Repolarization gradient induces local depolarization abnormalities in Brugada Syndrome

Abstract

Abstract Background Transmural voltage gradient in right ventricular outflow tract (RVOT) induces diagnostic ECG-phenotype in Brugada syndrome(BrS). Moreover, RVOT depolarization abnormalities have been described as contributors to BrS phenotype and arrhythmogenesis. Purpose To investigate the effect of ajmaline administration on J-elevation of RVOT unipolar signals in BrS patients. Moreover, we wanted to assess whether ajmaline-induced unipolar J-point elevation variations induced local depolarization abnormalities. Methods 21 BrS patients with spontaneous type-1 ECG pattern were enrolled. Due to the absence of BrS ECG pattern at the study, patients underwent RV endocardial mapping with the CARTO3 system, before (PRE) and after (POST) ajmaline administration. The PRE and POST data were exported from CARTO and converted into Matlab format using OpenEP. J-elevation for each point was calculated as the amplitude of the unipolar signal at J wave with respect to baseline. Activation time (AT) of each point was defined as the difference between local depolarization (minimum dV/dt of the unipolar signal) and surface ECG depolarization (time of the minimum signal on V2). With an automatic algorithm, corresponding PRE and POST points were selected. The difference between POST and PRE of each parameter was calculated to obtain the differential values delta-J and delta-AT. Differential values were then interpolated on the mesh of each subject to obtain 3D maps. The deltaJ map was divided into four intervals based on quartiles. We then selected a ROI 'IN' on a region with the greatest deltaJ variation, and a second ROI 'OUT' on the zone of lowest variation. The same ROIs were applied to the deltaAT map. The mean value of the respective differential parameters was extracted in each ROI. Results Greatest delta-J values were found in the RVOT/anterior wall. delta-J in the ROI 'IN' was greater than in the ROI 'OUT' (1.68 [1.11-2.28] vs 0.56 [0.38-0.93] mV, p<0.001). delta-AT in the ROI ‘IN’ was greater than in the ROI ‘OUT’ (27.96 [20.39-44.89] vs 7.62 [4.24-16.69] ms, p<0.001). A good correlation was found between delta-J and delta-AT, considering the data for the two ROIs together (Spearman R coefficient=0.71, p<0.001). Conclusions Our study shows that the repolarization gradient, evaluated by localized delta-J increase in RVOT, justifies BrS ECG phenotype and local depolarization abnormalities. A strong correlation was present in these RVOT areas between J-elevation variation and slow conducting zones.