THE NATURAL HISTORY OF THE DUCTUS ARTERIOSUS IN ASSOCIATION WITH OTHER CONGENITAL HEART DEFECTS DONALD E. CASSELS, M.D.,* SAROJA BHARATI, M.D.A AND MAURICE LEV, M.D.% I. Introduction Subsequent to Galen's description of the ductus arteriosus in a.D. 200 [1, p. 68], there was a hiatus in anatomical observation and speculation concerning the fetal circulation until Fallopius in 1561 [2] noted the ductus, and other descriptions followed during the sixteenth century. It remained for Harvey [3] to synthesize anatomical observations into a concept which included blood flow and perfusion to the lung as a separate circulation. The blood flow to the periphery was thought to occur subsequent to the return ofoxygenated blood from the lung to the systemic left ventricle. He remarked that the fetal circulation included supplementary channels not present in the mature circulation. The explanation of the purpose of the fetal channels was: ". . . the heart, in its beat, forces the blood through the wide open passages from the vena cava to the aorta through the two ventricles. The right ventricle, receiving blood from its auricle, propels it through the pulmonary artery and its continuation, called the ductus arteriosus, to the aorta. At the same time, the left ventricle contracts and sends into the aorta the blood which, received from the beat of its auricle, has come through the foramen ovale from the vena cava." In 1900, Gerard [4] consolidated information available into a reasonable proposal. Pohlman [5] reviewed the theories of the fetal circulation and perhaps too neatly classified these as follows: 1. Early theories suggested that mixed superior and inferior caval ?Professor of pediatrics, Pediatric Cardiology, Pritzker School of Medicine, University of Chicago. tHektoen Institute for Medical Research of Cook County Hospital, Chicago. !Director, Congenital Heart Disease Research and Training Center, Hektoen Institute for Medical Research, Chicago; career investigator and educator, Chicago Heart Association . This investigation was supported by grant HL 07605-12 from the National Heart and Lung Institute, National Institutes of Health. Perspectives in Biology and Medicine · Summer 1975 | 541 blood passed from the right atrium to the left, through the foramen ovale. 2.Some believed blood passed from the left atrium to the right. 3.One proposal stated that the inferior vena cava flow was divided, part to the right atrium and part to the left. The foramen ovale did not open into the two atria. 4.Others stated that all of the blood from the inferior vena cava flowed to the left atrium and blood from the superior vena cava went into the right atrium. This is the current concept. 5.It was also suggested that all blood of the left ventricle went to the head and upper extremities through the arch of the aorta and its branches, and all blood from the right ventricle went to the lungs, ductus , and descending aorta through the pulmonary artery. The aorta functioned as two parts, an upper and lower, connected by what is now called the isthmus ofthe aorta. This did not carry blood during fetal life. 6.One author speculated that blood flow through the superior vena cava was equal to the return through the pulmonary veins. The isthmus of the aorta carried the same amount of blood as the ductus arteriosus, each carrying one-half the contents of the left and right ventricle. The aortic arch system in the human embryo was studied in detail by Congdon [6]. The changes in arches 1, 2, and 3 are not pertinent. The left fourth aortic root becomes a segment of the left aortic arch in the human, the usual arrangement, although there may be a right arch and rarely a persistent double arch. The controversial fifth is usually ignored , and the sixth or pulmonary arch is concerned with the pulmonary artery. The ductus arteriosus is frequently described as the terminal segment ofthe sixth arch inserting into the aorta. It seems likely that the ductus arises as a dorsal sprout from the aorta and a ventral sprout from the primitive pulmonary artery [7, 8]. The ductus arteriosus as an isolated essential component of the fetal circulation has facets of great interest, (a) Its function and status as a conduit and bypass...