Ventricular Tachycardia With a Narrow QRS Complex: When the Improbable Is Possible.

BACKGROUND

Ventricular tachycardia (VT) is typically associated with wide QRS complexes; therefore, narrow QRS tachycardia in pacemaker-dependent patients represents a diagnostic challenge.

CASE SUMMARY: We report a 79-year-old man with permanent atrial fibrillation and complete atrioventricular block who presented with a regular narrow QRS tachycardia. Device interrogation confirmed ventricular pacing dependence. Electrophysiological studies demonstrated scar-related VT arising from the basal interventricular septum adjacent to the left bundle branch. The tachycardia was characterized by fragmented potentials and slow conduction channels and was entrainable with a short postpacing return cycle, supporting a reentrant mechanism. Targeted ablation rendered VT noninducible. No recurrent arrhythmic events occurred during follow-up.

DISCUSSION: VT may present with a narrow QRS morphology in pacemaker-dependent patients when reentrant circuits are located near the His-Purkinje system.

TAKE-HOME MESSAGE: Recognition of this uncommon mechanism and advanced electrophysiological mapping are essential for accurate diagnosis and targeted ablation.