TGA – Type I (ASD(+), VSD(-), PS(-))

Date
July 22, 2025
URL
https://x.com/WithAScalpel/status/1947622341002899482
Categories
TGA
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Transposition of the Great Arteries (TGA) – Type I

(ASD present, VSD absent, PS absent)

Preoperative Physiology: Parallel Circulation

In Type I TGA, the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating parallel circulations rather than the normal series arrangement. As a result, systemic blood remains desaturated.

Adequate intercirculatory mixing is essential for survival. In this subtype, the only natural communication is an atrial septal defect (ASD). When mixing is inadequate, infants present with severe cyanosis, and a balloon atrial septostomy (BAS) may be required to improve oxygenation.

A patent ductus arteriosus (PDA), maintained pharmacologically with prostaglandin E₁, can augment pulmonary blood flow. This increased flow imposes a volume load on the left ventricle (LV), but as pulmonary vascular resistance (PVR) falls after birth, the LV faces a reduced pressure load. Meanwhile, the right ventricle (RV) ejects against systemic vascular resistance (SVR) into the aorta, producing pressure overload and dilation of the RV.

Because of these hemodynamic conditions, an arterial switch operation (ASO) is required within the first 5–7 days of life, before the LV loses the capacity to support systemic circulation.

Postoperative Circulation: Arterial Switch Operation

The ASO restores normal physiology by reconnecting the aorta to the LV and the pulmonary artery to the RV. Following this repair, systemic and pulmonary circulations run in series, and oxygen saturation normalizes.

However, several postoperative risks remain:

  • Coronary artery stenosis or kinking, which may impair myocardial perfusion and lead to ventricular dysfunction.
  • Left ventricular dysfunction, particularly if the LV was deconditioned preoperatively.
  • Neo-aortic valve regurgitation, due to dilation or distortion of the reconstructed root.
  • Pulmonary artery stenosis, often related to compression from the reconstructed great arteries.
  • Persistent pulmonary hypertension (PH), which may precipitate a postoperative PH crisis.

Summary

TGA Type I with intact ventricular septum and no pulmonary stenosis represents a form of parallel circulation in which survival depends on atrial level mixing and ductal patency. Preoperatively, the LV is volume loaded while the RV faces systemic pressure overload. Definitive repair with an arterial switch operation within the first week of life is essential to establish normal circulation. Postoperatively, vigilance is required for coronary complications, ventricular dysfunction, valve regurgitation, and pulmonary hypertension.