Left bundle branch block-type ventricular tachycardia originating from the left ventricular septum in a patient with cardiac sarcoidosis.

This case report describes a left bundle branch block (LBBB)-type ventricular tachycardia (VT) with a unique reentrant circuit in a patient with cardiac sarcoidosis. The VT morphology and pace mapping supported an exit site of the VT from the basal posterior right ventricle (RV) septum. Nonetheless, concealed entrainment was established by pacing from a septal left ventricular (LV) site recording a diastolic potential, opposite site to the RV site. A point ablation at that LV site could successfully terminate the VT, suggesting that a critical isthmus was located on the LV side of the interventricular septum despite the demonstration of an LBBB-type VT.