Search

A total of 367 human fetuses and newborn subjects weighing from 60 to 5000 g provided the material for a morphometric study of the heart. A total of 17 interventricular parameters were measured in each specimen, one of the parameters representing an innovation with regard to the classically used set of measurements. A new anatomo-geometric configuration is described for each ventricle along with a new component for the left ventricular outflow tract, designated as the aortic outflow tract. The appropriate stereometric formulas were used to calculate real ventricular volumes rather than the previously studied volumetric indices. Additionally, correlation indices were calculated for ventricular wall thickness as well as the circumferences and diameters of the atrioventricular and arterial valves. The results show that, in fetuses of up to 2700 g in body weight, ventricular wall thickness is greater in the right than in the left ventricle, although the opposite is true in fetuses weighing above 2700 g. Throughout the range of weights studied, ventricular volume was greater in the left than in the right chamber. Tricuspid and pulmonary valve circumference and diameter were consistently greater than in the mitral and aortic valves, respectively. We believe the new morphometric data and their innovative interpretation to have immediate applications in both the morphological and functional areas of cardiology.

A pathogenetic mechanism for the formation of tetralogy of Fallot is postulated. We propose that the right ventricular ejection stream is divided into a transseptal aortic stream and an infundibular pulmonary stream during embryonic life before the ventricular septum is closed. The surgically unaltered hearts from 77 cases of tetralogy of Fallot were examined, and measurements made of certain morphologic features. A malformed, stenotic pulmonary valve was found in most all cases and accounts for a divided ejection stream. Infundibular stenosis is shown to be a postnatally acquired, progressive lesion. The detailed anatomic features of the heart and great vessels in tetralogy of Fallot are explained as a response of the developing heart and great vessels to the abnormal blood flow pattern of a divided right ventricular ejection stream. This pathogenetic mechanism, compared to previously proposed hypotheses, appears better able to account for the malformation complex of tetralogy of Fallot.

The development of human semilunar valves was studied in a range of specimens including embryos before the appearance of cellular semilunar valves at stage 17 and hearts after the attainment of mature fibroelastic valvular structure, which occurs around the time of birth. The valves develop by modification of endocardial cushion material at the downstream end of the cardiac tube and appear to grow at the margins, probably by cellular proliferation into a stagnant zone caused by boundary layer separation of blood flow. The flat endothelium on the ventricular aspect and the cuboidal endothelium on the arterial aspect of the valves correlate, respectively, with expected high and low shear forces produced by surface blood flow. Development of an aorta and pulmonary trunk with tricuspid semilunar valves appears to be contingent on the appearance of separate entwined ventricular ejection streams. The later fibroelastic phases of semilunar valve development show progressive increase in elastic and collagenous fibers, at sites which appear to be subjected, respectively, to fluctuating and static tensions.