QTc Calculator

How does this QTc calculator work?

This is a handy health tool that can estimate the QT corrected interval by using the heart rate expressed in beats per minute and QT interval expressed either in seconds or milliseconds. The QT values can be obtained from the ECG test.

This QTc calculator is designed to show the QT corrected interval for heart rate extremes because it returns the estimations by 4 different equations as presented below:  

QT corrected interval:

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

■ by Fridericia’s formula: QTc = QT/(RR^0.33)

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

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

Where:

RR interval = 60 / HR 

HR = Heart rate in beats per minute.

Moreover it returns the QT corrected interval expressed in both seconds and milliseconds.

As agreed upon by ACC / HRS the normal QTc interval is below 450 milliseconds for men and below 460 milliseconds for women.

No gender specific, any QTc greater than 500 milliseconds is considered highly abnormal, while any value of QTc smaller than 340 milliseconds may indicate short QT syndrome.

Please remember that this QTc calculator should NOT be considered as a substitute for any medical professional service.

Example calculation

For a heart rate/ Pulse of 72 beats per minute and a QT interval of 0.42 seconds the result is:

■ QTc Interval by Bazett’s method = 0.460 sec OR 460 msec

■ QTc Interval by Fridericia’s equation = 0.446 sec OR 446 msec

■ QTc Interval by Framingham’s algorithm = 0.446 sec OR 446 msec

■ QTc Interval by Hodges’s equation = 0.441 sec OR 441 msec

■ RR Interval = 0.833 sec OR 833 msec

What is the short QT syndrome?

This is a condition that can cause arrhythmia which is a disruption in the heart’s normal rhythm because the QT interval shortening means that the heart takes less time to recharge/ relax between beats but there is no underlying structural anomaly of the heart.

This is a relatively new discovery of the 21^st century medicine and there haven’t been numerous cases documented. It can be detected through EKG (electrocardiogram) that measures the electrical activity of the heart.

This condition that appears at any age, if left untreated leads to syncope which is fainting, feelings of dizziness and even to cardiac arrest and sudden death. On the other hand there are people, generally healthy that have shortened QT but don’t display any symptoms.

What if the QT is higher than normal?

The long QT syndrome is an uncommon condition, also put under arrhythmias and can pose a serious threat as the electrical activity of the heart is disrupted. There are also some individuals that have QT intervals longer but don’t develop serious arrhythmia while others experience moments in which their heart suddenly beats faster for no particular reason and this disruption of rhythm leads to the brain not being oxygenated properly and then fainting.

It is discussed that there is an inheritance pattern for this anomaly and that there are higher chances for it to appear to individuals that have cases of heart disease in the family.

References

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

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