Which manufacturing characteristics are predictors of outlet strut fracture in large sixty-degree Björk-Shiley convexo-concave mitral valves? The Björk-Shiley Study Group.

BACKGROUND Identification of predictors of outlet strut fracture is important for recipients of large (>/=29 mm) 60-degree Björk-Shiley convexo-concave mitral valves when it comes to decision making on prophylactic explantation. An association between the manufacturing process of Björk-Shiley convexo-concave valves and the risk of fracture has been suggested. OBJECTIVE The aim of this study was to determine which items from the manufacturing records, in addition to known risk factors, were predictive of fracture of large 60-degree Björk-Shiley convexo-concave mitral valves. METHODS All Dutch recipients (n = 2264) of Björk-Shiley convexo-concave valves were followed up until fracture, death, reoperation, or end of the study (July 1, 1996). Information was abstracted from the manufacturing records of large 60-degree Björk-Shiley convexo- concave mitral valves (n = 655) in Dutch recipients and included items that described the manufacturing process and items for which an association with strut fracture had been suggested. Manufacturing records were available for 637 valves (97%), including 25 fractured valves. RESULTS Multivariate analysis identified age at implantation (hazard ratio 0.95, 95% confidence interval 0.93-0.97), lot size (<175 valves versus >/=175 valves; hazard ratio 6.6, 95% confidence interval 2.2-20.1), number of hook deflection tests performed (0 or 1 versus >/=2; hazard ratio 4.7, 95% confidence interval 1.4-16.2), number of disks that were used (1 versus >/=2; hazard ratio 5.9, 95% confidence interval 1.9-18.5), and lot fracture percentage (hazard ratio 1.6, 95% confidence interval 1.4-1. 8) as independent predictors of fracture. Although the added predictive value of a model with these 5 variables was sizable compared with a model containing age only, it was only slightly better than a model with age, lot size, and lot fracture percentage. CONCLUSION If the serial number of a large 60-degree Björk-Shiley convexo-concave mitral valve is known, manufacturing information can add significantly to the prediction of fracture. Information on lot size and lot fracture percentage should be made available to clinicians for risk assessment of prophylactic explantation.

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