24-hour heart rate variability in patients with vasovagal syncope

Since alterations in the autonomic nervous system are thought to play a maj or role in the pathogenesis of vasovagal syncope, we characterized the chro nic autonomic profile of 44 patients with syncope and 20 healthy subjects b y means of heart rate variability using 24-hour Holter recordings (time- an d frequency-domain indexes), and evaluated whether the different types of r esponses to tilting (vasodepressive versus cardioinhibitory) could be assoc iated with different cardiac autonomic patterns. Twenty-three patients exhi bited a positive response to tilting, which was vasodepressive in 11 patien ts and cardioinhibitory in 12 patients. All vasodepressive patients had a s tandard deviation of the averages of NN (SDANN) intervals in all 5-minute s egments lower than 100 ms. Patients with vasodepressive syncope also had si gnificantly lower values of RMSSD (the 24-hour square root of the mean of t he sum of the squares of differences between adjacent normal RR intervals) than those with cardioinhibitory response, and lacked the day-night rhythm of the low frequency/high frequency ratio. However, only SDANN values corre ctly identified patients with vasodepressive response to tilting. We conclu de that (1) the population of patients with vasovagal syncope is heterogene ous, (2) patients with vasodepressive syncope have a peculiar chronic auton omic profile as assessed by 24-hour heart rate variability analysis, and (3 ) the evaluation of the autonomic profile in 24-hour Holter recordings coul d be of value in the diagnosis of patients with syncope.