MMP9 and pulmonary arterial hypertension: COPD-related hypoxia and systemic inflammation (e.g., HIF-1α/VEGF activation with downstream MMP-9/TGF-β1 signaling) and hypercapnia-related electrophysiologic alterations support atrial remodeling and arrhythmogenesis, while pulmonary hypertension and right-sided chamber enlargement increase atrial stretch and ectopy [6, 10, 11, 14, 15].