DEVELOPMENTAL-CHANGES IN THE MYOCARDIAL ARCHITECTURE OF THE CHICK

Background: Numerous studies describing myocardial architecture have b een performed on the adult heart but considerably fewer have been made during embryonic or fetal development. To serve as a basis for inters pecies comparison of ventricular morphology, and as a reference for st udying the effects of experimental perturbations, we examined the deve lopment of chick throughout the entire incubation period, Methods: Chi ck hearts from stage 14 (day 2) to stage 46 (day 21) were perfusion-fi xed, and sectioned in transverse, frontal and sagittal planes, The ven tricular myocardial architecture was examined and photographed in the scanning electron microscope, Results: At embryonic stage 16 and earli er, the smooth-walled heart loop had an outer myocardial mantle, cardi ac jelly, and endocardium, From stage 18, there was an outer compact a nd inner trabeculated myocardium. Trabeculated myocardium could be sub divided into the outer (basal) portion adjacent to the compact layer a nd the central (luminal) part, The outer basal layer could be distingu ished from the inner luminal by shorter and finer trabeculae with smal l, round intertrabecular spaces, From stage 24, the patterns of trabec ulae and intertrabecular spaces were ventricle-specific, Between stage s 24 to 31, abundant trabeculations were present throughout both ventr icular cavities, The trabeculae were initially radially arranged, but later adopted a spiral course, which persisted in a simplified form in to adulthood, Conclusions: The ventricular myocardium undergoes distin ctive morphogenesis, characterized by changes in trabecular patterning and orientation, We speculate that the embryonic trabecular architect ure reflects the directions of the main stresses, Unlike fetal and adu lt hearts, which rely mostly on the compact myocardial layer, the trab eculae play a crucial role in the contractile function of the embryoni c heart. (C) 1997 Wiley-Liss, Inc.