Planar Particle Image Velocimetry for in vitro analysis of a mitral valve replacement

The Epygon valve (Affluent Medical) is the first ‘physiological’ biological transcatheter mitral prosthesis specifically designed to restore the natural blood flow vortex in the left ventricle. Its asymmetric design, characterized by a pericardial tissue mono-leaflet combined with a D-shaped annular ring, aims to accommodate annulus dynamics and ensure physiological ventricular filling and ejection. The objective of this study is to investigate the intraventricular fluid dynamics induced by the presence of the Epygon valve in mitral position, through two-dimensional Particle Image Velocimetry (2D PIV), by observing the flow fields under two cardiac output conditions: 3.5 L/min and 5 L/min. To this purpose, the ViVitro Pulse Duplicator system, equipped with a silicon ventricles and transparent chambers, was employed to simulate the left heart circulation, reproducing working conditions in compliance with UNI EN ISO 5840:2021 — namely, a heart rate of 70 bpm, a mean aortic pressure of 100 mmHg and a systolic duration of 35% of the cardiac cycle. A 0.9% NaCl saline solution, seeded with polyamide tracer particles, was used as working fluid. Flow was measured with an electromagnetic flowmeter, while pressure signals were acquired using piezoelectric sensors. The PIV setup consisted of a high-resolution CMOS camera (Dantec Dynamics, Hisense Zyla CMOS) and a dual-pulse Nd:YAG laser. A phase-locked PIV approach was employed to acquire 48 distinct phases over the cardiac cycle, with 250 images pairs for each phase. From the computed velocity fields, several hemodynamic parameters were extracted to qualitatively and quantitatively assess the intraventricular flow characteristics and valve performance: velocity magnitude, vorticity, Turbulent Kinetic Energy (TKE), Reynolds Shear Stress (RSS), shear rate, circulation per unit area and viscous dissipation. The results show that the main intraventricular flow structures are qualitatively similar under both C.O. conditions: the transmitral flow generates a diastolic vortex in the mid-ventricular region, as typically observed in physiological conditions. However, from a quantitative standpoint, higher parameters values are observed at 5.0 L/min due to the increased flow rate. Velocity magnitude was consistently greater at 5.0 L/min during the diastolic filling and the early ejection phases, with peak velocities exceeding 0.6 m/s compared to approximately 0.5 m/s at 3.5 L/min. Vorticity fields at both C.O. revealed the formation of the physiological diastolic vortex, similar to that observed with the native mitral valve. However, at 5 L/??min, vorticity values surpass –100 s⁻¹ across multiple diastolic phases, while such levels were reached at 3.5 L/min only when the vortex was fully developed. This trend was confirmed by the circulation parameter, which showed more negative values at higher C.O., indicating a stronger and more coherent rotational structure. Similarly, RSS, shear rate and TKE showed greater values during diastolic filling at 5.0 L/min, highlighting increased shear forces and enhanced turbulent activity, particularly during vortex formation. In conclusion, the Epygon valve demonstrates the capability to restore flow structures within the left ventricular phantom that closely resemble physiological patterns, owing to its design, which more closely replicates the native mitral valve anatomy. Notably, this physiological similarity is maintained across both tested hemodynamic conditions.