HK1097435B - Prosthetic valves for medical application - Google Patents

Description

Prosthetic valve for medical applications

Technical Field

The present invention relates to prosthetic valves for medical applications. The valve of the present invention has been developed with particular reference to prosthetic heart valves and will therefore be described with particular reference to this use. However, it will be appreciated that the valve of the present invention may also be used in other medical applications (e.g. as a venous valve).

Background

Prosthetic heart valves are used to replace defective or damaged valves in patients themselves. Prosthetic heart valves currently in use fall into two broad categories: tissue valves and mechanical valves.

The tissue valve is a naturally occurring valve taken from a porcine heart or a valve formed from pericardial tissue taken from a bovine heart. Typically, tissue valves are well accepted by the patient's body and require only little anticoagulation treatment. However, tissue valves have the disadvantage that they wear out relatively quickly, with a lifetime of between 10 and 20 years.

The durability of the mechanical valve is excellent: accelerated testing has shown that mechanical valves can have a life of about 200 years. However, mechanical valves have the disadvantage that they are not readily accepted by the patient's body and require long-term anticoagulation treatment to prevent thromboembolic complications. This is undesirable in terms of the overall health of the patient.

It is therefore an object of the present invention to provide a prosthetic valve, and more particularly a heart valve, which has the durability of a mechanical valve, yet is compatible with the patient's body, as is a tissue valve, so that anticoagulation therapy is not required or is minimally required.

Disclosure of Invention

The present invention provides a prosthetic valve in the form of a flap valve comprising at least one flap arranged to permit liquid flow through the valve in only one direction, wherein the or each flap is made of a flexible mesh structure composed of a medically acceptable metal, said flexible mesh structure being selected from the group consisting of: a group of knitted metal wires and chain nails (chain nails).

The valve may comprise only a single flap arranged to lie snugly against the supporting wall, or two, three or more flaps arranged to lie snugly against each other.

Preferred materials are titanium or medically acceptable titanium alloys, e.g. Nitenol^TM. For use in knitted, woven, chain mail type structures, the metal used must be capable of being drawn into thin metal filaments.

Valves with two or more flaps may be stented or stentless.

Drawings

Preferred embodiments of the present invention will now be described in detail, by way of example only, with reference to the following drawings:

FIG. 1 is a plan view of a tricuspid prosthetic heart valve according to the invention;

FIG. 2 is a view of the valve of FIG. 1 from below;

FIG. 3 is a side view taken along the line of arrow III of the valve of FIG. 1;

FIG. 4 is a side view taken along the line of arrow IV of the valve of FIG. 1;

FIGS. 5a, b and c are side, plan and cross-sectional views, respectively, of a single-tipped valve according to the present invention;

FIGS. 6a, b and c are side, plan and cross-sectional views, respectively, of a bicuspid valve according to the invention; and

fig. 7a, b, c and d show sections of knitted material, woven material, chain mail material and perforated sheet material.

Detailed Description

Referring to the drawings, a tricuspid prosthetic aortic valve 2 is substantially similar in construction to a tissue valve, i.e. it is a flap valve comprising three equally sized flaps 3, 4, 5 of substantially flat material, each flap being formed, by scheme, to be slightly larger than a third of a circle. In this way, the flaps 3, 4, 5 can move apart to allow fluid to flow through the valve in the direction of arrow a (fig. 3), but in the opposite direction, the overlap of adjacent flaps closes the valve.

Each flap 3, 4, 5 is made of a flexible mesh structure composed of a medically acceptable metal. The term "medically acceptable" as used herein means a metal that is non-toxic to the body, and the metal is preferably inert in vivo, i.e., it does not elicit a "foreign body" response when implanted in vivo. It is envisaged that the valve of the present invention may have flaps 3, 4, 5 made of titanium or a medically approved titanium alloy, such as a nickel/titanium Nitenol (trade mark) alloy, but other medically acceptable metals may be used.

The flexible mesh structure can be made of metal wire, either by using a knitting type process (fig. 7a), or by producing a chain mail (fig. 7c), i.e. a series of separate, interlocking loops consisting of metal wire; a weaving type process (fig. 7b) may also be used. Another possibility is to use a thin, flexible sheet formed with a plurality of holes (fig. 7 d). The finished mesh structure must be able to flex without permanently flexing.

The woven or perforated flap provides a relatively stiff structure, however, the chain mail structure provides very flexible flaps; the stiffness of the knitted structure is between the stiffness of the woven structure and the stiffness of the chain mail structure.

Titanium and titanium alloy wires are preferred because they are known to be not only inert when implanted in the body, but also promote good tissue growth. Furthermore, evidence from titanium implants used elsewhere (e.g., the mouth) suggests that infections can be cleared from the titanium surface more easily than from other foreign materials.

Each flap 3, 4, 5 has an arcuate outer edge 3a, 4a, 5a from each end of which arcuate outer edge 3a, 4a, 5a side edges 6/7, 8/9, 10/11 extend inwardly such that adjacent side edges meet at an acute angle but with the apex between the side edges being arcuate.

As shown in fig. 3 and 4, the outer edge 3a, 4a, 5a of each flap is curved in side view, with the side edges 6/7, 8/9, 10/11 raised relative to the midpoint of the outer edge. This increases the overlap between adjacent flaps, with the adjacent side edges 6/8, 9/10, and 7/11 of adjacent flaps overlapping, which greatly reduces the risk of any reverse flow through the valve (i.e., in the direction opposite arrow a).

The valve shown in the drawings is of a semi-stented design, i.e. around the periphery of the valve, with a degree of reinforcement being provided by a peripheral rib 13, which peripheral rib 13 may simply be a thickened and/or reinforced region. For the sake of clarity, the ribs 13 are omitted in the views shown in fig. 3 and 4.

The valve can also be produced as a fully stented valve, i.e. with the three flaps 3, 4, 5 mounted on a rigid ring. Another possibility is to omit or reduce the peripheral reinforcement altogether and produce the valve as a completely stentless valve; for percutaneous insertion, i.e. by being inserted through the skin and then through a vein or artery to the aorta, a stentless design (or a minimally stented design) is advantageous. For percutaneous insertion, the valve has to be "crimped" (i.e. folded over on itself), and the obvious stent makes this impossible.

The tricuspid valve described above is the most common type of prosthetic valve, as it is in nature. However, according to the present invention, it is possible to form a valve with more than three valve flaps by the same general type design as a tricuspid valve.

Single-tipped and double-tipped valves are also possible; these valves are illustrated in figures 5 and 6, respectively.

Figures 5a, b and c show a single cusp valve 15 that is circular in plan and has a peripheral annular stent 16. A rigid, fixed wall 17 extends outwardly from the bracket, perpendicular to the plane of the bracket, approximately around one third of the circumference of the bracket. In side view, the single flap 18, consisting of flexible material, is U-shaped and fastened around its lower margin 19 to the edge of the fixed wall 17. The flap 18 is dimensioned such that when the flap 18 is pushed inwardly towards the fixed wall 17, the upper margin 20 of the flap may press against the wall 17, preventing fluid flow through the valve in the direction of arrow a. Fluid flowing through the valve in the direction of arrow B has a tendency to push the margin 20 of the flap away from the wall 17, allowing fluid to flow freely in that direction.

Referring to the flaps 3, 4, 5 above, the flaps 18 are made of the flexible mesh structure described above. The wall 17 is also made of a medically acceptable metal and may be solid or mesh.

Fig. 6a, b and c show a mitral valve 20 that is rounded according to a scheme and can be produced as a stented or stentless valve. In the stented version, the valve has a peripheral annular stent 21, the peripheral annular stent 21 supporting a rigid wall 22 extending outwardly from the stent and perpendicular to the plane of the stent. The shape of the wall 22 can most easily be imagined as an open-ended cylinder secured along its lower edge 23 to the bracket 21, while its upper edge (i.e. the edge furthest from the bracket 21) is formed with two opposing U-shaped cutouts, leaving the opposing sides of the wall 22 formed with U-shaped margins 25. Along the edges of the margin 25 on each side of the wall 22, a valve flap 24 made of a flexible mesh material is secured. In side view, each valve flap 24 is U-shaped so that its lower edge fits the margin of the cut-out portion of the wall 22, while the upper edge of the flap overhangs the central portion of the valve, so that fluid passing in the direction of arrow X pushes the valve flaps 24 together, closing the valve, but fluid in the direction of arrow Y has a tendency to push the flaps apart and can pass freely. The wall 22 may be made of a solid material or a mesh material.

In the stentless version, the stent 21 and wall 22 are omitted and the valve simply comprises two U-shaped valve flaps 24 arranged in opposed pairs, the upper ends 26 of which are secured together and the arcuate outer margin 25a of which is slightly stiffened, for example by a peripheral wire or peripheral rib, to maintain the correct shape of the valve. The stentless version functions in the same manner as the stented version.

The valve flaps 18 and 24 in the single-cusped and two-cusped versions may be made of any of the flexible mesh structures composed of a medically acceptable metal described with reference to the tricuspid valve.

It is envisaged that the valve described above with an initial coating of degradable sealing material over the flaps 3, 4, 5 may be implanted in the patient, which initial coating may prevent leakage through the open mesh structure of the flaps until the patient's own system has formed its own coating on the flaps by endothelialisation.

Claims (8)

1. A prosthetic valve in the form of a flap valve comprising at least one flap arranged to permit liquid flow through the valve in only one direction, wherein the or each flap is made of a flexible open mesh structure composed of a medically acceptable metal, said flexible open mesh structure being selected from the group consisting of: a set of knitted metal wires and chain mail.

2. The prosthetic valve of claim 1, wherein the valve comprises a single flap arranged to abut a support wall mounted on the peripheral stent.

3. The prosthetic valve of claim 1, wherein the valve comprises two flaps arranged to close against each other.

4. A prosthetic valve as claimed in claim 3, wherein said valve also includes a peripheral stent supporting a wall which extends at right angles to the plane of the stent and provides two opposed cutouts in which said flaps are mounted.

5. The prosthetic valve of claim 1, wherein the valve comprises three similarly sized flaps arranged to fit snugly against each other.

6. The prosthetic valve of claim 5, wherein the valve also includes a peripheral rib around the periphery of the valve.

7. The prosthetic valve of claim 5, wherein the valve also includes a peripheral stent to which the three flaps are mounted.

8. The prosthetic valve of any one of the preceding claims, wherein the medically acceptable metal is titanium or a titanium alloy.