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A multivariate analysis of cardiac growth in human embryos: endocardial cushions and ventricular myocardium
1State University of Rio de Janeiro (UERJ), Department of Anatomy, Brazil.
Study Objective:
In view of the controversy about the morphological significance of the endocardial cushion tissue and ventricular myocardium during cardiac development, the aim was to carry out quantitative studies of these structures.
Design:
Endocardial cushion tissue and ventricular myocardium were quantified by point count planimetry. The relative growth of the volume of these structures, and also the embryonic crown-rump length, was studied by multivariate allometry (principal components analysis) with the covariance matrix calculated from natural logarithms of the data.
Experimental Material:
27 serially sectioned human embryos were studied, ranging from stage 15 to stage 23 (Paris collection).
Measurements And Main Results:
The relative growth of endocardial cushion tissue, ventricular myocardium, and crown-rump length was discontinuous during the postsomitic period. The first component in principal components analysis measures overall size and, in the present analysis, accounts for 88.6% of the total variance. The growth vector isometry hypothesis was checked with the chi 2 test. This showed that differences in growth between cardiac structures and crown-rump length were allometric (p less than 0.01). Endocardial cushion tissue volume and crown-rump length grew with negative allometry during the second month of gestation, while ventricular myocardium volume grew with positive allometry.
Conclusions:
The results agree with those researchers who consider that endocardial cushion tissue functions only in causing initial cardiac fusion and partitioning, with little influence on the formation of definitive cardiac structures.