Cardiac arrhythmias are abnormal heart rhythms. These disorders are classified based on the area of the heart in which they originate. They originate either in the upper chambers of the heart, the lower chambers of the heart, the area of the heart responsible for creating the heart beat, or the electrical conduction system within the heart.

Each heartbeat originates as an electrical impulse in the upper right chamber of the heart (sinoatrial [SA] node). The impulse then travels across the upper chambers of the heart (atria), to an intermediate station (atrioventricular [AV] node), and finally to the lower chambers of the heart (ventricles). The electrical impulse generates the typical pattern seen on an electrocardiogram (EKG or ECG). Disturbance in the generation or transmission of the electrical impulse in the heart causes a cardiac arrhythmia. Some cardiac arrhythmias are temporary and do not cause illness. Others are serious and may be life threatening.

Cardiac arrhythmias may affect dogs of any age or sex. They may also affect any breed, but there are some breeds that are more at risk of developing arrhythmias than others. Giant breeds of dog are more prone to a type of arrhythmia known as atrial fibrillation, which is rapid abnormal beat originating in the atria. Labrador retrievers are prone to supraventricular tachycardia, which is a rapid heart rate originating just above the ventricles. Doberman pinschers and boxers are prone to ventricular tachycardia, which is a rapid abnormal heart beat originating in ventricles. Sick sinus syndrome is an abnormality that affects the SA node: It most commonly occurs in miniature schnauzers, dachshunds, cocker spaniels, and West Highland white terriers. Spaniels, German shepherds and Labrador retrievers are predisposed to certain types of heart block.

The prognosis (outlook) for animals with cardiac arrhythmias depends on the type of arrhythmia, the underlying cause of the arrhythmia, and the type and extent of any existing heart disease. Dogs in congestive heart failure have a guarded-to-poor prognosis.

What to Watch For

Weakness

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Slow heart rate

Fast heart rate

Erratic heart rate

Difficulty breathing

Lack of appetite

Diagnosis

Blood work, including a complete blood count and biochemical profile, should be performed to look for any underlying abnormalities. Some dogs may be anemic, have an elevated white blood cell count, or have organ dysfunction. Some diseases, such as hypothyroidism, may be the cause of cardiac arrhythmias.

Cardiac arrhythmias are diagnosed with an electrocardiogram (EKG, ECG). The type of arrhythmia can be diagnosed from an ECG oscilloscope or from a printout of the trace.

Thoracic (chest) radiographs (X-rays) may help determine if heart disease or heart failure are present.

A cardiac ultrasound (echocardiogram) is sometimes performed to determine evaluate cardiac function and identify any underlying heart disease.

Treatment

Treatment depends on the severity of the arrhythmia and the presence of any underlying disease. There are a variety of cardiac arrhythmias and each is managed differently. Some are serious and require medication or even electric shock treatment. Others are innocuous and do not require any treatment at all.

In addition to treating the cardiac arrhythmia, any underlying heart disease or other disease should also be addressed.

Home Care and Prevention

There is no home care for abnormal heart rhythms, except that you should administer any medications your veterinarian prescribes. If you suspect that your pet has an abnormal heart rate or rhythm, you should contact your veterinarian immediately.

Cardiac arrhythmias are difficult to prevent, but early diagnosis and treatment of predisposing causes can reduce the risk of arrhythmias developing.