QTc Calculator – Corrected QT Interval
Calculate corrected QT interval from ECG measurements
For informational purposes only. Consult a healthcare provider for ECG interpretation and clinical decisions.
Table of Contents
How to Use
- Measure QT interval from ECG in milliseconds
- Enter heart rate in beats per minute
- Select sex and preferred correction formula
- Click calculate to see QTc result and interpretation
What is QTc?
QTc (corrected QT interval) is a heart rate-corrected measurement of the QT interval on an electrocardiogram (ECG). The QT interval represents the time for ventricular depolarization and repolarization. Since the QT interval varies with heart rate, correction formulas are used to standardize the measurement.
A prolonged QTc indicates delayed cardiac repolarization, which can increase the risk of potentially life-threatening arrhythmias such as Torsades de Pointes.
QTc Correction Formulas
Three main formulas are used to calculate QTc:
- Bazett formula: Most commonly used, but can overcorrect at high heart rates
- Fridericia formula: More accurate at extreme heart rates
- Framingham formula: Linear correction, useful for heart rates near 60 bpm
Normal QTc Values
| Category | Male | Female |
|---|---|---|
| Normal | < 440 ms | < 460 ms |
| Borderline | 440-450 ms | 460-470 ms |
| Prolonged | > 450 ms | > 470 ms |
Clinical Significance
QTc prolongation can be:
- Congenital (Long QT Syndrome - LQTS)
- Acquired (medications, electrolyte imbalances)
- Associated with increased risk of sudden cardiac death
- A contraindication for certain medications
Always consult a cardiologist for proper evaluation and management of QTc abnormalities.
Frequently Asked Questions
- What is a normal QTc value?
- Normal QTc values are generally less than 440 ms for men and less than 460 ms for women. Values between 440-450 ms (men) or 460-470 ms (women) are considered borderline.
- Which QTc formula is most accurate?
- Bazett is most commonly used clinically, but Fridericia may be more accurate at extreme heart rates. The choice often depends on institutional preference and clinical context.
- What causes QT prolongation?
- QT prolongation can be caused by genetic conditions (Long QT Syndrome), medications (antiarrhythmics, antibiotics, antipsychotics), electrolyte imbalances (low potassium or magnesium), or structural heart disease.
- Is QT prolongation dangerous?
- Prolonged QT interval increases the risk of ventricular arrhythmias, particularly Torsades de Pointes, which can be life-threatening. Anyone with prolonged QTc should be evaluated by a cardiologist.
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