Abstract:
A transcatheter valve having an expandable frame and a collapsible multi-portion skirt within the frame are provided with seams between the portions of the skirt that are located to cooperate with features of the frame and thereby reduce the exposure of the seams.

Description:
TECHNICAL FIELD 
     This invention relates to transcatheter valves, such as heart valves, which have an expandable frame and a collapsible multi-portion skirt within the frame. Such assemblies are suitable for percutaneous transluminal delivery to replace a diseased aortic valve in patients suffering from cardiac valve dysfunction, such as aortic valve regurgitation or aortic stenosis. 
     BACKGROUND 
     Recently developed transcatheter valves conform to a patient&#39;s anatomy while providing a uniform degree of rigidity and protection for critical valve components. They are capable of deforming circumferentially to adapt to the shape of the pre-existing valve annulus, but are not susceptible to deformation or migration due to normal movement of the heart. In one type of design, the valve prosthesis has a multi-level component that is anatomically shaped when deployed, thereby enhancing anchoring of the valve and reducing the risk of migration and paravalvular leaks. A particularly successful assembly of this type is disclosed in U.S. Pat. No. 7,914,569, the entire contents of which is incorporated by reference. 
     SUMMARY 
     It has been discovered that the assembly of the type is disclosed in U.S. Pat. No. 7,914,569 may be improved by using differently formed components for the valve skirt, such that improved performance may be achieved without any departure from the successful design disclosed in that patent. Specifically, it has been discovered that the profile (diameter) of the assembly prior to deployment may be reduced by rearranging certain aspects of the assembly to reduce the bulk of the assembly and exploit the structure of the frame portion of the assembly to maintain the reduced bulk after deployment. 
     To accomplish these advantages, an improved valve prosthesis comprises a self-expanding frame having a longitudinal axis and an inflow end, and comprising a plurality of cells; a valve body having a skirt with a bottom edge sewn to the inflow end of the frame, a plurality of leaflets sewn to the skirt along a seam having upper and lower halves, a lower apex region, and at least one side seam between a point on the lower half of the seam (most preferably, the lower apex itself) and the bottom edge. The side seam may be substantially parallel to the longitudinal axis or it may make an acute angle with the longitudinal axis. 
     Regardless of angle, the skirt preferably has three substantially identical portions, with each portion being asymmetric about an axis substantially aligned with the longitudinal direction. However, in less preferred embodiments, non-identical portions are possible. 
     Or, alternatively, the skirt may have three substantially identical portions, the bottom edge of each portion having five end tabs symmetrically arranged about an axis of the skirt which is substantially aligned with the longitudinal direction and passes through an upper apex of the portion. In this case, the side seam extends between the tower apex region and an end tab which does not lie on the axis of the skirt. 
     Another variation has the skirt aligned with the frame such that the side seam substantially follows a line defined by three immediately adjacent nodes. 
     In any of the variations described above, it is preferred that the skirt be aligned with the frame such that the side seam and a line defined by three immediately adjacent nodes are aligned with each other within ±1 mm. 
     This summary of the claims has been presented here simply to point out some of the ways that the claims overcomes difficulties presented in the prior art, and to distinguish the claims from the prior art, but it is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages and features will be more readily understood from the following detailed description of various preferred embodiments, when considered in conjunction with the drawings, in which like reference numerals indicate identical structures throughout the several views, and in which: 
         FIG. 1  is a side view of a fully assembled valve body with the surrounding frame omitted for clarity. 
         FIG. 2  is a close-up side view of the inflow end of a fully assembled valve body, including the surrounding frame, according to the embodiment in which the side seam is essentially parallel with the direction of flow (bottom to top in the figure). 
         FIG. 3  is a close-up side view of the inflow end of a fully assembled valve body, including the surrounding frame, according to an alternative embodiment in which the side seam is angled with respect to the direction of flow (again, bottom to top in the figure). 
         FIG. 4  is a close-up inverted perspective view of the interior of the embodiment of  FIG. 3 . 
         FIG. 5  is a schematic plan view of a portion of the valve skirt according to the embodiment of  FIGS. 1 and 2 . 
         FIG. 6  is a schematic plan view of a portion of the valve skirt according to the embodiment of  FIGS. 3 and 4 . 
         FIG. 7  is a partially assembled valve skirt according to the embodiment of  FIG. 5 . 
         FIG. 8  is a partially assembled valve skirt according to the embodiment of  FIG. 6 . 
         FIGS. 9 and 10  are partially assembled valve skirts according to other embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, references are made to illustrative embodiments of methods and apparatus for carrying out the claims. It is understood that other embodiments can be utilized without departing from the scope of the claims. 
     By way of background, the currently successful transcatheter aortic valve prosthesis known by the tradename CoreValve® (Medtronic, Inc.) has a self-expanding multi-level frame which supports a valve body comprising a skirt and plurality of coapting leaflets. The frame has a contracted delivery configuration, in which the prosthesis may be stored within a catheter for percutaneous delivery, and an expanded deployed configuration having an asymmetric hourglass shape. The valve body skirt and leaflets preferably are constructed of porcine, bovine, equine or other mammalian tissue, such as pericardial tissue, and are sewn, welded, molded or glued together so as to efficiently distribute forces along the leaflets and to the frame. Alternatively, the valve body may comprise a synthetic or polymeric material. The frame comprises multiple levels, including a proximal conical inflow section, a constriction region and a flared outflow section. Each of the inflow and outflow sections is capable of deforming to a non-circular cross-section to conform to the patient&#39;s anatomy, while the constriction region is configured to retain a circular cross-section that preserves proper functioning of the valve body. The frame comprises a plurality of cells having a pattern that varies along the length of the frame to provide a high degree of anchoring and alignment of the valve prosthesis. The cell pattern further is selected to provide a uniform diameter where the commissural joints of the leaflets are attached to the frame, while permitting the inflow and outflow regions to expand to conform to the patient&#39;s anatomy. In this manner, optimal functioning of the valve body may be obtained even though the frame may be deployed in anatomies having a range of sizes. In addition, the frame resists deformation caused by movement of the heart and enables a functional portion of the valve body to be disposed supra-annularly to the native valve, with a portion of the valve prosthesis extending into the native valve annulus. For aortic valve replacement, the valve body comprises a skirt coupled to three leaflets. Each of the components preferably is formed of animal pericardial tissue or synthetic material, and then sewn, glued, welded or molded together. The lateral ends of the leaflets include enlarged regions that are folded to both form the commissural joints and fasten the commissural joints to the frame. The skirt and leaflets further are configured so that the joints align with contours of the cell pattern of the frame. In a preferred embodiment, the commissural joints are affixed to the frame at locations above the area of coaptation, to provide a selectable center of coaptation of the leaflets. This design provides a more efficient delivery configuration because the commissures are not compressed against the leaflets when the valve prosthesis is reduced to the contracted delivery configuration. Additionally, by lengthening the distance to the commissures, the design mimics the functioning of natural tissue valves by distributing forces along the coaptation edges and reducing horizontal forces transmitted to the commissural joints. 
     In general terms, the valve prosthesis includes a self-expanding frame which supports a valve body and 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. The proximal section constitutes the “inflow” portion of the valve prosthesis and is disposed in the aortic annulus of the patient&#39;s left ventricle, while the distal section constitutes the “outflow” portion of the valve prosthesis and is positioned in the patient&#39;s ascending aorta. 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. 
     The frame 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 which is impressed upon the metal alloy tube using conventional techniques. 
     Referring now to  FIG. 1 , the valve prosthesis of this application continues the successful features of the prosthesis described above but improves upon it. In more specific terms, the valve prosthesis comprises valve body  14 . Valve body  14  includes skirt  21 , and leaflets  22 . Leaflets  22  are attached along their bases to skirt  21 , for example, using sutures 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 an area of coaptation, as described more fully in U.S. Pat. No. 7,914,569, the entire contents of which are incorporated by reference. 
     The curve formed at joint  27  between the base of each leaflet  22  and skirt  21  follows the contour of the cell pattern of the frame (not shown in  FIG. 1 ), so that most of the length of joint  27  is directly supported by the frame, thereby transmitting forces applied to the valve body directly to the frame. 
     Skirt  21  and leaflet  22 , in preferred embodiments, may be cut from a sheet of animal pericardial tissue, such as porcine pericardial tissue, although synthetic or polymeric material may be used. Cutting may be done either manually or using a die or laser cutting system. The pericardial tissue may be processed in accordance with conventional techniques for processing, forming and treating tissue valve material. Alternatively, skirt  21  and leaflet  22  may be constructed on a synthetic or polymeric material. In a preferred embodiment, skirt  21  and leaflets  22  have a thickness of between 0.004 inch and 0.016 inch. The thicknesses of skirt  21  and leaflets  22  may or may not be equal to each other. 
     Skirt  21  comprises at least one side seam  43  where skirt  21  is joined upon itself (in a one-piece embodiment) or where two portions of material are joined to each other as part of the assembly of skirt  21  from separate components (three, in the preferred embodiment). In any case, side seam  43  extends downwardly from a point on the lower half of joint  27 , preferably from a point in the apex region (i.e., the immediate vicinity of the apex) and most preferably (as illustrated), from the lower apex of joint  27 . Side seam  43  extends downwardly towards the inflow portion of the prosthesis until it reaches the lower (or inflow) edge of skirt  21  located within the region indicated by  1 . Turning to  FIG. 2 , it may be seen that skirt  21  is attached to the frame such that the side seam  43  extends only the relatively short distance represented by a single cell of the frame. One advantage of such an embodiment is the reduction in the amount of any biological response to the seams, e.g., coagulation triggered by stitches or tissue folds. 
       FIGS. 3 and 4  illustrate an alternative embodiment in which side seam  43  is angled with respect to the vertical (i.e., the longitudinal axis lying along the direction of flow through the valve  10 ). In this embodiment, the side seam  43  is somewhat longer than in the embodiment of  FIG. 2 , because side seam  43  lies generally aligned with the diagonal struts  60  extending between three consecutive nodes  61  of the frame, as opposed to spanning the open portion of a cell. Nonetheless, side seam  43  is still significantly shorter than it would be if it extended to a a point on the upper half of joint  27  (e.g., locations where individual joints  27  come together). This embodiment has the advantage of orienting the side seam  43  behind the frame (compare  FIGS. 3 and 4 ) to avoid a “pillow” effect, i.e., a tendency for side seam  43  to bulge outwardly from the interior of the frame. 
       FIGS. 5 and 6  schematically illustrate various geometrical features of a portion of skirt  21  corresponding to the embodiments of  FIGS. 2 and 3-4 , respectively.  FIGS. 7 and 8  illustrate the assembly of the portions of  FIGS. 5 and 6 , respectively. 
     Skirt  21  preferably is constructed from the same material as leaflets  22 , and includes scalloped areas  37   a - b , reinforcing tabs  38   a - b  and multiple end tabs  39 . Each scalloped area  37   a - b  is shaped to be joined to each other and then joined to a body  33  of a respective leaflet  22 , as described illustrated earlier (see  FIG. 1 ). Reinforcing tabs  38   a - b  include fold lines (not shown in  FIG. 6  for clarity), except for reinforcing tabs  40  and  41  at the lateral ends of the skirt, which have only one fold apiece (see  FIGS. 7-8 ). 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. End tabs  39  are folded over the ends of the proximal-most row of cells of the frame to secure skirt  21  to the frame and seal against paravalvular bypass flows. 
     A line of symmetry S passes through a location substantially centered on the upper apex  50 , and is substantially parallel to the longitudinal direction of flow. Notably, in the embodiment of  FIG. 5 , line S symmetrically divides tabs  39   a - e  but does not symmetrically divide such tabs  39   b - f  in the embodiment of  FIG. 6 . This is due to the notable difference between the embodiments, i.e., the acute angle θ that side seam  43  makes from the direction of flow in  FIG. 6 , which enables side seam  43  (in that embodiment) to follow the frame as described above. Note that side seam  43  still originates in the lower apex region, specifically at lower apex  52  (the vertex of the acute angle). It may also be said that the side seam  43  extends between the lower apex  52  and an end tab which does not lie on the axis S, i.e., end tab  39   b  or  39   f , as opposed to end tab  39   c  which does lie on that axis. 
       FIGS. 9 and 10  schematically illustrate less preferred embodiments; for the sake of clarity, some details common to the preferred embodiments above are omitted. In these two embodiments, the angled seams originate at higher locations on the joints other than the lower apex but still in the lower half of the seams. As  FIG. 10  shows in particular, the portions of such embodiments do not necessarily have identical shapes. The embodiments of  FIGS. 9 and 10  are less preferred than other embodiments because of their relatively complicated configuration as compared to the preferred embodiments discussed above, and also because the side seams in these embodiments are generally not be a short as those in the preferred embodiments. 
     In general, assembly of valve body  14  from skirt  21  and leaflets  22  is performed as described in U.S. Pat. No. 7,914,569 as modified to accommodate the modifications described here. Adjoining leaflets  22  then are fastened together along adjacent seams, resulting in a leaflet assembly. 
     Referring again to  FIG. 1 , valve body  14  is shown as it would appear when affixed to the frame, but with the frame 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  and end tabs  39  are folded over and affixed to the most proximal row of cells of the frame, i.e., at the inflow end to the prosthesis. 
     Valve body  14  also is attached to the frame 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 and nodes that form the cells of the frame, so that joint  44  is affixed to and supported by the frame over most of the length of the joint. As discussed above, the configuration of the cells in the frame may be specifically customized to define a curved contour that supports joints  44  of the valve body. 
     When completely assembled to the frame, valve body  14  is affixed to the frame 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 the frame, thus reducing stress concentration and fatigue of the valve body components. 
     Implantation of the valve prosthesis is performed in a conventional manner. 
     White the description above uses preferred embodiments to describe certain details, the broadest scope of the disclosure includes other embodiments, as well as methods of carrying out the same principles that do not depend upon the specific physical components mentioned above but nonetheless achieve the same or equivalent results. Therefore, the full scope of the invention is described by the following claims.