TGA – Type II (ASD(+), VSD(+), PS(-))

Preoperative Physiology: Parallel Circulation with VSD

In Type II TGA, the aorta arises from the right ventricle (RV) and the pulmonary artery from the left ventricle (LV), maintaining the fundamental problem of parallel circulations. Unlike Type I, however, the presence of both an atrial septal defect (ASD) and a ventricular septal defect (VSD) creates additional mixing pathways.

• Mixing occurs primarily through the VSD, usually as a right-to-left shunt, and through the ASD, often as a left-to-right shunt driven by elevated left atrial pressure.
• The LV becomes volume overloaded due to increased pulmonary venous return entering via the ASD, VSD, and sometimes a PDA.
• The RV ejects into the aorta and thus faces systemic afterload, resulting in pressure overload and progressive dilation.
• When the VSD is large, left and right ventricular pressures equalize (LVP ≈ RVP), eliminating the pressure advantage of either ventricle.

A particularly important feature is the marked increase in pulmonary blood flow (PBF). The combination of high-pressure VSD shunting and unobstructed pulmonary circulation predisposes the pulmonary vasculature to injury and the early development of pulmonary hypertension (PH). If uncorrected, this may lead to irreversible vascular changes.

In some patients, an anteriorly malaligned VSD narrows the left ventricular outflow tract or results in a small aortic valve and ascending aorta, raising the possibility of needing aortic arch repair in addition to arterial switch.

Postoperative Management: Arterial Switch and VSD Closure

Definitive repair consists of an arterial switch operation (ASO) combined with VSD closure. This re-establishes physiologic circulation, with the LV supporting the systemic output and the RV ejecting into the pulmonary artery.

However, postoperative risks must be closely monitored:

• Coronary stenosis or malperfusion, a recognized complication of coronary transfer during ASO.
• Left ventricular dysfunction, particularly if preoperative conditioning was suboptimal.
• Neo-aortic valve regurgitation, which may develop over time.
• Pulmonary artery stenosis, often a result of distortion after the Lecompte maneuver.
• Persistent pulmonary hypertension, which can precipitate postoperative PH crisis and remains a critical concern in this subtype due to the preoperative pulmonary overcirculation.

Summary

TGA Type II differs from Type I by the presence of a VSD, which provides additional mixing but also imposes significant hemodynamic burdens. The LV experiences volume overload, the RV faces systemic pressure overload, and the pulmonary circulation is exposed to excessive flow and pressure, placing patients at high risk for pulmonary vascular disease. Definitive repair with ASO and VSD closure restores physiologic circulation, but vigilance for coronary complications, ventricular dysfunction, neo-aortic regurgitation, pulmonary artery stenosis, and persistent PH is essential in the postoperative period.