Canine atrial fibrillation.

Atrial fibrillation (AF) is the most commonly diagnosed supraventricular tachyarrhythmia in dogs. It typically develops when atrial enlargement occurs secondary to underlying cardiovascular disease. Electrocardiographically, AF is characterized by disorganized atrial electrical activity resulting in an absence of P waves and a rapid, irregular ventricular rate. The hemodynamic consequences of AF include decreased cardiac output and the development of clinical signs of heart failure. Therapeutic management focuses on controlling ventricular rate or restoring and maintaining sinus rhythm using antiarrhythmic medication and, in some cases, biphasic transthoracic electrical cardioversion. The prognosis varies and is especially guarded in the presence of significant underlying cardiac disease, such as dilated cardiomyopathy.