1. Department of Geriatrics, Xuanwu Hospital, Capital Medical University, Beijing 100053, P.R. China
2. Department of Cardiology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang�150081, P.R. China
3. Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, CA 90095, USA