Atrial inflammation and fibrosis are the critical processes involved in atrial fibrillation (AF) after myocardial infarction (MI). Fisetin is a dietary flavonoid that has shown forceful anti-inflammatory and anti-proliferative properties in diverse models of disease. However, fisetin's role in atrial inflammation, fibrosis, and AF vulnerability post-MI remains completely unknown.

Rats were subjected to MI surgery, by left anterior descending coronary artery ligation or sham operation, and treated with DMSO or fisetin via intraperitoneal injection. After 28 days, echocardiographic parameters were performed, and AF inducibility was tested. We further evaluated the inflammation, fibrosis of left atria (LA), and related signal pathways by RT-PCR, Western blot, and staining analysis.

Compared to the MI group, fisetin treatment improved cardiac function, inhibited macrophage recruitment into the LA and production of IL-1β and TNF-α, and attenuated adverse atrial fibrosis following acute myocardial infarction (AMI). Electrophysiological recordings, using an isolated perfused heart, showed that MI-induced higher inducibility of AF and prolonged AF duration, interatrial conduction time (IACT), atrial effective refractory period (AERP) were significantly alleviated by fisetin. Mechanistically, fisetin markedly increased phosphorylated AMPK (p-AMPK) levels and suppressed NF-κB p65, p38MAPK, and smad3 phosphorylation in the LA post-MI.

We demonstrate that fisetin improves LA expansion, cardiac function, atrial inflammation, fibrosis, and vulnerability to AF following MI by possibly regulating AMPK/NF-κB p65 and p38MAPK/smad3 signaling pathways.