Summary
Pulmonic stenosis is an inherited heart disease in which the pulmonic valve (or, alternatively, the pulmonary artery) is poorly formed, leading to a narrowing of the area through which blood travels as it makes its exit from the heart into the artery that enters the lungs.
In most cases of pulmonic stenosis, the defect is in the three-leafed pulmonic valve itself. "Valve dysplasia," this is called. And it's the result of a congenital malformation of the valve in which the leaflets that comprise it are too thickened or too fused together to allow blood past it properly. Sometimes, a ring of tissue around the valve is too narrow. This less common form of pulmonic stenosis is called annular "hypoplasia."
The least common form of the disease occurs when the pulmonary artery just above the valve is narrower in one spot than it should be. This is called "supravalvular stenosis." An even more rare version of this narrowing can happen in the heart just below the valve. It's called "subvalvular stenosis."
In all cases of this primarily canine condition, the right side of the heart (the one that receives blood from the body and pumps it into the lungs) becomes enlarged as the heart has to pump harder to move the blood through this narrowed area. (A heart that works harder, like any other muscle, gets bigger.)
Because this disease can be inherited with varying degrees of severity, some dogs will remain symptom free for their whole lives while others will die very young as a result of the heart's inability to move blood through the lungs for sufficient oxygenation, when it gets backed up in the rest of the body due to the high pressure that builds up as a result of the smaller opening in or near the pulmonic valve or because of major electrical disturbances in the heart.
Symptoms and Identification
Dogs with pulmonic stenosis are often identified by the significant heart murmur their veterinarian detects on a puppy's first physical examination. If a severe sufferer is not identified early, the first initial signs may be exercise intolerance (sluggishness), collapse (fainting) and ascites (fluid-build-up in the abdomen). Some, however, will never display any symptoms whatsoever, save a murmur.
After these dogs have been flagged as possibly sufferers of the problem, diagnosis is best achieved through simple chest X-rays (which may demonstrate an enlargement in the right side of the heart), electrocardiograms (EKG) and always echocardiography (ultrasound of the heart) with doppler (demonstrating the flow of blood) to elucidate the abnormal change in the dimensions of the heart and the blood flow through the region of the pulmonic valve.
An angiogram, a procedure to visualize the blood flow through the area, is also very helpful in determining the severity of the disease.
Affected Breeds
English Bulldogs and Mastiffs are most often affected. Pulmonic stenosis has also been described in higher incidences in the French Bulldog, Beagle, Wire-haired Fox Terrier, Chihuahua, Miniature Schnauzer, Samoyed, Boykin Spaniel, West Highland White Terrier, Cocker Spaniel, Airedale Terrier, and Scottish Terrier.
Treatment
Treatment for severe cases of pulmonic stenosis is now possible if the lesion occurs within the valve itself as long as other cardiovascular problems are not present.
Balloon valvuloplasty is a minimally-invasive interventional technique in which a catheter is placed through the jugular vein. An angiogram is performed to determine the exact location and severity of the defect. Finally, a balloon is inflated at the site of the valve, thereby widening the area. All but 15-20% of balloon valvuloplasty candidates may go on to live normal lives.
Other techniques (mostly surgical and quite invasive) have been attempted but most dogs don't tend to recover well in these cases.
Drug therapy may be the only approach for dogs when balloon valvuloplasty proves too expensive. Beta blockers and other cardiac drugs may decrease the symptoms, while exercise restriction remains a mainstay of our veterinary recommendations.
Veterinary Cost
Balloon valvuloplasty is a very expensive technique currently undertaken only by board-certified cardiologists in university settings, though that's beginning to change as a greater number of veterinary cardiologists learn the technique and apply it in their private practices across the country. Expect to pay $5,000 to $10,000 for this procedure.
Drug therapy is significantly less expensive and quite doable by most dog owners. Unfortunately, the cost of diagnosis can be insurmountable for some, especially if echocardiography and angiography are applied. Echocardiograms may cost as much as $500-$600 while angiograms may cost $500-$1,000 or more.
Prevention
Preventing pulmonic stenosis is all about careful weeding out of affected dogs from the breeding pool. Preventing reproduction in any affected pet is critical. Since very mild forms of the disease may be undetected through conventional means, screening dogs of highly affected breeds (with echocardiography) prior to breeding is strongly recommended.
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. 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.