Pulmonic valve stenosis
The pulmonic valve lies between the right ventricle and the pulmonary artery. Similar to the aortic valve, the pulmonic valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonic valve. The closure of the pulmonic valve contributes the P2 component of the second heart sound (S2). The
right heart is a low pressure system, so the P2 component of the second heart sound is usually softer than the A2 component of the second heart sound.
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.
Pulmonic stenosis is a relative narrowing of the valve from the right ventricle to the lungs. Initially, this congenital abnormality is usually silent - your doctor will not be able to hear anything abnormal even on careful examination. Eventually, a short ejection (crescendo-decrescendo) murmur will be heard in the area of the pulmonic valve, classically with a "click" which signifies the walls of the pulmonic valve snapping outward with each pumping stroke. Pulmonic stenosis is rarely cause for concern except for endocarditis prophylaxis. Pulmonic stenosis appears to be a polygenic threshold trait. Polygenic traits are controlled by an unknown number of genes. The gene expression is influenced by a variety of factors including gender, nutrition, breed, rate of growth, and amount of exercise. These traits are quantitative traits - that is, there is a wide range within the population. Such traits include height, weight, character, working abilities, and some genetic defects. Heritability varies within different breeds and within different populations of a particular breed. Because it is virtually impossible to determine the exact genotype for such traits, it is difficult to control defects with a polygenic mode of inheritance. The best attempts at control are based on a grading scheme for identification of the defect and a breed policy of recording and publishing the results for as many dogs as possible.
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.
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.