1 Department of Cardiology, West Suffolk Hospital NHS Foundation Trust, Bury St Edmunds, United Kingdom.
2 Department of Cardiology, Papworth Hospital NHS Foundation Trust, Cambridge University Health Partners, Papworth Everard, United Kingdom.
3 Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom.
4 Department of Cardiology, Royal Brompton and Harefield NHS Trust, London, and Imperial College London, London, United Kingdom; Norwich Medical School, University of East Anglia, Norwich, United Kingdom.