MXPA99006858A - Heart valve prosthesis - Google Patents

Abstract

The invention provides a prosthetic valve having a generally annular frame with three post and three scallops. The frame is tri-symmetric with an axis of symmetry defined by the axis of blood flow through the valve. The external surface of the frame is generally cylindrical with diameter D. Each leaflet has a truncated spherical surface adjacent to its free edge. The spherical surface is joined tangentially to a truncated conical surface. The half angle of the truncated cone is approximately 37.5°. The radius of the sphere is approximately D/2 - 0.5 (mm). The leaflet surface is axi-symmetrical with the axis of symmetry being perpendicular to the axis of the valve frame and blood flow.

Description

PROSTHESIS OF V CARDIAC LIVES The present invention relates to medical implants, particularly implants and cardiac and vascular prostheses. In mammals, the heart is the vital organ responsible for maintaining an adequate blood flow (and consequently, oxygen and nutrients) to all parts of the body. It prevents blood from flowing back through the heart through valves. Dysfunction of one or more of the valves in the heart can have serious medical consequences. Dysfunction of the heart valves can be the result of a congenital defect or damage or degeneration induced by a disease. The dysfunction results from stenosis or regurgitation (or a combination) of the valve, which leads to a high pressure upstream of the valve. To date, the only solution to treat some dysfunctions of the heart valves, is to replace the valve that malfunctions. The replacement operation of a valve is expensive and requires specialized facilities for open-heart surgery. The replacement of artificial valves with defects carries a higher risk and there are practical limits on the number of times a reoperation can be performed. This makes the design and operation life time of any replacement valve extremely important. Porcine aortic valves have been used for many years in human patients and it has been proposed (see for example EP-A-0, 02, 036 of Pro Medica International Ine) to use pulmonary pulmonary valves in human patients; however, valves derived from biological material have a finite life span and should generally be replaced ten years after implantation in younger patients. In third world countries, where rheumatic fever is still common, the problems of valve replacement in young patients are considerable. Anticoagulants (required for mechanical valves) are often not practical; Accelerated calcification (a problem of biological valves in young people), prevents the use of biological alternatives. In the Western world, the increase in life expectancy for humans results in a corresponding increase in patients requiring replacement of heart valves. Thus, there is an increasing need for heart valve prostheses that have a prolonged lifespan and also a low risk of inducing thrombosis in a recipient.

It is known that conventional flexible lamellae heart valves comprise an annular frame placed parallel to the blood flow. The annular frame generally has three posts extending in the downstream direction defining three openings or festoons generally U-shaped between the posts. The lamellae are generally attached to the frame between the posts along the edges of the festoons and detached at the free edges of the lamellae adjacent to the ends downstream of the posts. According to the present invention, there is provided a heart valve prosthesis comprising a frame and two or more lamellae attached to the frame, wherein at least one of the lamellae comprises a first portion, which has a generally spherical surface, and / or a second portion, which has a generally conical surface. The respective surfaces are preferably partially conical or spherical. The prosthesis may be an artificial valve and may be oriented in a particular direction in a heart (or other vascular tissue), to allow the flow of blood in a direction through the tissue, but to prevent reflux. The frame preferably has a generally circular cross section with two or more posts (in a number equal to the number of lamellae) extending in the same direction from a base. The prosthesis is preferably oriented with the frame posts extending in the downstream direction, so that the mouth of the valve formed by the base remains open. The lamellae are attached to the frame between the posts and each has a free edge adjacent to the ends of the posts, which can be sealed together to close the valve at the ends of the posts. The conical portion is preferably located adjacent the base of the prosthesis, and the spherical portion is preferably located adjacent the free edge. This is advantageous since the spherical surfaces at the edges of the lamellae seal more effectively than the flat or conical surfaces, and the conical portion at the base of the valve opens more easily after an increase in blood pressure in the vicinity. than an equivalent spherical portion. A valve embodying the invention has lower resistance to opening, because the conical portion reacts first to the pressure increase on the upstream side of the valve. When closed, the increase in pressure on the downstream side of the valve forces the free edges of the lamellae together, in a substantially parallel arrangement, thereby improving the seal between the lamellae and reducing the backflow of blood through the lamellae. The valve. The spherical portion adjacent to the base of the lamellae also confers advantages in the distribution of stress, when the valve closes and the pressure is greater downstream than upstream. The lamellae can (although it is not necessary), be identical. The number of lamellae is preferably three and the frame comprises three posts. The lamellae are preferably flexible. The lamellae may have a defined boundary between the first (spherical) portion and the second (conical) portion, or alternatively, the boundary between those two portions may be phased in, for example, by adopting a sphere of gradually increasing radius melting with the conical portion. This is acceptable as long as the free edge of the lamellae (or a portion thereof) has a generally conical surface. In one embodiment, the lamellae extend beyond the top of the frame posts. The lamellae can comprise any biostable, biocompatible thermoplastic elastomer, including, but not limited to, any polyurethane or silicone elastomer or any polymer or mixture based on those elements. The manufacturing route can be any suitable method, including not only dip molding, but also injection molding, transfer molding, and the like. Preferably, the lamellae comprise a biostable polyurethane, such as ELASTEON-CSIRO, CHRONOFLEX or TECOTHANE and are molded by immersion, thus integrating the lamellae to the support frame and the posts. The lamellae can be approximately 100-200 μm, but the thickness can vary with the material used. The lamellae can by themselves vary in thickness to incorporate thicker wall areas and adjacent thin-walled areas. Smooth ridges and / or progressions of thick-walled to thin-walled areas were contemplated. The surface of the lamella is preferably axisymmetric, with the axis of symmetry that is perpendicular to the axis of the valve frame and the intended direction of blood flow. Where the diameter of the frame is the distance D (mm), the radius of the sphere is preferably between D / 2 (mm) and (D / 2) -2 (mm).

The conical portion is generally truncated and has a half angle within the range of 30 ° to 45 ° (for example, preferably 37.5 °). The frame can be parallel or slightly inclined on the inside and the outside, to allow a slightly divergent flow. The pressure required to open the valve is Et3 defined by the equation, where E is the elastic modulus, R t is the thickness of the lamella and R is the radius of curvature. The inversion of the curvature in the center of the lamellae can also facilitate the opening of the valve. The prosthesis may have incorporated an escape route for trapped air, for example a purge hole in the frame and / or in one or more lamellae, optionally near the base of each lamella leading through the frame to the appearance of I influence to rebuff the space sublaminilla. The means to protect the valve from a posterior entrapment with an implantation suture is useful. These could take the form of a simple removable suture, which ties the tips of the posts, or a flexible polyurethane shield similar to a more sophisticated umbrella (not shown), which could be collapsed and extracted through the mitral prosthesis.

A metal frame can be used and the frame can be coated by immersion with polymer and with devices to improve metal-polymer adhesion. The metal may be titanium or a titanium alloy, although any implantable metallic material such as stainless steel or cobalt-chromium alloys may be suitable. Alternatively, a polymeric material for the frame can be used. Two preferred options are a rigid polyurethane and a PEEK, polyetheretherketone. Alternative polymers are Delrin (a polyacetal), polyethylene and polysulfone. Any rigid or semi-rigid thermoplastic polymer may be used, such as a polyurethane, PEEK, polyacetal, polyethylene, polysulfone, acrylic or similar materials. Surface modifications to improve biocompatibility can include whatever is useful in relation to the technology of medical devices in general. Surface modifications may be to control the interactions between the valve material and the blood to prevent protein adsorption, platelet binding and activation, activation of the coagulation cascade and calcification. It is preferable to coat any surface of the valve, primarily, including but not limited to, the material of the foil.

The surface modification that most likely results in a reduction in protein adsorption is that of the binding of the phospholipids to the polymer. The principle is that a phospholipid, such as phosphorylcholine, binds to the polymeric surface, this layer mimics the surface of cells and is resistant to the adsorption of plasma proteins. Since this adsorption is the first event in the blood-polymer interactions that triggers all reactions with the coagulation cascade and platelets, the inhibition of the process delays or prevents these other effects. Known technologies can be used to coat any type of synthetic prosthetic heart valve. The polymer used for the construction of the valve can be coated with any biomimetic substance, such as a glycoprotein or phospholipid analog protein, with the purpose of minimizing the adsorption of plasma protein on its surface. One more possibility involves the binding of antibodies with a surface to control the nature of a protein that is adsorbed. For example, it is known that surfaces covered with albumin layers are much less thrombogenic than surfaces covered with fibrinogen. Attempts have been made to coat polymers with these proteins, but there are many immunological problems associated with the use of proteins derived from sources other than the host. The best concept is to use anti-albumin antibodies, which can be bound to the surface, so that when the material comes into contact with the patient's blood, its own albumin is tightly bound to the binding antibody. Platelets tend to interact with all foreign surfaces, but this process can be reduced by controlling the composition and surface characteristics. It is important to prevent platelets from binding to the surface, but also to prevent any attached platelets from being activated at or near that surface. A process of superficial modification that could be beneficial involves the union of hydrophilic molecules on the polymeric surface. Polyethylene glycol or other similar substances can be covalently bound to polymers such as polyurethane and the hydrophilicity imparted will reduce the tendency of cell attachment. The binding of platelets can also be resisted by the use of pharmacologically active agents attached to the surface. Drugs such as prostaglandins, heparin, hirudin, plasminogen activator t and urokinase have been bound to functionalized polymeric surfaces or otherwise incorporated as leachable or diffusible components of the polymers for this purpose. It is known that these molecules have antiplatelet activity through their effect on the platelet membranes and / or their effect on the components of the coagulation cascade that interact with these membranes, and it is possible to reduce the binding and activation of platelets. One or more parts of the prosthesis can be transparent. Particularly preferred materials for use in the manufacture of prosthetic valves according to the present invention are based on those described in U.S. Patent Nos. 5,393,858 and 5,403,912, International Patent Application No. PCT / AU97 / 00619 and Patent Applications. Australian Provisional Nos P07002, P07616 and P07878. An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figures a and b show a valve in a perspective view; Figure 2 shows a perspective view of a valve of Figure 1 showing the spherical and conical portions; Figure 3 shows a sectional view through a lamella of the valves of Figure 1 and Figure 2; Figure 4 shows a side sectional view of the valve of Figure 1; Figure 5 shows a perspective view of the valve when it is open; Figure 6 shows a plan view and a perspective view of the frame; Figure 7 shows a perspective view of a second valve; Figure 8 shows a perspective view of the valve frame of Figure 7; Figure 9 shows a sleeve of the valve of Figure 7 in a perspective view; Figure 10 is a perspective view of a seam ring of the valve of Figure 7; Figure 11 shows a perspective view of the frame of Figure 8 partially cut away; Figure 12 shows a side sectional view of the lamellae of the valve of Figure 7; Figure 13 shows plan views (a, b, c and d) and a cross section (e) of the lamellae, indicating possible configurations of the lath; and Figure 14 shows a perspective view of integrally molded lamellae of the valve of Figure 7. Referring now to the drawings, a prosthesis according to the invention has a generally annular frame 1 with three posts 1P and three festoons ÍS. The shell of the valve 1 is preferably formed from a rigid polymer such as polyetheretherketone or polyurethane of high modulus, and is trisymmetric with an axis of symmetry defined by the axis of blood flow through the valve. The outer surface of the frame 1 is generally cylindrical with a diameter D, and diverges towards the tips of the poles P. For a given diameter D, the thickness of the frame of the valve 1 is typically 0.05 D. The three festoons ÍS and the poles 1P are equally spaced at 120 ° intervals around the frame. A lamella 10 is attached along the free edge of each festoon ÍS and is supported by adjacent poles 1P. The three lamellas 10 are thus also spaced at 120 ° intervals around the frame 1. Each lamella 10 is identical, and has a truncated spherical surface IOS adjacent to its free edge. The spherical surface IOS is tangentially connected to a truncated conical surface 10C. The truncated cone half angle is 37.5 °, but it can be any angle in the range of 30 ° to 45 °, as shown in Figure 3. The radius of the sphere is approximately D / 2 - 0.5 (mm), but it can be between D / 2 and D / 2-2 (mm). The surface of the lamella is ametrometric with the axis of symmetry that is perpendicular to the axis of the valve frame and the blood flow.

The free edge of each lamella lies in an XY plane perpendicular to the axis of the intended blood flow through the valve (Z). Figure 3b shows the geometry of the lamella in the XY plane, and Figure 4 shows the lamella geometry in the XZ plane. The valve is placed, for example, in the vascular tissue with the post 31 and the free edges of the lamellae pointing downstream. The geometry of the lamella is designed to encourage the opening of the valve foil at the base of the valve. An increase in pressure upstream of the valve causes the conical portions 10C at the base of the lamellae to diverge first. The conical surface can be deformed to an open position very easily with minimal resistance, and in this way, the valve can be opened under very low upstream pressures. The divergence of the conical sections 10C initiates the divergence of the IOS spherical portions. The spherical portions IOS of the lamellae 10 are easily opened after the divergence under the upstream pressure of the conical portions 10C, and under an increase of the downstream pressure, sealing each other more effectively than a conical or flat surface.

The sealing of the lamellae and the competition of the valves can be further improved by extending the lamellae 1 to 2 mm above the top of the valve posts, varying the geometry of the lamella above the pole slightly, to put the lamellas in direct opposition. Figures 7-13 show a second embodiment of a valve according to the invention. The second valve 20 has three lamellae 30 of flexible polyurethane, located on a support frame 21, a protective shield 24 for the lamellae 30, and a seaming ring 25 for surgical insertion. The frame 21 has three posts 21P, each tapering towards a point from a base 21B. The posts and base define three 21S scallops. The lower edge (upstream) of the base 21B is festooned to generally conform to the festoons 21S receiving the lamellae 30. A metal frame 21 is preferred and can provide maximum strength and minimum frame thickness; the frame 21 could be coated by immersion with polymer. Openings, gratings or a mesh surface, could increase metal / polymer adhesion. The main function of the frame 21 is to support the base of the lamellae 30, giving a stable and predictable geometry to the base of the lamellae 30. The origin of the lamellae of the frame must be at an optimized angle to minimize bending stresses during the movement of the foil, and to extend the transition zone from complete flexibility to complete rigidity, as widely as possible. A seamless connection of the foil 30 to the frame 21 is desirable to minimize the possibility of separation of the foil 30 from the frame 21. A degree of flexibility of the frame 21 will be desirable to reduce the stress on the foils, although the resistance to plastic thermoforming is important. An outer sleeve 24 is provided to surround the posts and the frame, and to provide protection to the lamellae 30 from contact with adjacent tissues, particularly the ventricular myocardium, in the case of the mitral valve, and the aortic wall in the case of the aortic valve. The sleeve extends beyond the edges of the posts. The frame 21 also provides a safe path for a seaming ring 25 to allow surgical insertion. Additionally, the frame can provide temporary support for a mounting system to allow for surgical manipulation during valve implantation. Ideally, the frame 21 should be attached to the seaming ring 21, in such a way as to allow the implanted valve 20 to be rotated by the surgeon to optimize the position of the frame poles. Ideally, to minimize the risk of damage to the lamellae 30 during surgical implantation, and to facilitate accurate and secure positioning of the seaming ring 25, the frame 21 should be detachable from the seam ring 25, and be attached in a easy and safe at the time of surgery, after completing the insertion of seam ring 25. The total height of the valve should be as low as is compatible, with good blade stability and reasonable effort. The base of the lamellae 30 should be located as close to the inflow aspect of the valve as possible, and the seaming ring 25 should be mounted at a distance from the inflow aspect to reduce the projection of the post as much as possible. The geometry of the lamellae 30 is preferably optimized for uniform diffusion of stress during opening and closing, and there should be three substantial areas of apposition of the lamella 30. The lamellae 30 should preferably be opened at low transvalvular pressure levels, to allow a satisfactory use in small sizes in the mitral position, as well as to gain an optimal hemodynamic function. The hydrodynamic operation in terms of pressure drop, should rival that of mechanical valves with two lamellae, more than with bioprosthetic valves, and that of bioprosthetic valves in terms of regurgitant flow. The three flexible leaflet valves have essentially two stable positions for the lamellae, open and closed. The transition between the open and closed positions implies a rapid deformation process, which infers rapid changes in the shape on the foil, accompanied by an abrupt angulation of the foil material and areas of high stress concentration. It is possible to minimize this source of highly repetitive, transient effort by carefully designing the lamella geometry. The foil 30 can be formed with "memory" 'for the optimized mean strain position, allowing minimal internal stresses in the most vulnerable part of its movement cycle. The lamellae 30 can be molded by immersion in a position of "moderate deformation". This offers a solution to the problem of dipping three lamellae 30 into a full frame 21. However, also helps to ensure that the deformation procis predictable and controlled, with the minimization and distribution of strain during deformation. To ensure that the valve assumes a closed position when it is discharged, a second dive could be applied while the valve is in the closed position. The same effect can be achieved by thermally annealing in the closed position. Whichever method is used, only enough memory can be induced in the foil to allow closure, but not so much as to require the level of the open transvalvular prre gradient that could be present if the foil was molded in the closed position. It may also be useful to carry out a third immersion molding in the open position (or additional thermal annealing) to impose a non-deformed, uniform geometry on the open valve. The thicknof the additional immersion coatings would be controlled by adjusting the concentration of the immersion solution. A further option is provided to reinforce the lamellae 30 and control the deformation by incorporating reinforcing edges 26 in the polyurethane foil 30. This has the effect of making the lamella 30 more rigid in one direction (the direction of the edges 26), than in the perpendicular direction. The anisotropic properties of the native aortic valve (and the porcine bioprosthetic valves) could be imitated through the circumferential beading on a polyurethane foil. The concept can be extended to the use of grid-like edges 26, or even concentrically placed circular or oval edges 26, which would influence the deformation of the foil in a predictable manner. Such edges 26 may be formed in a dip molded valve, for example, by carefully etching the dippers of the lamella 30. To avoid potential flow disturbances, it would be desirable to form the edges 26 on the lamella discharge, instead of the entrance surface. The foil 30 can be molded by separate immersion, to provide a suitable surface area for the lamellae 30, as well as the edged polyurethane pattern as an inherent part of the lamella 30. (projecting from the outflow aspect of the lamellae), and can be mounted on a frame 21 using bolts and locating holes. Alternatively, it is possible to immerse the three lamellae as a complete unit, which could be attached or fixed on a frame, for example, with the help of locating bolts and corresponding holes in the frame. The sleeve 24 may include a clamp and could extend beyond the posts to help protect the lamellae from impact with the myocardial or aortic wall.

Example 1 A valve was manufactured as shown in Figure 2. The base has an external diameter of approximately 23.8 mm, with an internal diameter of 22.4 mm. The posts extend approximately 17 mm from the base of the frame and in this mode, the width of the top of each post is 1.4 mm, with a thickness of 0.7 mm. The valve frame was manufactured from polyetheretherketone and coated with ELASTEON CSIRO at a thickness of 0.2 mm. To manufacture the coated valve, the frame was placed on a solid balloon and the lamellae were formed by immersion molding, thereby sticking to the frame.

The material of the foil is polyurethane ELASTEON CSIRO with a thickness between 100 to 200 μm. Alternative examples of a prosthetic valve according to the present invention involve using a high modulus polyurethane shell (E> 500 MPa) or using CHRONOFLEX or TECOTHANE polyurethane with an elastic modulus in the range of 5-15 MPa. Modifications and improvements can be incorporated without departing from the scope of the invention. For example, the framework can be made of a polymer, metal or biocompatible composition. The frame can be coated with polyurethane to allow the integration of the lamellae, and can be flexible to allow the post to bend (eg, about 0.05D) during closing of the valve under pressure.

Claims (19)

CHAPTER CLAIMEDICATORÍO Having described the invention, it is considered as a novelty and, therefore, what is contained in the following claims is claimed.

1. A cardiac valve prosthesis characterized in that it comprises a frame and two or more lamellae attached to the frame, wherein at least one of the valves comprises a first portion, which has a generally spherical surface, and a second portion, which has a surface generally conical The prosthesis according to claim 1, characterized in that the surfaces of the first and second portions are partially spherical or conical, respectively. 3. The prosthesis according to claim 1 or claim 2, characterized in that the frame has a generally circular cross-section, with two or more posts (in a number equal to the number of lamellae), which extend in the same direction of a base, so that the mouth of the valve formed by the base remains open. The prosthesis according to any of the preceding claims, characterized in that the lamellae are attached to the frame between the posts and each has a free edge adjacent to the ends of the posts, which can be sealed together at the ends of the posts . The prosthesis according to any of the preceding claims, characterized in that the conical portion is located adjacent to the base of the prosthesis, and the spherical portion is located adjacent to the free edge. The prosthesis according to any of the preceding claims, characterized in that the lamellae are identical. The prosthesis according to any of the preceding claims, characterized in that the prosthesis comprises three lamellae and three posts. The prosthesis according to any of the preceding claims, characterized in that the lamellae are flexible. The prosthesis according to any of the preceding claims, characterized in that the lamellae have a defined boundary between the first (spherical) portion and the second (conical) portion. The prosthesis according to any of claims 1 to 8, characterized in that the boundary between the first and second portions is in phase, adopting a sphere of radius that gradually increases joining with the conical portion, and the free edge of the Lamellae (or a portion thereof) have a generally spherical surface. The prosthesis according to any of the preceding claims, characterized in that the lamellae comprise a biostable material, such as a CSIRO biostable polyurethane, and are molded by immersion, thereby integrating the lamellae to the support frame and the posts. The prosthesis according to any of the preceding claims, characterized in that the lamellae are approximately 100-200 μm. The prosthesis according to any of the preceding claims, characterized in that the lamellae vary in thickness, so that they incorporate areas of thick walls and areas of adjacent thin walls. The prosthesis according to any of the preceding claims, characterized in that the surface of the prosthesis is axisymmetric, with the axis of symmetry that is perpendicular to the axis of the valve frame and the intended direction of blood flow. 15. The prosthesis according to any of the preceding claims, characterized in that the diameter of the frame is the distance D and the radius of the sphere is between D / 2 and D / 2-2 (mm). The prosthesis according to any of the preceding claims, characterized in that the conical portion is truncated and has a half angle within the range of 30 ° to 45 °. 17. The prosthesis according to any of the preceding claims, characterized in that the pressure required to open the valve is defined by the ET equation where? is the elastic modulus, t is the R thickness of the lamella and R is the radius of curvature. 18. The prosthesis according to any of the preceding claims, characterized in that the prosthesis incorporates an escape route for trapped air. 19. The prosthesis according to any of the preceding claims, characterized in that the prosthesis also comprises means for protecting the prosthesis from entrapment of the posts with an implantation suture.