WO1992021305A1

WO1992021305A1 - Composite curvature bileaflet prosthetic heart valve

Info

Publication number: WO1992021305A1
Application number: PCT/US1992/001158
Authority: WO
Inventors: Mark Shu
Original assignee: Medtronic, Inc.
Priority date: 1991-06-06
Filing date: 1992-02-12
Publication date: 1992-12-10
Also published as: US5314467A; AU2346992A

Abstract

A heart valve prosthesis having an annular valve housing (20) and two leaflets (26, 28). Each leaflet possesses a composite curvature shape with pivoting hinges offset to the hydraulic force center of the housing to provide fast response of the leaflets to flow direction change. The hinge mechanism includes modified serpentine-epicycloid curved hinge recesses (34, 36, 38, 40) in the housing for receiving elongated leaflet ears (42, 44, 46, 48) allowing the leaflets to change their motion modes approaching the closed position to reduce leaflet-edge tangential velocity and impact of the minor edges against one another and the major edges against the housing seat upon closure. The hinge mechanism contact surfaces change during rotation and translation of the leaflets in opening and closing, and thus do not rotate about fixed points subject to flow stagnation. The passage of blood through the central orifice and the two peripheral orifices washes both surfaces of the leaflets and the hinge mechanism.

Description

COMPOSITE CURVATURE BILEAFLET PROSTHETIC HEART VALVE

BACKGROUND OF THE INVENTION

1. Field of the Invention - The present invention is in the field of mechanical heart valve prostheses. More particularly, the present invention is directed to a composite curvature leaflet shape of a bileaflet prosthetic heart valve and a modified serpentine epicycloid curve hinge mechanism for such valve leaflets.

2. Brief Description of the Prior Art - Heart valve prostheses are well known in the art. Generally speaking, heart valve prostheses can be classified in two major types or categories. One type of prosthesis employs a tissue valve of animal (usually porcine) origin in its blood flow regulating valve mechanism. The other type of heart valve prosthesis utilizes a ball, a disc, valve leaflets or other mechanical valving devices to regulate the direction of blood flow through the prosthesis. The latter type of prosthesis is usually known in the art as "mechanical" heart valve prosthesis. For specific examples and detailed descriptions of the heart valve prostheses of the prior art, reference is made to U.S. Pat. Nos. 3,744,062; 3,835,475; 3,997,923; 4,364,126 and 4,106,129.

By their very nature, the mechanical heart valve prostheses have metal or plastic surfaces which, when exposed to the blood flow, are thrombogenic to some degree related to deficiencies in design, physical structure, operational characteristics and structural material. In

more recent years, pyrolytic carbon coated bileaflet heart valves having flat leaflets of the type shown in U.S. Pat. Nos. 4,276,658; Re. 31,040; 4,935,030; 4,863,458; 4,822,353; 4,888,010; 4,272,854; 4,451,937; 4,689,046; and 4,863,467, as well as PCT Publication No. W089/00841, have been published. Other prosthetic heart valves of the type shown in U.S. Pat. Nos. 4,484,365, 4,950,287 and 4,863,459, disclose leaflets curved in the downstream direction. A further group of designs employing conical or cylindrical surface bileaflets and pivot axes adjacent to or somewhat displaced from the center of the valve wherein the leaflets typically open away from the center of the valve to provide for central blood flow are disclosed in U.S. Pat. Nos.

4,808,180; 4,363,142; 4,274,437; 4,446,577; 4,328,592;

4,308,624; 4,443,894; 4,357,715; 4,308,624; 4,488,318; and

4,676,789.

Such heart valve designs having a variety of shapes of the leaflets and configurations of hinges have been

developed in an effort to improve reliability, hemodynamics, ease of surgical implantation, and the reduction or

elimination of the development of thrombi.

However, some of the prior art heart valve prostheses have designs which are functionally inefficient and

resistive to the free passage of blood. Others cause blood stagnation points or regions and turbulence which results in the formation of blood clots on the valve structure to obstruct the normal leaflet movement. Hemolysis

(destruction of blood elements) is still a concern in prior art valves that have fast closing contact speed and momentum by which blood elements are mechanically crushed.

In prior designs, considerable attention has been paid to the hinge mechanisms and particular shapes of the bileaflet valves in an effort to improve the blood flow characteristics through the valve orifice in its open position, to reduce the pressure drop and turbulence caused by the profiles of the leaflets to flowing blood. Designs intended to reduce noise of closure of the leaflets, and to provide for continuous cleaning of the valve surfaces and wiping of the hinges have also been advanced in the listed patents. The above listed patents depict various hinge mechanisms that provide rotation and in certain instances, translation of the leaflets during the opening and closing phases. However, most of these designs have never been utilized due to a variety of design shortcomings listed above.

In this regard, to avoid clotting of blood, it is desirable to make further improvements in mechanical heart valve prostheses with regard to these characteristics as well as with regard to simplicity and cost of construction, reliability of operation, and reduction of thrombogenecity. The mechanical heart valve of the present invention provides such improvements.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mechanical heart valve prosthesis which has a low profile and a bileaflet design which allows a large central orifice area to obtain optimal central flow characteristics. It is

another object of the present invention to provide a mechanical bileaflet prosthetic heart valve with composite curvature leaflets for eliminating boundary separation and associated turbulence along the blood flow stream direction.

It is still another object of the present invention to provide a bileaflet prosthetic heart valve having a modified serpentine-epicycloid curve hinge pivot mechanism to reduce the leaflet edge's tangential velocity near the closed position during the valve closing phase and hence reduce the impact of the leaflet edges against the annular housing and against each other on contact.

It is yet another object of the present invention to provide a bileaflet prosthetic heart valve with modified outflow section of the annular valve housing to eliminate leaflet impingement tendency.

It is a further object of the present invention to provide a moving leaflet heart valve hinge which provides for successive translation, rotation and translation of the valve leaflet(s) in the direction of blood flow during opening and closing phases, whereby the valve leaflet(s) accelerate and decelerate in a controlled fashion and the contacting surfaces of the hinge mechanism wipe one another so as to minimize blood clot formation in the region of the hinge mechanism.

It is still a further object of the present invention to provide a prosthetic heart valve that meets the above stated objectives, is reliable in use and is simple and inexpensive to manufacture.

The foregoing objects and advantages are attained by a mechanical heart valve prosthesis having an annular base defining a blood passageway and a pair of valve leaflets which are mounted through a hinge mechanism for closing and

opening the passageway for blood flow wherein the valve leaflets possess a composite curvature shape for eliminating boundary separation and associated turbulence of blood and are mounted through a hinge mechanism to the annular base so as to allow the leaflets to change their motion mode near the closed position to reduce leaflet edge tangential velocity upon approaching closure. The bileaflet prosthetic heart valve with composite curvature leaflets and a special hinge mechanism provides a maximal proportion of blood flow through the central opening defined by the interior facing surfaces of the bileaflets in their open phase in comparison to the peripheral blood flow between the interior surface of the annular valve body and the opposite surfaces of the leaflets.

In accordance with the present invention, the

preferred hinge mechanism is effected by a pair of elongated ear members formed on and by opposite sides of each valve leaflet at points purposely offset to hydraulic force center for providing a fast initial response of the leaflets to blood flow direction change. The elongated ear members are fitted into hinge point recesses in the interior surface of the annular base wherein each hinge recess provides an open recess position, a closed recess position, and a torque center cam for controlling the acceleration and deceleration of the leaflets as the elongated ear member bears against the torque center cam as blood flow change of direction swings the leaflets between their open and closed positions.

During operation of the mechanical valve prosthesis, the valve leaflets undergo limited axial and radial

translational movement limited by the contact of the ends of the elongated ears against the modified serpentine or epicycloid curved surfaces forming recess walls that meet at

the torque center cam. The contact of the ends of the elongated ears against the serpentine or epicycloid curved recess walls guides the movements of the valve leaflets from translation to rotation and then to translation again in the valve closing phase. The final contact motion of the valve leaflet edges against the annular base housing and against each other is completed by translation which causes soft closing of the major edges against the seat formed at an angle to the interior surface of the annular base. Lower valve closing noise and enhanced fatigue life of the valve are expected by this design.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention can be best understood, together with further objects and advantages thereof, by reference to the following description taken together with the appended drawings in which:

Figure 1 is a sectional view of an embodiment of a prior art heart valve design showing the left-hand leaflet in the closed position and the shape of the hinge recess without the right-hand leaflet in place;

Figure 2 is an inflow view of a preferred embodiment of the mechanical heart valve prostheses of the present invention depicting the composite curvature leaflets in the open position;

Figure 3 is a perspective view of a composite

curvature leaflet of the preferred embodiment of the present invention;

Figures 4A-4E are representations of the shape of the leaflet ear with respect to the shape of the hinge recess and provide illustrations of the geometric expression of the generation of the modified serpentine-epicycloid curve hinge recess outline;

Figure 5 is a cross-sectional view of the preferred embodiment of the present invention taken along lines A-A of Figure 2 with the valve leaflets in the open position;

Figure 6 is a cross-sectional view of the preferred embodiment of the present invention taken along lines A-A of Figure 2 with the valve leaflets intermediate the open position and closed position;

Figure 7 is a cross-sectional view of the preferred embodiment of the present invention taken along lines A-A of Figure 2 with the valve leaflets in the closed position;

Figure 8 is a perspective view of the preferred embodiment of the present invention depicting the composite curvature leaflets in the open position of Figure 2;

Figure 9 is a perspective view of the preferred embodiment of the present invention depicting the composite curvature leaflets in the closed position;

Figure 10 is a crosss-sectional view of a further embodiment of the present invention employing flat valve leaflets in conjunction with the modified serpentine-epicycloid curve hinge recess and elongated leaflet ears; and

Figures 11A and 11B are graphical depictions of the acceleration and deceleration characteristics of the leaflets of a prior art heart valve design compared to the preferred embodiments of the present invention,

respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following specification taken in conjunction with the drawing Figures 2-11 sets forth the preferred embodiment of the best mode contemplated by the inventor for carrying out his invention, although it should be understood that several modifications can be accomplished within the scope of the present invention.

Referring now to the drawing figures, and particularly to Figure 1, it depicts Figure 3 of the '658 patent listed above in order to illustrate the hinge mechanism of a widely implanted prior art bileaflet heart valve prosthesis. The element numerals from Figure 3 of the '658 patent are hyphenated in Figure 1, but otherwise find correspondence in the text of the '658 patent. The prior art heart valve of Figure 1 is formed of a base 10' and leaflets 11' and 12' (not shown). The base 10' is a generally annular member whose inner wall 13' defines the blood passageway. The blood passageway is alternately opened and closed by

movement of the leaflets 11' and 12' in response to the flow of blood. The base is provided with projections 14' having retaining means which cooperate with ears carried by the leaflets 11' and 12' to allow a pivotal movement of the leaflets between the open and closed positions.

The arrow 15' indicates the desired blood flow

direction. As illustrated in Figure 1, the projection 14' extends from the annular portion of base 10' in the upstream direction. The inner face of the projection 14' is provided with a flat portion 16' while the outlet or downstream terminus 17' of base 10' is generally circular, the portion 18' providing a transition between the circular

configuration of the outlet 17' and the flat portion 16'.

As is known in the prior art, pyrolytic carbon is coated on a substrate, the reference numeral 19' indicating the substrate throughout the figures while the pyrolytic carbon coating is indicated at 20'.

Flat portion 16' of projection 14' is provided with retaining means generally designated at 21'. The retaining means 21' are formed as recesses within the flat 16' having opposing arcuate ends 22' and 23' joined by side walls 24'-27', to form a bearing surface 28'. As will be

discussed more fully below, bearing surface 28' is a surface of revolution and preferably a spherical polygon. Except for their orientation within the flat 16', the retaining means 21' are identical.

The recesses which form the retaining means 21' may be formed by a cylindrical grinding wheel having the diameter desired for the bearing surface 28' by feeding the grinding wheel into the flat 16' to the desired depth thereby forming the side walls 24' and 26'. Such a grinding wheel (as well as the closed ear position of leaflet 12') is illustrated in phantom at 30'. The grinding wheel may then be swept through the arc defined by the ends 22'-23' to form the bearing surface 28' and the side walls 25' and 27'.

Leaflets 11' and 12' are provided with ears which are adapted to extend into the recesses forming retaining means 21' for pivotal movement therein. Any or all of the side walls 24'-27' may be adapted to serve as stops for the leaflets 11' and 12' as by limiting motion of the leaflet ears within the retaining means 21. That is, as illustrated in Figure 1, the side walls 25' and/or 27' may be position to prevent movement of the leaflet 11' past the illustrated position. An additional stop in the closed position is provided by engagement of the leaflet 11' with the inner

face 13' of base 10' as further illustrated in Figure 1. At least one of side walls 24' and 26' serve as a stop for the occluders 11' and 12' in the open position.

The configuration of the surface 28' and its

cooperation with the projections or ears of the leaflets 11' and 12' is described in the '658 patent such that the perimeter or terminus of the ear is shaped as the section of a sphere having a diameter closely approximating, but slightly smaller than, the diameter of the surface 28'. In this manner, portions of the perimeter of the ear engage surface 28' during movement of the leaflets 11' and 12' between the open and closed position to maintain the

leaflets in position retained by the side walls 24' and 26"and the end walls 22' and 23'.

In other figures of the '658 patent, such as Figure 5, it may be seen that there is very little if any play which would allow translational movement of the leaflets 11' and 12' in conjunction with their pivoting rotational movement between the open and closed positions. Consequently, as blood flow in the direction of the arrow 15' exerts a force against the closed leaflets 11', 12', they will swing open rapidly and shift from the position depicted with respect to the leaflet 11' to the phantom position 30'. The side walls 24' and 26' absorb the shock as the leaflets swing open to their full open position. Similarly, in pivoting from the open position to the closed position in response to a reversal of blood flow from the direction of the arrow 15', the leaflet ears rotate rapidly, gaining acceleration all of the way until the leaflet ears bear against the walls 27' and 25' and the minor edges 37' of the leaflets 11', 12' strike one another while the major edges 36' of the leaflets 11', 12' strike the inner wall 13' of the base 10'.

Figure 11A illustrates the edge tangential velocity of the valve leaflets 11', 12' of the Figure 1 type prior art heart valve between the time t_o and the time t_c which reflects the time elapsed for the leaflets 11', 12' to rotate from the open to the closed position. Figure 11B illustrates the leaflet edge tangential velocity associated with the translation, rotation and translation (with slight continued rotation) afforded by the hinge mechanism of the present invention in moving from the open to the closed position, to be described hereafter.

The prior art valve leaflet of Figure 1 is a flat leaflet and reference is made to Figure 18 of the

above-listed '592 patent which depicts a curved leaflet design employing a butterfly-shaped hinge mechanism similar to the above-described '658 patent hinge mechanism but apparently allowing for some degree of radial translation of the leaflets between the open and closed positions given the apparently shorter ear length than recess length. The '592 patent also depicts elongated recesses and spherical ears as well as pie-shaped recesses with elongated ears in further figures. In all embodiments of the '592 patent, therefore, a certain degree of rotational and translational motion is afforded but it is dependent not on the outline of the recess and matching leaflet ear but rather by the forces acting on the leaflets as they move from the open to closed positions and from the closed to the open positions.

The curvature of the '592 patent leaflets is properly that of a part of an ellipse formed by a plane cutting a right circular cylinder at an angle of about ten degrees to

about twenty degrees as described in the '592 patent. This and other prior art valve designs are improved upon in the context of the present invention and the specific

embodiments disclosed hereinafter.

The preferred embodiments of the present invention are depicted in Figures 2-11. The first preferred embodiment employs the composite curvature leaflets and hinge mechanism of the present invention although somewhat differing leaflet designs that provide different ratios of central orifice open and blood flow to total peripheral orifice area and blood flow and differing profiles in the open and closed position may be desirable in differing sized aortic and mitral valve applications. The second embodiment employs flat leaflets with the modified serpentine-epicycloid curve hinge recess and elongated leaflet ears also employed in the first embodiment.

Turning to Figure 2, the heart valve prosthesis of the present invention includes an annular valve base 20 having inner and outer surfaces 22 and 24 and first and second leaflets 26 and 28 shown in the open position and in the direction of blood flow. Although not specifically shown, it will be understood that the outer surface 24 may contact a further reinforcing metal ring and conventional sewing ring of the type shown, for example, in the Medtronic U.S. Patent No. 4,935,030 incorporated herein by reference. As is well known in the art, the annular valve base and its associated leaflets, reinforcing ring and sewing ring, may be provided in a variety of sizes to accommodate patients of varying ages and body sizes. The dimensions of the heart valve prosthesis also depend on whether the prosthesis is used in implantations replacing mitral, aortal or tricuspid heart valves. As is well known in the art, the sewing ring

is affixed by sutures (not shown) to the living tissue (not shown) when the heart valve prosthesis is implanted.

Returning to Figure 2 valve leaflets 26 and 28 having inner surfaces 30 and 32, and outer surfaces 31 and 33, respectively, are mounted into four recesses 34, 36, 38, 40 at hinge points defined by leaflet ears 42, 44, 46 and 48 so that the valve leaflets may swing from the open position depicted in Figure 8 to the closed position depicted in Figure 9.

Each valve leaflet possesses a composite curvature shape curved to present minor and major edges 49 and 50, respectively, of the leaflet 26 (depicted in Figure 3) and 52 and 54, respectively, of the leaflet 28. When the leaflets are closed as depicted in Figures 7 and 9, the major edges 50 and 54 seat against the inner seat surface 19 of the annular valve base 20 (shown in Figures 5-7) and the minor edges 48, 52 seat against one another.

During the open phase and in the open position, blood flows through the central orifice of the heart valve prosthesis defined by the facing inner surfaces 30, 32 of the leaflets 26 and 28 and through the outer orifices defined by the outer surfaces 31, 33 of the leaflets 26 and 28 and the inner surface 22 of the annular valve base 24. The ratio of the central orifice area to the total orifice area of the embodiment depicted in Figures 2-9 is

approximately fifty percent. However, the volumetric blood flow through the central orifice is approximately seventy percent or more due to fluid flow effects along the surfaces 22 of base 20 and outer surfaces 31 and 33 of the leaflets 26 and 28. The calculation of the ratio of the flow through the elliptic central orifice Q_E to total flow through the orifice Q_τ is set forth in the Appendix. The blood washing

action of the blood flow in the direction depicted in

Figures 5-7 passes over the inner and outer surfaces 30, 32 and 31, 33 of the leaflets 26 and 28 and the inner surface 22 of the annular valve base 20.

The composite curvature of the valve leaflets is depicted in Figures 3 and 5-9. The radius of curvature R_P of the inner and outer surfaces 30, 32 and 31, 33 extending from the major edges 50, 54 a distance toward the minor edges 49, 52 eliminates boundary separation and associated turbulence of the blood passing through the central and peripheral orifices in the open phase depicted in Figures 2, 5 and 8. It is generally desirable to have a central orifice area in the range of or greater than fifty percent of the total orifice area, but to have sufficient blood washing function along the circumferential interior surface 22 of the body 20 and the surfaces 31 and 33 of the leaflets 26 and 28 while minimizing pressure drop. Pressure drop is also minimized in the preferred embodiments of the present invention by providing the hinge point mechanism which allows the leaflets 26 and 28 to open to be virtually parallel to the blood flow (except along the major edges 50, 54 where the composite curvature afforded by radii R_P and R_Major is emphasized).

The radii of curvature of the major edges 50, 54 and the minor edges 49, 52 are represented by the arrows R_Major and R_Minor. The radius of curvature R_P is generally

perpendicular or transfers to the other radii of the

composite leaflet curvature.

Referring now to the hinge mechanisms of the present invention viewed in Figures 2 and in part in Figures 3-7, they preferably include the leaflet ears 42, 44 of leaflet 26 and 46, 48 of leaflet 28 which are positioned within

recesses 34, 36 and 38, 40, respectively. The recesses 34, 36, 38, 40 preferably have a generally flat bottom 58 bounded by curved side walls which curve concavely up from the flat bottom 58 to the flat surfaces 21, 23 to receive elongated ears 42, 44 and 52, 54 in a fashion as depicted in Figures 4A and 4B. Figures 5-7 specifically depict hinge recesses 34 and 38, although it will be understood that such hinge recesses are fashioned into flat surface 23 at 36 and 40 shown in Figure 2.

As described earlier and as shown in Figure 4B, each of the recesses 34, 36, 38, and 40 have a flat bottom and curved side and end walls which receive the leaflet ears which are also curved so that they present no abrupt or acute angles or edges subject to fracture or being worn as the leaflet ears traverse the recess.

In reference to Figure 4A, it depicts the general outline of the hinge mechanism recess 34 or 40 (as well as the mirror image of the recesses 36 and 38) of Figure 2 in relation to nine possible contact areas ("footprints") of an ear as the leaflet moves from the open position of Figure 5 to the closed position of Figure 7. In reference to Figures 5-7, nine successive positions of the leaflets 26 and 28 are shown corresponding to the footprints depicted in Figure 4A.

Turning to Figure 4B, it depicts a projection of the outline of the recess of Figure 4A and a leaflet ear resting in the closed position corresponding to footprint f1 in Figure 4A. The leaflet ear may, for example, be ear 42 of leaflet 26 resting in recess 34 of flat surface 21. Figure 4B depicts a generally flat recess bottom surface 58 against which the generally flat surface of the ear 42 rests. The ear 42 is also shown as including relatively rounded ends and corners which bear against the generally curved side

walls of recess 34. In this fashion, the ends of the elongated ears bear against the concave curved walls and the flat bottom of the recess 38 in pivoting through

translational, rotational and translational movement back and forth between the open and closed positions.

Returning to Figure 4A, the outline of the modified serpentine-epicycloid curve hinge recess is also shown in relation to the mathematical functions of Figures 4C, 4D and 4E which are used to generate the shape and in relation to the direction of downstream blood flow F (open leaflet position) and back flow F' (closed leaflet position) . Each hinge recess 34, 36, 38 and 40 includes the generally flat inner surface 58 and a pivoting edge or torque cam 60 that a side wall of the leaflet ears 42, 44, 46 and 48 bears against in the movement of the leaflets between the open position in Figure 5 to the closed position in Figure 7.

The pivoting edge or torque cam 60 is defined by one

epicycloid curved wall 62 and a flat wall 64 and curved wall 66 which are referred to as a serpentine curved wall. On the opposite side of each recess, the walls 72 and 70 meet at second pivoting edge or torque cam 74 against which the opposite side of the leaflet ears bear against in moving from the closed to the open position. It will be understood that each side edge of the leaflet ears may also be curved inward toward the flat inner surface 58 and that the torque cams 60 and 74 are curved in the same fashion as the other side walls 62, 64, 66, 70 and 72 between the surface of the flats 21 and 23 to the flat surfaces 58.

Referring now to Figures 4C to 4E, the epicycloid curve which shapes the wall 62 is generated as shown in

Figure 4D in accordance with the mathematical equations set forth in the Appendix.

Similarly the modified serpentine shape of walls 64 and 66 is developed in accordance with the Figure 4E projection from Figure 4C in accordance with the equations set forth in the Appendix.

Turning now to Figures 5-7, the leaflets 26 and 28 and elongated ears 42 and 46 are depicted in sectional views taken along the lines A-A from the top view depicted in Figure 2. A set of nine possible positions extending between the fully open position of Figure 5 and the fully closed position of Figure 7 are depicted in the phantom lines. The general outlines of the valve leaflets are depicted in dotted lines connecting the minor and major edges 49, 50 and 52, 54, respectively, of the two valve leaflets and the leaflet ear in the solid line position in each respective figure.

The recesses 34 and 38 depicted in Figures 5-7 are cut into a flat 21 on inner wall 22. Similarly, a flat 23 (as shown in Figure 2) on the opposite side of the inner surface 22 of annular valve base 20 bears the hinge mechanism recesses 36 and 40. The annular valve base 20 also includes a valve seating surface 19 which constitutes about a 15° surface cut from inner surface 22 and extending between the flats 21 and 23 (Figure 2) .

In the fully open position of the valve leaflets depicted in Figure 5, the leaflet surfaces over a major portion of each leaflet is parallel to the direction of downstream blood flow depicted by the arrow labeled F.

Similarly, the ears 42 and 46 are depicted parallel to the direction of blood flow and bear against the flat walls 64 and 72 of the recesses 34 and 38. The bicurvature of the trailing portion of the outer surfaces 31, 33 of leaflets 26, 28, respectively, approaching the major edges 50, 54

provides reduced boundary layer separation and reduces wake regions and turbulence downstream of the major edges 50, 54. The tangential flow of blood between the outer surfaces 31, 33 and the inner surface 22 of the valve body 20 washes those surfaces. At the same time, the flat inner surface 58 and the walls of the recesses 34, 38 are washed by blood except in the position occupied by the leaflet ears 42, 46.

If the valve depicted in Figures 5-7 is implanted as an aortic replacement, then the direction of blood flow F depicted in Figure 5 is attained on the pumping stroke of the heart, as a respective ventricle contracts. Pivoting movement in the direction of blood flow F is stopped on contact of the opposite edges of the ears 42 and 46 (and 44, 48) against the flat recess surfaces 64 and 72 of each recess 34, 38 (and 36, 40).

When, at the end of a ventricular stroke, the

respective ventricle relaxes to draw more blood into the chamber from the atrium, the back pressure (represented by the arrows F', F'_N, F'_T) within the aorta causes the

leaflets 26, 28 to quickly swing or pivot to the closed position depicted in Figure 7. In Figure 6, the leading edge of the elongated ears 42 and 46 is shown bearing against the serpentine walls 66 of recesses 34 and 38 and against the concave epicycloid wall 62. Continued blood flow in the direction F' will, through the application of tangential force F'_T along the inner surfaces 30 and 32, cause the valve leaflets to continue to rotate and translate to the fully closed position depicted in Figure 7.

As the valve leaflets begin to close, the tangential forces F'_T and normal forces F'_N applied against the inner surfaces 30 and 32 (shown in both Figures 5 and 6) rapidly accelerate the minor edges 48 and 52 of the valve leaflets

toward one another. But in doing so, the cosine value of tangential force F'_T reduces, and the normal force F'_N applied to the full exposed inner surface 30 and 32 tends to increase. The serpentine walls 66 of recesses 34, 38 guide the movement of the leading edge of the leaflet ears, and thus the movement of the entire leaflet. Therefore, the speed at which the leaflets pivot toward one another first accelerates and then decelerates. Consequently, the closing speed of the leaflets in the phantom line positions between the intermediate position depicted in Figure 6 and the fully closed position depicted in Figure 7, decelerate. The deceleration, allows the trapped blood between the

converging minor edges 48, 52 and the major edges 50, 54 and the seat 19 to escape being crushed.

Turning now to Figure 7, the leaflets 26 and 28 and the leaflet ears 42 and 46 are shown in the fully closed position. In viewing Figures 5-7 together, the successive rotation and translation of the valve leaflets 26 and 28 can be visualized. It can also be seen, that as the leaflet ears rotate and translate across the flat surfaces 58 of the hinge mechanism recesses, each opening and closing phase of the valve leaflets wipes the surface 58 as well as the walls defining the shape of the recess clean of blood cells. This wiping action reduces blood clotting in the vicinity of the hinge mechanism.

Turning now to the opening phase of the valve

leaflets, for example upon the next pumping stroke of the heart, blood pressure applied (as shown in Figures 7 and 6) in the downstream flow direction F against the leaflet outer surfaces 31 and 33 causes the leaflets 26 and 28 to pivot open rapidly because of the significant effect of the hinge mechanism toward the center of the valve body 20. Again,

the valve leaflets 26, 28 rapidly accelerate in both rotation and translation to the intermediate point depicted in Figure 6. As blood begins to flow in the direction F through the central orifice, the normal force F_N against the outer surfaces 31 and 33 of the leaflets begins to decrease and the leaflets 26, 28 decelerate as they rotate and translate toward the fully open position of Figure 5.

Although Figure 6 specifically depicts the rotation and translation of the leaflets and the leaflet ears against cam 60 and serpentine wall 66 as blood flow reverses direction from the downstream direction depicted in Figure 5, it may be imagined as illustrating an intermediate position which may be attained in the opening phase of the leaflets by translating the ear to bear against the cam 74 and epicycloid surface 62. The rapid acceleration and deceleration of the valve leaflets as they move from the open to closed and closed to open positions effectively use the dynamic normal and tangential forces to decrease closing velocity of and consequently increase fatigue life of the valve leaflets at the major and minor edges and at the hinge mechanisms. Particularly, in the closing of the valve leaflets, the deceleration decreases leaflet landing or contact velocity and any tendency of the major edges 50, 54 to stick by impacting the annular seat 19. In addition to reducing leaflet impingement tendency, the deceleration and low leaflet landing velocity provide a low closing noise and reduce hemolysis of trapped blood cells. The acceleration and deceleration thus minimize damage to the blood and reduce wear of the leaflets and annoying noise to the patient.

Turning now to Figures 8 and 9, perspective views of the valve leaflets 26, 28 and annular base 20 are presented

for purposes of illustration. Figure 9 in conjunction with Figure 7 shows that the overall profile of the valve in the closed position is relatively low and is unlikely to interfere with any cardiac structure in the desired

positions of implantation. Figure 8, viewed in conjunction with Figures 2 and 5, shows the relatively large central orifice with respect to the side orifices of the present invention.

Turning now to Figure 10, it depicts in cross-section a bileaflet prosthetic heart valve having a pair of flat leaflets 126, 128 mounted within the annular base 120 where the leaflet 126 is depicted in solid lines in the fully closed position and in dotted lines in the fully open position and the leaflet 128 is depicted in the fully open position. The embodiment of Figure 10 employs the modified serpentine-epicycloid hinge recess depicted in Figure 4A to 4E and the other figures of the first embodiment of Figures 2-9. For ease of description, elements which by

correspondence or similarity in the first embodiment are enumerated in a similar fashion.

In the Figure 10 embodiment, it will be understood that the Figure 4E depiction of the leaflet ears to the hinge recesses applies. Similarly, the description of the generation of the modified serpentine-epicycloid curve hinge recess outline and concave curve sidewalls also applies. In a similar fashion, as described above, the valve leaflet ears are guided by the recess shape and camming points to provide translational, rotational and translational movement in moving between the open and closed positions. The valve leaflets 126, 128 and leaflet ears 142, 146 may be of the general configuration depicted in the above-listed U.S.

Patent No. 4,689,046, incorporated herein by reference.

One aspect of the Figure 10 embodiment relating to the angle of the valve seat 119 is that the major leaflet edges 150, 154 bear against in the closed position. In Figure 10, the valve seat is an angular cut in the inner surface 122 at an angle of about 15° at a point equidistant from the flat surfaces 121, 123 and decreasing to about 11° where the seat 119 meets the flat surface 121, 123 this change in the angular cut into the surface 122 is necessary because of the oblique angle that the valve leaflets assume when in the closed position as depicted by leaflet 126 in Figure 10.

Although not specifically shown, it will be understood that the arcuate edges 150, 154 are similarly cut at 11° adjacent to the point where the leaflet ears protrude from the sides of the leaflets to 15° at the point depicted in Figure 10 where the major arcuate edges are equidistant from the leaflet ears. In this fashion, separate valve seats 119 are provided for each of the leaflets 126 and 128, both seats being cut into the inner surface 122 of the annular base 120 to accommodate the valve leaflets 126, 128 without allowing backflow leakage of blood or impingement of the leaflets in the closed positions.

One of the advantages of the embodiment in Figure 10 is that the leaflets in the fully open position are fully parallel with blood flow F. The reversal of blood flow in tangential forces acting on the inner and outer surfaces of the leaflets 126 and 128 will cause the leaflet ears to translate and bear against the serpentine curved sidewalls of the hinge recesses causing the leaflets to rotate toward the closed position, whereupon normal backflow force F' applied to the inner surfaces 130 and 132 accelerate the closure. Upon reaching a point in the closure approaching the fully closed position, the serpentine curvature again

causes the leaflets to translate toward one another and toward the central axis of the annular base 120 while decelerating. In this fashion, the flat leaflet embodiment employing the modified serpentine-epicycloid curve hinge recesses and elongated leaflet ears provides all of the benefits described above except that the blood flow volume is more equally distributed between the central orifice and the side orifices.

Returning now to Figures 11A and 11B, the approximate acceleration and deceleration characteristics of the heart valve of Figure 1 and the embodiment of the present

invention are depicted, respectively. The tangential velocity V_t over the time t_o-t_c that it takes for the leaflets to pivot between the open and closed positions are depicted. The characteristics of the Figure 1 prior art heart valve are derived from the publication entitled "The Closing Velocity of Baxter Duromedic Heart Valve

Prostheses," by G.X. Guo et al, ASAIO Transactions. 1990; 36:M529-M532, and in particular from the velocity data contained therein. The characteristics depicted in Figure 11B illustrate the effects of the translation, rotation and translation depicted in Figures 5-7 and 10 in conjunction with the normal and tangential forces exerted by the blood flow. The cooperation of the torque cams and the modified epicycloid-serpentine guide walls of the elongated hinge recesses provide the advantage of the rapid acceleration and deceleration depicted in Figure 11B and the consequent advantages of low closing noise, increased fatigue life, reduced fracture tendency of components, decrease in the possibility of cavitation at the trailing, major edges of the leaflets, full washing of the recessed surfaces and walls and the effective use of the dynamic forces to reduce

leaflet impingement tendency and damage to blood cells. In regard to impingement, it should be understood that

physicians on occasion loop sutures through the valve body orifice when affixing the valve in place and high velocity closure may cause the leaflet to stick against the suture and fail to open again as a result. The relationship of the angle of the seat 19 to the inner wall 22 of the base 20 and the angle of the downstream or major leaflet edges 50, 54 to the seat 19 angle, together with decreasing closure velocity of the major edges 50, 54 to seat 19, reduces the tendency of impingement, even if suture is placed through the orifice during implantation.

The annular valve body 24; 124 and the leaflets 26, 28; 126, 128 of the mechanical heart valve prosthesis embodiments of the present invention are preferably made entirely of pyrolytic carbon in accordance with processes which are known in the art. As is known, pyrolytic carbon material has very little thrombogenecity and is generally considered safe for use in mechanical heart valve

prosthesis.

What has been described above is an improved

mechanical heart valve prosthesis which is relatively simple to construct and which minimalizes the possibility for stagnation of blood flow and formation of incipient blood clots. Furthermore, the composite curvature of the leaflets of the first embodiment provides maximal flow through the central orifice defined by the leaflets in their open phase and provides consequent lower pressure drop with the

leaflets parallel to the flow stream during the open phase. The curved leaflet major or trailing edges in the open phase reduce boundary separation and associated turbulence along the flow stream direction.

In both embodiments, the passage of blood through the central orifice and the two peripheral or side orifices between the outer valve leaflet surfaces and the annular valve housing inner surface washes both sides of the leaflets and the hinge mechanism. The modified serpentine-epicycloid curve shape of the hinge recess and elongated leaflet ears provide acceleration and deceleration during the movement of the valve leaflets between the open and closed positions in order to minimize damage to blood cells, wear of the valve leaflets and hinge components,

impingement, and annoying noise to the patient.

Several modifications of the mechanical heart valve prosthesis of the present invention may become readily apparent to those skilled in the art in light of the foregoing disclosure. For example, it will be apparent that the modified serpentine epicycloid curve hinge recesses may be employed with valve bileaflets of flat or curved

configurations other than those shown in the figures and may be employed in single leaflet valve configurations, all of the types shown in the above listed prior art patents.

Therefore, the scope of the present invention should be interpreted solely from the following claims, as such claims are read in light of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A heart valve prosthesis comprising:

a generally annular base having an interior surface which defines a central passageway for blood flow in a downstream direction;

a pair of valve leaflets each having a first arcuate major edge which is configured to interface with the interior surface of said annular base in a blood flow sealing relationship therewith and a second, minor edge which is configured to interact with the minor edge of the other leaflet in a fluid flow sealing relationship therewith when in a closed position, each of said leaflets further having inner and outer opposite surfaces, wherein said first arcuate major edge possesses a first radius of arc, and at least said outer surface possesses a second radius of curvature extending over at least a portion of said outer surface from said first arcuate major edge, said second radius of curvature being generally transverse to at least said first radius of arc; and hinge means for supporting said pair of leaflets for substantially pivotable movements on eccentric axes between said closed position generally blocking blood flow through said central passageway and an open position allowing blood flow therethrough in said downstream direction.

2.The heart valve prosthesis of Claim 1 wherein said hinge means further comprises:

two pairs of recesses positioned within the interior surface of said annular base and having recess walls defining camming means; and

a pair of ears located proximally to and projecting from opposite side portions of each leaflet extending between said first and second edges of each leaflet and adapted to be fitted within a

respective pair of said recesses.

3. The heart valve prosthesis of Claim 2 wherein said leaflet ears are shaped to fit within said recesses in an open position whereby a portion of said inner and outer surfaces of said valve leaflets extending from said second, minor edge, in each leaflet, is generally parallel with downstream direction blood flow through said central passageway defined by said annular base interior surface and said inner and outer leaflet surfaces.

4. The heart valve prosthesis of Claim 3 wherein said hinge means and the curvature of the inner and outer surfaces of said valve leaflets provides a ratio of volumetric blood flow through the central orifice defined by the spatial volume between said facing inner surfaces of said valve leaflets in said open position and the total unobstructed passageway volume within said inner surface of said annular base in said open position that is equal to or greater than 70%.

5. The heart valve prosthesis of Claim 2 wherein said hinge means and the curvature of the inner and outer surfaces of said valve leaflets provides a ratio of volumetric blood flow through the central orifice defined by the spatial volume between said facing inner surfaces of said valve leaflets in said open position and the total unobstructed passageway volume within said inner surface of said annular base in said open position that is equal to or greater than 70%.

6. The heart valve prosthesis of Claim 1 wherein said hinge means and the curvature of the inner and outer surfaces of said valve leaflets provides a ratio of volumetric blood flow through the central orifice defined by the spatial volume between said facing inner surfaces of said valve leaflets in said open position and the total unobstructed passageway volume within said inner surface of said annular base in said open position that is equal to or greater than 70%.

7. The heart valve prosthesis of Claim 2 wherein said second minor edge of each leaflet possesses a third radius of arc extending between said opposite side portions of each leaflet.

8. The heart valve prosthesis of Claim 3 wherein said second minor edge of each leaflet possesses a third radius of arc extending between said opposite side portions of each leaflet.

9. The heart valve prosthesis of Claim 5 wherein said second minor edge of each leaflet possesses a third radius of arc extending between said opposite side portions of each leaflet.

10. A heart valve prosthesis comprising;

a generally annular valve body having an interior surface defining a central passageway

designed to be implanted to permit the flow of blood therethrough in a downstream direction and defining a valve leaflet seat;

a pair of valve leaflets which are supported for substantially pivotal movement on eccentric axes

between a closed position generally blocking blood flow through said central passageway and an open position allowing blood flow therethrough in said downstream direction,

said leaflets and said valve body including projecting ears and recesses, respectively, which receive said ears, said projecting ears and said recesses having complementary surfaces which mount said leaflets in a manner to allow pivotal movement relative to said annular valve body;

said recesses being elongated so that there is relative translational, rotational and

translational movement of said ears within said recesses as said leaflets pivot between the open

position and the closed position, and being formed in said interior surface at generally diametrically opposite locations wherein said ears are received;

each of said elongated recesses extending for a longitudinal distance greater than its

transverse dimensions and having a modified serpentine epicycloid curve shape defined by a serpentine curve guide wall extending toward one end of the elongated recess and an epicycloid curve guide wall extending toward the other end of said elongated recess, said guide walls oriented so that said ears move back and forth therealong at the same time they move

rotationally thereagainst, thereby defining a shifting pivot axis relative to said valve body as said leaflets pivot in each direction between the closed and open positions.

11. The heart valve prosthesis of Claim 10 wherein said recesses and said leaflet ears are configured to bear against said epicycloid curve guide wall in

rotational and translational movement of said leaflets from said closed to said open position and to bear against said serpentine curved wall in rotational and translational movement of said leaflets from said open to said closed position.

12. The heart valve prosthesis of Claim 10 wherein said epicycloid and serpentine curve guide walls are formed on a first recess side wall of said elongated recesses and form a first camming pivot for said leaflet ears at their juncture intermediate the ends of the

recesses.

13. The heart valve prosthesis of Claim 11 wherein said recesses and said leaflet ears are elongated with opposing sides and ends that are configured to bear against said epicycloid curve guide wall in rotational and translational movement of said leaflets from said closed to said open position and to bear against said serpentine curved wall and said first camming pivot in rotational and translational movement of said leaflets from said open to said closed position.

14. The heart valve prosthesis of Claim 10 wherein said epicycloid and serpentine curve guide walls are formed on a first recess side wall of said elongated

recesses and form a first camming pivot for said leaflet ears at their juncture intermediate the ends of the recesses and wherein said recesses have a second camming pivot formed on the second recess side wall generally opposed to said first recess side wall.

15. The heart valve prosthesis of Claim 14 wherein said recesses and said leaflet ears are elongated with opposing sides and ends that are configured to bear against said epicycloid curve guide wall and said second camming pivot in rotational and translational movement of said leaflets from said closed to said open position and to bear against said serpentine guide wall and said first camming pivot in rotational and translational movement of said leaflets from said open to said closed position.

16. A heart valve in accordance with Claim 10 wherein said leaflets are curved in cross section between said projecting ears having convex outer surfaces facing upstream and concave inner surfaces facing downstream when in the closed position.

17. The heart valve of Claim 16 wherein said leaflets each have an arcuate major edge which is configured to interface with said interior surface seat of said annular base in a generally blood flow sealing relationship

therewith when in said closed position and a second, minor edge which is configured to interact with the other minor edge of the other leaflet in a generally fluid flow sealing relationship therewith, each of said leaflets further having inner and outer surfaces, wherein said arcuate major edge possesses a first radius of arc, said second, minor edge possesses a second radius of arc and at least said outer surface possesses a third radius of curvature extending over at least a portion of said outer surface from said first arcuate major edge, said third radius of curvature being defined generally transverse to at least said first radius of arc.

18. A heart valve prosthesis comprising:

a generally annular base having an interior surface forming a central passageway therethrough of generally circular cross section for blood flow in a downstream direction; said base defining valve seat means;

a pair of valve leaflets proportioned to block blood flow downstream through said passageway when said leaflets are disposed in a closed position;

each of said leaflets having an arcuate major edge which abuts said valve body seat means and a minor edge which abuts the minor edge of the other leaflet in said closed position;

means for pivotably interconnecting each of said leaflets and said valve body for relative pivotal movement between the closed position and an open position wherein said arcuate major edges are situated in the blood flow downstream, which interconnecting means includes pairs of recesses formed in generally opposite locations in said interior wall and pairs of ears extending laterally from each of said leaflets;

said recesses each having a downstream section which is aligned substantially parallel to the centerline of said central passageway and an upstream section which connects at a point of connection to said downstream section and angles inward from the point of connection of the sections and wherein said recess upstream sections each have a first curved shape defined by a first wall section and said recess downstream sections each have a second curved shape defined by a second wall section; and

wherein said ears are configured with respect to said first and second curved shapes and walls such that, upon the beginning of backflow, said leaflet ears rotate about said point of connection and accelerate against said first curved shape wall section as tangential forces are applied to said leaflets in the vicinity of said major edges and then decelerate as normal forces of upstream blood flow direct said leaflet ears against said point of connection and toward the end of said upstream section, thus reducing the impact of said arcuate major and minor edges against said seat means and one another, respectively, upon reaching said closed position and so that the force created by backflow blood pressure between said ears and the wall sections of said recess is unloaded when said leaflets reach said closed position, whereby wear at the location of said interconnecting means is minimized.

19. The heart valve prosthesis of Claim 18 wherein said arcuate major edges of said leaflets possess a varying edge, said interior surface of said base is

generally parallel with said downstream blood flow

direction, and said seat means comprises first and second annular sections of said interior surface disposed opposite to one another and each formed at an angle to the direction of blood flow and formed at a further varying angle matching the varying angle of said leaflet edges into said interior surface downstream of said recesses, whereby said matching angles and said deceleration reduces the incidence of impingement of said leaflets against said seat means.

20. The heart valve prosthesis of Claim 19 wherein said arcuate major edges possess an angle that mates with the angle of said seat means when said leaflets are in said closed position.

21. The heart valve prosthesis of Claim 18 wherein said leaflet ears and said recess sections are configured to provide an angular rotation of said leaflets between said open and said closed position of about 50 degrees.