1 Department of Cardiology, Institute of Medicine, University of Tsukuba, Tsukuba, Japan.
2 Department of Cardiology, Institute of Medicine, University of Tsukuba, Tsukuba, Japan. Electronic address: kimisato@md.tsukuba.ac.jp.
3 Department of Cardiology, Institute of Medicine, University of Tsukuba, Tsukuba, Japan; Department of Cardiology, Keio University School of Medicine, Tokyo, Japan.