Development of the coronary arteries in the embryonic human heart

It is not known why the coronary arteries almost always originate only from the right and left aortic sinuses of Valsalva, since the structure and conditions appear to be the same for all six sinuses of the embryonic great arteries. We sought a possible mechanical explanation for the phenomenon by studying the development of the coronary vasculature in 351 staged, serially sectioned human embryos of Carnegie stages 9 through 23 from the Carnegie Embryological Collection. A plexus of blind epicardial capillaries appears on the heart in Carnegie stage 14 or 15 and acquires a coronary sinus connection in stage 15, 16, or 17. The connection of the proximal coronary arteries to the aorta does not appear until stage 18. We found no histologic features of the cardiac nerves or any other component of the tissues to account for the consistent origin of coronary arteries from the right and left aortic sinuses of Valsalva. However, serial section reconstructions showed that the two sinuses where coronary arteries develop acquire a positive transverse curvature and a negative longitudinal curvature, i.e., a catenoidal or saddle-shaped configuration, before the appearance of the coronary arteries. The four noncoronary sinuses also have a positive transverse curvature, but longitudinally, in contrast, they have a positive curvature or are straight. The results suggest that the coronary arteries originate from those sinuses of Valsalva where wall tension is increased by a catenoidal configuration.