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J Thorac Cardiovasc Surg 2001;121:1143-1149
© 2001 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

Outlet strut fracture of Björk-Shiley convexo-concave valves: Can valve-manufacturing characteristics explain the risk?

From the Departments of Cardiac Surgery and Epidemiology and Public Health, Imperial College of Science, Technology and Medicine, Hammersmith Hospital, London, United Kingdom^a; the International Epidemiology Institute, Rockville, Md^b; and the Department of Medical Physics and Clinical Engineering, The University of Sheffield, Royal Hallamshire Hospital, Sheffield, United Kingdom.^c

Supported by the Trustees for the Bowling Pfizer Heart Valve Settlement Funds.

Received for publication Aug 30, 2000. Revisions requested Oct 13, 2000;.revisions received Dec 11, 2000. Accepted for publication Dec 27, 2000. Address for reprints: Professor K. M. Taylor, Department of Cardiothoracic Surgery, Imperial College of Science, Technology, and Medicine, Hammersmith Hospital, Du Cane Rd, London W12 ONN, United Kingdom.

Background: Björk-Shiley 60° convexo-concave prosthetic heart valves (Shiley, Inc, Irvine, Calif, a subsidiary of Pfizer, Inc) continue to be a concern for approximately 35,000 nonexplanted patients worldwide, with approximately 600 events reported to the manufacturer to date. Fractures of the outlet struts of the valves began to appear in the early 1980s and have continued to the present, but their causes are only partially understood.
Methods: A matched case-control study was conducted evaluating manufacturing records for 52 valves with outlet strut fractures and 248 control subjects matched for age at implantation, valve size, and valve position.
Results: In addition to the risk factors recognized as determinants of outlet strut fracture, the United Kingdom case-control study has observed 7- to 9-fold increased risk with performance of multiple hook deflection tests. This test was performed more than once, usually after rework on the valve. Six valves in this study underwent multiple hook deflection tests, of which 4 experienced an outlet strut fracture. Cracks and further rework were noted for these valves. Significant associations were also observed between outlet strut fracture and disc-to-strut gap measurements taken before the attachment of the sewing ring.
Conclusions: It is our view that a combination of factors related to valve design, manufacturing process, and patient characteristics are responsible for outlet strut fractures of Björk-Shiley convexo-concave valves. Multiple hook deflection tests have emerged as a potential new risk factor for outlet strut fracture in both The Netherlands and the United Kingdom. This factor appears to be correlated with the presence of other abnormalities. A further study is needed to investigate the factors correlated with multiple hook deflection tests. On confirmation of risk, the presence of multiple hook deflection tests may be added to equations, quantifying the risk of outlet strut fracture for comparison against risk of mortality and serious morbidity from explant operations.

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