Origin and the embryonic transformations of vertebrate heart conducting system.

Abstract

As the embryonic structure, the cardiac conduction system must continue to develop in a coordinated manner at all embryonic stages. This requires not only the formation of distinct components of the conduction system, but the integration of these components into a functioning whole. The development of the chambered heart and a conduction system requires the proper arrangement of a number of embryonic building blocks, comprising inflow tract, atria, atrioventricular canal, compact and trabecular ventricular myocardium, and outflow tract. In the mammalian heart, the sinoatrial and atrioventricular nodes will aggregate in the slow-conducting inflow tract and atrioventricular canal. The ventricular conduction system may develop in its entirety from the trabecular ventricular myocardium, the remodeling of which results in a gradual transition toward the compact myocardium. So the development of the conduction system does not require the invention of new building components but a remodeling of existing components. Many details in the fashioning of the embryonic blocks of the heart into the conduction system of the formed heart still need to be worked out. The factors that specify the cardiac building blocks and regulate their coordinated morphogenesis have remained largely unknown. Their identification will benefit from combined molecular, genetic, and morphological approaches