Distinct platelet phenotype and reactivity in individuals with permanent atrial fibrillation treated with direct oral anticoagulants: a pilot study

Background: Atrial fibrillation (AF) is an age-related disease linked to an elevated risk of thromboembolic events. Despite the use of guideline-recommended direct anticoagulants (DOACs), a significant proportion of patients with AF show a residual risk of thromboembolic events, driven by mechanisms that are not fully understood. Objective: We conducted a pilot study to characterise the platelet phenotype and function in DOACs-treated AF patients, to explore whether an association between platelets and the residual thromboembolic risk exists. Methods: Within the Age-It project of the National Recovery and Resilience Plan, we examined by flow cytometry the platelet phenotype, reactivity and mitochondrial function of individuals with DOACs-treated permanent AF without a history of stroke (n=18, 66±13 years, 39% females), as compared to an age-, sex-, and comorbidity-matched control group without AF (n=18, 65±11 years, 39% females). Results: Unstimulated circulating platelets of DOACs-treated AF displayed a low-adhesive/quiescent phenotype compared to matched controls. Upon stimulation, platelets of DOACs-treated AF were hypo-reactive to ADP and PAR1 stimulation, but hyper-reactive to GPVI stimulation (median [IQR] of CTRL: 94.6 [13.4] %; AF: 96.9 [1.9] %; p=0.0014). Integrin activation positively correlated with dyslipidemia and higher mitochondrial membrane potential, which in turn correlated with serum TNF-α levels. Platelet surface receptor levels and TNF-α independently associated to an elevated CHA₂DS₂-VASc score. Conclusions: Individuals with DOACs-treated AF exhibit a distinct platelet phenotype, suggesting a potential mechanism behind their residual thromboembolic risk. Further well-powered studies are warranted to test whether platelet phenotyping can improve the prediction of thromboembolic events in DOACs-treated AF patients.