Two slits good, four slits bad? Assessing the hemodynamic impact of modifications to microvascular plugs in pulmonary flow restriction using a bench-top model

BACKGROUND: In patients with functionally univentricular circulations, the flow restriction achieved by modifying microvascular plugs (MVPs) during percutaneous stage I palliation has not been widely quantified. This study evaluates how progressive modification of the polytetrafuoroethylene (PTFE) membrane of MVPs alters flow restriction using a bench-top model of uni-ventricular physiology. METHODS: A 3D-printed model mimicking branch pulmonary arteries in parallel with a systemic outflow was connected to a Harvard pulsatile pump. Two MVP-9Q devices, each modified with one, two, three, or four slits in the PTFE membrane, were placed in limbs representing left and right pulmonary arteries. Mathematical scaling produced a valid hemodynamic model matching neonatal univentricuar physiology. Flow (L/min) was measured using sensors placed on both pulmonary arteries and the systemic limb. Flow distribution between systemic and pulmonary limbs was calculated as a percentage of fixed total flow to determine the pulmonary (Qp) to systemic (Qs) flow ratio (Qp:Qs). RESULTS: With a baseline model representing 2:1 Qp:Qs ratio, MVPs with one slit reduced pulmonary flow (Qp) by 23%. Two slits reduced Qp by 21% and produced a Qp:Qs ratio closest to 1:1. Additional slits progressively increased Qp and reduced restriction (three-slits: 18% reduction, Qp:Qs 1.1:1; four-slits: 15% reduction, Qp:Qs 1.3:1). CONCLUSIONS: Incremental PTFE membrane modification generated proportional but nonlinear effects on flow distribution in a simulated univentricular circulation. Creating one or two slits provided the optimal balance between pulmonary and systemic flow, while more than two slits produced minimal restriction.