Polymorphic ventricular tachycardia (a.k.a. Torsades de Pointes) is best treated with intravenous magnesium. Patients with a prolonged QT interval have a higher risk of developing polymorphic VT.

A prolonged QT interval increases the risk of polymorphic ventricular tachycardia (Torsades de Pointes) which can result in sudden cardiac death. Long QT 1: The ECG shows broad based T waves.