[Usefulness of the RR variability in the diagnosis of neurogenic syncope]

INTRODUCTION AND PURPOSES: Autonomic nervous system plays an important role in the pathogenesis of vasovagal/vasodepressor syncope and may also be assessed by the RR variability analysis. Head up tilt test (HUT) is a currently established tool to evaluate patients with neuromediated syncope. However, the relationship between heart rate variability and tilt induced syncope is not established. The purpose of this study was to assess the differences in heart rate variability among patients with syncope and negative or positive tilt test.

Fifty patients (mean age 33 +/- 17 years, 24 female, 26 male) with syncope underwent tilt test (20 min, 80 degrees tilt and 20 min more under isoproterenol infusion). Twenty-three patients have a negative tilt, the rest had a positive test. There were not significant differences in age or sex. Immediately after the HUT a 24-hour ambulatory electrocardiogram was performed (Marquette system 8000, 002A program). The parameters measured during Holter monitoring were: SDANN, SD, rMSSD, pNN50 and frequency analysis of heart rate spectrum (low frequency 0.04-0.15 Hz, high frequency 0.15-0.4 Hz and the relation low/high). No significant differences were detected in age and sex in patients with and without positive HUT.

pNN50 and rMSSD were the best predictors of the results of tilt (p = 0.006). SDANN and SDNN were not useful parameter. The finding of a value of pNN50 > 25% (value significantly different between patients with HUT--and +) have a specificity for predicting a positive HUT of 82.6%, with a sensibility of 51.8%. Positive predictive value was 77%. As can be easily understood, if the cut value of pNN50 is lowered, its sensibility increased and the specificity. decreased. In the frequency analysis only the relation low/high (L/H) was significantly different between both populations.

Heart rate variability is a useful tool in the evaluation of patients with vasovagal syncope, that may identify patients with chronically elevated vagal tone and thus may predict tilt test results.