Echocardiographic Findings in Congenitally Corrected Transposition of the Great Arteries (cc-TGA)
In cc-TGA, echocardiography demonstrates atrioventricular and ventriculoarterial discordance, where the morphologically right atrium connects to the morphologically left ventricle, the morphologically left atrium connects to the morphologically right ventricle, the morphologically right ventricle connects to the aorta, and the morphologically left ventricle connects to the pulmonary trunk. 1
Core Anatomic Features
The fundamental echocardiographic findings in cc-TGA reflect the double discordance that defines this condition:
Atrioventricular discordance: The right atrium connects to the morphologically left ventricle (identified by its smooth septal surface and bicuspid mitral valve), while the left atrium connects to the morphologically right ventricle (identified by its trabeculated septal surface and tricuspid valve with septal leaflet attachment) 1, 2
Ventriculoarterial discordance: The morphologically right ventricle gives rise to the aorta (positioned anteriorly and rightward), while the morphologically left ventricle gives rise to the pulmonary artery 1, 3
Ventricular geometry: The systemic right ventricle appears on the left side of the heart in four-chamber views, with characteristic trabeculations and moderator band visible 1
Associated Cardiac Anomalies
Echo must systematically evaluate for commonly associated lesions, as they occur in approximately 98% of cc-TGA cases:
Ventricular septal defect (VSD): Present in the majority of cases, requiring careful assessment of size, location, and hemodynamic significance 2, 4, 5
Pulmonary stenosis/outflow tract obstruction: Occurs frequently due to abnormal geometry of the left ventricle, which becomes distorted and compressed by the enlarged systemic right ventricle 1, 2, 4, 5
Systemic atrioventricular valve (tricuspid valve) abnormalities: Including Ebstein-like malformation, dysplasia, or regurgitation due to annular dilation 1, 2, 4, 5
Systemic Right Ventricle Assessment
Comprehensive echocardiographic imaging should be performed in a regional adult congenital heart disease center to evaluate the anatomy and hemodynamics of the systemic right ventricle. 1, 3
Critical parameters to assess include:
Systemic RV function: Challenging to quantify by standard echocardiography; utilize Doppler tissue indices of annular motion, myocardial performance index, and dP/dt of the atrioventricular regurgitant jet 1
Systemic RV size and wall thickness: Progressive dilation and hypertrophy occur due to chronic systemic pressure load 1
Tricuspid regurgitation severity: Generally due to annular dilation and systemic RV dysfunction, though may also result from Ebstein's anomaly; presents a volume load on the ventricle 1, 2
Additional Imaging Considerations
When echocardiographic windows are limited or additional detail is needed:
Transesophageal echocardiography (TEE): Effective for detailed evaluation of atrioventricular valve anatomy, baffle assessment in post-surgical patients, and detection of shunts 1, 3
Contrast echocardiography: Useful with agitated saline injection to evaluate baffle anatomy and shunting in patients with prior atrial baffle repair 1, 3
Complementary imaging: Additional imaging with CT or MRI should be performed to evaluate the great arteries, veins, and ventricular function when echocardiography is insufficient 1, 3
Common Pitfalls to Avoid
Misidentifying ventricular morphology: Always confirm ventricular identity by examining septal surface characteristics (smooth for LV, trabeculated for RV) and atrioventricular valve morphology (bicuspid mitral vs. tricuspid with septal attachment) 1
Underestimating tricuspid regurgitation: The systemic tricuspid valve is subject to progressive deterioration and requires quantitative assessment, as severity is linked to ventricular function and clinical outcomes 1
Missing conduction abnormalities: While not directly visualized on echo, be aware that complete heart block is common and may influence clinical management 2, 5
Overlooking coronary anomalies: Significant coronary artery anomalies are described in cc-TGA and should be evaluated when possible 6