This complex condition is a type of transposition of the great arteries (TGA) and accounts for 2 per cent of all congenital heart disease, but it attracts a disproportionate amount of attention due to the unusual physiology and variety of associated conditions. The condition is characterized by atrio-ventricular (A-V) and ventriculo-arterial (V-A) discordance such that the physiology is naturally corrected in that the systemic venous blood is directed to the lungs and the pulmonary venous blood to the systemic circulation (Figure 18.1). However, in achieving this, the systemic ventricle is the morphological right ventricle (mRV) and the sub-pulmonary ventricle is a morphologic left ventricle (mLV). The corrected physiology means that the patients are acyanotic and should be symptom free, but the clinical correlates are related to the high frequency of associated anomalies and the natural history of the mRV in the systemic position.
The associated conditions are listed in Table 18.1, with VSD being commonest at 60 per cent, together with the frequent combination of VSD with pulmonary stenosis or atresia (30 per cent in the Western world, up to 70 per cent in the East). The condition is also prone to conduction defects, with complete heart block developing in 40 per cent and abnormalities of the tricuspid valve (which is in the systemic circulation) causing regurgitation. The fascination with the condition is related to the natural history of the mRV in the systemic position, which is both unpredictable and partly dependent on the associated lesions.
|Associated lesions/conditions||Frequency (%)|
|VSD and pulmonary stenosis/atresia||40–70a|
|Ebsteinoid tricuspid valve||10–15|
|Bicuspid aortic valve||3|
|Abnormal mitral valve||3|
|Preoperative heart block||15–20|
a There are considerable variations in the pattern of lesions seen based on geographical variation. The table reflects typical lesions seen in the western hemisphere. In the eastern hemisphere, LVOT obstruction with VSD is commoner with a lower incidence of arch hypoplasia and Ebsteinoid tricuspid valve.
Presentation depends entirely on the associated lesions. Patients with a large VSD may present in heart failure, those with pulmonary stenosis or atresia will be cyanosed and those with arch hypoplasia or coarctation may present with circulatory collapse in the newborn period. Occasionally, patients are in complete heart block at birth and may present with heart failure secondary to profound bradycardia. Complete diagnosis can usually be made by echocardiography, and initial treatment is empirical, based on the nature of presentation to achieve a balanced circulation.
Patients with no significant associated lesions may be symptom free, and diagnosis may be made incidentally on a routine investigation such as an abnormal ECG (picking up conduction delay) or CXR (revealing an unusual position of the heart or the narrowed superior mediastinum characteristic of transposition). There are anecdotal cases diagnosed in their seventh or eighth decade, but most patients will develop some degree of right ventricular dysfunction (with or without tricuspid regurgitation) at some stage, with signs of congestive cardiac failure by age 50 in the majority of patients. Controversy remains over the management of symptom-less patients who develop echocardiographic signs of ventricular dysfunction and tricuspid regurgitation, and this is discussed later.
This will depend on the mode of presentation and the associated lesions: neonates with arch hypoplasia and coarctation require resuscitation, stabilization and urgent surgical repair. If there is associated VSD, then a pulmonary artery (PA) band may be placed at the same time to balance the circulation.
Patients with pulmonary stenosis or atresia require initial palliation with a Blalock-Taussig (BT) shunt, and those presenting with heart failure due to large VSD are usually initially managed with PA banding rather than VSD closure for reasons outlined below.
Traditional management of ccTGA was to address the clinically important lesions and achieve a ‘physiological’ repair, closing any intra-cardiac shunts and relieving any outflow tract obstruction. This is referred to as a ‘conventional repair’ because it leaves the mRV as the systemic ventricle. Conditions such as ccTGA with pulmonary atresia and VSD are treated by simple VSD closure and placement of an LV-PA conduit (since the mLV is the sub-pulmonary ventricle). This approach is successful at relieving immediate symptoms, but the medium- to long-term outcomes are disappointing due to the tendency to develop right ventricular failure. The 10-year freedom from congestive heart failure after conventional repair is only 50 per cent, with a similar likelihood for greater than moderate tricuspid regurgitation. Attempts at tricuspid valve repair in this setting have been universally disappointing, with even experienced centres having a 100 per cent failure rate at 10 years. As a consequence, there is now far less enthusiasm for ‘conventional’ repair, but it is still appropriate in older patients, in whom the mRV function remains good.