1 Department of Cardiovascular Medicine, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, West 7, North 15, Kita-ku, 060-8638 Sapporo, Japan.
2 Department of Cardiology, Gunma Chuo Hospital, Maebashi, Japan.
3 Department of Pathology and Laboratory Medicine, National Defense Medical College, Tokorozawa, Japan.
4 Division of Cardiology, Kisen Hospital, Tokyo, Japan.