Cardiac Arrhythmias in Dogs

Cardiac arrhythmias (irregular heartbeats) are not an uncommon health issue for dogs. While many dogs live long, healthy lives with this condition, unfortunately this is not always the case. Some arrhythmias can indicate underlying issues. In this post, our Kent vets discuss what can cause cardiac arrhythmias in dogs, signs and symptoms to watch for, and potential treatment options.

What are cardiac arrhythmias in dogs?

A cardiac (heart) arrhythmia is an abnormality in the rhythm of a dog's heartbeat. Abnormalities can occur in the speed, strength, or regularity of heartbeats. These are generally caused by unusual electrical activity within a dog's heart muscles, which can be caused by congenital issues (that originate from birth) or a condition, injury, or disease your dog acquired after they were born. 

While dogs of any age and breed can develop arrhythmias, but some types are more common in specific breeds (we'll explore types of arrhythmias and which breeds they tend to appear in below). 

If your dog displays signs of having an unusual heartbeat, contact your vet right away. An arrhythmia can indicate a serious underlying health condition that requires immediate treatment to avoid long-lasting complications. 

Here's what you should know about the signs, causes, and treatment options for dogs with heart arrhythmias. 

Signs of Cardiac Arrhythmias in Dogs 

Three common signs of cardiac arrhythmia in dogs include:

• Weakness
• Long pauses between heartbeats 
• Loss of consciousness 

Causes of Cardiac Arrhythmias in Dogs 

Several potential factors can cause a dog to develop an irregular heartbeat. These include:

Types of Heart Arrhythmias in Dogs

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

Atrial Fibrillation 

Atrial fibrillation, commonly found in Great Danes, Doberman pinschers, Newfoundlands, Irish Wolfhounds, Boxers, and other large breeds, often causes the heart to beat too fast and can occur even when the heart is structurally and functionally normal.

The condition may also be associated with underlying cardiomyopathy, which leads to poor heart function and heart enlargement. 

Heart Block 

The heartbeat is normally initiated by the sinus node, with the impulse being conducted through the atria and to the junction between the atrial and the ventricles. This junction is referred to as the atrioventricular (Av) node. The conduction is slowed at this point, allowing the atria time to fill the ventricles with blood before the ventricles are triggered to contract. 

Most dogs and other animals will have secondary pacemakers in the conduction system of the ventricles, which trigger the heart to beat when the conduction through the AV node is stopped. These secondary pacemakers discharge at a slower rate than the primary natural pacemaker of the sinus node. However, sometimes they discharge at a dangerously slow rate, causing weakness and potentially even collapse. Your dog may develop heart failure as a result of this abnormality, which can affect dogs of any breed. 

Ventricular Arrhythmias 

This type of arrhythmia tends to appear in boxers, bulldogs, and German shepherds. Bulldogs develop a variation of this disorder, and German shepherds have an inherited ventricular arrhythmia that affects young dogs between three and 24 months old. After 24 months of age, the arrhythmias tend to disappear in German shepherds and they will no longer be at risk. However, this condition can be passed on when these German shepherds are mated to a dog with a genetic background of risk for this condition. 

Arrhythmogenic right ventricular cardiomyopathy or ARVC (also referred to as Boxer Cardiomyopathy), occurs in the right ventricle. Boxers can also have arrhythmias develop in other areas of the heart. Ventricular arrhythmias that occur in rapid succession are called ventricular tachycardia, which can lead to a decrease in blood flow to the body. Dogs may collapse if perfusion to the brain (the amount of blood delivered to a unit of tissue per unit of time) decreases to a certain level.

These arrhythmias can degenerate into ventricular fibrillation, which is a fatal abnormal heart rhythm. Some dogs die suddenly of these arrhythmias, most often between five and nine months of age. 

Myocarditis 

While myocarditis can be diagnosed in any breed, it is typically found in medium to larger-sized dogs. Some dogs with heart block or ventricular arrhythmias may have myocarditis, or underlying inflammation of the heart. 

Sick Sinus Syndrome (Sinus Node Disease) 

West Highland White Terriers, Dachshunds, Miniature Schnauzers, boxers, and cocker spaniels are more likely to be diagnosed with sick sinus syndrome. This condition causes a heart rhythm where the sinus node (which typically initiates the beating heart) does not discharge an impulse to trigger the heart to contract. As a result, the heart stops beating. 

If the heart stops for more than eight seconds, the dog will faint or collapse. Sometimes, another part of the heart will initiate a beat to prevent complete cardiac arrest. Most of the time, the sinus node will eventually start working again, but there will be many long pauses in the dog's heart rhythm. 

Some dogs with sick sinus syndrome will have a more constant sinus bradycardia (too slow) because the sinus's firing rate is lower than normal. Other dogs with sick sinus syndrome will have periods of excessive tachycardia (rapid heartrate) in addition to pauses or bradycardia. 

Diagnosing Dogs With Cardiac Arrhythmia

If you suspect your dog may have any form of heart condition, book an appointment for an exam with your veterinarian as soon as possible. Early detection and treatment are vital to increasing your dog's chances of positive long-term prognosis. We can also refer you to a veterinary cardiologist for advanced testing and treatment.

A vet can perform diagnostic tests to confirm the diagnosis and gain insight into any other structural and functional problems in your dog's heart. Here are common diagnostic tests a vet or veterinary cardiologist may recommend:

Electrocardiogram 

While electrocardiograms are recorded, 24-hour electrocardiograms are monitored (Holter monitoring) are used to diagnose atrial fibrillation and dangerous arrhythmias. These same tests are used to understand disturbances in the heart's rhythm monitor your dog's response to treatment. 

In addition to treating the arrhythmia, your vet will need to perform other diagnostic tests to understand the structural and functional problems in your dog's heart. 

Troponin I (cTn1)

This cardiac biomarker is released when myocardial injury has occurred. It has a half-life of less than 70 minutes. Elevated circulating concentrations of Triponin I can point to chronic cardiac disease. 

C-Reactive Protein

This protein is produced by the liver in response to inflammation and can be measured in a dog's serum. Serum concentrations of C-reactive protein increase within 4 to 34 hours of onset of inflammation in dogs. 

Treating Dogs with Heart Arrhythmias

There are numerous treatment options for dogs with irregular heartbeats, including: 

• Prescription drugs (may include anti-inflammatory medications like corticosteroids, antiarrhythmic medications like sotalol to treat or prevent abnormal heart rhythms, or other prescription medications such as dilitiazem, atenolol and/or digoxin to treat atrial fibrillation). 
• Echocardiogram to monitor your dog's response to treatment
• 24-hour ambulatory electrocardiographic monitoring (Holter monitoring) to optimize treatment with the correct dose of medication 
• Radiography to help determine whether other medications are required 
• Pacemaker (implantation is now a common procedure for dogs, and your vet will likely refer you to a veterinary cardiologist for this surgery. Response to treatment is usually very good. 
• Cardioversion (electrical therapy) to stop tachyarrhythmias and restore sinus rhythm

Treatment of cardiac arrhythmias (irregular heartbeats) in dogs must be highly specific to each patient's medical status and individual requirements. At  Clover Veterinary Hospital, our vets are committed to detecting heart issues and other health conditions your dog may experience early, then developing a diagnostic and treatment plan to support the best possible outcomes for your pet's health. If you are referred to a veterinary cardiologist for further diagnostic testing and treatment, we will work closely with your specialist to ensure your dog receives the best possible cardiac care.  

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Do you suspect your dog may have an arrhythmia or other heart-related condition? Contact our Kent animal hospital today to book an appointment for an exam.