Modifications of Autonomic Activity and Baroreceptor Response on Posture Challenge in Patients with Vasovagal Syncope

Background: Vasovagal syncope (VVS) is diagnosed by medical history and confi rmed by a head-up tilt (HUT) test. The pathophysiology of VVS is controversial. Methods: In this study, we enrolled 30 VVS patients and compared normal study patients in Tri-Service General Hospital. We attempted to examine this controversy by evaluating heart rate variability and baroreceptor sensitivity of VVS in the upright posture. Results: The VVS patients had lower total peripheral vascular resistance, increased LF/HF (low frequency power / high frequency power) ratio, and decreased baroreceptor sensitivity in the HUT position. Conclusion: The VVS patients demonstrated postural vascular sympathetic dysfunction and cardiac sympathetic hyperactivity before syncope. The decreased baroreceptor sensitivity might be partly explained by the failure of the usual compensatory heart rate increase during orthostatic challenge.