Abstract:
This invention relates to the design and function of a single-tether compressible valve replacement prosthesis which can be deployed into a beating heart without extracorporeal circulation using a transcatheter delivery system. The design as discussed combats the process of wear on anchoring tethers over time by using a plurality of stent-attached, centering tethers, which are themselves attached to a single anchoring tether, which extends through the ventricle and is anchored to a securing device located on the epicardium.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 61/576,366, filed Dec. 16, 2011, which is incorporated by reference herein in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     No federal government funds were used in researching or developing this invention. 
     NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     SEQUENCE LISTING INCLUDED AND INCORPORATED BY REFERENCE HEREIN 
     Not applicable. 
     BACKGROUND 
     Field of the Invention 
     This invention relates to improved tethering for a transcatheter mitral valve replacement. 
     Background of the Invention 
     Valvular heart disease and specifically aortic and mitral valve disease is a significant health issue in the US. Recent advances have provided for the transcatheter deployment of a prosthetic cardiac valve. Compared to traditional valve replacement surgery which used an “open heart” surgical procedure and typically carries a 1-4% mortality risk in otherwise healthy persons, transcatheter deployment significantly reduces morbidity as well as reducing the cost of valve replacement therapy. 
     While replacement of the aortic valve in a transcatheter manner has been the subject of intense investigation, lesser attention has been focused on the mitral valve. This is in part reflective of the greater level of complexity associated to the native mitral valve apparatus and thus a greater level of difficulty with regards to inserting and anchoring the replacement prosthesis. 
     Several designs for catheter-deployed (transcatheter) aortic valve replacement are under various stages of development. The Edwards SAPIEN transcatheter heart valve is currently undergoing clinical trial in patients with calcific aortic valve disease who are considered high-risk for conventional open-heart valve surgery. This valve is deployable via a retrograde transarterial (transfemoral) approach or an antegrade transapical (transventricular) approach. A key aspect of the Edwards SAPIEN and other transcatheter aortic valve replacement designs is their dependence on lateral fixation (e.g. tines) that engages the valve tissues as the primary anchoring mechanism. Such a design basically relies on circumferential friction around the valve housing or stent to prevent dislodgement during the cardiac cycle. This anchoring mechanism is facilitated by, and may somewhat depend on, a calcified aortic valve annulus. This design also requires that the valve housing or stent have a certain degree of rigidity. 
     At least one transcatheter mitral valve design is currently in development. The Endo-valve uses a folding tripod-like design that delivers a tri-leaflet bioprosthetic valve. It is designed to be deployed from a minimally invasive transatrial approach, and could eventually be adapted to a transvenous atrial septotomy delivery. This design uses “proprietary gripping features” designed to engage the valve annulus and leaflets tissues. Thus the anchoring mechanism of this device is essentially equivalent to that used by transcatheter aortic valve replacement designs. 
     However, such designs still pose many unsolved problems such as heart remodelling, perivalvular leaking, inability to avoid fatigue failures, clotting, tissue damage, and so on. Accordingly, improvements are needed to address these and related problems in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to the design and function of a single-tether compressible prosthetic heart valve replacement which can be deployed into a closed beating heart using a transcatheter delivery system. The design as discussed focuses on the deployment of a device via a minimally invasive fashion and by way of example considers a minimally invasive surgical procedure utilizing the intercostal or subxyphoid space for valve introduction. In order to accomplish this, the valve is formed in such a manner that it can be compressed to fit within a delivery system and secondarily ejected from the delivery system into the target location, for example the mitral or tricuspid valve annulus. 
     In a preferred embodiment, there is provided a method of tethering a prosthetic heart valve during a transcatheter valve replacement procedure comprising the step of deploying a transcatheter prosthetic heart valve in a patient using as an anchor a single tether that is anchored within the heart between an apically affixed epicardial fastening device and a stent-based fastening system, wherein the transcatheter prosthetic heart valve comprises an expandable tubular stent having a cuff and an expandable internal leaflet assembly, wherein said cuff is comprised of wire covered with stabilized tissue or synthetic material, and wherein said leaflet assembly is disposed within the stent and is comprised of stabilized tissue or synthetic material. 
     In another preferred embodiment, there is provided wherein the prosthetic heart valve is tethered to the apex of the left ventricle using an interlocking tethering system comprised of a stent-based component and a single-tether distal component that cooperatively engages with the stent-based component to form a secure attachment of the prosthetic heart valve to the apex, and a single-tether proximal component that comprises or attaches to an epicardial tether securing device. 
     In another preferred embodiment, there is provided method of treating mitral or tricuspid regurgitation in a patient, which comprises the step of surgically deploying a single-tethered prosthetic heart valve into the mitral or tricuspid annulus of the patient. 
     In another preferred embodiment, the space between the cuff tissue and cuff dacron liner (inside-outside) may be used to create a cuff that is expandable, swellable or may be inflated and which provides an enhanced level of sealing of the cuff against the atrial trabeculations and annular tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The attached figures provide enabling and non-limiting example of certain features of the present invention. The figures are not intended to be limiting in any way to limit the description that is provided in the text. 
         FIG. 1A  is an illustration of one embodiment of an epicardial tether securing device. 
         FIG. 1B  shows an exploded side view of the device with the pinning structure and the plug-locking structure that fits into the securement disc.  FIG. 1C  shows a perspective view of the same device. 
         FIG. 2  is an illustration of one embodiment of the prosthetic valve of the present invention showing a mid-stent cuff design. 
         FIG. 3  is an illustration of one example of a locking tether connector having a tooth and groove design for attaching the ventricular tether to the stent body/stent-tether system. 
         FIG. 4  is an illustration of a prosthetic mitral valve being deployed within the left atrium (upper) and the left ventricle (lower), using endoscopic catheters fitted with positioning tethers. 
         FIG. 5  is an illustration of a two-way locking peg system for attaching the ventricular tether to the stent body/stent-tether system. 
         FIG. 6  is an illustration of one example of a single tether embodiment having an epicardial securing device at the apex connecting the single ventricular tether to a stent-tethering system of centering tethers. 
         FIG. 7  is an illustration of a prosthetic valve having a single ventricular tether connected to the stent body via a stent-tether system having two (2) centering tethers attached to the stent body portion of the valve. 
         FIG. 8  is an illustration of a prosthetic valve having a single ventricular tether connected to the stent body via a stent-tether system having three (3) centering tethers attached to the stent body portion of the valve. 
         FIG. 9  is an illustration of a prosthetic valve having a single ventricular tether connected to the stent body via a stent-tether system having four (4) centering tethers attached to the stent body portion of the valve. 
         FIG. 10  is an illustration of a prosthetic mitral valve deployed within the mitral annulus with the upper cuff located in the left atrium and lower stent body in or towards the left ventricle.  FIG. 10  shows a three (3) connection stent-tether system with three (3) tethers connected to the stent body and converging to a polymeric intra-ventricular connecting ring. The ventricular tether is in this embodiment actually two (2) ventricular tethers, both connected to the connecting ring, and both tethers attached to the apical epicardial securing device. 
         FIG. 11  is an illustration of a prosthetic mitral valve deployed within the mitral annulus with the upper cuff located in the left atrium and lower stent body in or towards the left ventricle.  FIG. 11  shows a three (3) connection stent-tether system with three (3) tethers connected to the stent body and converging to a polymeric intra-ventricular connecting ring. The ventricular tether is in this embodiment is a single (1) tether and is connecting the connecting ring to the apical epicardial securing device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention addresses problems concerning valve delivery and deployment, valve compliance, perivalvular leaking, hemodynamic issues such as LVOT and clotting, cardiac remodelling and so forth. 
     The present invention provides in one embodiment a tethering system for a prosthetic mitral valve that is designed to maintain integrity out to about 800 million cycles, or about 20 years. The use of a compressible prosthetic valve delivered via transcatheter endoscope techniques addresses the delivery issues. Deployment is addressed through the use of a prosthetic valve having a shape that features a tubular stent body that contains leaflets and an atrial cuff. This allows the valve to seat within the mitral annulus and be held by the native mitral leaflets. The use of a flexible valve attached using an apical tether provides compliance with the motion and geometry of the heart. The geometry and motion of the heart are well-known as exhibiting a complicated biphasic left ventricular deformation with muscle thickening and a sequential twisting motion. The additional use of the apically secured ventricular tether helps maintain the prosthetic valve&#39;s annular position without allowing the valve to migrate, while providing enough tension between the cuff and the atrial trabeculations to reduce and eliminate perivalvular leaking. The use of a single tether or a single paired-tether that is attached to a single apical location reduces or even eliminates the cardiac muscle remodelling that has been witnessed in prior art devices. These prior art devices were known to have a problem with unwanted change in tissue at the anchoring locations as well as heart-generated migration of the original anchoring locations to new locations that reduce or destroy the prior art valve&#39;s effectiveness. The use of a compliant valve prosthesis and the special shape and features help reduce or eliminate clotting and hemodynamic issues, including left ventricular outflow tract (LVOT) interference problems. Many prior art valves were not even aware of or were not able to address problems with blood flow and aorta/aortic valve compression issues. 
     Structurally, the prosthetic heart valve comprises a self-expanding tubular stent having a cuff at one end and tether loops for attaching tethers at the other end, and disposed within the tubular stent is a leaflet assembly that contains the valve leaflets, the valve leaflets being formed from stabilized tissue or other suitable biological or synthetic material. In one embodiment, the leaflet assembly may even include a wire form where a formed wire structure is used in conjunction with stabilized tissue to create a leaflet support structure which can have anywhere from 1, 2, 3 or 4 leaflets, or valve cusps disposed therein. In another embodiment, the leaflet assembly is wireless and uses only the stabilized tissue and stent body to provide the leaflet support structure, without using wire, and which can also have anywhere from 1, 2, 3 or 4 leaflets, or valve cusps disposed therein. 
     The upper cuff portion may be formed by heat-forming a portion of a tubular nitinol braided (or similar) stent such that the lower portion retains the tubular shape but the upper portion is opened out of the tubular shape and expanded to create a widened collar structure that may be shaped in a variety of functional regular or irregular funnel-like or collar-like shapes. In one preferred embodiment, the entire structure is formed from a laser-cut stent and collar design, as described further herein. 
     Functions of the Cuff 
     The cuff functions in a variety of ways. The first function of the cuff is to inhibit perivalvular leak/regurgitation of blood around the prosthesis. By flexing and sealing across the irregular contours of the annulus and atrium, leaking is minimized and/or prevented. 
     The second function of the cuff is to provide an adjustable and/or compliant bioprosthetic valve. The heart and its structures undergo complex conformational changes during the cardiac cycle. For example, the mitral valve annulus has a complex geometric shape known as a hyperbolic parabloid much like a saddle, with the horn being anterior, the seat back being posterior, and the left and right valleys located medially and laterally. Beyond this complexity, the area of the mitral annulus changes over the course of the cardiac cycle. Further, the geometry of the tricuspid valve and tricuspid annulus continues to be a topic of research, posing its own particular problems. Accordingly, compliance is a very important but unfortunately often overlooked requirement of cardiac devices. Compliance here refers to the ability of the valve to maintain structural position and integrity during the cardiac cycle. Compliance with the motion of the heart is a particularly important feature, especially the ability to provide localized compliance where the underlying surfaces are acting differently from the adjacent surfaces. This ability to vary throughout the cardiac cycle allows the valve to remain seated and properly deployed in a manner not heretofore provided. 
     Additionally, compliance may be achieved through the use of the tethers where the tethers are preferably made from an elastic material. Optionally, tethers may be made from polymer filaments known in the surgical field and exhibiting strength and resilience properties adequate for valve stabilization. Tether-based compliance may be used alone, or in combination with the cuff-based compliance. 
     The third function of the cuff valve is to provide a valve that, during surgery, is able to be seated and be able to contour to the irregular surfaces of the atrium. The use of independent tethers allows for side to side fitting of the valve within the annulus. For example, where three tethers are used, they are located circumferentially about 120 degrees relative to each other which allows the surgeon to observe whether or where perivalvular leaking might be occurring and to pull on one side or the other to create localized pressure and reduce or eliminate the leaking. 
     The forth function of the cuff is to counter the forces that act to displace the prosthesis toward/into the ventricle (i.e. atrial pressure and flow-generated shear stress) during ventricular filling. 
     Additional features of the cuff include that it functions to strengthen the leaflet assembly/stent combination by providing additional structure. Further, during deployment, the cuff functions to guide the entire structure, the prosthetic valve, into place at the mitral annulus during deployment and to keep the valve in place once it is deployed. 
     Cuff Structure 
     The cuff is a substantially flat plate that projects beyond the diameter of the tubular stent to form a rim or border. As used herein, the term cuff, flange, collar, bonnet, apron, or skirting are considered to be functionally equivalent. When the tubular stent is pulled through the mitral valve aperture, the mitral annulus, by the tether loops in the direction of the left ventricle, the cuff acts as a collar to stop the tubular stent from traveling any further through the mitral valve aperture. The entire prosthetic valve is held by longitudinal forces between the cuff which is seated in the left atrium and mitral annulus, and the ventricular tethers attached to the left ventricle. 
     The cuff is formed from a stiff, flexible shape-memory material such as the nickel-titanium alloy material Nitinol™ wire that is covered by stabilized tissue or other suitable biocompatible or synthetic material. In one embodiment, the cuff wire form is constructed from independent loops of wire that create lobes or segments extending axially around the circumference of the bend or seam where the cuff transitions to the tubular stent (in an integral cuff) or where the cuff is attached to the stent (where they are separate, but joined components). 
     Once covered by stabilized tissue or material, the loops provide the cuff the ability to travel up and down, to articulate, along the longitudinal axis that runs through the center of the tubular stent. In other words, the individual spindles or loops can independently move up and down, and can spring back to their original position due to the relative stiffness of the wire. The tissue or material that covers the cuff wire has a certain modulus of elasticity such that, when attached to the wire of the cuff, is able to allow the wire spindles to move. This flexibility gives the cuff, upon being deployed within a patient&#39;s heart, the ability to conform to the anatomical shape necessary for a particular application. In the example of a prosthetic mitral valve, the cuff is able to conform to the irregularities of the left atrium and shape of the mitral annulus, and to provide a tight seal against the atrial tissue adjacent the mitral annulus and the tissue within the mitral annulus. As stated previously, this feature importantly provides a degree of flexibility in sizing the a mitral valve and prevents blood from leaking around the implanted prosthetic heart valve. 
     An additional important aspect of the cuff dimension and shape is that, when fully seated and secured, the edge of the cuff preferably should not be oriented laterally into the atrial wall such that it can produce a penetrating or cutting action on the atrial wall. 
     In one preferred embodiment, the wire spindles of the cuff are substantially uniform in shape and size. In another preferred embodiment of the present invention, each loop or spindle may be of varying shapes and sizes. In this example, it is contemplated that the loops may form a pattern of alternating large and small loops, depending on where the valve is being deployed. In the case of a prosthetic mitral valve, pre-operative imaging may allow for customizing the structure of the cuff depending on a particular patient&#39;s anatomical geometry in the vicinity of the mitral annulus. 
     The cuff wire form is constructed so as to provide sufficient structural integrity to withstand the intracardiac forces without collapsing. The cuff wire form is preferably constructed of a superelastic metal, such as Nitinol™® and is capable of maintaining its function as a sealing collar for the tubular stent while under longitudinal forces that might cause a structural deformation or valve displacement. It is contemplated as within the scope of the invention to optionally use other shape memory alloys such as Cu—Zn—Al—Ni alloys, and Cu—Al—Ni alloys. The heart is known to generate an average left atrial pressure between about 8 and 30 mm Hg (about 0.15 to 0.6 psi). This left atrial filling pressure is the expected approximate pressure that would be exerted in the direction of the left ventricle when the prosthesis is open against the outer face of the cuff as an anchoring force holding the cuff against the atrial tissue that is adjacent the mitral valve. The cuff counteracts this longitudinal pressure against the prosthesis in the direction of the left ventricle to keep the valve from being displaced or slipping into the ventricle. In contrast, left ventricular systolic pressure, normally about 120 mm Hg, exerts a force on the closed prosthesis in the direction of the left atrium. The tethers counteract this force and are used to maintain the valve position and withstand the ventricular force during ventricular contraction or systole. Accordingly, the cuff has sufficient structural integrity to provide the necessary tension against the tethers without being dislodged and pulled into the left ventricle. After a period of time, changes in the geometry of the heart and/or fibrous adhesion between prosthesis and surrounding cardiac tissues may assist or replace the function of the ventricular tethers in resisting longitudinal forces on the valve prosthesis during ventricular contraction. 
     Stent Structure 
     Preferably, superelastic metal wire, such as Nitinol™ wire, is used for the stent, for the inner wire-based leaflet assembly that is disposed within the stent, and for the cuff wire form. As stated, it is contemplated as within the scope of the invention to optionally use other shape memory alloys such as Cu—Zn—Al—Ni alloys, and Cu—Al—Ni alloys. It is contemplated that the stent may be constructed as a braided stent or as a laser cut stent. Such stents are available from any number of commercial manufacturers, such as Pulse Systems. Laser cut stents are preferably made from Nickel-Titanium (Nitinol™), but also without limitation made from stainless steel, cobalt chromium, titanium, and other functionally equivalent metals and alloys, or Pulse Systems braided stent that is shape-set by heat treating on a fixture or mandrel. 
     One key aspect of the stent design is that it be compressible and when released have the stated property that it return to its original (uncompressed) shape. This requirement limits the potential material selections to metals and plastics that have shape memory properties. With regards to metals, Nitinol has been found to be especially useful since it can be processed to be austhenitic, martensitic or super elastic. Martensitic and super elastic alloys can be processed to demonstrate the required compression features. 
     Laser Cut Stent 
     One possible construction of the stent envisions the laser cutting of a thin, isodiametric Nitinol tube. The laser cuts form regular cutouts in the thin Nitinol tube. Secondarily the tube is placed on a mold of the desired shape, heated to the Martensitic temperature and quenched. The treatment of the stent in this manner will form a stent or stent/cuff that has shape memory properties and will readily revert to the memory shape at the calibrated temperature. 
     Braided Wire Stent 
     A stent can be constructed utilizing simple braiding techniques. Using a Nitinol wire—for example a 0.012″ wire—and a simple braiding fixture, the wire is wound on the braiding fixture in a simple over/under braiding pattern until an isodiametric tube is formed from a single wire. The two loose ends of the wire are coupled using a stainless steel or Nitinol coupling tube into which the loose ends are placed and crimped. Angular braids of approximately 60 degrees have been found to be particularly useful. Secondarily, the braided stent is placed on a shaping fixture and placed in a muffle furnace at a specified temperature to set the stent to the desired shape and to develop the martensitic or super elastic properties desired. 
     The stent as envisioned in one preferred embodiment is designed such that the ventricular aspect of the stent comes to 2-5 points onto which anchoring sutures are affixed. The anchoring sutures (tethers) will traverse the ventricle and ultimately be anchored to the epicardial surface of the heart approximately at the level of the apex. The tethers when installed under slight tension will serve to hold the valve in place, i.e. inhibit paravalvular leakage during systole. 
     Leaflet and Assembly Structure 
     The valve leaflets are held by, or within, a leaflet assembly. In one preferred embodiment of the invention, the leaflet assembly comprises a leaflet wire support structure to which the leaflets are attached and the entire leaflet assembly is housed within the stent body. In this embodiment, the assembly is constructed of wire and stabilized tissue to form a suitable platform for attaching the leaflets. In this aspect, the wire and stabilized tissue allow for the leaflet structure to be compressed when the prosthetic valve is compressed within the deployment catheter, and to spring open into the proper functional shape when the prosthetic valve is opened during deployment. In this embodiment, the leaflet assembly may optionally be attached to and housed within a separate cylindrical liner made of stabilized tissue or material, and the liner is then attached to line the interior of the stent body. 
     In this embodiment, the leaflet wire support structure is constructed to have a collapsible/expandable geometry. In a preferred embodiment, the structure is a single piece of wire. The wireform is, in one embodiment, constructed from a shape memory alloy such as Nitinol. The structure may optionally be made of a plurality of wires, including between 2 to 10 wires. Further, the geometry of the wire form is without limitation, and may optionally be a series of parabolic inverted collapsible arches to mimic the saddle-like shape of the native annulus when the leaflets are attached. Alternatively, it may optionally be constructed as collapsible concentric rings, or other similar geometric forms that are able to collapse/compress which is followed by an expansion to its functional shape. In certain preferred embodiments, there may be 2, 3 or 4 arches. In another embodiment, closed circular or ellipsoid structure designs are contemplated. In another embodiment, the wire form may be an umbrella-type structure, or other similar unfold-and-lock-open designs. A preferred embodiment utilizes super elastic Nitinol wire approximately 0.015″ in diameter. In this embodiment, the wire is wound around a shaping fixture in such a manner that 2-3 commissural posts are formed. The fixture containing the wrapped wire is placed in a muffle furnace at a pre-determined temperature to set the shape of the wire form and to impart it&#39;s super elastic properties. Secondarily, the loose ends of the wireform are joined with a stainless steel or Nitinol tube and crimped to form a continuous shape. In another preferred embodiment, the commissural posts of the wireform are adjoined at their tips by a circular connecting ring, or halo, whose purpose is to minimize inward deflection of the post(s). 
     In another preferred embodiment, the leaflet assembly is constructed solely of stabilized tissue or other suitable material without a separate wire support structure. The leaflet assembly in this embodiment is also disposed within the lumen of the stent and is attached to the stent to provide a sealed joint between the leaflet assembly and the inner wall of the stent. By definition, it is contemplated within the scope of the invention that any structure made from stabilized tissue and/or wire(s) related to supporting the leaflets within the stent constitute a leaflet assembly. 
     In this embodiment, stabilized tissue or suitable material may also optionally be used as a liner for the inner wall of the stent and is considered part of the leaflet assembly. 
     Liner tissue or biocompatible material may be processed to have the same or different mechanical qualities, e.g. thickness, durability, etc. from the leaflet tissue. 
     Deployment within the Valvular Annulus 
     The prosthetic heart valve is, in one embodiment, apically delivered through the apex of the left ventricle of the heart using a catheter system. In one aspect of the apical delivery, the catheter system accesses the heart and pericardial space by intercostal delivery. In another delivery approach, the catheter system delivers the prosthetic heart valve using either an antegrade or retrograde delivery approach using a flexible catheter system, and without requiring the rigid tube system commonly used. In another embodiment, the catheter system accesses the heart via a trans-septal approach. 
     In one non-limiting preferred embodiment, the stent body extends into the ventricle about to the edge of the open mitral valve leaflets (approximately 25% of the distance between the annulus and the ventricular apex). The open native leaflets lay against the outside stent wall and parallel to the long axis of the stent (i.e. the stent holds the native mitral valve open). 
     In one non-limiting preferred embodiment, the diameter should approximately match the diameter of the mitral annulus. Optionally, the valve may be positioned to sit in the mitral annulus at a slight angle directed away from the aortic valve such that it is not obstructing flow through the aortic valve. Optionally, the outflow portion (bottom) of the stent should not be too close to the lateral wall of the ventricle or papillary muscle as this position may interfere with flow through the prosthesis. As these options relate to the tricuspid, the position of the tricuspid valve may be very similar to that of the mitral valve. 
     In another embodiment, the prosthetic valve is sized and configured for use in areas other than the mitral annulus, including, without limitation, the tricuspid valve between the right atrium and right ventricle. Alternative embodiments may optionally include variations to the cuff structure to accommodate deployment to the pulmonary valve between the right ventricle and pulmonary artery, and the aortic valve between the left ventricle and the aorta. In one embodiment, the prosthetic valve is optionally used as a venous backflow valve for the venous system, including without limitation the vena cava, femoral, subclavian, pulmonary, hepatic, renal and cardiac. In this aspect, the cuff feature is utilized to provide additional protection against leaking. 
     Anchoring Tether, Tether Bundle, Positioning Tethers 
     In one preferred embodiment of the present invention, there is a tether-bundle that attaches to the extended points (two or three or four) of the stent and which converge to a central nexus point, to which the single tether is attached and leads to the apical tissue anchor location within the heart. In one preferred embodiment, the tether extends downward through the left ventricle, exiting the left ventricle at the apex of the heart to be fastened on the epicardial surface outside of the heart. Similar anchoring is contemplated herein as it regards the tricuspid, or other valve structure requiring a prosthetic. 
     In another preferred embodiment, there may be additional positioning-tethers optionally be attached to the cuff to provide additional control over position, adjustment, and compliance during deployment and possible for up to 30 days afterwards to ensure there is no leaking. It is contemplated that the positioning tethers may be kept and gathered outside of the patient body for a period of time until the interventionalist can verify by Echocardiography or Fluoroscopy that no further adjustment is necessary. In this preferred embodiment, one or more tethers are optionally attached to the cuff, in addition to, or optionally, in place of, the tethers attached to the stent. By attaching to the cuff and/or the stent, an even higher degree of control over positioning, adjustment, and compliance is provided to the operator during deployment. 
     During deployment, the operator is able to adjust or customize the tethers to the correct length for a particular patient&#39;s anatomy. The tethers also allow the operator to tighten the cuff onto the tissue around the valvular annulus by pulling the tethers, which creates a leak-free seal. 
     In another preferred embodiment, the tethers are optionally anchored to other tissue locations depending on the particular application of the prosthetic heart valve. In the case of a mitral valve, or the tricuspid valve, there are optionally one or more tethers anchored to one or both papillary muscles, septum, and/or ventricular wall. 
     The tethers, in conjunction with the cuff, provide for a compliant valve which has heretofore not been available. The tethers are made from surgical-grade materials such as biocompatible polymer suture material. Examples of such material include 2-0 exPFTE (polytetrafluoroethylene) or 2-0 polypropylene. In one embodiment the tethers are inelastic. It is also contemplated that one or more of the tethers may optionally be elastic to provide an even further degree of compliance of the valve during the cardiac cycle. Upon being drawn to and through the apex of the heart, the tethers may be fastened by a suitable mechanism such as tying off to a pledget or similar adjustable button-type anchoring device to inhibit retraction of the tether back into the ventricle. It is also contemplated that the tethers might be bioresorbable/bioabsorbable and thereby provide temporary fixation until other types of fixation take hold such a biological fibrous adhesion between the tissues and prosthesis and/or radial compression from a reduction in the degree of heart chamber dilation. 
     Further, it is contemplated that the prosthetic heart valve may optionally be deployed with a combination of installation tethers and the permanent tether, attached to either the stent or cuff, or both, the installation tethers being removed after the valve is successfully deployed. It is also contemplated that combinations of inelastic and elastic tethers may optionally be used for deployment and to provide structural and positional compliance of the valve during the cardiac cycle. 
     Pledget 
     In one embodiment, to control the potential tearing of tissue at the apical entry point of the delivery system, a circular, semi-circular, or multi-part pledget is employed. The pledget may be constructed from a semi-rigid material such as PFTE felt. Prior to puncturing of the apex by the delivery system, the felt is firmly attached to the heart such that the apex is centrally located. Secondarily, the delivery system is introduced through the central area, or orifice as it may be, of the pledget. Positioned and attached in this manner, the pledget acts to control any potential tearing at the apex. 
     Tines/Barbs 
     In another embodiment the valve can be seated within the valvular annulus through the use of tines or barbs. These may be used in conjunction with, or in place of one or more tethers. The tines or barbs are located to provide attachment to adjacent tissue. In one preferred embodiment, the tines are optionally circumferentially located around the bend/transition area between the stent and the cuff. Such tines are forced into the annular tissue by mechanical means such as using a balloon catheter. In one non-limiting embodiment, the tines may optionally be semi-circular hooks that upon expansion of the stent body, pierce, rotate into, and hold annular tissue securely. 
     Stabilized Tissue or Biocompatible Material 
     In one embodiment, it is contemplated that multiple types of tissue and biocompatible material may be used to cover the cuff, to form the valve leaflets, to form a wireless leaflet assembly, and/or to line both the inner and/or outer lateral walls of the stent. As stated previously, the leaflet component may be constructed solely from stabilized tissue, without using wire, to create a leaflet assembly and valve leaflets. In this aspect, the tissue-only leaflet component may be attached to the stent with or without the use of the wire form. In a preferred embodiment, there can be anywhere from 1, 2, 3 or 4 leaflets, or valve cusps. 
     It is contemplated that the tissue may be used to cover the inside of the stent body, the outside of the stent body, and the top and/or bottom side of the cuff wire form, or any combination thereof. 
     In one preferred embodiment, the tissue used herein is optionally a biological tissue and may be a chemically stabilized valve of an animal, such as a pig. In another preferred embodiment, the biological tissue is used to make leaflets that are sewn or attached to a metal frame. This tissue is chemically stabilized pericardial tissue of an animal, such as a cow (bovine pericardium) or sheep (ovine pericardium) or pig (porcine pericardium) or horse (equine pericardium). 
     Preferably, the tissue is bovine pericardial tissue. Examples of suitable tissue include that used in the products Duraguard®, Peri-Guard®, and Vascu-Guard®, all products currently used in surgical procedures, and which are marketed as being harvested generally from cattle less than 30 months old. Other patents and publications disclose the surgical use of harvested, biocompatible animal thin tissues suitable herein as biocompatible “jackets” or sleeves for implantable stents, including for example, U.S. Pat. No. 5,554,185 to Block, U.S. Pat. No. 7,108,717 to Design &amp; Performance-Cyprus Limited disclosing a covered stent assembly, U.S. Pat. No. 6,440,164 to Scimed Life Systems, Inc. disclosing a bioprosthetic valve for implantation, and U.S. Pat. No. 5,336,616 to LifeCell Corporation discloses acellular collagen-based tissue matrix for transplantation. 
     In one preferred embodiment, the valve leaflets may optionally be made from a synthetic material such a polyurethane or polytetrafluoroethylene. Where a thin, durable synthetic material is contemplated, e.g. for covering the cuff, synthetic polymer materials such expanded polytetrafluoroethylene or polyester may optionally be used. Other suitable materials may optionally include thermoplastic polycarbonate urethane, polyether urethane, segmented polyether urethane, silicone polyether urethane, silicone-polycarbonate urethane, and ultrahigh molecular weight polyethylene. Additional biocompatible polymers may optionally include polyolefins, elastomers, polyethylene-glycols, polyethersulphones, polysulphones, polyvinylpyrrolidones, polyvinylchlorides, other fluoropolymers, silicone polyesters, siloxane polymers and/or oligomers, and/or polylactones, and block co-polymers using the same. 
     In another embodiment, the valve leaflets may optionally have a surface that has been treated with (or reacted with) an anti-coagulant, such as, without limitation, immobilized heparin. Such currently available heparinized polymers are known and available to a person of ordinary skill in the art. 
     Alternatively, the valve leaflets may optionally be made from pericardial tissue or small intestine submucosal tissue. 
     Retrieval System 
     In another embodiment, a retrieval system is contemplated for quickly removing the prosthetic valve during an aborted surgical deployment using minimally invasive cardiac catheter techniques. In this embodiment, the tethers would be captured by a catheter having a snare attachment. Once the tethers were captured, an intra-ventricular funnel attachment would guide the prosthetic valve into a collapsed, compressed conformation by pulling on the tethers, thus pulling the compressed prosthetic valve into the removal catheter for subsequent extraction. 
     DESCRIPTION OF THE FIGURES 
     Referring now to the figures there is one embodiment of a single-tethered prosthetic heart valve according to the present invention. 
       FIG. 1A  shows a top view of one embodiment of a three-part epicardial tether securing device  100  wherein three tether holes  111  perforate the body of securement disc  110 .  FIG. 1B  shows an exploded side view of the device comprising securement disc component  110 , pinning component  120  and plug-locking component  120 . In this view, a plurality of pins  121  extend from the body of pinning component  120  and the plug-locking component  130  is gauged to fit snugly within the center hole  122  of the pinning structure  120  and the center hole  112  of securement disc component  110 , respectively.  FIG. 1C  shows a perspective view of the same device. 
       FIG. 2  is an illustration of one embodiment of the prosthetic valve  140  of the present invention showing a mid-stent cuff design. This design positions the top of the stent body  141  above the atrial floor at the mitral annulus, with the cuff  150  positioned over the atrial floor directly above the mitral annulus with the interior prosthetic leaflet structure (not pictured) installed at or near the top, atrial end of the stent body  160 . This design necessitates the use of a laser cut stent or a combination of a braided stent and an additional fused/joined collar component. 
       FIG. 3  is an illustration of one example of a locking tether connector  170  having a tooth and groove design for attaching the ventricular tether to the stent body/stent-tether system. The use of a connector to attach the single ventricular tether (not pictured) to the node of the tether-bundle (not pictured) emanating from the stent body is to reduce the wear that is observed on the tethers and/or to minimize the number of perforations required in the pericardial tissue to secure the tether(s). In this embodiment, each tether emanating from the stent body extends into a tether hole  181  in the toothed component  180 , which is fitted into the grooved barrel  190 . The tether holes  180  converge on the interior of the toothed component  180  such that they emerge from a single tether hole (not pictured) at the bottom of such toothed component  180  as a single, braided ventricular tether (not pictured). Wear on tethers and subsequent failure is known to have catastrophic consequences and result in death of the patient, while surgical alteration of the pericardial tissue, including at the apex, is known to have the effect, over time, of causing changes to the shape of the left ventricle 
       FIG. 4  is an illustration of a prosthetic mitral valve  140  being deployed within the left atrium (upper) and the left ventricle (lower), using endoscopic catheters  200  fitted with positioning tethers  210 . 
       FIG. 5  is an illustration of a two-way locking peg system  310  for attaching the single ventricular tether  270  to the epicardial securing device  100 . In the pictured embodiment, the tip of the braided single ventricular tether  270 , having passed through the epicardial securing device (not pictured), is inserted into cap component  320 . Pins  330  are then placed all the way through cap holes  321 , and are thusly passed through the braided filaments of tether  270  to hold such tether in place. Again, the use of a connector to attach the single ventricular tether to the node of the tether-bundle hanging from the stent body is to reduce the wear that is observed on the tethers, and avoid catastrophic device failure and death of the patient. 
       FIG. 6  is an illustration of one example of a single tether embodiment having the epicardial tether securing device  100  at the apex connecting the single ventricular tether  270  to a stent-tethering system of centering tethers. In this embodiment, the single ventricular tether  270  is tied to a single tether loop  280  at one end and secured to the epicardial tether securing device  100  at its other end, while the centering tethers  290  emanating from the stent body  160  are tied at a central point to a stent tether loop  300 , such stent tether loop remaining open until secured through single tether loop  280  during installation of the valve. 
       FIG. 7  is an illustration of a prosthetic valve  140  having a single ventricular tether  270  connected to the stent body portion of the valve  160  via a stent-tether system having two (2) centering tethers  290  attached to the stent body  160 , with the single ventricular tether  270  attached on its other end to the epicardial tether securing device  100 . 
       FIG. 8  is an illustration of a prosthetic valve  140  having a single ventricular tether  270  connected to the stent body portion of the valve  160  via a stent-tether system having three (3) centering tethers  290  attached to the stent body  160 , with the single ventricular tether attached on its other end to the epicardial tether securing device  100 .  FIG. 9  is an illustration of a prosthetic valve  140  having a single ventricular tether  270  connected to the stent body portion of the valve  160  via a stent-tether system having four (4) centering tethers  290  attached to the stent body  160 , with the single ventricular tether attached on its other end to the epicardial tether securing device  100 . 
     In each embodiment of  FIGS. 7-9 , centering tethers  290  are either tied to single ventricular tether  270 , or are braided together to form single ventricular tether  270 . 
       FIG. 10  is an illustration of a prosthetic mitral valve  140  deployed within the mitral annulus with the upper cuff  150  and leaflet assembly  152  located in the left atrium and lower stent body  160  in or towards the left ventricle.  FIG. 10  shows a three (3) connection stent-tether system with three (3) centering tethers  290  connected to the stent body  160  and converging to a polymeric intra-ventricular connecting ring  320 . The ventricular tether  270  is in this embodiment actually two (2) ventricular tethers, both connected to the connecting ring  320 , and both ventricular tethers  270  attached to the apical epicardial securing device. 
       FIG. 11  is an illustration of a prosthetic mitral valve deployed within the mitral annulus with the upper cuff  150  and leaflet assembly  152  located in the left atrium and lower stent body  160  in or towards the left ventricle.  FIG. 11  shows a three (3) connection stent-tether system with three (3) centering tethers  290  connected to the stent body and converging to a polymeric intra-ventricular connecting ring  320 . The ventricular tether  270  is in this embodiment is a single (1) tether and is connecting the connecting ring  320  to the apical epicardial tether securing device  100 . 
     Incorporation and Equivalents 
     The references recited herein are incorporated herein in their entirety, particularly as they relate to teaching the level of ordinary skill in this art and for any disclosure necessary for the commoner understanding of the subject matter of the claimed invention. It will be clear to a person of ordinary skill in the art that the above embodiments may be altered or that insubstantial changes may be made without departing from the scope of the invention. Accordingly, the scope of the invention is determined by the scope of the following claims and their equitable Equivalents.