Duct-dependent congenital heart disease: Case

This baby has hypoplastic left heart syndrome, the most severe of the duct-dependent systemic lesions. The left side of the heart is underdeveloped, and the right ventricle must pump blood both to the lungs through the pulmonary artery and to the body through the ductus arteriosus into the aorta. When the duct closes at day two to five the baby loses systemic blood flow and collapses in shock, which is exactly the presentation here. The history of a well baby at discharge, the collapse on day 3, the weak femoral pulses, the severe metabolic acidosis, and the cardiomegaly on chest X-ray together make the diagnosis before the echocardiogram confirms it. ^[1]

Clinical findings

The key findings in this case are the day-3 collapse in a previously well neonate, the signs of severe cardiogenic shock, and the echocardiographic confirmation of hypoplastic left heart syndrome. The baby was well on day 1 because the ductus arteriosus was still open and the right ventricle was perfusing the entire body through it. The progressive deterioration over 12 hours reflects the gradual anatomical closure of the duct as it loses its lumen and systemic blood flow falls. ^[1]

The physical signs are the signature of a left-sided duct-dependent lesion in collapse. The pallor and mottling with prolonged capillary refill reflect poor peripheral perfusion. The tachycardia and tachypnoea with grunting are the compensatory responses to shock and metabolic acidosis. The weak femoral pulses occur because the duct was the source of lower-body blood flow and it has closed. The hyperdynamic precordium reflects the single working ventricle doing the work of both. The severe metabolic acidosis with a base excess of minus 15 and a lactate of 9 is direct evidence of tissue hypoperfusion from loss of systemic cardiac output. ^[1]

The echocardiogram confirms the anatomy: a small or absent left ventricle, a hypoplastic aortic and mitral valve, and a diminutive ascending aorta. The ductus arteriosus is restrictive, which explains the collapse. The right ventricle is the dominant pumping chamber, and blood flows from the pulmonary artery through the duct into the descending aorta in a retrograde fashion to supply the head and neck vessels and the lower body. ^[3]