A cardiac valve prosthesis, particularly for replacement of the aortic valve

Abstract: A stentless prosthesis is made completely from material (10,12), for example bovine pericardium, other than valve material. The projection of the valve sleeve (10) allows any reparatory operations on surrounding tissues.

Description: The present invention relates to cardiac valve prostheses or, briefly, artificial cardiac "valves" as specified in the preamble of Claim 1. Such a prosthesis is known e.g. from GB-A-1 599 407 or DE-A-2 822 464. In the traditional approach, these artificial valves can essentially be separated into two basic categories, that is to say: the so-called "mechanical" valves, in which the blood flow through the valve is controlled by one or more obturators constituted by rigid bodies (for example, a lenticular core of graphite coated with biocompatible carbonaceous material) mounted so as to be able to oscillate in a respective annular stent or armature of rigid material (for example, titanium), and the so-called "biological" valves in which the blood flow is controlled by valve leaflets constituted by biological tissue mounted on a rigid, or only slightly flexible, stent or armature. The valve leaflets in question can be those of a natural cardiac valve taken from an animal (for example, a natural pig's valve) and mounted on the stent after treatment (stabilisation) to render it biologically inert. In other solutions, however, the biological tissue utilised to form the valve leaflets is biological tissue other than valve tissue (for example, bovine pericardium). A prosthesis of this latter type is described in European patent EP-B-0155245. This prior patent describes a cardiac valve prosthesis comprising an armature (or stent) of substantially rigid material of annular form within which is fitted a valve sleeve of biological tissue constituted by two sheets of biological material (for example, animal pericardial tissue) treated to render it biologically inert: in particular, the said sleeve, indicated 10, is illustrated on its own in Figure 6 of the drawings accompanying the patent. In this known solution, the sleeve in question is obtained by the technique illustrated schematically in Figures 1 and 2 of the appended drawings. In Figure 1, two sheets of biological material (for example, bovine pericardium) which have undergone a fixation in glutaraldehyde are indicated 10 and 12 respectively. The first sheet 10, intended to constitute the outer portion of the valve sleeve of an aortic valve prosthesis, has an approximately rectangular shape, whilst the other sheet 12, intended to constitute the internal or functional part of the valve sleeve (or rather, in practice, the valve flaps) is also generally rectangular. However, the sheet 12 has previously been subjected to a shaping process intended to give it three shaped portions 14 of approximately semi-circular, or half-moon, shape with arcuate edges and with a generally pocket or fingernail shape such that when the valve sleeve is closed into a tube (Figure 2), the leaflets or flaps 14 thus formed project in a convergent manner towards the internal orifice of the prosthesis. A detailed description of a process and of apparatus used for performing this shaping operation is provided in European patent EP-B-0133420. The two sheets 10 and 12 are then connected together by a line of stitching 16 (for example, with Dacron (a registered trade mark) thread coated with biocompatible carbonaceous material) which extends closely adjacent the outer peripheries of the half-moon portions forming the valve leaflets 14 and therefore has a festoon-like course. As already mentioned, the two sheets 10 and 12 connected together by the festoon-like line of stitching 16 are then closed into a tube and connected together along their facing edges by means of a further line 18 of stitching. All this gives rise - after mounting on the stent - to the structure illustrated schematically in Figure 2, in which the three valve leaflets 14 are able, alternately, to move apart so as to allow the blood to flow in one direction (upwardly with reference to Figure 2) and to fit together under the action of the blood pressure so as to prevent the blood from flowing in the opposite direction. All this accords with criteria widely known in the art and which do not require to be explained further herein. Preferably, the stitch line 18 is located at one of the so-called commissural faces (that is, the zone of maximum axial extent) of the sheets 10 and 12. In addition, the extreme edge of the outer sheet 10 intended to be situated downstream in the implanted position of the valve (that is, the extreme edge of the outer sheet 10 intended to face the output side of the valve) is slit, usually before closure of the tube, very close to the festoon stitch line 16, and thus very close to the arcuate edges of the valve flaps 14, so as to form an output edge 20 intended in turn to allow the valve sleeve to be fixed to the valve stent. In this respect one may again refer to the specification of European patent EP-B-0155245. Still with regard to Figure 2, it will again be noted that, for preference, the relative positions of fixing of the two sheets 10 and 12 is selected so that, when the tubular sleeve is closed into a tube, the inner sheet 12 (or functional sheet, this meaning the sheet which carries the valve leaflets 14) is made to project relative to the outer sheet in correspondence with the upstream edge of the prosthesis (or the input edge for the blood flow); all this facilitates the assembly on the valve stent. The more recent prior art has made headway with yet another line of progress, that is to say, that of attempting to form cardiac valve prostheses without the need for a stent. In other words one is dealing with valves termed "stentless" or "unstented", which do not have the rigid or substantially rigid annular structure present in most valves under current production. In general, it may be said that a presence of a stent is in fact imperative in mechanical cardiac valve prostheses. One has, however, been made to appreciate that, in itself, the presence of a stent if not strictly necessary in biological valve prostheses: in particular, the fact that the valve prosthesis as a whole has good characteristics of deformability renders valves of this type, formed from biological material of valvular origin (that is, in practice, with the use of natural valves taken from animals - typically pig valves), particularly suitable for implantation by the surgeon because of functional advantages and, in particular, a greater similarity to the anatomy of natural aortic valves. In GB-A-1 599 407 and DE-A-2 822 464, after which the preamble of Claim 1 was patterned, a valved prosthesis is disclosed in the form of a valved conduit comprising a biologically inert conduit into which a tube of tissue is attached to form a prosthetic valve within the lumen of the conduit. Also US-A-3 736 598 is of some interest for the invention. The present invention attempts specifically to make it possible to form stentless valves while avoiding the need to take cardiac valves from animals, and by constructing the valve prosthesis in accordance with an optimised design or model, not imposed by the anatomical configuration of animals which have considerable biological variations. All this may eventually make it possible to replace (either partially or completely) the natural biological tissue with a continuous, micro-porous and/or composite synthetic material (for example polyurethane), with the result that it will be possible to replace the connection of the parts by stitching with connection by gluing or welding, or indeed by moulding the prostheses in a single piece. According to the present invention, this object is achieved by means of a cardiac valve prosthesis having the further characteristics set forth in Claim 1 which follows. The invention will now be described, purely by way of non-limiting example, with reference to the appended drawings, in which: Figures 1 and 2, which relate to the prior art have already been described above, Figures 3 and 4 correspond substantially to Figure 1 and illustrate the criteria for the manufacture of the valve sleeve of biological tissue in an aortic valve according to the invention, Figure 5 illustrates a possible variant of a valve according to the invention, Figure 6 illustrates the structure of the valve of the invention in its configuration of use, Figure 7 is a view substantially similar to that of Figure 6 illustrating a further possible variant of the invention, and Figure 8 illustrates schematically the criteria of implantation of a valve of the invention. In Figures 3 to 8 the same reference numerals already used in Figures 1 and 2 have been used to indicate parts functionally similar to those already described. Thus, references 10 and 12 indicate respectively the outer and inner (or functional) sheets of biological material (or synthetic material, for example, polyurethane), while reference 14 indicates the half-moon, sack-shaped parts formed in the latter which will form the valve leaflets of the prosthesis; finally, reference 16 indicates the line of festoon stitching (or welding or gluing) connecting the two sheets 10 and 12 along the outer edges of the valve leaflets 14, while reference 18 indicates the line of stitching along which the valve sleeve is closed into a tube. An important characteristic of the solution of the invention lies in the fact that, in forming the edge of the outer sheet 10 intended to face the downstream end of the prosthesis, that is the outflow end with respect to the blood flow, this is not made to follow strictly the course of the line of festoon stitching 16, and hence the arcuate edges of the valve flaps 14, as it had in the prior art solution (Figure 2). In quantitative terms (without, however, wishing to attribute any limiting character thereto) one may state that, in the solutions adopted at present by the Applicant in the manufacture of the solution described in the prior European patent EP-B-0155245, the edge 20 of the outer sheet 10 is cut at an approximately constant distance of the order of 2mm from the festoon stitching 16. On the contrary, in the solution of the invention shown in Figures 3 and 4, the homologous edge, indicated 120, is located as a certain distance from the arcuate edges of the valve flaps 14: in practice, at a distance of the order of about 1 cm from the festoon stitching 16. In general, the distance separating the edge 120 from the stitching 16 is not constant and has a minimum value in correspondence with the cusps of the festoon stitching 16 (for example, about 1 cm) and a slightly greater value (for example, 1.2-1.5 cm) in correspondence with the loops of the stitching 16. With reference to Figures 3 and 4, it will also be noted that the upstream edge of the outer sheet 10, indicated 122, is not completely straight but has a generally undulating shape which follows the course of the stitching 16 to a certain extent. Again in the solution of the invention shown in Figures 3 and 4, and as already seen in the prior art solution, the arrangement of the relative fixing of the sheets 10 and 12 is selected so that, with the valve sleeve closed into a tube (see Figure 6), the edge of the inner or functional sheet 12 facing the upstream end of the valve projects to a greater or lesser extent relative to the homologous edge of the outer sheet 10. As illustrated schematically in the variant of Figure 5, this greater projection may, in effect take the form of an appendage 124 of the sheet 12, the position and dimensions of which can be varied selectively in dependence on specific applicational requirements so as to enable it to be sutured, for example, to the ventricular wall in a surgical reparatory operation. This appendage 124 of the sheet may, however, extend around the entire circumference of the prosthetic device in order to allow a repair or reinforcement of all or part of the annulus and/or of the adjacent ventricular wall. In the further variant shown in Figure 7, the downstream edge of the outer sheet 10 is not, in practice, subject to any cutting whereby the outer sheet 10 retains a generally rectangular shape (or slightly trapezoidal, for reasons which will be clarified below) so as to form a tubular jacket proper which surrounds the inner sheet 12 with the downstream edge (indicated 120′) of the outer sheet 10 extending annularly and being substantially coplanar with the free edges (that is those which project inwardly of the valve orifice) of the valve leaflets 14. In a further variant (not illustrated) the edge 120 may be located at a certain distance downstream of the edge plane of the valve leaflets so as to form a prosthetic duct proper, giving the prosthesis as a whole the character of an aortic valve prosthesis. As already stated, both with reference to the embodiments shown in Figures 3 to 5 and with reference to the variant of Figure 7, the two sheets 10, 12 of biological material (and particularly the outer sheet 10, at least in its starting configuration) may be generally trapezoidal whereby, when the valve sleeve is closed on itself into a tube as illustrated in Figures 6 and 7, it is possible to give it a generally frusto-conical shape. This latter, as seen in the direction of the free flow of blood may be selected to be convergent or divergent depending upon the specific requirements for the implant. In general, in all embodiments of the invention described, the extension of the outer sheet 10 for a certain distance beyond the line of festoon stitching 16 makes it possible to form a valve prosthesis constituted solely or substantially of biological tissue and, particularly, of biological tissue of non-valvular origin, without the support structure (armature or stent) of conventional valves. In other words, the invention enables a valve prosthesis of unstented type to be made without the need to make use of natural animal valves (for example, pigs' valves). The valve according to the invention may be anchored firmly in the implant position, with all the advantages resulting from its intrinsic character of deformability, without this giving rise to functional problems. Figure 8 shows schematically how this is possible and relates to a possible implant position of a prosthesis according to the invention in replacing a natural, malfunctioning aortic valve. In Figure 8, reference V indicates schematically the ventricle, while reference A indicates the aorta which extends from the so-called valve ring R of the ventricle V. In cardiac operations for the replacement of the natural valve by a prosthetic valve, the structure and the strength of the ring R may often be compromised both by the removal itself, effected surgically, and by septic or non-septic increase in endocarditis. These degenerative phenomena may even extend to adjacent tissue to a certain extent. By virtue of the axial extension of the outer biological sheet 10 relative to the valve (that is in the direction of flow of the blood) the valve according to the invention may be fixed firmly to the region of the ring and to the aortic wall with suture lines C so that, in addition to the necessary firm anchoring of the prosthesis in the implant site, it also repairs and consolidates the ring and the walls of the vessel. This effect may be made even more evident with the use of a solution such as that illustrated in Figure 7, with the downstream edge 120' of the outer sheet 10 located at a certain distance from the end edges of the valve leaflets 14 so as to give the prosthesis as a whole the character of an aortic valve prosthesis. In a complementary manner, the collar formed at the opposite end of the inner, or functional, sheet 12 may be fixed by further suture stitches T to the region of the ring R with a generally consolidating effect. Again, as appendages are present such as the appendage 124 in Figure 5 it is possible to extend the repair even to the walls of the ventricle V when, for example, these have been damaged by endocarditis, or to provide for reconstruction of the ring. Naturally, the possibility exists, as already indicated previously, of using a continuous, for example, micro-porous and/or composite synthetic material ( for example, polyurethane) for the sheets 10 and 12 instead of natural biological tissue (for example, bovine pericardium).

Claims: A cardiac valve prosthesis comprising a stentless valve sleeve made from two sheets of a material (10, 12), of which one sheet (12) is arranged on the inside of the sleeve to define the prosthetic valve leaflets (14) while the other sheet (10) is arranged on the outside of the sleeve and constitutes a formation for the suturing (C) of the prosthesis during implantation, characterized in that it includes valve leaflets (14) of a material selected from the group constituted by biological tissue other than biological valve tissue and synthetic material, in that, at the end of the prosthesis intended to be located flowdynamically upstream of the direction of free flow of the blood through the prosthesis, the said one sheet (12) projects axially a certain distance beyond the corresponding edge of the other sheet (10) and in that the sheets (10, 12) are connected together by at least one connecting line having a festoon course (16) with loops which follow the line of the arcuate edges of the valve leaflets (14) and in that the homologous end edges (120, 120') of the other sheet (10) are located at a certain distance of the order of at least about 1 cm from the said festoon line (16). A prosthesis according to Claim 1, characterized in that said other sheet (10) projects axially from the end edges of the valve leaflets (14) for a certain distance. A prosthesis according to Claim 1, characterized in that the prosthetic valve leaflets (14) have arcuate edges and in that the other sheet (10) has homologous end edges (120, 120') located at a certain distance, taken axially with respect to the prosthesis from the arcuate edges of the prosthetic valve leaflets (14). A prosthesis according to Claim 3 characterised in that the homologous end edges (120) of the other sheet (10) also have a generally festoon course which copies the course of the arcuate edges of the valve leaflets (14). A prosthesis according to Claim 3, characterised in that the homologous end edges (120') have a generally straight course. A prosthesis according to Claim 5, characterised in that the homologous end edges (120') are approximately complanar with the free end edges of the valve leaflets (14). A valve prothesis according to Claim 2 or Claim 5, characterised in that the other sheet (10) projects substantially in an axial direction from the end edges of the valve leaflets (14) whereby the prosthesis itself takes on the character of a vasco-valvular, preferably an aortic valve, prosthesis. A prosthesis according to any one of Claims 1 to 7, characterised in that said one sheet (12) has a projecting appendage (124) at the end of the prosthesis intended to be located flowdynamically upstream in the direction of free flow of blood through the prosthesis for use in a reconstructional operation . A prosthesis according to any one of Claims 1 to 7, characterised in that the said sheets (10, 12) have a generally trapezoidal shape whereby, when the sleeve is closed on itself to form the duct intended to be traversed by the blood flow, it assumes a generally frusto-conical shape. A prosthesis according to Claim 1, characterised in that the synthetic material is continuous and/or micro-porous and/or composite. A prosthesis according to Claim 1 or Claim 10, characterised in that the synthetic material is polyurethane. A prosthesis according to Claim 1, characterised in that the two sheets (10, 12) are connected together (16) by stitching and/or welding and/or gluing. A prosthesis according to any one of the preceding Claims made in a single piece of said material, for example by moulding. An aortic valve prosthesis according to any one Claims 1 to 13.

Inventors: CURCIO MARIA, RINALDI STEFANO, STACCHINO CARLA, VALLANA FRANCO, CURCIO, MARIA, RINALDI, STEFANO, STACCHINO, CARLA, VALLANA, FRANCO
Applicants: SORIN BIOMEDICA CARDIO SPA, SORIN BIOMEDICA CARDIO S.P.A.
Application year: 1992
Main classification: A61F2
IPC codes: A61F2