1. Department of Cardiovascular Surgery, University Medical Centre Freiburg, Faculty of Medicine, University of Freiburg , Freiburg, Germany
2. Department of Cardiovascular Surgery, University Hospital Düsseldorf, Heinrich Heine University , Düsseldorf, Germany
3. Department of Cardiothoracic Surgery, University Hospital Jena , Jena, Germany
4. Department of Cardiac Surgery, Inselspital, University Hospital Bern, University of Bern , Bern, Switzerland
5. Department of Cardiac and Vascular Surgery, University Hospital of Giessen and Marburg, Justus Liebig University of Giessen , Giessen, Germany