Cardiovascular rhythms in vasovagal syncope

Vasovagal syncope is a disorder of regulation in which different quantities of neural sympathetic and vagal activities interact, resulting in an unstable autonomic profile before the loss of consciousness. The functional state of the cardiovascular autonomic control is mirrored by the amplitude (power) of the spontaneous fluctuations in RR interval and blood pressure variability and in the pattern of the discharge activity of the post-ganglionic sympathetic fibers (muscle sympathetic nerve activity, MSNA). Power-spectrum and cross-spectrum analysis methodologies enable the identification of the frequency and the quantification of the amplitude of these fluctuations, giving a valuable insight into the autonomic changes preceding vasovagal events which may remain hidden when simple heart rate or blood pressure values are considered.