Ventricular overdrive pacing during narrow QRS tachycardia. What are the circuits involved?
A 57 year old lady with no underlying structural heart disease presented with recurrent episodes of paroxysmal palpitation with documented adenosine responsive narrow QRS tachycardia. 12 lead surface electrocardiograms showed no pre-excitation. She underwent an electrophysiology (EP) study. Anterograde study demonstrated dual AV physiology. A regular narrow QRS tachycardia similar to clinical tachycardia was induced in the EP study with atrial pacing protocols. Ventricular overdrive pacing (VOD) was performed during the tachycardia. What are the circuits involved in the tachycardia?