The ruler method yielded the lowest intraobserver (6 ± 2 ms) and interobserver (13 ± 3 ms) variability in QT measurement compared to caliper and computer methods.
Cross-Sectional (n=11)
Blinded observers
Does the ruler method reduce intra- and interobserver variability in QT measurement compared to caliper and computer methods in patients in sinus rhythm?
The ruler method using a 0.5-mm scale precision ruler with slope extrapolation yields the lowest intra- and interobserver variability for QT measurement compared to caliper and computer methods.
Absolute Event Rate: 6% vs 12%
p-value: p=> 0.01
Background: QT interval and QT dispersion are useful noninvasive measurements in clinical cardiology and can be measured by several methods. The comparative variability of these methods, however, is not well defined. Methods: We evaluated the intra‐ and interobserver variability of three simple methods of QT measurement: (1) ruler method: use of a 0.5‐mm scale precision ruler to measure QT with end of T wave determined by extrapolating its slope to baseline; (2) caliper method: use of a standard electrocardiogram (ECG) caliper and the standard ECG paper scale with QT determined by visual inspection; (3) computer method: use of a digitized computer software program with QT determined by cursor set manually by the user. QT intervals from 11 patients (total 44 ECG leads) in sinus rhythm without conduction defect were measured by five blinded, trained observers at two time points (a week apart) in a crossover manner. Results: The mean difference in intraobserver measurements were 6 ± 2, 12 ± 12, and 27 ± 2 ms by the ruler, caliper, and computer methods, respectively (P > 0.01, ruler vs caliper or computer). The mean differences in interobserver measurements were 13 ± 3, 16 ± 4, and 29 ± 3 ms for the same methods, respectively (P > 0.01, ruler vs caliper, computer). Enlargement of the ECG to 200% did not reduce the measurement variability. Conclusion: The ruler method as described yielded the lowest variability in QT measurement.
Tran et al. (Wed,) conducted a cross-sectional in Sinus rhythm without conduction defect (n=11). Ruler method vs. Caliper and computer methods was evaluated on Intraobserver measurement variability (mean difference in ms) (p=> 0.01). The ruler method yielded the lowest intraobserver (6 ± 2 ms) and interobserver (13 ± 3 ms) variability in QT measurement compared to caliper and computer methods.
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