Patent Publication Number: US-2016220366-A1

Title: Vascular implant

Description:
The present invention relates to a vascular implant, such as, but not limited to, a prosthetic heart valve. 
     Prosthetic heart valves have been an area of considerable research in recent years. Typically, the prosthetic valve comprises two elements: a support structure comprising a generally tubular framework surrounding a flow passage; and a flow control structure provided in the lumen of the support structure and providing the one-way valve action to permit blood flow in one direction through the valve, but preventing blood flow in the reverse direction. 
     However, a major problem with such implants has been the occurrence of mild to moderate paravalvular leakage. This can be particularly severe in the case of sutureless, percutaneous and transcatheter valves, that are not typically sutured to the host tissues, for which leakage has been shown to drastically reduce the hemodynamic efficiency of the valve. This can result in a significant increase in the load on the heart because any blood that leaks in the reverse flow direction, around the closed valve, does not contribute to the useful circulatory output of the heart. 
     Various proposals have been put forward to attempt to pack material to seal between the outside of the valve and the surrounding anatomy, but have not been entirely satisfactory, which is a problem. 
     A further problem is that it is undesirable for the implant to apply a high radial force to the surrounding anatomy to attempt to form a seal to avoid paravalvular leakage. 
     Another problem is that it is desirable for implants to be retrievable, so any sealing means that permanently hooks into the surrounding anatomy cannot achieve this. 
     The present invention seeks to alleviate, at least partially, some or any of the above problems. 
     The present invention provides a vascular implant comprising:
         a structure defining a flow passage, the flow passage having a first end and a second end; and   a skirt around at least a portion of the outer periphery of the structure,   wherein a portion of the skirt is fixed to the structure to form a seal with respect to the flow passage, and   wherein the skirt is compliant such that, in response to a higher fluid pressure at one of the ends of the flow passage, the skirt is configured to be urged against the anatomy at the site in which the implant is located, to span between the outer periphery of the structure and said anatomy.       

    
    
     
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic cross-section of an implanted valve to illustrate its operation as an embodiment of a vascular implant according to the invention; 
         FIGS. 2 and 3  are illustrations of a prosthetic heart valve of another embodiment of the invention; and 
         FIG. 4  shows the heart valve of  FIGS. 2 and 3  implanted at the location of the aortic valve. 
     
    
    
     An embodiment of the invention comprising an implantable valve will now be described with reference to the schematic cross-section shown in  FIG. 1 . In this embodiment, the implant comprises a structure  10  defining a flow passage  12  having a first end  12 A and a second end  12 B. The structure  10  sits within the native anatomy  14 . The structure  10  is generally approximately cylindrical, but in  FIG. 1  is, of course, shown in longitudinal cross-section. The structure  10  typically comprises a framework made from a metal tube or wire, but may take any suitable form known in the art. 
     The structure  10  supports a flow control device, in this case a valve comprising valve leaflets  16  located in the lumen of the flow passage  12 . Such valves are well known in the art, and can comprise one, two, three or more leaflets  16 . 
     According to preferred embodiments of the invention, the implant can be, for example, a prosthetic heart valve, such as an aortic valve, pulmonary valve, mitral valve or tricuspid valve. 
     In normal operation, fluid, in this embodiment blood, can flow from the first end  12 A to the second end  12 B of the flow passage  12  in the direction indicated by the arrow A because the leaflets  16  are flexible and the leaflets separate to permit flow. Flow in the reverse direction indicated by the arrow B is prevented by the closure by the leaflets  16 . 
     However, with conventional devices, it may be possible for paravalvular leakage to occur by flow of fluid around the exterior of the structure  10  where there are any gaps between the structure and the native anatomy. In  FIG. 1 , the clearance between the structure  10  and the native anatomy  14  is shown exaggerated for clarity. In practice, the implant will fit much more snugly in the implant site (which also helps anchor the implant in place). However, conventionally, some leakage may be unavoidable due to natural irregularities in the native anatomy and the inability to form a perfect seal all the way round. 
     As illustrated in  FIG. 1 , this embodiment of the present invention provides a skirt  18  around the outer periphery of the structure  10 . The skirt  18  may also be described as a flap, wing, parachute or similar. The skirt  18  is fixed to the structure  10  at a joining line  20  such that it forms a seal with respect to the flow passage  12 . 
     The joining line  20  can lie in a plane, as in this embodiment, or can take other shapes, regular or irregular. The skirt  18  and the joining line  20  are not limited to being in the particular location relative to the structure  10  illustrated in  FIG. 1 , but could, for example, be adjacent to the leaflets  16 , or could be positioned at either extreme end of the structure  10  or any intermediate position. If the joining line  20  is adjacent to the end of the structure  10  at the second end  12 B of the flow passage  12 , then the skirt  18  will extend beyond the end of the structure  10 . 
     The skirt  18  is compliant, for example being made of a flexible membrane. Suitable material for the skirt  18  includes biological tissue, polymer, fabric, or a combination thereof. For example, the skirt can be entirely synthetic, formed from artificial polymeric material, or can be biologically-derived, for example a xenograft of bovine pericardium or porcine pericardium, or a combination of synthetic and biologically-derived material. Any other bio-compatible material suitable to be formed into a membrane could be used. The skirt is substantially impermeable to prevent flow of the relevant fluid therethrough, or becomes impermeable after the implant, for example due to thrombus coating or cell proliferation. Although the skirt  18  is flexible, it can be elastic or inelastic. The skirt  18  is fixed to the structure  10  by any suitable technique, such as gluing or suturing or by being made as an integral component of the implant. 
       FIG. 1  illustrates the situation in which the fluid pressure at the second end of the flow passage  12 B is higher than the fluid pressure at the first end of the flow passage  12 A. In this case the leaflets  16  of the valve are urged together so that the valve is closed and reverse flow through the flow passage is prevented. If the implant is a replacement aortic valve or pulmonary valve, with the first end  12 A at the left or right ventricle, respectively, and the second end  12 B at the aorta or pulmonary artery, respectively, then this situation occurs during diastole when the pressure in the outlet artery rises above the ventricular pressure. If the implant is a mitral valve or tricuspid valve, with the first end  12 A in the respective atrium and the second end  12 B in the respective ventricle, then this situation occurs during systole, when the ventricular pressure exceeds the atrial pressure. 
     The higher pressure at the end  12 B can cause blood to flow around the implant where there are any gaps between it and the native anatomy  14 . The fluid pressure then urges the skirt  18  against the native anatomy  14 , as indicated by the small arrows in  FIG. 1 . This engages the skirt  18  against the anatomy at the implant site and occludes any gaps, and results in a seal against leakage. In effect, the skirt  18  acts like a parachute that becomes inflated when there is back pressure against the valve. 
     The compliance of the material of the skirt  18  means that it can conform to irregularities in the anatomy  14  at the location of the implant. The design of the skirt  18  means that damage to the native anatomy due to excessive radial force is avoided because the force urging the skirt into sealing engagement against the native anatomy  14  is provided by the fluid pressure to which the anatomy would be subjected to anyway in the absence of the implant. 
     A further specific embodiment of an implant according to the invention is illustrated in  FIGS. 2, 3 and 4 . Parts corresponding to those illustrated in  FIG. 1  are indicated with corresponding reference numerals, and so repetition of the description of those will be avoided. 
     The implant of  FIGS. 2 to 4  is a self-expanding prosthetic aortic valve. Further details of its structure can be obtained from WO 2010/112844. The implant has the addition of the skirt  18 . As illustrated in  FIGS. 2 and 3 , the joining line  20  at the closed edge of the skirt  18  where it is fixed to the structure, is curved such that it is scalloped. 
     In this embodiment, the open edge  22  of the skirt  18  is fixed at one or more points  24  to the structure  10 . This prevents complete reversal of the skirt, either when in use, or when being implanted. Fixing points  24  still enable the skirt  18  to “inflate” like a parachute to seal against the anatomy  14 , as illustrated in  FIG. 4 .  FIG. 4  also illustrates that a part of the anatomy around the implant site can be a native valve leaflet  14 . 1  that is displaced when the prosthetic valve is implanted. 
     Although a specific implant is illustrated in  FIGS. 2 to 4 , which is delivered percutaneously by trans-catheter techniques, the invention is not limited to those particular aspects. The implant in this particular embodiment is self-expanding, but it could equally be expandable or of fixed size. 
     Although the embodiments described have a single skirt  18  that surrounds the entire implant, an alternative is to have one or more individual skirts. The skirts could, in combination, surround the entire circumference of the implant, either with or without overlap. Alternatively, the or each skirt could be provided only at particular positions that are susceptible to leakage.