Congenital Heart Disease part 8

TRANSPOSITION OF THE GREAT ARTERY

Transposition of the great arteries is characterized by ventriculo arterial discordance, the left ventricle gives rise to the pulmonary artery, and the right ventricle to the aorta. There is atrioventricular concordance. If no significance additional cardiac lesion is present, it is referred  to as simple transposition of the great artery. A complex transition of the great artery has associated inracardiac anomalies including ventricle septal defect.

In general, it is not familial. There is no known association with syndromes or chromosomal abnormalities.

Adult patients are in general seen after surgical procedures. Because of the fundamental differences in presentation and clinical course, depending on the initial pathology and the type of operation these patients will have had, post-operative course will be described separetely.

Most adult patients with simple transposition of the great arteries will have had  a Mustard or a Senning atrial switch procedure. Most patients have a diminished exercise capacity when compared with the normal population. Dysfunction of the right ventricle, which serves as a systemic ventricle, is the most severe clinical problem. The prevalence increases substantially with longer duration of follow up. Tricuspid regurgitation often develops as a sign of right ventricle dilatation and progresses if cardiac failure becomes more prominent. Tachyarrhythmias occur frequently. Atrial flutter is the most typical presentation, but atrial fibrillation and all other types of supraventricular arrhythmias can occur. Ventricle tachycardia and ventricle fibrillation have been reported, and are associated with sudden cardiac death. With longer follow up, there is ongoing loss of sinus node function.

Bradycardia due to sinus node dysfunction necessating pacemaker therapy is common. The intra atrial tunnels are often referred to as baffles. They can leak with either left-right or right-left shunt, or can obstruct systemic venous and/or pulmonary venous drainage. The latter may lead to pulmonary hypertension. Systemic venous baffle stenosis, most often superior baffle, is reported to be present in up to 25% of the patients after Mustard repair. Superior vena cava obstruction may lead to venous congestion of the upper body half and necessitate  re-intervention. Obstruction of the systemic venous inferior baffle can cause venous congestion  of the lower body half, hepatic congestion, and hepatic cirrhosis. However, in either a superior or inferior baffle stenosis, clinical symptoms may be entirely absent, because of an effective collateral circulation provided by the azygos and hemiazygos vein. Narrowing of the subpulmonary outflow tract can occur due to leftward bulging of the interventricular septum. This can lead to a substantial gradient, which is often well tolerated by the subpulmonary  left ventricle. It may even be protective for systemic ventricular function due to ventricular septal shift to the right.  Other reported problems are residual ventricle septal defect or pulmonary arterial hypertention.