Cryptogenic ischemic stroke defines the situation where the cause of the thromboembolic event is not evident. Atrial fibrillation (AF) is a possible cause of cryptogenic stroke, even if asymptomatic. AF is the most common arrhythmia, and its incidence increases with age. AF is associated with an increased risk of ischemic stroke and systemic embolism, independent of the type of AF and also of the symptoms caused by the arrhythmia. The thromboembolic risk is associated to some clinical variables like age, hypertension, heart failure, diabetes, previous stroke, vascular diseases and gender. The mechanism of thrombosis in AF is complex, and comprises blood stasis in the left atrial appendage, but also atrial and endothelial damage, alteration of the extracellular matrix, and activation of humoral factors with prothrombotic significance.
AF is often asymptomatic or “silent”, as demonstrated in many clinical situations. Silent AF may be a frequent cause of otherwise unexplained stroke. The association between stroke and silent AF was demonstrated in many trials, especially in patients with an implanted device, like pacemakers, implantable cardiac defibrillators (ICD) and cardiac resynchronisation therapy (CRT) devices, where a reliable report of the arrhythmia is available. The best system to discover if a patient with cryptogenic stroke has AF is the continuous monitoring with an implantable loop recorder. However, the temporal relationship between AF and stroke is not often evident, so that the decision to prevent thromboembolisms in patients with silent AF should be based on the evaluation of risk with the appropriate score index. In the secondary prevention of stroke and transient ischemic attack (TIA), however, anticoagulation is generally indicated if a silent AF is demonstrated.