We report the case of a patient who had undergone implantation of a Bjork-Shiley Delrin valve in the aortic position 25 years earlier and who now presented with severe mitral stenosis. The patient underwent mitral valve replacement and aortic valve re-replacement. We review the justification for prophylactic replacement of Bjork-Shiley Delrin heart valves.

Since the 1st clinical use of the Bjork-Shiley Delrin (BSD) prosthetic heart valve in 1969, follow-up studies have shown that such valves continue to function satisfactorily for up to 27 years. It has been estimated that approximately 24,000 BSD heart valves were implanted from 1969 through 1981 and that 7,000 of the patients who received those valves were alive as of January 1996.¹

In October 2001, a 45-year-old woman was admitted to our institution with palpitations and dyspnea on exertion. She had a history of acute rheumatic fever, and her aortic valve had been replaced with a BSD valve 25 years earlier, when she was 20 years old. She was in New York Heart Association functional class II. Her heart sounds were arrhythmic, and a grade 2 --3/6 diastolic murmur was audible at the apex. She had pedal edema in both legs. Electrocardiography showed atrial fibrillation with a ventricular rate of 90 beats/min. She had mild cardiomegaly on chest radiography, and her cardiac silhouette was indicative of mitral stenosis. Echocardiography revealed severe mitral stenosis with a valve area of 1.4 cm² and a transvalvular maximum gradient of 20 mmHg. The mitral leaflets were thick in appearance, and the posterior leaflet was fixed. The patient also had severe tricuspid regurgitation. Her prosthetic aortic valve was found to be functioning well, although there was mild regurgitation and a transvalvular gradient of 25 mmHg. The pulmonary arterial pressure was 55 mmHg. The left ventricular (LV) dimensions were 45 mm at end-diastole and 27 mm at end-systole. Her LV ejection fraction was 0.70. Coronary angiography revealed normal coronary arteries. Replacement of the mitral valve was deemed necessary, and we decided to perform prophylactic replacement of the aortic valve prosthesis at the same time.

At surgery, the thorax was entered through the previous median sternotomy. Standard cardiopulmonary bypass was instituted with use of double venous cannulae. An aortic cross-clamp was applied, and the mitral valve was exposed through a left atriotomy. Commissural and chordal fusion and severe fibrosis of the leaflets were observed in the mitral valve. The mitral leaflets were excised and the valve replaced with a 31-mm mechanical prosthetic valve (Sulzer Carbomedics; Austin, Tex), with use of 2 --0 Ticron interrupted pledgeted sutures. After the left atriotomy was closed, the BSD valve was exposed through a transverse aortotomy (Fig. 1). The prosthesis was removed and replaced with a bi-leaflet 21-mm mechanical aortic prosthesis (Sulzer Carbomedics), with the same type of sutures used for the mitral valve. The aortotomy was closed, the heart de-aired, and the aortic cross-clamp removed. The tricuspid valve was exposed through a right atriotomy while the heart was beating, with both caval cannulae snared. There was no structural deformity of the tricuspid valve; the dilated annulus was reshaped by the DeVega annuloplasty technique. The patient was weaned from cardiopulmonary bypass with good hemodynamic function. Intraoperative transesophageal echocardiography showed normally functioning aortic and mitral prosthetic valves, and mild tricuspid regurgitation. The patient's postoperative course was uneventful, and she was discharged from the hospital on the 7th postoperative day. When last seen in June 2004, the patient was asymptomatic.

The BSD prosthetic heart valve was widely used from 1969 through 1981.¹ In the original Bjork-Shiley valve, the occluder disc was made of an acetal resin (Delrin). The Delrin disc was popular because of its high biocompatibility and low thrombogenicity. The disc was easy to manufacture, and Delrin was highly resistant to wear, with a predicted durability of more than 50 years.² However, there were occasional reports of shrinkage and deformation of the Delrin disc, as well as inlet strut fracture, which resulted in failure of the Bjork-Shiley prosthesis.³

Accelerated fatigue tests of heart valves manufactured for implantation in human beings showed major fatigue in the Bjork-Shiley Delrin discs at 140 million cycles.⁴ Those investigators concluded that the same components showed wear at identical sites in vitro and in vivo and that the degree of durability was the same in both instances.⁴ Our patient had a BSD valve with a life of approximately 920 million cycles in 25 years, assuming that the average heart rate was 70 beats/min. This estimate is far beyond the number determined by the above-mentioned fatigue tests. The present report pays tribute to the long-term durability of BSD valves.

It has been suggested that prophylactic removal of BSD valves is unnecessary, but that each case should be considered individually.⁵ The risk of mechanical failure is a concern in any patient with a prosthetic heart valve. Lindblom and colleagues⁶ discussed the management of patients with mechanical prosthetic valve failure. According to their report, which includes follow-up results of 3,334 cases of BSD valve implantation, patients with aortic valve failure experienced circulatory collapse and death within a much shorter period of time after mechanical failure than did those with prostheses in the mitral position. Those authors recommended emergent prophylac-tic re-replacement of prosthetic valves in the aortic position if any valvular malfunction was suspected.⁶ However, they did not recommend prophylactic re-replacement in general. There is no clear answer as to whether these BSD valves could be expected to continue to function indefinitely or whether prophylactic replacement is warranted. Even though the standard BSD valves in the aortic position have been very reliable, aortic valve replacement by a mechanical prosthesis has been suggested for patients whose BSD valves have been in place for a long time.⁷

Piehler and associates⁸ replaced prosthetic heart valves in a wide variety of patients. The authors analyzed age at reoperation, cardiac function, degree of valvular disease, co-morbidities, history of cardiac surgery, and concomitant procedures. When the risk was not adjusted for the above-mentioned factors, the in-hospital mortality rate for patients undergoing replacement of cardiac valve prostheses was 10.8%. However, in good-risk patients undergoing their 1st elective valve re-replacement, the risk-adjusted hospital mortality rate was just 1.3%.⁸ These findings emphasize the importance of prophylactic replacement of such valves.

In 2001, Jones and co-authors⁹ reported operative mortality rates for 1st-time reoperations: 11.5% for double-valve replacement (aortic and mitral), and 6.4% for aortic or 7.4% for mitral replacement alone. Studies comparing the results of 1st versus multiple reoperations^{10 --12} showed significant increases in the operative mortality rates in patients undergoing 2 or more valve reoperations; Ataka and colleagues¹¹ found the rate to be as high as 27.3%. It is clear that double-valve replacement increases the risk of death. In our patient, we replaced the 25-year-old, well-functioning mechanical valve (a BSD in the aortic position) to avoid the risk of a 2nd reoperation, which might otherwise have been required in the future because of structural valve deterioration or valve fatigue.

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10. Caus T, Mesana T, Mouly A, Guez P, Tapia M, Monties JR. Repeated heart valve replacements: prognosis and results [in French]. Arch Mal Coeur Vaiss 1995;88(1):35 --41.
    
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12. Husebye DG, Pluth JR, Piehler JM, Schaff HV, Orszulak TA, Puga FJ, Danielson GK. Reoperation on prosthetic heart valves. An analysis of risk factors in 552 patients. J Thorac Cardiovasc Surg 1983;86(4):543 --52.
    

Mechanical cardiac prostheses have the advantage of better durability over biologic types. Yet problems have arisen with fabrication of mechanical valves and with the materials that have been used in such valves to achieve optimum function and stability. Most of the problems of wear have been with the poppets or moving parts. Among the materials tried in early tilting-disc valves, Teflon and Delrin were considered satis-factory, although Teflon was more subject to wear. One disadvantage of the Delrin disc was its tendency to expand when body temperature rose substantially. There were a few reports of the leaflet's "sticking" when body temperatures reached high levels. Nevertheless, the Delrin disc was superior to others and provided good long-term function.

Since the introduction of carbon as the material of choice two decades ago, the poppets in most mechanical valves have been made with that element. Carbon is resistant to thrombosis, with good tissue tolerance and excellent long-term wear.

For a number of reasons, I agree with the decision of Badak and colleagues to replace the aortic prosthesis despite its satisfactory function and appearance. Compared with Delrin discs, the currently available prostheses with carbon poppets have greater durability and reliability. In contrast to the authors' procedure, I would have explored the aortic valve initially. Then when the decision was made to replace the mitral valve, I would have removed the aortic prosthesis. This sequence would have facilitated the mitral valve replacement, which is sometimes difficult with an aortic prosthesis in place.

Denton A. Cooley, MD

Surgeon-in-Chief, Texas Heart Institute, Houston