Congenitally corrected transposition of the great arteries

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Congenitally corrected transposition of the great arteries, also known as levo- or L-loop transposition (L-TGA), is a rare cardiovascular anomaly with inversion of the ventricles and great arteries.

Epidemiology

This anomaly comprises less than 1% of all congenital heart diseases .

Clinical presentation

Patients are usually asymptomatic when L-TGA is not associated with other anomalies or complications. Patients may present with congestive heart failure if there is an associated large ventricular septal defect (VSD) or with cyanosis if with associated VSD and pulmonary stenosis. If the anomaly is complicated by right ventricular or tricuspid valve dysfunction, patients can present with exertional dyspnea and easy fatigability.

ECG
  • absence of Q waves in the lateral precordium (V4-6)
    • physiologic Q waves in these leads often referred to as "septal" Q waves
  • prominent Q waves in right precordium (V1-3)
  • third degree atrioventricular (AV) conduction block

Pathology

In this anomaly, the right atrium communicates with the morphologic left ventricle, which gives rise to the pulmonary artery, while the left atrium communicates with the morphologic right ventricle, which gives rise to the aorta.  Thus, atrioventricular and ventriculoarterial discordance (double discordance) exists, and although blood flows in the normal direction, it passes through the wrong ventricular chambers. It is also called L-TGA because the morphologic right ventricle is in the levoposition. The aorta is also usually anterior and to the left of the main pulmonary artery.

Associations

The presence or absence of associated cardiac anomalies alters the natural history of the anomaly. Patients may have one or more associated anomalies which include:

  • ventricular septal defect (VSD)
    • occurs in approximately 70-80% of patients
    • usually perimembranous in location 
    • large VSDs may result in congestive heart failure during infancy or childhood 
  • pulmonary stenosis
    • occurs in approximately 40-50% of patients
    • commonly subvalvular in location
    • patients with both a VSD and pulmonary stenosis may present with cyanosis
  • pulmonary atresia
  • systemic atrioventricular (tricuspid) valve abnormalities
    • occurs in up to to 90% of patients
    • inferior displacement of the valve closer to the cardiac apex
  • abnormal conduction system
    • unusual position and course of the AV node and bundle of His 
    • dual AV nodes
    • complete AV block and paroxysmal supraventricular tachycardia
  • mirror-image coronary artery distribution
    • right coronary artery supplying the anterior descending branch and gives rise to a circumflex branch
    • left coronary artery resembles a right coronary artery 
  • situs inversus

Radiographic features

Plain radiograph

Chest radiographs may present with mesocardia or levocardia. Since there is an abnormal relationship of the great arteries, the vascular pedicle may appear abnormally straight. The left ventricular border may also appear more vertical than usual. In frontal radiographs, there could be an abnormal bulge along the upper left cardiac border produced by the inverted aorta and right ventricular outflow tract or by the right atrial appendage lying above the left atrial appendage (juxtapositioning of the atrial appendages).

In the absence of a VSD, pulmonary vasculature may be normal and the heart is not enlarged. Patients with VSD can present with pulmonary plethora and cardiomegaly.

Echocardiography

The diagnosis of L-TGA can be made using the segmental approach. The associated anomalies can also be detected and quantified.

CT

Allows direct visualization of abnormal atrioventricular and ventriculoarterial relationships. Cardiac-gated cine CT can additionally assess function.

MRI

Cardiac MRI is helpful in defining the anomalous anatomy, ventricular function and volumes.

Treatment and prognosis

Early surgical treatment was aimed only at repairing the associated anomalies (i.e. VSD, pulmonary stenosis or atresia and tricuspid valve abnormalities). Despite these repairs, patients still develop tricuspid valve insufficiency and right ventricular failure which complicate the anomaly. This has led to the development of the double switch procedure as the definitive surgical correction and to remove the systemic pressure load from the morphologic right ventricle . Prior to correction, patients may require pulmonary artery banding to train the morphologic left ventricle to receive the higher systemic pressure load.

In cases with associated severe pulmonary stenosis or pulmonary atresia, a modified Blalock-Taussig shunt is necessary .

Some patients with conduction abnormalities may require pacemaker insertion .

History and etymology

Rokitansky coined the term "corrected transposition" in 1875 while Schiebler et al introduced the term "congenitally corrected transposition" in 1961 . Although still commonly used in literature, in essence, both terms are misnomers due to the presence of double discordance in this anomaly.