AIMS: Risk-stratification of asymptomatic Brugada Syndrome (BS) patients remains a key-issue. A typical spontaneous BS-ECG pattern and ventricular tachycardia (VT)/ventricular fibrillation (VF) inducibility are two recognized risk markers. The aim of the study was to identify additional risk markers in asymptomatic BS. METHODS AND RESULTS: We have compared Holter recordings in symptomatic and in asymptomatic patients with BS. Heart rate variability (HRV), QT-interval rate-dependence and ST-segment elevation (ST-SE) were analysed. The study population included 47 BS patients (M=36, mean age=45+/-13 years) with a malignant ventricular arrhythmia in 11 cases, an unexplained syncope in 10 cases and no symptoms in the remaining 26 cases. A typical spontaneous BS-ECG was present in 21 cases and a drug-induced BS-ECG in 26 cases. A downward trend of the time domain variables of HRV was observed. During the nocturnal period, standard deviation (SD) of the 5min averaged NN intervals (SDANN) (46+/-13 vs 57+/-18ms, P=0.02) and ultra low frequency component (3287+/-2312 vs 5030+/-3270 ms(2), P=0.04) were significantly lower in symptomatic versus asymptomatic patients. In contrast, no difference was found in QT-interval rate dependence and in ST-SE. At multivariate logistic regression, VT/VF inducibility, typical spontaneous BS-ECG and a decreased nocturnal SDANN were associated with arrhythmic events (P=0.003). CONCLUSIONS: A decreased nocturnal SDANN was an independent marker of arrhythmic events in these BS patients.