HEART VALVE PROSTHESIS

Abstract: A heart valve prosthesis (1) has a substantially annular valve body (2) and two leaflets (3) which are disposed in the valve body (2) and, by means of a hinge mechanism (4, 5a, 5b), are pivotable between an open position and a closed position. The leaflets (3) are substantially semicircular and evenly curved in two perpendicular directions, one direction being perpendicular to the diameter of the semicircle, so as to bulge outward, as seen from the centre of the annulus (2). The leaflet edges (6) closest to the diameter of the semicircle are so curved that they, when the valve is closed, are applied against one another along their entire length. Further, two projections (7) are provided on the inside of the annulus (2), entirely within the width thereof, the corner portions (8) of the leaflets (3) being applied against these projections when the valve is closed.

Description: HEART VALVE PROSTHESIS The present invention relates to a heart valve pros¬ thesis having an annular valve body and two leaflets which are disposed in said member and, by means of a hinge mechanism, are pivotable between an open position and a closed position. None of today's many heart valve prostheses meets all the requirements made on such products, which have to function in an extremely reliable manner and withstand the constant wear caused by the heart beats. Since heart valve prostheses, hereinafter referred to as heart valves, are implanted in a very sensitive and 'cramped' space of the body, it is imperative that they do not damage or get tangled up in the surrounding tissue. Many of today's heart valves suffer from the inconvenience that either the leaflets proper or projections on the annulus protrude too far, so that the risk of surrounding tissue interfering with the valve function is imminent, especially if the valve is used in the mitral position. Projections on the annulus may further hinder the surgeon when implanting the heart valve. To emulate the function of the natural heart valve, a prosthesis should preferably have a central flow. It should in addition open and close rapidly and quietly, have an insignificant resistance against flow in the for¬ ward direction, and cause a minimum of turbulence. The artificial heart valve must of course be biocompatible, i.e. acceptable to the body, and be thrombo-resistant, i.e. not cause or be the residence of thrombosis. From this point of view, it is essential that all surfaces are well flushed by the blood, so that there are no hidden corners where clots may form. US-4, 078, 268 discloses a heart valve which has an annulus and two flat, semicircular leaflets. In one embodiment, the hinge is made up of pins projecting from the leaflets and corresponding holes in the annulus. In another embodiment, both the inside of the annulus and the leaflets are formed with projections which make up the hinges of the valve. The downstream side of the annu¬ lus is provided with triangular projections on which the leaflets rest when the valve is closed. US—4,274 Λ 437 discloses a heart valve which also has an annulus and two leaflets. These leaflets are sections of a hollow, straight and circular cylinder. The hinge mechanism includes a groove on the inside of the annulus, as well as two projections fitting in the groove and pro¬ vided one on each leaflet. The projections run freely in the groove, so that the leaflets can rotate in the annu¬ lus. These prior-art valves mainly suffer from the disad- vantage that some portions project much too far from the annulus, so that there is a considerable risk that they damage, or are themselves hindered by, the surrounding tissue. US-4, 863,459 discloses another heart valve which has an annulus and two curved semicircular leaflets. This valve has the advantage of not projecting as far as the other two valves described, but it nevertheless has quite a few drawbacks. Above all, it has no central flow and does not close quietly enough. One object of the invention is to provide a heart valve of this type, which has as low a structural profile as possible, i.e. has a minimum of elements projecting from the annulus, and which will not damage or get tangled up in the surrounding tissue, either in the open or in the closed position. This is achieved by a special design of the leaflets. Another object of the invention is to provide a heart valve which functions also when mounted in a slightly oblique position relative to the flow direction in the heart. When mounted in this manner, some prior-art heart valves cannot function properly, and as a result one of the leaflets stops working, with disastrous consequences for the patient. According to the invention, the heart valve pros¬ thesis is characterised in that the leaflets are substan- tially semicircular, that the leaflets are evenly, curved in two perpendicular directions, one direction being per¬ pendicular to the diameter of the semicircle, so as to bulge outward, as seen from the centre of the annulus, that the leaflet edges closest to the diameter of the semicircle are so curved that they, when the valve is closed, are applied against one another along their entire length, and that two projections are provided on the in¬ side of the annulus, entirely within the width thereof, the corner portions of the leaflets being applied against said projections when the valve is closed. One advantage of the heart valve according to the invention is the short path of movement of the leaflets, which is a result of the curved design of the leaflets and the relatively small angle between the closed position and the open position. Thus, the short path of movement con¬ tributes to the rapid function and quiet closing of the valve, and also reduces wear on the hinge mechanism. To some patients, the 'clicking' sound of a heart valve may • be deeply worrysome. Since the valve closes quietly and wear is distri¬ buted over a relatively wide area, the heart valve can be made of metal or other materials than pyrolytic carbon, which is the material most commonly used in today's heart valves. Pyrolytic carbon has many drawbacks, such as being expensive, brittle and invisible cr radiographs. A valve made of metal, on the other hand, -. ' ■. :nuch cheaper than a valve made of pyrolytic carbon and can be precision-worked to a much higher degree than a valve of pyrolytic carbon, which is a ceramic material. Finally, the metal surface can be coated with a substance (heparin) preventing throm¬ bosis. Another advantage is that the heart valve according to the invention can be implanted in all positions owing to its low profile and the fact that it can be easily turned in the suture ring after implantation. The preferred embodiment of the invention will now be described in more detail below, reference being had to the accompanying drawings, in which Fig. 1 is a perspective view as seen from the down¬ stream side of the heart .valve * according to the invention when closed, Fig. 2 is a corresponding view of the valve when open, Figs 3 and 4 are perspective views of a leaflet, Fig. 5 is a side view of a leaflet, Fig. 6 is a side view of the valve when closed, Fig. 7 shows the open valve from another angle than Fig. 2, Figs 8 and 9 illustrate parts of the valve as seen from the upstream side when the valve is open and closed, respectively, and Fig. 10 is a schematic view of the valve in the aor¬ tic and the mitral position. As shown in the drawings, the heart valve 1 has an annulus 2 and two leaflets 3 which are disposed in the annulus and, by means of a hinge mechanism 4, 5a, 5b, are pivotable between an open position and a closed position (see Figs 1 and 2) . The leaflets 3, which preferably are of equal size, are essentially semicircular, as appears from Fig. 5, and the leaflet edge 6 closest to the dia¬ meter of the semicircle is curved. As is apparent from Figs 3 and 4, the leaflets are evenly curved in two per¬ pendicular directions, one direction being perpendicular to the diameter of the semicircle. Thus, the leaflets bulge outward, as seen from the centre of the annulus. Closest to the diameter of the semicircle, the leaflet edges are so curved that they are applied against one another along their entire length when the valve is closed. Further, the inside of the annulus is formed with two projections 7 which are situated entirely within the width of the annulus and against which the corner portions 8 of the leaflets 3 are applied when the valve is closed. In the direction of its width, the annulus 2 co - prises three sections, the mid-section being circular- cylindrical and the other two sections having the shape of truncated cones widening towards the ends of the annulus. Since the annulus of the invention is of essentially the same construction as that disclosed in US 4,863,459, it will not be described in more detail here. Owing to the curvature of the leaflets 3 and the leaflet edges 6 as well as the provision of the projection 7, the corner portions 8 of the leaflets will not be as pointed and project as far as when flat and semicircular leaflets are used. As illustrated in Fig. 2, the leaflets 3 only project a short distance from the annulus 2 on the downstream side when the valve is open, and do not at all project beyond the envelope surface of an imaginary cylin¬ drical extension of the annulus. On the upstream side, the semicircular leaflet edges 9 only project very slightly from the annulus. As illustrated in Fig. 6, the leaflets 3 do not at all project beyound the annulus 2 on the upstream side when the valve is closed, and only project at the centre portion of the annulus on the downstream side. With this construction, there is practically no risk at .all that the heart valve may damage, or get tangled up in, the sur¬ rounding tissue. Tests have shown that the leaflet curvature should be more pronounced in the transversal direction and be in the range of 1:6-1:10, and less pronounced in the longitudinal direction where it should be in the range of 1:25-1:35. These figures are based on the ratio between, on the one hand, the distance between a line drawn between the leaf- let side edges and the leaflet upper and lower edges, respectively, and the leaflet crest, and, on the other hand, the distance between the leaflet side edges and the leaflet upper and lower edges, respectively, along said line. As shown in Figs 1 and 2 as well as Figs 7-9, the hinge mechanism of the heart valve according to the inven- tion includes two spaced-apart recesses 4 formed in the semicircular edge 9 of the leaflets 3, and a pair of pro¬ jections 5a, 5b corresponding to the recesses and provided on the inside of the annulus. The surface -of the leaflet portion moving downstream when the prosthesis is opened, is approximately twice as large as that moving upstream. The projections 5a, 5b - streamlined so as not to cause too much turbulence - are slightly off-set in relation to one another, in both cases relative to the centre plane of the annulus and an imagined vertical lin at each hinge. The projection 5a closest to the downstream side of the annulus extends substantially from the middle of the annu¬ lus obliquely towards the projection 7 in the downstream direction, and constitutes an abutment for the leaflet 3 when the valve is open. The inverse hinge construction, i.e. with recesses in the annulus and projections on the leaflets, is, how¬ ever, not outside the scope of the invention. In any case, it is preferred that the hinge mechanism is so positioned that about 2/3 of the leaflet surface is situated above an imagined axis through the hinge, and about 1/3 thereof is situated below said axis (on the influx side). As appears most clearly from Fig. 2, the heart valve 1 opens at the centre, so that the major part of the flow passes between the leaflets 3, thereby emulating the func¬ tion of the natural heart valve. Preferably, the hinges 4, 5a, 5b are so positioned that about 70% of the flow passes between the leaflets 3, i.e. through the central opening. When the valve is open, the leaflets 3 form an angle of about 75-86° with the annulus 2. The angle is measured between the plane of the annulus and an imagined line between the uppermost and the lowermost point of the leaf- let. The valve 1 may have different opening angles, e.g. about 80-85°, but preferably has an opening angle of about 85°. When the valve is closed, the leaflet still forms an angle with the annulus, which is about 25-35°. Owing to the short path of movement between the open and the closed position (a result of the curved design of the leaflets 3 and the relatively small angle between the open and the closed position) the valve 1 closes quietly. If the leaflets were to open too widely, i.e. form too large an angle with the annulus 2 in the open position, the blood would have time to accelerate back when the valve closes, and would then entrain the leaflets which at a high speed would strike the annulus 2. The more gently the leaflet is applied against the annulus 2, the lower is the sound level and the less is the wear on the heart valve. The leaflet curvature as well as the opening angle of the heart valve contribute to a gentle return of the leaflets, so-that the sound level and the wear are main¬ tained at a low level. This makes it possible to manufac- ture the outer valve from metal, with all the ensuing advantages. Another important parameter in the construction of heart valves is turbulence. It is imperative that the entire heart valve including the annulus 2 and the leaf- lets have a construction involving a minimum of turbu¬ lence. If the turbulence is too pronounced, the leaflets may come to 'flutter' in the open position, which may increase corpuscle decomposition. To minimise turbulence, the tangent of each leaflet 3 of the heart valve 1 half- way between the projections 7 in the open position of the valve is parallel to the annulus 2 where the distance between the leaflet 3 and the annulus 2 is the smallest. As a result, the tangent is parallel also to the flow direction where the highest velocity of the blood is to be expected. The projections 7, against which the corner portions 8 of the leaflets are applied when the valve is closed, are also designed for minimal turbulence. As seen from th centre of the annulus 2 in Fig. 7, the projections 7 have essentially the shape of an isosceles triangle, the apex between the equal sides being directed downstream, so tha the corner portions 8 of the leaflets can be applied against the projections 7 without any leakage. The equal sides extend all the way to the hinge projections 5b. Since the heart valve 1 should be as compact as possible, the projections 7 do not protrude beyond the width of the annulus 2. In Figs 8 and 9, the valve is shown as seen from the upstream side when open and closed, respectively. Fig. 9 illustrates that the semicircular leaflet edge 9, when th valve is closed, is applied against the inside of the annulus 2, that the recess 4 in the leaflet 3 is sealingl applied against the hinge projection 5b of the annulus 2, and that the corner portion 8 of the leaflet is applied against the projection 7 of the annulus 2. When the valve is open, as shown in Fig. 8, the leaflet can move slightl • in the flow direction, the hinge mechanism having a play to promote effective flushing thereof. The heart valve according to the invention is suit- ably implanted in the aortic as well as the mitral posi¬ tion, and may also be used in the pulmonary and the tri- cuspid position, if required. The aortic position 11 and the mitral position 10 are shown in Fig. 10. It should be observed that when the valve is used in the mitral posi- tion, the leaflets on the downstream side move in the sam direction as the valve leaflets of the natural mitral valve. Thus, the valve prosthesis according to the inven¬ tion can be used even if parts of or the entire mitral- valve assembly is retained, which results in an improved heart function after the operation. The blood flow is mor rapid in the aortic position 11 than in the mitral posi¬ tion 10, so that heart valves of different sizes and open ing angles may have to be implanted in the two positions. However, the heart valve according to the invention can be used in all of the positions mentioned above. For anatomical reasons, it may at times be necessary to implant the heart valve 1 in a slightly oblique posi¬ tion relative to the blood flow. With the heart valve according to the invention, this is easily done, since the curvature of the leaflets enables the heart valve accord¬ ing to the invention to function also if mounted in such an oblique position. To enable implantation in the heart, the heart valves mounted in a so-called suture ring. The heart valve 1 according to the invention can be turned in the suture ring 2 also after the implantation. Further, the projec- tions 7 form two parallel surfaces which * are perpendicular to the plane of the annulus 2 and which can be engaged by a tool for turning the heart valve in the suture ring. This can be done because of the compact design of the heart valve, leaving no projections which may damage the surrounding tissue.

Claims: CLAIMS 1. A heart valve prosthesis (1) having an annular valve body (2) and two leaflets (3) which are disposed in said member (2) and, by means of a hinge mechanism (4, 5a, 5b), are pivotable between an open position and a closed position, c h a r a c t e r i s e d in that the leaflets (3) are substantially semicircular, the leaflets (3) are evenly curved in two perpendicu¬ lar directions, one direction being perpendicular to the diameter of the semicircle, so as to bulge outward, as seen from the centre of the annulus (2), the leaflet edges (6) closest to the diameter of the semicircle are so curved that they, when the valve is closed, are applied against one another along their entire length, and two projections (7) are provided on the inside of the annulus (2), entirely within the width thereof, the corner portions (8) of the leaflets (3) being applied against said projections when the valve is closed. 2. A heart valve prosthesis as claimed in claim 1, c h a r a c t e r i s e d in that the hinges (4, 5a, 5b) are so -positioned that the leaflets (3) open at the centre and at least 70% of the flow passes between said leaflets (3). . 3. A heart valve prosthesis as claimed in claim 1 or 2, c h a r a c t e r i s e d in that the leaflets (3) form an angle of about 75-86° with the annulus (2) when the valve is open. 4. A heart valve prosthesis as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the annu¬ lus (2) in the direction of its width comprises three sec¬ tions, the mid-section being circular-cylindrical and the other two sections having the shape of truncated cones widening towards the ends of said annulus. 5. A heart valve prosthesis as claimed in claim 4, c h a r a c t e r i s e d in that the tangent of the leaflet (3) half-way between the projections (7) is, when the valve is open, parallel to the annulus (2) where the distance between the leaflet (3) and the annulus (2) is the smallest. 6. A heart valve prosthesis as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the leaflet curvature is more pronounced in the transversal direction than in the longitudinal direction. 7. A heart valve prosthesis as claimed in claim 6, c h a r a c t e r i s e d in that the transversal cur¬ vature is 1:6-1:10 and the longitudinal curvature is 1:25-1:35. 8. A heart valve prosthesis as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the hinge mechanism is so positioned that about 2/3 of the leaflet surface is situated above an imagined axis through the hinge, and about 1/3 thereof is situtated below said axis. 9. A heart valve prosthesis as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the projection (7) has the shape of an isosceles triangle, the apex between the equal sides being directed downstream and the equal sides extending to two of the hinges (4, 5a, 5b). 10. A heart valve prosthesis as claimed in any one of the preceding claims, which is mounted in a suture ring, c h a r a c t e r i s e d in that the projections (7) form two parallel surfaces which are perpendicular to the plane of the annulus (2) and which are engageable by a tool for turning the heart valve (1) in the suture ring also after implantation.

Inventors: OLIN CHRISTIAN, OLIN, CHRISTIAN
Applicants: OLIN CHRISTIAN, OLIN, CHRISTIAN
Application year: 1991
Main classification: A61F2
IPC codes: A61F2