1. Bristol Medical School, Faculty of Health Sciences, University of Bristol, Bristol, UK
2. Department of Cardiac Surgery, South Tees Hospital, Middlesborough, UK
3. Department of Cardiac Surgery, Northern General Hospital, Sheffield, UK
4. Department of Cardiothoracic Surgery, Blackpool Victoria Hospital, Blackpool, UK
5. Department of Cardiac Surgery/Cardiovascular Sciences, University of Bristol, Bristol, UK