A Novel Left Heart Simulator for the Multi-modality Characterization of Native Mitral Valve Geometry and Fluid Mechanics

Abstract

Numerical models of the mitral valve have been used to elucidate mitral valve function and mechanics. These models have evolved from simple two-dimensional approximations to complex three-dimensional fully coupled fluid structure interaction models. However, to date these models lack direct one-to-one experimental validation. As computational solvers vary considerably, experimental benchmark data are critically important to ensure model accuracy. In this study, a novel left heart simulator was designed specifically for the validation of numerical mitral valve models. Several distinct experimental techniques were collectively performed to resolve mitral valve geometry and hemodynamics. In particular, micro-computed tomography was used to obtain accurate and high-resolution (39 µm voxel) native valvular anatomy, which included the mitral leaflets, chordae tendinae, and papillary muscles. Threedimensional echocardiography was used to obtain systolic leaflet geometry for direct comparison of resultant leaflet kinematics. Stereoscopic digital particle image velocimetry provided all three components of fluid velocity through the mitral valve, resolved every 25 ms in the cardiac cycle. A strong central filling jet was observed during peak systole, with minimal out-of-plane velocities (V~0.6m/s). In addition, physiologic hemodynamic boundary conditions were defined and all data were synchronously acquired through a central trigger. Finally, the simulator is a precisely controlled environment, in which flow conditions and geometry can be systematically prescribed and resultant valvular function and hemodynamics assessed. Thus, these data represent the first comprehensive database of high fidelity experimental data, critical for extensive validation of mitral valve fluid structure interaction simulations.

Bench Models for Assessing the Mechanics of Mitral Valve Repair and Percutaneous Surgery

“…A third advance would be the development of simulators capable of multi-modality analyses similar to that describe by Rabbah et al 36 New simulators capable of being imaged using multiple modalities (micro-computed tomorgraphy, computed tomography, echocardiography, and magnetic resonance imaging) may provide key insight to the level of imaging detail required to fully assess MV function. This will provide new benchmarks for MV imaging and improve clinical analyses of patient MV function.…”

“…4). 36 In this method, the rigid model's chambers (with the MV mounted inside) are inserted into a micro-computed tomography scanner such that the MV is imaged in a configuration similar to that achieved during pulsatile ventricular filling. These scans have provided unprecedented details for leaflet geometry and chordae architectures which currently are not possible using computed tomography, magnetic resonance imaging, or echocardiography.…”

“…1a). 5,8,12,[18][19][20]22,23,[26][27][28][29][30][31][32][34][35][36][37][38][39]44,[46][47][48] These components are supplemented by systemic resistances and compliances to control cardiac output, systemic pressures, and dampen undesired flow and pressure oscillations within the rigid chambers of the system.…”

“…These models have been used to evaluate multiple repairs on a single MV, changes in leaflet mobility and coaptation, improvements in transmitral hemodynamics, and provide direct quantitative measures of tissue loading. [3][4][5]8,9,[11][12][13][14][17][18][19][20][22][23][24][26][27][28][29][30][31][32][33][34][35][36][37][38][39]41,42,44,[46][47][48] Within the limitation of each setup, these models are more risk averse, controlled, reproducible, and less expensive than clinical studies or large animal models. Understanding the advantages and limits of these models will aid the interpretation of their resulting data, inform future experimental evaluations, and further the translation of results to procedure and device development.…”

Multi-modal Pipeline for Comprehensive Validation of Mitral Valve Geometry and Functional Computational Models

“…A novel closed-loop left heart simulator ( Fig. 1) was utilized to carry out controlled in-vitro MV experiments [7,8]. It allows for precise control of annular and subvalvular MV geometry at physiological left heart hemodynamics.…”