1. Department of Cardiology, Norfolk and Norwich University Hospitals, Colney Lane, NR4 7UY, Norwich, UK
2. Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK
3. Imperial College London and Imperial College NHS Trust, South Kensington, SW7 2BX, London, UK
4. Department of Cardiology, Cambridge University Hospitals, Cambridge CB2 0QQ, UK