Heart rate variability analysis during head-up tilt testing in diagnostics of reflex syncope - review of problems and our experiences

Introduction: Participation of autonomic nervous system activity in the pathophysiology of neurally-mediated reflex syncope is a research topic for over three decades. Published papers on this topic vary in methods used, patient sets, as well as in the results. Aim: The aim of the study was to compare the analysis of heart rate variability generated during particular phases of head-up tilt testing with the analysis of selected time periods during testing in patients with syncope history. Patients and methods: 80 persons examined for reflex syncope were divided into 4 groups of 20 according to the results of head-up tilt testing as: reference, bradycardiac, tachycardiac and vasodepressor. Exclusion criteria were medicines interfering with heart rate and atrial fibrillation. Spectral analysis of heart rate variability was performed by evaluation of the whole duration of the particular phases (tilting, supine) and evaluation of the selected ultra-short time periods (1 or 2 min) with visual checking of the sinus rhythm. Results: Statistically significant changes in heart rate variability parameters were found only in the bradycardiac group: within the first minute after termination of tilting, a decrease in the low frequency component (P = 0.015), an increase in the high frequency component (P = 0.015), and a decrease in the ratio of both components (P = 0.003); analysis of the whole recovery supine position revealed only a decrease in the ratio of both components (P = 0.015). There were also statistically signifi cantly higher registered values of heart rate in the tachycardiac group and statistically signifi cantly lower blood pressure values in the vasodepressor group during tilting and in the first minute after termination of tilting. Conclusion: Ultra-short-term heart rate variability analysis in time periods directly related to syncope in comparison with the analysis of the entire test phases demonstrated a higher number of significant changes in the endpoints related to autonomic regulation of blood circulation. Spectral analysis of heart rate variability in subjects with cardio-inhibitory reflex syncope revealed a significant increase and prevalence of the high frequency component in the time period immediately after syncope.