Obstruction to right ventricle outflow increases the afterload on the right ventricle (Table 4.19, Figure 4.08). In order for the ventricle to eject normally it must increase systolic pressure; the resultant increase in wall stress leads to cardiac hypertrophy. If compensated, chamber volume remains normal, since flow is not increased. The stenosis may be subvalvular, valvular, or supravalvular.
Beyond the stenosis pulmonary resistance is normal, so a large pressure gradient is present across the obstruction. No shunt occurs unless there is a defect in the septa, thus no cyanosis. No symptoms occur unless the right ventricle cannot compensate to provide normal flow. Right ventricle enlargement is seen by echocardiography, ECG, and right ventricle heave, which can be felt externally. A loud, harsh systolic ejection murmur is heard; if the valve is compliant an early systolic click occurs. Valve area can be calculated by dividing stroke flow by 0.5 times the mean transvalve pressure gradient.
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