Corrected QT interval (QTc — Bazett & Fridericia)
- Category: General
- Version: v1.0.1
- Reviewed: Reviewed 6 Sep 2026
- Validation: Validation pending
RR in seconds = 60 ÷ HR, or the R–R interval as entered directly. Bazett QTc = QT ÷ √RR. Fridericia QTc = QT ÷ RR^(1/3). Both return the QTc in the unit the QT was entered in, and at a heart rate of 60 both equal the raw QT.
The bands are applied to the Bazett value only, because the pediatric thresholds were derived with Bazett and are not equivalent for Fridericia. QTc alone is never diagnostic; long QT syndrome requires full criteria (Schwartz score, symptoms, family history, genetics). Formula choice changes the answer: Bazett over-corrects at fast rates and so systematically over-calls prolongation in children. Outside roughly 60 to 100 bpm, Fridericia is the more defensible correction, and it is reported here without bands. Adult sex-specific cutoffs must not be applied to children. The QTc is only as good as the QT measurement (lead, tangent method, U-wave exclusion, machine vs manual).
| Result | Interpretation |
|---|---|
| ≤ 440 | ≤ 440 ms — At or below the pediatric upper limit of normal for a Bazett-corrected QTc (Andršová 2020; Phan 2015). |
| >440 to 460 | > 440 to ≤ 460 ms — Borderline zone between the pediatric upper limit of normal (~440 ms) and the prolonged threshold (460 ms) for a Bazett QTc (Andršová 2020; Phan 2015). |
| >460 to <480 | > 460 to < 480 ms — Above the pediatric prolonged-QTc threshold of 460 ms for a Bazett QTc (Phan 2015 endorsed 460 ms in infants/young children; Andršová 2020). |
| ≥ 480 | ≥ 480 ms — At or above the level Andršová 2020 cite as diagnostic of long QT syndrome for a Bazett QTc. QTc alone is not diagnostic — LQTS is established with full criteria (Schwartz score, symptoms, family history, genetics). |
References
- Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353–370. Reprinted Ann Noninvasive Electrocardiol. 1997;2(2):177–194.DOI 10.1111/j.1542-474X.1997.tb00325.x
- Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469–486. English translation Ann Noninvasive Electrocardiol. 2003;8(4):343–351.DOI 10.1111/j.0954-6820.1920.tb18266.x
- Phan DQ, Silka MJ, Lan Y-T, Chang R-KR. Comparison of formulas for calculation of the corrected QT interval in infants and young children. J Pediatr. 2015;166(4):960–964.PMID 25648293DOI 10.1016/j.jpeds.2014.12.037
- Andršová I, Hnatkova K, Helánová K, et al. Problems with Bazett QTc correction in paediatric screening of prolonged QTc interval. BMC Pediatr. 2020;20:558.PMID 33317470DOI 10.1186/s12887-020-02460-8
- Goldenberg I, Moss AJ, Zareba W. QT interval: how to measure it and what is "normal." J Cardiovasc Electrophysiol. 2006;17(3):333–336.PMID 16643414DOI 10.1111/j.1540-8167.2006.00408.x
Reproduction rights
Freely reproducible.Both corrections are mathematical formulas (√RR and RR^(1/3) normalizations) and the pediatric thresholds (440/460/480 ms) are numeric facts from the literature — neither is copyrightable (qtc.md IP status).
Independent clinical validation: pending
Two independent clinical validators will be named here once review is complete.
- 2026-09-03v1.0.0Initial releaseInitial published text.
- 2026-09-06v1.0.1ClarificationAdded a one-line description for the catalogue card. No rule, threshold or reference changed.
Other general scores
- APLS age-based weight estimateAge-based weight estimate for when a child cannot be weighed
- Body surface areaBody surface area from height and weight, for mg/m² dosing and cardiac index
- FOUR scoreComa assessment that stays complete in an intubated patient
- Ideal body weightIdeal body weight from height, by four published methods side by side
- Pediatric Glasgow Coma ScaleAge-adapted Glasgow Coma Scale for infants and children
Important. For use by qualified health professionals as an informational and educational aid. It supports clinical judgment and does not replace it. Verify every result independently before making a clinical decision. This is not a medical device.