1. Essex Cardiothoracic Centre, Basildon and Thurrock University Hospital NHS Foundation Trust, Nethermayne, Basildon, Essex, SS16 5NL, UK.
2. Freeman Hospital, Freeman Road, High Heaton, Newcastle upon Tyne, NE7 7DN, UK.
3. Newcastle University, 4th floor, William Leech Building, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.