| QTc Bazett: | |
|---|---|
| QTc Fredericia: | |
| QTc Framingham | |
| QTc Hodges: |
QTc Calculator – Estimate Corrected QT Interval
The QTc Calculator helps calculate the corrected QT interval (QTc) based on the QT interval and heart rate (or RR interval). QTc is an essential parameter in ECG interpretation to assess cardiac arrhythmia risk and detect Long QT Syndrome (LQTS).
How to Use the QTc Calculator
Enter the following ECG data:
- QT Interval (in milliseconds)
- Heart Rate (bpm) or RR Interval (in seconds)
- Select the correction formula: Bazett, Fridericia, Framingham, or Hodges
The calculator will display the QTc value with interpretation.
QTc Correction Formulas
- Bazett: QTc = QT ÷ √(RR)
- Fridericia: QTc = QT ÷ (RR)1/3
- Framingham: QTc = QT + 0.154 × (1 − RR)
- Hodges: QTc = QT + 1.75 × (HR − 60)
Example
QT interval: 420 ms
Heart Rate: 75 bpm
RR = 60 ÷ 75 = 0.8 seconds
Using Bazett:
→ QTc = 420 ÷ √0.8 ≈ 470 ms
(Borderline prolonged for males)
QTc Interpretation Guide
| QTc (ms) | Interpretation |
|---|---|
| < 350 | Short QT interval |
| 350–440 (men) | Normal range |
| 350–460 (women) | Normal range |
| 440–500 | Borderline prolonged |
| > 500 | Risk of torsades de pointes |
Common Use Cases
- Cardiology and ECG interpretation
- Screening for Long QT Syndrome
- Pre-drug therapy assessment (e.g. antipsychotics, antibiotics)
- Evaluating syncope or arrhythmia risk
- Critical care and emergency medicine
Why Use the QTc Calculator?
Accurate QT correction is crucial in assessing cardiac repolarization. Manual calculation can be error-prone, so this tool provides fast and accurate results with multiple correction options.
Frequently Asked Questions (FAQs)
Which QTc formula is most accurate?
Bazett is commonly used but overcorrects at high HR. Fridericia and Framingham offer better accuracy across a range of rates.
What is a dangerously prolonged QTc?
QTc above 500 ms increases the risk of ventricular arrhythmias like torsades de pointes.
Can QTc vary with gender?
Yes. Women naturally have longer QTc intervals than men by about 10–20 ms on average.
Can medications prolong QT interval?
Yes, many drugs (e.g. SSRIs, antihistamines, macrolides) can cause QT prolongation. Always monitor high-risk patients.
Is QTc valid at any heart rate?
No. At very high or low HR, Bazett’s formula may become inaccurate. Use Fridericia or Framingham instead.
Related tools: BPM Calculator, HRmax Calculator, PF Ratio Calculator.