1. Department of Thoracic, Cardiac and Vascular Surgery, Tuebingen University Hospital, Tuebingen, Germany
2. Department of Thoracic Surgery, Schillerhoehe Hospital, Schillerhoehe, Germany
3. Department of Thoracic, Cardiac and Vascular Surgery, Goettingen University Hospital, Goettingen, Germany
4. Department of Cardiothoracic Surgery, Magdeburg University Hospital, Magdeburg, Germany