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

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 ± 15.2 years, 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.