1. Faculty of Medicine, Imperial College London, Charing Cross Hospital, London W6 8RF, UK
2. Medical Sciences Division, University of Oxford, Oxford OX1 3AZ, UK
3. Department of Cardiothoracic Surgery, Imperial College NHS Trust, Hammersmith Hospital, London W12 0HS, UK
4. Department of Cardiothoracic Surgery, University of Thessaly, Biopolis, 41 110 Larissa, Greece
5. Unit of Quality Improvement, Department of Cardiothoracic Surgery, University of Thessaly, Biopolis, 41 110 Larissa, Greece
6. Department of Surgery and Cancer, Imperial College London, St Mary’s Hospital, London W2 1NY, UK