RELATION OF THE ATRIAL INPUT SITES TO THE DUAL ATRIOVENTRICULAR NODALPATHWAYS - CROSSING OF CONDUCTION CURVES GENERATED WITH POSTERIOR ANDANTERIOR PACING

Dual AV Nodal Pathways. Introduction: The usually accepted definition of the dual pathway electrophysiology requires the presence of conduct ion curves with a discontinuity (''jump''). However, AV nodal reentran t tachycardia has been observed in patients with ''smooth'' conduction curves, whereas discontinuity of the conduction curve does not guaran tee induction of stable reentry. We hypothesize that the duality of AV nodal conduction can be revealed by careful choice of stimulation sit es during the generation of AV nodal conduction curves. Methods and Re sults: In 21 rabbit heart atrial-AV nodal preparations, programmed ele ctrical stimulation with S1-S2-S3 pacing protocol was applied either p osteriorly at the crista terminalis input site (CrT) or anteriorly at the lower interatrial septum input site (IAS), or (in 8 preparations w ith surgically divided input sites) at both, We found that in intact p reparations with ''smooth'' conduction curves, pacing at long coupling intervals produced shorter AV nodal conduction times from the IAS (56 +/- 9.8 msec vs 69 +/- 10.1 msec; P < 0.01). At short coupling interv als, in contrast, shorter conduction times were obtained from the CrT (173 +/- 21.8 msec vs 188 +/- 22.8 msec; P < 0.01). This resulted in a characteristic crossing of the superimposed IAS and CrT conduction cu rves. After division of the inputs, the IAS site had rapid conduction to the His bundle but a longer refractory period, whereas the CrT site had long conduction times and shorter refractory periods. Wavefronts entering the AV node from these two inputs can summate, resulting in i mproved conduction. Conclusion: Pacing protocols designed to accentuat e the asymmetry between the AV nodal inputs can help to reveal the fun ctional difference between the dual pathways and thus to better assess the properties of AV nodal conduction.