Patients with atrial fibrillation (AF) are at increased risk for ischemic stroke. In patients who have suffered a stroke, screening for AF is routinely performed only for a short period after the stroke as part of the evaluation for possible causes. If AF is detected after an ischemic stroke, oral anticoagulation therapy is recommended for secondary stroke prevention. In 25% to 30% of stroke patients, the stroke mechanism cannot be determined (cryptogenic stroke). The incidence of paroxysmal AF undetected by short-term monitoring in patients with cryptogenic stroke is unknown, but has important therapeutic implications on patient care. The optimum monitoring duration and method of AF detection after stroke are unknown. The purpose of this study is to evaluate the incidence of AF and time to AF detection in patients with cryptogenic stroke using an insertable cardiac monitor.

The CRYSTAL AF trial is a randomized prospective study to evaluate a novel approach to long-term monitoring for AF detection in patients with cryptogenic stroke. Four hundred fifty cryptogenic stroke patients (by definition, without a history of AF) will be enrolled at approximately 50 sites in Europe, Canada, and the United States. Patients will be randomized in a 1:1 fashion to standard arrhythmia monitoring (control arm) or implantation of the subcutaneous cardiac monitor (Reveal XT; Medtronic, Inc, Minneapolis, MN) (continuous monitoring arm).

The primary end point is time to detection of AF within 6 months after stroke. The clinical follow-up period will be at least 12 months. Study completion is expected at the end of 2012.