Lutembacher's syndrome and a new concept of the dynamics of interatrial septal defect

Abstract

A report of a case of Lutembacher's syndrome (combination of interatrial septal defect and mitral stenosis) is presented. The currently held view of the dynamic changes in such a heart is discussed. It is pointed out that the fundamental disturbance in dynamics is the same whether or not the septal patency is complicated by a mitral lesion. According to previous investigators, the ultimate development of marked dilatation and hypertrophy of the right auricle and right ventricle, with minor involvement of the left auricle and left ventricle, is caused by shunting of blood through the communication, which in turn results from the fact that the pressure in the left auricle is higher than that in the right. Evidence is presented to show that this explanation is not tenable. A new concept of the dynamics of interatrial septal defect, based on a correlation between fundamental hydraulic principles and anatomic and experimental considerations, is proposed. It is shown that when two adjoining chambers have a source of constant and equal inflow, a free communication in their common wall, and outflow orifices of equal diameter, the gravitational orientation of the chambers determines their respective sizes, intraluminal pressures, and volume flows. If the chambers are placed one above the other, with the communication in a horizontal plane, the inferior chamber dilates and its outflow trajectory extends beyond that of the upper chamber, which indicates that there is a greater intraluminal pressure in the lowermost chamber. From an anatomic standpoint, evidence is presented to show that the auricular axis is such that the left auricle occupies a definitely more cephalad position that the right. Further, the plane of the foramen ovale (septal defect) is almost horizontal, and not vertical, as it is commonly represented. With the disposition of the chambers and septal defect in this relationship, filling of the right auricle is accomplished by the usual caval flow, and by a gravitational flow through the communication in the floor of the superiorly placed left auricle. Dilatation of the right auricle results, and, in due time, the right side of the heart shows dilatation and hypertrophy, whereas the left auricle and ventricle, which play almost no role in these events, remain essentially unaffected. The aorta becomes hypoplastic because of the decreased systemic volume of blood. The pulmonary arterial tree, on the other hand, necessarily dilates to accommodate the increased volume of blood in the lesser circuit. The presence of mitral stenosis simply exaggerates the flow differences. The proposed concept obviates the necessity of postulating a pressure gradient theory to explain the pathologic changes, and offers, instead, a well-correlated explanation of the entire progression of events which are associated with an interatrial septal defect.