Slow:fast and slow:slow AV nodal reentry in the rabbit resulting from longitudinal dissociation within the posterior AV nodal input.

Abstract

The anatomic and electrophysiologic bases for multiple forms of sustained AV nodal tachycardia were determined in the rabbit. Intracellular microelectrode recordings were used to identify antegrade and retrograde conduction limbs of sustained tachycardias observed in 23 of 152 superfused rabbit AV junctions. Slow:slow tachycardias (196 +/- 12 msec cycle length) with nearly equal AH and HA intervals (99 +/- 12; 97 +/- 11 msec, respectively) and early atrial activation near the coronary sinus os were observed in 14 preparations and slow:fast tachycardias (189 +/- 11 msec cycle length) with an AH > HA interval (141 +/- 12; 48 +/- 10 msec, respectively) and early atrial activation along the anterior limbus of the fossa ovalis were observed in 11 preparations. Both tachycardias were associated with longitudinal dissociation and localized reentry within the triangle of Koch. Slow:fast and slow:slow tachycardias exhibited counterclockwise and clockwise reentry circuits, respectively. Both circuits were present in two preparations. Slow:fast AV nodal reentrant tachycardias could be reset with stimuli introduced near the coronary sinus os and the anterior AV nodal input. Slow:slow tachycardias could be reset only by stimuli introduced near the coronary sinus os. The fraction of the tachycardia cycle length contained within the compact AV node was greater for slow:fast (0.35 +/- 0.07) than slow:slow reentry (0.15 +/- 0.05, p = 0.026), suggesting a longer lower common pathway for slow:fast tachycardia. Longitudinal dissociation within the posterior AV nodal input incorporating the AV node can provide the reentrant substrate for two different clinical forms of sustained AV nodal tachycardias.