https://doi.org/10.1007/s00392-025-02625-4
1Medizinische Hochschule Brandenburg Kardiologie/Angiologie Neuruppin, Deutschland; 2Marienhospital Herne, Klinikum der Ruhr-Universität Bochum Med. Klinik II, Kardiologie u. Angiologie Herne, Deutschland; 3Kerckhoff Klinik GmbH Herzchirurgie Bad Nauheim, Deutschland; 4Universitätsklinikum Brandenburg an der Havel GmbH Zentrum für Innere Medizin I Brandenburg an der Havel, Deutschland; 5Universitätsklinikum Ruppin-Brandenburg Med. Klinik A Schwerpunkt Kardiologie Neuruppin, Deutschland
Background and aim: The mechanisms of atrial fibrosis as an important factor in the initiation and maintenance of atrial fibrillation (AF) are not yet fully understood. We hypothesized that activated inflammasome and coronary microthrombosis lead to necrotic cardiomyocyte death, culminating in replacement atrial fibrosis.
Methods: We analyzed right atrial biopsies from 15 patients in SR, 17 patients with paroxysmal AF (pAF) and 17 patients with chronic sustained AF (cAF). The main components of the nod- like receptor family (pyrin domain-containing protein three (NLRP-3) inflammasome (NLRP-3, caspase-1, gasdermin-D, apoptosis-associated speck-like protein (ASC) and Il-1ß1) were analyzed by quantitative immunohistochemistry and Western blot. The occurrence of microthrombi and cardiomyocyte death was assessed by immunohistochemistry, confocal and electron microscopy.
Results: Compared to patients in SR, NLRP-3 expression was increased 2.3- and 3.6-fold in patients with pAF and cAF, respectively. Similarly, the number of NLRP-3 structures per 1 mm2 atrial area increased significantly from 171 ± 63 in SR to 443 ± 100 in pAF and 773 ± 145 structures in cAF patients. Both, the NLRP-3 protein levels and the mean numbers of NLRP-3 structures per atrial area were significantly higher in cAF than in pAF (p<0.01). Immunohistochemistry with antibodies against CD41b revealed 4.3 ± 1.1 microthrombi containing platelet aggregates per 1mm2 of atrial tissue in pAF patients and 8.1 ± 1.95 microthrombi in cAF patients. These values in both AF groups were statistically different (p<0.01) that those in SR patients (< 1 microthrombus per atrial area). These results were confirmed by electron microscopy (Figure 1), which revealed 6.4 ± 1.2 microthrombi in pAF patients, 3.6 ± 0.86 microthrombi in cAF patients and 0.6 ± 0.3 microthrombi per 1 mm2 of atrial area in patients SR. Membrane pore formation and irreversible cardiomyocyte damage were detected by electron microscopy and by immunohistochemistry with antibodies against complement 9. Necrotic cardiomyocytes were predominantly located in the atrial perivascular areas (Figure 2). Quantitative analysis revealed 3.55 ± 0.88 and 7.8 ± 1.77 necrotic cardiomyocytes per 1mm2 of atrial tissue in pAF and cAF patients, respectively. These values were statistically different (p < 0.01) from those in SR patients (1.06 ± 0.45 necrotic cardiomyocytes per 1mm2 of atrial tissue). The number of necrotic cardiomyocytes significantly correlated with the number of microthrombi per tissue area (r = +0.77, p < 0.01) and with the number of NLRP-3 structures (r = +0.76, p < 0.01).
Conclusion: This is the first study to link activated NLRP3-inflammasome and coronary microthrombosis to cardiomyocyte cell death and atrial replacement fibrosis in patients with AF.