1. Department of Cardiovascular Surgery, Chibanishi General Hospital, 107-1 Kanegasaku, Matsudo, Chiba 270-2251, Japan
2. Department of Cardiovascular Surgery, Omori Red Cross Hospital, 4-30-1 Chuo, Ota-ku, Tokyo 143-8527, Japan
3. Department of Cardiovascular Surgery, IMS Katsushika Heart Center, 3-30-1 Horikiri, Katsushika-ku, Tokyo 124-0006, Japan