Analysis of heart rate variability in paediatric patients with vasovagal syncope

Introduction
The aim of the study was to detect any abnormalities of the autonomic nervous system in children and adolescents with vasovagal syncope.

Material and methods
We studied 56 children, ages eight to 17 years, with a history of vasovagal syncope and 41 healthy volunteers. Heart rate variability was calculated over a 24-hour period for heart rate, standard deviations of the averages of the R-R intervals in all 5-min segments of R-R intervals (SDANN), the root of the 24-hour square (RMSSD), the proportion of adjacent normal R-R intervals < 50 ms (pNN50), the total power (TP), the low frequency index (LF), the high frequency index (HF), and the LF/HF ratio.

Results
Patients with vasovagal syncope had significantly reduced values of 24-hour (256.21 ±190.97 ms, 366.51 ±264.7 ms, p = 0.048) and night-time SDANN (168.56 ±140.59 ms, 251.54 ±189.92 ms, p = 0.034); 24-hour (292.96 ±226.25 ms, 390.49 ±254.06 ms, p = 0.046), daytime (349.52 ±298.32 ms, 479.23 ±350.39 ms, p = 0.040), and night-time RMSSD (188.47 ±161.07 ms, 271.05 ±200.70 ms, p = 0.029); daytime pNN50 (25.10 ±13.10%, 32.10 ±14.19%, p = 0.037); and increased value of night-time LF/HF ratio (1.43 ±1.50, 0.86 ±1.00, p = 0.015), in comparison to healthy subjects. In adolescents with vasovagal syncope we found significantly lower values of 24-hour (7578.29 ±5409.74 ms2, 12236.00 ±5651.45 ms2, p = 0.025) and daytime TP (4776.19 ±4146.56 ms2, 10488.70 ±8326.43 ms2, p = 0.039), 24-hour (2120.90 ±2057.00 ms2, 3634.22 ±3026.90 ms2, p = 0.015) and daytime HF (930.10 ±1101.66 ms2, 7832.90 ±18825.10 ms2, p = 0.015), in comparison with children. Males presented lower values of 24-hour (207.4 ±134.63 ms, 324.00 ±236.95 ms, p = 0.042) and daytime SDANN (264.56 ±208.16 ms, 432.65 ±320.52 ms, p = 0.044), and daytime RMSSD (282.54 ±248.94 ms, 446.28 ±342.35 ms, p = 0.041) compared with females.

Conclusions
Paediatric patients with vasovagal syncope had alterations in basal autonomic balance, which indicated an increased sympathetic modulation. More severe autonomic imbalance occurs in adolescent males.