Should atrial fibrillation burden be a feature to guide thromboembolism prophylaxis?

Atrial fibrillation (AF) is a well-known risk factor for cerebrovascular events and systemic emboli. However, the frequency and duration of AF necessary to be considered at risk for thrombus formation is unknown. This review summarizes the literature regarding AF burden and risk for thromboembolism. Previously, no distinction was made between patients who had paroxysmal versus persistent AF in regards to initiation of anticoagulation. Recently though, given an enhanced ability to detect even very brief paroxysms of AF via stored device diagnostics, the issue has been readdressed. However, despite multiple studies no clear threshold for AF burden to mandate anticoagulation has been established. In addition, there is a growing body of evidence which suggests that the pathophysiology of thrombus formation in AF involves mechanisms beyond just stasis due to protracted episodes of discoordinate atrial contraction. Therefore, once AF has been diagnosed and the risk-benefit ratio favors anticoagulation, therapy should be initiated and continued indefinitely unless a bleeding contraindication develops.