Pulmonary Stenosis

Congenital stenosis of the outflow segment of the right ventricle may be a sole malformation or part of a complex combination of defects. The simplest variety of pulmonary stenosis is fusion of the three leaflets of the pulmonary valve into a single membranelike structure with an opening in the center. As in other forms of valvular stenosis, the size of the opening directly determines its effect on circulatory dynamics. Pulmonary stenosis, if significant, places a pressure overload on the right ventricle analogous to the effect of aortic stenosis on the left ventricle (see chap. 9). The resistance to outflow from the right ventricle elevates the pressure inside that chamber, causing a pressure gradient between the ventricle and the pulmonary artery, where the pressure remains normal. In health identical pressures in the right ventricle and the pulmonary artery in systole average 15 mm Hg. In mild pulmonary stenosis right ventricular systolic pressure may rise to about 40 mm Hg; in moderate, to 70 mm Hg; and in severe, to 150 mm Hg. The right ventricle is quite able to adapt to the high pressure, particularly in infancy. However, in severe pulmonary stenosis the overloaded right ventricle may eventually produce right ventricular failure. In rate cases severe pulmonary stenosis may lead to serious emergencies in infancy requiring immediate surgical intervention.

Mild cases of pulmonary stenosis require no treatment other than preventive measures against endocarditis. Severe pulmonary stenosis requires surgical relief. Pulmonary valvotomy by means of open-heart surgery was the standard treatment until the late 1980s. Balloon dilatation of the pulmonary valve has now been applied successfully and is becoming the treatment of choice. The use of prosthetic valves in pulmonary stenosis is rarely necessary.