Interpretation
| Result | Meaning |
|---|---|
| ≤ 340 ms | Short |
| < 450 (men) / < 460 (women) | Normal |
| ≥ 450 (men) / ≥ 460 (women) | Prolonged |
| ≥ 500 ms | Markedly prolonged: high torsades risk |
Formula
RR (s) = 60 ÷ HR · Bazett: QT ÷ √RR · Fridericia: QT ÷ ∛RR · Framingham: QT + 154 × (1 − RR) · Hodges: QT + 1.75 × (HR − 60) · Rautaharju: QT × (120 + HR) ÷ 180 (QT in ms)
Clinical pearls
- Bazett over-corrects at fast heart rates and under-corrects at slow rates; Fridericia or Framingham are preferred above ~90–100 bpm.
- With QRS > 120 ms (bundle branch block, pacing), QTc overestimates repolarization; consider JT interval or a QRS-adjusted method.
- A QTc increase > 60 ms from baseline on a QT-prolonging drug is also a warning sign.
Examples
qtc qt 440 hr 88corrected qt for a qt interval of 0.42 s at heart rate 110 in a womanis a qt of 480 ms at 60 bpm prolonged
FAQ
What is a normal QTc?
Below 450 ms in men and below 460 ms in women; 500 ms or more is markedly prolonged with substantially increased torsades de pointes risk.
Bazett or Fridericia?
Bazett is the most widely used but is inaccurate at high or low heart rates; Fridericia is preferred in drug-safety monitoring and at faster rates.
Evidence
- 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. J Am Coll Cardiol 2009;53:982–91.
- 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.
- Luo S et al. A comparison of commonly used QT correction formulae: the effect of heart rate on the QTc of normal ECGs. J Electrocardiol 2004;37 Suppl:81–90.