Female sex

Hypokalemia

Bradycardia

Recent conversion from atrial fibrillation, especially with a QT-prolonging drug

Congestive heart failure

Digitalis therapy

High drug concentrations (with the exception of quinidine)

Rapid rate of intravenous infusion with a QT-prolonging drug

Baseline QT prolongation

Subclinical long-QT syndrome

Ion-channel polymorphisms

Severe hypomagnesemia