1. Department of Thoracic and Cardiovascular Surgery, University Hospital of Tuebingen, 72076 Tuebingen, Germany
2. Department of Thoracic and Cardiovascular Surgery, Johann-Wolfgang-Goethe University, 60590 Frankfurt am Main, Germany
3. Division for Cardiothoracic, Transplantation and Vascular Surgery, Hannover Medical School, 30625 Hannover, Germany
4. Department of Cardiac Surgery, University Hospital Zuerich, 8091 Zuerich, Switzerland