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Summary
Aortic stenosis is an inherited cardiovascular condition seen in a variety of large breed dogs. Affected dogs are born with a heart or aorta too narrow at the site via which the newly oxygenated blood exits as it's being pumped to the whole body (from the left ventricle into the aorta). Consequently, the heart has to work harder to pump past this area so that the entire body can receive all the oxygen-rich blood it requires to perform its normal functions (just as you would if your tube of toothpaste had a smaller opening than normal).
As the largest artery in the body, the aorta is the primary conduit for all this "fresh" blood. In some cases, the aorta is malformed so that it's narrower as it joins the heart at the left ventricle. More commonly, however, it's the ventricle itself that's faulty. This condition, a subset of aortic stenosis, is more appropriately termed "sub-aortic stenosis" or "sub-valvular aortic stenosis." In very rare instances, the actual valve located between the left ventricle and the aorta may be the site of this partial outflow obstruction.
Symptoms and Identification
The symptoms of aortic stenosis vary depending on the severity of the narrowing. Some dogs inherit only a mild, barely undetectable narrowing while others may suffer serious impediments to the outflow of blood from the heart.
The signs, therefore, are often consistent with an inability to feed the body the right amount of blood: fainting (when the brain doesn't get enough oxygen), poor growth and exercise intolerance or sluggishness.
Yet some dogs never display these more obvious symptoms. Instead, they suffer the secondary effects of a chronically overworked heart as it struggles to push blood through a smaller opening than is natural. Because an overtaxed heart (not unlike any hard-working muscle) responds by growing bigger over time, dogs born with this disease tend to develop symptoms like coughing (when the heart takes up too much room in the chest), difficulty breathing and dangerous heart rhythm abnormalities (when the heart's growth interferes with normal electrical activity). Sadly, sudden death is another possible outcome for these patients.
Identification of this disease is generally accomplished during a simple physical exam. Because the heart defect is accompanied by a characteristic heart murmur, veterinarians will generally identify the possibility of aortic stenosis during wellness visits within the first year of life.
Once the murmur is detected, most veterinarians will recommend a complete cardiac examination, including chest X-rays, an electrocardiogram (EKG), and most importantly, an ultrasound of the heart (echocardiogram). Definitive diagnosis of aortic stenosis always requires an echocardiogram to evaluate the narrowed structures that define the disease.
Affected Breeds
Though the mode of inheritance has been said to be autosomal dominant, it's possible this varies from one breed to the next. It's also been postulated that more than one gene is involved in its inheritance, hence the wide variability in severity from one individual to the next and the difficulty in determining the true mode of genetic transmission.
Newfoundland dogs have been found to carry the highest risk for this inherited disorder.
The Golden Retriever, Rottweiler, and Boxer have also been found to be at higher risk, relative to other breeds.
Though less so, it's also been associated with an increased risk for German Shepherds, German Shorthaired Pointers, Great Danes, Samoyeds and Bulldogs.
Treatment
Treatment of aortic stenosis isn't exactly where veterinary medicine shines. Indeed, we have made few strides in our ability to devise surgical modes of altering the configuration of this delicate area. Though techniques described in human patients have been attempted, these dangerous surgeries are not yet considered to be worth their extreme risk.
Instead, we veterinarians concentrate our efforts on medical solutions to the dilemma, largely by way of reducing the impact of the heart's inevitable work overload. That's why exercise restriction is a mainstay of treatment, along with beta blockers to reduce the blood pressure as the blood exits the heart.
Veterinary Cost
The cost of treatment is not high, given the low cost of beta blocking drugs. Diagnosis and necessary, follow-up evaluation of the heart throughout these patients' lives can add up, though. When each echocardiogram can cost as much as $500-$600, it's clear that treating these patients properly can get very pricey.
Prevention
Only through careful breeding programs will we achieve a lower incidence of this disease. Ideally, all dogs from affected breeds should be screened for this test with an echocardiogram before breeding. Though expensive, this becomes especially crucial if the trait has been identified in a future breeding dog's line. Additionally, all siblings and parents of affected animals should be spayed and neutered.
References
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.