Longitudinal Live Imaging-Derived 4D Hemodynamics and Dynamic Tissue Mechanics Across Outflow Tract Morphogenesis.

Growth and remodeling of the cardiac outflow tract (OFT) are poorly understood but associated with serious congenital heart defects (CHD). While only a minority of CHDs have identifiable genetic causes, the functional roles of mechanical forces in OFT remodeling are far less characterized. A key barrier has been the lack of longitudinal investigations examining the interplay between dynamic blood flow and wall motion across clinically relevant stages. Here, we developed a live high-frequency ultrasound-derived four-dimensional (4D) moving-domain computational fluid dynamics (CFD) simulation approach, enabling longitudinal quantification of OFT hemodynamics and tissue mechanics in the same ex ovo chicken embryos across Hamburger-Hamilton (HH) stage 21 to HH27. We found that wall shear stress (WSS) increases more than fourfold from HH21 to HH27, which strongly correlates with tissue extension in the distal OFT (R = 0.79, p < 0.05), whereas the proximal OFT experiences 20% larger expansive strains over development and higher hydrostatic stress than the distal OFT (dO) with heartbeats. Additionally, we identified a double-helical flow pattern with a ~ 3 degree flow direction shift in the OFT lumen, possibly contributing to the OFT septation and reflecting a streaming pattern associated with oxygenated and deoxygenated blood paths originated from extra-embryonic venous return and embryonic tissue return, respectively, before physical aorticopulmonary septation forms. We identified hemodynamic force and tissue mechanics as drivers of local tissue development and important stimuli for OFT remodeling and septation, advancing insights in how mechanical forces contribute to OFT development.