# What is the QTc?

Corrects the QT interval of an ECG for heart rate with the Bazett, Fridericia, Framingham, and Hodges formulas, and reads the result with the AHA/ACCF/HRS cut-offs for men and women.

- Page: https://www.acalculator.org/health/qtc-calculator
- JSON spec: https://www.acalculator.org/health/qtc-calculator.json
- Version: 38b4e5905a5f

## Default answer

Example with the default inputs (QT interval (ms) 400, Rate given as Heart rate, Heart rate (beats/min) 75, Headline formula Bazett, Sex Male): The Bazett QTc is 447 ms: Normal range.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| qt | QT interval (ms) | The measured QT interval on the ECG, in milliseconds. |
| mode | Rate given as | Enter the heart rate in beats per minute, or the RR interval in milliseconds. |
| hr | Heart rate (beats/min) | Heart rate at the time of the ECG, in beats per minute. |
| rr | RR interval (ms) | Time between two R waves, in milliseconds. |
| formula | Headline formula | Which formula the headline shows. The page shows all four. |
| sex | Sex | Sex at birth. The long-QTc cut-off is 450 ms for men and 460 ms for women. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| qtc | QTc | The corrected QT by the headline formula, in ms. |
| reading | Reading | Short, normal, or long QTc for the sex. |
| bazett | Bazett | QT ÷ √RR, in ms. |
| fridericia | Fridericia | QT ÷ ∛RR, in ms. |
| framingham | Framingham | QT + 154 × (1 − RR), in ms. |
| hodges | Hodges | QT + 1.75 × (heart rate − 60), in ms. |
| rate | Heart rate | Heart rate in beats per minute. |

## Method

RR (s) = 60 ÷ heart rate. Bazett: QT ÷ √RR. Fridericia: QT ÷ ∛RR. Framingham: QT + 154 × (1 − RR). Hodges: QT + 1.75 × (heart rate − 60). QT in ms.

## Assumptions

- A regular rhythm; each QTc is rounded to a whole millisecond and the reading uses the headline value.
- Long QTc: 450 ms or more in men, 460 ms or more in women; short: 390 ms or less (AHA/ACCF/HRS 2009). Over 500 ms is shown separately (Drew 2010, AHA/ACCF statement on torsade de pointes: highly abnormal).

## Worked examples

1. qt = 400, mode = hr, hr = 75, formula = bazett, sex = male gives qtc = 447, reading = Normal range, bazett = 447, fridericia = 431, framingham = 431, hodges = 426. Source: Bazett 1920: 400 ÷ √0.8 = 447.2; Fridericia 1920: 400 ÷ ∛0.8 = 430.9; Sagie 1992: 400 + 154 × 0.2 = 430.8; Hodges 1983: 400 + 1.75 × 15 = 426.25.
2. qt = 400, mode = hr, hr = 60, formula = fridericia, sex = female gives qtc = 400, bazett = 400, fridericia = 400, framingham = 400, hodges = 400.
3. qt = 360, mode = rr, rr = 600, formula = bazett, sex = female gives qtc = 465, reading = Long: 460 ms or more, fridericia = 427, framingham = 422, hodges = 430.
4. qt = 480, mode = hr, hr = 90, formula = hodges, sex = male gives qtc = 533, reading = Long: over 500 ms, bazett = 588.

## FAQ

### What is the QTc?

The QT interval is the time on an ECG from the start of the Q wave to the end of the T wave: how long the heart muscle takes to recharge after each beat. It gets shorter as the heart rate rises, so it is "corrected" to what it would be at 60 beats per minute. That corrected value is the QTc.

### What is a normal QTc?

The 2009 AHA/ACCF/HRS recommendations call a QTc of 450 ms or more long in men and 460 ms or more long in women, and 390 ms or less short. The 2010 AHA/ACCF statement calls a QTc over 500 ms highly abnormal: it goes with a 2 to 3 times higher risk of a dangerous rhythm called torsade de pointes.

### Which QTc formula is best?

Bazett (1920) is the most used, but it over-corrects at fast heart rates and under-corrects at slow ones. Fridericia, Framingham, and Hodges change less with heart rate, and the AHA/ACCF/HRS recommendations prefer a linear formula such as Framingham or Hodges. The page shows all four so you can compare them.

### What is the RR interval?

The time between two R waves on the ECG, the time of one heartbeat. RR in seconds is 60 divided by the heart rate: at 75 beats per minute, RR is 0.8 seconds (800 ms).

### Can I use the QTc with atrial fibrillation or a wide QRS?

With an irregular rhythm the RR changes from beat to beat, so the QTc from one beat is not reliable; clinicians average several beats. A wide QRS (for example bundle branch block) lengthens the QT for another reason and needs a different approach.

## Sources

- 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. https://doi.org/10.1111/j.0954-6820.1920.tb18266.x
- Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797-801. https://doi.org/10.1016/0002-9149(92)90562-D
- Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed: evidence that a linear QT correction for heart rate is better. J Am Coll Cardiol. 1983;1:694 (abstract).
- Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241-e250. https://doi.org/10.1161/CIRCULATIONAHA.108.191096
- Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the AHA and ACCF. Circulation. 2010;121(8):1047-1060. https://doi.org/10.1161/CIRCULATIONAHA.109.192704