Reproducibility of Minimum, Maximum and Median QT Intervals in the 12‐Lead Resting ECG

Abstract

Background: Heterogeneity in the recovery of ventricular refractory periods is an important factor in the development of ventricular arrhythmia. The QT dispersion (QTD) is increasingly used to measure this heterogeneity but its clinical value is limited due to methodological problems. QTD is defined as the maximum minus the minimum QT intervals that are suspected to be the least reproducible of the QT measurements.Objective: To analyze the reproducibility of the minimum, maximum and median QT intervals.Material: One database consisted of 356 subjects: 169 with diabetes and 187 nondiabetic control persons. The other database consisted of 110 subjects with remote myocardial infarction: 55 with no history of arrhythmia, and 55 with a recent history of ventricular tachycardia or fibrillation.Methods: 12‐lead surface ECGs were recorded with an amplification of 10 millimeters per millivolt at a paper speed of 50 mm/s. QT was measured manually by the tangent‐method. The reproducibility was calculated from measurements of QT in successive beats.Results: The standard deviation (SD) of QTs reproducibility was 9 ms for the arrhythmia data and 8 ms for the diabetes data. The reproducibility of QTmax and QTmin were on average 30% and 15% worse than for QTmedian. The SD of QTmax was significantly higher than for QTmedian in both database (P < 0.001), whereas SD of QTmin was only significantly higher than for QTmedian for the diabetes data (P < 0.001).Conclusions: The reproducibility of QTmin and in particular QTmax was significantly lower than for QTmedian. This indicates that the QT dispersion is based on the least reproducible of the QT measurements. A.N.E. 2000;5(4):354–357