1. Department of Cardiology, Xianyang Central Hospital, Xianyang, Shaanxi 712000, P.R. China
2. Department of Cardiology, Affiliated Hospital of Yan'an University, Yan'an, Shaanxi 716000, P.R. China
3. Department of Cardiology, Hanzhong People's Hospital, Hanzhong, Shaanxi 723000, P.R. China
4. Department of Cardiology, Yan'an City Hospital of Traditional Chinese Medicine, Yan'an, Shaanxi 716000, P.R. China