New methods of quantitative assessment of the extent and significance of serial ECG changes of the repolarization phase.

The authors present a method for optimally measuring variations in T wave shape and time intervals for the quantitative assessment of the significance of serial changes of the repolarization phase. The results, established on a healthy population, show the inadequacy of Bazett's formula, the constancy of maximum of T to the end of the T time interval, and good stability of the spatial T loops' morphotype. Residual intrasubject variability of corrected QT interval is mainly ascribable to physiologic, heart rate-independent changes in true onset of Q to a maximum of T time interval. The optimized mean quadratic deviation between two serial T loops is well correlated with changes in drug concentration.