Narrow-QRS Ventricular Tachycardia Due to Microreentry After Iatrogenic Right Bundle Injury

BACKGROUND: Ventricular tachycardia (VT) after ablation near the conduction system can present with a relatively narrow QRS complex and mimic supraventricular tachycardia (SVT), making diagnosis and management challenging. CASE SUMMARY: A 26-year-old man with 2 prior ablations for idiopathic premature ventricular complexes presented with incessant narrow-QRS tachycardia and left ventricular systolic dysfunction. Despite antiarrhythmic drugs and repeated cardioversion, the tachycardia persisted. Electrophysiologic study demonstrated ventriculoatrial dissociation, fixed His-His return intervals, and concealed fusion during atrial overdrive pacing. High-density mapping identified earliest activation at the mid-right bundle within a voltage border zone. Targeted radiofrequency ablation at this site terminated the VT and restored sinus rhythm, with complete recovery of ventricular function. DISCUSSION: This case illustrates an iatrogenic conduction system-related microreentrant VT masquerading as SVT, and it highlights the value of pacing maneuvers and high-density mapping for mechanistic diagnosis and precise ablation. TAKE-HOME MESSAGES: VT after prior right ventricular ablation may present with a narrow-QRS complex and mimic SVT. High-density mapping and pacing maneuvers can reveal an iatrogenic conduction system-related reentrant circuit and guide effective ablation.