AUTONOMIC IMBALANCE ASSESSED BY HEART-RATE-VARIABILITY ANALYSIS IN VASOVAGAL SYNCOPE

In this prospective study, the autonomic modulation of the sinus node of 12 patients (mean age 28 +/- 7 years) suffering from vasovagal sync ope (VVS) was compared to that of 11 sex and age matched control patie nts (mean age 32 +/- 4 years) by analysis of heart rate variability. S pectral indices (low frequency power [Plf], high frequency power [Phf] , total power [Pt], sympathovagal balance [LF/HF]) and temporal indice s, the mean of all coupling intervals between normal beats (mRR), the standard deviation about the mean (sdRR), the percentage of adjacent R to R intervals differing by more than 50 msec (pNN50), and the root m ean square of variations in successive R to R intervals (rMSSD) were c ompared at baseline and during head-up tilt between and within groups. Baseline results were similar in both groups. During tilt testing, co mparison of results between groups revealed only significantly higher sdRR and rMSSD and lower LF/HF ratio in WS patients. Within VVS patien ts, comparison of temporal and spectral analysis between baseline and tilt showed a significant increase of most indices (Plf, Phf, Pt, sdRR , and rMSSD) but a comparable LF/HF ratio; in contrast, control patien ts exhibited only a significant increase of LF/HF ratio. In conclusion , VVS patients who developed vasovagal syncope during head-up tilt dem onstrated a nonreciprocal modulation of the sinus node by the autonomi c nervous system indicative of a pronounced physiological sympathetic surge along with a paradoxical vagal input to the cardiovascular syste m.