Atrial Fibrillation in Dogs

The heart is a hollow, muscular organ with four separate chambers that pump blood throughout the body.

The bottom chambers are the right and left ventricles. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the rest of the body. 

The top chambers are the right and left atria. The right atrium accepts blood from the general circulation, and the left atrium accepts blood from the lungs.

When the heart relaxes, the valves between the atria and the ventricles open, allowing 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 acquired by the red blood cells.

What is atrial fibrillation?

Atrial fibrillation describes rapid, uncoordinated contractions of the heart muscle, specifically in the atria. The ventricles will then contract more rapidly than normal, but the rhythm may be either regular or irregular. Most of the time, atrial fibrillation in dogs occurs secondary to heart disease. 

In large and giant breed dogs (Irish wolfhound, Newfoundland, German shepherd, Bernese mountain dog), atrial fibrillation sometimes occurs as a primary heart problem.

What causes atrial fibrillation?

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

What are the signs of atrial fibrillation?

Most dogs who develop atrial fibrillation have underlying heart disease, so signs are often related to that underlying condition. 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 fluids balanced.

The dog may be exercise-intolerant, becoming exhausted after very little exertion. Syncope (fainting) may also occur due to inadequate blood flow to the brain. The dog may cough or have difficulty breathing due to fluid build-up in or around the lungs.

Atrial fibrillation causes an erratic heart rhythm when heard through a stethoscope (it may sound like “running shoes tumbling around a clothes dryer”). Your veterinarian may describe a pulse deficit: when they feel fewer pulses in an artery (like the femoral artery in the rear leg) than they hear through the stethoscope.

How is atrial fibrillation treated?

Treatment of atrial fibrillation in dogs involves medications that slow the electrical signals between atria and ventricles. Medications include beta-adrenergic blockers such as atenolol and sotalol, or calcium-channel blockers such as diltiazem. Digoxin is also sometimes used for treatment of this condition.

Dogs with atrial fibrillation also often have underlying heart disease, which means medical management also must focus on treatment of this condition. For congestive heart failure, medications are given to relieve the body of excess fluid, to control high blood pressure (if present), and to help the heart beat more effectively. For those dogs with primary atrial fibrillation (i.e., no other heart problems are present), cardioversion (using electrical or drug methods) can be attempted. This is a very specialized treatment and requires referral to a heart specialist.

Your veterinarian may recommend a special diet for your dog with atrial fibrillation. If your dog is experiencing congestive heart failure, then a mild to moderate restriction of sodium in the diet may be advised. Omega-3 fatty acids (DHA and EPA) may also be recommended for their anti-inflammatory effects and other benefits.

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

In dogs with atrial fibrillation, heart rates are monitored closely, and there will be follow-up ECGs to measure the success of treatment. Often, cardiologists recommend a 24-hour holter monitor, which is attached to your dog and monitors the ECG continuously. In addition, chest X-rays and heart ultrasounds are routinely recommended to assess heart health and monitor progression of the disease.

If your dog is being managed with digoxin therapy, your veterinarian will closely monitor blood levels of the medication to ensure no additional problems develop, as this drug has a narrow margin of safety. 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 a long time with medical management of their heart disease and atrial fibrillation.