The normal QT interval is controversial ... Due to the effects of heart rate, the corrected QT interval (QTc) is frequently used. The QTc is considered prolonged if greater than 450 ms in males ...

the certainty is considerably less for the otherwise asymptomatic person who happens to host a QTc value coined “borderline” (QTc ⩾440 ms). Although a normal QT interval imparts a much lower risk of ...