Sympathovagal Imbalance in Patients with Vasovagal Syncope

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 separately for data of the day time (6:00 AM-8:00 PM) and night time (8:00 PM-6:00 AM). Results: The results of the study demonstrated that patients who had a cardioinhibitory component of VVShad higher SDNN and ASDNN5 when compared to the vasodepressor type and SDNN and ASDNN5 tend to be higher than those with negative TTT. Significant differences were detected for the night time data between patients with a cardioinhibitory component of VVS compared with those who had vasodepressor type or a negative TTT. All of the spectral indices were not significantly different between these groups. Conclusions: The patients with VVS are heterogeneous and the patients with a cardioinhibitory component of VVS had high HRV for all 24 hours and night time. This study underlines the component of resting vagal tone in the pathophysiology of VVS. Vasovagal syncope, Heart Rate Variability, Spectral indices, Temporal indices, Autonomic nervous system