1. From the Boston Adult Congenital Heart and Electrophysiology Services, Children’s Hospital Boston, Boston, Mass (P.K., M.J.L., M.E.A., E.P.W.); Adult Congenital Heart Unit, Royal Brompton Hospital, London, UK (M.A.G.); Department of Cardiology, Centre Hospitalier et Universitaire de Nancy, Nancy, France (H.L., F.M.); and Department of Biostatistics, Montreal Heart Institute, Montreal, Canada (J.L.).