ABSTRACT
In order to perform the correct interpretation of corrected QT interval length (QTc), correct QT measurement (QT) is required. Inadequate QTc and QT measurements and calculations can lead to overdiagnosing, unjustified treatment for unaffected individuals, and underestimation of disease severity. This study investigates differences in length between manual and automated QT (QTc) on the ECG at rest and determines the causes of these differences. Analysis included 3925 ECG recordings of random men (age range 15+). QTc and QT intervals are measured with manual methods and automated algorithms. QTc and QT numeral values in 2 measurement methods matched in 4.3% of ECGs only. Most automated measurements (83.8%) were overestimated. Fraction of underdiagnosis of QTc prolongation cases over 440 msec for male for automated measurement and calculation was 20.4%, overdiagnosis share – 17.4%. Questionable automatic measurements of prolonged QT and QTc intervals should be supplemented by manual reevaluation and calculation of this interval. Most common differences in detecting QTc above 440 msec between manual and automated measurements involve the T wave (undetected T wave offset, T wave low amplitude, T wave alternation), altogether conditionated 53.3% of differences. 35% of those cases were connected with vague Q (R) wave. In 8.3% of cases, the cause of difference in QTc detection over 440 msec for manual and automated methods was not revealed.