[1] Papworth Hosp, Dept Cardiothorac Surg, Cambridge CB23 3RE, England
[2] Karolinska Univ Hosp, Dept Cardiothorac Surg, Stockholm, Sweden
[3] Univ Hosp, Dept Cardiothorac Surg, Liege, Belgium
[4] Hop La Pitie Salpetriere, Inst Cardiol, Paris, France
[5] Vicenzo Hosp, Dept Cardiac Surg, Vicenza, Italy
[6] Leiden Univ, Med Ctr, Dept Cardiothorac Surg, Leiden, Netherlands
[7] James Cook Univ Hosp, Dept Cardiothorac Surg, Middlesbrough, Cleveland, England