Significant Delayed Activation on the Right Ventricular Outflow Tract Represents Complete Right Bundle-Branch Block Pattern in Brugada Syndrome

Background The appearance of complete right bundle-branch block (CRBBB) in Brugada syndrome (BrS) is associated with an increased risk of ventricular fibrillation. The pathophysiological mechanism of CRBBB in patients with BrS has not been well established. We aimed to clarify the significance of a conduction delay zone associated with arrhythmias on CRBBB using body surface mapping in patients with BrS. Methods and Results Body surface mapping was recorded in 11 patients with BrS and 8 control patients both with CRBBB. CRBBB in control patients was transiently exhibited by unintentional catheter manipulation (proximal RBBB). Ventricular activation time maps were constructed for both of the groups. We divided the anterior chest into 4 areas (inferolateral right ventricle [RV], RV outflow tract [RVOT], intraventricular septum, and left ventricle) and compared activation patterns between the 2 groups. Excitation propagated to the RV from the left ventricle through the intraventricular septum with activation delay in the entire RV in the control group (proximal RBBB pattern). In 7 patients with BrS, excitation propagated from the inferolateral RV to the RVOT with significant regional activation delay. The remaining 4 patients with BrS showed a proximal RBBB pattern with the RVOT activation delay. The ventricular activation time in the inferolateral RV was significantly shorter in patients with BrS without a proximal RBBB pattern than in control patients. Conclusions The CRBBB morphology in patients with BrS consisted of 2 mechanisms: (1) significantly delayed conduction in the RVOT and (2) proximal RBBB with RVOT conduction delay. Significant RVOT conduction delay without proximal RBBB resulted in CRBBB morphology in patients with BrS.

Assessing the Malignant Ventricular Arrhythmic Substrate in Patients With Brugada Syndrome

BACKGROUND

Guidelines recommend the use of implanted cardioverter-defibrillators in patients with Brugada syndrome and induced ventricular tachyarrhythmias, but there is no evidence supporting it.

OBJECTIVES

This prospective registry study was designed to explore clinical and electrophysiological predictors of malignant ventricular tachyarrhythmia inducibility in Brugada syndrome.

METHODS

A total of 191 consecutive selected patients with (group 1; n = 88) and without (group 2; n = 103) Brugada syndrome-related symptoms were prospectively enrolled in the registry. Patients underwent electrophysiological study and substrate mapping or ablation before and after ajmaline testing (1 mg/kg/5 min).

RESULTS

Overall, before ajmaline testing, 53.4% of patients had ventricular tachyarrhythmia inducibility, which was more frequent in group 1 (65.9%) than in group 2 (42.7%; p < 0.001). Regardless of clinical presentation, larger substrates with more fragmented long-duration ventricular potentials were found in patients with inducible arrhythmias than in patients without inducible arrhythmias (p < 0.001). One extrastimulus was used in more extensive substrates (median 13 cm²; p < 0.001), and ventricular fibrillation was the more frequently induced rhythm (p < 0.001). After ajmaline, patients without arrhythmia inducibility had arrhythmia inducibility without a difference in substrate characteristics between the 2 groups. The substrate size was the only independent predictor of inducibility (odds ratio: 4.51; 95% confidence interval: 2.51 to 8.09; p < 0.001). A substrate size of 4 cm² best identified patients with inducible arrhythmias (area under the curve: 0.98; p < 0.001). Substrate ablation prevented ventricular tachyarrhythmia reinducibility.

CONCLUSIONS

In Brugada syndrome dynamic substrate variability represents the pathophysiological basis of lethal ventricular tachyarrhythmias. Substrate size is independently associated with arrhythmia inducibility, and its determination after ajmaline identifies high-risk patients missed by clinical criteria. Substrate ablation is associated with electrocardiogram normalization and not arrhythmia reinducibility. (Epicardial Ablation in Brugada Syndrome [BRUGADA_I]; NCT02641431; Epicardial Ablation in Brugada Syndrome: An Extension Study of 200 BrS Patients; NCT03106701).