Heart rate variability in childrenwith neurocardiogenic syncope

Abstract. In order to characterize the autonomic profile of syncopalchildren, we have studied heart rate variability (HRV) of 73children, ages 11–18, with neurocardiogenic syncope and apositive outcome of head-up tilt testing (HUT).HRV wascalculated over a 24-hour period for the time-domain indices(SDNN, SDANNi, SDNN, rMSSD, pNN50), and over 5-minute segmentsfrom night and day for frequency-domain indices (LF, HF, LF/HF).The obtained results were compared to reference valuescalculated for Polish children. 55% of the children had mixedresponse to HUT, 41% vasodepressor and 4% cardioinhibitory.Patients with syncope had significantly lower values of rMSSDand pNN50 in comparison to healthy children. Moreover, in thefrequency-domain analysis they exhibited significantly higher LFand lower HF values. The day-night rhythm of HRV and theage-related changes of HRV were, however, similar in syncopaland healthy children. In addition to this, we found asignificantly lower SDNN value in children with cardioinhibitoryresponse during HUT in comparison to children with mixedresponse. We concluded that 1) based on HRV analysis childrenwith neurocardiogenic syncope had alterations in basal autonomicbalance, which indicated an increased sympathetic modulation inthese patients, 2) syncopal children had adequate circadianrhythm of autonomic activity, 3) the changes of HRV indices withage in these groups are not altered in comparison to healthychildren, 4) syncopal children may exhibit differences in HRVindices values depending on the kind of vasovagal responseobserved during HUT.