Optical Mapping Can Reveal Two-Dimensional Morphology of Atrioventricular Insulation in the Foetal Avian Heart

Syndromes of ventricular pre-excitation or atrioventricular (AV) re-entry are believed to results from inappropriate formation of the AV junction (AVJ) during prenatal development. However, technical limitations pose challenge to study foetal heart electrophysiology and are hampering understanding formation of accessory pathways (APs) bypassing AVJ. Here, we present a novel approach of retrograde perfusion for optical mapping of chicken foetal heart. Together with embryonic heart mapping, we were able to investigate AVJ electrical remodelling during the entire prenatal period. AV electrical insulation was observed concomitant to functional deployment of the conduction system at the time of ventricular septation. However, persistence of ectopic AV electrical continuity was still detected in post-septation foetal hearts. APs registered in 40% of prenatal day 13 (localised in the central anterior or left posterior side) were progressively resolved and none were detected on prenatal day 18. The optical mapping approach thus proved its ability to track AVJ electrical remodelling during whole prenatal chicken development and spatiotemporally localise electrically active APs.