Aortic Stenosis
In aortic stenosis, there is a partial obstruction to the flow of blood as it leaves the left side of the heart (the left ventricle) through the main blood vessel (the aorta) that carries blood to the rest of the body.
In aortic stenosis, partial obstruction to the flow of blood ranges from small nodules to a fibrous band, most commonly just below the aortic valve ("subvalvular aortic stenosis"). Due to the obstruction, the heart must work harder to pump out an adequate blood volume. Clinical signs and long-term outcome depend on the degree of narrowing, or stenosis.
How Is Aortic Stenosis Inherited?
In Newfoundlands, this defect has been shown to have an autosomal dominant mode of inheritance, with variable expression.
In the mildest form, the condition is undetectable and will
not cause any problems for the dog. However the defect may still be passed on to offspring. The challenge for breeders and veterinarians is to identify affected dogs with very mild or no clinical signs of the disorder.
What Breeds Are Affected by Aortic Stenosis?
Congenital aortic stenosis is probably the most common heart
defect seen in large breed dogs. Newfoundland dogs have the highest risk for this disorder. It is also important in the golden retriever, Rottweiler, and boxer.
There is a mildly increased risk of aortic stenosis in the
German Shepherd, German short-haired pointer, Great Dane, Samoyed and Bulldog.
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 aortic stenosis mean to your dog and
you?
Dogs with mild stenosis will generally show no clinical
effects and have a normal life expectancy. With moderate to severe stenosis,
signs will be variable. Because of the narrowing in the aorta as the blood
leaves the left ventricle, your dog's heart must work harder to pump an adequate
volume of blood to the rest of the body. Depending on the degree of obstruction,
your dog's heart may be able to compensate at rest but not keep up with the
body's demands during exercise. Thus you may see reduced exercise tolerance -
your dog just seems to run out of steam - or fainting due to inadequate blood
supply to the brain.
In response to the obstruction to blood flow, the heart
muscle becomes thicker over time (left ventricular hypertrophy). As the
condition progresses, your dog's heart becomes less able to compensate and you
and your veterinarian may see signs associated with left-sided heart failure
such as tiring on exercise, difficulty in breathing, coughing, and/or poor
growth. Changes in the heart muscle can also lead to abnormal heart rhythms
(cardiac arrythmias) and sudden death.
Your veterinarian can do various tests (see below) to
determine the severity of the defect. Based on the results, he or she will
discuss with you the long-term prognosis, and ways to manage this condition in
your dog.
How is aortic stenosis diagnosed?
In young animals (less than 6 months of age) there may be no
clinical signs. Thus the first indication that your dog may have a problem may
come when your veterinarian hears a heart murmur during physical examination.
Some low-grade murmurs are "innocent" and disappear by 6 months of age, but if
the murmur is significant, your veterinarian will suggest a diagnostic workup to
determine the cause. He or she will listen very carefully to your dog's heart to
determine the point of maximal intensity of the murmur and when the murmur
occurs during the cardiac cycle. Other diagnostic aids include chest x-rays, an
electrocardiogram (ECG) and/or ultrasonography if available. To determine the
extent of the narrowing, the pressure gradient across the aortic valve (between
the left ventricle and the aorta) can be measured using special procedures for
which your veterinarian can refer your dog to a specialist.
In an older animal or when the obstruction is pronounced
there may be clinical signs associated with left-sided heart failure.
Based on the results of these various tests, your
veterinarian will discuss with you the prognosis and long term management of
your pet. He/She will also be able to tell you if any (and how much) change has
occurred in the heart already as a result of the stenosis.
Re-printed with permission from
Canine Inherited Disorders Database, a valuable resource on dog health where you will find find a description of the condition, information about how the disorder is inherited, consequences of the condition for you and your dog, and recommended or required care by both owner and veterinarian.
Please address any comments to Dr. Alice Crook, BSc, DVM at CIDD@upei.ca
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
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