1. Department of Cardiology, The Second Affiliated Hospital of Xi'an Medical University, Center for Clinical Medical Research of Cardiovascular Diseases in Shaanxi Province, Xi'an, Shaanxi 710038, P.R. China
2. Electrocardiographic Room, Ankang Central Hospital, Ankang, Shaanxi 725000, P.R. China
3. Department of Cardiology, Xingyuan Hospital, Yulin, Shaanxi 719000, P.R. China