Nonreentrant supraventricular tachycardia due to simultaneous conduction over fast and slow AV node pathways:...

A 55-year-old woman with frequent problematic supraventricular tachycardia is presented. The tachycardia was irregular with predominantly normal QRS morphology and was refractory to multiple antiarrhythmic drugs. At electrophysiology study, the tachycardia was inducible with atrial or ventricular extrastimuli and dual pathways were observed. In contrast to the situation usually seen with dual atrioventricular node physiology, the slow pathway had a longer effective refractory period than the fast pathway and reentrant tachycardia was not induced. Simultaneous conduction over the fast and slow pathways during sinus rhythm was shown to be the mechanism for clinical tachycardia. The tachycardia was successfully treated using radiofrequency ablation of the slow pathway.