Sick Sinus Syndrome
Sick sinus syndrome is a disturbance of the normal rhythm of the heart. The electrical impulse that drives the heart beat starts in the sinoatrial (SA) node of the heart, and then spreads through specialized conduction pathways, causing orderly depolarization and contraction of the heart muscle. This can be traced on an electrocardiogram.
Sick sinus syndrome is the name given to a number of arrhythmias (irregular rhythmns) that arise because of abnormal function of the SA node. Clinically, the arrhythmias may cause weakness and fainting.
How is sick sinus syndrome inherited?
The mode of inheritance is unknown.
What breeds are affected by sick sinus syndrome?
This is seen most often in miniature Schnauzers, particularly in female dogs.
It occurs less commonly in Pomeranians, dachshunds, pugs, boxers and cocker spaniels.
For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a general consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does sick sinus syndrome mean to your dog & you?
The most common clinical signs with this disorder are weakness and fainting.
How is sick sinus syndrome diagnosed?
The first indication of this disorder may be that your veterinarian finds your dog has an unusually slow heart rate, which is not increased by exercise. To diagnose this further, your veterinarian will likely perform an electrocardiogram which will show certain distinguishing features for this condition.
Your dog may have no clinical signs of this disorder, or may experience fainting or weakness.
FOR THE VETERINARIAN:
- ELECTROCARDIOGRAM: any combination of severe and persistant sinus bradycardia, SA block with or without escape rhythms, supraventricular premature complexes or tachycardia, bradycardia-tachycardia syndrome (periods of severe sinus bradycardia alternating with ectopic supraventricular tachycardias).
- Neither exercise nor intravenous atropine elevates the heart rate significantly.
How is sick sinus syndrome treated?
With no or only minimal signs, treatment is not necessary. Treatment should be considered where there are marked electrocardiographic changes and/or significant clinical signs such as frequent fainting. Certain drug therapies may cause temporary improvement; however the treatment of choice is to implant a permanent artificial pacemaker. The prognosis with a pacemaker is very good.
Even though the mode of inheritance is not known, it is preferable not to breed affected individuals and their parents and siblings.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: October 30, 2001.