1. From the Cardiovascular Magnetic Resonance Unit (M.A.T., G.C.S., M.A.W., R.A., D.J.P.) and Health Services Research Unit (M.R.), Royal Brompton Hospital, London, UK; Ospedale Regionale per le Microcitemie, Cagliari, Italy (R.G., C.D., A.A.); and Department of Cardiology, University College Hospital, London, UK (S.V.N., J.M.W.).