[1] Univ London Imperial Coll Sci Technol & Med, Natl Heart & Lung Inst, Royal Brompton Hosp, Dept Cardiac Med,Hlth Serv Unit, London SW3 9RP, England
[2] Univ London Imperial Coll Sci Technol & Med, Natl Heart & Lung Inst, Royal Brompton Hosp, Dept Cardiac Surg, London SW3 9RP, England
[3] Univ London Imperial Coll Sci Technol & Med, Natl Heart & Lung Inst, Royal Brompton Hosp, Hlth Serv Res Unit, London SW3 9RP, England
[4] Univ London Imperial Coll Sci Technol & Med, Natl Heart & Lung Inst, Royal Brompton Hosp, Acad & Clin Unit Sleep & Breathing, London SW3 9RP, England
[5] Umea Univ, Umea Heart Ctr, S-90187 Umea, Sweden
[6] John Radcliffe Hosp, Oxford Heart Ctr, Dept Cardiac Surg, Oxford OX3 9DU, England