Corrected QT

What This Calculator Measures

Corrects the QT interval for heart rate using the Bazett formula to assess QT prolongation risk.

How to Use

1. Measure the QT interval from the ECG (from the start of the QRS complex to the end of the T wave).
2. Enter the QT interval in milliseconds.
3. Enter the heart rate in beats per minute.
4. Select the patient's sex (thresholds differ between men and women).
5. Review the corrected QTc value and its interpretation.

Interpretation Guide

QTc <450 ms (men) or <460 ms (women) is normal. 450–499 ms (men) or 460–499 ms (women) indicates prolongation. ≥500 ms indicates marked prolongation and increased risk of Torsades de Pointes.

Clinical Significance

QT prolongation is a risk factor for Torsades de Pointes, a potentially fatal ventricular arrhythmia. Identifying prolonged QTc allows clinicians to address modifiable risk factors such as electrolyte abnormalities and QT-prolonging medications.

When to Use

• Assessment of QT prolongation risk
• Patients with electrolyte abnormalities (hypokalemia, hypomagnesemia, hypocalcemia)
• Medication review for QT-prolonging drugs
• Pre-operative cardiac risk assessment
• Evaluation of syncope or family history of sudden cardiac death

When Not to Use

• As a standalone risk assessment without clinical context
• When the ECG tracing quality is poor and QT measurement is unreliable

Limitations

• The Bazett formula tends to over-correct at high heart rates and under-correct at low heart rates.
• QT measurement itself has significant inter-observer variability.
• Does not replace clinical assessment of arrhythmia risk.
• Other correction formulas (Fridericia, Framingham) may be more appropriate in certain clinical settings.

Worked Example

A 45-year-old woman has a QT interval of 460 ms and a heart rate of 72 bpm.

QTc ≈ 504 ms (using Bazett formula). This is markedly prolonged (≥500 ms) and indicates increased risk of Torsades de Pointes.

Evidence

Source

Original Bazett Description / AHA ECG Guidelines

Reference

Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Bazett HC. Heart. 1920;7:353-370.
2. AHA ECG Guidelines for the Interpretation of the Resting 12-Lead ECG.

References

1. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370. (Original Description)
2. AHA ECG Guidelines for the Interpretation of the Resting 12-Lead ECG. (Guideline)