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.