Atrial Fibrillation in Dogs

My dog went to her veterinarian to have her teeth cleaned. She had an ECG prior to anesthesia because she is 10 years old and my veterinarian wanted to be sure she would be OK. The ECG showed an abnormal heart rhythm that my veterinarian called “atrial fibrillation.” We did not proceed with anesthesia. What does atrial fibrillation mean?

The heart is a hollow organ with four separate chambers that are involved in pumping blood around the body. The bottom chambers are the right and left ventricles; the right pumps the blood to the lungs, and the left pumps blood to the rest of the body. The top chambers are the right and left atria; the right accepts blood from the general circulation, and the left accepts blood from the lungs. When the heart relaxes, the valves between the atria and the ventricles open, allowing the blood to move from the atria to the ventricles. When the heart is beating normally, the contractions of the atria and the ventricles are coordinated to move the blood smoothly around the body, as well as into the lungs where carbon dioxide is exhaled, and oxygen is picked up by the red blood cells.

Atrial fibrillation describes very rapid contractions or twitching of the heart muscle, specifically in the atria. Most of the time, atrial fibrillation in the dog occurs secondary to heart disease. Sometimes, in large breed dogs, atrial fibrillation will occur as a primary heart problem. The ventricles will then contract more rapidly than normal, but the rhythm may be either regular or irregular.

My dog had no signs there was anything wrong with his heart.  What signs are typical in a dog with atrial fibrillation?

Most dogs who develop atrial fibrillation have underlying heart disease, so the signs that are observed are related to the disease. If the dog is experiencing congestive heart failure, the heart cannot pump blood effectively enough to provide adequate oxygen to the tissues and to keep the body’s fluid balance as it should be. The dog may be exercise intolerant, becoming exhausted after very little exertion. The dog may cough or have difficulty breathing. Atrial fibrillation causes an erratic heart rhythm that may sound like an extra heart sound is present when heard through a stethoscope. Your veterinarian may mention a “pulse deficit.”  This describes the situation in which there are fewer pulses felt in an artery (like the femoral artery in the rear leg) than are heard through a stethoscope.

What causes atrial fibrillation?

Sometimes, no specific cause is determined for atrial fibrillation. In that case it is called “idiopathic.” Atrial fibrillation can be the result of chronic heart valve disease, or disease of the heart muscle itself. Atrial fibrillation can also be caused by heart disease that is present at birth, but this is rare.

Is atrial fibrillation treatable?

For a dog with secondary atrial fibrillation, the focus of medical management is to treat the underlying heart disease. In cases of congestive heart failure, medication is given to relieve the body of excess fluid, to control hypertension (if present), and to help the heart beat more effectively. Another goal of therapy is to slow the contraction rate of the ventricles to help the blood circulate better. It is best to restrict the dog’s activity until the rapid heart rate is under control.

Is there any monitoring or follow-up for dogs with atrial fibrillation?

Heart rate is monitored closely, and there will be follow-up ECGs to measure the success of treatment. Over time, heart function will deteriorate, ultimately leading to congestive heart failure that cannot be managed. Eventually, euthanasia will be appropriate. That said, many dogs can live quite a long time with medical management of their congestive heart failure and atrial fibrillation.