1. ECG Room, Weifang Maternal and Child Health Hospital, Weifang, Shandong 261000, P.R. China
2. ECG Room, Qianfoshan Hospital Affiliated to Shandong University, Jinan, Shandong 250014, P.R. China
3. ECG Room, Shengli Oilfield Central Hospital, Dongying, Shandong 257034, P.R. China
4. ECG Room, The Second Affiliated Hospital of Shandong First Medical University, Tai'an, Shandong 271000, P.R. China
5. ECG Room, Weihai Municipal Hospital, Weihai, Shandong 234200, P.R. China
6. ECG Room, Tai'an Traditional Chinese Medicine Hospital, Tai'an, Shandong 271000, P.R. China
7. ECG Room, Dongying People's Hospital, Dongying, Shandong 257091, P.R. China
8. ECG Room, Weifang People's Hospital, Weifang, Shandong 261041, P.R. China