Advanced age promotes atrial ectopy and atrial fibrillation stabilization: the role of activated coagulation factors and the atrial inflammasome

Background

Age is a risk factor for atrial fibrillation (AF) and for stroke in patients with AF. Activated coagulation factors and their receptors (PARs), can promote NLRP3-inflammasome activation, which is involved in the pathogenesis of AF.

Objectives

To investigate the effect of aging on atrial ectopy, AF substrate development, and AF stabilisation, as well as AF-mediated activation of coagulation and the atrial inflammasome.

Methods

Four groups of goats were studied: Young (<3 years) sinus rhythm (Y-SR, n=9), Young AF (Y-AF n=7), Old (>8 years) sinus rhythm (O-SR, n=6), and Old AF (O-AF, n=8). Atrial ectopy and AF stabilisation were monitored during 4 weeks of atrial burst pacing. Clotting potential was measured using thrombin generation assays at baseline and 4 weeks (final). Hemodynamics and AF characteristics were assessed at the final experiment. Atrial samples were collected for histological, gene and protein expression analyses.

Results

Old goats exhibited faster AF stabilization (179 ± 374 AF paroxysms vs.1487 ± 614 AF paroxysms required for persistent AF development) and more frequent premature atrial contractions (PACs, ~4-fold increase) compared to young goats, but no increased AF complexity. Old goats showed higher constitutive atrial NLRP3 inflammasome activity (Casp1-p20: ~1.8-fold increase, GSDMD-NT: ~1.7-fold increase, and IL-1β: ~2.7-fold increase) relative to young goats. Thrombin generation potential did not differ between young and old goats at baseline.

While age alone did not alter AF complexity and thrombin generation, AF exerted a stronger effect on electrophysiology and coagulation in old goats than in young goats. Four weeks of AF increased systemic thrombin generation in old (baseline 178.8 ± 35.6 nM vs. final 219.5 ± 52.2 nM), but not in young goats. Moreover, in old goats, AF elicited atrial myocyte hypertrophy (O-AF: 13.79 µm [95% CI: 13.06, 14.53] vs. O-SR: 12.17 µm [95% CI: 11.32, 13.02]) and left atrial epicardial endomysial fibrosis (cell to cell distance, O-AF: 3.15 µm [95% CI: 2.83, 3.47] vs. O-SR: 2.91 µm [95% CI: 2.59, 3.24], along with increased atrial pro-fibrotic ( COL1A1: ~8.9-fold increase) and pro-hypertrophic (NPPA: ~2.9-fold increase, and NPPB: ~12.9-fold increase) gene expression compared to age-matched controls. Four weeks of AF upregulated atrial PAR-2 protein expression in both age groups and enhanced atrial NLRP3 inflammasome signalling particularly in young goats.

Conclusions

This study shows that aging accelerates AF stabilization, possibly through enhanced atrial ectopy and faster development of conduction alterations. In old goats, the greater AF susceptibility was accompanied by elevated baseline activation of the atrial NLRP3 inflammasome, which may have contributed to enhanced atrial ectopy and conduction disturbances. Finally, in older animals AF increased thrombin generation, which may have accelerated the development of a structural substrate for AF.