From Metabolic Syndrome to Atrial Fibrillation: Linking Inflammatory and Fibrotic Biomarkers with Atrial Remodeling and Imaging-Based Evaluation-A Narrative Review.

Atrial fibrillation (AF) is the most prevalent sustained arrhythmia worldwide and is now increasingly regarded as a disease of chronic inflammation and progressive atrial fibrosis. Understanding of molecular mechanisms that mediate the linkage between systemic metabolic dysregulation, inflammation, and structural atrial changes is crucial for informing risk stratification and targeting of prevention strategies. This review provides evidence from 105 studies focusing on the contributions of transforming growth factor-β1 (TGF-β1), tumor necrosis factor-a (TNF-α), interleukin-6 (IL-6), galectin-3, and galectin-1 to cardiac fibrogenesis, atrial fibrosis, and AF pathogenesis. We also link metabolic syndrome to these biomarkers and to atrial remodeling, as well as echocardiographic correlates of fibrosis. TGF-β1 is established as the central profibrotic cytokine and promotes Smad-based fibroblast activation, collagen accumulation, and structural atrial remodeling. Its role is highly potentiated by thrombospondin-1 by turning latent TGF-β1 into its potent form. TNF-α and IL-6 also play an integral role in the inflammatory fibrotic continuum by activating NF-κB and STAT3 signaling, promoting fibroblast proliferation, electrical uncoupling, and extracellular matrix accumulation. Galectin-3 is a potent profibrotic mediator that promotes TGF-β signaling and is a risk factor for negative outcomes, whereas Gal-1 seems to regulate inflammation resolution and may exert context-dependent protective or maladaptive roles. Metabolic syndrome is strongly associated with excessive levels of these biomarkers, chronic low-grade inflammation, oxidative stress, and ventricular and atrial fibrosis. Chronic clinical findings show that metabolic syndrome (MetS) increases AF risk, exacerbates atrial dilatation, and is associated with worse postoperative outcomes. Echocardiographic data are connected to circulating biomarkers and are non-invasive for evaluating atrial remodeling. The evidence to date supports that atrial fibrosis should be considered an end point of systemic inflammation, metabolic dysfunction, and activation of profibrotic molecular pathways. Metabolic syndrome, due to its chronic low-grade inflammatory environment and prolonged levels of metabolic stress, manifests as an important upstream factor of fibrotic remodeling, which continuously promotes the release of cytokines, oxidative stress, and fibroblast activation. Circulating fibrotic biomarkers, in comparison with metabolic syndrome, serve separate yet interdependent pathways that help orchestrate atrial structural remodeling through the simultaneous process but can also provide a long-term indirect measure of ongoing profibrotic activity. The integration of these biomarkers with superior atrial imaging enables a broader understanding of the fibrotic substrate of atrial fibrillation. This combined molecular imaging approach can facilitate risk stratification, refine therapeutic decisions, and facilitate early identification of higher-risk metabolic phenotypes, thus potentially facilitating directed antifibrotic and anti-inflammatory therapy in atrial fibrillation.