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J Thorac Cardiovasc Surg 2003;126:832-836
© 2003 The American Association for Thoracic Surgery

Surgery for acquired cardiovascular disease

Use of flexibility tests in the manufacturing process of 60° björk-shiley convexo-concave valves and the risk of outlet strut fracture

^a Department of Cardiac Surgery, Imperial College School of Medicine, Hammersmith Hospital, London, United Kingdom
^b Department of Statistical Science, University College London, London, United Kingdom
^c Medical Statistics Unit, R & D Directorate, University College Hospital NHS Trust, London, United Kingdom
^d Department of HIV and GU Medicine, Kings College London, London, United Kingdom

Received for publication October 10, 2002; revisions received November 18, 2002; revisions received February 5, 2003; accepted for publication February 11, 2003.

^* Address for reprints: Professor Kenneth M. Taylor, Hammersmith Hospital, Imperial College School of Medicine, Department of Cardiac Surgery, Du Cane Road, London W12 ONN, United Kingdom
k.m.taylor{at}ic.ac.uk

OBJECTIVES: Outlet strut fracture remains a concern for 30,000 patients living with a Björk-Shiley convexo-concave heart valve (Shiley, Inc, Irvine, Calif, a subsidiary of Pfizer, Inc). Previous studies (Netherlands and United Kingdom) investigating valve manufacturing aspects identified multiple performance of the hook deflection test as a risk factor for 60° valves. The present study validated this finding using new data with a greater number of valves implanted worldwide. Risks of outlet strut fracture associated with other manufacturing aspects were also investigated.

METHODS: A matched case-control study design was used including 416 outlet strut fracture cases and 803 controls.

RESULTS: Analyses similar to that of the Dutch and United Kingdom studies produced odds ratios of 3.4 (95% confidence interval [CI]: 1.1-10.3) and 2.8 (95% CI: 1.1-7.3), respectively, for multiple hook deflection tests. Load deflection test, which replaced the hook deflection test, showed a statistically significant association with outlet strut fracture: odds ratio of 5.0 (95% CI: 2.1-11.8) and 6.2 (95% CI: 2.2-18.0) for single and multiple load deflection tests, respectively. An analysis where hook deflection tests were separated from load deflection tests showed significantly elevated odds ratios with performance of any type of flexibility test, and the highest odds ratio was observed with a combined performance of load and hook deflection tests.

CONCLUSIONS: Multiple hook deflection tests can now be considered for inclusion in the risk model used for guidelines on explant surgery to improve prediction of outlet strut fracture and provide patient reassurance. Load deflection tests and combined performance of hook and load deflection tests were found to be significant risk factors. No outlet strut fractures were reported for valves manufactured after March 1984 when the load deflection test was still in place. Examining manufacturing documents for these valves may identify new risk factors that could be responsible for the outlet strut fractures risk that remains unexplained to date.

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