The Anatomy, Development, and Evolution of the Atrioventricular Conduction Axis.

Robert Anderson,Diane Spicer,Bjarke Jensen,Damian Sanchez-Quintana,Shumpei Mori

doi:10.3390/jcdd5030044

Abstract

It is now well over 100 years since Sunao Tawara clarified the location of the axis of the specialised myocardium responsible for producing coordinated ventricular activation. Prior to that stellar publication, controversies had raged as to how many bundles crossed the place of the atrioventricular insulation as found in mammalian hearts, as well as the very existence of the bundle initially described by Wilhelm His Junior. It is, perhaps surprising that controversies continue, despite the multiple investigations that have taken place since the publication of Tawara’s monograph. For example, we are still unsure as to the precise substrates for the so-called slow and fast pathways into the atrioventricular node. Much has been done, nonetheless, to characterise the molecular make-up of the specialised pathways, and to clarify their mechanisms of development. Of this work itself, a significant part has emanated from the laboratory coordinated for a quarter of a century by Antoon FM Moorman. In this review, which joins the others in recognising the value of his contributions and collaborations, we review our current understanding of the anatomy, development, and evolution of the atrioventricular conduction axis.

Highlights

The identification of the atrioventricular conduction axis by Sunao Tawara, in 1906 [1] ushered in the correct understanding of cardiac conduction [2,3]
Taking advantage of our experiences in these various fields, we review here the anatomy, development, and evolution of the atrioventricular conduction axis
Generations of scientists have built an ever-larger body of knowledge on the foundational observations on the atrioventricular conduction axis by Wilhelm His Jr. and Sunao Tawara

Summary

Introduction

The identification of the atrioventricular conduction axis by Sunao Tawara, in 1906 [1] ushered in the correct understanding of cardiac conduction [2,3]. The axis itself, the substance of the ventricular septum to emerge beneath the medial papillary muscle of the tricuspid valve (Figure 4—left-hand panel). This component is part of the initial ring of primary myocardium that surrounded the embryonic interventricular communication It is the remnant of this ring, lying with the vestibule of the right atrium, that were mistakenly taken by Kent to represent multiple pathways for atrioventricular conduction in the normal heart [7]. The remnants do exist, but are sequestrated within the vestibular myocardium on the atrial aspect of the insulating plane in individuals with normal atrioventricular conduction [17] It is these remnants that produce the anomalous atrioventricular nodes found in situations when the heart is congenitally malformed, such as congenitally-corrected transposition or straddling tricuspid valve [18,19]

The Retroaortic Node

Development of the Cardiac Chambers

The Development of the Atrioventricular Conduction Axis

Molecular Characterization of the Atrioventricular Conduction Axis

Conclusions