The normal heart rate of dogs should be 60 to 100 beats per minute. However, small dogs and puppies tend to have a higher heart rate, sometimes averaging 100 to 160 and even 180 beats per minute.
Bradycardia is what happens when a dog’s heart beats slower than expected. It can be caused by a wide range of factors, and it is more or less physiological in some breeds. Read on to find out more about low heart rates in this species, sinus bradycardia, and what to do if you think your pooch has it.
When can a low heart rate be normal?
First of all, your dog’s heart beats differently when they are engaged in any form of exercise and when they are at rest. The numbers that we have mentioned at the beginning of this article are for the resting heart rate, so when your dog has been sitting still or even sleeping for more than 5-10 minutes.
Some dog breeds can have a lower heart rate compared to others, and in their case, it is completely physiological. Here are a few examples:
- West Highland White Terriers
- Cocker Spaniels
- Pugs
- Dachshunds
What causes a low heart rate in dogs?
There are two pathological reasons why a dog’s heart might beat slower than normal, and they consist of a heart block and a sick sinus syndrome. A heart block happens when the AV node isn’t functioning normally, whereas a sinus syndrome is caused by a malfunction of the sinoatrial node.
In both of these cases, there is an emergency mechanism that kicks in so that the heart does continue to work and the pet remains alive. However, since it is not functioning at its normal capacity, the dog will show a number of symptoms, such as sudden collapse, weakness, fainting, or severe exercise intolerance.
Sinus bradycardia is somewhat more common than heart block, which is why we will discuss it more in the following sections.
Symptoms of sinus bradycardia in dogs
We’ve already mentioned some typical clinical signs that can be noticed in this condition, but here are a few more that pets might show:
- Slow breathing
- A decrease or lack of muscle coordination
- Confusion
- Exhaustion
Dogs can be suspected to have sinus bradycardia when their heart rate is lower than some specific limits. For example, for large dogs, that threshold is 60 beats per minute, but for small ones, it’s 100 beats per minute. Because the heart rate of puppies is normally higher than that of adults, in their case, bradycardia can happen when they have fewer than 150 to 160 heartbeats per minute.
What causes sinus bradycardia?
There is no general cause, so every dog is different, and their clinical picture might also be unique.
Pets that are extremely athletic can experience sinus bradycardia merely because their organs get properly oxygenated without their hearts having to work as hard as those of animals that don’t regularly engage in exercise.
Other causes of sinus bradycardia are listed below:
- Hypocalcemia
- Hypomagnesemia
- Hypothermia
- Hypothyroidism
- Diseases that affect the normal function of the heart (whether they be digestive, respiratory, or neurological)
- Anesthesia
How is a low heart rate diagnosed?
You can measure your dog’s heart rate at home by placing your hand on their chest and counting the number of pulses that you can feel over a 10 or 15-second period.
The vet will do the same at the clinic but will use a stethoscope – especially since this device allows them to hear any heart murmurs or particular changes in the heart rhythm.
As for the additional diagnostic methods that a veterinarian can utilize in this case, they consist of an ECG and an echocardiogram – the second being elected, especially in cases where the vet feels that the dog might need to have an artificial pacemaker installed.
How is canine sinus bradycardia treated?
Because bradycardia can occur physiologically in some cases, that also means that your dog might not have to receive any specific treatment. Rest is highly recommended to all pets that are diagnosed with a lower heart rate than normal, but if no underlying cause is detected and there’s no change in either the way the AV or sinus node functions, no type of additional therapy may be required.
There are medications that can help your dog’s heart work normally, but sometimes installing a pacemaker might prove to be much more effective, especially because it works so well when it comes to ‘rewiring’ the heart.
Unfortunately, the procedure itself is risky as pets have to be put under. The operation also has risks, including infection and abnormal heart rhythms. Therefore, depending on the dog’s age and general health status, they might first have to be stabilized with intravenous medication and only then be considered for the placement of an artificial pacemaker.
Every sedation comes with a share of risks, and they range from hypotension and arrhythmias to hypothermia and hypoventilation, so talk to your veterinarian about what they feel is the right solution for your pet.
References:
Short-Term Heart-Rate Variability in Healthy Small and Medium-Sized Dogs Over a Five-Minute Measuring Period, Radu Andrei Baisan, Eusebiu Ionut Condurachi & Vasile Vulpe, J. Vet. Res., 2020: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7105988/
Indications for Permanent Pacing in Dogs and Cats, R. A. Santilli et al, J. Vet. Cardiol., 2019: https://pubmed.ncbi.nlm.nih.gov/30709617/
Outcome and Survival in Canine Sick Sinus Syndrome and Sinus Node Dysfunction: 93 cases (2002-2014), J.L. Ward et al, J. Vet. Cardiol., 2016: https://pubmed.ncbi.nlm.nih.gov/27286907/
