Risk of arterial and venous thromboembolism in patients with atrial fibrillation or flutter: A nationwide population-based cohort study.

BACKGROUND: Patients with atrial fibrillation or flutter (AFF) are at increased risk of ischemic stroke, but their risk of other thromboembolic events remains less clear.

METHODS: During 2004-2013, we conducted a nationwide population-based cohort study using Danish medical registries. We identified all patients with first-time AFF and sampled a sex-, age-, and calendar year-matched general population comparison cohort without AFF. For myocardial infarction, peripheral embolism, ischemic stroke, hemorrhagic stroke, deep venous thrombosis, and pulmonary embolism, we computed cumulative risks and adjusted incidence rate ratios (aIRRs) adjusted for comorbidity and medication.

RESULTS: The study population consisted of 103,989 patients with AFF and 519,935 individuals without AFF from the general population. Ten-year cumulative risks in the AFF cohort were 3.5% for myocardial infarction, 0.5% for peripheral embolism, 6.7% for ischemic stroke, 1.3% for hemorrhagic stroke, 1.0% for deep venous thrombosis, and 1.3% for pulmonary embolism. During the first 30days following AFF, aIRRs were markedly (4 to 16-fold) increased for all outcomes and similarly elevated for myocardial infarction (aIRR=8.0, 95% confidence interval (CI): 6.8-9.5) and ischemic stroke (aIRR=9.9, 95% CI: 8.5-11.5). Thereafter, aIRRs decreased gradually, reaching unity after 5years for myocardial infarction, deep venous thrombosis, and pulmonary embolism, but remained 1.6 to 3.5-fold increased for peripheral embolism, ischemic stroke, and hemorrhagic stroke.

CONCLUSIONS: AFF was a risk factor for all arterial and venous outcomes during the first year of follow-up, but only for peripheral embolism, ischemic stroke, and hemorrhagic stroke thereafter.