Formulae for correction of QT interval: Calculation of QTc

Formulae for correction of QT interval: Calculation of QTc

QT interval on ECG

Various formulae have been used for the correction of QT interval with respect to the heart rate, even though the most popular one is the Bazett’s formula. Generally the QT intervals are corrected for a heart rate of 60 per minute. Some formulae use logarithmic parameters while others are linear.

Logarithmic formulae for correction of QT interval (Log-linear)

Bazett’s formula: QT / (RR)^0.5
[Observed QT interval divided by root of RR interval, in seconds]

Fridericia’s formula: QT / (RR)^0.33
[Observed QT interval divided by cube root of RR interval, in seconds]

Baseline correction: QT / (RR)^0.37
[Observed QT interval divided by RR interval, in seconds raised to the power of 0.37]

Linear formulae for correction of QT interval

Framingham formula: QT + 0.154 (1 – RR)

Hodges formula: QT + 1.75 (HR – 60)