title: 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?
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Acad, G, Bonchev str., block 105, 1113 Sofia, Bulgaria. Ivaylo.Christov@clbme.bas.bg
authors.forename: Ivaylo
authors.initials: I
authors.lastname: Christov
authors.forename: Ivan
authors.initials: I
authors.lastname: Dotsinsky
authors.forename: Iana
authors.initials: I
authors.lastname: Simova
authors.forename: Rada
authors.initials: R
authors.lastname: Prokopova
authors.forename: Elina
authors.initials: E
authors.lastname: Trendafilova
authors.forename: Stefan
authors.initials: S
authors.lastname: Naydenov
mesh_terms: D000465:Algorithms; D016208:Databases, Factual; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D015588:Observer Variation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity