1. Department of Cardiology, Binzhou Medical University Hospital, Binzhou, Shandong 256600, P.R. China
2. Department of Obstetrics, Jiaozhou Central Hospital of Qingdao, Jiaozhou, Shandong 266300, P.R. China
3. Department of Emergency, Binzhou Medical University Hospital, Binzhou, Shandong 256600, P.R. China
4. Department of Continuing Education, Binzhou Medical University Hospital, Binzhou, Shandong 256600, P.R. China