The mechanism of AV junctional reentry: Role of the atrio-nodal junction

Mapping of atrial-AV nodal (AVN) activation patterns was performed in 10 superfused rabbit AVN preparations utilizing 3 bipolar electrodes placed simultaneously at the crista terminalis (CT), interatrial septum (IAS) and His bundle (H) regions in close proximity to the AVN, along with two or three microelectrodes in the AN, N and NH regions of the AVN. Basic and premature stimuli were introduced at either or both the CT and IAS regions of the AVN. The timing of the premature stimuli was varied to induce close interaction of inputs to the AVN. Summation and/or cancellation, as evidenced by changes in the morphology of the action potentials and alteration of H1–H2 intervals, were observed. Apparent reentry phenomena could be induced or terminated by appropriately timed stimulation at the CT and IAS inputs. Reentry was critically related to both the patterns and timing of the spread of excitation within AVN and surrounding atrial tissue. Slow conduction and unidirectional block were observed in various portions of the reentry circuit. It is concluded that (1) interaction between input waves engaging the AVN produced either summation or fragmentation; (2) slow conduction and reentry resulted from a critical collision of wavefronts: (3) in this preparation, AVN reentry circuits always appeared to involve conduction through atrial tissue immediately surrounding AVN; and (4) remarkably, reentry confined to the intranodal region was never observed.