**5.1 Prenatal diagnosis**

Fetal diagnosis of many forms of CHD continues to improve. However the fetus with ccTGA and mild or no additional intracardiac anomalies may be overlooked by routine ultrasound screening. Distinct features notable on prenatal ultrasound that may improve detection of ccTGA are parallel course of the great arteries in combination with dextrocardia, abnormal insertion of the papillary muscles, and/or an abnormal TV (McEwing & Chaoui, 2004; Paladini et al., 2006; Shima et al., 2009). A retrospective review by Wan et al. found no difference in the number of cardiac interventions, timing of surgery, or survival between a cohort of ccTGA patients diagnosed prenatally (n = 14) and postnatally (n = 26). However, because 70% of this cohort required cardiac intervention prior to 3 years of age, the authors suggest prenatal diagnosis is important for preparation and counseling of the family (2009). A recent review of 11 cases of fetal ccTGA diagnoses describes the use of four-dimensional echocardiography and spatiotemporal image correlation (STIC), in which the relationship of the great arteries can be assessed in several different orthogonal planes by placement of a reference dot on images reconstructed from acquired volume data sets (Zhang et al., 2011).

#### **5.2 Early presentation and diagnosis**

Diagnoses of infants and children may occur after murmur evaluation, as VSDs are commonly associated lesions. In cases of large VSDs or severe TV regurgitation, some infants may present in CHF with diaphoresis, pallor, tachypnea, inability to gain weight, hepatomegaly, and a gallop on exam. Auscultation of the ccTGA patient may also reveal a loud, single second heart sound (S2) at the left 2nd intercostal space, with absence of S2 over the right 2nd intercostal space (Friedberg & Nadas, 1970). The presence of VSD combined with LVOTO may lead to a cyanotic presentation from decreased pulmonary blood flow. However, some degree of LVOTO may be protective of the lung bed in patients with large VSDs, and may delay a CHF presentation despite the normal decrease in pulmonary vascular resistance.

Congenitally Corrected Transposition of the Great Arteries 167

presence and direction of shunting, as well as the severity of LVOTO (Carey & Ruttenberg,

The ECG in patients with ccTGA is most significant for a superior QRS axis and atypical septal activation. As discussed previously, the conduction system in ccTGA consists of inverted AV bundles. Therefore the septum is activated from right to left, demonstrating presence of septal Q waves in the right precordial leads (QR pattern in leads V4R and V1) and absence of Q waves in the left precordial leads (rS pattern in lead V6). In fact, undiagnosed ccTGA patients with such a pattern on ECG have been diagnosed with remote inferior infarcts (Jennings et al., 1984; Warnes, 2006). Preexcitation may be observed in those patients with ccTGA and Wolff-Parkinson-White. Finally, varying degrees of AV block may

Transthoracic echocardiography (TTE) as an imaging modality is relatively inexpensive, widely available, and noninvasive. As with many types of CHD, TTE is the first line and most useful modality in the diagnosis of ccTGA. The anatomical designation (most commonly {S,L,L} as discussed previously), is first assigned by demonstrating atrial position, ventricular looping, and arterial looping. Morphology of the RV is seen on TTE by the presence of coarse trabeculations and a moderator band, whereas the LV has a smoothwalled endocardium and a funnel-shaped appearance. The level of the TV is inferior to the MV, which may also give a clue to ventricular inversion. In evaluation of the outflow tracts, the aorta in ccTGA is usually anterior and to the left of the PA. Once the diagnosis of ccTGA is made through demonstration of discordance between atria and ventricles as well as ventricles and great arteries, several anatomic objectives should be defined in the TTE evaluation. Semilunar and AV valve morphology as well as presence and severity of regurgitation warrant full description. Coronary origins should be identified and their proximal courses described. The degree of LVOTO is important as well as any additional defects present, as these will impact whether and what type of surgical repair is necessary (Oechslin, 2009). Transesophageal echocardiography (TEE) has been shown to have greater accuracy over TTE in correctly defining atrial situs and chordal AV valve attachments in adult patients with ccTGA (Caso et al., 1998). TEE is also more useful for investigation of intracardiac vegetations in cases of suspected endocarditis and in evaluation of thrombus in the atrial appendages, which may be applicable to the ccTGA patient with sustained atrial

Rather than a modality for diagnosis, cardiac catheterization (Figure 4) is typically reserved for the post-surgical patient who would benefit from an intervention such as LV to pulmonary artery (PA) conduit dilation or stent placement. For patients undergoing surgical palliation for single-ventricle ccTGA anatomy, catheterization is performed to assess pressure, function, and valve regurgitation prior to surgery. Most interesting, however, is the adult patient who presents with ischemic heart disease and is discovered on cardiac catheterization to have ccTGA after abnormal catheter passes or inversion of coronary

be present, as well as patterns of right or left-sided chamber enlargement.

1964).

**6.2 Electrocardiogram** 

**6.3 Echocardiography** 

arrhythmias.

**6.4 Cardiac catheterization** 

arteries on angiography (Jennings et al., 1984).
