1. Department of Paediatric Cardiology, Royal Brompton Hospital, London, United Kingdom (J.S., G.D.S., S.K., A.F., C.P., V.B., M.J., J.P., D.S., I.V., S.P., P.D.).
2. National Heart and Lung Institute, Imperial College, London, United Kingdom (G.D.S., S.P., A.F., P.D.).
3. Department of Cardiology, Magna Graecia University, Catanzaro, Italy (C.I.).