- QT interval corrected (QTc) Criteria: QTc <450 milliseconds (msec) or QTc <480 msec for patients with bundle branch block The QTc is the QT interval corrected for heart rate according to either Bazett's formula (QTcB), Fridericia's formula (QTcF), or another method, machine or manual overread. For subject eligibility and withdrawal, QTcF will be used. For purposes of data analysis, QTcF will be used as primary. The QTc should be based on single or averaged QTc values of triplicate Electrocardiogram (ECGs) obtained over a brief recording period.