[The structural organization of the human myocardium: the interrelation between myocardial fibers and interstitial...

The complex tridimensional structure of the human ventricular myocardium has rarely been studied in the past. In the normal heart, in the lapse of time of few weeks of the embryonic life, a radical transformation from a chaotic plexiform organization to a complex tridimensional structure occurs. From then on, the ulterior growth of the myocardial fibres will only be dimensional and quantitative, because the spatial geometry is to be considered definitive. The role of the interstitial connective tissue in following the development of the myocardium, possibly inducing or influencing it, is still unclear. We have performed an histologic study on serial sections of the ventricular mass of 7 human embryos and fetuses, from 5 to 20 weeks of gestational age. The sections have been evaluated for their morphologic characteristics as evidentiated by histochemical (PAS, trichrome, Gomori silver technique) and immunohistochemical (myosin, actin, desmin, myoglobin, vimentin, fibronectin, smooth muscle cell, endothelial factor VIII) stainings. The results show that myocardial growth is mantellar, proceeding from the epicardium toward the endocardium, with progressive structural organization in strata, variably related one to the other depending upon the considered site of the ventricular mass. The interstitium grows in parallel to the myocardial growth, beginning with a thin network surrounding each fibre that progressively in time is transformed in a complexly arranged and more densely packed structure. The collagen fibres appear initially at epicardial level, particularly around the coronary vessels.(ABSTRACT TRUNCATED AT 250 WORDS)