Abstract:
A method for delivering a heart valve prosthesis to a native valve annulus comprises expanding an expandable frame at the native valve annulus and positioning a replacement heart valve within the expandable frame. The expandable frame preferably includes a first anchoring portion that is positioned on a first side of the native valve annulus and a second anchoring portion that is positioned on a second side of the native valve annulus. The first anchoring portion engages tissue on the first side of the native valve annulus and the second anchoring portion engages tissue on the second side of the native valve annulus for securing the expandable frame to the native valve annulus. The replacement heart valve comprises a plurality of leaflets for replacing the function of the native valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/309,680, which is a national stage entry of International Application No. PCT/US2007/016855, filed Jul. 27, 2007, which designates the United States and was published in English by the International Bureau on Jan. 31, 2008 as WO 2008/013915, which claims the benefit of U.S. Provisional Application No. 60/833,791, filed Jul. 28, 2006, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to heart valve prostheses, preferably to aortic valve prostheses. More specifically, the invention relates to heart valve prostheses that can be implanted percutaneously by means of a catheter from a remote location without opening the chest cavity. 
         [0004]    2. Related Art 
         [0005]    Heart valve surgery is used to repair or replace diseased heart valves. Valve surgery is an open-heart procedure conducted under general anesthesia. An incision is made through the patient&#39;s sternum (sternotomy), and the patient&#39;s heart is stopped while blood flow is rerouted through a heart-lung bypass machine. 
         [0006]    Valve replacement may be indicated when there is a narrowing of the native heart valve, commonly referred to as stenosis, or when the native valve leaks or regurgitates. When replacing the valve, the native valve is excised and replaced with either a biologic or a mechanical valve. Mechanical valves require lifelong anticoagulant medication to prevent clot formation around the valve, which can lead to thromboembolic complications and catastrophic valve failure. Biologic tissue valves typically do not require such medication. Tissue valves can be obtained from cadavers (homografts) or can be from pigs (porcine valve) and cows (bovine pericardial valves). Recently equine pericardium has also been used for making valves. These valves are designed to be attached to the patient using a standard surgical technique. 
         [0007]    Valve replacement surgery is a highly invasive operation with significant concomitant risk. Risks include bleeding, infection, stroke, heart attack, arrhythmia, renal failure, and adverse reactions to the anesthesia medications, as well as sudden death. Two to five percent of patients die during surgery. 
         [0008]    Post-surgery, patients temporarily may be confused due to emboli and other factors associated with the heart-lung machine. The first two to three days following surgery are spent in an intensive care unit where heart functions can be closely monitored. The average hospital stay is between one and two weeks, with several more weeks to months required for complete recovery. 
         [0009]    In recent years, advancements in minimally invasive, endoaortic, surgery interventional cardiology, and intervention radiology have encouraged some investigators to pursue percutaneous replacement of the aortic heart valve. Percutaneous Valve Technologies (“PVT”) of Fort Lee, N.J., has developed a balloon-expandable stent integrated with a bioprosthetic valve, which is the subject of U.S. Pat. Nos. 5,411,552, 5,840,081, 6,168,614, and 6,582,462 to Anderson et al. The stent/valve device is deployed across the native diseased valve to permanently hold the valve open, thereby alleviating a need to excise the native valve and to position the bioprosthetic valve in place of the native valve. PVT&#39;s device is designed for delivery in a cardiac catheterization laboratory under local anesthesia using fluoroscopic guidance, thereby avoiding general anesthesia and open-heart surgery. The device was first implanted in a patient in April of 2002. 
         [0010]    PVT&#39;s device suffers from several drawbacks. Deployment of PVT&#39;s stent has several drawbacks, including that there is very little control over its deployment. This lack of control can endanger the coronary ostea above the aortic valve and the anterior leaflet of the mitral valve below the aortic valve. 
         [0011]    Another drawback of the PVT device is its relatively large cross-sectional delivery profile. This is largely due to fabricating the tri-leaflet pericardial valve inside a robust stainless steel stent. Considering they have to be durable, the materials for the valve and the stent are very bulky, thus increasing the profile of the device. The PVT system&#39;s stent/valve combination is mounted onto a delivery balloon, making retrograde delivery through the aorta challenging. An antegrade transseptal approach may therefore be needed, requiring puncture of the septum and routing through the mitral valve, which significantly increases complexity and risk of the procedure. Very few cardiologists are currently trained in performing a transseptal puncture, which is a challenging procedure by itself. 
         [0012]    Another drawback of the PVT device is its lack of fixation provision. It in effect uses its radial force to hold the stent in the desired position. For this to work, sufficient dilatation of the valve area has to be achieved; but this amount of dilation can cause damage to the annulus. Also, due to its inability to have an active fixation mechanism, the PVT device cannot be used to treat aortic regurgitation. 
         [0013]    Another drawback to this system is that it does not address the leakage of blood around the implant, after its implantation. 
         [0014]    Other prior art replacement heart valves use self-expanding stents that incorporate a valve. One such device is that disclosed in U.S. Pat. No. 7,018,406 to Seguin et al. and assigned to and made by CoreValve SA. In the endovascular aortic valve replacement procedure, accurate placement of aortic valves relative to coronary ostia and the mitral valve is critical. Standard self-expanding systems have very poor accuracy in deployment, however. Often the proximal end of the stent is not released from the delivery system until accurate placement is verified by fluoroscopy and the stent typically jumps once released. It is therefore often impossible to know where the ends of the stent will be with respect to the native valve, the coronary ostia, and the mitral valve. The anchoring mechanism is not actively provided (that is, there is no method of fixation other than the use of radial force and barbs that project into the surrounding tissue and not used as positioning marker (that is, markers seen under fluoroscopy to determine the position of the device). 
         [0015]    A simple barb as used in the CoreValve device relies mainly on friction for holding the position. 
         [0016]    Another drawback of prior art self-expanding replacement heart valve systems is their lack of radial strength. In order for self-expanding systems to be easily delivered through a delivery sheath, the metal needs to flex and bend inside the delivery catheter without being plastically deformed. In arterial stents, this is not a challenge, and there are many commercial arterial stent systems that apply adequate radial force against the vessel wall and yet can collapse to a small enough of a diameter to fit inside a delivery catheter without plastically deforming. However, when the stent has a valve fastened inside it, as is the case in aortic valve replacement, the anchoring of the stent to vessel walls is significantly challenged during diastole. The force required to hold back arterial pressure and prevent blood from going back inside the ventricle during diastole will be directly transferred to the stent/vessel wall interface. Therefore the amount of radial force required to keep the self expanding stent/valve in contact with the vessel wall and prevent it from sliding will be much higher than in stents that do not have valves inside of them. Moreover, a self-expanding stent without sufficient radial force will end up dilating and contracting with each heartbeat, thereby distorting the valve, affecting its function and resulting in dynamic repositioning of the stent during delivery. Stent foreshortening or migration during expansion may lead to improper alignment. 
         [0017]    Additionally, the stent disclosed in U.S. Pat. No. 6,425,916 to Garrison simply crushes the native valve leaflets against the heart wall and does not engage the leaflets in a manner that would provide positive registration of the device relative to the native position of the valve. This increases an immediate risk of blocking the coronary ostia, as well as a longer-term risk of migration of the device post-implantation. Further still, the stent comprises openings or gaps in which the replacement valve is seated post-delivery. Tissue may protrude through these gaps, thereby increasing a risk of improper seating of the valve within the stent. 
         [0018]    In view of drawbacks associated with previously known techniques for endovascularly replacing a heart valve, it would be desirable to provide methods and apparatus that overcome those drawbacks. 
         [0019]    Sadra et al. (U.S. published application No. 20050137701) describes a mechanism for anchoring a heart valve, the anchoring mechanism having an actuation system operated remotely. This mechanism addresses the fixation issue; however, considering the irregular shape of the aortic annulus there is a real potential for deforming the prosthetic valve annulus; this may require additional balloon angioplasty to give it its final shape, and also make the new valve more prone to fatigue and fracture. Moreover if full expansion of the stent is prone to deformation, the leaflet coaptation of the valve will be jeopardized. 
         [0020]    Sadra et al. (U.S. published application No. 20050137691) describes a system with two pieces, a valve piece and an anchor piece. The valve piece connects to the anchor piece in such a fashion that it will reduce the effective valve area considerably. Valve area, i.e., the inner diameter of the channel after the valve leaflets open, is of prime importance when considering an aortic valve replacement in a stenotic valve. Garrison&#39;s valve is also implanted in the inner portion of the stent, compromising the effective valve outflow area. Sadra et al.&#39;s and Garrison&#39;s valves overlook this very critically important requirement. 
         [0021]    The technologies described above and other technologies (for example, those disclosed in U.S. Pat. No. 4,908,028 to Colon et al.; U.S. Published Application No. 2003/0014104, U.S. Published Application No. 2003/0109924, U.S. Published Application No. 2005/0251251, U.S. Published Application No. 2005/0203616, and U.S. Pat. No. 6,908,481 to Cribier; U.S. Pat. No. 5,607,469 to Frey; U.S. Pat. No. 6,723,123 to Kazatchkov et al.; Germany Patent No. DE 3,128,704 A1 to Kuepper; U.S. Pat. No. 3,312,237 to Mon et al.; U.S. Published Application No. 2005/0182483 to Osbourne et al.; U.S. Pat. No. 1,306,391 to Romanoff; U.S. Published Application No. 2005/0203618 to Sharkcawy et al.; U.S. Published Application No. 2006/0052802 to Sterman et al.; U.S. Pat. No. 5,713,952; and U.S. Pat. No. 5,876,437 to Vanney et al.) also use various biological, or other synthetic materials for fabrication of the prosthetic valve. The duration of function and physical deterioration of these new valves have not been addressed. Their changeability has not been addressed, in the percutaneous situation. 
         [0022]    It is to the solution of these and other problems that the present invention is directed. 
       SUMMARY OF THE INVENTION 
       [0023]    It is accordingly a primary object of the present invention to provide to methods and apparatus for endovascularly replacing a heart valve. 
         [0024]    In is another object of the present invention to provide methods and apparatus for endovascularly replacing a heart valve with a replacement valve prosthesis using a balloon expandable and/or self expanding valve cage stent upon which a bi-leaflet or tri-leaflet elastic valve is inserted. 
         [0025]    It is also a feature of this invention that the valve piece of the implant is removable, and thus exchangeable, in the event of long or medium term failure of the implanted valve. 
         [0026]    It is another object of this invention to provide maximal valve area to the out flow tract of the left ventricle, thus minimizing the gradient across the valve, by using a supra annular implant of the valve piece to the valve cage stent. 
         [0027]    These and other objects are achieved by a heart valve prosthesis comprising a cylindrical valve cage stent constructed to be implanted percutaneously in the planar axis of a native valve annulus, the valve cage stent having a superior rim; and an elastic and compressible, multi-leaflet valve insertable percutaneously into the body, the valve including a valve frame made from a memory metal and a tissue cover attached to the valve frame; and attachment means for attaching the valve to the superior rim of the valve cage. 
         [0028]    The valve can be a bi-leaflet or a tri-leaflet valve. The bi-leaflet valve includes a frame, a tissue cover, a deformable hinge, and means for detachably connecting the valve to the valve cage stent. The frame has two substantially semicircular, expandable, and compressible parts, and the tissue cover is configured to cover the two parts of the frame with the straight sides of the two parts in spaced-apart relation. The tissue cover has a central aperture and the two parts of the frame have respective slots. The deformable hinge has oppositely extending arms extending through the slots and a stem received through the aperture. The superior rim of the valve cage stent has a valve mount affixed thereto for receiving a mating part on the hinge, thereby defining the attachment means. 
         [0029]    The tri-leaflet valve includes a frame, a tissue cover, and means for detachably connecting the valve to the valve cage stent. The frame is cylindrical and has three commissural posts mounted thereon. The tissue cover has three cusps fitted and sewn to the valve frame, the commissural posts being sized to maintain the commissural height of the cusps. The valve cage stent has three commissural pins extending from the superior rim thereof, and the commissural posts of the frame are cannulated to receive the commissural pins of the valve cage stent, thereby defining the attachment means. 
         [0030]    Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which: 
           [0032]      FIG. 1  is a diagram of a valve prosthesis in accordance with the present invention. 
           [0033]      FIG. 2A  is a diagrammatic plan view of a frame for a bi-leaflet percutaneous heart valve in accordance with the present invention. 
           [0034]      FIG. 2B  is a diagrammatic plan view of a tissue cover for the frame of  FIG. 2A . 
           [0035]      FIG. 2C  is a diagrammatic plan view of an assembled bi-leaflet percutaneous heart valve in accordance with the present invention, incorporating the frame of  FIG. 2A  and the tissue cover of  FIG. 2B . 
           [0036]      FIG. 2D  is a diagrammatic side elevational view of the bi-leaflet percutaneous heart valve of  FIG. 2C  in the open position. 
           [0037]      FIG. 2E  is a diagrammatic side elevational view of the bi-leaflet percutaneous heart valve of  FIG. 2C  in the closed position. 
           [0038]      FIG. 2F  is a top perspective view of an assembled bi-leaflet percutaneous heart valve in accordance with the present invention, in the closed position. 
           [0039]      FIGS. 2G and 2H  are top and side perspective views of the bi-leaflet percutaneous heart valve of  FIG. 2F  in the open position. 
           [0040]      FIGS. 2I and 2J  are side perspective views of the valve cage stent for use with the bi-leaflet percutaneous heart valve of  FIG. 2F . 
           [0041]      FIG. 2K  is a partial perspective view of the bi-leaflet percutaneous heart valve of  FIG. 2F  mounted on the valve cage stent of  FIG. 2I , with the valve in the closed position. 
           [0042]      FIG. 2L  is a partial perspective view of the bi-leaflet percutaneous heart valve of  FIG. 2F  mounted on the valve cage stent of  FIG. 2I , with the valve in the open position. 
           [0043]      FIG. 3A  is a diagrammatic perspective view of a frame for a tri-leaflet percutaneous heart valve in accordance with the present invention. 
           [0044]      FIG. 3B  is a perspective view of a tissue cover for the frame of  FIG. 3A . 
           [0045]      FIG. 3C  is a perspective view of an assembled tri-leaflet percutaneous heart valve in accordance with the present invention, incorporating the frame of  FIG. 3A  and the tissue cover of  FIG. 3B   
           [0046]      FIG. 3D  is a side perspective view of the valve cage stent for use with the tri-leaflet percutaneous heart valve of  FIG. 3C . 
           [0047]      FIGS. 3E and 3F  are top perspective views of the valve cage stent for use with the tri-leaflet percutaneous heart valve of  FIG. 3C . 
           [0048]      FIG. 3G  is a diagrammatic view of a portion the valve cage stent for use with the tri-leaflet percutaneous heart valve of  FIG. 3C , which as been opened up and flattened for purposes of illustration. 
           [0049]      FIG. 3H  is a partially cut-away perspective view of the tri-leaflet percutaneous heart valve of  FIG. 3C  mounted on the valve cage stent of  FIG. 3D , in the undeployed condition. 
           [0050]      FIG. 3I  is a partially cut-away perspective view of the tri-leaflet percutaneous heart valve of  FIG. 3C  mounted on the valve cage stent of  FIG. 3D , in the deployed condition. 
           [0051]      FIGS. 4A-4G  show the sequence of steps in implantation of the bi-leaflet percutaneous heart valve prosthesis of  FIG. 2C  in an aorta, in which the valve is attached to the valve cage stent outside the delivery catheter. 
           [0052]      FIGS. 5A-5I  are diagrammatic representations of the sequence of steps in implantation of the bi-leaflet percutaneous heart valve of  FIG. 2C , the aorta being omitted from all of  FIGS. 5A-5I  and the valve cage being omitted from  FIGS. 5A-5F  for clarity. 
           [0053]      FIGS. 6A-6J  show the sequence of steps in implantation of the tri-leaflet percutaneous heart valve of  FIG. 3C  in an aorta, in which the valve is attached to the valve cage stent outside the delivery catheter. 
           [0054]      FIGS. 7A and 7B  are exploded and assembled views, respectively, of the delivery system apparatus used in implantation of the bi-leaflet and tri-leaflet valves in accordance with the present invention. 
           [0055]      FIG. 7C  is an end view of the flexible sheath of the delivery system apparatus of  FIGS. 7A and 7B . 
           [0056]      FIG. 8  is a side view of a valve cage stent mounted on a balloon catheter. 
           [0057]      FIGS. 9A-9T  show the sequence of steps in implantation of the tri-leaflet percutaneous heart valve of  FIG. 3C  in an aorta, in which the valve is attached to the valve cage stent within the delivery catheter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0058]    In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0059]    The present invention relates to heart valve prostheses that can be implanted percutaneously by means of a catheter from a remote location without opening the chest cavity. As shown in  FIG. 1 , the valve prosthesis  10  comprises two parts, (1) a valve cage stent  20  constructed to be implanted in the planar axis of the native valve annulus, (2) an elastic and compressible valve  30 , and (3) an attachment mechanism for attaching the valve  30  to the superior rim of the above mentioned valve cage stent  20 . In accordance with the present invention, two types  110  and  210  of heart valve prosthesis  10  are contemplated, one type  110  incorporating an elastic and compressible bi-leaflet hinged valve  130  (shown in  FIGS. 2A-2E ) and the other type  210  incorporating an elastic and compressible tri-leaflet biologic valve  230  (shown in  FIGS. 3A-3C ). A system and method for implanting the valves (shown in  FIGS. 4A-4G, 5A-5I, and 6A-6J ) is also encompassed by the invention. 
         [0060]    Referring now to  FIGS. 2A-2H , the bi-leaflet tissue valve  130  comprises a two-part (that is, a two-leaflet) frame  132  made from a memory metal wire or strip and a tissue cover  133 . As best shown in  FIG. 2A , each part  132   a  and  132   b  of the frame  132  is substantially semicircular. Portions of each part  132   a  and  132   b  of the frame  132  (for example, the straight side and the center portion of the curved side) are configured (for example, by having a sinusoidal configuration, shown by broken lines in  FIGS. 2A and 2C ) so that each part  132   a  and  132   b  of the frame  132 , as well as the frame  132  as a whole, is expandable and compressible, while the remaining portions of the frame  132  are not expandable and compressible. 
         [0061]    Each part  132   a  and  132   b  of the frame  132  includes a slot  134  for receiving a hinge  135  having a shape when deployed that is similar to a lower-case “t”, as shown in  FIGS. 2D and 2E , having two aims  135   a  and  135   b  and a stem  135   c.  The slot  134  is formed unitarily with the frame  132 . The “t”-shaped hinge  135  is stamped out of memory metal (for example, nitinol) sheeting so that it is deformable. The arms  135  and  135   b  of the hinge  135  have projections  135   d  at their ends, which function as stops for the leaflets. The stem  135   c  of the hinge  135  has a snap-on or screw-in mechanism  141  for attachment to a valve mount  142  (shown in  FIGS. 2I-2L ), as described below. 
         [0062]    The tissue cover  133  (shown in  FIG. 2B ) is made, for example, of equine or bovine pericardium, or various synthetic materials, for example, or medical grade silicone, fabric, or other compressible, materials, and is configured to cover the two parts  132   a  and  132   b  of the frame  132  with their straight sides in spaced apart relation, with a central aperture  133   a  in the center for receiving the stem of the “t”-shaped hinge  135  and two side apertures  133   b  in alignment with the slots  134  for receiving the arms  135   a  and  135   b  of the hinge  135 . The tissue cover  133  is sewn to each part  132   a  and  132   b  of the frame  132 , as shown in  FIGS. 2C and 2F-2H , and thus connects the two parts  132   a  and  132   b  of the frame  132  in spaced-apart relation. 
         [0063]    As discussed in greater detail below, in use, the bi-leaflet valve  130  is detachably connected to a valve mount  142  (shown in  FIGS. 2I and 2I ) via the “t”-shaped hinge  135 , as shown in  FIGS. 2K-2N, 4D-4G, and 5G-5I . The valve mount  142  is also made from a memory metal so that it is collapsible. More specifically, the valve mount  142  has arms  142   a  and  142   b  on either side of a receptacle  142   c,  which are folded up vertically when the valve cage stent  120  is in its compressed (undeployed) condition, the ends of the arms  142   a  and  142   b  being affixed to the valve cage stent  120 . 
         [0064]    The detachable and collapsible bi-leaflet construction of the valve  130  enables the valve  130  in conjunction with its entire delivery system to be sized down so that it can be inserted percutaneously using a catheter, as described below. 
         [0065]    Referring now to  FIGS. 3A-3C , the tri-leaflet tissue valve  230  comprises an expandable and compressible valve frame  232  (shown in  FIG. 3A ) made from a memory metal wire or strip and a tissue cover  233  (shown in  FIGS. 3B and 3C ). The tissue cover  233  is made from the individual cusps of a porcine aortic valve sewn to appropriate fabric. Three identical cusps are selected. Two or more pigs are used to get ideal sized aortic cusps. The muscle bar cusp is preferably not used; and all of the sinus and surrounding tissue is S discarded. The commissural height is maintained at all cost. The tissue cover  233  (that is, the cusps sewn to the fabric) is fitted and sewn to the valve frame  232 . The valve frame  232  has three cannulated commissural posts  240   a,    240   b,  and  240   c  mounted thereon, and the tissue cover  233  is sewn to the commissural posts  240   a,    240   b,  and  240   c  to complete the tri-leaflet valve  230  ( FIG. 3C ). 
         [0066]    As shown in  FIGS. 3A-3C , the tri-leaflet valve  230  is mounted on commissural pins  240   aa ,  240   bb , and  240   cc  provided on a valve cage stent  220  of the type disclosed in provisional application No. 60/735,221, which is incorporated herein by reference in its entirety. More specifically, the commissural posts  240   a,    240   b,  and  240   c  of the valve frame  232  are cannulated to receive the commissural pins  240   aa ,  240   bb , and  240   cc , respectively, of the valve cage stent  220 , thereby connecting the valve frame  232  (and thus the valve  230 ) to the valve cage stent  220 . As described below, the heart valve prosthesis  210  incorporating the tri-leaflet valve  230  is delivered using a catheter. 
         [0067]    As shown in  FIG. 3G , the valve cage stent  220  for use with the tri-leaflet valve  230  has three different zones  221 ,  222 , and  223  along its longitudinal axis, the different zones having different geometric configurations so as to perform different functions. The first, or center, zone  221  functions as the stent connector, which is identical to the stent disclosed in Int&#39;al Patent Application No. PCT/US2006/043526, filed Nov. 9, 2006 (which is based on U.S. Provisional Application No. 60/735,221), and which connects to the native valve annulus. The second and third zones  222  and  223 , at either end of the center zone  221 , function respectively as the superior valve rim carrying the commissural pins in the tri-leaflet valve prosthesis  210  or the valve mount in the bi-leaflet valve prosthesis  110 , and the inferior valve skirt. The valve skirt  223  provides additional support, as well as a fabric/tissue attachment area to minimize leaking. 
         [0068]    The present invention also encompasses a system and method for implanting the above-described percutaneous valve prostheses  10  in the body. In a first embodiment, the system comprises a valve cage stent  20  for implantation in the body by the use of a first catheter of a delivery system  500  (shown in  FIGS. 8A and 8B , and as described in greater detail hereinafter) to provide a stable, fixed, and sturdy frame within which an elastic, compressible valve  30  can be inserted and secured by a second catheter (not shown), and the valve  30  is attached to the valve cage stent  20  after they are discharged from their respective catheters. Performing the procedure in two parts at the same session downsizes the devices considerably, so that the procedure can be performed percutaneously. In a second embodiment, the system comprises a valve cage stent  20  and an elastic, compressible valve  30  which are inserted using the same catheter, and the valve  30  is attached to the valve cage stent  20  within the catheter, as shown in  FIGS. 9A-9T . 
         [0069]    The valve cage stent  20  is a self-expanding or balloon expandable cylindrical valve cage stent  20 , made from memory metal, or stainless steel respectively. The self-expanding valve cage stent and the balloon expandable valve cage stent are structurally the same (that is, they differ only in the material from which they are made). The valve cage stent  20  is fabricated from metal tubing (memory metal or stainless steel), so that it is cylindrical in shape, with the stent pattern being cut into the tubing by laser. 
         [0070]    The expansion of the valve cage stent  20  produces maximal foreshortening of the ovals in the mid portion of the stent and thus provides active fixation of the stent to the annulus of the valve being replaced. The valve cage stent  20  has a fabric covering on its interior and parts of its exterior surfaces so in its expanded state it forms a complete seal and does not allow any leakage of blood. 
         [0071]    For delivery, the valve cage stent  20  is mounted on a balloon  600  ( FIG. 8 ), or in a restraining sheath if self-expandable. The delivery system apparatus  500  is shown in  FIGS. 7A-7C . The delivery system apparatus  500  comprises a flexible outer sheath  510 , in which the valve cage stent  20  is inserted with a first set of guide wires  520  attached thereto, followed by a slotted nosecone  530  having another set of guide wires  540  attached thereto. 
         [0072]    The valve cage stent  20  has provisions for the attachment of the prosthetic valve, depending on the type of prosthetic valve contemplated to be used. For example, in the case of a bi-leaflet valve, the valve is attached to the valve cage stent  120  via a valve mount affixed to the valve cage stent  120 , as shown in  FIGS. 4D-4G and 5G-5I . In the case of a tri-leaflet valve, the valve is attached to the valve cage stent  220  via engagement of the valve commissural posts  240   a,    240   b,  and  240   c  with the commissural pins  240   aa ,  240   bb , and  240   cc  of the valve cage stent  220 , as shown in  FIGS. 6H-6J . 
         [0073]    The delivery system employs a two stage procedure, both stages of which can be performed at the same session, only minutes apart. The first stage is insertion of the valve cage stent  20 . In the case of a bi-leaflet valve, as shown in  FIG. 4A , the valve cage stent  120  has a valve mount connected thereto and a guide wire connected to the valve mount. In the case of a tri-leaflet valve, as shown in  FIGS. 6A-6G  and as described above, the valve cage stent  220  has three commissural pins  240   aa ,  240   bb , and  240   cc  provided thereon and guide wires connected thereto. 
         [0074]    The second stage is insertion of the elastic and compressible valve, which is restrained in another catheter (not shown) for delivery into the valve cage stent  20 . As shown in  FIGS. 4A-4D, 5A-5F, and 6A-6H , in the second stage, the valve is placed over the guide wire (in the case of a bi-leaflet valve) or guide wires (in the case of the tri-leaflet valve) connected to the valve cage stent  20  in order to ensure proper positioning of the valve relative to the stent. Once the valve is seated, the guide wire or wires are withdrawn ( FIGS. 4D-4G, 5G-5I, and 6I-6J ). 
         [0075]    Because the bi-leaflet valve is detachable from the valve mount, it can be replaced when necessary. The valve mount has a snap-on or screw-in mechanism for attachment of the “t”-shaped hinge  135  thereto, as well as the above-described guide wire attached to it for placement of the valve. The use of a valve cage  20  allows for fabrication of a tri-leaflet tissue valve. 
         [0076]    In addition, the connection of valve  30  to the valve cage stent  20  provides the best effective flow dynamics, the flexibility of the whole system  500  is greatly increased, and the profile of the whole system  500  is reduced so that it can be inserted through a small opening in the access vessel. 
         [0077]    Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.