1. Division of Cardiovascular Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA, USA
2. Department of Cardiovascular Surgery, Heart Centre Freiburg University, Faculty of Medicine, University of Freiburg, Freiburg, Germany
3. Department of Cardiothoracic Surgery, Yale University, New Haven, CT, USA
4. Department of Cardiovascular Surgery, Jichi Medical University, Saitama Medical Centre, Saitama, Japan