Clinical Experience with a Dacron Velour-Covered Teflon-Disc Mitral- Valve Prosthesis

Transcription

1 Clinical Experience with a Dacron Velour-Covered Teflon-Disc Mitral- Valve Prosthesis Arthur C. Beall, Jr., M.D., Robert D. Bloodwell, M.D., Domingo Liotta, M.D., Denton A. Cooley, M.D., and Michael E. De Bakey, M.D. P rosthetic replacement of cardiac valves now has become a reliable method of management for advanced cardiac valve disease. Despite continued improvements in prosthetic design, however, incidence of late complications has remained significant, particularly those associated with thromboembolic phenomena. Recent evidence suggests that cloth coverage of these prostheses may encourage more complete healing with subsequent reduction in such complications [3]. A theoretical disadvantage to this approach is that tissue buildup on the cage legs of a totally cloth-covered valve prosthesis might impinge on ball or disc travel [l]. Additionally, thrombus formation following valve replacement usually originates at the cloth sewing ringmetal seat interface, where complete healing probably never occurs [9]. In order to eliminate this cloth sewing ring-metal seat interface, prevent possible tissue buildup on the cage legs, and circumvent possible complications associated with in vivo Silastic changes [ll], a new Teflon-disc mitral-valve prosthesis was developed with the caged legs covered with Teflon and the entire sewing ring and base covered with Dacron velour (Fig. 1). EXPERIMENTAL EVALUATION Design of the prosthesis is such that diameter of the disc (line A, Fig. 2) is greater than the diagonal from the orifice on one side to the distal portion of the cage legs on the opposite side (line B, Fig. 2), so that cocking of the disc is impossible. Frustrum area (measured at line C, Fig. 2) in the 4 available" sizes From the Cora and Webb Mading Department of Surgery, Baylor University College of Medicine, and the Methodist, St. Luke's Episcopal, Texas Children's, Ben Taub General, and Veterans Administration Hospitals, Houston, Tex. Supported in part by the U.S. Public Health Service (HE-01117) and (HE-05415) and the Texas and Houston Heart Associations. Presented at the Fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, La. Jan , *Surgitool Inc., Pittsburgh, Pa. 402 THE ANNALS OF THORACIC SURGERY

2 Dacron Velour-Covered Valve FIG. I. Current model of Dacron velour-covered Teflon-disc mitral-valve prosthesis. equals 120% of the orifice area (measured at line D, Fig. 2). Accelerated fatigue testing of the final model in excess of 1,000,000,000 cycles has demonstrated no evidence of significant wear of the Teflon disc or Teflon cage legs. In vivo experiments then were begun using calves for mitral-valve replacement. No anticoagulants were employed after neutralization of heparin required for extracorporeal circulation. Animals have been sacrificed up to 6 months following operation and have demonstrated rapid tissue encapsulation of the Dacron velour-covered sewing ring and base without evidence of thrombus formation or fibrous-tissue proliferation onto the cage legs (Fig. 3). Based on these encouraging experimental results, clinical trial was initiated. CLINICAL EXPERIENCE During the 11-month period from February 1, 1967, through Uecember 31, 1967, one or more of these prostheses were employed in 128 clinical cases in the Baylor University College of Medicine Affiliated Hospitals. In 8 patients the tricuspid valve was replaced, alone in 2, in conjunction with mitral-valve replacement in 5, and in conjunction with replacement of the mitral and aortic valves in 1. Thirty patients underwent mitral- and aortic-valve replacement. Isolated replacement of the mitral valve was carried out in 90 patients. All of these patients were in Class 111 or Class IV of cardiac function, according to the New York Heart Association Classification, and no patient was denied operation because of far-advanced, end-stage cardiac deteriorization. A number of opera- FIG. 2. Valve dimensions (see text). VOL. 5, NO. 5, MAY,

3 BEALL ET AL. A B FIG. 3. Prosthesis from calf at time of sacrifice 6 months after operation (A) from atrial side and (B) from ventricular side. Note complete encapsulation of base and absence of thrombus formation or fibrous tissue buildup on clear Teflon-covered cage legs. tions, particularly for multiple-valve replacement, were performed as salvage procedures on moribund patients. The technique of cardiopulmonary bypass employed for all operations consisted in the use of disposable plastic oxygenators* primed with 5% dextrose in distilled water under normothermic conditions [51. A right-sided approach to the mitral valve was preferred, entering the left atrium anterior to the right pulmonary veins. The diseased mitral valve was excised, including chordae tendinae and tips of the papillary muscles. Selection of size of the mitral prosthesis for use in each case was based upon size of the left ventricular cavity and ideal cardiac output, rather than upon size of the mitral-valve annulus. This method of sizing was considered important, in order to prevent use of too large a prosthesis in which the disc might result in subannular obstruction. Prosthetic fixation was accomplished by interrupted figure-of-eight sutures of double-armed 1-0 or 2-0 Tevdek or Tycron, passing both ends of the suture through the outer thin portion of the sewing ring and tying on the atrial side. This placed the mounting diameter of the prosthesis within the mitral-valve annulus and the "hat brim" portion of the sewing ring on the atrial side where it covered raw annular surfaces. A similar technique of insertion was employed for tricuspid-valve replacement. Among the 90 patients undergoing isolated mitral-valve replacement there were 11 deaths within 30 days of operation, an operative mortality rate of 12.1%. There were no deaths in either of the patients in whom isolated tricuspid-valve replacement was performed. Operative mortality rate in patients undergoing multiple-valve replacement approximated one-third, related primarily to severity of illness in patients selected for replacement. These figures are essentially the same as those previously reported from these institutions using other types of mitral-valve prostheses, and causes of operative deaths likewise were similar [2, 6, 71. Of particular significance, there have been only 2 late deaths during this 11-month period, and one of these was caused by two gunshot wounds of the head 2 months after operation. The other late death occurred 4 months following use of this prosthesis to replace a malfunctioning prosthesis of another type "Travenol Laboratories, Inc., Morton Grove, Ill. 404 THE ANNALS OF THORACIC SURGERY

4 Dacron Velour-Covered Valve FIG. 4. Prosthesis in patient 6 months after insertion at time of successful reoperation for repair of perivalvular leak. and was related to an uncontrollable arrhythmia in association with uppergastrointestinal-tract hemorrhage. At autopsy in both patients there was no evidence of prosthetic malfunction, thrombus formation on the prosthesis, or fibrous-tissue extension onto the cage legs. The base of the prosthesis which had been in place for 4 months was well encapsulated, and the prosthesis which had been in place for 2 months was almost completely covered. One of the first patients in whom this prosthesis was employed developed a perivalvular leak, and at successful reoperation for repair of the leak 6 months later, this prosthesis was otherwise well healed with no evidence of thrombus formation (Fig. 4). Furthermore, there have been only two thromboembolic complications. One patient, who died 6 days after mitral-valve replacement, had experienced a cerebrovascular accident 2 days prior to death; at autopsy no thrombotic material was seen on the prosthesis, a myocardial infarction appeared to be the cause of death, and there was a large mural thrombus on the ventricular surface of the infarct. The other patient had sudden onset of right hemiparesis 5 days following mitral-valve replacement, but complete recovery ensued spontaneously, and he has remained asymptomatic. Several patients now have returned for recatheterization 6 months or more after operation. Findings have demonstrated impressive return to or toward normal hemodynamics. Significantly, one of these patients had a small-sized prosthesis in place, and there was no end-diastolic gradient across the prosthesis at a cardiac output of 5.5 liters per minute. These prostheses, however similar to all cardiac-valve prostheses, do not function efficiently at rates of 150 per minute or more, as was produced in one of these patients during catheterization by extremely strenuous exercise on an ergometer. Another patient stopped taking digitalis 4 weeks after mitral-valve replacement and reentered the hospital in pulmonary edema secondary to atrial fibrillation, with a ventricular response of 180 per minute. Pulmonary edema immediately cleared upon rapid redigitalization, with resumption of a normal ventricular rate, and has not recurred. DISCUSSION Development of caged-ball prostheses, and subsequent experience with their use, now allows successful valve replacement in most pa-

5 BEALL ET AL. tients with acquired valvular heart disease. During the more than 7 years which have passed since the first successful mitral-valve replacement with a caged-ball prosthesis [12], design changes have been numerous, including development of both double-caged [4] and disc [8, 101 prostheses, in an effort to improve hemodynamic characteristics and to reduce complications. Despite such improvements in prosthetic design, thromboembolic complications following mitral-valve replacement have remained a serious problem, even in patients well regulated on anticoagulant therapy, and must be weighed seriously in accepting patients for valve replacement. Although duration of use of the mitral prosthesis reported still is too short for long-term statistical validity, results of its use over the past 11 months strongly suggest that elimination of the sewing ring-metal seat interface significantly reduces incidence of thromboembolic complications. During essentially similar periods of study two previous types of mitral prostheses employed in these same institutions resulted in a 9% [6] and a 14% [7] incidence of such complications. Without consideration of whether or not they were related to the mitral prosthesis itself, only 2 thromboembolic episodes in 128 patients certainly appears within the range of acceptability, and for the past 9 months none of the patients operated upon by one of us (A. C. B.) has received anticoagulants. If this low incidence of thromboembolic complications is maintained, and particularly if the suggestive evidence that anticoagulants are not required with this mitral prosthesis proves to be true, then recommendation of mitral-valve replacement earlier in the course of valve disease may become more acceptable. Far too often such patients are not referred for operation until an end-stage of cardiac decompensation has been reached, at which time functional recovery of the myocardium may no longer be possible. Only by operation earlier in the course of disease can the current operative mortality rate associated with mitral-valve replacement be significantly reduced. SUMMARY Despite numerous modifications in mitral-valve prostheses, incidence of thromboembolic complications has remained significant. Recent evidence has suggested that elimination of the sewing ring-metal seat interface of a prosthesis may reduce such complications by allowing endothelial coverage of this area. Therefore, a Teflon-disc mitral prosthesis was developed with the entire sewing ring and seat covered with Dacron velour. After accelerated fatigue testing and animal investigations, clinical trial of this prosthesis was begun, and over the past 11 months has included 128 cases. Operative mortality rate has 406 THE ANNALS OF THORACIC SURGERY

6 Dacron Velour-Covered Valve been similar to that for other mitral-valve prostheses, but there have been only 2 late deaths, one due to two gunshot wounds of the head. Only two thromboembolic complications have occurred, and one of these was in a patient dying from a myocardial infarction with a mural thrombus. Such results strongly suggest significant advantages of employing this prosthesis for mitral-valve replacement. REFERENCES Beall, A. C., Jr., Bloodwell, R. D., Liotta, D., Cooley, D. A., and De Bakey, M. E. Elimination of sewing ring-metal seat interface in mitral valve prostheses. Circulation. In press. Beall, A. C., Jr., Bricker, D. L., Cooley, D. A., and De Bakey, M. E. The use of valve replacement in the management of patients with acquired valvular heart disease. Amer. J. Surg. 110:834, Bronchek, L. I., and Braunwald, N. S. Thrombus resistant rigid prosthetic heart valves covered with porous synthetic fabric. Trans. Amer. SOC. Artif. Intern. Organs 13:101, Cartwright, R. S., Smeloff, E. A., Davey, T. B., and Kaufman, B. Development of a titanium double-caged full-orifice ball valve. Trans. Amer. SOC. Artif. Intern. Organs 10:231, Cooley, D. A., Beall, A. C., Jr., and Grondin, P. Open heart operations using disposable oxygenators, 5 per cent dextrose prime, and normothermia. Surgery 52:713, Cooley, D. A., Bloodwell, R. D., Beall, A. C., Jr., Gill, S. S., and Hallman, G. L. Total cardiac valve replacement using SCDK-Cutter prosthesis. Ann. Surg. 164:428, Cooley, D. A., Bloodwell, K. D., and Hallman, G. L. Mitral valve replacement with a discoid prosthesis. Ann. Thorac. Surg. 5:487, Cross, F. S., and Jones, R. D. A caged-lens prosthesis for replacement of the aortic and mitral valves. Ann. Thorac. Surg. 2:499, De Bakey, M. E., Jordan, G. L., Jr., Beall, A. C., Jr., O Neal, R. M., Abbott, J. P., and Halpert, B. Basic biologic reactions to vascular grafts and prostheses. Surg. Clin. N. Amer. 45:477, Kay, J. H., Kawashima, Y., Kagawa, Y., Jsuji, H. K., and Redington, J. V. Experimental mitral valve replacement with a new disc valve. Ann. Thorac. Surg. 2:485, Pierie, W. R., Hancock, W. D., Koorajian, S., and Starr, A. Materials and heart valve prostheses. Bull. N.Y. Acad. Sci. In press. Starr, A,, and Edwards, M. L. Mitral replacement: Clinical experience with a ball valve prosthesis. Ann. Surg. 154:726, DISCUSSION DR. FREDERICK S. CROSS (Cleveland, Ohio): I think that it is apparent that the low-profile disc valves are becoming the valves of choice for use in the mitral area. The current problems related to all valve prostheses are wear and thrombus formation on the cage. Early criticism of the disc valve suggested that there would be edge wear because of the relatively fixed position of the disc in the cage in contrast to a free tumbling ball. It has been our observation, in over three years experience with disc valves, that the disc does not wear unless something, such as thrombus accumulation on the cage, causes abnormal function. This leaves the problem of thrombus on the valve, and, like everyone else, VOL. 5, NO. 5, MAY,

7 BEALL ET AL. we are interested in further reducing the already decreasing incidence of thromboembolic problems related to the use of prosthetic valves. In order to accomplish this we have taken our existing disc mitral valve, enlarged the orifice to compensate for the cloth covering, and covered the cage, exclusive of the legs, with a thin Dacron mesh. We have chosen this material on the basis of the work done by Dr. Nina Braunwald at the National Institutes of Health. It is felt that this modified valve will decrease the incidence of thrombus formation because it eliminates the cloth-metal interface in the ring. For many years Dr. Richard Jones and I have been attempting to make the dog the animal of choice for valve research by overcoming the high incidence of thrombus formation on prosthetic valves. I think we have finally arrived at this goal and now can test valves in large numbers inexpensively and conveniently. For instance, disc valves with completely cloth-covered rims of several designs have been in place in dogs for as long as one year. There has been good tissue ingrowth into the cloth with no fibrin accumulation on the legs of the cage unless a leg has been in contact with the ventricular wall. Such long-term observations have encouraged us to make the valve with the completely covered rim available for clinical use. We are also evaluating total cloth-covered disc valves in the dog; however, we have found, as Dr. Braunwald has in the calf, that there is abrasion of the disc by the cloth-covered cage legs. This can be alleviated partially by the use of an undersized disc. In order to eliminate the abrasion problem seen with silicone and polypropylene discs, hollow titanium discs are now being evaluated in the totally cloth-covered cage. I would like to reemphasize the use of the dog in our valve studies. We recently have over a 90% survival rate for one month or more following valve insertion without postoperative anticoagulants. This increased survival has been made possible by eliminating postoperative bacteremia in the dogs by preoperative sterilization of the bowel with diet and antibiotics, and postoperative use of cephaloridine. In those dogs in which bacteremia is eliminated survival is high and, in turn, the incidence of thrombus accumulation on the valves is low. This is in marked contrast to dogs with demonstrable postoperative bacteremia. DR. JEROME H. KAY (Los Angeles, Calif.): We have inserted approximately 250 disc valves into the mitral and tricuspid areas of dogs and cows. During the past 2 years we have inserted our Kay-Shiley disc valve into approximately 125 cows. This valve was first presented two years ago at the meeting of this Society. This valve had a fair amount of exposed metal. Forty-four patients have been discharged following insertion of this original valve during the past 2% years. Four patients had peripheral emboli. In 3 patients, the cerebral symptoms were transient, but in one, the patient was left with a permanent hemiplegia and aphasia. Following the work of Drs. Nina Braunwald and A. Glenn Morrow at the National Heart Institute, we have been covering our disc valve with different types and amounts of cloth. Cows with this valve in the mitral area were sacrificed from 2 weeks to 6 months following surgery. Of the cows that we operated upon, 90% survived and were sacrificed. With the 100% Dacron clothcovered flange there was a marked decrease in the orifice size, about 35 to 40%. For this reason, we thought it would be important to leave a small amount of metal on the inside of the flange to prevent the overgrowth of tissue and the decrease in orifice size. With the same experimental valve covered with the same Dacron velour as used clinically by Dr. Beall, there was thrombus formation on the valve in the majority of these animals. In fully one-third of the animals there was marked thrombus formation and pronounced overgrowth of tissue. We feel very strongly that Dacron velour cloth was by far the poorest of all the materials tested. 408 THE ANNALS OF THORACIC SURGERY

8 Dacron Velour-Covered Value In some experiments we covered the struts with Dacron cloth; in these animals there was irregular growth of neointima and at many areas there was marked overgrowth of the neointima on the struts. I have my doubts as to the wisdom of completely cloth-covering the struts of any valve. We do not think that our parallel struts are a source of emboli. In the experimental animal we have used metal discs, as well as Teflon discs. We have also used our original Silastic disc in many experiments. We feel strongly from our experimental and clinical results that the Silastic disc is still the best of all. I am quite convinced that a Silastic disc will not produce the difficulties seen with the Silastic ball in the aortic area. In a disc valve that we have been most impressed with in our experiments with dogs as well as cows the cloth is knitted Teflon. There is a very small amount of metal present at the inside of the orifice of the flange. This is to prevent overgrowth of neointima that always occurs in such large amounts with the completely cloth-covered flange such as that Dr. Beall demonstrated today. we have used this valve since April, 1967, in 40 patients. There have been no emboli in these 40 patients. We feel strongly that one should not completely cover the flange, but should only cover it enough so that a small amount of metal is present inside the orifice to prevent overgrowth of tissue. I do not think one should completely cover the struts of any valve and one should definitely not use Dacron velour on a valve. From our animal experiments I am quite sure that there will be a high incidence of emboli and valve thrombosis if a Dacron velour-covered valve is used clinically as suggested by Dr. Beall. DR. ALBERT STARR (Portland, Ore.): Certainly any consideration of lowprofile mitral prostheses should take into account what has been achieved and can be achieved with the ball-valve prostheses. The extended cloth prosthesis (or a model 6120 Starr-Edwards valve) has now been followed up to 33 months (to January, 1968) and has an overall incidence of thromboembolic complications of 7%. The completely cloth-covered mitral prosthesis (or model 6300) has been in clinical trial since March, 1967; there have been 25 implantations with no deaths or late emboli despite the absence of anticoagulant treatment in half the patients who are participating in the double blind study. Edge wear and ease of interference of poppet motion by clot are two of the main disadvantages of the low-profile prosthesis. Nevertheless, there may be a few rare instances in which a small size ball valve may be too large to fit into a small left ventricle. In three such cases we have employed a hollow metallic disc valve in the mitral position providing hemodynamic function comparable to the same size ball valve. The low-profile valve (or model 6100) has a felt-padded Teflon cloth orifice. A Dacron sewing ring, enclosing a silicone insert, provides a great deal of compressibility to the prosthesis, an important feature in reducing the incidence of leak. The polished stellite struts provide a broad bearing area for the heathardened poppet, thereby minimizing the possibility of strut wear. While we are very pleased with the design of this prosthesis, there is some additional risk in the use of all low-profile prostheses over a prosthesis that encompasses a freely tumbling poppet such as a ball valve. I think that these low-profile valves will find their best application in situations where there is some anatomic disproportion between the ventricular aspect of the ball valve and the size of the left ventricle. Otherwise, the risk of using these prostheses would be unwarranted, considering the results that we can achieve with a freely tumbling poppet in a ball valve. DR. JOHN S. VASKO (Columbus, Ohio): I would like to congratulate Dr. Beall and his associates for their work, which appears to be a significant evolutionary VOL. 5, NO. 5, MAY,

9 BEALL ET AL. step in the development of the ideal prosthetic mitral valve. Dr. Beall emphasized the nonthrombogenic characteristics of this valve; however, the use of a more durable occluder may also be extremely important. We have been worried about some of the characteristics of Silastic occluders, and a recent experience of mine has amplified this concern. A 26-year-old young woman, who had a mitral valve placed elsewhere two and a half years ago, was brought to our emergency room moribund, in shock, with pulmonary edema, and anuric. The sound of the artificial valve was not audible. We operated on her as an emergency and found that the mitral-valve Silastic disc was incarcerated in the valve cage orifice in the open position. The Silastic disc showed severe circumferential wear, and it was roughened, severely discolored, and impregnated with a cloudy yellow material. I replaced this valve with a ball-valve prosthesis but she did not recover. The history was interesting in that approximately six months after her first operation, and after a relatively uneventful course, she had developed increasing signs of mitral regurgitation including a systolic murmur. We speculate that this early regurgitation was a result of the extreme edge wear of the Silastic disc which then was seating in an eccentric position. Later this wear decreased the disc valve sufficiently to permit its wedging into the valve orifice. The valve was a Hufnagle discoid mitral-valve prosthesis with a cage of polycarbonate and a disc of Silastic-coated polycarbonate. The Silastic peeled from the edges of the disc and may have embolized, and it possibly accounted for the multiple infarcts observed in the kidneys and spleen at autopsy. DR. BEALL: I would certainly like to thank the discussants for their remarks, and I am happy to see that, even though he still opposes the low-profile valves, Dr. Starr does have one of his own now. I have been asked about the use of anticoagulants in these patients, and I don t know the answer. All I can say at the present time is that within the series I presented, I personally have not used anticoagulants on my patients. The use by my associates has been variable. In regard to use of the Dacron velour covering, I feel just as strongly that it is good as Dr. Kay does that it is bad. Changes in the variant Silastic disc, or the possibility of this occurring, was our reason for going to the use of a Teflon disc and Teflon covering of the cage legs-thus having Teflon against Teflon. I don t think we can ever eliminate wear, but Teflon against Teflon certainly reduces wear, and we have had enough experience with Teflon to be reasonably certain that it won t absorb fatty acid esters. Again, I think the field of valve replacement is changing rapidly now in that we are getting improved valves from many different directions. It appears that one of these directions is toward more and more coverage of metal, and the incidence of thromboembolic phenomena is going down. One case has been reported to us in which one of the prostheses which I presented to you has become occluded with thrombus, but this is in an overall clinical series around the country of somewhere between 700 and 800 valves. We are seeing lower incidences of thromboembolic phenomena, but I doubt that we will ever eliminate them entirely. 410 THE ANNALS OF THORACIC SURGERY