Transposition of the Great Arteries

Ventriculoarterial discordance: the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, so the systemic and pulmonary circulations run in parallel. Survival requires a mixing communication (patent foramen ovale, atrial septal defect, ventricular septal defect, ductus arteriosus).

• About 5 to 7% of congenital heart disease, about 0.2 to 0.3 per 1000 live births, male to female about 2 to 3:1. A ventricular septal defect is present in about 25 to 45% and left ventricular outflow obstruction in about 10 to 15%.
• Untreated, about 30% die in the first week, 50% in the first month and 90% within the first year.

• Cyanosis within hours to days (earlier with an intact septum), with tachypnoea but little distress, in a usually term, well grown male infant.
• Single loud second heart sound, often no murmur.
• With a large ventricular septal defect: mild cyanosis and heart failure at 3 to 6 weeks.
• Deterioration at ductal closure: profound hypoxaemia, acidosis, collapse.
• Differential diagnosis: persistent pulmonary hypertension of the newborn, pulmonary atresia, tricuspid atresia, total anomalous pulmonary venous return, truncus arteriosus, neonatal sepsis, congenitally corrected transposition.
• Complications: severe hypoxaemia and acidosis, heart failure, coronary artery abnormalities, pulmonary vascular disease if repair is delayed, and the late problems after repair.

• Hyperoxia test: PaO2 does not rise to more than 150 mmHg on 100% oxygen; PaO2 is often 20 to 40 mmHg.
• Chest X-ray: "egg on a string" cardiac silhouette (narrow mediastinum), increased pulmonary markings. ECG: right axis deviation, right ventricular hypertrophy.
• Echocardiography: parallel great arteries, aorta anterior and rightward, atrial septal communication size, ventricular septal defect, outflow obstruction, ductus, coronary artery origin and course.
• Arterial blood gas and lactate to assess hypoxaemia and acidosis.

• Alprostadil 0.05 to 0.1 micrograms/kg/min IV to keep the ductus open, then 0.01 to 0.05 micrograms/kg/min; prepare for apnoea and ventilation.
• Balloon atrial septostomy (Rashkind procedure), under echocardiographic guidance and usually at the bedside, when SpO2 stays less than 70 to 75% despite alprostadil or the atrial septum is intact or restrictive. Expected saturation after septostomy is about 80 to 90%.
• Correct acidosis, maintain glucose and temperature; use inotropes only when needed.
• Definitive surgery: arterial switch (Jatene) operation with transfer of coronary arteries:
  • Intact septum: ideally in the first 2 to 3 weeks of life, before the left ventricle loses its ability to support the systemic circulation (retraining is needed after about 4 weeks).
  • With ventricular septal defect: by 3 months, usually 4 to 6 weeks, to avoid pulmonary vascular disease.
  • With ventricular septal defect and pulmonary stenosis: Rastelli procedure (ventricular septal defect closed to the aorta, right ventricle to pulmonary artery conduit) at 3 to 5 years, or other repairs.
• Operative mortality for arterial switch is about 2 to 5% in modern units; 20-year survival is about 90%.
• Late complications after arterial switch: supravalvular pulmonary stenosis (about 10 to 25%, intervene if peak gradient is 40 to 50 mmHg or more), neo aortic root dilatation with regurgitation (valve surgery if severe), coronary artery stenosis (about 3 to 7%, silent ischaemia possible), residual ventricular septal defect, pulmonary artery branch stenosis, arrhythmia.
• Atrial switch (Mustard or Senning), the older operation: the right ventricle supports the systemic circulation. Complications include baffle obstruction or leak, sinus node dysfunction, atrial flutter, ventricular dysfunction and tricuspid regurgitation. Management in adults: bisoprolol 1.25 to 10 mg daily for rate control, diuretics for failure (furosemide 20 to 40 mg daily), pacemaker for sinus node disease, defibrillator for ventricular arrhythmia or ejection fraction of 35% or less with symptoms, baffle stenting, and cardiac transplantation for end stage failure.
• Endocarditis prophylaxis: amoxicillin 2 g orally (50 mg/kg in children) 30 to 60 minutes before dental procedures for 6 months after surgery and afterwards if residual defects are next to prosthetic material.
• Special groups: pregnancy (arterial switch with normal function is usually tolerated; atrial switch carries risk of heart failure and arrhythmia, so assess ventricular function and baffle before conception); children (exercise tolerance is usually good; yearly neurodevelopmental review); elderly after atrial switch (progressive failure).
• Red flags: SpO2 less than 70% despite alprostadil, absent atrial mixing, new murmur, exertional chest pain or syncope after switch (coronary ischaemia), sustained tachycardia.
• Follow up: echocardiography at discharge, 6 months, yearly in childhood, then every 1 to 2 years; coronary assessment (CT angiography or stress imaging) in adolescence and adulthood for arterial switch; yearly review for atrial switch with baffle imaging by MRI or CT.