The nurse is conducting an admission assessment of an 11-month-old infant with heart failure who is scheduled for repair of restenosis of coarctation of the aorta that was repaired 4 days after birth. Findings include blood pressure higher in the arms than the lower extremities, pounding brachial pulses, and slightly palpable femoral pulses. Which pathophysiologic mechanism supports these findings?

Choice A reason: Obstruction at the aortic semilunar valve (aortic stenosis) would cause left ventricular outflow obstruction, leading to decreased systemic circulation overall. However, this condition does not explain the discrepancy between upper and lower extremity blood pressures or the diminished femoral pulses. Choice B reason: Pulmonic valve obstruction would impair blood flow into the pulmonary circulation, leading to cyanosis and right-sided heart strain. This does not explain the clinical findings of stronger pulses and higher blood pressure in the arms compared to the legs. Choice C reason: An atrial septal defect (ASD) produces a left-to-right shunt, which can cause a murmur and increased pulmonary blood flow. However, it does not cause differential blood pressures between upper and lower extremities or diminished femoral pulses. Choice D reason: Coarctation of the aorta involves narrowing of the aortic lumen, typically distal to the subclavian artery. This narrowing reduces blood flow to the lower extremities, resulting in weaker femoral pulses and lower blood pressure in the legs compared to the arms. The pounding brachial pulses and hypertension in the upper extremities are classic findings of coarctation, making this the correct pathophysiologic mechanism.