Atrial Fibrillation in Dogs

Atrial fibrillation (AF) is a common electrical disturbance or arrhythmia of the heart, marked by rapid randomized contractions of the atrial heart muscle causing a totally irregular, often rapid , ventricular rate. In this arrhythmia the normally coordinated electrical activity in the upper heart chambers, the right atrium and left atrium, is lost. The muscle of these chambers begins to wiggle like a "bag full of worms." Atrial flutter is similar to AF, but the atrial contractions are rapid but regular. Both rhythms are very abnormal and reduce heart function. 

AF can occur as a single problem (lone AF) or more often as a complication of heart muscle disease (cardiomyopathy) or chronic heart valve disease. It occurs in both dogs and cats but is much more common in dogs. Many dogs with AF are also in congestive heart failure (CHF). 

Giant breed dogs, such as the Saint Bernard and the Irish wolfhound are predisposed to this rhythm disturbance. In general, the larger the dog or the more severe the heart disease, the greater the risk for atrial fibrillation or atrial flutter.

Excessive doses of thyroid hormone supplements can lead to AF in dogs. 

Once established, these heart arrhythmias are often permanent.