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.
The obstruction 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.
S/he 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.
FOR VETERINARIAN:
MURMUR: systolic, left hemithorax, radiates into thoracic inlet
and up the neck, PMI left heart base (3rd to 4th intercostal space),
may be equally loud at right heart base.
ECG: may be normal, over time shows left ventricular
enlargement, left axis shift, may show ST depression, may show
ventricular arrhythmias
RADIOGRAPHS: may see left ventricular enlargement, cranial
aortic enlargement, left axis shift. Pulmonary vasculature is normal.
ECHOCARDIOGRAPHY: left ventricular hypertrophy, subvalvular
fibrous ring, post-stenotic dilation of aorta
The arterial pulse may be of reduced intensity and slow to rise.
Echocardiography (with Doppler) or cardiac catheterization is usually
required to determine the severity of the defect.
How is aortic stenosis treated?
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.
Various 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.
Breeding advice
Affected individuals should not be used for breeding, and littermates
should be carefully screened.
FOR MORE
INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Resources
Bussardori, C. 1998. Breed related echocardiographic prognostic
indicators in pulmonic and subaortic stenosis. ACVIM-Proceedings of the
16th Annual Veterinary Medical Forum: 140-142.
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.
Patterson, D.F. 1996. The genetics of canine congenital heart
disease. ACVIM-Proceedings of the 14th Annual Veterinary Medical
Forum: 225-226. This reference has good information for
breeders
and veterinarians regarding screening and genetic counselling for
congenital heart defects.
Copyright © 1998 Canine Inherited
Disorders Database. All rights reserved.Revised: August 18, 2003.
This database is funded jointly by the Animal Welfare Unit at the
Atlantic Veterinary College, University of Prince Edward Island, and
the
Canadian Veterinary Medical Association.
reprinted
with kind permission from:- Alice
Crook, DVM,Coordinator, Sir James Dunn Animal Welfare Centre,
Atlantic Veterinary College,University of Prince Edward Island,
550 University Ave.Charlottetown, PEI C1A 4P3
http://www.upei.ca/cidd
********************
The above information is simply
informational. It's intent is not to replace the advice of a
veterinarian nor to assist you in making a diagnosis of your pet.
Please consult with your own veterinarian for confirmation of any
diagnosis. Your pets life may depend on it.
