Morphological changes in the normal pattern of ventricular myoarchitecture in the developing human heart.

Background: The aim of the present study was to describe the morphological changes in the normal pattern of ventricular myoarchitecture in the prenatal and adult human heart, to understand the three-dimensional organization of the muscle fibers and their active functional role in valvular dynamics.

Methods: We used dissection and histological techniques in 56 human hearts from fetuses and adults of both sexes.

Results: In all hearts, the ventricular wall was arranged in three different layers: superficial (subepicardial), middle, and deep (subendocardial) myocardium. The superficial and deep layers are present in both ventricles, whereas the middle layer is found only in the left ventricle. Age-related differences were noted in the pattern of myoarchitecture of the superficial layer, mainly in the fetal period, and especially in the right ventricle; however, the middle layer always shows a circumferential pattern, which is specially evident in elderly hearts. The ventricular fibers in the superficial and deep layers are anchored in the ventricular orifices.

Conclusions: Our findings reveal that muscle fiber architecture showed age- but not sex-related differences. These variations may reflect a mechanism of adaptation of the heart to functional demands throughout life.