WO1988002263A1

WO1988002263A1 - Scleral bioprosthetic heart valves

Info

Publication number: WO1988002263A1
Application number: PCT/GB1986/000580
Authority: WO
Inventors: Joseph Fahmy Khalil
Original assignee: Joseph Fahmy Khalil
Priority date: 1986-09-29
Filing date: 1986-09-29
Publication date: 1988-04-07

Abstract

A scleral bioprosthetic heart valve is a "new" biological material suitable for replacement of the diseased heart valves. Its morphological characteristics allows for "new" designs to be utilized. The frame on which the valve can be mounted adopts various shapes to suit different positions in the heart. Its functional characteristics allow for "new" concept to be forwarded in mechanism of valve function and therefore conventional tri-leaflet valves or nonconventional bi-leaflet and single-leaflet valves are demonstrated. The collective "new" capabilities accounts for easy manufacture, easy operative plantation and preservation of maximum myocardial function.

Description

DESCRIPTION

SCLERAL BIOPROSTHETIC HEART VALVES

This invention relates to the use of "sclera" as an appropriate substitute for the diseased heart valves.

Surgical management of valvular heart disease has progressed over the past 30 years, however when it necessitates replacement of the native heart valve which is severely diseased beyond any possibility of repair, of the currently available devices for replacement, despite considerable progress, unfortunately none is "ideal" in all circumstances, this makes the continuous search for better substitute necessary.

Biological material of various nature is used with some advantages over mechanical devices except that the failure rate at 7 - 10 years compromises its use in certain circumstances. It was therefore thought that the present invention provides a valve of biological advantages and nearing the mechanical valves in design and durability.

According to the present invention the "sclera" is prepared by freeing it from the episclera and the attached eye muscles and after removal of the cornea, conjunctiva, optic nerve, choroid and retina and after fixation using gluteraldehyde, the prepared sclera is fashioned into spherical cusps in different sizes and these are mounted, as described later, to make the valves in either of four designs.

The advantages of the sclera as a tissue used to substitute for diseased heart valves are:-

1 Scleral tissue is available from human cadavers who carry donation cards for corneal transplant, also animal sclera of porcine origin and probably canine is also available and suitable, however, availability of the latter may be limited. The bovine sclera although widely available is particularly not suitable on the account of its thickness and stiffness. The sclera is made of 95% Collagen orientated in a spherical displayand therefore when treated with gluteraldehyde, its shape is preserved but "deformation" by complete reversal of its curvature for valve opening to execute valve function is allowed and it undergoes "reformation" of the natural spherical curvature for valve competence in closed position.

Deformation - reformation mechanism is in a concavo-convex configuration which, has excellent hoemodynamic properties.

The sclera is known not to calcify in the body and is avascular in contrast with, other tissues currently used. Therefore long-term durability is expected to be superior.

The "normal" intra-ocular pressure of 18-23mm Hg. makes the sclera adapted to a certain degree of tension and therefore the stress induced by the circulatory pressures and flows should be less deliterious on the sclera than on the tissues originally not meant to be under any tension.

In common with other available biological material the following is achieved compared with mechanical devices:- i. no hoemolysis ii. no emboli iii decreased anti-coagulant-related morbidity and mortality iv decreased incidence of sudden valve failure culminating into death.

The shape and configuration αf the sclera allows for versatility in valve design as described later, which therefore achieves.- i. easy manufacture ii. easy implantation iii. excellent flow characteristics with no gradient, i.e. entirely non-obstructive valves. A specific embodiment of the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 shows the conventional tri-leaflet valve, O-shaped frame but non- stented;

Figure 2 illustrates an axial-mounted bi-leaflet valve on a D-shaped frame far the mitral position;

Figure 3 shows another axial-mounted bi-leaflet valve on a Z-shaped or I- shaped frame for the aortic position;

Figure 4 illustrates a single-leaflet C-shaped valve.

The best mode for carrying out the invention would be in the form of a conventional tri-leaflet valve, however, referring to the drawing, figure 1, the valve is mounted circumferentially on a circular O-shaped frame (which could be made flexible) dispensing with the need of any stents because by virtue of the spherical morphology of the sclera the cusps would co-apt without need to be fixed at another level than that of the frame.

However, as the valve function would rely an the mechanism of Deformation, i.e. complete reversal of the curvature in the open position and on Reformation, i.e. reverting to the natural curvature namely sphere, the valve mechanism could be achieved by coaptation of the cusps and the wall of the heart and major vessels rather than coaptation of the cusps to each other to achieve valve competence. This allows the design of the valve in a nonconventional way to be based on the axis.

Referring to the drawing, figure 2, the bi-leaflet valve is mounted on a D- shaped frame with the leaflets built on the straight side of the D and the curved semi-circle would be used for valve implantation into the mitral and tricuspid positions.

The fibrous annulus of the native mitral valve is a thin and incomplete ring of fibrous tissue only well formed antero-medially, also the active motion of the mitral "annulus" contributes to the valve competence and enhances the left ventricular functions which would be impaired in fixation with complete ring in conventional mitral valve replacement. Therefore, this type of design has the purpose of utilization of the strong tissue of the annulus for valve implantation and to leave, the deficient half for annular contraction to preserve the left ventricular function and help in the mechanism of valve competence.

Referring to drawing, figure 3, the valve mechanism is similar to the above-mentioned design but because the anatomy of the aortic and pulmonary valves is different, the bi-leaflet valve is mounted on a Z- shaped or I-shaped frame with the leaflets built on a "longitudinal" straight bar and the "transverse" bars are used for valve implantation in those positions.

Referring to the drawing, figure 4, using the same principle of valve competence, reliance an coaptation between the valve tissue and the native walls, a single-leaflet (mono- cuspid) valve is mounted on a C-shaped frame. The global sclera minus 1/6 at each pole (i.e. areas corresponding to the sectors occupied by the cornea and the optic nerve) laid open and size-adjusted, is mounted on a C-shaped frame approximately 2/3 the circumference of a circle with, the free end forming the valve mechanism with the wall at the opposite side of the "cylinder".

It is therefore concluded that the sclera as a biological tissue to be used far manufacturing heart valves is very versatile as all four designs could be applicable industrially for clinical utilization.

Claims

1. Scleral bioprosthetic heart valves comprising spherical cusps fashioned from human, porcine or canine sclera, in different sizes and mounted in various designs comprising a frame in the shape of 0, D, Z or I, and C and the scleral cusps built in a conventional tri-leaflet or axial bi-leaflet and single-leaflet valves.

2. A conventional scleral bioprosthetic heart valve as claimed in claim 1 wherein the circular O-shaped frame is used for the tri-leaflet cuspid valve is mounted on the frame but dispensing with the use of any stents, Fig 1.

3. An axial scleral bioprosthetic heart valve as claimed in claim 1 wherein the D-shaped frame is used and the bi-leaflet cuspid valve is mounted on the straight bar, Fig 2.

4. An axial scleral bioprosthetic heart valve as claimed in claim 1 wherein the Z-shaped or I shaped frame is used and the bi-leaflet cuspid valve is mounted on the longitudinal bar, Fig 3.

5. A single-leaflet scleral bioprosthetic heart valve as claimed in claim 1 wherein the C-shaped frame is used and the monocuspid valve is mounted on it, Fig 4.