Atrial Fibrillation in Cats

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 the 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. In cats, atrial fibrillation occurs secondary to severe heart disease. In most cases, the ventricles also contract more rapidly than normal.

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?

Cats who develop atrial fibrillation have underlying heart disease, so signs are often related to that underlying condition. If the cat 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 cat may be exercise-intolerant, becoming exhausted after very little exertion. The cat may cough or have difficulty breathing due to fluid build-up in or around the lungs. Rapid breathing and open-mouth breathing while resting are commonly noted.

Atrial fibrillation causes an erratic heart rhythm when heard through a stethoscope (it may sound like “tennis shoes in the 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.

When the heart is not beating normally, as with atrial fibrillation, the blood inside the heart does not flow well, which can lead to blood clots (thrombi) forming inside the heart chambers. These small clots can lodge in blood vessels where they narrow or branch, restricting blood flow to affected areas of the body, a condition called thromboembolism. A common site for thromboembolism is where the aorta divides into the femoral arteries that supply blood to the back legs. Signs of this life-threatening complication include sudden paralysis, cold limbs, and pain.

How is atrial fibrillation treated?

Treatment of atrial fibrillation in cats 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.

Cats with atrial fibrillation 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. Anticoagulant medications such as clopidogrel may also be prescribed to help stop blood clots from forming in the heart.

Your veterinarian may recommend a special diet for your cat with atrial fibrillation. If your cat 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 cats with atrial fibrillation?

In cats with atrial fibrillation, heart rates are monitored closely, and there will be follow-up ECGs to measure the success of treatment. In addition, chest X-rays and heart ultrasounds are routinely recommended to assess heart health and monitor progression of the disease. Over time, heart function will deteriorate, ultimately leading to congestive heart failure that cannot be managed. Eventually, euthanasia will be appropriate. That said, many cats can live a long time with medical management of their heart disease and atrial fibrillation.