CA1143904A

CA1143904A - Prosthetic heart valve

Info

Publication number: CA1143904A
Application number: CA000366659A
Authority: CA
Inventors: Shlomo Gabbay
Original assignee: Shelhigh Inc
Current assignee: Shelhigh Inc
Priority date: 1979-12-13
Filing date: 1980-12-12
Publication date: 1983-04-05
Also published as: NO151847B; NO803731L; AU6529780A; US4275469A; EP0030826B1; IL61754A; ES497740A0; EP0030826A1; DK152951B; DK152951C; ZA807783B; JPS571338A; ES8106652A1; DE3065920D1; DK532080A; AU537209B2; NO151847C

Abstract

GAB-3. A PROSTHETIC HEART VALVE

ABSTRACT OF THE INVENTION
A prosthetic heart valve consists of a tubular membrane having a flexible generally circular inlet end adapted to be attached to the annulus of a heart with one side of the tube held to the heart cavity as by attachment to the papillary muscle while the other side of the tube is formed as an extended single flap adapted to move toward and away from the membrane on the attached side to provide a closed or open valve at the outlet end.

Description

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BACKGROUND OF THE INVENTION - FIELD OF APPLICATION
This invention relates to valves for the human heart and more particularly to a prosthetic heart valve.

BACKGROUND OF THE INVENTION - DESCRIPTION OF THE PRIOR ART
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In the field of heart valves there have been many attempts to produce a valve that is similar or substantially similar to the natural heart valve. The reason is that if the replacement valve differs in any substantial way from the natural valve, its reaction in the heart muscle might be so detrimental as to cause failure of the heart itself. One approach is known as the S~arr-Edwards valve. It utilizes vertical struts, a steeL or plasltic ball movably entrapped in ;~
cage and having a larger diameter than the opening in a circular ring. The pressure of blood flowing through the rin8 moves~the ball away from the ring and permits blood flow through~the valve. The reversal of pressure causes the ball to be sea~ed again against the ring to block flow through the valve. There .
are many problems with the Starr-Edwards type valve. The flow is not axial since it must flow arourid the ball. Such a flow quite often creates a very serious problem since it tends to cause turbulence (eddy currents) which restricts the flow of ~ ~
blood and may cause blood clots. The presence of blood clots ~ ' in turn leads to thromboembolisms and improper seating of the valve, and anticoagulants must be used continually. The ~3~

projecting cage member can cause scarring of the heart wall;
the clicking sound of the valve can be emotionally disturbing.
There has been some work done in attempting to produce~
a valve which more closely simulates the shape and axial flow characteristics of the natural heart valve, and, of course, eliminates the ball. Most of these have been directed to tricuspid or three lip valves.
Tricus'~id valves may require the use of certain heart valves from swine. One of the problems encountered is that hu~ reds of pigs have to be slaughtered before one or two perfect valves can be found. Secondly, in a tricuspid valve, as will be explained hereinafter, if there is slight damage or shrinkage to one of the cusps, the valve does not close properly.
Also, swine valves are not particularly large and because of mounting problems, onLy about 30% of the area of the mounting~
ring can be used for the opening in the valve. Thus, much of the internal diameter of the normal heart valve is lost~with this type of valveO
Moreover, tricuspid valves have an inherent problem~
in that the three lips must close in exact alignment or the;
valve does not properly close. If one lip is slightly out of line or misshapen, the other two lips cannot make up for the difference and, therefore, leakage occurs. Likewise, after the valve has been used for some period of time, one of the cusps may become slightly inflexible and immobile, causing tissue to build up on that cusp and further reduce its mobility.

The result is stenosis or total lack of movement of the cusp.
This reduces the size of the opening and the amount of blood flowing through the valve. Also, the stenosis may cause turbulence in the flow of blood and improper closure which almost invariably leads to failure of the valve. Some more of the problems and description of many types of heart valves are discussed in detail ln th~ Jo~rnal of Tho~acic and Cardiovascul~r Surgery, Vol~ 68, No. 3~ September, 1974, pages 261 to 269 and b~ applicant in Vol~ 76, ~o. 6, December, 1978, pages 771 to 787.
There has been some effort to produce a two cusp valve which attempts to simula~e the shape and flow of the natural heart valve. However, the principal problems with such a valve (as shown in U. S. Patent 3,739,402 to Cooley et a~ ~e the lack of an adequate volume of blood fLow through the valve and the inability to obtain complete cLosure.
This patent specifies that the lips can only open to approximately 2 millimeters, or only open to a small fraction (20%) of the valve passage area. Thus, only 20% of the amount of blood entering the valve can exit and the result is a tremendous strain on the heart and the va1ve, which may possibly lead to failure of both. Reduction in flow also causes high back pressure within the heart and may seriously damage the inside of the heart.

The inflexibility of the lips of the device disclosed in the ~ooley et al patent causes them to close along a thin narrow line at their leading edge. This closing creates two serious problems. With a narrow line of closurer the slightest deformity in either lip prevents complete closing and causes leakage through the valve. Second, since the valve closes only along this narrow line, the val-ve is often unable to remain closed when sub~ected to the extreme pressures in the heart. This is especially important when the valve is used in the mitral position in the heart, since the pressure differen-tial across the valve in that position is substantial, and any leakage could lead to cardiac failure.
A heart valve is needed which closely simulates the natural heart valve by having the flexlbility to open to substantially the same size as the natural opening and the flexibility to completely close and to remain closed asainst the force of large pressure differentials.

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It is~ therefore, an object of this invention to provide a prosthetic heart valve which closely resembles the natural heart valve.
It is a further object of this invention to provide a heart valve having full axial laminar flow through a tubular member.
A still further object of this invention is to provide a heart valve having sufficien~ flexibility to open to the full diameter of the valve and to fully close and remain completely closed.
Another object of this invention is to provide a heart valve which moves in conjunction with the annulus of the opening in which i~ is placed.
Still another object of this invention is to provide a heart valve which is strong enough to resist the pressure of the heart without failure.
Yet still anoth~r object of this invention is to provide a heart valve having proper closure and minimal resistance to flow.
Another object of this invention is to provide a heart valve with a single movable lip.
To the above ends, I have provided a prosthetic valve for a heart comprising a tubular membrane having an inlet ~ ~ ~ 3~ ~ ~

opening at one end adapted to attach the valve to the annulus of a heart and an outlet opening at a second end. A support structure is adapted to attach the membrane to the heart for preventing the second end from protruding through the inlet opening when the valve closes.

BRIEF DESCRIPTION OF THE D~WINGS
Fig. 1 is a schematic cross section view of a human heart~
Fig. 2 illustrates a prosthetic heart valve according to the present invention;
Fig. 3 is a schematic view of the left ventricle of a human heart with a prosthetic valve of this invention implanted therein;
Fig. 4 is a view similar to that of Fig. 3 with the left ventricle in the contracted position;
Fig. 5 is an illustration of the support element of the present invention;
Fig. 6 illustrates a second embodiment of the present ;~
invention;
Fig. 7 is an illustration of the support structure in the second embodiment; and `
Fig. 8 is an illustration of a still further embodiment of a support structure.

The manner in whlch th~ valve according to the present invention operates can best be understood by reference to Fig. 13 diagrammatically illustrating the anatomy of the human heart. As there shown, there are four basic chambers, the right atrium 10, the right ventricle 12, the left atrium 14 and the left ventricle 16. Normally, blood flows into the heart from the superior vena cava (not shown).into the right atrium 10, ~hrough tricuspid valve 18 and into right ventricle 12.
It continues through pulmonary valve 20, pulmonary trunk 22, A right and left pulmonary arteries 24 and ~, and finally into the lungs 28. From lungs 28 the blood comes back through left atrium 147 mitral valve 30, left ventricle 16~ aortic valve 32, aorta 34 and thence through the rest of the body. The two most~
important valves are mitral valvle 30 and aortic valve 32.~ The basie reason is that left ventricle 16 is the basic pumping part of the heart. The walls 35 and 36 of left ventricle 16 are much ~hicker and more muscular than anywhere else in the heart. The pressures in left ventricle 16 range from 0-5 and 90-180 m.m. Hgr~ whereas in the other parts of the heart, such~
as right ventricle 12, they range between 0-5 and 2-30 m.m. Hg.
When blood fLcws from left atrium 14 to left vent~icle 16, mitral valve 30 opens and aortic valve 32 closes. Next, left - -ventricle 16 contracts with mitral valve 30 closing. Then, aor~ic valve 32 opens allowing blood to flow into aorta 34. If mi~ral valve 30 leaks oxygenated blood into left atrium 14, a reduction of hlood flowing through aorta 34 may be caused and substantially less oxygenated blood reaches the rest of the body. Additionally, leakage through aortic valve 32 causes an increase in the size of the heart muscle which may eventually lead to cardiac failure. Thus, even slight leakage in mitral valve 30 or aortic valve 32 causes blood to flow in the wrong direction through the heart and may result in the eventual death of the person involved.
There are many reasons for failure of heart valves.
Some of the most common are rheumatic diseases, such as rheumatic fever and congenital defects, such as birth defects.
In these diseases, the cusp of one of the valves becomes stiff and may either be permanently open or permanently closed and ~mable to function. ';ubstantial leakage occurs and may eventually result in death. This leakage is often referred to as heart murmur because of the sound of the flow of blood through the valve in the wrong direction. `~
When a mitral valve 30 becomes defective, it may be replaced by prosthetic valve 40 according to the present invention, as hereinafter described with reference to Fig. 2.

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The valve 40 is primarily constructed of a tubular membrane 42 having substantiaLly the same diameter throughout.
More specifica]ly, the cross-sectional area of the opening throughout the tubular membrane 42 from the inlet 44 to the outlet opening 46 is substantially the same. Therefore, blood readily flows through valve 40 without any significant loss of pressure. As such, there is no substantial impediment and a minimal amount of friction to ~he passage of blood. Since the outlet 46 and the inlet 44 are substantially equal~ they dlffer from those prior art valves in which the outlet area was less than the inlet area. In those valves1 due to this difference in area, a venturi effect was created causing a substantial amount of frictional resistance to the flow of blood and a substantial drop in the flow rate. This puts pressure on the heart and may eventually lead to its failure. In the present valve, that pressure differ~ntial is substantially eliminated.~ ;
The end of the tubular membrane forming inlet 44 may be made by folding over a portion of the membrane 42 as at 48, i.e.g by doubling the thickness so that the end wilI have~
the additional strength required to hold the sutures which are sewn in to connect the membrane to the annulus of the heart, as will be further described. The amount of material foLded down may be relatively smalL and it is within the scope of the present invention to eliminate this fold if desired.

The outlet end 46 of the membrane includes a first portion 50 which is attached to the support structure or stent 52~
shown in more detail in Fig. 5. More specific~lly, this section may be folrled over to cover the support structure and prevent the latter from contacting the blood or heart wall. Although it is not absolutely necessary to provide this fold of material about the support structure, it provides an additional advantage of strengthening the membrane near the support structure at the location where sutures connect the support structure and the membrane to the wall of the heart, as will be further described.
A second portion 54 at the outlet end of the membrane preferably extends below the first portion 50 and thereby provides a free flap of material depending from one side 56 thereof.
At its end, this flap is preferably but not necessarily semicircular in shape. This additional material is provided to increase the surface area of ~.he side 56 in order to provide .
better closure of the valve as will be described. Although this is the preferable embodiment, it is within the scope of the present invention to form the sides S6 and 58 of a uniform length, the side 56, howeverl being in the form of a free unsupported flap. In addition, the flap 54 may also be folded up along its bottom.
The membrane is mad~ of a biological material such as dura mater (the membrane surrounding the human brain). The dura mater is taken from cadavers and processed so that it is ~ ~ ~ 3~ ~ ~

totally inert and thus not be subject to rejection by the human body. This material is e~tremely strong and flexible and has a high modulus of elasticity so that the valve can be continuously opened and closed with the membrane still retaining its original configuration. Other biologically acceptable materials, such as animal pericardium with gluteraldehyde and dura mater of animals such as pigs, sheep and calves treated by gluteraldehyde may be used.
Gluteraldehyde is useful because the cross linking -increases the strength of the dura mater. Also gluteraldehyde ~ ;
is an antiseptic and sterilizes the material before use.
While the membrane forming the valve of the present invention has been illustrated as a continuous tubular structure, it is obvious that the tube can be formed of two half-tubes sewn longitudinally together along their adjoining sides. In this case,~
the junc~ure line preferably wouLd rise vertically ~rom the ~free ends 62 and 64 of the stent 52.
The support structure 52 (Fig. 5),which may be rnade of high-grade surgical steel, includes a curved element 60,;whlch~is formed with substantially the same radius as the tubular mcrnbrane and preferably is long enough to extend around slightly more than half of the circurnference of the membrane.
At its ends, the curved element 60 has two upward projecting ~;
struts 62 and 64 bent over at its ends as at 66 and 68. The ends of the struts may have other configurations, such as, for example, triangular~ circularl semicircular, square, `rectangular, or any other desired shape. The important consideration in forming the struts is to make th~m high enough to support the membrane when the valve closes and low enough to prevent their touching and interfering with the inlet opening of the valve.
The support structure 52 is preferably formed from a unitary length of wire stock which may be any suitable strong material, such as 7 for example, a high-grade surgical steel like "Eligiloy". This material must be both strong and flexible. Generally, it is not necessary to cover the support structure with any other material, since it is covered with the membrane. However, it is within the scope of the present invention to cover it with any desired material, such as, for example, plastic lilce a medical grade silicone~

The manner in which the prosthetic valve according tQ the prescnt invention is utiLized will now be described with reference to Figs. 2 and 3.
It is attached after removal of the defective valve by sewing (stitches 60~ the inlet end 48 of the valve on to the remaining tissue around the circumference or annulus of the natural valve.
The outLet end 50 of the valve is held in position by means of one or more sutures 62 which may be stitched around the covered curved element 52 and connected to the papillary muscle 64 to hold the valve in place, as will be further ~ 3~ ~ ~

described. If desired, the sutures 62 may be connected to any suitable part of the heart, such as, for example, by runnlng the sutures 1~ through the wall 35 of the heart and sewing the ends through a plaget or fabric or in any other desired manner.
With the valve in place, as shown in Fig. 3, blood 1~
from the left atrium ~ can easily flow into the left ventricle 16 through the inlet opening 44 of the valve 40. Since the opening of the valve is formed of an extremely thin membrane material which is merely folded down at 48, the flow can be substantially the same as through a normal mitral valve. This aspect of the invention :i9 very important because the amount of flow area affects the amount of activity in whieh an individual m~y engage.
Referring to F;g. 4, the heart is illustrated with a left ventricle 16 in a somewhat contracted pumping position wi~h the aortic valve 32 in open position and the ar~ificial valve 40 (replacing the mitral valve) in a closed position.
The end of the valve has become smaller because the annulus of the heart surroundin~ tlle inlet opening 44 is a sphincter muscle which closes approximately 30%. The contraction of the ventricle 16 forces the blood against the side 56 and moves the material forming this wall and more particularly flap 54 against the inner wall of the side 58 9 whereby the valve 40 is closed and blood located in the left ventricle cannot pass back through the valve to the left atrium 14. When the pressure within the left ventricle builds to a high enough level, the aor~ic valve 32 opens and the blood is pumped into the aorta 34 and on to the rest of the body as previously explained.
A number of significant advantages are achieved wlth ~he pros~hetic valve of the present invention. Since the-inlet opening 44 of the tubular membrane 42 is completely flexible, there is no impedance to the restric~ion of the mitral valve opening as was present in prior prosthetic heart valves. Therefore, there is a significant reduction in the many complications caused by pr~or art prosthetic h~art valves~
Due to ~he flexibility of the inlet opening 44, the heart can open and close in a normal manner without any restrictions created by the implanted valve. The stitches 60 are not under strain as in valves with rings having a less flexible annulus where the stitche6 were subjected to a strain when the mitral ~
annulus opened and closed~ This advantage substantially reduces .
the chance for tearing and leakage across the valve perimeter.
Alsog in the past, it was dangerous to use a large valve because of the difficulty in contracting the big valve during the pumping of the heart. With the present invention, it is ~
feasible to use a large valve which may provide an orifice area which is substantially the same size as that orifice area ~ 3~

of the natural valve belng replacedO Since the flow area through the membrane is substantially equal throughout the present valve, turbulence is minimized and the blood flows without any significant loss of pressure. Thus, a primary cause of blood coagulation is eliminated and avoids the need to give the patient anticoagulants for the remainder of his or her life as with many prior heart valves. In addition, the flow area through the valve is substantially equal from the inlet ~o the outlet and the two factors together virtually eliminate any excess pressure on the heart which might eventually lead to its failure.
The flap 54 on the first side 56 is preferably slightly longer than the second side 58. When the valve 40 closes, this 1ap provides more closure area and provides an extra safety precaution that the valve does not leak. Since the present valve has only a single flap, even if it were to shrink slightly or become stiff, the valve will still tightly close. The length~, and diameter of the valve 40 may be sized according to the heart in which it is to be placed. One important llmitation~
is ~hat the support structure 52 is joined to the heart so that it does not contact ~he inlet opening 44 and interfere with the closing of the heart valve. Further, the support structure must be long enough (usually either half or slightly more than half the circumference of the tubular membrane 423, so that the first side 56 is not able to protrude through or even contact the inlet opening 44 and thereby interfere with 3~

~he closing of the inlet opening or the opening and closing of the valve itself.
The prosthetic valve as disclosed may also be used to replace other valves such as the aortic valve 32. In this event, the inlet opening 44 would be sewn in at the annulus left from the removed, damaged, original aortic valve and the outlet portion would extend into the aorta 34 where it would be fastened.
A second embodiment of the present invention, as seen in Figs. 6 and 7, provides a prosthetic heart valve 70 with a tubular membrane 72 substantially the same as in the first embodiment. The major difference lies in the support-member 74 which is placed within the tubular membrane as will be described, and forms a firmer supporting structure. ~ ;
The support member 74 may be formed from a single piece of material with the inlet end 76 formed as a complete circleO The outlet end 78 is preferably a semicircle and~may vary Erom 40 to 70% oE a circle. The vertical struts 80 and 82 of the support structure are preferably parallel to each other and at an obtuse angle with respect to the two ends. The support structure may be constructed of any desired strong but highly flexible material 3 such as, for example, a synthetic material like polyprop~lene, ~elrin or ~eflon, or metal.

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~, The membrane 72 similar to the type described in the Eirst embodiment is placed over the support structure 74 and may be Eolded at each end so as to completely encase the support structure within the membrane which is sutured thereto about ends 76 and 78 and struts 80 and 82. As provided in the first embodiment, the nonsupported side of the membrane may have an extended flap 84 adjacent the outlet opening for providing extra security when the valve closes. As in the form of invention shown in Figs. 2-5, the membrane may be made of two pieces which in the present case would be sewn together along the line of the struts 80, 82.
The completed valve may be installed in place of a mitral~ aortic or tricuspid valve of the heart as in the first embodiment. The compLeted valve with the support structure 74 may be affixed to the mitral annulus by sewing about the inlet end. Several sutures may affix the outlet end to the papillary muscle of the heart or through the wall thereof as previously explained.
In operation, the valve performs in a similar manner to the first embodiment in that when the annulus of the mitral vaLve contracts, the flexible support structure also easily adapts i~self to such contraction. Also, the nonsupported side of ~he membrane, and more particularly flap 84, is readily ~ ~ ~ 3~

moved by the blood against the opposite facing wall of the membrane which is supported by the support structure 74 to close the valve~ This struc~ure9 at the same time, prevents the flap from protruding into the tubular configuration and interfering with the inlet opening.
A modified form of stent or support 100 is illustrated in Fig. 8. In place of an open framework, the stent is made of solid structure of highly flexible material, preferably a syn~hetic such as polypropylene, delrin or teflon, or even of thin metal in the form of a tube open at opposite ends and along one side. The upper end 102 preferably extends about two thirds of the circumference while the lower end 104 about one half oE the circumference with slanting edges 106 and 108 interconnecting the same, the resulting stent thus having the general shape of the open frame of Fig. 7. The tubular membrane such as 7~ in Fig. 6 is placed over support 100, the latter being provided with a series of openings 110 at top and bottom for att~ching the membran2 thereto. The resulting valve will ba~
substantially identical in outward appearance to that shown;in igo 6 and will be attached to the hear~ annulus at the top and to the heart wall at the bottom in the manner previously described.

While specific embodiments of the invention have been described, it will be appreciated that the invention is not limited -~thereto as many modifications thereof may be made by one skilled in the art, which fall within the true spirit and scope of the invention. In addition, while there have been shown the preferred forms of my invention, it should be understood that such modifications may be made without departing from the spirit as comprehended by the following claims.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A prosthetic heart valve comprising a tubular membrane having an inlet end and an outlet end, the inlet end being adapted to be attached about the annulus of the heart, and a substantially semicircular supporting structure attached to a semicircular section of the outlet end of said tubular membrane and adapted to be attached to the wall of the heart, whereby the remaining section of the tubular membrane at the outlet end remains free and is movable toward and away from the supported portion thereof to close or open the outlet end of the tubular membrane.

2. A prosthetic heart valve according to claim 1, in which the unsupported end of said tubular membrane is of greater length than the supported end.

3. A prosthetic heart valve according to claim 2, in which said unsupported end is formed as a semicircular flap.

4. A prosthetic heart valve according to claim 1, in which the inlet end of said tubular membrane is folded back upon itself to provide a firm support for attachment to the annulus of the heart.

5. A prosthetic heart valve according to claim 1, in which the ends of the semicircular supporting structure are formed with smooth raised ends, and in which the outlet end of the tubular membrane attached to said supporting structure is folded thereover.

6. A prosthetic heart valve according to claim 1, in which the diameter of said semicircular supporting structure is substantially equal to the diameter of the inlet end of said tubular membrane.

7. A prosthetic heart valve according to claim 1, in combination with a flexible ring enclosed by and supporting the inlet end of said tubular membrane, and a pair of upwardly and forwardly extending struts respectively connecting the ends of said semicircular supporting structure to said flexible ring.

8. A prosthetic heart valve according to claim 7, in which the unsupported end of said tubular membrane is of greater length than the supported end.

9. A prosthetic heart valve according to claim 8, in which said unsupported end is formed as a semicircular flap.

10. A prosthetic heart valve according to claim 7, in which the diameter of said flexible ring is substantially equal to the diameter of said semicircular supporting structure.

11. A prosthetic heart valve according to claim 7, in which said ring, said struts and said supporting structure are formed as a unit of semirigid flexible material.

12. A prosthetic heart valve according to claim 11, in which said material is wire stock.

13. A prosthetic heart valve according to claim 12, in which said wire stock is surgical steel.

14. A prosthetic heart valve according to claim 11, in which the diameter of said flexible ring is substantially equal to the diameter of said semicircular supporting structure.

15. A prosthetic heart valve comprising a tubular membrane having an inlet end and an outlet end, the inlet end being adapted to be attached about the annulus of the heart, a supporting structure for said membrane comprising a sheet of semirigid flexible material having a length substantially equal to the length of said tubular membrane, and positioned within said tubular membrane, said sheet having a circumference at its upper end substantially equal to two thirds of the circumference of the tubular membrane and a circumference at its lower end substantially equal to one half of the circumference of said tubular membrane, and means attaching the inlet and outlet ends of said tubular membrane to the respective corresponding circumferences at the upper and lower ends of said supporting structure, whereby the unattached portion of the outlet end of said tubular membrane is movable toward and away from the attached portion thereof to close or open the outlet end of the tubular membrane.

16. A prosthetic heart valve according to claim 15, in which the unattached portion of the outlet end of said tubular membrane is of greater length than the attached portion thereof.

17. A prosthetic heart valve according to claim 16, in which said unattached end is in the form of a semicircular flap.

18. A prosthetic heart valve according to claim 15, in which the diameters of the upper and lower ends of said supporting structure are substantially equal.