1. In this randomized controlled trial, apixaban lowered the risk of stroke or systemic embolism significantly more than aspirin in patients with subclinical atrial fibrillation.
2. Apixaban was associated with a higher risk of major bleeding than aspirin.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Symptomatic atrial fibrillation is a leading cause of stroke and stroke-related disability and mortality, for which oral anticoagulants are established prophylactic therapies. Conversely, subclinical atrial fibrillation can be asymptomatic or only produce short-lasting symptoms and is only diagnosed by continuous cardiac rhythm monitoring with a pacemaker or defibrillator. It is associated with a 2.5-time increase in the risk of stroke or systemic embolism, yet the role of oral anticoagulation in this population is uncertain. This randomized controlled trial assessed the safety and efficacy of apixaban against aspirin in patients with subclinical atrial fibrillation and CHA2D2-VASc score ≥3. By a mean follow-up of 3.5 years, apixaban resulted in a lower risk of stroke or systemic embolism than apixaban. Nevertheless, apixaban was also associated with an increased risk of major bleeding, although fatal bleeding occurred in comparably small numbers across both groups. The study results were limited to patients with implanted cardiac electronic devices. However, it offered evidence demonstrating the benefits of apixaban over aspirin in preventing stroke and systemic embolism in this population, even when bleeding risk was considered.
Click here to read the study in NEJM
Relevant Reading: Anticoagulation with Edoxaban in Patients with Atrial High-Rate Episodes
In-Depth [randomized controlled trial]: The current study was a randomized controlled trial to assess the safety and efficacy of apixaban for patients with subclinical atrial fibrillation at increased risk of stroke. Patients who had subclinical atrial fibrillation lasting between six minutes and 24 hours detected by an implanted pacemaker, defibrillator, or cardiac monitor and a CHA2D2-VASc score ≥3, indicating an elevated risk of stroke, were eligible for inclusion. Exclusion criteria included age below 55 years of age (after protocol amendment), clinical atrial fibrillation, ongoing oral anticoagulation, uncorrected major bleeding, and creatinine clearance of less than 25 mL/min. Overall, 4,012 patients with a mean age of 76.8 years and a mean CHA2D2-VASc score of 3.9 were randomized to receive apixaban 5mg twice daily or aspirin 81mg daily. The primary efficacy outcome was stroke or systemic embolism and measured in the intention-to-treat population. The primary safety outcome was major bleeding, as defined by the International Society on Thrombosis and Haemostasis, assessed in the on-treatment population. A stroke or systemic embolism occurred in 55 patients in the apixaban group (0.78% per patient-year) and 86 in the aspirin group (1.24%, per patient-year; Hazard Ratio [HR], 0.63; 95% Confidence Interval [CI], 0.45-0.88; p=0.007). Ischemic stroke occurred at a significantly lower rate in the apixaban group (0.64% per patient-year) than the aspirin group (1.02% per patient-year). Major bleeding occurred in 1.71% per patient-year in the apixaban group and 0.94% per patient-year in the aspirin group (HR, 1.80; 95% CI, 1.26 to 2.57; p=0.001). The overall rates of all-cause mortality and death from cardiovascular causes were not significantly different between the two groups. This study demonstrated that apixaban may reduce the risk of stroke or systemic embolism in subclinical atrial fibrillation as compared to aspirin.
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