More than 15 authors. Background/Introduction: Pulsed-field ablation (PFA) has emerged as a promising alternative to radiofrequency and cryoballoon ablation, offering fewer complications and high acute success rates. However, the long-term impact of PFA on left atrial (LA) functional remodelling remains unclear. Purpose: This study aimed to assess changes in global and regional LA function after PFA using 4D CT, and to determine whether posterior wall isolation (PWI) contributes to additional impairment of LA strain. Methods: We retrospectively analysed 41 atrial fibrillation patients treated with PFA at UZ Brussel (April 2024–May 2025). Twenty-five underwent pulmonary vein isolation (PVI) alone, and sixteen received PVI plus PWI. All patients underwent contrast-enhanced 4D CT before and after ablation (20 phases per heartbeat; mean interval 65days). LA segmentation was performed, and a reference mesh at end-diastole was deformed across phases using a deformation vector field. Area, longitudinal, and circumferential strains were calculated with a universal atrial coordinate (UAC) system, enabling regional analysis (septal, lateral, anterior, posterior). (Figure Presented).Results: Global LA area strain declined after PFA. In the PVI-only group, reductions were most pronounced in the posterior and septal segments, whereas in the PVI+PWI group, strain decreased more diffusely across all regions. LA maximum volume increased post-procedure (mean +7.2mL in PVI vs. +9.0mL in PVI+PWI). Strain indices also decreased more in the PVI+PWI group, with area strain falling by −0.09 vs. −0.15 and alpha strain by −0.17 vs. −0.22. (Figure Presented).Conclusion(s): Comprehensive 4D CT analysis demonstrated that PFA leads to a measurable decline in LA function, with regional heterogeneity. Additional posterior wall isolation was associated with further impairment of posterior atrial strain. These findings highlight the importance of assessing regional LA function after ablation and suggest that advanced imaging may guide tailored ablation strategies.