Just like in humans, the dog’s heart is extremely important. It is a powerful muscle that works constantly to pump oxygenated blood throughout the body and return deoxygenated blood to the lungs.
The nervous system plays an important role in this process, as the electrical signal sent from the heart tissue is responsible for telling the heart to contract to pump. But what happens when this signal changes and what can be done about it?
What is an arrhythmia?
A heart that pumps at a normal rate usually has a normal rhythm, which is a pattern that repeats itself regularly. If the heart is pumping too fast or too slow, there may be a heart rhythm problem. This is the definition of arrhythmia. Similarly, the time between heartbeats also plays a role. A rhythm with a steady beat between beats is called an asynchronous rhythm. Anything that causes an irregular rhythm between beats causes an arrhythmia.
Your dog’s heart rate (the number of beats per minute) may increase due to stress or exercise, but this is usually temporary. A healthy heart will return to a normal heart rate at rest. In small dogs, this number may be between 120 and 160 beats per minute. In large breed dogs, the normal resting heart rate is between 60 and 120 beats per minute. If your dog’s heart rate stays too slow or too fast, he or she may have an arrhythmia or be at increased risk of developing one.
What causes cardiac arrhythmias in dogs?
There are many types of cardiac arrhythmias in dogs. Some mainly affect large breed dogs, while others may affect certain breeds. Boxer dogs are most likely to develop arrhythmogenic right ventricular cardiomyopathy (ARVC), a type of arrhythmia that can be fatal if left untreated. Boxers are also at risk for atrial fibrillation, as are Great Danes, Doberman Pinschers, Irish Wolfhounds and Newfoundlands. Atrial fibrillation can be treated with medications that slow the heart rate. Smaller breeds, such as Cocker Spaniels, Dachshunds, Miniature Schnauzers and Westies, are at increased risk of developing sick sinus syndrome, which causes the heart to beat so slowly that surgical implantation of a pacemaker is necessary.
Structural changes in the heart can cause arrhythmias. For example, in dogs with dilated cardiomyopathy (DCM), the walls of the heart become very thin and literally bulge outward. As a result, the heart cannot pump blood efficiently and the body lacks oxygen. This forces the heart to pump harder and the heart rate becomes so fast that arrhythmias such as supraventricular tachycardia (SVT) and atrial fibrillation can occur.
An infection or inflammation of the heart, acamyocarditis, can increase the risk of ventricular arrhythmia or heart block. Heart block occurs when the electrical signal that flows through the heart to cause its contraction eventually stops. Most dogs are able to overcome this signal stoppage with a natural “secondary pacemaker”, but it still results in a slow heart rate. As a result, dogs with heart block may appear very lethargic. Neurological disorders, respiratory disorders, gastrointestinal disorders, and certain medications (especially those involving general anesthesia) can increase the risk of heart block in dogs.
Symptoms of arrhythmia
Dogs with arrhythmias may show subtle signs at first. They may appear more tired than usual or try to avoid exercise. For example, you may notice that your pup is easily fatigued and can’t run as much as he used to. If he is trying to sleep, he may seem more restless, but a more telling sign is if his respiratory rate exceeds 40 breaths per minute during sleep. This is common with underlying heart disease.
Dogs with heart disease tend to cough a lot, especially at night. If heart problems progress, your dog may have difficulty breathing throughout the day. Severe heart disease can lead to fluid accumulation in the abdomen and weight loss due to generalized muscle wasting, or cachexia.
In some cases, you may be able to detect an arrhythmia yourself. To check your dog’s heart rate, you should place your hand on his chest or listen with a stethoscope if you have one. You will then count the number of beats in a fifteen-second window. Once you have this total, multiply it by four to get the number of beats per minute. When palpating or auscultating, you should hear regular repeated beats. If the beats occur abnormally or you hear more than two heart sounds (e.g., more than the typical “lub dub” sound), contact your veterinarian immediately!
CLICK NEXT PAGE BELOW TO CONTINUE READING …