1. Department of Cardiovascular Medicine, Sapporo Cardiovascular Clinic , North 49, East 16, 8-1, Higashi Ward, Sapporo, Hokkaido 007-0849 , Japan
2. Department of Cardiovascular Medicine, Chiba University Graduate School of Medicine , 1-8-1 Inohana, Chuo-ku, Chiba-shi, Chiba 260-8670 , Japan