Two slits good, four slits bad? Assessing the hemodynamic impact of modifications to microvascular plugs in pulmonary...

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.

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).

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).

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.