QTc calculator (Bazett, Fridericia, Framingham, Hodges)

The QT interval shortens as heart rate rises, so it is corrected to a rate of 60 beats per minute (RR = 1 s). RR in seconds is 60 / heart rate.

Bazett (1920):      QTc = QT / √RR
Fridericia (1920):  QTc = QT / ∛RR
Framingham (Sagie et al. 1992): QTc = QT + 154 × (1 − RR)   (ms)
Hodges (1983):      QTc = QT + 1.75 × (heart rate − 60)   (ms)

Assumptions and limits

• Measure QT in the lead with the longest interval, averaged over several beats; the result is only as good as that measurement.
• Bazett over-corrects at fast heart rates and under-corrects at slow ones; Fridericia and Framingham are often preferred for monitoring.
• The AHA/ACCF/HRS recommendations consider a QTc of 450 ms or more in men and 460 ms or more in women prolonged, but interpretation belongs to a clinician with the full ECG.

Worked example

QT 400 ms at 75 beats/min (RR 0.8 s): Bazett 447 ms, Fridericia 431 ms, Framingham 431 ms, Hodges 426 ms.

References

• Vandenberk B et al. Which QT correction formulae to use for QT monitoring? J Am Heart Assoc 2016;5:e003264
• Rautaharju PM et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the ECG, part IV: the ST segment, T and U waves, and the QT interval. Circulation 2009;119:e241–e250
• Sagie A et al. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol 1992;70:797–801