1. From the Royal Brompton Hospital (A.N.S., H.U., J.P., M.R., S.Y.H., K.P.M., S.J., L.S., M.L.R., P.E.F.D.) London, United Kingdom; National Heart and Lung Institute (A.N.S., H.U., S.Y.H., K.P.M., P.E.F.D.), Imperial College, London, United Kingdom; Queen Charlotte's and Chelsea Hospital (A.N.S.), London, United Kingdom; Children's Hospital of Pittsburgh (S.A.W.), Pittsburgh, Pa; Queen Silvia Children's Hospital (J.S., H.B.), Gothenburg, Sweden; Lund University Hospital (K.H., S.J.), Lund, Sweden; and...