1. Department of Cardiovascular Surgery, University Hospital Giessen , Giessen, Germany
2. Medical Faculty, Justus-Liebig-University , Giessen, Germany
3. Department of Cardiac Surgery, Heidelberg University , Heidelberg, Germany
4. University Department of Cardiac Surgery, Leipzig Heart Center , Leipzig, Germany
5. Department of Cardiac Surgery, Schüchtermann-Klinik Bad Rothenfelde , Bad Rothenfelde, Germany
6. Department of Cardiovascular Surgery, University Hospital Freiburg , Freiburg, Germany
7. Department of Cardiovascular Surgery, University Heart & Vascular Center Hamburg UKE , Hamburg, Germany
8. Department of Cardiac Surgery, LMU University Hospital Munich , Munich, Germany
9. Department of Cardiac Surgery, University Hospital Frankfurt , Frankfurt, Germany
10. Department of Cardiac Surgery, University Hospital Augsburg , Augsburg, Germany
11. Department of Thoracic and Cardiovascular Surgery, University Hospital Tübingen , Tübingen, Germany
12. Institute of Medical Biometry, University Hospital Heidelberg , Heidelberg, Germany