US20100131055A1 - Artificial valve prosthesis with improved flow dynamics - Google Patents

Abstract

An expandable venous valve having a support structure configured to enlarge the area adjacent the valve structure. The enlarged pocket areas can be created by forming an artificial sinus adjacent the valve structure in an unsupported section of vessel wall between two support frame sections.

Description

TECHNICAL FIELD
• This invention relates to medical devices, more particularly to intravascular valve prostheses and the like.
BACKGROUND OF THE INVENTION
• The venous system includes a series of valves that function to assist the flow of blood returning to the heart. These natural valves are particularly important in the lower extremities to prevent blood from pooling in the lower legs and feet during situations, such as standing or sitting, when the weight of the column of blood in the vein can act to prevent positive blood flow toward the heart. This condition, commonly known as ‘chronic venous insufficiency’, is primarily found in individuals in which gradual dilation of the veins, thrombotic events, or other conditions prevent the leaflets of the native valves from closing properly. This leads to significant leakage of retrograde flow such that the valve is considered ‘incompetent’. Chronic venous insufficiency is a potentially serious condition in which the symptoms can progress from painful edema and unsightly spider or varicose veins to skin ulcerations. Elevation of the feet and compression stocking can relieve symptoms, but do not treat the underlying disease. Untreated, the disease can impact the ability of individuals to perform in the workplace or maintain their normal lifestyle.
• To treat venous valve insufficiency, a number of surgical procedures have been employed to improve or replace the native valve, including placement of artificial valve prosthesis. These efforts have met with limited success and have not been widely adopted as a method of treating chronic venous insufficiency. More recently, the search has been to find a suitable self-expanding or radially-expandable artificial valve that can be placed using minimally invasive techniques rather than requiring open surgery and its obvious disadvantages. Thus far, use of prosthetic venous valves has remained experimental only.
• While attempts have been made to mimic the function of the natural valve, there is no expandable valve for venous transcatheter placement that includes a combination of the native structural features that individually or collectively, may prove highly advantageous or critical for a successful valve. One common problem evident from early experiences with prosthetic valves is the formation of thrombus around the base of the leaflets, probably due at least in part to blood pooling in that region. In a natural valve, the leaflets are typically located within a sinus or enlargement in the vein. There is some evidence that the pockets formed between the leaflets and the walls of the sinus create vortices of flowing blood that help flush the pocket and prevent blood from stagnating and causing thrombosis around the valve leaflets, which can interfere with the function of the valve. It is thought that the stagnating blood prevents oxygen from reaching the endothelium covering the valve cusps, leading to hypoxia of the tissues which may explain increased thrombus formation typical in that location. Expandable-frame valve prostheses typically are of a generally cylindrical in shape and lack an artificial sinus or pocket space that is sufficient for simulating these natural blood flow patterns. What is needed is an intravenously placed artificial valve that is configured to create more effective flow patterns around the valve structure to circulate the blood or bodily fluids and reduce the likelihood of stagnation and the potential clinical problems that may result.
SUMMARY OF THE INVENTION
• The foregoing problems are solved and a technical advance is achieved in an illustrative valve prosthesis, such as an artificial venous valve, having a valve structure and a self-expanding or otherwise expandable support structure that upon deployment within the vein, helps create an artificial sinus or larger pocket in the vessel surrounding the valve structure of sufficient size and shape to stimulate flow patterns or vortices which facilitate clearing of the blood or other bodily fluid that would otherwise pool therein. The structural adaptations result in more turbulent flow, increased velocity of flow, larger and/or more numerous vortices, other factors, or a combination of the above that prevent stagnant, hypoxic areas from occurring around the valve structure. Furthermore, the modified flow may also contribute to helping close the leaflets to form a seal and prevent leakage of fluid back through the valve. The artificial sinus or enlarged pockets simulate the function of the natural sinus that exists at the site of most natural valves in the deep veins of the lower legs and which may explain why the problem of thrombus forming around the valve structure has been observed to be a common problem in prosthetic venous valve designs lacking such a sinus area.
• In one aspect of the invention, the collapsible support structure of the valve prosthesis is expandable to a particular diameter upon deployment, with the valve prosthesis being configured such that the prosthesis includes an intermediate, substantially ‘open’ section such that the artificial sinus is created by a portion of the duct or vessel that is substantially unsupported by the support structure. The unsupported portion of the vessel can advantageously assume a diameter that is larger than the deployment diameter of the vessel-anchoring or ‘closed’ sections or portions of the collapsible support structure, thereby creating an artificial sinus as blood (or bodily fluid) exerts pressure on the unsupported portion of the vessel wall. In one exemplary embodiment, the expandable support structure comprises a first, proximal portion and a second, distal portion that are interconnected by one or more thin members or struts, such that the largely unsupported region between the first and second (proximal and distal) sections of the support structure forms an artificial sinus (proximal being defined herein as have the same positional orientation as the orifice or opening of the valve structure, which is typically toward the heart in a venous valve). The valve structure is attached about the support structure such that it is largely situated within the unsupported region forming the artificial sinus. For example, the valve structure (defined herein as one or more cooperating leaflets, tubular members, or any flexible structure adapted to seal a passageway in response to changing fluid pressure differentials thereacross) may be attached to the interconnecting members, which can comprise oppositely placed struts having attachment points, (e.g., suture or any suitable structure or method) to facilitate attachment of the valve material.
• In another aspect of the invention, the expandable support structure of the valve prosthesis comprises a framework or anchoring portion having an intermediate region that includes an enlarged diameter configured to create an artificial sinus about the valve structure, which is attached inside the intermediate region. In one embodiment, the support structure is made of a superelastic material, such as nitinol, and the intermediate region comprises an expanded or bulging portion that is formed by heat setting the nitinol tubular frame around a mandril or other fixture of the desired configuration using a method well known in the medical arts. The intermediate portion expands to a diameter larger than the proximal and distal portions when the prosthesis is deployed from the delivery system, thereby producing larger pockets around the valve structure which create more effective flow patterns to reduce pooling. In another embodiment, the proximal, distal, and intermediate sections are separate, interconnected sections, such as zig-zag frame or other expandable or self-expanding support or anchoring frames. The intermediate section comprising the artificial sinus includes a first and a second radially expandable or self-expanding portions in which the adjoining ends of each are larger in diameter than the ends which adjoin the proximal and distal sections, respectively. The frustoconical shape of the respective intermediate sections can be accomplished by either forming the section into that shape (i.e., plastic deformation of a tubular prosthesis, heat setting nitinol, laser cutting a frustoconical section of tubing, etc.) or a constraining means, such as a suture or thin wire, can be used to manipulate the relative diameters by feeding the constraining means through the apices of the bend or apertures therein and applying the appropriate amount of tension to create the desired shape. Optionally, a tubular or band-like section can be positioned between opposing frustoconical sections to create a longer artificial sinus.
• In yet another aspect of the invention, the proximal end of the collapsible support at which the valve structure is located is expanded (e.g flared outward) such that the expanded end or a combination of the expanded end and adjacent area of the vein forms the artificial sinus.
• In still yet another aspect of the invention, the proximal and distal sections are configured to include a substantially open area between them with the valve structure being attached to the distal section such that it is positioned just below the artificial sinus. Optionally, a sleeve of a biomaterial (e.g a bioremodelable material such as small intestinal submucosa (SIS) or another collagenous extracellular matrix) or fabric can be attached over the proximal and distal sections such that it forms a seal between the prosthesis and the vessel wall, including the artificial sinus.
• In still yet another aspect of the present invention, the support structure of the prosthesis is configured such that the attachment pathway (defined herein as the interface between the lateral, outer edges of the leaflets and the struts and/or vessel walls to which they are attached to establish and define the shape and configuration of the plurality of leaflets comprising the valve structure as deployed) has a first, proximal portion in which the one or more longitudinal attachment struts extending from the proximal bends or commissures that carry and support the proximal outer edges of the leaflets (and span the orifice) have a strongly longitudinal orientation with respect to the longitudinal axis of the prosthesis and valve structure, and a distal portion of the attachment pathway that extends circumferentially (laterally) and distally from the longitudinal axis to form the bottom or distal edge of the outer leaflet edge or perimeter. When viewed from the side, the support frame and attached leaflet is configured such that the angle (angle .alpha.) formed between the opposing leaflets, as carried along the proximal attachment pathway, is substantially less than the angle (angle .beta.) formed between distal attachment pathways and the vessel walls. This configuration results in leaflets having large coaptable area relative to the overall surface area, which improves sealing (including reducing the effects of retraction by the valve material) and allows for larger pockets surrounding the leaflets which, like the sinus, facilitate the creation of larger, stronger vortices of retrograde flow that help close the leaflets and clear away blood or fluid that could otherwise stagnate under conditions where the surrounding pockets are smaller in size. As used herein, the term ‘retrograde flow’ is defined as bodily fluid traveling in a distal direction (toward the feet), whether due to gravitational forces, redirection due to contact with the prosthesis or bodily lumen walls, or by some other means.
• A first embodiment of this aspect of the invention includes a frame comprising a pair of longitudinal attachment struts originating from each commissure bend. The struts extend in generally longitudinal direction, diverging relatively or not at all toward the distal end of the prosthesis before more acutely diverging as they curve laterally and circumferentially away from the proximal strut portions such that the transition between the proximal and distal portions of attachment pathway comprises a bend having a radius that is distinctly smaller than that of the adjacent strut portions (the proximal portions being straight some embodiments). The distal attachment pathways converge to define the bottom outer edge of each leaflet. In a second embodiment of this aspect of the invention, the support frame of the prosthesis includes a pair of substantially parallel longitudinal attachment struts to which the leaflets are attached to form the proximal portion of the attachment pathway, and distal attachment struts extending circumferentially and laterally outward from the substantially parallel struts to form the distal portion of the attachment pathway. The support frame carrying the valve structure may be advantageously comprised of radial sections (e.g., quadrants in a bicuspid valve) that are of an identical pattern but with alternating orientation such as to provide for radial stability and better expandability characteristics. The radial section not carrying the leaflet proximal outer edges serves as lateral support structure for adding longitudinal stability and help protecting the leaflets from adhering to the vessel walls. The parallel struts provide for advantageous bending and torsional characteristics such that the frame has utility as a stent. In an alternate embodiment of the support structure, the lateral outer edges of the opposing leaflets can be attached to single longitudinal attachment strut having a pair of distal struts extending laterally outward and circumferentially to carry the bottom half of the leaflet and define the overall shape thereof. The strut may be thicker than adjacent struts and include aperture therealong for facilitating attachment of the valve structure.
• In still yet another aspect of the present invention, the proximal section of the valve is wider in diameter at its proximal end, which anchors the prosthesis in the vessel, and narrower at the interface between the proximal and intermediate sections. This, in combination with a leaflet structure that maximizes pocket size, results in retrograde flow being subject to a Venturi effect which increases flow and the strength of the vortices to close the valve and clear the pockets of potentially stagnating fluids.
• The configuration of the basic units of the support structure and valve structure is not particularly critical for an understanding of the invention. Numerous examples are well known in the prior art and may be found in the disclosure of Applicant's provisional application Ser. No. 60/403,783 entitled, ‘Implantable Vascular Device,’ filed Aug. 15, 2002 which is expressly incorporated by reference herein.
BRIEF DESCRIPTION OF THE DRAWING
• Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
• FIG. 1 depicts a cross-sectional view of a native venous valve and retrograde blood flow pattern;
• FIG. 2 depicts a schematic view of an illustrative embodiment of the present invention in which the prosthesis includes interconnecting proximal and distal sections defining an intermediate, substantially open section for creating an artificial sinus in the vessel;
• FIG. 3 depicts a schematic view of a second illustrative embodiment of the present invention in which the proximal and distal sections are interconnected by a frame that is incorporated into the valve structure of the prosthesis;
• FIG. 4 depicts a schematic view of an illustrative embodiment of the present invention in which the intermediate section of the prosthesis comprises an expanded portion of the support structure;
• FIG. 5 depicts a schematic view of an illustrative embodiment of the present invention in which the proximal end is expanded to create an artificial sinus about the valve structure;
• FIGS. 6-7 depict side views of embodiments of the present invention in which artificial sinus comprises a plurality of separate support sections;
• FIG. 8 depicts a partially sectioned side view of an embodiment of the present invention that includes an external sleeve of material;
• FIG. 9 depicts a perspective view of a support structure of the present invention adapted to increase coaptation of leaflets and pocket size within the vessel;
• FIGS. 10-11 depict side views comparing the flow patterns in a standard valve leaflet configuration with those of the embodiment ofFIG. 9; and
• FIG. 12 depicts an embodiment of the present invention having a combination of a narrowed intermediate section and the valve structure configuration ofFIG. 9.
• FIG. 13 depicts a side view of an embodiment of the present invention in which the leaflets are attached to the parallel struts to increase the area of coaptation;
• FIG. 14 depicts a side view of the embodiment ofFIG. 13 that is rotated 90.degree. therefrom.
• FIG. 15 depicts a top view of the embodiment ofFIG. 13.
• FIG. 16 depicts an unrolled view of the support frame of the embodimentFIG. 13;
• FIGS. 17-18 depict unrolled views of additional embodiments of the present invention for increasing the area of leaflet coaptation;
• FIGS. 19-20 depict plan views of adaptations in the support structure for affixing the valve structure thereto; and
• FIG. 21 depicts a partially sectioned perspective view of an embodiment in which the support structure does not co-extend along the entirety of the leaflet outer edges.
DETAILED DESCRIPTION
• The present invention, selected examples of which are illustrated inFIGS. 2-9,11-20, comprises a collapsible, self expanding or otherwise expandableartificial valve prosthesis10 that is deployed within abodily passageway20, such as a vessel or duct, of a patient typically delivered and implanted using well-known transcatheter techniques for self-expanding prostheses, the valve prosthesis having a first orproximal end13 and a second ordistal end14, with the normal, antegrade fluid flow typically traveling from the distal end to proximal end of the prosthesis, the latter being located closest to the heart in a venous valve when placed within the lower extremities of a patent. Thevalve prosthesis10 comprises asupport structure11 and avalve structure12, such as the illustrative valve structure, attached about the support structure and configured to selectively restrict fluid flowing therethrough by closing with changes in the fluid pressure differential, such as in the presence of retrograde flow. The present invention includes structural features that modify the flow dynamics within the prosthesis such that fluid collecting inpockets35 near the base of theleaflets26 is more likely to be flushed away or effectively mixed with fresher incoming bodily fluid on a continual basis.
• It should be understood that the materials used to comprise thesupport structure11 can be selected from a well-known list of suitable metals and polymeric materials appropriate for the particular application, depending on necessary characteristics that are required (self-expansion, high radial force, collapsibility, etc.). The materials used for thevalve structure12 can comprise a synthetic material or biologically-derived material appropriate for the clinical application; however, investigational studies have demonstrated that a bioremodelable material (such as an collagenous extracellular matrix (e.g., small intestinal submucosa), pericardial, or a growth factor-enhanced material may have superior anti-thrombogenic properties within the body as the native cells and tissue gradually replace the original leaflet material. The number of leaflets possible for embodiments of the present invention can be two, three, four, or any practical number, but bi-leaflet valves may prove advantageous in low-flow venous situation as compared to tri-leaflet embodiments, such the type used as heart valves which are subject to high-flow situations where thrombus formation is far less of a problem.
• In the embodiments ofFIGS. 2-8, thesupport structure11 is configured such that when the device is deployed within thebodily passage20, such as a vein of the lower legs or feet, anartificial sinus34 is formed adjacent to and surrounding thevalve structure12 such that the blood or other bodily fluids collecting within thepockets35 formed around the bases of thevalve leaflets26 is more likely to be flushed out on a continual basis due to the advantageous geometry created by theartificial sinus34. The principle is illustrated in the example ofFIG. 1 which shows a naturalvenous valve21 in whichretrograde blood22 flowing or falling back down and closing the valve is thought to create a series ofvortices23 as it contacts the leaflets. It is believed that the rounded shape of the enlargednatural sinus37 surrounding thevalve21 facilitates creation of these vortices, thereby preventing blood from pooling or stagnating within thepockets35 at the base of thevalve21, which may lead to thrombus formation or other problems. The present invention, by virtue of the configuration of thesupport structure11, creates anartificial sinus34 that attempts to reproduce the function served by thenatural sinus37 in the vein.
• FIG. 2 depicts a side view of an illustrative embodiment of the present invention in which theprosthesis10 includes a first orproximal section15 and a second ordistal section17 that are spaced apart from one another, defining an intermediate, substantiallyopen section16 for creating theartificial sinus34 in thevessel20. The term ‘substantially open’ is used herein to define a largely unsupported portion of the bodily passage in which at least some minimal interconnecting structure (e.g., thin or flexible elements aligned with the leaflet commissures) is present that traverses the unsupported portion of the bodily passage, but it comprises very limited surface area and typically supplies minimal, if any, force against the walls of the passageway lateral to thevalve structure12. The proximal anddistal sections15,17, which preferably comprise a pair of radially expandable or self-expandinganchoring portions24, are joined by an interconnecting means36, such as the illustrative pair of connection struts18,19 that allows theintermediate section16 to be otherwise open and free of scaffolding so that thevein walls38 along that section of thevessel20 are able to expand due to pressure exerted by the blood flowing within the vein.
• In the embodiments of the present invention, the anchoringportions24 may function as stents to help the bodily passage remain patent, but their primary function is limited to engaging the bodily passage to anchor the prosthesis thereagainst. Thesupport structure11 and anchoringportions24 also may be configured to be readily collapsible as with a normal vein. Since the diameters of the proximal anddistal sections15,17 generally assume a fixed diameter after deployment, the intermediate section, which is mostly unsupported or covered by structure, expands to form a bulging region of the vessel that functions as anartificial sinus34. Although the interconnecting means36 advantageously permit the proximal anddistal sections15,17 to be deployed together at a fixed distance from one another, it is within the scope of the invention to have thevalve prosthesis10 comprise separate unconnected sections that are deployed sequentially at an effective distance from one another to create anartificial sinus34 therebetween. Additionally, the interconnecting means36 can comprise suture, fabric, or some other non-rigid material to join the proximal anddistal sections15,17 and define the optimal length of theintermediate section16, without interfering with the creation of theartificial sinus34. To deploy aprosthesis10 having a flexible interconnecting means36, one of either the proximal or thedistal sections15,17 can be deployed first with the delivery system then being slowly withdrawn until the interconnecting means36 becomes taut, whereby the opposite section is then deployed.
• In the illustrative embodiment, thevalve structure12 comprises a pair ofleaflets26 that are situated in the intermediate section and attached to theproximal section15 at twocommissural points27,28, each located at the proximal ends of the interconnecting struts18,19, using an appropriate attachment means30, such as suture, adhesive, fasteners, tissue welding using heat and/or pressure, etc. Theleaflets26 are attached about theirdistal ends29 to thedistal section17 of thesupport structure11 using the same or an other suitable attachment means30. Thevalve structure12 is configured so that it advantageously expands with the deployment of the proximal anddistal sections15,17 such that theouter edges39 thereof contact the vessel wall sufficiently to at least substantially prevent leakage of bodily fluid around thevalve structure12. Optionally, the wall-engaging outer edges of theleaflets26 can be reinforced with aseparate frame32 that is attached to or incorporated into theouter edges37 to improve sealing with thevessel wall38. An example of such aframe32 is depicted in embodiment shown inFIG. 3 in which theframe32 also serves as the interconnecting means36 between the proximal anddistal section15,17 of thesupport structure11, with thestruts18,19 being laser cut from the same tube used to form the remainder of thesupport structure11. The valve frame32 (that portion of thesupport structure11 that reinforces the valve structure12) can either be configured to exert relatively little radial force beyond what might be required to ensure adequate contact with thevessel wall38, or it may be configured such that theframe32 exerts sufficient radial force such that it assists in creating anartificial sinus34 in the portion of the vein along theintermediate section16 of thevalve prosthesis10.
• Another method of creating theartificial sinus34 is depicted inFIGS. 4-5, whereby thesupport structure11 includes an expandedportion31, larger in diameter than the remainder of thesupport structure11, that upon deployment, creates anartificial sinus34 surrounding thevalve structure12. The diameter of theartificial sinus34 caused extending thevessel wall38 is, at its widest point, preferably about 10-120% larger than the diameters of the proximal anddistal sections15,17 when fully deployed (unrestrained from within the delivery sheath), with a more preferred differential of about 30-80% and a most preferred difference of 50-70% larger, depending on the diameter of the vein, the valve structure geometry, fluid column pressures at that location, and other factors. In the illustrative embodiments, the transition between the proximal anddistal section15,17 and the expandedintermediate section16 is curvilinear, creating a bulge-like or flared configuration (FIGS. 4 and 5, respectively). In the examples depicted, the support structure comprises a singletubular anchoring portion24 that is plastically, resiliently, or otherwise deformed into a second configuration that includes the expandedportion31. For example, the anchoringportion24 can be laser cut from a tube of nitinol, placed around a mandril having the desired shape, and heat set to produce the final desired shape. In the embodiment ofFIG. 4, the expandedportion31 comprises theintermediate section16 of theprosthesis10, such that theartificial sinus34 is created between the proximal anddistal sections15,17 and thevalve structure12 is located therein. InFIG. 5, the expandedportion31, which comprises theproximal section15 of thesupport structure11, includes a flared configuration that extends outward from the distal section17 (no separately functionalintermediate section16 is present). Thevalve structure12 is attached about theproximal end13, while the flared, expandedportion31 thereabout causes thevessel20 to bulge outward, thus creating anartificial sinus34 about the proximal end of theprosthesis10. Theartificial sinus34 comprises a combination of a supported and an unsupported portion in the embodiment ofFIG. 5. In both illustrative embodiments thevalve structure12 is sewn to thestruts33 of the support structure within the passageway of the anchoringportion24. Other alternative methods of attachment include adhesives, staples or other fasteners, wire, engagement barbs on the frame, tissue welding, etc.
• FIGS. 6-7 depict embodiments similar to that ofFIG. 5, except that the proximal, intermediate, anddistal sections15,16,17 comprise separate anchoring portions24 (having a serpentine or ‘zig-zag’ configuration in the illustrative embodiment) that are attached to one another in well-known manner, such as by feeding theillustrative thread material42 or suture through theapices45 of adjoining bends and securing it therearound. In the embodiment ofFIG. 6, theintermediate section16 comprises a first and a secondintermediate subsection40,41 of opposing frustoconical-shapedanchoring portion24 that are coupled to form theartificial sinus34. The first andsecond subsections40,41 can be manipulated into a frustoconical shape by plastically deforming the anchoringportion24 into that shape, or by increasing constraint of the frame about the distal end of a cylindrical-shapedproximal portion15 and the proximal end of a cylindrical-shapeddistal portion17 with a constrainingmeans42, such as thread, suture, wire, band, covering, etc., so that therespective sections15,17 assume a frustoconical shape. Additional constrainingmeans42 may be included at the first and second ends13,14, as depicted, to maintain the cylindrical shape of the proximal and distal15,17 sections. The thread or suture30 (constraining means) at theinterface46 interconnecting the first and secondintermediate subsections40,41 may or may not function to tension theapices45 of those respective subsections. The illustrative embodiment ofFIG. 7 is similar to that ofFIG. 6 except that theintermediate section16 also comprises a thirdintermediate subsection43, located betweenintermediate subsection40 and41, that extends the length of the artificial sinus. The illustrative thirdintermediate section43 comprises a short cylindrical or band-shaped portion whose width can be adjusted to create the desired geometry of theartificial sinus34. Additional subsections can be added as well, if so desired.
• FIG. 8 depicts an embodiment in which thesupport structure11 comprises aproximal portion15 joined to adistal portion17 by a interconnectingstrut36, the entire support structure being cut from a single piece of cannula, such as stainless steel or nitinol. Thevalve structure12, comprising a plurality ofleaflets26, is attached to thedistal portion17 such that theartificial sinus34 is formed in the largely open, unsupported region between the proximal anddistal sections15,17 by virtue of thevessel20 bulging outward, as in the embodiment ofFIG. 2. Thevalve prosthesis10 further includes anoptional covering44, such as an outer sleeve of SIS (or other suitable biological or synthetic material), that is attached to both the proximal anddistal sections15,17 of thesupport structure11, which helps seal the prosthesis to prevent leakage of retrograde fluid therearound. The covering44 is preferably of a constitution and configuration such that it does not interfere with the creation of theartificial sinus34.
• FIGS.9,11, and13-20 comprise embodiments of anartificial valve prosthesis10 in which supportstructure11 carrying theleaflets26 is configured to increase the leaflet contact (coaptable)area57 about the proximal portion of thevalve structure12 without relying on built-in slack within the material to bring the leaflets in closer proximity and provide for a extensive sealing area, longitudinally. As defined in this application, theleaflet contact area57 comprises a longitudinal portion along thevalve structure12 in which the facing surfaces of opposing leaflets26 (two or more) coapt or lie in close proximity to one other while in a dry or resting, neutral state (i.e., the pressure differentials across the valve orifice are essentially equalized such that the leaflets are not being forced together or apart due to external forces, such as fluid flow), when the prosthesis is an expanded or deployed configuration. Thesupport frame11 may be configured for maximizing the extent of theleaflet contact area57 by including one or more longitudinal attachment struts49,50 that define at least theproximal portion75 of theattachment pathway74 of each leaflet lateralouter edge87,88 (the termsouter edge39 and lateralouter edges87,88 being defined herein as the area or zone along the leaflet that comprises the sealing interface). The longitudinal attachment struts49,50/proximal attachment pathways75 have a substantially longitudinal orientation (e.g., substantially parallel) with respect to thelongitudinal axis64 of the prosthesis (and valve structure12). At a point generally proximate thedistal end89 of the leaflet contact area57 (theproximal portion96 of the leaflet), thedistal portions76 of the adjacent attachment pathways74 (which are joined proximally about a commissural point) diverge from one another (forming a generally Y-shaped pathway configuration) and assume a much more circumferential orientation than that of theproximal portion75 of the pathway such that the outer leaflet lateral edges87,88 of each leaflet converge at a point lateral to the freeinner edge84 thereof to seal the passageway and form thedistal portion96 of the leaflet that defines the bottom96 or ‘floor’ of thepocket55 or intravascular space adjacent the outer surfaces of each of the leaflets, which generally assumes a strongly cupped or curved shape such that the leaflet assumes a generally ‘folded’ appearance due to the acutelyangled attachment pathway74 with the proximal portion of the leaflet having a strong longitudinal orientation with respect to the prosthesis and vessel and thebottom portion96 having a strongly perpendicular orientation relative to the longitudinal axis of the vessel and prosthesis. It should be noted that thecommissures27,28, while located about theproximal end13 of theillustrative prosthesis10, may be located proximal thereto such thatadditional support structure10 extends proximally, such as in the embodiments of FIGS.2-8,12.
• By extending or maximizing the leaflet contact area and decreasing the radius of the curvature of the leaflet (increasing curvature) about the distal portion thereof, the basal or distal portion of thepocket35 adjacent each leaflet is enlarged to facilitate and maximize the size and/or velocity of theflow vortices55,56 formed therein during retrograde flow. During pre-clinical investigations, these broader pockets have been shown to be especially advantageous in bi-leaflet artificial valve designs implanted in the venous system, these valves exhibiting a marked reduction in thrombus formation as compared to earlier designs. The improvement in flow dynamics for the purpose of clearing thepocket35 of stagnant blood that can thrombose and compromise valve function or lead to other complications is depicted in a comparison ofFIGS. 10 and 11. Laboratory analysis of the patterns of retrograde flow within a valve has shown that multiple vortices are typically created. In the embodiment ofFIG. 10, which has a generally (inverted) V-shapedattachment pathway74, afirst vortex55 is created below which a second,smaller vortex56 is usually present, usually having opposite flow, which may be at least partially inadequate for clearing away blood pooling about the base of theleaflets60,61 in a venous valve. In the embodiment of the present invention depicted inFIG. 11, which has a generally (inverted) Y-shapedattachment pathway74, the larger pocket (at least at the basal portion) allows for a larger and strongersecond vortex56 of fluid created by retrograde flow that is more optimal for clearing away any pooling blood that would otherwise collect there and potentially provide for greater downforce on theleaflets60,61 to improve closure of the valve.
• FIGS. 9 and 11 depict an artificialvenous valve prosthesis10 in which theframe32 of thesupport structure11 is configured such that the pair of longitudinal attachment struts49,50 extending from each of thecommissures27,28 that represent the proximal attachment points for the valve structure (not shown) form afirst angle47 (.alpha.) with respect to one another that is less than thesecond angle48 (.beta.) that is formed between the distal attachment struts51,52, which comprise continuations of the longitudinal attachment struts49,50 (together comprising thelegs58 of the frame32), and the inside63 of thevessel wall38. Thefirst angle47 is preferably between −10 and 30.degree. (a negative angle being possible with a sufficiently large-radius bend about the commissure) with a more preferred angle being 0-25.degree. and a most preferred angle of 0-10.degree. The longitudinal attachment struts49,50 may both diverge and converge at various points therealong (i.e., bow inward or outward), which in case, the first angle may be relevant for only theproximal portion75 or is measurable between vectors representing the best straight line longitudinally traversing eachstrut49,50. The illustrative embodiment also includes a pair of optional stabilizingarms53,54 that extend laterally from thelegs58,59 to help center theprosthesis10 within thevessel20. Ideally, the angles depicted in theframe32 configuration ofFIG. 11 results in the opposingleaflets60,61 being much more in alignment (e.g., parallel) with one another than in a prosthesis where theangles47,48 are relatively the same, such as the prior art valve shown inFIG. 10, particularly over the proximal half of theleaflets60,61. The result is the creation of a larger pocket around the base of theleaflets60,61 that helps create larger and/or stronger vortices of retrograde blood flow. A second clinical benefit is that there is a larger area of coaptation between theleaflets60,61, which helps provide a better seal against possible reflux through the valve orifice.
• FIGS. 13-18 depict another group of embodiments configured for maximizing the coaptation distance or region between the leaflets in which theattachment pathway74 comprises aproximal portion75 that generally extends along one or more longitudinal attachment struts49,50 that are generally aligned with thelongitudinal axis64 of the prosthesis and adistal portion76 that is angled laterally from the longitudinal attachment struts and generally follows the distal attachment struts51,52 which unlike the embodiment ofFIG. 9, extend laterally outward from thelongitudinal struts49,50 as separate struts. As with the embodiment ofFIG. 9, the distal attachment struts/portions converge at a point oppositely facing eachleaflet60,61 where they attach to thelateral support structure53,54, which helps center the prosthesis in the vessel and protects the leaflets from adhering to the vessel wall. In the embodiments ofFIGS. 13-17, thesupport frame11 further includesproximal support arms77,78 that attach to and extend from the longitudinal attachment struts49,50 about the commissure points27,28 and provide an interconnection with thelateral support structure53,54 (also shown inFIG. 15).
• The embodiment depicted inFIGS. 13-14 comprises a pair of longitudinal attachment struts49,50, generally parallel to one another, which are adapted for attaching therespective leaflets26 therealong, thus creating a large leaflet contact orcoaptable area57 that extends over half of the length of the prosthesis. As depicted inFIG. 16, Thelateral support structure53,54 shares or mirrors the configuration of the longitudinal attachment strut regions which they interconnect, except that they are located 90.degree. therefrom and oriented oppositely thereto, such that thesupport structure11 generally forms a serpentine configuration adapted to be readily collapsible and expandable. In the illustrative embodiment, thesupport structure11 or frame can be divided into four sections orquadrants70,71,72,73 that are identical except for their orientation,sections70 and72 being oriented with thecommissures27,28 and longitudinal attachment struts49,50 carrying thevalve structure12 being oriented proximally toward thefirst end13 of theprosthesis10. The repeating, uniform design of thesupport structure11 of the illustrative embodiment advantageously provides better structural stability, compressibility/expandability, and overall integrity than a support structure that does that comprise a non-uniform, non-repeating frame pattern.
• Thelateral arms77,78 of thelateral support structure53,54, that connect to the longitudinal attachment struts49,50 each include astrut68 that carries a proximalradiopaque marker67 used to facilitate orientation of thedevice10 and provide additional support. An identicaldistal strut90 and an optionalradiopaque marker91 is located distal to the longitudinal attachment struts49,50 and attached to the distal attachment struts51,52 to serve a similar orientation and stabilization function. Anintegral barb25 is located about the commissural bends27,28 that interconnect the longitudinal attachment struts49,50. The parallel longitudinal attachment struts49,50 are also interconnected about their distal ends by ashort interconnecting strut81 such that an elongateclosed cell92 is formed. The width ofcell92 is not critical, although it may be made sufficiently narrow such that it serves to further pin or anchor theleaflets60,61 to thestruts49,50, which could be especially advantageous in fixation if the leaflet material retracts during the remodeling process. A preferred width between the twostruts49,50 would be between 0-5 mm, with 0-3 mm being more preferred and 0-1 mm being most preferred. If the spacing is too wide, gaps may be created between the opposing leaflets which could allow for an unacceptable amount of reflux through the valve.
• A similar frame design is shown inFIG. 17 which includes a singlelongitudinal attachment strut49 to which bothleaflets60,61 are sewn or otherwise attached allowing for similar extended coaptation between leaflets. Theleaflets60,61 can be attached such that each abuts the strut49 (and sewn or attached without being wrapped over the strut) or the first lateral leaflet edge (not shown) is wrapped around thestrut49 while the second leaflet lateral edge of the opposite leaflet is sewn over the first lateral leaflet edge and strut49. The single attachment strut can be of a width that is generally uniform with respect to the other support structure or it may be made substantially thicker, such as shown inFIG. 19. Furthermore, athicker strut49 could includeapertures93 or slots of any shape or length distributed therealong for receiving sutures orother attachment elements30, such as clips, rings, etc., for affixing or anchoring the leaf outer edges thereto.FIG. 20 depicts an embodiment having a pair of longitudinal attachment struts49,50 with anchoringstructure95, such as the illustrative scalloped edge that is strategically configured therealong to help prevent or limit theattachment element97 and the valve structure itself, from sliding down the longitudinal attachment struts49,50, especially during any retraction that may occur with a bioremodelable material. The anchoring structure can comprise any projections or other structure that provides a shoulder or irregularities along the edges of the struts that helps limit sliding of the leaflets along the longitudinal attachment struts49,50. Further examples of adaptations for limiting movement or migration of attachment elements (e.g., sutures) and covering material are disclosed in an application to Case et al. (U.S. Ser. No. 10/820,918), entitled ‘Intraluminal Support Device with Graft’ and filed Apr. 8, 2004, which is expressly incorporated by reference herein.
• FIG. 18 depicts an embodiment having generally, but not absolutely parallel longitudinal attachment struts49,50 which slightly converge toward thedistal end14 of the prosthesis10 (and are spaced more distant from each other than the embodiment ofFIGS. 13-14. The commissural bends27,28 anddistal bends82 interconnect the longitudinal attachment struts and form aclosed cell92 as in the embodiment ofFIGS. 13-16. The distal attachment struts51,52 provide the interconnection between the oppositeclosed cells92 as well as thedistal portion76 of theattachment pathway74. They also carry alateral arm93 and together comprise thelateral support structure83,84 that provide longitudinal support/stabilization and leaflet protection. The embodiment ofFIG. 18 lacksproximal support arms77,78 of the embodiment ofFIGS. 13-16.
• Theillustrative support structure11 inFIGS. 9,11,13-18 is not critical to achieve the optimal leaflet angles in thevalve structure12 for creating larger pockets, as depicted. For example, theattachment pathway74 of thevalve structure12 can comprise an attachment to an outside support frame to form the illustrative configuration with theframe32 that is not necessarily extending along theouter edges39 of theleaflets60,61, but rather attached to selected strut that cross theattachment pathway74, especially along thedistal portion76 of the pathway. Furthermore, at least a portion of theouter edges39 can be directly affixed to the vessel wall (such as being sutured, heat welded, or anchored with barbs, adhesives, etc.) with theframe11 being absent or reinforcing or shaping only a limited portion of the leafletouter edges39, thus allowing for the vein to naturally collapse (at least partially) when not filled with blood. In the example depicted inFIG. 21, theframe11 comprises apartial support98 of a hair-pin configuration that includes a proximal bend about eachcommissure27,28 with free-ended longitudinal attachment struts49,50 extending therefrom which help form theleaflet angle47, while thedistal portion76 of theattachment pathway74 comprises an alternative attachment that does not result in the leaflet material being urged thereagainst by a radially expandable frame. Methods include surgical attachment, tissue welding, adhesives, barbs and other well-known methods, teachings of which is included in a co-pending U.S. patent application entitled, ‘Percutaneously Deployed Vascular Valves with Wall-Adherent Adaptations (Case et al.) filed Apr. 1, 2004 (Ser. No. to be added by amendment), the disclosure of which is expressly incorporated by reference herein. The angle of theleaflets60,61 relative to thelongitudinal axis64 of the prosthesis and vessel (half of thefirst angle47 or .alpha./2) is preferably −5-15.degree. with a more preferred angle of 0-10.degree. and a most preferred angle of 0-5.degree. The relatively small or shallow angles of the longitudinal attachment struts49,50 about thecommissures27,28 allows for a larger space adjacent theleaflets60,61 andbroader pockets35 at the base of the leaflets. The longitudinal attachment struts49,50 of the support structure can be formed generally parallel to one another along the proximal portions of the longitudinal attachment struts49,50 to create the maximum pocket size and greater coaptation of the leaflets. For example, thepocket35 areas would be maximized in anattachment pathway74 whereangle47 is zero (or a negative angle) andangle48 is at least 90.degree., such that the attachment pathway along each leaflet lateralouter edge87,88 is generally L-shaped such that thedistal portion76 of the attachment pathway angles abruptly from the proximal portion rather than assuming a dog-leg configuration as shown in the illustrative embodiments.
• The amount of contactable orcoaptable area57 can be expressed in different ways. In the present invention, the length of the leaflet contact area57 (orproximal portion75 of the attachment pathway) in a typical venous valve prosthesis is preferably at least 2 mm and as much as 50 mm (depending on the configuration of the valve prosthesis), with a more preferred length of 5-30 mm and a most preferred range of 5-15 mm. In an average sized venous valve having a length of 25 mm, the preferred range of theleaflet contact area57 orproximal attachment pathway75 would be 10-80% of the prosthesis length (2.5-20 mm), assuming thevalve structure12 is generally as long as thesupport frame11. A more preferredleaflet contact area57 would comprise 30-60% with 35-55% being most preferred in a prosthesis of the same general type as depicted. The relationship between leaf contact area and the diameter of the vessel may be a factor in optimizing the functionality of thevalve prosthesis10. Preferably, the length of the longitudinal attachment struts49,50 and/orleaflet contact area57 is 25 to 250% of the nominal vessel diameter with a more preferred range of 25-150%.
• The amount of slack in the leaflet material also helps determine how well the leaflets coapt during retrograde flow and how large of an opening they permit during antegrade flow. Preferably, but not essentially, the prosthesis is configured such that the distance formed between the leaflets in their fully open position and the vessel diameter remains preferably between 0-100% of the vessel diameter, with a more preferred range of 20-80% of the vessel diameter and a most preferred range of 50-70%. By substantially orienting the longitudinal attachment struts49,50 with thelongitudinal axis64 of the prosthesis, less slack is necessary for optimal or extended coaptation. Not having the leaflets regularly contact the outer walls of the vessel can be especially important when using a bioremodelable material, such as an ECM, which can partially or completely adhere to the wall over time as tissue grows into the leaflets, thus compromising the functionality of the valve.
• FIG. 12 depicts an embodiment having different structural configuration to after retrograde fluid flow patterns within the pocket to prevent pooling of blood or bodily fluid. Thesupport structure11 includes proximal anddistal sections15,17 which are sized and configured to expand and engage thewalls38 when thevalve prosthesis10 is deployed within thebodily passage20. Theintermediate section16, which includes thevalve structure12, is narrower than each of the adjoining proximal anddistal sections15,17. A covering of biologically-derived or synthetic biocompatible orbioremodelable material44, such as a collagenous extracellular matrix (ECM) (e.g., SIS), pericardial tissue, or fabric, such as DACRON, ePTFE, etc., is attached over or inside the support structure to enclosepassageway62 and to help seal the prosthesis with the vessel. The proximal anddistal sections15,17 are generally frustoconical or bowl-shaped with theinterface46 with the proximal or distal end of theintermediate section16 being smaller in diameter than the proximal or distal ends13,14 of the prosthesis. By narrowing thepassageway62 of theprosthesis10 at the point where it transitions between theproximal section15 and theintermediate section17, a Venturi effect is created in which the retrograde flow is accelerate, which advantageously produces enhanced flushing action (e.g., stronger vortices) within thepockets35 surrounding theleaflets60,61. The ability of thevalve prosthesis10 to prevent pooling of blood or fluid around thepockets35 is further enhanced in the illustrative embodiment by configuring theleaflets61,62 as in the example shown inFIG. 11. It is not necessary to the invention that the proximal and distal sections share the same configuration. Therespective sections15,16,17 may be separate, attached units, as shown, or represent subsections of asingle anchoring portion24, similar to the embodiment ofFIG. 4.
• It should be noted that the support structure and valve structure shown in each of the figures in the application are merely exemplary of the numerous well-known possibilities, many others of which are disclosed in U.S. patent application Ser. No. 10/642,372 entitled, ‘Implantable Vascular Device,’ filed Aug. 15, 2003 and whose disclosure is expressly incorporated by reference herein. For example, the valve structure may comprise more than the illustrative two leaflets or comprise leaflets of other shapes and configuration. The valve structure may also comprise a non-leaflet valve such as one or more tubular sleeves or other configurations adapted to restrict fluid flow. With regard to the support structure, it may be formed from wire, cut from a section of cannula, molded or fabricated from a polymer, biomaterial, or composite material, or a combination thereof. The pattern (i.e., configuration of struts and cells) of the anchoring portion(s) that is selected to provide radial expandability to the prosthesis is also not critical for an understanding of the invention. Any other undisclosed or incidental details of the construction or composition of the various elements of the disclosed embodiment of the present invention are not believed to be critical to the achievement of the advantages of the present invention, so long as the elements possess the attributes needed for them to perform as disclosed. The selection of these and other details of construction are believed to be well within the ability of one of even rudimentary skills in this area, in view of the present disclosure. Illustrative embodiments of the present invention have been described in considerable detail for the purpose of disclosing a practical, operative structure whereby the invention may be practiced advantageously. The designs described herein are intended to be exemplary only. The novel characteristics of the invention may be incorporated in other structural forms without departing from the spirit and scope of the invention. The invention encompasses embodiments both comprising and consisting of the elements described with reference to the illustrative embodiments. Unless otherwise indicated, all ordinary words and terms used herein shall take their customary meaning as defined in The New Shorter Oxford English Dictionary, 1993 edition. All technical terms shall take on their customary meaning as established by the appropriate technical discipline utilized by those normally skilled in that particular art area. All medical terms shall take their meaning as defined by Stedman's Medical Dictionary, 27^thedition.

Claims (29)

1-29. (canceled)

30. A radially expandable artificial valve prosthesis for implantation in a vessel having a vessel wall, comprising:

a support structure, comprising:

a proximal section comprising a first radially expandable anchoring portion having a plurality of struts interconnected by bends;

a distal section comprising a second radially expandable anchoring portion having a plurality of struts interconnected by bends;

the proximal and distal sections spaced apart from one another to define an intermediate section disposed between the proximal and distal sections, the intermediate section comprising a substantially open section of the support structure;

a first connection strut connected with the proximal and distal sections and spanning the intermediate section; and

a second connection strut connected with the proximal and distal sections and spanning the intermediate section; and

a valve structure attached to the support structure and configured to selectively restrict fluid flow through the support structure by closing with changes in the fluid pressure differential across said valve prosthesis.

31. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure is situated in the intermediate section of the support structure.

32. The radially expandable valve prosthesis ofclaim 31, wherein the intermediate section has a first length the extends along a lengthwise axis of said valve prosthesis;

wherein the valve structure has a second length that extends along the lengthwise axis of said valve prosthesis; and

wherein the first length is greater than the second length.

33. The radially expandable artificial valve prosthesis ofclaim 30, wherein the proximal section defines a first circumference and the first connection strut is connected with a first attachment point on the first circumference; and

wherein the distal section defines a second circumference and the first connection strut is connected with a second attachment point on the second circumference; and

wherein the first and second attachment points lie on a first longitudinal axis of said artificial valve prosthesis.

34. The radially expandable artificial valve prosthesis ofclaim 33, wherein the second connection strut is connected with a third attachment point on the first circumference; and

wherein the second connection strut is connected with a fourth attachment point on the second circumference; and

wherein the third and fourth attachment points lie on a second longitudinal axis of said artificial valve prosthesis that is different than the first longitudinal axis.

35. The radially expandable artificial valve prosthesis ofclaim 34, wherein the first and second longitudinal axes are disposed substantially opposite each other with respect to a centrally-disposed longitudinal axis of said valve prosthesis.

36. The radially expandable artificial valve prosthesis ofclaim 30, wherein the proximal section defines a first circumference and the first connection strut is connected with a first attachment point on the first circumference; and

wherein the distal section defines a second circumference and the first connection strut is connected with a second attachment point on the second circumference; and

wherein the first attachment point lies on a first longitudinal axis of said artificial valve prosthesis and the second attachment point lies on a second, different longitudinal axis of said valve prosthesis.

37. The radially expandable valve prosthesis ofclaim 36, wherein the first and second attachment points are approximately 90° out of phase with each other relative to a centrally-disposed longitudinal axis of said valve prosthesis.

38. The radially expandable valve prosthesis ofclaim 36, wherein the second connection strut is connected with the first attachment point on the first circumference and a third attachment point on the second circumference;

wherein the third attachment point lies on a third, different longitudinal axis of said artificial valve prosthesis.

39. The radially expandable valve prosthesis ofclaim 30, wherein the first and second connection struts comprise linear struts disposed substantially opposite each other with respect to a centrally-disposed longitudinal axis of said valve prosthesis.

40. The radially expandable valve prosthesis ofclaim 30, wherein the intermediate section includes interconnecting structure consisting of the first and second connection struts.

41. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure is attached to the first and second connection struts.

42. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure comprises a single leaflet.

43. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure comprises two leaflets.

44. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure comprises a synthetic material.

45. The radially expandable valve prosthesis ofclaim 44, wherein the valve structure comprises DACRON.

46. The radially expandable valve prosthesis ofclaim 44, wherein the valve structure comprises ePTFE.

47. The radially expandable valve prosthesis ofclaim 30, wherein the valve structure comprises a biologically-derived material.

48. The radially expandable valve prosthesis ofclaim 47, wherein the valve structure comprises a bioremodellable material.

49. The radially expandable valve prosthesis ofclaim 48, wherein the valve structure comprises an extracellular matrix material.

50. The radially expandable valve prosthesis ofclaim 49, wherein the valve structure comprises small intestine submucosa.

51. The radially expandable valve prosthesis ofclaim 30, wherein the support structure comprises a metal.

52. The radially expandable valve prosthesis ofclaim 51, wherein the support structure comprises stainless steel.

53. The radially expandable valve prosthesis ofclaim 51, wherein the support structure comprises a superelastic material.

54. The radially expandable valve prosthesis ofclaim 53, wherein the superelastic material comprises nitinol.

55. The radially expandable valve prosthesis ofclaim 30, wherein the support structure comprises a polymeric material.

56. A radially expandable artificial valve prosthesis for implantation in a vessel having a vessel wall, comprising:

a support structure, comprising:

a proximal section comprising a first radially expandable anchoring portion having a plurality of struts interconnected by bends and defining a first circumference;

a distal section comprising a second radially expandable anchoring portion having a plurality of struts interconnected by bends and defining a second circumference;

the proximal and distal sections spaced apart from one another to define an intermediate section disposed between the proximal and distal sections, the intermediate section comprising a substantially open section of the support structure; and

first and second connection struts spanning the intermediate section and connected with the proximal and distal sections, each of the first and second connection struts connected with a first attachment point on the first circumference; and

a valve structure attached to the support structure and configured to selectively restrict fluid flow through the support structure by closing with changes in the fluid pressure differential across said valve prosthesis.

57. A radially expandable artificial valve prosthesis for implantation in a vessel having a vessel wall, comprising:

a support structure, comprising:

a proximal section comprising a first radially expandable anchoring portion having a plurality of struts interconnected by bends and defining a first circumference;

a distal section comprising a second radially expandable anchoring portion having a plurality of struts interconnected by bends and defining a second circumference;

the proximal and distal sections spaced apart from one another to define an intermediate section disposed between the proximal and distal sections, the intermediate section comprising a substantially open section of the support structure; and

first and second curvilinear connection struts spanning the intermediate section and connected with the proximal and distal sections, each of the first and second curvilinear connection struts connected with a first attachment point on the first circumference and a second attachment point on the second circumference; and

a valve structure attached to the support structure and configured to selectively restrict fluid flow through the support structure by closing with changes in the fluid pressure differential across said valve prosthesis.

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