The difference between extreme Tetralogy of Fallot (T4F) and pulmonary atresia with ventricle septal defect (PA/VSD) is the anterograde pulmonary blood flow. It is speculated that the association of modified Blalock-Taussig shunt (mBTs) and additional pulmonary blood flow favours shunt thrombosis but promotes better pulmonary arterial (PA) growth. This study sought to compare (PA) growth after mBTs shunt between T4F and AP/VSD.

From 1995 to 2018, 79 mBTs were performed in infants (<1 years), 45 for T4F and 34 for AP/VSD. Using a 1:1 propensity score match analysis, 38 patients were included (n=19 in each group). The primary outcome was operative mortality, mBTs thrombosis, and PA growth.

After matching, the preoperative Nakata was similar (101±8mm²/m²in T4F; 106±8 in AP/VSD P=0.75). The age and weight were similar (24,3±5 days, 3.3±0.5kg in T4F; 24,15±4, 3.3±0.9 in AP/VSD P=0.84 and P=0.77 respectively). The mBTs size was similar (4.15±0.5mm in T4F; 4.3±0.5 in PA/VSD P=0.35). There was no difference in in-hospital mortality (n=0, in T4F; n=2, 11% in AP/VSD, P=0.14) and mBTs thrombosis (3,16% in T4F; 2,11% in AP/VSD, P=0.18). The time to extubation tended to be longer in T4F (5±1days vs. 2±1 P=0.06). The left and right PA diameter at time of biventricular repair were similar (7.5±0.5mm, 7±0.2 in T4F; 8.1±0.7mm, 7±1 in AP/VSD P=0.43 and P=0.78, Fig. 1) and the Nakata delta (112±23mm²/m²in T4F; 110±17 in AP/VSD P=0.78). Median time to complete repair was the same in the PA/VSD (12.26 [3.9-25] months) compared with T4F (9.7 [6.2–41.1] months) P=0.87). The interstage reintervention were similar (3.16% in T4F; 4.22% in AP/VSD, P=0.9).

Anterograde blood flow with mBTs did not increase the risk of mBTs thrombosis. We could not show benefit of anterograde blood flow with mBTS versus mBTS for pulmonary arteries growth. Anterograde blood flow did increase the time to extubation, probably by increasing total pulmonary blood flow.