**7. Diagnosis**

Antenatal diagnosis of TGA by fetal echocardiography has improved since the visualization of outflow tracts to evaluate the major arteries' relationship is regularly performed. Postnatally, any baby failing the CCHD test or presenting with tachypnea and cyanosis that does not improve with 100% oxygen supplementation should raise the suspicion of a shunting cardiac lesion. A Hyperoxia test confirms the fixed shunting and differentiates between cardiac and pulmonary etiology of hypoxia [13].

Echocardiography with Doppler Study is confirmatory. The procedure should include evaluating atrioventricular and ventricular arterial connections and the presence of other anatomical cardiac anomalies, including those of coronary arteries. In D-TGA, two-dimensional echocardiography in the subcostal view demonstrates a great artery arising from the posteriorly situated left ventricle and bifurcating into left and right pulmonary arteries, while in the short-axis or parasagittal view, the aorta is visualized coming out anteriorly from the right ventricle [7, 8, 13, 14]. The atrial evaluation is important to confirm the presence of FO or ASD and the degree of interatrial flow, which determines the critical intercirculatory mixing. The presence of a VSD assures mixing but suggests the possibility of aortic arch anomalies. Complex TGA with VSD and coarctation have worse surgical outcomes and mortality. The presence of patent DA and the degree and direction of shunting blood are important information to obtain. Coronary artery anatomy and its variations must be ascertained via echocardiography, angiography or cardiac magnetic resonance imaging (MRI) prior to surgery. Atrioventricular valvular anomalies and chordae tendineae's relationship with interventricular septum and ventricles are other important features to evaluate before surgery.

Electrocardiography in TGA is generally normal with right-axis deviation and right ventricular hypertrophy. Biventricular hypertrophy may be noted if DTGA is complicated with large VSD, PDA, PS, or LVOO. Chest radiography may show normal or slightly increased heart size or the typical "egg on a string" appearance with

**Figure 5.** *Chest radiograph in DTHA showing "egg on string appearance".*

a narrow mediastinum, created by the anteroposterior positioning of the aorta and pulmonary artery and by involuted thymus (**Figure 5**) [7, 8, 13, 14]. The pulmonary vascular markings may be normal or increased. In the presence of a large VSD or straddling tricuspid valve, the pulmonary flow is increased, and cardiomegaly with congestive heart failure may supervene soon after birth. Cardiac catheterization (CC) and coronary angiography should be done to determine the origin, anatomy, and course of CA, espy if the echocardiography fails to visualize it well before surgery. CC is also used for performing balloon septostomy as a palliative measure to establish mixing of blood.

The conditions which should be clinically differentiated from DTAG are other cyanotic congenital cardiac defects, such as double-outlet right ventricle with malposed great arteries; tricuspid atresia; pulmonary atresia with an intact ventricular septum or with VSD; Tetralogy of Fallot with absent pulmonary valve, pulmonary atresia or severe pulmonary valve stenosis; TAPVR and truncus arteriosus.
