Hydraulic characterisation of a micro vascular plug for the pulmonary flow reduction in patients with congenital heart disease

Abstract

Purpose- Univentricular heart condition, such as the Hypoplastic Left Heart Syndrome (HLHS), denotes a severe Congenital Heart Disease (CHD). Newborn patients who are ineligible for a palliative surgical correction often suffer from pulmonary overperfusion and reduced systemic flow. This project aimed to hydraulically characterise a commercially available vascular plug (MVP - Medtronic, MN, USA) modified as a Pulmonary Flow Restrictor (PFR) and to investigate its personalisation towards a patient-specific approach to restore a balanced pulmonary-to-systemic (Q_p/Q_s) flow ratio.Methods- First we focused on assessing the hydraulic resistance of Micro Vascular Plugs (MVPs) in a Mock Circulatory Loop (MCL). We measured the pressure drop across three different device configurations (no, one and two holes) for flow rates up to 2 L/min at steady-state conditions. Additionally, we tested varying pipe diameters and compliances. To have a more realistic environment, the measurements were also performed in a 3D-printed geometry obtained from a HLHS patient's Computed Tomography (CT) scan. Additional Computational Fluid Dynamics (CFD) simulations allowed to look further into hemodynamics, washout of passive scalar analysis and thrombus risk model implementation based on platelets' activation.Results- The in vitro experiments revealed two key behaviours of the MVP in relation to flow rate. At low flow rates, hydraulic resistance is primarily determined by hole size, while at high flow rates, the pressure drop is mainly influenced by the ratio of MVP diameter to pipe diameter. The experimentally obtained results for hydraulic performance showed agreement with CFD simulations (RMSE = 2.5 mmHg for one hole and RMSE = 2.0 mmHg for two holes) and with analytical formulation (RMSE = 3.8 mmHg) at low flow rates (0 to 0.4 L/min). No major differences in washout time were observed between the one and two holes configurations of the MVP (approximately 0.48 s). Similarly, the thrombus risk model indicated minimal variation, with the scaled volume average of active platelet (AP) concentration increase differing by only 7\% between the two configurations. The scaling was implemented such that the part per million (ppm) increase to the initial value of 25e12 m-3 was monitored.Conclusion- Through in vitro and in silico investigations, we demonstrated that the hydraulic properties of the MVP can be personalized by adjusting the number of perforations and the MVP-to-pipe diameter ratio. Future studies will need to incorporate patient-specific parameters to tailor the MVP to individual needs towards improved patient outcomes.