RISK OF STRUT FRACTURE OF BJORK-SHILEY VALVES

The incidence of and factors that predispose to outlet strut fracture of Bjork-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-degrees convexo-concave (60-degrees-CC) or a 70-degrees convexo-concave (70-degrees-CC) Bjork-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-degrees), large valve size (greater-than-or-equal-to 29 mm diameter), and young age (< 50 years) as risk factors for outlet strut fracture. For large 70-degrees-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-degrees-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-degrees-CC and 70-degrees-CC valves (aortic and mitral) was constant over time. Overall survival since implantation was better for patients with 60-degrees-CC prostheses than for those with 70-degrees-CC prostheses; the adjusted hazard ratio for mortality for patients receiving a 70-degrees-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-degrees-CC valves is an underestimate. The data indicate that prophylactic replacement of 60-degrees-CC and 70-degrees-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 Bjork-Shiley heart-valve failure should be referred without delay to a cardiothoracic centre.