Can dogs develop heart arrhythmias?

What is an arrhythmia?

Arrhythmia refers to an irregular beat or rhythm of the heart. The abnormality may be in the speed, regularity, or strength of the heartbeats. The condition is caused by abnormal electrical activity in the heart muscles of dogs which can be brought about by hereditary problems that are already present at birth, infections, injuries, stress, and a whole lot of other issues.

Signs of Heart Arrhythmia in Dogs

The prominent sign of heart arrhythmia is an irregularity in the heartbeat - the heartbeat may be too fast or too slow, the rhythm may be irregular, beats may be skipped from time to time, or the heartbeat may not be pronounced enough.

Many cases of heart arrhythmia in dogs are incidental findings during a dog’s regular health and wellness check. Most dogs with the condition don’t exhibit any tell-tale signs. Some may appear weak or may suddenly lose consciousness, but these symptoms are uncommon.

Types of Heart Arrhythmia in Dogs

Dogs of any breed or age can develop arrhythmias but some types are more common in specific breeds.

Ventricular Arrhythmias

This type is most common among German Shepherds, Boxers, and Bulldogs.

In Boxers, it’s called ‘Boxer Cardiomyopathy’ or arrhythmogenic right ventricular cardiomyopathy (ARVC). In these dogs, the arrhythmia is primarily associated with the heart’s right ventricle, though it may also be from other areas of the heart.

The arrhythmia is called ventricular tachycardia when irregular heartbeats occur in rapid succession. When this happens, it may lead to a decrease in the flow of blood to the body. The dog may collapse when there is not enough blood (and oxygen) reaching the brain.

Without proper medical intervention, ventricular arrhythmia can worsen into ventricular fibrillation, an abnormal heart rhythm that is fatal.

In German Shepherds, an inherited form of ventricular arrhythmia affects those that are between 3 and 24 months of age. The condition generally disappears after 24 months of age and the dogs are no longer at risk. But these dogs should never be used for breeding because they can pass the condition to their offspring.

Atrial Fibrillation

Dog breeds that are more prone to developing atrial fibrillation include Boxers, Doberman Pinschers, Great Danes, Newfoundlands, and other large breeds. Atrial fibrillation causes a dog’s heart to beat too fast (tachycardia).

The condition may be brought about by an underlying heart problem (cardiomyopathy) caused by a defect in the function or structure of the heart. But there are also cases in which atrial fibrillation occurs without any defect in the heart structure and function.

Sick Sinus Syndrome (Sinus Node Disease)

Most cases of sick sinus syndrome are diagnosed in older Cocker Spaniels, Miniature Schnauzers, and West Highland White Terriers.

The condition is brought about by the failure of the sinus node to discharge an impulse that triggers the contraction of the heart. The sinus node is a part of the heart that normally initiates the beating of the heart. Without heart contraction, the beating stops, and the dog may collapse if the pause is more than 8 seconds. Most of the time, the sinus node will start functioning again, but the heart rhythm has considerably long pauses.

Some dogs with sick sinus syndrome may experience bradycardia (heartbeat is too slow) while others have periods of tachycardia (rapid heartbeat) accompanying the heartbeat pauses and bradycardia.

The gold standard in treating sick sinus syndrome in dogs is the implantation of a pacemaker. The response to the procedure is usually very good. Medications may still be given to dogs that still experience tachycardia even after implantation.

Heart Block

In dogs with heart block, the ventricles don’t contract because of a problem in the atrioventricular node (AV node). Weakness and collapse of affected dogs may occur. Heart failure is also a concern. Pacemaker implantation is also the treatment of choice for this type of arrhythmia.

Commonly affected breeds include the Pug, Cocker Spaniel, Labrador Retriever, German Wirehaired Pointer, and Chow Chow.

Myocarditis

Myocarditis can affect any breed, but medium and large dog breeds are more predisposed to developing inflammation of the heart. In most cases, the cause of myocarditis cannot be fully established. Affected dogs can die suddenly.

Causes of Heart Arrhythmia in Dogs

Cardiac causes of arrhythmia in dogs include:

• Heart muscle disease - dilated cardiomyopathy, hypertrophic cardiomyopathy, ARVC
• Congenital heart defects - subaortic stenosis
• Severe valve leakage
• Enlargement of the heart chambers - chronic degenerative mitral valve disease
• Myocarditis - inflammation of the heart
• Trauma to the heart - vehicular accidents
• Age-related changes in the heart
• Replacement of the heart muscle with cancer cells or inflammatory cells

Non-cardiac causes of arrhythmia in dogs include:

• Gastric dilatation and volvulus - bloat and stomach torsion
• Pancreatitis (inflammation of the pancreas)
• Hypomagnesemia (low magnesium in the blood)
• Severe anemia
• Neurologic disease - brain tumors
• Diseases of the spleen, liver, or gastrointestinal tract
• Endocrine disease - problems of the thyroid gland, adrenal glands, etc.
• Muscular dystrophy
• Certain Medications
• Anesthetic agents
• Toxins - chocolate or caffeine (theobromine toxicity)

Diagnosis and Treatment of Heart Arrhythmia in Dogs

The diagnostic protocol to determine the presence of heart arrhythmia in dogs include the following:

• Complete physical exam - Your vet will listen to your dog’s heart using a stethoscope.
• Electrocardiogram

Sometimes, there is a need to record the electrocardiograms and monitor them for 24 hours (Holter monitoring). The 24-hour monitoring period is necessary to determine the frequency and severity of the rhythm disturbance.

In the management of heart arrhythmia in dogs, it is important that follow-up Holter monitoring, echocardiography, and radiography be used to monitor treatment including determining the correct dose and if there is a need for other medications.

My dog has a heart murmur. Will he be ok?

The prognosis will depend to a large extent on the type of arrhythmia and if it’s a treatable cause. Pacemaker implantation is often associated with a good prognosis if there is no severe underlying heart disease.

Read more:

Is diet important for my dog’s heart health?

Heart Murmurs in Dogs

Common Causes of Coughing in Dogs

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