Ventricular trabeculations in the chick embryo heart and their contribution to ventricular and muscular septal development.

Abstract

Sixty-two chick embryo hearts were studied at incremental stages of development (Hamburger-Hamilton stages 16 to 39) by scanning electron microscopy following 3% glutaraldehyde fixation and critical point drying. Early in cardiac development, the primitive ventricle becomes homogeneously trabeculated with highly organized sheets of myocytes lined by endocardial cells, with the trabeculae generally oriented in the dorsoventral direction. Coalescence of these trabecular sheets begins at stage 26, initially at the area of the bulboventricular flange, and later proceeding caudally toward the floor of the ventricle. The fusion process is finished by stage 30, resulting in a muscular ventricular septum that has now divided the primitive ventricle into right and left ventricles. Further growth of the ventricular septum is by continued fusion of the adjoining trabecular sheets. Remnants of the apposing trabecular sheets are found in the solidified muscular septum in the form of endocardial channels. We suggest that persistent patency of these channels results in muscular ventricular septal defects.

Congenital heart defects through 30 years

“…Spontaneous closure of 76% of the defects occurred during the first year of life, consistent with our data. The developmental pattern of the muscular ventricular septum includes multiple intervenetricular channels, which are gradually obliterated during intrauterine life by coalescence of the trabecular sheets [21]. From this perspective, closure of small muscular VSDs during the first months after birth may be regarded as a protracted normal developmental process.…”

Building the vertebrate heart - an evolutionary approach to cardiac development

“…Trabeculae are highly organized sheets of cardiomyocytes that form muscular ridges or projections lined by endocardial cells (Ben-Shachar et al, 1985). Trabeculae will progressively become part of papillary muscles, the interventricular septum, and part of the conduction system (Moorman and Christoffels, 2003).…”

The heart exhibits right to left communication between the fibres of the muscular part of the interventricular septum

“…The homogeneous left central muscular part of the IVS had no canals and the dye stained the fibres of the muscle through the septum. The stripe filled with tightly packed black dye was under the endocardium like the endocardial-lined channels presented by Ben-Shachar et al [4]. The black dye also stained the route through the endocardium slightly black (Figs.…”

“…The interventricular foramen is closed by the membranous part of the IVS at the end of the 7 th week [5]. Ben-Shachar et al [4] use scanning electron microscopy combined with critical point drying of the tissue. They find the smooth endocardial-lined channels to be oriented left-right and craniocaudal directions in the middle of the muscular part of the IVS of the stage 30 chick embryo heart.…”

“…The trabecular endocardial surface becomes apposed and forms into channels through coalescence of the trabecular sheets. They speculate that highly organised ventricular trabeculations may regulate the systolic and diastolic functions of the primitive ventricle and that the muscular ventricular septal defects (VSD) are due to continued patency of the channels in the muscular part of the IVS of the fully developed heart [4].…”