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.


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