Young Male With Incessantly Wide Complex Tachycardia: What Is the Substrate of the Arrhythmia?

A 26-year-old male with no past medical issues presented with 24-hour sudden onset palpitations, chest discomfort, and dizziness. He was hemodynamically stable and his heart rate was 189 bpm, with no other remarkable findings on physical examination. A 12-lead ECG (Figure 1) showed regular wide complex tachycardia with right bundle-branch block and extreme superior axis. Stepwise management was provided with vagal maneuvers, escalating doses of adenosine, uptitrated intravenous verapamil, and cardioversion with serial discharges ≤270 J of biphasic energy. However, all interventions were ineffective, and the tachycardia remained incessant. What is the arrhythmia, and what cardiac structure is involved in its origin? Figure 1. Twelve-lead ECG recorded in the emergency department showing a regular wide complex tachycardia with right bundle-branch block morphology and right superior axis deviation. Please turn the page to read the diagnosis. The ECG shows a regular wide complex tachycardia with right bundle-branch block morphology and right superior axis, suggesting a fascicular ventricular tachycardia (VT), poor responsiveness to intravenous verapamil, and cardioversion is not characteristic of this …