Background Brugada syndrome (BrS) is a highly arrhythmogenic cardiac disorder, associated with an increased incidence of sudden death. Its arrhythmogenic substrate in the intact human heart remains ill-defined. Methods and Results Using noninvasive ECG imaging (ECGI), we studied 25 BrS patients to characterize the electrophysiologic substrate, and 6 patients with right bundle branch block (RBBB) for comparison. Seven normal subjects provided control data. Abnormal substrate was observed exclusively in the right ventricular outflow tract (RVOT) with the following properties (compared to normal controls; p<0.005): (1)ST-segment elevation (STE) and inverted T-wave of unipolar electrograms (EGMs) (2.21±0.67 vs. 0 mV); (2)delayed RVOT activation (82±18 vs. 37±11 ms); (3)low amplitude (0.47±0.16 vs. 3.74±1.60 mV) and fractionated EGMs, suggesting slow discontinuous conduction; (4)prolonged recovery time (RT; 381±30 vs. 311±34 ms) and activation-recovery intervals (ARIs; 318±32 vs. 241±27 ms), indicating delayed repolarization; (5)steep repolarization gradients (ΔRT/Δx= 96±28 vs. 7±6 ms/cm, ΔARI/Δx= 105±24 vs. 7±5 ms/cm) at RVOT borders. With increased heart rate in 6 BrS patients, reduced STE and increased fractionation were observed. Unlike BrS, RBBB had delayed activation in the entire RV, without STE, fractionation, or repolarization abnormalities on EGMs. Conclusions The results indicate that both, slow discontinuous conduction and steep dispersion of repolarization are present in the RVOT of BrS patients. ECGI could differentiate between BrS and RBBB.

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Background-The relationship of atrioventricular nodal reentrant tachycardia to congenital heart disease (CHD) and the outcome of catheter ablation in this population have not been studied adequately. Methods and Results-A multicenter retrospective study was performed on patients with CHD who had atrioventricular nodal reentrant tachycardia and were treated with catheter ablation. There were 109 patients (61 women), aged 22.1±13.4 years. The majority, 86 of 109 (79%), had CHD resulting in right heart pressure or volume overload. Patients were divided into 2 groups: group A (n=51) with complex CHD and group B (n=58) with simple CHD. There were no significant differences between groups in patients' growth parameters, use of 3-dimensional imaging, and type of ablation (radiofrequency versus cryoablation