Abstract:
In general, the present invention comprises an holding apparatus for facilitating implantation of a prosthetic heart valve within a mammalian heart. The holding apparatus generally comprises a cage or enclosure having a heart valve prosthesis retention space defined therewith. The proximal end of the holding apparatus is releasably attached to the proximal end of the heart valve prosthesis such that, when the holding apparatus is advanced in a forward direction, a “pulling” force will be exerted upon the proximal end of the prosthesis, rather than a “pushing” force being exerted upon the distal end of the prosthesis. The releasable attachment of the prosthesis to the holding apparatus may be accomplished by any suitable attachment member, and preferably comprises a number of suture threads which are passed through the prosthesis and threaded upon the holding apparatus at locations which are easily accessible such that the surgeon may cut the suture threads to effect release of the heart valve prosthesis, during the prosthesis implantation procedure. Also described and claimed are associated methods for utilizing the above-described holding apparatus to effect implantation of a prosthetic heart valve.

Description:
This is a Continuation, of application 8/723,420, filed Sep. 30, 1996, now U.S. Pat. No. 5,800,531. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices, and more particularly to an apparatus for facilitating the implantation of a stentless bioprosthetic, (e.g., xeno raft, homograft, allograft) heart valve, and associated methodology. 
     BACKGROUND OF THE INVENTION 
     Among the various types of prosthetic heart valves which have heretofore been known are certain “stentless” bioprosthetic valves. One example of a stentless bioprosthetic heart valve is described in U.S. Pat. No. 5,197,979 (Quintero, et. al.), the entire disclosure of which is hereby expressly incorporated by reference. 
     One such stentless bioprosthetic valve is commercially available as the Edwards® PRIMA™ stentless aortic bioprosthesis (Baxter Edwards AG, Spierstrasse 5, GH6048 Horn, Switzerland). This stentless aortic bioprosthesis generally comprises a chemically-tanned porcine aortic heart valve having an adjacent segment of aorta connected thereto. An inflow annulus is defined at the proximal end of the bioprosthesis and an outflow annulus is defined at the distal end thereof. The porcine coronary arteries are cut away from the aortic portion of the bioprosthesis, thereby forming coronary openings in the bioprosthesis. Woven polyester cloth is sewn around the inflow annulus of the bioprosthesis to facilitate suturing of the proximal end of the bioprosthesis to a surgically prepared endogenous aortic valve root of the recipient patient. Thereafter, in cases wherein the entire bioprosthesis is implanted the distal end of the bioprosthesis may be anastomosed to the patient&#39;s aorta, and the coronary openings of the bioprosthesis are aligned with, and sutured to, the patient&#39;s coronary ostia. 
     In an alternative implantation procedure, the surgeon may elect to trim or cut away the distal portion of the cylindrical prosthesis body (e.g., that portion above the valve leaflets), and to implant only the proximal portion of the bioprosthesis. In such modified “partial” implantation procedure, it is unnecessary for the surgeon to anastomose that distal end of the distal end of the bioprosthesis and/or the coronary openings to the patient&#39;s aorta because such distal portions of the bioprosthesis have been trimmed or cut away prior to its implantation. 
     The above-described stentless aortic bioprosthesis of U.S. Pat. No. 5,197,979 (Quintero, et al.) was provided with a holding fixture which was attached to the outflow (i.e., distal) end of the bioprosthesis. An elongate handle was connectable to the holding fixture. Such handle was intended to be grasped and manipulated by the surgeon to maneuver the stentless aortic bioprosthesis to its desired implantation position. Certain problems or shortcomings were, however, associated with this holding fixture attached to the outflow (i.e., distal) end of the bioprosthesis. First, the holding fixture was of a configuration which tended to substantially block the outflow end of the prosthetic valve root cylinder, thereby preventing the surgeon from visualizing the valve leaflets from a distal vantage point, during the implantation procedure. Second, because the holding fixture was attached only to the outflow (i.e., distal) end of the stentless bioprosthesis, the exertion of forward pressure against the holding fixture tended to cause the cylindrical body and/or leaflets of the stentless bioprosthesis to compressively deform or buckle, due to the pliable or flexible nature of such stentless bioprosthesis. Such buckling or deformation of the stentless bioprosthesis could be problematic if one were to attempt, in accordance with standard operative technique, to advance the stentless bioprosthesis over a series of pre-placed suture threads which have been passed through the inflow annulus at the inflow (i.e., proximal) end of the bioprosthesis. 
     In view of the above-described problems associated with the prior art holding fixtures used in conjunction with stentless bioprosthesis, it is desirable to develop an improved holding apparatus which is attachable to the inflow annulus located at the inflow (i.e., proximal) end of the bioprosthesis such that, when proximally directed pressure is exerted against the holding apparatus, such pressure will be transferred through the holding apparatus so as to effect a “pulling” action upon the inflow annulus at the inflow (i.e., proximal) end of the bioprosthesis, rather than a “pushing” action upon the outflow (i.e., distal) end of the bioprosthesis. Furthermore, it is desirable for such improved holding apparatus to be configured and constructed in a manner which does not substantially block the outflow opening at the outflow (i.e., distal) end of the bioprosthesis, thereby allowing the surgeon to clearly view and properly orient the valve leaflets and commissurae of the bioprosthesis during the implantation procedure. Also, it is desirable that the holding apparatus be constructed in a manner which firmly holds the stentless bioprosthesis during any trimming or cutting away of the distal portion of the bioprosthesis, as is sometimes done in the modified or partial implantation technique described hereabove. 
     SUMMARY OF THE INVENTION 
     In general, the present invention provides a prosthetic heart valve holding apparatus which comprises a cage or enclosure which substantially surrounds a prosthetic heart valve, and which is releasably attachable to the proximal end of the prosthetic heart valve. A handle may be attachable to the holding apparatus to facilitate advancement of the heart valve to its desired implantation site. Because the cage or enclosure of the holding apparatus is attached to the prosthetic heart valve at or near its proximal end, the exertion of forwardly directed advancement force upon the holding apparatus (e.g., by pushing on a handle attached to the holding apparatus) will be converted into a “pulling” force on the proximal portion of the prosthesis rather than a “pushing” force on the distal end thereof. 
     In accordance with the invention, the holding apparatus may generally comprise a) a distal hub member and b) a plurality of strut members which extend downwardly from said distal hub member at spaced-apart locations around. The downwardly extending strut members define a prosthetic heart valve receiving space beneath the distal hub member and inboard of the strut members. A bioprosthetic heart valve (e.g., a stentless bioprosthesis) having an annular sewing ring (e.g., a dacron mesh ring) at its proximal end is insertable within the receiving space such that the bottom ends of the strut members may be connected or attached to or immediately above the sewing ring, at the proximal end of the prosthesis. A handle may be formed upon, or may be attachable to, the distal hub member of the holding apparatus such that the handle extends upwardly therefrom. A surgeon may then grasp the handle, and may utilize the handle to advance the holding apparatus (with the heart valve prosthesis releasably mounted therewithin) to the intended implantation site. Because the holding apparatus is connected at or near the proximal (inflow) end of the prosthesis, the exertion of pushing force on the handle will cause a “pulling” force to be applied to the proximal (inflow) end of the prosthesis rather than exerting a “pushing” force against the distal (outflow) end of the prosthesis. In this manner, the holding apparatus allows the bioprosthesis to be advanced into position without compressively deforming or collapsing the prosthesis, and without any need for use of extraneous instruments (e.g., forceps) to grasp and pull the proximal (inflow) end of the bioprosthesis into place. After the proximal (inflow) end of the bioprosthesis has been positioned immediately adjacent the endogenous valve root or other intended site of implantation, sutures may be tied in place to affix the sewing ring at the proximal (inflow) end of the prosthesis to the endogenous valve root or other host tissue. Thereafter, the prosthesis is disconnected and detached from the holding apparatus, and the holding apparatus is extracted and removed thereby removing the bioprosthesis in its implanted position within the host body. 
     Further in accordance with the invention, a proximal ring member may be formed at the proximal end of the holding apparatus, and sutures or other releasable connections may be formed directly between the proximal ring member of the holding apparatus and the proximal (inflow) end of the prosthesis. In this manner, the proximal ring member formed on the holding apparatus will serve to rigidly maintain the proximal (inflow) end of the prosthesis in a rigidly fixed open configuration during placement of the sutures through the sewing ring of the prosthetic valve, and throughout the implantation procedure. The surgeon may then effectively suture the proximal mesh ring of the prosthesis (e.g, the portion which protrudes below the proximal ring member of the holding apparatus (to the body of the patient) while the proximal ring member of the holding apparatus holds the proximal (inflow) opening of the prosthesis in it&#39;s intended open configuration. Additionally, when the holding apparatus is being used in conjunction with a stentless aortic bioprosthesis or other aortic valve prosthesis of the type having openings which are intended to be sutured to the aortic tissue of the patient about the coronary ostia, it may be desirable to provide a proximal ring member on the holding apparatus which is transectable or severable into a plurality of segments. In this manner, the bioprosthesis may be sutured or otherwise affixed to the coronary ostia of the patent before detachment and removal of the holding apparatus is accomplished, and the gaps or openings which exist between separate segments of the inferior ring member may be utilized as passageways through which the sutured interconnection between the bioprosthesis and the coronary artery of the patient may pass. This will permit the holding apparatus to be extracted and removed from the patient even after the bioprosthesis has been securely sutured to the coronary ostia of the patient. The openings which are created by segmenting of the proximal ring member may be utilized as passageways through which the previously-created interconnections between the bioprosthesis and the body of the patient may pass. This allows the holding apparatus to be extracted and removed after the aortic bioprosthesis contained therewithin has been suture or otherwise affixed to the coronary ostia of the patient. 
     Still further in accordance with the invention, the holding apparatus operates to rigidly support and hold the proximal end of the bioprosthesis in a fully opened, non-disfigured condition during the implantation procedure. This aspect of the invention is particularly prominent in embodiments which incorporate the above-described proximal ring member which is literally attached fully around the proximal end of the bioprosthesis. By rigidly holding and supporting the bioprosthesis in its desired, open, non-disfigured condition the holding apparatus of the present invention serves to prevent the phenomenon of multiple plications during implantation of the stentless bioprosthesis. By rigidly supporting and holding the proximal end of the bioprosthesis, the holding apparatus allows the surgeon to apply pressure to the sewing ring portion of the bioprosthesis during passage of sutures and implantation of the bioprosthesis without forming unwanted folds, plications, indentations or invaginations in the bioprosthesis. This ensures that, when finally implanted, the bioprosthesis will be in its desired non-deformed configuration, thereby providing for optimal functionality of the bioprosthesis after implantation. 
     Still further in accordance with the invention, the holding apparatus may be releasably connected to the bioprosthesis contained therewithin by any suitable type of releasible connecting member, apparatus, or substance. For example, the bioprosthesis may be releasably connected to the holding apparatus by way of suture thread(s), clasp(s), clip(s), clamp(s), hook(s), strap(s), ligature(s), adhesive(s), magnet(s), etc. In the preferred embodiment described herebelow, suture threads are utilized to releasably attach the bioprosthesis to the holding apparatus. Such suture threads are passed through apertures or holes formed at various locations on the holding apparatus, and are stitched through the body of the bioprosthesis such that the proximal (inflow) end of the bioprosthesis is attached to the proximal end of the holding apparatus, and further such that several points adjacent the distal end of the bioprosthesis are also attached to adjacent distal locations on the holding apparatus. These suture threads are strung over adjacent locations on the holding apparatus, such adjacent locations being readably accessible during the implantation procedure to permit the surgeon to cut or sever the suture threads at such locations. Such cutting or severing of the suture threads serves to release the bioprosthesis from the holding apparatus, thereby allowing the holding apparatus to be extracted and removed. 
     Still further in accordance with the invention, the holding apparatus may incorporate one or more hinges or bendable regions which permit flexing or relaxation of the functional shape of the holding apparatus to facilitate its intended use, extraction and removal. 
     Still further in accordance with the invention, the holding apparatus may be constructed such that open areas are formed about the lateral sides of the bioprosthesis to permit the surgeon to optionally trim or cut away the distal portion of the bioprosthesis in cases wherein the surgeon has elected to perform a modified “partial” bioprosthesis implantation procedure. In this regard, suture threads or other markings may be formed on the bioprosthesis to mark a line above the distal-most location(s) of the valve leaflets so that the surgeon may safely cut away that portion of the bioprosthesis which extends above such suture threads or other markings, without damaging the valve leaflets and without impairing the hemodynamic valving capability of the bioprosthesis. 
     Still further in accordance with the present invention, the holding apparatus may comprise a hub member positionable adjacent the distal end of the prosthesis body, and a plurality of elongate strut members having proximal ends and distal ends which are attached to the hub members such that the strut members extend substantially downward therefrom so as to define a hollow prosthesis retention space inboard of the strut members and beneath the hub member. Disposed on the proximal end of the strut members is an attachment ring for maintaining the prosthesis within the retention space. The proximal inflow end of the prosthesis is releasably connected to the attachment ring to allow the holding apparatus to be selectively disengaged from the prosthesis. 
     The attachment ring itself preferably comprises an inner ring member which is attached to the proximal ends of the strut members, and an outer ring member which is releasably attached to the inner ring member. In this respect, a portion of the prosthesis is frictionally captured between the inner and outer ring members. The application of a force in a distal direction to the hub member subsequent to the detachment of the inner ring member from the outer ring member facilitates the distal movement of the inner ring member relative to the outer ring member, thereby resulting in the separation of the inner and outer ring members from each other and the release of the portion of the prosthesis from therebetween. 
     The inner and outer ring members of the attachment ring are releasably attached to each other by at least one suture thread extending therebetween. In this respect, the inner and outer ring members each include at least one pair of suture passage apertures formed therein, with the suture passage apertures of one pair being coaxially aligned with respective ones of the suture passage apertures of the other pair for allowing the suture thread to be extended between the inner and outer ring members. Additionally, the inner and outer ring members each preferably include at least one enlarged attachment region formed thereon, with each pair of suture passage apertures being formed within a respective attachment region. The attachment region formed on the inner ring member preferably includes a cutting instrument receiving notch formed therein which is sized and configured to permit a cutting instrument to be inserted thereinto for purposes of cutting the suture thread. 
     The inner ring member of the attachment ring defines a beveled outer surface portion, with the outer ring member defining a beveled inner surface portion having a configuration which is complementary to the outer surface portion of the inner ring member. In this respect, the portion of the prosthesis is frictionally captured between the outer and inner surface portions when the inner and outer ring members are releasably attached to each other. Additionally, the outer ring member of the attachment ring preferably includes at least one tab portion extending distally therefrom which is sized and configured to engage the inner ring member subsequent to the distal movement of the inner ring member relative to the outer ring member in an amount sufficient to release the portion of the prosthesis from therebetween. The outer ring member preferably includes three (3) pairs of tab portions extending distally therefrom, with the tab portions of each pair being disposed on either side of a respective one of the three (3) strut members of the holding apparatus when the inner and outer ring members are attached to each other. 
     Further aspects and advantages of the invention will become apparent to those skilled in the art upon reading and understanding of the detailed descriptions of preferred embodiments set forth herebelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative and presently preferred embodiments of the invention are shown in the accompanying drawings in which: 
     FIG. 1 is a perspective view of a first embodiment of a bioprosthetic aortic heart valve implantation system of the present invention; 
     FIG. 2 is a bottom plan view of the implantation system of FIG. 1; 
     FIG. 3 is an exploded perspective view of the implantation system of FIG. 1; 
     FIG. 4 is an enlarged perspective view of a portion of the implantation system of FIG. 1; 
     FIG. 5 a  is a perspective view of a bioprosthetic aortic heart valve implantation system and its packaging; 
     FIG. 5 b  is a perspective view of the system of FIG. 5 a  with a handle; 
     FIG. 5 c  is an enlarged perspective view of a retainer portion of the packaging of FIG. 5 a;    
     FIG. 5 d  is a perspective view of the implantation system of FIG. 5 a  being prepared for use; 
     FIG. 5 e  is a perspective view of removal of an identification tag of the implantation system of FIG. 5 a;    
     FIG. 5 f  is a perspective view of a preparation step for the implantation system of FIG. 5 a;    
     FIG. 5 g  is a perspective view of placed suture thread between the implantation system of FIG. 5 a  and an aortic root; 
     FIG. 5 h  is a perspective view similar to that of FIG. 5 g  except with the implantation system at the site of aortic root implantation; 
     FIG. 5 i  is an enlarged perspective view of a portion of the system of FIG. 5 a  showing a suture thread retainer with suture thread therein; 
     FIG. 5 j  is an enlarged elevation view along line  5   j — 5   j  of FIG. 5 i;  and 
     FIG. 5 k  is a perspective view of an implanted heart valve of the implantation system of FIG. 5 a  along with the holding apparatus thereof being withdrawn after valve prosthesis placement. 
     FIG. 6 a  is an exploded, perspective view of a second embodiment of the bioprosthetic aortic heart valve implantation system of the present invention. 
     FIG. 6 b  is an assembled perspective view of the second embodiment of the bioprosthetic heart valve implantation system of the present invention shown in FIG. 6 a.    
     FIG. 6 c  is an enlarged perspective showing of the upper end of one of the strut members of the apparatus of FIG. 6 a,  wherein a tab formed on the upper end of the strut member has been bent over to facilitate attachment of the strut member to the distal hub of the apparatus. 
     FIG. 7 is a perspective view of a third embodiment of a bioprosthetic aortic heart valve implantation system of the present invention. 
     FIG. 8 is an exploded, perspective view of the third embodiment of the bioprosthetic heart valve implantation system shown in FIG.  7 . 
     FIG. 9 a  is an enlarged, partial perspective view of the region  9   a  encircled in FIG.  7 . 
     FIG. 9 b  is a cross-sectional view taken along  9   b — 9   b  of FIG. 9 a,  showing the attachment ring of the implantation system as releasably attached to the bioprosthetic aortic heart valve. 
     FIG. 9 c  is a cross-sectional view similar to FIG. 9 b,  but showing the attachment ring of the implantation system as detached from the bioprosthetic aortic heart valve. 
     FIG. 10 a  is a cross-sectional view taken along line  10   a — 10   a  of FIG.  7 . 
     FIG. 10 b  is a cross-sectional view similar to FIG. 10 a,  but showing the attachment ring of the implantation system as detached from the bioprosthetic aortic heart valve. 
     FIG. 11 a  is a cross-sectional view taken along line  11   a — 11   a  of FIG.  7 . 
     FIG. 11 b  is a cross-sectional view similar to FIG. 11 a,  but showing the attachment ring of the implantation system as detached from the bioprosthetic aortic heart valve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The accompanying figures show three (3) different embodiments of the implantation system  10 ,  10   a,    10   b  of the present invention. The individual elements and aspects of these embodiments are independently combinable and interchangeable. However, it will generally be appreciated that the first embodiment shown in FIGS. 1-5 is routinely useable in procedures wherein the implantation system  10  of the present invention is detached and removed from the bioprosthetic heart valve before the body of the bioprosthesis is sutured to or otherwise connected to the coronary ostia of the patient. On the other hand, the second and third embodiments of the implantation system  10   a,    10   b  are primarily usable in procedures wherein the implantation system  10   a,    10   b  is permitted to remain attached to the bioprosthesis during the process of suturing or otherwise attaching the bioprosthesis to the coronary ostia, and thereafter, the implantation system  10   a,    10   b  is detached and removed from the patient without disrupting the previously-formed anastomosis or connection between the bioprosthesis and the coronary ostia. 
     i. First Embodiment 
     FIGS. 1-5, show a first embodiment of a bioprosthetic heart valve implantation system  10  of the present invention. The implantation system  10  shown in FIG. 1-5 includes a holding apparatus  12  having a stentless bioprosthetic heart valve  54  mounted therewithin. 
     The preferred holding apparatus  12  comprises a distal central hub member  14  whose center is in alignment with a longitudinal axis LA of the holding apparatus  12 , and an proximal ring member  20  having a series of apertures  22  formed therein, at spaced apart locations therearound. Each aperture  22  is capable of having a suture thread passed therethrough. Although the embodiment shown in the drawings includes a total of 24 apertures  22  formed in the proximal ring member  20 , the actual number of such apertures  22  may vary, and may in some embodiments number fewer than 24. Typically 18-24 of these apertures  22  will be utilized. 
     The preferred holding apparatus  12  has three strut members  24  which extend outwardly and downwardly (i.e., in the proximal direction) from the central hub member  14  to the ring member  20 . Each of the three strut members  24  may be positioned directly opposite one of the three cusps or commissurae of the prosthetic valve. It will be appreciated, however, that the specific number of strut members  24  may not be critical to the invention, and various designs of the holding apparatus  12  may be employed wherein, as an alternative to the use of individual strut members  24 , the holding apparatus body may be a cylindrical or bulbous cage or enclosure formed of solid, perforated, mesh or other suitable material, configured to substantially surround the distal end and sides of the prosthesis retention space  52 . 
     Also, it will be appreciated that the proximal ring member  20  shown in the drawings is an optional feature. Such proximal ring member  20  serves to substantially distribute the pulling force evenly around the inflow annulus at the proximal end of the prosthesis. Various alternative embodiments of the invention may be devised which do not include such proximal ring member  20  and wherein the proximal ends of the strut members themselves, are sewn or otherwise attached to the prosthesis  54 , at discrete points or locations therearound, or the proximal end of any continuous cage or enclosure used to form the holding apparatus  12  may be releasably attached at individual, discrete locations around the inflow annulus of the prosthesis  54 . 
     As is apparent from the figures, the diameter of the ring member  20  is preferably larger than the diameter of the distal hub member  14 . In the embodiment shown, each strut member  24  is made up of a substantially vertical first segment  26  and a substantially horizontal second segment  30 . The substantially vertical first segments  26  of the strut members  24  extend upwardly from the proximal ring member  20 . The substantially horizontal second segment  30  of each strut member  24  extends laterally outward from the distal hub member  14 . 
     A suture thread retainer  28  is formed on each strut member  24 . Each suture thread retainer  28  incorporates a traversing notch or channel  38  within which a plurality of suture threads may be retained. A cutting instrument entrance slot  46  is formed within each strut member  24  to permit scissors and other types of suitable instruments to be inserted thereinto, for the purpose of simultaneously cutting one or more suture threads which are disposed within the channel  38 . 
     As shown in significant detail of FIG. 5 j,  each channel  38  formed by each suture thread retainer  36  comprises an outer wall  40 , an inner wall  42  and a floor  44 . The manner in which the first and second suture threads  70 ,  78  are disposed within channels  38  is described more fully herebelow. 
     The distal hub member  14  is, in the embodiments shown, a generally cylindrical member having a threaded bore  48  formed therein. The threaded bore  48  is sized and configured to receive a handle member  50  (FIGS. 5 b - 5   f ). Examples of handle members  50  which may be used include handle Model 1108 or handle Model 1111 available from Baxter Healthcare Corporation, Edwards CVS Division, 17221 Red Hill Ave., P.O. Box 11150, Irvine, Calif. 92711-1150. The outer diameter of the distal hub member  14  is sufficiently small so as not to substantially block or obscure the outflow opening at the distal end of the prosthesis  54  when the prosthesis  54  is positioned within the prosthesis retention space  52  of the holding apparatus  12 . 
     The prosthesis retention space  52  is formed between or inboard of the strut members  24  and ring member  20 , and below (i.e., proximal to) the distal hub member  14 . The bioprosthesis  54  is releasably mounted within the retention space  52  of the holding apparatus  12 . The bioprosthesis  54  shown in the drawings is a stentless aortic bioprosthesis which comprises a cylindrical prosthesis body  56  having a plurality of valve leaflets  62  disposed therein. The outer surface of these cylindrical prosthesis body  56  may incorporate a marking thread, such as a green-colored thread, which is located immediately distal to the valve leaflets  62  This marking thread  60  will thus serve as a guide to permit optional trimming away of the distal portion of the cylindrical prosthesis body  56  without injuring the valve leaflets  62 . 
     A ring of woven polyester mesh  64  is sewn to the inflow annulus of the prosthesis  54 , and may extend beneath the proximal ring  20  of the cage, as shown. Such ring of polyester mesh material  64  facilitates suturing of the prosthesis  54  to the endogenous aortic root. An additional flap  68  of woven polyester mesh material may be sewn on a portion of the outer surface of the cylindrical prosthesis body  56 , to further enhance the suture-holding of the prosthesis to specific endogenous tissue. As used herein, reference to the cylindrical body  56  of the prosthesis  54  is intended to include the polyester mesh ring  64  and polyester mesh flap  68  attached to the tissue of the prosthesis  54 . 
     The prosthesis  54  is releasably mounted within the retention space  52  by first  70  and second  78  suture threads. The specific manner in which the first  70  and second  78  suture threads are utilized to releasably attach the bioprosthesis  54  to the holding apparatus  12  can be seen from FIGS. 1 and 4. As shown, the first suture thread  70  is initially tied about the upper surface of the proximal ring member  20 , immediately adjacent one of the suture package apertures  22 . Thereafter, the first suture thread  70  is alternately laced in and out of the apertures  22 , and is thereby passed through the under-lying cylindrical prosthesis body  56 , as shown. Upon exiting the suture passage aperture  22  which is closest to each strut member  24 , the first suture thread  70  is pulled upwardly, and is passed through the channel  38  of the suture thread retainer  36  formed on that strut member  24 . Thereafter, the first suture thread  70  is pulled downwardly adjacent the opposite side of that strut member  24  and is then laced in and out of the previously unused suture passage apertures  22  adjacent that side of the strut member  24 , to grasp the underlying cylindrical prosthesis body  56 . The free end of the first suture thread  70  is then tied and knotted over the upper surface of the proximal ring member  20 , in the same manner as had been done with the other end of that first suture thread  70 . This is shown in FIG.  4 . 
     The second suture thread  78  is knotted around the undersurface of the upper arm  30  of each strut member  24 , and is then passed through the underlying cylindrical body  56  of the prosthesis  54 , and through the channel  38  of the suture thread retainer  36 , as shown, The leading end of the second suture thread  78  may optionally then be again passed through the underlying cylindrical body  56  of the prosthesis  54  a second time, and will thereafter be passed through the adjacent suture passage aperture  34  and tied beneath the undersurface of the upper arm  30  of the strut member  24 , as shown. In this regard, the second suture thread  78  serves to accomplish releasable attachment of the distal aspect of the bioprosthesis  52  to the holding apparatus  12 . 
     The specific manner in which the first suture thread  70  and second suture thread  78  are disposed within the suture retainer  36  are shown in detail in FIGS. 5 i - 5   j . With reference to FIGS. 5 i - 5   j  it can be seen that the channel  38  formed within the suture retainer  36  is defined by an inner wall  42 , a base  44 , and an outer wall  40 . The first suture thread  70  and second suture thread  78  are positioned within the channel  38  of the suture retainer  36  in side-by-side juxtaposition. Thus, the surgeon may insert a single cutting instrument  108 , such as scissors, into the cutting instrument receiving slot  46  of each strut member  24  for the purpose of simultaneously severing both the first suture thread  70  and the second suture thread  78  associated with that particular strut member  24 . In this regard, only three cutting operations are necessary to effectively sever all three of the first suture threads  70  and all three of the second suture threads  78 , thereby releasing the bioprosthesis  54  from its attachment to the holding apparatus  12 . 
     The preferred methodology by which the first embodiment of the implantation system  10  may be utilized to facilitate surgical implantation of the bioprosthesis  54  is shown in FIGS. 5 a - 5   j.  With reference to FIGS. 5 a - 5   j,  the implantation system  10  is packaged as shown in FIG. 5 a  in a sterile plastic jar  86  with a plastic retainer  88  having a tab  90 . The jar  86  contains buffered glutaraldehyde  92 . A gloved hand  93  is used to remove the system  10  from the jar  86  by grasping the tab  90  of the retainer  88 . The retainer  88  has a track  94  which releasably retains the hub member  14  by engaging a groove  16  thereof. Once the implantation system  10  is removed from the jar  86 , the handle member  50  is threaded into the threaded bore  48  of the hub member  14 . The handle member  50  is then grasped and, as shown in FIG. 5 c , the retainer  88  is discarded. The valve prosthesis  54  housed within the prosthesis retention space  52  is rinsed in several fresh sterile saline solutions  96  as known in the art and exemplified in FIG. 5 d,  and its identification tag  98  is removed as shown in FIG. 5 e  and retained for record keeping. To prevent drying of the prosthesis  54  prior to implantation, sterile saline may be applied, as illustrated in FIG. 5 f,  every one to two minutes until implantation. 
     FIGS. 5 g - 5   h  show one method of initially positioning and securing the inflow annulus of the prosthesis  54  at a supra-annular implantation site immediately above the endogenous aortic root  100 . As shown, the bioprosthesis  54 , while it remains releasably mounted within the holding apparatus  12  is positioned at an exteriorized location immediately above the upper scissor receiving notch  102 . Suture threads  104  are passed through the polyester mesh ring  64  sewn to the inflow annulus of the prosthesis  54 , through the endogenous aortic root  100 , and again upwardly through the polyester mesh ring  64 . After such suture threads  104  have been installed all the way around the endogenous aortic root  100  and the prosthesis  54 , proximally directed pressure is applied to the handle  50 , so as to advance the holding apparatus  12  and the prosthesis  54  downwardly over the pre-positioned suture threads  104 , to a point (FIG. 5 h ) where the inflow annulus of the prosthesis  54  is in its desired supra annular position immediately above the endogenous aortic root  100 . 
     Thereafter, as shown in FIGS. 5 i - 5   j,  scissors  108  will be inserted into each of the cutting instrument receiving slots  46 , and will be utilized to simultaneously cut the first  70  and second  78  suture threads extending through the channel  38  of the suture retainers  36  formed on each strut member  24 . In this regard, only three scissor snips will be required to effect cutting of all three first suture threads  70  as well as all three second suture threads  78 . Because both ends of each first suture thread  70 , and both ends of each second suture thread  78 , are tied and anchored to the holding apparatus  12 , the subsequent extraction and pulling away of the holding apparatus  12  will also serve to draw the first suture threads  70  and second suture thread  78  out of the prosthesis  54 . In this regard, the severed first suture thread  70  and second suture thread  78  will be withdrawn and carried away with the used holding apparatus  12 , as shown in FIG. 5 k.    
     After the holding apparatus  12  has been removed and discarded, the surgeon may tie and cut away excess quantities of the suture threads  104 , and may effect any additional suturing required to secure the distal end of the prosthesis  54  and/or the coronary openings  55  to the patient&#39;s coronary ostia. 
     ii. Second Embodiment 
     In the second embodiment of the holding apparatus  12   a,  as shown in FIGS. 6 a - 6   c,  the proximal ring members  20   a  is segmented or divided into a plurality of separate portions. The vertical strut members  24   a  are capable of being splayed or bent outwardly in directions which are generally divergent from one another, so as to cause the individual segments or portions of the proximal ring member  20   a  to spread apart from one another. This results in the formation of gaps or openings in the proximal ring member  20   a,  so as to allow the proximal ring member  20   a  to be extracted from the patient even after the bioprosthesis contained within the holding apparatus  12   a  has been sutured to the coronary ostia of the patient. 
     More specifically, the second embodiment of the holding apparatus  12   a  may be constructed as a single molded piece, or alternately may be fabricated from a plurality of individual components as is specifically illustrated in the exploded view of FIG. 6 a.  With reference to FIG. 6 a,  the individual components of which the holding apparatus  12   a  is formed comprise a central hub member  14   a  and three (3) strut members  24   a  having respective segments of the proximal ring member  20   a  formed on the basal or proximal end thereof. 
     In the embodiment shown, the central hub member  14   a  is provided with three outwardly extending attachment legs  90  each such attachment leg  90  has a substantially horizontal, planar central portion  92  with vertical flanges or lips  90  formed on either side thereof. Scissor-receiving notches or cut-away areas  96  extend inwardly into each of the horizontal flat center portions  92  of the attachment legs  90 . 
     Pass-through slots  97  are formed in each of the attachment legs  90 , inboard of each horizontal flat central portions  92 . Corresponding bendable tab members  100  are formed on the upper ends of the strut members  24   a,  and such tab members  100  are passable downwardly through the pass-through slots  97  of the attachment legs  90 . Thereafter, such tab members  100  may be bent upwardly such that they abut against the under surface of the horizontal flat portion  92  of each attachment leg  90 . This effectively and firmly attaches each strut member  24   a  to the central hub member  14   a.    
     Separate upper scissor receiving notches  102 ,  104  are formed in the upper ends of the strut members  24   a.  As the tab members  100  are bent over, each of these upper scissor receiving notches  102 ,  104  becomes aligned with the corresponding notch  96  formed in the adjacent attachment leg  90  of the central hub member  14   a,  to facilitate insertion of scissors or other cutting instruments to sever the upper suture thread  116  passed through suture passage apertures  112  or other attachment member or apparatus by which the upper end of each strut member  24   a  is attached to the bioprosthesis  54  positioned within the prosthesis retention space  52   a  holding apparatus  12   a.  The preferred manner in which such upper suture threads  116  are deployed and positioned is shown in detail in FIG. 6, and is more fully described herebelow. 
     Each of the three (3) segments of the proximal ring member  20   a  shown in FIG. 6 a  have ends  110  which are abutable against one another such that the proximal ring member  20   a  will assume the assembled shape of a substantially round or circular ring. Locator projections  113  extend from some of the segment ends  110  of the proximal ring member  20   a  to assist in guiding and locating the ends  110  into direct abutment to form the desired ring structure. 
     As shown in FIG. 6, individual lower suture threads  120  may be utilized to secure the assembled proximal ring member  20   a  to a bioprosthesis  54  contained within the interior prosthesis receiving space  52   a  of such holding apparatus  12   a.    
     In this regard, discrete groups of suture passage apertures  112  are located at specific locations on the holding apparatus  12   a  to facilitate releasible attachment of the holding apparatus  12   a  to a bioprosthesis which is positioned within the prosthesis retention space  52   a  of the holding apparatus  12   a.    
     Preferably, a group of four (4) suture passage apertures  112  is formed in a substantially rectangular array near the upper end of each strut member  24   a,  at a location immediately adjacent the basal end of each upper scissor-receiving notch  102 . In this manner, the upper suture threads  116  may be tied or otherwise anchored to the strut members  24   a,  and passed alternately in and out of the four (4) suture passage apertures  112 , as shown in FIG. 6 b,  to thereby stitch or couple the upper end of each strut member  24   a  to a bioprosthesis  54  contained within the prosthesis retention space  52   a.  When it is desired to disconnect the bioprosthesis from the holding apparatus  12   a,  scissors may be inserted downwardly into the upper scissor receiving notches  102 , so as to cut the upper suture thread  116 , thereby releasing the bioprosthesis from the upper ends of the strut members  24   a.    
     Similarly, groups consisting of four (4) suture passage apertures  112  are formed at spaced-apart locations around the proximal ring member  20   a,  and individual lower suture threads  120  may be tied or otherwise anchored to the suture passage aperture  112 , and may be passed alternately in and out of the adjacent four (4) suture passage apertures  112  to stitch the bioprosthesis  54  within the retention space  52   a  to the proximal ring member  20   a,  as shown in FIG. 6 b.  Because the lower scissor receiving notches  118  extend downwardly into the upper edges of the proximal ring member  20   a,  at the locations between the suture passage apertures  112  of a discrete group, the tip of a pair of scissors or other cutting instrument may be inserted into each such scissor receiving notch  118  to cut each lower suture thread  120  by which the proximal ring member  20   a  is attached to the proximal end of the bioprosthesis, in this regard, six separate scissor snips may be utilized to completely severe all of the individual lower  120  suture threads  120  which attach the proximal ring member  20   a  to the proximal end of the bioprosthesis  54 . 
     As with the first embodiment of the invention shown in FIGS. 1-5, the bioprosthesis  54  is positioned within the prosthesis retention space  52   a  of the holding apparatus  12   a  such that the proximal mesh ring  64  of the bioprosthesis  54  protrudes below the lower edge of the proximal ring member  20   a.  Such mounting of the bioprosthesis  54  within the retention space  52   a  is preferably accomplished prior to packaging within a storage container  86 , as shown in FIG. 5 a.  This enables the surgeon to easily use the holding apparatus  12   a  to facilitate proper placement and suturing of the proximal sewing ring  64  of the bioprosthesis  54  to the patient prior to release or removal of the holding apparatus  12   a.    
     In operation, the second embodiment of the holding apparatus  12   a  shown in FIGS. 6 a - 6   c  operates in substantially the same way as described hereabove with respect to the first embodiment shown in FIGS. 1-5. However, the second embodiment of the holding apparatus  12   a  has the added capability of being removed after the coronary openings  55  (see FIG. 3) of the bioprosthesis  54  have been anastomosed or otherwise attached to the coronary ostia of the patient. For example, after the holding apparatus  12   a  of the second embodiment (along with a bioprosthesis  54  mounted within its prosthesis retention space  52   a ) has been advanced to a point where the proximal mesh ring  64  of the bioprosthesis is located at its intended implantation site (e.g., the aortic annular or supra-annular position) and sutured in place, the surgeon may then proceed to suture, or otherwise attach the peripheries of the coronary openings  55  of the bioprosthesis to the aortic tissue surrounding the coronary ostia of the patient. Thereafter, scissors are inserted downwardly into the upper scissor receiving notches  102  and may be utilized to cut the upper suture thread  116 , thereby enabling the upper suture thread  116  to be pulled through the body of the prosthesis such that the holding apparatus may be extracted and removed from the prosthesis. Also, scissors are inserted downwardly into each of the lower scissor receiving notches  118  formed in the proximal ring member  20   a,  and will be utilized to cut each of the lower suture thread  120 , thereby enabling the lower suture thread  120  to be pulled through and removed from the body of the prosthesis as the holding apparatus  12   a  is extracted and removed. 
     After all of the upper suture threads  116  and lower suture threads  120  have been cut, the surgeon will splay or outwardly bend the strut members  24   a  away from one another so as to cause the ends  110  of the proximal ring member  20   a  segments to separate or part from one another. This creates gaps or openings between the adjacent ends  110  of the separate segments of the proximal ring member  20   a . After such gaps or openings have been created in the proximal ring member  20   a,  the surgeon will lift upwardly on a handle which is attached to the central opening  48   a  of the central hub member  14   a,  thereby lifting the entire holding apparatus  12   a  upwardly. Such upward lifting of the holding apparatus  12   a  causes the previously severed upper suture threads  116  and lower suture threads  120  to be drawn or pulled through the adjacent tissue of the prosthesis, thereby freeing the holding apparatus  12   a.  Furthermore, as the holding apparatus  12   a  is lifted upwardly, the points at which the prosthesis are connected to the aortic tissue surrounding the coronary ostia will pass through the gaps or openings created between the adjacent ends  110  of separate segments of the proximal ring member  20   a.  in this manner, the holding apparatus  12   a  is extracted and removed from the body of the patient while the bioprosthesis remains in its implanted position with the coronary openings  55  of the bioprosthesis  54  being anastomosed or otherwise attached to the patient. 
     iii. Third Embodiment 
     Referring now to FIGS. 7-11 b,  there is depicted a holding apparatus  12   b  constructed in accordance with a third embodiment of the present invention. As shown in FIG. 7, the holding apparatus  12   b  includes the stentless bioprosthetic heart valve or prosthesis  54  mounted therewithin. 
     Such mounting of the prosthesis  54  within the holding apparatus  12   b  is preferably accomplished prior to packaging of the bioprosthesis  54  within a storage solution  92 , as shown in FIG. 5 a.  As in the holding apparatus  12 ,  12   a  constructed in accordance with the first and second embodiments of the present invention, the holding apparatus  12   b  includes a central hub member  14   b.  The hub member  14   b  itself includes a female retention bore  130  formed therein to facilitate the attachment of the previously described handle member  50  to the holding apparatus  12   b.  Extending radially outward from the hub member  14   b  in equidistantly spaced intervals of approximately 120 degrees are three (3) identically configured attachment legs  132 . 
     In addition to the hub member  14   b  and integral attachment legs  132 , the holding apparatus  12   b  includes three (3) elongate strut members  134  having distal ends which are attached to the outermost ends of respective ones of the attachment legs  132 . As best seen in FIG. 8, the strut members  134  may define arcuately contoured, outwardly bowed central portions. The strut members  134  extend substantially downward from the attachment legs  132  so as to define a hollow prosthesis retention space inboard of the strut members  134  and beneath the hub member  14   b.  As seen in FIG. 7, this retention space is sized and configured to accommodate the prosthesis  54 . 
     The holding apparatus  12   b  of the third embodiment further comprises an attachment ring  136  which is disposed on the proximal ends of the strut members  134  for maintaining the prosthesis  54  within the retention space defined within the holding apparatus  12   b.  As will be discussed in more detail below, the proximal inflow end of the prosthesis  54  is releasably connected to the attachment ring  136  in a manner allowing the holding apparatus  12   b  to be selectively disengaged from the prosthesis  54  subsequent to the placement thereof into a desired site. 
     In the third embodiment, the attachment ring  136  itself comprises an inner ring member  138  which is attached to the proximal ends of the strut members  134 . The inner ring member  138  includes a lower, beveled outer surface portion  140  and an upper, beveled inner surface portion  142  which defines the top rim  144  of the inner ring member  138 . Formed on the top rim  144  of the inner ring member  138  are three (3) attachment lugs  146  which are used to facilitate the attachment of the proximal ends of the strut members  134  to the inner ring member  138 . As such, the attachment lugs  146  are oriented about the periphery of the top rim  144  in equidistantly spaced intervals of approximately 120 degrees. 
     In addition to the attachment lugs  146 , formed on the top rim  144  of the inner ring member  138  are three (3) enlarged attachment regions  148 . In the third embodiment, each attachment region  148  is centrally positioned between a respective pair or the attachment lugs  146 . As such, like the attachment lugs  146 , the attachment regions  148  are preferably separated from each other by equidistantly spaced intervals of approximately 120 degrees. As best seen in FIG. 9 a,  each attachment region  148  includes a spaced pair of suture passage apertures extending therethrough which are separated by a cutting instrument receiving notch  150 , the use of which will be discussed in more detail below. 
     In addition to the inner ring member  138 , the attachment ring  136  of the holding apparatus  12   b  includes an outer ring member  152  which is releasably attached to the inner ring member  138 . As will also be discussed in more detail below, a portion of the prosthesis  54  is frictionally captured between the outer and inner ring members  152 ,  138  when they are releasably attached to each other. The outer ring member  152  is adapted to receive the inner ring member  138  in a nesting fashion, and includes a beveled inner surface portion  154  having a configuration which is complementary to the outer surface portion  140  of the inner ring member  138 . Additionally, as with the inner ring member  138 , formed about the top edge of the outer ring member  152  in equidistantly spaced intervals of approximately 120 degrees are three (3) enlarged attachment regions  156 . As best seen in FIG. 9 a,  extending through each of the attachment regions  156  is a spaced pair of suture passage apertures  158 . 
     In the third embodiment, the releasable attachment of the inner and outer ring members  138 ,  152  to each other is facilitated by initially inserting the inner ring member  138  into the outer ring member  152  such that the attachment regions  148  of the inner ring member  138  are vertically aligned with respective ones of the attachment regions  156  of the outer ring member  152 . When so aligned, the suture passage apertures of each pair disposed within a respective attachment region  148  are coaxially aligned with respective ones of the suture passage apertures  158  of the corresponding attachment region  156 . As further seen in FIG. 9 a,  a suture thread  159  is extended through the coaxially aligned suture passage apertures of each corresponding pair of attachment regions  148 ,  156  to facilitate the releasable attachment of the inner and outer ring members  138 ,  152  to each other. 
     As best seen in FIGS. 7 and 8, the outer ring member  152  of the attachment ring  136  further includes three (3) spaced pairs of tab portions  160  which extend distally from the top rim thereof. Each pair of tab portions  160  is centrally positioned between a respective pair of attachment regions  156 . In this respect, when the inner and outer ring members  138 ,  152  are releasably attached to each other in the aforementioned manner, each pair of tab portions  160  is oriented so as to receive a respective one of the attachment lugs  146  of the inner ring member  138  therebetween. As such, when the inner and outer ring members  138 ,  152  are releasably attached to each other, the tab portions  160  of each pair extend upwardly along either side of a respective strut member  134  of the holding apparatus  12   d.  Each tab portion  160  of the outer ring member  152  has a generally hook-shaped configuration, and defines a channel  162  which is directed downwardly toward the beveled inner surface portion  154  of the outer ring member  152 . 
     Referring now to FIGS. 9 b - 11   b , the prosthesis  54  with which the holding apparatus  12   b  is preferably utilized includes the layer of mesh  64  which is sewn to and extends about the inflow annulus thereof. Importantly, the mesh  64  defines an excess end portion  164  which extends along, but is not secured to, the outer surface of the prosthesis  54  adjacent the inflow annulus thereof. As previously explained, the prosthesis  54  is maintained within the retention space of the holding apparatus  12   b  by the releasable connection of the attachment ring  136  to the prosthesis  54 . In the holding apparatus  12   b,  the releasable connection of the attachment ring  136  to the prosthesis  54  is facilitated by the frictional capture of the end portion  164  of the mesh  64  between the complementary beveled outer and inner surface portions  140 ,  154  of the inner and outer ring members  138 ,  152  when releasably attached to each other in the aforementioned manner. The frictional retention of the end portion  164  between the inner and outer ring members  138 ,  152 , and in particular the outer and inner surface portions  140 ,  154  thereof, is shown in FIGS. 9 b,    10   a  and  11   a.  When it is desired to disengage the holding apparatus  12   b  from the prosthesis  54  subsequent to the placement thereof in a desired site, the inner and outer ring members  138 ,  152  are detached from each other so as to allow the end portion  164  of the mesh  64  to be released from compression between the beveled outer and inner surface portions  140 ,  154 . 
     The detachment of the inner and outer ring members  138 ,  152  from each other is facilitated by cutting each of the three (3) suture threads  159  extending between corresponding pairs of the attachment regions  148 ,  156 . Such cutting is accomplished by inserting the end of a cutting instrument into the notches  150  of the attachment regions  148  in succession, and severing the suture threads  159 . After the suture threads  159  have been severed by the cutting instrument, the application of force in a distal direction to the hub member  14   b  facilitates the distal movement of the inner ring member  138  relative to the outer ring member  152 . Such distal movement results in the separation of the inner and outer ring members  138 ,  152  from each other, and the release of the end portion  164  from therebetween. Such distal movement of the inner ring member  138  relative to the outer ring member  152  which facilitates the release of the end portion  164  from therebetween is best shown in FIG. 9 c.    
     As will be recognized, subsequent to the release of the end portion  164  from between the inner and outer ring members  138 ,  152 , it is still necessary that the outer ring member  152  be withdrawn from within the operative site along with the inner ring member  138 . Despite the detachment of the inner ring member  138  from the outer ring member  152  facilitated by the severing of the suture threads  159 , the outer ring member  152  is pulled from the operative site by the inner ring member  138  due to the inclusion of the tab portions  160  on the outer ring member  152 . 
     As best seen in FIGS. 10 a - 11   b,  the tab portions  160  of the outer ring member  152  engage the inner ring member  138  subsequent to the distal movement of the inner ring member  138  relative to the outer ring member  152  in an amount sufficient to release the end portion  164  of the mesh  64  from therebetween. In this respect, subsequent to such distal movement of the inner ring member  138 , the top rim  144  thereof is received into the channels  162  of the tab portions  160 , thus causing the continued distal movement of the inner ring member  138  to effectively draw the outer ring member  152  therewith. As a result, when the top ring  144  of the inner ring member  138  is received into the channels  162  of the tab portions  160 , a sufficient gap is defined between the outer and inner surface portions  140 ,  154  so as to facilitate the release of the end portion  164  from therebetween. Thus, the holding apparatus  12   b  moves independently of the prosthesis  54 . 
     It is to be appreciated that the invention has been described hereabove with reference to certain presently preferred embodiments and examples only, and no effort has been made to exhaustively describe all possible embodiments and examples of the invention. Indeed, various adaptations and modifications may be made to the specific embodiments described hereabove, without departing from the intended spirit and scope of the invention. Accordingly, it is intended that all reasonable modifications and alterations to the above-described embodiments and examples, be included within the scope of the following claims.