CA2080138A1

CA2080138A1 - Artificial heart valve

Info

Publication number: CA2080138A1
Application number: CA 2080138
Authority: CA
Inventors: Jose Benito Garcia Gonzalez-Moro
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-02-07
Filing date: 1992-02-06
Publication date: 1992-08-08
Also published as: AU1261292A; BR9204120A; ES2028611A6; WO1992013502A1; EP0532719A1

Abstract

The artificial heart valve is comprised of a flexible frame consisting of a valve ring (1) and posts (2) extending from the ring and defining some recesses, said ring having the shape of a shell;
voiles (4) for opening and closing the valve are fixed to said frame and project beyond the apex of said posts (2); a calf heart sac coating applied to said frame with a thickness from 16 to 22 mm; and a ring for fixing the valve to the heart tissues of the patient. The valve of the invention is useful as substituent for failing or dysfunctional human valves.

Description

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~0 92/13502 PCT/ES92/OOQ14 ARTIFICIAL HEART VALV~3 FIELD OF TBE INVENTION
The invention relates to a new artificial heart valve to be substituted for diseased or malfunctioning human valves, and which belongs to the group of biologi-cal valve sub~titute~ or "bioprostheses" also known a~
valve xenograft~, that i8 to say valve~ fabricated from biological tissues, and in this case from calf pericar-dium treated with glutaraldeXyde''an'd attached to a flexible frame composed of a polymer known as Celcon.

BACRGP~OUND OF THE INVENTION
At the beginning of the seventies, Dr Mari6n Ionescu of LeedR, England, devised the 3-velum calf pericardium valve, treated with glutaraldehyde and mounted on the outside of a rigid titanium ring. Subse-quently, the valve was modifisd, reducing its profile and also changing the rigid ring to a flexible one made of plastic (Delrin). These modifications of the pericardium valve brought about a hydraulla lmprovement which was demonstrated in studies per~ormed in vitro by Reul, and subsequently in vivo by various investigators (Cardiac Prostheses Symposium, Montreux, Switzerland, 1985), including the inventor.
It was also found that the Ionescu-Shiley peri-cardium bioprostheses, which was the name under whichthey were marketed, were of very low thrombogenicity, probably due to their excellent hydrodynamics, there being no need to administer anticoagulants for life as was the case with other biological v21ves implanted in the mitral position or with mechanical valve substitutes.
Studies carried out by the inventor (Biologic Bioprosthetic Valvea, Yorke Medical Books, 1986) have confirmed this highly beneficial a~pect clinically.
Designs si~;lar to the Ionescu-Shiley valve, th~t is to say with the pericardial vela mounted on the out-side of the frame of the valve, with a few modification~, were appearing on the market for clinical use at the beginning of the eighties.
Nevertheless, the excellent hydraulics of this type of pericardium bioprosthesis was not accompa-nied by a proportionate durability, since holes gradu-ally began to appear in the vela, ostensibly through frictional abrasion against the lining of the valve supports, as well as tearing of the vela at the points of attachment to the supports, as was published by Ionescu himself and others (Cardiac Prostheses Sympo-sium, Montreux, Switzerland, 1985).
These malfunctions have been demonstrated in vitro by means of fatigue accelerators, it being found that abrasion or friction of the pericardial velum against the inside of the lining of the valve frame eventually wears a hole in the tissue after about one hundred million cycles. In addition, the inventor, af-ter 14 years of experience with this type of valve, has demonstrated the incompetence of the latter through loss of the suture which attaches the vela to the frame or through tearing of the vela as a result of the su-ture which encircles the velum to attach it to the frame.
This problem was not solved by the modifica-tions of a new pericardium valve designed by Ionescu and known as "low profile", because the clinical expe-rience of the University of Santiago (Spain) reveals that these valves continue breaking down in the same way and in the same proportion as Ionescu's earlier design.
There was consequently a need for a biologi-cal valve which, in the opening and closing movements of the vela, would avoid abrasion by causing friction of pericardium with pericardium and not against the in-ner lining of prosthetic material of the valve, the ~ A
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, latter at the same time retaining good hydraulic behaviour.
In this respect the university of Glasgow designed a new pericardium valve completely coated in-side with pericardium with a circular support ring.
That valve, marketed under the name Bioflo, was evalu-ated by the inventor and his collaborators at the University of Santiago (chief researcher of the Spanish multicentres study) and was shown to have hydraulics much inferior to the traditional pericardium valves which mount the tissue outside the support or frame, so that, in the small sizes and specifically for aortic valve substitution they are highly stenotic and clini-cally unacceptable (Gonzales Juanatey, J.R., vega, M., Rubio, J., et al. Echo-Doppler, Early Hemodynamic Evaluation of the New Bioflo Pericardial Bioprosthesis:
A Reason for Alarm, Mediterranean Association of Cardi-ology and Cardiac Surgery, 4th Annual Meeting, Antalya, Turkey, 1990, p. 33. Echo-Doppler Evaluation of Various Pericardial Bioprostheses in Small Aortic Annuli.
Gonzales Juanatey, J.R., et al., Cardiovascular Update 4, Ed. R. Rivera, Ediciones ELA, 1991, p. 273).
This problem has been fulfilled by the pre-sent invention, which has created a highly durable heart valve having excellent blood circulation hydraulic characteristics by lining the inside of the frame to avoid selective type abrasion, i.e., only on the posts almost up to the base of the latter, whereby the excellent hydraulics of this design is preserved.
This ~act has been corroborated by the in vitro studies conducted for such purpose by Dr. Reul, Helmholtz Institute, Aachen, Germany. Similarly, the design of the ring and the frame of the valvular support is of anatomical configuration and completely flexible, with-out any prosthetic material on the outside of the posts, which contributes to readily adapt it to the an-..
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nulus of the patient to bP implanted, providing better hydraulics compared with other pericardium valves de-signed earlier.
According to the present invention, an arti-ficial heart valve is provided which comprises a flex-ible frame composed of a valve ring and some posts which stand up from the ring and which define recesses between them, the part of the ring corresponding to each recess being shell-shaped or scalloped; some vela for opening and closing the valve which are attached to the said frame and which are dimensioned in such a way that they project beyond the apex of the said posts; a facing or lining of pericardium applied to only the posts or support of the said frame; and some means of attachment of the valve to the patient's heart tissue.
Preferably, the frame is made of a highly fatigue-resistant acetate copolymer, specifically the polymer known as Celcon, and has between five and six holes in each recess and in the posts for attaching therein each velum preselected from pericardial tissue.
The means of attachment of the valve con-sist, for their part, of a ring of silicone rubber, specifically Silastic, coated with tubular polyester fabric, specifically Dacron, to accept the stitches for suture of the patient's ring and thus to implant the valve.
Lastly, the selective facing of pericardium consists of calf pericardial tissue treated with puri-fied glutaraldehyde in solution buffered with phosphate salt at pH 7.4, without pressure, and is 1.6 to 2.2 mm in thickness. The attachment of the pericardial tissue under pressure O has to be stressed, improvement which, apart from the valvular design, enables distortion of the tissue fibers to be avoided at the stage of at-taching the same during manufacture, preserving their elasticity in a natural manner and facilitating mould-, , . .
' - -ing of the valvular recesses. This involves better con-figuration of the same and hence of the coaptation area of the vela, reducing the mechanical stress. The use of polarized light has allowed the natural direction of the tissue fibers to be obtained, as well as a greater concentration of fibers in the stress areas close to : the posts and in the coaptation areas.
The valve of the invention has been sub-jected to various tests of functioning. Thus, in vitro studies (Prof. H. Reul, Helmholtz-Institute for Biomedical Eng., Aachen Germany) have demonstrated ; that, with the valve's internal lininy of treated peri-,j cardium, the durability of the valve is increased to the point of attaining four hundred million cycles, which means a three-fold increase in mechanical dura-bility. In addition, and to eliminate failure through the wearing of holes or loss of attachment of the vela to the posts of the frame, the profile of the velum has been increased with respect to the profile of the posts and the assembly has been covered with pericardium, a new approach to attachment of the pericardial vela to the posts of the frame, so that there are no suture stitches around the post to attach the vela and keep them competent, new concept which eliminates the loss of attachment of the suture to the posts, further in-creacing the coaptation area of the vela having been developed also. Furthermore, and given the hydraulic characteri~tics of pericardium valves mounted on the outside of the frame, which are always superior to other biological valves, the thickness of the pericar-dium of the lining has been reduced, the latter being made so that the valve preserves its effective internal orifice to the maximum extent. That is to say, its me-chanical durability has been increased by means of the selective internal lining of the pericardium and the :. , A

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attachment to the posts of the frame, and the optimal hydraulics of these designs are preserved.
For the purpose of presenting a more de-tailed disclosure of the invention, a preferred embodi-ment of the latter will next be described, reference being made to the attached diagrammatic drawings, wherein:
Figure 1 illustrates the frame of the valve of the invention;
Figure 2 shows the selective facing of the frame with treated calf pericardium:
Figure 3 is a sagittal section of the valve of the invention;
Figure 4 shows the valve now mounted with the pericardial vela; and Figure 5 illustrates the internal projec-tion of the valve with the semicircular shape of the three recesses faced with pericardium in the inner part of the posts.
As seen in Figures 1 to 5 of the drawings, the valve of the invention includes a frame made of highly fatigue-resistant acetate copolymer, known by the name of Celcon, which is composed of a valve ring 1 and some posts 2 which stand up from the ring and de-fine recesses between them, between five and six holes 3 being made in each recess and in the posts for attaching therein each velum 4 preselected from peri-cardial tissue and according to the valve sizes. The scalloped or shell-like shape of the ring for each re-cess of the valve is observed in Figure 1.
Figure 2 shows a velum 4 separated from the valve, while the vela applied to the valve are shown in broken lines. In this figure, A has been used to desig-nate the attachment of the pericardium to the posts 2 of the frame, as well as the internal facing or lining, and each velum 4 of pericardium preselected to be at-:. .
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- tached to the posts 2 is shown by B. Once the vela 4 have been mounted, the external positioning of each velum and its projection with respect to the posts are observed, as well as the profile of the latter.
In Figure 3, A has been used to designate the calf pericardium of the velum 4, B the attachment of the pericardium to the frame, C the valve ring faced with tissue, D the suturing ring made of silicone rub-ber (Silastic) coated with tubular polyester fabric (Dacron), to accept the stitches for suture of the pa-tient's ring and thus to implant the valve, and E the pericardium now attached to the frame.
In Figure 4, the vela 4 now attached at the base and along the whole length of the scallop and of the posts 2 of the frame are shown at A and B. All of the pericardial tissue of the vela is treated with pu-rified glutaraldehyde in solution buffered with phosphate salt at pH 7.4 and without pressure.
Lastly, Figure 5 illustrates the semicircu-lar shape of the three recesses of the valve with a se-lective internal facing of pericardium which has been designated 5 and which, as stated, has been applied by sewing to the frame a treated pericardium tissue be-tween 1.6 and 2.2 mm in thickness.
As examples of specific embodiment of the heart valve of the invention, it is appropriate to point out that this valve is structured in such a way that the thickness of each pericardial velum varies be-tween 0.3 and 0.45 mm for valves with external diame-ters of 19 to 23 mm, between 0.42 and 0.52 mm forvalves with external diameters of 25 to 29 mm and be-tween 0.50 and 0.62 mm for valves with external diame-ters of 31 to 33 mm. Consequently, the sizes of the valves which are to be implanted vary between 19 mm in external diameter, including the Dacron coating, and 33 mm.

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Furthermore, the projection from the base of the valve to the top of the posts of the frame with the vela already mounted is, in millimeters, 7 for size 19, 8 for sizes 21 and 23, 9 for size 25, 10 for sizes 27 and 29 and 11 for sizes 31 and 33. The coated internal - diameters, in millimeters, are 15 for size 19, 17 for size 21, 19 for size 23, 21 for size 25, 23 for size 27, 25 for size 29, 27 for size 31 and 29 for size 33.
The foregoing description relates to what is considered to be the preferred embodiment of the heart valve of the invention. Nevertheless, experts will un-derstand that it will be possible to make various modi-fications of detail in the structure of the valve de-scribed and illustrated without departing from the spirit and scope of the invention. Consequently, it is maintained that the scope of the invention is limited only by the content of the attached 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. Artificial heart valve to be substituted for diseased or malfunctioning human valves, characterised in that it comprises a flexible frame composed of a valve ring (1) and some posts (2) which stand up from the ring and define recesses between them, the part of the ring corresponding to each recess being shell-shaped or scalloped; some vela (4) for opening and closing the valve, attached to the said frame, the said vela being dimensioned in such a way that their profile projects beyond the profile of the said posts, without there being any prosthetic material on the outside of the said posts;
a selective facing or lining of pericardium (5) applied to the said frame; and some means (D) of attachment of the valve to patient's heart tissue.

2. Heart valve according to Claim 1, characterised in that the frame is made of a highly fatigue-resistant copolymer and has between five and six holes in each recess and in the posts (2) for attaching therein each velum (4) preselected from pericardial tissue.

3. Heart valve according to any one of the preceding claims, characterised in that the means (D) of attachment of the valve consist of a ring of silicone rubber coated with tubular polyester fabric, to accept the stitches for suture of the patient's ring and thus to implant the valve.

4. Heart valve according to any one of the preceding claims, characterised in that the selective internal facing of pericardium (5) consists of calf pericardial tissue treated with purified glutaraldehyde in solution buffered with phosphate salt at pH 7.4, without pressure, and is 1.6 to 2.2 mm in thickness.