Statistical
Corrected QT Interval (QTc) ECG formulas: Bazett (SQRT) vs Fridericia (Cube Root)
Compare Bazett and Fridericia heart-rate corrections using QT in milliseconds and heart rate in beats per minute.
Compare correction methods with explicit units
For a regular rhythm, RR in seconds is 60 divided by heart rate in beats per minute. Bazett divides QT by sqrt(RR), while Fridericia divides it by RR^(1/3). With QT supplied in milliseconds, both results are displayed in milliseconds under these conventional correction formulas.
The formulas are population corrections, not individualized guarantees. Bazett can overcorrect at higher heart rates and undercorrect at lower rates. Fridericia also has limitations; drug-study guidance does not make one formula universally valid in every patient or mandate the simple alarm in this worksheet.
This arithmetic example cannot validate ECG measurement, rhythm, QRS duration or clinical risk. Do not infer absence of risk from a result below a threshold. Appropriate interpretation considers the tracing, symptoms, medicines and other clinical information.
| ECG QTc Formula | Spreadsheet Expression | QT = 420 ms, HR = 75 (RR = 0.80s) | At HR = 60 bpm (RR = 1.0s) |
|---|---|---|---|
| Bazett QTc (Square Root) | B2 / SQRT(60 / B3) | 420 / 0.89443 = 469.6 ms | 420.0 ms |
| Fridericia QTc (Cube Root) | B2 / ((60 / B3) ^ (1 / 3)) | 420 / 0.92832 = 452.4 ms | 420.0 ms |
| Illustrative threshold comparison | Compare unrounded Bazett QTc with 500 ms | QT=460, HR=75 gives 514.3 ms after rounding | At 60 bpm, the same QT gives 460 ms |
Bazett Corrected QT Interval: QTc_B = QT_ms / SQRT(60 / HR_bpm)
Uses the square root of RR in seconds. A numeric positive QT and heart rate are required.
=IF(COUNT(B2:B3)<>2,"Invalid inputs",IF(OR(B2<=0,B3<=0),"Invalid inputs",ROUND(B2 / SQRT(60 / B3), 1)))Fridericia Cube-Root Corrected QT Interval: QTc_F = QT_ms / ((60 / HR_bpm) ^ (1/3))
Uses the cube root of RR in seconds. At 60 bpm both correction formulas return the supplied QT.
=IF(COUNT(B2:B3)<>2,"Invalid inputs",IF(OR(B2<=0,B3<=0),"Invalid inputs",ROUND(B2 / ((60 / B3) ^ (1 / 3)), 1)))Compare an unrounded Bazett result with an example threshold
This labels the arithmetic comparison only; it neither diagnoses torsades nor determines treatment. The comparison uses the unrounded result so display rounding does not change the branch.
=IF(COUNT(B2:B3)<>2,"Invalid inputs",IF(OR(B2<=0,B3<=0),"Invalid inputs",IF((B2 / SQRT(60 / B3)) >= 500, "Bazett QTc at least 500 ms", "Bazett QTc below 500 ms")))Try the example
Use the original values or change them to test your understanding.