Induction of sinus node reentry: Its relation to inhomogeneous atrial conduction

Abstract

The conduction pattern in the region of thesinus node (SN) was investigated using the extrastimulus method in the in vivo canine heart. The stimulating electrode was placed in the SN 5–10 mm distant from a recording electrode in the high right atrium (HRA). Multiple electrograms were simultaneously recorded from different atrial sites for evaluation of activation sequence. SN reentry was induced in eleven of fourteen dogs with achievement of a critical delay (20–80 msec) in conduction time from the SN to the recording electrode in the HRA. In these cases, induction of SN reentry was associated with the appearance of fragmentation of the HRA electrograms. In two dogs, at critical coupling intervals (S1-S2), the conduction time to the HRA suddenly increased from 45 to 80 msec and 20 to 50 msec, respectively, resulting in discontinuous HRA1-HRA2 vs S1-S2 curves compatible with the idea of longitudinal dissociation of atrial conduction. All premature impulses conducted through the “slow pathway” were associated with sinus node reentry. Inhomogeneous conduction from the SN to HRA was also suggested by fragmentation of the HRA electrogram into several distinct components. Decreasing the S1-S2 interval produced diminution of the initial component of the HRA electrogram with associated further delay of the second component suggesting unidirectional block in one pathway and slow conduction in another. In conclusion, (1) atrial conduction in andaround the SN could undergo longitudinal dissociation as evidenced by the appearance of fragmentation of the HRA electrogram and discontinuous curves, and (2) critical conduction delay from the SN to HRA was clearly related to the appearance of SN reentry.