Arrhythmia, in basic terms, refers to an abnormal heart rate. This may sound a little scary, but an arrhythmia often happens as a variation of your dog’s typical heartbeat. Plenty of dogs with arrhythmias will live a long and otherwise healthy life.
“An arrhythmia is simply an irregular heartbeat or a heart rate that’s slower or faster than normal,” says Dr Lori Siemens, DVM, DACVIM, a board-certified veterinary cardiologist. “Some arrhythmias are harmless and require no treatment, and some are dangerous and need medication.”
Arrhythmias in dogs may remain symptomless for years before presenting as a more serious heart problem. But in some cases, your dog may have other symptoms, too. Your veterinarian may notice these symptoms at their regular checkup, which means they can prescribe medication to help your dog stay healthy.
Read on to learn everything you need to know about arrhythmias in dogs, including their symptoms and causes, the main types, and the treatments your vet may recommend.
What Is A Normal Heart Rate for Dogs?
Dogs tend to have faster heart rates than humans—though sometimes, their heartbeat may slow down to match yours!
A dog’s typical resting heart rate is typically around 70-120 beats per minute (bpm). Yours, however, will usually fall somewhere between 60 and 100 bpm.
Evidence also suggests your dog’s size, age, and breed can affect their heart rate, with an average difference of 10.5 beats per minute between dogs weighing 5 kilograms (kg) and those weighing 55 kg. Chihuahuas, for example, generally have a faster heart rate than larger dogs.
As for what your dog’s heartbeat should sound like, Dr Siemens says it should consist of a first heart sound and a second heart sound, often described as “lub-dub.” The heartbeats should be regular in rhythm and not too fast or too slow.
Symptoms Of Arrhythmias In Dogs
Sometimes, a dog with an arrhythmia will show symptoms, though this can depend on the underlying condition causing the arrhythmia.
If your dog has a type of arrhythmia that causes a faster heart rate, they could have some of the following symptoms:
- exercise intolerance (they may seem weak or get tired easily)
- effort intolerance (showing little interest in activities like walks or play)
- shortness of breath or panting
- presyncope (can cause them to feel lightheaded and dizzy, with ‘wobbling’ and weakness in their back legs)
If your dog has an arrhythmia that causes a slower heart rate, they could have some of the following symptoms:
- general weakness
- extreme tiredness
- slower movements
- seeming ‘spacey’
- collapsing or fainting
Keep in mind, though, that Dr Siemens says dogs commonly don’t show any symptoms, even when they have significant arrhythmias. They may act pretty much as they always have, despite their irregular heart rate.
How Can You Tell If a Dog Has an Arrhythmia?
While it’s possible to check your dog’s vital signs at home, your vet is the only one who can confirm whether your dog has an arrhythmia.
They may hear the arrhythmia while listening to your dog’s heart as part of a wellness exam or when treating your dog for another condition. If you have a dog whose breed is prone to arrhythmia, your vet can also perform a 24-hour electrocardiogram (EKG) called a Holter monitor to help detect an arrhythmia.
Why Do Arrhythmias In Dogs Happen?
To understand what causes arrhythmias, it may help to first understand how your dog’s heart should function.
Dr Siemens explains:
A normal heartbeat starts with pacemaker cells in the sinus node, located in the upper right part of the heart. These cells send an electrical current down through the atria, or top of the heart, and then through the AV node, a specialised area of conduction tissue in the middle of heart. Finally, the current passes through the ventricles, the powerful muscle at the bottom of the heart.
This electrical current causes the muscle cells of the ventricles to contract. This contraction pushes blood from the heart to the body and to the lungs. Any disease that disrupts this pathway of electrical conduction can cause an arrhythmia. Examples include heart disease, cancer, or electrolyte imbalance, along with other health concerns that put stress on the body.
Some arrhythmias are just normal responses to things happening in the body—like exercise, fever, or nervousness—speeding up the heart rate temporarily. A respiratory sinus arrhythmia can also cause a dog’s heart rate to speed up when they breathe in and slow down when they breathe out. Pathological arrhythmias, however, are truly abnormal and may require treatment.
Common Types Of Arrhythmias In Dogs
Vet experts recognise five main types of arrhythmias in dogs. These include:
Atrial fibrillation
The most common form of arrhythmia is atrial fibrillation. It most commonly affects large and giant breeds, like Great Danes, Newfoundlands, Labrador Retrievers, Mastiffs, and Rottweilers.
If your dog has a structurally normal heart, this type of arrhythmia may not cause any noticeable symptoms. But they might develop an intolerance to exercise over time.
On the other hand, if your dog has cardiomyopathy—an enlargement of the heart that often causes atrial fibrillation—or another underlying condition, they may have symptoms like:
- exercise intolerance
- lethargy and general weakness
- loss of appetite
- shortness of breath
- cou
- coughing
- fainting
Your veterinarian may prescribe a medication to slow your dog’s heart rate, like diltiazem, atenolol, or digoxin. They’ll continue to monitor your dog to make sure the medication works at the dosage they prescribed.
Ventricular arrhythmia
This type of arrhythmia most commonly affects Bulldogs, Boxers, and German Shepherds.
In some dogs, ventricular arrhythmias may happen rapidly, one after the other. Known as ventricular tachycardia, this can cause heart palpitations and decreased blood flow in your dog’s body. Eventually, diminished blood flow to the brain may lead to collapse. In some cases, a ventricular arrhythmia may lead to ventricular fibrillation, which is fatal.
Your vet may recommend an electrocardiogram to better diagnose the arrhythmia and determine treatment options. They may prescribe anti-arrhythmic drugs, like sotalol, to help prevent ventricular fibrillation.
If your dog’s ventricular arrhythmia relates to underlying heart problems, your vet will recommend treating these as well.
In German Shepherds, an inherited ventricular arrhythmia could show up around 12 weeks of age. This arrhythmia can be fatal, so your vet may recommend monitoring your dog carefully. Once they reach the age of two, the arrhythmia will likely clear up on its own.
Sick sinus syndrome
This type of arrhythmia causes the heart to stop beating. It’s most common in Dachshunds, Boxers, West Highland White Terriers, Miniature Schnauzers, and Cocker Spaniels.
The sinus node is the part of the heart that makes it beat. A sinus node malfunction can disrupt the heartbeat and cause an arrhythmia where your dog’s heart may temporarily stop beating. That said, sick sinus syndrome can cause both a slower or faster heartbeat, depending on the underlying cause. Your dog’s heart rate may speed up at times and slow down at other times.
If your dog’s heart stops for longer than eight seconds, they’ll collapse or faint—which probably sounds quite alarming! But in most cases, the sinus node will start up again after a pause, or another part of the heart will ‘jump start’ it so it resumes beating.
Treatment for sick sinus syndrome involves a pacemaker—now a common surgery for dogs. What’s more, dogs typically respond well to pacemakers.
A veterinary cardiologist can implant a pacemaker. They may also recommend medication.
Heart block
A heart block can affect both dogs and cats.
In a healthy heart, impulses that run between the atria and the ventricles tell the heart to contract and pump blood throughout the body. If this doesn’t happen, the ventricles don’t contract and the heart stops beating.
A dog with heart block may seem weak or collapse. They may, in time, develop heart failure.
If your vet detects any concerns with your dog’s heart rate during an exam, they’ll recommend an echocardiogram. If this test confirms heart block, a veterinary cardiologist can fit your dog with a pacemaker to trigger the contraction of the ventricles and help their heart function as it should.
Myocarditis
While myocarditis isn’t a type of arrhythmia itself, it can cause them. This inflammation of the heart often develops due to an underlying health issue. Experts have linked it to viral, bacterial and protozoal infections, but they have yet to determine the exact cause.
It generally affects medium and large breed dogs. Many dogs with heart block or ventricular arrhythmias also have myocarditis.
Beyond having an arrhythmia, your dog may not show any symptoms of myocarditis. But over time they may develop:
- weakness and fainting
- exercise intolerance
- difficulty breathing
- abdominal swelling
This serious condition can be fatal, which is what makes it so important to schedule regular wellness checkups for your dog. Catching the condition early may improve your dog’s chances of survival.
If your vet detects an arrhythmia and connects it to myocarditis, they can monitor the condition and prescribe anti-arrhythmic medications or anti-inflammatory drugs like corticosteroids.
Can Dogs Get Better After An Arrhythmia Diagnosis?
It’s natural to feel a little frightened if your dog has an arrhythmia, but keep in mind that the diagnosis can help your vet continue monitoring your dog’s condition. Many dogs never get a diagnosis in the first place, and an undetected arrhythmia could increase their risk of sudden death down the line.
An arrhythmia doesn’t automatically lead to sudden death—but if your dog does have a potentially concerning arrhythmia, treatment can make a difference. Both medications and pacemakers can improve your dog’s heart function and raise their chances of a long and healthy life.
As soon as you notice any symptoms that could point to an arrhythmia, it’s best to make an appointment with your vet as soon as possible. Make sure to share all of your concerns so they can order the right tests to check for arrhythmias or other heart issues.