Transposition of the great arteries
The normal ‘figure of eight’ systemic/pulmonary blood flow circuit is replaced by two separate parallel circuits, i.e. systemic venous blood pass-ing through the right side of heart returns directly to the systemic circu-lation via a connecting aorta. Pulmonary venous blood returning to the left side of the heart is retuned directly to the pulmonary circulation via a connecting pulmonary artery. This condition is not compatible with life unless there is adequate mixing of the blood from both circulations via an ASD or PDA.
Infants usually present in the first few hours or days with worsening duct-dependent cyanosis. Hypoxia is usually severe, but heart failure is not a feature. This is a medical emergency and early diagnosis and intervention are required to avoid severe hypoxia.
Once diagnosed care is needed to maintain body temperature as hypo-thermia will worsen the metabolic acidosis of hypoxaemia. Prompt cor-rection of acidosis and hypoglycaemia is essential. Before cardiac surgery, systemic arterial oxygenation can be improved with prostaglandin E infu-sion and balloon atrial septostomy. Definitive arterial switch procedure is performed in the first 2wks of life.