Stresses induced in an embryonic heart by blood flow have been visualized for the first time in 3-D using an optical coherence tomography (OCT) method. The technique could provide new insight into how and why heart defects develop. Biomedical engineers at Case Western Reserve University investigated shear stress — the parallel force of one material sliding along another — using a modified Doppler OCT technique. In the developing heart, shear stress is induced in the heart’s own endocardial cells as blood cells rush past them. A quail embryo. The bulge on the middle left side of the embryo is its developing heart. Images courtesy of Biomedical Optics Express. This stress typically helps to control and regulate cellular processes involved in heart development. Even tiny aberrations in the heartbeat, however, can alter blood flow patterns and change these developmental forces, leading to congenital heart defects such as abnormal valve formation. “All previous attempts at shear-stress mapping have been two-dimensional, but the 3-D geometry of the embryonic heart is changing hour by hour at these early stages, and the shape of the heart twists and turns as it develops, so a 2-D projection doesn't really provide a good approximation,” said Andrew M. Rollins, an associate professor of biomedical engineering. Rollins and colleagues directly measured the heart structure and blood flow within the developing hearts of quail embryos with their modified OCT method. The data collected was used to create 4-D images (3-D movies), which showed that “locations of high shear correspond with locations of future valve formation,” he said. A map of the shear stress on a developing heart at four evenly spaced time points during a heart cycle. Red indicates areas of greater stress. The team currently is investigating the effects of abnormal shear on valve development caused by alcohol exposure, Rollins said. Next, they hope to adapt the technique based on the information gathered from their preliminary animal tests and apply it to humans. Their goal is a tool that doctors could use to identify whether early intervention could prevent defects in developing hearts. The research appeared in Biomedical Optics Express (http://dx.doi.org/10.1364/BOE.3.003022). For more information, visit: www.case.edu