Evaluation of the difference between automated and measured QTc intervals in children

The corrected QT interval (QTc) is obtained through automated ECG computations or manual physician measurements. We hypothesized that differences exist in children between the measured and automated QTc intervals within and between Healthy and hypertrophic cardiomyopathy (HCM) subjects with greater differences for HCM due to structural abnormalities.

QT measurements - Bazett correction- automated (aQTc) and measured (mQTc), were extracted from the GE MUSE database for 385 Healthy pediatric (single ECG) and 208 HCM subjects (2 ECGs), stratified by age < 12 and ≥ 12 yrs., sex, race, and ethnicity. QTc means (SD), automated and measured differences, and the difference of the differences of aQTc and mQTc were analyzed overall and by subgroups. All ECGs were read by one pediatric cardiologist with a second cardiologist reading a random subset of HCM ECGs to evaluate intraclass correlations and agreement.

The mQTc intervals were shorter than aQTc intervals within Healthy (p < 0.001) and within first HCM ECGs (p < 0.001) with both aQTc and mQTc shorter in Healthy than HCM (p < 0.001). The difference in these differences was significant overall using HCM ECG 1 but not HCM ECG 2. Healthy subject aQTc and mQTc intervals differed by age, sex, and race (p < 0.002). HCM ECG 1 aQTc- mQTc intervals differed for age < 12 yrs., as well as by sex and race. HCM ECG 2 intervals differed only for age < 12 yrs.

Compared to measured values, automated QTc values were significantly longer in both Healthy and HCM subjects. Automated measurements may overestimate the QTc.