|Title of Invention||
"ARTIFICAL MITRAL HEART VALVE"
|Abstract||An artificial heart valve for human patients is disclosed. The structure of the artificial valve of the invention is a replica of the natural mitral valve and comprises of the following parts: a) a valve body with an interior valve surface; b) an annulus for suturing the valve to the native annulus of the mitral valve in its natural position; c) cusps that are identical or substantially similar in thickness, dimension, number and configuration similar to the natural human mitral valve. d) chordae made of the same material strong enough to support the functioning of the artificial valve of the invention in exactly the same manner as in a natural mitral valve.|
|Full Text||ARTIFICIAL MITRAL HEART VALVE Field of the invention
The present invention relates to artificial mitral heart valve. More particularly, the present invention relates to artificial heart valves that simulate human mitral valves and resemble human mitral valve both in terms of design and function. Background of the invention
A wide variety of artificial heart valves are known in the prior art for the replacement of natural heart valves, which are no longer capable of performing their normal functions. In fact, the prior heart teaches a variety of mechanical or prosthetic heart valves for operating hemodynamically in conjunction with the pumping action of the heart. Typically such valves comprise of a valve body and valve members capable of opening in a single direction. Such valve members or occluders may be in the form of a single leaflet or multiple leaflets. These leaflets are hinge mounted in such a way that they hinge along eccentric axes to open and close a central blood passageway.
In its open position, the prosthetic heart valve should ideally provide a central blood passageway with good flow characteristics so that the blood flows freely though the passageway with minimum drag or obstruction. A prosthetic heart valve mounted at the aortic position should be very responsive to blood flow. It should be capable of opening quickly during the pumping stroke of the heart and closing quickly when the heart relaxes so that regurgitation or reverse flow of the blood is avoided. The opening and closing of the valves should also be soft as the wings of a butterfly so that the patient is not unduly disturbed by the unwanted sounds. The components of the valve are required to be made of biocompatible material and in the mounted position, should be completely washed by blood so that stagnation of blood in the crevices of the valve and their eventual clotting is avoided. Most importantly, the prosthetic heart valve should be capable of opening and closing countless number of times without jamming or malfunctioning.
Towards achieving some of above-mentioned requirements, the prior art teaches a variety of designs and construction of heart valves. For example, US Patent 4,383,854 Qune 16, 1981) teaches a bileaflet heart valve having an ear extending from each lateral side of
each leaflet. The ear pivots in a recess and is guided in part by a knob traveling in a longitudinal slot that is cut more deeply into the sidewall of the valve body.
US Patent 4,363,142 (December 14, 1982) discloses a bileaflet heart valve wherein the leaflets have laterally extending ears in the form of generally oval or spherical projections that are received in recesses of complementary design.
US Patent 4,373,216 (February 15, 1983) discloses a bi-leaflet heart valve wherein protrusions extend generally radially inward from a pair of flat sidewall sections of the valve body guide valve members which have slots in their lateral edges which fit about such protrusions.
US Patent 4,451,934 (June 5, 1984) show a generally similar bileaflet heart valve where the pivot arrangement is formed with a reversal of these parts so that the leaflets have laterally protruding ears which are received within the slot and also in US Patent 4,443,894 (April 24, 1984) wherein the slots are of kidney bean shape.
US Patent 4,808,180, (February 28, 1989) discloses a bileaflet heart valve wherein the leaflets each have a semi-conical shape. By virtue of such shape, they inherently provide significant resistance to blood flow through the valve in the open position. The leaflets are guided by generally C — shaped rails that protrude from the valve body sidewall and are received in recesses of complementary shape in the lateral edges of the semi-conical leaflets.
US Patent 5,207,707 (January 16, 1992) discloses a trileaflet heart valve wherein the leaflets translate between open and closed positions guided by ears. These ears travel along curved grooves carved in walls of a pivot structure which are open at their downstream ends.
US Patent 4,820,299 and 5,123,198 also disclose similar trileaflet prosthetic heart valves. US Patent 5,123,918 illustrates a construction wherein specially configured edge guides arcs are formed in the respective faces of three triangular projections that protrude from the interior surface of the valve body. These arcs extend from the downstream edge of the valve body in a circular section that swings radially inward and then back in a direction toward the interior surface of the valve body and they guide such leaflets in moving between the open and the closed positions.
Commercially developed mechanical heart valves have frequently employed valve members oriented at a significant angle to the valve centerline in the open position, so that when backflow of blood begins, it preferentially impinges strongly upon the outflow surfaces of such valve members. This arrangement initially imparts a strong pivotal force component in the direction of the closing movement, which contributes to prompt closing and minimal regurgitation. It is now felt that it is particularly important for a mechanical heart valve prosthesis to provide a passageway through which blood can freely flow in the open position with a minimum of drag, and to accomplish this desired objective, it is presendy believed that valve members should be able to follow the flow and, when required assume orientations parallel or nearly parallel to the longitudinal axis of the passageway. Of course such valves should promptly close with only a small amount of regurgitation and without creating any significant cavitation.
According to US Patent 6,059,826 (May 9, 2000), it is particularly important for a mechanical heart valve prosthesis to provide a passageway through which blood can freely flow in the open position with a minimum of drag, and to accomplish this desired objective, it is presently believed that valve members should be able to follow the flow and, when required assume orientations parallel or nearly parallel to the longitudinal axis of the passageway. Of course such valves should prompdy close with only a small amount of regurgitation and without creating any significant cavitation. Accordingly, US Patent 6,059,826 discloses a trileaflet heart valve which includes a generally annular valve body having an interior wall of normally circular cross section into which extend three wedge shaped projections. These wedge shaped projections provide three pairs of flanking flat surfaces between which three leaflets are pivotably supported.
While the valve taught by the aforesaid US Patent addresses some of the prior art problems, the major disadvantage associated with the mechanical valves still remains. Mechanical heart valves are quite durable but require continuous anticoagulation therapy to prevent blood clotting.
Prior art also teaches a "ball and cage" type prosthetic heart valve, which essentially comprises of a ring or annulus the inner diameter of which is substantially equal to the inner
diameter of the blood vessel. A ball made of synthetic material sits on the annulus, the diameter of ball being such that it sits firmly on the annulus but does not pass through it. The misalignment of the ball from the annulus is prevented by a wire cage supported on the annulus in such a manner that the ball is capable of one way vertical movement inside the cage but is incapable of falling off the annulus. Other types of mechanical valves are tilting disc and bileaflet valves but again these valves suffer from the disadvantage that they are expensive and require life long anticoagulation therapy to prevent blood clotting which can be hazardous.
Therefore, there has been an increased preference to "bioprosthetic" or tissue valves. Unfortunately, the commonly employed "bioprosthetic" or tissue valves also have their limitations. One of the serious disadvantages reported is the homografts from human donors are extremely difficult to obtain in exact sizes. They are difficult from human donors are extremely difficult to obtain in exact sizes. They are difficult to sterilize and have to undergo numerous tests to rule out chances of infection and donor incompatibility. Therefore, prior art also envisages "xenografts", i.e., bioprosthesis obtained from non-human donors such as pigs, cattle, ostriches and kangaroos. Xenografts offer a better alternative to homografts because of their easier availability in higher numbers in variety of sizes.
Animal valves are commonly trimmed to size by cutting away the aortic valves between the leaflets and leaving only the tissue to which the leaflets are attached. These tissues are then supported by metallic or plastic stents. These stents are frames, which support the tissues that form the valve and are covered by cloth. The stent is often augmented by an annular ring usually sewn to the exterior of the prosthesis to aid in the surgical attachment of the prosthesis to the patient's aorta. These unfortunately occupy space leading to the reduction in size of the patient's annulus, which in turn leads to increased blood turbulence. Also, the stents tend to be rigid. As a result, much of the "shock" of the opening and closure of the valves are absorbed by the leaflets, thereby greatly reducing their life.
Towards overcoming some of the disadvantages of stents, US Patent 6,304,905 (April 2, 2002) discloses stentless valves of mammalian origin. While such stentless valves do overcome some of the disadvantages of the mechanical valves, they are of animal origin and are sometimes liable to be rejected by the patient's body. Also there are increased incidents infections hitherto thought to be unique to animals being transmitted to humans. Thus, prosthetic valves of animal origin always present a severe danger of either passing on some dreadful infection to the patient or being entirely rejected by the patients' body. Chemical treatments to render them inert reduces their life span to less than 20 years rendering them suitable only for patients over 60 years of age.
Another alternative is the homografts obtained from human cadavers and autografts obtained from the patients themselves. From a cadaver heart, aortic, pulmonary and Mitral valve homografts may be taken out and sterilized, stored and used for replacement in a patient. However, these valves face a tremendous short supply. These may function for 20 to 25 years. Although they are the best substitute for diseased valves, their limited supply and need for technical skills in implanting them make them unavailable to most patients. In addition, tissue valve bank facility has to be developed to sterilize and store these valves. Recent results have shown that the mitral homograft is not a suitable substitute for diseased mitral valves. While the autograft is today considered a good substitute for a select group of patients who need mitral valve replacement, technical skill and availability of tissue valve bank limits the use of this autograft.
In mitral valve surgery is necessary to retain the majority of the diseased mitral valve apparatus. This means retaining part of the cusp, the chordae tendinae and its attachment to the papillary muscles. It has now been well established and recognized that retaining the mitral valve apparatus and its continuity with the ventricular muscle provides superior left ventricular function and long term survival. However it is commonly believed that the prosthetic valve and some bioprosthetic valves will be obstructed if the subvalvular apparatus is retained. It is therefore common practice to remove the diseased mitral apparatus. This results in a problem peculiar to mitral valve replacement in that the patient often not only suffers from heart failure but also loses long-term benefits.
Objects of the invention
It is therefore the primary object of the present invention to provide prosthetic valves, which overcome the disadvantages of the prior art valves.
It is another object of the present invention to provide prosthetic valves, which are easy to use, simple to produce, and which simulates the functions and appearance of the human heart valve.
It is yet another object of the present invention to provide prosthetic valves, which do not employ any metal parts.
It is yet another object of the present invention to provide prosthetic valves, which are one piece integral valves incapable of jamming during operation.
It is another important object of the present invention to provide prosthetic valves, which are of non-animal origin.
It is still another important object of the present invention to provide prosthetic valves, which do not require the use of any anti-coagulants. Summary of the invention
The above and other advantages of the present invention are achieved by the artificial
valve of the present invention which simulates and is an exact copy of the natural mitral valve.
The structure of the artificial valve of the invention is a replica of the natural mitral valve and comprises of the following parts:
a) a valve body with an interior valve surface;
b) an annulus for suturing the valve to the native annulus of the mitral valve in its
c) cusps that are identical or substantially similar in thickness, dimension, number and
configuration similar to the natural human mitral valve.
d) chordae made of the same material strong enough to support the functioning of the
artificial valve of the invention in exactly the same manner as in a natural mitral valve. Brief description of the accompanying drawings
Figure 1 is a depiction of the artificial heart valve of the invention in closed position; and
Figure 2 is a depiction of the artificial heart valve of the invention in an open position.
Figure 3 is a depiction of the artificial mitral heart valve made of expanded polytetrafluoroethylene in an open position.
Figure 4 is a depiction of the artificial mitral heart valve made of expanded polytetrafluoroethylene in a closed position.
Figure 5 is a depiction of a natural human heart mitral valve.
Figure 6 is another depiction of a natural human mitral valve.
Figure 7 is a depiction of the artificial heart mitral valve of the invention made of expanded polytetrafluoroethylene implanted in a cadaver heart.
Figure 8 is another depiction of the artificial heart mitral valve of the invention made of expanded polytetrafluoroethylene implanted in a cadaver heart. Detailed description of the invention
The artificial heart valve of the invention will now be described with reference to the accompanying drawings which are illustrative and should not be construed as limiting the scope of the invention in any manner.
Figure 1 depicts the artificial heart mitral valve of the invention in a closed condition. The artificial heart valve comprises a valve body (1) which has an interior valve surface (2). The valve body defines a central passageway which permits blood flow therethrough. An annulus (3) is provided at one end of the valve body (1) for suturing to the natural annulus of the mitral valve in its natural position. The valve body (1) is also provided with a plurality of cusps (4) which are flexibly mounted within said valve body (1) on the annulus (3) to alternately move from an open position to permit blood flow downstream through the valve body and a closed position to prevent blood flow upstream through the valve body. The cusps (4) are identical or substantially similar in thickness, dimension, number and configuration similar to those of a natural human mitral valve. Chordae (5) are provided connected with the cusps (4) to support the functioning of the artificial mitral valve of the invention.
Figure 2 is a depiction of the artificial heart valve of the invention of figure 1 but in a cut open condition.
Referring now to Figure 3, the valve of the invention is depicted based on the line drawing of Figure 1 but made of a biocompatible material expanded polytetrafluroethylene. In the alternative, raw silk may also be used. As shown in the figures, the valve of the present invention has a valve body made of biocompatible material such as expanded polytetrafluoroethylene or raw silk. The valve body (31) has an interior surface (32). An annulus (33) is provided for suturing to the natural annulus of the mitral valve in its natural position. The valve of the invention is also provided with cusps (34) that are identical or substantially similar in thickness, dimension, number and configuration similar to the natural
human mitral valve. The cusps (34) are preferably constructed on the basis of known and measured normal human mitral valve cusps. Chordae (35) are provided made of the same material as the cusps (34) and strong enough to support the functioning of the artificial valve of the invention in exactly the same manner as in a natural mitral valve.
The chordae (35) are integrated into small pieces of the same material in four different divisions. These four divisions are used for implanting into the native papillary muscles of the patient's own heart. The technique for implantation is similar to the technique used in the implantation of the homograft mitral valve.
The valve as shown in Figures 3 and 4 (closed and cut open condition respectively) is made using a expanded polytetrafluoroethylene membrane, which was obtained commercially. The membrane was cut to the desired dimensions based on prior measurements of the natural human valve.
Figures Sand 6 depict natural human mitral valves based on which the artificial mitral valves of the invention are made.
Figure 7 and figure 8 depict successful implantation of the artificial mitral valve of the invention in a human cadaver. The expanded polytetrafluoroethylene mitral valve of the invention was sutured in a cadaver human heart for the purpose of testing whether such an implantation could be successfully carried out. It was observed that there was no difficulty in such implantation. The functioning of the artificial valve was tested manually and the functioning was observed to be satisfactory with proper movement of both the anterior and the posterior leaflets.
The material for the artificial heart valve of the invention is Raw Silk and/or expanded polytetrafluroethylene (EPTFE). While other inert biocompatible and/or blood friendly synthetic material can also be used, raw silk or EPTFE are the most preferred.
The valve of the present invention conveniently employs this material to reproduce the entire construction of a human valve without employing any stents or other material. This material has been demonstrated to satisfy the following requirements for synthetic blood conduits such are:
(a) chemical inertness;
(b) resistance to dilatation;
(c) biocompatibility with tissue and blood elements which are prerequisites for such a valve.
When used alone in fabricating this valve it will provide uniform structure and will have the above mentioned properties. This integral monomaterial design eliminates the drawbacks of combining different materials in a design.
Silk is commonly used as a suture and as a cloth material for performing surgery on human beings. Silk as a material has several advantages such as versatility (lending itself for use as a suture even in vascular anastomosis), strength, excellent tensile strength, high flexibility. Another distinct advantage that silk possesses is that it can be produced in very fine thickness from 8-0 onwards. Silk is a natural material and has excellent properties which are highly suitable for construction of artificial heart valves. Its relatively high abundance and capability of being mass produced also renders the material relatively inexpensive. The structure of the valve of the invention can be made by templates either by hand or machine. The silk can be woven to produce low porosity while retaining its tensile strength. Being a
natural material it is biodegradable unlike other man made materials. This advantage is unique especially considering the recent interest in biocompatible materials for human use.
The entire structure of the mitral valve including the annulus, the cusps, the chordae tendinae and the extension for suture to the papillary; muscle may be produced with silk thread of a know caliber without knots. The technology involves weaving either by hand weaving machine or mechanical weaving machine.
EPTFE is available as a resin. The manufacturing process is by paste extrusion and Die casting. The die is made to exact measurements obtained from normal living and cadaver mitral valves and includes in design all of the components of the design described earlier. It is made in different sizes and lengths to suit each individual patient's needs.
Cusps made form PTFE and mounted on a frame with a cloth sewing ring were tested in earlier experiments. Although the material performed reasonably, the combination of different materials and the design which copies only partially the natural valve design failed to perform satisfactorily. These drawbacks with PTFE valves tested so far are overcome in the present invention using a single material without suture, stent and obstructive sewing rings.
The valve and material of the invention provide a natural design and function. The material is blood friendly and provide a scaffold for cellular growth make it non-obstructive and does not require anticoagulants. The valve of the invention is also inexpensive to produce. The structure of the valve of the invention is fail safe and structural failure is unlikely. Another significant advantage of the valve of the invention is that it provides
continuity between mitral valve and ventricular muscle retaining normal heart function while providing long term benefits.
The valve of the invention is comprised of a single material, which provides a friendly surface for endocardial growth. The valve structure and material characteristics combine to provide long term trouble free function. This is suitable for use in all ages. The valve of the invention can also be made available in all sizes and can be mass produced. There is no need for a valve bank. The valve of the invention uses a single blood friendly material.
The valve of the present invention based entirely on natural design using a single, blood compatible material already tested in the human circulation will have the following advantages:
(a) in function such a valve will have the natural physical and physiological properties and
therefore will function like the natural valve;
(b) the material is blood compatible and will not require lifelong anti-coagulation;
(c) there is no likelihood of sudden mechanical failure as happens with prosthetic and
bioprosthetic valves, because there are no mechanical parts;
(d) this will not produce any annoying noise;
(e) it allows endothelial growth and therefore, thrombogenic complications are unlikely;
(f) it will be less expensive than currently available substitutes
(g) it can be impregnated with antibiotics to make it infection resistant;
(h) it will not cause genetic abnormalities in the fetus when implanted in pregnant women. (i) The material used may be silk which is biocompatible and will not pollute the environment.
1. An artificial mitral heart valve for human patients which comprises a valve body (1,
Figure 1) provided with an interior valve surface (2), the valve body defining a central
passageway for blood flow therethrough, an annulus (3) being provided at one end of the
valve body (1) for suturing to the natural annulus of the mitral valve in its natural
position in the human patient, a plurality of cusps (4) being provided flexibly mounted
within said valve body (1) on the annulus (3) to alternately move from an open position
to permit blood flow downstream through the valve body and a closed position to
prevent blood flow upstream through the valve body, the cusps (4) being identical or
substantially similar in thickness, dimension, number and configuration similar to those
of a natural human mitral valve, a set of chordae (5) being provided connected with the
cusps (4) to support the functioning of the artificial mitral valve.
2. An artificial mitral heart valve as claimed in claim 1 wherein the valve body, annulus,
cusps and chordae are integral with each other and are made of a blood compatible
3. An artificial mitral heart valve as claimed in claim 1 and 2 wherein the valve body,
annulus, cusps and chordae are similar to the mitral valve in a human in terms of shape
4. An artificial mitral heart valve as claimed in any preceding claim wherein the chordae
comprise different pieces of the same material in four different divisions in order to
implant the artificial heart valve into the native papillary muscles of the patients heart.
5 An artificial mitral heart valve as claimed in any preceding claim wherein the valve is
made of expanded polytetrafluorethylene or raw silk. 6. An artificial mitral heart valve substantially as described hereinbefore and with reference to the accompanying drawings.
|Indian Patent Application Number||1049/DEL/2002|
|PG Journal Number||50/2007|
|Date of Filing||21-Oct-2002|
|Name of Patentee||ALL INDIA INSTITUTE OF MEDICAL SCIENCES|
|Applicant Address||ANSARI NAGAR, NEW DELHI 110 029, INDIA.|
|PCT International Classification Number||A61F 2/24|
|PCT International Application Number||N/A|
|PCT International Filing date|