1. From the Department of Clinical Sciences, Pediatrics (A.W., M.L., J.P., A.R.) and Department of Public Health and Clinical Medicine, Heart Centre (U.-B.D.), Umeå University, Umeå, Sweden; Pediatric Clinic, Visby Hospital, Visby, Sweden (I.F.); Department of Pediatrics and Pediatric Cardiology, University of Lund, Lund, Sweden (G.W.); and Department of Physiology, University of Auckland, Auckland, New Zealand (A.W.).