Heart rate correction of the QT interval using five formulas. Enter the measured QT and RR (or heart rate).
ms
Enter by
ms
Sex
Enter the QT and RR (or heart rate) to see the QTc by all five formulas.
Cutoffs
Men
≥ 450 ms
Women
≥ 470 ms
Both
≥ 500 ms · TdP
A tool to support learning and decision-making. The result does not replace clinical evaluation of the patient.
About: Corrected QT (QTc)
The QT interval shortens as heart rate rises and lengthens as it falls. To compare the QT with reference values, it must be corrected for heart rate: the result is the corrected QT (QTc).
This calculator shows the QTc by five formulas at once (Bazett, Fridericia, Framingham, Hodges and Rautaharju), which helps you see when the choice of formula changes the interpretation.
How to use
Measure the QT from QRS onset to the end of the T wave, preferably in lead II or V5, using the tangent method when the end of the T wave is not clear.
Enter the RR interval (in ms) of the preceding cycle or the heart rate.
Select the patient's sex: the prolongation cutoff differs between men and women.
How to interpret
Men: a QTc ≥ 450 ms is prolonged (borderline in the calculator).
Women: a QTc ≥ 470 ms is prolonged.
In both sexes, a QTc ≥ 500 ms indicates a high risk of torsades de pointes.
Bazett overestimates the QTc at high heart rates and underestimates it at low heart rates; in these settings, Fridericia and Framingham are more reliable.
Limitations
With a wide QRS (bundle branch block, paced rhythm), part of the QT reflects depolarization and the QTc is overestimated; use the modified QT. In atrial fibrillation, average several cycles.
References
Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353–70.
Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469–86.
Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797–801.
Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram. Part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241–50.
