Which manufacturing characteristics are predictors of outlet strut fracture in large sixty-degree Bjork-Shiley convexo-concave mitral valves?

Background: Identification of predictors of outlet strut fracture is important for recipients of large (greater than or equal to 29 mm) 60-degree Bjork-Shiley convexo-concave mitral valves when it comes to decision making on prophylactic explantation. An association between the manufacturing process of Bjork-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 Bjork-Shiley convexo-concave mitral valves. Methods: All Dutch recipients (n = 2264) of Bjork-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 Bjork-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 greater than or equal to 175 valves; hazard ratio 6.6, 95% confidence interval 2.2-20.1), number of hook deflection tests performed (0 or 1 versus greater than or equal to 2; hazard ratio 4.7, 95% confidence interval 1.4-16.2), number of disks that were used (1 versus greater than or equal to 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 Bjork-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.