# Cyanotic Congenital Heart Disease and Transposition of the Great Arteries > Cyanotic congenital heart disease and transposition for NEET-PG Medicine, covering X-ray silhouettes, ductal dependence and prostaglandin E1 use. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/cyanotic-congenital-heart-disease-and-transposition - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Nelson Textbook of Pediatrics; Hurst's The Heart; Braunwald's Heart Disease - How to cite: "Cyanotic Congenital Heart Disease and Transposition of the Great Arteries", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/cyanotic-congenital-heart-disease-and-transposition ## Direct answer Transposition of the great arteries is a common cause of neonatal cyanosis in which the aorta arises from the right ventricle and the pulmonary artery from the left, creating parallel circulations that need mixing. Its chest X-ray shows an egg-on-string silhouette, unlike the boot-shaped heart of tetralogy of Fallot. Ductal-dependent lesions are kept open with prostaglandin E1, and transposition is corrected by an arterial switch operation in the neonatal period. ## What you must remember - **The five Ts:** tetralogy of Fallot, transposition of the great arteries, truncus arteriosus, tricuspid atresia and total anomalous pulmonary venous connection, the classic cyanotic lesions. - **Egg on string:** a narrow vascular pedicle with an egg-shaped heart, typical of transposition, often with increased pulmonary vascularity. - **Boot-shaped heart:** an upturned apex from right ventricular hypertrophy with a concave pulmonary artery segment, typical of tetralogy of Fallot with decreased pulmonary vascularity. - **Snowman sign:** a dilated vertical vein and superior vena cava forming a snowman silhouette in supracardiac total anomalous pulmonary venous connection. - **Parallel circulations:** survival in transposition depends on mixing through a patent ductus arteriosus, atrial septal defect or ventricular septal defect. - **Prostaglandin E1:** keeps the ductus open in ductal-dependent lesions, and its common adverse effect is apnoea, so it is given with airway support available. - **Hyperoxia test:** little rise in PaO2 on 100 per cent oxygen points to a fixed cardiac shunt, whereas a large rise suggests lung disease. - **Arterial switch:** the definitive repair for transposition in the neonatal period, re-connecting the great arteries and transferring the coronary arteries. ## A stepwise approach to a cyanosed neonate A three-day-old term neonate is cyanosed with a normal-looking chest, no obvious murmur, and little response to oxygen. The sequence below narrows the diagnosis and protects the circulation while the cause is confirmed. 1. **Test the oxygen response:** Give 100 per cent oxygen and measure PaO2, because little rise suggests a cardiac cause, while a large rise points to lung disease. 2. **Read the chest film:** An egg on a string suggests transposition, a boot-shaped heart suggests tetralogy of Fallot, and a snowman silhouette suggests supracardiac anomalous venous drainage. Pulmonary vascularity is then judged, since it separates the lesions further. 3. **Judge pulmonary blood flow:** Increased vascularity favours transposition or truncus, whereas decreased vascularity favours tetralogy with pulmonary stenosis. This flow pattern guides whether the ductus must be kept open. 4. **Start prostaglandin E1 if the lesion is ductal-dependent:** The infusion keeps the ductus open and is started in a monitored setting, since apnoea is the characteristic danger. Ventilatory support must be ready before the first dose is given. 5. **Arrange echo and definitive care:** Echocardiography confirms the anatomy, and transposition with poor mixing needs urgent balloon atrial septostomy. The arterial switch operation is then planned in the neonatal period. ## Where the examiner sets the traps Cyanotic heart questions usually test the X-ray sign or the first drug. - **Trap:** reading egg-on-string as a sign of tetralogy — **Correct:** a narrow mediastinum with an egg-shaped heart belongs to transposition, whereas the boot-shaped heart belongs to tetralogy of Fallot. - **Trap:** giving 100 per cent oxygen to prove a cyanotic lesion is benign — **Correct:** lack of response suggests a cardiac shunt, and the test helps separate cardiac from lung causes. - **Trap:** choosing an atrial switch as the modern repair for transposition — **Correct:** the arterial switch operation is the standard neonatal repair, and atrial switch procedures are now largely historical. ## Frequently asked questions ### What is the egg-on-string sign on a chest X-ray? The egg-on-string sign is the narrow mediastinal silhouette with an egg-shaped heart seen in transposition of the great arteries. It reflects the narrow vascular pedicle and is one of the classic features used to distinguish this lesion from other cyanotic heart disease. ### Which cyanotic lesion gives a boot-shaped heart on chest X-ray? Tetralogy of Fallot gives the boot-shaped heart on chest X-ray, produced by right ventricular hypertrophy with an upturned apex and a concave pulmonary artery segment. The lung fields in tetralogy of Fallot typically show decreased pulmonary vascularity, which contrasts with transposition. ### Why is prostaglandin E1 given to neonates with transposition? Prostaglandin E1 keeps the ductus arteriosus open in ductal-dependent lesions, including transposition with poor mixing, so that blood can still reach the lungs or the body. Its common adverse effect is apnoea, so the infusion must be given in a monitored setting with airway support available. ### What is the definitive surgical treatment for transposition of the great arteries? The definitive surgical treatment for transposition of the great arteries is the arterial switch operation, usually performed in the neonatal period. It reconnects the aorta to the left ventricle and the pulmonary artery to the right ventricle, and it transfers the coronary arteries.