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Pacing Clin Electrophysiol. 2006 Nov;29(11):1277-84.

Precision of QT interval measurement by advanced electrocardiographic equipment.

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Department of Cardiac and Vascular Sciences, St. George's University of London, London, UK.


The costs of clinical investigations of drug-induced QT interval prolongation are mainly related to manual processing of electrocardiographic (ECG) recordings. Potentially, however, these costs can be decreased by automatic ECG measurement. To investigate the improvements in measurement accuracy of the modern ECG equipment, this study investigated QT interval measurement by the "old" and "new" versions of the 12SL ECG algorithm by GE Healthcare (Milwaukee, WI, USA) and compared the results to carefully validated and reconciled manual measurements. The investigation used two sets (A and B) of ECG recordings that originated from large clinical studies. Sets A and B consisted of 15,194, and 29,866 10-second ECG recordings, respectively. All the recordings were obtained with GE Healthcare recorders and were available in digital format compatible with ECG processing software by GE Healthcare. The two sets of recordings differed significantly in ECG quality with set B being substantially more noise polluted. Compared to careful manual QT interval readings in recording set A, the errors of the automatic QT interval measurement were (mean +/- SD) +3.95 +/- 5.50 ms, and +0.51 +/- 12.41 ms for the "new" and "old" 12SL algorithm, respectively. In recording set B, these numbers were +2.41 +/- 9.47 ms, and -0.17 +/- 14.89 ms, respectively (both differences were highly statistically significant, P < 0.000001). In recording set A, 95.9% and 76.6% of ECGs were measured automatically within 10 ms of the manual measurement by the "new" and "old" versions of the 12SL algorithm, In recording set B, these numbers were 83.9% and 59.5%. The errors made by the "new" and "old" version of 12SL algorithm were practically independent each of the other (correlation coefficients of 0.031 and 0.281 in recording sets A and B, respectively). The study shows that (a) compared to the "old" version of the 12SL algorithm, the QT interval measurement by the "new" version implemented in the most recent ECG equipment by GE Healthcare is significantly better, and (b) the precision of automatic measurement by the 12SL algorithm is substantially dependent on the quality of processed ECG recordings. The improved accuracy of the "new" 12SL algorithm makes it feasible to use modern ECG equipment without any manual intervention in selected parts of drug-development program.

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