Congenitally Corrected Transposition of the Great Arteries

Congenitally corrected transposition of the great arteries (ccTGA, also called L-TGA) combines atrioventricular discordance with ventriculo arterial discordance. The right atrium opens through a mitral valve into a morphologic left ventricle that gives rise to the pulmonary artery.

The left atrium opens through a tricuspid valve into a morphologic right ventricle that supports the aorta. Blood flows in the correct sequence, but the right ventricle is the systemic ventricle. It accounts for about 0.5% of congenital heart disease.

Situs solitus with levocardia is the usual arrangement, though dextrocardia and situs inversus occur.

Associated lesions are ventricular septal defect (60 to 80%), pulmonary stenosis or atresia (30 to 50%), and an Ebstein like abnormality of the left sided tricuspid valve (the systemic atrioventricular valve), present in most cases. Isolated ccTGA may remain undetected until adult life.

Pathophysiology. The right ventricle is not built for systemic afterload. Over decades it dilates and fails. Systemic atrioventricular valve regurgitation worsens this.

Perfusion defects from a supply demand mismatch add to the damage. The atrioventricular node and His bundle are abnormally positioned and elongated, so complete heart block develops at about 2% each year. Accessory conduction connections accompany the Ebstein like valve and can cause pre-excitation.

• Often asymptomatic until the third to fifth decade.
• Syncope or presyncope from heart block.
• Palpitations from atrial arrhythmias.
• Exertional dyspnoea and fatigue from systemic ventricular dysfunction.
• With a ventricular septal defect and pulmonary stenosis: cyanosis or heart failure in childhood.
• Examination: a single loud second sound from the anterior leftward aortic valve, a holosystolic apical murmur of systemic atrioventricular valve regurgitation, bradycardia in heart block, and dextrocardia in some.
• ECG: Q waves in V1 to V3 with absent septal Q waves in V5 and V6, first degree or higher atrioventricular block, and sometimes a pre-excitation pattern.
• Chest X-ray: straight left heart border from the leftward ascending aorta and absent pulmonary knuckle.

Red flags.

• Syncope or presyncope
• New heart failure symptoms
• New or worsening systemic atrioventricular valve regurgitation
• Rapid atrial tachyarrhythmia with 1:1 conduction
• Cyanosis
• Systemic ventricular ejection fraction under 40%

• Echocardiography with segmental analysis: establish atrial situs, ventricular morphology (the right ventricle has a moderator band and coarse trabeculation, with the tricuspid valve inserting lower on the septum than the mitral), atrioventricular discordance and ventriculo arterial discordance. The aorta lies anterior and to the left of the pulmonary artery, and the great arteries run in parallel in the short axis. Assess systemic atrioventricular valve regurgitation, associated defects and strain.
• Cardiac MRI: systemic ventricular volumes, ejection fraction and scar. Systemic right ventricular ejection fraction under 40% denotes dysfunction.
• Ambulatory ECG and exercise testing: heart block, atrial arrhythmias, chronotropic response.
• Cardiac CT or catheterisation: for coronary anatomy and haemodynamics before intervention.
• NT-proBNP: adjunct for decompensation.

Differential diagnosis.

• Complete (dextro-) transposition after atrial switch repair, which also has a systemic right ventricle
• Isolated Ebstein anomaly
• Dextrocardia with situs inversus
• Double outlet right ventricle
• Univentricular heart
• Dilated cardiomyopathy
• Other causes of heart block in young adults

• No associated lesions and normal function: no intervention. Regular surveillance.
• Pacing: complete or advanced atrioventricular block, and symptomatic bradycardia, need a pacemaker. Conventional right ventricular pacing worsens systemic ventricular function, so when much ventricular pacing is expected use biventricular or conduction system pacing.
• Systemic atrioventricular valve regurgitation: repair or replace for moderate to severe regurgitation, ideally before systemic ventricular ejection fraction falls under 40% and before the ventricle dilates.
• Anatomic repair (double switch): atrial plus arterial switch for selected children whose subpulmonary left ventricle is trained to systemic pressure (often by pulmonary artery banding). A Rastelli type repair applies when ventricular septal defect and pulmonary stenosis coexist.
• Heart failure drugs have no proven survival benefit in a systemic right ventricle. Diuretics are used for congestion. An ACE inhibitor is commonly used in practice: ramipril 1.25 to 2.5 mg orally once daily, increased every 1 to 2 weeks to 10 mg once daily, maximum 10 mg daily (5 mg daily at creatinine clearance under 30 mL/min). Check potassium and creatinine 1 to 2 weeks after each change, and stop or reduce for creatinine rise over 30% or potassium over 5.5 mmol/L. Contraindicated in pregnancy and bilateral renal artery stenosis. Beta blockers are used with caution because of heart block.
• Atrial fibrillation or flutter: anticoagulation with apixaban 5 mg orally twice daily, reduced to 2.5 mg twice daily when at least two of age 80 years or over, weight 60 kg or under and serum creatinine 133 micromol/L or over are present. Also 2.5 mg twice daily at creatinine clearance 15 to 29 mL/min, and avoided under 15 mL/min. Maximum 10 mg daily. Catheter ablation in a specialist centre.
• Antibiotic prophylaxis for endocarditis only with prosthetic valves or material, previous endocarditis, or unrepaired cyanotic disease.

Special groups. Pregnancy is usually tolerated with normal systemic ventricular function, no significant regurgitation and NYHA class I to II. Risk rises with systemic ejection fraction under 40%, severe regurgitation or NYHA class III to IV. Counsel before conception. ACE inhibitors are stopped before conception.

Monitoring. ECG and clinical review at least annually. Echocardiography annually. Cardiac MRI every 2 to 3 years for systemic ventricular size and function. Ambulatory ECG yearly or with symptoms. NT-proBNP when symptomatic.

Referral and escalation. Refer to an adult congenital heart disease centre for diagnosis. Urgent for syncope, heart block, new heart failure or rapid arrhythmia.