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

Growth and remodeling of the cardiac outflow tract (OFT) is 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 4D moving-domain computational fluid dynamics (CFD) simulation approach, enabling longitudinal quantification of OFT hemodynamics and tissue mechanics in the same embryos across Hamburger-Hamilton (HH) stage 21 to HH27. We found that rising wall shear stress (WSS) strongly correlates with tissue extension in the distal OFT, whereas the proximal OFT experiences increasing expansive strains and higher hydrostatic stress with heartbeats. Additionally, we identified a double-helical flow pattern in the OFT lumen, possibly reflecting an evolutionary legacy for directing oxidized and non-oxidized blood flow before great vessel septation. Together, our results advanced insights in how hemodynamic forces and tissue stress contribute to OFT remodeling and septation.