1. Department of Cardiovascular Surgery, The Sakakibara Heart Institute of Okayama, 2-5-1 Nakai-cho, Kita-ku, Okayama City, 700-0804 Okayama, Japan
2. Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama City, 700-8558 Okayama, Japan