Influence of psychological stress on QT interval

This paper investigates the influence of psychological stress due to driving in city traffic condition on beat-to-beat QT interval. Electrocardiogram (ECG) signal of 16 subjects were analyzed from Physionet "drivedb" database. Total 32 segments of ECG signal was selected from all subjects. 16 of which were recorded during "Stressed" condition and rest 16 were in "Unstressed" states. Each segment was 5 minutes long and QT intervals were extracted using Berger's template matching algorithm. Heart rate corrected QT (QTc) intervals was calculated using methods proposed by Bazett, Fridericia and Framingham. The mean and standard deviation of each QTc interval time series was calculated as a feature describing average length and variability of QTc interval. The results showed that the mean QTc was lower in "Stressed" condition than "Unstressed", however none of the differences were statistically significant. In contrast, the variability of QTc intervals were higher in "Stressed" segments than the "Unstressed" ones and the difference was statistically significant. However, such difference was not present in RR intervals. In summary, QT was not prolonged due to stress but beat-to-beat QT variability increased in "Stressed" condition and this can be an effective marker to detect psychological stress.