Corrected QT Interval (QTc)

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Clinical Use

Estimate QT interval when a heart is beating at 60 bpm.

Reference Values

QTc categorized by the European regulatory guideline5
QTc (ms)
Male Female
Normal ≤430 ≤450
Borderline 431-450 451-470
Prolonged >450 >470


Short QTc: ≤ 340 ms6


\[QTc\hspace{0.1cm} Bazett = QT \times RR^{-1/2}\]

\[QTc \hspace{0.1cm} Fredericia = QT \times RR^{-1/3}\]

\[QTc\hspace{0.1cm} Framingham\hspace{0.1cm} (Sagie) = QT + 0.154 \times(1-RR)\]

\[QTc \hspace{0.1cm} Hodges= QT + \frac{105}{RR} -105 \]


  • Bazett formula is commonly used because it offers a simple approach to determining QTc. However, it undercorrects at heart rates below 60 bpm and overcorrects at heart rates above 100 bpm.
  • At heart rates outside of the 60 – 100 bpm range, the Fredericia or Framingham formulas are more accurate and should be used instead.


1 Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920;7:353-370.
2 Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. [The duration of systole in the electrocardiogram of normal subjects and of patients with heart disease.] Acta Medica Scandinavica 1920;53:469–486. Link
3 Hodges M, Salerno D, Erlien D. Bazett’s QT correction reviewed. Evidence that a linear QT correction for heart is better. J Am Coll Cardiol 1983;1:694.
4 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;70:797–801. Abstract
5 CPMP/986/96. The Assessment of the Potential for QT Interval Prolongation by Non-Cardiovascular Medicinal Products. London: Committee for Proprietary Medicinal Products; 1997.
6 Giustetto C, Di Monte F, Wolpert C, Borggrefe M, et al. Short QT syndrome: clinical findings and diagnostic-therapeutic implications. Eur Heart J. 2006;27(20):2440. Epub 2006 Aug 22. Full text


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Developer: Sirikarn Napan, MD, FACC