Heart Disease of the Sinus Node in Dogs

The sinus node, located within the heart, is responsible for keeping the heart rate consistent and regular. In heart disease of the sinus node in dogs, the sinus node does not function properly. The electrical impulse is discharged irregularly and the heart does not contract at the same time, each time. These actions cause a longer than normal break between beats to the point where the heart actually stops beating. The pauses between beats are also very irregular, and if the heart pauses for more than a few seconds, the initial beats that come back are very rapid. The heart may beat regularly for a while, and then become irregular again. Sick sinus syndrome also is characterized by a regular, yet very slow, heartbeat because of the sinus node sending electrical impulses at a very low rate. On the contrary, dogs may have a very rapid, yet consistent, heartbeat, mixed with long pauses.

Heart disease of the sinus node in dogs occurs as a result of the sinus node and its ability to regulate the heartbeat. It is characterized by long pauses in between heartbeats, which essentially is the heart stopping before it irregularly resumes again.

With sick sinus syndrome, many dogs show no symptoms. Dogs that live a sedentary lifestyle definitely show the least amount of symptoms, if any. Symptoms can include:

• Slow heart rate
• Fast heart rate
• Long pauses between beats of the heart
• Weakness
• Intolerance to exercise
• Fainting
• Collapse
• Lethargy
• Coughing
• Difficulty breathing

Types

Certain breeds are more susceptible to acquiring sick sinus syndrome. Predisposed breeds include:

• Pugs
• West Highland White Terriers
• Cocker Spaniels
• Miniature Schnauzers
• Dachshunds

Sick sinus syndrome has a cause that is unknown. Possible causes include:

• Genetics
• Heart disease
• Cancer in the chest area

If your dog is showing any symptoms it is important to make an appointment with the veterinarian. The veterinarian will do a complete examination with the blood work to check for any metabolic abnormalities, urinalysis, and biochemistry profile to check the functioning of all the organs of the dog. The veterinarian will also ask questions about specific symptoms and the onset of the symptoms.

After listening to the report of your dog’s symptoms, the veterinarian will begin to focus on the heart. She will listen to the dog’s heart with a stethoscope and may possibly hear long pauses between the beats or some sort of irregularity, whether it is a slow, inconsistent beating heart or a rapid and inconsistent beating. The veterinarian will use an electrocardiogram or a heart monitor which your dog wears for a longer period of time to acquire more accurate information on the functionality of the heart. The monitor will also allow the veterinarian to rule out any other cardiac diseases.

The veterinarian will perform additional testing to evaluate the functionality of the dog’s sinus node. This is accomplished by using a provocative atropine response examination where atropine, a drug which stimulates the sinus node’s electrical activity, is given to the dog. The veterinarian will be looking for the heart to either speed up or stay the same. In sick sinus syndrome, the heart will not respond to the atropine. Imaging of your dog’s chest area will also allow the veterinarian to take a closer look at the heart. It will help the veterinarian check for any abnormalities in the chambers, and will also check for heart failure.

There are a few methods of treatment that have proven successful  for sick sinus syndrome. Treatment methods include: 

Pacemaker

The veterinarian may recommend that your companion have a pacemaker implanted in order to regulate the heartbeat and keep it consistent. Pacemakers have proven to be a successful method of treatment.

Medications

Medications can be prescribed according to your dog’s diagnosis and the severity of his condition. There are medications that can help keep the heartbeat consistent and regular. The medical professional will give specific instructions on how and when to administer the medication. He will also communicate with you any adverse side effects to watch for.

If your dog has heart disease of the sinus node, or sick sinus syndrome, with medications or a pacemaker, the prognosis is good. It is important to listen to your veterinarian’s instructions on any at-home care for your companion. The medical professional may recommend that the dog takes it easy and does not perform any strenuous exercise activity. Every dog is different, as is every diagnosis. If your dog has a mild case of sick sinus syndrome, he may be able to exercise and live a very normal life. It is important to understand the disease and to be aware of any behavioral changes and symptoms as they develop. Be sure to ask the physician any questions if you see any type of symptoms develop in your loved one.