Assessment of autonomic function at rest and during tilt testing in patients with vasovagal syncope.

This study evaluated autonomic nervous system function in 30 patients with syncope and a positive tilt test result, 20 with a negative test result, and 20 healthy controls. Indexes of heart rate variability were measured during the intervals immediately before and after tilt, while all subjects were asymptomatic, and over a 24-hour period. There were no significant differences among the groups in any of the indexes of heart rate variability over the 24-hour period. In patients with a positive tilt result, tilting caused a decrease in low-frequency (LF) and high-frequency (HF) bands, although the LF/HF ratio did not significantly change. In patients with a negative tilt result there was a decrease in the HF band but no other significant changes. In the controls there was an increase in the LF band and LF/HF ratio and a decrease in the HF band. Our findings showed that patients with vasovagal syncope have no chronic differences from normal subjects in autonomic nervous system activity, but that these patients respond differently to the orthostatic stimulus.