Repolarization lability measured on 10-second ECG by spatial TT' angle: reproducibility and agreement with QT variability

J Electrocardiol. Sep-Oct 2014;47(5):708-15. doi: 10.1016/j.jelectrocard.2014.06.003. Epub 2014 Jun 9.


Background: Reproducibility of spatial TT' angle on the 10-second ECG and its agreement with QT variability has not been previously studied.

Methods: We analyzed 2 randomly selected 10-second segments within 3-minute resting orthogonal ECG in 172 healthy IDEAL study participants (age 38.1±15.2years, 50% male, 94% white). Repolarization lability was measured by the QT variance (QTV), short-term QT variability (STV(QT)), and spatial TT' angle. Bland-Altman analysis was used to assess the agreement between different log-transformed metrics of repolarization lability, and to assess the reproducibility.

Results: The heart rate showed a very high reproducibility (bias 0.14%, Lin's rho_c=0.99). As expected, noise suppression by averaging improves reproducibility. Agreement between two 10-second LogQTV was poor (bias -0.04; 95% limits of agreement [-1.89; 1.81]), while LogSTV(QT) (0.04 [-1.01; 1.10]), and especially LogTT' angle (-0.009 [-0.84; 0.82]) was better.

Conclusion: TT' angle is a satisfactory reproducible metric of repolarization lability on the 10-second ECG.

Keywords: ECG; Repolarization; Spatial TT′ angle.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Electrocardiography / methods*
  • Female
  • Heart Conduction System / physiology*
  • Heart Rate / physiology
  • Humans
  • Male
  • Reproducibility of Results