Abstract:
An improved holder, system and method for implanting a tissue-type prosthetic heart mitral valve that constricts the commissure posts of the valve and allows the user to detach the handle of the holder prior to withdrawing the holder itself. The ability to remove the handle allows a surgeon greater access to suturing the prosthetic valve to the mitral annulus. The holder may include two relatively movable plates, one of which attaches to the valve sewing on the inflow end of the valve ring and the other which attaches via sutures to the valve commissures on the outflow end. Separation of the plates places the sutures in tension and constricts the commissures. An adjusting member or adapter is interposed between the handle and holder to enable separation of the two plates and removal of the handle. The adjusting member or adapter may be packaged with the valve and holder combination, or may be sold as a separate unit, possibly with the handle, so that prior art holders can be retrofit.

Description:
RELATED APPLICATION 
     The present application is a continuation-in-part of U.S. application Ser. No. 09/626,570, filed Jul. 27, 2000 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices, and more particularly to an apparatus for facilitating the implantation of a bioprosthetic replacement heart valve, and associated methodology. 
     BACKGROUND OF THE INVENTION 
     In mammalian animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary valves and have leaflets to control the directional flow of blood through the heart. The valves are each mounted in an annulus that comprises a dense fibrous ring attached either directly or indirectly to the atrial or ventricular muscle fibers. Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. 
     Two primary types of heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a ball and cage arrangement or a pivoting mechanical closure to provide unidirectional blood flow. The other is a tissue-type or “bioprosthetic” valve which is constructed with natural-tissue valve leaflets which function much like a natural human heart valve&#39;s, imitating the natural action of the flexible heart valve leaflets which form commissures to seal against each other to ensure the one-way blood flow. In tissue valves, a whole xenograft valve (e.g., porcine) or a plurality of xenograft leaflets (e.g., bovine pericardium) provide occluding surfaces that are mounted within a surrounding stent structure. In both types of prosthetic valves, a biocompatible cloth-covered sewing or suture ring is provided on the valve body, for the mechanical type of prosthetic valve, or on the inflow end of the stent for the tissue-type of prosthetic valve. 
     In placing a tissue type prosthetic valve in the mitral position, the commissure posts are on the blind side of the valve and may become entangled with pre-installed sutures, and may damage the annulus or tissue during delivery. The difficulty of the delivery task is compounded if the surgery is through a minimally-invasive access channel, a technique that is becoming more common. The problem of entanglement is termed “suture looping,” and means that the suture that is used to attach or mount the valve to the heart tissue is inadvertently wrapped around the inside of one or more of the commissure post tips. If this occurs, the looped suture may damage one of the tissue leaflets when tightly tied down, or at least may interfere with valve operation and prevent maximum coaptation of the valve leaflets, resulting in a deficiency in the prosthetic mitral valve. 
     Some attempts have been made to overcome these problems in current holders for prosthetic mitral valves. An example of such a holder is U.S. Pat. No. 4,865,600, Carpentier, et al., incorporated herein by reference. Carpentier provides a holder having a constriction mechanism that constricts the commissure posts inwardly prior to implantation. The Carpentier device provides an elongate handle to both hold the valve/valve holder combination during implantation, as well as to cause the commissure posts to constrict inwardly. The valve is connected to the valve holder by the manufacturer using one or more sutures, and the combination shipped and stored as a unit. During the valve replacement procedure, the surgeon connects the handle to the holder and locks a locking nut to hold the commissure posts at a given constricted position. The surgeon then attaches the sewing ring of the valve to the native valve annulus with an array of sutures that has been pre-embedded in the annulus and extended outside the body. The valve is then advanced along the array of sutures to its desired implantation position and the sutures tied off. When the holder is cut free, the commissure posts are released to expand and the holder may be removed using the handle. The inability to remove the elongate handle while maintaining commissure constriction is a detriment. The handle must be attached to the holder so that the commissure posts remain in a constricted position during attachment of the array of sutures to the sewing ring. This can be awkward for manipulation of the valve/valve holder combination during this time-constrained operation. Further, the relatively wide holder periphery may interfere with the attachment step. 
     What is needed then is an improved tissue-type prosthetic valve holder attachable to the inflow end of the valve that can constrict the commissure posts with or without a handle being attached, yet provides improved visibility and accessibility to the surgeon during the valve attachment steps. 
     SUMMARY OF THE INVENTION 
     The present invention provides a holder for a tissue-type prosthetic heart valve having an inflow end and an outflow end and a flow axis therebetween. The valve includes an annular suture ring at the inflow end attached to a stent having posts circumferentially-spaced about the flow axis that support occluding tissue surfaces of the valve. In this type of valve the posts are cantilevered generally in the outflow direction. 
     The holder includes a valve abutment portion sized and shaped to abut the suture ring at the inflow end of the valve. The holder further includes a commissure post constriction mechanism adapted to constrict the commissure posts radially inward from a relaxed position to a constricted position when actuated by a handle adapted to operatively connect to the commissure post constriction mechanism. A retaining mechanism is also provided that retains the commissure post constriction mechanism in the constricted position after the handle is removed. 
     In one embodiment the commissure post constriction mechanism comprises an adjusting portion and an adjusting member adapted to adjust the distance between the adjusting portion and the valve abutment portion and one or more filaments attached to the adjusting portion and sutured through the end of the commissure posts distal the adjusting portion. When the adjusting member is operated to separate the adjusting portion from the valve abutment portion the adjusting portion pulls the filaments, which in turn urge the end of the commissure posts distal the adjusting portion radially inwardly, to the constricted position. 
     The valve abutment portion may be of a planar shape, with the adjusting portion of a substantially complementary planar shape to the valve abutment portion. It is preferred that the planar shape of the valve abutment portion be comprised of a plurality of tangs radiating from a central body to each cover a portion of the suture ring. In this manner a sufficient amount of the suture ring is left exposed to allow for suturing the suture ring to the native annulus. 
     Adjustment of the distance between the valve abutment portion and the adjusting portion may be achieved by providing a central threaded aperture in the adjusting portion and an adjusting member that cooperates with this threaded aperture. In this construction the end of the adjusting member proximal the valve abutment portion abuts the valve abutment portion during operation. When the adjusting member is advanced through the central aperture of the adjusting portion it pushes the valve abutment portion and the two portions separate. 
     A handle may be operatively connected to the adjusting member to turn it by providing a handle that has an externally threaded end portion and an adjusting member having a central longitudinal threaded bore sized to receive the threaded end of the handle. When the handle is introduced into the bore it is rotated in a first direction and will seat in the threaded bore of the adjusting member. Further rotation of the adjusting member separates the adjusting portion from the valve abutment portion, as recited above, and causes the commissure posts to constrict inwardly. 
     In the prior art the handle would have to remain attached during suturing of the suture ring to the host tissue to keep the commissure posts in the constricted position. The holder with the handle connected were removed by severing the filament(s). and removing the holder, handle and filaments together. 
     In accordance with the present invention, the adjusting member itself may be adapted to be the retaining mechanism. Preferably, the adjusting member threads create a greater frictional resistance with the threaded aperture of the adjusting portion than that between the threaded end of the handle and the threaded bore of the adjusting member. This frictional resistance between the adjusting member and the central aperture allows the handle to be further rotated in a second, opposite direction, and the handle will detach or unscrew from the adjusting member without moving the adjusting member, leaving the commissure posts in the constricted position. The tug of the filaments themselves on the adjusting portion when the commissure posts will cause the adjusting member/central aperture thread interface to bind and so may be used to achieve the requisite additional frictional resistance required for allowing the handle to be unscrewed. 
     In alternative embodiments other mechanisms may be used in accordance with the invention to act as the retaining mechanism. For example, a ratchet assembly may be provided to lock the valve attachment and adjusting portions apart, allowing the handle to be removed while leaving the commissure posts in the constricted position. A ratchet assembly may be comprised of a one or more toothed members affixed to the valve abutment portion that each engage a complementary notch, opening or, for example, a pawl affixed to the adjusting portion. As the valve abutment portion and the adjusting portion are separated by the adjusting member the successive teeth of the toothed member engage the notch, opening or pawl affixed to the adjusting portion, locking the two portions apart. 
     The present invention further provides a method for retrofitting a holder for a tissue-type prosthetic mitral heart valve attachable to a surgical delivery handle. The heart valve is of the type having an inflow end and an outflow end and a flow axis therebetween, and includes an annular suture ring at the inflow end and radially flexible commissure posts circumferentially-spaced around the outflow end that support occluding tissue surfaces of the valve. The holder has a commissure post constriction mechanism releasably attached to the sewing ring at the inflow end of the valve, the mechanism adapted to constrict the valve commissure posts radially inward from a relaxed position to a constricted position when actuated by the delivery handle. The method includes providing a retaining mechanism that retains the commissure post constriction mechanism in the constricted position after the delivery handle is removed. The retaining mechanism may be provided during the holder assembly process so that the retaining mechanism is attached to and shipped as a unit with the prosthetic valve. Alternatively, the retaining mechanism may be provided separately from the holder and valve combination and the method includes coupling the retaining mechanism to the holder at the time of surgical implantation of the valve. The retaining mechanism and delivery handle may be packaged and sold as a unit. The retaining mechanism desirably comprises an adapter that is interposed between and threadingly engaged to the holder and the handle. 
     Further in accordance with the invention a method for replacing a heart valve is provided, comprising the steps of removing an existing heart valve to leave an annulus of that heart valve, attaching a holder of the invention to a prosthetic tissue-type heart valve and constricting the commissure posts of the prosthetic heart valve with a handle; inserting the valve through the annulus of the heart valve; removing the handle while leaving the commissure posts in the constricted position; suturing the tissue-type heart valve to the heart annulus, and detaching the holder from the prosthetic heart valve. 
     After suturing the heart valve to the annulus the surgeon severs the filament, causing the posts of the stent to open to the relaxed, operational position. The severing of the filament(s) also releases the holder from the prosthetic heart valve, allowing it to be removed. 
     A further understanding of the nature and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a heart valve holder of the present invention assembled to the inflow side of a tissue-type heart valve; 
     FIG. 2 is a perspective view of the holder/heart valve assembly, showing an actuating and delivery handle attached to the holder; 
     FIG. 3 is a perspective view of the holder/heart valve assembly showing an adjusting portion retracted to cause inward movement of the valve commissure posts; 
     FIG. 4 is a perspective view of the valve holder of the present invention exploded from a tissue-type heart valve; 
     FIG. 5A is a plan view of an adjusting portion of the holder of the present invention; 
     FIG. 5B is a sectional view through the adjusting portion of the holder, take along line  5 B— 5 B of FIG. 5A; 
     FIGS. 6A and 6B are partial sectional views of the holder of the present invention attached to a heart valve wherein the commissure posts of the valve are, respectively, relaxed and biased inwardly; 
     FIGS. 7A-7C illustrates several steps in the implantation of a tissue-type valve in the mitral position using the holder of the present invention; 
     FIGS. 8A and 8B are partial sectional views of an alternative holder of the present invention attached to a heart valve wherein the commissure posts of the valve are, respectively, relaxed and biased inwardly; 
     FIG. 9A is a perspective view of an exemplary storage and handling clip that attaches to a holder of the present invention; 
     FIGS. 9B-9F are various views of the handling clip of FIG. 9A; 
     FIG. 10 is a perspective view of the handling clip attached to a holder and valve combination and placed within a storage container shown in phantom; 
     FIG. 11A is a plan view of a heart valve holder of the prior art attached to a heart valve and delivery handle during a step of implantation into a valve annulus; 
     FIG. 11B is a plan view of a heart valve holder of the present invention attached to a heart valve and delivery handle during a step of implantation into a valve annulus; 
     FIG. 12A is an exploded perspective view of a valve, holder, handle and adapter combination of the present invention; 
     FIGS. 12B-12C are perspective assembled views of the combination of FIG. 12A showing two steps of operation thereof to constrict commissures of the heart valve; 
     FIGS. 13A-13C are sectional views of the holder, handle, and adapter combination of FIG. 12 showing several steps of operation; 
     FIGS. 14A-14C are several views of an alternative adapter for use with a valve holder of the present invention; 
     FIG. 15 is a partial elevational view of the interaction between a pawl on the adapter of FIG. 14 and a raised feature on a valve holder to ensure positive engagement therebetween; and 
     FIGS. 16A-16F are several sectional views of a portion of an alternative holder of the present invention showing a further apparatus for maintaining commissure constriction. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides an improved heart valve holder for tissue-type prosthetic heart valves that facilitates implantation and reduces the chance of suture entanglement. The holder of the present invention is particularly useful for prosthetic mitral heart valves having commissure posts on the outflow side supporting flexible leaflets therebetween. The mitral position is such that the outflow side (and commissure posts) projects distally toward the left ventricle during implantation, and thus the holder must be attached to the inflow (i.e., accessible) side of the valve. Delivery of the valve to the mitral position involves sliding the valve down a plurality of sutures that have been pre-installed around the annulus and then passed through the valve sewing ring. The holder of the present invention constricts the commissure posts radially inward and thus helps prevent the posts from becoming entangled in the array of pre-installed sutures. This benefit is thus particular to the situation where the outflow side (and commissure posts) of the heart valve extends distally during delivery, which is the case in the mitral position. Nonetheless, the holder of the present invention may prove useful for the implantation of heart valves in other than the mitral position, and thus the invention may be applicable thereto. 
     With reference now to FIGS. 1-3 an exemplary holder  20  of the present invention is shown attached to a tissue-type heart valve  22 . The heart valve  22  includes an annular sewing ring  24  on an inflow side, and a plurality of commissure posts  26  projecting generally axially in the outflow direction. The holder  20  attaches to the sewing ring  24  on the inflow side of the valve  22 , which also is the proximal (i.e., accessible) side during implantation. That is, commissure posts  26  project distally toward the outflow side of the valve  22 . 
     FIGS. 2 and 3 illustrate a plurality of flexible leaflets  28  that are supported by and extend between the commissure posts  26 . The leaflets  28  provide the occluding surfaces of the valve  22 , and may be made of individual pieces of bovine pericardium, for example. Alternatively, the leaflets  28  may be part of an entire xenograft, or homograft. In the former instance, natural porcine (pig) valves are particularly useful. Therefore it should be understood that the leaflets  28  may be formed of a variety of materials, none of which is limiting with respect to the present invention. In addition, there are preferably three such leaflets  28  corresponding to three commissure posts  26 . 
     Various constructions for the heart valve  22  are known, which may include metallic or plastic stent elements, a silicone or urethane insert for the sewing ring  24 , biocompatible fabric (i.e., polyester) covering around one or more of the elements, etc. In a preferred embodiment, the heart valve  22  includes an internal metallic wireform (not shown) having an undulating shape with a plurality of arcuate cusps connected by upstanding commissures. The wireform commissures provide internal structure for the commissure posts  26  of the valve, and are somewhat flexible so as to be able to flex or cantilever inward. The holder  20  of the present invention facilitates this flexing, though the invention is generally directed toward causing the inward movement of the commissure posts. Of course, other internal constructions of heart valve  22  having movable commissure posts are available, with which the holder  20  of the present invention may function equally as well. 
     With reference still to FIGS. 1-3, and also FIG. 4, the holder  20  of the present invention includes three relatively movable elements. A plate-like valve abutment portion  40  lies against the inflow side  32  of the sewing ring  24 , and includes a plurality of through holes  42  around its periphery. A plate-like commissure adjusting portion  44  generally mirrors the shape of the valve abutment portion  40 , and also includes a plurality of peripheral through holes  46 . The adjusting portion  44  further includes a centrally located and internally threaded boss  48  that projects in a proximal direction from the otherwise generally planar adjusting portion. Finally, an adjusting member  50  having external threads  52  thereon is sized to mate with the internal threads  54  of the boss  48   
     A plurality of filaments or sutures  60  are shown in FIGS. 1-3 partly extending between the tips  62  of the commissure posts  26 . Because there are three commissure posts  26 , there are at least three lengths of sutures  60  extending therebetween in a triangular configuration. Each length of suture  60  spans two of the commissure posts  26 , and threads proximally along the post and through the sewing ring  24  to be attached to the holder  20 . This is seen best in the perspective view of FIG.  1 . Specifically, each suture  60  passes through the holes  42  in the valve abutment portion  40  and attaches to the adjusting portion  44 . The specifics of the attachment of each suture  60  will be explained below. 
     As mentioned, the abutment portion  40 , adjusting portion  44 , and adjusting member  50  are relatively movable. That is, the adjusting portion  50  is adapted to cause relative axial displacement between the abutment portion  40  and the adjusting portion  44 . Because the abutment portion  40  remains against the sewing ring  24 , the adjusting portion  44  translates proximally away from the abutment portion, and attached valve  22 . This is seen in FIG.  3 . Because the sutures  60  attach to the adjusting portion  44 , they are also pulled in the proximal direction. Moreover, because each suture  60  threads in a distal direction along and between two of the commissure posts  26 , proximal movement of the adjusting portion  44  thus shortens the amount of each suture between the commissure post tips  62 . This shortening causes radially inward movement of the tips  62 , with the commissure posts  26  eventually flexing inward from their structural point of attachment within the valve  22  adjacent the sewing ring  24 . 
     Now with reference to FIGS.  4  and  5 A- 5 B, structural details of the holder  20  of the present invention will be explained. As mentioned above, the valve abutment portion  40  is generally plate-like, and preferably includes a central, generally triangular body  70  having three outwardly extending tangs  72  at the apices thereof Two through holes  42  are providing in each of the tangs  72 , spaced apart along an imaginary circle centered in the triangular body  70 . Three upstanding pins or legs  74  having hooks  76  project from the proximal face of the body  70 , preferably inward and between each two tangs  72 . 
     The adjusting portion  44 , as best seen in FIG. 5A, also includes a generally triangular plate-like body  80  that is sized similar to the body  70  of the abutment portion  40 . In this regard, the adjusting portion  44  includes a plurality of channels  82  on the face opposite the valve abutment portion  40  that received the hooks  76  of the upstanding legs  74  such that the plate-like bodies  70  and  80  can be juxtaposed against one another, though their separation distance is limited. The hooks  76  thus effectively prevent disengagement of the attaching portion  44  and the abutment portion  40  once the two are coupled together. The adjusting portion  44  also includes three outwardly extending tangs  84  at the apices of the triangular body  80 . Like the abutment portion  40 , two through holes  46  are provided on each of the tangs  84 , and are spaced apart along an imaginary circle centered in the body  80 . Preferably, each through hole  46  in the adjusting portion  44  aligns with a through hole  42  in the valve abutment portion  40  when the holder  20  is assembled. 
     Each tang  84  features a suture cutting guide  86  that projects from the proximal face of the body  80 . Each cutting guide  86  includes a central cutting recess  88  defined between a pair of suture grooves  90 . A cutting recess  88  extends generally radially, while the suture grooves  90  are angled with respect thereto. The depth of the suture grooves  90  is less than the depth of the cutting recess  88 , as seen in FIG. 5B, and thus a length of suture  60  can be strung between the grooves  90  so as to be suspended over the cutting recess  88 . As seen in FIG. 5A, the suture grooves  90  lead into both of the through holes  46  on either side of the cutting guide  86 , such that each suture bridges the cutting recess  88  and may be bent to be secured to or pass through one of the through holes  46 . The specific arrangement of the sutures  60  will be more fully described below. 
     With reference still to FIG. 5A, the adjusting portion  44  further includes means for receiving clips on a removable transport template that secures the holder  20  and heart valve  22  assembly within a storage jar during transportation. Specifically, three clip-receiving notches  100  are equidistantly spaced around the periphery of the body  80 . In the illustrated embodiment, the notches  100  are disposed in a counter-clockwise direction adjacent each of the tangs  84  (as seen from the proximal face). Each of the notches  100  is spaced from the center of the body  80  a radial distance  102 , as indicated. As seen in the left of FIG. 5A, progressively larger holders will have progressively larger tangs  84   a ,  84   b ,  84   c  so as to enable attachment to larger valve sizes. Advantageously, the notch distance  102  remains constant for all the various sizes of the holder  20  to provide a one-size-fits-all template attachment means. That is, the same size of storage template can be used for a set of different sizes of holders. This arrangement also reduces the radial profile of the holders for larger sized valves, as the dimension of the template notches with respect to the overall perimeter is progressively reduced. This size reduction further helps to prevent snags as the holder and valve are delivered to the implantation site. 
     With reference again to the perspective views of FIGS. 1-3, the arrangement of the discrete lengths of sutures  60  will now be described. There are desirably three equal lengths of sutures  60 , each being secured at its free end to the adjusting portion  44 . Each length of suture  60  attaches to a first tang  84  of the adjusting portion  44 , passes through the aligned holes  46  and  42  (in a first tang of the abutment portion  40 ) and through the sewing ring  24  to a first commissure post  26 . From there, the suture  60  continues axially to the tip  62  of the post  26 , and extends across the outflow side of the valve  22  to the tip of a second commissure post  26 . The suture then passes proximally along the second commissure post  26 , again through sewing ring  24 , and through aligned holes  42  and  46  in second tangs  72 ,  84 , respectively, of the abutment portion  40  and adjusting portion  44 . It should be noted that each of the commissure posts  26  desirably has a fabric covering, and the sutures  60  pass at least once through the fabric covering at the tip  62  of each post. 
     At one of its free ends, the suture  60  passes between the suture grooves  90  within one of the cutting grooves  86 . Each length of suture  60  is secured at both ends to different through holes  46  in the adjusting portion  44 . Additionally, each two adjacent lengths of suture  60  are secured to the same through hole  46 . That is, as seen in FIG. 1, two lengths of suture,  60   a  and  60   b , are seen extending along the closest commissure post  26  to the adjusting portion  44 . The first length  60   a  passes through the left through hole  46   b , over the cutting guide  86 , and is secured to the right through hole  46   b . The second length  60   b  is secured to the right through hole  46   b  and passes distally through sewing ring  24  to the commissure post  26 . The second length  60   b  does not cross the cutting guide  86 , but instead continues to the next commissure post  26  before extending proximally to the holder  20  and over its associated cutting guide  86 . In this manner, the lengths of sutures  60  can be completely disengaged from the valve  22  by simply making three scalpel cuts in each of the three cutting guides  86 . 
     The holder  20  of the present invention works in conjunction with a delivery handle  110 , as seen in FIGS. 2 and 4. As seen in FIG. 4, the handle  110  includes a shaft  112  terminating in a distal externally threaded rod  114 . The adjusting member  50  is tubular and includes internal threads  116  that are sized and configured to receive the threaded rod  114 . In addition, as mentioned above, the adjusting member  50  is externally threaded so as to mate with internal threads  54  on the boss  48  of the adjusting portion  44 . By coupling the adjusting member  50  to the boss  48 , and then the handle  110  to the adjusting member, the handle  110  connects to the holder  20 . 
     With reference to FIGS. 6A and 6B, use of the holder  20  to radially constrict the commissure posts  26  is shown. Specifically, FIG. 6A illustrates the holder  20  assembled to the heart valve  22  using the aforementioned lengths of suture  60 . In its relaxed configuration, the adjusting portion  44  lies flush against the abutment portion  42 . In this state, the adjusting member  50  is threaded part way into the boss  48  such that a distal end contacts the cavity  78  in the abutment portion  40 , but can be further advanced a distance A, as indicated. The handle  110  is shown also part way engaged with the adjusting member  50 , with the threaded rod  114  still partly showing. 
     Now with reference to FIG. 6B, the handle  110  has been completely screwed into the adjusting member  50 , at which point further rotation of handle  110  causes relative rotation between the adjusting member  50  and the adjusting portion  44 . In other words, actuation of the handle  110  causes relative axial movement between the adjusting member  50  and adjusting portion  44 . This axial movement is caused by advancement of the adjusting member  50  within the boss  48 , which causes the distal end of the adjusting member to push against the abutment member  42 . Because the adjusting member  50  is thus prevented from relative movement with respect to the abutment member  42 , further advancement of the adjusting member causes the adjusting portion  44  to displace away from the abutment portion  42 , as indicated by the arrows  120 . The adjusting portion  44  rides upward along the adjusting member  50  until it contacts a proximal shoulder  122 , with the resulting spacing B between the adjusting portion  44  and abutment portion  42 . Because of the attachment of the lengths of suture  60  to the adjusting portion  44 , relative movement of the adjusting portion with respect to the abutment portion  42  pulls each length of suture out of the valve  22 . This, in turn, causes inward radial contraction of the commissure posts  26 , as indicated by the arrows  124 . 
     In a preferred embodiment, the frictional resistance to rotation between the adjusting member  50  and the adjusting portion  44  is greater than the frictional resistance to rotation between the handle  110  and the adjusting member  50 . Consequently, once the commissure posts  26  have been radially constricted, as indicated in FIG. 6B, the handle  110  can be removed (unscrewed) from within the adjusting member  50  without causing relative rotation between the adjusting member and the adjusting portion  44 . Therefore, the holder  20  maintains the radially constricted configuration of the commissure posts  26 . This inequality in frictional rotation can be obtained in a number of ways. For example, the threaded rod  114  and associated internal threads  116  of the adjusting member  50  have a smaller diameter than the external threads  52  and associated internal threads  54  of the boss  48 . Simply by virtue of this size relationship, and corresponding lower surface area in contact, less resistance to rotation of the threaded connection between handle  110  and adjusting member  50  is obtained, all else being equal. 
     To insure the handle  110  can be removed without reversing the adjusting member  50  with respect to the adjusting portion  44 , however, the materials are chosen to enhance the inequality in frictional resistance, as mentioned above. That is, the materials of the adjusting member  50  and adjusting portion  44  are chosen so as to have a greater frictional resistance to relative sliding movement than between the materials of the handle  10  and adjusting member  50 . In one embodiment, the adjusting member  50  and adjusting portion  44  are made of the same or different polymers, while handle  110  is metal. Resistance to relative sliding movement between metal and polymer is generally less than that between two polymers. In a preferred embodiment, both the adjusting member  50  and adjusting portion  44  are made of DELRIN, while handle  110  is made a stainless-steel. 
     FIGS. 7A-7C illustrate several steps in the use of the valve holder  20  the present mentioned. FIG. 7A illustrates a portion of the heart H in cross-section, and specifically the left ventricle LV into which the mitral annulus MA opens. A plurality of sutures  130  is shown pre-installed within the mitral annulus MA. In a typical procedure, the sutures  130  are brought outside the body and passed through the sewing ring  24  of the prosthetic valve  22 . The handle  110  attaches to the holder  20  of the present invention which in turn is coupled to the valve  22  and operably engaged therewith to radially constrict the commissure posts  26 . During delivery of the valve  22 , this radial constriction of the commissure posts  26  helps prevent entangled of the posts with the array of pre-installed sutures  130 . Indeed, the access passageway to the mitral annulus MA can be somewhat narrow and nonlinear, making the possibility of suture entanglement problematic. However, radial constriction of the commissure posts  26 , in conjunction with the barrier provided by the triangular suspension of sutures  60  between the commissure posts, greatly reduces the chance of entanglement. Moreover, the sutures  130  are entirely prevented by the triangular suspension of sutures  60  from contacting the valve leaflets  28 . Not only does the radial constriction of the commissure posts  26  reduce the chance of suture entanglement, but it also reduces the chance of contacting one of the posts with the surrounding anatomy. 
     After all the sutures  130  have been pre-installed in the mitral annulus MA and threaded through the sewing ring  24 , the valve  22  is lowered along the plurality of sutures  130  so that the sewing ring  24  contacts and lies flush against the mitral annulus MA, as seen in FIG.  7 B. At this stage, the handle  110  is removed from the holder  20  to facilitate tying off of each of the sutures  130  to secure the valve  22  against the mitral annulus MA. Again, removal of the handle  110  is facilitated by the small frictional resistance to rotation between the handle and holder  20 , relative to that between the actuating portions of the holder. 
     Finally, after securing the valve  22  within the mitral annulus MA, each of the lengths of suture  60  is severed at the cutting guides  86  to facilitate removal of the holder  20  from the valve  22 . FIG. 7C shows the severed free ends of the points of suture  60  being pulled from within the valve  22 . The holder  20  can be removed using forceps, or handle  110  may be reattached to facilitate the removal. 
     The present invention contemplates a number of different structures that cause constriction of tissue-type valve commissure posts using a handle, while also permitting removal of the handle without releasing the commissure posts. FIGS. 8A and 8B illustrate a second embodiment of a holder  150  that utilizes a ratchet methodology. Without going into great detail concerning elements of the holder  150  that are similar to those described above, the alternative holder relies on one or more toothed or ratchet members  152  extending proximally from the abutment portion  40  to engage complementary opening(s) in the adjusting portion  44 . As the adjusting portion  44  is displaced away from the abutment portion  42 , ratchet members  152  retain that spacing, as indicated FIG.  8 B. In this way, the relative frictional rotation between handle  110 , adjusting portion  44 , and adjusting member  50  is not important. Indeed, the handle  110  and adjusting member  50  can be formed as one-piece, rather than two as shown. 
     Now with reference to FIGS. 9A-9F and  10 , use of a clip  160  as mentioned above to attach to holders  20  of the present invention during shipping and storage of an attached valve is illustrated. As illustrated, each clip  160  includes a generally planar C-shaped disk portion  162  having a semi-circular handle  164  attached thereto. The clip  160  is desirably molded of a suitable polymer, with the handle  164  being formed by a semi-circular strip pivotable with respect to the disk portion  162 , with its ends attached by living hinges  165  to a pair of upstanding bosses  166 . In this respect, the handle  164  lies generally parallel to the plane of the disk portion  162  until pulled upward by the user. 
     Three fingers  168  depend downwardly from the disk portion  162  in the direction opposite the direction that the handle  164  may be lifted. Each finger  168  includes an inwardly directed pawl  170  sized to couple with a holder  20  of the present invention. More specifically, the three fingers  168  are circumferentially spaced 120° around a common axis of the holder  20  and clip  160  so as to engage the peripheral notches  100  on the adjusting portion  44  of the holder. As mentioned previously, the peripheral notches  100  for different sized valve holders are radially spaced a consistent distance from the axis. Therefore, the same size clip  160  may be used to couple to a plurality of holders for different sized valves, thus reducing the inventory of clips required. After coupling the clip  160  to the holder  20  (or adjusting member  50 ), the handle  164  may be used to lower the valve  22  into a storage and shipping container  172 , as seen in FIG.  10 . The periphery of the disk portion  162  is sized to closely fit within the container  172 , and thus prevents the valve from movement in the container during shipping. 
     The mitral valve holder  20  of the present invention provides an additional advantage over earlier mitral valve holders, such as the holder shown in U.S. Pat. No. 4,865,600 to Carpentier, et al. Specifically, prior holders such as that shown in the Carpentier patent were relatively wide in dimension so as to unnecessarily interfere with attachment of the sutures to the valve and the valve to the annulus. 
     The holder shown in the Carpentier patent, for example, includes a disk-shaped outer holder plate to which a delivery handle attaches. FIG. 11A illustrates a prior art holder  180  attached to the inflow end of a mitral valve during delivery of the valve into position in an annulus  182 . Various means are known for obtaining access to the annulus  22 , such as by using a pair of retractors  184  as illustrated to pull surrounding tissue away from surgical field. The outer disk-shaped plate  186  of the holder  180  may be seen occluding all of the mitral valve except for an outer peripheral portion  188  of the sewing ring. A plurality of sutures  190  is shown extending out of the surgical field through the sewing ring  188 . These sutures  190  were previously embedded in the annulus  182 , and threaded through the sewing ring  188  at a location outside the patient. Though accomplished more conveniently outside the patient, this pre-threading operation must be done after the surgical site has been exposed, and thus time is of the essence. To prevent perivalvular leakage, the array of sutures must be relatively evenly circumferentially spaced and located along a radial line, and this delicate operation may be impeded by the relatively large sized holder body  186 , and attendant reduced sewing ring visibility. 
     After the pre-threading is complete, the surgeon connects a handle  192  to the holder  180  and slides the valve and holder combination down the array of sutures  190  into position in the annulus  182 . Because the disk-shaped outer plate  186  is so large, as seen in FIG. 11A, the surgeon cannot see the leaflets from the inflow side of the valve. Problems sometimes arise when the forwardly directed commissures of the valve become entangled in one or more of the sutures in the array. Such entanglement may be visible through the inflow end of the valve, but as mentioned, that view is blocked by the outer plate  186 . 
     The present invention provides a holder permitting greater visibility of the valve to help alleviate the aforementioned problems associated with the time-critical processes of pre-threading and then sliding the valve and holder into place. FIG. 11B illustrates the holder  20  of the present invention attached to the inflow end of a prosthetic valve having a peripheral sewing ring  200 . The holder  20  is as described above, and like reference numerals for the various elements will be used. Namely, the holder  20  has the approximately triangular-shaped body  80  of the adjusting portion  44  with three outwardly extending tangs  84  at the triangle apices. The tangs  84  feature a pair of through holes  46  through which sutures (not shown for clarity) pass to attach the adjusting portion  44  to the sewing ring  200  of the valve. 
     The body  80  includes three generally linear sides  202  extending between the tangs  84  (although each side is interrupted by the aforementioned clip-receiving notches  100 ). The sides  202  separate from and expose the surrounding portions of the sewing ring  200 . Indeed, the sides  202  expose the inner volume of the valve, such that leaflets  204  of the valve can be seen from the inflow end thereof. It will therefore be appreciated that the task of pre-threading the array of sutures around the sewing ring  200  is facilitated by the increased visibility of the sewing ring provided by the triangular-shaped holder  20 . More specifically, the surgeon can pre-thread the array of sutures around the sewing ring  200  with greater confidence that no sutures are placed too far radially inward or outward, and that they are evenly circumferentially spaced. At a minimum, the time needed to complete this task is reduced. Furthermore, as the valve is introduced to the surgical site along the array of sutures, the surgeon can inspect the leaflets  204  from the inflow side thus enhancing early detection of any suture looping or entanglement that will be visible from the inflow side in the form of a deformed leaflet. 
     The present invention may provide an improved valve holder as described above, or adapters as described below may be used to retrofit valve holders of the prior art. In particular, FIGS. 12A-12C and  13 A- 13 C illustrate several embodiments of an adapter system of the present invention for use with a prior art valve holder such as that shown in U.S. Pat. No. 4,865,600 to Carpentier, et al. FIG. 12A shows a tissue-type mitral heart valve  210  having a sewing ring  212 , a plurality of upstanding commissures  214  with distal tips  216 , and a plurality of tissue-type leaflets  218  forming the occluding surfaces of the valve. A conventional holder such as shown in Carpentier, et al. includes a lower plate  220  configured to abut and attach to the sewing ring  212 , and an upper plate  220  that works in conjunction with the lower plate  220  to pull the commissure tips  216  of the valve  210  inward. The lower plate  220  has a generally triangular body  224  having three outwardly projecting tangs  226  each with a pair of through holes  228 . 
     As seen in FIGS. 12B and 12C, three guide posts  230  on the lower plate  220  and three locking posts  232  having outwardly directed pawls  234  pass through and mate with apertures  236  evenly circumferentially spaced around a disk-shaped body  238  of the upper plate  222 . The upper plate  222  further includes three outwardly directed flanges  240  having through holes aligned with the through holes  228  in the lower plate  220 , and three cutting guides  242  projecting upward from the disk-shaped body  238 . In addition, a central internally threaded boss  244  is adapted to receive a delivery handle of the prior art, such as shown at  246  having a male threaded end  248 . 
     The present invention provides an adapter  250  to be interposed between the delivery handle  246  and internally threaded boss  244 , having a distal male threaded portion  252  and a proximal female threaded portion  254 . The distal male threaded portion  252  is configured to mate with the internally threaded boss  244 , while the proximal female threaded portion  254  receives the threaded end  248  of the handle  246 . 
     Use of the adapter  250  is seen best in FIGS. 13A-13C, and generally parallels the function of the adjusting member  50  previously described. As has been described previously, and in the earlier patent to Carpentier, et al., the lower plate  220  and upper plate  222  work in conjunction with the threaded delivery handle to pull the commissure tips  216  inward. FIG. 12C illustrates the two plates  220 ,  222  separated such that a plurality of sutures connected to the upper plate  222  and passing into the valve and between the commissures (seen at  260 ) are placed in tension causing the commissure tips  216  to be pulled inward in the direction of the arrows  262 . FIGS. 13A-13C illustrate the holder in cross-section and isolated from the valve to better illustrate this plate separation. In contrast to the present invention, in the prior art the delivery handle  246  had to remain threadingly engaged with the upper plate  222  to maintain the plate separation. 
     In contrast, the adapter  250  of the present invention permits the delivery handle  246  to be removed while maintaining plate separation. FIG. 13A shows the adapter  250  threadingly attached to the delivery handle  246 . The combination handle  246  and adapter  250  is then coupled to the upstanding boss  244  on the upper plate  222  and advanced so that a distal end  264  on the adapter contacts a central pin  266  on the lower plate  220 . Further advancement of the handle  246  and adapter  250  combination causes separation between the lower and upper plates  220 ,  222 . The separation may be limited by contact between the enlarged proximal portion  254  with the upstanding boss  244 , or by engagement of each of the three pawls  234  with corresponding features on the upper plate  222 , both shown in FIG.  13 B. Subsequently, the delivery handle  246  may be reversed from engagement with the adapter  250  and removed from the surgical site, as seen in FIGS. 12C and 13C. The adapter  250  remains in the position shown in FIG. 13C, maintaining the separation between the lower and upper plates  220 ,  222 , but not interfering with the implantation operation. 
     There are number of ways to ensure that the handle  246  may be retracted from engagement with the adapter  250  while leaving the adapter in place. For example, and as mentioned above in conjunction with the earlier embodiment, the coefficient of friction between the materials of the engaging threads can be such that the handle  246  can be easily removed. For example, the upper plate  222  is typically molded from a polymer such as Delrin, and the adapter  250  can be formed of a similar material to produce a relatively high coefficient of friction between the respective threads. At the same time, the handle  246  may be made of stainless-steel, for example, which produces a lower coefficient friction between the male threads  248  and the female threads of the proximal adapter portion  254 . If the adapter  250  is made a suitable polymer, such as the material of the holder, it may be coupled to the holder prior to packaging, shipping and storage. Many tissue-type heart valves are stored in a preservative solution, such as glutaraldehyde, and material of the holder and adapter  250  must be able to withstand long periods of immersion in such solutions. 
     Alternatively, the adapter  250  may also be made of stainless-steel, with the relative coefficients of friction being favorable for reversal and removal of the handle  246 . In this configuration, the adapter  250  may be sold as a separate article to be coupled with existing delivery handles to retrofit prior art systems. In this manner, both the handle  246  and adapter  250  are able to withstand the high temperatures of steam sterilization, and may be reused. 
     Another way to ensure that the adapter  250  remains coupled to the upper plate  222  while the handle  246  can be removed is to provide slightly dissimilar thread patterns on the adapter and female threads of the upper plate boss  244 . As the handle  246  and adapter  250  are threadingly engaged to the boss  244 , the dissimilar threads tend to bind and lock the adapter to the upper plate  222 . Consequently, the handle  246  can be easily reversed and de-coupled from the adapter  250 . 
     A still further method of preventing the coupling of the adapter  250  and upper plate  222 , while permitting removal of the handle  246 , is to provide a groove, raise rib, or similar expedient on the adapter that engages with a mating feature on the upper plate. For example, although not shown, the lower surface of the proximal portion  254  may include a raised radially-directed rib that mates with a groove or similar rib on the upper surface of the boss  244 . After the two parts  250 ,  222  are threadingly engaged, as seen in FIG. 13B, the raised ribs interfere and prevent disengagement, at least to the extent of withstanding the torque applied upon removal of the handle  246  from engagement with the adapter  250 . 
     A still further configuration in accordance with the present invention is illustrated FIGS. 14A-14C and  15 . In this embodiment, an adapter  280  is provided that includes a distal male threaded portion  282 , a proximal female threaded portion  284  and a generally disk-shaped flange  286  interposed therebetween. The flange  286  includes at least one distally-directed tooth or pawl  288  close to a peripheral edge. The adapter  280  is shown in FIG. 14C in an orientation in which it may be coupled with a holder located below, and a handle located above. In particular, the handle will couple to the female threaded portion  284 , while the male threaded portion  282  couples with a boss on the holder and causes the aforementioned inward movement of the associated valve commissures. 
     FIG. 15 is a partial cutaway that shows engagement of the pawl  288  with an upstanding feature on the valve holder  290 , such as a cutting guide  292 . That is, rotation of the adapter  280  in the direction of arrow  294  causes the pawl  288  to cam up and over the cutting guide  292 . Because of the shape of the pawl  288 , the adapter  280  cannot be rotated in the opposite direction. Thus, the adapter  280  is maintained in its threading engagement with the holder, which maintains the aforementioned inward bias of the valve commissures, and permits removal of the handle. The positive engagement of the pawl  288  with the cutting guide  292  ensures that the adapter  280  cannot be removed from the holder once coupled thereto. The illustrated adapter  280  is representative of one type of adapter that can be used to retrofit existing valve holders. Specifically, the adapter  280  can be sold in combination with the valve holder, and be stored with the valve, or can be sold as a separate item to be coupled with handle at the time of surgery. 
     FIGS. 16A-16F illustrate portions of an alternative holder of the present invention having an alternative structure for maintaining valve commissure constriction. A segment of a valve abutment portion  300  is shown interacting with a segment of an adjusting portion  302 . The abutment portion  300  and adjusting portion  302  may in other respects be identical to those illustrated in FIGS.  4  and  5 A- 5 B. Indeed, the abutment portion  300  includes at least one upstanding leg  304  having a hook  306 , as described previously. In addition to the leg  304 , an upstanding gap retainer  308  is provided, preferably adjacent thereto. The gap retainer  308  includes a stop member  310  having a lower angled surface  312 . In preferred embodiment, there are two or more, preferably three, pairs of legs  304  and gap retainers  308 . Furthermore, although the leg  304  and gap retainer  308  are illustrated as separate elements, they may be incorporated into a single upstanding element or leg. 
     FIGS. 16A-16C illustrate a process of assembling the holder by insertion of the leg  304  and gap retainer  308  through an aperture  314  provided in the adjusting portion  302 . As seen, the leg  304  and gap retainer  308  are cantilevered and spaced apart so that they may be biased toward one another and fit through the aperture  314 . Both the hook  306  and stop member  310  are axially aligned so as to normally interfere with respective sides of the aperture  314 , and the leg  304  and gap retainer  308  must be bent to permit passage through the aperture  314 . 
     FIGS. 16D-16F illustrate operation of the holder. FIGS. 16D shows the relative positioning of the valve abutment portion  300  and adjusting portion  302  during storage and shipping of the bolder and attached valve. Prior to delivery of the valve along a surgical pathway, the valve abutment portion  300  and adjusting portion  302  are separated so as to constrict the valve commissures, as was described previously. This separation is desirably accomplished using a handle with or without an adapter. As the adjusting portion  302  moves relatively away from the abutment portion  300 , depicted in FIGS. 16E, the aperture  314  contacts the lower angled surface  312  of the stop member  310  and cams the cantilevered gap retainer  308  inward. Subsequently, the gap retainer  308  springs upright to its relaxed position, as seen in FIGS. 16F, such that the stop member  310  again interferes with and contacts the face of the adjusting portion  302  and prevents it from moving back toward the abutment portion  300 . In this manner, a simple and reliable mechanism for maintaining separation of the holder elements provides a positive stop and insurance against inadvertent commissure expansion. 
     It will be appreciated that the invention has been described hereabove with reference to certain examples or preferred embodiments as shown in the drawings. Various additions, deletions, changes and alterations may be made to the above-described embodiments and examples without departing from the intended spirit and scope of this invention. Accordingly, it is intended that all such additions, deletions, changes and alterations be included within the scope of the following claims.