Deterioration of ventricular tachycardia to ventricular fibrillation after rapid intravenous administration of magnesium sulfate

We report the case of a patient who had development of ventricular fibrillation following rapid intravenous administration of magnesium sulfate (2 g over 5 s) for treatment of sustained monomorphic ventricular tachycardia. Initial slowing of the tachycardia was followed by gradual widening of QRS complexes and electrical alternans, leading to ventricular fibrillation within 3 min of magnesium administration.