1 Adult Congenital Heart Centre and National Centre for Pulmonary Hypertension, Royal Brompton Hospital, London, United Kingdom; Department of Cardiology, St Vincent's Hospital Melbourne, Australia. Electronic address: t.roberts2@rbht.nhs.uk.
2 Adult Congenital Heart Centre and National Centre for Pulmonary Hypertension, Royal Brompton Hospital, London, United Kingdom; NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College London, United Kingdom; National Heart and Lung Institute, Imperial College School of Medicine, London, United Kingdom.