Sympathovagal Imbalance in Patients with Vasovagal Syncope

Background: Vasovagal syncope (VVS) is one of the most frequent causes of unexplained syncope and can be assessed by a Tilt Table Test (TTT). The pathophysiology of VVS is related to an imbalance of the autonomic nervous system (ANS). The aim of this study was to compare the autonomic status by Heart Rate Variability (HRV) during asymptomatic periods in patients with syncope who have positive and negative TTT. Methods: We retrospectively studied patients with a history of syncope who underwent a tilt table test and 24-hour Holter monitoring between January 2004 and November 2007. We compared patients with a positive and negative TTT. The following HRV parameters were acquired from Holter monitoring: spectral indices which included low frequency power (LF), high frequency power (HF) and low-high frequency ratio (LF/HF) and temporal indices which included standard deviation for all analyzed N-N intervals (SDNN), average of all five minute standard deviations (ASDNN5), standard deviation of all five minute averages (SDANN5) and root mean square of the difference between successive RR intervals (RMSSD). The spectral and temporal indices of HRV analysis were performed from 24-hour data and separatel