflet overhang while a prosthetic valve having a height of over 18 mm is likely to extend beyond the STJ line. 
       FIGS.  3 A- 3 B  show the frame  102  with the valvular structure  122  and skirt  120  removed for purposes of illustration. As best seen in  FIG.  3 A , the struts  112  form a plurality of closed cells  130  arranged in a plurality of circumferentially-extending rows  132  of cells. Each row  132  of cells  130  can get progressively larger from the inflow end  104  to the outflow end  106 . In the illustrated embodiment, the struts  112  define three rows of cells, including a first row  132   a  adjacent the outflow end  106  of the frame, a second row  132   b,  and a third row  132   c  adjacent the inflow end  104  of the frame  102 . In other embodiments, the frame  102  can have a greater or fewer number of rows  132 . 
       FIG.  3 B  illustrates a partial view of the frame  102 . While only one side of the frame  102  is depicted in  FIG.  3 B , it should be appreciated that frame  102  forms an annular structure as shown in  FIG.  3 A  having an opposite side that is identical (or substantially identical) to the portion shown. As shown in  FIG.  3 B , the cells  130  in the row  132   a  adjacent the outflow end  106  of the frame  102  can have a relatively larger open cell area compared to the cells of rows  132   b  and  132   c.  Accordingly, the cells  130  in row  132   a  can be referred to as “larger” or “elongated” cells  134 . In the illustrated embodiment, the elongated cells  134  have a height H 1  greater than a height H 2  of the cells  130  of row  132   b,  and/or a height H 3  of the cells  130  of row  132   c.  The elongated cells  134  can have a width W 1  that is at least twice the width of a coronary catheter (e.g., a 6 Fr coronary catheter). The height of the elongated cells  134 , in combination with the positioning of the valvular structure  122  within the frame  102  defines a gap G ( FIG.  1   ) between the outflow end  136  of the elongated cells  134  and the outflow edge  138  of the leaflets  124  configured to accommodate a coronary catheter there-through, as described further below. 
     The smaller cells, such as the cells in rows  132   b,    132   c  in the illustrated embodiment, can have a relatively stronger structural strength than larger cells  134 . Accordingly, the frame  102  can be positioned within the native annulus such that the smaller cells  130  in rows  132   b,    132   c  bear a greater amount of the radial force applied by the native annulus than the larger cells. 
     As mentioned previously and shown in  FIGS.  1 - 2   , the prosthetic valve  100  can also include a valvular structure  122  (shown in the open configuration) which is coupled to and supported by the frame  102 . The valvular structure  122  can include, for example, a leaflet assembly comprising one or more leaflets  124  made of a flexible material. The leaflets  124  can be made in whole or in part, from biological material, bio-compatible synthetic materials, or other such materials. Suitable biological material can include, for example, bovine pericardium (or pericardium from other sources). 
     The leaflets  124  can be secured to one another at their adjacent sides to form commissures  126 , each which can be secured to a respective commissure post  128 . Selection of the height of the individual leaflets is an important consideration for smaller diameter prosthetic valves. Generally speaking, the leaflets should be high enough to promote full closure of the leaflets during diastole, for example, to prevent unwanted back flow through the prosthetic valve. On the other hand, the leaflets should also be low enough as to not block access to the coronary arteries when in an opened and closed configuration. 
     Referring to  FIG.  2   , each leaflet  124  can have a curved, scallop shape including a lower cusp portion  140  extending between first and second tabs  142  of the leaflet  124  and an outflow edge  138  (also referred to as a coaptation edge) that contacts respective outflow edges of the other leaflets during diastole. The lower cusp portion  140  can comprise an inflow edge  144  offset from the outflow edge  138  along a longitudinal axis of the valve  100 . The inflow edge  144  can be aligned with (or substantially aligned with) and coupled to the inflow end  104  of the frame  102 , and the outflow edge  138  can be disposed such that it is located between the inflow end  104  and the outflow end  106  of the frame  102 , defining a gap G between the outflow edge  138  of the leaflet  124  and the outflow end  106  of the frame when the valvular structure  122  is in the open configuration. The gap G can remain open and accessible during the working cycle of the prosthetic valve  100 , thereby reducing potential blockage of the coronary arteries. 
     The valvular structure  122  can be coupled to the frame  102  via one or more commissure posts  146 . As shown in  FIG.  3 B , selected struts  112  of the elongated cells  134  can be configured as commissure posts  146 . Each commissure post  146  can comprise a plurality of apertures  148 . The commissure post  146  can be disposed such that it is spaced apart from the outflow end  106  of the frame  102  along a longitudinal axis  118  of the valve  100 . In the illustrated embodiment, an outflow edge  148  of the commissure post  146  can be disposed such that it substantially aligns with a plane P that is perpendicular to the longitudinal axis of the frame and bisects each of the elongated openings  134 . However, in other embodiments, the commissure post  146  can be disposed at any location along the height of the elongated cell  134 . 
     In the illustrated embodiment, the frame  102  can comprise three commissure posts  146  spaced apart from one another about the circumference of the frame  102 . However, in other embodiments, the frame  102  can comprise a greater or fewer number of commissure posts and the commissure posts  146  can be disposed at any position about the circumference of the frame  102 . In the illustrated embodiment, each commissure post  146  comprises three apertures  148  extending along a height of the commissure post  146 . One or more leaflets  124  of the valvular structure  122  can be sutured to the frame  102  via the plurality of apertures  148 , as shown in  FIGS.  1 - 2   . 
     Coupling the leaflets  124  to the apertures  148  of the commissure post  146  advantageously does not require the use of an intermediate cloth layer. Rather, each tab  142  of a leaflet  124  can be coupled to a tab  142  of an adjacent leaflet  124  to form a commissure  150 . Each commissure  150  can be sutured directly to the frame  102  at a respective commissure post  146 . Likewise, the cusp edge  140  of each leaflet  124  can be sutured along the scallop line directly to the frame  102 . Eliminating intermediate cloth portions by suturing the leaflets  124  directly to the frame  102  can advantageously prevent or mitigate tissue ingrowth along the cusp edge portion  140  and/or the commissures  150 . Such a configuration is feasible in small-diameter prosthetic valves, such as prosthetic valve  100 , due to the relatively lower stresses experienced by the leaflets  124  in such prosthetic valves, the lower stresses resulting from systolic and/or diastolic pressure being applied over a relatively smaller area, when compared to a non-small diameter prosthetic valve. 
     In some embodiments, the valvular structure  122  can be coupled to the frame  102  using, for example, a wide, thick suture  152  ( FIG.  2   ). Such a suture  152  can advantageously prevent or mitigate tearing of the leaflets  124  along the portions of the leaflets coupled to the frame. 
     The height H 1  of the elongated cells  134  in combination with the position of the commissure posts  146  and thereby the outflow edges  138  of the leaflets  124  allows access to the coronary vessel when the prosthetic valve  100  is implanted within the native annulus of a patient. For example, in some instances a patient may require implantation of a coronary stent (or other procedure that requires access to the coronary vessel) after a prosthetic heart valve, such as prosthetic valve  100 , has been implanted. In such instances, the physician may access the coronary vessel through the outflow end  106  of the prosthetic valve by passing through the elongated cells  134 . This allows a physician to access the coronary vessel without needing to remove or displace the prosthetic heart valve  100 . For example,  FIG.  22    illustrates prosthetic valve  100  (with the skirt  120  and valvular structure  122  removed for purposes of illustration) implanted within a patient&#39;s native aortic heart valve  800 . As shown, the frame  102 , once expanded, can retain the native leaflets  802  in an open position against the aortic walls  804 . The elongated cells  134  allow a coronary catheter  806  to access to the coronary vessels  808  via the coronary ostia  810 . The height of the elongated cells  134  can be selected such that the outflow ends  106  of one or more elongated cells  134  abut the ceiling of the native sinus positioning the prosthetic valve  100  within the native aortic valve  800  and the aortic root such that the coronary vessels  808  remain accessible. Further details of leaflet heights and ratios with prosthetic valve frames can be found, for example, in International Application No. PCT/US2021/025869, incorporated herein by reference in its entirety. 
     In some instances, it may be necessary to implant a second prosthetic valve within a previously-implanted prosthetic valve in what is known as a valve-in-valve (VIV) procedure. Such a procedure can be used to augment or replace a previously-implanted valve (e.g., if the previously-implanted valve is failing or otherwise compromised). Implantation of the second prosthetic valve or “guest valve” within the first prosthetic valve or “host valve” can be challenging with smaller diameter valves because it can be difficult to properly align and orient the guest valve within the host valve while maintaining access to the coronary ostia. The configuration of prosthetic valve  100  can advantageously retain access to the coronary ostia regardless of the positioning of the guest valve within the host valve. 
     Referring to  FIG.  21   , a delivery apparatus  900  including a handle  902  can be used to deliver and implant the prosthetic valve  100  in the following exemplary manner. The prosthetic valve  100  can be disposed on a distal end portion  906  of the delivery apparatus  900  in a radially compressed state. The prosthetic valve  100  can be crimped on an inflatable balloon  904  or another type of expansion member that can be used to radially expand the prosthetic valve  100 . The distal end portion  906  of the delivery apparatus  900 , including prosthetic valve  100 , can be advanced through the vasculature to a selected implantation site (e.g., within a previously implanted host valve and/or within a native valve). In the illustrated embodiment, the distal end portion of the delivery apparatus  900  and the prosthetic valve  100  are inserted into a femoral artery and advanced through the femoral artery and the aorta and positioned within the native aortic valve  800  or a host valve previously implanted within the native aortic valve  800 . The prosthetic valve  100  can then be deployed at the implantation site, such as by inflating the balloon  904 . Further details of delivery apparatuses that can be used to deliver and implant plastically expandable prosthetic valves, such as the prosthetic valve  100  (or any other prosthetic valves disclosed herein) are disclosed in U.S. Pat. Nos. 10,588,744, 10,076,638, and 9,339,384, which are incorporated herein by reference in their entireties. 
     If the prosthetic valve  100  being implanted is a self-expandable prosthetic valve, the prosthetic valve can be retained in a radially compressed state within a delivery capsule or sheath of the delivery apparatus when inserted into and advanced through the patient&#39;s vasculature to the desired implantation site. Once positioned at the desired implantation site, the prosthetic valve can be deployed from the delivery capsule, which allows the prosthetic valve to self-expand to its radially expanded, functional size within the native valve or a previously implanted host valve. Further details of delivery apparatuses that can be used to deliver and implant self-expandable prosthetic valves (including any of the prosthetic valves disclosed herein when the frames are constructed of a self-expandable material such as Nitinol) are disclosed in U.S. Pat. Nos. 9,867,700 and 8,652,202, which are incorporated herein by reference in their entireties. 
     In a particular example, the prosthetic valve  100  can be deployed within a previously implanted host valve  200 , as shown in  FIG.  23   .  FIG.  4    illustrates the result of a valve-in-valve procedure using an exemplary balloon-expandable prosthetic valve  200  as the host valve and prosthetic valve  100  as the guest valve. The back-left leaflet  124  (in the orientation shown in  FIG.  4   ) of the guest valve&#39;s  100  valvular structure is shown transparently for purposes of illustration. Examples of balloon-expandable prosthetic valves can be found, for example, in U.S. Pat. No. 9,393,110. Host valve  200  can comprise a frame  202  including a plurality of struts  203  forming cells  204  arranged in a plurality of circumferentially extending rows  206 . In the illustrated embodiment, the host valve  200  has four rows of cells including an outflow row of cells  206   a,  two middle rows of cells  206   b,  and an inflow row of cells  206   c . The host valve  200  can further comprise a valvular structure, and inner and/or outer skirts, however, such components are not shown for purposes of illustration 
     Ideally, the guest valve  100  is implanted in a rotationally aligned position relative to the host valve  200 . However, in some instances, the guest valve  100  can be implanted in a rotationally offset position and/or become rotationally offset from the host valve  200  during or after the implantation procedure. As used herein the term “rotationally aligned” means that the struts  112  of the outflow row of cells  130  (the elongated cells  134 ) of the guest valve  100  are in a rotational position such that they are aligned with the struts  203  of the outflow row of cells  206   a  of the host valve  200 . The term “rotationally offset” means that the struts  112  of the elongated cells  134  are in a rotational position such that they are offset from the struts  203  of the outflow row of cells  206   a  of the host valve  200  (see e.g.,  FIG.  4   ). 
       FIG.  4    illustrates the guest valve  100  in a “worst-case” rotationally offset position relative to the host valve  200 . As used herein, a “worst-case” position means a rotationally offset position in which the struts  112  of the guest valve  100  align with the center of the cells  204  of the outflow row  206   a  of the host valve  200 , or vice versa, resulting in a relatively smaller opening through which a coronary catheter can be inserted. However, the elongated cells  134  of the guest valve  100  have a width W 1  ( FIG.  3 B ) configured such that even when the host valve  200  and guest valve  100  are in a “worst-case” position a coronary catheter  250  (e.g., a 6 Fr coronary catheter) can extend through both the guest valve  100  and the host valve  200 , as shown in  FIG.  4   . The height H 1  ( FIG.  3 B ) of the elongated cells  134  can be selected such that the outflow end  106  of the guest valve frame  100  can abut the ceiling of the native sinus. The gap G between the outflow end  106  of the frame and the outflow edge  138  of the leaflets  124  can serve to allow access to the coronary ostia. 
     In some embodiments, such as when the host valve  200  comprises a valvular structure aligned with (or substantially aligned with) the outflow end  208  of the frame  202 , it may be necessary to cut or remove the valvular structure of the host valve  200  prior to implantation of the guest valve  100 . If such action is not taken, the valvular structure can cover the outflow row  206   a  of cells, obstructing the sinus and potentially harming the patient. However, in the illustrated embodiment, the height H 1  of the elongated cells  134  can further serve as a spacer between the outflow edge of the host valve&#39;s  200  valvular structure and the outflow end  106  of the guest valve  100 . Accordingly, even if the valvular structure of the host valve  200  is retained by the guest valve  100  in an open configuration against the frame  202 , the elongated cells  134  define a space between the ceiling of the native sinus and the outflow edge of the host valvular structure such that the host valvular structure does not occlude the coronary sinus. 
     For example,  FIG.  23    illustrates a guest prosthetic valve  100  (including frame  102 , skirt  120 , and valvular structure  122 ) implanted in a valve-in-valve configuration within a host valve  200  in a patient&#39;s native aortic heart valve  800 . As shown, the previously implanted host valve  200  retains the native leaflets  802  in an open position against the aortic walls  804 . The soft components of the host valve  200  (the leaflets and the skirts) are omitted for purposes of illustration. The valve-in-valve configuration can abut the ceiling  812  of the native sinus and serve as a spacer such that the coronary vessels  808  remain accessible. Accordingly, the coronary vessels  808  remain accessible and blood can flow through the frames  102 ,  202  and into the coronary vessels  808  as shown by arrows  814 . 
     As shown, the width W 1  ( FIG.  3 B ) of each elongated cell  134  is configured to be at least twice as wide as the outer diameter of the selected coronary catheter  250  (e.g., a 6 Fr coronary catheter). Accordingly, the coronary catheter  250  can be disposed through the outflow end row  132   a  of cells of the guest valve  100  (e.g., the elongated cells  134 ) and the host valve  200  regardless of the relative rotational orientation between the guest valve  100  and the host valve  200 . 
       FIG.  5    illustrates the result of a valve-in-valve procedure using a first small diameter valve  100   a  as the host valve and a second small diameter valve  100   b  as the guest valve. Guest valve  100   b  can comprise a valvular structure, an inner skirt, and/or an outer skirt, however such components are not shown for purposes of illustration. Further, the back-left leaflet (in the orientation shown in  FIG.  5   ) of the host valve  100   a  is not shown for purposes of illustration.  FIG.  5    illustrates the guest valve  100   b  in a “worst-case” rotationally offset position relative to the host valve  100   a  such that the struts  112   b  of the guest valve  100   b  align with the center of the elongated cells  134   a  of the host valve  100   a.    
     As shown, the elongated cells  134   b  of the guest valve  100   b  have a width W b  and the elongated cells  134   a  of the host valve  100   a  have a width W a  such that a coronary catheter  250  (e.g., a 6 Fr coronary catheter) can be inserted through the host and guest elongated cells  134   a,    134   b,  respectively, regardless of the rotational position of the host valve  100   a  and the guest valve  100   b  relative to one another. The height of each set of elongated cells  134   a,    134   b  can be selected such that the outflow end  106   a,    106   b  of the host valve frame  100   a  and the guest valve frame  100   b  can abut the ceiling of the native sinus when implanted in a patient. 
     The valvular structure  122   a  of the host valve  100   a  can be sized such that the gap G a  between the outflow edge  138   a  of each leaflet  124   a  and the outflow end  106   a  of the frame  102   a  allows the coronary catheter  250  to extend therethrough when the valvular structure  122   a  is fully open (e.g., as shown in  FIG.  5   ). Such a configuration advantageously allows the guest valve  100   b  to be implanted within the host valve  100   a  (thereby maintaining the valvular structure  122   a  in the fully open configuration) without needing to remove or cut the valvular structure  122   a  of the host valve  100   a.    
     As shown in  FIG.  5   , the width W a , W b  of each elongated cell  134   a,    134   b  is configured to be at least twice as wide as the outer diameter of the selected coronary catheter  250  (e.g., a 6 Fr coronary catheter). Accordingly, the coronary catheter  250  can be disposed through the elongated cells  134   a,    134   b  of the guest valve  100   b  and the host valve  100   a  regardless of the relative rotational orientation between the guest valve  100   b  and the host valve  100   a.    
       FIG.  6    illustrates result of a VIV procedure using an exemplary balloon-expandable prosthetic valve  200  as the host valve, a first small diameter prosthetic valve  100   a  as a first guest valve, and a second small diameter prosthetic valve  100   b  as a second guest valve. The host valve  200  and the second guest valve  100   b  can each include a valvular structure, an inner skirt, and/or an outer skirt, however these components are omitted for purposes of illustration. Further, the back-left leaflet (in the orientation shown in  FIG.  6   ) of the first guest valve  100   a  has been omitted for purposes of illustration. 
     As shown in  FIG.  6   , regardless of the rotational orientation between the host valve  200 , the first guest valve  100   a,  and the second guest valve  100   b,  a coronary catheter  250  (e.g., a 6 Fr coronary catheter) can be disposed through the elongated cells  134  of the first and second guest valves  100   a,    100   b  and the outflow end row of cells  206   a  of the host valve  200 . In some embodiments, the host valve  200  can also be configured as a small diameter prosthetic valve. 
     In the illustrated embodiment, the host valve  200  has a 12 cell configuration, and each of the small diameter guest valves  100  can have a 9 cell configuration. “12 cell” and “9 cell” configurations refer to the number of cells in each circumferentially extending row.  FIGS.  7 - 8    illustrate an exemplary prosthetic valve  300  including a frame  302  having a  9  cell configuration.  FIG.  7    illustrates the frame  302  of the prosthetic valve  300  coupled to an exemplary valvular structure  304 .  FIG.  8    illustrates the frame  302  without the valvular structure  304 . The prosthetic valve  300  can further comprise inner and/or outer skirts, however, such components are not shown for purposes of illustration. The frame  302  can comprise a plurality of commissure windows  310  and can further comprise three circumferentially-extending rows  306  of cells  308 . For example, the frame  302  can comprise an outflow row  306   a,  a middle row  306   b,  and an inflow row  306   c.  Similar to frame  202  described above, the cells  308  outflow row  306   a  can have a relatively larger open cell area compared to the cells of rows  306   b,    306   c,  and can be referred to as elongated cells  314 . The height of the elongated cells  314  in combination with the positioning of the valvular structure  304  within the frame  302  defines a gap between the outflow end of the elongated cells  314  and the outflow edge  316  of the valvular structure  304  configured to accommodate a coronary catheter there-through. As shown in the illustrated embodiment, an outflow edge  312  of the commissure window  310  can be disposed such that it substantially aligns with a plane P ( FIG.  8   ) that is perpendicular to the longitudinal axis of the frame  302  and extends through each of the elongated openings  314 . 
       FIGS.  9 - 10    illustrate an exemplary prosthetic valve  400  having a 12-cell configuration.  FIG.  9    illustrates the frame  402  of the prosthetic valve  400  coupled to an exemplary valvular structure  404 .  FIG.  10    illustrates a portion of the frame  402  without the valvular structure  404 . While only one side of the frame  402  is depicted in  FIG.  10   , it should be appreciated that frame  402  forms an annular structure having an opposite side that is identical (or substantially identical) to the portion shown. The frame  402  can comprise four circumferentially-extending rows  406  of cells  408 . For example, the frame  402  can comprise an outflow row  406   a,  two middle rows  406   b,  and an inflow row  406   c.  Similar to frames  202  and  302  described above, the cells  408  outflow row  406   a  can have a relatively larger open cell area compared to the cells of rows  406   b,    406   c,  and can be referred to as elongated cells  414 . The height of the elongated cells  414  in combination with the positioning of the valvular structure  404  within the frame  402  defines a gap between the outflow end of the elongated cells  414  and the outflow edge  416  of the valvular structure  404  configured to accommodate a coronary catheter there-through. As shown in the illustrated embodiment, an outflow edge  412  of the commissure window  410  ( FIG.  10   ) can be disposed such that it substantially aligns with a plane P ( FIG.  10   ) that is perpendicular to the longitudinal axis of the frame  402  and extends through each of the elongated openings  414 . 
     Though the above frame embodiments are described in the context of small-diameter valves, it should be understood that elongated cells and commissure posts such as those described can be used on prosthetic valves having any of various diameters. 
       FIGS.  11 - 14    illustrate another embodiment of a small-diameter prosthetic valve  500 . The small diameter prosthetic valve  500  can comprise a frame  502  having an inflow end portion  504  and an outflow end portion  506  and a valvular structure  508  coupled to and supported by the frame  502 . The prosthetic valve  500  can further comprise inner and/or outer skirts, however, such components are not shown for purposes of illustration. 
     The valvular structure  508  is configured to regulate the flow of blood through the prosthetic valve  500  from the inflow end portion  504  to the outflow end portion  506 . The valvular structure  508  can include, for example, a leaflet assembly comprising one or more leaflets  510  made of flexible material. The leaflets  510  can be made in whole or in part, from biological material, bio-compatible synthetic materials, or other such materials. Suitable biological material can include, for example, bovine pericardium (or pericardium from other sources). The leaflets  510  can be secured to one another at their adjacent sides to form commissures  512 , each which can be secured to a commissure support member, as discussed further below. As shown in  FIG.  12   , each leaflet can have an inflow edge portion  514  (also referred to as a cusp edge portion) that can be mounted to the frame  502  and an outflow edge portion  516  (also referred to as the free edge portion) that contacts respective outflow edges of the other leaflets during closure of the leaflets (e.g., during diastole). 
     During typical valve operation, the leaflets  510  transition between a closed state in diastole, with their outflow edges  516  coapting against each other, and an open state (see e.g.,  FIG.  11   ) allowing blood to flow through the prosthetic valve  500 . The outflow orifice through which the blood can flow determines the pressure gradient across the valve. Known valves can have valvular structures attached to the frame in such a manner that the outflow edges of each leaflet are spaced radially inward of the frame to prevent leaflet abrasion when the leaflets open under the flow of blood. In such valves, the effective outflow orifice (e.g., as determined by the position of the leaflets), also referred to as the geometric orifice area (GOA), can be narrower than the inflow orifice, producing a relatively high pressure gradient across the prosthetic valve. The increased pressure gradient can lead to prosthesis-patient-mismatch (PPM) where the prosthetic valve is essentially undersized for the patient, which has been shown to be associated with worsened hemodynamic function and more cardiac events. Accordingly, and particularly when small diameter valves are used, it is preferable to provide a large outflow orifice during systole to prevent elevated pressure gradients. 
     As shown in  FIG.  13   , the valvular structure  508  of prosthetic valve  500  advantageously defines a relatively large GOA  518  when compared to the size of the outflow orifice  520  defined by the outflow end  506  of the frame. The term “GOA,” as used herein, is defined as the open space through which blood can flow when the valvular structure is in the open configuration. The GOA  518  of the outflow orifice  520  can be sized to provide a selected pressure gradient across the prosthetic valve  500 . Such a configuration can be achieved by attaching the leaflets  510  to the frame  502  in such a manner that the radial distance S 1  between the outflow edges  516  of the leaflets  510  and the frame  502  is minimized. 
     Referring again to  FIG.  12   , the cusp edge portion  514  terminates at its upper ends at two laterally projecting integral lower tabs  522 . The lower tabs  522  can extend from a body  524  of the leaflet  510  such that an upper or outflow edge  526  of each lower tab  522  is positioned at an angle θ relative to a longitudinal axis A of the leaflet  510 . The angle θ can be selected such that the radially outer edge  528  of each lower tab  522  corresponds to the draft angle of the frame  502 . The “draft angle” of the frame, as used herein, means the degree of taper from the outflow end  506  of the frame  502  to the inflow end  504 , which can be a measure of the angle between a longitudinal axis of the frame and a line drawn tangent to the outer surface of the frame  502 . For example, in a cylindrical valve, the draft angle is about 0 degrees. In a non-cylindrical, tapered valve (e.g., a frustoconical, V-shaped, or Y-shaped valve), the draft angle can be, for example, between about 2 degrees and about 15 degrees. 
     In the illustrated embodiment, the frame  502  has a cylindrical shape and the lower tabs  522  are positioned such that the radially outer edge  528  corresponds to (e.g., is substantially parallel to) the draft angle of the frame  502 . Accordingly, the lower tabs  522  extend from the body portion  524  such that the angle θ is a 90 degree angle. Such a configuration can advantageously allow for a greater GOA  518  while preventing or mitigating abrasion of the leaflets  510 . 
     In other embodiments wherein the frame has a non-cylindrical shape, the lower tabs  522  can be disposed such that an upper edge  526  of each tab  522  extends at a non-90 degree angle relative to the longitudinal axis of the leaflet (e.g., as shown in  FIG.  20   ). In such embodiments, the angle θ can be less than or greater than 90 degrees. For example, a non-cylindrical valve can have a draft angle between about 2 degrees and about 5 degrees. In such embodiments, the angle θ can be between about 88 degrees and about 85 degrees. 
     Each lower tab  522  can have a height Hi. The height H 1  can be shorter than the height of a conventional leaflet tab in order to provide a greater GOA during systole. For example, a conventional commissure opening can have a height of about 3.3 mm and conventional leaflets can have a height of 3.7 mm. Accordingly, a conventional leaflet tab must be squeezed in order to fit into a conventional commissure opening, which can form a rigid portion of leaflet that extends radially inward toward the longitudinal axis of the prosthetic valve. In contrast, the height H 1  of lower tabs  522  can be selected to minimize squeezing, and therefore minimize rigid portions formed by the leaflets  510 . In some embodiments, the height H 1  of the lower tabs can substantially correspond to the height of the commissure opening. For example, the height of a tab “substantially corresponds” with the commissure opening if the height H 1  of the tab is between 0.1 mm to 0.5 mm greater or less than of the height of the opening. For example, in some particular embodiments, the height H 1  of each lower tab  522  can be 3.4 mm, and the height of the commissure opening can be 3.3 mm. 
     As shown in  FIG.  12   , each lower tab  522  can be coupled to an upper tab  530  via a respective neck portion  532 . In the illustrated embodiment, each upper tab  530  and neck portion  532  are formed integrally with the leaflet  510 . However, in other embodiments, the upper tabs  530  and/or neck portions  532  can be formed separately from the leaflet  510  and coupled to the leaflet  510 . In the illustrated embodiment, the upper tab  530  can have a substantially rectangular shape including a radially inner edge portion  534  that tapers from the neck portion  532  to a free edge  533 . However, in other embodiments, the upper tab  530  can have any of various shapes. As shown in  FIG.  11   , when the valvular structure  508  is coupled to the frame  502 , each upper tab  530  is folded downward (e.g., toward the inflow end  504  of the frame  502 ) along the neck portion  532  such that the free edge  533  faces the inflow end  504  of the prosthetic valve  500 . 
     As best seen in  FIG.  13   , the neck portion  532  can be sized such that when the upper tab  530  is folded downwards (e.g., toward the inflow end  504  of the frame  502 ), a rigid portion  535  is formed by the folded neck portion  532  that extends radially into the outflow orifice a distance S 1 , thereby preventing the leaflets  510  from hitting the frame  502  (preventing or mitigating abrasion and/or other damage to the leaflets) while maximizing the GOA  518  of the outflow orifice  520 . Such a configuration advantageously improves the pressure gradient across the valve  500  while minimizing wear along the hinge line  536  ( FIG.  12   ) (e.g., the portion of the leaflet  510  where the lower tab  522  meets the body  524 ). 
     In some embodiments such as the illustrated embodiment, the neck portion  532  can have a width W 1  that is less than half the width W 2  of the lower tabs  522  and/or the upper tabs  530 . For example, in some particular embodiments, each neck portion  532  can have a width of about 0.70 mm and each lower tab can have a width of about 2.0 mm. In other embodiments, the width W 1  of the neck portion  532  can be half the width W 2  of the lower tabs  522  and/or the upper tabs  530 . 
     Furthermore, the size of the neck portion  532  (and therefore the size of the rigid portion  535  and of the distance S 1 ) can be varied depending on the specific anatomical needs of the patient. For example, for larger prosthetic valves mounted against dilated anatomical structures, it may be beneficial to reduce the GOA of the outflow orifice. In such cases, the neck portion  532  can be enlarged such that the rigid portion  535  and therefore the space S 1  between the frame  502  and the leaflets  510  extends radially a greater distance into the outflow orifice  520 , thereby limiting the flow through the outflow end of the valve  506 . In other embodiments, the GOA  518  can also be reduced by, for example, varying the angle of the lower tabs  522  and/or enlarging the height of the lower tabs  522 . 
     Referring to  FIG.  14   , in some embodiments, the valvular structure  508  can be secured to the frame  502  in the following exemplary manner. Adjacent lower tabs  522  of two adjacent leaflets  510  can be coupled together, and the upper tabs  530  can be folded downward along the neck portions  532  such that the lower tabs  522  are disposed between them. The lower tabs  522  can then be inserted through a commissure window in the frame  520  and folded along the radially outer surface  538  of the frame  502 . Each lower tab  522  can be coupled to a respective upper tab  530  along a suture line. In some embodiments, a wedge (not shown) can be disposed between the lower tabs  522  where they fold along the radially outer surface  538  of the frame  502 . The wedge can be secured to the lower tabs  522  using one or more sutures. 
       FIGS.  15 - 17    illustrate another embodiment of a small-diameter prosthetic valve  600  having a frame  602  coupled to a valvular structure  604  configured to provide a selected GOA (e.g., a maximized GOA) at the outflow orifice  606 . As shown in  FIG.  15   , the frame  602  can have an inflow end portion  608  and an outflow end portion  610 . The valvular structure  604  can be coupled to and supported by the frame  602 . The prosthetic valve  600  can further comprise inner and/or outer skirts, however, such components are not shown for purposes of illustration. 
     The valvular structure  604  can be similar to the valvular structure  508 , described previously, except that the leaflets  612  of valvular structure  604  do not include upper tabs. Referring to  FIG.  16   , each leaflet  612  can comprise an inflow edge portion  614  (also referred to as a cusp edge portion) that can be mounted to the frame  602  and an outflow edge portion  616  (also referred to as the free edge portion) that contacts respective outflow edges of the other leaflets during closure of the leaflets (e.g., during diastole). 
     The cusp edge portion  614  of each leaflet  612  terminates at its upper ends at two laterally projecting integral tabs  618 . The tabs  618  can extend from a body portion  620  the leaflet  612  such that an upper or outflow edge  622  of each tab  618  is positioned at an angle θ relative to a longitudinal axis A of the leaflet  612 . The angle θ can be selected such that the radially outer edge  624  of each tab  618  corresponds to the draft angle of the frame  602 . For example, in the illustrated embodiment, the prosthetic valve  600  comprises a cylindrical frame  602  having a draft angle of about 0 degrees. As shown, the tabs  618  extend from the body  620  of the leaflet  612  such that the angle θ is a 90 degree angle relative to a longitudinal axis A of the leaflet  612 . In other words, the tabs  618  are positioned such that the radially outer edge  624  corresponds to the draft angle of the frame  602 . Such a configuration can result in “streamlining” where the end of the hinge line  626  of each tab  618  is tangent with the commissure folding line, which therefore does not create a rigid portion of the leaflet  618 . 
     Referring still to  FIG.  16   , each tab  618  can have a height H 2 . The height H 2  can be shorter than the height of a conventional leaflet tab in order to provide a larger GOA during systole. A conventional commissure opening can have a height of about 3.3 mm and conventional leaflets can have a height of, for example, about 3.7 mm. Accordingly, a conventional leaflet tab must be squeezed in order to fit into a conventional commissure opening, which can form a rigid portion of leaflet that extends radially inward toward the longitudinal axis of the prosthetic valve. In contrast, the height H 2  of tabs  618  can be selected to minimize squeezing, and therefore minimize rigid portions of the leaflets  612 . In some embodiments, the height H 2  of the lower tabs can substantially correspond to the height of the commissure opening. For example, the height of a tab “substantially corresponds” with the commissure opening if the height H 2  of the tab is between 0.1 mm to 0.5 mm greater than or less than of the height of the commissure opening. For example, in some particular embodiments, the height H 2  of each lower tab  522  can be 3.4 mm, and the height of the commissure opening can be 3.3 mm. 
     Each tab  618  can comprise a step portion  628  disposed between the outflow edge  616  of the leaflet  612  and the upper edge  622  of each tab  618 . The step portion  628  is configured to offset the folding area to the junction between the tab&#39;s upper edge  622  and the step portion  628 , rather than positioning the fold at the upper edge of the leaflet  612 . The step portion  628  can further provide a visual indicator to facilitate proper positioning of the tab  618  within the commissure window  630  ( FIG.  17   ) during assembly of the prosthetic valve  600 . 
     In some embodiments, the valvular structure  604  can be secured to the frame  602  in the following exemplary configuration.  FIG.  17    illustrates a cross-sectional view of a portion of the frame  602  and valvular structure  604  showing the tabs  618  of adjacent leaflets  612  secured to a commissure window  630 . The commissure window  630  can comprise two members  632  defining an opening  634  between them. The tabs  618  can be inserted through the opening  634  and can be folded along the radially outer surface  636  of the frame  602 . A flexible connector  638  can extend around each member  632 , around the outer edges  624  of each tab  618  and across the radially outer surface of the tabs  618 . A wedge  640  can be disposed radially between the flexible connector  638  and the tabs  618  and between the adjacent tabs  618 . The various components can then be coupled together using one or more sutures  642 . 
     As best seen in  FIG.  18   , the configuration of the leaflets  612  advantageously allows the valvular structure  604  to be coupled to the frame  602  such that the GOA  644  is nearly the entire area of the outflow orifice  646 , thereby maximizing the GOA. In other words, when the valvular structure  604  is in the open configuration, at least a portion of the leaflets  612  abut the frame  602 . Such a configuration advantageously improves the pressure gradient across the valve  600 . The leaflet parameters, including tab angle and tab height, can be varied to provide a selected GOA  644 , for example, to maximize the GOA  644  in a small-diameter prosthetic valve. In some particular embodiments, the configuration of prosthetic valve  600  can result in a GOA of about 216 mm 2 , which can result in a pressure gradient of about 5 mmHg across the prosthetic valve  600 . 
     In some cases, the leaflets  612  can be configured to deliberately reduce the GOA  644 , for example, by enlarging the height H of the tabs  618  and/or angling the tabs  618  relative to the draft angle of the frame  602 . Reduction of the GOA can be advantageous for, for example, large frames mounted against dilated anatomical structures. 
       FIGS.  19 - 20    illustrate another embodiment of a small-diameter prosthetic valve  700  including a valvular structure  704  configured to provide a selected GOA  706  at the outflow orifice  708 . As shown in  FIG.  19   , the prosthetic valve  700  can comprise a frame  702  having an inflow end portion (not shown) and an outflow end portion  710 , the valvular structure  704  can be coupled to and supported by the frame  702 . The prosthetic valve  700  can further comprise inner and/or outer skirts, however, such components are not shown for purposes of illustration. 
     The valvular structure  704  can be similar to the valvular structures  508  and  604 , described previously, except that the leaflets  710  of the valvular structure  704  have tabs  712  that are angled relative to the draft angle of the frame such that the GOA  706  of the prosthetic valve  700  is reduced when compared to the GOAs of prosthetic valves  500  and  600 . 
     Referring to  FIG.  20   , each leaflet  710  can comprise an inflow edge portion  714  (also referred to as a cusp edge portion) that can be mounted to the frame  702  and an outflow edge portion  716  (also referred to as the free edge portion) that contacts respective outflow edges of the other leaflets during closure of the leaflets (e.g., during diastole). 
     The cusp edge portion  714  of each leaflet  710  terminates at its upper ends at two laterally projecting integral tabs  712 . The tabs  712  can extend from a body portion  718  the leaflet  710  such that an upper or outflow edge  720  of each tab  712  is positioned at an angle θ relative to a longitudinal axis A of the leaflet  710 . In some embodiments, it may be desirable to create a GOA  706  that is narrower than the outflow orifice  708 . For example, in embodiments wherein relatively larger frames are mounted against dilated anatomical structures. In such embodiments, the tabs  712  can extend from the body  718  of the leaflet at a non-90 degree angle such that the radially outer edge  722  of each tab  712  does not correspond to the draft angle of the frame  702 , thereby forming rigid portions  724  ( FIG.  19   ) where the tabs  712  are coupled to the frame  702 . The rigid portions  724  can extend radially inward toward a longitudinal axis of the prosthetic valve  700 , as shown in  FIG.  19   . 
     In the illustrated embodiment, the outflow edge  720  of each tab  712  is positioned such that the angle θ is less than 90 degrees. In other embodiments, the outflow edge  720  can be positioned such that the angle θ is greater than 90 degrees. As shown in  FIG.  19   , when coupled to the frame  702 , the tabs  712  form rigid portions  724  that extend radially inwardly toward a longitudinal axis of the prosthetic valve  700 . The rigid portions  724  space the outflow edge  716  of the leaflets  710  inwardly by a distance S 2 , thereby reducing the GOA  706  of the outflow orifice  708 . The angle θ can be selected to provide rigid portions  724  of a selected size, thereby selecting a specific GOA for the prosthetic valve  700 . The leaflet parameters, including tab angle and tab height, can be varied to provide a selected GOA  706 , for example, a reduced GOA. 
     Additional Examples of the Disclosed Technology 
     In view of the above described implementations of the disclosed subject matter, this application discloses the additional examples enumerated below. It should be noted that one feature of an example in isolation or more than one feature of the example taken in combination and, optionally, in combination with one or more features of one or more further examples are further examples also falling within the disclosure of this application. 
     Example 1. An implantable prosthetic device, comprising: 
     a frame movable between a radially compressed configuration and a radially expanded configuration, the frame having an inflow orifice, an outflow orifice, and comprising one or more commissure windows; 
     a valvular structure comprising a plurality of leaflets, each leaflet comprising a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet to form a commissure tab assembly, each commissure tab assembly being coupled to a respective commissure window; and 
     wherein each tab extends from the main body at an angle such that a radially outer edge of the tab corresponds to a draft angle of the frame. 
     Example 2. The prosthetic device of any example herein, particularly example 1, wherein an outflow edge of each tab is spaced apart from the outflow edge of the leaflet by a stepped portion. 
     Example 3. The prosthetic device of any example herein, particularly any one of examples 1-2, wherein the tabs have a height selected such that the commissure tab assembly fits within a respective commissure window without forming a radially-extending rigid portion. 
     Example 4. The prosthetic device of any example herein, particularly any one of examples 1-3, wherein each tab has a height that substantially corresponds with a height of the commissure window. 
     Example 5. The prosthetic device of any example herein, particularly any one of examples 1-4, wherein an outflow edge of the tab is disposed at a 90 degree angle relative to a longitudinal axis of the leaflet. 
     Example 6. The prosthetic device of any example herein, particularly any one of examples 1-5, wherein each tab is a lower tab and wherein each leaflet further comprises a pair of upper tabs extending from the main body and coupled to the main body via a neck portion, each upper tab comprising a radially inner edge, a radially outer edge, and a free edge. 
     Example 7. The prosthetic device of any example herein, particularly example 6, wherein each neck portion has a first width and each lower tab has a second width, and wherein the first width is less than half the second width. 
     Example 8. The prosthetic device of any example herein, particularly any one of examples 6-7, wherein the radially inner edge of each upper tab tapers toward a free edge of the upper tab. 
     Example 9. The prosthetic device of any example herein, particularly any one of examples 6-8, wherein the upper tabs and neck portions of each leaflet are formed integrally with the main body of the respective leaflet. 
     Example 10. The prosthetic device of any example herein, particularly any one of examples 6-9, wherein each upper tab is folded along the neck portion toward the inflow edge of the leaflet to form a rigid portion that extends radially inwardly toward a longitudinal axis of the frame. 
     Example 11. The prosthetic device of any example herein, particularly any one of examples 6-10, wherein a width of the neck portion is selected to provide a selected geometric orifice area (GOA) of the outflow orifice. 
     Example 12. An implantable prosthetic device, comprising: 
     a cylindrical frame movable between a radially compressed configuration and a radially expanded configuration; 
     a valvular structure comprising a plurality of leaflets, each leaflet comprising a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body; and 
     wherein each tab extends from the main body such that an outflow edge of the tab is disposed at a 90-degree angle relative to a longitudinal axis of the leaflet. 
     Example 13. The prosthetic device of any example herein, particularly example 12, wherein an outflow edge of each tab is spaced apart from the outflow edge of the leaflet by a stepped portion. 
     Example 14. The prosthetic device of any example herein, particularly any one of examples 12-13, wherein the frame comprises one or more commissure openings, and wherein each tab has a height 0.1 mm greater than a height of the commissure opening. 
     Example 15. The prosthetic device of any example herein, particularly any one of examples 12-14, wherein the tabs are lower tabs and wherein each leaflet further comprises opposing upper tabs coupled the outflow edge of the leaflet via a neck portion, wherein each lower tab is paired with an adjacent lower tab of an adjacent leaflet to form a commissure, and wherein each upper tab is folded toward an inflow end of the frame such that the neck portion forms a rigid portion extending radially inwardly toward a longitudinal axis of the frame. 
     Example 16. The prosthetic device of claim 15, wherein each neck portion has a first width and each lower tab has a second width, and wherein the first width is less than half the second width. 
     Example 17. The prosthetic device of any example herein, particularly example 16, wherein the radially inner edge of each upper tab tapers toward a free edge of the upper tab. 
     Example 18. The prosthetic device of any example herein, particularly any one of examples 15-17, wherein the upper tabs and neck portions of each leaflet are formed integrally with the main body of the respective leaflet. 
     Example 19. The prosthetic device of any example herein, particularly any one of examples 15-18, wherein each upper tab is folded along the neck portion toward the inflow edge of the leaflet to form a rigid portion that extends radially inwardly toward a longitudinal axis of the frame. 
     Example 20. The prosthetic device of any example herein, particularly any one of examples 15-19, wherein a width of the neck portion is selected to provide a selected geometric orifice area (GOA) of the outflow orifice. 
     Example 21. The prosthetic device of any example herein, particularly any one of examples 15-20, wherein the lower tabs have a height selected such that the lower tab fits within a respective commissure window without forming a radially-extending rigid portion. 
     Example 22. The prosthetic device of any example herein, particularly any one of examples 15-21, wherein each lower tab has a height that substantially corresponds with a height of the commissure window. 
     Example 23. The prosthetic device of any example herein, particularly any one of examples 12-22, wherein each tab is paired with an adjacent tab of an adjacent leaflet to form a commissure, the commissure further comprising a flexible connector configured to extend around one or more struts of the frame to couple the commissure to frame. 
     Example 24. An implantable prosthetic device, comprising: 
     a cylindrical frame movable between a radially compressed configuration and a radially expanded configuration, the frame comprising an inflow orifice and an outflow orifice; and 
     a valvular structure comprising a plurality of leaflets, each leaflet comprising 
     a main body having an inflow edge and an outflow edge, 
     a pair of opposing lower tabs extending from opposite sides of the main body, and 
     a pair of opposing upper tabs extending from and coupled to the outflow edge of the leaflet via respective neck portions; 
     wherein each lower tab extends from the main body such that an outflow edge of the lower tab is disposed at a 90-degree angle relative to a longitudinal axis of the leaflet; and 
     wherein each lower tab is paired with an adjacent upper tab of an adjacent leaflet to form a plurality of commissures, and wherein each upper tab is folded toward the inflow orifice of the frame such that the neck portion forms a rigid portion extending radially inwardly toward a longitudinal axis of the frame such that the outflow edge of the leaflet defines a selected geometric orifice area (GOA) within the outflow orifice. 
     Example 25. The prosthetic device of any example herein, particularly example 24, wherein each neck portion has a first width and each lower tab has a second width, and wherein the first width is less than half the second width. 
     Example 26. The prosthetic device of any example herein, particularly any one of examples 24-25, wherein each upper tab has an angled radially inner edge. 
     Example 27. The prosthetic device of any example herein, particularly any one of examples 24-26, wherein the upper tabs and neck portions of each leaflet are formed integrally with the main body of the respective leaflet. 
     Example 28. The prosthetic device of any example herein, particularly any one of examples 24-27, wherein a width of the neck portion is selected to provide a selected geometric orifice area (GOA) of the outflow orifice. 
     Example 29. The prosthetic device of any example herein, particularly any one of examples 24-28, wherein an outflow edge of each lower tab is spaced apart from the outflow edge of the leaflet by a stepped portion. 
     Example 30. The prosthetic device of any example herein, particularly any one of examples 24-29, wherein the lower tabs have a height selected such that the lower tab fits within a respective commissure window without forming a radially-extending rigid portion. 
     Example 31. The prosthetic device of any example herein, particularly any one of examples 24-30, wherein each lower tab has a height that substantially corresponds with a height of the commissure window. 
     Example 32. The prosthetic device of any example herein, particularly any one of examples 24-31, wherein each neck portion has a first width and each lower tab has a second width, and wherein the first width is less than half the second width. 
     Example 33. The prosthetic device of any example herein, particularly any one of examples 24-32, wherein a radially inner edge of each upper tab tapers toward a free edge of the upper tab. 
     Example 34. The prosthetic device of any example herein, particularly any one of examples 24-33, wherein the frame comprises one or more commissure openings, and wherein each lower tab has a height 0.1 mm greater than a height of the commissure opening. 
     Example 35. The prosthetic device of any example herein, particularly any one of examples 24-34, wherein each lower tab is paired with an adjacent lower tab of an adjacent leaflet to form a commissure, the commissure further comprising a flexible connector configured to extend around one or more struts of the frame to couple the commissure to frame. 
     Example 36. An implantable prosthetic device, comprising: 
     a non-cylindrical frame having an inflow orifice and an outflow orifice, the frame movable between a radially compressed configuration and a radially expanded configuration, the frame having a shape in the radially expanded configuration that tapers from a first diameter at the outflow orifice to a second diameter at the inflow orifice, the second diameter being larger than the first diameter; 
     a valvular structure comprising a plurality of leaflets, each leaflet comprising a main body having an inflow edge, an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body; and 
     wherein each tab extends from the main body at an angle such that a radially outer edge of the tab corresponds to a draft angle of the frame. 
     Example 37. The prosthetic device of any example herein, particularly example 36, wherein each tab extends from the main body such that an outflow edge of the tab is disposed at an angle relative to a longitudinal axis of the leaflet, the angle being less than 90 degrees. 
     Example 38. The prosthetic device of any example herein, particularly example 37, wherein the angle of the tabs is selected to provide a selected geometric orifice area (GOA) of the outflow orifice. 
     Example 39. The prosthetic device of any example herein, particularly any one of examples 37-38, wherein the angle of the tabs is between about 88 degrees and about 85 degrees. 
     Example 40. The prosthetic device of any example herein, particularly any one of examples 36-39, wherein each tab is coupled to an adjacent tab of an adjacent leaflet to form a commissure, and wherein each commissure is coupled to the frame such that the tabs form rigid portion that extends radially inwardly toward a longitudinal axis of the frame. 
     Example 41. The prosthetic device of any example herein, particularly any one of examples 36-40, wherein an outflow edge of each tab is spaced apart from the outflow edge of the leaflet by a stepped portion. 
     Example 42. The prosthetic device of any example herein, particularly any one of examples 36-41, wherein each tab has a height that substantially corresponds with a height of a commissure window defined in the frame. 
     Example 43. The prosthetic device of any example herein, particularly example 36, wherein an outflow edge of the tab is disposed at a 90 degree angle relative to a longitudinal axis of the leaflet. 
     Example 44. The prosthetic device of any example herein, particularly any one of examples 36-43, wherein each tab is a lower tab and wherein each leaflet further comprises a pair of upper tabs extending from the main body and coupled to the main body via a neck portion, each upper tab comprising a radially inner edge, a radially outer edge, and a free edge. 
     Example 45. The prosthetic device of any example herein, particularly example 44, wherein each neck portion has a first width and each lower tab has a second width, and wherein the first width is less than half the second width. 
     Example 46. The prosthetic device of any example herein, particularly any one of examples 44-45, wherein the radially inner edge of each upper tab tapers toward a free edge of the upper tab. 
     Example 47. The prosthetic device of any example herein, particularly any one of examples 44-46, wherein the upper tabs and neck portions of each leaflet are formed integrally with the main body of the respective leaflet. 
     Example 48. The prosthetic device of any example herein, particularly any one of examples 44-47, wherein each upper tab is folded along the neck portion toward the inflow edge of the leaflet to form a rigid portion that extends radially inwardly toward a longitudinal axis of the frame. 
     Example 49. The prosthetic device of any example herein, particularly any one of examples 44-48, wherein a width of the neck portion is selected to provide a selected geometric orifice area (GOA) of the outflow orifice. 
     Example 50. The prosthetic device of any example herein, particularly any one of examples 44-49, wherein the frame comprises one or more commissure openings, and wherein each lower tab has a height 0.1 mm greater than a height of the commissure opening. 
     Example 51. An implantable prosthetic device, comprising: 
     an annular frame that is movable between a radially compressed configuration and a radially expanded configuration, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame; 
     a valvular structure comprising a plurality of leaflets, each leaflet having a main body including an inflow edge and an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet and secured to the frame to form a commissure assembly; 
     wherein the valvular structure is secured to the frame such that a gap is defined between the outflow edges of the leaflets and the outflow end of the frame; and
         wherein each cell of the first row of cells is configured to be at least twice as wide as a selected coronary catheter.       

     Example 52. The implantable device of any example herein, particularly example 51, wherein one or more struts of the first row of cells are commissure posts comprising a plurality of apertures. 
     Example 53. The implantable device of any example herein, particularly example 52, wherein each commissure post comprises three apertures. 
     Example 54. The implantable device of any example herein, particularly any one of examples 51-53, wherein the inflow edges of the leaflets are coupled to an inflow end of the frame by one or more sutures extending through the leaflets and around struts of the frame that define the inflow end of the frame. 
     Example 55. The implantable device of any example herein, particularly any one of examples 51-54, wherein the prosthetic device is devoid of any fabric material inside of the frame. 
     Example 56. The implantable device of any example herein, particularly any one of examples 51-55, wherein the commissure assemblies are devoid of any fabric material. 
     Example 57. The implantable device of any example herein, particularly any one of examples 51-56, wherein the cells in the first row of cells each have a height greater than the cells in the second and third rows of cells. 
     Example 58. The implantable device of any example herein, particularly any one of examples 51-57, wherein the cells in the first row of cells have a height selected to allow access to the coronary vessel through the gap when the implantable device is implanted within a native annulus. 
     Example 59. A method, comprising: 
     inserting a distal end of a delivery apparatus into the vasculature of a patient, the delivery apparatus releasably coupled to a guest prosthetic valve movable between a radially compressed and a radially expanded configuration, the prosthetic valve including a frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame and configured to be at least twice as wide as a selected coronary catheter, and a valvular structure disposed within the frame and coupled to the frame such that a gap is defined between the outflow edges of the valvular structure and an outflow end of the frame; 
     advancing the guest prosthetic valve to a selected implantation site comprising a previously implanted host prosthetic valve, the host prosthetic valve comprising a host frame and a host valvular structure disposed within the host frame; 
     positioning the guest prosthetic valve within the host prosthetic valve; and radially expanding the guest prosthetic valve within the previously implanted host prosthetic valve. 
     Example 60. The method of any example herein, particularly example 59, further comprising inserting the selected coronary catheter through the gap of the guest prosthetic valve and through the frame of the host prosthetic valve. 
     Example 61. The method of any example herein, particularly any one of examples 59-60, further comprising cutting the host valvular structure prior to radially expanding the guest prosthetic valve. 
     Example 62. The method of any example herein, particularly any one of examples 59-61, wherein the host frame comprises first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the host frame and configured to be at least twice as wide as a selected coronary catheter, and the host valvular structure is coupled to the host frame such that a gap is defined between the outflow edges of the host valvular structure and an outflow end of the host frame. 
     Example 63. The method of any example herein, particularly example 62, further comprising inserting the selected coronary catheter through the gap of the guest prosthetic valve and the gap of the host prosthetic valve. 
     Example 64. The method of any example herein, particularly any one of examples 59-63, wherein the guest prosthetic valve is rotationally offset relative to the host prosthetic valve. 
     Example 65. A method of assembling a prosthetic heart valve, comprising: 
     forming a valvular structure from a plurality of leaflets, each leaflet comprising an inflow edge, an outflow edge, and two opposing tabs, wherein the valvular structure is formed by coupling adjacent tabs of adjacent leaflets to one another to form respective commissures; 
     positioning the valvular structure within a radially expandable and compressible frame, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame and configured to be at least twice as wide as a selected coronary catheter; and 
     coupling the valvular structure to the frame such that a gap is defined between the outflow edges of each leaflet and an outflow edge of the frame when the valvular structure is in an open configuration. 
     Example 66. An assembly, comprising: 
     a first implantable prosthetic device and a second implantable prosthetic device, each implantable prosthetic device comprising:
         an annular frame that is movable between a radially compressed configuration and a radially expanded configuration, the frame comprising first, second, and third circumferentially-extending rows of cells, the first row of cells disposed adjacent an outflow end of the frame,   a valvular structure comprising a plurality of leaflets, each leaflet having a main body including an inflow edge and an outflow edge, and a pair of opposing tabs extending from opposite sides of the main body, each tab being paired with an adjacent tab of an adjacent leaflet and secured to the frame to form a commissure assembly, the valvular structure secured to the frame such that a gap is defined between the outflow edges of the leaflets and the outflow end of the frame; and       

     wherein each cell of the first row of cells is configured to be at least twice as wide as a selected coronary catheter; and 
     wherein the first implantable prosthetic device is disposed withing the annular frame of the second implantable prosthetic device. 
     Example 67. The assembly of any example herein, particularly example 66, wherein the first prosthetic device is rotationally offset relative to the second prosthetic device. 
     Example 68. The assembly of any example herein, particularly any one of examples 66-67, wherein the selected coronary catheter can extend through the gap in the first prosthetic device and the gap in the second prosthetic device. 
     In view of the many possible embodiments to which the principles of the disclosure may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope. Rather, the scope is defined by the following claims. We therefore claim all that comes within the scope and spirit of these claims.