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What is pulmonic stenosis?
As part of normal circulation in the body, the right side
of the heart (the right ventricle) pumps blood to the lungs to receive oxygen.
The oxygenated blood goes back to the left side of the heart from which it is
pumped out to the rest of the body.
Blood flows from the right ventricle of the heart through
the pulmonic valve into the pulmonary artery and thence to the lungs. With
pulmonic stenosis, there is partial obstruction of normal blood flow, most
commonly due to a malformation of the pulmonic valve ("pulmonic valve
dysplasia") but the abnormality may be immediately above or below the valve
as well.
The effect of this partial obstruction is to force the
heart to work harder to pump blood to the lungs. The extent to which a dog will
be affected depends on the degree of narrowing (stenosis) of the valve area.
With severe stenosis the dog will likely develop congestive heart failure due to
the increased workload of the heart.
How is pulmonic
stenosis inherited?
Pulmonic stenosis appears to be a polygenic threshold
trait.
What breeds are affected by
pulmonic stenosis?
Pulmonic stenosis is one of the most common congenital
heart defects in all species. There is a breed predisposition in the following
breeds of dog:
The English bulldog and the mastiff are at most risk for
pulmonic stenosis. In English bulldogs, pulmonic stenosis occurs commonly
with an abnormal left main coronary artery branch, arising from a single right
coronary artery. In this breed the condition is more common in males.
There is also an increased risk of pulmonic stenosis in
the beagle, wire-haired fox terrier, chihuahua, miniature Schnauzer, samoyed,
Boykin spaniel, West Highland white terrier, cocker spaniel, Airedale terrier,
and Scottish terrier.
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 pulmonic
stenosis mean to your dog & you?
In its milder forms, the slight thickening of the
pulmonary valve will cause minimal or no obstruction and your dog will not be
affected. However with more severe thickening of the valve, the obstruction to
blood flow from the right side of the heart will cause varying degrees of heart
damage which worsens with age. With moderate-to-severe pulmonic stenosis, your
dog may experience signs associated with low cardiac output and/or right-sided
heart failure, such as respiratory difficulties, fainting, tiring with exercise,
abnormal cardiac rhythms, abdominal swelling due to an enlarged liver or the
accumulation of fluid because of failing circulation, or sudden death.
Based on your dog's physical examination and diagnostic
tests such as chest x-rays and an electrocardiogram, your veterinarian will
discuss with you the severity of the pulmonic stenosis. If there are significant
changes evident, he or she will suggest further tests to determine the pressure
gradient across the pulmonic valve. (Normally there is no pressure difference
between the right ventricle of the heart, and the pulmonary artery to the
lungs.) Where there is a pronounced pressure gradient, surgery to correct the
stenosis should be considered.
How is pulmonic
stenosis diagnosed?
The first indication that your dog has a problem may be
when your veterinarian hears a heart murmur on an early physical examination.
Alternately, you may see signs in your dog related to heart disease, such as
fainting or fatigue with exercise. Your veterinarian will listen carefully to
try to determine the location of the murmur and to differentiate it from an
"innocent" murmur which disappears by about 6 months of age. If the
murmur is significant, your veterinarian will suggest further tests such as a
chest x-ray, electrocardiogram, and cardiac ultrasound to help determine the
cause, and to see what changes if any have already occurred in the heart as a
result of the defect. Once pulmonic stenosis has been diagnosed, Doppler
echocardiography or cardiac catheterization can be done to measure the pressure
gradient between the right ventricle and the pulmonary artery, to determine the
severity of the obstruction. Based on these test results your veterinarian will
discuss with you the long term prognosis for your dog and whether surgical
correction of the defect should be considered.
FOR THE VETERINARIAN:
- MURMUR: systolic ejection murmur, loudest in pulmonic
area near left cranial sternal border, often equally loud along right
cranial sternal border.
- ELECTROCARDIOGRAM: RV hypertrophy and right axis shift,
right atrial enlargement, possibly arrhythmia associated with hypertrophy.
- RADIOGRAPHS: right ventricular hypertrophy ,
poststenotic dilation of pulmonary artery with distal pulmonary vessels
reduced in size.
- ECHOCARDIOGRAPHY: primary means of diagnosis of
pulmonic stenosis, typically see mild to moderate right atrial dilation,
concentric RV hypertrophy, deformity and narrowing in the pulmonic valve
region, and poststenotic dilation of the pulmonary artery.
- jugular pulses may be evident.
In English bulldogs, pulmonic stenosis is commonly
associated with a left coronary artery anomaly which has important
implications for surgical correction.
How is pulmonic
stenosis treated?
With mild-to-moderate stenosis, your veterinarian will
monitor your dog. No other treatment is necessary unless clinical signs develop
which are associated with heart disease. Surgery is an option in dogs with
moderate-to-severe pulmonic stenosis, with different techniques recommended
depending on the site of the stenosis. Because of the expertise and technical
equipment required and the surgical risk involved, surgery to correct pulmonic
stenosis is generally performed in a referral centre.
Surgery is more risky if atrial fibrillation or congestive
heart failure have developed. These conditions should be treated medically and
the dog stabilized before surgery is considered.
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.
Breeding advice
Affected individuals and their parents should not be used
for breeding. Siblings should only be used after careful screening. If any
affected offspring are born, breeding of the parents should be discontinued.
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.
Thomas, W.P. 1995. Therapy of congenital pulmonic
stenosis. In J.D. Bonagura and R.W. Kirk (eds.) Kirk's Current
Veterinary Therapy XII Small Animal Practice, p. 817-821. W.B. Saunders,
Toronto.
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