Patent Publication Number: US-7722667-B1

Title: Two piece bioprosthetic heart valve with matching outer frame and inner valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 09/203,169, filed Dec. 1, 1998, now U.S. Pat. No. 6,074,418, and entitled “DRIVER TOOL FOR HEART VALVE PROSTHESIS FASTENERS”, which is a continuation-in-part of application Ser. No. 09/062,822, filed Apr. 20, 1998, now U.S. Pat. No. 6,176,877, and titled “TWO PIECE PROSTHETIC HEART VALVE.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to mechanical heart valve prostheses. More specifically, the invention relates to a driver tool for attaching and implanting heart valve prostheses. 
     BACKGROUND OF THE INVENTION 
     Implantable mechanical heart valves are used for replacement of defective valves in hearts of patients. One common method employs a sewing ring or suture cuff which is attached to and extends around the outer circumference of the mechanical valve orifice. The sewing cuff is made of a biocompatible fabric suitable for allowing a needle and suture to pass therethrough. The valves are typically sutured to a tissue annulus that is left when the surgeon removes the existing valve from the patient&#39;s heart. The sutures are tied snugly, thereby securing the valve to the heart. 
     Sewing cuffs are labor intensive, difficult to manufacture and may be difficult to secure to the valve orifice. Further, attaching the suture cuff to the tissue annulus is time consuming and cumbersome. The complexity of suturing requires a patient to be on cardiopulmonary bypass for a lengthy period. It is also desirable to provide a large lumen through the valve orifice relative to the overall valve diameter for blood flow. However, techniques for attaching the sewing cuff to the valve orifice typically require that the area of the valve lumen be reduced to accommodate an attachment mechanism. For example, the sewing cuff is typically retained between two rims of the valve orifice. One of the rims normally defines the outside diameter of the valve orifice and thus limits the size of the valve lumen. 
     Another technique for attaching heart valves uses a series of pins which pierce the tissue annulus of the heart. The pins are crimped or bent, thereby locking the valve to the heart tissue and preventing the valve from separating from the heart. This technique is described in U.S. Pat. Nos. 3,574,865 and 3,546,710. Another technique for attaching a prosthetic heart valve to the heart tissue is shown in U.S. Pat. No. 4,705,516 in which an outer orifice ring is sutured to the tissue annulus and an inner orifice ring is then screwed into the outer orifice ring. However, the rings are not locked together and may become unscrewed after extended use. 
     Implantable heart valves can require fasteners to hold them securely to surrounding tissue in the body. Suturing has been used. However, the use of suturing is time consuming and increases the duration of the implantation surgical procedure. The use of helical fasteners or screws is disclosed in the above cited pending application. However, access one at a time to the multiple helical fasteners used with an implant can be difficult and time consuming. The fasteners face in different directions and a simple tool must be positioned multiple times to approach the implantable heart valve component from several difficult angles around the heart, some of which may be obstructed by adjoining tissue. There is a need for an improved technology for screwing helical fasteners through a heart valve component into a tissue annulus of the heart. 
     SUMMARY OF THE INVENTION 
     A bioprosthetic heart valve includes an inner bioprosthetic valve and an outer frame configured to attach to a tissue annulus of a heart. The inner bioprosthetic valve has an exterior shape which substantially matches an interior shape of the outer frame. The exterior shape of the inner valve mates in substantial alignment with the interior shape of the outer frame. An outer frame-inner valve attachment mechanism is configured to couple the inner valve to the outer frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded cross-sectional view of a prosthetic heart valve. 
         FIG. 2  is a cross-sectional view of the heart valve of  FIG. 1 . 
         FIG. 3  is a perspective view of an attachment mechanism for the prosthetic heart valve of  FIGS. 1 and 2 . 
         FIG. 4  is a side cross-sectional view of an implantation tool for implanting the heart valve prosthesis shown in  FIGS. 1 and 2 . 
         FIG. 5  is a side cross-sectional view of the tool of  FIG. 4  in which a holder portion of the tool is moved to an open position. 
         FIG. 6  is a side perspective view of an outer orifice ring in accordance with another embodiment. 
         FIG. 7A  is a side plan view and  FIG. 7B  is a side cross-sectional view of the outer orifice ring shown in  FIG. 6 . 
         FIG. 8  is a side perspective view of a suture securing tool. 
         FIG. 9  is a perspective view of a holder for use in implanting an outer ring of a heart valve. 
         FIG. 10  is a side cross sectional view of a driver tool engaging a heart valve outer ring and coupled to helical fasteners in accordance with the present invention. 
         FIG. 11  is a side cross sectional view of a driver tool engaging a heart valve outer ring and coupled to helical fasteners in accordance with the present invention. 
         FIG. 12  is an enlarged cross sectional view of the distal end of the driver tool of  FIG. 10  or  11 . 
         FIG. 13  is an end view of a distal end of the driver tools of  FIGS. 10 and 11 . 
         FIG. 14  is a cross sectional view along line  14 - 14  of  FIG. 12 . 
         FIG. 15  is an enlarged cross sectional view of an alternate distal end of the driver tools of  FIGS. 10 and 11 . 
         FIG. 16  is a further enlarged cross sectional view of a portion of the alternate distal end of the driver tool of  FIG. 15 . 
         FIG. 17  is an enlarged cross sectional view of an alternate distal end of the driver tools of  FIGS. 10 and 11 . 
         FIG. 18  is an enlarged drawing of front and end views of a helical screw fastener with its last coil turned into the center of the coil. 
         FIG. 19  is an enlarged drawing of a front and an end view of a driver tip for use with the helical screw fastener of  FIG. 18 . 
         FIG. 20  is a perspective view of a bioprosthetic valve. 
         FIG. 21  is an exploded view of the valve of  FIG. 20  and an outer frame. 
         FIG. 22  is a side cross-sectional view of an implantation device and the outer frame of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Heart valve prosthesis  10  shown in  FIG. 1  includes inner orifice ring  12  and outer orifice ring  14 .  FIG. 1  is a side cross-sectional exploded view of valve  10  and  FIG. 2  is a side assembled cross-sectional view of valve  10 . 
     Inner orifice ring  12  includes locking recess  16  (or, in another embodiment, a ridge) formed around its outer circumference. Leaflets (or occluders)  18  provide an occluding mechanism and are pivotably coupled to ring  12  at pivot guard  20 . Leaflets or occluders  18  move between an open position (not shown) and a closed position as shown in  FIGS. 1 and 2  in which flow of fluid through lumen  22  is blocked. Leaflets  18  rotate within pivots  24  formed in pivot guards  20 . In one preferred embodiment, inner ring  12  comprises a prosthetic heart valve available from St. Jude Medical, Inc. of St. Paul, Minn., without a sewing cuff carried thereon. However, in some embodiments it may be preferable to use a specially designed inner ring  12 . 
     Outer orifice ring  14  includes locking ridge  30  (or, in another embodiment, a recess) formed on an inner annulus circumference thereon. Inner annulus  32  of ring  14  is sized to have approximately the same radius as outer annulus  34  of inner ring  12 . Similarly, locking ridge  30  of outer ring  14  substantially conforms to locking recess  16  of inner ring  12 . Locking recess  16  and locking ridge  30  cooperate to provide a ring coupling mechanism adapted to couple the outer orifice ring to the inner orifice ring. Outer orifice ring  14  also includes tissue annulus attachment locking mechanism  40  which, in one preferred embodiment, comprises helical screws carried through holes  29  around the circumference of outer ring  14 . Other types of attachment mechanisms include staples, pins, rivets, “nails”, barbs, hooks, etc. These mechanisms could be coupled to or integral with the outer orifice ring. As illustrated in  FIGS. 1 and 2 , locking mechanism  40  attaches to the natural heart tissue annulus  42  of the patient. 
     In  FIG. 3  a perspective view of locking mechanism  40  is shown in greater detail. Locking mechanism  40  is a helical screw preferably made of a biocompatible material. For example, locking mechanism  40  may be formed from a platinum-iridium alloy, MP35N (a Wrought cobalt-nickel-chromium-molybdenum alloy), stainless steel, titanium or other biocompatible materials. As shown in  FIG. 3 , tool  44  includes engaging tip  46  which fits into screw head  48 . Locking mechanism  40  may be turned by rotating tool  44 . In one embodiment, there are between 8 and 16 substantially equally spaced locking mechanisms  40  around the circumference of inner orifice ring  12 . However, any number may be used. Locking mechanism  40  typically extends between about 0.050 to about 0.200 inches into the tissue annulus  42 . 
       FIG. 4  is a side cross-sectional view of tool  60  for use in snapping inner ring  12  into outer ring  14  of heart valve prosthesis  10  shown in  FIGS. 1 and 2 . Tool  60  includes elongated handle  62  including proximal gripping end  64 . Actuator rod  66  extends through a center opening  68  in handle  62 . Holder  70  is coupled to a distal end of handle  62 . Holder  70  includes moveable half  72 A and fixed half  72 B coupled at pivot  74 . Halves  72  include lower lip  76  adapted to abut outer ring  14 . Distal end  80  of actuator rod  66  couples to actuator cable  82  which is connected to half  72 A. Spring  84  is coupled to actuator rod  66  and pushes actuator rod  66  in an axial direction away from holder  70  holding halves  72  in the closed position as shown in  FIG. 4 . Rod  66  includes actuator button  90 . Proximal end  64  of handle  62  includes handle grip  93 . 
     Orifice pushing mechanism  91  is aligned axially with handle  62  and coupled to handle  62  by threads  92 . Mechanism  91  includes gripping portion  94  and orifice abutting surface  96 . As shown in  FIG. 4 , orifice abutting surface  96  is adapted to abut inner orifice ring  12 . 
       FIG. 5  is a side cross-sectional view of a portion of tool  60  showing holder  70  in an open position in which half  72 A is rotated about pivot  74 . In this position, heart valve prosthesis  10  is freed from holder  70  such that heart valve prosthesis may be selectively removed from, or engaged with holder  70 . 
     In operation, pressure is applied to actuation button  90  while grasping handle grip  93 . This causes actuator rod  66  to move downward, towards the distal end of tool  60  whereby cable  82  causes half  72 A to rotate about pivot  74 . When pressure is released from actuator button  90 , spring  84  pushes actuator rod  66  in a direction away from holder  70  such that half  72 A is moved back into a closed position by cable  82  as shown in  FIG. 4 . After outer orifice ring  14  has been attached to the natural tissue annulus of the patient&#39;s heart, tool  60  containing pre-loaded ring  12  is inserted through implantable ring  14  by depressing actuator button  90 . This engages lip  76  under ring  14 . Mechanism  94  is then rotated whereby lip  76  and surface  96  work in opposing directions such that no axial force is applied to helical screws  40  or the patient&#39;s tissue annulus. Outer orifice ring  14  is held against lower lip  76  such that a relative pressure is applied between rings  12  and  14 . This causes locking ridge  30  to seat within locking recess  16 . When inner ring  12  has been “snapped” in place with ring  14 , ring  12  prevents locking mechanisms  40  from unscrewing or disengaging. Force may then be applied to actuator button  90  such that half  72 A of holder  70  rotates as shown in  FIG. 5  so that tool  60  may be removed from prosthesis  10 . 
       FIG. 6  is a perspective view of outer orifice ring  100  in accordance with another embodiment which is coupled to suture cuff  102 . In the embodiment of  FIG. 6 , ring  100  includes a plurality of suture holes  104  formed therein for receiving sutures  106 . Further, the inner annulus of ring  100  includes suture receiving groove  108 .  FIG. 7A  is a side plan view of outer ring  100  and  FIG. 7B  is a side cross-sectional view of outer ring  100 . As shown in  FIG. 7A , the outer annulus of ring  100  includes cuff retaining grooves  110  formed therein. In one preferred embodiment, O-rings  101  are provided to prevent leakage between the orifice rings as shown in  FIG. 7B . Retaining sutures are wound circumferentially through cuff  102  and within cuff retaining grooves  110  binding or clamping cuff  102  to ring  100 . 
     Ring  100  is sutured to tissue annulus  42  using sutures  106  which extend radially through cuff  102  and suture holes  104 . Preferably, sutures  106  are metal sutures of a biocompatible material such as stainless steel. After the sutures  106  are threaded through the patient&#39;s natural tissue annulus and outer orifice ring  100 , the surgeon secures the suture using knots  114  which may be formed by twisting the suture  106  as shown in  FIG. 6 . Excess suture material is then trimmed and knots  114  are folded into suture grooves  108 . 
       FIG. 8  is a side perspective view of a suture securing tool  130  for use in twisting sutures  106  shown in  FIG. 6 . Tool  130  includes elongated body  132  carrying shaft  134  therethrough between an actuator  136  and a hook  138 . Spring  140  pushes on end cap  144  and body  132  such that hook  138  presses against end cap  142 . By pressing on actuator  136 , hook  138  may be extended to hook both ends of suture  106 . When actuator  136  is released, suture  106  is trapped between hook  138  and cap  142 . Tool  130  is then rotated to twist sutures  106  together forming twisted knots  114  shown in  FIG. 6 . 
     Following implantation of ring  100  into the tissue annulus  42 , inner orifice ring  12  as shown in  FIG. 1  is coupled to ring  100  as described with respect to  FIGS. 1-5 . 
       FIG. 9  is a perspective view of implantation tool  150  for use in implanting orifice ring  100 . Tool  150  includes legs  152  having coupling tips  154  which are configured to couple to ring  100 . Tool  150  may be used by the surgeon to hold ring  100  during suturing such that force may be applied to ring  100 . Tips  154  may be fit into suturing grooves  108 . Tool  150  includes handle attachment opening  156  which may be used to selectively engage an elongated handle (not shown). Opening  156  can be as shown or can be a threaded hole, a snap fit hole or other opening adapted to selectively engage an elongated handle. 
     In  FIG. 10 , driver tool  210  is shown engaging outer ring  212  of a two piece prosthetic heart valve. Driver tool  210  couples to helical screw fasteners  214  which pass through holes in outer ring  212 . Helical fasteners  214  can be any fastener that advances along its central axis by being turned about that axis, i.e., anything that goes in by twisting, such as a screw. Helical screw fasteners  214  attach outer ring  212  to tissue annulus  213  during an implantation procedure using driver tool  210 . Driver tool  210  includes tool housing  216 , which is generally cylindrical in shape, or round in cross section, and extends from distal end  218 , which engages outer ring  212 , to proximal end  220  spaced away from the distal end  218 . Drive shaft  222  at proximal end  220  has a handle  224  that can receive a twisting or driving force for transmission to helical screw fasteners  214 . Handle  224  can also be actuated or pulled away from the proximal end  220  to disengage driver tool  210  from helical screw fasteners  214 . 
     In  FIG. 10 , handles  226 ,  228  project laterally from proximal end  220 . Handles  226 ,  228  can be manually squeezed together to retract or disengage driver tool  210  from outer ring  212 . When handles  226 ,  228  are squeezed together, tool housing  216  slides relative to tube  232 . Handles  226 ,  228  pivot on pin  227 . Handle  226  is rigidly coupled to tube  232 . Handle  228  has slot  229  engaging a pin in tool housing  216 . When handles  226 ,  228  are squeezed together, tool housing  216  moves toward outer ring  212  while other parts of drive tool  210  remain stationary relative to handle  226 . Tool housing  216  pushes outer ring  212  away from tool  210 , releasing outer ring  212  from tool  210  when handles  226 ,  228  are squeezed together. Spring  225  maintains handles  226  and  228  in the open or spread apart position and prevents accidental dislodgement of ring  212 . 
     As an alternative to the handles  226 ,  228  of  FIG. 10 , a release button, along with additional springs can be disposed on the proximal end of tool  210 . With this alternative, when the installation of helical fasteners  214  is complete, the release button can be pressed, releasing a catch to retract driver tool  210  from outer ring  212 . 
     In  FIG. 11 , another alternative embodiment of a tool  211  is shown where there are no handles  226  and  228  as in  FIG. 10 , and spring  225  prevents accidental dislodgement of ring  212  while the health professional grasps tool housing  216 . In  FIG. 11 , components which are similar to those in  FIG. 10  are identified with the same reference numerals used in connection with the description of  FIG. 10 . 
     In  FIG. 11 , after helical screw fasteners  214  are driven in by tool  211  in the same manner that helical screw fasteners  214  are driven in by tool  210  ( FIG. 10 ), the handle  224  is lifted or pulled up relative to tool housing  216  while the surgeon holds tool housing  216 . This lifting action first lifts drive shaft  222 , compresses spring  272 , thereby disengaging helical screw fasteners  214  from the flexible shafts  262  ( FIG. 12 ) of the tool  211 . When spring  272  is fully compressed, lifting force is transferred through the compressed spring  272  to tube  232 . When the handle is lifted further, tube  232  lifts relative to tool housing  216 , compressing spring  225  while tube  232  remains in contact with outer ring  212 . Spring  225  is made stiffer than spring  272  so that the flexible shafts  262  ( FIG. 12 ) disengage from the helical screw fasteners  214  before the tube  232  lifts to release outer ring  212  from tool  211 . Tool housing  216  moves toward outer ring  212  while other parts of driver tool  211  retract or move away from outer ring  212 . The tool  211  is thus fully disengaged from outer ring  212  and helical screw fasteners  214  after use. 
     In  FIG. 12 , distal end  218  is shown in more detail. At distal end  218 , cylindrical end  234  of tool housing  216  abuts outer ring  212 . Struts  236  of tube  232  extend beyond cylindrical end  234  to engage outer ring  212  with a snap fit between groove  238  of struts  236  and locking ridge  240  of outer ring  212 . Outer ring  212  is thus retained securely on distal end  218 . Helical screw fasteners  214  pass through holes  242  in outer ring  212  and into tissue annulus  213 . In one embodiment, there are approximately eight to sixteen helical fasteners although any number can be used, each passing through a separate hole  242  in outer ring  212 . Helical screw fasteners  214  can be formed of metal wire compatible with implantation, and have a hub portion  244  which is wound in a polygonal shape, typically a hexagon, and the remainder  246  of the helical fastener is wound in a helix with a sharp point  247  at the end. In another embodiment, the last coil of the hub portion  244  turns into the center of the coil (as described later in  FIGS. 18-19 ). 
     In  FIG. 12 , drive shaft  222  couples to drive train  250 . Drive shaft  222  may be narrowed to form a gear shaft  252  on its end. Gear plate  254  is assembled on gear shaft  252  so that gear shaft  252  is free to spin. Gear  256  is attached to gear shaft  252  so that gear shaft  252  drives gear  256 . Satellite gears  258  are assembled on plate  254  with gear hubs  259  extending through holes in plate  254  so that they engage or mesh with gear  256 . Plate  261  is also assembled onto gear shaft  252  with gear hubs  257  extending through holes in plate  261  so that gear shaft  252  is free to spin. Retaining ring  260  is then attached to gear shaft  252  to keep gears  256  and satellite gears  258  caged between gear plates  254 ,  261 . Gear plates  254  and  261  are provided with multiple tabs  263  which are shaped to mate with slots  265 . This arrangement prevents drive train  250  from rotating within tube  232  when drive shaft  222  is rotated. Satellite gears  258  are coupled to flexible shafts  262  which extend to helical screw fasteners  214 . There are multiple satellite gears  258  and multiple flexible shafts  262 , however, for clarity only two of each are illustrated in  FIG. 12 . In one embodiment, if a second gear  256  is provided to drive some of the fasteners. For example, eight shafts  262  could be driven by gear  256  and a second gear (not shown) located above gear  256  could drive eight more shafts  262  which extend vertically through the spaces shown in  FIG. 14 . Flexible shafts  262  pass through holes in plate  264  and in housing  270 . Plate  264  and housing  270  are fixed relative to tube  232  and retain flexible shafts  262  in a favorable orientation to transmit twisting motion from the vertical axis of drive shaft  222  to the axis of each helical screw fastener  214 . With the satellite gears  258  held in relatively fixed locations relative to tube  232 , when drive shaft  222  is twisted relative to tube  232 , gear  256  drives satellite gears  258  so that they distribute twisting motion to all eight, or more, flexible shafts  262  simultaneously. Flexible shafts  262 , in turn, couple this twist or drive to the helical screw fasteners  214  (only two are shown in  FIG. 12 ). Driver tips  266  on the ends of flexible shafts  262  are shaped to engage the hub portions  244  of helical screw fasteners  214 . Typically, driver tips  266  have a hexagonal, square or cylindrical slotted shape and slidingly engage a correspondingly hexagonal or square or cylindrical slotted hub shape of helical screw fasteners  214  to transmit torque. Torsional drive is thus distributed from drive shaft  222  (or handle  224 ) through drive train  250  to drive helical screw fasteners  214  into tissue annulus  213 . Helical screw fasteners  214  advance at approximately right angles to the hand twisting motion and at approximately right angles to tool housing  216 . Driver tool  210  is inserted in a convenient straight direction down the aorta toward the tissue annulus  213 , avoiding having to approach individual helical screw fasteners  214  at awkward or difficult angles and at different radial directions. All of helical screw fasteners  214  advance simultaneously, avoiding delay in completing the implantation. 
     In  FIG. 12 , cylindrical housing  270  is snap fit in tube  232  and serves as a guide for flexible shafts  262 , which reduces binding or tangling of flexible shafts  262 . Compression spring  272  presses drive train  250  toward distal end  218  to keep driver tips  266  engaged with helical screw fasteners  214 . Handle  224  ( FIG. 10 ) can be pulled away from tool housing  216 , compressing spring  272  and moving drive train  250  away from distal end  218 . When drive train  250  is moved away from distal end  218 , driver tips  266  are slid out of or decoupled from helical screw fasteners  214 . 
     In  FIG. 13 , an enlarged end view of distal end  218  is shown. In  FIG. 13 , outer ring  212  has been omitted from the drawing for clarity. End  234  of tool housing  216  is generally cylindrical in shape and houses tube  232  which, in one embodiment, has four struts  236  extending from it. Flexible shafts  262  pass through holes  271  in cylindrical housing  270  and couple with hub portions  244  of helical screw fasteners  214 . Helical screw fasteners  214  have a helical portion  246  for engaging tissue. Helical portion  246  also couples with the holes  242  in outer ring  212  ( FIG. 12 ) such that helical screw fasteners  214  are self-advancing when twisted about their central axis. Hub portion  244  of helical screw fasteners  214  slides along driver tips  266  to accommodate the advancing motion. This arrangement keeps the helical screw fasteners  214  retained to the tool  210 , preventing the fasteners from becoming prematurely detached from the tool. In one embodiment, shafts  262  extend directly in a radial direction or bend to go to a drive tip  266  at a different location due to space limitations in housing  270 . In  FIGS. 10-13  all of the helical screw fasteners  214  can be advanced simultaneously into tissue when handle  224  is twisted relative to tool housing  216 . Each flexible shaft  262  turns or bends in a different radial direction. 
     In  FIG. 14 , internal construction of drive train  250  is shown.  FIG. 14  is a sectional view along line  14 - 14  of  FIG. 12 . In this embodiment, gear  256  is shown attached to gear shaft  252  and engaging all (e.g. eight or more) satellite gears  258 . Gears  256 ,  258  are spur gears which mesh with each other as shown only partially at  274 . The satellite gears are attached to flexible shafts  262  which serve as axles for the satellite gears  258 . Drive train  250  is housed within tube  232  which, in turn, is housed in tool housing  216 . The use of flexible shafts permits coupling around sharp, approximately right angle turns with multiple radial directions of drive for the multiple helical fasteners. 
     The tissue annulus of the heart has been prepared to receive the heart valve prosthesis pursuant to techniques known in the art. Driver tool  210  has been preloaded with outer ring  212  snapped on its distal end  218  and helical screw fasteners  214  inserted in outer ring  212  and coupled to driver tips  266 . Distal end  218  is then advanced toward prepared tissue annulus  213  until outer ring  212  is aligned within the tissue annulus. Handle  224  is twisted to advance helical screw fasteners  214  into the tissue annulus. When outer ring  212  is attached by helical screw fasteners  214  to the tissue annulus, handle  224  is lifted relative to tool housing  216 . This compresses spring  272  and disengages driver tips  266  from helical screw fasteners  214  if they have not already been disengaged by the advance of the helical fasteners. Handles  226  and  228  are squeezed together, unsnapping outer ring  212  of the heart valve from the tool  210 . The tool  210  is removed, leaving outer ring  212  attached to the tissue annulus of the heart by multiple helical fasteners. 
     In  FIGS. 15 and 16 , an alternative embodiment  300  of the distal end of the driver tool shown in  FIGS. 10 and 11  is shown. In  FIG. 15 , drive shaft  322 , corresponding to drive shaft  222  in  FIGS. 10 and 11 , has a tapered portion  302  and a splined tip  304  at the distal end. The splined tip  304  engages a central hub  306  of a turntable  308  for rotating the turntable  308 . Turntable  308  has a circular gear rack  310  spaced radially outward from the central hub  306 . A plurality of spur gears  312  engage the circular gear rack  310  with loose tolerances, allowing for any misalignment between the spur gears  312  and the turntable. Each spur gear  312  has a hub  314  surrounding a throughhole  316  along a central axis of spur gear  312 . Each hub  314  is flared or swaged outwardly to secure it to mounting tube  318  such that it is free to spin when driven by circular gear rack  310 . Turntable  308  is free to spin in a circular groove  309  formed on the end of mounting tube  318 . Each throughhole  316  is shaped to receive and loosely engage a driver tip  324 . When driver tips  324  are hexagonal, then throughhole  316  has a corresponding hexagonal shape and is slightly larger than driver tip  324 . A spring arrangement  326  coupled to the plurality of driver tips  324  provides axial force to the driver tips  324  for driving helical fasteners  214 . Turntable  308  and spur gears  312  comprise a drive train for driving the driver tips  324 . Spring arrangement  326  comprises a plurality of springs  330  which can be formed from flat strips of spring steel or other suitable material. Each spring  330  is attached to mounting tube  318  with a fastener  339 . Each spring is also attached to a driver tip  324  with a fastener  335  so that driver tip  324  rotates easily on fastener  335  when it is driven by spur gear  312 . Each spring  330  engages tapered portion  302  at contact point  332 . When drive shaft  322  is down (as illustrated in  FIG. 15 ) the spring arrangement  326  applies a radially outward force to the driver tips assisting with engagement of tissue  334 . When drive shaft  322  is lifted up, the contact points  332  engage a narrower cross-section  333  of the tapered portion  302 , resulting in a radially inward retraction force on the driver tips  324 . Also, when drive shaft  322  is lifted, the turntable  308  disengages from spline  304 , allowing the turntable  308  to rotate easily, which facilitates disengagement of driver tips  324 . Drive shaft  322  is held in a position for driving by coil spring  336 , which is compressed between lip  337  on driveshaft  322  and tube  232 . When drive shaft  322  is lifted, spring  336  is compressed first to provide disengagement, and then as drive shaft  322  is lifted further, fully compressed spring  336  transfers lifting force to tube  232 , and secondly then, spring  225 , which is stiffer than spring  336 , is compressed to allow disengagement of struts  236  from protruding ring  240  of outer ring  212 . 
     In the embodiments shown in  FIG. 15 , the springs  330  can be assisted by additional coil springs secured at location  331 , if desired. 
     In  FIG. 17 , a further embodiment  350  is shown which is similar to the embodiment shown in  FIGS. 15-16 , except that the gears  352  are beveled gears and the circular gear rack  354  is correspondingly beveled to engage the beveled gears  352 . Parts in  FIG. 17  which are similar to those in  FIGS. 15-16  have the same reference numbers that are used in  FIGS. 15-16 . 
     In the embodiments shown in  FIG. 17 , the springs  330  can be assisted by additional coil springs secured at location  331 , if desired. 
     In  FIG. 18 , a further preferred embodiment of a helical screw fastener  400  is shown, and a corresponding driver tip  402  is shown in  FIG. 1.9 . Helical screw fastener  400  has a hub  404  which includes a last coil which turns into the center of helical screw fastener  400  to form a drive lug  406  which can receive a torsional force. Helical screw fastener  400  has a helical main body  408  ending in a sharp point  410  for engaging a tissue annulus such as tissue annulus  213  of  FIG. 12 . The driver tip  402  of  FIG. 19  includes a slot  420  with a slot base  422  for slidingly engaging drive lug  406 . The driver tip  402  includes a round shaft  424  which slidingly engages the main body  408  of helical screw fastener  400 . The driver tip  402  also includes a shoulder  426  which, along with the slot base  422  provides an axial driving force to helical screw fastener  400 , urging the sharp point  410  toward the tissue annulus  213  of  FIG. 12 . Preferably, helical screws  214  may be coupled with outer ring  212  such that they are self advancing, thereby needing no axial driving force and simply advance into tissue annulus  213  as they are turned. Helical screw fastener  400  and driver tip  402  can be used in the tools shown in  FIGS. 10-17 . 
     For convenience, a driver tool  210  as shown in any of  FIGS. 10-17 , outer ring  212  and multiple helical screw fasteners  214  are provided assembled in a package as a sterilized kit. The tool is preloaded by having outer ring  212  snapped in place on the distal end, helical fasteners preloaded in holes in the outer ring and the driver tips coupled to the helical fasteners. 
     Preferably, the rings set forth herein are formed of biocompatible materials. The outer ring is generally made of material more flexible than the inner ring, such as polyethylene terephthlate (PET), polyetheretherketones (PEEK), ultrahigh molecular weight polyethylene, Nitinol® (a nickel-titanium alloy), and polyurethane. The inner ring is made preferably of a material more rigid than the outer ring such as titanium, MP35N (wrought cobalt-nickel-chromium-molybdenum alloy), ceramic, Elgiloy® (cobalt-chromium-nickel-molybdenum iron alloy), pyroltic carbon or other rigid polymers for the inner ring. The particular shapes of the orifice rings and attachment mechanisms may be modified as appropriate. The ring coupling mechanism for coupling the two rings may be any mechanism as desired and is not limited to the particular “snap” coupling techniques set forth herein. For example, the coupling techniques may include screws, wires, bayonet locking mechanism, and nails which extend axially and engage the rings. Further, the configuration of the inner orifice ring and its occluding mechanism may be other than those set forth herein. 
     Implantation time is short and relatively simple implantation techniques can be used. Further, the angular positioning of the leaflets in the inner ring is easily accomplished by rotating the inner ring with respect to the outer ring. The invention allows surgical access to subvalvular features prior to coupling the inner ring to the outer ring without the possibility of damaging the occluding mechanism, for example. The inner valve ring can be removed and replaced without excising the entire prosthesis. The complexity of surgery is reduced because manual suturing may not be required. The area of the lumen is increased over typical prior art designs and a lower profile results because the cuff attachment mechanism requires less area. With the inner ring coupled to the outer ring, the outer ring attachment mechanisms are prevented from “backing out” and completely shielded from blood flow where they could otherwise initiate formation of thrombus. Any type of occluding mechanism may be used and the attachment mechanism may be integral with the ring body. The invention also eliminates suturing such that the implantation procedure is faster. Further, there are no suture tails which could lead to thrombus formation. The invention is also useful in minimally invasive surgery because the attachment is with a single elongate tool which can be placed through a trocar in the patient and the entire valve attached in a single step. 
     The component parts of tools depicted in  FIGS. 10-17  can be constructed of biocompatible polymers such as polyurethane, delrin, polysulfone, of metals such as stainless steel, or of other biocompatible materials. Gears are preferably constructed of nylon, teflon or stainless steel. The completed tool or kit can be gamma sterilized and disposable, if desired. Flexible shafts can be formed of stainless steel and coated with nylon or teflon for lubricity. Helical screw fasteners can be made of platinum-iridium alloy, MP35N (a wrought cobalt-nickel-chromium-molybdenum alloy), stainless steel, titanium or other biocompatible materials. If desired, an electric motor can be used to provide the torsional force rather than manually twisting a handle. 
     The present invention is also applicable to stentless bioprosthetic heart valves.  FIG. 20  is a perspective view of such a stentless bioprosthetic heart valve  510 , such as the Toronto SPV® valve from St. Jude Medical. Valve  510  includes a covering  512  and is adapted for implantation in the aortic position. Valve  510  includes three leaflets  516 , 518  and  520  which meet along coaptation surfaces  522 . Covering  512  can comprise a flexible or fabric sheath which is contoured to the external surface of the valve  510 . In such an embodiment, covering  512  consists of a generally annular base  524  and three axially projecting and circumferentially-spaced commissure supports  526 ,  528  and  530 . Sutures  534  along inflow edge  536  and outflow edge  538  are used to attach covering  512  to valve  510 . Covering  512  can be a biocompatible polymer such as polyester or polytetrafluoroethylene (PTFE). 
       FIG. 21  shows an exploded view of valve  510  and outer frame  550 . Outer frame  550  has a shape which substantially matches the outer shape of valve  510  such that valve  510  fits securely within outer frame  550 . Outer frame  550  can be secured to the native tissue annulus using any appropriate technique such as sutures, staples or screws, as discussed above, or other techniques. As outer frame  550  does not include the valve structure, it provides improved access to and visibility of the annular and sub-annular regions for the surgeon during the implantation procedure such that the orientation and location of the valve is more accurate. Outer frame  550  is a substantially flexible structure. In one embodiment, it is relatively thin, on the order of about 0.01 to about 0.05 inches (about 0.25 mm to about 1.27 mm), and is made from a flexible biocompatible polymer such as polyester or PTFE in a molded or fabric form. The wall of outer frame  550  can be continuous, meshed, or have perforations. 
     After outer frame  550  has been implanted, valve  510  is attached to frame  550 . This attachment can also be through suturing or other attachment techniques. In one embodiment, an adhesive is used to secure valve  510  to frame  550 . One such adhesive is described in U.S. patent application Ser. No. 09/235,138, filed Jan. 22, 1999. For example, a chemically activated adhesive can be used in which the activating chemical is applied to outer frame  550  or valve  510  separately or combined together on either the frame  550  or valve  510  just prior to implantation. If an adhesive is used, a holder can be provided to hold the valve against frame  550  during the adhesion process. Preferably, the holder would have a shape which substantially matches the shape of outer frame  550 . Such a holder preferably maintains pressure between the valve  510  and the outer frame  550 . For example, the holders can include an inflatable membrane similar to a balloon such that a force can selectively be applied from the valve  510  to the outer frame  550  while the adhesive cures. 
     These configurations allow the surgeon to use an adhesive without requiring the adhesive itself to be accurately applied to the native tissue during implantation. Further, as the adhesive will be placed on the frame  550  and/or valve  510 , the adhesive will not drift into undesirable areas in the internal part of the valve such as the coronary ostia or into the left ventricle. A stronger and more consistent bond can be obtained because the adhesive will bond between similar materials as opposed to trying to bond the valve  510  directly to the native tissue. The invention reduces the time required to implant the valve, provides improved control of adhesive placement and improves bond reliability between similar materials. 
     A continuous or partial ridge  552  can be provided along the inflow edge of frame  550  to aid in the alignment and placement of valve  510  within frame  550 . For example, the inflow edge  536  of valve  510  abuts ridge  552  when valve  510  has been accurately placed, and commissure supports  526 ,  528 ,  530  are in vertical alignment with the corresponding features of outer frame  550 . Valve  510  can be rotated to the correct alignment before the adhesive cures. During implantation, the inner valve  510  mates in substantial alignment with outer frame  550 . 
     The outer frame  550  can be implanted using the techniques set forth herein. For example,  FIG. 22  is a side cross sectional view similar to  FIG. 11  showing tool  211  carrying outer frame  550  at distal end  218 . Screws  214  extend through outer frame  550  and can be used to attach outer frame  550  to the native tissue annulus as discussed above. Although  FIG. 22  illustrates screws  214  located in a single plane near the inflow edge of outer frame  550 , additional screws can be positioned at other locations on frame  550  to provide improved attachment. In such an embodiment, additional flexible shafts  262  such as those shown in  FIG. 12  can be provided to simultaneously actuate additional screws. Once the valve  510  is coupled to outer frame  550 , the heads of screws  214  are covered by valve  510  and secured in place. Sutures or staples can also be used to implant outer frame  550 . In one aspect, any type of surgical attachment mechanism can be used to implant outer frame  550 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.