Patent Publication Number: US-2023149157-A1

Title: Transcatheter Prosthetic Atrioventricular Valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to the filing date of U.S. Provisional Patent Application No. 63/280,673, filed Nov. 18, 2021, the disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     The heart has four native valves, including the aortic valve, the pulmonary valve, the mitral valve (also known as the left atrioventricular valve), and the tricuspid valve (also known as the right atrioventricular valve). When these valves begin to fail, for example by not fully coapting and allowing retrograde blood flow (or regurgitation) across the valve, it may be desirable to repair or replace the valve. Prosthetic replacement heart valves may be surgically implanted via an open-chest, open-heart procedure while the patient is on cardiopulmonary bypass. However, such procedures are extremely invasive and frail patients, who may be the most likely to need a prosthetic heart valve, may not be likely to survive such a procedure. More recently, prosthetic heart valves have been trending to less invasive procedures, including collapsible and expandable heart valves that can be delivered through the vasculature in a transcatheter procedure. 
     The aortic valve and the pulmonary valve typically have a relatively circular shape and a relatively small diameter compared to the left and right atrioventricular valves. As a result, transcatheter prosthetic heart valves designed for the mitral and tricuspid valve may have significantly larger challenges that need to be overcome compared to transcatheter prosthetic heart valve designs for the aortic and pulmonary valves. 
     Another challenge in designing transcatheter prosthetic atrioventricular valves is avoiding or limiting conduction disturbances. When a transcatheter prosthetic atrioventricular valve is expanded into the native mitral or tricuspid valve, the device may press against tissue and result in disturbances of the natural conduction system of the heart. Because of this, pacemakers are frequently implanted along with prosthetic atrioventricular valves in order to help override any such conduction disturbances. 
     Another challenge in designing transcatheter prosthetic atrioventricular valves is allowing for the prosthetic valve to be recaptured (e.g., re-collapsed into a delivery device) after it has been at least partially expanded. Due to the typical size of a prosthetic atrioventricular valve being relatively large, as well as the potential inclusion of both an outer anchoring frame and an inner valve frame, the forces involved in recapturing a prosthetic atrioventricular valve may be relatively large, rendering such recapture relatively difficult. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     This disclosure is generally directed to collapsible and expandable prosthetic atrioventricular valves that may limit conduction disturbances while providing for effective fixation. These valves may be best suited for replacing native mitral valves, and particularly native tricuspid valves. These prosthetic transcatheter atrioventricular valves may be generally include a collapsible and expandable stent, a collapsible and expandable valve assembly coupled to the stent. The stent may include an outer stent, generally meant to achieve fixation within the native valve annulus, and an inner stent, generally meant to provide a support for bioprosthetic leaflets of the valve assembly. The inner stent may be generally cylindrical and may be attached to the outer stent in a way which allows the bioprosthetic valve assembly to maintain a generally cylindrical shape, even when forces applied to the outer stent distort the shape of the outer stent. The valve assembly may include a plurality of bioprosthetic leaflets (typically three leaflets, although two leaflets or more than three leaflets may be provided). The valve assembly may include one or more skirts or cuffs on inner and/or outer surfaces of the inner and/or outer stent to help provide a seal between the inside of the native valve annulus and the outside of the bioprosthetic leaflets. 
     According to one aspect of the disclosure, a collapsible and expandable prosthetic atrioventricular valve includes an outer stent having an atrial disc, a ventricular disc, and a plurality of posts coupling the atrial disc to the ventricular disc, and an inner stent. A plurality of connectors may extend between the inner stent and the outer stent to couple the inner stent to the outer stent. A plurality of prosthetic leaflets may be mounted within the inner stent. The outer stent may be devoid of metal in a space circumferentially extending between adjacent ones of the plurality of posts, the space extending approximately one-third of a circumference of the outer stent. The atrial disc may have two circumferential rows of cells, and the ventricular disc may have one circumferential row of cells. The atrial disc may have one circumferential row of cells, and the ventricular disc may have two circumferential rows of cells. The plurality of posts may includes three posts, each of the three posts including two struts extending from the atrial disc to the ventricular disc. The two struts of each of the three posts may have a first end coupled to a respective first apex of a cell in the atrial disc, and a second end coupled to a respective second apex of a cell in the ventricular disc. Each of the three posts may include a tine between the two struts. An aperture may be formed in one of the two struts or the tine of each of the three posts, each of the plurality of connectors being coupled to the outer stent via a corresponding one of the apertures. In an expanded condition of the prosthetic atrioventricular valve, a diameter of the outer stent at the plurality of posts may be smaller than diameters of the outer stent at the atrial disc and the ventricular disc. The inner stent may include a circumferential row of first cells having a total number, and the outer stent may include a circumferential row of second cells having a total number, the total number of second cells being a whole number multiple of the total number of first cells. The total number of second cells may be twenty-seven, and the total number of first cells may be nine. 
     According to a second aspect of the disclosure, a method of replacing a native atrioventricular valve of a heart may include delivering a prosthetic atrioventricular valve to the native atrioventricular valve while the prosthetic atrioventricular valve is collapsed within a delivery catheter, the prosthetic atrioventricular valve including an outer stent, an inner stent coupled to the outer stent, and a plurality of prosthetic leaflets mounted within the inner stent. The prosthetic atrioventricular valve may be deployed from the delivery catheter to allow the prosthetic atrioventricular valve to self-expand. Allowing the prosthetic atrioventricular valve to self-expand may include positioning an atrial disc of the outer stent on an atrial side of the native atrioventricular valve and positioning a ventricular disc of the outer stent on a ventricular side of the native atrioventricular valve. After the prosthetic atrioventricular valve has self-expanded into the native atrioventricular valve, a gap in the outer stent between an adjacent pair of posts that connect that atrial disc to the ventricular disc may be aligned with a conduction system of the heart. 
     According to a third aspect of the disclosure, a prosthetic atrioventricular valve system may include an outer stent having an atrial portion and a ventricular portion, an inner stent, a plurality of connectors extending between the inner stent and the outer stent to couple the inner stent to the outer stent, and a plurality of prosthetic leaflets mounted within the inner stent. The outer stent may include one or more circumferential rows of cells and a plurality of rails extending in an axial direction from the atrial portion to the ventricular portion. The cells of the one or more circumferential rows of cells of the outer stent may be diamond-shaped. Each of the plurality of rails may include a connector at a terminal end thereof. At least one flexible control member may be coupled to the connector of each of the plurality of rails. The flexible control member may be a suture. In a retrieval condition of the prosthetic atrioventricular valve system, the outer stent may be at least partially deployed from a delivery catheter, and the flexible control member may extend proximally through an interior of the delivery catheter. 
     According to a fourth aspect of the disclosure, a method of recapturing a prosthetic atrioventricular valve may include delivering the prosthetic atrioventricular valve to a native atrioventricular valve while the prosthetic atrioventricular valve is collapsed within a delivery catheter, the prosthetic atrioventricular valve including an outer stent having an atrial portion and a ventricular portion, an inner stent coupled to the outer stent, and a plurality of prosthetic leaflets mounted within the inner stent, the outer stent including one or more circumferential rows of cells and a plurality of rails extending in an axial direction from the atrial portion to the ventricular portion. The prosthetic atrioventricular valve may be deployed from the delivery catheter to allow the prosthetic atrioventricular valve to at least partially self-expand. After allowing the prosthetic atrioventricular valve to at least partially self-expand, the prosthetic atrioventricular valve may be retrieved into a retrieval catheter. Retrieving the prosthetic atrioventricular valve may include causing the prosthetic atrioventricular valve to collapse into the retrieval catheter by manipulating at least one flexible control member coupled to a plurality of connectors, each of the plurality of connectors coupled to a corresponding one of the plurality of rails. The retrieval catheter may be the delivery catheter. The retrieval catheter may be a separate device from the delivery catheter, and after deploying the prosthetic atrioventricular valve from the delivery catheter, and before retrieving the prosthetic atrioventricular valve, the retrieval catheter may be advanced along or through delivery catheter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic illustration of the right atrioventricular valve. 
         FIG.  2    is a side perspective view of an outer stent of a prosthetic atrioventricular valve according to one aspect of the disclosure. 
         FIG.  3    is a side perspective view of an outer stent of a prosthetic atrioventricular valve according to another aspect of the disclosure. 
         FIG.  4    shows the outer stent of  FIG.  3   , with annotations illustrating relative positioning of structures of a native tricuspid valve following implantation. 
         FIG.  5    shows a side perspective view of an outer stent of a prosthetic atrioventricular valve according to a further aspect of the disclosure. 
         FIG.  6    shows a side view of the outer stent of  FIG.  5   . 
         FIG.  7    shows an enlarged view of the ventricular disc of the outer stent of  FIG.  5   . 
         FIG.  8    is a developed view of an inner stent according to an aspect of the disclosure. 
         FIG.  9    is a top-down view of the outer stent of  FIG.  5    coupled with an inner stent similar to that shown in  FIG.  8   . 
         FIG.  10    shows the configuration of  FIG.  9    with additional features provided. 
         FIG.  11    is a top-down view of an outer stent similar to  FIG.  5    coupled with the inner stent of  FIG.  8   . 
         FIG.  12    is a top-down view of an outer stent coupled to an inner stent similar to that of  FIG.  8   . 
         FIG.  13    is a highly schematic illustration of an outer stent similar to those of  FIGS.  2 - 3    positioned within a native tricuspid valve. 
         FIG.  14    is a highly schematic cross-section of the heart showing an outer stent similar to those of  FIGS.  2 - 3    positioned within a native tricuspid valve. 
         FIG.  15    is a highly schematic cross-section of the heart. 
         FIG.  16    is a top-down schematic view of a retrieval system coupled to a prosthetic heart valve according to an embodiment of the disclosure. 
         FIG.  17    is a side view of the prosthetic heart valve of  FIG.  16    being re-collapsed using the retrieval system of  FIG.  16   . 
         FIGS.  18 A-B  are schematic views of alternate constructions of a stent having rails for interaction with a retrieval system. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
       FIG.  1    is a schematic illustration of the right atrioventricular valve (commonly referred to as the tricuspid valve). The tricuspid valve separates the right atrium RA from the right ventricle RV and typically has three leaflets, including a posterior leaflet PL, an anterior leaflet AL, and a septal leaflet SL. The septal leaflet SL is positioned nearest the interventricular septum IVS. The tricuspid valve annulus may include conduction nodes near the connection point between the annulus and the septal leaflet, including for example the atrioventricular (“AV”) node. Electrical impulses may be conducted from the AV node, via the bundle of His, to the Purkinje fibers that provide electrical conduction to the ventricles. Papillary muscles PM along the right ventricular wall RVW may support chordae tendineae coupled to the tricuspid valve leaflets to prevent inversion of the leaflets during normal physiological operation. The left atrioventricular valve (commonly referred to as the mitral valve) may have a generally similar structure as the tricuspid valve, although many differences do exist—including for example mitral valve typically includes two leaflets (an anterior and posterior leaflet) and has the general shape of a hyperbolic paraboloid or “saddle”-type shape. Both the mitral valve annulus and tricuspid valve annulus may be very large compared to the aortic and pulmonary valves. For example, the tricuspid valve may have a diameter of between 45-50 mm in a patient with moderate tricuspid valve disease, and a diameter of between 50-60 mm in a patient with severe tricuspid valve disease. Depending on the stage of tricuspid regurgitation, the tricuspid valve annulus may have an enlarged diameter of up to 70 mm. 
       FIG.  2    is a side perspective view of an outer stent  100  of a prosthetic atrioventricular valve according to one aspect of the disclosure.  FIG.  2    shows the outer stent  100  in isolation from the rest of the prosthetic heart valve and omits structures such as an inner stent and prosthetic leaflets carried by the inner stent, and one or more sealing cuff and/or skirts on the inner and/or outer surfaces of the inner and/or outer stent. The outer stent  100  of  FIG.  2    is collapsible and expandable and may be formed of a shape memory metal such as nitinol. The outer stent  100  of  FIG.  2    may be generally circular (and/or rotationally symmetric) when in the illustrated expanded condition. The outer stent  100  may include one or more rows of cells (e.g., diamond-shaped cells) in an atrial disc section  110  (which may also be referred to as an atrial flare or atrial anchor section), and one or more rows of cells (e.g. diamond-shaped cells) in a ventricular section  120  (which may also be referred to as a ventricular flare or ventricular anchor section). In the illustrated embodiment, the atrial section  110  includes two rows of diamond-shaped cells, including a first row of cells  110   a  and a second row of cells  110   b  positioned downstream (in an outflow direction) of the first row of cells  110   a.  In the illustrated embodiment, the ventricular section  120  includes a single row of diamond-shaped cells  120   a . However, in other embodiments, the atrial section  110  may include more or fewer rows of cells, the ventricular section  120  may include more than one row of cells, and the cells may form shapes other than diamond shapes. 
     The atrial section  110  may be coupled to the ventricular section  120  only at selected locations around the circumference of the outer stent  100 , with a large amount of space  140  remaining devoid of metal stent structure circumferentially between those connection points. In  FIG.  2   , the connection points include three double clips  130 . As shown, the double clips  130  are positioned at equidistant locations around the circumference of the outer stent  100 , but in other embodiments the positioning may be other than equidistant. Each double clip  130  may include a first generally axial stent post  130   a  extending from a top apex of a first ventricular stent cell  120   a  to a bottom apex of a first atrial stent cell in the second row  110   b , and a second generally axial stent post  130   b  extending from a top apex of a second ventricular stent cell  120   a  to a bottom apex of a second atrial stent cell in the second row  110   b.  The first atrial stent cell may be directly adjacent to the second atrial stent cell, and the first ventricular stent cell may be directly adjacent to the second ventricular stent cell. If three double clips  130  are provided, the space  140  devoid of metal stent structure extends approximately one-third the circumference of the outer stent  100  (but slightly less due to the size of the double clips  130 ). If two double clips  130  were provided, the space  140  devoid of metal stent material would be approximately half the circumference of the outer stent  100 . If four double clips  130  were provided, the space  140  devoid of metal stent material would be approximately one-fourth the circumference of the outer stent  100 , etc. 
     In the embodiment illustrated in  FIG.  2   , the atrial disc  110  includes two rows  110   a,    110   b  of stent cells, with 27 cells each, and the ventricular disc  120  includes one row of stent cells  120   a  with 27 cells. However, as noted above, more or fewer rows may be provided in the atrial section  110 , and more rows may be provided in the ventricular section  120 . Fewer rows in the ventricular section  120  may be desirable in some embodiments to minimize the amount of structure extending into the right (or left) ventricle, and thus minimize the amount of structure available to block the right ventricular outflow tract (“RVOT”) (or the left ventricular outflow tract (“LVOT”)). In some embodiments, it may be desirable to include a number of cells in each row  110   a,    110   b,    120   a  that is a multiple of three or a multiple of nine, particularly if the inner stent (which may be similar or the same as any of the inner stents described below) includes rows of 3 or 9 cells (or multiples thereof), as such correspondence may maximize the ability to provide regular positioning of members that couple the inner stent to the outer stent  100 . However, it should be understood that more or fewer than 27 cells may be provided in each row  110   a,    110   b,    120   a.  Also, if the inner stent includes a number of cells per row that is different than 9, it may be desirable for each row of cells  110   a,    110   b,    120   a  in the outer stent  100  to include a multiple (e.g., an integer or whole number multiple) of that different number. However, in still other embodiments, such correspondence between the numbers of cells in each row of the inner stent to the number of cells in the rows of the outer stent  100  need not be provided. 
     The connectors between the atrial disc  110  and ventricular disc  120  may be utilized as anchor points to couple the inner stent to the outer stent  100 . For example, in  FIG.  2   , a total of three or six connection points may be utilized to couple the inner stent to the outer stent  100 , since there are three double clips  130 . 
     As shown in  FIG.  2   , there is no metal stent structure positioned axially between the ventricular disc  120  and the atrial disc  110  in the circumferential direction between circumferentially adjacent double clips  130 . The atrioventricular valve pseudo-annulus may generally align with this void space  140  (and with the double clips  130 ), when the prosthetic valve is implanted. This large void space  140  reduces the contact between the outer stent  100  and the native valve annulus, particularly reducing metal-to-tissue contact in these areas. Preferably, when implanted, the void space  140  is aligned with the base of the septal leaflet SL (if implanting into the tricuspid valve) to reduce or eliminate contact with the AV node, thus minimizing or eliminating the likelihood of conduction disturbances. The same or similar positioning may be used if implanting the prosthetic valve into the native mitral valve annulus to avoid conduction disturbances. In some patients, a pacemaker may already be implanted into the heart, or it may nonetheless be desirable to implant a pacemaker despite the reduced disturbance to the conduction system. The conduction gaps  140  in the outer stent  100  may, in those circumstances, additionally help to avoid interfering with any pacemaker leads near the prosthetic heart valve. 
     When implanted, the outer stent  100  of  FIG.  2    may provide suitable fixation despite the voids  140  provided in the outer stent. For example, the outflow end of the atrial disc  110  may “bite into” the native annulus upon deployment, and the inflow end of the ventricular disc  120  may “bite into” the native leaflets, in order to provide good engagement with the native tissue. For example, the outflow apices of the second row  110   b  of atrial cells and the inflow apices of the first row  120   a  of ventricular cells may engage with native tissue. It should be understood that expansion forces of the outer stent  100  may also provide an amount of fixation within the native valve. Because the prosthetic valves described herein are intended for transcatheter implantation, these prosthetic valves would typically not be sutured to the native annulus, and thus must maintain sufficient fixation without sutures or similar fixation mechanisms typically used in surgical valve implantations. The connectors between the atrial disc  110  and the ventricular disc  120  (e.g., the three double clips  130  shown in  FIG.  2   ) will also push against the native annulus to assist with fixation. Although not shown, the outer stent  100  shown in  FIG.  2    may include a skirt or cuff (e.g., a synthetic fabric like PET or PTFE) to provide sealing between the outer stent  100  and the native valve annulus. The skirt or cuff may extend over the entire outer stent  100 , including in the spaces  140  that are void of metal structure. The existence of the skirt or cuff in this area is not expected to cause any significant conduction disturbances, even when aligned with the AV node, at least because the material is a generally soft, non-metallic material. 
     Also, although not shown in  FIG.  2   , other anchoring features may be provided to help maintain engagement of the prosthetic heart valve within the native valve annulus once deployed. For example, needles, hooks, barbs, paddles, tines, etc. may be provided on the outer stent  100 , with those features engaging native tissue to provide even further fixation. 
     In some circumstances, the areas  140  of the outer stent  100  that are void of metal may create potential issues when loading the prosthetic heart valve into a catheter for delivery, or when deploying the prosthetic heart valve from the catheter. This discontinuity in metal structure may tend to cause the ventricular disc  120  to “want” to invert upon deployment (as it is the first section that is released from the catheter during transseptal delivery), or upon loading into the catheter for insertion into the patient. The inflow apices of the ventricular cells  120   a  may also tend to result in the ventricular disc  120  biting into, or otherwise not smoothly loading into, the delivery catheter upon loading of the prosthetic heart valve into the delivery catheter. For example, as the prosthetic heart valve is collapsed and drawn into the catheter (e.g., via a funnel), the inflow apices of the ventricular stent cells  120   a  may tend to hook over or bite into structures of the loading funnel and/or the catheter during loading. In order to minimize the likelihood of one or more of the above issues occurring, additional fixation structures may be provided to couple the atrial disc  110  to the ventricular disc  120 . For example, one or more suture lines may be provided to couple the inflow apex of one or more ventricular cells  120   a  to the outflow apex of one or more atrial cells in the second row  110   b.  Such fixation structures may extend longitudinally or diagonally, and any number may be provided. Such fixation structures may tend to allow for a smoother deployment and loading of the prosthetic heart valve, despite the areas  140  devoid of metal between the ventricular disc  120  and atrial disc  110 . However, as noted above, these fixation structures are preferably soft and/or non-metal, so that such structures do not create any conduction disturbances that might otherwise occur if metal structure was pressing into native annulus at or near the AV node. It should further be understood that, if these fixation structures are provided, they would preferably only be provided where the stent cells are “free-floating”—e.g., not in the areas where the double clips  130  are provided. 
       FIG.  3    is a side perspective view of an outer stent  200  of a prosthetic atrioventricular valve according to another aspect of the disclosure. The outer stent  200  of  FIG.  3    is identical to the outer stent  100  of  FIG.  2    in most respects, and thus for brevity, only the differences will be described. Reference numbers for stent  200  used in  FIG.  3    that refer to similar or identical components in stent  100  are increased by  100  (e.g., atrial rows  210   a,    210   b  correspond to atrial rows  110   a,    110   b,  respectively). Whereas the outer stent  100  of  FIG.  2    is shown with three double clips  130  that couple the atrial disc  110  to the ventricular disc  120 , the outer stent  200  of  FIG.  3    is shown with similar double clips  230  with an additional tine  230   c  in between the double clips or posts  230   a,    230   b.  These additional tines  230   c  may provide for additional anchoring by pressing against and/or engaging native tissue for fixation during deployment of the outer stent  200  into a native valve annulus. Also shown in  FIG.  3    at the clips/posts  230  (e.g., near a base of tines  230   c ) is an aperture  230   d  that may be utilized for coupling a coupling member, with the other ends of the coupling members attaching to the inner stent, as shown in other figures below. 
       FIG.  4    shows the outer stent of  FIG.  3   , with annotations illustrating relative positioning of structures of a native tricuspid valve, including the anterior leaflet AL, septal leaflet SL, and posterior leaflet PL, following implantation. As shown, in one implanted condition, the clips/posts  230  generally align with the native commissures, and one of the conduction gaps  240  aligns with the base of the septal leaflet SL where the AV node is expected to be located. In other words, the forces F of the outer stent  200  pressing on the native valve annulus are mostly concentrated at the clips/posts  230 , with little or no force F being applied directly to the base of the septal leaflet SL, minimizing or eliminating the likelihood of conduction disturbances. 
       FIG.  5    shows a perspective view of an outer frame  300  according to a further aspect of the disclosure.  FIG.  6    shows a partial side view of the outer stent  300  of  FIG.  5   .  FIG.  7    shows an enlarged view of the ventricular disc  320  of the outer stent  300  of  FIG.  5   . The outer stent  300  of  FIGS.  5 - 7    is generally similar to that shown in  FIG.  2   , with certain differences. For the purpose of brevity, only the differences are described here. Reference numbers for outer stent  300  used in  FIGS.  5 - 7    that refer to similar or identical components in stent  100  are increased by 200 (e.g., atrial disc  310  and ventricular disc  320  correspond to atrial disc  110  and ventricular disc  120  respectively). One difference is that, instead of including two rows of cells  110   a,    110   b  at the atrial disc  110  and one row of cells  120   a  at the ventricular disc  120 , the outer stent  300  of  FIGS.  5 - 7    includes one row of cells  310   a  at the atrial disc  310  and two rows of cells  320   a,    320   b  at the ventricular disc. As best shown in  FIGS.  6 - 7   , the ventricular disc  320  may include an outward flare  322 , particularly at the outflow end of the ventricular disc  320 , including at the outflow end of the outflow row of cells  320   b.  This outward flare  322  may help better engage tissue on the ventricular side of the valve annulus, such as tissue of the native leaflets. The inclusion of two rows of cells  320   a,    320   b  at the ventricular disc  320  may provide additional surface area for anchoring or fixing the outer stent  300  within the native valve annulus. As best shown in  FIG.  6   , the posts  330   a,    330   b  coupling the atrial disc  310  to the ventricular  320  disc may have a “C” or “U”-shape in the expanded condition, with the “C” or “U”-shape configured to receive portions of the native valve annulus therein to better anchor the prosthetic heart valve within the native valve annulus. In other words, the posts  330   a,    330   b  may define a diameter that is smaller than the diameters of both the atrial and ventricular discs in the expanded condition of the outer frame  300  (and in the expanded condition of the prosthetic heart valve that incorporates the outer frame  300 ). 
       FIG.  8    is a developed view of an inner frame or stent  400  according to an aspect of the disclosure as if cut longitudinally and laid flat on a table. In an expanded or deployed condition, the inner stent  400  may be generally cylindrical and be positioned radially inside the outer stent (e.g., outer stents  100 ,  200 ,  300  or other outer stents). As with the outer stent, the inner stent  400  may be formed from a collapsible and expandable material, such as a shape memory metal, including nitinol. In the illustrated embodiment, the inner stent  400  includes two rows of generally diamond-shaped cells, including a top inflow row  410  and a bottom outflow row  420 , with nine cells in each row. However, as noted above, the inner stent  400  may include more or fewer cells in each row  410 ,  420 , and in some embodiments may include more or fewer rows of cells. A plurality of connectors  430  may be provided with the inner stent  400 . In the illustrated embodiment, three connectors  430  are provided within every third cell in the inflow row  410 , although more or fewer connectors  430  may be provided. Preferably, the number of connectors  430  is the same as the number of posts or other connecting features that couple the atrial disc of the outer stent to the ventricular disc of the outer stent. In the expanded condition of the inner stent  400 , each connector  430  may extend radially outwardly and couple to the outer stent at the outer stent posts. In the illustrated embodiment, each connector  430  includes an aperture  430   d  near a terminal end thereof, and each post of the outer stent may include a corresponding aperture (e.g., aperture  230   d  of double clips  230  of outer stent  200 ), with rivets, sutures, or other fasteners coupling the inner stent connectors  430  to the outer stent posts via the apertures. However, it should be understood that other fastening modalities may be appropriate. In the illustrated embodiment of the inner stent  400 , the connectors  430  are formed of the same material as the inner stent  400  and may be integral therewith. The connectors  430  may be formed, for example, by laser cutting a tube of nitinol to create the inner stent  400  shown in  FIG.  8   . The inner stent may include commissure attachment features  440 , illustrated as generally rectangular or square stent features at the outflow end of every third cell in the ventricular row  420 . The commissure attachment features (“CAFs”)  440  may include apertures and may be used to couple (for example via sutures) two adjacent bioprosthetic leaflets to the inner stent  400  at the CAFs  440 . Three CAFs  440  are shown in  FIG.  8    because the prosthetic heart valve incorporating the inner stent  400  of  FIG.  8    includes three prosthetic (e.g., bioprosthetic or synthetic) leaflets. Some or all of the ventricular cells  420  that do not have CAFs  440  may include stent extensions  450  that may extend radially outwardly when expanded and attach to the ventricular disc of the outer stent in order to help stabilize the ventricular disc of the outer stent when the prosthetic heart valve is implanted. The length of the stent extensions  450  of the inner frame  400  could be increased and, instead of coupling to the outer frame, engage with native anatomical structures, such as native leaflets or chordae tendineae, to help further secure the prosthetic heart valve in place. In other embodiments, the outer stent may instead or additionally include stent extensions similar to those shown for the inner stent in  FIG.  8   . 
       FIG.  9    illustrates a top-down view of the outer stent  300  of  FIG.  5    coupled to an inner stent  500  similar to that shown in  FIG.  8   . The only difference between inner stent  500  and inner stent  400  is that inner stent  500  omits the stent extensions  450  that are part of inner stent  400 . Notably, the three connectors  530  of the inner stent  500  extend outwardly from the inner stent  500  and couple to an individual post  330   a  or  330   b  of each double clip  330 . However, in other embodiments, the three connectors  530  of the inner stent  500  could separate, branch, or split near a terminal end thereof so that each of the three connectors  530  of the inner stent  500  could attach to each post  330   a,    330   b  of each double clip  330 . In this particular embodiment, it should be understood that there is rotational symmetry of the inner stent  500  and the outer stent  300 , allowed at least in part by including nine cells in each row of the inner frame  500  and a multiple of nine cells (27 in this embodiment) in each row of the outer frame  300 .  FIG.  10    shows the same configuration as shown in  FIG.  9   , with certain additional features shown. In particular,  FIG.  10    illustrates that either post  330   a  or  330   b  of each clip  330  (if only one post is being used) of the outer stent  300  may serve as an attachment site  335  of the inner stent connectors  530 .  FIG.  10    also shows that, as noted above, a skirt or cuff and/or suture materials  350  may be provided between the atrial disc  310  and the ventricular disc  320  of the outer frame  300 , spanning the areas  340  void of metal between the atrial disc  310  and the ventricular disc  320 . And although  FIG.  10    only shows a single void area  340  covered by skirt and/or cuff and/or suture materials, it should be understood that all of the void areas  340  may be covered by skirt and/or cuff and/or suture materials. Although embodiments herein are generally disclosed and/or shown with rows of cells having nine cells, or a whole-number multiple of nine cells, it should be understood that other numbers (and whole-number multiples) may be suitable. For example, particularly when the inner stent (e.g.,  400  or  500 ) includes a set of three prosthetic leaflets mounted therein, the inner stent preferably includes a total number of cells that is a whole-number multiple of three (e.g., 3, 6, 9, 12, 14, 18, 21, etc.). In such an embodiment, it may also be preferable for the outer stent to have rows of cells having a number of cells that are a whole-number multiple of three, and particularly a whole-number multiple of the number of cells in the rows in the inner stent. 
       FIG.  11    illustrates a top-down view of an outer stent  600  that is similar to outer stent  300  of  FIG.  5   , in that the atrial disc  610  includes one row of cells  610   a  and the ventricular disc  620  includes two rows of cells with the same configuration as outer stent  300 , but having double clips  630  that are substantially similar or identical to double clips  230  of outer stent  200 .  FIG.  11    shows outer stent  600  coupled to inner stent  500 . As can be seen, the three inner stent connectors  530  extend radially outward to couple to the clips or posts  630  of the outer stent  600 . 
       FIG.  12    is another top-down view showing that an inner stent  800  may include more than three connectors  830 . In  FIG.  12   , the inner stent  800  is generally similar or identical to the inner stent  500  of  FIG.  8   , except that a total of nine connectors  830  are provided to couple the inner stent  800  to the outer stent  700 . The outer stent  700  may be generally similar to other outer stents described herein, with the main exception that there are additional connection points  730  to account for the additional connectors  830 . The additional connection points  730  may be defined by or include a continuous row of cells between the atrial disc and ventricular disc. In other words, instead of having a large gap or void space between the atrial disc and ventricular disc, outer stent  700  may have complete or substantially complete circumferential rows of cells extending between the terminal ends of the outer stent. 
     The connectors  430 ,  530 ,  830  shown and described in connection with  FIGS.  8 - 12    may all have a generally similar purpose. As noted earlier, the connectors  430 ,  530 ,  830  may help to mechanically isolate the generally cylindrical inner frame from the outer frame so that, even when the outer frame is distorted (for example as a result of forces applied by the native valve annulus to the outer stent during normal operation), the inner frame is able to remain substantially cylindrical, allowing the prosthetic leaflets to maintain a desirable geometry which allows for good coaptation of the bioprosthetic leaflets. 
       FIG.  13    is a highly schematic representation of an outer stent similar to those of  FIGS.  2 - 3    positioned within a native tricuspid valve. This illustration may also apply to the outer stent of  FIG.  5   . As shown in  FIG.  13   , the three posts/clips coupling the atrial disc to the ventricular disc are configured to be positioned at a clip location L, which is where the main outward forces F are applied to the valve annulus VA from the outer stent. On the other hand, the spaces devoid of metal between the posts do not provide significant force against the annulus, because there is no metal structure of the outer stent in those areas. One of those areas is preferably aligned with the conduction system CS, which includes the atrioventricular node AVN and/or Bundle of His (not separately labeled in  FIG.  13   ). 
       FIG.  14    is a highly schematic cross-section of the heart showing an outer stent similar to those of  FIGS.  2 - 3    positioned within a native tricuspid valve TV. This illustration may also apply to the outer stent of  FIG.  5   . As shown in  FIG.  14   , the ventricular disc  120  (or  220 ,  320 ) assist with anchoring on the ventricular side of the tricuspid valve TV, while the atrial disc  110  (or  210 ,  310 ) assists with positioning and/or anchoring on the atrial side of the tricuspid valve TV, with the posts/clips  130  (or  230 ,  330 ) spanning the two discs. For outer frames with more rows of cells in the ventricular disc than the atrial disc (such as that shown in  FIG.  5   ), the landing zone on the ventricular side may be larger than on the atrial side. 
       FIG.  15    is a highly schematic cross-section of the heart. As indicated in the figure, any of the outer stents described herein may include a ventricular disc section that may function, at least in part, to engage the chordae tendineae CT of the tricuspid valve (or the mitral valve), to push against the chordae tendineae CT in an outward direction D and provide enhanced anchoring within the native valve annulus. 
     During the process of delivering heart valve replacement and repair devices, and in particular collapsible and expandable prosthetic heart valves, it is typically useful to be able to partially or completely recapture the device after an initial partial or complete deployment of the device from a delivery catheter. For example, if the initial deployment of a prosthetic heart valve results in undesirable or suboptimal positioning of the prosthetic heart valve relative to the failing heart valve, it may be desirable to pull the prosthetic heart valve back into the delivery catheter and to either attempt a second deployment of the prosthetic heart valve to achieve a more desirable position relative to the failing heart valve, or otherwise to abort the procedure and completely remove the prosthetic heart valve from the patient. Various difficulties may be encountered when attempting to recapture an expandable prosthetic heart valve into a delivery catheter, or into a separate recapture. For example, the forces required to collapse a partially or fully expanded prosthetic heart valve to a small enough diameter to fit within a catheter may be relatively large. The forces may be even larger when the prosthetic heart valve includes a double-stent configuration, such as an any of the prosthetic heart valves described herein with an inner stent connected to an outer stent. Further, relatively flexible and relatively long intravascular delivery catheters may have more difficulty handling such recapture forces, compared to shorter and more rigid transapical catheters. Still further, recapture of a partially or fully deployed prosthetic heart valve may be more difficult when the prosthetic heart valve includes a double-flanged or hour-glass-shaped frame, compared to a frame that has a generally continuous taper from a larger diameter to a smaller diameter. Embodiments are described in greater detail below that may solve or mitigate some or all of these issues, and these solutions may be implemented for any of the prosthetic heart valves described above, as well as other specific designs of prosthetic heart valves not described above. 
     A prosthetic heart valve  1000  is illustrated in  FIGS.  16 - 17   . Prosthetic heart valve  1000  may include an outer frame  1100  and an inner frame  1200 . The inner frame  1200  may be substantially similar or identical to inner frames  500  or  800 , and thus is not described in greater detail here. The outer frame  1100  may be substantially similar to outer frame  700 . In other words, outer frame  1100  does not include significant gaps or voids between the atrial disc  1110  and the ventricular disc (not separately labeled), but rather outer frame  1100  defines complete or substantially complete rows of cells, which may be generally diamond-shaped cells, extending between the atrial and ventricular discs. It should be understood that, although outer frame  1100  does not include significant gaps tailored for the avoidance of conduction disturbance, the rail system described below may be applicable to various other frame designs, including designs similar or identical to outer frames  100 ,  200 ,  300 , or  600 . And as with other embodiments described herein, parts of the prosthetic heart valve  1000  are omitted from the figures for purposes of clarity, such as prosthetic leaflets mounted within the inner frame  1200 , and sealing skirts of cuffs provided on interior and/or exterior surfaces of the outer frame  1100  and/or inner frame  1200 . 
     As shown in  FIGS.  16 - 17   , the outer frame  1100  may include one or more rails  1170  in addition to the general diamond-shaped cell structure of the outer frame  1100 . In the illustrated embodiment, a total of nine rails  1170  are illustrated, with the rails being positioned at substantially equal intervals around the circumference of the outer frame  1100 . In particular, each rail  1170  is illustrated as being positioned between (in the circumferential direction) a pair of adjacent connectors  1230  of the inner frame  1200 . However, the number and configuration of rails  1170  shown in  FIGS.  16 - 17    is merely exemplary. For example, the outer frame  1100  may include more or fewer than nine rails  1170 . In some embodiments, the number of rails  1170  may be equal to the number of connectors  1230 , but in other examples, the number of rails  1170  may be different from the number of connectors  1230 . Further, although it may be desirable for the rails  1170  to be positioned at substantially equal intervals around the circumference of the outer frame  1100 , other relative positioning may be suitable. Further, although each rail  1170  is shown as being positioned at about the circumferential midpoint between a pair of adjacent connectors  1230 , other relative positioning may be suitable, including radial alignment between the connectors  1230  and the rails  1170 . 
     In some embodiments, the rails  1170  are formed of the same material as the outer frame  1100 , such as a shape memory metal such as nickel-titanium alloy, including nitinol. Each rail  1170  may be formed separately from the outer frame  1100  and attached to the interior or the exterior of the outer frame via any suitable mechanism, such as fasteners (e.g., sutures) or adhesives. In other embodiments, each rail  1170  may be formed integrally with the outer frame  1100 , for example via laser cutting the cells and rails  1170  of the outer frame  1100  from a single tube, such as a tube of nitinol. Whether the rails  1170  are formed separately from, or integrally with, the outer frame  1100 , each rail  1170  has an axial extent that is substantially parallel to the central longitudinal axis of the prosthetic heart valve  1000 . In other words, when the prosthetic heart valve  1000  is collapsed, the rails  1170  are substantially parallel to the central longitudinal axis of the prosthetic heart valve  1000 . When the prosthetic heart valve is expanded, the rails  1170  may be contoured along with the inflow-to-outflow contours of the outer frame  1100 , but preferably the rails  1170  do not have significant contouring in the circumferential direction of the outer frame  1100 . 
     As shown in  FIGS.  15 - 16   , a connector  1180  may be provided at an end of each post or rail  1170 . For example, each rail  1170  may include a loop or similar structure at a terminal end thereof, which may be on the side of the atrial disc  1110  which is generally collapsed first during a retrieval procedure. However, in embodiments where the ventricular disc is collapsed first during a retrieval procedure, the connectors  1180  may be positioned on the end of the rails  1170  on the side of the ventricular disc. In some embodiments, a connector  1180  may be provided on each end of the rails  1170  to allow for optionality in which end of the prosthetic heart valve  1000  is collapsed first during a retrieval procedure. Although the connectors  1180  are shown as loops or rings formed integrally with the rails  1170 , in other embodiments, the connectors  1180  may take other shapes suitable for connection with control element(s)  1300 , and in other embodiments the connectors  1180  may be formed on the outer stent  1100  adjacent the rails  1170 . 
     In use, one or more control elements  1300  may be coupled to the rails  1170  via connectors  1180 . For example, control elements  1300  may be flexible elements, such as wire, cords, sutures, etc. In some embodiments, a single control element  1300  may be coupled to each rail  1170 . In other embodiments, a single control element  1300  may be coupled to more than one, or all, of the rails  1170 , for example by looping through the connectors  1180 . The control elements  1300  may extend proximally through a catheter device  1400 , which may be the delivery device used for the initial deployment of the prosthetic heart valve  1000 , or a separate retrieval catheter specifically designed for a retrieval and/or repositioning procedure. In some embodiments, the catheter device  1400  may include a funnel-shaped member  1410  at the end of the catheter  1400 , the funnel  1410  tapering from the leading end to the trailing end where it meets the distal end of the main portion of the catheter  1400 . 
     In one exemplary use, a delivery catheter (which may be the same as, or different than, catheter  1400 ) is used to deliver the prosthetic heart valve  1000  to the native tricuspid or mitral valve annulus, for example via the femoral vein, while the prosthetic heart valve  1000  is collapsed within the delivery catheter. The ventricular end of the prosthetic heart valve  1000  may be deployed first by pushing the prosthetic heart valve  1000  distally out of the delivery catheter, or by withdrawing the delivery catheter proximally relative to the prosthetic heart valve  1000 . As the prosthetic heart valve  1000  exits the delivery catheter, it begins to self-expand for placement on the ventricular side of the native valve annulus. At some point after the process of deployment has begun, the operator may determine that it would be desirable to either reposition the prosthetic heart valve  1000  or remove the prosthetic heart valve  1000  from the patient entirely. If such a determination is made, the operator may pull the control element(s)  1300  in the proximal direction P relative to catheter  1400 , and/or push the catheter  1400  distally relative to the control element(s)  1300 . It may be more preferably to push the catheter  1400  distally while the control elements  1300  stay generally in a static position relative to the anatomy, compared to pulling the control elements  1300  proximally while the catheter  1400  stays in generally a static position relative to the anatomy, although it should be understood that either option is viable. The preference for pushing the catheter  1400  distally for retrieval may be based on the possibility that the ventricular disc is already expanded enough where pulling the ventricular disc relative to the native valve annulus may cause damage to the annulus. As noted above, this retrieval process may be performed with the original delivery catheter, or via another retrieval catheter that may be, for example, delivered over or through the original delivery catheter. This action draws the prosthetic heart valve  1000  back into the catheter  1400 , forcing the expanded portions to re-collapse back into the catheter  1400 . As the prosthetic heart valve  1000  is drawn into the catheter device  1400  and collapses, the rails  1170  help to distribute the re-sheathing forces, allowing the prosthetic heart valve  1000  to more easily and uniformly collapse into the catheter device  1400 . 
     As noted above, in some embodiments that employ rails  1170 , the rails  1170  may be formed integrally with the outer frame  1100 , for example via laser cutting the cells and rails  1170  of the outer frame  1100  from a single tube, such as a tube of nitinol.  FIG.  18 A  illustrates one exemplary mechanism of forming rails  1170   a  integrally with an outer frame  1100   a.  As shown in  FIG.  18 A , outer frame  1100   a  may include one or more rows of generally diamond-shaped cells  1190   a,  where each row is “free-floating” in the sense that the upper and lower apexes of one row of cells  1190   a  are not directly coupled to upper or lower apexes of the adjacent row or cells  1190   a.  Each rail  1170   a  couples the side apex of one cell in a row to a side apex of an adjacent cell in the same row of cells  1190   a.  Although  FIG.  18 A  illustrates three rows of cells  1190   a,  with a rail  1170   a  after every second cell (e.g., two cells  1190   a  between each circumferentially adjacent pair of rails  1170   a ), it should be understood that other numbers of rows of cells  1190   a  may be used, and a different spacing of the rails  1170   a  (e.g., one cell  1190   a  between each circumferentially adjacent pair of rails  1170   a,  or three or more cells  1190   a  between each circumferentially adjacent pair of rails  1170   a ) may be suitable. Finally, it should be understood that  FIG.  18 A  illustrates only a representative section of the outer frame  1170   a.    
       FIG.  18 B  illustrates a section of an outer frame  1170   b  which is similar in concept to outer frame  1170   a,  but instead of having rows of “free-floating” cells  1190   a,  outer frame  1170   b  includes rows of struts  1190   b  that each have a “zig-zag” pattern, with each pair of adjacent struts forming a general “V” shape with the apex of the “V” pointing in an alternating direction. Although outer frame  1100   b  is shown with five rows of zig-zag struts, with four struts between each pair of adjacent rails  1170   b,  it should be understood that the frame could include more or fewer than five rows of zig-zag struts, and each row may include more or fewer than four struts between each pair of circumferentially adjacent rails  1170   b.  And, although not shown, rails  1170   a  and  1170   b  may include connectors similar to those described above, including alternates described below. 
     As with frame  1100   a,  frame  1100   b  may be formed as an integral member—e.g., laser cut from a single tube of nitinol. The rails  1170   a  and  1170   b  do not foreshorten as the frame expands since the rails are effectively straight lines that have no capability to foreshorten. However, the “free-floating” cells  1190   a  may individually foreshorten upon expansion, but because adjacent rows are not directly coupled to each other, this foreshortening does not interfere with the rails  1170   a.  Similarly, each row of zig-zag struts  1190   b  may foreshorten as the frame  1100   b  expands, but this foreshortening does not interfere with the rails  1170   b.    
     In the embodiments described above that include rails for retrieval and/or repositioning, it should be understood that the retrieval may be performed prior to the full release of the atrial section of the outer frame from the delivery catheter. However, in some embodiments, the retrieval may be performed after full release (e.g., complete expansion) of the prosthetic heart valve from the delivery catheter. Although it may be more difficult to retrieve the prosthetic heart valve after it has been fully released, because the required forces for retrieval would be higher than if the prosthetic heart valve has only partially expanded, it is still an option. For example, applying retrieval forces at the distal end of the catheter may assist with such retrieval. Also, while it may be generally more difficult to perform such retrieval while the delivery catheter is deflected in multiple planes, the prosthetic valve may be partially collapsed, and then moved to be positioned in the right atrium, at which the catheter may be straightened to more easily complete the retrieval. 
     Further, although the rails  1170  are generally shown each with a single connector  1180  at a terminal end thereof, other connector options may be suitable. For example, the rails may each include multiple connectors or eyelets along their length (e.g., at any junction where a row of “free-floating” cells  1190   a  is positioned, or where a row of zig-zag struts  1190   b  is positioned). With this embodiment, wires or sutures or other control elements may run circumferentially through eyelets of rails that are aligned so that the control elements, upon tensioning, help to force the circumferential collapse of the frame. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.