The Multiple Causes of Stroke in Atrial Fibrillation: Thinking Broadly

Atrial fibrillation (AF) is numerically the most important risk factor for stroke. It is well established that patients with AF have a 5-fold increased risk of stroke relative to those without and that anticoagulation reduces the risk of stroke by approximately two-thirds. Definitively attributing the mechanism of an individual stroke to AF is more problematic, however. In fact, there is no way to reliably establish the etiology of any ischemic infarction. This necessitates screening for all potential stroke risk factors and treating accordingly. The pattern of infarction is often used to classify the presumed mechanism of infarction as thrombotic or embolic, although even this is approach is based on association and increasingly is recognized as not completely reliable. Furthermore, it should not dictate management-patients with perforating arterial territory infarcts with AF also require and benefit from anticoagulation. Likewise, if other potential embolic sources beyond AF are identified, anticoagulation remains the standard of care. The traditional conceptual model of the mechanistic link between AF and cardioembolic infarction is likely oversimplified. Long-term cardiac rhythm recording studies indicate an inconsistent temporal relationship between AF and infarction. This suggests that cardioembolic stroke in patients with AF may result from the underlying atrial cardiopathy, rather than the rhythm disturbance leading to atrial stasis and thromboembolism. We reviewed traditional and current concepts, as well as evidence for the role of AF in ischemic stroke.