Corrected Transposition of the Great Vessels with Ebstein Malformation of the Left Atrioventricular Valve: an Embryologic Analysis and Two Case Reports.

CORRECTED transposition is commonly considered to be the resuilt of a leftward l)ending of the bulboventricular loop instead of a rightward bending, with concomitantly abnormal development of the trtuncuis septum.'-3 Recently an embryologic study was carried out by one of u-s of normal eight to 19 somites hulman embryos (Streeter's age groups horizon X and XI) and a 6.6-mm. human embryo with an abnormally bent lheart (age group horizon XIV*).4 From this study, interesting supplementary information was gained regarding the sequence of events in the formation of the bent heart-tube and the possible consequtences in case of a disturbance in the first step of the bending. Moreover, the fate of the atrioventricular endocardial cushions was followed throughout horizons XVII to XX in order to understand some of the characteristics of the right and left atrioventricular valves in the normal heart, in the heart with corrected transposition, and in the heart with the Ebstein-type malformation.