Insights into atrioventricular nodal function from patients displaying dual conduction properties: interactive and orthogonal pathways.

BACKGROUND There is a significant variability observed in the conduction properties of the atrioventricular node. In a subset of hearts, impulse transmission tends to fall into two distinct conduction regions, termed the slow and fast pathway, and a further subset are capable of dual conduction of a single input stimulus, termed double firing. METHODS AND RESULTS In this article, we closely characterize two distinct responses in patients with double firing properties of the atrioventricular node, separating these into discrete types: those with slow and fast pathway interaction and interdependence (interactive), and those with independent pathway properties (orthogonal). We use novel mathematical techniques to evaluate the relative decrement and unique properties of conduction during the overlapping slow and fast pathway conduction zones. CONCLUSIONS Our analysis demonstrates two distinct patterns of pathway conduction in double firing patients, termed interactive and orthogonal. We show parallel overlapping segments of slow and fast pathway decremental conduction curves in interactive pathways, with no such findings with orthogonal conduction. These findings suggest anatomic correlates of pathway conduction, with interactive pathways likely having a common distal segment and orthogonal pathways able to independently activate downstream structures.