Revisiting the development of the atrioventricular conduction axis.

Area of Science:

• Cardiovascular Development
• Human Embryology
• Cardiac Anatomy

Background:

• The development of the atrioventricular conduction axis is not fully understood despite extensive research.
• Recent advancements in imaging and human specimen availability provide new insights.

Purpose of the Study:

• To elucidate the morphological remodeling and insulation of the atrioventricular conduction axis during human embryonic and fetal development.
• To investigate the fate of nodoventricular and fasciculo-ventricular pathways.

Main Methods:

• Analysis of serial histological sections and micro-computed tomographic datasets from Carnegie stages 17-23 and fetal specimens.
• Inclusion of a newborn specimen (42 weeks) and data from human developmental biology resources.
• Assessment of reproducibility through blinded interobserver evaluation.

Main Results:

• The atrioventricular conduction axis originates from trabecular cardiomyocytes on the septal crest, forming bundles and the primary ring.
• Fetal development leads to the centralization of the atrioventricular node and disruption of most nodoventricular pathways.
• Fasciculo-ventricular connections largely persist, with some remaining throughout gestation; part of the primary ring forms the retro-aortic node.

Conclusions:

• Atrioventricular conduction axis remodeling involves dynamic reorganization and selective insulation of cardiomyocytes.
• The persistence of fasciculo-ventricular pathways and loss of nodoventricular connections are key findings.
• These changes have significant implications for understanding postnatal conduction system anatomy and arrhythmogenic substrates.