- Patients at high risk for QT/QTc prolongation, e.g. Baseline prolongation of QTcF >/=500 msec; Risk factors for Torsade de Pointes (e.g. uncompensated heart failure, abnormal potassium or magnesium levels that cannot be corrected, any unstable cardiac condition during the last 30 days, or a family history of long QT syndrome); The use of concomitant medications that prolong the QT/QTc interval.