Subaortic Stenosis

Note: We do not currently have a health liaison for this disorder. If you would like to volunteer, please contact president@samoyedhealthfoundation.org and we will be happy to answer any of your questions. For a description of the position, please click on disorder health information liaison or health information reviewer.

Thank you to Joy Ritter for putting together this article for SCARF.

Summary

The left ventricle (chamber) of the heart pumps oxygenated blood through the aorta, a large blood vessel, to the rest of the body. In aortic stenosis there is a narrowing (stenosis) of the aorta. The most common type in dogs is subaortic stenosis (SAS) where the narrowing is just below the aortic valve (thus the full technical name - subvalvular aortic stenosis). The narrowing can be minor – a few small nodules, or major – a fibrous band constricting the entire aorta. The heart must work harder to pump blood past the constriction. SAS is NOT usually present at birth, but develops as the dog ages.

Diagram of canine heart anatomy

Signs and Symptoms

The clinical signs depend on the degree of stenosis. With a mild stenosis, the dog may not show any ill effects, and may have a normal lifespan. With moderate to severe stenosis, the clinical effects are greater. Because the heart must work harder to pump blood to the body, it may not be able to pump enough, especially during exercise. The dog may seem fine at rest, but fatigue easily during exercise, or even faint due to an inadequate blood/oxygen supply to the brain.

Because of working harder, over time the heart muscle becomes thicker (left ventricular hypertrophy). Eventually the heart is less and less able to compensate for the narrow aorta and the dog may show signs of left-sided (congestive) heart failure. These can include tiring during exercise, difficulty breathing, coughing, and/or poor growth. Changes in the heart can also cause abnormal heart rhythms (arrythmias) and/or sudden death.

Causes

It is inheritable (genetic) in some breeds. The mode of inheritance in Samoyeds is unknown at this time.

Risk Factors

Parent(s) with disease, if inheritable. Otherwise unknown at this time.

Diagnostic Tests

In young dogs (< 6 months), or those with a mild stenosis, there may be no outward signs. The first indication that a dog has a problem may be during a routine physical examination, when a veterinarian hears a heart murmur. There are other defects that can cause heart murmurs and some “innocent” murmurs may disappear by the time the dog is 6 months old. However, if a veterinarian thinks the murmur is significant, or if the murmur persists, he may suggest additional tests. In SAS the murmur is caused by turbulence as the blood passes the aortic valve. By listening very carefully to a dog’s heart, a veterinarian can determine when during the heartbeat the murmur is heard, and from where it can be most easily heard. This helps determine where the defect is in the heart. Other non-invasive tests include x-rays, ultrasound, and electrocardiograms (ECGs). Cardiac catheterization can be done by a specialist to determine just how narrow the aorta is, but it is an invasive procedure with its own risks, and usually requires a general anesthetic.

It has been recommended by cardiologists that reevaluation of breeding animals be performed at a minimum of 1, 2, 4, and 6 years of age due to the late onset of some of the murmurs associated with the SAS.

Treatment Guidelines

Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.

Prognosis and long term management depend on the severity of the stenosis and how much change has occurred in the heart. With mild SAS, routine treatment may not be required. Antibiotics may be given at times to treat/prevent infections since even mild infections can be serious in a dog with a heart defect.

With moderate or severe stenosis, dogs may be given a type of drug called a “beta-blocker” to minimize the effects of left-ventricular hypertrophy. Additional drug therapy and dietary restrictions may be needed if the dog shows signs of left-sided heart failure.

Attempts to correct stenosis through surgery have met with limited success.

Management

These tips are from an owner’s perspective:

Basically, special care should be given to preventing infections; even a mild skin infection can be very serious with any dog with a heart defect. Anesthesia should be avoided unless absolutely necessary. Dogs with moderate to severe SAS WILL die suddenly usually between 2-6 years of age. Dogs with mild SAS may live to their full lifespan.

It has been found to be genetic in other breeds; therefore, it would seem to be of genetic origin in Samoyeds. If genetic, a dog with mild SAS could produce ANY degree of SAS in their offspring, which would indicate that the affected animal is not a candidate to remain in the breeding pool.

This heart defect is relatively painless and the affected dogs seem to limit themselves through fatigue or by being on medication.

References

Aortic Stenosis – Canine Inherited Disorders Database

http://cidd.discoveryspace.ca/disorder/aortic-stenosis-0.html 3 bones

Bussardori, C. 1998. Breed related echocardiographic prognostic indicators in pulmonic and subaortic stenosis. ACVIM-Proceedings of the 16th Annual Veterinary Medical Forum: 140-142. 2bones

Bonagura, J.D. and Darke, P.G.G. 1995. Congenital heart disease. In S.J. Ettinger and E.C. Feldman (eds.)Textbook of Veterinary Internal Medicine, p. 892-943. W.B. Saunders, Toronto. four bonesrating

Patterson, D.F. 1996. The genetics of canine congenital heart disease. ACVIM-Proceedings of the 14th Annual Veterinary Medical Forum: 225-226. 2 bones Includes information for breeders and veterinarians on screening and genetic counseling for congenital heart defects