Abstract:
A stentless aortic bioprosthesis having patent, non-ligated coronary artery segments extending therefrom, and methods for surgical replacement of aortic and/or non-aortic (e.g., pulmonary) heart valves with such stentless aortic bioprosthesis. The presence of the patent, non-ligated coronary segments facilitates end to end anastomosis of the patient&#39;s native coronary arteries and/or existing coronary artery bypass grafts to the coronary segments of the bioprosthesis even when such native coronary arteries (or coronary grafts) are too short to reach the wall of the aortic segment of the bioprosthesis. The presence of such patent, non-ligated coronary segments also eliminates the need for removal of a “button” or segment of the native aorta in connection with the native coronary artery segments prior to implantation of the bioprosthesis, and is thus advantageous for patients whose ascending aorta is diseased or otherwise compromised.

Description:
This is a continuation of application Ser. No. 08/998,318, filed on Dec. 24, 1997, now U.S. Pat. No. 6,001,126. 
    
    
     FIELD OF INVENTION 
     The present invention pertains generally to medical devices and methods, and more particularly to a bioprosthetic heart valve device and related methods for surgical implantation of such bioprosthetic device. 
     BACKGROUND OF THE INVENTION 
     Heart valve replacement surgeries have been performed in human beings for many years. Most frequently, these valve replacement procedures are utilized to replace the mitral or aortic valves of patients who suffer from valvular heart disease. 
     In particular, surgical replacement of the aortic valve has proven to be a successful mode of treatment of patients who are diagnosed with a) obstruction (i.e., stenosis) of the aortic valve or b) leakage (i.e., regurgitation, incompetence or insufficiency) of the aortic valve. In some patients, symptoms of both obstruction and leakage are present, this being known as “mixed disease” or “combined lesions”. These types of aortic valvular heart disease may be caused by a number of factors, including congenital deformations, infections, degenerative calcification, and certain rheumatological disorders. 
     Surgical replacement of the aortic valve is typically performed under general anesthesia, with full cardiopulmonary bypass. An incision is made in the aorta adjacent to the heart, and the leaflets of the endogenous aortic valve are removed along with any calcified surrounding tissue, thereby creating an annular opening (i.e. the “aortic annulus”) at the site previously occupied by the endogenous aortic valve. Thereafter, a prosthetic aortic valve is selected and sutured into the aortic annulus, as a prosthetic replacement for the surgically-removed endogenous valve. 
     The available types of prosthetic aortic valves have heretofore included mechanical valves as well as valves formed of preserved animal tissue (i.e., “bioprosthetic” valves). Of the bioprosthetic valves, some (known as “stented” bioprosthetic valves) incorporate a man-made stent or support frame upon which the preserved biological tissue is mounted. Others (known as “stentless” bioprosthetic valves) do not include any man-made stent or support frame, and are formed entirely of preserved biological tissue. 
     Tissues for use in bioprosthetic heart valves are typically harvested from the hearts of donor animals and such tissues typically contain large amounts of connective tissue proteins (e.g., collagen and elastin). After the desired tissues have been harvested from the donor animals, they undergo a chemical “fixing” process wherein the connective tissue proteins within the tissue are exposed to one or more chemical cross linking agents capable of forming chemical cross linkages between amino groups present on the connective tissue protein molecules. The types of chemical cross linking agents useable for this purpose include: formaldehyde, glutaraldehyde, dialdehyde starch, hexamethylene diisocyanate and certain polyepoxy compounds. 
     Examples of commercially available stented bioprosthetic valves include the Carpentier-Edwards®, PERIMOUNT™ Pericardial Bioprosthesis (Baxter Healthcare Corporation, Edwards CVS Division, Post Office Box 11150, Santa Ana, Calif. 92711-1150) as well as the Carpentier-Edwards® Porcine Bioprosthesis (Baxter Healthcare Corporation, Edwards CVS Division, Post Office Box 11150, Santa Ana, Calif. 92711-1150). 
     Examples of commercially available stentless bioprosthetic valves include the Edwards Prima™ Stentless Bioprosthesis (Baxter Edwards A G, Spierstrasse 5, CH-6848 Horw, Switzerland), the Medtronic Freestyle™ Aortic Root Bioprosthesis (Medtronic, Inc. 7000 Central Avenue NE, Minneapolis, Minn. 55432-3576) and the St. Jude Toronto™ SPV Stentless Bioprosthesis (St. Jude Medical, Inc. One Lillehei Plaza, St. Paul, Minn. 55117). 
     The stentless bioprosthetic valves may offer superior hemodynamic performance when compared to their stented counterparts, due to the absence of flow restrictions which can be created by the presence of a stent and/or sewing ring. Also, the stentless bioprosthetic valves may exhibit better post-implantation durability than the stented bioprosthetic valves, because they provide a more flexible structure which serves to dissipate stress during the cardiac cycle. 
     At least one of the previously available aortic bioprostheses (i.e., the Medtronic Freestyle™ Aortic Root Bioprosthesis referred to hereabove) has included a segment of the donor animal&#39;s ascending aorta, along with ligated remnants of the donor&#39;s coronary arteries extending outwardly therefrom. However, because the coronary artery remnants included in this bioprosthesis have been ligated prior to fixation, the lumens of these coronary artery segments are substantially collapsed and occluded. As a result, it is typically necessary for the surgeon to trim away a substantial portion of each coronary artery remnant, prior to anastomosis of the patient&#39;s endogenous coronary arteries thereto. 
     It is desirable to devise a new stentless aortic bioprosthesis which includes coronary artery remnants which have been fixed in an unligated, natural configuration, such that the lumens of such coronary artery remnants remain patent, and the patient&#39;s endogenous coronary arteries may be anastomosed directly thereto. 
     SUMMARY OF THE INVENTION 
     The present invention is a stentless aortic bioprosthesis having patent coronary artery protuberances, and related methods for surgical implantation of such bioprosthesis. 
     In accordance with the invention, there is provided a stentless heart valve bioprosthesis formed of fixed biological tissue, comprising a segment of mammalian aorta having an aortic lumen extending longitudinally therethrough, an inflow end, an outflow end, a plurality of aortic valve leaflets disposed within the aortic lumen. The bioprosthesis includes right and left coronary sinuses, a non-coronary sinus which is situated adjacent to and between the coronary sinuses, and right and left coronary artery segments having coronary artery segment lumens extending therethrough. The coronary artery segments extend outwardly from the coronary sinuses, and the segment of mammalian aorta is fixed with the right and left coronary artery segments defining patent lumens therethrough such that some of the blood which enters the lumen of the aortic segment may flow outwardly through the coronary lumens. 
     Further in accordance with the invention, mandrel members such as short segments of plastic tubing may be inserted into the lumens of the coronary artery segments, prior to tanning of the tissue, to maintain the patency of the lumens of the coronary artery segments. Ligatures may be tied about the coronary artery segments to hold the mandrel members in place during the tanning (i.e., chemical fixation) process. The mandrel members and any accompanying ligatures may then be removed after completion of the tanning process. 
     Still further in accordance with the invention, there is provided a method of surgical implantation of an aortic bioprosthesis of the foregoing character to effect a “total root” aortic valve replacement. Such method generally comprises the steps of: 
     1. surgically transecting the patient&#39;s right and left coronary arteries at locations which are spaced distances away from the wall of the patient&#39;s ascending aorta; 
     2. surgically removing a segment of the patient&#39;s ascending aorta, along with at least the leaflets of the endogenous aortic valve; 
     3. anastomosing the aortic bioprosthesis to the patient&#39;s native tissues such that the aortic bioprosthesis replaces the removed segment of the ascending aorta; and, 
     4. either, a) anastomosing the patient&#39;s native coronary arteries (or coronary artery bypass grafts) to the coronary segments of the bioprosthesis, at spaced distances from the wall of the aortic segment of the bioprosthesis or b) ligating or otherwise closing the lumens of the coronary segments and attaching the coronary patient&#39;s native coronary arteries (or coronary artery bypass grafts) at other locations as may be desirable in certain patients. 
     Still further in accordance with the invention, there is provided a method of surgical implantation of an aortic bioprosthesis of the foregoing character to effect replacement of a defective pulmonary valve. Such method generally comprises the steps of: 
     1. surgically removing the patient&#39;s pulmonary valve along with an adjacent segment of the pulmonary artery; 
     2. closing (e.g., ligating, embolizing or placing purse string sutures in) the coronary segments of the bioprosthesis to prevent leakage of blood out of the lumens of such coronary segments; and, 
     3. anastomosing the aortic bioprosthesis to the patient&#39;s native tissues such that the aortic bioprosthesis replaces the removed pulmonary valve and adjacent segment of pulmonary artery. 
     Still further in accordance with the present invention, there are provided methods of using the aortic bioprosthesis of the foregoing character to effect “mini-root” or “sub-coronary” replacement of a malfunctioning aortic valve. Such mini-root and sub-coronary aortic applications of the bioprosthesis are carried out in accordance with known techniques, by selectively cutting away distal portion(s) of the bioprosthesis and using the remaining portion of the bioprosthesis to carry out a mini-root or sub-coronary aortic implantation procedure. 
     Further aspects and elements of the present invention will become apparent to those skilled in the art, upon reading and understanding of the detailed description which follows, and viewing of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side perspective view of a stentless aortic bioprosthesis of the present invention having a handle-connection fixture mounted on the outflow end thereof. 
     FIG. 2 is a bottom perspective view of the stentless aortic bioprosthesis of FIG.  1 . 
     FIG. 3 a  is a plan view of the inflow end of a stentless aortic bioprosthesis of the present invention. 
     FIG. 3 b  is a plan view of the outflow end of a stentless aortic bioprosthesis of the present invention. 
     FIG. 4 is a longitudinal section view of the aortic bioprosthesis, through line  4 — 4  of FIG.  1 . 
     FIG. 4A is a longitudinal section view of the aortic bioprosthesis, as in FIG. 4, and showing a coronary protuberance closed; 
     FIGS. 5 a - 5   c  are step-wise illustrations of a preferred technique for performing a full-root replacement of a defective aortic valve with a stentless aortic bioprosthesis of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A. The Preferred Aortic Bioprosthesis having Coronary Protuberances 
     Turning now to FIGS. 1-4 of the drawings, there is seen a stentless aortic bioprosthesis  10  in accordance with this invention. This aortic bioprosthesis  10  is formed of a preserved segment of mammalian aorta  12  having an inflow rim or inflow end IE, an outflow rim or outflow end OE and the donor animal&#39;s aortic valve leaflets  20  positioned therewithin. Segments of the donor animal&#39;s right and left main coronary arteries  14   a,    14   b  extend from the aortic segment  12 , and such coronary artery segments  14   a,    14   b  have open, patent lumens extending therethrough. 
     The aortic bioprosthesis  10  of the present invention is preferably of porcine origin. After the tissue of which the bioprosthesis is formed has been harvested from the donor animal, the coronary artery segments  14   a,    14   b  are trimmed to a desired length, such as 1-6 mm and preferably as long as possible (i.e., up to the first coronary bifurcation present on each main coronary artery of the donor animal). Thereafter internal or external support members are inserted or attached to the coronary segments  14   a,    14   b  to maintain patency of the coronary segment lumens  15   a,    15   b  during subsequent tanning. Examples of internal supports which may be used to maintain such patency of the coronary segment lumens  15   a,    15   b  are mandrel members  16  which are sized and configured to be inserted into the lumens  15   a,    15   b  of the coronary artery segments  14   a,    14   b,  as shown in FIG.  1 . Such mandrel members  16  may comprise solid members of generally cylindrical configuration, or may comprise segments of tubular members as specifically shown in the drawings, such tubular members having bores  17  extending longitudinally therethrough. The presence of such bores  17  in the tubular mandrel members  16  can be used as passageways for pins or support members which are used to hold or suspend the bioprosthesis  10  during the tanning process. In instances where internal mandrel members  16  are used to maintain patency of the coronary lumens  15   a,    15   b,  ligatures  18  may be tied about the coronary artery segments  14   a,    14   b  following insertion of the mandrel members  16  therein, to frictionally retain the mandrel members  16  within the coronary artery segments  14   a,    14   b.  In the preferred embodiment shown in the drawings the mandrel members  16  are formed of silicone tubing, but they may be formed of other materials such as polyurethane, polyester, polytetraflouroethylene (PTFE), polyethylene, stainless steel, titanium or a metal alloy. 
     The bioprosthesis  10  having the mandrel members  16  inserted in its coronary segments  14   a,    14   b  is then exposed to a chemical agent (i.e., a fixative agent or tanning agent) which will form chemical cross linkages between connective tissue protein molecules present in the tissue of the bioprosthesis  10 . The chemical tanning agents which are useable for this purpose, formaldehyde, dialdehyde starch, hexamethylene diisocyanate and certain polyepoxy compound(s), as well as combinations of these agents. The presently preferred embodiment, shown in the drawings, is by immersion in a solution of 0.625% HEPES buffered glutaraldehyde at pressures of less than approximately 10 mmHg, as described in detail in U.S. Pat. No. 5,800,531, entitled System, Apparatus and Method for Chemical Fixation of Stentless Cardiac Valvular Bioprostheses, which is hereby expressly incorporated by reference. 
     After the tanning process is complete, the bioprosthesis  10  is removed from the tanning solution and the internal or external support members (e.g., mandrel members  16 ) are removed. As specifically shown in FIG. 4, in applications wherein internal support members such as the mandrel members  16  have been secured by ligatures  18 , such ligatures  18  will typically be removed prior to extraction of the mandrel members  16 . Thereafter, if necessary, any distal portions  19  of coronary artery segments  14   a,    14   b  of length L 2  located beneath or distal to the ligatures  18  may be cut away and discarded, so as to leave remaining coronary segments  14   a,    14   b  of length L 1  and of substantially normal anatomical configuration attached to the bioprosthesis  10 . In this regard, it is desirable that such ligatures  18  be placed as distal as possible, so as to maximize the length L 1  of the coronary artery segments  14   a,    14   b  which remain after the distal coronary segments  19  have been cut away and discarded. Preferably, the length L 1  of the coronary artery segments remaining after final trimming will be at least 2 mm and typically in the range of 2-6 mm, while the length L 2  of the discarded distal coronary segments  19  is preferably less than 5 mm. 
     After the internal or external support members (e.g., mandrels  16 ) have been removed and the coronary artery segments  14   a,    14   b  have undergone final trimming (if necessary), the bioprosthesis  10  is sterilized by a suitable technique, such as immersion in a biocompatible sterilization solution. The bioprosthesis is then measured to determine its outside diameter, usually rounded off to the nearest millimeter. For commercial applications, bioprostheses  10  which have outside diameters which would round off to an odd number of millimeters (e.g., 15, 17, 19, 21, 23, 25 , 27 and 29 mm) may be rejected. 
     After the bioprosthesis  10  has been sized, it is subjected to a second trimming step in which substantially all of the myocardial tissue is shaved away, leaving a thin cartilage rim adjacent to the right coronary septal shelf for reinforcement. The left and right coronary artery segments  14   a,    14   b  are allowed to remain. All trimming is conducted with the goal of leaving an intact aortic wall segment above the protruding coronary segments  14   a,    14   b,  such intact aortic wall segment being of sufficient width to a) maintain proper alignment of the commissure, b) prevent distortion of the bioprosthesis  10  during suturing, and/or c) permit replacement of a supracoronary segment of the patient&#39;s ascending aorta (e.g., a “total root replacement”) if so desired. 
     Finally, the inflow end IE of the bioprosthesis  10  is trimmed on the same plane as the cusps of the valve leaflets  20 , usually leaving an intact segment of about 3 to 4 mm in width as measured from the hinge of the leaflet. All of the fatty tissue in the aorta is trimmed away. As shown in FIGS. 3 a  and  3   b,  the resulting aortic segment contains three valve leaflets  20 , each of which is affixed to the aortic segment at a juncture. The inner edges  25  of the valve leaflets  20  meet when the leaflets  20  are in their closed positions, as shown in the drawings. Also, the leaflets  20  form commissures at their junctions with the aortic wall, and the leaflets are joined to the aortic segment  12  along a leaflet junctures  29 . The wall of the aortic segment  12  adjacent junctures  29  forms the Sinus of Valsalva (not shown). The leaflet  20  closest to the right coronary artery segment  14   a,  is positioned somewhat asymmetrically with respect to the other two leaflets  20 . 
     A fabric covering  28  may optionally be disposed about the inflow end IE of the bioprosthesis  10  and/or upon a portion of one side of the bioprosthesis  10  which corresponds to the right coronary septal shelf, as shown in FIG.  1 . This fabric covering  28  enhances the strength of the bioprosthesis  10  which is sutured to the native aortic annulus, and thus serves to deter the sutures from tearing through the tissue of the bioprosthesis  10 . This fabric covering  28  may be formed of a thin, biocompatible material which is strong enough to hold sutures. For example, such fabric covering  28  may be formed of woven polyester having a thickness of 0.008 inch″ and a weight of 72 grams per square meter. The fabric used for the covering  28  is preferably cut on the diagonal to assure a snug fit around curved surfaces. The fabric is then sewn to the bioprosthesis  10  by hand, using a nonabsorbable, biocompatible thread. 
     Mid-cusp markings  32 , such as stitches formed of thread of a color which contrasts with the body of the bioprosthesis  10 , may be formed on the fabric covering  28  along the inflow rim, preferably at the mid-cusp point of each leaflet  20 , to aid the surgeon in aligning the bioprosthesis  10  with the patient&#39;s natural aorta. For instance, if the cloth is white, the markings  32  may be stitches of navy blue thread, and the like. An exemplary light green marking thread is Polyester PTFE-Coated thread of 6.0 size, having a denier of 110-130. 
     Additional commissure markings  33  may also be formed on the fabric covering and/or inflow end of the bioprosthesis  10  at the locations of the valvular commissures to aid the surgeon in aligning the bioprosthesis with the patient&#39;s native anatomical structures. These optional commissure markings  33  may be formed in the same manner as described hereabove with respect to the mid-cusp markings  32 , but will preferably of a color which is different from the mid-cusp markings  32  so as to permit the surgeon to easily distinguish between the mid-cusp markings  32  and commissure markings  33 . 
     A valve retainer fixture  34  may be attached to the outflow end OE of the bioprosthesis, as shown, to facilitate the attachment of an elongate handle thereto. Such valve retainer fixture  34  may be of the type described in U.S. Pat. No. 5,336,258 (Quintero et al.). Alternatively, in lieu of the use of such valve retainer fixture  34 , the bioprosthesis may be mounted within a cage-like holding apparatus of the type described in copending U.S. patent application Ser. No. 08/723,420, entitled Bioprosthetic Heart Valve Implantation Device. 
     B. Methods of Implanting the Preferred Aortic Bioprosthesis having Coronary Protuberances: 
     The currently used methods for surgical implantation of the bioprosthesis  10  of the present invention typically require that the patient be placed under general anesthesia and on cardiopulmonary bypass. An incision is made in the patient&#39;s chest wall (e.g., a median stemotomy) and the heart is exposed. The malfunctioning endogenous valve (typically the aortic valve but possibly another cardiac valve such as the pulmonary valve located between the right ventricle and the pulmonary artery) is then removed and the bioprosthesis  10  (or a portion thereof) is sutured into place to act as a prosthetic replacement for the previously-removed endogenous valve. 
     The bioprosthesis  10  shown in FIGS. 1-4 will typically be implanted at the aortic position to replace the endogenous aortic heart valve. However, in some instances the bioprosthesis  10  may also be utilized to replace another heart valve such as a malfunctioning pulmonary valve located between the right ventricle and pulmonary artery. When used to replace a heart valve other than the aortic valve, the lumens  15   a,    15   b  of the coronary segments  14   a,    14   b  will typically be closed off (as seen in FIG. 4A) by suitable closure means such as ligation, embolization, or placement of a purse string suture. 
     i Subtotal Aortic Applications of the Bioprosthesis: 
     In the mini-root and sub-coronary techniques previously known in the art, a bioprosthesis  10  of appropriate size is selected and is either a) trimmed along marker thread  30  or at some other location selected by the surgeon to separate the aortic root portion of the bioprosthesis  10  (i.e., the base of the aortic segment  12  having the leaflets  20  disposed therein) from the remainder of its aortic segment  12  and coronary segments  14   a,    14   b  or  b ) the lumens  15  of the coronary segments  14   a,    14   b  are closed by ligation, placement of a purse string suture thereabout, embolization of other suitable means to prevent blood from subsequently leaking out of the lumens  15  of those coronary segments  14   a,    14   b.  Thereafter the bioprosthesis  10  may be implanted at the aortic location to replace the patient&#39;s endogenous aortic valve, without attachment of coronary arteries or other vessels or grafts to the coronary segments  14   a,    14   b.    
     ii. Total-Root Aortic Applications of the Bioprosthesis: 
     In other applications, the entire bioprosthesis  10 , including the entire aortic segment  12  and coronary artery segments  14   a,    14   b  may be implanted at the aortic location, in accordance with the procedure shown in FIGS. 5 a - 5   c.  In this procedure, the patient&#39;s right coronary artery RCA and left coronary artery LCA are transected at locations which are spaced distances away from the wall of the patient&#39;s ascending aorta AO and a segment of the patient&#39;s ascending aorta AO is removed and the native aortic valve leaflets are surgically excised and removed. 
     A bioprosthesis  10  of correct size is selected, and a handle (not shown) is attached to the handle connection fixture. The handle (not shown) is then used to position the bioprosthesis  10  such that its inflow end IE is in juxtaposition to the aortic annulus, and a proximal anastomosis PA is formed to secure the inflow end IE of the bioprosthesis  10  to the native aortic annulus. 
     Thereafter, the native right coronary artery RCA is trimmed to length, if necessary, and a right coronary anastomosis CAR is formed between the transected end of the right coronary artery RCA and the distal end of the right coronary segment  14   a  of the bioprosthesis  10 . The native left coronary artery LCA is then trimmed to length, if necessary, and a left coronary anastomosis CAL is formed between the transected end of the left coronary artery LCA and the distal end of the left coronary segment  14 b of the bioprosthesis  10 . The patient&#39;s coronary arterial vasculature is thereby connected to the aortic segment  12  of the bioprosthesis  10  such that a portion of the arterial blood which subsequently flow is into the aortic segment  12  of the bioprosthesis  10  will flow into the right and left main coronary arteries RCA, LCA to perfuse the patient&#39;s myocardium in accordance with normal hemodynamics. 
     In patients where coronary artery bypass graft(s) are present, one of more openings may be made in the aortic segment  12  of the bioprosthesis, and the ends of the bypass graft(s) may be sutured to such openings in accordance with well known surgical technique. 
     Finally, the outflow end of the handle (not shown) and valve retainer fixture  34  are disconnected and removed, and to end approximation with the outflow end of the bioprosthesis  10 . A distal anastomosis DA is then formed therebetween, as shown in FIG. 5 c.    
     Thereafter, the patient may be removed from cardiopulmonary bypass and the chest incision may be closed. 
     The invention has been described hereabove with reference to certain presently preferred embodiments only, and no attempt has been made to exhaustively describe all possible embodiments of the invention. For example, with respect to the method for implantation of the bioprosthesis  10 , it may be possible to accomplish implantation of the bioprosthesis by a minimal access (e.g. “keyhole”) technique without the need for forming large incisions in the patient&#39;s chest wall, but rather by forming a plurality of small minimal access incisions—and using a thoracoscopic technique to perform the implantation surgery. Accordingly, it is intended that the above-described preferred embodiments as well as all possible other embodiments of the invention be included within the scope of the following claims.