1 Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center Essen, University Hospital of Essen, Hufelandstr 55, 45147 Essen, Germany.
2 Thoracic and Cardiovascular Surgery, West German Heart and Vascular Center Essen, University Hospital of Essen, Hufelandstr 55, 45147 Essen, Germany. Electronic address: konstantin.zhigalov@yahoo.com.