TU wave area-derived measures of repolarization dispersion in the long QT syndrome.

The purpose of this study was to evaluate area-derived parameters of repolarization dispersion in LQTS patients and their unaffected family members and to use this analysis to challenge the concept of dispersion of repolarization in surface ECG. The area under the curve between the J point and the next P wave was measured automatically in 12 leads of the digital ECG in 34 LQTS patients and 22 unaffected family members. The area-derived measures of repolarization included total repolarization area, T wave amplitude, time to accumulate the first (tA50) and the median (tA25-75) 50% of the total area, and the time to accumulate 97% of the total repolarization area (tA97). In comparison with unaffected family members, LQTS patients had significantly higher dispersion of tA50 (tA50-SD = 34 +/- 18 ms vs 11 +/- 6 ms, respectively, P < .001) and tA25-75 (t[A25-75]-SD = 44 +/- 19 ms vs 24 +/- 15 ms, respectively, P < .001), whereas no significant difference was observed in the dispersion of total repolarization area, T wave amplitude, and time to accumulate total repolarization area (tA97-SD = 44 +/- 20 ms vs 53 +/- 19 ms, respectively, ns). It is concluded the analysis of area-derived parameters of repolarization showed that LQTS patients have increased interlead variability of the repolarization morphology (tA50-SD and t[A25-75]-SD), whereas they do not have increased dispersion of the total repolarization duration (tA97-SD). This observation indicates that an increase in traditional measures of dispersion (QT dispersion) may represent a heterogeneity of repolarization shape, whereas the true dispersion of the total duration of repolarization, which is related to electrocardiographic lead projection, is similar in patients and healthy subjects.