Outlet strut fracture of Bjork-Shiley convexo concave heart valves: the UKcohort study

Objective-To investigate the risk of outlet strut fracture (OSF) in Bjork-S hiley convexo concave (BSCC) valves in relation to patients' clinical and v alve characteristics. Design-A cohort of 2977 patients with 3325 valves with a follow up of 18 ye ars. Setting-38 cardiac implantation centres in the UK. Results-56 OSF events were reported with 43 occurring in mitral and 13 in a ortic valves. The overall OSF rate was 0.17%/year. No dominant clinical fac tor of risk was found, but multiple regression analysis identified age, bod y surface area, valve size, shop order fracture rate, and manufacturing per iod as risk factors for OSF. A 4% (95% confidence interval (CI) 2% to 6%) d ecrease in the risk of OSF was observed for each advancing year of age and a fivefold (95% CI 2 to 13) increase in risk for a 0.5 m(2) increase in bod y surface area. The association between the risk of OSF and valve size was not constant over time. Excess risks among 31 mm and 33 mm sizes (mainly mi tral valves) decreased over time while that for 23 mm (almost all aortic va lves) increased. The risk of OSF increased by 40% (95% CI 20% to 50%) for a unit increase in the fracture rate of other valves in the same batch. For valves manufactured during 1981 to 1984 the risk of OSF was 4 (95% CI 2 to 12) times greater than for valves manufactured before 1981. Conclusions-The OSF rates for 60 degrees BSCC valves observed in the UK are the highest among all monitored populations. The changing patterns of mitr al and aortic valve OSF rates over time observed in this study have not bee n identified previously and highlight the need for continued monitoring of patients with the BSCC valve.