1. Department of Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center, University of Duisburg-Essen, Hufelandstraße 55, 45122 Essen, Germany
2. Department of Cardiothoracic, Transplant and Vascular Surgery, Hannover Medical School, 30625 Hannover, Germany
3. Medical Sciences Division, University of Oxford, Oxford OX3 9DU, UK