Background: Inadequate pulmonary blood flow through a right ventricle-to-pulmonary artery (RV-PA) shunt early after the Norwood operation can be remedied by adding a modified Blalock-Taussig (mBT) shunt. We used multiscale computational modeling to determine whether the stenotic RV-PA shunt should be left in situ or removed.
Methods: Models of the Norwood circulation were constructed with (1) a 5-mm RV-PA shunt, (2) a RV-PA shunt with 3- or 2-mm stenosis at the RV anastomosis, (3) a stenotic RV-PA shunt plus a 3.0- or 3.5-mm mBT shunt, or (4) a 3.5-mm mBT shunt. A hydraulic network that mathematically describes an entire circulatory system with pre-stage 2 hemodynamics was used to predict local dynamics within the Norwood circulation. Global variables including total cardiac output, mixed venous oxygen saturation, stroke work, and systemic oxygen delivery can be computed.
Results: Proximal stenosis of the RV-PA shunt results in decreased pulmonary blood flow, total cardiac output, mixed venous saturation, and oxygen delivery. Addition of a 3.0- or 3.5-mm mBT shunt leads to pulmonary overcirculation, lowers systemic oxygen delivery, and decreases coronary perfusion pressure. Diastolic runoff through the stenotic RV-PA shunt dramatically increases retrograde flow into the single ventricle. Removal of the stenotic RV-PA shunt balances systemic and pulmonary blood flow, eliminates regurgitant flow into the single ventricle, and improves systemic oxygen delivery.
Conclusions: Adding a mBT shunt to remedy a stenotic RV-PA shunt early after a Norwood operation can lead to pulmonary overcirculation and may decrease systemic oxygen delivery. The stenotic RV-PA shunt should be taken down. Conversion to an optimal mBT shunt is preferable to augmenting a stenotic RV-PA shunt with a smaller mBT shunt.