Atrial Fibrillation (AF) in Dogs

Overview of Canine Atrial Fibrillation

Atrial fibrillation (AF) is a common electrical disturbance or arrhythmia of the heart, marked by rapid randomized contractions of the atrial heart muscle causing a totally irregular, often rapid , ventricular rate. In this arrhythmia the normally coordinated electrical activity in the upper heart chambers, the right atrium and left atrium, is lost. The muscle of these chambers begins to wiggle like a “bag full of worms.” Atrial flutter is similar to AF, but the atrial contractions are rapid but regular. Both rhythms are very abnormal and reduce heart function.

AF can occur as a single problem (lone AF) or more often as a complication of heart muscle disease (cardiomyopathy) or chronic heart valve disease. It occurs in both dogs and cats but is much more common in dogs. Many dogs with AF are also in congestive heart failure (CHF).

Giant breed dogs, such as the Saint Bernard and the Irish wolfhound are predisposed to this rhythm disturbance. In general, the larger the dog or the more severe the heart disease, the greater the risk for atrial fibrillation or atrial flutter.

Excessive doses of thyroid hormone supplements can lead to AF in dogs.

Once established, these heart arrhythmias are often permanent.

What to Watch For

The symptoms of atrial fibrillation are not very specific.

• Congestive heart failure with fluid accumulation in the chest or abdomen
• Reduced exercise tolerance
• Rapid heartbeat
• Chaotic heart rhythm

Diagnosis of Atrial Fibrillation in Dogs

Diagnostic tests are needed to recognize AF, and exclude other diseases. The evaluation of a dog with AF is similar to that needed to evaluate any cardiac patient. These tests may include:

• Complete medical history and physical examination, including auscultation with a stethoscope
• An electrocardiogram (EKG) to diagnose the rhythm with certainty
• Chest radiographs to assess heart size and detect evidence of congestive heart failure
• An echocardiogram for definitive diagnosis of underlying heart disease
• Serum biochemical tests with special interest on kidney function and electrolytes
• Thyroid function in dogs receiving supplementation with thyroxine
• Heartworm (HW) antigen test if appropriate for your geographic area

Treatment of Atrial Fibrillation in Dogs

Treatments for AF depend on the underlying heart condition. In most cases, heart failure is also evident and must be managed medically.

Hospital control of congestive heart failure includes:

• Furosemide – a diuretic drug.
• Possible use of a nitrate to dilated blood vessels
• Oxygen if needed
• Digoxin to improve heart function and decrease the heart rate
• Thoracocentesis, which is a procedure to remove chest fluid by inserting a needle into the chest and removing excess fluid by syringe

Home therapy includes:

• Oral digoxin (Lanoxin, Cardoxin).
• Addition of either a beta blocker drug or a calcium channel antagonist (diltiazem) to control heart rate
• Treatment for CHF such as oral furosemide, enalapril or benazepril and dietary sodium restriction

Home Care and Prevention

Administer all medications as prescribed by your physician. Learn the side effects of each medication; for example, digoxin can lead to loss of appetite or vomiting. Alert your veterinarian if there are signs of difficult breathing, loss of appetite, exercise intolerance, coughing or other symptoms.

There is no specific preventative measure for atrial fibrillation. It is important to give all medication for any existing heart condition. See your veterinarian for routine examinations to monitor the progress of the disease.

In-depth Information on Canine Atrial Fibrillation

Both atrial fibrillation (AF) and the related rhythm, atrial flutter, originate in the top chambers of the heart called the atria. Both rhythms can lead to a decrease in heart function related to chaotic rhythm and excessively rapid heart rates. These electrical disturbances can rarely be “cured” back to normal because the majority of dogs with AF have progressive underlying heart disease. When AF occurs as the only heart problem (lone atrial fibrillation) or suddenly develops in a hospitalized patient, there is a greater likelihood that the rhythm can be made “normal” again. However, over 95 percent of cases maintain AF for life.

A number of other heart rhythm disturbances can also lead to a rapid heart rate and deterioration in heart function. Ventricular tachycardia is a good example; this is a rapid heart rate that originates in the lower chambers of the heart called the ventricles. These disturbances are readily distinguished by an electrocardiogram (EKG) examination.

A key to management of AF is the medical control of co-existing congestive heart failure (CHF) when present.

Veterinary care should include diagnostic tests and subsequent treatment recommendations.

Diagnosis In-depth of Atrial Fibrillation in Dogs

Diagnostic tests are needed to recognize all AF, and exclude all other diseases. These tests may include:

• Complete medical history and physical examination
• Physical examination and examination of the heart and lungs with a stethoscope. This will identify the chaotic rhythm and prompt an electrocardiogram (EKG). The presence of congestive heart failure can also be determined from this examination.
• An EKG is needed to diagnose the rhythm with certainty and to exclude other electrical disturbances of the heart. This study is done in a manner similar to that used in people.
• Chest X-rays are important to gauge the size of the heart and detect congestive heart failure. This will appear as fluid accumulation in the lungs, called pulmonary edema, or fluid accumulation in the chest cavity, called pleural effusion.
• An echocardiogram, or ultrasound of the heart, is needed to diagnosis the underlying heart disease with certainty. This noninvasive, painless examination can display heart size, disease (lesions) and heart muscle function.
• Serum biochemical tests (blood tests) and a urinalysis should be obtained with special interest directed to kidney function and blood electrolytes.
• Thyroid function should be measured in dogs receiving supplementation with thyroxine.
• An heartworm(HW) antigen test should be done if appropriate for geographic area.
• Your veterinarian may recommend additional diagnostic tests or refer you to a specialist to insure optimal medical care. These are selected on a case-by-case basis.

Treatment In-depth of Atrial Fibrillation in Dogs

The principles of therapy for AF include the following:

• Control congestive heart failure if present
• Control the heart rate to prevent excessively rapid heart beats
• Provide home therapy to slow the progression of heart disease

Initial treatment for heart failure may require hospitalization with administration of a diuretic, oxygen and other treatments. Vasodilator drugs such as nitroglycerine or , which cause dilatation of blood vessels, may be administered. In some forms of heart failure, the use of dobutamine or other potent stimulators of the heart muscle may be necessary. Fluid accumulation around the lungs (pleural effusion) may require drainage with a needle (thoracocentesis). Additional treatment may include:

• A diuretic such as the drug furosemide (Lasix®). Diuretics prevent the kidney from retaining excessive salt (sodium) and water leading to increased volume of urine produced. Diuretics are usually prescribed for home care to prevent fluid retention. The dose must be sufficient to prevent fluid retention but at the same time cannot be so high as to cause kidney failure or excessive loss of potassium.
• Other diuretics may be prescribed in selected patients. For example, spironolactone prevents fluid retention and may protect the heart muscle for further damage in dilated cardiomyopathy.
• A potassium supplement may be recommended in some patients.
• Most patients with atrial fibrillation are treated with an angiotensin converting enzyme inhibitor such as enalapril (Enacard®) or benazepril. Enalapril, benazepril and related drugs block some of the harmful hormones that circulate in heart failure, prolong life and reduce clinical symptoms in canine heart failure. This class of drug treatment, sometimes called ACE-inhibitors, prevents salt retention as well. Dosing is critical as these drugs can lower blood pressure excessively or lead to kidney failure.
• The diet may be modified to limit sodium intake and prevent fluid retention. There are specialized diets available for this purpose though some senior diets are also relatively low in sodium. Fish oil supplements may be of value in dogs with weight loss – ask your veterinarian about these.
• Dietary supplements are used in some forms of cardiomyopathy. The amino acids taurine is sometimes prescribed for cardiomyopathy in spaniel breeds. L-carnitine is sometimes recommended for treatment of dilated cardiomyopathy. Other nutritional supplements such as vitamin E and coenzyme Q10 are recommended by some veterinarians, but there is no evidence of their benefit for heart failure in dogs.
• The drug digoxin (Lanoxin®, Cardoxin®) is prescribed to improve heart function and reduce the heart rate. The dose of this drug must be critically determined to prevent side effects such as loss of appetite and vomiting.
• Beta-blockers such as metoprolol, propranolol or atenolol are usually be prescribed to control heart rate, to control arrhythmias and protect the heart muscle in atrial fibrillation, but these must be dosed very carefully – doses must be started low and gradually increased. The calcium channel blocker, diltiazem, is used by some in place of beta-blockers to slow the heart rate.
• Complications of blood clots are not a big problem in dogs with AF.

Follow-up Care for Dogs with Atrial Fibrillation

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical. Administer prescribed medication(s) as directed, and be certain to alert your veterinarian if you are experiencing problems treating your dog. Optimal follow up veterinary care for atrial fibrillation often involves the following:

• Regular examinations that include an interview about clinical symptoms and quality of life. Be prepared to answer questions about your dog’s activity, appetite, ability to sleep comfortably, breathing rate and effort, coughing, exercise tolerance, and overall quality of life.
• Bring your medications with you to show your veterinarian. Dosing is critical for heart medication.
• Measurement of arterial blood pressure is often done when dogs are in heart failure.
• Blood tests to examine kidney function and blood electrolytes are routinely recommended.
• A blood digoxin test should be done periodically if that drug is prescribed.
• A chest X-ray may be needed to evaluate the lungs for fluid.
• A periodic electrocardiogram is recommended to evaluate the heart rhythm and verify heart rate control in AF.