The natural history of ccTGA aside from the coexisting abnormalities is mainly dictated by the systemic RV function, so the regular assessment of ventricular function is vital. In addition to routine echocardiography examination, cardiac magnetic resonance imaging (MRI) is considered to be the method of choice for a comprehensive evaluation of both asymptomatic patients and those after surgery.
Compared to echocardiography, the major advantage of MRI is the ability to assess cardiac anatomy in multiple planes with high spatial resolution. Since the main feature of ccTGA is RV dysfunction, the MRI as the „gold standard“ for volumetric assessment of the systemic RV is the most relevant and precise method in patient follow-up.
Inverted coronary arteries anatomy can be analyzed with cardiothoracic computed tomography (CT), which also remains a method of choice in patients with contraindications for MRI and in specific clinical cases.
A standard protocol for evaluating ccTGA includes cine steady-state free precession (SSFP) images in standard cardiac planes for ventricular analysis and analysis of the interatrial baffle patency in Senning and intraventricular tunnel in Rastelli procedure [8] Postcontrast MR angiography is used to evaluate the extracardiac vessels, and flow measurement through the aortic and pulmonary valve is used to quantify the insufficiency of the atrioventricular valves and the possible baffle leak.
Flow measurement can also be used to investigate and quantify the baffle stenosis. Late gadolinium enhancement can depict myocardial scarring of the systemic right ventricle.
- Standard report concerning a pre/postoperative ccTGA patient should include:
A. Anatomy
Analyzing the acquired images defines the “double discordance” of heart chambers and other co-existing cardiovascular malformations (VSD, valvular anomaly, etc.). High spatial resolution images help to analyze the morphological features of systemic RV - more apical position of the tricuspid valve, the moderator band and the septal insertion of papillary muscles. ( Fig. 1 , Fig. 2 , Fig. 3 , Fig. 4 , Fig. 5 ). The anatomy of the coronary arteries inversion can be imaged with cardiothoracic CT ( Fig. 6 ).
B. Volumes, myocardial mass and systolic function of both ventricles
MRI is the gold standard for the measurement of the end-diastolic volume and an ejection fraction of the systemic RV ( Fig. 7 ). This is especially important in longitudinal follow-up of the RV function decline and proper timing of surgical treatment.
C. Analysis of intra-atrial and intra-ventricular conduit stenosis, obstruction or leak.
Using CT or MR angiography, conduit stenosis and obstruction can be detected ( Fig. 8 ). MRI flow velocity measurement can evaluate baffle stenosis which is frequent after Senning procedure, measuring the peak velocity after the correction.
D. Quantification of the systemic atrioventricular valve regurgitation.
Tricuspid valve insufficiency is usually combined with progressive RV dysfunction in ccTGA, and the regurgitant volume can be calculated as the difference between systemic RV stroke volume and forward flow through ascending aorta, and regurgitant fraction as the ratio between regurgitant volume and systemic ventricular stroke volume ( Fig. 9 ).
E. Gadolinium-enhanced MR angiography (MRA). MRA can be performed to evaluate anomalies of the extra-cardiac vascular structures.
F. Late gadolinium enhancement is useful for myocardium replacement fibrosis detection due to ventricle dilatation and possible post-operative scarring after double-switch surgery.
CT and MRI both have roles in different clinical settings, MRI depicts superior cardiac anatomy with high spatial resolution, while the ECG-gated cardiac CT is helpful in patients with contraindications for MRI - its advantages over MRI are better spatial resolution and imaging of coronary arteries, while the speed is useful in acute settings.
A high dose of ionizing radiation is the main flaw of CT in lifelong follow-up, including no possibility to quantify valvular disease and shunt.
The most common findings and complications after double switch procedure are systemic RV dysfunction leading to dilation, baffle leak or stenosis, insufficiency of the systemic tricuspid valve and sinus-node dysfunction.