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.

Background-The risks of sports participation for implantable cardioverter-defibrillator (ICD) patients are unknown. Methods and Results-Athletes with ICDs (age, 10-60 years) participating in organized (n=328) or high-risk (n=44) sports were recruited. Sports-related and clinical data were obtained by phone interview and medical records. Follow-up occurred every 6 months. ICD shock data and clinical outcomes were adjudicated by 2 electrophysiologists. Median age was 33 years (89 subjects <20 years of age); 33% were female. Sixty were competitive athletes (varsity/junior varsity/traveling team). A pre-ICD history of ventricular arrhythmia was present in 42%. Running, basketball, and soccer were the most common sports. Over a median 31-month (interquartile range, 21-46 months) follow-up, there were no occurrences of either primary end point-death or resuscitated arrest or arrhythmia-or shock-related injury-during sports. There were 49 shocks in 37 participants (10% of study population) during competition/practice, 39 shocks in 29 participants (8%) during other physical activity, and 33 shocks in 24 participants (6%) at rest. In 8 ventricular arrhythmia episodes (device defined), multiple shocks were received: 1 at rest, 4 during competition/practice, and 3 during other physical activity. Ultimately, the ICD terminated all episodes. Freedom from lead malfunction was 97% at 5 years (from implantation) and 90% at 10 years. Conclusions-Many athletes with ICDs can engage in vigorous and competitive sports without physical injury or failure to terminate the arrhythmia despite the occurrence of both inappropriate and appropriate shocks. These data provide a basis for more informed physician and patient decision making in terms of sports participation for athletes with ICDs.