Changes of the RR interval and the QRS morphology in AV nodal tachycardia : further evidence for extranodal involvement

A young patient with AV nodal tachycardia was referred for ablation. During electrophysiological testing, a stable succession of up to four different RR intervals with comcomitantly changing QRS morphologies were recorded. This observation might reflect the conduction of the reentry circuit through different extranodal ''pathways'' in the low right atrium. Radiofrequency current was applied near the ostium of the coronary sinus; this abolished conduction through the slow pathway, as dual AV conduction was no longer present. She remains free of recurrences for a follow-up period of 8 months