Brugada Syndrome Substrate Characterization and Ablation: Insights From ECG BrS Type I Pattern, Novel Prognostic Index dST-Tiso and High Density Mapping

Most of the patients with a diagnosis of Brugada syndrome (BrS) have no history of syncope or resuscitated cardiac arrest at the time of the diagnosis. Risk stratification in these patients is of utmost importance because cardiac arrest may be the presenting symptom. Individuals with a spontaneous electrocardiogram (ECG) BrS type I pattern (J-point and coved ST-segment elevation in the right precordial leads) are at higher risk of life-threating arrhythmic events than those with ECG abnormalities induced by sodium channel blocking agents. However, in the latter category, there may be subgroups of patients more exposed to the risk of arrhythmias. To date, a clear answer to this question has not yet emerged. Although controversial, programmed ventricular stimulation (PVS) is still central in the complex decision-making algorithm used to manage these lower risk BrS patients. A recent pooled analysis has confirmed the predictive role of PVS inidentifying BrS patients at increased risk of cardiac arrest6. Recently, Iacopino et al. demonstrate that the novel dST-Tiso interval >300 msec is a powerful predictor of ventricular arrhythmias inducibility (sensitivity 92% specificity 90%) in subjects with drug-induced BrS type I ECG pattern7. Radiofrequency ablation (RFA) of arrhythmogenic zones in the right ventricular epicardium has emerged over the past decade as a possible future curative treatment option for BrS. However, only a small number of studies with limited follow-up periods have reported successful results with RFA in symptomatic Brugada patients. The first to describe a successful RFA procedure in Brugada were Nademanee et al. using a selected cohort of nine high-risk patients with frequent ICD shocks for ventricular arrhythmias. More recently, Brugada et al.and Nademanee et al. described an improved technique for successful elimination of the Brugada syndrome phenotype with epicardial RFA. The mapping was performed before and after administration of flecainide/ajmaline which resulted in identification of more extensive arrhythmogenic segments in the RV epicardium beyond the RVOT.

Most recently, Iacopino et al. proposed a successful epicardial ablation of the arrhythmogenic substrate in BrS by using a novel and feasible technique with hybrid mini-thoracotomic approach and a 0-fluoroscopy strategy. The novel workflow combines both electrophysiological and surgical skills in a hybrid fashion with the aim to overcome their respective limitations.

Bipolar electrogram (BiEGM)-based substrate maps are heavily influenced by direction of a wavefront to the mapping bipole. Recently, Porta-Sanchez et al. evaluate high-resolution, orientation-independent peak-to-peak voltage (Vpp) maps obtained with an equi-spaced electrode array and omnipolar EGMs (OTEGMs), measure its beat-to-beat consistency, and assess its ability to delineate diseased areas within the myocardium compared against traditional BiEGMs on two orientations: along (AL) and across (AC) array splines and demonstrate that an equi-spaced electrode grid when combined with omnipolar methodology yielded the largest detectable bipolar-like voltage and is void of directional influences, providing reliable voltage assessment within infarcted and non-infarcted regions of the heart.

To date, there is no study that characterized the arrhythmogenic substrate of Brugada patients with the equi-spaced electrode array and omnipolar EGMs (OTEGMs) that are available nowadays.

The published studies regarding epicardial substrate ablation in Brugada patients describe an electrophysiological substrate characterized by abnormal fragmented prolonged low-frequency ventricular electrograms. We believe that the low resolution and the greater electrode dimensions of the conventional catheter can impact on both the duration and morphology of these signals.