This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other hea diseases in children, Subject name: Pediatrics
A five-day-old, full term male infant was severely cyanotic at bih. His chest X ray showed 'Egg-on -side' appearance. Prostaglandin E1 was administered initially and later balloon atrial septosomy was done which showed improvement in oxygenation. The most likely diagnosis of this infant is: 
Select and explain. 
A. Tetralogy Fallot, B. Transposition of great vessels, C. Truncus aeriosus, D. Tricuspid atresia
B: Transposition of great vessels
Answer: B: Transposition of great vessels 
Explanation: - Given features suggests towards diagnosis of TGA Transposition of the great vessels with an intact ventricular septum presents with early cyanosis, normal-sized hea, normal or slightly increased pulmonary vascular markings, and an ECG showing right-axis detion and right ventricular hyperophy - Balloon atrial septostomy: Helpful in a baby with TGA with intact ventricular septum for initial stabilization, It creates a communication between the left and right atria - helps in mixing blood of systemic and pulmonary circulations & maintain relatively better oxygenation. -TREATMENT OF TGA: PGE1 analogue - Keep ductus aeriosus open Balloon atrial septostomy / Rashkind procedure - Emergency procedure Aerial switch operation / Jatene's repair - Definitive surgery