MECHANICAL HEART VALVE ASSEMBLY WITH SUPER-ELASTIC LOCK WIRE

Abstract: A mechanical heart valve assembly includes an orifice (2) coupled with a stiffening ring (12) and sewing cuff (20) by a lock wire (26). The lock wire (26) is made from a super-elastic material, e.g., a nickel-titanium alloy, and pre-formed into a "C" shape. The lock wire (26) is inserted between the orifice (2) and stiffening ring (12) by piercing the sewing cuff (20) that surrounds the ring (12), and passing the lock wire (26) into a window (22) in the stiffening ring (12) and into the aligned lock wire grooves (6, 24) on the orifice and stiffening ring. Once seated in the lock wire grooves, the lock wire (26) retains its "C" shape, providing a secure coupling between the orifice (2) and stiffening ring (12).

Description: Mechanical Heart Valve Assembly With Super-Elastic Lock Wire Description Technical Field The present invention relates to a mechanical heart valve and method for manufacturing the same. Background Art Mechanical heart valves are used to replace native valves which no longer function properly due to disease or other factors. Mechanical valves typically include an orifice having one or more occulders, which regulate blood flow. Also, mechanical valves typically include a stiffening ring that helps the valve assembly resist the compressive annular loads to which it is exposed when implanted. The stiffening ring can be made integral to the valve orifice or mechanically attached to the valve orifice. When the stiffening ring is mechanically attached to the valve orifice, a coupling mechanism is required. One coupling mechanism includes a lock wire. For example, the family of Sulzer Carbomedics Prosthetic Heart Valves utilize a titanium lock wire positioned in grooves on the outer wall of the orifice and inner wall of the stiffening ring. A window in the stiffening ring allows insertion of the lock wire when the groove on the orifice is aligned with the groove on the stiffening ring. A prior art valve of this type is described in Walker et al., U.S. Patent 5,397,346. Typically, the stiffening ring is incorporated with the sewing cuff. Therefore, in order to perform the mechanical attachment of orifice and ring, the cuff must be cut or otherwise partially disassembled to allow the lock wire to be passed through the window of the stiffening ring and into the aligned grooves. Once the lock wire is inserted, the cuff must be stitched closed again. This process of cutting and repairing the sewing cuff is time consuming. Further, this process leads to rejection of valve assemblies due to visual discrepancies caused by the cut/sew process. Therefore, there is a need for a mechanical heart valve assembly and method for manufacturing, which reduces the manufacturing time and reduces the rejection of valve assemblies due to visual discrepancies. Disclosure of Invention The present invention is directed toward a mechanical heart valve assembly. The mechanical heart valve assembly includes a generally annular valve orifice. The outer surface of the valve orifice has a circumferential lock wire groove. A generally annular valve support ring surrounds at least a portion of the valve orifice. The support ring includes an inner surface with a circumferential lock wire groove. The orifice lock wire groove and support ring lock wire groove are positioned generally opposite each other. A lock wire is positioned in the grooves, operably coupling the orifice and support ring. The lock wire comprises a super-elastic material. In one embodiment, the lock wire comprises nickel-titanium alloy, e.g., SE508 alloy. The lock wire includes a first and a second end and is generally "C" shaped. In one embodiment, the distance between the first and second ends of the lock wire is about 0.115 inches. In one embodiment, the lock wire has a cross-sectional diameter of about 0.0135 inches. The support ring includes a window for receiving the wire. In one embodiment, a sewing cuff is disposed circumferentially about at least a portion of the support ring, covering the window. Additionally, the present invention is directed toward a method of manufacturing a mechanical heart valve assembly. The mechanical heart valve assembly includes an orifice, a stiffening ring, and a lock wire. The lock wire is formed into a super-elastic "C" shape. The stiffening ring is aligned with the orifice so that the stiffening ring surrounds at least a portion of the orifice and so that a lock wire groove on an inner wall of the stiffening ring is generally aligned with a lock wire groove on an outer wall of the orifice. A first end of the lock wire is inserted through a window in the stiffening ring and into the generally aligned lock wire grooves until all of the lock wire is seated in the lock wire grooves. In one embodiment, a sewing cuff is positioned circumferentially about at least a portion of the stiffening ring. The first end of the lock wire pierces the sewing cuff before it is inserted into the window of the support ring. The present invention provides several advantages. First, there is no need to cut or otherwise disassemble the sewing cuff in order to insert the lock wire. Consequently, the number of manufacturing steps is reduced and the number of rejections based on visual discrepancies in the cuff is reduced. Both of these reductions help lower the manufacturing cost of the heart valve assembly. Additionally, the super-elastic lock wire is relatively easy to insert and returns to its memory shape when seated in the lock wire grooves. The lock wire will retain its pre-formed shape in a wide range of temperatures and after repeated sterilizations. Brief Description of Drawings Figure 1 is an exploded view of a mechanical heart valve assembly; Figure 2 is bottom view of a stiffening ring; Figure 3 is a top view of a lock wire; and Figure 4 is a side, cross-sectional view of a lock wire. Best Mode for Carrying Out the Invention An exploded view of a mechanical heart valve assembly is shown in Figure 1. A generally annular valve orifice 2 includes an outer wall 4 having a circumferential lock-wire groove 6. Occluders 8 are disposed within valve orifice 2 and coupled with inner wall 10. The embodiment shown in Figure 1 includes two occluders 8. Other embodiments may include one occluder or three or more occluders. A generally annular stiffening or support ring 12 includes an outer wall 14 (Fig. 2) and an inner wall 16. In the embodiment shown in Figure 1, sewing cuff 20 includes a seating lip or flange 18 that is useful for seating the heart valve assembly in a valve annulus. Other embodiments include a sewing cuff 20 without a flange. As shown in Figure 2, the sewing cuff 20 is positioned circumferentially around outer wall 14. When the heart valve assembly is seated in a native valve annulus, sutures are passed through the sewing cuff 20 and the surrounding annulus tissue to securely fix the valve assembly in place. The sewing cuff 20 is made from polyester knit, PTFE knit, ePTFE knit, or other biocompatible material that promotes tissue growth about the valve assembly, providing a long-term, secure attachment. Stiffening ring 12 also includes window 22 extending from outer wall 14 to inner wall 16. A circumferential lock-wire groove 24 on inner wall 16 intersects window 22, as shown in Figure 1. Lock wire 26 mechanically couples orifice 2 and stiffening ring 12 as described below. Lock wire 26 is made from a biocompatible, super-elastic material. In one embodiment, lock wire 26 is made from a nickel titanium alloy, commonly known as nitinol. One example of a suitable alloy is SE508 alloy available from Nitinol Devices & Components, Inc., Fremont, California. Referring to Figure 3, the pre-formed of lock wire 26 is generally in the shape of a C . The length of wire 26 is selected for the specific size of the valve being used, and the gap 28 in lock wire 26, which defines the open part of the "C" shape, is about 0.115 inches. For example, a valve sized for a 29-mm annulus has a lock wire with a length of about 3.0203 inches and gap of about 0.115 inches. Referring to the embodiment shown in Figure 4, the cross-sectional shape of lock wire 26 is generally circular with a diameter of about 0.0135 inches +/- .0005 inches. The manufacturing process of a heart valve assembly according to the present invention is as follows. First, lock wire 26 is pre-formed into a "C" shaped ring of the appropriate diameter for the selected valve size. This is accomplished by wrapping the generally straight lock wire around a rod of appropriate diameter and annealing the lock wire into the desired "C" shape. Other methods for working with super-elastic materials may also be used. Stiffening ring 12 is disposed about orifice 2 so that lock wire grooves 6, 24 are generally aligned. One end 30 or 32 of lock wire 26 is used to pierce cuff 20. The end then passes through cuff 20 into window 22 of stiffening ring 12. Lock wire 26 then slides into the generally opposed grooves 6, 24 and passes around the circumference of both stiffening ring 12 and orifice 2 in grooves 6, 24. When lock wire 26 is fully inserted in grooves 6, 24 it returns to its pre-formed "C" shape, providing a secure mechanical coupling between orifice 2 and stiffening ring 12. Since cuff 20 has been pierced by wire having a small diameter, e.g., 0.0135 inches, there is no significant damage to cuff 20 that might require repair. Due to the super-elastic characteristics of lock wire 26, it will retain its shape within the physiological temperature range commonly found in an implantation. In the embodiment using the SE508 alloy, the lock wire will retain its shape to temperatures as low as 20 degrees Celsius. Further, the lock wire will retain its shape after multiple steam sterilizations to which it may be exposed during manufacture and prior to implantation. Other embodiments are within the scope of the following claims.

Claims: WHAT IS CLAIMED IS: 1. A method of manufacturing a mechanical heart valve assembly comprising an orifice (2), a stiffening ring (12), a sewing cuff (20) disposed around said stiffening ring (12), said sewing cuff (20) being comprised of a flexible biocompatible material, and a lock wire (26), said lock wire (26) having a cross section, the steps comprising: forming the lock wire (26) in a pre-formed "C" shape; aligning the stiffening ring (12) and sewing cuff (20) with the orifice (2) so that the stiffening ring (12) surrounds at least a portion of the orifice (2) and so that a lock wire groove (24) on an inner wall of the stiffening ring (12) is generally aligned with a lock wire groove (6) on an outer wall (4) of the orifice (2); and inserting a first end of the lock wire (26) through a window (22) in the stiffening ring (12) and into the generally aligned lock wire grooves until all of the lock wire is seated in the lock wire grooves characterized by inserting said lock wire (26) through said window (22) through said flexible material of said sewing cuff (20) without creating a hole in said flexible material significantly larger than said cross section of said lock wire (26). 2. The method according to claim 1 wherein the biocompatible material is a knit fabric and said lock wire (26) is inserted through said fabric without cutting said fabric. 3. The method according to claim 2 wherein said first end of said lock wire (26) is used to pierce said fabric. 4. The method according to any of the foregoing claims wherein said forming step further comprises forming said lock wire (26) of a super-elastic material. 5. The method according to claim 4 wherein the lock wire (26) comprises nickel-titanium alloy. 6. The method according to any of the foregoing claims wherein said lock wire (26) returns to its preformed "C" shape when it has been seated in the lock wire grooves. 7. A mechanical heart valve assembly constructed according to the method of any of claims 1 through 6. 8. A mechanical heart valve assembly, comprising: a generally annular valve orifice (2) having an outer surface (4), the outer surface including a circumferential groove (6); a generally annular valve stiffening ring (12) having an inner surface (16) and surrounding at least a portion of the valve orifice (2), the inner surface (16) including a circumferential groove (24), wherein the orifice groove (6) and stiffening ring groove (24) are generally opposite each other; a sewing cuff (20) disposed circumferentially about at least a portion of said stiffening ring (12); and a lock wire (26) positioned in the grooves (6, 24) and having a cross section, said lock wire (26), operably coupling the orifice (2) and stiffening ring (12), characterized by the lock wire (26) comprising a super-elastic material, said lock wire (26) being inserted through a hole in said sewing cuff (20), which hole is substantially the same size as said cross section of said lock wire. 9. The assembly of claim 1, wherein the lock wire (26) comprises nickel-titanium alloy. 10. The assembly of claims 8 or 9, wherein the lock wire (26) includes a first and a second end and is generally "C" shaped. 11. The assembly of claim 10, wherein the distance between the first and second ends of the lock wire (26) is about 0.115 inches. 12. The assembly of any of claims 8 through 11 , wherein the lock wire (26) has a cross-sectional diameter of about 0.0135 inches. 13. The assembly of any of claims 8 through 12, wherein the stiffening ring (12) includes a window (22).

Inventors: COLVIN JAMES L, DEBUTTS JACK, JONES MELANIE E, KELLEY TIMOTHY A, MORTON MICHAEL C, NELSON KATHRYN M, NOETH CARRIE, SAUTER JOSEPH A, SCOGGINS REBECCA, SINGLETON BILL, WILSON ANNE, COLVIN, JAMES, L., DEBUTTS, JACK, JONES, MELANIE, E., KELLEY, TIMOTHY, A., MORTON, MICHAEL, C., NELSON, KATHRYN, M., NOETH, CARRIE, SAUTER, JOSEPH, A., SCOGGINS, REBECCA, SINGLETON, BILL, WILSON, ANNE
Applicants: SULZER CARBOMEDICS INC, SULZER CARBOMEDICS INC.
Application year: 1999
Main classification: A61F2
IPC codes: A61F2, A61L27