Atrial pacing-induced reverse alternating Wenckebach periods. A common electrophysiologic phenomenon in patients with dual atrioventricular nodal pathways.

ABSTRACT

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) 32 AH block, which thereafter were followed by runs of 21 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.