Figure 3 Phenomena observed during diagnostic process of patient 3
3A: Tachycardia switched between LBBB, RBBB and normal QRS morphology, accompanied by cycle length change. 3B: Antegrade conduction of His bundle during tachycardia. 3C: A His bundle refractory period ventricular stimulus reset the tachycardia and antegrade conduction of His bundle during ventricular pacing revealed the existence of accessory pathway. 3D: Progressive QRS fusion and perfect PPI during RVA entrainment. LBBB=left bundle branch block; RBBB=right bundle branch block; PPI=post pacing interval.