Corrected QT (QTc) Calculator
Adjust QT interval based on heart rate
Bazett formula: QTc = QT / √RR
Fridericia formula: QTc = QT / 3√RR
Framingham formula: QTc = QT + 154 x (1 – RR)
Hodges formula: QTc = QT + 1.75 x (HR – 60)
Rautaharju formula: QTc = QT + (120 + HR) / 180
* QTc[msec], QT[msec], RR[sec], RR interval(=60/HR), HR[beats/min]
Why Correct the QT Interval (QTc)?
The QT interval represents the entire duration of ventricular systole. However, it can vary depending on heart rate, electrolyte abnormalities, age, and sex. In particular, the QT interval increases when the heart rate decreases and shortens when the heart rate increases. Therefore, correction for heart rate is necessary — this corrected value is known as the QTc (corrected QT interval).
A normal QTc interval is typically around 410 milliseconds. A QTc exceeding 419 milliseconds is considered prolonged. QT prolongation can indicate a risk for arrhythmias, especially Torsades de Pointes.
An additional simple way to assess the QT interval :
The QT interval should be shorter than half of the R-R interval.