Looking for more details? Read our comprehensive QTc guide
What is the QTc Interval?
The QT interval represents electrical depolarization and repolarization of the ventricles. Because the QT interval naturally shortens at faster heart rates, it must be corrected for heart rate (QTc) to accurately assess the risk of arrhythmias, specifically Torsades de Pointes (TdP).
Reference Ranges
- Normal (Men) ≤ 440 ms
- Normal (Women) ≤ 460 ms
- Borderline 441-470 ms (Men) / 461-480 ms (Women)
- Prolonged (High Risk) > 500 ms
Comparison of Formulas
Bazett: Most widely used, but overcorrects at fast heart rates (>90 bpm) and undercorrects at slow heart rates (<60 bpm).
Fridericia: More accurate than Bazett at extremes of heart rate.
Framingham & Hodges: Linear correction formulas that provide more consistent results across different heart rates.
How to Use
Enter the patient's uncorrected QT interval (in milliseconds) and their current Heart Rate. Select the preferred correction formula (Bazett is most common). The tool provides the QTc.
Case Example
Patient: ECG shows a QT interval of 400 ms with a heart rate of 90 bpm.
Calculation: Using Bazett's formula: QTc = 400 / sqrt(60/90) = 489 ms.
Interpretation: The QTc is prolonged (>440 ms for men, >460 ms for women), increasing the risk of arrhythmias.
Frequently Asked Questions
Bazett's formula tends to overcorrect at fast heart rates and undercorrect at slow rates. Formulas like Fridericia or Framingham may be more accurate at extremes of heart rate.
References
- Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram. J Am Coll Cardiol. 2009.
- Vandenberk B, Vandael E, Robyns T, et al. Which QT Correction Formulae to Use for QT Monitoring? J Am Heart Assoc. 2016.