Method and apparatus for replacing a mitral valve with a stentless bioprosthetic valve

A stentless bioprosthetic valve includes at least one piece of biocompatible material comprising a bi-leaflet conduit. The conduit has a distal end and a proximal end that defines a first annulus for suturing to the valve annulus of a heart. The conduit further includes first and second leaflets that mimic the anterior and posterior leaflets of the native mitral valve. The first and second leaflets extend between the proximal and distal ends. The distal end defines a second annulus at which the first and second leaflets terminate. The second annulus is for suturing to free edges of the anterior and posterior leaflets of the native mitral valve that remain intact following resection of the native mitral valve so that the native chordae tendineae continue to provide prolapse prevention and left ventricular muscle support functions in addition to maintaining the continuity between the valve annulus and the papillary muscles. A method for replacing the native mitral valve with a stentless bioprosthetic valve is also provided.

TECHNICAL FIELD

The present invention relates to a method and apparatus for replacing a native mitral valve with a stentless bioprosthetic valve.

BACKGROUND OF THE INVENTION

The mitral valve is a functional unit composed of multiple dynamically interrelated units. During cardiac cycle, the fibrous skeleton, the anterior and posterior leaflets, the papillary muscles, the chordae tendineae, and the ventricular and atrial walls all interplay symphonically to render a competent valve. The complex interaction between the mitral valve and the ventricle by the subvalvular apparatus (the papillary muscles and the chordae tendineae is essential in that it maintains the continuity between the atrio-ventricular ring (which is part of the fibrous skeleton of the heart) and the ventricular muscle mass, which is essential for the normal function of the mitral valve.

The chordae tendineae, which connect the valve leaflets to the papillary muscles (PM) act like “tie rods” in an engineering sense. Not only do the chordae tendineae prevent prolapse of the mitral valve leaflets during systole, but they also support the left ventricular muscle mass throughout the cardiac cycle.

To function adequately, the mitral valve needs to open to a large orifice area and, for closure, the mitral leaflets need to have an excess of surface area (i.e. more than needed to effectively close the mitral orifice). On the other hand, systolic contraction of the posterior ventricular wall around the mitral annulus (MA) creates a mobile D-shaped structure with sphincter-like function which reduces its area by approximately 25% during systole, thus exposing less of the mitral leaflets to the stress of the left ventricular pressure and flow.

Although the primary function of the mitral valve is to act as a one-way no return valve, it has been postulated that the structural integrity of the MA-PM continuity is essential for normal left ventricular function.

Since it was first suggested in the mid-1960's that preservation of the subvalvular apparatus during mitral valve replacement might prevent low cardiac output in the early postoperative period, this important observation was largely overlooked by most surgeons for many years.

There is now considerable laboratory and clinical evidence to corroborate this position, as evidence has demonstrated that chordal excision is associated with a change in left ventricular shape from oval to spherical, which can lead to a significant increase in postoperative left ventricular end systolic volume and wall stress, along with a decline in ejection fraction.

The majority of evidence appears to support the concept that preservation of the subvalvular apparatus with the MA-PM continuity in any procedure on the mitral valve is important for the improved long-term quality and quantity of life after mitral valve surgery. Reparative techniques to correct mitral valve disease are often the best surgical approach for dealing with mitral valve abnormalities, however mitral valvuloplasty is not always feasible because of extensive fibrosis, leaflets calcification, or massive chordal rupture. Mitral valve replacement using either a mechanical valve or a bioprosthetic valve thus remains the best surgical solution for severe mitral valve disease.

However, there are many additional problems that face patients after valve replacement with a prosthestic valve. Valve-related problems include limitation of the mitral flow (due to a small effective orifice area) during exercise and high cardiac output imposed by a smaller size artificial valve as compared with the natural valve orifice area.

Further, the rigid structure of an artificial valve prevents the physiologic contraction of the posterior wall of the left ventricle surrounding the MA during systole. Surgical interruption of the MA-PM continuity accounts for changes in geometry mechanics and performance of the left ventricle. Myocardial rupture, a lethal complication of mitral valve replacement, results from excision or stretching of the papillary muscle in a thin and fragile left ventricle. Myocardial rupture can also be caused by a strut of a stented bioprosthetic valve eroding into or protruding through the posterior left ventricle wall. Maintaining the MA-PM continuity appears to provide a substantial degree of protection from this devastating complication. Also, the difficulties in controlling adequate anticoagulation for a mechanical valve bring a high morbidity risk factor of thromboembolic and hemorragic complication and endocarditis.

Stented tissue valves, although less thrombogenic, are not reliably durable and, because of the rigid stent, they are less hemodynamically efficient. Stentless valves are considered to have the potential advantages of superior hemodynamic performance and enhanced durability and have already showed satisfactory mid-term results in the aortic position. From these points of view, it is expected that new stentless valves in the mitral position will be developed. However, stentless mitral valves are not yet commonly available for clinical use because of the anatomical and functional complexity of the mitral valve and the subvalvular apparatus, resulting in the difficulties of the design and implantation procedures of the stentless mitral valves. The present invention provides and apparatus and method for replacing a native mitral valve with a stentless, bioprosthetic valve that maintains the anatomical and functional complexity of the mitral valve and the subvalvular apparatus.

SUMMARY OF THE INVENTION

The present invention is a stentless bioprosthetic valve for replacing a native mitral valve resected from a valve annulus in a heart. The bioprosthetic valve comprises at least one piece of biocompatible material comprising a bi-leaflet conduit having dimensions that correspond to the dimensions of the native mitral valve. The conduit has a proximal end and a distal end. The proximal end defines a first annulus for suturing to the valve annulus of the heart. The conduit further includes first and second leaflets that mimic the three-dimensional anatomical shape of the anterior and posterior leaflets of the native mitral valve. The first and second leaflets extend between the proximal end and the distal end of the conduit. The distal end of the conduit defines a second annulus at which the first and second leaflets terminate. The second annulus is for suturing to free edges of the anterior and posterior leaflets of the native mitral valve that remain intact following resection of the native mitral valve so that the native chordae tendineae, which are attached to the papillary muscles, continue to provide prolapse prevention and left ventricular muscle support functions in addition to maintaining the continuity between the valve annulus and the papillary muscles.

In accordance with one aspect of the invention, the at least one piece of biocompatible material comprises harvested biological tissue.

In accordance with another aspect of the invention, the harvested biological tissue comprises pericardial tissue.

In accordance with yet another aspect of the invention, the harvested biological tissue comprises a porcine mitral valve.

In accordance with still another aspect of the invention, the harvested biological tissue comprises a homograft mitral valve.

In accordance with yet another aspect of the invention, the at least one piece of biocompatible material comprises an artificial tissue.

In accordance with another feature of the invention, the bioprosthetic valve further comprises a biocompatible, unstented ring connected to the first annulus for supporting the first annulus and for suturing to the valve annulus of the heart. The ring, when sutured to the valve annulus, impedes dilatation of the valve annulus and preserves motion of the valve annulus.

The present invention also provides a method for replacing a native mitral valve having anterior and posterior leaflets with a stentless bioprosthetic valve. According to the inventive method, at least one piece of biocompatible material that comprises a bi-leaflet conduit having dimensions that correspond to the dimensions of the native mitral valve being replaced is provided. The conduit has a proximal end and a distal end. The proximal end defines a first annulus and the distal end defines a second annulus. The conduit further includes first and second leaflets that mimic the three-dimensional shape of the anterior and posterior leaflets of the native mitral valve. The first and second leaflets extend from the proximal end and terminate at the distal end of the conduit. The majority of the anterior and posterior leaflets of the native mitral valve are resected from the valve annulus but the free edges of the anterior and posterior leaflets are left intact along with the native chordae, tendineae which are attached to the papillary muscles, so that the native chordae tendineae can provide prolapse prevention and left ventricular muscle support functions for the bioprosthetic valve in addition to maintaining the continuity between the valve annulus and the papillary muscles. The first and second leaflets at the second annulus of the conduit are sutured to the free edges of the anterior and posterior leaflets of the native mitral valve that remain following resection of the native mitral valve. The first annulus of the conduit is then sutured to the valve annulus of the native mitral valve to secure the bioprosthetic valve to the valve annulus.

In accordance with another aspect of the inventive method, a biocompatible, unstented support ring encircles the first annulus. The support ring is sutured to the valve annulus of the heart to secure the bioprosthetic valve to the valve annulus and to impede dilatation of the valve annulus and preserve motion of the valve annulus.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a method and apparatus for replacing a native mitral valve with a stentless bioprosthetic valve. As representative of the present invention,FIG. 1illustrates an apparatus10comprising a stentless bioprosthetic valve12for replacing a native mitral valve14(FIG. 4) in accordance with a first embodiment.

The bioprosthetic valve12shown inFIG. 1is made from one or more pieces of biocompatible material formed into a bi-leaflet conduit20having dimensions that correspond to the dimensions of the native mitral valve14. The conduit20has a proximal end22and a distal end24. The proximal end22defines a first annulus26for suturing to the valve annulus of the native mitral valve14, as described further below.

The conduit20further includes first and second leaflets30and32(FIG. 2) that mimic the three-dimensional anatomical shape of the anterior and posterior leaflets34and36(FIG. 4), respectively, of the native mitral valve14. The first and second leaflets30and32extend between the proximal end22and the distal end24of the conduit20.

The distal end24of the conduit20defines a second annulus40at which the first and second leaflets30and32terminate. The second annulus40is for suturing to free edges of the anterior and posterior leaflets34and36of the native mitral valve14, as described further below.

The biocompatible material of the bioprosthetic valve12may be a harvested biological material including, but not limited to, bovine pericardial tissue, horse pericardial tissue, porcine pericardial tissue, a porcine mitral valve, or a homograft (or allograft) mitral valve. The biocompatible material may also be suitable synthetic material including, but not limited to, polyurethane or expanded PTFE.

In the case of, for example, bovine pericardial tissue, the tissue is harvested in slaughterhouses and kept in cold saline solution for transport to minimize the effects of autolysis and bacterial/enzymatic reactions on the tissue. The pericardial tissue is dissected to be clean of all fatty and other biological materials. The pericardial material is then formed into a tri-dimensional shape of what will be the leaflet structure of the bioprosthetic valve12by attaching the pericardial tissue to a mold (not shown) having such a shape.

The molds are produced in different sizes to render valves of different sizes to match the needs of the different patients (i.e., sizes between 23 and 35 mm in diameter). The molds can have either a male shape of what will be the inflow aspect of the valve12, or a female aspect of the same. The pericardial tissue is applied to the molds and accommodated to ensure the complete comformability to the mold's shape. The bioprosthetic valve12can be made with only one piece of pericardial tissue, as shown inFIGS. 1 and 2. Alternatively, the bioprosthetic valve12can be made with two pieces of pericardial tissue, one of which will form the first leaflet30and the other forms the second leaflet32of the prosthetic valve, as may be seen inFIG. 2A.

Once the pericardial piece(s) is fully conformed on the mold, the biological material is tanned by immersion in an adequate fixation solution (e.g. 0.65% glutaraldehyde solution buffered at pH 7.4). This tanning can be achieved with an ample range of glutaraldehyde concentrations (e.g. between 0.4% and 5%).

When the pericardial tissue is already fixed with the fixation agent, it is then separated from the mold and the lateral edges50and52(FIG. 2) are sutured together along a seam54to form the tubular conduit20. In the alternate embodiment ofFIG. 2Awhere two pieces of pericardial tissue are used, it is necessary to suture the tissue in two locations, thereby forming two seams56and58. The seams54,56, and58are always placed at what will be the commissures of the prosthetic valve12, where the first leaflet30meets the second leaflet32.FIG. 2Billustrates another alternate embodiment for the valve12in which there are no seams because the valve is a harvested porcine mitral valve.

In accordance with the first embodiment of the present invention, the valve12further includes a flexible, unstented, biocompatible ring60(FIG. 3) that is sutured about the first annulus26along a proximal edge62at the proximal end22of the conduit20. The ring60is for supporting the first annulus26and for suturing the valve12to the valve annulus in the heart. The ring60may be made from a biological material such as, for example, bovine or porcine pericardial tissue, or from a suitable synthetic material, such as the material marketed under the tradename DACRON or the material marketed under the tradename TEFLON. In the embodiment ofFIG. 3, the ring60is positioned underneath the proximal edge62of the conduit20. Alternatively, the ring60could be positioned on top of the proximal edge62, as shown inFIG. 3A, or wrapped around the proximal edge, as shown inFIG. 3B, and subsequently sutured in place.

According to an alternate construction for the valve12shown inFIG. 3C, a ring70is formed at the proximal end22of the conduit20by folding an additional portion72of the conduit20located at the proximal end22over onto itself and suturing the folded portion to the conduit.

Replacement of the native mitral valve14(FIG. 4) with the bioprosthetic valve12begins by taking either direct or echocardiographic measurements of the height of the anterior and posterior leaflets34and36of the native mitral valve. The size of the bioprosthetic valve12to be implanted is determined based on a measurement of the distance between the right and left trigones on the valve annulus. Four stay-sutures (6-0 silk) may be placed on the annulus of both mitral commissures and on the centers of the anterior and posterior leaflets34and36to help make sure that the bioprosthetic valve12is implanted in the proper anatomical orientation.

As may be seen inFIGS. 4 and 5, the native mitral valve14is then dissected from the heart. The proximal end80of the native mitral valve14is resected from the valve annulus82. At the distal end84of the native mitral valve14, the anterior and posterior leaflets34and36are resected in such a manner that the free edges86and88of the anterior and posterior leaflets, respectively, remain intact and connected to the native chordae tendineae90which, in turn, remain attached to the two papillary muscles100.

Next, the prosthetic valve12is moved into the position shown inFIG. 6. The second annulus40of the conduit20(at the distal end24where the first and second leaflets30and32terminate) is then sutured to the free edges86and88of the anterior and posterior leaflets34and36of the native mitral valve14that were preserved during the resection of the native mitral valve. According to one technique, 5-0 Ethibond continuous over-and-over sutures110may be used to secure the distal end24of the prosthetic valve12to the free edges86and88. The sutures110may be started from the apex of the first and second leaflets30and32and extended toward both commissural sides to help prevent any folds from occurring in the first and second leaflets.

To complete the replacement procedure, the ring60at the proximal end22of the bioprosthetic valve12is sewn to the native mitral annulus82as shown inFIGS. 6 and 7with sutures120. The sutures120may be three 4-0 Prolene running sutures or other suitable means. Once it is sutured to the valve annulus82, the ring60functions to impede dilatation of the valve annulus and preserve the motion of the valve annulus.

The prosthetic valve12and associated method for replacing the native mitral valve14described above are useful in treating dilated cardiomyopathy, ischemic cardiomyopathy, ischemic mitral valve regurgitation, and infected mitral valve endocarditis. By suturing the second annulus40at the distal end24of the valve12to the free edges86and88of the anterior and posterior leaflets34and36of the native mitral valve14that are intentionally left intact when the native mitral valve is resected, the native chordae tendineae90, which remain attached to the papillary muscles100, continue to provide prolapse prevention and left ventricular muscle support functions. Significantly, the bioprosthetic valve12and the method for implanting the bioprosthetic valve described herein accomplish the goal of maintaining the continuity between the valve annulus82and the papillary muscles100.

Additional benefits of the bioprosthetic valve12and associated method for implanting include:A) a large orifice with an adequate circumference correlated with the size of the patient's body surface area, unrestrictive to a central free flow, compatible with high cardiac output at exercise, a low pressure required to open the valve, and without an increased gradient across the valve;B) rapid opening and closure at all pressure ranges, without regurgitate flow and obstruction of the left ventricle outflow tract;C) no rigid support or stent in the mitral area to allow the physiologic contraction of the left ventricular posterior wall around the mitral annulus during systole, flexible to adapt precisely to the mitral annulus reducing the tissue stress and allowing a uniform distribution of stress on the prosthetic valve which provides longer life and a higher resistance to wear, tear, and calcification; andF) anticoagulation treatment is not required and no trauma of the blood elements is produced.

FIGS. 8–10illustrate an apparatus10′ comprising a stentless bioprosthetic valve12′ in accordance with a second embodiment of the present invention in which the bioprosthetic valve comprises a homograft mitral valve. InFIGS. 8–10, reference numbers that are the same as those used inFIGS. 1–7indicate structure that is the same as described above for the previous embodiment, while reference numbers that have apostrophe (′) indicate similar, but not identical, structure.

In accordance with the second embodiment, the homograft valve12′ to be implanted must be harvested. To harvest the valve12′, the left atrium of the donor heart is opened and the mitral valve annulus82, the leaflets30′ and32′, and the subvalvular tissues (the chordae tendineae90and the papillary muscles100) are anatomically evaluated. The valve12′, and in particular the heights of the leaflets30′ and32′, are measured.

The left ventricle is then opened and the entire valve12′ is excised or removed by incision of the valve circumferentially (not shown). The incision is placed near the fibrous valve annulus82of the valve12′ and then through the myocardium of the left atrium and ventricle to ensure that the valve annulus is preserved intact. The donor chordae tendineae that remain attached to the valve leaflets30′ and32′ are removed from the tips of the papillary muscles and the valve12′ is placed on ice. After the mitral valve12′ is thawed, the donor chordae tendineae are trimmed to form the distal edges of the homograft leaflets30′ and32′ that will be attached to the free edges86and88of the native mitral valve14. The myocardium of the atrium and ventricle is then cut away from the first annulus26′ of the valve12′, leaving just enough tissue to allow sewing of the homograft valve, without damaging the leaflets30′ and32′, to the native mitral valve annulus82.

In an identical fashion to the first embodiment, the native mitral valve14is dissected from the heart as shown inFIG. 4. The proximal end80of the native mitral valve14is resected from the valve annulus82. At the distal end84of the native mitral valve14, the anterior and posterior leaflets34and36are resected in such a manner that the free edges86and88of the anterior and posterior leaflets, respectively, remain intact and connected to the native chordae tendineae90which, in turn, remain attached to the two papillary muscles100.

Next, the valve12′ is moved into the position shown inFIG. 9. The second annulus40′ (at the distal end24′ where the first and second leaflets30′ and32′ terminate) is then sutured to the free edges86and88of the anterior and posterior leaflets34and36of the native mitral valve14that were preserved during the resection of the native mitral valve. According to one technique, 5-0 Ethibond continuous over-and-over sutures110′ may be used to secure the distal end24′ of the homograft valve12′ to the free edges86and88. The sutures110′ may be started from the apex of the first and second leaflets30′ and32′ and extended toward both commissural sides to help prevent any folds from occurring in the first and second leaflets.

The proximal end22′of the valve′12is then sewn to the native mitral annulus82as shown inFIGS. 9 and 10with sutures120′. The sutures120may be 4-0 Prolene or polypropylene running or continuous sutures or other suitable means. A ring, such as the ring60described above or another suitable annuloplasty ring may be sutured in at the valve annulus82to impede dilatation of the valve annulus and preserve the motion of the valve annulus.

The homograft valve12′ and the associated method for replacing the native mitral valve14described above are useful in treating dilated cardiomyopathy, ischemic cardiomyopathy, ischemic mitral valve regurgitation, and infected mitral valve endocarditis. By suturing the second annulus40′ at the distal end24′ of the valve12′ to the free edges86and88of the anterior and posterior leaflets34and36of the native mitral valve14that are intentionally left intact when the native mitral valve is resected, the native chordae tendineae90, which remain attached to the papillary muscles100, continue to provide prolapse prevention and left ventricular muscle support functions. Significantly, the homograft valve12′ and the method for implanting the homograft valve described herein also maintain the continuity between the valve annulus82and the papillary muscles100.