1. National Heart and Lung Institute, Imperial College London , London W12 0HS , UK
2. Department of Cardiology, Harefield Hospital, Guy's and St Thomas' NHS Foundation Trust , Hill End Road, London UB9 6JH , UK
3. College of Engineering, Design and Physical Sciences, Brunel University London, Kingston Lane , Uxbridge UB8 3PH , UK
4. Department of Cardiothoracic Surgery, Harefield Hospital, Guy's and St Thomas' NHS Foundation Trust , Hill End Road, London UB9 6JH , UK