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Aortic valve stenosis (AS) is a valvular heart
disease caused by the incomplete opening of the aortic valve.
The aortic valve controls the direction of blood flow from the left
ventricle to the aorta. When in good working order, the aortic valve
does not impede the flow of blood between these two spaces. Under some
circumstances, the aortic valve becomes narrower than normal, impeding
the flow of blood. This is known as aortic valve stenosis, or aortic
stenosis, often abbreviated as AS.
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.
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.
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 dogs with mild aortic stenosis,there is no
special treatment required. The dog should not be used for breeding
and littermates should be carefully screened. Your veterinarian may
suggest antibiotics in certain circumstances as a precaution against
infection of the abnormal valve tissue.
With moderate to
severe stenosis, the dog's exercise should be restricted.
Beta-blocking drugs may be prescribed by your veterinarian to try to
minimize the effects of left ventricular hypertrophy. Your
veterinarian will recommend other therapy if required to manage
congestive heart failure. Medical management for congestive heart
failure is similar no matter what the cause, and consists of
medications to support the heart muscle and decrease the work load of
the heart, together with dietary recommendations.
surgeries have been attempted to alleviate the obstruction with
limited success. The surgery itself carries a high risk, and there is
little, if any, increase in survival rates compared with dogs whose
condition is managed medically.
Understand your dog's physical restraints. A
dog with aortic stenosis may need to reduce activity to protect from
heart failure. Ask your doctor what a safe level of exercise is for
your dog. Make sure that anyone caring for the dog knows of the
condition and reduced activity requirement.
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