Biology subjects

Wang, V. Y.

Publications and source records attributed to Wang, V. Y..

4 recordsLinked to original sources

bioRxiv2021

A Framework for Evaluating Myocardial Stiffness Using 3D-Printed Hearts

MRI-driven computational modeling is increasingly used to simulate in vivo cardiac mechanical behavior and estimate subject-specific myocardial stiffness. However, in vivo validation of these estimates is exceedingly difficult due to the lack of a known ground-truth in vivo myocardial stiffness. We have developed 3D-printed heart phantoms of known myocardium-mimicking stiffness and MRI relaxation properties and incorporated the heart phantoms within a highly controlled MRI-compatible setup to simulate in vivo diastolic filling. The setup enables the acquisition of experimental data needed to evaluate myocardial stiffness using computational constitutive modeling: phantom geometry, loading pressures, boundary conditions, and filling strains. The pressure-volume relationship obtained from the phantom setup was used to calibrate an in silico model of the heart phantom undergoing simulated diastolic filling. The model estimated stiffness was compared with ground-truth stiffness obtained from uniaxial tensile testing. Ultimately, the setup is designed to enable extensive validation of MRI and FEM-based myocardial stiffness estimation frameworks.

bioengineering↗

bioRxiv2019

A novel MRI-based finite element modeling method for calculation of myocardial ischemia effect in patients with functional mitral regurgitation.

BackgroundFunctional Mitral Regurgitation (FMR) affects nearly 3 million patients in the United States. Conventional indices are limited for predicting FMR response to coronary revascularization (REVASC). Uncertainty as to which patients will respond to REVASC alone impedes rational decision-making regarding FMR management. Determination of myocardial material parameters associated with ischemic myocardium will address knowledge gaps regarding the impact of ischemia on regional cardiac muscle.\n\nMethodWe proposed a novel MRI-based finite element (FE) modeling method to determine the effect of ischemia on myocardial contractility. The method was applied to two patients with multi-vessel coronary disease and FMR and one healthy volunteer. Cardiac MRI (CMR) included cine-MRI, gadolinium-enhanced stress perfusion, late gadolinium enhancement (LGE), and non-invasive tagged MRI (CSPAMM). The left ventricular (LV) FE model was divided into 17 sectors. Sector-specific circumferential and longitudinal end-systolic strain and LV volume from CSPAMM were used in a formal optimization to determine the sector based myocardial contractility, Tmax.\n\nResultsThe FE optimization successfully converged with good agreement between calculated and experimental end-systolic strain and LV volumes. Specifically, the optimized TmaxH for Patient 1, Patient 2, and the volunteer was 336.8 kPa, 401.4 kPa, and 259.4 kPa and for Patient 1 and Patient 2 was 0.44 and 0.\n\nConclusionWe developed a novel computational method able to predict the effect of myocardial ischemia in patients with FMR. This method can be used to predict the effect of ischemia on the regional myocardium and promises to facilitate better understanding of FMR response to REVASC.

bioengineering↗

bioRxiv2019

Mechanical effects of MitraClip on leaflet stress and myocardial strain in functional mitral regurgitation: A finite element modeling study.

PurposeMitraClip is the sole percutaneous device approved for functional mitral regurgitation (MR; FMR) but MR recurs in over one third of patients. As device-induced mechanical effects are a potential cause for MR recurrence, we tested the hypothesis that MitraClip increases leaflet stress and procedure-related strain in sub-valvular left ventricular (LV) myocardium in FMR associated with coronary disease (FMR-CAD).\n\nMethodsSimulations were performed using finite element models of the LV + mitral valve based on MRI of 5 sheep with FMR-CAD. Models were modified to have a 20% increase in LV volume ({uparrow}LV_VOLUME) and MitraClip was simulated with contracting beam elements (virtual sutures) placed between nodes in the center edge of the anterior (AL) and posterior (PL) mitral leaflets. Effects of MitraClip on leaflet stress in the peri-MitraClip region of AL and PL, septo-lateral annular diameter (SLAD), and procedure-related radial strain (Err) in the sub-valvular myocardium were calculated.\n\nResultsMitraClip increased peri-MitraClip leaflet stress at end-diastole (ED) by 22.3{+/-}7.1 kPa (p<0.0001) in AL and 14.8{+/-}1.2 kPa (p<0.0001) in PL. MitraClip decreased SLAD by 6.1{+/-}2.2 mm (p<0.0001) and increased Err in the sub-valvular lateral LV myocardium at ED by 0.09{+/-}0.04 (p<0.0001)). Furthermore, MitraClip in {uparrow}LV_VOLUME was associated with persistent effects at ED but also at end-systole where peri-MitraClip leaflet stress was increased in AL by 31.9{+/-}14.4 kPa (p=0.0268) and in PL by 22.5{+/-}23.7 kPa (p=0.0101).\n\nConclusionsMitraClip for FMR-CAD increases mitral leaflet stress and radial strain in LV sub-valvular myocardium. Mechanical effects of MitraClip are augmented by LV enlargement.

bioengineering↗

bioRxiv2019

Left Ventricular Chamber Shape During Vena Caval Occlusion: Improved MRI-based Measurement of the End-Systolic Pressure-Volume Relationship in Normal Sheep

The left ventricular (LV) end-systolic pressure volume relationship (ES; ESPVR) is the cornerstone of systolic LV function analysis. Recently, it became possible to measure 2D LV chamber shape during vena cava occlusion (VCO) with MRI. We used an improved level-set semi-automatic segmentation method (LSSM) to determine the effect of VCO on LV geometry, ES pressure area (PA) and ESPVR. 10 healthy adult sheep were anesthetized. LV pressure transducer and inferior vena cava (IVC) balloon catheter were percutaneously inserted. Ferumoxytol (0.125 ml/kg iv; AMAG Pharmaceuticals, Waltham, MA) was given to enhance blood pool contrast. LV pressure and 2D retrospectively-gated cine MRI of LV cross sections 25 (Apex), 50 (Mid) and 75% (Base) of the distance from the apex to the base of the LV were obtained during separate IVC balloon inflations (VCO). LV pressure was digitally filtered and LV chamber segmented with the LSSM. Cross sectional area, major and minor axes, major axis orientation, ESPAR and ESPVR were calculated. The LSSM had excellent reliability. All cross sections became more elliptical during VCO. The orientation (angle) of each major axis relative to the anterior RV insertion shifted during VCO. However, the orientation remained toward the septum. There was chamber collapse (LV area < 0.25 cm2) at the apical level during VCO (7 cases). ESPAR was non-linear at all levels. ESPVR was non-linear because of apical collapse. In conclusion, MRI-based measurement of LV geometry, ESPAR and ESPVR during VCO is a valuable method that may lead to improved understanding of systolic LV function. New and NoteworthyReal-time MRI was used to continuously measure the LV PA relationship as loading conditions were transiently varied in anesthetized sheep. All three examined cross-sections became more elliptical during VCO. The ESPAR were non-linear at all three cross-sections. Chamber collapse at the apical level during VCO resulted in a non-linear ESPVR. The heart contracted in a non-concentric manner during VCO which could inform modeling studies and elucidate mechanisms underlying LV adaptations to sudden load changes.

bioengineering↗