Heart valve prosthesis

A medical device in cardiac surgery for replacement of the diseased native heart valves in humans increases thromboresistance of heart valve prosthesis. A heart valve prosthesis comprising an annular housing with the inner surface defining the blood flow I through the valve prosthesis and leaflets mounted within the annular housing with the possibility to pivot around the reference axis between an open position which allows the passage of the direct blood flow I, and a closed position which restricts the blood backflow II. Each leaflet has an upstream surface facing the direct blood surface I, a downstream surface facing the blood backflow II, a coaptation surface, and a side surface.

BACKGROUND OF THE INVENTION

The invention relates to medical devices and can be used in cardiac surgery for replacement of the diseased native aortic and mitral heart valves in humans. This invention can also be successfully used for replacement of the diseased tricuspid valve.

There is a certain heart valve prosthesis [1] comprising an annular housing with fixing elements restricted by support surfaces facing the direct and reverse blood flow and a side surface facing the central axis of the housing, and leaflets mounted within the annular housing with the possibility to pivot between an open position, which allows the passage of the direct blood flow, and a closed position which restricts the blood backflow, each leaflet has an outer side surface having projections with support surfaces facing the direct blood flow, which interact with the corresponding support surfaces of said fixing element of the housing, a coaptation surface interacting with the corresponding coaptation surface of the other leaflet in the closed position, with projections having support surfaces facing the blood backflow and interacting with the support surface of the fixing element of the housing, an upstream and a downstream surfaces respectively facing the direct blood flow and the blood backflow, while the downstream surfaces of the leaflets have projections-cams which prevent the coaptation of the leaflets in the open position and restrict the opening angle of the leaflets.

This prosthesis, as experience of its clinical application had shown, has good hemodynamic characteristics and a small percentage of thrombotic and thromboembolic complications. However, its leaflets, which divide the hydraulic orifice of the housing into three segments, disrupt the homogeneous laminar structure of blood flow with creation of blood stagnation zones and thus preserving the possibility of thrombotic complications.

There is a certain heart valve prosthesis [2] comprising an annular housing, leaflets with the possibility to pivot and form a major zone of central passageway of the housing, and leaflet pivoting limiters. The leaflet pivoting limiters are represented by two pairs of projections located at the end surface of the housing facing the downstream blood flow, and which ensure limiting of their pivoting angle and permanent link with the housing by interacting with the side surfaces of the leaflets.

This prosthesis provides withdrawal of the leaflets from the housing orifice and therefore increases the homogeneousness of the flow structure. However the provision of the leaflet pivoting limiters at the end surface of the housing increases the prosthesis overall dimensions and risk of restriction of leaflet mobility by the internal heart structures.

This heart valve prosthesis was chosen by us as prototype prosthesis.

The objective of the proposed invention is to increase thromboresistance of prosthetic heart valve.

SUMMARY OF THE INVENTION

Proposed is a heart valve prosthesis comprising an annular housing with an inner surface defining the blood flow through the prosthesis, and leaflets mounted within the annular housing with the possibility to pivot around the reference axis of rotation between an open position, which allows the passage of the direct blood flow, and a closed position which restricts the blood backflow, each leaflet has an upstream surface facing the direct blood flow, a downstream surface facing the blood backflow, a coaptation surface interacting with the corresponding coaptation surface of the other leaflet in the closed position, and a side surface interacting with the inner surface of the housing. At least two console projections radially oriented and directed mainly perpendicular to the reference axis of leaflet rotation are provided at the inner surface of the housing, and a slot embracing the corresponding console projection of the housing is provided at each leaflet. The surfaces interacting with the leaflet slots and forming a supporting part of the hinge are provided at the lateral sides of the console projections and the counterpart surfaces forming a mobile part of the hinge and facing the side surfaces of the corresponding console projection are provided at the slot inner sides of each leaflet.

Furthermore the inner surface of the housing is mainly cylindrical and the downstream surface of each leaflet is formed by the crossing cylindrical and conical surfaces. In this connection the diameter of the cylindrical downstream surface of the leaflet corresponds to the diameter of the inner surface of the housing, and in the closed position of the leaflet the generatrix of the cylindrical downstream surface is approximately parallel to the central axis of the housing.

The upstream surface of each leaflet is provided in the form of cylindrical surface with diameter equal to or somewhat bigger than the diameter of the inner surface of the housing, and in the open position of the leaflet the generatrix of the cylindrical upstream surface is approximately parallel to the central axis of the housing.

The optimal embodiment of the hinges between the leaflets and the housing is an embodiment where the surfaces forming the supporting part of the hinge of the console projections are made as a segment of the spherical recess and the counterpart surfaces forming the mobile part of the hinge are made as a segment of the spherical projection.

However the above-mentioned embodiment of the hinges does not restrict the subject matter of the invention and the interacting hinge surfaces may be of any other form, for example as segments of cylindrical surfaces.

Ledges interacting with the side surfaces of the leaflets in the closed position are also provided on the inner surface of the housing.

Without restricting the subject matter of the invention, two, three or more leaflets may be mounted within the heart valve prosthesis. It would be reasonable to mount two leaflets for mitral and tricuspid prostheses and three leaflets for aortic prosthesis.

In the proposed heart valve prosthesis there are no elements which introduce disturbances into the blood flow or generate stagnation zones, thus ensuring higher thromboresistance of the prosthesis.

The provision of the console projections radially oriented and directed mainly perpendicular to the reference axis of rotation of the leaflets at the inner surface of the housing and the counterpart slot embracing the corresponding console projection of the housing at each leaflet ensures the mobile connection of leaflets with the housing. Moreover, if compared to the prototypes, the number of the hinged joints for one leaflet is twice as less. Due to this the thromboresistance of the prosthesis is increased because said hinged joints are the major potentially dangerous locations for thrombus formation and traumatization of blood elements.

The provision of the surfaces, which interact with the leaflet slots at the lateral sides of the console projections of the housing and form the supporting part of the hinge, and the counterpart surfaces, which face the side surfaces of the corresponding console projection of the housing and form the mobile part of the hinge at the inner slot sides, allows the leaflet to pivot around the hinge axis between the open and closed positions. Thus fulfilling the major intended function of the valve, i.e. to pass the direct blood flow and restrict the blood backflow.

The provision of the mainly cylindrical inner surface of the housing together with the downstream surface of each leaflet in the form of crossing cylindrical and conical surfaces with the diameter equal to the diameter of the inner surface of the housing ensures mutual conformity of said surfaces. Namely: because the central axis of the cylindrical downstream surface of the leaflet in the open position is parallel to the central axes of the housing, its cylindrical downstream surface fits closely to the inner surface of the housing practically along its whole perimeter, thus preventing the possibility of generation of any obstacles to the blood flow. Because the other part of the cylindrical downstream surface is conical it provides a surface inclined to the flow axis, which facilitates quick leaflet pivoting and valve closure under the influence of the blood backflow. The proposed embodiment of the downstream leaflet surface is an optimal one, but, without restricting the subject matter of the invention, it may be formed with other surfaces, for example, spherical, toroidal, conical ones, or in the form of two crossing cylindrical surfaces.

The provision of the upstream surface of each leaflet in the form of the cylindrical surface with the diameter equal or somewhat bigger than that of the inner surface of the housing ensures creation of the approximately cylindrical hydraulic orifice which allows the direct blood flow to pass freely through it when the leaflets are in the open position. The provision of the central axis of the upstream cylindrical surface of the leaflet in the open position approximately parallel to the central axis of the housing prevents creation of the extra orifice confuserness which can lead to additional energy losses.

The provision of the ledges at the inner surface of the housing, which interact with the side surfaces of the leaflets in the closed position, prevents leaflet escape from the housing.

Said features of the prosthesis ensure the creation of positive effect, that is a higher thromboresistance, better structure of the blood flow, and less trauma to formed elements of the blood.

DETAILED DESCRIPTION

For convenience in the drawings the direct blood flow is shown by the arrow I and the blood backflow by the arrow II.

The heart valve prosthesis comprising of the annular housing1with the inner surface2, defining the blood flow I through the valve prosthesis, and the leaflets3mounted within the annular housing1with the possibility to pivot around the reference axis of rotation (shown by the dash-and-dot line0-0) between the open position, which allows the passage of the direct blood flow I, and the closed position which restrict the blood backflow II. Each leaflet3has the upstream surface4facing the direct blood flow I, the downstream surface5facing the blood backflow II, the coaptation surface6, and the side surface7.

The console projections8radially oriented are provided at the inner surface2of the housing1, and the slot9, which corresponds to the projection, is provided at each leaflet.

The concave spherical surfaces11forming the supporting part of the hinge are provided at the lateral sides10of the console projections8, while the counterpart convex spherical surfaces13are provided at the inner sides12of the slot9of each leaflet3.

The inner surface2of the housing1is mainly cylindrical, and the downstream surface5of each leaflet3is in the form of the crossing cylindrical5aand conical5bsurfaces, in this connection the generatrix (shown by the dash-and-dot line1-1) of the cylindrical5adownstream surface5, is parallel to the central axis (shown by the dash-and-dot line2-2) of the housing1(seeFIG. 4).

The upstream surface4of each leaflet3is cylindrical, and when the leaflet3is in the open position its generatrix (shown by the dash-and-dot line3-3) is approximately parallel to the central axis2-2of the housing1.

The ledges14are provided at the inner surface2of the housing1.

The heart valve prosthesis functions as follows.

When excess pressure is created at the inlet of the prosthesis the leaflets3pivot around the axis of rotation0-0, and the convex spherical surfaces13in the leaflet slots9interact with the concave spherical surfaces11of the console projections8at the inner surface2of the housing1forming a hinge which provides a mobile connection of the leaflets3with the housing1. When the cylindrical surfaces5aof the leaflets3contact the inner surface2of the housing the pivoting of the leaflets3around the axis0-0stops. The heart valve prosthesis opens and allows the passage of the direct blood flow I. In this connection the direct blood flow I is restricted by the cylindrical upstream surfaces4of the leaflets3, which define the central axisymmetric laminar blood flow I without introduction of any disturbances by the valve elements. As a result there are minimal energy losses, minimal pressure drop across the valve and prevention of trauma to the blood. Furthermore the walls of the housing1limit not only the pivoting of the leaflets3but also inhibit penetration of the connective tissue and surrounding heart structures inside the housing1, thus preventing restriction of mobility of the leaflets3.

When excess pressure is created at the outlet of the prosthesis the blood backflow II starts to form, which works on the conical surfaces5bof the leaflets3and causes the leaflets3to pivot around the axis0-0into the closed position, because the surface generatrix5bof the leaflets3is located at an angle to the axis of the blood backflow II. In this connection the convex spherical surfaces13in the leaflet slots9interact with the concave spherical surfaces11of the console projections8at the inner surface2of the housing1forming a hinge which provides a mobile connection of the leaflets3with the housing1. When the side surfaces7contact the ledges14at the inner surface2of the housing1the pivoting of the leaflets3stops and the heart valve prosthesis closes. The leaflets3interact among themselves with the coaptation surfaces6and simultaneously with the ledges14at the inner surface2of the housing1by their side surfaces restricting the blood backflow II and sealing the heart valve prosthesis. The presence of small clearances between the surfaces13and11in the hinge joints of the leaflets3within the housing1, as well as between the surfaces7and2in the zone of location of the projection8, and also at portions of the surfaces6ensures the reduction of the mechanical trauma to the formed elements of the blood and provision of the clinically insignificant blood backflow II which washes out the surfaces2,6,11, and13and prevents the initiation of the thrombus formation process.

Information sources:1. Heart valve prosthesis. RF Patent No. 21131912. Heart valve prosthesis. Application for RF Patent No. 2006110832 A