12-lead electrocardiogram (ECG) during electrophysiologic study showing pace mapping of an idiopathic RVOT tachycardia

Left panel: 12 lead ECG of spontaneous ventricular tachycardia (VT) in a patient with a structurally normal heart. The VT has a left bundle branch block (LBBB) and an inferior axis morphology, suggesting that the origin is in the right ventricular outflow tract (RVOT). Right panel: A mapping catheter has been positioned in the RVOT and pacing is performed from its tip during sinus rhythm. The "pace map" closely approximates the QRS morphology of the spontaneous VT in all 12 leads, suggesting that the mapping catheter is at or near the VT focus.