Figure 3.

(A) Wide complex tachycardia at the beginning of the EP study. (B) During programmed atrial stimulation, a shift in QRS morphology from LBBB (second circle) to RBBB (first circle) can be observed. (C) Fusion between A and V potentials in the distal coronary sinus suggesting a left lateral AP. (D) The first two arrows show the presence of the AP – fusion between A and V potentials; the last two arrows show the disappearance of the fusion – successful ablation of the AP. Also, a wider QRS complex after ablation can be observed on surface ECG (V1-3).