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J Thorac Cardiovasc Surg 1994;107:318-319
© 1994 Mosby, Inc.
LETTERS TO THE EDITOR |
Department of Cardiovascular Surgery
University of Padova Medical School
Padova, Italy
To the Editor:
We describe here a patient in whom severe mitral regurgitation developed 20 years after mitral valve replacement with a Björk-Shiley prosthesis (Shiley, Inc, Irvine, Calif.). Prosthetic incompetence was attributed to a concentric wear of the Delrin occluder (Du Pont Company, Wilmington, Del.), which prevented normal valve closure.
A 69-year-old man underwent aortic valve replacement in 1966 with a Starr-Edwards prosthesis. Five years later, he underwent mitral valve replacement with a Delrin disc Björk-Shiley prosthesis and tricuspid annuloplasty; 1 year after that, the Starr-Edwards aortic valve was replaced with a Delrin disc Björk-Shiley prosthesis because of periprosthetic leak. In 1988, a transthoracic two-dimensional echocardiogram showed marked left atrial and ventricular dilatation, a left ventricular ejection fraction of 51%, and mild incompetence of the mitral prosthesis. A hemodynamic investigation showed pulmonary hypertension (45, 25, and 30 mm Hg) and elevated pulmonary wedge pressure (40, 15, and 25 mm Hg). Subsequently, progressive worsening of his clinical status with onset of fatigue and exertional dyspnea and appearance of signs of overt cardiac failure prompted reevaluation. On admission, mild peripheral edema and jugular vein distention were present: The liver was palpable 4 cm below the costal border and diffuse pulmonary basal rales were present. Heart rate was 110 beats/min and blood pressure was 120/80 mm Hg; a grade 3/6 holosystolic apical murmur radiating to the axilla was noted. The electrocardiogram revealed atrial fibrillation and left ventricular hypertrophy and a chest radiograph revealed marked cardiomegaly and signs of pulmonary congestion. A transesophageal two-dimensional echocardiogram showed severe mitral regurgitation with mild aortic and moderate tricuspid valve incompetence.
At reoperation in September 1991, there was no periprosthetic leak and the movement of the disc was unimpeded. Although no evident cause of valve regurgitation could be detected, the mitral prosthesis was excised and replaced uneventfully with a 29 mm Sorin Biomedica tilting-disc prosthesis (Sorin Biomedica Spa, Saluggia, Italy). At gross inspection, no deformation or wear of the Delrin occluder was present and the housing was intact and not distorted. It appeared, however, as though concentric wear of the occluder had occurred, creating a significant clearance between the disc and the prosthetic ring and allowing the disc to slide excessively between the struts, thus preventing normal closure of the prosthesis (Fig. 1).
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1 In the original valve, the occluder was made of an acetal resin (Delrin), a material that showed excellent resistance to wear, allowing a prediction for such prostheses of a durability in excess of 50 years. 2 The only drawback of Delrin was its recognized propensity toward absorbing moisture during sterilization by steam autoclaving. 2 As a consequence, the disc could become larger or partially deformed, causing irregular valve function. Shrinkage and deformation of the Delrin disc have been occasionally reported as causes of failure of the Björk-Shiley prosthesis. 3, 4 For such reasons, the Delrin disc wasreplaced in 1971 by an occluder made of pyrolytic carbon. 5
Nevertheless, reported durability of the standard Björk-Shiley prosthesis has been excellent, regardless of the disc material. In fact, large clinical series (which also include patients with the Delrin disc valve) have shown an extremely low rate of structural valve deterioration or even absence of this complication at long-term follow-up. 6,7
The particular mode of failure of a Delrin disc Björk-Shiley prosthesis that occurred in the patient described here has apparently not been reported previously. At reoperation, performed 20 years after the original mitral valve replacement, undue clearance between the disc and the prosthetic ring was evident, preventing complete prosthetic closure during systole. Additionally, the disc could slide excessively between the struts, contributing to increased regurgitation. This was recognized as the only possible mechanism accounting for hemodynamically severe prosthetic incompetence. These findings, together with the progressive deterioration of patient condition, indicate that valve incompetence was most likely caused by even, concentric wear of the Delrin occluder, a potential complication that occurred in this case much earlier than initially predicted by Björk. 1
Because of the excellent long-term durability of the Delrin disc Björk-Shiley prosthesis, many patients with this device are still alive. Awareness of this potential, if rare, complication is important for those who perform follow-up studies on recipients of prosthetic valves. Such complications justify a continuous, noninvasive reevaluation of patients with this specific prosthetic model.
References
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