United States Patent [191
`Girard et a].
`
`USOO571641
`[11] Patent Number:
`[45] Date of Patent:
`
`5,716,417
`Feb. 10 1998
`a
`
`[54] INTEGRAL SUPPORTING STRUCTURE FOR
`BIOPROSTHETIC HEART VALVE
`
`-------- ~- 623/2
`4,351,000 7/1939 Gupta
`5,258,023 11/1993 Reger .................... .. 623/900
`5,411,552
`5/1995 Andersen et a]. .................... .. 623/900
`
`[75] Inventors: Michael J. Girard. Lino Lakes; Todd
`D. Campbell. White Bear; M. William
`Mir-sch, II. Roseville; Kristen
`Swanson. St. Paul, all of Minn.
`
`[73] Assignee: St. Jude Medical, Inc.. St, Paul. Minn.
`
`[21] Appl. Nu; 472,744
`
`[22] Filed:
`
`Jun. 7, 1995
`
`[51] Int. Cl.6 ...................................................... .. A61F 2/24
`[52] US. Cl. ................................... .. 623/900; 623/2
`[58] Field of Search .................................. .. 623/900. 2. 3.
`623/66
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`1264471
`2/1972 United Kingdom ..................... .. 623/2
`2279134 121994 United Kingdom ..................... .. 623/2
`
`Primary Examiner—John G. Weiss
`Assistant Examiner—Bruce E. Snow
`Attorney, Agent, or Firm—l-Iallie A. Finucane
`
`[571
`
`ABSTRACT
`
`A Stem fol‘ receiving and Supporting *1 tissu? hem Valv? for
`ultimate implantation into a humam th? heart valve includ
`“1g ‘issue '“?m 30in“ a‘ circumfercmiauy 5PM“
`commissures. wherein the stent includes at least one com
`missure support post and at least one sinus support structure
`each sinus support structure being disposed between but not
`functionally connected to an adjacent commissure support
`post.
`
`3/1971 Hancock ............................... .. 623/900
`3,570,014
`4,626,255 12/1986 Reichart et al. ...................... .. 623/900
`
`3 Claims, 4 Drawing Sheets
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`22
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`KN}
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`'
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`NORRED EXHIBIT 2127 - Page 1
`Medtronic, Inc., Medtronic Vascular, Inc., & Medtronic
`Corevalve, LLC v. Troy R. Norred, M.D.
`Case IPR2014-00111
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`

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`US. Patent
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`Feb. 10, 1998
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`Sheet 1 of 4
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`5,716,417
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`NORRED EXHIBIT 2127 - Page 2
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`U.S. Patent
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`Feb. 10, 1998
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`Sheet 2 of 4
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`NORRED EXHIBIT 2127 - Page 3
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`US. Patent
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`Feb. 10, 1998
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`Sheet 3 of 4
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`NORRED EXHIBIT 2127 - Page 4
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`US. Patent
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`Feb. 10, 1998
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`Sheet 4 of 4
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`NORRED EXHIBIT 2127 - Page 5
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`5.716.417
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`1
`INTEGRAL SUPPORTING STRUCTURE FOR
`BIOPROSTHETIC HEART VALVE
`
`FIELD OF THE INVENTION
`
`This invention relates generally to replacement heart
`valves for use in humans. and more particularly is directed
`to an integral supporting structure for use in a bioprosthetic
`tissue valve.
`
`BACKGROUND OF THE INVENTION
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`Prosthetic heart valves are typically used to replace dis
`eased natural heart valves in either the aortic or mitral
`position. Several categories of prosthetic heart valves are in
`existence. One category includes what may be referred to as
`mechanical heart valves. Such valves typically have a rigid
`ori?ce ring and rigid hinged lea?ets coated with a blood
`compatible substance such as pyrolytic carbon. Other
`con?gurations. such as ball-and-cage assemblies. have also
`been used for such mechanical valves.
`A second category of prosthetic heart valves comprises
`assemblies having various amounts of biological or natural
`material. As described in more detail below. some of these
`valves include lea?ets derived from natural material
`(typically porcine) and still include the natural supporting
`structure or ring of the aortic wall. In other valves. lea?ets
`derived from natural material (typically bovine pericardium)
`are trimmed and attached to a synthetic. roughly annular
`structure or ring that mimics the function of the natural
`aortic wall. In still other valves. both the lea?ets and the
`annular support ring are formed of synthetic polymers or
`biopolymers (e.g.. collagen and/or elastin). For ease of
`description. these valves will be referred to herein as bio
`prosthetic valves.
`Many bioprosthetic valves include an additional support
`structure or stent for supporting the lea?ets, although
`so-called stentless valves are also used. The stent provides
`structural support to the cross-linked valve. and provides a
`suitable structure for attachment of a sewing cult to anchor
`or suture the valve in place in the patient.
`Bioprosthetic valves which include a stent are typically of
`two types. In one type. an actual heart valve is retrieved from
`either a deceased human (“homograft”) or from a slaugh
`tered pig or other mammal (“xenograft”). In either case. the
`retrieved valve may be trimmed to remove the aortic root. or
`the aortic root or similar supporting structure may be
`retained. The valve is then preserved and/or sterilized. For
`example. homografts are typically cryopreserved and
`xenografts are typically cross-linked. typically in a glutaral
`dehyde solution. The tissue valve may then be attached to
`the stent.
`The other type of stented bioprosthetic valve includes
`individual valve lea?ets which are cut from biological
`material. e.g.. bovine pericardium. The individual lea?ets
`are then positioned on the stent in an assembly that approxi
`mates the shape and function of an actual valve.
`In the case of either type of stented bioprosthetic valve.
`the function of the stent is similar. Primarily. the function of
`the stent is to provide a support structure for the prosthetic
`valve. Such a support structure may be required because the
`surrounding aortic or rnitral tissue has been removed in
`harvesting the valve. The support o?‘ered by a stent in a
`valve is important for several reasons. First of all. a valve is
`subject to signi?cant hemodynamic pressure during normal
`operation of the heart. Upon closing the valve the lea?ets
`close to prevent back?ow of blood through the valve. In the
`
`2
`absence of any support structure. the valve cannot function
`properly and will be incompetent. One function of the stent
`is to assist in absorbing the stresses imposed upon the
`lea?ets by this hemodynamic pressrn'e. This is typically
`achieved in existing stents through the use of commissure
`support posts to which the valve commissures are attached.
`Some known stents have been designed such that the
`commissure support posts absorb substantially all the
`stresses placed on the valve by hemodynamic pressure. One
`such stent is a formed piece of spring wire which is bent to
`form three vertically-extending commissure support posts.
`each having a U-shape and being connected to the other
`commissure support posts via arcuate segments of wire.
`Such a stent is described in U.S. Pat. No. 4.106.129 to
`Carpentier. et al. In that stent. the lea?et stresses are borne
`by the commissure posts rotating around and exerting a
`torque upon the arcuate wire sections between the posts. The
`composition and structure of this stent also provides for
`deforrnability of the ori?ce-de?ning elements. A separate
`insert element in the form of a plastic web is positioned
`around the wire stent prior to attachment of the valve.
`In other types of stents. the commissure posts are ?xed to
`a rigid base and are designed to be substantially ?exible
`along their entire length so that the posts bend in the manner
`of a ?shing pole in response to the stresses imposed upon the
`lea?ets by hemodynamic pressure. An example of such a
`stent is shown in U.S. Pat. No. 4.343.048 to Ross. et al.
`Other stents. for example the stent shown in U.S. Pat. No.
`4.626.255 to Reichart. et al.. include further support struc
`ture connected to and disposed between the commissure
`support posts. Such support structure prevents a given
`commissure post from being resilient along its entire length.
`Still other stents. such as in U.S. Pat. No. 5.037.434 to Lane.
`include an inner support frame with commissure posts
`resilient over their entire length. and a relatively more rigid
`outer stent support which begins to absorb greater stress as
`the associated commissure support bends further inward.
`Although all of these stents provide support to the bio
`prosthetic valves to which they are attached. the stress
`distributions are often unnatural. leading to premature wear
`or degradation of over-stressed portions of the valve.
`Accordingly. the need exists for stents which more closely
`approximate the stress response of a natural aortic or mitral
`valve. Furthermore. the stents which include several parts
`are mechanically complex and require multiple assembly
`steps. A stent which includes a stress response that approxi
`mates a natural valve would thus also desirably have an
`integral constmcn‘on.
`Another function of a stent is to serve as a framework both
`for attachment of the valve. and for suturing of the valve into
`place in the recipient. e.g.. a human patient. Toward that end.
`the stent. or a portion of the stent. is typically covered with
`a sewable fabric or membrane. and may have an annular
`sewing ring attached to it. This annular sewing ring serves
`as an anchor for the sutures used to attach the valve to the
`patient.
`A variety of different stent designs have been employed in
`an effort to render valve attachment. and implantation of the
`valve simpler and more e?icient Design trade-offs have
`often occurred in designing these stents to have the desirable
`stress and strain characteristics while at the same time
`having a structure which facilitates assembly and implanta
`tion.
`In the stentless valves previously referred to. the unsup
`ported valve is sewn into the recipient's aorta in such a way
`that the aorta itself helps to absorb the stresses typically
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`3
`absorbed by a stent. Current porcine aortic stentless valves.
`such as porcine aortic stentless valves. are typically intended
`for use in the aortic position and not in the mitral position.
`A mitral valve would require a support structure not pres
`ently available with porcine aortic valves. and recently.
`stentless porcine rnitral valves for placement in the mitral
`position have been developed.
`Indeed. the stented valves used in the mitral position
`utilize the stent to provide support for normal valve function.
`In these stented mitral valves. a “low pro?le” stent having
`generally shorter commissure posts has been used. so as to
`prevent the ventricle wall from impinging on the valve.
`However. use of a lower pro?le stent often requires that the
`bioprosthetic valve be somewhat distorted upon attachment
`to the low-pro?le stent. ‘This. in turn. can lead to reduced
`functionality of such valves. While the “higher pro?le”
`stents can avoid this distortion. care must be given to valve
`placement so as to avoid the referenced impingement by the
`ventricle wall. A need exists for a stent for use in the mitral
`position that includes the advantageous stress/strain and
`attachment characteristics previously described.
`Known stents for bioprosthetic valves have been formed
`from a variety of materials including both metals and
`polymers. Regardless of the material employed. the long
`term fatigue characteristics of the material are of critical
`importance. Unusually short or uneven wear of a stent
`material may necessitate early and undesirable replacement
`of the valve. Other material characteristics are also consid
`ered in selecting a stent material. including: rate of water
`absorption. creep. and resilience to the radiation which may
`be used for sterilization. Further. it may be highly desirable
`to form the stent of a radio-opaque material to allow the
`stented valve to be viewed by x-ray imaging. Of course. the
`selected material must also be biocompatible and have the
`required physical characteristics to provide the desired
`stress/strain characteristics. Furthermore. most existing
`stents are formed of a material having a constant cross
`sectional dimension. Formed wire stents and stents formed
`from stamped metal are examples. Use of a material of
`variable cross section would allow stress and strain charac
`teristics to be carefully controlled by adding or subtracting
`cross sectional area in cm'tain regions of the stent. as may be
`required.
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`SUMMARY OF THE INVENTION
`Accordingly. it is a general aim of the present invention
`to provide an improved stent for use in combination with
`bioprosthetic heart valves. Any valve or lea?et. Whether
`mechanical or natural tissue. may be used with the stents of
`the present invention. ‘Typical natural valves include. but are
`not limited to horse. kangaroo. rabbit. bear. cow. pig. boar
`and human. The preferred valve or lea?et is porcine-derived
`In accordance with that aim. it is a primary object of the
`present invention to provide an integral stent that more
`closely approximates the stress and strain response of a
`natural valve than has been provided by known stents.
`It is a related object of the invention to provide such a
`stent that closely mimics the natural valvular anatomy and
`allows the three commissures of the valve to work in unison.
`It is a further related object to provide such a stent having
`adequate support in the commissure region. while approxi
`mating the constraints placed on the valve by the natural
`compliance of the aorta.
`A further object of the invention is to provide an integral
`stent having the desirable stress-strain characteristics. and
`having a structure that facilitates assembly of the valve to the
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`stent. It is another object of the invention to provide a stent
`having a structure that facilitates the implantation of the
`assembled valve in the patient. It is a related object of the
`invention to provide such a stent with easy and complete
`commissure attachment.
`It is further related object to provide such a stent that
`allows easy attachment of the other components associated
`with the stented valve including the sewing ring.
`A further object of the invention is to provide an integral
`stent composed of a material that has improved performance
`characteristics. particularly. superior long-term performance
`characteristics.
`An integral stent for use in a bioprosthetic valve in
`accordance with the present invention achieves the afore
`mentioned object.
`The stent includes a plurality of oornmissure support
`posts. preferably asymmetrically circurnferentially spaced to
`duplicate or approximate the spacing between valve com
`rnissures that occurs in nature. Each commissure support
`post includes an in?ow edge. an out?ow edge. and side rails
`connected between the edges. The side rails and edges
`preferably enclose a longitudinally-extending central open
`ing that allows attachment of the comrnissures of the valve
`to the commissure support posts. In some embodiments of
`the invention. the stent also may include in?ow rail seg
`ments connected between the in?ow edges of the commis
`sure support posts. See. for example. FIGS. 1 and 4. The
`in?ow rail segments and the in?ow edges of the support
`posts form a circumferentially continuous annular in?ow
`surface.
`In other embodiments of the invention. the in?ow surface
`and the in?ow rail segment may be discontinuous. In this
`embodiment of the invention. for example. the area between
`and under the commissure support posts may be open or
`substantially open. An exemplary embodiment of an open
`stent is shown in FIG. 3.
`The stent may also include one or a plurality of sinus
`support structures. Each sinus support structure is disposed
`between adjacent commissure support posts. In preferred
`embodiments of the invention. the sinus support structure(s)
`are not functionally connected to the adjacent commissure
`support post. See. for example. FIGS. 3 and 4. As used
`herein. functionally connected refers to no connection. or a
`connection that does not share or relieve stress distribution
`with the support post. as described in more detail below.
`In accordance with the present invention. each of the sinus
`support structures typically include a pair of diverging side
`arms. A ?rst side arm is attached to the in?ow rail and
`extends toward. but does not functionally connect to. one of
`the adjacent commissure support posts. A second side arm is
`also functionally attached to the in?ow rail and extends
`toward. but does not functionally connect to. the other
`adjacent commissure support post. Connecting the pair of
`diverging side arms is a top rail which curvedly extends
`between the pair of side arms. One or more supports may
`connect the top rail to the in?ow rail.
`The resulting structure closely approximates the stress
`strain response and dynamics of a natural valve. The com
`missure support posts are preferably ?exible along their
`entire length and can form an arcuate bend. e.g.. in the
`manner of a ?shing pole.
`In devices according to the present invention. in attaching
`the valve to the stent. tissue of the valve may connect the
`commissure support posts and the intermediate sinus support
`structures. As a result. the commissure support posts and the
`sinus support structures o?‘er two different mechanism for
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`5,716,417
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`5
`absorbing the hemodynamic stress imposed upon the leaf
`lets. The result is a more accurate approximation of the stress
`performance of a natural valve. since the sinus support
`regions and the means by which they are attached to the
`valve. mimic the constraints placed on the valve by the
`natural compliance of the aorta. As a result. the individual
`commissures work in unison and are made dependent upon
`each other. Furthermore. the stent is integrally formed and
`includes a relatively open structure; these features. among
`others. ease attachment to other parts of the valve. and the
`implantation of the completed assembly is easier and more
`reliable.
`Other objects and advantages will become apparent from
`the following detailed description and appended claims. and
`upon reference to the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a perspective view of a stent according to one
`embodiment of the invention.
`FIG. 2 is a top representative view of the relative place
`ment of the commissure support posts according to some
`embodiments of the invention.
`FIG. 3 is a perspective view of a stent according to
`another embodiment of the invention.
`FIG. 4 is a photograph of a stent according to the
`embodiment of the invention shown in FIG. 1.
`FIG. 5 is a photograph of a stent according to an embodi
`ment of the invention showing a stent covered with a
`sewable fabric.
`FIG. 6 is a photograph of a stent of FIG. 5 showing the
`attachment of the sewing ring.
`DETAIIED DESCRIPTION oF THE
`PREFERRED EMBODIMENTS
`Turning now to the drawings, FIG. 1 shows an integral
`tissue valve stent 10 according to one embodiment of the
`present invention. As a point of reference. arrow 11 shows
`the direction of blood ?ow through the stent and valve. The
`stent 10. as illustrated, includes three commissure support
`posts 20. 30 and 40. It is intended that the invention should
`not be limited by the number of commissure support posts.
`The number used is primarily a product of the number of
`lea?ets being used. For example. there are typically three
`porcine-derived lea?ets. so the stent would typically include
`three commissure support posts. Other systems may have a
`di?’erence number of lea?ets. and mechanical systems typi
`cally have one to three lea?ets. Also. the placement of the
`valve. e.g.. aortic or mitral. may dictate the number of
`lea?ets used.
`According to one aspect of the invention. these support
`posts are asymmetrically circumferentially spaced about the
`generally cylindrical stent 10. It will be appreciated that
`support posts 20. 30. 40 are each adapted to receive a
`commissure of the bioprosthetic valve. Each support post
`includes a central opening 21. 31. 41 that runs along the
`length of the respective support post. The central opening as
`shown is preferably oblong. but any shape may be used
`Also. each support post may include more than one central
`opening. Each oblong central opening may be bordered on
`either side by side rails. preferably tapered side rails. FIG. 1
`shows ?rst side rail 23 and second side rail 24. The remain
`der of the oblong central opening 21 is bordered by an in?ow
`edge 26 and an outflow edge 27. The in?ow edge and/or an
`upstream portion of the commissure support post may also
`include radially thickened areas. These radially thickened
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`6
`areas may provide additional structure as needed to avoid.
`channel. distribute. or reduce stress caused during operation
`of the valve assembly. In attaching the tissue valve to the
`stent. sutures would pass through the central openings. One
`skilled in the art will thus appreciate that the presence of
`these central openings facilitates attachment of the valve.
`In a preferred embodiment of the invention. each of the
`side rails 23. 24 may also taper from the in?ow edge to the
`out?ow edge. This taper helps distribute stress more evenly
`and provides the support post with some of its advantageous
`functional features. as will be discussed in greater detail
`below. The three support posts. each having side rails. an
`in?ow edge. and an oudlow edge. are connected together by
`in?ow rail segments 51. 52 and S3. The in?ow rail segments
`and the in?ow edges of the three support posts 20. 30. 40
`may form a circumferentially continuous in?ow surface 50.
`as shown in FIG. 1. or may be discontinuous. as shown in
`FIG. 3.
`According to an embodiment of the invention. the in?ow
`surface may be planar or may be scalloped to match or
`approximate the aortic or mitral valve anatomy. As shown in
`FIG. 1. the in?ow surface 50 may be sinuous or sinusoidal.
`with each support post 220. 30. 40 having a corresponding
`downstream directed maximum 22. 32. 42. respectively. The
`area corresponding to a maximum is also the area where the
`greatest amount of material is removed when the stent is
`produced using a laser machining process. as explained in
`more detail below. Between each maximum is a downstream
`directed minimum 74. 84. 94. respectively. Likewise. each
`sinus support structure 70. 80. 90 has a corresponding
`downstream-directed minimum 74. 84. and 94. respectively.
`The area corresponding to a minimum is also the area where
`no material is removed. or the smallest amount of material
`is removed. when the stent is produced using a laser machin
`ing process. as explained in more detail below.
`As shown more clearly in FIG. 2. an embodiment of the
`invention includes spacing commissure support posts 20. 30.
`40 in a predetermined circumferential or angular distribu
`tion. In a preferred embodiment of the invention. support
`post 20. 30. and 40 are asymmetrically distributed. with only
`one support post being equi-angled or equidistant to the
`others. For example. for porcine-derived valves. the right
`cusp and the left cusp are typically about the same size. and
`the non-coronary cusp is typically smaller than the other
`two. FIG. 2 shows support post 40 equidistant from both
`support post 30 and support post 20. but neither support post
`30 or support post 20 are equidistant from the other two
`posts. Example 1 provides various factors involved in
`choosing a speci?c support post distribution. The primary
`factors are the number of lea?ets. the typical size of the
`lea?ets. and the source of the lea?ets. For example. porcine
`derived valves typically have three lea?ets. with two usually
`being larger than the other. To most closely approximate the
`spacing of the natural valve. a porcine-derived replacement
`valve may have two lea?ets spaced from about 121° to about
`125°. preferably from about 122° to about 124°. and most
`preferably approximately 123". As one sldlled in the art will
`appreciate. this spacing may change according to the nature
`of the actual lea?et chosen.
`For example. when implanting porcine valves. it may be
`desirable to evaluate the speci?c porcine valve geometry in
`comparison to the recipient heart sinus region in order to
`match stent post height and width. and sinus height and
`width. etc.. in order to more closely match the porcine
`geometry to the recipient’s geometry and to avoid or mini
`mize blocking the patient’s ostium or ostia.
`In accordance with the invention. one skilled in the art
`may also distribute stress/strain resistance by choosing a
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`7
`predetermined post sti?ness. Post sti?ness is partly a prod
`uct of the size. shape. and materials used in a particular stent.
`in support posts 20. 30. and 40. and in their respective side
`rails. Stress resistance and/or distribution may also be a
`product of the interaction of the various structures of a stent
`or stent assembly according to the present invention. As
`described above. tapering the side rails of each post also
`helps distribute stress through the support post more evenly.
`Example 2 provides various factors involved in choosing
`post stiffness. It will be appreciated by those skilled in the
`art that selecting a maximum stress well below the endur
`ance limit of the material prevents premature failure of the
`stent. For example. in a stent made from
`polyetheretherketone. a post stilfness from about 0.59 N/mm
`to about 0.73 N/mm has been found acceptable.
`A stent according to the invention may also include a
`fabric covering or wrap. and/or a sewing ring or cuff. The
`construction. design. and placement of these features are
`well-known in the art.
`The support post geometry and angular distribution noted
`above can adequately handle the stress and strain imposed
`upon the stent by the operating valve. Stent 10 also includes
`sinus support structures 70. 80. 90 in the sinus regions
`between support posts. It will be appreciated that these
`open-structured sinus support structures facilitate the physi
`cal attachment of the valve to the stent. As would be evident
`to one skilled in the art. the base of a lea?et would be
`attached to the fabric covering the stent approximately in the
`curve from the downstream end of a commissure support
`post. across a side arm of the adjacent sinus support
`structure. across the trough between two side arms. up the
`other side arm of the sinus support structure. and over to the
`downstream end of a second commissure support post. This
`roughly corresponds to an arced region running from the
`downstream distal end of a commissure support post. into
`the trough formed by the sinus support arms. and up to the
`downstream distal end of another commissure support post.
`The sinus support structures also place constraints on the
`stented valve that allow it to perform more like a natural
`valve as constrained by the surrounding tissue. e.g.. an aortic
`valve constrained by the aorta. As opposed to known stents
`that permit the lea?ets or cusps to function independently of
`each other. a stent according to the present invention mimics
`naturally occurring heart valves by tying the function of one
`lea?et to the function of another. In an assembled stent of the
`present invention. the lea?ets all function together. Pressure.
`stress. or constraints on one lea?et will be shared or affect
`another lea?et.
`In an embodiment of the invention shown in FIGS. 1 and
`4. each sinus support structure 70. 80. 90 is composed of two
`side arms 72. 73 (only the side arms for sinus support
`structure 70 are labelled). Each diverging side arm has a ?rst
`end attached to an in?ow rail segment. and a second end
`extending toward. but not connected to. an adjacent com
`missure support post. For example. sinus support structure
`70 has ?rst side arm 72 and second side arm 73. both of
`which have an end attached to in?ow rail segment 51. First
`side arm 72 extends toward side rail 24 of adjacent support
`post 20. and second side arm 73 extends toward side rail 33
`of adjacent support post 30.
`Each sinus support structure may also include a top rail 75
`connected to and extending between the diverging side arms
`72 and 73. and. as is shown in FIG. 3. one or more additional
`posts may connect the top rail to the in?ow rail segment.
`In accordance with a preferred embodiment of the
`invention. the side arms are not functionally connected to the
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`adjacent support posts to which they are closest. As noted
`above. if there is any minimal connection. it is preferred that
`such connection does not affect the natural stiffness of the
`adjacent support post. nor do the arms alfect the stress
`response of the free-standing stent. It will be appreciated.
`however. that the presence of a tissue valve sutured to the
`stent provides an indirect tissue connection between a given
`support post and an adjacent side arm.
`This indirect tissue connection is believed important for
`several reasons. In the case of sinus support structure 70. the
`indirect tissue connection between support post 20. sinus
`support structure 70. and support post 30 places a constraint
`condition on movement of the two support posts 20 and 30.
`Indeed. all three support posts 20. 30. and 40 are similarly
`constrained by the presence of the other two sinus support
`structures 80 and 90. This constraint causes the three support
`posts to act in unison when the valve is properly attached to
`the stent That is. as hemodynarnic pressure is applied to the
`valve and transferred to the stent. the indirect tissue con
`nection causes the three support posts to work in unison. as
`constrained by the tissue connecting the commissures. and
`as also constrained by their connection to the sinus support
`structures. Such constraint. causing the three comrnissures to
`work in unison. is present in a natural valve. In a natural
`valve. this natural constraint is provided by the structure and
`compliance of the surrounding tissue. For example. it may
`be desirable to have an even higher commissure post
`?exibility. then have a sinus ring side arm connected to the
`commissure post for the additional stiifness. This may be
`accomplished by having a stiif side rail and no contact with
`the side arm. or by having a ?exible side rail that is made
`more stiff by connection with a side arm.
`In accordance with the invention, the commissure support
`post or posts are preferably ?exible along the entire length
`of the side rails. In this and the embodiments noted below.
`it may be desirable for the commissure support post ?ex
`ibility to approximate the physiological ?exibility of the
`natural valve. It may also be desirable to minimize tissue or
`lea?et stress in the assembled valve. particularly under
`conditions when physiological ?exibility can not be
`achieved.
`In other embodiments of the invention. the commissure
`support post or posts may have a predetermined ?exibility
`characteristic along its length. or may have a predetermined
`?exibility characteristic that is variable along its length.
`Areas of greater or lesser ?exibility may be achieved. for
`example. by using different thicknesses of the same material.
`or by using materials of diiferent ?exibility as a composite.
`In contrast. however. following harvesting of a biopros
`thetic valve. the aortic root is trimmed to adequately expose
`the valve to allow for attachment of the valve to the stent. As
`such. the portion of the aorta which would normally provide
`this constraint is typically missing. Moreover. for placement
`of a bioprosthetic tissue valve in the mitral position. there is
`no surrounding vascular anatomy which would provide the
`necessary constraint. The sinus support sn'uctures 70. 80. 90
`and the indirect tissue connection are therefore believed to
`mimic the constraints placed on the valve by the natural
`compliance of the aorta. without interfering with the stress/
`strain characteristics of the free-standing commissure sup
`port posts.
`Furthermore. the preferably open geometry of the sinus
`support structures facilitates the assembly process. during
`which the tissue valve is typically sutured or attached to the
`fabric covering the stent. and a sewing ring is typically
`sutured or attached to the fabric covering the stent. It will be
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`appreciated that the assembly process is also facilitated by
`the preferred integral or unitary structure of the stent. Since
`multiple parts do not need to be assembled to each other or
`to the valve. the complexity of the assembly process is
`reduced. An integral or unitary design also prevents relative
`movement between separate stent segments which may lead
`