Thrombotic complications associated with atrial fibrillation in three dogs.

Atrial fibrillation (AF) is the most common chronic pathologic arrhythmia in dogs, and whereas thromboembolism is a common complication of AF in humans, this complication has not been previously reported in dogs. This report describes thrombotic complications associated with AF in three dogs. A spherical left atrial mass consistent with a thrombus was identified in two dogs during echocardiographic examination. A third dog experienced arterial thromboembolism confirmed with ultrasound and postmortem examination. These cases provide a unique antemortem description of intra-atrial thrombus formation and cardioembolic disease associated with AF in dogs, and raise awareness of the importance of thorough echocardiographic evaluation of the atria for thrombus prior to pharmacologic cardioversion or direct current cardioversion.