Anatomy of the defect and surgical correction
In classical transposition of the great arteries, severe ventriculoarterial discordance is observed. The aorta originates from the right ventricle (RV), and the pulmonary artery abnormally arises posterior to the left ventricle (LV). These anatomical features are clearly visualized on cardiac MRI using the b-SSFP sequence (oblique sagittal view of the outflow tracts is used).
For treatment, arterial switch operation (arterial switch repair) is used. The key stage of the intervention is the Le Compte maneuver (Le Compte manoeuvre). It consists of the translocation (mutual relocation) of the aorta and pulmonary artery. In this process, the ostia of the coronary arteries are carefully excised from the old aortic root as small patches (so-called "buttons" — coronary artery button) and reimplanted into the root of the neo-aorta.
Postoperative tomograms normally show the pulmonary artery branches anterior and lateral to (straddling) the ascending aorta. However, due to tissue tension, bilateral stenosis of the proximal pulmonary artery branches is a frequent long-term consequence of the Lecompte maneuver. This complication is reliably detected using MR angiography with volumetric 3D reconstruction.
Congenitally corrected transposition (ccTGA)
Congenitally corrected transposition of the great arteries (CCTGA) is a rare variant of the defect characterized by the simultaneous presence of atrioventricular and ventriculoarterial discordance. Blood flow follows this pathway: from the right atrium to the left ventricle and further into the pulmonary artery; from the left atrium to the right ventricle and then into the aorta.
Physiologically, the circulatory loops are separated correctly, so cyanosis is absent, and systemic circulation is maintained by the morphological right ventricle. The disease may be asymptomatic and an incidental finding, but over time, the vast majority of patients develop heart failure of the systemic right ventricle. Its anatomy is simply not adapted to the high resistance of the systemic circulation.
ccTGA is rarely encountered in isolation. Frequent associated pathologies:
- Ventricular septal defect (VSD) is the most common anomaly.
- Pulmonary stenosis (PS) is diagnosed in approximately 50% of cases. Fibrous tissue tags (fibrous tissue tags) may be found in the outflow tract.
- Anomalies of the left-sided tricuspid valve (e.g., Ebstein's anomaly with apical displacement of the leaflets) are identified in 20% of cases.
Role of diagnostic imaging
Cardiac MRI plays a crucial role in the management of patients with TGA and ccTGA. Tomograms (especially in the SSFP sequence) clearly show that the morphological left ventricle is located anteriorly, and the right ventricle is on the right.
Key imaging goals:
- Precise description of all atrioventricular and ventriculoarterial connections.
- Detection of associated VSD and tricuspid valve anomalies.
- Identification of any outflow tract obstruction.
- Assessment of fibrosis or scarring of the systemic right ventricle. Late gadolinium enhancement (LGE) is used for this purpose.
Pulmonary atresia as a related pathology
As part of evaluating associated disorders, it is important to consider pulmonary atresia, a condition characterized by complete absence of the lumen and blood flow from the right ventricle to the pulmonary trunk. Treatment strategy and prognosis depend on the presence of a VSD.
The variant with VSD (PA-VSD) is more common and is considered a severe form of Tetralogy of Fallot. It is characterized by a subaortic defect and an overriding aorta. Pulmonary blood supply is provided via collateral pathways—major aortopulmonary collateral arteries (MAPCAs) or a patent ductus arteriosus (PDA).
Surgical treatment consists of defect closure, collateral unifocalization, and creation of a connection between the right ventricular outflow tract and the pulmonary artery using a homograft (conduit). In the postoperative period, the radiologist must evaluate conduit function. The main problem is its dysfunction (stenosis and regurgitation), leading to RV overload. Stenosis frequently occurs secondarily due to calcification of non-viable homograft tissue.
Important diagnostic nuance: calcium deposits are extremely difficult to visualize on cardiac MRI (CMR); computed tomography (CT) should be used to detect them.
Briefly: answers to topical questions
What hemodynamic variants of pulmonary atresia with intact ventricular septum exist?
Hemodynamic variants of pulmonary atresia with an intact ventricular septum depend on the size and shape of the right ventricular cavity.
- Biventricular repair is possible if a right ventricular infundibulum (infundibulum) is present.
- Single ventricle physiology develops if the right ventricular cavity is small (large venous sinusoids are visualized in the wall).
What standard cardiac MRI views, in addition to the oblique sagittal view, are used to evaluate congenital heart defects?
The following standard MRI views are used to evaluate cardiac anatomy:
- Vertical long axis (Vertical long axis, VLA) plane intersects the mitral valve and cardiac apex.
- Horizontal long axis (Horizontal long axis, HLA) intersects the vertical long axis, mitral valve, and apex.
- Short-axis views (Short-axis) are positioned perpendicular to the horizontal long axis at the mid-ventricular and basal levels.
- Four-chamber view (Four-chamber) intersects both ventricles.
- Two-chamber view (Two-chamber) is positioned strictly perpendicular to the four-chamber view.
- Three-chamber view is used to evaluate the left ventricle.
How is pulmonary atresia with VSD classified depending on the sources of pulmonary blood supply?
In pulmonary atresia, the sources of pulmonary blood flow can be a patent ductus arteriosus (PDA) or major aortopulmonary collateral arteries (MAPCAs).
To understand the hemodynamics of corrected TGA (ccTGA), remember the "double error" principle: the atria are connected to the wrong ventricles (error #1), and the ventricles to the wrong great arteries (error #2). Two negatives make a positive—venous blood still reaches the lungs, and arterial blood reaches the aorta.
Class and exam questions
What is the Lecompte maneuver in TGA?
This is a surgical translocation procedure in which the aorta and pulmonary artery are repositioned relative to each other. As a result, the pulmonary artery branches normally "straddle" the ascending aorta anteriorly and laterally.
Why is there no cyanosis in congenitally corrected TGA?
Due to double discordance (atrioventricular and ventriculoarterial), venous blood is still directed to the lungs, and oxygenated blood to the systemic circulation. Physiologically, hemodynamics remain normal.
Why does heart failure eventually develop in ccTGA?
Systemic circulation is maintained by the morphological right ventricle. Since it is not anatomically designed for high loads and systemic vascular resistance, decompensation develops over time.
Which diagnostic imaging method best detects conduit calcification post-surgery?
CT is used to detect calcification of homograft (conduit) tissue. Calcium deposits are visualized very poorly on MRI.
What else to study on this topic
- Anatomy and variations of coronary artery origins in classical TGA
- Principles of b-SSFP MRI and late gadolinium enhancement (LGE) in cardiology
- Echocardiographic criteria for Ebstein's anomaly in ccTGA
- Surgical unifocalization of major aortopulmonary collateral arteries (MAPCAs)
- MRI quantitative assessment of right ventricle-to-pulmonary artery conduit function
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