- Risk of prolonged interval between Q and T (QT) on an electrocardiogram (ECG) corrected for heart rate (QTc) as defined by: (1) Current therapy with any medication known to be associated with Torsades de pointes or potent inducers of cytochrome CYP3A4. (2) History of QT prolongation. (3) Congenital long QT syndrome. (4) QT interval corrected for heart rate by the Bazett's method (QTcB) correction unmeasurable or greater than 480 ms on screening ECG.