Influence of thrombocytopenia on bleeding and vascular events in atrial fibrillation.

Whether thrombocytopenia substantively increases the risk of hemorrhage associated with anticoagulation in patients with atrial fibrillation (AF) is not established. The purpose of this study was to compare rates of bleeding in patients with AF and thrombocytopenia (platelet count <100,000/µL) to patients with AF and normal platelet counts (>150,000/µL). We performed a propensity score-matched, retrospective cohort study of adults (n=1,070) with a new diagnosis of AF who received a prescription for an oral anticoagulant between 2015 and 2020. The thrombocytopenia cohort was defined as having at least two platelet counts on separate days <100,000/μL in the period spanning the 12 weeks preceding the initiation of anticoagulation to 6 weeks following the initiation of anticoagulation. The primary endpoint was the 1-year cumulative incidence of major bleeding; secondary endpoints included clinically relevant bleeding, arterial and venous thrombotic events, and all-cause mortality. Patients with AF and thrombocytopenia experienced a higher 1-year cumulative incidence of major bleeding (13.3% vs. 5.7%, P<0.0001) and clinically relevant bleeding (24.5% vs. 16.7%, P=0.005) compared to controls. Thrombocytopenia was identified as an independent risk factor for major bleeding (hazard ratio 2.20; CI, 1.36-3.58; P=0.001), with increasing risk based on severity of thrombocytopenia. The cumulative incidence of arterial thrombosis at 1 year was 3.6% in the group with thrombocytopenia and 1.5% in controls (Gray test, P=0.08). These findings suggest that baseline platelet counts are an important biomarker for hemorrhagic outcomes in AF and that degree of thrombocytopenia is an important factor in determining the level of risk.