Long PR Interval Leads to Atrial Remodeling, Fibrosis and Inducible Atrial Fibrillation in Swine

Abstract 2277430, presented at Western Atrial Fibrillation Symposium 2026

Pacing algorithms have been developed to minimize the risk of pacing-induced ventricular dysfunction at the expense of a prolonged PR interval. However, a long PR interval has been associated with incident atrial fibrillation (AF) and the impact of a prolonged PR interval on atrial remodeling remains unclear. We investigated the effects of standard vs. long atrioventricular delay (AVD) on atrial function in swine.Twenty-four Yucatan mini-swine were divided into 3 groups: control (AAI 90 bpm, n=8), standard (160/180ms, n=8) and long (350ms, n=8) AVD groups. All animals underwent baseline electrophysiological studies followed by implantation of a dual-chamber pacemaker with left bundle branch area leads for the standard and long AVD groups. Swine in the standard and long AVD groups underwent atrioventricular junctional (AVJ) ablation to allow 100% pacing at the programmed AVD. Atrial and ventricular function was assessed by monthly speckle-tracking echocardiography. At the terminal study, repeat electrophysiology and echocardiography studies were performed followed by tissue histology.Baseline paced QRS durations after AVJ ablation (control, 76.8 ± 3.5; standard, 77.1 ± 4.1; long, 77.9 ± 3.8 ms; P = 0.835), left ventricular dyssynchrony (control, 7 [0–11]; standard, 7 [0–10]; long, 9 [2–9] ms; P = 0.986) and left ventricular ejection fraction (control, 81.1 ± 7.4; standard, 85.9 ± 5.6; long, 82.4 ± 7.4%; P = 0.373) did not differ among the groups. At 4 months, the long AVD group exhibited greater left atrial (LA) dyssynchrony (control, 25.8 ± 12.3; standard, 23.6 ± 12.0; long, 81.1 ± 19.5 ms; P < 0.001), decreased LA peak strain (control, 39.6 ± 4.5; standard, 37.4 ± 5.3; long, 22.3 ± 5.4%; P < 0.001), greater AF inducibility (control, 0 [0–8]; standard, 0 [0–0]; long, 39 [25–64]%; P < 0.001), slower conduction velocity (control, 1.9 ± 0.1; standard, 1.8 ± 0.2; long, 1.5 ± 0.2 m/s; P < 0.001) and higher atrial fibrosis burden (control, 6.2±1.0; standard, 6.6±0.6; long, 10.6±1.3%, P < 0.001) than the other groups.A long AVD led to worsening atrial function, inducible AF and fibrosis in this model, suggesting that conduction system pacing with a standard AVD may be better for atrial mechanics and the future risk of AF than allowing intrinsic conduction with a long PR interval.