Overview of Cardiac Arrhythmias in Dogs
Cardiac arrhythmias are abnormal heart rhythms that can occur in dogs. 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 heartbeat, 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
- Slow heart rate
- Fast heart rate
- Erratic heart rate
- Difficulty breathing
- Lack of appetite
Diagnosis of Cardiac Arrhythmias in Dogs
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 of Cardiac Arrhythmias in Dogs
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 dog 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.
Information In-depth on Canine Arrhythmias
Normal heart rhythms begin in the sinoatrial (SA or sinus) node, which is located in the right upper chamber (atrium) of the heart. While abnormalities of the sinus node are typically a consequence of a systemic disorder, such as hypo- or hyperthyroidism, primary sinus disease is common and can lead to a type of arrhythmia known as sick sinus syndrome. Other arrhythmias arising outside of the SA node may occur. Among the most serious of these is atrial fibrillation. Arrhythmias arising from the ventricles include premature ventricular contractions and ventricular tachycardia. More serious arrhythmias sometimes lead to cardiac decompensation and acute or chronic heart failure. Some arrhythmias worsen to the point of fibrillation and eventually the absence of any heartbeat (asystole).
Cardiac arrhythmias can lead to a very slow heart rate (potentially as slow at 40 beats per minute), termed bradycardia; very fast heart rate (potentially over 200 beats per minute in a dog), termed tachycardia; or an erratic heart beat. Numerous different types of arrhythmias may occur. Some of the more common ones include:
- Atrial fibrillation
- Atrial tachycardia
- Ventricular escape rhythm
- Ventricular premature complex
- Ventricular tachycardia
- Ventricular fibrillation
- First-degree heart block
- Second-degree heart block
- Third-degree heart block
Often, cardiac arrhythmias are associated with underlying heart disease, such as dilated cardiomyopathy, congestive cardiac failure, or cardiac birth defects. In addition, a variety of other diseases or events may cause cardiac arrhythmias including:
- Hypothyroidism (under active thyroid gland)
- Chronic lung disease
- An overdose of certain medications such as digoxin, narcotics, xylazine
- Administration of anesthetic agents
- High or low blood potassium
- Tumors of the heart
- Toxicity, such as chocolate poisoning
- Hypoadrenocorticism (Addison’s disease – a disease of the adrenal glands)
- Urinary obstruction
- Lyme disease
- Smoke inhalation
- Head trauma
- Low blood pressure (hypotension)
- Gastric dilatation-volvulus
- Diseases of the spleen
- Severe infections
Cardiac arrhythmias are often detected during physical examination. Your veterinarian will listen to your dog’s heart with a stethoscope to determine if its heart rate is too slow, too fast, or erratic. If an arrhythmia is detected or suspected, it is confirmed by means of an electrocardiogram (ECG, EKG). Your dog will be positioned on his right side and will have clips or pads attached to his arms and legs. This procedure is painless. The ECG is then turned on and a tracing is obtained of the electrical activity of the heart. The tracing is examined to determine if the heart rate and rhythm.
Sometimes, a simple ECG is inadequate to evaluate the significance of an arrhythmia. Other methods of evaluating the heart rhythm include post-exercise ECG, hospital telemetry, ambulatory (Holter) ECG, and the use of a cardiac event monitor. These methods are particularly useful in assessing the overall frequency of an arrhythmia, the relationship of an arrhythmia to clinical signs, or the effectiveness of treatment.
In addition, other diagnostic tests are performed to determine the overall health of your dog:
- Complete blood count – This is performed to evaluate the red blood cells, white blood cells and platelets. Some dogs may be anemic or have an elevated white blood cell count.
- Biochemical profile – This blood work is performed to determine the function of the body’s organs and electrolyte levels.
- Some dogs may have a high or low potassium level, low thyroid levels or evidence of kidney or liver disease.
- Radiographs – X-rays of the chest help determine if congestive heart failure is present or if there some underlying heart disease.
- Ultrasound – An ultrasound of the heart (echocardiogram) helps determine the adequacy of cardiac function and the existence of any underlying heart disease.
Treatment varies and depends on the type of arrhythmia and presence and extent of any underlying disease. Some arrhythmias do not require treatment and spontaneously convert to normal. Other arrhythmias are serious and require treatment. Some of the treatment options include:
- Medications to control the arrhythmia, treat underlying heart disease, or normalize cardiac function. Medications used include digoxin, diltiazem, propranolol, enalapril, procainamide, lidocaine, and atropine.
- Certain types of cardiac arrhythmias require the placement of a pacemaker to control the arrhythmia. Severe heart blocks often require a pacemaker to keep the heart rate and rhythm normal.
- Dogs in congestive heart failure may need treatment with a diuretic (e.g. furosemide) and possibly nitroglycerine.
- Dogs with underlying medical diseases often require additional medication. For example, dogs with hypoadrenocorticism may require steroid supplementation.
Follow-Up Care for Dogs with Cardiac Arrhythmias
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical and may include the following:
- Administer any prescribed veterinary medications as directed and be certain to contact your veterinarian if you are experiencing problems treating your dog.
- Dogs with cardiac arrhythmias will require frequent veterinary evaluation (including listening to the heart with a stethoscope [cardiac auscultation].
- Repeat ECGs may be called for to monitor your dog’s response to therapy.
- If a cardiac arrhythmia can be resolved, veterinary check-ups may not need to be as frequent.
- Periodic chest X-rays and cardiac ultrasound are sometimes indicated.