Circulation and sepsis
Corrected QT interval (QTc)
QT corrected for heart rate, by the Bazett and Fridericia formulas.
For education. Check against your unit's guidance and a second clinician before use.
ms
beats per minute
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Before you use this
- Measure QT in lead II or V5, from the start of the QRS to the end of the T wave, averaged over several beats.
- In children, a QTc over about 460 ms is usually taken as prolonged, and over 500 ms as high risk. Discuss with paediatric cardiology.
- Common PICU causes of a long QT: low potassium, magnesium or calcium, and QT-prolonging medicines.
How this is calculated
- RR interval (seconds) = 60 ÷ heart rate
- Bazett: QTc = QT ÷ √RR
- Fridericia: QTc = QT ÷ ∛RR (cube root)
Sources
- 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.
- Rautaharju PM, et al. 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:e241–50.
Checked by PICUlearn, 21 Sept 2026.