The heart is a hollow organ with four separate chambers that pump blood throughout the body. The bottom chambers are the right and left ventricles. 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 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 acquired by the red blood cells.
Prior to having anesthesia, my senior cat had an electrocardiogram (ECG). The ECG showed an abnormal heart rhythm that my veterinarian called atrial fibrillation. What is atrial fibrillation?
Atrial fibrillation describes very rapid contractions, or twitching, of the heart muscle, confined to the atria, or the top chambers of the heart. Most of the time, atrial fibrillation in cats occurs secondary to heart disease. Sometimes, in large breed cats, atrial fibrillation will occur as a primary heart problem. In those cases, the ventricles will contract more rapidly than normal, and the rhythm may be either regular or irregular.
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 (cardiomyopathy). Atrial fibrillation can also (rarely) be caused by heart disease that is present at birth.
What are the signs of atrial fibrillation?
Most cats who develop atrial fibrillation have underlying heart disease, so the signs that are observed 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.
Atrial fibrillation causes an erratic heart rhythm that may sound like an extra heart sound is present, when heard through a stethoscope (“tennis shoes in the clothes dryer”). Your veterinarian may describe what is called a pulse deficit. This is when there are fewer pulses felt in an artery (like the femoral artery in the rear leg) than are heard through a stethoscope.
What are treatment options for atrial fibrillation?
For a cat with atrial fibrillation, medications that slow the rate of conduction of electrical signals between the atria and the ventricles are used. These include beta-adrenergic blockers such as atenolol (brand name: Tenormin®), or calcium-channel blockers such as diltiazem (brand names: Cardizem®, Dilacor XR®, Tiazac®, Diltia XT®, Taztia XT®, Dilt-XR®).
Cats with atrial fibrillation also often have underlying heart disease, meaning the focus of medical management also needs to center on treatment of this condition. For 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.
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 in order.
Is there any monitoring or follow-up for cats with atrial fibrillation?
Heart rate is monitored closely, and there will be follow-up ECGs to measure the success of treatment. In addition, radiographs of the chest (X-rays) and heart ultrasounds to assess heart health are recommended to monitor progress 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 quite a long time with medical management of their congestive heart failure and atrial fibrillation.