# Hypoplastic Left Heart Syndrome > Hypoplastic left heart syndrome for NEET-PG Paediatrics, covering ductal-dependent systemic flow, neonatal shock, prostaglandin E1 and the Norwood pathway. - Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/hypoplastic-left-heart-syndrome - Exam / course: NEET-PG · Subject: Paediatrics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-15 - Last updated: 2026-10-15 - Reference basis: Nelson Textbook of Pediatrics; Moss and Adams Heart Disease in Infants, Children and Adolescents - How to cite: "Hypoplastic Left Heart Syndrome", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/hypoplastic-left-heart-syndrome ## Direct answer Hypoplastic left heart syndrome is a congenital malformation in which the left ventricle, mitral valve, aortic valve and ascending aorta are severely underdeveloped. Systemic blood flow therefore depends on the patent ductus arteriosus, and the baby usually looks well at birth. Ductal closure in the first days causes shock, and the standard bridge is a prostaglandin E1 infusion followed by surgery. ## What you must remember - **Anatomy:** a small left ventricle with atresia or stenosis of the mitral and aortic valves, and a hypoplastic ascending aorta. - **Circulation:** systemic output depends on right-to-left flow through the ductus arteriosus, with mixing through a patent foramen ovale or atrial septal defect. - **Presentation:** day 2 to 3 of life, with pallor, poor perfusion, weak pulses, metabolic acidosis and shock as the duct closes. - **Heart sounds:** a single loud second sound; the murmur may be absent, so a normal examination does not exclude the diagnosis. - **Initial drug:** alprostadil, a prostaglandin E1 infusion, keeps the duct open; its main serious adverse effect is apnoea. - **Oxygen caution:** excess inspired oxygen raises pulmonary blood flow at the expense of systemic flow, so moderate saturations are deliberately accepted. - **Stage 1 surgery:** the Norwood procedure rebuilds the aorta from the pulmonary trunk and provides a systemic-to-pulmonary shunt, usually in the first weeks of life. - **Prenatal clue:** fetal echocardiography allows delivery planning at a centre with neonatal cardiac surgery. ## A stepwise approach to the shocked neonate A term neonate on day 3 is pale and mottled, with weak femoral pulses and tachypnoea. The sequence below moves from recognition to definitive surgery without losing the ductus. 1. **Recognise the ductal emergency.** Think of HLHS in any neonate with shock and a single loud second sound, even when the chest X-ray looks unremarkable. 2. **Start prostaglandin E1.** The infusion keeps the ductus open, and the team must be ready to ventilate for apnoea. 3. **Confirm with echocardiography.** Define the mitral and aortic valves, the left ventricle and the atrial communication. 4. **Avoid excess oxygen.** Commonly used targets are moderate saturations, because high oxygen shifts flow to the lungs. 5. **Correct acidosis and perfusion.** Treat metabolic acidosis, support perfusion with fluids and inotropes, and prevent hypothermia. 6. **Refer for Norwood surgery.** Early transfer to a centre experienced in single-ventricle care is the priority. Each step protects the same thread, which is systemic flow through the ductus. Delay at any point usually shows up as falling perfusion and rising lactate before it shows up as a murmur. ## Where the exam tries to catch you Most HLHS questions test whether you understand that the circulation is duct dependent. - **Trap:** giving high-flow oxygen to a cyanosed neonate and expecting a large rise in saturation. **Correct:** the lesion depends on ductal and atrial mixing, so a modest rise is expected and high oxygen can reduce systemic flow. - **Trap:** stopping prostaglandin once the baby looks stable. **Correct:** the ductus must stay open until surgery, or systemic flow collapses. - **Trap:** calling it coarctation whenever femoral pulses are weak. **Correct:** both are duct dependent, but echocardiography separates them by the size of the left ventricle and the mitral and aortic valves. - **Trap:** expecting a loud murmur before suspecting HLHS. **Correct:** the murmur may be absent, so shock with a single second sound is the clue. ## Frequently asked questions ### Which prostaglandin keeps the ductus open in hypoplastic left heart syndrome? Alprostadil, a prostaglandin E1 analogue, is infused to keep the ductus arteriosus patent in hypoplastic left heart syndrome until surgery. Its most important serious adverse effect is apnoea, so ventilatory support must be immediately available. ### What is the Norwood procedure? The Norwood procedure is the first-stage palliative operation for hypoplastic left heart syndrome. It reconstructs the aorta using the pulmonary trunk, provides a shunt to supply the lungs, and performs an atrial septectomy to allow free mixing. ### Why should high-flow oxygen be avoided in hypoplastic left heart syndrome? High-flow oxygen lowers pulmonary vascular resistance and increases pulmonary blood flow in hypoplastic left heart syndrome. Because the single ventricle supplies both circulations, that diversion reduces systemic flow and worsens perfusion. ### How does hypoplastic left heart syndrome differ from coarctation of the aorta in a shocked neonate? In coarctation of the aorta the left ventricle and mitral and aortic valves are of normal size, while the aortic arch narrows. Hypoplastic left heart syndrome has an underdeveloped left-sided heart, and echocardiography distinguishes the two.