In ductal steal due to a significant PDA, which description best reflects the pathophysiology?

• A. Redistribution of systemic blood flow into the lungs due to retrograde aortic flow
• B. Increased systemic blood flow to all organs
• C. Decreased pulmonary blood flow with preserved systemic flow
• D. No change in regional blood flow

Answer: (A)

A large patent ductus arteriosus creates a left-to-right shunt from the aorta into the pulmonary artery, providing a low-resistance pathway for blood to flow into the lungs. This diastolic runoff lowers aortic diastolic pressure and can even cause retrograde flow in the aorta distal to the ductus, effectively pulling systemic blood toward the pulmonary circulation to feed the lungs. The net effect is a redistribution of systemic blood flow into the lungs, with decreased perfusion to systemic organs. In other words, blood is diverted from the body to the lungs through the PDA, which is the essence of ductal steal.