1. Department of Cardiothoracic Surgery, University Hospital of Cologne, Kerpener Str. 62, Cologne 50937, Germany
2. Department of Cardiothoracic Surgery, University Hospital of Cologne, Cologne, Germany
3. Department of Vascular Surgery, University Hospital of Cologne, Cologne, Germany
4. Department of Cardiothoracic Surgery, University Hospital of Magdeburg, Magdeburg, Germany