# QTc Calculator

Corrects the QT interval based on its duration on ECG test and the patient’s heart rate.

In the text below the tool you can read more about the four QTc equations that are used.

The QTc calculator is aimed at determining the corrected QT interval. This is based on the use of the QT interval, as extracted from an ECG test and the pulse rate of the patient, measured in beats per minute.

The QT interval is one of the most important pieces of information provided by the ECG and represents the electrical depolarization and repolarization of the ventricles.

Normal values are considered to be below maximum 0.46s. Abnormally long intervals may indicate ventricular tachyarrhythmias.

The corrected QT interval is estimated through 4 different formulas:

■ Bazett’s formula: QTc = QT/√(RR in seconds)

■ Fridericia’s formula: QTc = QT/(RR0.33)

■ Framingham’s formula: QTc = QT + 0.154(1-RR)

■ Hodges’s formula: QTc = QT + 1.75(HR - 60)

According to the ACC/HRS, normal values are lower than 450 milliseconds for men and below 460 milliseconds for women.

Heart rate/Pulse (HR)
QT interval (QT)
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Steps on how to print your input & results:

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## Variables considered

The QTc calculator is based on heart rate (pulse rate) in beats per minute and QT interval, either in seconds or miliseconds.

■ Heart rate is defined as the number of subsequent contractions of the heart during one minute, in which blood is pumped from the ventricles to the arteries.

■ The QT interval is a cardiologic term used for the time in the heart’s electrical cycle between the start of the Q wave and the end of the T wave. This is measured in seconds or in miliseconds, the latter for more precision.

## QTc formulas

The corrected QT interval is calculated based on the following:

■ Bazett’s formula: QTc = QT/√(RR in seconds)

■ Fridericia’s formula: QTc = QT/(RR0.33)

■ Framingham’s formula: QTc = QT + 0.154(1-RR)

■ Hodges’s formula: QTc = QT + 1.75(HR - 60)

According to the ACC/HRS:

■ Normal values are lower than 450 milliseconds for men and below 460 milliseconds for women;

■ Any QTc value greater than 500 milliseconds is abnormal;

■ Any QTc value lower than 340 milliseconds is abnormal and may indicate short QT syndrome.

After one comparison study, it was concluded that Fridericia and Framingham correction formulas have the best rate correction and significantly improved prediction while Bazett’s formula overestimated QTC prolongation.

## Abnormally high or low QTc

Values lower than normal may be caused by short QT syndrome which is a condition that in turn leads to arrhythmia. This is not considered to have to do with any underlying structural anomaly of the heart and can appear at any age.

A shorter QT interval basically means that the heart takes less time to relax between contractions. This can lead to syncope, dizziness and even complicate to cardiac arrest and sudden death.

Prolonged QT syndrome is also indicative of an arrhythmia type and is characteristic by moments in which the heart suddenly beats faster for no particular reason.

This increase in contraction frequency that has not been supported by other physiological adaptation can lead to impaired tissue perfusion of the brain.

## References

1. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920; (7): 353–37

2. Vandenberk B, Vandael E, Robyns T, Vandenberghe J, Garweg C, Foulon V, Ector J, Willems R. Which QT Correction Formulae to Use for QT Monitoring? J Am Heart Assoc. 2016; 17;5(6).

3. Indik JH, Pearson EC, Fried K, Woosley RL. Bazett and Fridericia QT correction formulas interfere with measurement of drug-induced changes in QT interval. Heart Rhythm. 2006; 3(9):1003-7.

4. Kujanik S. Comparison and recalculation of the very different QTc interval durations in young healthy women. Acta Physiol Hung. 2011; 98(3):262-72.

Specialty: Cardiology

System: Cardiovascular

Objective: Determination

Type: Calculator

No. Of Variables: 2

Abbreviation: QTc

Article By: Denise Nedea

Published On: March 16, 2017

Last Checked: March 16, 2017

Next Review: March 10, 2023