DE2807467A1 - VALVE PROSTHESIS - Google Patents

Description

QR.-rWG. DIPU-ING.M. SC. DirL-PHiS. CS. UIPL-HHVS.

HQQER - LEGAL RIGHTS - GRSESSBACH - HAECKER

Applicant Robert Bernard Davis

_A α? ία ·? h ¹¹ “Michael Road

k-163 Framingham, Mass. 01701, USA

February 20, 1978 John Skelton

11, Alden Street Sharon, Mass. 02067, USA

Richard Edwin Clark

6, Thorndell Drive

St. Louis, Miss ο 63117, USA

Wilbur Milton Swanson

2301, Parkridge Avenue

St "Louis" Miss ο 63144, USA

Description heart valve prosthesis

The invention relates generally to cardiovascular prostheses with synthetic fabric. In particular, the invention is concerned with a heart valve prosthesis that comprises a tissue or tissue parts which are held on a frame and form a three-lobed heart valve arrangement.

The replacement of heart valves with prostheses is part of everyday surgery today. The currently available prostheses are however not entirely satisfactory. Currently, most prosthetic heart valves work with a ball or valve, which is applied to a sealing ring to close the heart valve or the valve opening. With this construction the ball or valve is in the bloodstream when the valve is opened. This is disadvantageous for two important reasons. First of all, the pressure drop across the open artificial heart valve is greater than the pressure drop across a natural one Heart valve, which leads to a weak but permanent and therefore cumulative overload of the heart. Besides that

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the presence of the ball or the flap leads to areas of turbulent flow where there is a tendency for a There is damage to the red blood cells.

In view of the above-described disadvantages of the known heart valve prostheses, stabilized heart valves from pigs have also recently been used as a replacement for damaged human heart valves. Pig heart valves are similar in some properties to human heart valves, but on the other hand, collecting, sorting, sterilizing , restraining and storing pig heart valves are complicated and expensive.

Based on the prior art and the problems identified above, the invention is based on the object of an improved Specify heart valve prosthesis, in particular a prosthesis made entirely of synthetic materials in the form of a tri-lobed heart valve. A natural human heart valve should function as precisely as be imitated at all possible and a long service life of the artificial heart valve can be guaranteed.

When solving the given task, the following had to be taken into account:

A human heart valve contains thin, flexible membranes which, when the heart valve is open, lie flat against the wall of the adjacent one Create a blood vessel and consequently cause minimal disruption of the blood flow. When closed the membranes or wings form three adjacent one another

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Bags caused by blood pressure in a tight and fluid-tight Keeping in contact »With regard to the extremely low weight and the extremely high flexibility of the wings the natural heart valve has a short response time and quickly goes from fully closed to fully open above. In this way, there is little energy loss in the bloodstream, while at the same time a minimal amount of undesirable Backflow is achieved.

The functional characteristics of the heart valves specified above in humans arise due to the complex structure of the natural heart valve leaflets. Such a wing represents one Arrangement of collagen fiber bundles, which are embedded in a softer tissue material. This composition of the Wing fabric leads to a good resilience of the wing, to a high tensile strength and to a sufficient Softness and flexibility for achieving a good seal with the heart valve closed. When the peak occurs of a blood pressure pulse, a heart valve leaflet withstands a load of 150 g / cm along a load perpendicular to the load Line.

The tissue of the heart valve leaflets is also elastic Properties anisotropic, i.e. the deformation under load differs from that under load in one direction when loaded in a different direction. In the context of the present application, it has proven useful to have two to define certain directions, namely a direction parallel to the free edge of a heart valve wing and a direction to it perpendicular direction. These directions correspond to the circumferential

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direction or the radial direction, of which in the technical literature is commonly spoken.

When loaded in a parallel to its free edge In the direction of the natural heart valve leaflet, it expands very easily with increasing load up to a load from 1 to 2 g / cm of the wing width an elongation between 10 and 12% is achieved. If the load increases further the resistance to further stretching increases considerably. If the load is perpendicular to the free edge, this is sufficient Range of easy extensibility up to an elongation of approx. 20% with a load of approx. 2 g / cm. With another If the load increases, the resistance to further stretching increases, but is not as great as with load parallel to the free edge.

The task set is taking into account the properties of a natural heart valve and described above their wings solved by a heart valve prosthesis, which according to the invention is characterized by the combination of the following features:

(a) A frame is provided with three mutually equidistant, parallel legs, each of which is a pair of rod parts which are connected to one another at one end and the other ends of which diverge in such a way that that they form arches that connect neighboring legs and those between each other limit an opening and

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(b) there are three heart valve leaflets made of flexible tissue provided, each of which is inserted between the rod parts of two legs and attached to them and is attached to the arch connecting them and has a free edge between the legs, such that the free edges can be brought into contact with one another to seal the opening »

According to the invention a heart valve prosthesis is therefore formed by flexible fabric vanes which are inserted in a frame with three arches _f holding the wings in the proper orientation and equal to each other is a means, x ^ hich suturing of the prosthesis to the wall of the surrounding blood vessel The fabric is preferably shrunk in a compacting manner, that is, compressed in a first direction to form crimps in the threads, the crimps that are formed being thermally fixed so that they lie in planes that are essentially parallel to »The threads are also fanned out in the spaces between the filaments so that openings of different shapes and sizes result between the filaments» This compacting shrinkage is then repeated in a second direction that forms an angle with the first direction. The fabrics are preferably made as ribbons with selvedges, on which there are no severed threads and which form the free edges of the heart valve leaflets. "

Further details and advantages of the invention are provided below explained in more detail with reference to drawings and / or are the subject matter of the subclaims. Show it:

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1 shows a perspective illustration of a main frame of a preferred embodiment of a heart valve prosthesis according to the invention;

FIG. 2 is a perspective illustration of a fabric tape in the form that it would have after it has been inserted into adopts the main frame according to FIG. 1;

3 shows another frame;

FIG. 4 shows a plan view of the frame according to FIG. 1;

FIG. 5 shows a plan view of the frame according to FIG. 3;

6 shows a perspective illustration of the partially completed heart valve prosthesis in which the fabric inserted into the main frame and cut open in preparation for gluing is;

7 shows a development of the partially completed heart valve prosthesis according to FIG. 6;

Figure 8 is a cross-sectional view taken along line 8-8 in Figure 7;

Fig. 9 shows a flat braided tape as a fabric for

a heart valve prosthesis according to the invention;

Fig. 10 is a photographic representation of a flat woven fabric made of multifilaments of polymeric material before compacting shrinkage and

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Figure 11 is a photographic representation of the fabric

according to FIG. 10 after carrying out a compressing Shrinkage in the warp and weft directions.

10 of the drawing shows a preferred embodiment of a fabric 12 which can be used as a starting material for the production of an artificial heart valve according to the invention consist of untwisted filaments 18
from a polyester, for example us polyethylene terephthalate. The fabric 12 can, for example, in both directions
each about 100 threads per 2.5 cm are woven, the threads having a linear density of about 30 denier. Each thread 30 can comprise filaments 18, each filament 18 having a diameter of approximately 10 μm.

Since the threads have no twist, they have a flat shape in the fabric, as shown in FIG. 10. The fabric is consequently only about 3 to 4 filament diameters thick. The mesh
is furthermore, as will be explained below, preferably woven in such a way that at least one fabric edge results without severed threads. For this reason the fabric is preferably made in the form of a ribbon, although this is not absolutely necessary.

Commercially available polyester yarns generally contain a number of impurities which are potentially beneficial to the Bodies could prove harmful if such yarns are used in the manufacture of implanted prostheses.

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Contaminants include, for example, catalyst residues from the polymerization process, oligomers, and antioxidants and other stabilizers, matting agents and finishing agents. Consequently, it is important that only a pure polymeric material is used for the purposes of the invention.

As Fig. 10 shows, the threads 14 and 16 are woven so that there are gaps 20 that play a role in the subsequent shrinkage and texturing steps, which the fabric according to FIG. 10 is subjected to an in to obtain two-way textured fabric as shown in FIG. In the course of further procedural steps the tissue is shrunk in two directions by compressing it while applying a compressive force in the plane of the tissue each of these steps being carried out essentially as described in U.S. Patent 3,001,262 is. A machine similar to that described in US Pat. Nos. 2,765,513 and 2,765,514 can be used. In the shrinking steps, crimps are created in the filaments or texturing generated, the threads fan out in the interstices of the fabric.

In order to achieve the desired easy stretchability in both directions, the stretch characteristics of a natural one Is similar to a heart valve, the same tissue is compacted sequentially in both the warp and weft directions. In this respect, the method to be used according to the invention is in contrast to the method according to US Pat 3 001 262, according to which the threads of a first fabric are textured in the warp direction, whereupon the fabric is dissolved

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and the warp threads are used as weft threads or fill threads for a subsequently woven fabric, which is again crimped in the direction of the warp thread in order to achieve a certain extensibility characteristic in both directions. The illustrated difference between the two processes leads to f that the crimp of threads in both the warp direction and the weft direction in planes produced and is thermally fixed, the "wherein the threads are fanned out in the gaps 20 extend substantially parallel to the plane of the fabric, so that openings of different sizes and directions arise between the filaments. A considerable number of these openings have dimensions between 20 and 40 μm, which is preferred for rapid tissue ingrowth, these openings also being evenly distributed throughout the tissue compares finished fabric according to US Pat. No. 3,001,262, where the crimps and the fanned filaments of the weft or fill threads present in the end product are necessarily shifted and realigned with respect to the main plane of the fabric and the position of the spaces in the finished fabric during the second weaving process are"

The fact that a thin fabric is more desirable than a thick fabric has been recognized as a result of the desired functional properties, particularly with regard to flexibility and elongation properties, the property not to lead to the formation of thrombosis, and the ability to handle many millions of bending cycles without being able to withstand fatigue fractures. The property of not leading to the formation of thromboses, is given to the fabric according to the invention in that the

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The ingrowth of body tissue is promoted _/ so that the blood flowing past only comes into contact with compatible surfaces, as they are also found in nature. The filaments of the tissue described are analogous to the collagen fiber bundles in the natural heart valves when natural tissue grows and form a textile support structure or lattice on which the body can settle natural tissue in order to maintain the membrane function of the heart valve and the desired sealing properties. Although blood clots at the interface between the tissue and the blood, the natural tissue ingrowth occurs in such a way that the clotted blood is firmly anchored in the tissue and does not dissolve in the bloodstream. In this way, the artificial tissue is completely embedded in a layer of living tissue, which is thin enough to be able to be nourished by diffusion processes.

From the above description it is clear that the process of ingrowth of natural tissue affects the thickness and thus the flexibility and rigidity of the working heart valve. However, these properties now influence in turn, the sensitivity to fatigue fractures and the ability to control the amount of flow back when closing Reduce blood to a minimum. In order for it to be useful for an artificial heart valve, the tissue must also have one have a very easily expandable area up to an elongation of 10 to 20%. In particular, each heart valve leaflet is involved closed heart valve curved along a line perpendicular to its free edge with a relatively small radius, as will become clear from the following description of FIGS. 1 to 8. Along this line is a

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Area of high stress concentration.

An additional advantage of the method according to the invention is from Fig. 11 clearly, where it can be seen that the individual threads are fanned out in the area of the spaces 20, which means that the individual filaments are open locally in the area of these interspaces, so that a more finely distributed matrix is distributed Openings gives what different size and orientation own. These openings encourage the ingrowth of living Tissue. In contrast, a fabric as shown in Fig. 10 has a regular pattern of im Spaced openings with larger fixed ones Dimensions provided, whereby the ingrowth of natural tissue is not promoted as well.

The fabric produced according to the invention was with regard to the Ingrown tissue of natural tissue was investigated and it was found that there are other available tissues in this regard is superior. In addition, the fabric can according to the invention with specific elongation properties are produced, as they are required for use as heart valve leaflets, with the elongation properties may be different in two directions, for example in the warp direction and in the weft direction can.

The following is a more detailed description of the crimping or densification process used in accordance with the present invention is applied. Using the machine described in U.S. Patents 2,765,513 and 2,765,514, a belt of the Fabric according to FIG. 10 with a width of about 3.8 cm and

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a length of about 15 cm between two sheets of paper and then passed in the warp direction through the nip between an upper roller and a lower roller. The top roller has a peripheral speed of about 1.6 m / s, while the lower roller has a peripheral speed of about 0.34 m / s having. In this compression pass, the warp threads are shrunk or compressed in such a way that they curl, the curl being forced into a plane by the pressure between the rollers which is essentially parallel to the plane of the tissue. At the same time, the filaments of the warp threads are moved apart in the gaps; the threads are fanned out in the area of the gaps so that openings of different sizes and orientations are created result, as shown in FIG. 11. After this compression step, the fabric is removed from between the sheets of paper.

A second compression run is then carried out in essentially the same way as described above, however, the fabric passes through the nip between the rollers in the weft direction.

If desired, any of the compaction runs described above can be repeated with the fabric tape after is preferably rotated by 90 ° for each pass.

The compression steps in two directions can be with respect to the number of passes and the amount of compaction can be varied to accommodate stress in each of the to achieve the desired elongation characteristic in both directions and in this way the corresponding characteristic

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approximate natural heart valve wing. In any case it will be the compression steps carried out in such a way that up to an elongation of 10 to 20% there is a very slight extensibility is.

After a series of compression cycles, the tissue in the unloaded state is thermally fixed at a temperature ,, under the fusion temperature "is Polyäthylentherephtalat example, can be worked with a temperature of about 21O ⁰ C» The heat fixation is preferably carried out in a hot air oven, the typical Dwell time is between 1 and 1 * 5 minutes »

In some cases it is desirable to pretreat the threads before weaving, in order to prevent damage to the filaments during weaving. A suitable pretreatment is to provide a coating with a 5% solution of polyvinyl alcohol » After weaving, this additive on the fabric is washed off in an aqueous washing bath _β

The following is now a preferred embodiment of a artificial heart valve will be explained in more detail with reference to FIGS.

In detail, Fig. 1 of the drawing shows a main frame 22, which is bent from a single piece of round polypropylene rod with a diameter of 1 mm to the shape shown is such that there are three equidistant parallel legs 24, 26, 28, of which two are each at a small distance

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having mutually extending rod parts which are connected to one another at one end and the other ends of which diverge. The diverging ends of the rod parts form three arcs 30, 32 and 34. The ends connected to one another of each pair of rod parts form loops 36, 38 and 40. Fig. 4 shows a plan view of the main frame 22 "

A second frame 42 (FIGS. 3 and 5) consists of a single piece of round polypropylene rod with a diameter of 1 mm, which is bent so that three arcs 44, 46 and 48 result, which have essentially the same shape such as the arches 30, 32 and 34 _t so that they can be fitted closely to them, as FIG. 7 shows.

When assembling the artificial Hersklappe, one begins with that one that is curled and compacted in both directions Belt 50, which is produced by the method described above and has the structure shown in FIG. 11, threaded between the three pairs of rod parts to obtain the arrangement shown in FIG. The main frame 22 is shown separately in FIG. 1 in such a way to improve clarity that FIGS. 1 and 2 together represent a Form an exploded view. The upper edge of the tape 50 is a selvedge without severed threads and forms three free ones Edges 52, 54 and 56 of the heart valve leaflets.

Between everyone. Pair of rod parts, which form the parallel legs 24 to 28, is thus a double one Fabric layer. It is now necessary to use the band or /. whose Parts - in short, the tissue - to be firmly attached to the legs 24 to 28 and also to which the legs are connected to one another.

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binding arches 30 to 34. To simplify this fastening, the tissue is first severed on the outside of each of the legs 24 to 28, as FIG. 6 shows.

An adhesive, such as tetrahydrofuran dissolved in polyurethane, is then used to adhere the fabric as follows the individual legs 24 to 28 to be attached. First of all, the outwardly protruding strips, for example the strips 58 and 60, spread out, whereupon the adhesive on the outside of the gap between the rod parts along a continuous line between points a and b is plotted. The adhesive penetrates the fabric strips 58, 60 along them Line and reaches the outer surface of the main frame 22; i.e. the adhesive only comes into contact with the outside of the rod parts of the main frame. The heart valve leaflets are only supported by the pieces of tissue on the inside of the main frame 22 which are not soaked with the adhesive. This way it is avoided that the tissue through penetration is stiffened by glue in the areas forming the heart valve leaflets, which could lead to flexural fractures.

In the above-described method for applying the adhesive, the bending forces are also evenly applied to the The edges of the heart valve leaflets are distributed, thereby avoiding excessive stress concentrations. The edges can curve around the round surface of the rod parts on the inside of the main frame 22 during each bending process and are not soaked with the glue.

The method described for applying the adhesive is reduced

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also the contact of the blood with the glue.

Next, the fabric is then attached to the arches 30, 32 and 34 by first placing the two frames 42 opposite one another aligns the main frame 22 in such a way that the fabric is located between the two frames 22, 42, as shown in FIG. and 8 show. Then the adhesive 61 is through the fabric with the surface of the main frame 22 and with the Surface of the second frame 42 brought into contact along a continuous line, which the points b on the legs 24,26,28 connects with each other. As in the previous step, care is taken to ensure that the adhesive does not reach any area of the tissue which lies within the main frame 22 so that it does not come into contact with the blood which flows through the heart valve.

After performing the steps described above, the manufacture of the heart valve leaflets is essentially complete. The further manufacturing steps now serve to simplify the sewing of the artificial heart valve to the blood vessel. For example, the fabric available on the outside of the frame 22 can be rolled and attached the connection line between the main frame 22 and the second frame 42 are strengthened to provide attachment points in this way for the sutures to be placed when performing the heart operation.

As mentioned, the frames 22, 42 are preferably made of polypropylene; however, other materials have also been used with success. Polypropylene has an excellent flexural alternation

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strength and chemical stability, but is difficult to attach to other materials using an adhesive. Around The two frames 22 and 42 can be coated with polyurethane by multiple dip-coating to improve the adhesion will. It has been shown that the sheathed frame parts then have the desired properties of the polypropylene, without structural defects or breaks in the area of the adhesive connections.

Artificial heart valves with the tissue described above were examined in accelerated fatigue testers to to check their long-term stability. It was found that fatigue fractures generally occurred in the area of the greatest deflection of the tissue, i.e. in each heart valve wing along a line which is perpendicular to its free edge and is substantially the same distance from the adjacent leg. The fatigue fractures showed up in the generally in the filaments of the threads of the heart valve leaflets that run parallel to the free edges. To achieve a For improved fabric strength along the lines mentioned, one can use fabric which is larger in this direction Have number of the load-absorbing threads.

However, there is a limit to such reinforcement when considering a flat woven fabric as shown in FIG Does not want to seriously affect the geometry of the spaces.

Another way of building up tissue to achieve a improved strength against fatigue fracture is shown in FIG. 9

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shown. The fabric shown there is a flat braided band 62 with three groups of threads, namely a first diagonal group 64, a second diagonal group 66 and a longitudinal group 68 made of inserted threads. The threads in each of the three groups are preferably untwisted multifilament threads similar to those used for the fabric according to FIG. The tape 62 is braided on a conventional flat braiding machine. It can be seen that both band edges are not cut Sutures on v / iron and both can serve as free edges for the heart valve leaflets. This way it will be like the one before described example, a fraying of the free edges of the heart valve leaflets avoided. Take over for the band under consideration the thread groups 64 and 66, i.e. the two diagonal groups, the load, which in the case of the initially described Tissue has to be taken over by a single thread group. As a result, the result is that a greater number of threads absorbs a considerable load component parallel to the free edge.

The tape 62 according to FIG. 9 is preferably produced by the threads of the diagonal groups 64 and 66 being laid over the Longitudinal threads of thread group 68 are interwoven in a known manner in order to obtain a kind of three-axial fabric. Such Flat braided fabrics have the additional advantage over conventionally woven fabrics that they are in In the transverse direction, i.e. perpendicular to the longitudinal threads 68, are inherently extremely extensible. Enable such tissue It allows for two-way stretchability with any desired combination of the single-directional stretchabilities achieve if only the longitudinal threads 68 are compressed or crimped.

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Claims (13)

- sr - DB. -INTO THE. DIPL-INS. M. SC. DIl L-PH CS. OR. DIP '. -PHYS. HQGER - LEGAL RIGHTS - GR! E £ SBÄCH - HAECKSa / ~ ~ PATENT LAWYERS IN STUTTGART Applicant Robert Bernard Davis A 42 747 b ^{11f Michael Road} ' k-163 Framingham, Mass. ΟΊ7Ο1, USA February 20, 1978 John Skelton 11, Alden Street Sharon, Mass "02067, USA Richard Edwin Clark 6, Thorndell Drive St ₀ Louis, Miss »63117, USA Wilbur Milton Swanson 2301, Parkridge Avenue St »Louis, Miss ο 63144, USA Patent claims % Heart valve prosthesis, characterized by the combination following features: (a) It is a frame (22) with three mutually equidistant, parallel legs (24 to 28) are provided, each of which has a pair of rod members connected at one end to each other connected and the other ends of which diverge in such a way that they have arcs (30 to 34) form, the adjacent legs (24 to 28) connect with each other and one between each other Limit opening and (b) three heart valve leaflets made of flexible tissue are provided, each of which inserted between the rod parts of two legs (24 to 28) and on these and the one connecting them Arch (3O to 34) is attached and between the legs (24 to 28) a free edge (52 to 56) in such a way that the free edges ö - ^ ö34 / 0 854 I LU k - 163 February 20, 1978 - 2 - (52 to 56) can be brought into contact with one another for sealing the opening. 2. Heart valve prosthesis according to claim 1, characterized in that that the heart valve leaflets are parallel to the direction of their free edge (52 to 56) and perpendicular to it these are elastically yielding. 3. Heart valve prosthesis according to claim 2, characterized in that the elastic resilience of the heart valve leaflets parallel to its free edge (52 to 56) from the elastic resilience of the same perpendicular differs from their free edge (52 to 56). 4. Heart valve prosthesis according to claim 1, characterized in that the rod parts of each leg (24 to 28) have a distance from each other. 5. Heart valve prosthesis according to one of claims 1 to 4, characterized in that a second frame (42) is provided, which is made of a rod-shaped material and substantially congruent in shape with the arcs (30 to 34) of the first frame (22) connecting the legs (24 to 28) and that the heart valve leaflets are glued to the frame (22, 42) and between them. 6. Heart valve prosthesis according to one of claims 1 to 5, characterized in that the heart valve leaflets with at least one of the frames (22, 42) are glued with the aid of an adhesive (61) which is attached to the outside of the Opening is attached. 809834/0854 February 20, 1978 - 3 - 7. Heart valve prosthesis according to one of claims 1 to 6, characterized in that the rod parts are rounded Have surface on which the heart valve leaflets roll when they are deflected, and that the "heart valve leaflets are glued to the rod parts by means of an adhesive on the outer surfaces of the same, which lie on the outside of the rounded surface areas on which the heart valve leaflets roll. 8. Heart valve prosthesis according to one of claims 1 to 7, characterized in that the flexible fabric of the heart valve leaflets is woven mulcifilament threads made of polymeric Having material. 9. Heart valve prosthesis according to claim 2 and 8, characterized in that that the threads are separated from one another by gaps (20) and crimped in both directions are, wherein the crimps are substantially in one plane with the fabric (7) and wherein the filaments the threads are fanned out in the area of the intermediate spaces (20) to form openings of different sizes and to form orientation between the filaments. 10. Heart valve prosthesis according to claim 9, characterized in that that each heart valve wing has threads which run parallel to its free edge (52 to 56) and those threads which run perpendicular to this free edge (52 to 56). 11. Heart valve prosthesis according to one of claims 1 to 10, characterized in that the free edges (52 to 56) 809834/0854 k - 163 February 20, 1978 - 4 - the heart valve wing · (woven) edges with not severed threads. 12. Heart valve prosthesis according to one of claims 1 to 11, characterized in that each heart valve leaflet consists of a flat braided band (62) and that the free edge (52 to 56) is an edge without cut threads. 13. Heart valve prosthesis according to claim 12, characterized in that that each heart valve wing has longitudinal threads (68) which are parallel to the free edge (52 to 56) run as well as oblique threads (64,66) which run at acute angles to the free edge (52 to 56). 809834/0854