Heart valve prosthesis and methods of manufacture and use

Abstract

A heart valve prosthesis is provided having a self-expanding multi-level frame that supports a valve body comprising a skirt and plurality of coapting leaflets. The frame transitions between a contracted delivery configuration that enables percutaneous transluminal delivery, and an expanded deployed configuration having an asymmetric hourglass shape. The valve body skirt and leaflets are constructed so that the center of coaptation may be selected to reduce horizontal forces applied to the commissures of the valve, and to efficiently distribute and transmit forces along the leaflets and to the frame. Alternatively, the valve body may be used as a surgically implantable replacement valve prosthesis.

Claims

1. A valve prosthesis comprising: a valve body comprising a plurality of leaflets affixed to a skirt, adjoining leaflets affixed together to form commissures; and a self-expanding frame comprising an inflow section having a first row of cells in a circumferentially repeating pattern defining an inflow edge of the frame, and an outflow section having a second row of cells in a circumferentially repeating pattern and including a plurality of eyelets; wherein the area of individual cells in the first row of cells is less than the area of individual cells in the second row of cells; wherein the frame has a contracted delivery configuration and an expanded deployed configuration, wherein, when the frame is in the expanded deployed configuration, the outflow section diameter is larger than the inflow section diameter; wherein the frame supports the valve body, wherein a portion of the skirt is folded over the inflow edge of the frame and affixed to the first row of cells and the commissures are sewn to the frame between the first and second rows of cells.

2. The valve prosthesis of claim 1, wherein the frame comprises a middle region between the inflow section and the outflow section, wherein in the expanded deployed configuration, a middle region diameter of the middle region is smaller than the inflow section diameter.

3. The valve prosthesis of claim 1, wherein the outflow section includes two eyelets.

4. The valve prosthesis of claim 1, wherein the skirt further comprises a plurality of end tabs, wherein the end tabs are folded over the inflow edge of the frame and affixed to the first row of cells.

5. The valve prosthesis of claim 1, wherein the frame has inflow and outflow ends and a plurality of cell patterns that vary in size between the inflow and outflow ends.

6. The valve prosthesis of claim 1, wherein the leaflets comprise porcine, bovine, equine or other mammalian pericardial tissue, synthetic material or polymeric material.

7. The valve prosthesis of claim 1, wherein the valve prosthesis is configured to hold a patient's native valve permanently open in the expanded deployed configuration.

8. The valve prosthesis of claim 1, wherein the outflow section diameter is between 30 mm and 55 mm and the inflow section diameter is between 19 mm and 34 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which:

(2) FIGS. 1A, 1B and 1C are, respectively, side and top end views of an exemplary valve prosthesis of the present invention in the expanded deployed configuration and an enlarged region of the frame of the valve prosthesis;

(3) FIG. 2 is a side view of the frame of the valve prosthesis of FIG. 1 in a contracted delivery configuration;

(4) FIGS. 3A and 3B are, respectively, plan views of a leaflet and the skirt employed in the valve body of the present invention;

(5) FIGS. 4A, 4B, 4C, and 4D are, respectively, a perspective view of a leaflet with its enlarged regions folded, a plan view of an embodiment of the valve body of the present invention in which the leaflets are fastened to the skirt, a perspective view of an alternative embodiment of a skirt, and a perspective view of another alternative embodiment of a skirt;

(6) FIG. 5 is a side view of the valve body of FIG. 4B fully assembled; and

(7) FIG. 6 is a side view depicting the valve prosthesis of the present invention deployed atop a patient's aortic valve.

DETAILED DESCRIPTION OF THE INVENTION

(8) The present invention is directed to a heart valve prosthesis having a self-expanding frame that supports a valve body. In a preferred embodiment, the frame has a tri-level asymmetric hourglass shape with a conical proximal section, an enlarged distal section and a constriction region having a predefined curvature when the frame is deployed. In the context of the present application, the proximal section constitutes the inflow portion of the valve prosthesis and is disposed in the aortic annulus of the patient's left ventricle, while the distal section constitutes the outflow portion of the valve prosthesis and is positioned in the patient's ascending aorta.

(9) In a preferred embodiment the valve body comprises three leaflets that are fastened together at enlarged lateral end regions to form commissural joints, with the unattached edges forming the coaptation edges of the valve. The leaflets are fastened to a skirt, which is in turn affixed to the frame. The enlarged lateral end regions of the leaflets permit the material to be folded over to enhance durability of the valve and reduce stress concentration points that could lead to fatigue or tearing of the leaflets. The commissural joints are mounted above the plane of the coaptation edges of the valve body to minimize the contracted delivery profile of the valve prosthesis, while the configuration of the edges permits uniform stress distribution along the coaptation edges.

(10) Referring to FIG. 1, an exemplary embodiment of a valve prosthesis constructed in accordance with the principles of the present invention is described. Valve prosthesis 10 comprises expandable frame 12 having valve body 14 affixed to its interior surface, e.g., by sutures. Frame 12 preferably comprises a self-expanding structure formed by laser cutting or etching a metal alloy tube comprising, for example, stainless steel or a shape memory material such as nickel titanium. The frame has an expanded deployed configuration that is impressed upon the metal alloy tube using techniques that are per se known in the art. Valve body 14 preferably comprises individual leaflets assembled to a skirt. All of the components of valve body 14, i.e., the skirt and leaflets, may be formed of a natural or man-made material. Alternatively, the leaflets may be formed from a natural material, such as porcine, equine or bovine pericardium, while the skirt comprises a synthetic or polymeric material, such as Dacron, ePTFE, or similar material.

(11) Frame 12 preferably includes multiple levels, including outflow section 15, inflow section 16 and constriction region 17. As depicted in the enlarged view of FIG. 1B, the frame comprises a plurality of cells having sizes that vary along the length of the prosthesis. As indicated by dotted lines a, b and c, each cell comprises two zig-zag structures having unequal-length struts, wherein the vertices of the zig-zags are coupled together. For example, zig-zag 18 has length z.sub.1 whereas zig-zag 19 has greater length z.sub.2. This cell design permits each level of cells between the proximal and distal ends of the frame to be tailored to meet specific design requirements, such as, compressibility, expansion characteristics, radial strength and so as to define a suitable contour for attachment of the valve body.

(12) The cell pattern of frame 12 also enables the frame to expand to the tri-level asymmetric hourglass shape depicted in FIG. 1A, having conical inflow section, enlarged outflow section and fixed diameter constricted region. Each section of frame 12 has a substantially circular cross-section in the expanded deployed configuration, but in addition the cell patterns of the inflow and outflow sections permit those sections to adapt to the specific anatomy of the patient, thereby reducing the risk of migration and reducing the risk of perivalvular leaks. The cell patterns employed in the constriction region are selected to provide a uniform circular cross-section area for the constriction region when deployed, and a pre-determined radius of curvature for the transition between the constriction region and outflow section of the frame. In particular, the convex-concave shape of frame 12 within the constriction region ensures that the frame is held away from the opposing sinus wall in the ascending aorta, thus ensuring adequate blood flow to the coronary arteries and facilitating catheter access to the coronary arteries.

(13) Enlarged outflow section has nominal deployed diameter D.sub.o, inflow section has nominal deployed diameter D.sub.I, and constriction region has deployed substantially fixed diameter D.sub.c. The conical shape of the inflow region and smooth transitions between adjacent sections of frame 12 are expected to be particularly advantageous in directing blood flow through the valve body with little or no turbulence, as compared to step changes in diameter observed for surgically implanted replacement valves.

(14) The above-described cell pattern permits each of the inflow and outflow sections of frame 12 to expand to a diameter within a range of deployed diameters, while retaining constriction region 17 at a substantially constant diameter. Thus, for example, outflow diameter D.sub.o may range from 30 to 55 mm, while inflow diameter D.sub.I may vary from 19 to 34 mm. Illustratively, frame 12 may be manufactured in four sizes having a range of diameters D.sub.o, D.sub.I and D.sub.c as set forth in Table 1 below:

(15) TABLE-US-00001 TABLE 1 Size A Size B Size C Size D D.sub.O 40 mm 50 mm 40 mm 50 mm D.sub.C 22 mm 22 mm 24 mm 24 mm D.sub.I 26 mm 26 mm 29 mm 29 mm

(16) Advantageously, these four frame sizes are expected to cover a wide range of patient anatomies, while requiring construction of only two sizes of valve bodies (22 and 24 mm). Compared to previously-known commercially available surgical valves, which vary from approximately 17 mm to 31 mm in one millimeter increments, it is expected that the above four sizes of valve prosthesis of the present invention could be used for more than 75% of the patient population, thus greatly reducing the costs associated with manufacturing and inventorying large numbers of parts.

(17) When configured as a replacement for an aortic valve, inflow section 16 extends into and anchors within the aortic annulus of a patient's left ventricle and outflow section 15 is positioned in the patient's ascending aorta. Importantly, the configuration of outflow section 15 is expected to provide optimal alignment of the valve body with the direction of blood flow. In addition, the cell pattern of outflow section also serves to anchor the outflow section in the patient's ascending aorta to prevent lateral movement or migration of frame 12. As depicted in FIG. 1C, the use of relatively larger cells in the outflow section of frame 12, combined with the convex-concave shape of constriction region 17, ensures that the frame does not obstruct blood flow to the patient's coronary arteries when deployed and allows for catheter access to the coronary arteries. Frame 12 also may include eyelets 20 for use in loading the heart valve prosthesis 10 into a delivery catheter.

(18) Still referring to FIG. 1, valve body 14 includes skirt 21 affixed to frame 12, and leaflets 22. Leaflets 22 are attached along their bases to skirt 21, for example, using sutures 23 or a suitable biocompatible adhesive. Adjoining pairs of leaflets are attached to one another at their lateral ends to form commissures 24, with free edges 25 of the leaflets forming coaptation edges that meet in area of coaptation 26.

(19) As depicted in FIG. 1A, the curve formed at joint 27 between the base of each leaflet 22 and skirt 21 follows the contour of the cell pattern of frame 12, so that most of the length of joint 27 is directly supported by frame 12, thereby transmitting forces applied to the valve body directly to the frame. As further depicted in FIG. 1C, commissures 24 are configured to span a cell of frame 12, so that force is evenly distributed within the commissures and to frame 12.

(20) Referring to FIG. 2, valve prosthesis 10 is shown in the contracted delivery configuration. In this state, valve prosthesis may be loaded into a catheter for percutaneous transluminal delivery via a femoral artery and the descending aorta to a patient's aortic valve. In accordance with one aspect of the present invention, commissures 24 are disposed longitudinally offset from coaptation edges 25 of the valve body, thereby permitting a smaller delivery profile than achievable with previously-known replacement valves. In addition, because frame 12 self-expands upon being released from the delivery catheter, there is no need to use a balloon catheter during placement of valve prosthesis 10, thereby avoiding the potential for inflicting compressive injury to the valve leaflets during inflation of the balloon.

(21) Referring now to FIGS. 3A and 3B, skirt 21 and leaflet 22 of a preferred aortic valve embodiment of the present invention are described. In one preferred embodiment, skirt 21 and leaflet 22 are cut from a sheet of animal pericardial tissue, such as porcine pericardial tissue, either manually or using a die or laser cutting system. The pericardial tissue may be processed in accordance with tissue processing techniques that are per se known in the art for forming and treating tissue valve material. In a preferred embodiment, skirt 21 and leaflets 22 have a thickness of between 0.008 and 0.016, and more preferably between 0.012 and 0.014.

(22) In an alternative preferred embodiment, leaflets 22 are formed from animal pericardial tissue as described above, while skirt 21 is cut from a sheet of synthetic or polymer material, such as Dacron, ePTFE, or other similar material as known in the art. In this case, skirt 21 has a thickness of between 0.004 and 0.012, and more preferably between 0.006 and 0.008, and may thus be compressed to a substantially smaller delivery profile. Alternatively, skirt 21 and leaflets 22 may be constructed of a synthetic or polymeric material.

(23) Leaflet 22 includes enlarged lateral ends 30 and 31 disposed at either end of free edge 32, and body 33. Free edge 32 forms coaptation edge 25 of the finished valve body 14, while lateral ends 30 and 31 are folded and joined to adjacent leaflets to form commissures 24. In accordance with one aspect of the present invention, free edges 32 assume the form of catenaries when the valve body is affixed to frame 12, thereby providing uniform loading along the length of the coaptation edge in a manner similar to a suspension bridge. Body 33 is joined to skirt 21 as described below. Lateral ends 30 and 31 illustratively are shown in FIG. 3A as having fold lines d, e and f, to define flaps 34, 35 and 36.

(24) In the embodiment of FIG. 3B, skirt 21 includes panels 21a, 21b and 21c, each panel having scalloped area 37, reinforcing tab 38, and end tab 39. Scalloped area 37 or each panel 21a, 21b and 21c is joined to a body 33 of a respective leaflet 22. Reinforcing tabs 38 illustratively include fold lines g, h and i, between panels 21a-21b and 21b-21c, except for reinforcing tabs 40 and 41 at the lateral ends of the panels 21a and 21c, which have only one fold apiece. As described below, reinforcing tabs 40 and 41 are joined to one another, e.g., by sutures or gluing, so that skirt 21 forms a frustum of a cone. In one preferred embodiment, panels 21a, 21b and 21c are cut conjoined from a single piece of animal pericardium, as depicted in FIG. 3B.

(25) End tabs 39 are folded over the ends of the proximal-most row of cells of frame 12 to secure skirt 21 to the frame and seal against perivalvular bypass flows (see FIG. 1A). Because end tabs 39 are directly supported by the last zig-zag row of cells of frame 12, there is no opportunity for an unsupported edge of the skirt to flap or otherwise extend into the flow path along the inflow edge of skirt 21. Thus, the design of the valve prosthesis not only ensures that there are no flaps to disrupt flow or serve as sites for thrombus formation, but also reduces the risk that hemodynamic flow against such flaps could cause frame 12 to migrate.

(26) It has been observed that when panels 21a-21c are cut conjoined from a single piece of animal pericardium, the skirt has a tendency to bunch-up or accordion when the valve body is collapsed to its reduced delivery configuration. However, applicants have discovered that if panels 21a-21c are severed along fold lines h in FIG. 3B, or individually cut from a piece of animal pericardium, this phenomenon is not observed, and the skirt can be collapsed to a substantially smaller profile. In particular, whereas a tissue-based skirt comprising conjoined panels 21a-21c, as shown in FIG. 3B, fits within a 21 French delivery catheter, forming skirt 21 of individual panels 21a-21c enables the device to fit within an 18 French catheter, resulting in a reduction in the delivery profile of about twenty-five percent (25%).

(27) As a still further alternative, skirt 21 may be formed of a synthetic or polymeric material, such as Dacron, ePTFE, or similar material selected for its properties and biocompatibility. As opposed to leaflets 22, which provide a mechanical function through movement, skirt 21 functions primarily to create a seal to prevent perivalvular leaks. Accordingly, a thin synthetic material may be used in place of thicker mammalian tissue to serve this purpose. As a result, the device may be compacted to a reduced delivery profile by virtue of the decreased volume of the skirt. For example, use of a synthetic skirt with a valve body having tissue-based leaflets may enable the device to fit within a catheter having even less than an 18 French diameter.

(28) Referring to FIGS. 4A and 4B, assembly of valve body 14 from the above-described embodiments of skirt 21 and leaflets 22 is described. In FIG. 4A, flap 34 first is folded along line d. Flap 35 is folded along line e so that it lies atop flap 34, forming seam 42 comprising a triple thickness of the tissue. Flap 36 then is folded along line f. Adjoining leaflets 22 then are fastened together along adjacent seams 42, resulting in a leaflet assembly.

(29) Reinforcing tabs 38 are folded along lines g, h and i to form seams 43 comprising a double thickness of tissue, or in the case of separate panels 21a-21c, joined to form seams along tabs 38. Next, the leaflet assembly is attached to skirt 21 along the bottom edges of bodies 33 of the leaflets to form joints 44. At this stage of the assembly, prior to attaching reinforcing tab 40 to 41 and the remaining seam 42 of leaflets 22, the valve body appears as depicted in FIG. 4B. Reinforcing tabs 40 and 41 then are fastened together to form another seam 43 along skirt 21 and the remaining seam 42 between leaflets 22. Valve body 14 then is ready to be affixed to frame 12.

(30) Referring to FIG. 4C, alternative embodiment of a synthetic skirt for a valve body of the present invention is described. Skirt 45 of FIG. 4C is formed from tube 47 of commercially available synthetic material, such as described above. Tube 47 is cut at one end to form scalloped areas 37, while notches are cut at the other end of the tube to form end tabs 39. Leaflets 22, which may comprise natural or synthetic material, then are assembled and attached to skirt 45 in a manner similar to that described above. Because skirt 45 is essentially cylindrical, it preferably comprises a material that is sufficiently flexible to stretch to conform to the desired shape of frame when end tabs 39 are attached to frame 12.

(31) In FIG. 4D, another alternative embodiment of a synthetic skirt for a valve body of the present invention is described. In this case, the skirt first is cut from tube 47 into a shape shown in FIG. 4C, and then formed into a shape resembling the frustum of a cone by creating triangular pleats 48. In particular, prior to the attachment of a leaflet assembly, the apices of the scalloped areas 37 are folded upon themselves and joined, such as by sewing, bonding, welding, molding, or gluing together to form pleats 48. As illustrated in FIG. 4D, pleats 48 may be formed by seams 49, and may have a width selected to impart any desired amount of taper to the skirt 46. The leaflets then may be assembled and attached to the skirt, and the valve body attached to frame 12, as described above. Advantageously, pleats 48 provides strengthened attachment points to secure skirt 46 to frame 12.

(32) Referring to FIG. 5, valve body 14 is shown as it would appear when affixed to frame 12, but with frame 12 omitted to better illustrate where the valve body is affixed to the frame. During the step of affixing the valve body to the frame, flaps 36 of adjacent leaflets are affixed, e.g., by sutures, to span a cell of the frame to support commissures 24 (compare to FIG. 1B) and end tabs 39 are folded over and affixed to the proximal-most row of cells of the frame 12 (compare to FIG. 1A). Valve body 14 also is attached to frame 12 along seams 43 formed by the reinforcing tabs. Each joint 44 is aligned with and fastened to (e.g., by sutures or glue) to a curved contour defined by the struts of the cells of frame 12, so that joint 44 is affixed to and supported by frame 12 over most of the length of the joint. As discussed above, the configuration of the cells in frame 12 may be specifically customized define a curved contour that supports joints 44 of the valve body.

(33) When completed assembled to frame 12, valve body 14 is affixed to frame 12 along the edges of flaps 36 of the commissures, end tabs 39, leaflet seams 42, reinforcing tab seams 43 and joints 44. In this manner, forces imposed on leaflets 22, commissures 24 and joints 44 are efficiently and evenly distributed over the valve body and transferred to frame 12, thus reducing stress concentration and fatigue of the valve body components. Moreover, the use of multiple thicknesses of material along seams 42 and 43 is expected to provide a highly durable valve body that will last for many years once implanted in a patient.

(34) In accordance with another aspect of the present invention, the center of coaptation of leaflets 22 is a distance L below the point at which the commissures are affixed to the frame, as shown in FIG. 5. Compared to previously-known designs, in the present invention the overall lengths of the coaptation edges are increased, while leaflets 22 coapt along a shorter portion of those lengths. Several advantages arise from this design: the leaflets require only minimal pressure to open and have a rapid closing time. the valve demonstrates better washing dynamics when open, i.e., less turbulence along the free edges of the leaflets. the valve provides a more uniform distribution of stresses along the coaptation edges of leaflets 22. the angle at which force is transmitted to the commissures is increased, thereby substantially reducing the horizontal forces applied to the commissures that tend to pull the commissures away from the frame. controlling the center of the height of coaptation allows the commissures to be located distal of the center of coaptation, thereby reducing the contracted delivery profile of the valve prosthesis.

(35) All of the foregoing benefits are expected to reduce non-uniform loads applied to the valve body, and substantially enhance the durability of the valve prosthesis.

(36) As will of course be apparent to one of skill in the art of prosthetic valve design, the assembly steps described above are merely illustrative, and a different order of assembling the leaflets and skirt to form valve body 14 may be employed. In an alternative embodiment, a conventional sewing ring may be attached to valve body 14 and frame 12 may be omitted. In this case, the valve prosthesis may be implanted surgically, rather than by percutaneous transluminal delivery. In this case, commissures 24 may be attached to the ascending aorta by sutures ox other means as described above.

(37) Referring now to FIG. 6, implantation of valve prosthesis 10 of the present invention is described and is shown having skirt 46 from FIG. 4D. As discussed above, valve prosthesis preferably comprises a self-expanding multilevel frame that may be compressed to a contracted delivery configuration, as depicted in FIG. 3, onto an inner member of a delivery catheter. The valve prosthesis and inner member may then be loaded into a delivery sheath of conventional design, e.g., having a diameter of 18-20 French or less. Due in part to the fact that commissures 24 are longitudinally offset from the coaptation edges of the leaflets, the ability to customize the cell pattern along the length of the frame, and the construction of the skirt, it is expected that valve prosthesis may be designed to achieve a significantly smaller delivery profile than previously-known percutaneously-deliverable replacement valves.

(38) The delivery catheter and valve prosthesis are then advanced in a retrograde manner through a cut-down to the femoral artery and into the patient's descending aorta. The catheter then is advanced, under fluoroscopic guidance, over the aortic arch, through the ascending aorta and mid-way across the defective aortic valve. Once positioning of the catheter is confirmed, the sheath of the delivery catheter may be withdrawn proximally, thereby permitting the valve prosthesis to self-expand.

(39) As the valve prosthesis expands, it traps native leaflets LN of the patient's defective aortic valve against the valve annulus, retaining the native valve in a permanently open state. As further illustrated in FIG. 6, outflow section 15 of the valve prosthesis expands against, and aligns the prosthesis within, the ascending aorta, while inflow section 16 becomes anchored in the aortic annulus of the left ventricle, so that skirt 21 reduces the risk of perivalvular leaks.

(40) As also seen in FIG. 6, the deployed configuration of constriction region 17 holds valve body 14 in a supra-annular position, away from the heart walls, thereby ensuring that the constriction region expands to the predetermined fixed diameter. This in turn ensures that the valve body does not experience any unexpected lateral loads and therefore expands to its design diameter, e.g., illustratively either 22 or 24 mm as in Table 1 above.

(41) Because outflow section 15 of frame 12 employs relatively larger cells than the remainder of the frame, valve prosthesis 10 does not disrupt blood flow into coronary arteries CA when deployed, and also does not obstruct subsequent catheter access to the coronary arteries. Accordingly, a clinician may readily gain access to the coronary arteries, for example, to perform angioplasty or stenting, simply by directing the angioplasty or stent delivery system guide wire through the openings in the cell pattern of frame 12.

(42) While preferred embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.