CA1154553A - Catenary mitral valve replacement - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A novel one-way valve, preferably a substitute mitral heart valve, is provided herein. The mitral heart valve comprises a stent including a circular base and a pair of upstanding,diametrically opposed struts, separating a pair of diametrically opposed,arcuately shaped, depressed re-liefs, each such relief being bounded by a smooth curve interconnecting the struts to the circular base. A flexible, durable, biocompatible covering is secured to the stent and provides two equal,opposed,molded flexible,flappably-movable,valve leaflets secured along the smooth curve defining the upper perimeter of the reliefs. The valve leaflets each are preformed and molded so that the free margin of the biocompatible leaf-lets along the free edges of each of the leaflets between the tips of each associated strut is so related to the circumference of the circular base that, when the valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of the circular base. When the valve is in its relaxed and natural closed position, the shape of the leaflets is such that the free edges of the leaflets drop down and sealingly meet in substantially wrinkle-free form at a curve of apposition in the plane defined by the tips of the struts and the axis of the valve and follow the approximate shape of a catenary curve.

Description

~154553 This invention relates to fluid valves, and more p~rticular-ly, to such fluid valves which permit fluid flow in one directlon and ~, .
prevent fluid flow in the opposite direction. Such a valve may be used as a replacement valve in a human heart or in artificial heart pumps . , ~eart valve disease in advanced forms causes severe disability and ultimately death. The quality and length of life for patients suffering from valve disease can be remarkably improved by surgical treatment, which usually involves the total replacement of the diseased valve with a prosthetic valve.
In the two decades since the first successful implantation in a human, nearly 50 different valve types have been introduced and many have been discarded; of those remaining, two basic types are in use - those constructed of human or animal tissues (tissue valves) and those constructed of cloth, metals, carbon, and plastic components (nontissue or mechanical valves).
These devices have come ln various forms of flexible unicusp, bicuspid, and tricuspid valves, ball valves and "butterfly"
or flapper valves.
Significant late complications following implantation of these valves can occur and are related to valve design and materials.
Present valve replacements do not permit restoratlon of normal

- 2 - ~

1~L54553 pressure-flow dynamics at all levels of cardiac f~mction. Thus, there is still no clearcut choice for the surgeon and the search for the ideal replacement heart valve is continuing.
In addition artificial heart pumps are now known which have been developed to simulate the action of the human heart. Critical components in the artificial heart pump include the fluid control valves and they must operate faultlessly for an indefinite period of time with a mechani-cal action that does not produce excessive blood damage (haemolysis).
Stented tissue valves, that is, supported valvular grafts which may be either xenografts (heterografts) or allografts (homografts), have been used as replacement heart valves. (See, for example, Carpentier et al., J. Thorac. Cardiovasc. Surg. 68:771 (1974); Zuhdi et al., Ann. Thorac.
Surg. 17:479 (l974); Horowitz et al., J. Thorac. Cardiovasc. Surg. 767:
885 (1974)). In general, such grafts have been mounted on supporting frames (stents) which provide rigid orifice rings (See Weldon et al., J.
Surg. Research 6:548 (1966)). Some stents have included struts capable of flexing inwardly to a limited extent, thereby reducing stresses im-posed on the grafts and decreasing possible erosion of surrounding tissues of the patient (See Sugie et al., J. Thorac. Cardiovasc. Surg. 57:455 (1969); and Hardy, Human Organ Support and Replacement, 333 et. seq.).
Despite the encouraging results with prosthetic tissue heart valves and in contrast to non-tissue prosthetic valves, there is a continuing need for improvement, particularly with regard to the 1154~

hydrodynamic performance and lony-range durability of the tissue valve.s.
The art is still faced with the desirability of providing an im-proved stent for a tissue (xenograft or allograft) heart valve which is capable of yielding to a limited extent in response to forces which tend to alter the configuration and circumference of the orifice ring, thereby improving the long-range reliability of the valves. Accordingly, con-tinued efforts are being made to develop more efficient, reliable and biocompatible prostheses.
The results of such continued efforts are evidenced in heart valves which are disclosed in issued United States Patents.
United States Patent No. 2,832,078 issued April 29, 1958 to D.T.
Williams discloses an aortic heart valve including a slotted cylindrical shell with an internal three-sac membrane to provide opening and closing ports, which seal at the centre of the cylindrical shell.
United States Patent No. 3,199,788 issued August 3, 1965 to F.J.
Segger, provides an aortic heart valve including a deformable cone-shaped cusp-supporting ring, with the cusps having smooth curved surfaces.
~nited States Patent No. 3,548,418 issued December 22, 1970 to W.W.
Angell et al., provides a graft-supporting ring for grafting porcine aortic valves in which the ring is generally in the form of the residual portion of a conical shell, having three struts, the ring being completely covered and having three internal depressed valve cusps.
United States Patent N0. 3,570,014 issued March 16, 1971 to W.D.
Hancock provides a stent for aortic and mitral heart valves in which the stent includes a ring and three support arms rising therefrom, to which commissures and cusps of a heart valve are attached.
United States Patent No. 3,714,671 issued February 6, 1973 to W.S.
Edwards et al. provides a stent for supporting a tricuspid heart valve, in .,:.

~.154553 which the ring comprises portions of ellipses, in which the upstanding por-tions are covered with fabric and which terminate in radial wings, and to which three valve cusps are sutured, the valve cusps having straight trimmed edges, and being supported without tension.
United States Patent No. 3,736,598 issued June 5, 1973 to B.J.
Bellhouse et al. provides ab aortic valve including a ring having three legs folded to U-shaped sections to which are attached three valve cusps whose free edges meet in radial planes of abutment.
U-ited States Patent No. 3,739,402 issued June 19, 1973 to D.A.
Cooley et al., provides a graft support for a bicusp valve which includes a frusto-conical ring and a pair of inverted frusto-conical segments defin-ing struts, all provided with a fabric cover, to,which are secured a pair of cusps whose upper edges lie adjacent to each other to form the valve opening.
Vnited States Patent No. 3,744,062 issued July 10, 1973 to V.
Parsonnet provides a heart valve construction including a stent having three lower arcuate protions and three upstanding posts, to which a fabric sheath is secured, and from which three valve leaflets, each having an arcuate edge and a straight edge are secured, so that the straight edges provide an upper meeting closure.
Vnited States Patent No. 3,755,823 issued September 4, 1973 to W.D. Hancock provides a stent for heart valves in the form of a flexible stent including a ring having three spaced-apart apexes to which a cloth sleeve is attached and to which three valvc cusps are attached, so that the free edges sag towards the centre, at which point they meet at a central,~
slightly raised point. This valve utilizes a whole porcine aortic valve which is pretreated before mounting on the stent.

115~S53 Vnited States Patent No. 3,938,197 issued Pebruary 17, 1976 to S.
~i]o provides a heart valve including a ring to which are attached a plurality of flat valve flaps whose free edges all meet in abutting rela-tion.
United States Patent No. 3,983,581 issued October 5, 1976 to W.W.
Angell et al. provides a heart valve stent of a particular shape, to which a covering is attached, and from which three valve cusps are attached so that their free edges meet at three commissures, and so that their common points meet at a central depression. A whole porcine xeno-graft is mounted to the stent.
United States Patent No. 4,035,849 issued July 19, 1977 to W.W.
Angell et al. provides; a heart valve stent of a particular shape, to which a covering having a bead along its perimeter is attached and from which three valve cusps are attached, so that their free edges meet at three commissures and so that their common points meet at a central depres-sion. A whole porcine xenograft is mounted to the stent.
United States Patent No. 4,084,268 issued April 18, 1978 to M.I.
Ionescu et al. provides a heart valve including a dish-shaped cloth-covered stent having three upright posts, to which three cusps are attached,the cusps meeting at their upper edges at a flat closed portion, and in which the knots of the stitches are covered by a pledget and cover. This valve uses pretreated bovine pericardium for its three leaflets.
United States Patent No. 4,106,129 issued August 15, 1978 to A.F.
Carpentier et al. provides a heart valve including a deformable wire-frame stent having three inverted V-shaped commissure supports, to which are se-cured a cover, and from which are suspended three valve leaflets meeting along the commissures. A whole porcine xenograft is mounted to the stent.

1:154553 United States Patent No. 4,164,046 issued August 14, 1979 to ~.A.
Cooley provides a mitral or tricuspid valve replacement which i.s based on an open ring stent.
United States Patent No. 4,172,295 issued October 30, 1979 to R.J.
Batten provides a tricuspid heart valve dish-shaped cloth-covered stent having three upright ports to which are attached three cusps meeting at their upper edges at a flat closed position, in /

//////'// .

~1~455;3 which the knots of the stitches are covered by a pledget and cover, and in which securing holes are provided between the cusps.
~ nited States Patent No. 4,178,639 issued December 18, 1979 to J.C. Bokros provides a heart valve having an annular valve body and a pair of pivotally secured valve leaflets.
In spite of all these prior patents, improvements are still required to provide improved valves which: provide minimal obstruction to the flow of blood; have smooth surfaces to minimize haemolysis; must not be too slow in closing, thereby permitting a substantial and undesirable reflux caused by the relatively high head pressure of the pump system; in opening and closing, there should be a minimum amount of mechanical stress and strain to the valve which wou~.d materially contribute to shortening the life of the valve; provide adequate support for attachment within the heart; minimize adverse clotting effects; should not create significant turbulence in the blood stream in both systole and diastole, which can damage blood elements; provide acduracy in the si~e and shape of the cusps; provide accuracy in the shape and size of the stent ring;
have improved reliability by minimizing stresses in the flexing cusps tissue; incorporate flexibility and deformability in their functional operation; and improve the structural alignment of the tissue relative to the stent.

~1~455~3 Accordingly, an object of a msin aspect of this invention is to provide an improved one-way valve~
An object of another aspect of this invention is to provide an improved one-way valve which may be used in artifi~ial heart pumps as well as for heart valve replacements.
Objectives of further aspects of this invention are to provide heart valves having the following characteristics:

1. free flow central orifice configuration;
2. rapid opening and closing;

3. potent~al mimimal compressive and tensile stress distrlbution on flexing leaflets and hence improved valve reliability;

4. high ratio of available valve flow area to implant site area;
. relative ease of fabrication of all sizes compared to other tissue type valves;
6. mimimal obstruction to the left ventricular outflow tract;
7. negligible retrograde flow;
8. maximal conformity to the natural anatomic valve configuration;
9. mimimal thromboembolic potential;
; 20 10. e~se of handling and insertion; snd 11. silent operatlon.

l~LS4~53 By one aspect of ehis invention, a one-way valve is provided corn-prising: a stent including a circular base and a pair of diametrically opposed struts, separating a pair of diametrically opposed, arcuately shaped, depressed reliefs, each such relief being bounded by a smooth curve interconnecting the struts to the circular base; a flexible, durable, covering secured to the stent, and providing two equal, opposed, molded, flexible, flappably-movable, valve leaflets secured along a smooth curve defining the upper perimeter of the reliefs; the valve leaflets each being preformed and molded so that the free margins of the covering along the free edges Of each of the leaflets between the tips of each associated strut is so related to the circumference of the circular base that, when the valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of the circular base; and, when the valve is in its relaxed and natural, closed position, the shape of the leaflets is such that the free edges of the leaflets drop down and sealingly meet in substantially wri.nkle-free form at a curve of apposition in the plane defined bv the tips of the struts and the axis of the valve, and follow the approximate shape of a catenary curve.
By another aspect of this invention, a mitral heart valve com-prising: a stent including a circular base and a pair of upstanding,diamet-rically opposed struts, separating a pair of di.ametrically opposed, arcu-ately shaped, depressed reliefs, each such relief bcing bounded by a smooth curve interconnecting the struts to the circular base; a flexible, durable, biocompatible covering secured to the stent and providing a pair of equal, opposed, molded, flexible, flappably-movable, valve leaflets secured along the smooth curve defining the upper perimeter of the reliefs; the valve leaflets each being preformed and molded so that the free margins of the biocompatible covering along the free edges of each of the leaflets be-~s~s~

tween the tips of each associated strut is so related to thc circurn-ference of the circular base that, when the valve is in ils open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of the circular base, and, when the valve is in its relaxed and natural closed position, the shape of the leaf-lets is such that the free edges of the leaflets drop down and sealingly meet in substantially wrinkle-free form at a curve of apposition in the plane defined by the tips of said struts, and the axis of the valve and follow the approximate shape of a catenary curve.
By a variant of these aspects the struts are substantially identi-cal.
By another variant, the reliefs are symmetrically disposed equi-distant from the struts.
By another variant of these two aspects of this invention, the struts are made to be flexibly elastically deformable to minimize stresses on the valve leaflets when the valve closes.
By a further variant thereof, the free edges of the leaflets follow a precise catenary curve in the closed position.
By yet another variant thereof, the reliefs are disposed equidis-tant from the struts.
By yet another variant of the second aspect of this invention, the valve leaflets are formed of pcricardium trcated with glutaral-dehyde.
By a variation thereof, the valve leaflets are formed of other flexible materials, e.g., polyurethane-type compounds.
By a further variant, the leaflets of pericardium are secured to each other and to the struts by sutures.
By another variant, the struts lie within the surface of a cone having the circular stent base as the conic base.

1154~5~3 By a further variant, the smooth curve inLerconnecting the struts is a parabola.
By yet another variant, the stent is formed of a ~lexible, elas-tically deformable material, so that the struts may llex slightly.
By still another variant, the material is polypropylene of is an acetal copolymer.
By a still further variant, the valve cusps are formed of bovine, porcine or human fascia lata or dura mater, or of polyurethane.
By another aspect of this invention, a method is provided for mak-ing a mitral heart valve comprising the steps of: (a) providing a stent in-cluding a circular base:and a pair Of upstanding, diametrically opposed, struts separating a pair of diametrically opposed~arcuately shaped~depressed reliefs, each releif being bounded by smooth curve interconnecting the struts to the circular base, the hei~ht of the struts bein~ a selected value derived from the outside circumference of the circular base; (b) pro-viding a shape for the valve leaflets in their closed position by requiring that the length of leaflet tissue from the strut to the free èdge provides the apprcximate shape of a catenary or other curve; (c) generating the sectional contours of the leaflets in the closed position; (d) provide a mold of the shape selected around which a leaf].et is to be formed; (e) mold-ing the leaflets on the mold so that the free margins of a biocompatible covering along the free edge of each of the leaflets between the tips of each associated strut is so related to the circumference of the circular base that, when the valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of the circular base, and, when the valve i.s in its relaxed and natural closed position, the shape of the leaflets is such that the free edges of the leaflets drop down and sealingly meet in substantially wrinkle-llS4SS;~

free form at a curve of apposition in t-he plane defined by the tips of the struts, and the axis of the valve and follow the approximate shape of a catenary curve; (f) securing the molded, leaflets so formed to the circular base and securing the leaflets to each other and to the struts; and (g) fixing the valve in the closed position while maintaining the leaflets in their shaped condition.
By a variant of this aspect of this invention, the height of the struts is one-quarter of the outside circumference of the circular base.
By yet another variant thereof, the leaflets are secured to each other and to the struts by sutures.
The heart valve provided herein in one preferred embodiment is designed specifically for the mitral position which has the bicuspid character of the natural mitral valve. Such a design more likely takes advantage of the anatomic configuration and flow patterns of the natural left ventricle then, for example, a tricuspid tissue valve or a non-tissue valve in the mitral position. When closed, a bicuspid or bi-leaflet valve has the advantage of presenting minimal obstruction of the ventricular outflow tract.
In the accompanying drawings, Figure 1 is a perspective view of the stent forming part of the mitral valve replacement of an embodiment of this invention;
Figure 2 is a perspective view of the mitral valve of an embodi-ment of this invention, in the open position; and Figure 3 is a perspective view of the mitral valve of an embodi-ment of this invention in the closed position.
As seen in Figure 1, the stent includes diametrically opposed reliefs which are slightly splayed from the vertical axis of the valve to allow for tissue anchoring at the valve outlet without causing obstruction 11545~3 to flow with the valve fully open. The stent also includes a low cylindri-cal base member or ring 11. Disposed about the cylindrical base member or ring 11 are a pair of identical, diametrically opposed struts 12 between which are a pair of identical, diametrically opposed reliefs 13. The struts can, of course, be less than true conical segments and still provide a stent 10 which can be used in providing the mitral valve replacement of an embodiment of this invention.
The stent 10 is made as light and unbulky as is compatible with the needed strength and with avoidance of sharp edges. Preferably it is made of a flexible elastically deformable material, i.e., synthetic ~plastic materials, e.g.Jpolypropylene or acetal copolymer~ so that the struts 12 may flex slightly. The struts 12 have rounded extremities 14 and are connected to the cylindrical base member or ring 11 by smooth curvés 15 to give the reliefs 13 an arcuate shape. Each strut 12 has an-chor openings 16.
The mitral valve 18 is`formed on the stent 10 by a suitable cover-ing material so secured to the cylindrical base member or circle 11 to pro-vide a pair of opposed surfaces 21 secured to the struts 12 of the stent 10 and a pair of opposed cusps or leaflets 22 which are flexible and flappably movable. The free margin or perimeter 23 at the free edges of the cusps or leaflet 22 is preferably of such length that when the free edges of the leaflets meet, the valve is closed to form the approximate shape of catenary curve 24 or lenyth equal to the perimeter 23.
In the embodiment of this invention as shown in Figures 2 and 3, the mitral valve 18 in its closed position has two equal or leaflets cusps 22 which form a curve of apposition in the plane defined by the tip of each stent strut 12 and the axis of symmetry of the valve 18. In the open position, the valve 18 provides an approximately cylindrical shape of tis-:llS45r~

sue with an exit area equal to the inside area of the cylindrical memberor circular base 11 of the stent lO.
In this embodiment, the length 23 of tissue between the tips of each stent strut 12 in the closed position equals half the circumference of the exit aperture of the valve 18. This is achieved by having a curved closure line which appears to be like a line dropping from the stent strut tips 14 towards the cylindrical base member or ring 11. The curve is preferably a catenary, i.e., the curve formed by a uniform chain hanging freely between two points but may assume other curved configurations pro-vided the specified tissue length is adhered to.

Calf pericardium was selected as the material for construction of the valve or cusps leaflets since, when treated with glutaraldehyde, it has acceptable durability and biocompatibility. Other naturally-occurring materials, e.g., bovine, porcine, human (pericardium, fascia lata, dura mater) or synthetic materials, e.g. polyurethanes e.g. that known by the Trade Mark of AVCOTHANE of acceptable durability and biocompatibility may also be used. A flexible stent made of acetal copolymer, is preferably used since it allows flexibility and thereby provides greater valve dura-bility.
In the preparation of one variant embodiment of this invention, a prototype stent 10 was machined from an acetal copolymer rod. The height of the s~rut 12 above the cylindrical base member or ring 11 was equal to one-quarter of its outside circumference. The shape of the cusps or leaf-lets 22 in the closed position was determined by requiring that the lengths of tissue shown for the open valve 18 from the tip 14 of the strut 12 to the free edge of the cusps or leaflets 22 should form catenar-ies in the closed position. The sectional contours of the cusps or leaf-lets 22 in the closed position were then generated. A mold was then made ~5~S5~3 around which each cusps or leaflet 22 could be formed. The moist tissue for the cusps or leaflets 22 was attached to the stent 10, then sutures 25 were used to secure the cusps or leaflets 22 to each other and to the tips 14 of the stent struts 12. The valve 18 was fixed in the closed position using 0.625~ glutaraldehyde solution while the shape of the cusps or leaflets 22 was maintained by cotton batting and by a negative mandrel shape. The shape was further maintained after initial fixation by cotton batting once the negative mandrel molding was removed.
The mitral replacement valve 18 of an embodiment of this inven-tion was compared against different conventional types of prostheses using a hydromechanical apparatus which provided a realistic simulation of heart geometries, pressures, and flows. The hydrodynamic performance of each of the valves tested was compared at three different pulse rates (60, 80, and 120 beats per minute). The three measures used to characterize valvular performance were:
- Table I, mean and maximum transmitral pressure difference - Table II, observed and calculated open valve area - Table III, total transmitral energy loss per cycle - 15 a -~1~45~;~

TABLE I
Transmitral. pressure difference; mean, maximum ~mmHg) at Valves 60 80 120 beats/min beats/minbeats/min (1) ~icusp ~ 1.3, 11.5 1.8, 12.02.9, 11.0 (2) Bjork-Shiley, c.c. 1.2, 14.22.1, 13.3 4.8, 13.0 (3) St. Jude Medical 1,3, 13.62.9, 15.0 5.0, 13.4 (4) Hall-Kaster 1.4, 16.0 1.9, 14.45.5, 15.8 (5 ) Ionescu-Shiley 1.6, 7.83.0, 11.0 5.9, 13.4 (6) Omniscience 1.8, 15.6 2.5, 14.76.2, 16.8 (7) Bjork-Shiley 1.6, 14.2 2.9, 14.46.9, 13.9 (8) Lillehei-Kaster 3.9, 18.23.5, 14.1 8.4, 17.0 (9) C~rpentier-Edwards 2.9, 15.54.6, 17.5 8.7, 18.7 (10) Starr-Edwards 4.1, 14.1 6.2, 18.111.4, 22.1 (11) Hancock 4.4, 16.9 6.7, 20.413.4, 25.4 Note: Bracketed numbers indicate order of merit with (1) being the best value and (ii) the worst.

~:~54S5~3 ~ABLE II
._ Open valve area; calculated, o~served (cm ) at Valves 60 80 120 beats/min beats/min beats/min (1) Bicusp 3.0, 3 9 3.6, 4.1 5.3, 4.7 (2) Bjork-Shiley, c.c. 3.6, 4.2, 4.2 (3) St. Jude Medical 2.8, 3.5, 3.8, 10(4) Hall-Kaster 2.9, 3.7, 3.3,

(5) Omniscience 2.7, 3.2, 3.0,

(6) Ionescu-Shiley 2.7, 2.9 2.4, 3.2 2.9, 3.2

(7) Bjork-Shiley 2.8, 3.5, 2.8,

(8) Lillehei-Kaster 2.0, 2.7, 2.3,

(9) Carpentier-Edwards 2.1, 2.0 2.1, 2.0 2.2, 2.1

(10) Hancock 1.9, 1.5 1.5, 1.6 1.9, 1.7

(11) Starr-Edwards 1.7, 1.7, 1.7, .. ... . ... _ _ . ... _ _ No-te: -Bracketed numbers indicate order of merit with (1) being the best valve and (11) the worst.
-Non tissue type valves do not have an observed area.

~S9tS5~

TABLE III
Total transmitral energy loss (~) at Valves 60 80 120 beats/min beats/min beats/min (1) Bicusp 7 8 7 (2) Ionescu-Shiley 7 9 11 (3) Carpentier-Edwards 9 9 11 (4) Omniscience 9 10 12 (5) Hall-Kaster 10 11 12 (6) St. Jude Medical 10 12 13 (7) Bjork-Shiley, c.c. 12 12 13 (8) Starr--Edwards 7 8 14 (9) Bjork-Shi.ley15 16 18 (10) Lillehei-Kaster 15 17 18 (11) Hancock 12 13 19 Total model ventricular 0.935 1.066 1.105 energy (Joules) . ____ _ 20 Note: Bracketed numbers i.ndicate order of merit with (1) being the best valve and (11) the worst.

~15~55;~
The B~ork--Shiley may be descrlbed as a -valve which uti1izes a single spherical tilting disc occluder. The dLsc is made fro~
pyrolytic carbon and the metal housing ls made of a mctal known by the Trade Mark STELI.ITE. Cloth of a polytetrafluoroethylene known by the Trade Mark TEFLON is used for the s~lturing ring.

~le Omniscierlce may be described as a valve wh;ch utilizes a single pivoting curvilinear - shell occluder. The disc is made from pyrolytic carbon and the metal housing is made of titanium. The suturing ring is made of knitted polyester.

The Bjork-Shiley (cc) may be described as a valve which utilizes a single convexo-concave tilting disc occluder. ~e disc is made of pyrolytic carbon and the metal housing is made of STELLITE. The sutu~~ing r;ng is made of knitted TEFLON. (See Canadian Patent 1,066,853) The ~all-~aster may be described as a valve wllich utilizcs a single spherical pivoting disc occluder. The disc is made from pyrolytic carbon and the metal housing is made of titanillm. The suturing ring is mL~de of knitted TEFLON.

The Starr-Edwards may be describcd as a valvc which u~ilizes a silicone rubber ball occluder. The netal housing is made of STELLITE. The suturing ring is m~de of knitted ~EFLON and polypropylene .

llS4S5~3 me Carpentier-Edwards may be described as a valve which u-tilizes a glutaraldehyde preserved flexible support mounted porcine xenograft.
m e flexible support is comprised of wire frame formed of a wire known by the Trade Mark ELGILOY, having an insert of a material known by the Trade Mark REEMAY, with a support of a synthetic plastic known by the Trade Mark MYLAR and a TEFLON cloth. (See Canadian Patent 1,069,652 and V.S. Patent 4,106,129).

m e Hancock may be described as a valve which utilizes a glutaraldehyde preserved flexible support mounted porcine xenograft. The fle-xible support is comprised of polypropylene, STELLITE, silicone foam, and knitted synthetic fabric known by the Trade Mark DACRON. (See U.S.
Patent 3,755,823).

me St. Jude Medical may be described as a valve which utilizes two center opening tilting disc occluders. The discs and housing are made from pyrolytic carbon. m e suturing ring is made of a D~CRON velour.
(See U.S. Patent 4,178,639).

The Ionescu-Shiley may be described as a valve which utilizes bovine pericardial xenograft material for construction of three equal cusps mounted on a symmetrlcal titanium frame covered with DACRON cloth. The suturing ring is also made of DACRON cloth. (See U.S. Patent 4,084, 268).

_ 20 -~L~X4~

The Lillehei-Kaster may be described as a valve which utilizes a free -floating pyrolytic carbon disc for an occluder. The housing is made from titanium and the suturing ring is made from DACRON cloth.
The Bicusp or Bi-leaflet Mitral Valve of an embodiment o the present invention as described in Figures 1-3.
From the results shown in the Tables, the bicusp or bi-leaflet mitral valve of an embodiment of this invention, tested under simulated conditions in a model left heart as described have shown significantly re-duced obstruction to flow through the valve demonstrated by showing the smallest transmitral pressure, largest open area, and least transvalvular energy loss as compared to existing devices.
As noted above, the hydrodynamic performance of the bicusp valve has been assessed by comparison with existing prostheses, namely, with seven non-tissue valves and three tissue valves. The parameters measured were: mean and maximum transvalvular pressure difference; maximum observed or calculated open area; and total transmitral energy loss. The bicusp mitral valve of an embodiment of this invention demonstrates performance superior to all tested prosthesis as assessed by these parameters.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A one-way valve comprising: a stent including a circular base and a pair of diametrically opposed struts, separating a pair of diametrical-ly opposed, arcuately shaped, depressed reliefs, each said relief being bounded by a smooth curve interconnecting said struts to said circular base;
a flexible, durable, covering secured to said stent, and providing two equal, opposed, molded, flexible, flappably-movable, valve leaflets secured along a smooth curve defining the upper perimeter of said reliefs; said valve leaflets each being preformed and molded so that the free margins of said covering along the free edge of each of said leaflets between the tips of each associated strut is so related to the circumference of the circular base that, when the valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of said circular base; and, when the valve is in its relaxed and natural closed position, the shape of the leaflets is such that the free edges of the leaflets drop down and sealingly meet in substantially wrinkle-free form at a curve of apposition in the plane defined by the tips of said struts and the axis of the valve, and follow the approximate shape of a catenary curve.

2. The valve of claim 1 wherein said struts are substantially identical.

3. The valve of claim 1 wherein said reliefs are symmetrically disposed equi-distant from said struts.

4. A mitral heart valve comprising: a stent including a circular base and a pair of upstanding diametrically opposed struts, separating a pair of diametrically opposed, arcuately shapecd, depressed reliefs, each said relief being bounded by a smooth curve interconnecting said struts to said circular base; a flexible, durable, biocompatible covering secured to said stent and providing a pair of equal, opposed, molded, flexible, flappably-movable, valve leaflets secured along said smooth curve defining the upper perimeter of said reliefs; said valve leaflets each being preformed and molded so that the free margins of said biocompatible covering along the free edge of each of said leaflets between the tips of each associated strut is so related to the circumference of the circular base that, when the valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of said circular base, and, when said valve is in its relaxed and natural closed position, the shape of said leaflets is such that the free edges of said leaflets drop down and sealingly meet in substantially wrinkle-free form at a curve of apposition in the plane defined by the tips of said struts, and the axis of the valve and follow the approximate shape of a catenary curve.

5. The valve of claim 4 wherein said struts are substantially identical.

6. The valve of claim 5 wherein said reliefs are symmetrically disposed equidistant from said struts.

7. The valve of claim 5 wherein the free edges of said leaflets follow a precise catenary curve.

8. The valve of claim 7 wherein the valve leaflets are formed of pericardium treated with glutaraldehyde.

9. The valve of claim 8 wherein said leaflets of pericardium are secured to each other and to said struts by sutures.

10. The mitral heart valve of claim 4 wherein said struts lie within the surface of a cone having the circular stent base as the conic base.

11. The mitral heart valve of claim 10 wherein said smooth curve interconnecting said struts is a parabola.

12. The mitral heart valve of claim 4 wherein said stent is formed of a flexible, elastically deformable material, so that said struts may flex slightly.

13. The mitral heart valve of claim 12 wherein said material is se-lected from the group consisting of polypropylene and an acetal copolymer.

14. The mitral heart valve of claim 4 wherein the valve leaflets are formed from a material selected from the group consisting of bovine, porcine or human fascia lata or dura mater, and of polyurethane.

15. A method of making a mitral heart valve comprising the steps of:
(a) providing a stent including a circular base and a pair of upstanding, diametrically opposed, struts separating a pair of diametrically opposed, arcuately shaped, depressed re-liefs, each said relief being bounded by smooth curve inter-connecting said struts Lo said circular base, the height of said struts being a selected value derived from the out-side circumference of the circular base;
(b) providing a shape for the valve leaflets in their closed position by requiring that the length of leaflet tissue from said strut to said free edge provides the approximate shape of a catenary curve;
(c) generating the sectional contours of said leaflets in the closed position;
(d) provide a mold of the shape selected around which a leaflet is to be formed;
(e) molding said leaflets on said mold so that the free margins of said biocompatible covering along the free edge of each of said leaflets between the tips of each associated strut is so related to the circumference of said circular base that, when said valve is in its open position, the cross-sectional area of the exit is substantially equal to the cross-sectional area of the inside of said circular base, and, when said valve is in its relaxed and natural closed position, the shape of said leaflets is such that the free edges of said leaflets drop down and sealingly meet in substantially wrinkle-free form at a curve of apposition in the plane defined by the tips of said struts, and the axis of the valve and follow the approximate shape of a catenary curve;
(f) securing the molded, leaflets so formed to the circular base and securing the leaflets to each other and to the struts; and (g) fixing the valve in the closed position while maintaining the leaflets in their shaped condition.

16. The method of claim 15 wherein the height of the struts is one-quarter of the outside circumference of the circular base.

17. The method of claim 15 wherein the cusps are secured to each other and to the struts by sutures.