Reliability and reproducibility of advanced ECG parameters in month-to-month and year-to-year recordings in healthy subjects

Advanced resting ECG parameters such the mean vector angle between the QRS complex and T wave (spatial QRS-T angle), and the QT interval variability index (QTVI) have important diagnostic and prognostic utility, but their reliability and reproducibility (R&R) are not well characterized. We hypothesized that the spatial QRS-T angle would have relatively higher R&R than parameters such as QTVI that are more responsive to transient changes in the autonomic nervous system. The R&R of several conventional and advanced ECG parameters were studied via intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) in: (1) 15 supine healthy subjects from month-to-month; (2) 27 supine healthy subjects from year-to-year; and (3) 25 subjects after transition from the supine to the seated posture. As hypothesized, ICC for the spatial mean QRS-T angle was higher than QTVI (0.95 vs. 0.61), and CV lower (3.8 vs. 8.1%, respectively), suggesting that the former parameter is more reliable and reproducible.