Quantifying cardiovascular flow dynamics during early development

Pulmonary Annulus Growth Pattern in Patients with Tetralogy of Fallot Prior to Surgical Repair

Objectives

The size of the pulmonary valve annulus often determines the feasibility of pulmonary valve preservation at the time of intracardiac repair of Tetralogy of Fallot. Currently, there is limited available data regarding the growth pattern and the determining factors that contribute towards pulmonary valve annulus growth.

Methods

This retrospective study included patients who underwent surgical repair of Tetralogy of Fallot with or without prior palliation. These patients had an echocardiogram at the time of initial diagnosis and a second echocardiogram prior to intracardiac repair. The sizes of the pulmonary annulus, the right and left pulmonary arteries with z-scores were recorded. Patients with improvement in the pulmonary annulus z-scores between the 2 echocardiographic examinations were allocated in Group I (n = 46) and Group II (n = 68) were those with no improvement.

Results

A total of 114 patients were included in the study. The right and left pulmonary arteries size and z scores improved significantly between the 2 echocardiograms. Although the median size of the pulmonary annulus increased between the 2 echocardiograms (6 and 7.9 mm; P<0.001), there was no significant change in the z-score (-2.2, -2.34; P = 0.185). Multivariate logistic regression analysis showed that gender, blood group, presence of collaterals, and palliation with Blalock-Taussig shunt had no impact on the improvement in pulmonary annulus z-score.

Conclusion

In Tetralogy of Fallot, the pulmonary valve annulus z-score may not change significantly prior to the intracardiac repair. Although in certain subgroups there may be an improvement, there was no specific factor that could be identified and had an influence on this improvement.

In Utero Programming of Testicular Cancer

It is well established that the intrauterine biological environment plays important roles in fetal development. In this review, we re-visit the hypothesis that testicular germ cell cancer (TGCC), especially in adolescents and young adults, has been programmed in utero. The origin for extreme in utero environments is mostly maternal driven and may be due to nutritional, physical and psychological stressful conditions that alter the optimal molecular and biophysical in utero environments. Moreover, precursors for TGCC may originate as early as during fertilization or implantation of the blastocyst. Further investigations of human developmental biology, both in vivo and in vitro, are needed in order to establish better understanding of in utero programming of future wellbeing or diseases.

A hybrid of light-field and light-sheet imaging to study myocardial function and intracardiac blood flow during zebrafish development

Biomechanical forces intimately contribute to cardiac morphogenesis. However, volumetric imaging to investigate the cardiac mechanics with high temporal and spatial resolution remains an imaging challenge. We hereby integrated light-field microscopy (LFM) with light-sheet fluorescence microscopy (LSFM), coupled with a retrospective gating method, to simultaneously access myocardial contraction and intracardiac blood flow at 200 volumes per second. While LSFM allows for the reconstruction of the myocardial function, LFM enables instantaneous acquisition of the intracardiac blood cells traversing across the valves. We further adopted deformable image registration to quantify the ventricular wall displacement and particle tracking velocimetry to monitor intracardiac blood flow. The integration of LFM and LSFM enabled the time-dependent tracking of the individual blood cells and the differential rates of segmental wall displacement during a cardiac cycle. Taken together, we demonstrated a hybrid system, coupled with our image analysis pipeline, to simultaneously capture the myocardial wall motion with intracardiac blood flow during cardiac development.

During the conception of the heart, cardiac muscular contraction and blood flow generate biomechanical forces to influence the functional and structural development. To elucidate the underlying biomechanical mechanisms, we have embraced the zebrafish system for the ease of genetic and pharmacological manipulations and its rapidity for organ development. However, acquiring the dynamic processes (space + time domain) in the small beating zebrafish heart remains a challenge. In the presence of a rapid heartbeat, microscopy is confined by temporal resolution to image the cardiac contraction and blood flow. In this context, we demonstrated an integrated light-sheet and light-field imaging system to visualize cardiac contraction along with the flowing blood cells inside the cardiac chambers. Assuming the periodicity of the cardiac cycle, we synchronized the image data in post-processing for 3-D reconstruction. We further quantified the velocity of the various regions of cardiac muscular contraction, and tracked the individual blood cells during the cardiac cycles. The time-dependent velocity maps allow for uncovering differential segments of cardiac contraction and relaxation, and for revealing the patterns of blood flow. Thus, our integrated light-sheet and light-field imaging system provides an experimental basis to further investigate cardiac function and development.

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.

Influence of blood flow on cardiac development

The role of hemodynamics in cardiovascular development is not well understood. Indeed, it would be remarkable if it were, given the dauntingly complex array of intricately synchronized genetic, molecular, mechanical, and environmental factors at play. However, with congenital heart defects affecting around 1 in 100 human births, and numerous studies pointing to hemodynamics as a factor in cardiovascular morphogenesis, this is not an area in which we can afford to remain in the dark. This review seeks to present the case for the importance of research into the biomechanics of the developing cardiovascular system. This is accomplished by i) illustrating the basics of some of the highly complex processes involved in heart development, and discussing the known influence of hemodynamics on those processes; ii) demonstrating how altered hemodynamic environments have the potential to bring about morphological anomalies, citing studies in multiple animal models with a variety of perturbation methods; iii) providing examples of widely used technological innovations which allow for accurate measurement of hemodynamic parameters in embryos; iv) detailing the results of studies in avian embryos which point to exciting correlations between various hemodynamic manipulations in early development and phenotypic defect incidence in mature hearts; and finally, v) stressing the relevance of uncovering specific biomechanical pathways involved in cardiovascular formation and remodeling under adverse conditions, to the potential treatment of human patients. The time is ripe to unravel the contributions of hemodynamics to cardiac development, and to recognize their frequently neglected role in the occurrence of heart malformation phenotypes.

Main pulmonary artery cross-section ratio is low in fetuses with tetralogy of Fallot and ductus arteriosus-dependent pulmonary circulation

OBJECTIVES

This study aimed to determine fetal echocardiographic features of tetralogy of Fallot in association with postnatal outcomes.

METHODS

The Z-scores of the main and bilateral pulmonary arteries and the aorta were measured, and the following variables were calculated in 13 fetuses with tetralogy of Fallot: pulmonary artery-to-aorta ratio and main pulmonary artery cross-section ratio - the main pulmonary artery diameter squared divided by the sum of the diameter squared of the left and right pulmonary arteries. Fetuses were classified as having ductus arteriosus-dependent or ductus arteriosus-independent pulmonary circulation.

RESULTS

We included two infants with pulmonary atresia and six infants with ductus-dependent pulmonary circulation, who underwent systemic-to-pulmonary shunt surgeries at ⩽1 month of age. The Z-scores of the main pulmonary artery and the pulmonary artery-to-aorta ratio in fetuses with ductus-dependent pulmonary circulation were lesser than those in fetuses with ductus independence, but not significantly. The main pulmonary artery cross-section ratio in fetuses with ductus dependence was significantly lesser (0.65±0.44 versus 1.56±0.48, p<0.005). Besides, the flow of the ductus arteriosus was directed from the aorta to the pulmonary artery in the ductus arteriosus-dependent group during the fetal period.

CONCLUSIONS

The main pulmonary artery cross-section ratio was the most significant variable for predicting postnatal outcomes in fetuses with tetralogy of Fallot.

Heart function and hemodynamic analysis for zebrafish embryos

The Zebrafish has emerged to become a powerful vertebrate animal model for cardiovascular research in recent years. Its advantages include easy genetic manipulation, transparency, small size, low cost, and the ability to survive without active circulation at early stages of development. Sequencing the whole genome and identifying ortholog genes with human genome made it possible to induce clinically relevant cardiovascular defects via genetic approaches. Heart function and disturbed hemodynamics need to be assessed in a reliable manner for these disease models in order to reveal the mechanobiology of induced defects. This effort requires precise determination of blood flow patterns as well as hemodynamic stress (i.e., wall shear stress and pressure) levels within the developing heart. While traditional approach involves time-lapse brightfield microscopy to track cell and tissue movements, in more recent studies fast light-sheet fluorescent microscopes are utilized for that purpose. Integration of more complicated techniques like particle image velocimetry and computational fluid dynamics modeling for hemodynamic analysis holds a great promise to the advancement of the Zebrafish studies. Here, we discuss the latest developments in heart function and hemodynamic analysis for Zebrafish embryos and conclude with our future perspective on dynamic analysis of the Zebrafish cardiovascular system. Developmental Dynamics 246:868-880, 2017. © 2017 Wiley Periodicals, Inc.

Four-dimensional live imaging of hemodynamics in mammalian embryonic heart with Doppler optical coherence tomography

Hemodynamic analysis of the mouse embryonic heart is essential for understanding the functional aspects of early cardiogenesis and advancing the research in congenital heart defects. However, high-resolution imaging of cardiac hemodynamics in mammalian models remains challenging, primarily due to the dynamic nature and deep location of the embryonic heart. Here we report four-dimensional micro-scale imaging of blood flow in the early mouse embryonic heart, enabling time-resolved measurement and analysis of flow velocity throughout the heart tube. Our method uses Doppler optical coherence tomography in live mouse embryo culture, and employs a post-processing synchronization approach to reconstruct three-dimensional data over time at a 100 Hz volume rate. Experiments were performed on live mouse embryos at embryonic day 9.0. Our results show blood flow dynamics inside the beating heart, with the capability for quantitative flow velocity assessment in the primitive atrium, atrioventricular and bulboventricular regions, and bulbus cordis. Combined cardiodynamic and hemodynamic analysis indicates this functional imaging method can be utilized to further investigate the mechanical relationship between blood flow dynamics and cardiac wall movement, bringing new possibilities to study biomechanics in early mammalian cardiogenesis. Four-dimensional live hemodynamic imaging of the mouse embryonic heart at embryonic day 9.0 using Doppler optical coherence tomography, showing directional blood flows in the sinus venosus, primitive atrium, atrioventricular region and vitelline vein.

4D subject-specific inverse modeling of the chick embryonic heart outflow tract hemodynamics

Blood flow plays a critical role in regulating embryonic cardiac growth and development, with altered flow leading to congenital heart disease. Progress in the field, however, is hindered by a lack of quantification of hemodynamic conditions in the developing heart. In this study, we present a methodology to quantify blood flow dynamics in the embryonic heart using subject-specific computational fluid dynamics (CFD) models. While the methodology is general, we focused on a model of the chick embryonic heart outflow tract (OFT), which distally connects the heart to the arterial system, and is the region of origin of many congenital cardiac defects. Using structural and Doppler velocity data collected from optical coherence tomography, we generated 4D ([Formula: see text]) embryo-specific CFD models of the heart OFT. To replicate the blood flow dynamics over time during the cardiac cycle, we developed an iterative inverse-method optimization algorithm, which determines the CFD model boundary conditions such that differences between computed velocities and measured velocities at one point within the OFT lumen are minimized. Results from our developed CFD model agree with previously measured hemodynamics in the OFT. Further, computed velocities and measured velocities differ by [Formula: see text]15 % at locations that were not used in the optimization, validating the model. The presented methodology can be used in quantifications of embryonic cardiac hemodynamics under normal and altered blood flow conditions, enabling an in-depth quantitative study of how blood flow influences cardiac development.

Systems biology and biomechanical model of heart failure

Heart failure is seen as a complex disease caused by a combination of a mechanical disorder, cardiac remodeling and neurohormonal activation. To define heart failure the systems biology approach integrates genes and molecules, interprets the relationship of the molecular networks with modular functional units, and explains the interaction between mechanical dysfunction and cardiac remodeling. The biomechanical model of heart failure explains satisfactorily the progression of myocardial dysfunction and the development of clinical phenotypes. The earliest mechanical changes and stresses applied in myocardial cells and/or myocardial loss or dysfunction activate left ventricular cavity remodeling and other neurohormonal regulatory mechanisms such as early release of natriuretic peptides followed by SAS and RAAS mobilization. Eventually the neurohormonal activation and the left ventricular remodeling process are leading to clinical deterioration of heart failure towards a multi-organic damage. It is hypothesized that approaching heart failure with the methodology of systems biology we promote the elucidation of its complex pathophysiology and most probably we can invent new therapeutic strategies.

Biomechanics of early cardiac development

Biomechanics affect early cardiac development, from looping to the development of chambers and valves. Hemodynamic forces are essential for proper cardiac development, and their disruption leads to congenital heart defects. A wealth of information already exists on early cardiac adaptations to hemodynamic loading, and new technologies, including high-resolution imaging modalities and computational modeling, are enabling a more thorough understanding of relationships between hemodynamics and cardiac development. Imaging and modeling approaches, used in combination with biological data on cell behavior and adaptation, are paving the road for new discoveries on links between biomechanics and biology and their effect on cardiac development and fetal programming.

Fluid dynamics of heart development

The morphology, muscle mechanics, fluid dynamics, conduction properties, and molecular biology of the developing embryonic heart have received much attention in recent years due to the importance of both fluid and elastic forces in shaping the heart as well as the striking relationship between the heart's evolution and development. Although few studies have directly addressed the connection between fluid dynamics and heart development, a number of studies suggest that fluids may play a key role in morphogenic signaling. For example, fluid shear stress may trigger biochemical cascades within the endothelial cells of the developing heart that regulate chamber and valve morphogenesis. Myocardial activity generates forces on the intracardiac blood, creating pressure gradients across the cardiac wall. These pressures may also serve as epigenetic signals. In this article, the fluid dynamics of the early stages of heart development is reviewed. The relevant work in cardiac morphology, muscle mechanics, regulatory networks, and electrophysiology is also reviewed in the context of intracardial fluid dynamics.

Blood velocity pulse quantification in the human conjunctival pre-capillary arterioles

Axial red blood cell velocity pulse was quantified throughout its period by high speed video microcinematography in the human eye. In 30 conjunctival precapillary arterioles (6 to 12 microm in diameter) from 15 healthy humans, axial velocities ranged from 0.4 (the minimum of all the end diastolic values) to 5.84 mm/s (the maximum of all the peak systolic values). With the velocity pulse properly quantified, two parameters can be estimated: (1) the average velocity of the pulse during a cardiac cycle AVV (average velocity value) and (2) the magnitude of the pulsation using Pourcelot's resistive index RI. These parameters are important for the estimation of other hemodynamic parameters such as the average volume flow and the average shear stress. The results of this study revealed that the AVV in the human precapillary arterioles ranged between 0.52 and 3.26 mm/s with a mean value for all microvessels of 1.66 mm/s+/-0.11(SE). The RI ranged between 35.5% and 81.8% with a mean value of 53.1%+/-2.2. Quantitative information was obtained for the first time on the velocity pulse characteristics just before the human capillary bed.

Zebrafish genetic models for arrhythmia

Over the last decade the zebrafish has emerged as a major genetic model organism. While stimulated originally by the utility of its transparent embryos for the study of vertebrate organogenesis, the success of the zebrafish was consolidated through multiple genetic screens, sequencing of the fish genome by the Sanger Center, and the advent of extensive genomic resources. In the last few years the potential of the zebrafish for in vivo cell biology, physiology, disease modeling and drug discovery has begun to be realized. This review will highlight work on cardiac electrophysiology, emphasizing the arenas in which the zebrafish complements other in vivo and in vitro models; developmental physiology, large-scale screens, high-throughput disease modeling and drug discovery. Much of this work is at an early stage, and so the focus will be on the general principles, the specific advantages of the zebrafish and on future potential.

The development of the heart and microcirculation: role of shear stress

It is evident that hemodynamic factors have a dominant function already during early cardiogenesis. Flow and ensuing shear stress are sensed by endothelial cells by, ciliary modified, cytoskeletal deformation which then activates a number of subcellular structures and molecules. Shear stress dependent changes mostly converge towards NF kappa B signaling and DNA binding, thereby altering metabolic paths and influencing differentiation of the cells. Geometry of the vascular system heavily affects the flow and shear patterns, as is the case in the adult vasculature where atheroprone areas nicely coincide with the frequency of the primary cilium as shear stress sensor.

The role of shear stress on ET-1, KLF2, and NOS-3 expression in the developing cardiovascular system of chicken embryos in a venous ligation model

In this review, the role of wall shear stress in the chicken embryonic heart is analyzed to determine its effect on cardiac development through regulating gene expression. Therefore, background information is provided for fluid dynamics, normal chicken and human heart development, cardiac malformations, cardiac and vitelline blood flow, and a chicken model to induce cardiovascular anomalies. A set of endothelial shear stress-responsive genes coding for endothelin-1 (ET-1), lung Krüppel-like factor (LKLF/KLF2), and endothelial nitric oxide synthase (eNOS/NOS-3) are active in development and are specifically addressed.