1 Freeman Hospital, The Newcastle upon Tyne Hospitals NHS Foundation Trust, NE7 7DN, UK.
2 Critical Care and Cardiology, Royal Brompton Hospital (Part of Guy's and St Thomas' NHS Foundation Trust), Sydney Street, London, SW3 6NP, UK.
3 National Heart & Lung Institute, Imperial College, Guy Scadding Building, Dovehouse St, London, SW3 6LY, UK.
4 Department of Cardiology, Faculty of Medicine, School of Health Sciences, University of Ioannina and University Hospital of Ioannina, 45110 Ioannina, Greece.