Abstract Body: Background: Congenital heart defects (CHDs) occur in approximately 1% of all live births with nearly 25% of these characterized as critical. Ventricular Septal Defects (VSDs) are among the most common forms of CHDs and occur when the left and right ventricles do not properly separate. Currently, the biophysical conditions that lead to abnormal ventricular septation remain poorly understood. To address this, we constructed three-dimensional profiles of gene expression patterns at stages of cardiac development just preceding the initiation of ventricular septation. This revealed that genes associated with vascular wall shear stress displayed spatially heterogeneous expression. Specifically, we identified that the myocardial region that demarcates the site of ventricular septation generally lacks wall shear stress-activated gene expression. This led to the hypothesis that spatial differences in hemodynamic forces that emerge during cardiac morphogenesis actively control ventricular septation.
Methods: To test this hypothesis, we have developed a non-surgical, non-genetic animal model system to acutely elevate wall shear stress in the early embryonic heart, and we have used unbiased geometric morphometric analysis to identify conditions that lead to altered ventricular septation.
Results: Using full three-dimensional reconstructions of the entire developing heart, we have identified that elevating blood viscosity triggers defects in cardiac anatomy. Quantification of the reconstructed heart luminal geometry confirmed that the positioning and alignment of the ventricular septum is disrupted when blood viscosity falls outside of specific tolerances. In addition, atrioventricular cushion morphology was altered, ventricle lumen volume reduced, and cardiac trabeculation became highly disordered when blood viscosity was increased. Initial unbiased geometric morphometric methods further demonstrated that the three-dimensional architecture of the developing heart was far more variable when blood viscosity was increased, demonstrating that blood rheology is an essential variable that controls the possible anatomical configurations the developing heart can attain.
Conclusions: We have developed a novel non-surgical animal model to measure the sensitivity of the embryonic heart to shear stress and generated a quantitative, three-dimensional imaging pipeline for determining the array of CHDs that may form in response to abnormal shear stress.