Myocardial Biomechanics and the Consequent Differentially Expressed Genes of the Left Atrial Ligation Chick Embryonic Model of Hypoplastic Left Heart Syndrome

Fig. 1. Schematic summary of our methodology. The LAL surgery was conducted at HH21. At HH25, when biomechanical changes manifested, we imaged the embryonic heart, performed segmentation the myocardium, tracked myocardial strains, and performed image-based FE modeling of the heart. At HH30, we performed single-cell RNA sequencing of embryonic LV

Fig. 2. Three-dimensional reconstruction of the chick embryonic ventricle, segmented from 2D stack of ultrasound cine-images for a LAL embryo at HH25. 3D geometries at other time points of the cardiac cycle were re-animated using motion-tracking data. t time, T cardiac cycle duration, ES end-systole, mid mid-systole-diastole, ED end-diastole

Fig. 3. a 3D reconstructed ventricle epicardial and endocardial boundary, superimposed onto the quadratic ensemble averaged ultrasound image at HH25. b Average ventricle thickness of Normal and LAL hearts for the left and right ventricles at HH25

Fig. 4. a Reconstruction of the blood spaces in the chick embryonic heart at HH25, superimposed on the myocardial segmentation of the ventricle. Definitions of the myocardial circumferential and longitudinal axes are indicated as well. b Directions of maximum strain in the ventricle, calculated via the minimum eigenvector of the strain tensor. c, d The spatial-averaged strains in the minimum eigenvector direction for normal and LAL hearts in c LV and d RV respectively. Results were obtained from image motion-tracking

Fig. 5. a Pressure–volume loops obtained from FE model for 4 normal and 4 LAL samples. Active tension magnitude (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathbf{T}}_{\max}$$\end{document}Tmax) is tuned for each simulation to satisfy the maximum pressure criteria of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathbf{P}}_{\max}=$$\end{document}Pmax= 3.1 mmHg for Normal and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathbf{P}}_{\max}$$\end{document}Pmax = 2.6 mmHg for LAL cases. b The myocardial active tension that enabled a good fit to the maximum pressure criteria is compared

Fig. 6. Spatial distribution of Cauchy stress tensor magnitude obtained from FE models, plotted at the end-diastolic time point for samples Normal 1 and LAL 1

Fig. 7. a Spatially averaged stress in the minimum eigenvector direction (direction of maximum shortening) obtained from subject-specific FE models, plotted over the cardiac cycle, for 4 normal and 4 LAL chick embryonic ventricles. b, c Average temporal peak stress in minimum eigenvector direction in normal and LAL embryos for b LV and c RV, respectively

Fig. 8. Selected differentially expressed genes obtained from single-cell RNA sequencing of the normal and LAL chick embryonic heart at HH30 that are potentially important for mechanobiological origins of the hypoplastic LV morphogenesis