QTc Calculator — Free Online Calculator
Input
QTc (Bazett)
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QTc (Fridericia)
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About This Calculator
The corrected QT interval (QTc) adjusts the measured QT interval for heart rate, since the QT interval naturally shortens at faster heart rates. A prolonged QTc increases the risk of ventricular arrhythmias, including Torsades de Pointes. Bazett's formula is the most commonly used but tends to overcorrect at high heart rates; Fridericia's formula is more accurate at extreme heart rates.
Formula
Interpretation
| QTc (ms) | Interpretation |
|---|---|
| ≤ 440 (male) / ≤ 460 (female) | Normal |
| 441–499 (male) / 461–499 (female) | Borderline prolonged |
| ≥ 500 | Prolonged — high risk |
References
- Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.
- Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469-486.
- Goldenberg I, et al. QT interval: how to measure it and what is "normal". J Cardiovasc Electrophysiol. 2006;17(3):333-336.
Frequently Asked Questions
What is a prolonged QTc interval?
A QTc interval >450 ms in males or >470 ms in females is generally considered prolonged. QTc >500 ms significantly increases the risk of torsades de pointes, a potentially fatal ventricular arrhythmia.
Which QTc correction formula is more accurate?
The Bazett formula is most commonly used but overcorrects at high heart rates and undercorrects at low heart rates. The Fridericia formula is considered more accurate, especially when heart rate is outside 60–100 bpm. Many guidelines now recommend Fridericia.
What medications can prolong the QT interval?
Many drugs can prolong QT, including antiarrhythmics (sotalol, amiodarone), antibiotics (azithromycin, fluoroquinolones), antipsychotics (haloperidol, ziprasidone), and antiemetics (ondansetron). CredibleMeds.org maintains a comprehensive list.
What electrolyte abnormalities affect QTc?
Hypokalemia, hypomagnesemia, and hypocalcemia all prolong the QT interval. Correcting these electrolyte imbalances is essential before attributing QT prolongation to other causes.
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⚠ Medical Disclaimer
This tool is for educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for clinical decisions.