Stable patterns of AH block arising from longitudinal dissociation and reentry within the superfused rabbit AV junction.

Introduction: Multiple forms of antegrade AH Wenckebach block (WB) observed in 14 of 221 superfused rabbit AV junctions.

Methods: Bipolar and microelectrode recordings were used to examine the mechanism of multiple forms of AH WB.

Results: Each of the 14 preparations demonstrated typical 3:2 and 2:1 AV block, but also demonstrated longitudinal dissociation within the slow pathway input (N = 11) or compact AV node (N = 3). A 3:2 WB in one pathway and 1:1 conduction in a parallel pathway summated to provide antegrade conduction of the third atrial beat. Retrograde conduction (reentry) blocked conduction of the fourth impulse (4:3 block). A 5:4 block was similarly observed, with summation providing for antegrade AH activation of the third and fourth atrial beats. Retrograde activation observed with the fourth beat, terminated antegrade conduction of the fifth beat.

Conclusions: The studies demonstrate multiple AH WB patterns consistent with rate-dependent longitudinal dissociation, summation of dissociated AV conduction pathways, and retrograde conduction block within the AV junction.