Revisiting the anatomy of the atrial chambers in light of knowledge of their development

Abstract

We reasoned that knowledge of the developmental components might provide the basis for clarifying controversial issues regarding atrial anatomy and would provide the background for recent clinical segmentation of the walls. We have revisited the interactive pdf files created by Hikspoors and colleagues to provide a pictorial account of human cardiac development, supplementing this information with the data available in the Human Developmental Biology Resource. We then revisited the multiple dissections of human hearts available in our joint archives. When first identified, the atrial component of the primary heart tube receives the systemic venous tributaries caudally and continues ventrally as the atrioventricular canal. The appendages then balloon laterally and ventrally from the primary component. The systemic venous tributaries are committed to the developing right atrium, with the pulmonary vein initially canalising from a solitary strand before becoming incorporated into the left atrium. The primary component of the atrial septum is reinforced by a second component formed by muscularisation of the mesenchymal cap and vestibular spine. The remaining rims of the oval fossa are interatrial folds. Each definitive atrium possesses a part of the body, a venous component, an appendage, and a vestibule, with the septum separating its cavities. Apart from the nodes of the conduction system, the atrial walls are composed of working myocardium, with the alignment of the myocytes underscoring preferential conduction.

Keywords: appendages; atrial development; atrial septum; inferior pyramidal space; left atrium; right atrium; vestibules.