4-D Computational Modeling of Cardiac Outflow Tract Hemodynamics over Looping Developmental Stages in Chicken Embryos

Segmentation of beating embryonic heart structures from 4-D OCT images using deep learning

Optical coherence tomography (OCT) has been used to investigate heart development because of its capability to image both structure and function of beating embryonic hearts. Cardiac structure segmentation is a prerequisite for the quantification of embryonic heart motion and function using OCT. Since manual segmentation is time-consuming and labor-intensive, an automatic method is needed to facilitate high-throughput studies. The purpose of this study is to develop an image-processing pipeline to facilitate the segmentation of beating embryonic heart structures from a 4-D OCT dataset. Sequential OCT images were obtained at multiple planes of a beating quail embryonic heart and reassembled to a 4-D dataset using image-based retrospective gating. Multiple image volumes at different time points were selected as key-volumes, and their cardiac structures including myocardium, cardiac jelly, and lumen, were manually labeled. Registration-based data augmentation was used to synthesize additional labeled image volumes by learning transformations between key-volumes and other unlabeled volumes. The synthesized labeled images were then used to train a fully convolutional network (U-Net) for heart structure segmentation. The proposed deep learning-based pipeline achieved high segmentation accuracy with only two labeled image volumes and reduced the time cost of segmenting one 4-D OCT dataset from a week to two hours. Using this method, one could carry out cohort studies that quantify complex cardiac motion and function in developing hearts.

Effect of Blood Flow on Cardiac Morphogenesis and Formation of Congenital Heart Defects

Congenital heart disease (CHD) affects about 1 in 100 newborns and its causes are multifactorial. In the embryo, blood flow within the heart and vasculature is essential for proper heart development, with abnormal blood flow leading to CHD. Here, we discuss how blood flow (hemodynamics) affects heart development from embryonic to fetal stages, and how abnormal blood flow solely can lead to CHD. We emphasize studies performed using avian models of heart development, because those models allow for hemodynamic interventions, in vivo imaging, and follow up, while they closely recapitulate heart defects observed in humans. We conclude with recommendations on investigations that must be performed to bridge the gaps in understanding how blood flow alone, or together with other factors, contributes to CHD.

Hemodynamic and Structural Comparison of Human Fetal Heart Development Between Normally Growing and Hypoplastic Left Heart Syndrome-Diagnosed Hearts

Congenital heart defects (CHDs) affect a wide range of societies with an incidence rate of 1.0–1.2%. These defects initiate at the early developmental stage and result in critical health disorders. Although genetic factors play a role in the formation of CHDs, the occurrence of cases in families with no history of CHDs suggests that mechanobiological forces may also play a role in the initiation and progression of CHDs. Hypoplastic left heart syndrome (HLHS) is a critical CHD, which is responsible for 25–40% of all prenatal cardiac deaths. The comparison of healthy and HLHS hearts helps in understanding the main hemodynamic differences related to HLHS. Echocardiography is the most common imaging modality utilized for fetal cardiac assessment. In this study, we utilized echocardiographic images to compare healthy and HLHS human fetal hearts for determining the differences in terms of heart chamber dimensions, valvular flow rates, and hemodynamics. The cross-sectional areas of chamber dimensions are determined from 2D b-mode ultrasound images. Valvular flow rates are measured via Doppler echocardiography, and hemodynamic quantifications are performed with the use of computational fluid dynamics (CFD) simulations. The obtained results indicate that cross-sectional areas of the left and right sides of the heart are similar for healthy fetuses during gestational development. The left side of HLHS heart is underdeveloped, and as a result, the hemodynamic parameters such as flow velocity, pressure, and wall shear stress (WSS) are significantly altered compared to those of healthy hearts.

Computational Modeling of Blood Flow Hemodynamics for Biomechanical Investigation of Cardiac Development and Disease

The heart is the first functional organ in a developing embryo. Cardiac development continues throughout developmental stages while the heart goes through a serious of drastic morphological changes. Previous animal experiments as well as clinical observations showed that disturbed hemodynamics interfere with the development of the heart and leads to the formation of a variety of defects in heart valves, heart chambers, and blood vessels, suggesting that hemodynamics is a governing factor for cardiogenesis, and disturbed hemodynamics is an important source of congenital heart defects. Therefore, there is an interest to image and quantify the flowing blood through a developing heart. Flow measurement in embryonic fetal heart can be performed using advanced techniques such as magnetic resonance imaging (MRI) or echocardiography. Computational fluid dynamics (CFD) modeling is another approach especially useful when the other imaging modalities are not available and in-depth flow assessment is needed. The approach is based on numerically solving relevant physical equations to approximate the flow hemodynamics and tissue behavior. This approach is becoming widely adapted to simulate cardiac flows during the embryonic development. While there are few studies for human fetal cardiac flows, many groups used zebrafish and chicken embryos as useful models for elucidating normal and diseased cardiogenesis. In this paper, we explain the major steps to generate CFD models for simulating cardiac hemodynamics in vivo and summarize the latest findings on chicken and zebrafish embryos as well as human fetal hearts.

New Concepts in the Development and Malformation of the Arterial Valves

Although in many ways the arterial and atrioventricular valves are similar, both being derived for the most part from endocardial cushions, we now know that the arterial valves and their surrounding structures are uniquely dependent on progenitors from both the second heart field (SHF) and neural crest cells (NCC). Here, we will review aspects of arterial valve development, highlighting how our appreciation of NCC and the discovery of the SHF have altered our developmental models. We will highlight areas of research that have been particularly instructive for understanding how the leaflets form and remodel, as well as those with limited or conflicting results. With this background, we will explore how this developmental knowledge can help us to understand human valve malformations, particularly those of the bicuspid aortic valve (BAV). Controversies and the current state of valve genomics will be indicated.

Label-free optical imaging in developmental biology [Invited]

Application of optical imaging in developmental biology marks an exciting frontier in biomedical optics. Optical resolution and imaging depth allow for investigation of growing embryos at subcellular, cellular, and whole organism levels, while the complexity and variety of embryonic processes set multiple challenges stimulating the development of various live dynamic embryonic imaging approaches. Among other optical methods, label-free optical techniques attract an increasing interest as they allow investigation of developmental mechanisms without application of exogenous markers or fluorescent reporters. There has been a boost in development of label-free optical imaging techniques for studying embryonic development in animal models over the last decade, which revealed new information about early development and created new areas for investigation. Here, we review the recent progress in label-free optical embryonic imaging, discuss specific applications, and comment on future developments at the interface of photonics, engineering, and developmental biology.

Characterisation of the developing heart in a pressure overloaded model utilising RNA sequencing to direct functional analysis

Cardiogenesis is influenced by both environmental and genetic factors, with blood flow playing a critical role in cardiac remodelling. Perturbation of any of these factors could lead to abnormal heart development and hence the formation of congenital heart defects. Although abnormal blood flow has been associated with a number of heart defects, the effects of abnormal pressure load on the developing heart gene expression profile have to date not clearly been defined. To determine the heart transcriptional response to haemodynamic alteration during development, outflow tract (OFT) banding was employed in the chick embryo at Hamburger and Hamilton stage (HH) 21. Stereological and expression studies, including the use of global expression analysis by RNA sequencing with an optimised procedure for effective globin depletion, were subsequently performed on HH29 OFT-banded hearts and compared with sham control hearts, with further targeted expression investigations at HH35. The OFT-banded hearts were found to have an abnormal morphology with a rounded appearance and left-sided dilation in comparison with controls. Internal analysis showed they typically had a ventricular septal defect and reductions in the myocardial wall and trabeculae, with an increase in the lumen on the left side of the heart. There was also a significant reduction in apoptosis. The differentially expressed genes were found to be predominately involved in contraction, metabolism, apoptosis and neural development, suggesting a cardioprotective mechanism had been induced. Therefore, altered haemodynamics during development leads to left-sided dilation and differential expression of genes that may be associated with stress and maintaining cardiac output.