WO1990004367A1

WO1990004367A1 - Heart valve prosthesis

Info

Publication number: WO1990004367A1
Application number: PCT/GB1989/001227
Authority: WO
Inventors: Duncan +Di Winnard
Original assignee: Winnard, Muriel +Hf
Priority date: 1988-10-20
Filing date: 1989-10-17
Publication date: 1990-05-03
Also published as: GB8824608D0; AU4422389A

Abstract

A heart valve prosthesis comprises an occluder ring (10) and two planar leaflets (12, 12) which pivot between a closed position in which they lie at an angle of 25°-60° (preferably 45°) to the plane containing their pivotal axes (14, 14) and an open position in which they lie at a greater angle (preferably 85°) to that plane. The leaflets therefore open and close quickly. The pivotal axes (14, 14) are inset a relatively short distance from the outer edges (16, 16) of the leaflets and so do not obstruct the centre region of the valve when open. The occluder ring may be formed from polycrystalline alumina or from titanium, and the leaflets from polycrystalline or single crystal alumina, all of which materials are substantially biologically inert, mechanically strong and wear resistant.

Description

HEART VALVE PROSTHESIS

This invention relates to a heart valve, or heart valve prosthesis.

Heat valve prostheses are known which comprise an occluder ring and two leaflets mounted to the ring for pivotal movement between closed and open positions. In the closed position, the leaflets lie generally in a transverse plane, and they must turn through a considerable angle in order to open the valve. In some of these valves, the flow of blood is rendered turbulent owing either to the shape of the leaflets or to the locations which they occupy when open. Some of these valves take a relatively long time to close, because of the large angle through which the leaflets must turn, such that a significant return flow (or reflux flow) of blood occurs during the time taken for the valve to close.

I have now devised a bileaflet heart valve prosthesis which opens and closes quickly, minimises turbulence in the blood flow when open and minimises reflux flow.

In accordance with this invention, there is provided a heart valve prosthesis comprising an occluder ring forming a through-passage for the flow of blood and two generally planar leaflets mounted to the occluder ring for pivotting movement between a closed position and an open position, each leaflet in the closed position lying at an angle of 25°-50° to a plane containing the pivotal axes of the two leaflets, and in the open position lying at a greater angle to said plane, the pivotal axes being inset from the opposite outer edges of the two leaflets by 5-40% of the length of each leaflet.

Preferably in the open position, each leaflet lies at substantially 85° to the plane containing the pivotal axes of the two leaflets.

In providing that each leaflet opens and closes between an angle of 25°-60° and an angle of e.g. 85° to the plane containing the two pivotal axes, advantage is taken of the fact that the change in the cross-sectional area of the flow passage per degree of rotation of the leaflet is relatively large throughout the opening and closing movement. The leaflets therefore open and close very quickly. Preferably in the closed position each leaflet lies at an angle of substantially 45° to the plane containing the two pivotal axes.

The pivotal axes are inset from the opposite outer edges of the two leaflets, so as effectively to increase the span of the respective hinges and reduce the freedom of the leaflets to rock about these. However the amount of inset is relatively small so that the leaflets are positioned close to opposite peripheral portions of the ring when in the open position, thus minimising the obstruction which the leaflets present to the flow of blood. Preferably the pivotal axis of each leaflet is inset from its outer edge by 10-20% (most preferably 15%) of the length of the leaflet.

The occluder ring may comprise two identical half-rings which are brought together in order to mount the two leaflets pivotally therebetween: the mating surfaces of the two half- rings are then bonded together. The hinge of each leaflet may comprise integral pins projecting from the leaflet (or from the ring) and received in sockets in the ring (or in the leaflet). The ring may be provided with inserts formed with the hinge sockets (or pins), in which case the occluder ring may be formed in one piece.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIGURE 1 is an isometric view of a heart valve prosthesis in accordance with the invention shown closed;

FIGURE 2 is a cross-section through the heart valve prosthesis shown closed;

FIGURE 3 is a cross-section through the heart valve prosthesis shown fully open;

FIGURE 4 is a side view of the occluder ring of an example of valve in which socket bearing inserts are bonded int bores provided in the ring;

FIGURE 5 gives a plan view and an end view of such bearing insert; and

FIGURE 6 is a plan view of a leaflet for the valve o Figure 4.

Referring to Figures 1 to 3 of the drawings, there i shown a bileaflet heart valve prosthesis which comprises a occluder ring 10 and two leaflets 12,12 pivotally mounted to th ring. Each leaflet is substantially planar and its pivotal axi 14 is inset by a distance d from its outer edges 16 by 10-20 (preferably 15%) of the length 1 of the leaflet from its outer edge 16 to its inner edge 18. The pivotal axes 14,14 of the tw leaflets lie in a median plane of the occluder ring.

In the closed position, each leaflet 12,12 lies at a angle of 25-60° (preferably 45° as in the example shown) to the plane containing the axes of the two leaflets.

The shape of each leaflet is substantially one half of an ellipse, with the inner edge 18 of the leaflet being straight and corresponding to the minor axis of the ellipse. In the closed position, the straight, inner edges 18,18 of the two leaflets seat against rim portions 20,20;22,22 of the ring. The rim portions 20,20 project from the ring in the downstream direction of blood flow, whilst the rim portions 22,22 project from the ring in the opposite direction, the cross-sections of these seating rims being formed to provide sealing edges.

In the open position, each leaflet 12,12 lies at an angle of substantially 85° to the plane containing the axes 14,14 of the two leaflets, as shown in Figure 3.

In use, the heart valve opens and closes very quickly, the leaflets in the example shown moving through only 40° between their 45° closed position and their 85° open position, and acted upon through a relatively large leaflet area whose centre of pressure is substantial upstream of the leaflet axis.

In the closed position, the leaflets seat against the rim portions 20,20;22,22 of the occluder ring and seal the valve in an effective manner against the formed sealing edges. In the open position, the leaflets present little obstruction to the flow of blood because they lie nearly parallel to the direction of flow and because they are positioned close to opposite peripheral portions of the ring rather than towards the centre of the ring. Further the smooth surfaces of. the leaflets and of the inner periphery of the occluder ring ensure that the blood flow through the heart valve is relatively free of turbulence. Although close to the opposite peripheries of the occluder ring, the leaflets are still sufficiently spaced from those peripheries so that, when the leaflets are opening or closing, any turbulence in the blood flow between the leaflets and the opposite peripheries of the ring is minimised. Because the leaflets close rapidly and seat on formed sealing edges, there is little return flow of the blood (or reflux flow) during the closure movement and after closure there is little regurgitation between the leaflets and the sealing edges on the occluder ring.

The occluder ring may comprise two identical half rings which are brought together to mount the two leaflets pivotally therebetween, and then their mating surfaces are bonded. The two half-rings may be moulded from polycrystalline alumina. In this case the mating surfaces are polished to an optical finish before the two half-rings are brought together, and then these surfaces are bonded by an optical contact thermo-diffusion bonding technique. This produces a very strong bond.

The occluder ring may instead be formed by milling from titanium. The leaflets may be formed of polycrystalline alumina or of single crystal alumina, in which case the occluder ring may have bearing inserts of either of the latter materials.

Figures 4 to 6 show a valve in which the occluder ring 40 is formed with circular bores 42 which receive bearing inserts 44 preferably bonded to the occluder ring by thermo-diffusion bonding. The inserts 44 are formed with bearing sockets 46 which receive pivot pins 48 formed on the leaflets 50 (Figure 6) by cutting notches 52 into the edges of the leaflets. The occluder ring may be formed in one piece.

The materials specified above are all substantially biologically inert and exhibit a high Young's modulus and a high transf lexural strength. They are furthermore very hard and so extremely resistant to wear and can be polished to a very high finish.

The use of fully dense, high purity polycrystalline alumina also makes the use of the reported characteristic of overgrowth of non-vascular fine (lOOjim) tissue, such growth being facilitated mechanically by the sub-micron surface etching along grain boundaries that is a side effect of controlled thermo- diffusion bonding and thus particularly appropriate to the occluder ring. Such overgrowth aids leaflet sealing and camouflages the underlying material from thrombogenic and haemolytic reaction.

In another embodiment the outer surface of the occluder ring may be formed with only one retaining lip for the location and retention of the sewing ring, in this case the corresponding lip may comprise a separate ring of high tensile strength metal (e.g. stellite), having an interference fit with the occluder ring and having the sewing ring connected to it. This separate ring is preferably contracted about the occluder ring and so relies upon the high compressive strength of the material of which the occluder ring is made. The separate ring not only serves to attach the sewing ring to the occluder ring but also acts as a reinforcement for the occluder ring.

Claims

1. A heart valve prosthesis comprising an occluder ring forming a through-passage for the flow of blood and two generally planar leaflets mounted to the occluder ring for pivotting movement between a closed position and an open position, each leaflet in the closed position lying at an angle of 25°-60° to a plane containing the pivotal axes bf the two leaflets, and in the open position lying at a greater angle to said plane, the pivotal axes being inset from the opposite outer edges of the two leaflets by 5-40% of the length of each leaflet.

2. A heart valve prosthesis as claimed in claim 1 in which in the open position each leaflet lies at substantially 85° to the plane containing the pivotal axes of the two leaflets.

3. A heart valve prosthesis as claimed in claim 1 or 2, in which in the closed position each leaflet lies at an angle of substantially 45° to the plane containing the pivotal axes of the two leaflets.

4. A heart valve prosthesis as claimed in claim 1, 2 or 3, in which the pivotal axes are inset from the opposite outer edges of the two leaflets by 10-20% (preferably substantially 15%) of the length of each leaflet.

5. A heart valve prosthesis as claimed in any preceding claim in which the occluder ring comprises two identical half rings brought together to mount the two leaflets pivotally therebetween.

6. A heart valve prosthesis as claimed in claim 5, in which the two half rings are bonded together by thermo-diffusion bonding .

7. A heart valve prosthesis as claimed in any preceding claim, in which the occluder ring receives bearing inserts with which the leaflets are pivotally engaged.

8. A heart valve prosthesis as claimed in any preceding claim in which the occluder ring is formed of polycrystalline alumina or of titanium.

9. A heart valve prosthesis as claimed in any preceding claim, in which the leaflets are formed of polycrystalline or single crystal alumina.

10. A heart valve prosthesis as claimed in any preceding claim, further comprising a separate reinforcing ring disposed around the occluder ring and having a sewing ring connected thereto.