Spontaneous termination of reciprocating tachycardia owing to interaction of dual atrioventricular nodal pathways in patients with an accessory pathway.

Retrospective analysis of the electrophysiologic recordings from 125 consecutive patients with reciprocating tachycardia involving an accessory atrioventricular (AV) pathway suggested, by the mode of spontaneous termination of reciprocating tachycardia, the coexistence of dual AV nodal pathways in 7 patients. Three different modes of spontaneous tachycardia termination were observed. In 2 patients with antidromic tachycardia, termination was a result of AV nodal reentry, preceded by a decrease in retrograde AV nodal conduction. In 3 other patients with antidromic tachycardia, termination occurred after a sudden switch from a slow to a fast AV nodal pathway, leading to conduction block in either the accessory pathway or the His-Purkinje system. In 2 patients with orthodromic tachycardia, termination was caused by a sudden change of anterograde conduction from a fast to a slow AV nodal pathway, eliciting an AV nodal echo beat. The interaction of dual AV nodal pathways within the reentry circuit incorporating the accessory pathway always inhibited sustained reciprocating tachycardia.