1. Centre for Cardiovascular Imaging, University College London, United Kingdom (J.A.H., V.M., A.M.T.).
2. Department of Paediatrics and Adolescent Medicine, Division of Paediatric Cardiology, Medical University of Vienna, Austria (J.A.H.).
3. Institute of Cardiovascular and Medical Sciences, University of Glasgow, United Kingdom (N.S.).
4. Department of Paediatrics, University of Oxford, United Kingdom (A.J.).