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