The right outflow tract sulcus in embryonic human hearts

The right outflow tract sulcus occurs in a region of complex and rapidly changing embryonic anatomy where cardiac septa and valve rings fuse, but its importance in cardiogenesis is unknown. Regions of the heart which include this sulcus were reconstructed from nine normal human embryos from the Carnegie Embryological Collection using images of serial histological sections and a computer-based three-dimensional (3-D) reconstruction system. The sulcus appears in Carnegie stage 9 as one of the paired cardiogenic folds and persists through stage 19. It maintains a consistent position on the right lateral aspect of the outflow tract, where the outflow tract bends posteriorly. The sulcus elongates in proportion to the increased diameter of the outflow tract to stage 16. With rotation of the outflow tract and division into separate circulations in subsequent stages, the right outflow tract sulcus becomes related only to the left ventricular outflow tract. Between stages 10 and 16, the portion of the outflow tract extending from the right outflow tract sulcus to the aortic sac or great arteries elongates. Subsequent to outflow tract rotation and division, this distance decreases. The right outflow tract sulcus appears to be of importance in contributing to the final cardiac topography where interatrial, atrioventricular, interventricular, and outflow tract sulci meet and where the junction of atrioventricular and semilunar valve rings occurs.