Abstract: Objective　To explore the diagnostic value of heart rate deceleration (DC) in asymptomatic vasovagal syncope (VVS). Methods　Forty-five children diagnosed with VVS from January 2018 to December 2019 were selected as the VVS group, and 45 healthy children who underwent outpatient physical examination during the same period were selected as the control group. The 24h dynamic electrocardiogram was performed. The changes of baseline DC value, heart rate deceleration runs (DRs) and heart rate variability (HRV) between VVS and healthy children were compared, and the above indicators were compared by age and gender groups. At the same time, the correlation between DC and HRV related-indicators, and the predictive value of DC for VVS diagnosis were analyzed. Results　The DC value, DR8, and the ratio of low frequency power to high frequency power (LF/HF) in the VVS group were significantly higher than those in the control group, and the differences were statistically significant (P<0.05). In VVS group, DC value, DR4 and LF of school-age children were significantly lower than those of adolescent children (P<0.05). However, there was no statistically significant difference in DC value, DRs and HRV indexes between male and female children (P>0.05). The control group was divided into groups by age and gender, and there were no statistically significant differences in DC value, DRs and HRV indexes between different groups (P>0.05). In school-age children, the DC value of VVS group was significantly higher than that of control group. In adolescent children, DC value, DR4, DR8 and LF of VVS group were significantly higher than those of control group (P<0.05). DC was positively correlated with HRV indexes (r=0.31~0.67, P<0.05), and negatively correlated with LF/HF (r=－0.36, P<0.05). Binary logistic regression analysis showed that only DC was associated with VVS in adolescent children (P<0.05). The receiver operating characteristic curve (ROC) was used to analyze the predictive value of DC, and it was found that when the DC value was 7.72 ms in school age children and 8.36 ms adolescent chidlren, there was good sensitivity and specificity. Conclusion　The autonomic nerve function was abnormal in asymptomatic stage of VVS children, and it became more significant with age. Both school-age and adolescent children with VVS had increased vagus nerve tension, and adolescent VVS children had a certain degree of increased sympathetic nerve tension. The DC has an obvious positive correlation with vagus nerve tension and has a good predictive value for the diagnosis of VVS.

Key words: vasovagal syncope;　heart rate deceleration;　heart rate deceleration runs;　heart rate variability;　 autonomic nerve function