In vitro characterisation of a biological monoleaflet mitral valve prosthesis through particle image velocimetry

Epygon valve is the first biological transcatheter mitral prosthesis which can restore the natural blood flow vortex in the left ventricle, optimizing the ejec- tion function.The aim of the study is to in vitro investigate the fluid dynamic that develops inside a left ventricle (LV) phantom in presence of the Epygon prosthesis valve in the mitral position through two-dimentional Particle Im- age Velocimetry (PIV). In particular, the valve is tested in an anatomical and in an non anatomical orientation (180° valve rotation). To this purpose, a commercially-available cardiovascular simulator (Vivitro PulseDuplicator) was employed to simulate the left heart and to reproduce working conditions ac- cording to the ISO 5840-2021 standard. The working fluid is 0.9% w/v NaCl solution dispersed with polyamide particles. The flow rate was measured using an electromagnetic flowmeter (model 501, Carolina Medical Electronics), and pressure signals using piezoelectric sensors (model 6069, Utah medical). Firstly, a hydraulic characterization of the testbench was performed by varying the CO in the range 2 – 6.5 l/min. Secondly, a high-resolution camera and a dual-pulse Nd:YAG laser allowed to acquire images of the fluid domain of inter- est. The hydraulic behaviour of the prosthesis was assessed in terms of Effective Orifice Area (EOA) and regurgitation fraction. Upon determining the correct functioning of the setup, the acquisitions were performed with test parameters according to the ISO 5840 standard (cardiac output, CO, of 5 L/min, heart rate of 70 bpm, systolic duration of 35% of the period, mean aortic pressure of 100 mmHg). In order to assess the velocity and vorticity vector fields 600 images were acquired, examining nine time instants during the cardiac cycle, which provide detailed information about the development of the flow. In the anatomical configuration of the valve regarding the left ventricular flow, it results characterized by the formation and evolution of a clockwise-rotating vortex throughout the cardiac cycle, which, as expected, facilitates fluid ejection from the ventricle. Converserly with an 180° valve rotation, as expected, the vortical structures formed rotate in the opposite direction. These results show how a mispositioning of the Epygon valve can compromise its fluid dynamic performance, in particular by obstructing the anatomical vortex development, restricting the LV blood ejection to the aortic valve, and also impacting velocity range values.