Device Interrogation Unmasking Flecainide-Induced Wide Complex Tachycardia.

backgroundWide-complex tachycardia poses diagnostic and therapeutic challenges, particularly when class IC antiarrhythmic toxicity mimics ventricular tachycardia (VT). CASE SUMMARY: An 85-year-old woman with a dual-chamber pacemaker, paroxysmal atrial fibrillation on flecainide, and chronic kidney disease presented with dyspnea and a wide-complex tachycardia initially diagnosed as VT. Intravenous amiodarone was administered. Initial device interrogation revealed ventricular sensing at 496 ms cycle length without atrial tracking. Ventricular overdrive pacing demonstrated that the atrial cycle length did not accelerate to the pacing rate, confirming an independent atrial tachycardia at 551 ms and excluding atrioventricular reentrant tachycardia and VT with retrograde conduction. The Ventricular Intrinsic Preference algorithm subsequently demonstrated intact atrioventricular conduction, proving the wide QRS was aberrancy. Recognition of potential amiodarone-flecainide interaction prompted drug cessation and sodium bicarbonate therapy, leading to clinical recovery. DISCUSSION: This case demonstrates how pacemaker diagnostics can differentiate flecainide-induced aberrancy from VT and highlights the important drug-drug interaction between amiodarone and flecainide via CYP450 inhibition. TAKE-HOME MESSAGE: In patients with pacemakers presenting with wide-complex tachycardia, device interrogation and knowledge of programmed parameters are helpful to differentiate supraventricular tachycardia with aberrancy from VT.