Heart Rate Variability In Children With Vasovagal Syncope

Objective To investigate the heart rate variability (HRV) in children with vasovagal syncope (WS), and to explore whether the basal autonomic profile has been altered in children with VVS, and the effect of age, gender and response type on children with VVS.Methods Eighty-two children (33 males, 49 females, age 4-17 yrs, mean 10.85±2.58yrs) were enrolled in this study, who came from syncope outpatient department or in-patient department of the Second Xiangya Hospital of Central South University during Jan 2003 to Dec 2006. According to the result of head-up tilt table test (HUTT) they were further divided into HUTT-positive group and HUTT-negative group. Fifty healthy children were as control group, who were matched in age and gender. All children experienced 24 hour dynamic electrocardiogram and Holter recordings were analyzed in the computer. HUTT was performed in syncope group in the consecutive day. According to different standard these children were divided, and time domain and frequency domain indexes were compared between groups. SPSS 11.0 software was used for the statistical analysis of these data.Results Gender and age had no significant differences between syncope group and control group. HUTT was positive in 48 children and negative in 34 children in syncope group. Among 48 HUTT-positive children(16 males), 20 were less than 12 years, 32 were vasodepressor response, 14 were mixed response and 2 were cardio-inhibitory response. Comparing with the controls, SDNN,VLF,HF (p<0.05) and TT,LF (p<0.01) were significantly lower and SDANN,rMSSD,pNN50,LF/ HF were slightly lower in syncope group (p>0.05). HRV indexes were lower in HUTT-positive group compared to the control group, but only LF was significant (p<0.05). SDANN was significantly lower (p<0.05) in children with no more than twelve years than the others in HUTT-positive group, but other HRV indexes had no evident differences (p>0.05). Among children with VVS, HRV indexes were lower in females than males, but only TP (p<0.01) and VLF,LF,SDNN (p<0.05) reached statistical significance. Time domain and frequency domain indexes were higher in mixed type than vasodepressor type, but none of them was significant (p>0.05).Conclusions The function of sympathetic and parasympathetic nerve has been altered and autonomic activity is diminished in children with unexplained syncope. The basal autonomic profile is abnormal in children with VVS. Following the increase of age, the activity of autonomic nervous system is increased, but sympathetic activity is dominant in children with VVS. Among children with WS, the activity of autonomic nervous system is weaker in females than males. The children of vasodepressor and mixed response have similar pattern of change in autonomic activity.