CA1184703A - Low profile prosthetic xenograft heart valve - Google Patents

Abstract

LOW PROFILE PROSTHETIC XENOGRAFT
HEART VALVE

Abstract Prosthetic heart valves having a low profile are disclosed which comprise an annular, right cylindrical, metal stent covered with fabric around which a glutaraldehyde-stabilized pericardial valving element is attached. The valving element is formed of three leaflets, each having a plateau on a truncated triangle extending higher at the center than at the edges, and formed as a cylinder having a diameter substantially equal to the diameter of the stent. In a preferred embodiment of the invention, the stent has upright legs which have radiused upper tips which are approxi-mately one-half the width of prior art stent legs.
These narrow tipped stent legs reduce stress induced in the leaflets by curvature of the leaflets around the tips of the stent legs in the closed position, extending the service life of the valve. Tabs are added to the tips of the stent legs to add structural strength. These tabs can be tapered or straight but their bottom portions must be narrower than the stent legs. The tabs have a plurality of holes in them through which coaptation stitches are passed. The coaptation stitch can be two separate stitches, one in a first plane and one in a second plane at 90°
to the first plane, or, in the preferred embodiment, a single figure eight stitch passing through the holes in the tab in a plane coincident with the long axis of the stent leg.

Description

P.C. 6349 LOW PROFILE PROSTHETIC XENOGRAFT
.
HEART VALVE
The early development of prosthetic heart valves is well documented in papexs given at symposia in 1960 and in 1968, published in PROSTHETIC HEART VALVES, Lyman A. Brewer III, Ed., Charles C. Thomas Publishing Co., Springfiled, Illinois (1969), Second National Con~erence on Prosthetic Heart Valves; PROST~ETIC
VALVES FOR CARDIAC SURGERY, K. Al~in Merendino, Ed.,~ Charles C. Thomas Publishing Co., Springfield, Illinois ~19ol).
Lefrak and Starr recently surveyed the develop-ment of cardiac valve prostheses, E.A. Lefrak and A. Starr, CARDIAC V~LVE P~OSTHESES, Appleton-Cen-tury-l~rofts, New York, 1979 and the development of tissue heart valves has been comprehensively reviewed by : Ionescu, Marian I., TISSUE HEART VALVES, Butterwor-ths, Boston, 1979.
Great efforts have been expended in the develop~
ment of tissue heart valve prostheses and in the development of supportive structures, or stents, ~or tissue valves. Representative of ef~ots to develop stents for tissue valves are the disclosures in the ~ollowing United S-tates patents: Patent 3,570,014, W. D. Hancock, March 16, 1971; Patent 3r7141671, Willi.am Sterliny Edwards et al, February 6, 1973;
Patent 3,755,823, W. D. Hancock, September 4, 1973;
Patent 3,983,581, William W. Angell, October 5, 1976;
Patent 4,035,849, William W. ~ngell e-t al, July 19, 1977; Patent 4,079~468, Domingo Santo Liotta, Marc~a 21 1978; Patent 4,084,268, ~arian I. Ionescu et al.~
April 18, 1978; Patent 4,106,129, Alain F. Carpentier et al, August 15, 1978; Patent 4,172,295, Richard J.
Ba~ten, October 30, 1979 and Paten~ 4,192,a20, Richard B. Davis e~ al, March 11~ 1980~ Other structures are also reported in the aforementioned treatisçs on heart valve develop~ents.
A number of specific tissue valves are described in the following publications:
o w~ Sterling Edwards et al, MITRAL AND AORTIC VALVE
R~PLACEMENT WIT~. FASCIA LAmA ON A FRA~IE, Jou~al of Thor~cic & Cardiovascular Surgery, Vol~ 5B, N~. 6, Dece~ber 1969r Pages 854-858; Ionescu, M.I. et al, EEART VALVE REPLACEMENT WITH IOMESCU-SHILEY PERICARDIAL
~E`~OGRAFT, Cardiology_Di~est, June 1977, Page 45;
Ionescu, M.I. et al, HEART VALVE REPLACEME~IT WITH THE
ESCU-SHILE~ PERICARDI~L XENOGRAFT, The Journal of ~h~racic and Cardiovascular Surgery, Volume 73, Pages _ 31 - 4Z, 1977; Tandon, A. P. et al, ~ONG-TERM
~AE?~!ODYNAMIC EVALUATION OF AORTIC PERICARDIAL XENOGRAFT, British ~eart. Journal, Volume 40, Pages 602-~07, 1978;
Ionescu, M.I. et al, LONG-TERM CLXNICAL AND HAEMO~YNAMIC
E~ALUATION OF THE IONESCU-SHILEY PERICARDIAL XENOGRAFT
ElEA~T VALVE, ThOraXChirU~ie~ VO1Ume 26, PageS 250-258, 1978; Ionescu, M. I. et al, LONG-TERM SEQUENTIAL
HEMODYNAMIC EVALUATION OF RIGHT VE~TRICUI.AR OUTFLOW
TRACT RECONSTRUCTION USIMG A VALVE, MECHANISM, The Annals of Thoracic Sur~ery, VO1Ume 27, No. 5, ~a~ 1979;
RQSS, D. N., FLEXIBLE BIOPROSTHETIC PERICARDIAL HE~RT
VALVE, Thoracic & Cardiovascular Sur~ery, Volume 28, Pages 150-152, 1980.
Particular techniques for preparing, handling and storing tissue valves are disclosed in U.S. Paten~s Nos .

3,966,401, Hancock et al, June 29, 1976, and 4,182,446, Penny, January 1980.
Some of -the earliest heart valve prostheses were flexible two-or three-cusp valves in which the cusps wexe constructed of vaxious types of fabric. Some of thQse flexible leaflet valves had good flow charactPristics but most failed early.
The leaflets tore, separated from the annulus, or become rigid due to fibrous tissue ingrowth. From about 1960 into the 1970's the trend was to mechanical ~alves. These ranged from the mecahnically quite simple Starr-Edwards valve to the relatively sophisticated Bjork-Shiley valve and includPd a nwmber of disc poppet valves. These ~echanical ~alves generally dominated the market and are still ~ery satisfactory for many applications. Tissue valves are hcwever the preferred treatment where anticoagulation therapy is not tolerated by the patient.
~n 1962, Donald Ross and Sir Brian B~rratt-Boyes, working independently, were performing implanatations o~ homograft tissue valves, some of which were free graft implants and some of which were ~ounted on supporting stents. Fully clothed covered rigid stents were used in some of these homograf-t valves.
In 19~5, Drs. Binet and Carpentier, and their associates, implanted a specially prepared porcine aortic valve xenograft. These porcine valves were sterilized and treated, e.g. with formaldehyde, and were commonly attached to a metal stent. Experience showed that these valves were of short life, largely because formaldehyde w~s used as -the cross-linking agent. Formaldehyde was found to create reversible cross links in the tissue, thereby allowing ear~y breakdown of the tissue. ~r~ Carpentier, in about .,~ ~

3 ~ 3 1968, established th~ concept oE the bioQrosthesLs by substantially eliminating anti~enicity of the tissue, principally by changing the preservative from formaldehyde to glutaraldehyde. Glutaraldehyde has been shown to create cross links of a more permanent nature than those created by for~aldehyde.
A number of porcine bioprostheses and specially designed stents for supporting these prostheses resulted from the efforts of Warren Hancock e~ al.
Generally, pig aortic valves are procured under clean conditions, placed in a cold, balanced electrolyte solution, ~xcess tissue is trimmed and the xenogra~ts are immers~d in 0.2~ glutaraldehyde. The leaflets are held in ~heir nor~.al valving position under pressure during the tanning process and each valve :i5 sutured to a cloth covered stent by sutures. A
nu~ber of clesigns and stent constructions for the ~ancock type valve are exemplified in the a~orementioned United States Pa~.ents Nos. 3,570,014 and 3,7S5,823.
Stents for poxcine valves were developed ~y a number of other workers also, see, e.g., U.S. Patents Nos.
3,983,581; 4,035,849; 4,079,4~8 and 4,106,129.
Stents for supporting cusp val~es of other tissue members, e.g. fascia lata and pericardium, have been developed by a number of workersr see, e.g., U.S. Patent 3,714,671, and Edwards et al, MITRAL AND AORTIC VALVE REPLAC~MENT WITH FASCIA
LATA ON A FRAME, supra. Much of the pioneering work in this area of valve development was done by Dr. Martin I~ Ionescu and his associat~s, see, e.g., Bartek et al, FRAME-MOUNTED TXSSUE HEART VALVES:
TECHNIQUE OF CONSTRUCTION, Thorax, Volume 29, Pages 51-55, 1974; Ionescu et al, HEART ~ALVE REPLACEMENT
WITH IONESCU-SHILEY PERICARDIAL XENOGRAFT, Cardiolo~y 1~~7~3 Di~est, June 1377; Ionescu et al, HEART VALVE
REPLACEi!~ENT r~ITH IONESCU-SHILEY PERICA~I~IAL XE~iOGRAFT, The Journal of Thoracic and Cardiovascular Surgery, Volume 73, Pages 31~42, 1977; Tandon et al, ~ONG-TERM
:
S ~AEI`~ODYNAMIC EVALUATION OF AORTIC PERICARDIAL XENOGRAFT, British Heart Journal, Volume 40, Pages 602-607, 1978;
Ionescu et al, LONG-TERM CLINICAL AND HAEMODYNAMIC
~VALUATIO~ O~ THE IO~ESCU-SHILEY PERICARDIAL XENOGRAFT
~ART VALVE, Thoraxchirugie, Volume 26, Pages 250-258, 1378; Ionescu, et al, LONG-TERM SEQUE~TIAL
~EMODY~AMIC EVAL~ATION OF RIGHT VENTRICULAR OUTFLOW
TRACT RECONSTRUCTION USI~G A VALVE MECHANISM, The Annals of Thoracic Surgery, 27, 425-434, 1979i and IonPscu, Editor, TISS~E HEART VALVES, Butterwort~s, 1979 A number o-f improvements in the basic Ionescu tissue heart valve have been made. For example, a tissue heart valve has been developed which has a cloth-covered stent of special construction, in which tha outflow annulus diameter of the valve is defined and limited by the positioning of a coaptation stitch on ~he inside o~ the supporting legs of the stent, as has been the practice since the early developmen~
of the Ionescu type tissue heart valve. Another improvement in the method for aligning the tissue of the cusps of the Ionescu type heart valve is described in U.S. Patent No. 4,172,2~5, which also discloses the coaptat.ion stitch inside the stent legs.
It has been the practice, in order to achieve a maximum flo-~ orifice in valves oE implantation diametexs less than or equal to 23 mm, to splay the stent legs outwardly in an effort to achieve a full-flow orifice inside the coaptation stitches.

~ hile these various modifications and improve~
ments in the basic Ionescu valve over the years have solved some of the problems, there remains a number of problems which have not been solved. One potential problem is that stress is concen-trated in the tissue in some areas where sharp bending of the tissue around the stent occurs. Some measures can be taken to relieve this stress. The s~ress tends to be highest at points o~ maximum curv~ture such as around the tips of the stent legs because o the pinching o~ the tissue leaflets together inside and above the tip of the sten-t leg.

The problems described above are largely or entirely solved by the present invention.
According to a broad aspect of the present invention, there is provided a prosthetic heart va]ve comprising: a) a stent comprising: 1) a ring with scallops formed therein defining an aperture with inflow and outflow ends; and 2) a plurality of legs coupled to said ring extending upwardly toward said outflow end, said stent being dimensioned such that the quotient of the radius of curvature of mobile tissue measured at the point of greatest curvature divided by the thickness of said tissue is greater than or equal to five at all points of contact between said tissue and said stent; b) a plurality of tissue leaflets attached to said stent and to each other to form a valving ele-, ..
ment; and c) a plurality of coaptation means in the vicinityof the tips of said stent legs for causing joining of the edges of said tissue leaflets.
More specifically, the present invention comprises an improved tissue valve prosthesis of the Ionescu type. The improved prosthetic heart valve of this invention comprises a stent which includes an annular base integrally formed with three legs which extend upwardly to the outflow ends of the legs. The space between the legs is configured to form genera~ly ellipti-cally shaped scallops having a depth ~ measured from the top of the legs to the bottom of the scallop. The stent, circumferen-tially, forms a right cylinder having a uniform interior diameter D, the legs extending parallel to the axis of the righ-t cylinder.
The lower edge of the stent forms scallops which correspond gen-7~-erally to the arc of the scallops between the legs. The scallops of the lowex edge of the base and the scallops between the legs vertically define three generally elliptically shaped one-third portions of the base between their respective upright legs. A
fabric covering totally encompasses and follows the configuration of the stent and an annular sewing ring is attached to the fabric covering and extends outwardly from the base. A tissue valve element is formed of three tissue leaflets, joined -to form a generally cyllndrical three-cusp valving element, each of the leaflets having a top edge forming a truncated triangle with a central high plateau tapering down on each side of the plateau to the corners adjacent the sides of the leaflet, giving the top of each leaflet a generally very obtuse, flat topped general-ly truncated triangular configuration. Conventional stitching or other means are utilized to attach the tissue valve element around i,~
" p .

the fabric covered stent to the fabric, around the annulus for~ed by the stent and up the outside surface o the fabric covered stent legs. A co-aptation stitch through the tissue leafl~ts adjacent the upper edge thereof, and disposed directly above the top of the fabric covered stent, fixes the leaf-lets in position to form three cusps each having an upwardly extending point, extending in the outflow direction, midway between -the legs. The upper edges, or outflow edges, of the cusps meet, in -the closed position of the valve, with the points adjacent each other. In -the open position, the tissue valve element forms a cylinder having an inside diam~-ter ak the top o~ the valve substantially equal to the inside diameter of the fabric covered s-t~nt, the flow path through the valve generally being in the con-fi~uration of a right cylinder with the axis of the cylinder corresponding to the flow axis oE the valve, the legs and the stent forming a circumferentially right cylindrical surface around the axis, with the suture or sewing ring forming an annulus around the stent~
For convenience, in describing the valve, the outflow end of the valve is depicted at the top of the drawings and the valve is described in this con-Eiyura-tion; thus, the upward or top portion oE the valve would,correspond to the ou-tflow portion of the valve and the bottom would correspond to the inflow end of the valve.

. .. . . _ -- . .. . _ .. . ..

A significant feature of th~ prescnt invention resides in -the preferred configuration of the s-tent legs wherein the ra-tio defined as the value of the radius of curvature of tissue around the inside top of said leg measured at the point of greatest curvature divided by the thickness of the tissue is approximately five or more. The width o~ the post top is approximately from 0.760 to 1.05 millimeters and the thickness of the cloth covered post top is approximately 2 millimeters. The tissue thickness in the pre~erred embodiment is approximately 0.3 milli-met~rs. The tissue does not pinch together inside such narrow pos-ts during closure at physiological pressure and an inside radius of curvature equal to or greater than 1.5 millimeters is obtained. The life of a valve using such a sten-t will be extended beyond that of a valve with a smaller radius of curvature.

.

7~3 The i~proved stent is also designed so tnat the ratio of the radius of curvature o~ the tissue around the fabric-covered stent at a point between the up~
right stent legs divided by the khickness of the tissue is greater than or equal to five.
~ dditional strength to the legs is provided by inwardly projecting tabs whiLch are, preferably, inte-gra1ly for~ed at the tips of the legs, conforming to tke width of the stent leys at their tips but narrower than the stent legs at the botto~ of the tabs, said ta~s extending both vertically down the leg for a pre~
determined distance and inwardly toward the center axis of the stent. Apertures are formed in the tabs through which the coaptation stitches ~ass to register the coaptation stitch directly above the stent leg.
The coaptation stitches can be in either of t~o e.~badim2nts. Tne first embodiment consists of two separate stitches, one passing through one aperture in the tab and defininy a plane generally parallel to the long axis of the stent legs and tied off abo~e the tips o~ the stent legs, and the other stitch passing through another aperture in the tabs and defining a plane which is generally perpendicular to the plane defined ~y the first stitch, said second stitch belng tied off at the outside ed~e of the stent leg. The second embodiment of the coaptation stitch is a single stitch passing through a plurality of holes in the tabs which deEines a plane which is parallel to the long axis oE the stent leg.
The second embodiment is the preEerred emhodiment and generally defines a figure eight pattern -through a pair of holes in each tab.
The inward projection of the tabs -toward the center of the flow aperture of the valve is also limited to preven~ touching between -the tissue leafle-ts and the bottom of the tabs. Generally this 47~3 distance of inward projection is li~ited to forth thousan~ths of an inch in the naked stent, i.e., no more -than forty thousandths inward projection of the bare plastic tab. The width of the tabs is also limited to aid in preventing the bottoms of the tabs from touching the tissu~ leaflets.
In the preferred e~odiment, the widths of the ta~s re~a1ns constant throughout their length while the widths o the stent le~s increases at points farther f~o~ the tips of the stènt legs. In another embodiment, the widths of the tabs decrease at points further ~ro.~ the tips of the stent legs irrespective of the widths of the stent legs.
FIGURE 1 is a perspective view of a completd va~ve of th.is inventio~.
FIGURE 2 iS an exploded view of the cloth covered stent and the valving ele~ent ~ormed of three leaflets prior to attachment to the sten-t.
FIGURE 3 is a perspective view o~ t'ne preferred s~ent configuration.
FIGURE 4 is a sectional view of the curvature o~ tissue around the covered stent leg taken along line 4-4 in FIGURE 2.
FIGURE 5 is a top view of the stent shown in perspective in FIGURE 3.
FIGURE 6 is a sectional view taken along section line 6-6 in FIGURE 5.
FIGURE 7 is a partial perspective view of ~he coaptation of the tissue lea~lets with the stent leg and coaptation stitch.
FIGURE 8 is another partial perspective view showing the view of FIGURE 7 in a later stage of manufac-ture.

gJ 3 FIGUR~ 9 is a t~p plan view, vie~ed ~rom the outflow en~, of the completed va~ve in the fully open position.
FIGURE 10 is a section~l vîew of tne cur~ature Or tissue around the stent taken along s~ction line 10-10 in FIGURE 2.
FIGURE 11 is a detailed view of an embodiment of the coaptation stitching.
FIGURE 12 is a detailed view of the preferred e.~odim~nt of the coaptation stitching.
FIGURE 13 is a detailed view of a typical tab a~d stent leg tip showing the relative widths of each.
FIGURE 14 is a detailed view of another embodi-~nt of a typical tab and stent leg tip s~owing t~e relative widths of eacn.
FIGURE 15 is a top view and a sectional view, t Xen along the section line in the top view, of a ~rior art stent utilized in one of the improvements of the basic Ionescu valve, with the measurements thereof shown for purposes of co~parison with the present in~/en-tion.
FIGURE 16 is a flat plan view of the outline of one of the leaflets used in the present valving element, before the sewing of three such leaflets toge~her ~o Eorm a cylindrical valving me~ber.
FIGURE 17 is a top plan view, viewed from the outflow end, of the completed valve in -the ful~ly closed position.
FIGURE 18 is a partial cross-section taken along line 1%-18 in FIGURE 8 showing the closed cusps of the valve leafle~s along the closure line.

71~3 FIGURE 1 snows a low profile pericardial xenogra~t heart valve 10 which comprises a valving elemen-t 20, a stent asse~bly 102 and a suture or se~ing ring assembly 200. The coaptation stitches 130, 132 and 134 cause coaptation or joining of the edges of the -tissue leaflets of valving element 20 in the vicinity of the tips of the stent legs thereby forming xadial coaptation lines 133 in PIGURE 1.
FIGURE 2 depicts an exploded view oE the tissue ~alving elemen-t 20 prior to attachment of the stent 102, and generally shows the three stitch seams 22, ~ and 26 which jOill the three tissue leaflets 30, 5~~ and 70 into a right cylindrlcal valving element.
This valving ele~ent is then sewn to the cloth-covered stellt 102.
FIGTJRE 16 deplcts one of the leaflets, leaflet 30, of the valving element 20, as exemplary o~ all of the leaflets 30, 50 and 70, all of which are sub-s~antially identical. The leaflet 30 is a generally ~lat layer ~r sheet of pericardium tissue, trea-ted as will be aescribed and discussed in more detail hereinafter, and includes a curved bottom 32 and curved sides 34 and 36 with a top, or outflow edge generally indicated a~ 40. The top 40, however, comprises three distinct portions. Edges 42 and 44 converge upwardly like symmetrical sides of a triangle to a central plateau 46 at the top and form obtuse corners with the sides 34 and 36, respectively, on the bottom. Each o~ the lea~lets 50 and 70 are to be understood as including corresponding elements, `~ 76~3 including the top or outflow edges 60 and 80, as shown in FIGURE 2, for exa~ple, and plateaus 5 and 86 correspondins to plateau 46. The three leaflets 30, 50 and 70 are in all essential respects identical, although there will be some ~inor variation in the exact shape and size oE these leaflets because they are made from naturally occllrring tissue and considerable manual dexterity and skill is required in production. Minor ~riations, so long as the function is not irnpaired, ~re readily tolerated in the present valve cons~ruction.
The shape of the leaflets 30, 50 and 10 is ve~y i~portant to the proper functioning of the ~-alve, although precise dimensions are not critical 1~ because minor deviations and di~ensions can be compensated f:or in the final joinder of the leaflets into the valving element and in Eitting the valving ~le~ent over the stent. One portion of -the con-figura~ion of the leaflets is of vital importance to the optimum fun~tioning of the present invention, although the invention will function in an improved manner over t:he prior art even if vexy minor devia-tions are permitted~ This important portion of the configuration is the truncated triangular top edge converging to the plateau 46 in FIGURE 16 and to plateaus 66 and 86 in the leaflets 50 and 70. The base of the triangle is, of course, an imaginary line joining the lower corners of the top edge.
Plateau 46 is centrally located between the juncture of the outElow edge portion 42 with side 34 and out-flow edge portion 44 with side 36. The best deEinition of the shape of this ob-tuse truncated triangle defined by the plateau 46 and the juncture of the top edges 42 and 44 with the sides of the leaElet, is that this truncated triangle is so configured and dimensioned that when the three leaflets are sewn together at their respective edges to form a cylinder, and fitted over a s-tent, with a coaptation stitch posi-tioned directly over the end of the stent when thevalve is closed, the plateau 46 of the leaflet 30 to~ches, or substantially touches, the corresponding plateaus 66 and 86 of the leaflets 50 and 70, with no more than about l mm of face-to-~ace contact, in the center o~ t'ne flow path of the valve with s~bstantial face-to-face contact, i.e~ from about

2 .~m to about 6 or 7 mm, between the interior surfaces of the edges intermediate the center and the outer diameter of the valve~ Exactitude is not - 15 pe~îectly required, but it is required t~at the p~ateaus ~6, 66 and 86 be in touching or substantially in touching relationship when the valve is ~losed, a~d that there be substantial surface-to-sur~ace co~tact alony the central portion of the xadial coaptation lines of cusp contact. This relationshi~
is. shown in FIGURE 18 which depicts the valve of FIG~RE l cut perpendicular the radius de~ined by the cusp coaptation line 133, the area Qf contact being shown at 90. The maximum face-to-face contact is about halfway be-tween the center and the legs and would be at .least 2 or 3 mm but not more than 9 or 10 m~, optimally from 3 to 7 mm dependiny on valve size .
It is neither necessary nor possible to ~ive exact shape and dimensional definitions to the leaflets exemplified by leaflet 30, but -the configura-tion may be described, realizing that the truly ~8~7~;~

critical. relationship is t~e interrela~ionship of the three obtuse truncated triangular portions.
The maximum width of the leaflet lies about midheigh-t thereof. The height of the leaflet is, af course, of no criticality whatever, and so this is merely a general relationship~ Thus~ the surn of S~, Sb and Sc (see FIGURE 16) is approximately equal to one-half of the total vertical height of ~he leaflet, Sa representing the mean altitude o~ the obtuse truncated triangle formed by plateau 46~
converging edge portions 42 and 44 and ~he base ~e~ined by the junctures of -top ed~e 40 with side 34 and side 36, respectively, Sb plus Sa being equal to about 35% plus or minus 3 to 5~ of the total ~3tical height, and the sum of Sa, Sb and Sc being about 50~ plus or rninus around lO~ of the total vertical height. The width of the leaflet, ~a, measured Sa down frorn the plateau 46 is about 85%
plus or minus 10% of the maximum width, ~c~ of the lea~letr Sa being around 12 to 17% of the total - vertical height. The width Wb measured at Sa plus Sb from the plateau 46 is about 95% plus or minus about 5% of the ma~imum width. The exact width and height ratios depend yenerally upon the overall size of the valve and will usually fall within the ranges indicated, although the firs~ deEinition by function is the best and rnost rneaninyEul description pre~ently comprehended. In a speci~ic embodiment, the valving member for the size 23 valve is a section of pericardium 0~012 inch thick, with a maximum height of ~l millimeters and a maximum width Wc of 26.5 millimeters at about 526 of total height. The ~.

4~3 width Wa of the obtuse trlangle is 22.5 millimeters measured at Sa down about 14% of the total height from the topJ the intermediate width Wb being 25.5 millime~ers at Sb7 35% from the top. Again, this is merely one example of one size of a valve and the dimensions are not the critical factor; it is the interrelationship of the top edges of the lea-flet that is critical.
Glutaraldehyde has been used effectively to stabilize connective tissue for clinical heart valve substitutes for several years. The tissue leaflets of the present invention are cut from lQ pericardium tissue, although other tissues may be used. The use of formaldehyde and glutaraldehyde tanning in preservation of tissue is described by E. Aubrey Woodruff, The Cllemistry and Biology of Aldehyde Treated Tissue Heart yalve Xenografts, in lonescuJ TISSUE
HEART VALVES, Butterworths, 1979. ~oodruff and other contributors to TISSUE HEART VAL~ES discuss in detail the glutaraldehyde tanning and preservation of connective tissue. In the preferred embodiment of the present invention, pericardium treated with .5% glutaraldehyde at pH 7.~ without fixing the tissue in a prestressed condition is preferred; however, it is to be understood that the invention dis-closed and claimed here relates to the configuration of the valving leaflets and element and the supporting stent, and any suitably preserved tissue may be utilized in the present invention.

7~

The stent ass~mbly refers generally to the entire stent asse~ly which includes a biolo~ically compatible metal or plastic stent 102. The s-tent 102 defines the configuration o~ the stent assem31y.
S Thè stent 102 may be considered as three one-third protions of a stent integrally formed of one piece of material although, of co~rse, the method of - formation or the number of pieces is of no conse~uence rovided the completed stent is as described ~erein.
L~e stent 102 co~prises an annular base or ring 10~
S.~ich extends aro~nd and defines the Elow orifice of ~9 valve. Coupled to the ring or integrally formed t~erewith are a plurality of stent legs extendi~g upwardly a dis-t2nce H toward the outflow end of the valve from the lo~ermost portion o~ the base. There are three substan-tially identical legs 106, 108 a~d ilO~ each separated from its neighboring legs hy sc~llops 112 as best shown in FIGURE 3. The bottom or inflow edge o the stent 102 is also scalloped to c-onorm generally to the ar_ of the scallops betw~en t~e legs. rrhese bottom scallops generally follow the configuration of the scallops 11~ of the outflow edge so as to generally ~orm parallel edges defining ring or base 104. The scallops of the lower or inflow edge of the base and the scallops of the out~low edge between the legs vertically de~ine three generally elliptical shaped one-third portions o~ the base between the centerlines of the respective upright l~gs which together circu~ferentially form a right cylinder oE constant diameter having an inside diameter D with the legs extending parallel to the axis of the cylinder as shown in FIGURE 5.

76~3 The stent assembly, in the preferred embodiment, also includes a fabric covering which totally or at least substantially encloses the stent 102. It is not essential to the functioning of the presen~ valve that the stent be cloth-covered, but it has been long recognized that there are structural and biological advantages to the use of fully cloth-covered stents for supporting tissue valves. This concept predates the present invention and constitutes no part thereof but is simply adopted as part of the best mode in carrying out the present invention. The fabric covering described in detail by Ionescu et al in United States Patent ~,084,268 has been generally adopted, and the same techni-ques are applied in the present in~ention as are taught in United States Patent 4,084,268 e~cept for the improvements dis-closed herein. Reference is made to United States Patent 4,084,268 for specific details of the fabrics, knots, sewing and techniques. It IS sufficient here to describe the stent assem-bly as including a cloth covering which encloses or substantially encloses and conforms to the stent.
FIGURE 7 is a partial cross-section depicting a fabric 120 enclosing the outside of the stent~ a fabric 122 which encloses the inside of the stent, with a suitable seam area 124 joining the fabrics along the top or outflow edge of the stent.
A fabric 126 is joined along the lower edge o the stent and exten~ls outwardly forming part of and attaching a sewing or suture ring generally indicated at 200 which may be of any of the forms used in the prior ar*.

~I 19 Generally, sucn sl~ture rings co~prise a plurality of layers oF fabric and paddiny, 202, 204 and 206, enclosed in layer 126~ soft enough to permit ~he suturing needle to be readil~ inserted through it and yet rigid and strong enough to provlde firm ~ounting of the prosthesis in the heart valve area.
The suture ring 200 o:E this inven~ion differs from th~ prior art suture rings only in ~hat it curves and confor~s to the scalloped contour o~ the valv~
r}ng or base derined by the portion 10~ of the stent 102~
The tissue leafle.s, after being sewn to form a cylinder as shown in FIGURE 2, may be sewn to the stent assem~ly in any conventional mann~r, as, for example, ~y running stitches shown in 210 in FIG~R2 7.
FI~URE 7 depicts the val~e in a partially completed con~iguration with the tissue leaElets 3C ~nd 70 joined by seam 22, the upper edges 80 and ~C suDstan-tially touching or just to-lching, wi-thout a large or ~ignificant surface-to-surface contact or the two leaflets. Coaptation stitch 130 is disposed directly over the tip 109 o~ the stent leg 108 and passes through a hole 121 in the tab 123 to form the radial coaptation line 133.
FIGURE 8 shows another stage in the construction of the valve shown in FIG~RE 7 by the addition oE the pledget and cover 220. This cover is sewn by stitches 222 to the stent leg through the tissue as described by Ionescu e-t al in U.S. Patent 4,08a,268, or it can be connected in any other co.nvenien-t rnanner. The fabric covering, the pledget, and the sewing, all as disclosed - 21 ~

with great particularity by Ionescu et al, supra, are utilized in carrying out the invention in its preferred embodiment, but they are not part of the invention per se.
Coaptation of the tissue leaflets is caused by the action of coaptation stitches 134, 130 and 132 shown in FIGURE
1. The present invention departs frorn the prior art in a very important and significant manner in the way in which the coapta-tion of the ed~es 40 and 60, the edges 40 and 80, as best shown in FIGURE 18, and the edges 60 and 80 abut in touching relation-ship. This coaptation is defined generally by the placementof the coaptation sti-tches 134, 130 and 132 directly above the respective stent legs 106, 108 and 110, the placement of the coaptation stitch 130 being depictedas exemplary in FIGURES 7 and 8. In prior art valves such as the one disclosed in U.S.
Patent 4,084,268, the coaptation stitch had been placed inside the circumference of the circle defined by the tips of the stent legs. Placement of the coaptation stitch directly above the tips of the stent legs tends to allow the orifice diameter of the fully open valve to equal the inside diameter of -the covered stent. FIGURE 9 illustrates a tissue valve in -the fully open position.
~ nother extrernely significant departure from the prior art is the relative height El of the stent 102, the depth U of the scallops between the legs of the stent 102, and the inside diameter D of the stent.
In the prior art it was considered necessary, or at least very importan-t, -that in smaller valve sizes, e.g. 23 mrr ., ~ (r ``~d,~

or less, the legs may be splayed outwardly from the base. Thus, referring to FIGURE 15, in the prior art stent 102', the input diameter Din was smaller -than the outflow diameter DoUt, DoUt being the diameter of the circle in which the legs at the outflow end of the valve lie. The coaptation stitches of the prior art were formed inside the legs, and the diameter of the circle on which these coaptation stitches were made to lie was made, or attempted to be made 7 approximately equal to Din. Thus, the stent, viewed circumferentially, e.g. from the end, was not a right cylinder, but was generally frustoconical because OL- the splaying. Sometimes, of course, the splaying of the legs was accomplished by bending the legs out from another wide cylindri-cal base, but the result was substantially -the same as a frusto-conical imaginary figure derived from the diameter of the inflow and the outflow ends of the valve.
In cont:rast to the prior art, the stent 102 of the present invention is, viewed circumferentially, a right cylinder, with the axis of the cylinder lying in the center of the flow path and the legs extending from the inflow end toward the out-flow end (the top as vlewed in the figures) of the valve parallelto the axis of the right cylinder. Thus, Din becomes equal to out-Also of great significance is the ratio U/D, D being equal, of course, to the inner diameter of the stent. As com-pared with what is regarded as the Glosest and most pertinent prior art, the Ionescu type valve described by Ionescu et al in U.S. ~'a-ten-t 4,084,268, various features oE which are also des-.~ .
,..~

1~47~3 cribed in U.S. Patent No. 41172,295 to Batten, the scallop depth U measured from the scallop bottom on -the outflow edge of the stent base 104 to the upper or ou-tflow end of the stent legs (see FIGURE 6), is very much less, Eor a given valve diameter, than the corresponding distance U' in the prior art stent depicted in FIGURE 15. In particular, the ratio of U/D in the present valve is between about .50 and about .65, and optimally from about .55 to .62.
It is important, of course, to obtain and maintain as low a profile valve as can be made to operate; but that alone is not the only significance of the a:Eoresaid ratio of U/D.
This result, long sought for but heretofore unattainable, is obtained by reason of the unique combinatlon of elements, config-urations, relationships, and dimensional ratios, which, acting together in a unique way, make it possible to provide a heart valve prosthesis, in which the valving element is a generally cylindrical tissue element, which has a profile of less than two-thirds the profile of prior art valves, which closes more rapidly than prior art valves of rela-ted cons-truction, and in which the stresses in the cusps of related prior art valves have been wholly or substantially avoided. This new result comes about by reason of the interac-tion and cooperative action and function o:E the U/D ratio of the stent, the posltioning of the coaptation stitch above the end of the stent leg, and -the unique configuration of the cusp leaflets of the valving element.

76~
- 2~ -As will be seen in FIGURE 9, when -the valve is in the fully open position, the flow path is substantially a right cyl-inder through the valve, with the coaptation stitches being placed directly above the legs. This has two functions. The first is of significance but, comparatively, of lesser significance than the other. The first result of this placement of the coaptation stitches is that a larger flow orifice i.s obtained without the necessity for splaying the legs of the valve. More importantly, the stresses of the prior art tissue valves at four o'clock and at eight o'clock, i.e. at the lower right and the lower left-hand portions of the cusp, when viewing the cusp straight on laterally, have been avoided without fluttering, rolling and floating of the edges of the tissue at the outflow end of the valve. This is a new and extremely desirable result which foll.ows from -the combination of configurations described. This result is accom-plished by reason of the unique configuration of the leaflets in which the valve element comprises three tissue leaflets joined to form a generally cylindrical valve element having three points which extend centrally of each of the custs respectively toward the outflow end of the valve and centrally between the ends of the legs, the valve element forming in the open position a cylin-der havlng three points on the outflow end thereof and, in the closed posltion, forming three cusps which arc inwarclly between the legs with the outflow end of the leaflets touching with the three points adjacent each other in the center oE the out:Elow end of the valve. It will be apparent from a consideration of the structure of the lea~lets -that, while in the preferred embodiment they are Eormed of three separate pieces, they may very well be formed of a single integral piece of tissue with appropriate cuttin~ and stitching such that the end result, the valving element, has the proper configura-tion~ mhu5, while it is convenient to star-t with three pieces of tissue r the same invention may be practiced with only one piece in which the three leaflets are inteyrally joined.
The shortening of the implant depth, to less than about two-thirds of the prior art stent heights of corresponding valves, and the adoption of the coaptation stitch directly above the ends of the legs, permit the use of the above described valving element while providing a substantial area of face-to-face overlapping contact along the radial contact lines of the cusps and obvia-ting the tenaency of the outflow ends of the leaflets -to roll, flutter, and atherwise to delay in closing or to twist and deform by minimizing the coaptation, at the center of -the valve, of the plateaus 46, 66 and 86.
A preferred stent design for tissue heart valves is depicted in detail in E'IGURES 3, 5 and 6.
FIGURE 3 shows the improved stent in perspective.
FIGURE 5 shows a top view of the stent, and FIGURE 6 is a sectional view of the stent taken along section line 6-6 in FIGURE 5. It is advantageous to use this preferred stent design in conjunction with the valving element 20 described above. Such a combination is a preferred method of valve construction in the present invention. However, the preferred sten-t design may he employed with other valving elements.

7~;~

The width W~ of the stent legs 106, loa and 110 at their tips 107, 109 and 111, as viewed in FIGURE
5, is substantially less than the width oE the tips of prior art stent legs. As shown in FIGURE 4, which is a detailed sectional view of the ~ip 107 of stent leg 106, the width Wt is equal to the diameter of the half circle defining the -tip if the tip is rounded.
In other embodiments where the tip is not rounded, Wt is measured between the points near the tip where the edges of the s-tent leg first start to curve in toward the center line oE the stent leg.
In the preferred embodiment of the stent design, the stent legs are rounded at their tips. The width of ~he stent legs at the tips thereof has been reduced from approximately 2.032 milli~eters in prior stents to a substantially narrower range of widths -from about G.76 mm to about 1.14 mm. This reduced width of the stent legs at their tips has the effect of in-creasiny the radius of curvature of the tissue inside the stent leg and tip. This cuxvature is caused by the action of the coaptation stitches 134, 130 and 132 in FIGURE 1 and by closure of the valve which causes collapse of the cusps 30, 50 and 70 toward the center of the valve under res-triction of the coaptation stitches. That is, the tissue leaflets 30, 50 and 70 curve less sharply together at the tips 107, 109 and 111 of the stent legs when the tips of the legs are narrower. This increased radius of curvature translates into reduced stress in the tissue of the cusps and a lonyer service life Eor the valve.

However, this reduced w:idth of -the tips of the stent legs 106, 108 ancl 110 in FIGURE 3 leaves less material in the stent legs to carry the s-tructural loading of the closed leaflets caused by the impulse pressure in the flow of blood caused by intermittent pumping action of the heart. To compensate for cne reduced width in the leg tips, tabs 120, 123 and 125 (see FIGURES

3 and 5) are added at the outflow end or -tip of each of the stent legs to add structural strength to the legs. These tabs prefer-ably project inwardly toward the center of the stent and are integrally formed with the stent legs and preferably conform to the width WT at the tips of the stent legs as seen in FIGURE 5.
The tabs extend both vertically down the stent leg for a distance Ht1, FIGURE 6, and toward the center of the aperture defined by the stent ring for a distance Tt.
The exact dimensions of the tabs,Wt, [-Itl, Ht2 and T
in FIGURES 5 and 6, are, within the parameters of this aspect of the invention, matters of design choice~ The strength of material used in constructing the stent will affect the choice.
Typical dimensions in the preferred embodirnent of the stent design are given in Table I below.
The tabs 120, 123 and 125 have apertures 12:L formed therein through which the coaptation stitches pass, It is pre-ferred that the coaptation stitches be passed throughthe holes 121 in the tabs since this registers the position of the coapta-tion stitch at a positive, repeatable location. The diameter of the holes 121 in the preferred embodiment is 0.813 mm, and the dimension Tt in FIGURE 6ischosen togive sufficient strength. The use of holes 121 ir. the tabs located as describod above insures good repeatability of manufacture because different assenbly t~orkers cannot change the ori ice diameter or induce stresses in the tissue by inadvert nt mislocation of the coaptation stitch too far toward or away from the center of the aperturer The tabs 120, 123 and 125 are included in the preferred embodimont because they have been found to be highly desirable and necessary, in many instances~ for surficient strength; however, the tabs are not al~ays necessary. With refined ~anufacturing techniques ~ adaptation of stronger materials, the tabs are e~p~cted to be eliminated or reduced in size. The ~unda;~ental concept disclosed herein is extension of t`r~e se-vlce life of the valve by reducing stress levels ~n the tissue by, among other things, utilizing narro~er, rou~;ded stent leg tips 107, 109 and 111 as shown in FIGU~S 3 and 4. Ideally, a substantially zero tip width woIld be desirable, but structurally this is impossible at present. The t`~i dth of the stent leg at its tip is made ~,ore narrow than heretofore known; however, the stated widtn of the tips of the sten-t legs in the preferred embodiment should not be understood as limiting the invention in any way.
A general guideline -for the narrowness of the stent leg tip is that the tip should be sufficiently narrow so that the quotient of the radius oE curvature of tissue together inside the stent ley tip divided by the thickness of the tissue is ~reater than or equal to five. The radius of curvature Rc of the tissue inside a typical stent leg tip is illustra-ted in FIGURE 4. This curvature is caused by the coaptation o-f the leaflets under pressure and tends to concentra-te shear stresses in the tissue a-t points 135 and 137 ~847~3 -- 2~ -where curvature is greatest. In the preferred embo~iment, -this ratio should be a minimum of approxima-tely five. That is, if the radius of curvature of the tissue around the -tip of the stent leg lS less than approximately five times the thickness T of -the tissue, then the tips of the stent legs are too wide. This gen-eral guideline has been shown to increase the service life of the valve; but the foregoing statement should not be understood as limi-ting the invention to a ratio of five.
It is critical that the stent dimensions be selected such that touching between the tissue and the stent is substan--tially eliminated or minimized, and the radius of curva-ture of the tissue around the stent is not smaller than a predetermined value. That is, touching between the tissue and -the sten-t is substantially eliminated or minimized, and the radius of curva-ture of the tissue around the stent measured at the point of greatest curvature divided by the thickness of the tissue should be greater than or equal to five. This curvature at two of -the various places on the stent where it occurs is illustrated in FIGURES 4 and 10. FIGURE 4 is a sectional view taken along sec-tion line 4-4 in FIGURE 2 looking down on the top o:E the stent leg. The center of the stent is toward the top of FIGURE 4.
The radius lines Rc illustrate -the radius oE curvature oE the tissue 21 -together inslde the stent leg -ti.p:L07 and the fabric covering 113 surroundiny the ti.p. The coaptation stitch 134 is seen to pass through -the hole 121 in the s-tent leg tip and is approximately centered above the tip of the leg.

4~76}3~

The points of maximum curvature 135 an~ 137 are seen to '~2 in the tissue at a point just inside of the center~ost cxtremity of the cloth covering 113. The thickness OL the tissue is desi~nated as T. The xatio

5 OL Rc~ should be greater than or eq~lal to fiv~ for e~tended durabilit~.
FIGURE 10 is another sectional view o~ a place of curvature oE the tissue around the stent taken along sec~ion line 10-10 in FIGURE 2~ ~gain, Rc indicates th- radius o curvature or the tissue 21 over t~le to~ of the clotn covering 124 surrounding the base rlng 104 of the stent. T indicates the thickness OL the tissue ana, fo- extended durability, the ratio RC/T should be ~r~ter than or equal to Ei~Je.
The reason for the above stated criteria oF tip narrowness is that most curvature of the tissue around t'ne stent leg occur~ at -the tips 107, 109 and 111 of the ste~t legs where the coaptation stitches 134, 130 and 132 in IGU~ 1 pull the cusps together. Thus, stress in the tlssue is concentrated ~here the radius oE curvature ls smallest as can be visualized in examining FIGURES 7 and 4. B~cause the tissue formed around the legs and inside oE the coaptation stitches is mobile, a large radius through which the tissue can flex helps to reauce the r~sk of fatigue failures.
P~eLerring to FIGURE 11, there is shown another embodiment of a coaptation stitch arrangement typical for all three stent legs. This embodi~ent includes a separate coaptation stitch 134 passing throu~h the tissue leaElets 50 and 70, through the top hole 121a in the tab 120, and up and over the tip 107 oE the stent 7~3 leg 106. Coapt~tion stitGh 134 could be a g-oup of stitches~ Another coaptation sti-tch 135, or group of stitches, passes through the tissue leaflets 50 and 70, throuyh the bottom `nole 121b in t7ne tab 120J and QUt an~
around the outside edge 133 of the stent leg 106.
Thus, the top coa~tation s~itch 134 lies in a plane parallel to the long axis of the stent leg 106.. The top stitch 134 or group of stitches is tied off above t~e ~ip 107 of the stent legO The bottom coaptation s~i~ch 135 lies in a plane generally perpendicular to the plane of the top stitch or s~itches 134 ana is tie~ ofr at the outside edge 138 of t'ne stent leg 1~6. These stiiches are placed.so that they do not in~erfere with the no~mal operation of the valve in the open position.
Because the thread is smaller in diam~ter than the holes 121~ the thread o~ coaptation stitches 134 and 135 will pull to the side o~ the holes 121 closest to the stitch knot when the thread is pullea tight. At 2C ti~es during manu~acture, the thread may be passed tnrough the tissue leaflets along an axis not par~llel to the axis o~ the bottom hole 121b. Thu~t when tne thread i5 pulled tight the tissue leaflet on one side of the ho~e is moved farther toward the knot at the outside edge 138 of the stent leg 106 than is the tissue leaflet on the other side . Thus uneven pulling can cause wrinkling oE the tissue lea:Elets.
~ An improvement of the coaptation stitching o~
FIGURE ].1 is illustrated in FIGU.RE 12 which snows the preferred embodiment of -the coaptation stitching arrangement. FIGURE 12 shows a coaptation stitch or stitches 140 residing generally in a plane parallel to the long a~ls of the stent leg 106 and passing through bo-th the top and bottom holes 121a and 121b and through 7~3 .

the tissue leaflets 50 and 70. The stitch can be either a single figure sigh~ stitch as shown in ~IGURE 1~ or it can be two separate stitches, each passing through both tissue leafle-ts and through Gne of the holes 121a or 121b. Each stitch 140 is tied together above the tip 107 of the stent leg 106. The figure eight stitch shown in FIGURE 1~ is the preferred e~odiment, however, because it is simpler and faster ~o i~plement than two separate stitches bo-th in a v~rtical plane. The figure eight stitch is simpler b~cause only one ~not need be tiedO
The coaptation stitch illustrated in FIGURE 12 te~Zs to eliminate the tendency for variations in st~tch placement during manufacturing which can cause wri.~kling of the tissue l~afle-ts.
Referring again to FIGURE 12, it has been found e~par-imentally that the width, ~T~ of the tab and the amount of inward projection or protuberance, P, ol the tab from the inside edge of the hole toward the center of the flow aperture of the valve is important in preventing abrasion of the tissue leaflets on the inside edges of the tab. ~hen the tissue leaflets coa~t together during the closing action of the valve, if the t..a~s 120, 123 and 125 protrude too ~ar in toward the center of the flow aperture, abrasion can occur in the area generally marked 142 in FIGURE 8.
To prevent this abrasion, the dimension P shown in FIGURES 5 and 12 is, in the preEe.rred embodiment, .restricted to a maximum of forty thousandths of an inch (0.040 inches or 1.016 millimeters~. However, any embodiment will be satisEactory wherein the distance which the tab extends towàrd the center of .

_3~_ the aperture is restricted to a distance ~ihich sub-stantially eliminates tcuching bet~een th2 tissue leaflets and the bottom surfaces or lower 20% of the tab under ~aximum backpressure conditions, The bottom of the tab surfaces refers generally to those portions of the tab surfaces below the midway point in the height of the tab designated HT2 in FIGURES
67 13 and 14~
The area or coaptation of the tissue leaflets, deslgnat2d generally as 144 in FIGURE 8~ tends to g~w larger during higher backpressure conditions.
Thi~ ~heno~enon can be visualized in placing the fingertips on each hand together fingerprint to firg2rprint with the fingertips on the other hand to ~orm a roof shaped arrangement. The fin~erprint area of contact represents the area of coaptation 1 ~k in FIGURE 3 . As the hands are pressed together keeping the fingers stiff, the fingers tend to flex toward each other such that the opposing first and second knuckle areas tend to come close- together.
~his represents the situation when higher backp~essure exists on the tissue leaElets during closin~.
As the tissue leaflets come closer together under increased backpressure, ~he area of contact between the lea~lets tends to increase by expanding in the downward direction, i.e. toward the stent riny 104 in FIGURE 7. If the tabs 120, 123 and 125 e~;tend too far in toward the center, abrasion between the mobile areas of the tissue leaflets just inside the tabs and 3Q the bottom portions of the tabs can occur. Restrlction of -the distance which the tabs protrude into the flo~
aperture tends to elimina-te the aforestated abrasion.

4'7~3 ~ .
~3~-The sa~e reasoning applies to restriction o~
t~le :Lelative widths, WT, of the tabs 120, 123 and 125 throllghout their heigh-t HT2 as compared to the relative width of the s-~ent le~s 106, 108 and 110 as 5 the stent legs descend from tips 107, 109 and 111~
Referring to FIGUR3 13, there is shown a detail view o~ the preferred embodim~n~ ~or the tabs and stent le~
tips~ As seen in FIGU~E 13, the width, WT, of the tab 120 remains constant throughout its height, ~T2~
10 regardless of the width of the stent ie~ 106. It is seen in FIGURE 13 that the width of -the stent leg 106 ~s in~reasing at polnts farther away froin the tip 10~.
FIGURE 14 shows another em'oodiment for the tabs wherein the width, WT, of the tab 120 decreases a-t 15 polnts farther down from the tip 107 irrespecti.ve of the width of said stent leg.
The purpose of maintaining a constant or de-creasing width for the ta~s 120, 123 and 125 is to minimize the possibility of abrasion of the tissue 20 leaflets on the tabs during closure af the valve and coaptation of the tissue leaflets just inside the tabs.
The increasing width of the stent legs 106, 108 and 110 tend to give shape and support to the tissue lea~lets to form the CUSp5 of the valve. The increasing width of 25 the stent legs versus the constant or decreasing wid-th of the tabs -tends to keep the tissue leaflets away from the lcwer sur~aces of the -tabs during co~ptat.ion thereby minimi2ing abrasion~ Any shape or form for the tabs which accomplishes the purpose of minimizi.ng or 30 eliminating this abrasion will be satisfactory and is intended to be included within the scope oE the claims appended thereto.

L8~7~3 As exe~plary only and not in any li~iting sellse, optimum stent dimensions for the stent depicted in FIGURE~ 5 and 6 are given in ~able I.
In FIG~RES 5 and 6, D refers to -the inside diameter of the stent ring and Do refers to the outside diameter thereof. U refers to the depth o~ scallop 112 and W re~ers to t`ne width of stent ring 104.
Ri refers to the ilside radius oE the scallop 112 and ~O refe~s to the outside radius of the scallop forming .he bottom of stent rlng 104. Finally HT2 re__~s to the total height of the tabs.
It wil 1 be apparent that the foregoing descrlption, gi~ in considerable detail as to the method o~
carrying out the best mode of the invention as conte~plated by the inventor, is given to exemplify the cor.cepts and prlnciples of the invention and not to limit it. The stent may be made of titanium, Delrin (T~), polyacetal, polypropylene or Elgiloy with the fabric covering of Dacron or Teflon but tne invention is not li~ited to t'nese ma-terials nor is it limited to any particular covered stent; indeed, the ~resent invention can be carried out without a coversd st2nt. Similarly, the structures and elements of the ir.vention have been described, in their best mode embodiments, as integral, in the case o~ the stent, and separate, in the case of the leaflets. ~lowever, whether formed of one or many pieces, i~ the structure which results functions in the manner as descrihed herein, it is the same invention. Thus, it is contemplated that the scope of the invention will be as de~ined in the following claims read in light of the principles of the invention as disclosed herein and not limited by the best mode.

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Claims (6)

1. A prosthetic heart valve comprising:
a) a stent comprising:
1) a ring with scallops formed therein defining an aperture with inflow and outflow ends;
and 2) a plurality of legs coupled to said ring extending upwardly toward said outflow end, said stent being dimensioned such that the quotient of the radius of curvature of mobile tissue measured at the point of greatest curvature divided by the thickness of said tissue is greater than or equal to five at all points of contact between said tissue and said stent;
b) a plurality of tissue leaflets attached to said stent and to each other to form a valving element; and c) a plurality of coaptation means in the vicinity of the tips of said stent legs for causing joining of the edges of said tissue leaflets.

2. The prosthetic heart valve of Claim 1 further including inwardly projecting tab means at the out-flow end of each stent leg for adding structural strength to said legs, with the distance that said tab means project inwardly toward the center of said aperture being restricted to a distance which substantially eliminates touching between the tissue leaflets and the bottom surfaces of said tab means.

3. The prosthetic heart valve of Claim 2 further including means on said tab means coupled to said coaptation means for fixing the position of said coaptation means, with said means for fixing the position of said coaptation means comprising a plurality of holes through said tab means.

4. The valve of Claim 3 wherein each of said coaptation means comprises a coaptation stitch lying generally in a plane parallel to the long axis of the stent leg and passing through said plurality of holes and said tissue leaflets, and which stitch is tied off above the tip of said stent leg, with each of said tabs having two holes therein and each of said coaptation stitches defining a figure eight pattern through said two holes.

5. The valve of Claim 2 wherein the width of said tab means remains constant throughout its length while the width of said stent legs increases at points removed from the tips of said stent legs.

6. A prosthetic heart valve comprising:
a stent comprising an annular base integrally formed with three upwardly extending legs, the space between the legs configured to form generally elliptically shaped scallops having a depth U measured from the top of the legs to the bottom of the scallop, the stent circumferentially forming a substantially right cylinder having an interior diameter D with the legs extending parallel to the axis of the cylinder, the lower edge of the base forming scallops corresponding generally to the arc of the scallops between the legs, the scallops of the lower edge of the base and the scallops between the legs vertically defining three generally elliptically shaped one-third portions of the base between the respective upright legs;
a fabric covering encompassing and following the configuration of the stent;
an annular sewing ring attached to the fabric covering and extending outwardly from the base;
a tissue valve element formed of three tissue leaflets joined to form a generally cylindrical three-cusp valving element, each leaflet having a top edge forming a raised truncated triangular form with a central plateau and two sides diverging from each side of the plateau to corners at their junctures with the sides of the leaflet;

means attaching the tissue valve element around the fabric covered stent; and a plurality of coaptation stitches through the tissue leaflets adjacent the upper edges thereof disposed directly above the tops of the fabric covered stent legs fixing the leaflets to form three cusps, with said plateaus extending upwardly midway between the legs in the open position of the valve, the upper edges of the cusps meeting in the closed position of the valve with the plateaus adjacent each other, and in the open position of the valve the tissue valve element forming a cylinder having an inside diameter at the top of the valve sub-stantially equal to the inside diameter of the fabric covered stent, and with said stent being dimensioned such that the quotient of the radius of curvature of mobile tissue measured at the point of greatest curvature divided by the thickness of said tissue is greater than or equal to five at all points of contact between said tissue and said stent.