Cardiology
Corrected QT (QTc, Hodges)
Linear heart-rate correction of QT.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The Hodges formula corrects the measured QT interval for heart rate, producing a rate-corrected QT (QTc) that allows comparison across different heart rates. It uses a linear correction — QTc = QT + 1.75 × (heart rate − 60) — rather than the square-root relationship of Bazett. Linear corrections such as Hodges tend to perform better than Bazett at the extremes of heart rate, where Bazett can over- or under-correct. The result is reported in milliseconds.
Interpreting the result
A QTc up to about 440 ms is generally normal, 441–470 ms is borderline, and above 470 ms is prolonged and associated with an increased risk of ventricular arrhythmia, including torsades de pointes. Thresholds differ slightly by sex and source, and a marked change from a patient's own baseline is clinically important even within the "normal" range. The corrected value guides decisions about QT-prolonging drugs and electrolyte correction.
Worked example
A patient has a measured QT of 420 ms at a heart rate of 100 bpm. Using Hodges: QTc = 420 + 1.75 × (100 − 60) = 420 + 70 = 490 ms — a prolonged QTc that warrants review of QT-prolonging drugs and electrolytes.
Pearls / pitfalls
- No correction formula is perfect; Hodges is more reliable than Bazett at very fast or very slow rates, where Bazett notably overcorrects.
- Measure the QT in the lead with the longest interval and a clearly defined T-wave end, avoiding U-waves.
- A wide QRS (for example bundle branch block) inflates the QT — a QRS-corrected approach may be needed.
- Trends matter: a significant rise from a patient's own baseline QTc is meaningful even if still within the normal band.
Evidence & validation
The Hodges correction was described as one of several rate-correction formulae and is recognised for its more stable performance across heart rates compared with Bazett. Multiple comparative studies support linear corrections such as Hodges and Framingham over Bazett at extreme rates, and society guidance acknowledges the limitations of any single formula.
Frequently asked questions
How is the Hodges QTc different from Bazett?
Hodges uses a linear correction based on heart rate, whereas Bazett divides the QT by the square root of the RR interval. Hodges is generally more reliable at very high or very low heart rates, where Bazett tends to over- or under-correct.
What QTc is considered prolonged?
A QTc above about 470 ms is generally regarded as prolonged and carries an increased arrhythmia risk. Values of 441–470 ms are borderline, and exact thresholds vary slightly by sex and reference.
Does a normal QTc rule out risk?
Not entirely. A significant increase from a patient's own baseline can be important even within the normal range, and other factors such as electrolyte disturbance and QT-prolonging drugs also contribute to risk.
Which heart rate should I use?
Use the heart rate corresponding to the ECG on which the QT was measured. An irregular rhythm such as atrial fibrillation makes any single-beat correction less reliable, so interpret with caution.
References
- Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed: evidence that a linear QT correction for heart rate is better. J Am Coll Cardiol. 1983;1:694.
- Postema PG, Wilde AAM. The measurement of the QT interval. Curr Cardiol Rev. 2014;10(3):287–294.
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