Coarctation of the aorta

A 5-day-old boy comes to the emergency department because of altered mental status. His mother called an ambulance after finding him grey and unarousable in his crib. He was born via Cesarean section due to preterm premature rupture of the membranes. Since birth, the infant has gained little weight and has been generally fussy. His temperature is 37ºC (98.6ºF), pulse is 180/min, respirations are 80/min, blood pressure is 50/30 mmHg, and oxygen saturation is 80% on room air. Physical examination shows a mottled, cyanotic infant who is unresponsive to stimulation. Cardiopulmonary examination shows prominent heart sounds, wet rales to the inferior lungs bilaterally, strong brachial pulses but absent femoral pulses. Endotracheal intubation is performed immediately and successfully. Which of the following is the most appropriate next step in management?