Increased intermittency and decreased nonstationarity of heart rates during the daytime in patients with neurocardiogenic syncope.

ABSTRACT

INTRODUCTION: During head-up tilt (HUT) test, patients with neurocardiogenic syncope show a sudden severe decrease in heart rate at the beginning of their induced syncopal attacks (termed intermittency). They also exhibit slow and progressive increases in their mean heart rates long before the induced syncopal attacks (termed nonstationarity). The aim of this study was to test our hypothesis that during daily activity, although not as prominently as during HUT test, patients show different degrees of intermittency and nonstationarity compared to healthy persons. METHOD AND RESULTS: Thirty patients with a positive HUT test and 30 healthy controls without a history of syncope were studied. The RR intervals of their 24-hour ambulatory ECGs were analyzed. To quantify the intermittency (C1) and nonstationarity (H1) behavior, multifractal analysis was performed using Mexican hat and Haar wavelet function, respectively. In the syncope group, C1 and H1 were significantly higher at 6 A.M.-6 P.M. and lower at 6 A.M.-midnight, respectively. However, the values were not different at midnight-6 A.M. The significant night-day circadian change shown in the control group was lost in C1 and diminished in H1. CONCLUSION: Patients with neurocardiogenic syncope show increased intermittency and decreased nonstationarity of heart rates in the daytime during daily activity, and abnormal night-day circadian changes of the intermittency and nonstationarity. These findings may be useful in the early identification of patients with neurocardiogenic syncope and in the investigation of abnormalities in heart rate regulating mechanisms.