Atrial fibrillation in dogs

Atrial fibrillation is an abnormal heart rhythm caused by rapid irregular contractions of the upper chambers of the heart, called the atria. Because the heart is beating faster and more irregularly than normal, it does not fill or pump blood properly. Failure to pump blood normally can result in fluid accumulation in the lungs, chest or abdomen, and can lead to weakness and heart failure.

The most common cause of AF is advanced heart disease, with enlargement of one or both atria. AF can occur spontaneously for unknown reasons in giant-breed dogs such as the great Dane and Irish wolfhound. Clinical signs of AF include weakness and inability to exercise. Fainting episodes may occur. Breathing may be faster and labored, and coughing may be noted. An electrocardiogram (ECG) is needed to confirm the presence of AF. Additional tests, such as chest X-rays and a heart ultrasound, are then done to search for any underlying cause. Any fluid removed from the chest or abdomen may be sent for analysis.

Treatment is initially directed at any underlying heart disease or heart failure and may include drugs to increase contractility or decrease fluid retention. Diltiazem is a calcium channel blocker commonly used to decrease heart rate in animals with AF. Multiple beta-blockers are also used in dogs, which slow the heart rate, allowing the heart to fill properly and pump blood efficiently. In some cases, a procedure called electrical cardioversion may be performed with the animal underneath anesthesia to try and convert the AF back to a normal rhythm. Although the rate of conversion is good, recurrences are common.

Many dogs with AF can live for years; dogs with underlying heart disease live much shorter lives. The large-breed dogs such as Irish wolfhounds and great Danes can develop a disease of the heart called dilated cardiomyopathy, which is commonly fatal. If you feel like your dog has an abnormal heart rhythm, please contact your veterinarian and have your dog examined thoroughly.

Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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