Significance of Early Onset and Progressive Increase of Activation Delay During Premature Stimulation in Brugada Syndrome

BACKGROUND: The relationship between the activation delay during programmed stimulation and the inducibility of ventricular fibrillation (VF) and filtered QRS duration on signal-averaged ECG (SAECG) were assessed in patients with Brugada syndrome (BS). METHODS AND RESULTS: The activation delay was assessed using the interval between the stimulus and the QRS complex during programmed stimulation in 25 patients with BS and 10 with idiopathic ventricular tachycardia (controls). The mean increase of delay (MID) was used to characterize the conduction curves. The filtered QRS duration (fQRSd) in leads V(2) (RfQRSd) and V(5) (LfQRSd) were also evaluated using SAECG. Both MIDs at the right ventricular outflow tract (RVOT) were significantly greater in symptomatic and asymptomatic BS patients than in the control group (symptomatic, 7.1 +/-2.7 ms vs control, 2.5 +/-1.2 ms, P<0.001, asymptomatic, 7.3 +/-3.3 ms vs control, P<0.001, respectively). The MID correlated with the His-ventricular interval; however, there were no significant correlations between the MID and RfQRSd or RfQRSd - LfQRSd. CONCLUSIONS: The MID, which indicates an increase of the St-QRS during premature stimulation, was much greater in patients with BS (regardless of clinical symptoms) than in the control group, especially in the RVOT, which might be related to the easy inducibility of VF from the RVOT.