Orthostatic Hypotension: QTc Interval Prolongation during Head-Up Tilt

Abstract

Background: The QT interval shortens in response to sympathetic stimulation. Head-up tilt-table (HUT) testing is a straightforward way to achieve brisk sympathetic stimulation. There is not enough information about the response of the QT interval to HUT, particularly, in patients with orthostatic hypotension (OH). Objective: Analyse the response of the RR, QT and QTc intervals in patients with OH and reflex syncope (NM) during HUT and find differences between groups. Methods: We reviewed the electrocardiograms and compare the RR and QT/QTc intervals during 1) baseline; 2) HUT plus hyperventilation; 3) positive test. Results: We studied 137 patients, 62 control group (no syncope and negative HUT). On average, the RR HUT interval was shorter than the resting RR by −171 ± 110.4 ms in controls; −228.6 ± 119.4 ms (NM) and −194 ± (OH) (P < 0.0001). However, in the positive tests, the RR increased by 137.4 ± 377 ms in the NM group and in the OH group, the RR decreased by −141.1 ± 176 ms (P = 0.002). When the test was positive, the QTc interval shortened −27 ± 48 ms in the NM group, and in the OH group prolonged by 15 ± 32 ms (P = 0.00001). Furthermore, the longest QT and QTc interval values were seen in the OH group. Conclusion: Significant differences between the reflex group and the OH during a positive test, the QTc decreased in the NM group, but in the OH population increased. This observation has not been described. We hypothesize that QTc prolongation could reflect autonomic nervous system downregulation and could explain to a degree, the increased mortality in this group.