Abnormal Nocturnal Heart Rate Variability and QT Dynamics in Patients with Brugada Syndrome

Background: In Brugada syndrome (BSY), most of the ventricular arrhythmic events are nocturnal, suggesting an influence of the autonomic nervous system.
Methods: In 46 patients (mean age = 41 ± 14 years, 43 men) with electrocardiograms (ECG) consistent with BSY and structurally normal hearts, we measured heart rate variability (HRV) and QT dynamics (QT/RR slopes) on 24-hour ambulatory ECG. Type 1 BSY-ECG was spontaneous in 23 (50%) and induced in 23 patients.
Results: History of syncope was present in 23 patients (50%). Programmed ventricular stimulation induced ventricular tachyarrhythmias (VTA) in 13 patients (28%). A single patient developed ventricular tachycardia during a mean follow-up of 34 months. Compared to a control group matched for age and sex, HRV was decreased over 24 hours and during nighttime in patients with BSY (SDNN 122 ± 44 vs 93 ± 36 ms, P = 0.0008 and SDANN 88 ± 39 vs 54 ± 24 ms, P < 0.0001). QTend /RR slopes were decreased over 24 hours in patients with BSY (0.159 ± 0.05 vs 0.127 ± 0.05, P = 0.003) and particularly at night (0.123 ± 0.04 vs 0.089 ± 0.04, P = 0.0001). QTend /RR slopes were significantly decreased during nighttime in patients with spontaneous versus provoked BSY-ECG patterns. By contrast, HRV and QT/RR slopes were similar in symptomatic and asymptomatic patients, whether VTA were induced or not.
Conclusions: Patients with a BSY-ECG pattern had lower HRV and QT/RR slopes than control subjects during nighttime. High-risk patients with spontaneous BSY-ECG patterns had the lowest nocturnal QTend/RR slopes. These unique repolarization dynamics might be related to the frequent nocturnal occurrence of VTA in BSY.