1. Department of Cardiovascular Surgery, Sapporo Medical University Hospital, Sapporo-shi, Japan
2. Department of Cardiovascular Surgery, Hakodate Municipal Hospital, Hakodate, Japan
3. Department of Surgery, Yamaguchi Prefectural Grand Medical Center, Yamaguchi, Japan
4. Department of Cardiology, Japanese Red Cross Kyoto Daini Hospital, Kyoto, Japan
5. Department of Cardiovascular Surgery, Kushiro Kojinkai Memorial Hospital, Kushiro, Japan
6. Department of Cardiovascular Surgery, Nishinomiya Watanabe Cardiovascular Center, Nishinomiya, Japan
7. Department of Cardiovascular Surgery, Kanazawa Medical Center, National Hospital Organization, Kanazawa, Japan
8. Department of Cardiovascular Surgery, Southern Tohoku General Hospital, Kouriyama, Japan