Atrial fibrillation is an abnormal heart rhythm caused by rapid irregular contractions of the upper chambers, or atria, of the heart. Because the heart is beating faster and more irregularly than normal, it does not fill or pump blood properly. Failure to pump blood normally can result in fluid accumulation in the lungs, chest, or abdomen, and can lead to weakness in heart failure.

The most common cause of atrial fibrillation is advanced heart disease. Advanced heart disease in dogs may include degeneration and leakage of heart valves, diseases of the heart muscle which is called cardiomyopathy, and certain congenital heart deformities. It is especially common in large breed dogs. Clinical signs are primarily weakness and inability to exercise. Fainting episodes may occur.

An electrocardiogram is needed to confirm the presence of atrial fibrillation. Additional tests, such as chest x-rays and cardiac ultrasounds may be performed. Treatment is initially directed at any underlying heart disease or heart failure and may include drugs to increase cardiac contractility and decrease fluid retention. Drugs such as pimobendan, furosemide, digoxin, diltiazem, beta blockers are commonly used. In people, a procedure called electrical cardioversion is performed. This procedure is not always successful in our canine patients, as recurrence of atrial fibrillation is common after the procedure.

Dogs with advanced heart disease and atrial fibrillation may live 3-12 months, depending on the type and severity of their heart disease. Giant breed dogs with idiopathic atrial fibrillation can live for years; however their atrial fibrillation can progress to serious heart disease, especially dilated cardiomyopathy. Every dog should have its heart checked annually by a veterinarian, especially if there are signs of weakness and episodes of fainting.


Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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