CA2123824A1

CA2123824A1 - Bioprosthetic valve

Info

Publication number: CA2123824A1
Application number: CA002123824A
Authority: CA
Inventors: Ivan Vesely; Slawomir Krucinski; Gordon Campbell; Derek Boughner; Mohan Dokainish
Original assignee: London Health Association
Current assignee: London Health Services Centre
Priority date: 1993-06-18
Filing date: 1994-05-18
Publication date: 1994-12-19
Also published as: GB9410549D0; GB9312666D0; GB2279134A; GB2279134B; US5549665A

Abstract

ABSTRACT

A bioprosthetic valve comprising a support ring having three spaced apart end stops projecting upwardly therefrom, a stent post ring having three spaced apart stent posts pivotally connected thereto and adapted to engage respective ones of the end stops so as to permit outward pivoting of the stent posts and to prevent inward pivoting thereof, a leaflet valve having three generally triangular leaflets defining respective cusps, the leaflets being joined at respective commissures, and a sewing ring for attaching the leaflet valve to the stent post ring and support ring.

Description

-~ 2~2~24 BIOPROSTHETIC VALVE

Field of the Invention This invention relates in general to bioprosthetic valves, and more particularly to a nov~l bioprosthetic heart valve with pivoting supporting stent posts for holding valve leaflets therebetween.

Backqround_of the Invention ~hen a patient's own heart valve becomes diseased, it can be either r~paired or surgically replaced with an artificial valve. There are two basic types of artificial heart valves, mechanical valve~ and tissue valves. ~echanical valYes are ~ade o~ metal or hard plastic, whereas ti55ue valves con~ist o~ chemically preserved animal tissue, usually extracted from pig ~porcine) or cow (bovine). The animal tissue valves are mounted on a supporting frame or "stent". The stent enables the surgeon to in ert and mount the valve into the heart with minimal difficulty. The stents themselves a.re constructed from a polymer material and are covered with ~AC~ON0 cloth that contains a ~ewing ring.
Typically, thre~ stent po~t~ project upwardly from the sewing ring and hold the three valve leaflets suspended in the required geometry.

Animal tissue valves have soma inherent advantages over mechanical valves since they do not require the pati~nt to be on chronic an~icoagulants. UnfortunatPly, ~ 30 ti~ue valves aventually suf~er from failure in a manner I similar to human heart valve~, and therefore need I periodic replacement~ Currently, the survival rate of I biopro~thatic tis~ue valves i~ approxi~ately 95% a~ter l five year~ from surgery, but only 40~ after fifteen years 1 35 from urgery.

. The failure of these animal tissue valves results ¦ fro~ poor mechanical properties. Specifically, the supporting stents ar~ relatively rigid, and cannot mimic 2~ 2382~

the cyclic expansion and contraction of the natural aorta where the valve sits. It is believed that mounting of the valves on such non-physiological stents contributes to mechanical damage caused by repetitive sharp bending at the stent posts. Much of the damage to the valve tissue occurs during valve opening because the supporting stents cannot dilate with the recipient~s aorta. Such unnatural behaviour induces sharp curvatures within the leaflats and very high local stresses that damage the leaflet material and ultimately cause it to fail through flexural fatigue.

The inventors hav~ recognized the desirability of providing a bioprosthetic heart valve with a flexible or expansive supporting stent. In Krucinski S., Vesely I., Dokainish M.A., Campbell G. "Numerical Simulation of Leaflet Flexure in Biopro~th~tic Valves Mounted on Rigid and Expansile Stents", Journal of Biomechanics (26(8):929 943, 1993), thQ inventor# de~cribe a simulated stent with posts that pivot about their respective bases for reducing compressive co~missural stressing in a bioprosthetic heart valve. Pivoting stent posts reduce flexural stresses in pericardial bioprosthetic valves: A
numerical analysi~", presented at the 1993 conference of ASAIO, New Orleans, May, 1993. The concep~ of pivoting stents wa~ disclos~d.

Another prior ~rt bioprosthetic valve is disclosed in U.S. Patent 5,258,023 (Reger). Thi~ valve incorpora~es a stent compri~ing a ~rame which is fully covered by a biochem.ically in~rt or phy~iologically compatible shroudO The ~ram~ i~ in the form o~ a hollow cylinder of r~ctangular cro~-section which i~ machined ¦ or trimmed to provide a ~uturing ~upport ring, extended 1 35 cusp stanchions, and interferencs free blood flow to the coronary arterie~. The fra~e is joint ~re~ but is made slightly dcforsab1o to confor~ to contraotile changes of 2~23~2l~

th~ heart. The Reger Patent discloses that such deformity and expansion permits the frame to compliantly respond to expansion and contraction of the native valve orifice of the beating heart in which the aortic valve is implanted in order to reduce beat-by-beat stress on the aortic valve and anchoring sutures, thereby reducing the likelihood of eventual valve d~hiscence.

As indicated above, the inventors have realized that while outward movement of the stent posts reduces local stresses on the leaflet material, it i~ also extremely important to limit th~ inward movement of the stent posts in order to reduce compre6sive ~lexural stre~se~ on the valve leaflets.
Accordingly, althouyh the provision of flexible stent posts is known in the prior art, no practical heart valve has yet been provided ~or allowing limited outward movement o~ the stent po~ts during systole while also preven~ing inward movement o~ the stent po~ts during diastole 50 as to reduce commi~sural stresses in the valve leafl~ts.

I Moreover, the in~entors' mathematical modelling (see J. Biomechanics article discussed above) ha~ shown that a compliant supporting frame c~nnot derorm sufficiently outward to enable the required amount of expansion to reduce stre~ses, and still provide structural rigidity to prevent collaps~ of the frame inward during valve closure.
1 Summary of thç Inve~tion !J According to the present invention, a bioprosthetic .1 valve is provided with a plurality of pivoting stents for supporting the valve lea~lets or cusps. According to the pr~ferred embodi~ent, th~ bioprosth~tic valve of the pre~ent invention is used a~ a replacement for the human .~ .

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21~382ll ,~

heart valve, although the valve o~ the present invention may be used to replace other valves in the human body with only minor modifications in design and size. In the preferred heart valve embodiment, the tips o~ the stents are attached to the aortic wall, which causes outward pivoting as the aorta expands during systole, to facilitate significant reduction of local stresses in the valve leaflets. The valve also includes end stops for preventing the stents from moving ~xcessively inward during diastole and ensuring a properly ~unctioning valve that seals well. A truly, fre~ly pivoting ~rame wikh inward acting end stops provides both unrestricted outward movement, and controlled inward rigidity. Thus, the bioprosthetic heart valve according to the present invention provides a more natural opening for th~ valve leaflets and reduces leAflet bending and the associated ~tresses which are characteristic of prior art heart valves.

Brie~ De~cription o~ the Drawings A description of the prior art and of the preferred embodiment of thQ present invention i~ provided in greater dstail below with referenca to the following drawings, in which:
Figure 1 i8 a per~pective view of a prior art biopro3thetic heart valve;
Figur~ 2 i8 an exploded perspective view of the bioprosthetic heart valve according to the preferred embodiment of th~ present invention;
Figura 3 shows connec~ion of a leaflet cusp supporting wire frame to individual stent posts of the heart valv~ shown in Figure 2;
Figure 4 i8 ia perspective view of an assembled heart valve according to the pre~erred embodiment;
Figur~ 5 is a detailed cro~s-sectional view showing pivoting of the ~tant posts in the heart valve of the preferred embodiment; and ~12~ 2~

Figure 6 is a detail in perspective of an alternative embodiment of pivoting post and stop member.

Detailed Description of the Invention_and Prior Art With reference to Figure i, a prior art bioprosthetic valve (e.g. pig aortic valve or calf pericardium) i~ shown mounted to a rigid support ~rame with stent posts 1 projecting upwardly from a sewing ring 5, so that the valve leaflets meet to form cusps 3 through which blood is intended to flow. While some prior art frame~ or stents claim to be flexible, such as disclosed in U.S. Patent 5,258,023 (Reg~r), the po ts 1 in prior art devices have been found to flex only inward during valve closure. Since the base o~ each ~tent post 1 has a fixed diameter the stent posts generally do not move outward during systolic valve opening.

In contrast, the natural aortic root expands con~iderably during valve opening. Medical studies have shown that proper functioning of the aortic valve depends on aortic root expansion. The natural expansion of the aortic root at the onset o~ systole enable the commi~sure~ to move apart, and initiate the opening of tha aortic valve. When the roo~ is fully expanded, the ~ree edge o~ the lea~le~ ln a natural aortlc valve is pulled taught between the commi~sures creating a rough triangular shaped orifice ~or the majori~y of systoleO
The slight tension on the leaflets in systole eliminates compres~ive strQsses and minimizes circumferential bending.

Prior art stented biopros~hetic valves such as shown in Figure 1, by virtue o~ kheir de~ign, cannot expand in ~sy~tole. The valve opens through central reverse i35 flexing, and the leaflets o~ten e~perience sharp bends and very high curvatures which eventually lead to valve failure.

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2123~
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Turning now to the preferred embodiment of the invention, a bioprosthetic heart valve is shown in Figures 2-5. The valve comprises a preferably rigid support ring 7 into which a flexible stent post ring 9 is inserted for snap-fit engagement. The stent post ring 9 is preferably fabricated from a suitable ~lexible polymer and includes a plurality of stent posts 11 interconnected via a connecting brace 13. Each of the stent posts 11 comprises a main body portion whioh~ according to the illustrated preferred a~bodiment, i~ generally flat, although in alternatiYe embodiments may be of variable cross-~ection. The stent po~t ~ain body portions are connected to the connecting brace 13 adjacent a lower end o~ each stent post as shown in detail with reference to Figure 5. The lower end oP each stent post l~ ha~ an outward protrusion 14, the purpose o~ which is discussed in greater detail below. Each stent poct has an oblong hole 12 extending therethrough to facilitate attachment o~ tissue and/or cloth covering by suturing.
The support ring 7 include~ threa end stops. Each end ~top compris3~ a first memb~r 17 projecting upwardly fro~ an outsr diam~t~r o~ th~ support ring and be.ing of generally ~pherical ~egment shape defining a hollow internal portion 19. Each of the ~nd ~tops also comprisas a second me~b2r 21 projacting ~rom the outer diameter of th~ support ring toward an inner diameter o~
the support ring in the ~orm o~ an arch. The support ring 7 ~urther includee a scalloped extension 22 from the bottom ~urface thereo~ which i8 adapted to conform to the correct geometry of ~he aortic roo~
:: .
During as~embly, a3 shown be~t with reference to ~ Figure~ 3 and 5, the upper di~tal end~ of stent posts 11 ¦ 35 are inserted through the support ring 7 ~rom beneath and then are moved ~urther upwardly through the opening between end stop ~irst member 17 and second member 21 ~' V .'. , . '' . ' ~' ' ` '' I ' ' ' .~:''`,.1', . ' ~ ~ , '~ ! 2382~
. . .

until protrusion 14 hooks into the hollow internal portion 19 of the first member 17, thereby completing the snap-fit engagement of the stent post ring 9 to the support ring 7.

Next, a wire fram~ 23 i~ received in a ~lot 25 disposed in the upper distal end of Pach stent post 11.

Finally, the anim~l leaflet valve 27 is placed over the ~upport ring 7, stent po~t rin~ 9 and wlre ~rame 23.
As discu~sed abov~, the animal ti~ ue leaflet valve 27 typically compri~es a pig aortic valve of calf perlcardium d~fining three l~aflet~ 29, 31. and 33, to which ~ cloth cover 35 i~ ~ewn. Th~ cloth cover 35 may be ~ewn into either or both o the lea~let valve 27 or stent po~ts 11, with the ~tent po~t~ 11 being covered both inside and out. A3 in the prior art, the valve leaflets 29, 31 and 33 meet to ~ine re~pective cusps (such as cusp 34) which open and close during systole and diastole, respec~ively. A ~o~t sewing ring 37 is provided at the base o~ the animal ti~sue valve 27 by which the animal tissue valve 27 may be ~ewn to the support ring 7, as shown be~t with re~erence to Figure 4.

In thQ asqembled form ~hown in Figure 4, the wire ~rame Z3 (Figures 2 and 3) provide ~upport for the lea~let valve 27 on the stent post ring 9.

A~ shown be~t with reference to Figure 5, ~he bottom portion o~ each stent po~t 11 is adapted to slide along the support ring 7 during pivoting in sy~tole (~hown in I phantom) and to hook insid~ the hollow internal portion 19 during diastole (~olid lines). Fur~hermore f a portio~
of thQ main body of the st~n~ po~t 11 abuts the second member 21 a~ove the pivot point provided by conn~cting brace 13 during diaskole, further limiting the inward . movement of th~ stent post 11.

2 1 2 ~

According to the preferred embodiment, the stent posts 11 and connecting brace 13 are fabricated as a single unit from suitable material in ~uitable dimensions to limit the pivoting of the stent posts ll about the connecting brace 13 to approximately 10 off of vertical, in the preferred embodiment, so as to minimize tensile stresses in the leaflets 29, 31 and 33. However, the pivot angle may vary in other embodiments depending on the relationship between the height o~ post 11 above brace 13 and the radial excursion of th0 top post 11. As will be appreciated from tha Figure~ and the description above, pivoting of the stent posts 11 oacurs as a result o~ twisting or torsional movement of the connecting brace 13. Generally, the amount o~ pivoting i8 limited by the exp~nsion of the aor~a. Al~o, the g20~etry of the valve leaflets prevents pivoting of the st~nt po8t5 11 past a certain point (Q.g. 16 expansion of commissural diameter), since generated tension limits outward movement of the posts 11. It i~ contemplated that the rigidity of the stent posts and end stops can be designed to limit pivoting by varying the shape o~ the cro~s-section of the stent posts.

According to the alternative embodiment o~ Figure 6, the outward protrusion has bean eliminated and the shape of the stop member 17A ha~ be2n straightened to eliminate the hollow internal portion 19. Also, instead of using a connecting brace, each pos.t llA is provided with a pair o~ pivot arms 13A which are received within a respective pair o~ hole~ 22A in the stop member 21A.
.1 In summary, whereas prior art heart valve~ having ~ totally rigid stent posts experience magnitude~ o~
?1 35 flexural stresse~ and degrees of bending which are l su~icient to produce compressive buckling and leaflet I tearing, the valve accor~ing to the present inven~ion is :i '.'~
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21~38?,~
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characterized by signi~icantly reduced leaflet curvatures and associated stresses. Furthermore, in contrast with prior art bioprosthetic valves in which the stent post8 flex inwardly during diastole, the heart valve of the present invention allows for considerable outward pivoting during systole but prevents excessive inward pivoting during diastole in order to reduce the compressive flexural stresses normally associated with the function of exi~ting pexicardial biopro3the~
Modifications and alternative embodiments of the invention are pos~ible. For example, it i~ contemplated that human tis3ue may be used in~tead o~ an$mal tissue for valve 27. Also, the human or animal ti~sue may be modi~ied in various ways to prevent i~une reaction.
Furthermore, as di~cu~sed above it i~ contemplated that the biopro¢thetic valve o~ the present invention may be u3ed to replace other valve~ in the human body. For example, according to one alternative embodiment, the valve of the pre~ent invention may be modified for use in the urinary tract to replace a defectiv~ urinary sphincter muscle in order to treat incontinence. Also, the valve may be used in the eye or in the brain to reduce ~luid pressure.
All such modification~ and embodiments are believed 25 to b~ with in the sphere and scope Or the present :.
inv~ntion as derined by the claims appended hereto~

Claims

1. A bioprosthetic heart valve comprising:
a) a support ring having three spaced apart end stops projecting upwardly therefrom;
b) three spaced apart stent posts adapted to pivot outwardly relative to said supporting and to engage respective ones of said end stops so as to prevent inward pivoting thereof;
c) leaflet valve means formed from an aortic root and having three generally triangular leaflets defining respective cusps which are adapted to open and close during heart systole and diastole, respectively, said leaflet being joined at respective commissures adjacent said aortic root; and d) means for attaching said leaflet valve means to said stent posts and said support ring.

2. The bioprosthetic heart valve of claim 1, further comprising a stent post ring to which said stent posts are connected for pivoting movement.

3. The bioprosthetic heart valve of claim 2, wherein each of said end stops further comprises a first member projecting from an outer diameter of said support ring, said first member being of generally spherical segment shape defining a hollow internal portion, and a second member projecting from said outer diameter toward an inner diameter of said support ring, said second member extending substantially above said first member and being of generally arcuate shape.

4. The bioprosthetic heart valve of claim 3, wherein each of said stent posts further comprises a main body portion connected to said stent post ring at a pivot point adjacent a lower end of said stent post such that a portion of said main body moves inwardly no further than said second member above said pivot point during diastole, said lower end having an outward protrusion below said pivot point adapted to hook into said hollow internal portion of said first member during diastole, whereby said stent post is prevented from excessive inward pivoting during diastole while being permitted said stent post to pivot outwardly by twisting of said stent post ring during systole.

5. The bioprosthetic heart valve of claim 1, further comprising a wire frame conforming in shape to said respective cusps of said leaflet valve means and connected to an upper distal end of each of said stent posts, for supporting said leaflet valve means on said stent post ring.

6. The bioprosthetic heart valve of claim 5, wherein said wire frame is received within cooperatively dimensioned slots disposed in the distal end of each of said stent posts.

7. The bioprosthetic heart valve of claim 1, wherein said support ring further incorporates a scalloped extension from a bottom surface thereof so as to conform said bottom surface to aortic valve geometry.

8. The bioprosthetic heart valve of claim 1, further comprising a sewing ring circumscribing said leaflet valve means for attaching said leaflet valve means to said support ring.

9. The bioprosthetic heart valve of claim 1, further comprising a cloth covering sewn onto said leaflet valve means.

10. The bioprosthetic heart valve of claim 1, further comprising a cloth covering sewn onto said stent posts.

11. The bioprosthetic heart valve of claim 1, wherein said leaflet valve means consists of one of either animal tissue or human tissue.

12. The bioprosthetic heart valve of claim 10, wherein said animal tissue is chemically treated pig aortic valve.

13. The bioprosthetic heart valve of claim 10, wherein said animal tissue is chemically treated calf pericardium.

14. The bioprosthetic heart valve of claim 1, wherein said stent post ring is fabricated from a flexible polymer.

15. The bioprosthetic heart valve of claim 1, wherein said stent post ring is adapted to limit said outward pivoting of said stent posts to approximately 16°
from vertical.

16. The bioprosthetic heart valve of claim 1, wherein each of said stent post has a pair of pivot arms projecting from opposite sides thereof, and wherein each of said end stops includes a pair of holes for receiving respective ones of said pivot arms so as to permit said outward pivoting of said stent posts.

17. A bioprosthetic valve comprising;
a) a support ring having three spaced apart end stops projecting upwardly therefrom;
b) three spaced apart stent posts adapted to pivot outwardly relative to said supporting and to engage respective ones of said end stops so as to prevent inward pivoting thereof;

c) leaflet valve means having three generally triangular leaf lets defining respective cusps which are adapted to open and close; and d) means for attaching said leaflet valve means to said stent posts and said support ring.