Role of the perinodal region in atrioventricular nodal reentry: Evidence in an isolated rabbit heart preparation

To evaluate the role of perinodal tissue in the genesis of atrioventricular (AV) nodal reentry, echo beats were induced by programmed stimulation in nine superfused rabbit atrial-atrioventricular nodal preparations. In these preparations, extracellular bipolar electrograms were recorded simultaneously from the crista terminalis, interatrial septum and His bundle, along with microelec-trode action potentials from cells in the AV node and perinodal tissues. Three patterns of AV reentry were observed: 1) In four preparations, with the introduction of basic and premature stimuli at the crista terminalis input region to the AV node, block occurred within the AV node, anterograde conduction continued along the perinodal fibers and entered the AV node by way of the interatrial septal input region. Reentry occurred via retrograde nodal conduction. 2) In two other preparations, with the introduction of basic and premature stimuli at the interatrial septal input region, conduction blocked in retrograde manner within the AV node, and retrograde conduction occurred via the perinodal tissues. It subsequently entered the node by way of the crista terminalis input region, and continued in an anterograde direction through the AV node, with reentry via the interatrial septal region and perinodal fibers. 3) In three preparations, basic and premature stimuli at the crista terminalis region blocked in the perinodal tissue near the crista terminalis, but conducted slowly in an anterograde fashion through the AV node. To complete the reentry circuit, the stimuli exited at the interatrial septal region and conducted in retrograde fashion via the perinodal tissues to reenter the node at the crista terminalis. Moreover, in four other preparations, surgical interruption of the perinodal tissue prevented reinitiation of reentrant phenomena. These studies demonstrate the critical role of the perinodal tissues as a necessary link in the AV nodal reentrant mechanism in this preparation