The circadian rhythm of syncopal episodes in patients with neurally mediated syncope

To explore the circadian rhythm of neurally mediated syncope (NMS).

411 patients with NMS (165 males and 246 females aged from 3 to 68years) were included in the study. All subjects underwent head-up tilt test (HUTT) and were carefully asked about the number of syncopal attacks and the periods (morning 06:00am-12:00am, afternoon 12:00am-18:00pm, evening 18:00pm-24:00pm, night 00:00am-06:00am) in which episodes occurred in.

(1) Syncopal attacks of all patients tended to occur in the morning (P=0.010); there was a statistical difference in the frequency of episodes in four periods through the day in HUTT positive patients (P=0.001), but there was no significant change of episodes within a day in HUTT negative group; and there was no statistical difference in circadian syncope distribution between HUTT negative and HUTT positive group or among patients with different HUTT responses (the orthostatic hypotension (OH) and orthostatic hypertension (OHT) patients were excluded). (2) The syncopal attacks of morning hours occurred more in males than females, but the episodes in the evening occurred more in females than males (P=0.034). (3) The younger the patients were, the chance of syncopal attacks in the morning increased; the older the patients were, they may have more episodes at night (P<0.001).

A distinct circadian variation in the frequency of syncopal episodes exists, with a peak in the morning, and there were statistical differences in circadian rhythm of syncopal episodes regarding gender and age.