CA1154903A

CA1154903A - Bileaflet valve with improved pivot

Info

Publication number: CA1154903A
Application number: CA000355273A
Authority: CA
Inventors: Jack C. Bokros
Original assignee: CARBO MEDICS Inc
Current assignee: CARBO MEDICS Inc
Priority date: 1979-07-30
Filing date: 1980-07-03
Publication date: 1983-10-11
Also published as: IT1128539B; FR2462149B1; GB2055452B; DE3028981A1; FR2462149A1; GB2055452A; IT8049317A0

Abstract

ABSTRACT OF THE DISCLOSURE

A bi-leaflet heart valve wherein two complementary leaflets open and close a passageway of generally circular cross section through an annular valve body. Each of the leaflets is pivoted by interengaging means at opposite locations on the annular valve body. The valve body is provided with arcuate seat means having a downstream facing surface, and the leaflets are formed with a major arcuate edge which seals against the interior surface of the valve body and with a planar minor edge. In the closed position, the upstream surface of the leaflets lies in abutting contact with the downstream surface of the seat, and the planar surfaces abut each other along a plane diametric of the passageway, thus positively closing the center.
The proportioning of the leaflets and the location of the seats are such that the load on the interengaging means is relieved in the closed position, wherein the load is supported primarily by the contact between the leaflets and the seat.

Description

~S49~)3 BACKGROUND TrlE INVENTION
This invention is related to heart valve prostheses for replacement of defective natural valves and more particularly to hear~ valve prostheses employing a pair of pivotal valve members.
Various types of heart valve prostheses have been developed which operate hemodynamically as a result of pumping action of the heart and in essence function as check valves. Some of these valves which have been used employ a ball-and-cage arrangement, whereas others have used a disc-type valve member. U. S. Patent No.
3,534,411, issued October 20, 1970 is exemplary of a valve which employs a disc oE the free-floating variety. A number of valves using a pivoting disc arrangement have been developed, such as that shown in U.S. Patent No. 3,546,711 to Bokrcs, issued December 15, 1970, and that shown in U.S. Patent No. 3,859,~6~, issued January 14, 1975.
Disc-type heart valves have also been developed which use two valve members or leaflets, instead of a single disc, which leaflets rotate about parallel axes as a part of the opening and closing action of the valve. British Patent No. 1,160,00g, issued July 30, 1969, is exemplary of a valve of this general type, and it is this general ~ype of heart valve prosthesis to which the present invention is directed.
SUMMARY OF THE INVENTION
The invention provides improvements in heart valve prostheses which employ a pair of pivoting leaflets or valve members which are supported via interengaging means within an annular valve body having a generally circular cross section. Arcuate seat means having a downstream-facing surface is provided, generally as a part of the interior wall surface o the annular valve body. The leaflets each have a planar ~15~ 3 minor edge and an arcuat~ major edge, and the upstream surface of the arcuate edge abuts against the downstream surface of the arcuate seat ~eans while the planar minor edge surfaces abut against each other. The valve is proportioned so as to relieve the load upon the interengaging means when the leaflets are in the closed position and thus has improved wearability at these points. By employing an elongated arcuate seat in association with each leaflet, an excellent seal is assured both in the center and along the periphery which greatly reduces backflow through the check valve during the time it is in the closed position.
BRIEF DESCRIPTION OF THE ~RAWINGS
FIGURE 1 is a perspective view of a heart valve embodying various features of the invention employing a pair of l~aflets which are shown in the open position;
FIGURE 2 is a sectional view taken generally along the line 2-2 o~ FIGURE l;
FIGURE 3 is a partial sectional view similar to FIGURE 2 showing the leaflets in a closed position;
FIGURE 4 is a plan view of the valve of FIGURES
1 through 3 with the leaflets shown in the closed position and with a portion broken away;
FIGURE 5 is a sectional view enlarged in size taken along the line 5-5 of FIGURE 3;
~ IGURE 6 is a perspective view of an alternative embodiment of a heart valve embodying features of the invention which has a pair of leaflets shown in the open position;
FIGURE 7 is a partial sectional view taken generally along the line 7-7 of FIGURE 6;
FIGURE 8 is a sectional view similar to that shown in FIGURE 7 illustrating the leaflets in the closed position;
FIGURE 9 is a plan view, slightly reduced in 1;~54L~)3 size of the valve shown in FIGURE 8 with the leaflets in the closed position;
FIGURE 10 is a fragmentary, exploded perspective view of the valve shown in FIGURE 6 illustrating the interrelationship of one of the leaflets and the valve body;
FIGURE 11 is a fragmentary sectional view taken generally along the line 11-11 of FIGURE 9; and FIGURE 12 is a fragmentary sectional view, enlarged in size, taken along the line 12-12 of FIGURE
8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Illustrated in FIGURE 1 is a heart valve 11 -which.has an annular valve body OL housing 13~and which carries a pair of pivoting leaflets or valve members 15 that open and close to control the flow of blood through a central passageway 17. The normal flow of blood is in the direction of the arrows 19 in FIG. 2. The leaflets 15 are supported about eccentric axes in a pair of diametrically opposed supports or standards 21 which extend upwardly from the annular valve body 13. Of course the valve 11 can operate in any orientation because it is not significantly affected by gravity;
however, for ease of explanation, the valve 11 is shown and described with the supports 21 upstanding from the annular valve body 13.
The valve body is formed with a peripheral grove 23 about its exterior surface which accommodates a suturing ring tnot shown), which may be any of the various tyPes already well known in the art. The -suturing ring facilitates the sewing or suturing of the heart valve to the heart tissue. The passageway 17 through the valve body 13 is preferably circular, and the internal wall surface 25 of the valve body which defines the passageway will have the general shape of a 3 ~591C5~Q3 right circul2r cylinder.
The valve body 13 and the leaflets 15 may be made of any suitable material that is biocompatible and non-thrombogenic and that will stand up under the wear to which these elements will be subjected during countless openings and closings of the leaflets. The components may be made from isotropic graphite, such as that sold under the tradename POCO, which has been suitably coated wlth pyrocarbon, preferably that sold under the trademark P~ROI,ITE which gives excellent compatibility and wear-resistance.
The illustrated leaflets 15 are flat and have a uniform thickness throughout. A minor edge 29 of each leaflet is straight and is formed as a planar surface;a major edge 31 is curved in a manner to match the inner surface of the passageway 17. The outline of the arcuate major edge 31 is generally defined by a plane cutting the right cylindrical interior wall surface 25 of the valve body and is thus that of a section of an ellipse. The angle at which the planar minor edge 29 is oriented to the flat surfaces of the leaflet lS is determined so that the planar edges abut in substantially complete surface-to-surface contact when the leaflets are in the closed position (FIG. 3), as explained in more detail hereinafter.
The upstanding supports 21 each contaln a pair of spherical depressions 33 which receive ears 3S that project outward from opposite sides of the leaflets 15.
The ears 35 have end surfaces 37 which are sections of a spherical surface having a radius of curvature equal to or just slightly less le.g., about 1-2%) than the radius of curvature of the spherical depressions 33. Thus, the ears and spherical surfaces constitute interengaging means which ~uides the rotation of the leaflets during pivoting and defines the eccentric pivotal axes about .

. .

1~54903 which the leaflets rotate. E~owever, the sidewise or lateral thrust of the leaflets is not borne by the ears 35, but instead flat bearing surfaces 39 are provided in the location between the ears and the minor planar edges 29, and these flat edge surfaces 39 bear against a flat surface 41 provided on the int~erior facing portions of the standards 21. The length of each ear 3S is such that its apex does not quite reach the wall of the spherical depression 33, as best seen in F~GURE 5.
A pair of surfaces 43 perpendicular to the plane of the flat surface 41 are also provided in the standards 21 which serve as stops for the leaflets in the open position.
- As best seen in FIGURE 2, when the leaflets have rotated during opening movement so that the major portions thereof have swung downward in a downstream direction, the upstream surfaces 45 of the-leaflets in the region adjacent the short, flat edge surfaces 29 come into abutting contac~ with the stops 43 and limit the opening movement of the lea~lets to the orientation shown in FIGURE 2. Inasmuch as the leaflets are nearly parallel to the flow of blood downward through the passageway 17 in this open position, there is little force causing the leaflets 15 to bear against the stops 43 and accordingly wear at this location is not a problem.
In order to achieve a seal along the major arcuate edge 31 of the leaflets in the closed position and to further improve the longevity and operating characteristics of the valve, a ledge or arcuate seat 47 is formed in diametrically opposite regions of the valve body 13. In the illustrated embodiment, the interior surface 25 of the annular body is cut away to form this seat 47 which is essentially elliptical to match with the elliptical arcuate edge 31 of the leaflets. The ,:
,: ' , radius of curvature of the end edge regions of the leaflets (between the flat upstream and downstream surfaces) along the major edge 31 is preferably slightly less, e.g., 2-5%, than the corresponding radius of curvature of the curved surface of the seat 47. This relationship assures a line contact in the closed position which minimizes backflow leakage along this major perimeter section of the leaflets~
As can be seen from FIGURE 2, the diameter of the passageway 17 upstream of the seat 47 is smaller than in the region downstream of the seat, and the seat 47 is located to serve as the stop for the leaflets in the closed position. The location of the seat 47 also achieves another purpose, i.e. that of unloading the ~orce on the ears 35 in the closed position b~
substantially eliminating contact between the spherical surfaces 33 of the depression and the spherical surfaces 37 of the ears. As the leaflets 45 rotate to the closed position, the major edges 31 come in contact with the curved surface 47 of the seat halting further rotational movement. If the planar edge surfaces 29 of the leaflets are now in contact, no further movement of the leafIets occurs; however, should there be a slight gap therebetween because of the tolerance provided between the ears 35 and the depressions 33, the back pressure of the blood against the underside or downstream flat surfaces of the leaflets causes them to quickly slide slightly into abutting contact, which sliding movement is permitted by the curved contact in the region of the seats 47. The valve is constructed so that the downstream surfaces are at an angle of between about 45 and about 80 to a plane through the passageway centerline in the closed position.
The location of the seat 47 relative to the depressions 33 is such that the ears 35 are aligned ~59~()3 substantially precisely centrally within the depressions 33. As a result, as depicted in F~GURE 5, there is a slight gap between the end surface 37 of the ears and the spherical surface 33 o~ the depressions. It is this elimination of the normal physical contact between these surfaces, which occurs when the leaflets are either in the open position or pivoting between open and closed positions, that eliminates wear at the tilne during the cycle when the opportunity for wear is the greatest, .i.e., in the nearly closed position when the leaflets are in motion and the pressure across the valve is approaching the maximum.
In this position illustrated in FIGURE 3, the baclc pressure of the blood against the downstream sur~aces of the leaflets 15 creates forces which can be resolved into vectors in two directions, i.e.j ;n the plane of the leaflets and perpendicular to the leaflets. The force vectors in the plane of the leaflets are resisted by the abutting contact or the planar minor edge surfaces 29. The forces perpendicular to the surfaces of the leaflets are resisted by the abutting contact against the curved do~nstream-facing surface of the seat 47 along the entire length of the major edge 31.
Inasmuch as substantially the entire downstream surface of the leaflets 15 is exposed to the back pressure of blood, the force will be acting uniformly against this surface, and the arcuate seat is located so as to resist the force so that it will not be otherwise borne by the ears contacting the surface of the spherical depressions 33 where wear would be concentrated. In order to achieve this result, it is important that the surfaces of the seat 47 are located so as to be intersected by a line parallel to the axis of rotation defined by the ears 35 which divides the ~15~03 downstream surface into two regions of equal surface area, which line is referred to as the geometric or geographic center line of the leafl.ets 15 is labeled GCL
in FIGURE 4. It can be seen that this line GCL
intersects the seat 47. The effect of this relationship is shown in relationship to the left~hand leaflet in FIGURE 4 wherein a line S drawn between the ends of the arcuate seat, which divides the surface of the leaflet into regions ~1 and A2, lies inward of the line GCL. Although illustrated upon the upstream surface that is visible in FIGURE 4, the relative relationship of these lines is the same on the downstream surface which is the important one for this aspect. The region Al is larger in area than the re~ion A2, and the contact between the leaflet and seat along the edge of the region Al will resist the force exerted by the back pressure of blood against the leaflets and unload the ears 35 within the spherical depressions 33~
Illustrated in FIGURES 6 through 12 is a heart valve 51 which generally resembles the valve 11 but has a different pivotal support arrangement for the leaflets and a slightly different seat arrangement for the major edge thereof. The valve 51 includes an annular valve body 53 and a pair of leaflets 55 which control the flow of blood through a central passageway 57 that normally flows in the direction of the arrows 59 in FIGURE 7.
The leaflets 55 each have a pair of ears 61 which are received in generally triangular or pie~shaped depressions 63 formed in upstanding supports or standards 65.
The passa~eway 57 through the valve body is defined by the internal wall surface 67 which is essentially the surface of a right circular cylinder interrupted only in the region of the standards 65 and in the reyion of arcuate seats 69 discussed hereinafter. I'he leaflets 55 are flat and have a uniform thickness, being defined generally about their periphery by a minor planar surface 71 and a major arcuate edge 73. Again, the major edge 73 is essentially that of a section of an ellipse formed by a plane cutting the right circular cylinder. The end surface of the maJor edge 73 i6 curved so that it bears against the cylindrical interior wall in substantially line contact.
The pivotal axis of each of the leaflets is also eccentric to the leaflet being defined by the ears 61, which each have a generally rectangular cross ~section and rounded corners and edges. The lower end of each ear has a suitable radius of curvature that facilitates its pivotal movement in the depression 63 and serves as the pivotal axis of the leaflet. The depressions 63 have rear surfaces 75 which are preferably flat and which complement flat end surfaces 77~formed on the ears (see FIG. 12); however, compleme'ntary arcuate surfaces might be used. As in the valve ll, the ears 61 are dimensioned so ~hat there is a very slight gap between the flat end surface 77 of the ear and the rear surface 75 of the depressions.
Accordingly, the leaflets are each provided with short f~lat bearing surfaces 79 (see FIG. 10~ in the region between the ears 61 and the planar minor edges 71 and in the region just below the ears, which bear against the planar interior surfaces 81 of the upstanding standards ~5.
The periphery of each depsession 63 consists of an upper curved edge 83 which bridges an outer straight edge 85 and an inner straight edge 87. The straight edges 85 and 87 converge to a rounded vertex which has a radius of curvature substantially matched to that of the bottom end of the ear 61 to provide the desired pivot ~lS49~3 surfaces. The radius of curvature o~ th~ verte~ is preferably not more than about 3% longer than the radius o~ curvature of the bottom end of the ear. The distance between the vertex and the upper curved edge 83 is such to provide sufficient clearance to allow ~ree movement of the ear within the depression 63, e.g., about 5% of the length of the ear.
The outer edge 85 of each depression 63 serves as a stop for the leaflets in the open position illustrated in FIG. 7. In this position, blood is flowing downward through the valve, and the bottom end of the ear 61 will be seated in the vertex. Because the leaflets 55 are nearly parallel to the flow path of blood in this position, there will be little force urging the ear 61 against the straight edge surface 85, and wear is no~ a problem.
At the end of ~he pumping stroke, the respective ventricle relaxes to draw more blood into the chamber from the atrium, and the back pressure within the aorta causes the leaflets of a valve in the aortic position to begin to swing to the closed position. In the orientation depicted in FIGURE 7, the force of the blood attemptinq to flow upward against the major area of the downstream surface 89 of the leaflets which lies below the pivot axis causes the leaflets to promptly swing outward. The upper curved surface 83 provides a guide surface for the movement of the upper curved edge of the ears 61, inasmuch as the bottom ends of the ears will tend to lift above the vertex during the closing pivotal movement.
To stop the leaflets in the closed position, the four stops 69 are provided which are strategically located about the interior surface 67 of the valve body. Each of the stops 69 has an undersurface 91 which faces generally downstream and which is curved with a 1~54~

radius of curvature s]ightly larger than ~he radius o~
curvature o the upstream edge surface of the major edge 73 of the leaflets so that there is line contact therebetween as generally seen in FIGURE 11. The positioning of the surfaces 91 is such that, as contact is made between the curved, upstream-facing sections of the major arcuate edges 73 of the leaflets and the curved downstream surfaces of the stops, the minor planar edges 71 will be urged into abutting contact, positively preventing blood leakage through the diametrical center of the valve and also eliminating contact between the upper curved end of the ears 79 and the arcuate surface 83 of the depressions.
The stops 69 are strategically located so that they are intersected by the line parallel to the pivotal axis which divides the downstream surface 89 into two regions of eq~al surface area, again marked GCL in FIG.
9. The strategic location of the stops 69 provides downward-facing curved under surfaces 91 which flank the points of intersection of the line GCL of each leaflet with the stops and assures that the force of the back pressure of blood against the downstream surface 89 of the leaflets is borne by the undersurfaces 91 of the stops. Otherwise, the force vector of the back pressure o~ blood in the direction perpendicular to the surface of the flat leaflets would be borne by contact between each ear, at a location near its curved lower end, and the outer straight wall 85 of the depressions, which would have a fairly high propensity for the occurrence of wear. A line S is again drawn on the right hand leaflet of FIG. 9 which connects the inner ends of the stops 69 and divides the leaflet into regions Al and A2. Because the surface area of Al is larger-than - - -the surface area of A2, the force of the blood pressure on the underside of the leaflet is borne by the ~L~54~

stops.
Although the inventic)n has been described with regard to certain preferred embodiment, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing rom the scope of the invention which is definecl in the claims appended hereto. For example, although it is preferred to provide the depressions in the flat internal walls of the valve body and to form the protruding guides upon the lateral surfaces of the leaflets, these interengaging parts could be reversed so that the depressions are cut in the lateral surfaces of the leaflets and the protruding guides are formed at opposite locations on the opposed flat sections of the valve body. Moreover, the invention is not limited to flat leaflets but could similarly be incorporated in a valve having a pair of curved leaflets. Particular features of the invention are emphasized in the claims which follow.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A heart valve prosthesis comprising an annular valve body having a passageway therethrough of generally circular cross section, a pair of leaflets proportioned to block blood flow through said passageway when said leaflets are disposed in the closed position, said valve body being formed with arcuate seat means having a surface facing generally downstream with respect to the the normal direction of flow of blood therethrough, each of said leaflets having an arcuate major edge which abuts said seat surface and a planar minor edge, and interengaging means which pivotally interconnects each of said leaflets and said valve body for relative pivotal movement between the closed position and an open position, said leaflets being so oriented in the closed position that the downstream surfaces thereof are at an acute angle to the axis of said passageway such that the backflow pressure of blood causes said minor edges to abut each other and positively close the center of said passageway while said major edges engage said seat means, and said seat means being so located that the force upon said interengaging means created by backflow blood pressure is unloaded when said leaflets reach said closed position whereby wear at the location of said interengaging means is minimized.

2. A heart valve in accordance with Claim 1 wherein the outline of said leaflet arcuate edge is substantially that defined by a plane cutting a section of a cylindrical surface.

3. A heart valve in accordance with Claim 1 wherein said downstream-facing surface of said seat means is formed with a predetermined radius of curvature and where said arcuate major edge, in the region where it abuts said seat means, is formed with a shorter radius of curvature.

4. A heart valve in accordance with Claim 3 wherein said outline of said edge is a section of an ellipse.

5. A heart valve in accordance with Claim 1 wherein, in said closed position, said downstream surfaces are oriented at an angle of between about 45°
and about 80° to a plane through the passageway centerline.

6. A heart valve in accordance with Claim 1 wherein separate arcuate seat means, disposed at generally diametrically opposite locations along the interior surface of said annular valve body, is provided for abutting contact along a major of the length of the arcuate edge of each leaflet.

7. A heart valve in accordance with Claim 6 wherein each of said separate arcuate seat means extends to those locations of the intersection of the GCL line of each of said leaflets with said valve body interior surface.

8. A heart valve in accordance with Claim 1 wherein said seat means includes a pair of seats associated with each leaflet at locations where the GCL
line of the downstream surface intersects said annular body.

9. A heart valve in accordance with Claim 8 wherein the upstream edge region of said leaflet arcuate edge has a radius of curvature slightly less than the radius of curvature of the downstream surface of said seat means.

10. A heart valve in accordance with Claim 1 wherein said interengaging means includes a pair of projections extending from opposite lateral sides of said leaflets which are received in generally diametrically opposite depressions formed in the interior surface of said annular valve body.

11. A heart valve prosthesis comprising an annular valve body having a central passageway extending therethrough, a pair of valve leaflets, means supporting said pair of leaflets for substantially pivotal movement on a pair of eccentric axes between a closed position blocking blood flow through said central passageway and an open position allowing blood flow therethrough, said leaflets each including guides projecting in opposite directions along the pivotal axis, said guides having a rounded bottom end, said support means including pairs of generally triangular depressions at generally diametrically opposite locations, each of said depressions having a curved top edge and generally straight outer and inner edges which meet at a vertex, said leaflet guides being received in said depressions with said bottom ends at the vertex thereof, said vertex being formed with a radius of curvature matched to the radius of curvature of said bottom ends and providing pivot points for each bottom end, whereby said leaflets each move between an open position wherein said guides are located generally adjacent said outer edges and a closed position wherein said guides are located generally adjacent said inner edges.

12. A prosthesis in accordance with Claim 11 where the radius of curvature of said vertex is equal to or not more than 3% longer than the radius of curvature of said bottom end.