For QTc interval calculation, in addition to Bazett’s formula, linear and parabolic heart rate correction formulas with two separate α values were used. Beat-to-beat QT interval variability was calculated using QTV index (QTVI) formula. Polysomnographic recordings of 30 patients were analyzed. In athletes and children sometimes the R-R interval shows beat-to-beat variability – it may affect the QTc, so longer ECG recordings and several measurements should be considered.The aim of the study was to determine whether different sleep stages, especially REM sleep, affect QT interval duration and variability in male patients without obstructive sleep apnea (OSA).When the heart rate is lower than 50 bpm or higher than 120 bpm longer – it may affect the QTc, so longer ECG recordings and several measurements should be considered.Irregular rhythm – this makes it difficult to get a consistent QT measurement.

Interpretation of the T wave end point is one of the main issues faced when interpreting the QT interval either manually or automatically.A wide QRS complex – may give an impression that the QT interval is prolong.However even with automated QT interval measurement several problems have been identified which gives an inaccurate measurement. Therefore automated QT interval measurement technology has been introduced. This is a usual human error and it’s difficult to correct this error. The QT interval measurement in an ECG can differ from one interpreter to another. E.g.: QT interval is 40s, Heart rate is 80 bpm.R-R interval = 60/ heart rate (it can also be measured by measuring the distance from one R wave to the next R wave manually in an ECG).Fredericia’s formula – QTcF = QT/√3(R − R).At heart rates outside of the 60 – 100 bpm range, the Fredericia corrections are more accurate and should be used instead. It provides an adequate correction for heart rates ranging from 60 – 100 bpm but over-corrects at heart rates > 100 bpm and under-corrects at heart rates < 60 bpm. Out of these two Bazzet’s formula is used commonly due to its simplicity. There are several formulas but the common used formulas are Bazzet’s formula and Fredericia’s formula. This allows comparison of QT values over time at different heart rates and improves detection of patients at increased risk of arrhythmias. QTc estimate the QT interval at a heart rate of 60 bpm.

How to calculate qtc manually