Abstract:
A ring prosthesis provides suitable flexibilities/stiffness three-dimensionally at various points about the circumference of an associated heart valve, and is shaped proportionally to fit about the annulus of the associated heart valve. The ring prosthesis also provides a certain flexibility to conform to the natural non-planar shape of the annulus (e.g., saddle shape for mitral valve surface) with or without preformation of the ring prosthesis. The prosthesis can also be used as an artificial annulus for further valve anchoring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a support prosthesis for use in medical applications, and in particular, to an annuloplasty ring that is adapted for use in supporting a heart valve.  
         [0003]     2. Description of the Prior Art  
         [0004]     Annuloplasty rings for use as heart valve prostheses are well known in adult patients. Most such annuloplasty rings are substantially planar. Recently, an interest in non-planar (e.g., saddle-shaped) annuloplasty rings has developed. The conventional non-planar annuloplasty rings tend to be substantially rigid throughout the annuloplasty ring. Unfortunately, uniformly rigid annuloplasty rings do not conform to the natural non-planar shape of the human valve annulus. As a result, these uniformly rigid annuloplasty rings do not move with the valve tissue, thereby increasing the stress to the leaflet or surrounding tissue.  
         [0005]     In addition, many patients who suffer from disfunction of the mitral and/or tricuspid valves(s) of the heart, surgical repair of the valve (i.e., “valvuloplasty”) is a desirable alternative to valve replacement. One problem associated with the annuloplasty rings of the prior art is that when such annuloplasty rings are implanted into children or adolescents (such as pediatric patients with CVA or RVD), the subsequent growth of the patient may render the annuloplasty ring too small for its intended function, thereby abnormally constricting the annulus. Follow-up surgery would be necessary to replace the originally implanted annuloplasty ring with a larger annuloplasty ring suitable for the then-current size of the patient. However, the tissue of the heart valve annulus grows into the fabric of the annuloplasty ring by design, so that the annuloplasty ring is soon embedded in living tissue, thereby making such replacement surgery problematic.  
       SUMMARY OF THE DISCLOSURE  
       [0006]     It is an object of the present invention to provide a ring prosthesis that has varying flexibility to conform to the natural non-planar shape of a human valve annulus.  
         [0007]     It is another object of the present invention to provide a ring prosthesis that reduces stress to the leaflet and surrounding tissue due to annuloplasty.  
         [0008]     It is yet another object of the present invention to provide an expandable annuloplasty ring for implantation in a heart valve annulus.  
         [0009]     In order to accomplish the objects of the present invention, the present invention provides an annuloplasty ring having a frame member that has varying three-dimensional flexibility/expandability at different regions of the frame member. The ring also includes a suture-permeable outer layer that covers the frame member, and a soft sleeve surrounding the frame member.  
         [0010]     The ring prosthesis according to the present invention is also adapted to expand upon natural growth of the patient&#39;s annulus, or upon application of a dilatation force surgically applied. The outer layer can be provided in the form of a fabric covering that is preferably radially expandable. The ring prosthesis may also be implanted percutaneously and secured to the dilated natural human valve annulus.  
         [0011]     According to the present invention, the ring prosthesis provides suitable flexibilities/stiffness three-dimensionally at various points about the circumference of an associated heart valve, and is shaped proportionally to fit about the annulus of the associated heart valve. The ring prosthesis also provides a certain flexibility to conform to the natural non-planar shape of the annulus (e.g., saddle shape for mitral valve surface) with or without preformation of the ring prosthesis. The prosthesis can also be used as an artificial annulus for further valve anchoring. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a top plan view of one embodiment of a mitral annuloplasty ring prosthesis according to the present invention, with the covering material and insert being partially removed to expose the individual segments.  
         [0013]     FIGS.  2 ( a ),  2 ( b ) and  2 ( c ) are enlarged cross-sectional views of the section A-A′ of the ring prosthesis of  FIG. 1  according to different embodiments thereof.  
         [0014]      FIG. 3  is a perspective view of one embodiment of the frame member for the ring prosthesis of  FIG. 1 .  
         [0015]      FIG. 4  illustrates a conventional saddle-shape mitral annulus.  
         [0016]      FIG. 5  is a bottom view of another embodiment of a mitral annuloplasty ring prosthesis according to  FIG. 2 ( b ) of the present invention, which has a wire or drawstring running through the sleeve.  
         [0017]      FIG. 6  is a side view of the ring prosthesis of  FIG. 1  pre-formed to the natural mitral valve shape (e.g., saddle shape).  
         [0018]      FIG. 7  is a perspective view of yet another embodiment of a mitral annuloplasty ring prosthesis according to the present invention, with the covering material and insert being partially removed to expose the individual segments.  
         [0019]      FIG. 8  is a perspective view of the frame member of the ring prosthesis of  FIG. 7 .  
         [0020]      FIG. 9  is the perspective view of the ring prosthesis of  FIGS. 7-8  implanted on the top of a natural mitral valve.  
         [0021]      FIG. 10  is a perspective view of the frame member of  FIG. 3  modified to include interlocking elements.  
         [0022]     FIGS.  11 ( a )- 11 ( c ) illustrate how different types of interlocking struts can be used in connection with the frame member of  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims.  
         [0024]     Inasmuch as the human mitral valve is far more likely to require repair than the tricuspid, aortic and pulmonary valves, the description of the present invention herein will be based on the repair of a mitral valve. However, the same principles discussed herein in connection with the repair of a mitral valve also apply to the repair of all other heart valves.  
         [0025]      FIGS. 1-3  illustrate a ring prosthesis  100  according to one embodiment of the present invention. The ring prosthesis  100  is illustrated herein as an annuloplasty ring  100 . The annuloplasty ring  100  can be made of a single inner frame member  10  that is covered by a suture-permeable outer layer  30 , and which has a soft expandable insert or sleeve  20  (hereinafter “insert”) surrounding the frame member  10 . This is best shown in  FIG. 2 ( a ), which shows the frame member  10  completely embedded in a soft insert  20 , and then further covered by a biocompatible material as the outer layer  30 . The covering material for the outer layer  30  may be folded and sealed, as shown at  31 . The ring prosthesis  100  can be secured to a valve annulus by suture or staples.  
         [0026]     The frame member  10  can be made of a material having shape memory, such as Nitinol. The frame member  10  can also be made of other biocompatible materials, such as Cobalt-Chromium alloys, and titanium alloys. The structural pattern for the frame member  10  can be cut from a flat sheet or tube and then heat or cold formed into a three-dimensional shape.  
         [0027]     The biocompatible material for the outer layer  30  can be made from a suture-permeable material such as tissue, Dacron or ePTFE cloth, or other synthetic material that allows selected expansion of the insert  20  and frame member  10 . The soft expandable insert  20  can be made of silicone, cotton, and other similar biocompatible filling materials.  
         [0028]     As shown in FIGS.  2 ( b ) and  5 , the ring prosthesis  100  can optionally include a wire  40  that extends adjacent to, and along the circumference of, the frame member  10 . The wire  40  can be a metallic wire or a drawstring, and may be used to control or restrict the dimension of the metallic frame member  10  either permanently or temporarily. Specifically, if the wire  40  is biodegradable, it is disappear after a period of time after implantation, so that the restriction of the dimension is temporary. Conversely, if the wire  40  is not biodegradable, then the restriction of the dimension is permanent.  FIG. 2 ( b ) shows the wire  40  tied to the outside of the ring prosthesis  100  to restrict the expansion of the ring prosthesis  100 . In the embodiment of  FIG. 2 ( b ), the soft insert  20  can be positioned so that it only partially covers the frame member  10 , and defines an opened inner space  21  that receives the wire  40 .  
         [0029]     If a drawstring  40  is used, the drawstring  40  extends through the inner space  21  of the insert  20  and can be pulled or released to constrict and remodel the orifice of the ring prosthesis  100  so as to secure the ring prosthesis  100  in place at a valve annulus. The two ends of the drawstring  40  may be tied during the surgical procedure. The drawstring  40  can be made of non-stretchable wire or tape, and also can be made of an elastic material, such as silicone. The constriction applied to the frame may be permanent or temporary, as described above.  
         [0030]      FIG. 2 ( c ) illustrates an alternative embodiment where both the frame member  10  and the restriction wire  40  are completely embedded in the soft insert  20 .  
         [0031]      FIG. 3  illustrates the frame member  10  of the mitral annuloplasty ring  100  of  FIG. 1 . The shape of the frame member  10  is designed based on the natural planar shape of a valve annulus, which is a slight D shape for a mitral valve. The frame member  10  may be flat or pre-formed into a saddle shape. The expandability and flexibility may not be uniform throughout the frame member  10 . Specifically, the expandability and flexibility of the frame member  10  at each location can be designed to match the need for that particular location. For example, regions  14 ,  17  and  18  can have different expandabilities and flexibilities because the natural human mitral valve has different anatomies and movement dynamics at the anterior, posterior and side regions. This variable expandability and flexibility is achieved by providing different structural patterns, or varying the thickness of the material within the prosthesis (e.g., the frame member  10  and the insert  20 ), which allows certain movement within its elasticity.  
         [0032]     The present invention provides different ways for varying the flexibility and expandability of the prosthesis ring  100 . In this regard, it is the construction of the frame member  10  which allows the ring prosthesis  100  to experience bending and deformation in three dimensions. In a first example, as shown in  FIG. 3 , the frame member  10  defines a thin-walled tubular member configured with a pattern of alternating struts or zig-zags  35  that define a plurality of slots  15  formed therebetween, with the slots  15  being disposed substantially parallel to the longitudinal axis LA of the tubular ring  100 . The slots  15  can be formed by cutting away portions of the material that is used for the frame member  10 . It is the provision of a pattern of structural modifications to the frame member  10  (such as, but not limited to, the zig-zags  35 , slots  15  and/or the cells  19  described below) which allows the annuloplasty ring  100  to be bent during cardiac cycles, and to conform to the non-planar surface of the valve annulus.  
         [0033]     As another example, the frame member  10  defines a thin-walled tubular member that has a plurality of cells  19  formed therein. The cells  19  may be deformed to allow the annuloplasty ring  100  to expand upon stretching by circumferential external forces. The cells  19  can be formed by cutting material away from the frame member  10  to form openings that make up the cells  19 .  
         [0034]     On the top of the frame member  10  in  FIG. 3 , additional material may be bent outwardly to form a flange  36  to facilitate the securing of the ring prosthesis  100  to the valve annulus. The flange  36  can be made up of a plurality of U-shaped elements. The flange  36  can be used to further control the flexibility of the annuloplasty ring  100 . For example, configuring the flange  36  with a greater number of U-shaped elements will cause the frame menber  10  to be less flexible, while configuring the flange  36  with a lesser number of U-shaped elements will cause the frame menber  10  to be more flexible.  
         [0035]     In addition to the cells  19  and slots  15  described above, additional structures can be provided to vary the flexibility and expandability of the ring prosthesis  100 , to cause structural deformation, or to function as locking mechanisms to prevent the retraction of the structure of the frame member  10  when there are no external stretching forces (e.g., when the natural valve annulus is not expanding). Additional interlocking struts or bars shaped as arcs, zig-zags, and similar alternating elements may be added to the top or bottom of the frame member  10 . For example,  FIGS. 10 and 11 ( a )- 10 ( c ) illustrate how additional struts can be provided on the frame member  10  to function as one-way locking mechanisms that prevent the retraction of the frame member  10 .  
         [0036]     Referring first to  FIG. 10 , locations  120  and  125  can be provided on the zig-zags  35  of the frame member  10 , and locations  120 ′ and  125 ′ can be provided on the flange  36 , for receiving the struts described in connection with FIGS.  11 ( a )- 11 ( c ). These struts can have the same material as the frame member  10 , and can even be cut from the material used to form the frame member  10 . These struts can have different configurations or patterns to obtain the desired flexibility, expandability and anti-retraction for the ring prosthesis  100 . For example, in  FIG. 11 ( a ), the strut  129  has a center coil that is unwrapped permanently during the expansion (i.e., outward motion) of the locations  120  and  125  of the zig-zag  35 . This expansion of the locations  120 ,  125  allows the segment  128  to rotate into a more horizontal position, thereby making it more difficult for the locations  120 ,  125  to return to their original positions. In  FIG. 11 ( b ), the expansion of the locations  120 ,  125  pulls on the strut  130 , causing the strut  130  to straighten itself to form a straight segment. The resisting forces applied by the strut  130  against the zig-zag  35  at the locations  131  and  132  will make it more difficult for the locations  120 ,  125  to return to their original positions. In  FIG. 11 ( c ), the expansion of the locations  120 ,  125  pulls on the strut segments  136 ,  137 ,  139  and  140 , causing them to form a larger radius segment. The resisting forces applied by the strut segments  136  and  137  against the locations  120 ,  125  will make it more difficult for the struts  120 ,  125  to return to their original positions. These struts can also function to vary the flexibility and expandability of the ring prosthesis  100  because their provision or absence at certain locations of the ring prosthesis  100  will cause these locations to be more rigid (where the struts are provided) or more flexible (where the struts are absent).  
         [0037]      FIG. 4  shows the mitral annular shape of a natural valve. Mitral leaflets concave towards the left ventricle during systolic pressure. The leaflets form a saddle shape.  
         [0038]      FIG. 6  is a side view of the mitral annuloplasty ring prosthesis  100  pre-formed to the natural mitral valve shape (saddle shape).  
         [0039]      FIG. 7  illustrates a modification that can be made to the mitral annuloplasty ring prosthesis  100 , where the ring prosthesis  100   a  can be the same as the ring prosthesis  100  except that hooks  155  are now provided to anchor the ring prosthesis  100   a  to the annulus of the natural valve. The frame member  10   a  of the ring prosthesis  100   a  is shown in greater detail in  FIG. 8 , with the hooks  155  extending in the longitudinal direction LA.  
         [0040]     The ring prosthesis  100 / 100   a  can be implanted percutaneously. To carry out the percutaneous procedure, the ring prosthesis  100 / 100   a  is delivered to the valve annulus by a catheter or other known delivery means, and then mechanically expanded to the size of the dilated natural valve annulus by means of a holder and/or a balloon using techniques that are well-known in the art. The expansion of the ring prosthesis  100 / 100   a  is tailored to the expanded natural valve annulus; for example, greater expansion in the posterior section of the mitral valve annulus than in the anterior section because the anterior section does not change much in a diseased case or during the growth of a pediatric patient. If hooks  155  are provided, the ring prosthesis  100   a  is then attached on top of the annulus  160  by means of the hooks  155  that are specifically placed to allow the ring prosthesis  100   a  to adapt to the three-dimensional shape of the annulus. See  FIG. 9 . Otherwise, the ring prosthesis  100  can be stapled or sutured to the valve annulus  160 . As the mechanical expansion force is removed, the ring prosthesis  100 / 100   a  returns to its unexpanded dimension, which in turn reshapes the dilated natural annulus. The retraction forces of the ring prosthesis  100 / 100   a  around its circumference are designed to have different values to provide the optimum reshaping of the annulus.  
         [0041]     The ring prosthesis  100 / 100   a  may be used as an artificial annulus for anchoring or receiving future artificial valve (e.g., a self-expanding heart valve) that is to be deployed within the ring prosthesis  100 / 100   a.    
         [0042]     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.