United States Patent [191
`Vesely et al.
`
`lIlllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005549665A
`[11] Patent Number:
`5,549,665
`[45] Date of Patent:
`Aug. 27, 1996
`
`[54] BIOPROSTETHIC VALVE
`
`[75] Inventors: Ivan Vesely; Slawomir Krucinski;
`Gordon Campbell; Derek Boughner;
`Mohan Dokainish, all of London,
`Canada
`
`[73] Assignee: London Health Association, London,
`Canada
`
`[21] Appl. No.: 261,983
`_
`Jun. 17, 1994
`[22] F1led:
`[30]
`Foreign Application Priority Data
`,
`_
`Umted Kmgdom ................. .. 9312666
`
`Jun. 18, 1993 [GB]
`
`[56]
`
`[51] Int. Cl.6 ...................................................... .. A61F 2/24
`[52] US. Cl. .......... ..
`.. 623/2; 623/900
`[58] Field of Search ................................. .. 623/2, 66, 900
`.
`References cued
`U_S_ PATENT DOCUMENTS
`.
`.............................. ..
`LlOtta et
`4,725,274
`2/1988 Lane et a1. ..
`623/2
`4,851,000
`7/1989 Gupta . . . . . . . . .
`. . . .. 623/2
`5163 953 11/1992 Vince ........................................ .. 623/2
`5,258,023 11/1993 Regcr _
`5,326,370
`7/1994 Love et al. ................................ .. 623/2
`
`4
`
`8300617 3/1983 WIPO ...................................... .. 623/2
`WO94/01060 1/1994 WIPO .
`
`OTHER PUBLICATIONS
`_
`_
`_
`_
`_
`_
`“Numencal S1mulat10n of Lea?et Flexure 1n B1oprosthet1c
`Valves Mounted on Rigid and Expansile Stents,” 28 Dec.
`1992, by 5- Kmcinski, I- Veley, M~ A- Dokainish, and G
`Campbell.
`“Pivoting Stent Posts Reduce Stresses in Pericardial Bio‘
`prosthetic Valves: A Numerical Analysis,” by I. Vesely and
`S. Krucinski.
`
`Primary Examiner—Michael Milano
`Attorney, Agent, or Firm-Fay, Sharpe, Beall, Pagan, Min
`nich & MCKe6
`_
`
`.
`
`ABSTRACT
`[57]
`Abioprosthetic valve Comprising asuppon n-ng having three
`spaced apart end stops projecting upwardly therefrom, a
`stent post ring having three spaced apait 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
`pivoting thereof’ a lea?et valve
`h .
`th
`an t .
`1
`l n t d ? .
`t.
`“mg m gen“ y nangua‘ ea es 6 nmgrespec‘ve
`cusps’ the lea?ets being joined a‘ respective commissures’
`and a sewing ring for attaching the lea?et valve to the stent
`P051 ring and support ting.
`
`FOREIGN PATENT DOCUMENTS
`
`220097 3/1987 European Pat. 01f. ................. .. 623/2
`
`21 Claims, 4 Drawing Sheets
`
`NORRED EXHIBIT 2105 - Page 1
`Medtronic, Inc., Medtronic Vascular, Inc.,
`& Medtronic Corevalve, LLC
`v. Troy R. Norred, M.D.
`Case IPR2014-00110
`
`

`

`US. Patent
`
`Aug. 27, 1996
`
`Sheet 1 of 4
`
`5,549,665
`
`NORRED EXHIBIT 2105 - Page 2
`
`

`

`US. Patent
`
`Aug. 27, 1996
`
`Sheet 2 of 4
`
`5,549,665
`
`NORRED EXHIBIT 2105 - Page 3
`
`

`

`US. Patent
`
`Aug. 27, 1996
`
`Sheet3 0f 4
`
`5,549,665 Q
`
`NORRED EXHIBIT 2105 - Page 4
`
`

`

`US. Patent
`
`Aug. 27, 1996
`
`Sheet 4 of 4
`
`v 5,549,665
`
`NORRED EXHIBIT 2105 - Page 5
`
`

`

`5,549,665
`
`1
`BIOPROSTETHIC VALVE
`
`FIELD OF THE INVENTION
`
`This invention relates in general to bioprosthetic valves,
`and more particularly to a novel bioprosthetic heart valve
`with pivoting supporting stent posts for holding valve leaf
`lets therebetween.
`
`BACKGROUND OF THE INVENTION
`
`When a patient’s own heart valve becomes diseased, it
`can be either repaired or surgically replaced with an arti?cial
`valve. There are two basic types of arti?cial heart valves,
`mechanical valves and tissue valves. Mechanical valves are
`made of metal or hard plastic, whereas tissue valves consist
`of 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 insert and mount the valve into the
`heart with minimal difficulty. The stents themselves are
`constructed from a polymer material and are covered with
`DACRON® cloth that contains a sewing ring. Typically,
`three stent posts project upwardly from the sewing ring and
`hold the three valve lea?ets suspended in the required
`geometry.
`Animal tissue valves have some inherent advantages over
`mechanical valves since they do not require the patient to be
`on chronic anticoagulants. Unfortunately, tissue valves
`eventually suffer from failure in a manner similar to human
`heart valves, and therefore need periodic replacement. Cur
`rently, the survival rate of bioprosthetic tissue valves is
`approximately 95% after ?ve years from surgery, but only
`40% after ?fteen years from surgery.
`The failure of these animal tissue valves results from poor
`mechanical properties. Speci?cally, the supporting stents are
`relatively rigid, and cannot mimic the cyclic expansion and
`contraction of the natural aorta where the valve sits. It is
`believed that mounting of the valves on such non-physi
`ological 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 recipi
`ent‘s aorta. Such unnatural behaviour induces sharp curva—
`tures within the lea?ets and very high local stresses that
`damage the lea?et material and ultimately cause it to fail
`through ?exural fatigue.
`The inventors have recognized the desirability of provid
`ing a bioprosthetic heart valve with a ?exible or expansive
`supporting stent. In Krucinski S., Yesely I., Dokainish M. A.,
`Campbell G. “Numerical Simulation of Lea?et Flexure in
`Bioprosthetic Valves Mounted on Rigid and Expansile
`Stents”, Journal of Biomechanics (26(8):929—943, 1993),
`the inventors describe a simulated stent with posts that pivot
`about their respective bases for reducing compressive com
`missural stressing in a bioprosthetic heart valve. Also, in
`pivoting stent posts reduce ?exural stresses in perieardial
`bioprosthetic valves: A numerical analysis, presented at the
`1993 conference of ASAIO, New Orleans, May, 1993 the
`concept of pivoting stents was disclosed.
`Another prior art bioprosthetic valve is disclosed in US.
`Pat. No. 5,258,023 (Reger). This valve incorporates a stent
`comprising a frame which is fully covered by a biochemi
`cally inert or physiologically compatible shroud. The frame
`is in the form of a hollow cylinder of rectangular cross
`section which is machined or trimmed to provide a suturing
`
`15
`
`25
`
`30
`
`35
`
`2
`support ring, extended cusp stanchions, and interference free
`blood ?ow to the coronary arteries. The frame is joint free
`but is made slightly deformable to conform to contractile
`changes of the heart. The Reger Patent discloses that such
`deformity and expansion permits the frame to compliantly
`respond to expansion and contraction of the native valve
`ori?ce 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 dehiscence.
`As indicated above, the inventors have realized that while
`outward movement of the stent posts reduces local stresses
`on the lea?et material, it is also extremely important to limit
`the inward movement of the stent posts in order to reduce
`compressive ?exural stresses on the valve lea?ets.
`Accordingly, although the provision of ?exible stent posts
`is known in the prior art, no practical heart valve has yet
`been provided-for allowing limited outward movement of
`the stent posts during systole while also preventing inward
`movement of the stent posts during diastole so as to reduce
`commissural stresses in the valve lea?ets.
`Moreover, the inventors’ mathematical modelling (see J.
`Biomechanics article discussed above) has shown that a
`compliant supporting frame cannot deform sufficiently out
`ward to enable the required amount of expansion to reduce
`stresses, and still provide structural rigidity to prevent col
`lapse of the frame inward during valve closure.
`
`SUMMARY OF THE INVENTION
`
`According to the present invention, a bioprosthetic valve
`is provided with a plurality of pivoting stents for supporting
`the valve lea?ets or cusps. According to the preferred
`embodiment, the bioprosthetic valve of the present invention
`is used as a replacement for the human heart valve, although
`the valve of the present invention may be used to replace
`other valves in the human body with only minor modi?ca
`tions in design and size. In the preferred heart valve embodi
`ment, the tips of the stents are attached to the aortic wall,
`which causes outward pivoting as the aorta expands during
`systole, to facilitate signi?cant reduction of local stresses in
`the valve lea?ets. The valve also includes end stops for
`preventing the stents from moving excessively inward dur
`ing diastole and ensuring a properly functioning valve that
`seals well. A truly, freely pivoting frame with 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 the valve lea?ets and reduces lea?et
`bending and the associated stresses which are characteristic
`of prior art heart valves.
`
`55
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`A description of the prior art and of the preferred embodi
`ment of the present invention is provided in greater detail
`below with reference to the following drawings, in which:
`FIG. 1 is a perspective view of a prior art bioprosthetic
`heart valve;
`FIG. 2 is an exploded perspective view of the biopros
`thetic heart valve according to the preferred embodiment of
`the present invention;
`FIG. 3 shows connection of a lea?et cusp supporting wire
`frame to individual stent posts of the heart valve shown in
`FIG. 2;
`
`65
`
`NORRED EXHIBIT 2105 - Page 6
`
`

`

`5,549,665
`
`3
`FIG. 4 is a perspective view of an assembled heart valve
`according to the preferred embodiment;
`FIG. 5 is a detailed cross-sectional view showing pivoting
`of the stent posts in the heart valve of the preferred embodi—
`ment; and
`FIG. 6 is a detail in perspective of an alternative embodi~
`ment of pivoting post and stop member.
`
`DETAILED DESCRIPTION OF THE
`INVENTION AND PRIOR ART
`
`15
`
`4
`adapted to conform to the correct geometry of the aortic
`root.
`During assembly, as shown best with reference to FIGS.
`3 and 5, the upper distal ends of stent posts 11 are inserted
`through the support ring 7 from beneath and then are moved
`further upwardly through the opening between end stop ?rst
`member 17 and second member 21 until protrusion 14 hooks
`into the hollow internal portion 19 of the ?rst member 17,
`thereby completing the snap-?t engagement of the stent post
`ring 9 to the support ring 7.
`Next, a wire frame 23 is received in a slot 25 disposed in
`the upper distal end of each stent post 11.
`Finally, the animal lea?et valve 27 is placed over the
`support ring 7, stent post ring 9 and wire frame 23. As
`discussed above, the animal tissue lea?et valve 27 typically
`comprises a pig aortic valve or calf pericardium de?ning
`three lea?ets 29, 31 and 33, to which a cloth cover 35 is
`sewn. The cloth cover 35 may be sewn into either or both of
`the lea?et valve 27 or stent posts 11, with the stent posts 11
`being covered both inside and out. As in the prior art, the
`valve lea?ets 29, 31 and 33 meet to de?ne respective cusps
`(such as cusp 34) which open and close during systole and
`diastole, respectively. A soft sewing ring 37 is provided at
`the base of the animal tissue valve 27 by which the animal
`tissue valve 27 may be sewn to the support ring 7, as shown
`best with reference to FIG. 4.
`In the assembled form shown in FIG. 4, the wire frame 23
`(FIGS. 2 and 3) provide support for the lea?et valve 27 on
`the stent post ring 9.
`As shown best with reference to FIG. 5, the bottom
`portion of each stent post 11 is adapted to slide along the
`support ring 7 during pivoting in systole (shown in phantom)
`and to hook inside the hollow internal portion 19 during
`diastole (solid lines). Furthermore, a portion of the main
`body of the stent post 11 abuts the second member 21 above
`the pivot point provided by connecting brace 13 during
`diastole, further limiting the inward movement of the stent
`post 11.
`According to the preferred embodiment, the stent posts 11
`and connecting brace 13 are fabricated as a single unit from
`suitable material in suitable dimensions to limit the pivoting
`of the stent posts 11 about the connecting brace 13 to
`approximately 10° off of vertical, in the preferred embodi
`ment, so as to minimize tensile stresses in the lea?ets 29, 31
`and 33. However, the pivot angle may vary in other embodi
`ments depending on the relationship between the height of
`post 11 above brace 13 and the radial excursion of the top
`post 11. As will be appreciated from the Figures and the
`description above, pivoting of the stent posts 11 occurs as a
`result of twisting or torsional movement of the connecting
`brace 13. Generally, the amount of pivoting is limited by the
`expansion of the aorta. Also, the geometry of the valve
`lea?ets prevents pivoting of the stent posts 11 past a certain
`point (eg 15% expansion of commissural diameter), since
`generated tension limits outward movement of the posts 11.
`It is contemplated that the rigidity of the stent posts and end
`stops can be designed to limit pivoting by varying the shape
`of the cross-section of the stent posts.
`According to the alternative embodiment of FIG. 6, the
`outward protrusion has been eliminated and the shape of the
`stop member 17A has been straightened to eliminate the
`hollow internal portion 19. Also, instead of using a connect
`ing brace, each post 11A is provided with a pair of pivot
`arms 13A which are received within a respective pair of
`holes 22A in the stop member 21A.
`In summary, whereas prior art heart valves having totally
`rigid stent posts experience magnitudes of ?exural stresses
`
`NORRED EXHIBIT 2105 - Page 7
`
`with reference to FIG. 1, a prior art bioprosthetic valve
`(e.g. pig aortic valve or calf pericardium) is shown mounted
`to a rigid support frame with stent posts 1 projecting
`upwardly from a sewing ring 5, so that the valve lea?ets
`meet to form cusps 3 through which blood is intended to
`?ow. While some prior art frames or stents claim to be
`?exible, such as disclosed in U.S. Pat. No. 5,258,023
`(Reger), the posts 1 in prior art devices have been found to
`?ex only inward during valve closure. Since the base of each
`stent post 1 has a ?xed diameter the stent posts generally do
`not move outward during systolic valve opening.
`In contrast, the natural aortic root expands considerably
`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 of systole enables the commissures to move apart, and
`initiate the opening of the aortic valve. When the root is fully
`expanded, the free edge of the lea?et in a natural aortic valve
`is pulled taught between the commissures creating a rough
`triangular shaped ori?ce for the majority of systole. The
`slight tension on the lea?ets in systole eliminates compres
`sive stresses and minimizes circumferential bending.
`Prior art stented bioprosthetic valves such as shown in
`FIG. 1, by virtue of their design, cannot expand in systole.
`The valve opens through central reverse ?exing, and the
`lea?ets often experience sharp bends and very high curva
`tures which eventually lead to valve failure.
`Turning now to the preferred embodiment of the inven
`tion, a bioprosthetic heart valve is shown in FIGS. 2-5. The
`valve comprises 21 preferably rigid support ring 7 into which
`a ?exible stent post ring 9 is inserted for snap-?t engage
`ment. The stent post ring 9 is preferably fabricated from a
`suitable ?exible 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 which,
`according to the illustrated preferred embodiment, is gen
`erally ?at, although in alternative embodiments may be of
`variable cross—section. The stent post main body portions are
`connected to the connecting brace 13 adjacent a lower end
`of each stent post as shown in detail with reference to FIG.
`5. The lower end of each stent‘post 11 has an outward
`protrusion 14, the purpose of which is discussed in greater
`detail below. Each stent post has an oblong hole 12 extend
`ing therethrough to facilitate attachment of tissue and/or
`cloth covering by suturing.
`The support ring 7 includes three end stops. Each end stop
`comprises a ?rst member 17 projecting upwardly from an
`outer diameter of the support ring and being of generally
`spherical segment shape de?ning a hollow internal portion
`19. Each of the end stops also comprises a second member
`21 projecting from the outer diameter of the support ring
`toward an inner diameter of the support ring in the form of
`an arch. The support ring 7 further includes a scalloped
`extension 22 from the bottom surface thereof which is
`
`35
`
`40
`
`50
`
`55
`
`60
`
`

`

`5
`and degrees of bending which are sufficient to produce
`compressive buckling and lea?et tearing, the valve accord
`ing to the present invention is characterized by signi?cantly
`reduced lea?et curvatures and associated stresses. Further
`more, in contrast with prior art bioprosthetic valves in which
`the stent posts ?ex inwardly during diastole, the heart valve
`of the present invention allows for considerable outward
`pivoting during systole but prevents excessive inward piv
`oting during diastole in order to reduce the compressive
`?exural stresses normally associated with the function of 1
`existing pericardial bioprosthesis.
`Modi?cations and alternative embodiments of the inven
`tion are possible. For example, it is contemplated that human
`tissue may be used instead of animal tissue for valve 27.
`Also, the human or animal tissue may be modi?ed in various
`ways to prevent immune reaction.
`Furthermore, as discussed above it is contemplated that
`the bioprosthetic valve of the present invention may be used
`to replace other valves in the human body. For example,
`according to one alternative embodiment, the valve of the
`present invention may be modi?ed for use in the urinary
`tract to replace a defective urinary sphincter muscle in order
`to treat incontinence. Also, the valve may be used in the eye
`or in the brain to reduce ?uid pressure.
`All such modi?cations and embodiments are believed to
`be with in the sphere and scope of the present invention as
`de?ned by the claims appended hereto.
`We claim:
`1. A bioprosthetie 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 out
`wardly relative to said support ring and to engage
`respective ones of said end stops for preventing inward
`pivoting thereof;
`c) lea?et valve means formed from an aortic root and
`having three generally triangular lea?ets de?ning
`respective cusps which are adapted to open and close
`during heart systole and diastole, respectively, said
`lea?ets being joined at respective commissures adja
`cent said aortic root; and
`d) means for attaching said lea?et valve means to said
`stent posts and said support ring.
`2. 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.
`3. The bioprosthetic heart valve of claim 1, further com
`prising a sewing ring circumscribing said lea?et valve
`means for attaching said lea?et valve means to said support
`ring.
`4. The bioprosthetic heart valve of claim 1, further com
`prising a cloth covering sewn onto said lea?et valve means.
`5. The bioprosthetie heart valve of claim 1, further com
`prising a cloth covering sewn onto said stent posts.
`6. The bioprosthetic heart valve of claim 1, wherein said
`lea?et valve means consists of one of either animal tissue or
`human tissue.
`7. The bioprosthetic heart valve of claim 6, wherein said
`animal tissue is chemically treated pig aortic valve.
`8. The bioprosthetic heart valve of claim 6, wherein said
`animal tissue is chemically treated calf pericardium.
`9. The bioprosthetic heart valve of claim 1, wherein each
`of said stent posts 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
`
`5
`
`20
`
`25
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`5,549,665
`
`6
`pivot arms so as to permit said outward pivoting of said stent
`posts.
`10. The bioprosthetic heart valve of claim 1, wherein the
`three generally triangular lea?ets are arranged in a geometry
`which prevents the pivoting of the stent posts beyond a 15%
`expansion of comrnissural diameter.
`11. The bioprosthetic heart valve of claim 1, wherein each
`of said end stops further comprises a pair of members
`projecting from said support ring on opposite sides of a
`respective one of said stent posts for preventing said inward
`pivoting thereof.
`12. 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 out
`wardly relative to said support ring and to engage
`respective ones of said end stops for preventing inward
`pivoting thereof;
`0) lea?et valve means having three generally triangular
`lea?ets de?ning respective cusps which are adapted to
`open and close; and
`d) means for attaching said lea?et valve means to said
`stent posts and said support ring.
`13. The bioprosthetic heart valve of claim 12, wherein the
`three generally triangular lea?ets are arranged in a geometry
`which prevents the pivoting of the stent posts beyond a 15%
`expansion of cornrnissural diameter.
`14. 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 out
`wardly relative to said support ring and to engage
`respective ones of said end stops for preventing inward
`pivoting thereof;
`-
`c) a stent post ring to which said stent posts are pivotally
`connected for pivoting movement, wherein said stent
`post ring is adapted to limit said outward pivoting of
`said stent posts to approximately 10° from vertical;
`d) lea?et valve means formed from an aortic root and
`having three generally triangular lea?ets de?ning
`respective cusps which are adapted to open and close
`during heart systole and diastole, respectively, said
`lea?ets being joined at respective commissures adja
`cent said aortic root; and
`e) means for attaching said lea?et valve means to said
`stent posts and said support ring.
`15. 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 out
`wardly relative to said support ring and to engage
`respective ones of said end stops for preventing inward
`pivoting thereof;
`c) a stent post ring to which said stent posts are pivotally
`connected for pivoting movement;
`d) lea?et valve means formed from an aortic root and
`having three generally triangular lea?ets de?ning
`respective cusps which are adapted to open and close
`during heart systole and diastole, respectively, said
`lea?ets being joined at respective comrnissures adja
`cent said aortic root; and
`e) means for attaching said lea?et valve means to said
`stent posts and said support ring.
`16. The bioprosthetic heart valve of claim 15, wherein
`each of said end stops further comprises a ?rst member
`
`NORRED EXHIBIT 2105 - Page 8
`
`

`

`5,549,665
`
`7
`projecting from an outer diameter of said support ring, said
`?rst member being of generally spherical segment shape
`de?ning a hollow internal portion, and a second member
`projecting from said outer diameter toward an inner diam
`eter of said support ring, said second member extending
`substantially above said ?rst member and being of generally
`arcuate shape.
`17. The bioprosthetic heart valve of claim 16, 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 ?rst
`member during diastole, whereby said stent post is pre
`vented from inward pivoting during diastole while said stent
`post being permitted to pivot outwardly by twisting of said
`stent post ring during systole.
`
`15
`
`8
`18. The bioprosthetic heart valve of claim 15, further
`comprising a wire frame conforming in shape to said respec
`tive cusps of said lea?et valve means and connected to an
`upper end of each of said stent posts, for supporting said
`lea?et valve means on said stent post ring.
`19. The bioprosthetic heart valve of claim 18, wherein
`said wire frame is received within cooperatively dimen
`sioned slots disposed in the upper end of each of said stent
`posts.
`20. The bioprosthetic heart valve of claim 15, wherein
`said stent post ring is fabricated from a ?exible polymer.
`21. The bioprosthetic heart valve of claim 15, wherein the
`three generally triangular lea?ets are arranged in a geometry
`which prevents the pivoting of the stent posts beyond a 15%
`expansion of commissural diameter.
`
`NORRED EXHIBIT 2105 - Page 9
`
`