Endo-Epicardial Electrical Disarray in Arrhythmogenic Cardiomyopathy with Ventricular Arrhythmias

Arrhythmogenic cardiomyopathy (ACM) is a hereditary condition frequently presenting with ventricular arrhythmias (VA). VA burden may be disproportionate to detectable structural alterations. To quantify local disorganisation of electrical propagation using the Vector Field Heterogeneity (VFH) metric in patients with ACM and to assess whether VFH may unmask sub-clinical substrate missed in conventional voltage maps. High-density endo-epicardial substrate maps acquired with a 16-pole grid catheter in patients with ACM were retrospectively reviewed. Directional vector maps of electrical propagation were computed offline from 4x4 unipolar arrays. VFH, ranging from 0 (perfect planar wave) to 1 (maximal disorganisation), was estimated as a quantitative measure of local propagation heterogeneity. VFH values were compared between endo- and epicardial maps and across omnipolar voltage (OV)-defined regions: normal (OV>1.5mV), border zone (0.3mV-1.5mV), scar (<0.3mV), as well as isochronal deceleration zones (DZ). 23 patients were included. VFH differed significantly across voltage categories (p<0.001) with highest VFH observed in regions OV<0.3mV (epi 0.57 [0.28] vs. endo 0.56 [0.30]). In border zone regions, epicardial VFH exceeded endocardial (0.41 [0.42] vs 0.39 [0.45]), whereas in normal OV areas, endocardial VFH was higher than epicardial (epi 0.17 [0.27] vs. endo 0.29 [0.34]). Highest VFH were recorded at sites of DZs (0.59 [0.25]), with a trend towards increased electrical disarray during sensed extras (0.62 [0.28], p=ns). Notably, in epicardial regions with normal voltage directly adjacent to low-voltage substrate, VFH was significantly elevated compared to overall normal voltage areas (0.26 [0.32] vs.0.17 [0.27], p<0.001). Heterogeneous electrical propagation quantified by VFH is significantly increased in patients with ACM at sites of scar and DZs, but also in normal voltage areas adjacent to low-voltage areas and on the endocardium. This could indicate microstructural alterations and/or transmural disease progression that are missed in traditional assessments but unmasked by VFH and could complement existing substrate mapping approaches in ACM.