Which feature of Tetralogy of Fallot contributes to decreased pulmonary blood flow due to obstruction of the right ventricular outflow tract?

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The key idea is that pulmonary blood flow in Tetralogy of Fallot is limited primarily by the narrowing of the right ventricular outflow tract. This obstruction (infundibular stenosis) blocks the path from the right ventricle to the pulmonary artery, so less blood reaches the lungs for oxygenation. As a result, blood tends to shunt from right to left across the VSD, mixing deoxygenated blood into systemic circulation and causing cyanosis. Right ventricular hypertrophy develops as a consequence of the chronic pressure load from this obstruction, not as the direct cause of reduced lung blood flow. The VSD and overriding aorta are important features of the syndrome and contribute to its hemodynamics, but the specific factor that directly decreases pulmonary flow is the outflow tract obstruction.