1. Department of Cardiology, Royal Brompton & Harefield Hospitals, Guy's and St Thomas' NHS Foundation Trust, Hill End Rd, Harefield, Uxbridge UB9 6JH, UK
2. Faculty of Medicine, Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, Royal Brompton Campus, Guy Scadding Building, Cale Street, London SW3 6LY, UK