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

Hypoplastic left heart syndrome-a scoping review

Background

An estimated 3% of all newborns with congenital heart disease develop hypoplastic left heart syndrome (HLHS), making it a prominent cause of mortality in this group if surgical procedures or a heart transplant are not implemented. While compelling evidence supports a genetic element, identifying a particular genetic cause is limited to a subgroup of patients, indicating a complex and multifaceted origin for this condition. The objective of this scientific contribution was to identify, synthesize, and analyze the scientific knowledge produced regarding the implications of researching on HLHS in a scoping review.

Methods

The search for articles was diligently conducted between January 1, 2019 and February 20, 2025 on the PubMed/MEDLINE, Scopus, Web of Science, and Cochrane databases. This search was assiduously complemented by a gray search. It included internet browsers (e.g., Google) and medical textbooks. The following research question steered our study: "What are the basic data on the etiology and pathogenesis on HLHS?" All stages of the selection process were iwis carried out by the single author.

Results

Of the 1,364 articles found, 75 were included in the sample for analysis, which was implemented with an additional 25 articles from references and gray literature. The studies analyzed indicated that HLHS is one of the most complex congenital heart defects, characterized by small or hypoplastic left-sided heart structures and a dominant right ventricle. The Fontan circulation and the phased surgical technique that it entails have been the cornerstones of HLHS patient care since its debut some 40 years ago. Although there is considerable genetic evidence for HLHS, the exact genetic cause of this cardiologic entity is still not well known. HLHS remains genetically heterogeneous. There is evidence of incomplete penetrance for the C57Bl/6J-b2b635Clo/J (Ohia) mice.

Conclusions

HLHS is a complex and complicate congenital heart disease, which requires further investigation. In this article, I further explore the involvement of the endocardium in the progression of ventricular hypoplasia, therefore offering a potential explanation for the morphological alterations observed in the disease as a result of compromised blood flow to the developing ventricle. These findings may support a new paradigm for the complicated genetics of this congenital heart defect and there is some evidence that HLHS can originate genetically in a combinatorial approach.

Identification of Hypoplastic Left Heart Genotypes and Phenotypes; The Window toward Future Cell-Based Therapy: A Narrative Review

Hypoplastic left heart syndrome (HLHS) is a prevalent and lethal type of single ventricle anomaly. During early prenatal evaluations, left heart hypoplasia may be neglected due to its progressive features. It is a heterogeneous congenital heart disease with different phenotypes. Currently, there is no definite treatment for HLHS. This is in part due to its heterogeneous phenotypes that require different management. In addition, hindrances in recognizing the etiologic factors do not allow early preventive or therapeutic procedures. Phenotypic determination is fundamental to identifying the etiologic factors and therapeutic strategies. This review article introduces comprehensive information about different phenotypes and genotypes of HLHS and their novel molecular strategy. Genetic defects and flow-mediated mechanisms are the main known factors of HLHS. Recent studies reported additional data about its nonmendelian genetic origins associated with heterogeneous phenotypes. The genetic defects influence endocardium or cardiomyocyte development to yield early or late valve deformities and myocardial malformations. The new molecular therapeutic methods are essentially based on genetic etiologies. The principal therapeutic purpose is reinforcing the function of the right ventricle in patients with nonfunctional left ventricles. The ultimate desire is to create a biventricular heart in selected cases.

Developmental and Evolutionary Heart Adaptations Through Structure-Function Relationships

While the heart works as an efficient pump, it also has a high level of adaptivity by changing its structure to maintain function during healthy and diseased states. In this Review, we present examples of structure-function relationships across species and throughout embryonic development in mammals and birds. We also summarize current research on avian models aiming at understanding how biophysical and biological mechanisms closely interact during heart formation. We conclude by underscoring similarities between cardiac adaptations and structural changes over developmental and evolutionary time scales and how understanding the mechanisms behind these adaptations can help prevent or alleviate the effects of cardiac malformations and contribute to cardiac regeneration efforts.

In Vivo and In Vitro Approaches to Modeling Hypoplastic Left Heart Syndrome

PURPOSE OF REVIEW

Hypoplastic left heart syndrome (HLHS) is a critical congenital heart defect characterized by the underdevelopment of left-sided heart structures, leading to significant circulatory challenges, and necessitating multiple surgeries for survival. Despite advancements in surgical interventions, long-term outcomes often involve heart failure, highlighting the need for a deeper understanding of HLHS pathogenesis. Current in vivo and in vitro models aim to recapitulate HLHS anatomy and physiology, yet they face limitations in accuracy and complexity.

RECENT FINDINGS

In vivo models, including those in chick, lamb, and mouse, provide insights into hemodynamic and genetic factors influencing HLHS. In vitro models using human induced pluripotent stem cells offer valuable platforms for studying genetic mutations and cellular mechanisms. This review evaluates these models' utility and limitations, and proposes future directions for developing more sophisticated models to enhance our understanding and treatment of HLHS.

Computational approaches for mechanobiology in cardiovascular development and diseases

The cardiovascular development in vertebrates evolves in response to genetic and mechanical cues. The dynamic interplay among mechanics, cell biology, and anatomy continually shapes the hydraulic networks, characterized by complex, non-linear changes in anatomical structure and blood flow dynamics. To better understand this interplay, a diverse set of molecular and computational tools has been used to comprehensively study cardiovascular mechanobiology. With the continual advancement of computational capacity and numerical techniques, cardiovascular simulation is increasingly vital in both basic science research for understanding developmental mechanisms and disease etiologies, as well as in clinical studies aimed at enhancing treatment outcomes. This review provides an overview of computational cardiovascular modeling. Beginning with the fundamental concepts of computational cardiovascular modeling, it navigates through the applications of computational modeling in investigating mechanobiology during cardiac development. Second, the article illustrates the utility of computational hemodynamic modeling in the context of treatment planning for congenital heart diseases. It then delves into the predictive potential of computational models for elucidating tissue growth and remodeling processes. In closing, we outline prevailing challenges and future prospects, underscoring the transformative impact of computational cardiovascular modeling in reshaping cardiovascular science and clinical practice.

Role of tissue biomechanics in the formation and function of myocardial trabeculae in zebrafish embryos

Cardiac trabeculae are uneven ventricular muscular structures that develop during early embryonic heart development at the outer curvature of the ventricle. Their biomechanical function is not completely understood, and while their formation is known to be mechanosensitive, it is unclear whether ventricular tissue internal stresses play an important role in their formation. Here, we performed imaging and image-based cardiac biomechanics simulations on zebrafish embryonic ventricles to investigate these issues. Microscopy-based ventricular strain measurements show that the appearance of trabeculae coincided with enhanced deformability of the ventricular wall. Image-based biomechanical simulations reveal that the presence of trabeculae reduces ventricular tissue internal stresses, likely acting as structural support in response to the geometry of the ventricle. Passive ventricular pressure-loading experiments further reveal that the formation of trabeculae is associated with a spatial homogenization of ventricular tissue stiffnesses in healthy hearts, but gata1 morphants with a disrupted trabeculation process retain a spatial stiffness heterogeneity. Our findings thus suggest that modulating ventricular wall deformability, stresses, and stiffness are among the biomechanical functions of trabeculae. Further, experiments with gata1 morphants reveal that a reduction in fluid pressures and consequently ventricular tissue internal stresses can disrupt trabeculation, but a subsequent restoration of ventricular tissue internal stresses via vasopressin rescues trabeculation, demonstrating that tissue stresses are important to trabeculae formation. Overall, we find that tissue biomechanics is important to the formation and function of embryonic heart trabeculation. KEY POINTS: Trabeculations are fascinating and important cardiac structures and their abnormalities are linked to embryonic demise. However, their function in the heart and their mechanobiological formation processes are not completely understood. Our imaging and modelling show that tissue biomechanics is the key here. We find that trabeculations enhance cardiac wall deformability, reduce fluid pressure stresses, homogenize wall stiffness, and have alignments that are optimal for providing load-bearing structural support for the heart. We further discover that high ventricular tissue internal stresses consequent to high fluid pressures are needed for trabeculation formation through a rescue experiment, demonstrating that myocardial tissue stresses are as important as fluid flow wall shear stresses for trabeculation formation.