Inappropriate ventricular pacing-induced ventricular fibrillation in a long QT type 3 syndrome patient with implantable cardioverter-defibrillator

•Ventricular pacing in patients with implantable cardioverter-defibrillator (ICD) has potentially proarrhythmic effects.•Timely ventricular pacing due to an automatic ventricular threshold testing and atrial undersensing played an important role in the occurrence of ventricular fibrillation (VF) by forming short-long-short sequence.•In patients with long QT syndrome, discontinuation of an automatic ventricular threshold testing and appropriate lead management are essential to prevent iatrogenic VF.