OBJECTIVES This study aimed to evaluate the progression of electrophysiotogicat phenomena in a cohort of patients with paroxysmal atrial fibrillation (PAF) and persistent atrial fibrillation (PsAF). BACKGROUND Electrical remodeling has been conjectured to determine atrial fibrillation (AF) progression. METHODS High-density electroanatomic maps during sinus rhythm of 20 patients with AF (10 PAF, 10 PsAF) were compared with 5 healthy control subjects (subjects undergoing ablation of a left-sided accessory pathway). A computational postprocessing of electroanatomic maps was performed to identify specific electrophysiological phenomena: stow conductions corridors, defined as discrete areas of conduction velocity <50 cm/s, and pivot points, defined as sites showing high wave-front curvature documented by a curt module >2.5 1/s. RESULTS A progressive decrease of mean conduction velocity was recorded across the groups (111.6 +/- 55.5 cm/s control subjects, 97.1 +/- 56.3 cm/s PAF, and 84.7 +/- 55.7 cm/s PsAF). The number and density of slow conduction corridors increase in parallel with the progression of AF (8.6 +/- 2.2 control subjects, 13.3 +/- 3.2 PAF, and 20.5 +/- 4.5 PsAF). In PsAF the atrial substrate is characterized by a higher curvature of wave-front propagation (0.86 +/- 0.71 1/s PsAF vs 0.74 +/- 0.63 1/s PAF; P = 0.003) and higher number of pivot points (25.1 +/- 13.8 PsAF vs 9.5 +/- 6.7 PAF; P < 0.0001). Slow conductions: corridors were mostly associated with pivot sites tending to cluster around pulmonary veins antra. CONCLUSIONS The electrical remodeling hinges mainly on corridors of slow conduction and higher curvature of wave-front propagation. Pivot points associated to SC corridors may be the major determinants for functional localized re-entrant circuits creating the substrate for maintenance of AF. (C) 2022 by the American College of Cardiology Foundation.