[1] Royal Edinburgh & Associated Hosp, Dept Cardiothorac Surg, Edinburgh, Midlothian, Scotland
[2] Univ Edinburgh, Edinburgh, Midlothian, Scotland
[3] Royal Edinburgh & Associated Hosp, Dept Clin Neurosci, Edinburgh, Midlothian, Scotland
[4] Royal Edinburgh & Associated Hosp, Dept Clin & Surg Sci, Edinburgh, Midlothian, Scotland
[5] Royal Edinburgh & Associated Hosp, Dept Anaesthet, Edinburgh, Midlothian, Scotland
[6] Royal Edinburgh & Associated Hosp, Edinburgh, Midlothian, Scotland