1. West of Scotland Heart and Lung Centre, Golden Jubilee National Hospital, Clydebank, Scotland (H.B., D.C., M.M., M.C.P., H.E., S.H., S.W., M.L., A.M., K.G.O., C.B.).
2. Norfolk and Norwich University Hospital, Norwich, England (H.B.).
3. British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences (J.C., D.C., S.W., C.B.), University of Glasgow, Scotland.
4. Robertson Centre for Biostatistics (I.F.), University of Glasgow, Scotland.