The Bjork-Shiley Prosthesis

Transcription

1 The Bjork-Shiley Prosthesis A Significant Advance in Aortic Valve Replacement Javier Fernandez, M.D., Vladir Maranhao, M.D., Alden S. Gooch, M.D., Dryden Morse, M.D., and Henry T. Nichols, M.D." ABSTRACT Replacement of the aortic valve with the new tilting-disc Bjork- Shiley prosthesis was performed in 133 patients during the period May, 197, to September, Thirty-two of these had simultaneous implantation of a Beall mitral valve prosthesis. None of the 13 early deaths (9.8%) or 7 late deaths (5.2%) were attributable to malfunction of the prosthesis or embolic complications. Objective evidence of improvement was noted by cardiac catheterization and treadmill exercise tests following operation. Clinical improvement was found in 97% of the survivors during the three to nineteen months of follow-up. S ince 1961 we have employed a variety of different prostheses for aortic valve replacement. Because of the early complications-particularly low cardiac output syndrome-and unfavorable late results due to thromboemboli, ball variance, and hemolysis with the use of several models of the Starr-Edwards aortic prosthesis [2, 4, 7, 91, a clinical trial with calf aortic valve transplantation was undertaken in 1967 [ 121. Late degeneration and failure of the heterografts produced catastrophic results [8]. As an alternative, in May, 197, we turned to the tilting-disc Bjork- Shiley aortic valve prosthesis [l]. This report relates our clinical results in 133 consecutive patients undergoing aortic valve replacement with the prosthesis. Clinical Material From May, 197, to September, 1971, 133 patients underwent aortic valve replacement with the Bjork-Shiley prosthesis? at the Hahnemann Medical College Hospital in Philadelphia and the Deborah Hospital in Browns Mills, New Jersey. Twenty patients had had previous mitral commissurotomy, 2 had undergone a previous Beall mitral valve prosthesis implantation, 1 had received an aortic calf valve heterograft, and 5 had From the Deborah Hospital, Browns Mills, N.J., and Hahnemann Medical College Hospital, Philadelphia, Pa. *Deceased. Presented at the Eighth Annual Meeting of The Society of Thoracic Surgeons, San Francisco. Calif., Jan , We wish to acknowledge the assistance of Miss Bernadette Brennan, R.N., in the preparation of this paper. Address reprint requests to Dr. Fernandez, Deborah Hospital, Browns Mills, N.J tshiley Laboratories Inc., Santa ha, Calif.

2 FERNANDEZ ET AL. TABLE 1. NATURE OF PRIMARY AORTIC AND CONCOMITANT VALVULAR LESIONS Lesion Primary aortic (total 133 patients) AS AR AS 8c AR concomitant Mitral (total 6 patientsa) MS MR MS & MR Tricuspid (total 4 patients) TR No. of Patients "Thirty-two had mitral valve replacement; 16 had commissurotomy. AS = aortic stenosis; AR = aortic regurgitation: MS = mitral stenosis; MR = mitral regurgitation; TR = tricuspid regurgitation. had a Starr-Edwards aortic prosthesis inserted. Of the total group, 11 patients had isolated aortic valve replacement and 32 had combined aortic and mitral replacement. There were 87 men and 46 women ranging in age from 17 to 69 years. The selection of patients for operation was based on clinical findings supplemented by cardiac catheterization data, aortography, and coronary cineangiograms as indicated. More than 5% of our patients underwent graded treadmill exercise testing 161 as an additional means of arriving at an objective measure of their cardiac disability. Of the 133 patients, 18 (81%) were considered to be in Functional Class I1 or 111 according to the New York Heart Association (NYHA) classification. Fourteen (1.5%) patients who had had various manifestations of heart failure in the past and significant hemodynamic changes were in Class I. The other 11 patients (8.2%) were in Class IV. Sixty-two patients had combined aortic stenosis and regurgitation, 37 had predominant regurgitation, and 34 had predominant stenosis (Table 1). Associated mitral valve disease was observed in 6 patients, of whom 32 required concomitant mitral valve replacement with a Beall prosthesis* and 16, mitral commissurotomy. Eight patients required additional procedures: tricuspid plication in 3, resection of an aneurysm of the sinus of Valsalva in 2, excision of an ascending aortic aneurysm in 1, and coronary revascularization with a bypass vein graft in 2. The valvular lesions appeared to be of rheumatic origin in 117 patients. In another 15, the aortic valve was bicuspid or a small third rudimentary 'Surgitool Co., Pittsburgh, Pa THE ANNALS OF THORACIC SURGERY

3 Bjork-Shiley Prosthesis cusp was present, a configuration most likely of congenital origin. One patient had Marfan s syndrome. In 7 patients there was a history of acute or subacute bacterial endocarditis. These included several patients with a severe degree of left ventricular enlargement preoperatively, 1 with acute lesions of subacute bacterial endocarditis, another with wide-open aortic regurgitation from a previous calf valve heterograft, and 1 with coronary artery disease that necessitated a vein bypass graft to his left anterior descending coronary artery. Surgical Technique The aortic valve was approached through a midsternal incision. Total cardiopulmonary bypass with hemodilution and mild hypothermia was employed, and the coronary arteries were perfused continuously in all patients. The aortic prosthesis was anchored to the annulus by means of multiple interrupted sutures. Care was taken to avoid having the cut end of the sutures interfere with the motion of the prosthetic disc. The disc was usually oriented so that it opened toward the noncoronary cusp. When a concomitant mitral valve operation was indicated, the mitral valve was approached through the right interatrial groove. All patients received anticoagulation with warfarin postoperatively, starting within one week of operation. An attempt was made to maintain the prothrombin time between 25 and 32 seconds. Immediate nonfatal postoperative complications were similar to those found with other types of open-heart operations, but none appeared related to the valve in the present series. Three patients manifested signs of neurological damage soon after anesthesia. Two recovered totally within a few days, and 1 still had a minor speech defect eight months after operation. All had severe calcification of the aortic valve. Operative Mortality The overall operative mortality up to one month postoperatively was 13 deaths, or 9.8% (Table 2). No death was directly related to the mechanical performance of the prosthetic valve. The postmortem examination done in 12 patients showed an intact, well-functioning prosthesis in situ in each case. The greater proportion of the deaths occurred as a result of mechanical failure of the heart or persistent acute or subacute bacterial endocarditis, which had been confirmed by blood cultures in 6 patients. Only 1 patient had evidence of recent lesions at the time of operation. Most of the deaths occurred in the operating room or in the intensive care unit within 48 hours after operation. Further causes of death included acute pulmonary insufficiency, thrombosis of the abdominal aorta, postoperative shock, and massive gastrointestinal hemorrhage. VOL. 14, NO. 5, NOVEMBER,

4 FERNANDEZ ET AL. TABLE 2. ANALYSIS OF OPERATIVE MORTALITY AVR AVR & MVR Cause of Death (11 patients) (32 patients) Total Deaths Myocardial failure Irreversible ventricular fibrillation 1 1 Acute myocardial infarction 1 1 Postoperative shock 1 1 Acute pulmonary insufficiency 1 1 Thrombosis of abdominal aorta 1 1 Massive gastrointestinal hemorrhage 1 1 Total 6 (6%) 7 (22%) 13 (9.8%) AVR = aortic valve replacement; MVR = mitral valve replacement. Table 2 demonstrates the marked difference between the 6% mortality (6 of 11 patients) among those who required single aortic valve replacement and the 22% mortality (7 of 32 patients) in the aortic and mitral valve replacement group. Similarly, those patients who presented a more severe degree of cardiac disability clinically had a higher mortality. In 64 Class I and I1 patients who had single aortic valve replacement there were 2 deaths (3.1%), as opposed to 4 (1.8 /o) of 37 patients in Class I11 and IV. In the combined replacement group the differences were more striking (Table 3). Late Mortality During the study period up to December, 1971, there were 5 (5%) late deaths among the patients having single aortic valve replacement and 2 (6.2%) among those having combined aortic and mitral replacement. The overall late mortality was 5.2%. TABLE 3. OPERATIVE MORTALITY ACCORDING TO FUNCTIONAL CLASSIFICATION AND TYPE OF OPERATION No. of Class Patients Deaths Percent Aortic value replacement I & I1 I11 & IV Total Aortic and rnitral valve replacement I & I1 I11 & IV Total THE ANNALS OF THORACIC SURGERY

5 B jork-s h iley Prosthesis TABLE 4. ANALYSIS OF LATE MORTALITY AVR AVR & MVR Cause of Death (11 patients) (32 patients) Total Myocardial infarction 2 2 Cerebral emboli, intraoperative 1 1 Subacute bacterial endocarditis 1 1 Aspiration pneumonitis 1 1 Hepa ti tis 1 1 Arrhythmia 1 1 Total 5 (5%) 2 (6.2%) 7 (5.2%) AVR = aortic valve replacement; MVR = mitral valve replacement. The causes of these deaths are tabulated in Table 4. Two patients suffered acute myocardial infarction three and six months, respectively, after operation. One patient who underwent double valve replacement developed cerebral damage possibly due to calcium air emboli at the time of operation. He died seven weeks later of pulmonary complications. At postmortem examination the two prostheses were found to be intact and free of thrombi. One patient developed subacute bacterial endocarditis due to pneumococcus two months postoperatively. At postmortem examination a perivalvular abscess was seen extending into the ventricular septum. Another patient had successful reoperation for closure of a paravalvular leak and simultaneous bypass vein graft to his left anterior descending coronary artery. He died three months later, however, from accidental food aspiration while eating a heavy meal. The postmortem examination demonstrated an intact prosthesis and a patent vein graft. The other deaths were due to hepatitis after four months in 1 patient and to intractable arrhythmia after six months in another. Follow-up information was obtained by interview in SO% of the patients and by letter or telephone in the remaining 2%. The follow-up ranged from three to nineteen months. As of December 15, 1971, there were 113 surviving patients, of whom 9 had had aortic valve replacement and 23 had had combined aortic and mitral replacement. The majority showed marked clinical improvement, with relief of symptoms and increased exercise tolerance. The heart size had not changed except in a few who showed a definite decrease in the cardiac silhouette by roentgenogram. Forty-eight patients (42.5%) were considered to have an excellent result. They had resumed their normal levels of activity, and many had returned to productive employment. Fifty-seven (5%) were asymptomatic but did not feel quite ready to return to their previous level of activity. Seven patients (6.2%) manifested mild dyspnea with effort. One patient was considered to VOL. 14, NO. 5, NOVEMBER,

6 PERNANDEZ ET AL. have a poor result because of persistent congestive heart failure ten months after operation. No embolic complications occurred during the follow-up period. All patients received routine anticoagulation. Significant paravalvular regurgitation occurred in 3 patients. One was the patient mentioned previously who died some time after successful repair of the leak. Due to mild aortic regurgitation, many of the other patients have a diastolic murmur-without symptoms and of insignificant proportionalong the left sternal border. Two patients have required coronary bypass graft operations. Both developed angina some time after their aortic valve replacement. In 1, the lesion in the left main coronary artery appeared secondary to trauma from coronary cannulation. This patient required a single bypass graft to the left anterior descending coronary artery. In the other patient the lesions were discovered during the preoperative studies; this second patient required a triple bypass graft to her right coronary artery, left anterior descending artery, and marginal vessels. Both patients are alive and well four and six months, respectively, after their second operation. Preoperative treadmill exercise tests were conducted in 9 patients, Seven showed improvement in their exercise tolerance or disappearance of arrhythmic patterns. One manifested no change, and in the others the test was stopped because of frequent premature ventricular contractions. As determined by cardiac catheterization, the preoperative systolic gradients across the aortic valve in 5 patients ranged from 2 to 79 mm. Hg. Following valve implantation the gradient almost totally disappeared ( to 4 mm. Hg) (Table 5). Aortic regurgitation was graded from to 4+ in the 9 patients studied before and after operation. All except 2 had had a significant preoperative regurgitant lesion. Seven of these patients showed marked reduction in the amount of regurgitation, from an average of 3+ preoperatively to 1+ postoperatively. In 1 patient (A. J.) the aortogram confirmed 3+ paravalvular regurgitation, although the patient is now asymptomatic. Except for 1 patient (C. M.), all who were studied demonstrated a return of the pulmonary artery pressure and left ventricular end-diastolic pressure to normal levels. Comment Since 1961 we have used various types of aortic prosthetic valves and even calf valve heterografts. We have shared with others the complications associated with the use of these valve substitutes [24, 7, 8, 111. The initial encouraging report by Bjork [ 11 with the use of his central-flow tilting-disc valve, and especially its attractive hydrodynamic characteristics, caused us to begin a clinical trial with this prosthesis in May, 197, in patients with aortic valve disease. In those patients who required simultaneous mitral valve replacement, the Beall valve with no exposed metal surfaces was used. 532 THE ANNALS OF THORACIC SURGERY

7 I- c p M w co 4 N csr w, w, TABLE 5. PREOPERATIVE AND POSTOPERATIVE HEMODYNAMIC FINDINGS Aortic Regurgi- BA LV Pulmonary tationa Patient, Age, Pressure. Pressurea Aortic Pressure (Scale Bjork Aortic & Sex (mm. HE) (mm. HE) Gradien ta (mm. HE) to 4+) Valve Size Remarks - C.M., I13156 (83) 13/6b 137/56b 88/4 (61) (93) (72) K.W., L,L., 58,M 54,M 5,M A. J., 46,M 97/6 (75)b 1516 (8) G.M., 55,M (96Ib N.H., 67,M D.L., 59,M McC. J.. 26, M 68/53 (7Ib (88) 1516 (78) 116 (75) /54 (85) / / / / / /15 26/ No No No No No No mo., asymptomatic 1 mo., asymptomatic RCA occ. & LAD dis. 11 mo., asymptomatic MR l+; residual AR, asymptomatic, 12 mo. 8 mo., asymptomatic Triple bypass graft; 6 mo., asvmdtoma tic 2+ No mo.; asymptomatic 1+ No. 25 Bjork, then 1+ angina; bypass graft to LAD; 4 mo. postop. no angina No. 25 Ao. commissuro tomy 1962: valvulo- plasty 1968; Biork 197; aiymptoma tic 12 mo. Values listed are, first, preoperative; second, postoperative. In the case of McC. J., the last BA pressure and aortic regurgitation values are postoperative and all other values are preoperative. bascending aortic pressure (mm. Hg). BA = brachial artery; LV = left ventricular; RCA = right coronary artery; LAD = left anterior descending coronary artery; MR = mitral regnrgitation; AR = aortic regurgitation; A =aortic.

8 FERNANDEZ ET AL. The overall early and late mortality was 9.8 and 5.2%, respectively. A significant fact was that no deaths could be attributed directly to the prosthesis. There were no embolic complications and no deaths due to emboli from the valve. No instances of mechanical malfunction and no hematological abnormalities have been encountered in the survivors. The clinical improvement seen at follow-up has been gratifying; 97% of the survivors were symptom-free, and many had returned to gainful employment. Immediate postoperative complications in this series were relatively few in number [5] except for the 3 patients who developed neurological deficit in connection with removal of calcific deposits from the aortic valve at the time of operation. Of the 2 patients who underwent reoperation for coronary bypass grafting, 1 had preexisting coronary disease, and in the other, the lesion in the left main coronary artery seemed to be the result of trauma from the coronary cannula at the time of operation. Both patients are alive and well four and six months after reoperation, respectively. We have had no cases of low cardiac output syndrome with the Bjork- Shiley valve. During the period 1963 to 197 there were 3 deaths as a result of low-output syndrome among 267 patients who had Starr-Edwards ball valves of the silicone ball-metal cage type. There were 4 deaths due to lowoutput syndrome among 14 patients who received Starr-Edwards prostheses of the type with a metal ball and cloth-covered cage. The low-output syndrome, characterized by inability to maintain blood pressure in the presence of adequate blood volume and apparently adequate myocardial contractions, only occurred in patients with the smaller-sized aortic prostheses. The incidence of persistent postoperative anemia due to hemolysis among the survivors with Starr-Edwards prostheses was approximately 1%. Only 2 required reoperation for replacement with a Bjork-Shiley valve. There were no instances of hemolytic anemia among the patients with Bjork- Shiley valves. The theoretical factors accounting for the absence of thromboemboli may be the hydraulic characteristics of a prosthesis with central flow [4] and the mild built-in regurgitation seen in postoperative aortograms. (The Delrin+ disc of the prosthesis used in this series has a clearance of.3 inch from the valve ring.) The present Bjork-Shiley valve, 1972 model, has a Pyrolite-t disc with a.1-inch clearance and, thus, less regurgitation. Only 1 death due to bacterial endocarditis could have been related to the presence of the prosthesis, although we are not sure whether the infection started at the time of the operation or some time later. Most deaths, as in other series [3,41, were related to the extent to which the valvular disease had affected the myocardial reserve and to any associated coronary artery disease. Myocardial function is a critical consideration in operative mortality. The subjective evaluation of cardiac disability is not accurate. Emphasis E. I. du Pont de Nemours & Co., Inc., Wilmington, Del. tculf General Atomic Inc., San Diego, Calif. 534 THE ANNALS OF THORACIC SURGERY

9 Bjork-Shiley Prosthesis should be placed on the objective results such as those obtained from treadmill exercise tests [ 11 and preoperative hemodynamic data. Although most patients in our series underwent cardiac catheterization -including aortogram and coronary cineangiograms-before operation, only 9 were studied postoperatively. This is mainly due to the reluctance of the patients to be subjected to another catheterization when they are still feeling well or have returned to work. The data obtained after operation in this small group of patients demonstrated abolition of the systolic ejection gradient across the prosthesis similar to that reported by Bjork [l]. Except in 1 patient (C. M.), the left ventricular end-diastolic pressure and pulmonary artery pressures returned to normal in those patients in whom these determinations were made. The amount of aortic regurgitation seen in the aortograms was considered to be mild and has been largely eliminated in the present Pyrolite model of the valve. Considering that the time of follow-up is still relatively short, at present we cannot draw any long-term conclusions or predictions about the Bjork- Shiley prosthesis. For the time being, however, it remains our first choice for aortic valve replacement because of a clear superiority over the commonly used, somewhat obstructive ball-valve prostheses. Addendum Since this paper was presented, 55 additional aortic valve replacements with the Pyrolite disc Bjork-Shiley prosthesis have been performed, with no deaths. References 1. Bjork, V.. A new central-flow tilting disc valve prosthesis: One year s clinical experience with 13 patients. J. Thorac. Cardiovasc. Surg. 6:355, Bloodwell, R. D., Okies, J. E., Hallman, G. L., and Cooley, D. A. Aortic valve replacement: Long-term results. J. Thorac. Cardiovasc. Surg. 58:457, Fleming, J., Hamer, J., Hayward, G., Tubbs,. S., and Hill, I. Long-term results of aortic valve replacement with the Starr-Edwards valve. Br. Med. J. 1:139, Fraser, R. S., and Waddell, J. Systemic embolization after aortic valve replacement. J. Thorac. Cardiovasc. Surg. 54:81, Gooch, A. S., Maranhao, V., Ablaza, S. G. G., and Goldberg, H. Medical complications following open-heart surgery. Arch. Intern. Med. 12:672, Gooch, A. S., and McConnell, D. Analysis of transient arrhythmias and conduction disturbances during submaximal treadmill exercise testing. Progr. Cardiovasc. Dis , Kastor, J. A., Akbarian, M., Buckley, M. J., Dinsmore, R. E., Sanders, C. A., Scannell, J. G., and Austen, W. G. Paravalvular leaks and hemolytic anemia following insertion of Starr-Edwards aortic and mitral valves. J. Thorac. Cardiovasc. Surg , Morse, D. P. Discussion of S. W. Buch, J. C. Kosek, and W. W. Angell, Deterioration of formalin-treated aortic valve heterografts. J. Thorac. Cardiovase. Surg. 6:68, 197. VOL. 14, NO. 5, NOVEMBER,

10 FERNANDEZ ET AL. 9. Morse, D. P. Discussion of C. W. Lillehei, Aortic valve replacement, describing first case of ball variance. J. Thorac. Cardiovasc. Surg. 5:497, Patterson, J. A., Naughton, J., Pietras, R. J., and Gunnar, R. M. Treadmill exercise in the assessment of functional capacity of cardiac patients. Circulation 43 (Suppl. II):29, Roberts, W. C., and Morrow, A. G. Fatal degeneration of the silicone rubber ball of Starr-Edwards prosthetic aortic valve. Am. J. Cardiol. 22:614, Yang, S. S., Maranhao, V., Ablaza, S. G. G., Morse, D. P., Nichols, H. T., and Goldberg, H. Clinical and hemodynamic findings following calf aortic valve transplantation for human aortic valve. Am. J. Cardiol. 23: 199, Discussion DR. DENTON A. COOLEY (Houston, Tex.): The paper presented by Dr. Fernandez and his associates was reviewed before the meeting, and his results with the Bjork prosthesis were compared with our own series. We first used this prosthesis in September, 1969, and during the ensuing period up to December 31, 1971, the valve was used for aortic replacement in 647 patients. The aortic prosthesis has good hemodynamic features, a low late incidence of thromboembolism, and no late hemolysis. Mortality in 528 patients having single aortic valve replacement was 7.8%. In 37 patients of Functional Class I or 11, no deaths occurred. Among 491 patients of Functional Class I11 or IV, 41 died after operation, a mortality of 8.3%. Among 119 patients undergoing aortic and mitral valve replacement, 21 died, a mortality of 17.6%. The mortality in the entire group of 647 was 9.6%-62 patients. Only 37 (5.7%) were in Functional Class I or 11, and the remainder were in Functional Class I11 or IV. Review of the age distribution revealed that 19 patients were less than 2 years old, the youngest being 1 years of age. Twenty-nine patients were more than 71 years old. About 7% were between 4 and 7 years of age. While this series of aortic replacements was being accumulated, 321 patients underwent insertion of the Bjork mitral prosthesis with a mortality of 15.3%; 231 had a single mitral replacement with a 13% mortality; 82 had combined mitral and aortic prosthetic replacement with a 19.5% mortality, and 4 had mitral and tricuspid valve replacement with 2 deaths. While we had expected the Bjork mitral prosthesis to have the same low incidence of thromboembolism as the aortic prosthesis, we discovered that the valve had a substantial incidence of this complication, necessitating constant anticoagulant therapy for control. We therefore, along with the group from Cutter Laboratories, designed a new full-orifice discoid mitral prosthesis which we believe will give more favorable results. The valve was fabricated by Cutter Laboratories and has now been used in 48 patients. It has a self-washing principle, and we believe its overall design will significantly reduce the incidence of posto erative thromboembolism. In additional feature which we have recently added is an eccentric sewing ring so the disc will not impinge upon the surrounding ventricular myocardium, a problem that is particularly important in patients with pure mitral stenosis, in whom the left ventricular cavity is small. Finally, I would like to report the successful use of the Bjork aortic prosthesis in 3 patients with truncus arteriosus. The prosthesis was inserted in a woven Dacron tube graft and used as a composite pulmonary artery and valve prosthesis. These patients had the operation we reported ten years ago. Our original efforts, reported eight years ago, failed for technical and physiological reasons, including pulmonary hypertension. We believe that the Bjork prosthesis may be well suited for pulmonic valve 536 THE ANNALS OF THORACIC SURGERY

11 Bjork-Shiley Prosthesis replacement and may obviate the need for homograft valves in that anatomic location. DR. DERWARD LEPLEY, JR. (Milwaukee, Wis.): I congratulate the authors on their work with this new prosthesis. We have been using it since about May of 197, and we have put 15 valves in 133 patients. We did not come out so well with the aortic valves, in that our mortality was 2%. All deaths were in patients of Functional Class IV, however. I would also point out that of the 6 patients having aortic valve replacement, 12 had concomitant direct coronary revascularization, and we lost 6 of them. In our hands, one of the severest problems has been the 6 to 9 gm. heart with associated severe aortic stenosis and significant coronary artery disease. In the mitral position we have replaced 56 valves with an operative mortality of 5.3%. There has been only 1 late death in that group. I would like to comment from the standpoint of both these valves, aortic and mitral. We have had 3 instances of embolus from the mitral valve, and all have resolved completely. No emboli have occurred from aortic valves. All the patients received anticoagulants. It is interesting that, for the first time, I am seeing regression of left ventricular hypertrophy on electrocardiograms in the aortic stenosis group, which I did not commonly see when using the ball valves. The patients we have recatheterized show hemodynamics that are very good, better than with any prosthesis used to date. Also, with 1 exception we have not had any paravalvular leaks in these 15 patients; the patient who did develop a leak had a great amount of calcium in the aortic wall. We use a method of sewing in which Teflon-patch-reinforced mattress sutures are placed from above downward, and even in 15 ball valves placed prior to the time when we began using the Bjork prosthesis, we did not have paraprosthetic leaks. DR. C. WALTON LILLEHEI (New York, N.Y.): I wish to discuss the choice of prosthetic valves and to describe our pivoting-disc valve, which is the result of a five-year period of developmental testing. Both the aortic and mitral (tricuspid) models are identical in design, featuring a low profile and central flow with a free-floating disc (to distribute wear evenly) that opens to 8 degrees and closes to 18 degrees. The latter increases rapidity of response and reduces cardiac work and regurgitation without sacrificing flow. The disc is Pyrolite carbon with a titanium housing. Extensive accelerator and animal tests showed that carbon discs consistently outperformed polypropylene, polycarbonate, Delrin, stainless steel, and titanium. Pyrolite carbon is formulated at 1 C. and is chemically inert and impervious to autoclaving. Accelerator studies indicated a projected wear halfway through the disc in 25 years at physiological heart rates. Gott, in his vena caval ring studies, found Pyrolite carbon to be the most antithrombogenic substance of some 2 studied. We have used this prosthesis for aortic, mitral, and tricuspid single or double valve replacement in 61 patients with a hospital mortality of 4.9%. There has been no early or late valve-related mortality. In a survey for this meeting, we found that 25 of these valves have been implanted by fifteen surgeons with no known valve-related complications to date. In conclusion, this valve incorporates advantages not present in any other prosthesis. DR. ARTHUR C. BEALL, JR. (Houston, Tex.): At prior meetings of this Society we have tried to keep everyone up-to-date with the work we have been doing on a mitral prosthesis which shows an exceedingly low incidence of thromboembolic complications. We have been continually searching for materials that would be more durable, and, as have many others, we began working with Pyrolite carbon several years ago. After several design changes, a valve was produced that uses Pyrolite carbon for not only the disc, but also the struts. VOL. 14, NO. 5, NOVEMBER,

12 FERNANDEZ ET AL. At the same time, according to data developed at our center by Dr. Alan Reid some years ago that he belatedly reported at the American Heart Association meeting last November, with the smaller-sized prosthesis the gradient was somewhat higher than was desirable. However, since 1969 a 2% increase in the orifice area of the Model 14 and a 25% increase in the frustum area of the medium- and small-sized prostheses has been made. With the Model 15, which incorporates the Pyrolite carbon disc and struts, the same increased orifice and frustum area was put into all sizes. At that point we began calf studies, which showed complete healing of the entire base and sewing ring one year after implantation. The metal seat-sewing ring interface had been eliminated from the ventricular side after one year in the animal. We began employing this valve clinically some nine months ago. For the past months it has also been used by Drs. Jay Ankeney of Cleveland and Jack Greenberg of Miami, and the valve is now available commercially. DR. FERNANDEZ: As far as the mitral valve is concerned, we have accumulated a large experience with the use of the Beall valve and at the present time have no reason to change to another prosthesis. The incidence of fatal emboli that we reported recently at the American College of Chest Physicians was 1.5%. There were also 4.5% nonfatal emboli in 298 survivors followed up to four years. I congratulate Dr. Lillehei for his fine results. His valve seems to have very good hemodynamic characteristics, and we will await further follow-up. 538 THE ANNALS OF THORACIC SURGERY