Abstract:
A valve retainer is connected to an elongate delivery member. The valve retainer is configured to releasably secure a prosthesis (e.g., a heart valve prosthesis) to the delivery member during delivery to a target site in a body (e.g., a native valve annulus). The valve retainer includes a rotational identifier that identifies the rotational orientation of the valve retainer when the valve retainer is positioned proximate to the target site. A heart valve prosthesis can include a commissural post that has a predetermined rotational position relative to the rotational identifier, such that the heart valve prosthesis can be rotationally aligned with the native commissures of the native valve by rotating the delivery member and the valve retainer until the commissural post is aligned with a native valve commissure and the rotational identifier is visible.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/423,386, filed Dec. 15, 2010, the entire disclosure of which is incorporated in its entirety herein by reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to prosthetic heart valves, and specifically to techniques for accurately positioning such valves during implantation procedures. 
         [0004]    2. Background 
         [0005]    Aortic valve replacement in patients with severe valve disease is a common surgical procedure. The replacement is conventionally performed by open heart surgery, in which the heart is usually arrested and the patient is placed on a heart bypass machine. In recent years, prosthetic heart valves have been developed which are implanted using minimally invasive procedures such as transapical or percutaneous approaches. These methods involve compressing the prosthesis radially to reduce its diameter, inserting the prosthesis into a delivery tool, such as a catheter, and advancing the delivery tool to the correct anatomical position in the heart. Once properly positioned, the prosthesis is deployed by radial expansion within the native valve annulus. 
         [0006]    While these techniques are substantially less invasive than open heart surgery, the lack of line-of-sight visualization of the prosthesis and the native valve presents challenges because the physician cannot see the actual orientation of the prosthesis during the implantation procedure. Correct positioning of the prosthesis is achieved using radiographic imaging, which yields a two-dimensional image of the viewed area. The physician must interpret the image correctly in order to properly place the prostheses in the desired position. Failure to properly position the prosthesis can lead to device migration or to improper functioning. Proper device placement using radiographic imaging is thus important to the success of the implantation. 
         [0007]    PCT Publication WO 05/002466 to Schwammenthal et al., which is incorporated herein by reference, describes prosthetic devices for treating aortic stenosis. 
         [0008]    PCT Publication WO 06/070372 to Schwammenthal et al., which is incorporated herein by reference, describes a prosthetic device having a single flow field therethrough, adapted for implantation in a subject, and shaped so as to define a fluid inlet and a diverging section, distal to the fluid inlet. 
         [0009]    U.S. Patent Application Publication 2006/0149360 to Schwammenthal et al., which is incorporated herein by reference, describes a prosthetic device including a valve-orifice attachment member attachable to a valve in a blood vessel and including a fluid inlet, and a diverging member that extends from the fluid inlet, the diverging member including a proximal end near the fluid inlet and a distal end distanced from the proximal end. A distal portion of the diverging member has a larger cross-sectional area for fluid flow therethrough than a proximal portion thereof. 
         [0010]    U.S. Patent Application Publication 2005/0197695 to Stacchino et al., describes a cardiac-valve prosthesis adapted for percutaneous implantation. The prosthesis includes an armature adapted for deployment in a radially expanded implantation position, the armature including a support portion and an anchor portion, which are substantially axially coextensive with respect to one another. A set of leaflets is coupled to the support portion. The leaflets can be deployed with the armature in the implantation position. The leaflets define, in the implantation position, a flow duct that is selectably obstructable. The anchor portion can be deployed to enable anchorage of the cardiac-valve prosthesis at an implantation site. 
         [0011]    U.S. Patent Application Publication 2010/0121436 (“the &#39;436 publication”) to Tuval et al., which is incorporated, herein in its entirety by reference, describes a heart valve with three commissural posts and a delivery system therefore. During implantation, the valve prosthesis, including the commissural posts, is initially collapsed within a delivery tube. Before expanding the valve prosthesis, a physician uses radiographic imaging, such as x-ray fluoroscopy, to provide visual feedback that aids the physician in rotationally aligning the commissural posts with respective native commissures of a native semilunar valve. The identifiers strongly contrast with the rest of the commissural posts and the valve prosthesis, which comprise a radiopaque material. Without such identifiers, it is generally difficult to three-dimensionally visually distinguish the commissural posts from one another and from the rest of the valve prosthesis, because the radiographic imaging produces a two-dimensional representation of the three-dimensional valve prosthesis. When the valve prosthesis is in a collapsed state, the elements thereof overlap in a two-dimensional image and are generally indistinguishable. 
         [0012]    The &#39;436 publication describes a procedure during which the physician selects one of the commissural posts having a radiographic identifier, and attempts to rotationally align the selected post with one of the native commissures, such as the commissure between the left and right coronary sinuses. Because the radiographic image is two-dimensional, all of the posts appear in the image as though they are in the same plane. The physician thus cannot distinguish between two possible rotational positions of the posts: (1) the desired rotational position, in which the selected post faces the desired native commissure, and (2) a rotational position 180 degrees from the desired rotational position, in which the selected post faces the side of the native valve opposite the desired native commissure. For example, if the desired native commissure is the commissure between the left and right coronary sinuses, in position (2) the post is rotationally aligned with the non-coronary sinus, although this undesired rotation is not apparent in the radiographic image. To ascertain whether the posts are in rotational position (1) or (2), the physician slightly rotates the valve prosthesis. If the radiographic identifier on the selected post appears to move in the radiographic image in the same direction as the rotation, the selected post is correctly rotationally aligned in the desired position (1). If, on the other hand, the radiographic identifier appears to move in the direction opposite the direction of rotation, the selected post is incorrectly rotationally aligned in position (2). To correct the alignment, the physician may rotate the valve prosthesis approximately 60 degrees in either direction, thereby ensuring that one of the two other posts is now rotationally aligned in position (1). 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    Heart valve prostheses and systems and methods of delivering heart valve prostheses are provided. The delivery systems and methods herein seek to simplify implantation of heart valve prostheses by reducing the amount of time and the number of steps necessary to implant prostheses. A heart valve prosthesis can include three commissural posts to which are coupled a prosthetic valve. The commissural posts can be shaped so as define therethrough respective openings that serve as radiographic identifiers during an implantation procedure. During the procedure, the valve prosthesis, including the commissural posts, is initially collapsed within a delivery tube. Before expanding the valve prosthesis, a physician uses radiographic imaging, such as x-ray fluoroscopy, to provide visual feedback that aids the physician in rotationally aligning the commissural posts with respective native commissures of a native semilunar valve. The identifiers strongly contrast with the rest of the commissural posts and the valve prosthesis, which comprise a radiopaque material. Without such identifiers, it is generally difficult to three-dimensionally visually distinguish the commissural posts from one another and from the rest of the valve prosthesis, because the radiographic imaging produces a two-dimensional representation of the three-dimensional valve prosthesis. When the valve prosthesis is in a collapsed, state, the elements thereof overlap in a two-dimensional image and are generally indistinguishable. 
         [0014]    A valve retainer is connected to an elongate delivery member, wherein the valve retainer is configured to releasably secure the prosthesis to the elongate delivery member during delivery to a target site in a body. The valve retainer includes a rotational identifier configured to allow a user to identify the rotational orientation of the valve retainer, and thereby the rotational orientation of the commissural posts of the prosthesis, when the valve retainer is positioned proximate to the target site in the body. 
         [0015]    The physician selects one of the comimissural posts having a radiographic identifier, and attempts to rotationally align the selected post with one of the native commissures, such as the commissure between the left and right coronary sinuses. Because the radiographic image is two-dimensional, all of the posts appear in the image as though they are in the same plane. The physician thus cannot distinguish between two possible rotational positions of the posts: (1) the desired rotational position, in which the selected post faces the desired native commissure, and (2) a rotational position 180 degrees from the desired rotational position, in which the selected post faces the side of the native valve opposite the desired native commissure. For example, if the desired native commissure is the commissure between the left and right coronary sinuses, in position (2) the post is rotationally aligned with the non-coronary sinus, although this undesired rotation is not apparent in the radiographic image. 
         [0016]    To ensure proper rotational alignment, a fluoroscopic image of the heart valve prosthesis, the valve retainer, and the native valve commissures is generated. The heart valve prosthesis is then rotationally aligned by rotating the elongate delivery member and the valve retainer until a commissural post is aligned with a native valve commissure and the rotational identifier is visible on a predetermined side of the valve retainer such that the rotational position of the commissural post with respect to the rotational identifier is known. 
         [0017]    The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0018]      FIG. 1  is a schematic illustration of a fully-assembled valve prosthesis, in accordance with an embodiment of the present invention; 
           [0019]      FIGS. 2A and 2B  are schematic illustrations of a collapsible outer support structure and a collapsible inner support structure, respectively, prior to assembly together into the valve prosthesis of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0020]      FIG. 3  is a schematic illustration of a subject undergoing a transapical or percutaneous valve replacement procedure, in accordance with an embodiment of the present invention; 
           [0021]      FIG. 4  shows an exemplary transverse plane MRI of an aortic root demonstrating the projection angle of a left anterior oblique projection; 
           [0022]      FIG. 5  shows an exemplary transverse plane MRI of an aortic root demonstrating the projection angle of a right anterior oblique projection; 
           [0023]      FIG. 6  shows an exemplary transverse plane MRI of an aortic root demonstrating the projection angle of an anteroposterior projection; 
           [0024]      FIG. 7  illustrates a two-dimensional view of a heart valve prosthesis and delivery system according to an embodiment of the present invention at one stage of delivery; 
           [0025]      FIG. 8  illustrates a two-dimensional view of a heart valve prosthesis and delivery system according to an embodiment of the present invention at a second stage of delivery; 
           [0026]      FIG. 9  illustrates a two-dimensional view of a heart valve prosthesis and delivery system according to an embodiment of the present invention at a third stage of delivery; 
           [0027]      FIG. 10  is a profile view of a valve retainer according to an embodiment of the present invention; 
           [0028]      FIG. 11  is a perspective view of the valve retainer of  FIG. 10 ; 
           [0029]      FIG. 12  illustrates a valve prosthesis in a crimped configuration connected to the valve retainer shown in  FIGS. 10 and 11  at a first rotational orientation; 
           [0030]      FIG. 13  illustrates a valve prosthesis in a crimped configuration connected to the valve retainer shown in  FIGS. 10 and 11  at a second rotational orientation; 
           [0031]      FIG. 14  illustrates a two-dimensional view of a heart valve prosthesis and delivery system according to an embodiment of the present invention at one stage of delivery. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The following detailed description of heart valve prostheses and systems and methods of delivering heart valve prostheses refers to the accompanying figures that illustrate exemplary embodiments. Other embodiments are possible. Modifications can be made to the embodiments described herein without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not meant to be limiting. Further, it would be apparent that the systems and methods described below can be implemented in many different embodiments of hardware. Any actual hardware described is not meant to be limiting. The operation and behavior of the systems and methods presented are described with the understanding that modifications and variations of the embodiments are possible given the level of detail presented. For example, while the description provided is directed to heart valve prostheses and systems and methods of delivering heart valve prostheses, the systems and methods described herein should not be limited to delivery of heart valve prostheses. One of skill in the art would readily understand how to incorporate the features and structures described herein into delivery systems and methods for other types of prostheses. For example, the systems and methods described herein can be used for other types of procedures, such as delivery of stents, valves, or other prostheses to a variety of areas in the body. 
         [0033]      FIG. 1  is a schematic illustration of a fully-assembled valve prosthesis  10  in accordance with an embodiment of the present invention. Typically, valve prosthesis  10  comprises exactly three commissural posts  11 , arranged circumferentially around a central longitudinal axis  13  of valve prosthesis  10 . Valve prosthesis  10  can also be provided with two commissure posts, e.g., for placement in a native mitral valve annulus, or could be provided with more than three commissural posts. Valve prosthesis  10  further comprises a prosthetic valve  104  coupled to commissural posts  11 . Valve  104  typically comprises a pliant material  105 . Pliant material  105  can include, e.g., animal pericardial tissue or artificial tissue. Pliant material  105  of valve  104  is configured to collapse inwardly (i.e., towards central longitudinal axis  13 ) during diastole, in order to inhibit retrograde blood flow, and to open outwardly during systole, to allow blood flow through the prosthesis. For some applications, valve prosthesis  10  comprises a collapsible inner support structure  12  that serves as a proximal fixation member, and a collapsible outer support structure  14  that serves as a distal fixation member. 
         [0034]    The commissural posts  11  are shaped so as define therethrough respective openings  16  that serve as radiographic identifiers during an implantation procedure, as described hereinbelow. Although  FIG. 1  illustrates openings  16  on each of the three commissural posts, it is understood that openings  16  may be provided only on one or two of the commissural posts. The openings may assume any convenient shape, for example, slits, as shown in FIGS.  1  and  2 A-B. In some embodiments, the openings are shaped to be reflection-asymmetric along respective post axes generally parallel with central longitudinal axis  13  of prosthesis  10  when the posts assume their collapsed position. For some applications, in addition to serving as the radiographic identifiers, openings  16  are used for coupling valve  104  to support structures  12  and  14 . Although pliant material  105  of valve  104  at least partially fills openings  16 , the pliant material is substantially more radiolucent than commissural posts  11 , and thus does not reduce the radiographic visibility of the radiographic identifiers. One or more of posts  11  can be formed without openings  16 , and the one or more posts can instead comprise radiographic identifiers comprising a material having a radiopacity different from (greater or less than) the radiopacity of posts  11 , such as gold or tantalum. 
         [0035]    Valve prosthesis  10  is configured to be placed in a native diseased valve of a subject, such as a native stenotic aortic or pulmonary valve, using a minimally-invasive approach, such as a beating heart transapical procedure, or a retrograde transaortic procedure. As used in the present application, including in the claims, a “native valve” is to be understood as including: (a) native valves that include their native leaflets, and (b) native valves in which one or more of the native leaflets have been surgically excised, are otherwise absent, or are damaged or stenosed. 
         [0036]    Reference is made to  FIG. 2A , which is a schematic illustration of collapsible outer support structure  14  prior to assembly with inner support structure  12 , in accordance with an embodiment of the present invention. In this embodiment, outer support structure  14  is shaped so as to define a plurality of distal diverging strut supports  20 , from which a plurality of proximal engagement arms  22  extend radially outward in a proximal direction. Engagement arms  22  are typically configured to be at least partially disposed within aortic sinuses of the subject, and, for some applications, to engage and/or rest against floors of the aortic sinuses, and to apply an axial force directed toward a left ventricle of the subject. Outer support structure  14  comprises a suitable material that allows mechanical deformations associated with crimping and expansion of valve prosthesis  10 , such as, but not limited to, nitinol or a stainless steel alloy (e.g., AISI 316). 
         [0037]    Reference is made to  FIG. 2B , which is a schematic illustration of collapsible inner support structure  12  prior to assembly with outer support structure  14 , in accordance with an embodiment of the present invention. For some applications, inner support structure  12  is shaped so as to define a plurality of distal diverging inner struts  30 , and a bulging proximal skirt  32  that extends from the struts. A proximal portion  34  of proximal skirt  32  is configured to engage a left ventricular outflow tract (LVOT) of the subject and/or periannular tissue at the top of the left ventricle. A relatively narrow throat section  36  of proximal skirt  32  is configured to be positioned at a valvular annulus of the subject, and to engage the native valve leaflets. Inner support structure  12  comprises, for example, nitinol, a stainless steel alloy, another metal, or another biocompatible material. Inner support structure  12  also includes one or more fixation hooks  38  extending from the proximal end of inner support structure  12 . Preferably, inner support structure  12  includes three fixation hooks  38 . However, it is understood that fewer or greater than three fixation hooks  38  can be provided with inner support structure  12 . Fixation hooks  38  extend from the proximal end of inner support structure  12  and include eyelets at their proximal end. Fixation hooks  38 , which are optional, can be formed in various configurations other than that shown. For example, fixation hooks  38  can be J-shaped hooks or eyelets  38 , and can take on any number of sizes or shapes while remaining compatible with the delivery methods and systems described herein. 
         [0038]    Reference is again made to  FIG. 1 . Inner and outer support structures  12  and  14  are assembled together by placing outer support structure  14  over inner support structure  12 , such that outer strut supports  20  are aligned with, and typically support, respective inner struts  30 , and engagement arms  22  are placed over a portion of proximal skirt  32 . Inner struts  30  and outer strut supports  20  together define commissural posts  11 . 
         [0039]    Although exactly three commissural posts  11  are shown in the figures, for some applications valve prosthesis  10  comprises fewer or more posts  11 , such as two posts  11 , or four or more posts  11 . 
         [0040]    Typically, valve prosthesis  10  further comprises a graft covering  106  which is coupled to proximal skirt  32 , such as by sewing the covering within the skirt (configuration shown in  FIG. 1 ) or around the skirt (configuration not shown). Inner support structure  12  thus defines a central structured body for flow passage that proximally terminates in a flared inlet (proximal skirt  32 ) that is configured to be seated within an LVOT immediately below an aortic annulus/aortic valve. For some applications, graft covering  106  is coupled at one or more sites to pliant material  105 . 
         [0041]    In an embodiment of the present invention, a portion of valve prosthesis  10  other than commissural posts  11 , e.g., proximal skirt  32 , is shaped so as to define openings  16  that serve as radiographic identifiers. Alternatively or additionally, the commissural posts or the selected other portion of the prosthesis comprise radiographic identifiers comprising a material having a radiopacity different from (greater or less than) the radiopacity of other portions of the prosthesis. For some applications, the radiographic identifiers are radially aligned with commissural posts  11 . 
         [0042]    Additional features of valve prostheses suitable for use in conjunction with the present invention are described in U.S. Patent Publication Nos. 2008/0071361, 2008/0071366, 2008/0071368, 2008/0071369, 2010/0131054, 2010/0137979, and 2010/0262231, each of which is incorporated, in its entirety by reference herein. 
         [0043]      FIG. 3  is a schematic illustration of a subject  200  undergoing a transapical or percutaneous valve replacement procedure in accordance with an embodiment of the present invention. A fluoroscopy system  210  comprises a fluoroscopy source  213 , a fluoroscopy detector  212 , and a monitor  214 . Fluoroscopy source  213  is positioned over subject  200  so as to obtain a left anterior oblique (LAO) projection. Preferably, the LAO projection is at an angle between 30 and 45 degrees, such as between 30 and 40 degrees, with a 30-degree cranial tilt (for orthogonal projection of the annulus). Typically, imaging is enhanced using an ultrasound probe  216 . It is understood that alternate fluoroscopy systems can be used in conjunction with the delivery systems and methods described herein. 
         [0044]      FIGS. 4-6  show exemplary transverse plane MRIs of an aortic root. Right coronary sinus R is generally positioned on the anterior side of the annulus. Left coronary sinus L and non-coronary sinus N are also shown.  FIGS. 4-6  further illustrate a commissure R/L between the right and left coronary sinuses R and L, a commissure N/R between the non-coronary sinus N and the right coronary sinus R, and a commissure N/L between the non-coronary sinus N and the left coronary sinus L. Commissure R/L is best shown in a LAO projection, as illustrated in  FIG. 4 . Commissure N/R is best shown in a right anterior oblique (RAO) projection, as illustrated in  FIG. 5 . Commissure N/L is best shown in an anteroposterior (AP) projection, as illustrated in  FIG. 6 . Commissures R/L, N/R, and N/L serve as clear anatomical landmarks during the replacement procedure, enabling the physician to readily ascertain the layout of the aortic root. 
         [0045]      FIG. 7  is a schematic view of valve prosthesis  10  in a collapsed, position in a catheter  300  inserted transapically and extending through a native annulus. Devices and methods for introducing a delivery system into a heart through the apex area of the heart are described by U.S. Patent Application Publication 2010/0121436, which is incorporated by reference herein in its entirely. In this embodiment, openings  16  in commissure posts  11  are shaped as slits. As noted above, openings  16  are clearly visible by fluoroscopy. Valve prosthesis  10  is contained within sleeve  314  at its distal end. Valve prosthesis  10  is held at its proximal end by valve retainer  308 , which is connected to inner delivery member  306 . Preferably, fixation hooks  38  on valve prosthesis  10  are engaged with valve retainer  308 . An auxiliary catheter  310  is introduced into the aortic root. Auxiliary catheter  310  is preferably a pigtail catheter thr introducing dyes into the aortic root area to facilitate imaging of the aortic root area. When the valve prosthesis  10  has been inserted, to the position illustrated in  FIG. 7 , the distal ends of engagement arms  22  are positioned downstream of the tips  320  of native valve leaflets  312 . Because  FIG. 7  is a two-dimensional view, only two native valve leaflets  312  are illustrated. It is also understood that the implantation devices and methods described herein can be used to implant prostheses in a native annulus that does not have three leaflets. For example, the devices and methods described herein can be used to implant prostheses in a mitral or pulmonary valve annulus. In addition, it is understood that the implantation devices and methods described herein can be used to implant prostheses in a native annulus from which one or more native leaflets have already been removed, or in which one or more of the native leaflets has been damaged. 
         [0046]    After valve prosthesis  10  has been inserted through a native annulus, the valve prosthesis is rotationally aligned with the native commissures and sinuses of the native valve. Preferably, an RAO projection is used for the rotational alignment procedure. Once an RAO projection has been established, initial alignment proceeds generally in the manner described in U.S. Patent Application Publication 2010/0121436, which is incorporated, by reference herein in its entirely. Specifically, the physician selects one of the commissural posts  11  having a radiographic identifier, and attempts to rotationally align the selected post with one of the native commissures, such as the commissure between the left and right coronary sinuses. Because the radiographic image is two-dimensional, all of the posts appear in the image as though they are in the same plane. The physician thus cannot distinguish between two possible rotational positions of the posts: (1) the desired rotational position, in which the selected post faces the desired native commissure, and (2) a rotational position 180 degrees from the desired rotational position, in which the selected, post faces the side of the native valve opposite the desired native commissure. For example, if the desired native commissure is the commissure between the left and right coronary sinuses, in position (2) the post is rotationally aligned with the non-coronary sinus, although this undesired rotation is not apparent in the radiographic image. To ascertain whether the posts are in rotational position (1) or (2), the physician slightly rotates the valve prosthesis. If the radiographic identifier on the selected post appears to move in the radiographic image in the same direction as the rotation, the selected post is correctly rotationally aligned in the desired position (1). If, on the other hand, the radiographic identifier appears to move in the direction opposite the direction of rotation, the selected post is incorrectly rotationally aligned in position (2). To correct the alignment, the physician may rotate the valve prosthesis approximately 60 degrees in either direction, thereby ensuring that one of the two other posts is now rotationally aligned in position (1). 
         [0047]    After rotational alignment has been achieved, the physician verifies that the distal end  316  of the valve retainer  308  is still approximately at the level of the curl of the pigtail catheter  310 , and that proximal ends  318  of the engagement arms  22  are still positioned downstream of the tips  320  of the native valve leaflets  312 . Once this position has been confirmed, sleeve  314  is moved in a distal direction, i.e., away from valve retainer  308 , to release engagement arms  22 . Engagement arms  22  are configured to radially expand when released from sleeve  314 , as shown in  FIG. 8 . Inner delivery member  306 , and thereby valve retainer  308 , are then retracted in a proximal direction (i.e., generally towards the apex of the heart) in order to position engagement arms  22  in their respective sinuses, as illustrated in  FIG. 9 . Although engagement arms  22  are shown in  FIGS. 9 and 10  as not fully extending to the base of the sinuses, it is understood that the arms can be formed in a variety of shapes and lengths, and may contact the base of the sinuses and/or contact the native leaflets  312  when implanted in a native annulus. U.S. Patent Publication Nos. 2008/0071361, 2008/0071366, 2008/0071368, 2008/0071369, 2010/0131054, 2010/0137979, and 2010/0262231, each of which is incorporated, in its entirety by reference herein, disclose heart valve prostheses having engagement arms suitable for use with the present invention. 
         [0048]    At this stage, commissural posts  11  can be released from sleeve  314  by further moving sleeve  314  in a distal direction relative to valve retainer  308 . Delivery catheter  300  is then moved proximally with respect to valve retainer  308 , thereby releasing the proximal skirt  32  of valve prosthesis  10 . Once released, proximal skirt  32  contacts the upper ventricle of the heart below the sinuses. Proximal skirt can contact the underside of native leaflets  312  in addition to or instead of contacting the upper ventricle. Sleeve  314 , valve retainer  308 , and inner delivery member  306  can then be withdrawn from the heart. 
         [0049]      FIG. 10  is a profile view of a valve retainer  408  according to another embodiment of the present invention. Unlike valve retainer  308 , which, as shown in  FIGS. 7-9 , is substantially radially symmetrical, valve retainer  408  is formed with a rotational identifier on one side thereof. As shown in  FIGS. 10-11 , the rotational identifier can be a physical identifier such as a notch  422  formed on one side of valve retainer  408 . As illustrated in  FIGS. 10-11 , notch  422  preferably extends from the proximal end  424  of valve retainer  408  towards distal end  416 , and extends approximately 180 degrees around the outer surface of valve retainer  408 . However, it is understood that notch  422  can be formed in a variety of shapes and locations consistent with the present invention. For example, notch  422  can be a narrow notch on one side of valve retainer  408 , i.e., a notch that extends only a small fraction of the length of valve retainer  408 . Notch  422  can extend to the proximal end  424  of valve retainer or can be formed only in the middle region of valve retainer  408 . It is also understood that other physical markings can be used consistent with the present invention. The term notch is used herein to refer to any of a variety of notch, slit, groove, or other physical alteration that is visible during a fluoroscopy procedure and that provides information on the rotational alignment of the valve retainer. For example, a hole formed in the valve retainer can serve as the physical alteration. 
         [0050]    As shown in  FIG. 11 , valve retainer  408  also includes three slots  426  at its distal end  416 . Slots  426  are configured to receive fixation hooks  38  of valve prosthesis  10 . Fixation hooks  38  serve to secure valve prosthesis  10  to valve retainer  408  when fixation hooks  38  are placed within slots  426  and valve retainer  408  is placed within a catheter, such as delivery catheter  300 . As shown in  FIG. 11 , slots  426  are evenly positioned around the perimeter of the distal end  416  of valve retainer  408 . Although three evenly spaced slots  426  are shown in  FIG. 11 , it is understood that fewer or more than three slots can be provided with retainer  408 , and that the slots can be spaced unevenly. 
         [0051]      FIGS. 12 and 13  illustrate valve prosthesis  10 , in its crimped configuration, connected to valve retainer  408 . In  FIG. 12 , notch  422  is positioned to the right. It should be noted that the circumferential locations of the commissure posts  11  of valve prosthesis  10  relative to the fixation hooks  38  of valve prosthesis  10  are known due to the geometry of valve prosthesis  10 . Specifically, commissure posts  11  and fixation hooks  38  are formed on valve prosthesis  10  such that when fixation hooks  38  are inserted, into slots  426  of valve retainer  408 , the circumferential position of each commissure post  11  is known based on the geometry of valve prosthesis  10  and valve retainer  408 . 
         [0052]    Thus, when valve prosthesis  10  is loaded into valve retainer  108  and viewed in a two-dimensional profile view, such as during an angiography procedure, and, when notch  422  is visible on the right side of valve retainer  408  in the profile view, as shown in  FIG. 12 , a user can identify that the central commissure post  428  is rotationally positioned on the anterior side of valve prosthesis  10 . This is because the location of the central commissure post  428  relative to fixation hooks  38  is known, and because the location of central commissure post  428  relative to slots  426  is known because the fixation hooks  38  are secured within slots  426 . As noted above, radiographic images are two-dimensional. Because of this, absent the additional information provided by the position relationship between notch  422  and central commissure post  428 , a user would be unable to distinguish between two possible rotational positions of the posts: (1) the desired rotational position, in which the selected central commissure post  428  faces the desired native commissure, and (2) a rotational position 180 degrees from the desired rotational position, in which the selected central commissure post  428  faces the side of the native valve opposite the desired native commissure. 
         [0053]    Although a particular commissure post  11  has been identified as a central commissure post  428  for purposes of describing  FIG. 12 , it is understood that any of the three commissure posts  11  can serve as a central commissure post during an implantation procedure. In any particular implantation procedure, the commissure post  11  that serves as the central commissure post is determined by aligning the opening  16  of one of the commissure posts  11  with the tip of the center of coaptation  440  (see  FIG. 14 ) of the native valve leaflets  312 . It is understood that the center of coaptation  440  refers to the point where the tips of the native valve leaflets  312  meet when the native valve is in a closed position. Once the opening  16  of one of the commissure posts  11  is aligned, with the center of coaptation in a chosen radiographic view, for example, using an RAO projection, that particular commissure post  11  serves as central commissure post  428  for that procedure. It is also understood that more or fewer than three commissure posts, fixation hooks  38 , and slots  426  can be utilized in the delivery devices described, herein while maintaining the advantages of the present invention. Valve retainers  408  and the delivery devices and methods described herein utilizing the described valve retainers  408  can be used to implant valve prostheses that are structurally different from the valve prostheses described, herein. For example, the delivery devices and, methods described herein can be utilized to delivery valve prostheses with no engagement arms. 
         [0054]    It is understood that openings  16  may be provided only on one or two of the commissural posts. The openings may assume any convenient, shape, for example, slits, as shown in  FIGS. 12-14 . In some embodiments, the openings are shaped, to be reflection-asymmetric along respective post axes generally parallel with central longitudinal axis  13  of prosthesis  10  when the posts assume their collapsed position. For some applications, in addition to serving as the radiographic identifiers, openings  16  are used for coupling valve  104  to support structures  12  and  14 . Although pliant material of a valve at least partially fills openings  16 , the material is substantially more radiolucent than commissural posts  11 , and thus does not reduce the radiographic visibility of the radiographic identifiers. As detailed above, one or more of posts  11  can be formed without openings  16 , and the one or more posts can instead comprise radiographic identifiers comprising a material having a radiopacity different from (greater or less than) the radiopacity of posts  11 , such as gold or tantalum. 
         [0055]    In the profile view of loaded valve prosthesis  10  shown in  FIG. 13 , notch  422  of valve retainer  408  is visible on the left, i.e., rotated approximately 180 degrees from the position shown in  FIG. 12 . When valve prosthesis  10  is loaded into valve retainer  408  and viewed in a two-dimensional profile view, such as during an radiography procedure, and when notch  422  is visible on the left side of valve retainer  408  in the profile view, as shown in  FIG. 13 , a user can identify that the central commissure post  428  is rotationally positioned on the posterior side of valve prosthesis  10 . This is because the location of the central commissure post  428  relative to fixation hooks  38  is known, and because the location of central commissure post  428  relative to slots  426  is known because the fixation hooks  38  are secured within slots  426 . 
         [0056]    It is understood that the rotational orientation of the identified central commissure post  428  with respect to notch  422  can be reversed, that is, notch  422  can be formed in valve retainer  408  such that when notch  422  is visible on the right side of an angiography projection, central commissure post  428  is posterior instead of anterior. In this configuration, when notch  422  is visible on the left side of an angiography projection, central commissure post  428  is anterior instead of posterior. 
         [0057]      FIG. 14  is a schematic view of valve prosthesis  10  in a collapsed position in a catheter  300  inserted transapically and extending through a native annulus. Devices and methods for introducing a delivery system into a heart through the apex area of the heart are described by U.S. Patent Application Publication 2010/0121436, which is incorporated by reference herein in its entirely. In this embodiment, openings  16  in commissure posts  11  are shaped as slits. As noted above, openings  16  are clearly visible by fluoroscopy. Valve prosthesis  10  is contained within sleeve  314  at its distal end. Valve prosthesis  10  is held at its proximal end by valve retainer  408  which is connected to inner delivery member  306 . Valve retainer  408  is provided with notch  422 , which is visible on the right side of valve retainer  408 . Preferably, fixation hooks  38  on valve prosthesis  10  are engaged with valve retainer  308 . An auxiliary catheter  310  is introduced into the aortic root. Auxiliary catheter  310  is preferably a pigtail catheter for introducing dyes into the aortic root area to facilitate imaging of the aortic root area. When the valve prosthesis  10  has been inserted to the position illustrated in  FIG. 14 , the distal ends of engagement arms  22  are positioned downstream of the tips  320  of native valve leaflets  312 , and therefore downstream of the center of coaptation  440 . Because  FIG. 14  is a two-dimensional view, only two native valve leaflets  312  are illustrated. It is understood that the implantation devices and methods described herein can be used to implant prostheses in a native arm ulus that does not have three leaflets. For example, the devices and methods described herein can be used to implant prostheses in a mitral or pulmonary valve annulus. In addition, it is understood that the implantation devices and methods described herein can be used to implant prostheses in a native annulus from which one or more native leaflets have already been removed, or in which one or more of the native leaflets has been damaged. 
         [0058]    After valve prosthesis  10  has been inserted through a native annulus, the valve prosthesis is rotationally aligned with the native commissures and sinuses of the native valve. Preferably, an RAO projection is used for the rotational alignment procedure. This rotational alignment is achieved by lining up the opening  16  of one of the commissure posts  11  with the center of coaptation  440  of the native valve leaflets  312  using an RAO projection to visualize the aortic root area (this post is marked as central commissure post  428  in  FIG. 14  for description purposes). Commissure N/R is the native commissure visible in an RAO projection, as shown in  FIG. 5 , and it is positioned on the anterior side of the heart. Thus, a user can properly align the commissure posts  11  of valve prosthesis  10  by first aligning an opening  16  of a commissure post  11  (thereafter designated central commissure post  428 ) with the native commissure N/R and verifying that notch  422  of valve retainer  408  is visible on the right side of the angiographic projection. As described with reference to  FIG. 12 , a user can identify that the central commissure post  428  is rotationally positioned on the anterior side of valve prosthesis  10  when notch  422  is visible to the right side of the profile view of valve retainer  408 . Because native commissure N/R is anterior in an RAO projection, rotationally aligning central commissure post  428  to the anterior position ensures that commissure  428  is aligned with native commissure N/R. The remaining commissure posts  11  are evenly distributed around the circumference of valve prosthesis  10  to approximately match the normal spacing of the native commissures a heart such that properly rotationally aligning one commissure post  11  is sufficient to ensure that the remaining two commissure posts  11  are also properly aligned with a respective one of the remaining two native commissures R/L or Nit. 
         [0059]    Alternately, an LAO or RAO projection can be used in conjunction with the implantation devices and methods disclosed herein. Native commissure R/L is visible when an LAO projection is utilized, as shown in  FIG. 4 . Therefore, when an LAO projection is used, a central commissure  428  is identified by alignment with the native commissure R/L. Because native commissure R/L is anterior in an LAO projection, central commissure  428  is properly rotationally positioned when notch  422  of valve retainer  408  is visible on the right side of valve retainer  408 . 
         [0060]    Native commissure N/L is visible when an AP projection is utilized, as shown in  FIG. 6 . Therefore, when an AP projection is used, a central commissure  428  is identified by alignment with the native commissure N/L. Because native commissure N/L is posterior in an AP projection, central commissure  428  is properly rotationally positioned when notch  422  of valve retainer  408  is visible on the left side of valve retainer  408 . 
         [0061]    In other embodiments, the rotational identifier of valve retainer  408  can include one or more radiopaque identifiers applied on the outer surface of valve retainer  408  or formed integrally with valve retainer  408 . When a radiopaque identifier is applied to the outer surface, valve retainer  408  may or not be formed with a notch or other physical rotational identifier. For example, instead of physically notching valve retainer  408 , a radiopaque identifier can be applied on one side of valve retainer  408 . The radiopaque identifier can, for example, be a vertical or a dot that contrasts with the rest of valve retainer  408  during radiographic imaging. The radiopaque identifier can extend approximately 180 degrees around the outer surface of valve retainer  408 . The radiopaque identifier can be positioned on valve retainer  408  in a known location relative to a commissure post of a valve prosthesis when the valve prosthesis is secured to valve retainer  408  for an implantation procedure. If the radiopaque identifier is visible when the commissure post is aligned with a native commissure, the user knows that the central commissure post is on the anterior side of the valve prosthesis. If the radiopaque identifier is not visible when the commissure post is aligned with a native commissure, the user knows that the central commissure post is on the posterior side of the valve prosthesis. As with the positioning of the notch  422  described above, the relation between the location of the radiopaque identifier and the anterior/posterior position of the commissure post can be reversed. That is, the radiopaque identifier can be positioned on valve retainer  408  such that if the radiopaque identifier is not visible when the commissure post is aligned with a native commissure, the user knows that the central commissure post is on the anterior side of the valve prosthesis. 
         [0062]    The foregoing description of the invention has been presented thr purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Other modifications and variations may be possible in light of the above teachings. The embodiments and examples were chosen and described in order to best explain the principles of the invention and its practical application and to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention.