TGA – Type III (ASD(+), VSD(+), PS(+))

Date
July 24, 2025
URL
https://x.com/WithAScalpel/status/1948347672823251050
Categories
TGAVSD
image

Transposition of the Great Arteries (TGA) – Type III

(ASD present, VSD present, PS present)

Preoperative Physiology: Parallel Circulation with VSD and PS

In Type III TGA, the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating parallel circulations as in other subtypes. Mixing occurs through both the ASD and VSD, and occasionally through a PDA if present.

The defining feature of this subtype is the coexistence of a ventricular septal defect with pulmonary stenosis (PS). Because of the obstruction at the right ventricular outflow tract, shunting across the VSD is predominantly left ventricle → right ventricle, but pulmonary blood flow is restricted by PS. As a result, pulmonary arteries are often hypoplastic, and patients present with cyanosis.

The left ventricle, which receives limited pulmonary venous return due to reduced pulmonary flow, is relatively volume-deprived and tends to remain small. In cases of posteriorly malaligned VSD, the aorta becomes enlarged while the pulmonary artery system remains underdeveloped, further exaggerating the imbalance between systemic and pulmonary circulations.

Surgical Strategies

The operative approach depends on the severity of pulmonary stenosis:

  • Mild PS: An arterial switch operation (ASO) with VSD closure can restore normal physiology, since pulmonary outflow is adequate.
  • Moderate to severe PS: More complex procedures are required, including the Nikaidoh procedure (aortic root translocation) or the half-turn truncal switch, both designed to realign the ventriculo-arterial connections while addressing RVOT obstruction.
  • Severe PS or pulmonary atresia: A Rastelli procedure is indicated, using the VSD to route LV output to the aorta and placing a conduit between the RV and pulmonary artery to restore pulmonary flow.

In neonates or infants with profound cyanosis and markedly hypoplastic pulmonary arteries, a systemic-to-pulmonary shunt (e.g., modified Blalock–Taussig shunt, BTTS) may be employed as an initial palliative measure. This increases pulmonary blood flow, improves oxygenation, and promotes pulmonary artery growth in preparation for definitive repair.

Summary

TGA Type III is characterized by parallel circulations with mixing through ASD and VSD, complicated by pulmonary stenosis. The physiologic consequences include reduced pulmonary blood flow, hypoplastic pulmonary arteries, cyanosis, and a volume-deprived left ventricle. Surgical management must be tailored to the degree of PS: ASO with VSD closure for mild cases, Nikaidoh or truncal switch for moderate to severe obstruction, and Rastelli repair for severe PS or atresia. In selected patients, initial palliation with a systemic-to-pulmonary shunt may be necessary to stabilize circulation and prepare the pulmonary vasculature for definitive repair.