Beat-to-beat determinants of the beat-to-beat temporal and spatial variability of repolarization

Background The goal of this study was to compare the time series predictors of beat-to-beat variability in repolarization in healthy individuals. Methods Spatial QRS- and T-vector amplitudes, spatial QRS-T, RR′ and TT′ angles, RR′ and QT intervals, and QRS- and T-loop roundness were measured on 453 consecutive sinus beats in 168 healthy subjects (mean age 39.8 ± 15.6 years; 50% men; 93% white). Panel time-series regression models were adjusted by age, sex, and race. Appropriate time series of ECG metrics served as predictors and outcomes. Results Increase in T-loop roundness index by 0.1 was associated with 1.1°(95%CI 0.9-2.2; P = 0.048) increase in corresponding TT′ angle. One unit increase in a respiration index was associated with 4 ms (95%CI 0.6-7.0; P = 0.021) increase in QT interval. Conclusions Spatial TT′ angle and beat-to-beat variability in T-loop roundness represent intrinsic measures of repolarization variability. QT interval variability characterizes the effect of respiration and heart rate variability.