Abstract:
A heart valve prosthesis having improved flow characteristics. A heart valve prosthesis includes a valve body and a pair of leaflet occluders. The valve body includes an interior surface that defines a central passage for blood flow. The pair of leaflet occluders are pivotably mounted in the passage via ears or tabs that are received in recesses formed in the interior surface that defines the central passage. The recesses are formed with sloped sidewalls to improve the blood flow therethrough. The recesses are also formed such that the leaflet occluder ears act against at least two surfaces that limit the motion of the leaflet occluder to provide a more stable movement that is less damaging to blood cells.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to heart valve prostheses and, in particular, to an improved pivot design for the pivotable leaflet occluders. 
     BACKGROUND OF THE INVENTION 
     A variety of heart valve prostheses have been developed for use in hearts, such as human or animal hearts. The typical heart value prosthesis generally includes a main body portion having an annular shape and a central passage for blood flow. One or more leaflet occluders 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 for effective replacement of a defective natural heart valve. 
     A common heart valve construction is the bi-leaflet design in which two leaflet occluders are pivotably mounted in the annular body in an opposed relationship. The leaflet occluders are mounted such that when the heart valve is closed, each leaflet occluder covers approximately half of the valve opening or passage. Typically, each leaflet occluder is generally semi-circular in shape and includes a rounded exterior which engages an inner surface of the main body that defines the central passage. Each leaflet occluder also includes a generally linear edge portion designed to move proximate the linear edge portion of the opposing leaflet occluder when the valve is closed. Each leaflet occluder is mounted for pivotable movement about an axis disposed generally parallel with the linear edge. 
     In operation, as blood pressure rises in response to heart contraction, the leaflet occluders are pivoted from a closed position to an open position. In the open position, blood flows past the leaflet occluders through the heart valve 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 leaflet occluders 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. 
     Conventional leaflet occluders include opposing tabs or ears that are received in corresponding recesses formed in the interior surface defining the flow passage. Each pair of opposed recesses constrain the leaflet occluder mounted therein, and the walls of the recesses serve as stops to limit the pivoting motion of the leaflet occluders at closed and open positions. Exemplary prior art designs are illustrated and described in such patents as Hanson et al., U.S. Pat. No. 4,276,658, Bokros, U.S. Pat. No. 4,689,046, and Campbell, U.S. Pat. No. 5,147,390. Such prior art valves have generally proved to be very reliable, and have a projected life expectancy exceeding that of the patient. However, it is desirable to continually increase or enhance the performance characteristics of heart valve prostheses. 
     For example, problems can develop because of the design of the recesses for receiving the leaflet occluder ears. In many applications, it is desirable to design recesses with a contour providing at least two stops that act against the leaflet ear to limit the pivotable motion of a given leaflet occluder. By separating the stops that act against the ear, the angle at which the leaflet occluders close and/or open can be better controlled. The Hanson et al. reference and the Bokros reference cited above utilize recesses having narrowed throat regions and expanded outlying regions to provide at least two stops separated by a given distance that act against the leaflet occluder ear to limit a given pivoting motion. 
     Though such designs provide two stopping surfaces, they are typically limited by wall surfaces that are generally perpendicular to the interior surface that defines the blood flow passage of the heart valve. Such perpendicular surfaces often exist throughout the throat region of the recess and limit the ability of the blood to freely flow through the recessed area. As a result, blood clotting can occur in the vicinity of the pivot recesses. 
     It would be advantageous to provide a heart valve prosthesis with uniquely designed leaflet occluder pivot recesses able to facilitate better blood flow characteristics while providing stable control of the opening and closing of the leaflet occluders. 
     SUMMARY OF THE INVENTION 
     The present invention features a heart valve prosthesis comprising a valve body and a pair of leaflet occluders. The valve body includes an interior surface that defines a central passage for blood flow therethrough. The leaflet occluders are proportioned to be pivotably mounted within the central passage. Each leaflet occluder includes a pair of mounting ears, and the valve body includes a plurality of recesses for receiving the pairs of mounting ears. Each recess is bounded by a base surface and a sidewall. The sidewall defines a narrowed throat region, an upstream expanded region on one side of the throat region, and a downstream expanded region on a generally opposite side of the throat region. The sidewall slopes outwardly from the base surface to form an angle with a central recess axis along the entire length of the sidewall. Thus, there are no surfaces generally perpendicular to the interior surface of the valve body. 
     According to another aspect of the present invention, a heart valve prosthesis is provided that includes a valve body having an interior surface defining a central passage for conducting blood flow. The heart valve prosthesis also includes at least one leaflet occluder pivotably mounted to the valve body by a pair of pivots. The interior surface that defines the central passage includes at least one pair of recesses to receive the pair of pivots. Each recess is bounded by a continuously sloped sidewall extending between the interior surface and a recess base. Each recess further includes a narrowed throat region disposed such that the continuously sloped sidewall forms at least one pivot stop on each opposing side of the narrowed throat region. The pivot stops cooperate to limit pivotal motion of the at least one leaflet occluder. 
     According to yet another aspect of the present invention, a method is provided for facilitating blood flow through a prosthetic heart valve. The prosthetic heart valve is of the type including a valve body having an interior surface defining a central passage through which blood flows and a leaflet occluder pivotably mounted in the central passage by a pair of pivot ears. The method includes creating a first recess and a second recess in the interior surface on generally opposite sides of the central passage to receive a pair of pivot ears of an individual leaflet occluder. The method further includes forming each of the first recess and the second recess with a pair of expanded regions separated by a narrower throat region. The method further includes defining the first recess by a first sidewall and the second recess by a second sidewall. Additionally, the sidewalls are oriented at an angle throughout the narrower throat region and the pair of expanded regions to prevent the formation of surfaces that would be generally perpendicular to the interior surface of the valve body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a perspective view of a heart valve prosthesis illustrating certain aspects of the present invention, and having one leaflet and a portion of the outer wall cut away to disclose a recess; 
     FIG. 2 is a cross-sectional view taken generally along the line  2 — 2  of FIG. 1, showing leaflets in a closed position; 
     FIG. 3 is a cross-sectional view similar to that of FIG. 2 but showing the leaflets in an open position; 
     FIG. 4 is an expanded front view of a recess, according to an exemplary embodiment of the present invention; 
     FIG. 5 is a cross-sectional view taken generally along line  5 — 5  of FIG. 4; 
     FIG. 6 is a cross-sectional view taken generally along line  6 — 6  of FIG. 4 
     FIG. 7 is a front view similar to that of FIG. 4 but showing a leaflet ear in dashed lines in a closed position; and 
     FIG. 8 is a front view similar to that of FIG. 4 but showing a leaflet ear in dashed lines in an open position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to FIG. 1, a heart valve prosthesis  10  is illustrated according to one preferred embodiment of the present invention. Valve  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 occluder, and in this embodiment a pair of leaflet occluders  18 , is pivotably mounted to valve body  12 . In the illustrated embodiment, each leaflet occluder  18  includes a perimeter edge  20  having a generally linear lead edge  22  and a generally arcuate, semicircular, edge  24  designed to engage interior surface  14  of valve body  12  when valve  10  is in a closed position, as illustrated best in FIG.  2 . Preferably, the leading edge  22  of each occluder  18  is formed at an angle that allows the two lead edges  22  to abut one another when valve  10  is in a closed position. (See FIG.  2 ). Similarly, arcuate edges  24  are formed at an angle to facilitate engagement with interior surface  14 . (See FIG.  2 ). Each leaflet occluder  18  is further defined by a pair of generally flat opposing surfaces  26  that extend from lead edge  22  to arcuate edge  24 . 
     Each leaflet occluder  18  includes a pair of pivot structures  28  that permit the leaflets to pivot between the closed position illustrated in FIG.  2  and the open position illustrated in FIG.  3 . In the particular embodiment illustrated, pivot structures  28  each include an ear  30  that is generally in the form of a flat tab extending outwardly from arcuate edge  24  a predetermined distance from lead edge  22 , as illustrated in FIGS. 1 through 3. 
     The exemplary valve body  12  is designed to facilitate blood flow therethrough and to pivotably receive leaflet occluders  18 . Specifically, valve body  12  includes an upstream edge  32  having a filleted region  34  and a downstream edge  36  having a filleted region  38 . Filleted regions  34  and  38  help provide a smooth transition of blood through central passage  16 . 
     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 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 occluder ears  30 . In the illustrated embodiment, 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 leaflet occluders  18 . The contour and placement of recesses  44  is selected to limit the range of movement of leaflet occluders  18  between the closed position illustrated in FIG.  2  and the fully open position illustrated in FIG.  3 . The unique design of recesses  44  provides for controlled movement of leaflet occluders  18  while enhancing the flow characteristics of blood flowing past recesses  44  as it moves through central passage  16 . 
     Referring generally to FIG. 4, a preferred, exemplary embodiment of one of the recesses  44  is illustrated. The illustrated recess is oriented the same as the rightmost recess illustrated in FIG.  3 . However, the leftmost recess illustrated in FIG. 3 is simply a mirror image of the rightmost recess, and the following description applies equally. In fact, the following description can be assumed to apply equally to each of the four recesses required for the embodiment illustrated in FIGS. 1-3. 
     Referring again to FIG. 4, recess  44  is bounded by a base surface  46  and a sidewall  48 . Sidewall  48  is a sloped sidewall that extends between base surface  46  and interior surface  14 . As illustrated, sidewall  48  slopes generally outwardly from base surface  46  to interior surface  14 . In other words, sidewall  48  forms an angle  50  (see FIGS. 5 and 6) with a central axis  52  disposed through recess  44  generally normal to base surface  46  and interior surface  14 . Angle  50  exists along the length of sidewall  48  to eliminate surfaces that are generally perpendicular with interior surface  14  i.e. generally parallel with central axis  52 . 
     Potentially, angle  50  can vary in degree at different points or locations along sidewall  48 , but typically it is substantially constant along the entire length of sidewall  48 . In any event, angle  50  preferably is in the range from approximately 1° to approximately 45°; more preferably in the range from approximately 10° to approximately 35°; yet more preferably in the range from approximately 25° to approximately 35°; and most preferably approximately 30°. 
     Sidewall  48  preferably includes an outermost edge or fillet  54  that is arcuate in shape to further facilitate the transition of blood through recess  44 . Preferably, the arcuate edge  54  also provides a rounded edge for contact with a given leaflet occluder ear  30  as the ear  30  pivots to the limit of its motion in recess  44 . Having arcuate edge  54  at the point of contact reduces the Hertzian contact stresses which, in turn, reduces the amount of impact wear on the components relative to a sharp edge contact. 
     Between base surface  46  and outermost edge  54 , sidewall  48  is illustrated as generally flat, but this should not be construed as limiting. Potentially, this sidewall can provide a slightly arcuate surface or other contour in the transition direction from interior surface  14  to base surface  46 . Also, an arcuate transition or fillet  55  is disposed between sidewall  48  and base surface  46 . Fillet  55  improves the fluid washing at the bottom of the recess  44 . 
     Furthermore, sidewall  48  includes a lengthwise contour that enhances the stability of the leaflet occluder  18  when it moves to a fully open or fully closed position. Specifically, the lengthwise contour of sidewall  48  forms recess  44  with a narrowed throat region  56 , an upstream expanded region  58 , and a downstream expanded region  60 . This configuration allows each recess  44  to be formed with multiple stops or stop areas  62 . Sidewall  48  is configured such that stop areas  62  exist on opposite sides of central axis  52  and throat region  56 . Preferably, a given leaflet occluder ear  30  contacts two stop areas whenever it reaches its limit of travel. 
     For example, as illustrated in FIG. 7, leaflet occluder  18  and its attached ear  30  are in a closed position abutting two stop areas  62 . Similarly, as illustrated in FIG. 8, ear  30  abuts sidewall  48  at two stop areas  62  when leaflet occluder  18  and ear  30  are in an open position. Downstream expanded region  60  may include an extended portion  64  that effectively increases the radius of curvature of sidewall  48  at the adjacent stop  62 . In this particular design, the extended portion  64  increases the leaflet/orifice contact area so the contact stresses are reduced and it also avoids over constraining the leaflets in the fully closed position when the straight edges  22  of the two leaflets are in contact, and the accurate edges of the leaflets  24  are in contact with the inside surface  14  of the orifice. 
     The combination of the sloped sidewall  48  with its unique overall contour provides for greater control of the leaflet occluders  18  via multiple stop areas  62  while reducing the risk of blood clotting proximate recesses  44  by providing the sidewall with an appropriate slope. As described above, the actual slope angle of sidewall  48  can vary, but a desirable, exemplary angle is approximately 30° from a normal axis, because this angle provides relatively smooth transition of the blood flowing past a given recess  44  while remaining steep enough to provide a solid abutment surface for the corresponding ear  30  at each stop area  62 . 
     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 configurations may be utilized; the number, shape and size of the leaflet occluders can be changed depending on the specific design; the materials utilized for the given components, e.g. pyrolytic carbon, are well known to those of ordinary skill in the art, but those materials can be changed according to specific applications or advances in material technology; and the contour of the leaflet occluder ears as well as the shape of the base and sidewall can be adjusted accordingly. 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.