Table III.

QTc prolongation grade and corresponding recommendations.

QTc prolongation grade	Definition	Recommendationa
1	Average QTc 450–480 msec	In patients with drug-induced LQTS, removal of the offending agent is indicated (I, A)
2	Average QTc 481–500 msec	In patients with drug-induced LQTS, removal of the offending agent is indicated (I, A)
3	Average QTc ≥501 msec; >60 msec change from baseline	In patients with drug-induced LQTS, removal of the offending agent is indicated (I, A)
4	Torsade de pointes; polymorphic ventricular tachycardia; signs/symptoms of serious arrhythmia	Intravenous magnesium sulfate for patients who take QT-prolonging drugs and present with few episodes of torsades de pointes pacing in which the QT remains long (IIa, B); atrial or ventricular or isoproterenol (IIa, B); potassium ion repletion to 4.5–5 mmol/l (IIb, C)

^aIn the parentheses, the Roman numeral represents the classification of the recommendation, and the letter represents the level of evidence. National Cancer Institute's toxicity definitions for corrected QT interval prolongation (78) and specific treatment recommendations according to the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology (ACC/AHA/ESC) 2006 guidelines (79). LQTS, long QT syndrome.