1 Department of Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center, University Hospital Essen, Hufelandstrasse 55, D-45147 Essen, Germany. Electronic address: zaki.haidari@uk-essen.de.
2 Department of Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center, University Hospital Essen, Hufelandstrasse 55, D-45147 Essen, Germany.