Dataset of manually measured QT intervals in the electrocardiogram

Abstract

Background: The QT interval and the QT dispersion are currently a subject of considerable interest. Cardiac repolarization delay is known to favor the development of arrhythmias. The QT dispersion, defined as the difference between the longest and the shortest QT intervals or as the standard deviation of the QT duration in the 12-lead ECG is assumed to be reliable predictor of cardiovascular mortality. The seventh annual PhysioNet/Computers in Cardiology Challenge, 2006 addresses a question of high clinical interest: Can the QT interval be measured by fully automated methods with accuracy acceptable for clinical evaluations?

Method: The PTB Diagnostic ECG Database was given to 4 cardiologists and 1 biomedical engineer for manual marking of QRS onsets and T-wave ends in 458 recordings. Each recording consisted of one selected beat in lead II, chosen visually to have minimum baseline shift, noise, and artifact.In cases where no T wave could be observed or its amplitude was very small, the referees were instructed to mark a 'group-T-wave end' taking into consideration leads with better manifested T wave.A modified Delphi approach was used, which included up to three rounds of measurements to obtain results closer to the median.

Results: A total amount of 2*5*548 Q-onsets and T-wave ends were manually marked during round 1. To obtain closer to the median results, 8.58 % of Q-onsets and 3.21 % of the T-wave ends had to be reviewed during round 2, and 1.50 % Q-onsets and 1.17 % T-wave ends in round 3. The mean and standard deviation of the differences between the values of the referees and the median after round 3 were 2.43 +/- 0.96 ms for the Q-onset, and 7.43 +/- 3.44 ms for the T-wave end.

Conclusion: A fully accessible, on the Internet, dataset of manually measured Q-onsets and T-wave ends was created and presented in additional file: 1 (Table 4) with this article. Thus, an available standard can be used for the development of automated methods for the detection of Q-onsets, T-wave ends and for QT interval measurements.

Figure 1

PTB Diagnostic ECG Database visualized by the Wave 6.8 program. Example of individual marking of QRS onset and T-wave end in lead II (the red vertical tracings).

Figure 2

PTB Diagnostic ECG Database visualized by the Wave 6.8 program. Example of group marking of the T-wave end (the red vertical tracing) in cases when no T-wave in lead II can be observed or its amplitude is very small.

Figure 3

Reviewing rounds in the manual determination of the QRS onset and T-wave end.

Figure 4

Example of the feedback forwarded to all the referees during 2nd and 3rd rounds. The black vertical dashed line is the median. The red vertical lines denote the most left and the most right marks made by the observers, with their name and deviation from the median shown as a text at the top of the figure.

Figure 5

Histogram of deviations between the markings of Referee 1 and the Q-onset and T-wave end medians. The mean referees' deviation is depicted by small red vertical line, the 99 % confidence interval is presented by green horizontal bar and the standard deviation is given by blue horizontal bar.

Figure 6

Histogram of deviations between the markings of Referee 2 and the Q-onset and T-wave end medians. The mean referees' deviation is depicted by small red vertical line, the 99 % confidence interval is presented by green horizontal bar and the standard deviation is given by blue horizontal bar.

Figure 7

Histogram of deviations between the markings of Referee 3 and the Q-onset and T-wave end medians. The mean referees' deviation is depicted by short red vertical line, the 99 % confidence interval is presented by green horizontal bar and the standard deviation is given by blue horizontal bar.

Figure 8

Histogram of deviations between the markings of Referee 4 and the Q-onset and T-wave end medians. The mean referees' deviation is depicted by small red vertical line, the 99 % confidence interval is presented by green horizontal bar and the standard deviation is given by blue horizontal bar.

Figure 9

Histogram of deviations between the markings of Referee 5 and the Q-onset and T-wave end medians. The mean referees' deviation is depicted by small red vertical line, the 99 % confidence interval is presented by green horizontal bar and the standard deviation is given by blue horizontal bar.

Figure 10

Example of manual marking in presence of electromyographic noise. The black vertical dashed line is the median. The red vertical lines denote the most left and right markings made by the observers, with their name and deviation from the median shown as a text at the top of the figure.

Figure 11

Example of referees marking in presence of mains interference. The black vertical dashed line is the median. The red vertical lines denote the most left and right markings made by the observers, with their name and deviation from the median shown as a text at the top of the figure.