1. Department of Cardiothoracic Surgery, Friedrich-Schiller-University of Jena, Jena, Germany
2. Wolfson Medical School, University of Glasgow, Glasgow, United Kingdom
3. Institute of Medical Statistics, Computer Sciences and Documentation, Friedrich-Schiller-University of Jena, Germany
4. Department of Cardiology, Katholisches Klinikum, Koblenz, Germany
5. Department of Cardiothoracic Survey, University of Cologne, Germany