Sick Sinus Syndrome in Dogs

This condition can be hereditary and certain breeds are found to be more prone to developing it. Your dog’s heart rate may decrease or increase to a dangerous level and the symptoms can wax and wane over time. The number one symptom noticed is your dog fainting (syncope).

This syndrome gets its name from the sinus node which initiates your dog’s heartbeat not working properly, causing his irregular heartbeat. There are many other conditions that can have an irregular heartbeat as a symptom and it may difficult for you to determine if your dog’s symptoms have an underlying cause.

Sick sinus syndrome goes by a few names including sinus node dysfunction and bradycardia-tachycardia syndrome. It is defined as abnormalities in the typical rhythm of older and adult dog's heart beats.

Symptoms are mostly generalized, however, there are a few more specific ones to be aware of. Some of these symptoms may only be detected by your veterinarian. 

• Fainting – without any other warning, signs or symptoms your dog may lose consciousness, this may happen after your dog’s heart stops for 8 seconds or more 
• Lethargy – you may notice your dog has an overall weakness and lack of energy with no explanation
• Bradycardia – an irregularly slow heartbeat, for dogs this would be anything below 40 beats per minute
• Tachycardia – an irregularly fast heartbeat, this would not be explained by exercise or any other causes and could be over 200 beats per minute
• Asymptomatic – your dog may present with no noticeable symptoms to you and only upon a visit to his veterinarian will sick sinus syndrome be caught

Types

The 2 types of sick sinus syndrome are bradycardia and tachycardia. These are based on how slow or how quick his heart rate is.

Bradycardia

• Abnormally slow heart rate
• Typical heart rate for a dog is around 40 beats per minute
• With sick sinus syndrome, this can go as low as 10 beats per minute

Tachycardia

• Abnormally high heart rate
• Typical heart rate for a dog at rest is around 40 beats per minute and can go up to the high 200’s per minute when he is involved with intense exercise or play
• With sick sinus syndrome, your dog at rest could have a heartbeat of 200+

There are a few possible causes for sick sinus syndrome and these include inheritance in certain breeds, and age of your dog. Female dogs are more susceptible to developing the syndrome and it is most often found in dogs that are 6 years old or above. 

Breeds most prone, although any dog is susceptible:

• West Highland White Terriers
• Dachshunds
• Miniature Schnauzers – females tend to inherit this syndrome more than males do 
• Boxers
• Cocker Spaniels

Age is a factor:

• Adult dogs tend to show signs of the syndrome more so than puppies or young dogs
• Older dogs have a higher risk of developing symptoms as they age versus their younger counterparts

If you are concerned that your dog is possibly suffering from sick sinus syndrome, it will be very important to get him to his veterinarian as soon as possible as this syndrome can be life-threatening if left untreated. Once at his veterinarian, your dog will most likely be given a physical exam and any symptoms you have noticed should be brought to the veterinarian’s attention.

It will be important to share if you noticed him fainting or losing consciousness or if you noticed a quick heart rate with no justification for it. Your veterinarian will want to perform some testing to determine the exact cause of your dog’s symptoms. Some of these tests included in the diagnosis will include electrocardiograph, echocardiogram, blood pressure and x-rays.

Your dog will be back on his feet relatively quickly after surgery. Your veterinarian will discuss any follow up appointments as necessary with you following treatment. When treatment is implemented quickly, his prognosis will be good. In up to 90% of dogs treated with surgery and pacemaker implantation, symptoms completely disappear. 

Ongoing follow up to ensure there are no further heart beat problems or concerns will be necessary for the remainder of his life. It will also be important to bring him in regularly for checkups of his pacemaker.