The shunt pathway in persistent pulmonary hypertension of the newborn is described as:

• A. Right-to-left
• B. Left-to-right
• C. Bidirectional
• D. No shunt

Answer: (A)

In PPHN, the pulmonary vascular resistance remains high after birth, so pressures on the right side of the heart stay higher than on the left. This drives blood to mix and bypass the lungs through fetal channels, especially the foramen ovale and the ductus arteriosus. Deoxygenated blood from the right heart crosses into the left heart and then into the systemic circulation, causing cyanosis and systemic hypoxemia. While shunting can be bidirectional at times, the classic and most characteristic pattern in persistent pulmonary hypertension of the newborn is right-to-left shunting.