Risk of strut fracture of Björk-Shiley valves

Abstract

The incidence of and factors that predispose to outlet strut fracture of Björk-Shiley heart valves are still not known. To obtain such information a retrospective cohort study was conducted on all 2303 patients in the Netherlands with a 60° convexo-concave (60°CC) or a 70° convexo-concave (70°CC) Björk-Shiley heart valve. Patients have been followed-up for a mean of 6·6 years (range 1-4271 days). 42 cases of mechanical failure due to outlet strut fracture have been recorded—6 of the 7 patients with fracture of the aortic valve died, as did 18 of the 35 patients with fracture of the mitral valve. Multivariate analysis identified wide opening angle (70°), large valve size (≥29 mm diameter), and young age (<50 years) as risk factors for outlet strut fracture. For large 70°CC mitral valves the cumulative risk of outlet strut fracture after 8 years was 17·4% (95% Cl 9·1-31·6). Unlike previous findings, this excessive risk applied to late as well as to early batches of valves. In patients with a large 60°CC mitral valve the cumulative risk after 8 years was 4·2% (95% Cl 2·7-6·5). The incidence rate of outlet strut fracture in 60°CC and 70°CC valves (aortic and mitral) was constant over time. Overall survival since implantation was better for patients with 60°CC prostheses than for those with 70°CC prostheses; the adjusted hazard ratio for mortality for patients receiving a 70°CC prosthesis was 1·5 (95% Cl 1·1-2·0). Together with the low (24%) necropsy rate, this ratio suggests that the reported incidence of strut fracture for the 70°CC valves is an underestimate. The data indicate that prophylactic replacement of 60°CC and 70°CC valves is advisable for selected groups of patients. Since the case-fatality rate is 50% for emergency replacement of faulty valves, patients suspected of Björk-Shiley heart-valve failure should be referred without delay to a cardiothoracic centre.