Figures Legend:
Figure 1. A single ventricular extrastimulus applied from the right ventricular apex (RVa) during the tachycardia. RVa p= Right ventricular apex proximal, HIS d= His bundle distal, HIS p= His bundle proximal, CS= Coronary sinus.
Figure 2. Annotated response to His refractory ventricular extrastimulus and a schematic diagram demonstrating the double loop. Arrows denoting potential retrograde P waves. RVa p= Right ventricular apex proximal, HIS d= His bundle distal HIS p= His bundle proximal, CS= Coronary sinus.