Regional specific changes in cardiac resident macrophages and fibroblasts modulate long-term atrial fibrillation maintenance

Abstract Background Most of the mechanistic insights into atrial fibrillation (AF) pathophysiology have been reported on cardiomyocytes, and it is commonly assumed that they apply in the same manner to different regions of the atria. Purpose This study aimed to investigate the differential regional features of non-myocyte populations in the atria of pigs and patients with persistent AF (PsAF) based on their functional relevance for AF maintenance. Methods We developed a porcine model resembling clinical PsAF without underlying structural heart disease (N=19), and a second PsAF model with infarct-related atrial cardiomyopathy (MI-PsAF, N=14). Animals with MI-PsAF underwent 3-hour ischaemia-reperfusion in the proximal circumflex artery 2 months prior to the initiation of the AF protocol. The latter aimed to resemble a common clinical scenario with underlying coronary artery disease. After long-lasting self-sustained PsAF, all animals underwent in vivo electroanatomical mapping to identify individual-specific atrial regions associated with AF maintenance (i.e., driver regions), which were further characterized in ex vivo studies by flow cytometry, single-cell RNA transcriptomics (Figure 1), proteomics, and immunolabeling. The results in animals were validated on atrial samples from patients with driver regions in the left atrial appendage (N=8). Results In a subset of 7 and 6 animals with PsAF and MI-PsAF, respectively, radiofrequency ablation at driver regions effectively terminated the arrhythmia in 100% and 67% of the cases. In patients, ablation of driver regions achieved 90% AF-free survival at 2-years of follow-up. Atrial remodeling during PsAF showed differential adaptative changes in non-myocyte populations, which depended on the functional relevance to sustain the overall arrhythmia. Both in animals and patients, driver regions showed overt compositional shifts in fibroblasts and myeloid populations. More specifically, driver regions were characterized by a phenotypic shift towards cardiac resident macrophages with an associated transcriptomic and proteomic profile favoring cardiomyocyte homeostasis and cell survival within a substrate prone to re-entry (Figure 2). In fibroblasts, PTX3 represented a transcriptional hallmark exclusively present in driver regions, which supports their role on modulating regional specific changes during PsAF. Conclusions The results reported herein provide a new perspective on the critical role of regional atrial differences in non-myocyte populations that contribute to sustain AF in the long-term.Figure 1 Figure 2