[1] Royal Brompton Hosp, Imperial Coll London, Natl Heart & Lung Inst, London, England
[2] Childrens Hosp Pittsburgh, Pittsburgh, PA 15213 USA
[3] Harefield Hosp, London, England
[4] Royal Brompton & Harefield Hosp, London, England
[5] Queen Silvia Childrens Hosp, Gothenburg, Sweden
[6] Univ Lund Hosp, S-22185 Lund, Sweden
[7] Cardiothorac Unit Southhampton Gen Hosp, Southampton, Hants, England