Wide and narrow QRS tachycardias: What is the mechanism?

A 50-year-old lady was referred for radiofrequency catheter ablation of narrow QRS tachycardia that was terminated with intravenous adenosine. Twelve-lead Electrocardiogram (ECG) was normal during sinus rhythm. The electrophysiological study showed an Atrio-Hisian (AH) interval of 104 ms and Hisio-Ventricular (HV) interval of 45 ms during sinus rhythm. Atrial pacing reproducibly induced regular broad (left bundle branch block morphology) and narrow QRS tachycardias. A spontaneous premature ventricular ectopic from right ventricular apex has resulted in transition of the tachycardia from wide to narrow. What are the likely mechanisms?