Atrial fibrillation newly diagnosed after a stroke: which came first, atrial fibrillation or stroke?

Atrial fibrillation (AF) is known to be a cause of ischemic stroke (1). However, paroxysmal AF (PAF) is often undetected because it is episodic, frequently asymptomatic, and has a short duration. In a meta-analysis, sequential stratified ECG monitoring detected AF in 11.5% of stroke survivors (95% confidence interval, 8.9–14.3%) (2). According to a report from the Framingham Study, most patients with AF diagnosed after stroke (AFDAS) eventually develop PAF or persistent AF (PerAF) (3). In other words, most cases of AFDAS are likely to be a cause rather than a consequence of stroke. Thus, anticoagulation therapy has been widely used for secondary prevention of stroke in these patients.