Corrected QT Interval

Formulas

• Bazett: QTc = QT / √(RR) — most commonly used, overcorrects at high HR
• Fridericia: QTc = QT / (RR)^(1/3) — preferred at extremes of HR
• Framingham: QTc = QT + 0.154 × (1 − RR) — linear correction
• Hodges: QTc = QT + 1.75 × (HR − 60) — linear, less rate-dependent bias
• Rautaharju: QTc = QT × (120 + HR) / 180 — age/sex refined

Wide QRS note: For LBBB, subtract 0.5 × (QRS − 100) ms from QT before correcting. For RBBB, subtract 0.5 × (QRS − 100) ms.

Normal Values

• Normal QTc: <450 ms (men), <460 ms (women)
• Borderline prolonged: 450–469 ms (men), 460–479 ms (women)
• Prolonged: ≥470 ms (men), ≥480 ms (women)
• High risk: ≥500 ms (any sex — associated with TdP risk)