Atrial fibrillation in cryptogenic stroke: look harder, look longer, but just keep looking.

D espite atrial fibrillation (AF) being the most common cardiac arrhythmia, its asymptomatic (and sometimes, paroxysmal) nature makes subsequent detection and diagnosis challenging. Ischemic stroke as a result of AF is usually more severe and results in greater functional loss, and patients with undetected AF will undoubtedly by at greater risk of recurrent stroke. The failure to diagnose AF after stroke also relegates this particularly vulnerable group to using antiplatelet agents, which are known to be only minimally effective in established AF, while placing them at similar risk of hemorrhagic complications as with oral anticoagulation therapy. Current guidelines (both European and American) recommend the use of short-term (usually 24 hours) cardiac monitoring among stroke and patients with transient ischemic attack for whom occult AF or paroxysmal AF is suspected, and no other causes for stroke are found. 1,2 However, even in selected high-risk patient group (such as the elderly, cryptogenic stroke patients, etc), the use of 24-hour ECGs only improve new AF detection rates to just >10%, 3 whereas extended monitoring (>24 hours) with external loop recorder or implantable device can further increase detection rates to >14%. This would suggest that longer cardiac monitoring among patients with cryptogenic stroke is indicated and would have important therapeutic and clinical implications. Therefore, current guidelines and strategies for AF detection may need to be reviewed. Until recently, the evidence-base for protracted cardiac monitoring among such patients relied on relatively small cohort studies that lacked a control group and, therefore, it was not possible to conclude whether extended monitoring would actually improve AF diagnosis over current practice. However, 2 randomized controlled trials recently published in the New England Journal of Medicine have provided compelling evidence in favor of longer ECG monitoring among patients with cryptogenic stroke. The first of these, the Cryptogenic Stroke and Underlying Atrial Fibrillation (CRYSTAL AF) trial, 4 included 441 patients newly diagnosed with cryptogenic stroke, half of whom were subsequently provided with an implantable cardiac monitor for continuous monitoring for ≥6 months; the others received usual care. The second study, the 30-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation After a Cerebral Ischemic Event (EMBRACE) trial, 5 involved 572 patients with cryptogenic stroke and subsequently randomized them to receive a 30-day event trigger cardiac monitor or 24-hour cardiac monitor. In both trials, patients were extensively investigated before a diagnosis of cryptogenic stroke was made, and before enrollment and randomization …