Sinus Bradycardia in Dogs
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Sinus bradycardia in dogs is an abnormally low heart rate caused by the impulses in the sinus node firing more slowly than normal. The sinus node is responsible for the electrical impulses in the heart that cause it to beat or contract. In most cases, this is a harmless condition that often occurs in athletic dogs. However, it can be dangerous if it is due to a serious underlying condition. Treatment depends on the original cause, and diagnosis is the key to the best treatment.
In the following AnimalWised article, you can learn more about what is bradycardia in dogs, as well as its symptoms, causes and treatment.
What is bradycardia in dogs?
Bradycardia or sinus bradycardia is a type of cardiac arrhythmia in which the affected dog has an abnormally low heart rate due to slowed activation of impulses in the sinus node of the heart. These impulses are what cause the contraction or heartbeat. The decreased activation of the impulses therefore leads to a decrease in beats per minute.
In very athletic dogs, or in dogs that exercise regularly, sinus bradycardia can be harmless and even beneficial because your dog's heart doesn't have to work as hard to move oxygen around the body. However, it becomes dangerous when the drop in heart rate is caused by a serious condition, as it can lead to syncope or unconsciousness.
The origin of bradycardia may be cardiac, with or without lesions such as cardiomyopathy or myocarditis. However, there are also numerous extracardiac causes that can lead to bradycardia, which we will discuss in the following sections.
Sinus bradycardia is characterized by an abnormally low heart rate at rest. Similar to humans, your dog's exact resting heart rate is influenced by several different factors, including their size and health. Here is a guideline for what an abnormally low heart rate in a dog means:
- Puppies: heart rate lower than 160 beats per minute.
- Small adult dogs: heart rate lower than 100 beats per minute.
- Large adult dogs: heart rate lower than 60 beats per minute
There are certain breeds with a greater genetic predisposition to suffer from bradycardia:
- Miniature schnauzer
- Cocker spaniel
- Highland White Terrier
It is also more common in younger animals, unless it is caused by an underlying condition, in which case it can affect a dog of any age.
If you want to learn more about heart failure in dogs, do not miss this other article, where we talk about the most common symptoms of heart failure in dogs.
Symptoms of bradycardia in dogs
There is a difference between physiologic and non-physiologic bradycardia in the way the symptoms occur. If your dog is active and athletic, it is likely that it will not show symptoms. However, as mentioned before, symptoms may occur if bradycardia is caused by an underlying cause.
Some common symptoms of sinus bradycardia include the following:
- Intolerance to physical exercise
- Reduced respiratory rate
- Uncoordinated movements
- Pale mucous membranes
In addition, in some cases, this condition can lead to:
- Heart failure
- Blood pressure fluctuations
- Altered blood flow to vital organs
Typically, the sinus bradycardia is most apparent when your dog is at rest.
Continue reading in this other article where we talk about taurine rich foods for dogs with heart problems.
Causes of bradycardia in dogs
Bradycardia can be caused by a number of pathological conditions. As we mentioned earlier, physiologic bradycardia may be present in athletic dogs, which allows the heart to pump oxygenated blood throughout the body with less effort during exercise. However, this condition can also be caused by cardiac or extracardiac problems, of which there are several:
Some of the heart problems that can cause bradycardia in dogs include:
- Myocarditis: an inflammation of the heart muscle, or myocardium.
- Pericarditis: an inflammation of the layer that covers the heart.
- Cardiomyopathy: Disease of the heart muscle that makes it difficult for the heart to pump blood to the rest of the body and can be either enlarged or hypertrophied.
On the other hand, extracardiac causes of bradycardia in dogs include:
- Hypothyroidism:causes the bodily functions to slow down.
- Hypokalemia: drop in blood magnesium or potassium levels.
- Liver or kidney failure: the kidneys filter waste from your puppy's bloodstream, while the liver filters waste from the digestive system. When either of these processes is impaired, it can alter the normal heart rate of dogs.
Other causes of sinus bradycardia in dogs include hypothermia or reduced body temperature, tracheal intubation, or sedation.
Continue reading this other article if you want to learn more about heart murmurs in dogs.
Diagnosis of Bradycardia in Dogs
The diagnosis of sinus bradycardia is relatively simple, as your veterinarian can easily detect it with a stethoscope by measuring the heartbeats per minute.
If an electrocardiogram (ECG) is performed, additional information can be obtained to determine if bradycardia is truly present and if it coexists with another type of arrhythmia.
The next step is to determine the cause of the bradycardia in your dog. To do this, your veterinarian will perform a thorough physical examination of your dog, taking into account the history of symptoms, your dog's general condition, and any incidents that may have led to the condition.
To examine the thyroid, kidneys, and liver, and to detect any electrolytic or hematologic changes, your veterinarian will need to perform blood and biochemical tests. Chest x-rays are also often recommended to assess the condition of the heart, although cardiac ultrasound and echocardiograms are preferable.
Treatment of bradycardia in dogs
Treatment is based on any underlying disease identified. Many dogs show no clinical signs and require no treatment. Therapeutic approaches vary widely and depend on the cause SB, heart rate, and severity of clinical signs. Below are some examples of how this disease is treated depending on the underlining condition:
- In the case of hypothyroidism, the dog should be treated with the missing thyroid hormone replacement.
- Cases of bradycardia as a consequence of intubation, sedation, or anesthesia resolve spontaneously after surgery.
- In cases of hypothermia, the dog's body temperature should be gradually increased to increase the heart rate that is causing this problem.
- In cases where bradycardia is sudden and critical, the dog must be hospitalized to control it and provide fluid therapy.
Depending on the final diagnosis, your doctor will order further monitoring. If signs are present, they should disappear with resolution of the causative underlying condition. As you can see, the treatment of bradycardia in dogs varies greatly depending on the cause, so be sure to consult a veterinarian as soon as the first symptom appears.
Continue reading this other article if you want to know more about what the normal vital signs are or should be in dogs.
This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.
If you want to read similar articles to Sinus Bradycardia in Dogs, we recommend you visit our Cardiovascular diseases category.
- Avepa continuing education. (2016). Canine cardiology, a practical update . Available at: https://avepa.org/pdf/proceedings/CARDIOLOGIA_CANINA_2016.pdf
- Ceron, J.; Fernandez, MJ; Garcia, C.; Hervera, M.; Angle, SM; Perez, D.; Perez, C.; Santamarina, G.. (2016). Clinical Manual of Small Animal Internal Medicine I. ESVPS, Ed. SM Publishing Ltd. Sheffield, UK.