Dr. Engle: When pulmonic stenosis occurs as an isolated congenital malformation of the heart, it usually is due to fusion of the valve cusps into a dome with a small hole in the center. In Figure 1 the pulmonary artery has been laid open so that one can see the three leaflets of the pulmonary valve are completely fused, and that there is only a small, central, pinpoint opening which permits blood to leave the right ventricle and enter the pulmonary circulation.
Valvular pulmonic stenosis is much more common than subvalvular or infundibular stenosis, where the obstruction to pulmonary blood flow lies within the substance of the right ventricle. There it may be due to a diaphragm of tissue which obstructs the outflow of the right ventricle, or to an elongated narrow tunnel lined with thickened endocardium, or to a ridge of fibrous or muscular tissue just beneath the pulmonary valve.
The changes in the cardiovascular system which result from obstructed pulmonary blood flow are so characteristic that they permit the ready recognition of this condition. Proximal to the constriction, these changes manifest the burden placed on the right ventricle, which enlarges and hypertrophies. On physical examination this is demonstrated by the precordial bulge and tapping impulse just to the left of the sternum, where the rib cage overlies the anterior (right) ventricle. Radiographically, both by fluoroscopy and in roentgenograms in the frontal and both oblique views, right ventricular enlargement is seen. In the electrocardiogram, the precordial leads show a pattern of right ventricular hypertrophy.
Functional infundibular stenosis.
