Patent Application
20100023119
The present invention relates to valve molds and prostheses for mammalian systems in general and more particularly, to a valve mold based on an improved template design and improved prosthesis formed therewith.
The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. All documents listed are hereby incorporated herein by reference.
Valves in mammalian systems are one-way valves that maintain the forward movement of the blood. The largest valves in mammalian systems include the aortic valve and the pulmonary valve. The treatment of valve disease is to either surgically repair or replace the damaged valve with a prosthesis. The two main types of valve substitutes are mechanical prosthesis and tissue valves. The main advantages of the mechanical prosthesis are their structural durability, availability, easy surgical implantation, guaranteed competence and excellent hemodynamic performance. The main drawbacks of such mechanical valves is the need for maintaining the patient permanently and adequately anticoagulated, which entails the risk of thromboembolism or hemorrhage. These problems are most significant in children, women of childbearing age and in patients living in areas of the world where drug availability or patient education is suboptimal. Finally, such mechanical valves tend to be expensive, and therefore beyond the economic possibilities for many patients.
Over the years, advances in tissue valves have been made, including valves made from porcine, bovine pericardium and homograft. These valves can either be stented or stentless. Initially tissue valve replacements were stented either porcine valves supported by a metallic or plastic stent or bovine pericardium valve supported by a metallic or plastic stent. One significant advantage of these stented tissue valves over mechanical valves is that they do not need permanent anticoagulation. The main disadvantage of stented tissue valves is limited durability. High stresses have been found along the edge of the rigid stent mounting area in these valves. The most widely used tissue valve is the porcine/bovine aortic valve treated with glutaraldehyde and supported within a metallic or plastic stent with a cloth flange for suturing it to the patient. These valves, or bioprosthesis, do not require anticoagulation, but have a limited durability in younger patients. As such, their use is typically limited to patients above 65 years of age.
The mold design disclosed in U.S. Pat. No. 6,491,511 (“Duran”) is used to shape biological tissue membrane, to form a reconstituted heart valve for replacement that closely resembles the native valve. Autologous tissue valves are made from the patient's own tissue and can be homologous or heterologous. One significant advantage of autologous tissue valves over other tissue valves is the lack of immune response from the body. However, the valves produced in accordance with Duran, like all stentless bioprosthesis, are difficult to work and can require on the order of 50-60 minutes to implant. The Duran mold has a pronounced curvature along the side to be sutured. In fact, the curvature of the mating surface of the cusps is described in Duran as an ellipse defined by the equation x2/a2+y2/b2=1, where ‘a’ has a value greater than zero and less than 22.0 (0<a<22.0), and ‘b’ has a value greater than zero and less than 14.0 (0<b<14.0). This highly curved attachment line requires the use of three continuous running sutures—one for each of the three cusp or valve leaflets. This method of suturing is not only clinically demanding, but also time consuming. Thus, there is a need in the art for an improved aortic valve mold and a prosthesis formed therewith which overcomes one or more of the aforementioned drawbacks.
The present invention relates to a valve mold and prosthesis for mammalian systems using an improved design. In one embodiment, a mold for forming a replacement tissue valve includes a first template comprised of a thin film polymer having three continuously linked cusps formed thereon in which the first template includes a first lower undulating side that is longer than a first upper side. The mold further includes a second template comprised of a thin film polymer having three continuously linked cusps formed thereon in which the second template includes a second lower undulating side that is longer than a second upper side. In one embodiment, the first and second templates interlock to accommodate a membrane interposed there between that is to be formed into the replacement tissue value.
Other embodiments are disclosed and claimed herein.
One aspect of the invention relates to a mold for replacement valves and instrumentation for the construction in the operating room of a sigmoid (for aortic or pulmonary) valve using a biological tissue membrane, such as the patient's own pericardium either autologous or porcine, bovine or other mammalian pericardium. In one embodiment, autologous pericardium decreases the incidence of immunological rejection of the valve.
Another aspect of the invention is to provide a valve mold design where a conical tube is anchored at a wider end to the inflow orifice, and its smaller or outflow end is minimally anchored to the walls of the great vessels. In one embodiment, the molds of the present invention comprises two thin film plastic templates having the molding shape of the valve to sandwich the pericardium to form the valve. After the pericardium is placed between the two thin film plastic templates, the template-pericardium sandwich can be trimmed or cut to the appropriate size and/or shape. In one embodiment, the lateral aspects of the trimmed pericardium can be joined together to form a truncated cone with a base (inflow) orifice that is larger than its upper (outflow) orifice. The base orifice may correspond to the base of the new valve, while the outflow orifice has three slight curvatures corresponding to the three free edges of the new prosthesis. The three points joining the three slight curvatures may correspond to the three commissures of the new prosthesis.
The general implantation time of a reconstructed aortic valve using Duran's 3-dimensional template would take about 60 minutes. Recent animal trials show that, when performed in accordance with the principles of the invention, the implantation process is simplified by allowing the inflow orifice of the reconstructed valve (using biological membrane) to be suture around the native aortic annulus and the commissures (outflow orifice) sutured at 3 points of the aortic wall using, for example, a U-stitch. Using this approach, the implantation time may be significantly reduced to 30 minutes or less. Reduction in implantation time directly reduces the cardio-pulmonary bypass time, which is a critical variable determining the outcome of every cardiac valve surgery.
In another embodiment, or in addition to one or more of the previous embodiments, a valve mold template may be a 3-dimensional geometry which, when folded and sutured to form a close-loop, resembles the geometry of a native valve. The attachment line of a template designed in accordance with the principles of the invention may have a slightly undulating edge.
Another aspect of the invention is to provide a valve mold design that includes three cusps which, when folded, create three “bulges” that resemble the native valve's three cusps. In one embodiment, these three cusps are linked continuously in that there is no narrow band or other flat connecting strip separating them. Heretofore, heart valve mold designs have interspersed connecting strips between the cusps to provide flat areas in order to suture the prosthetic heart valve to the aortic root of the patient. However, the heart valve mold design may similarly include interspersed connecting strips between three adjacent cusps.
In another embodiment, there may be a narrow band only at the outer end of the valve mold which is usable for suturing. Thus, when folded, the three cusps may be formed into a reconstructed valve with no connecting strips for suturing between the cusps.
Another aspect of the invention is to provide a valve mode design which, when extended, exhibits a fan-like design in that the length of the valve mold along the base (inflow) orifice is more than the length of the valve mold along the upper (outflow) orifice. In another embodiment, a valve mold design of the invention may be designed for a three-point attachment of the valve's upper orifice.
In another embodiment, a template designed in accordance with the principles of the invention may be made of a sufficiently thin polymer such that it is transparent allowing a clear view of the biological membrane. This thin polymer design may also allow an operator to effectively trim or cut through the pericardium-template sandwich to a desired size and/or shape. Thus, a single template design may be used once. Moreover, the thin film polymer valve mold may also include markings and guidelines that effectively guide the surgeon to trim/cut/fashion the membrane template-sandwich between the valve mold templates to the desired geometry. The thin and transparent mold allows the surgeon to easily cut through the sandwich with scissors or a scalpel directly.
Yet another aspect of the invention is to provide a single piece template that incorporates both the male/female (positive/negative) templates of the 3-dimensional geometry of the intended reconstructed valve.
Still another aspect of the invention is a vascular prosthesis constructed using a mold template as described herein.
Referring now to the figures,
Moreover, the attachment side of template 100 (which is side 120) is a slightly undulating edge, according to one embodiment. In another embodiment, the undulations of side 120, as measured by ‘d’, range from 0.0001 mm to 20 mm and preferably in the range of 1 to 15 mm. The slightly undulating side 120 may enable the production of a re-constructed valve that is nearly circular. This circular feature of the attachment line (corresponding to side 120) of the re-constructed valve may be advantageous since it enables a more effective suturing technique to be used. In particular, the technique of multiple interrupted suturing can be used to attach a replacement valve constructed with template 100. Molds of the prior art have highly non-circular attachment lines, necessitating the use of continuous running sutures, which is clinically demanding and time consuming.
In one embodiment, an aortic valve consistent with the principles of the invention includes a tri-leaflet, reed-like structure. In this fashion, the truncated cone may be supported at both ends by the two cables that maintain a circular flow and outflow orifices of the prosthesis. In one embodiment, these threads are removable after implantation. In such a case, after removal of the patient's diseased valve cusps, the base of the cylinder may be sutured to the patient's aortic base. The three commissural points of the cone in its outflow orifice may then be sutured with a pledget to the patient's aortic wall beyond the patient's own commissures. In one embodiment, a completely stentless prosthesis may be achieved by cutting and pulling out the inflow and outflow cords.
It should further be appreciated that the template 100 of
The lengths L1 and L2 of template 100 will depend on the size of the valve to be implanted. In one embodiment, when used as an aortic mold template, the final diameter of the valve will range from approximately 9 mm to approximately 35 mm. However, it should equally be appreciated that the diameter may be smaller or larger, depending on the size of the valve needed. It can also be customized for larger or smaller hearts such as in the case of an infant or for larger hearts if required.
The template 100 of
It should be appreciated that template 100 may be made of a sufficiently thin polymer such that it is transparent allowing a clear view of the biological membrane (including autologous pericardium) when it is “sandwiched” between a pair of the valve mold templates. A clear view of the biological membrane when sandwiched between the valve molds may be desirable because the surgeon would be able to ensure that the membrane is evenly spread, with virtually no air being trapped under or above the membrane to ensure complete treatment of the membrane, and that there is no overlapping or crumpling of the membrane within the valve mold. Any movement of the membrane (even during the trimming process) can be readily observed to allow the surgeon to make any necessary adjustments. Template 100 can be manufactured from a number of plastic materials, including high density polyethylene, polypropylene, polyesters, polyamides and other suitable plastic materials. In one embodiment, template 100 may be manufactured using an injection molding process or vacuum thermal forming or any other plastic-forming process.
In another embodiment, the thin film polymer valve mold template may be made of sufficiently thin film to allow easy trimming, and yet rigid enough to hold the membrane and to be molded according to the desired geometry provided by the valve mold. In contrast, the mold disclosed in Duran required the operator to trim the membrane along the peripheral of the valve mold template, which made it difficult to trim at narrow angles or in small radius regions.
In yet another embodiment, the thin film polymer valve mold may include markings and guidelines that effectively guide the surgeon to trim/cut/fashion the membrane sandwiched between the valve mold templates to the desired geometry.
Referring now to
Each cusp 110 is designed with a cusp angle θ formed by lines 130 and 135. In one embodiment, cusp angle θ may range from approximately 100 degrees to approximately 160 degree. Proper selection of the cusp angle θ will ensure that the three leaflets of the heart valve are molded and assembled in accordance with the invention, these leaflets should contact each other to properly close the heart valve during diastolic phase. In this embodiment, the three cusps 110 are continuously linked in that there is essentially no spacing or distance between the cusps 110, as shown in
The single piece template 300 may optionally include a series of inter-locking and matching stubs 150 on both the male/female (positive/negative) sides, as shown in
After the membrane has been treated, the excess membrane 410 may be trimmed along the edges of the templates 400 and 420. However, if where the templates are not of the required shape and/or size, the templates 400 and 420 themselves, along with the sandwiched membrane 410, may all be trimmed to a specific size and/or shape. This would enable a surgeon to use a universally designed template, yet still be able to tailor it to the needs of the specific patient. In this case, it should further be appreciated that the templates may be made of thin plastic having a thickness on the order of less than approximately 0.5 mm.
After the trimming process, the two loose ends of the trimmed tissue may then be attached to one another to form the prosthetic valve. Thereafter, the replacement heart valve may be sutured into the aortic or pulmonary valve root, which in one embodiment is done using a multiple interrupted suturing process. Once implanted, the autologous tissue will slowly regain the consistency of the surrounding tissue, and will function in a normal opening/closing valve fashion.
Molds of the invention were tested in two test groups of sheep. The first group was tested with prosthetic valves made with the sheep's autologous pericardium using a preferred embodiment of the valve mold of the invention. The constructed valve was placed in the pulmonary valve root. The valve implanted was constructed intra-operatively as an autologous pericardial heart valve made of the sheep's own pericardium, treated for 8 minutes with buffered Glutaraldehyde. In this first group, the valve was implanted in 6 sheep in pulmonary position and in 6 sheep in aortic position under cardiopulmonary bypass. After implant, all valves were immediately competent and no regurgitation was detectable. The hemodynamic study showed very low transvalvular pressure gradients after implantation. After six month, the sheep of the pulmonary implants were sacrificed showing promising results with competent valves. At time of sacrifice transvalvular gradient was 4.5+/−1.9 mmHg. There was no valvular or paravalvular leak, the leaflets were pliable and thin. Histology showed no tear or rupture at the Single Point Attached Commissures (SPAC). Subsequently the SPAC valve was implanted as autologous pericardial valve in the same manner in aortic position.
The second group consisted of 20 Merrino sheet in which molded autologous aortic valve prostheses were implanted. The valve prostheses were constructed from the sheep pericardium in less than 15 min. In each case, the native valve was removed and a prosthesis was implanted in less than 30 minutes using cardio pulmonary bypass. Epicardial echo demonstrated well working valve prostheses with insignificant regurgitation. Postmortem revealed all valve leaflets to be pliable with minor calcification in a few leaflets. Except for one incidence, the commissures were reliably anchored to the aortic wall. After changing the implantation technique by adding a pledged outside of the aorta at SPAC, no more disruption of SPAC occurred. Implants in this second group of sheep showed overall excellent results that appear to be as good a commercially available valve prostheses. In the A-Series, the commissures were implanted at the aortic wall with a 4/0 suture. In this series, one torn commissure was found. The suture at the commissure had been cutting through the aortic wall, the suture loop was still found to be anchored at the free-floating commissure and the pericardial leaflet structure was still intact at this location. Due to this incidence, the implantation technique of the commissures was changed by tying the 4/0 suture over a pledged outside of the aorta. Subsequently in the next series (H-series) all commissures were found to be intact, with no tears or alterations of the aortic wall and the pericardial leaflet.
According to another aspect of the invention, the mold may be prepared together as a kit that includes a sizer for accurate measurement of the diameter of a valve to the correct size required of a valve that is to be replaced and/or a tanning solution. These sizers may be any design that fit inside or across the valve root as long as they are capable of determining the diameter of the valve that needs to be replaced. One embodiment of the sizer 500 can be seen in
Referring now to
Continuing to refer to
At block 830, sutures may be placed at the commissures of the valve leaflets and passed through the conduit wall at three equidistant points at the sino-tubular junction. The 3-dimensional shaped pericardial flap may then be sutured together along the lateral side in a way that it will form a vascular graft at block 840.
In one embodiment, the commissural sutures may be pulled, thereby inverting the leaflets into the conduit. The sutures may then be securely tied outside of the conduit wall, forming a three-leaflet valve.
Process 800 may then proceed to block 850 where an optional strip of pericardium may be sutured to the base of the valved conduit to match the right ventricular outflow tract, if necessary. The lower part of the completed valved conduit is ready to be sutured to the right ventricular outflow tract, while the upper part may be sutured to the pulmonary trunk.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2006/003495 | 9/6/2006 | WO | 00 | 9/1/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60714629 | Sep 2005 | US |
