Atrial Pacing-Induced Reverse Alternating Wenckebach Periods. A Common Electrophysiologic Phenomenon in Patients with Dual Atrioventricular Nodal Pathways.

Reverse alternating Wenckebach periods (RAWP) have rarely been described, and the significance of dual AV nodal pathways in atrial pacing-induced RAWP is unknown. Forty-five of 50 consecutive patients (M/F = 23/27, mean age 40 +/- 5 years) with common type AV nodal reentrant tachycardia had discontinuous antegrade conduction curves. Atrial pacing revealed that pattern A RAWP (23 patients) had the fourth paced beat conducted over the fast pathway, and pattern B (18 patients) over the slow pathway. Four patients had both pattern A and B RAWP during different pacing cycle lengths. All episodes of atrial pacing-induced RAWP emerged from (or started as) 3:2 AH block, which thereafter were followed by runs of 2:1 AH block. Comparisons between patterns A and B showed (1) maximal atrial pacing cycle length with RAWP was longer in pattern A; (2) A2H2-A1H1 and A4H4-A1H1 were significantly greater in pattern B; (3) A2H2-A4H4 and H2A4/A2H2 were significantly greater in pattern A. It is concluded that atrial pacing-induced RAWP is a common electrophysiologic phenomenon in patients with dual AV nodal pathways. Furthermore, intermittent slow pathway conduction associated with different AnHn and HnAn+2 parameters helped the interpretation of different conduction patterns.