1. Department of Cardiothoracic Surgery, University Hospital Cologne , Kerpener Str. 62, 50937 Cologne , Germany
2. Department of Cardiac Surgery, Kerckhoff-Clinic, Campus Kerckhoff, Justus-Liebig-University of Giessen , Benekestr. 2-8, 61231 Bad Nauheim , Germany
3. Institute of Medical Statistics and Computational Biology, University Hospital Cologne , Cologne , Germany
4. Department of Cardiothoracic Surgery, Ruhr-University Hospital Bergmannsheil , Bochum , Germany
5. Department of Cardiac Surgery , Bad Neustadt a. d. Saale , Germany
6. Department of Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center Essen, University Hospital Essen , Essen , Germany
7. Clinic for Thoracic and Cardiovascular Surgery, Heart and Diabetes Center North Rhine-Westphalia, Ruhr University Bochum , Bad Oeynhausen , Germany
8. Department of Thoracic and Cardiovascular Surgery, University Hospital Aachen , Aachen , Germany
9. Department of Cardiac and Thoracic Surgery, University Hospital Münster , Münster , Germany
10. Department of Cardiovascular Surgery, University Heart Center Hamburg , Hamburg , Germany
11. Department of Cardiothoracic Surgery, Otto-von Guericke University , Magdeburg , Germany
12. Department of Cardiology, University Hospital Cologne , Cologne , Germany