CD4 and atrial fibrillation: T lymphocytes, particularly CD4+ and CD8+ subsets, emerge as key mediators: CD8+ T cell senescence marks AF atrial tissue and correlates with recurrence (Li et al., 2024); CD4+CD28null T cells predict postoperative AF and heart failure outcomes (Sulzgruber et al., 2017; Sulzgruber et al., 2018; Hammer et al., 2021); Th17/Treg imbalance associated with AF-related inflammation and fibrosis (Wu et al., 2016; He et al., 2018; Chen et al., 2020).