Abstract
BACKGROUND: The exact nature of the circuit and the existence of the upper and lower common pathways in Atrioventricular nodal re-entrant tachycardia (AVNRT) are not well defined. METHODS AND RESULTS: This report describes a case of re-entrant supraventricular tachycardia in which electrophysiologic manoeuvres confirmed an atypical AVNRT. During the tachycardia there was spontaneous variability in intracardiac intervals, and possible mechanisms are discussed. The tachycardia resolved after slow-pathway ablation. CONCLUSION: Atypical AVNRT can cause spontaneous intracardiac interval variability that complicates diagnosis but is effectively treated with targeted slow-pathway ablation.