WO2001006958A1

WO2001006958A1 - Hybrid prosthetic heart valve

Info

Publication number: WO2001006958A1
Application number: PCT/US2000/020124
Authority: WO
Inventors: Gregory James Hofmann; John Timothy Baldwin
Original assignee: Sulzer Carbomedics Inc.
Priority date: 1999-07-23
Filing date: 2000-07-24
Publication date: 2001-02-01

Abstract

A heart valve prosthesis (10) having improved leaflet occluders (18). A heart valve prosthesis (10) comprises a valve body (12) and a pair of leaflets (18). The valve body (12) includes an interior surface (14) that defines a central passage (16) for conducting blood flow therethrough. The leaflets (18) are pivotably mounted to the valve body (12) for pivotable motion within the central passage (16) between an open and a closed position. Each leaflet is formed from at least two unique materials (46, 51). Preferably, at least an outer arcuate edge (24) of each leaflet is formed from a softer, more pliable material (51) to better approximate the characteristics of natural heart valve tissue.

Description

Hvbrid Prosthetic Heart Valve

Description

Background Art

The present invention relates generally to heart valve prostheses and, in particular, to an improved leaflet occluder design for use in a prosthetic heart valve.

A variety of heart valve prostheses have been developed for use in hearts, such as human hearts. The typical heart valve prosthesis generally includes a main body portion having an annular shape and a central passage for conducting blood flow therethrough. One or more leaflet occluders, commonly called leaflets, are mounted to the annular body for pivotable movement within the central passage. Such heart valve assemblies operate hemodynamically in conjunction with the pumping action of the heart to effectively fulfill the role of a natural heart valve.

A common heart valve construction is the bi-leaflet design in which two leaflets are pivotably mounted in the annular body in an opposed relationship. The leaflets are mounted such that when the heart valve is closed, each leaflet covers approximately half of the valve opening or passage. Typically, each leaflet occluder is generally semi-circular in shape and includes a rounded exterior edge that engages an inner surface which defines the central passage of the main body portion. Each leaflet also includes a generally linear edge designed to move proximate the generally linear edge of the opposing leaflet when the valve is closed. Each leaflet is mounted for pivotable movement about an axis disposed generally parallel with the linear edge. Such heart valve assemblies can be used as aortic valves or mitral valves.

For example, when in operation as an aortic valve, as blood pressure rises in response to heart contraction, the leaflets are pivoted from a closed position to an open position. In the open position, blood flows past the leaflets as it moves through the heart valve central passage. When the heart contraction is complete, however, the blood tends to flow in the opposite direction in response to pressure in the aorta. This causes the leaflets to close and thereby maintain a pressure in the arterial system. Effectively, this type of heart valve prosthesis operates in substantially the same manner as a natural human heart valve. The leaflets often include opposing tabs or ears that are received in corresponding recesses or orifices formed in the interior surfaces that defines the flow passage. The cooperating ears and recesses are designed to allow each of the leaflets to pivot between open and closed positions over long periods of time. Accordingly, both the valve body and the leaflets have traditionally been formed from a relatively stiff, wear-resistant material, such as pyrolytic carbon. However, when the leaflet is formed from a relatively stiff material, the rounded exterior edge is not able to undergo coaptation with the inner surface of the main body as would tissue in a natural heart valve. Additionally, the stiffness of the leaflets can produce a "waterhammer" and/or "squeeze flow" effect when the leaflets move to a closed position. Potentially, this effect can damage the blood cells of blood flowing through the prosthetic heart valve. Furthermore, stiff leaflets can be prone to leakage along the perimeter and have greater potential for cavitation. It would be advantageous to have a prosthetic heart valve utilizing leaflets having an outer, arcuate edge formed of a pliable material that better approximates the characteristics of natural heart valve tissue. Disclosure of Invention

The present invention features a heart valve prosthesis. The heart valve prosthesis includes a valve body and a pair of leaflets pivotably mounted to the valve body. The valve body includes an interior surface that defines a central passage for blood flow therethrough. The leaflets are mounted such that they may pivot within the central passage. Each leaflet is formed from at least two unique materials to preserve wear characteristics while providing a more pliable material for engagement with the interior surface of the valve body.

According to another aspect of the present invention, a heart valve prosthesis is provided with a valve body and a leaflet. The valve body includes an interior surface that defines a central passage for blood flow therethrough. The valve body also includes orifices formed through the interior surface. The leaflet includes a pair of pivot mounts disposed for engagement with corresponding orifices that are positioned at appropriate locations along the interior surface. The leaflet also includes an arcuate distal edge disposed for engagement with the interior surface. The pair of pivot mounts comprise a first material, and the arcuate distal edge comprises a second material having different material characteristics than the first material. According to another aspect of the present invention, a method is provided for constructing a heart valve prosthesis. The method includes providing a valve body with an interior surface that defines a central passage through which blood may flow. The method further includes pivotably mounting a leaflet to the valve body for pivotable motion between an open position and a closed position with respect to the central passage. Further, the method includes forming a conformable distal edge along the leaflet to facilitate engagement with the interior surface. Brief Description of Drawings

The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: Figure 1 is a perspective view of a heart valve prosthesis illustrating certain aspects of the present invention, and showing one leaflet partially broken away;

Figure 2 is a cross-sectional view taken generally along the line 2-2 of Figure 1 , showing the leaflets in a closed position; Figure 3 is a cross-sectional view similar to that of Figure 2 but showing the leaflets in an open position;

Figure 4 is a top view of a leaflet, according to an exemplary embodiment of the present invention;

Figure 5 is a cross-sectional view taken generally along line 5-5 of Figure 4; and Figure 6 is a cross-sectional view similar to Figure 5 but showing an alternate embodiment of the leaflet. Best Mode for Carrying Out the Invention

Referring generally to Figure 1, a heart valve prosthesis 10 is illustrated according to a preferred embodiment of the present invention. Heart valve prosthesis 10 includes a valve body 12 having a generally annular shape. Valve body 12 includes an interior surface 14 that defines a central passage 16 for conducting blood flow therethrough.

At least one leaflet 18 is pivotably mounted to valve body 12 for pivotal motion within central passage 16. In the embodiment illustrated, heart valve prosthesis 10 is a bi-leaflet design having a pair of leaflets 18 pivotably mounted to valve body 12. In this preferred bi-leaflet design, each leaflet 18 includes a perimeter edge 20 having a lead edge 22 and a generally arcuate, semicircular edge 24 designed to engage interior surface of valve body 12 when valve 10 is in a closed position, as illustrated best in Figure 2. Each leaflet 18 is further defined by a pair of generally flat opposing surfaces 26 that extend from lead edge 22 to arcuate edge 24. In the closed position, the two lead edges 22 of the two leaflets 18 abut one another, and the arcuate edges 24 engage the interior surface 14. (In Figure 1, a portion of one leaflet 18 is broken away to more clearly illustrate the exemplary prosthetic heart valve design.)

Each leaflet 18 includes a pivot axle 28 that permits the leaflet to pivot between a closed position illustrated in Figure 2 and an open position illustrated in Figure 3. Each axle 28 includes a pivot member, such as a pair of ears 30, that extend outwardly from arcuate edge 24, generally on opposite sides of the leaflet 18 (see Figure 4). Ears 30 may be formed as flat tabs that extend from arcuate edge 24 at a predetermined distance from lead edge 22. Ears 30 permit leaflets 18 to be pivotably mounted to valve body 12 for regulating blood flow therethrough.

Valve body 12 includes an upstream edge 32 that may have a chamfered region 34 to facilitate the smooth transition of blood into central passage 16. Additionally, valve body 12 includes a downstream edge 36 that also may have a chamfered region 38 to facilitate the outflow of fluid from valve body 12.

The exemplary valve body 12 further includes a pair of thickened or reinforced regions

40 that are generally opposed to one another across central passage 16. Each reinforced region 40 is defined in part by an inward surface 42 that typically is generally flat. Inward surface 42 is part of overall interior surface 14 of valve body 12, but it interrupts the otherwise generally cylindrical configuration of interior surface 14.

Reinforced regions 40 are designed to accommodate a plurality of recesses 44 for receiving leaflet ears 30. In the embodiment illustrated, there are two pairs of opposed recesses 44, and each pair of opposed recesses is located to receive opposed ears 30 of one of the leaflets 18. The contour and placement of recesses 44 is selected to limit the range of movement of leaflets 18 between the closed position illustrated in Figure 2 and the fully open position illustrated in Figure 3. It should be noted that various recess designs are well known to those of ordinary skill in the art, and the configuration of ears 30 may vary depending on the particular recess design that is utilized in prosthetic heart valve 10.

To provide desirable wear characteristics and longevity of the leaflets 18, while providing a more advantageous seal between the leaflets and the interior surface 14 of valve body 12, each leaflet 18 is formed from at least two materials having different material characteristics. Preferably, at least distal edge 24 is formed from a more pliable material to facilitate better engagement with interior surface 14 along the extent of arcuate edge 24.

In the exemplary illustrated embodiment, ears 30 are part of the overall axle 28 formed from a stiffer, more wear resistant material 46, such as pyrolytic carbon. For example, the pivoting axle 28 may be formed from Pyrolite(r), a material utilized by Sulzer Carbomedics, Inc. of Austin, Texas. Preferably, axle 28 is formed as an integral unit having a beam 48 that extends at least substantially across the width of a given leaflet 18 proximate its lead edge 22. An exemplary beam 48 is a generally rectangular beam that extends beyond ears 30 an approximately equal distance on both sides of each ear 30. Ears 30 extend outwardly from opposing ends of beam 48 beyond edge 24, as best illustrated in Figure 4.

Referring also to Figure 5, the remainder of leaflet 18, i.e. a distal portion 50 of leaflet 18, is formed from a more pliable material 51 that is conformable during engagement with interior surface 14 and/or during exposure to the pressures/forces established by the fluid dynamics of the blood acting along or against leaflets 18. Preferably, distal portion 50 is formed from a polymeric material, such as a silicone material. Potentially, material 51 may comprise a bioprosthetic material or tissue. In any event, pliable material 51 is designed to change shape or conform sufficiently under the changing forces and pressures, that result from the fluid dynamics established during pumping of the heart, to reduce or eliminate detrimental effects, such as waterhammer, cavitation and peripheral leakage.

As illustrated in Figure 5, distal portion 50 may be attached to axle 28 by molding the second material 51 around beam 48. Alternatively, beam 48 may be formed from a pair of generally flat elongate members 52 that capture or sandwich a portion 54 of the second material therebetween, as illustrated in Figure 6. The elongate members 52 may be held against the second material by a fastener 56, such as a plurality of rivets 58.

In the embodiments illustrated, the pliable second material 51 extends beyond beam 48 towards lead edge 22, and, in fact, forms lead edge 22. Use of the second material 51 along lead edge 22 helps to form a better seal when leaflets 18 are in a closed position, as illustrated in Figure 2. Further, the second material may incorporate a fiber or fibers 60 to provide greater stiffness and/or improved wear characteristics (see Figure 6). For example, carbon fibers may be mixed with a polymer, e.g. silicone, to form a composite second material 51. The specific design of a given leaflet 18, however, can be adjusted in several ways. For example, first material 46 may be extended to form lead edge 22, as with a conventional leaflet. Additionally, beam 48 can be expanded into distal portion 50 a greater distance than illustrated. In fact, the more pliable, secondary material can be used to form only arcuate, distal edge 24, thereby enhancing the seal with interior surface 14 of valve body 12. Essentially, beam 48 can be made larger or smaller to fill varying degrees of the illustrated distal portion 50, depending on the overall design of prosthetic heart valve 10 and the desired application of the prosthetic heart valve.

It will be understood that the foregoing description is of preferred exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, a variety of valve body designs may be utilized; the number, shape and size of the leaflets can be changed depending on the overall design of the prosthetic heart valve; and the materials utilized in forming the leaflets can be changed or adjusted while still obtaining the desirable results of the present invention. For example, the ears potentially can be made of the stiffer material with the remainder of the leaflet formed of a softer material. Alternatively, the two materials utilized may be of the same general type of material but having different degrees of stiffness and/or hardness to accomplish the desirable wear and fluid dynamic characteristics. Further, the shape and size of the axle assembly can be adjusted for a given application. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A heart valve prosthesis (10), comprising: a valve body (12) having an interior surface (14) that defines a central passage (16) for a flow of blood therethrough; and a pair of leaflets (18) pivotably mounted within the central passage, wherein each leaflet of the pair of leaflets is formed from at least two different materials (46,51) that are exposed to the flow of blood.

2. The heart valve as recited in claim 1, wherein each leaflet includes an axle portion (28) formed of a first material (46) and a distal leaflet portion (50) formed of a second material (51).

3. The heart valve as recited in claim 2, wherein the first material has a greater stiffness than the second material.

4. The heart valve as recited in claim 3, wherein the second material is a composite material.

5. The heart valve as recited in claim 3, wherein the first material comprises a pyrolytic carbon.

6. The heart valve as recited in claim 3, wherein the second material comprises a polymer.

7. The heart valve as recited in claim 5, wherein the second material comprises a polymer.

8. The heart valve as recited in claim 6, wherein the polymer is reinforced with a fiber.

9. The heart valve as recited in claim 6, wherein the polymer comprises silicone.

10. A heart valve prosthesis (10), comprising: a valve body (12) having an interior surface (14) that defines a central passage (16) for blood flow therethrough, the interior surface (14) comprising at least one pair of opposed surfaces (40); and a leaflet (18) having a pair of pivot mounts (30), disposed for receipt by the at least one pair of opposed surfaces (40), and an arcuate distal edge (24) disposed for engagement with the interior surface (14), wherein the pair of pivot mounts (30) comprise a first material (46) and the arcuate distal edge (24) comprises a second material (51) having different material characteristics than the first material (46).

11. The heart valve prosthesis as recited in claim 10, further comprising a beam extending between the pair of pivot mounts.

12. The heart valve prosthesis as recited in claim 11 , wherein the beam comprises the first material.

13. The heart valve prosthesis as recited in claim 10, wherein the first material is a stiffer material than the second material.

14. The heart valve prosthesis as recited in claim 10, wherein the second material comprises a polymer.

15. The heart valve prosthesis as recited in claim 10, wherein the second material comprises a bioprosthetic material.

16. A method for constructing a heart valve prosthesis (10), comprising: providing a valve body (12) with an interior surface (14) that defines a central passage (16) through which blood may flow; providing a composite leaflet (18) formed from at lease two differing materials (46, 51); pivotably mounting the leaflet (18) to the valve body (12) for pivotable motion between an open position and a closed position with respect to the central passage (16); and forming a conformable distal edge (24) along the leaflet for engagement with the interior surface.

17. The method as recited in claim 16, wherein constructing includes forming a beam and a pair of pivot ears from a first material and forming a remaining portion of the leaflet from a second material.

18. The method as recited in claim 16, wherein forming includes utilizing a polymeric material for the conformable distal edge.

19. The method as recited in claim 17, further comprising molding the second material to the first material.