QTc interval is significant because prolongation may lead to ventricular dysrhythmia. Computerized electrocardiogram machines typically measure QT interval length and, using an algorithm assessment of multiple leads, calculate a QTc value. Manual measurement of the QT interval used to calculate the QTc value is more time-consuming but potentially more accurate. In this study, we compare the automated QTc calculation with the QTc value calculated using manual QT measurements.
We prospectively obtained 350 resting 12-lead electrocardiograms (ECGs) in children aged 2 to 14 years in an academic pediatric emergency department. Manual measurement of the QT interval was performed and the QTc was calculated using the 2 most commonly used correction methods, Bazzet and Fridericia formulas. The paired values were used to perform a Bland-Altman analysis and create a receiver operating characteristic curve.
Bland-Altman analysis determined that QT-automated and QTc-Bazett had an average difference of 3.8 milliseconds, with a standard deviation of 86 milliseconds (95% confidence interval = −161 to 176). An automated QTc value of 455 milliseconds was sensitive to detect manual QTc values of greater than 480 milliseconds.
In children with resting ECGs, there is a poor agreement between the automated QTc produced by a computerized electrocardiogram and the QTc value obtained using manual QT measurement. Statistically and clinically relevant discrepancy between the automated QTc and QTc values calculated after manual QT measurement was present. Automated QTc values may be used as a screening tool to detect prolonged QTc, but for accurate determination of QTc, manual measurement is necessary.