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  • Title: Semiautomated QT interval measurement in electrocardiograms from a thorough QT study: comparison of the grouped and ungrouped superimposed median beat methods.
    Author: Hingorani P, Karnad DR, Ramasamy A, Panicker GK, Salvi V, Bhoir H, Kothari S.
    Journal: J Electrocardiol; 2012; 45(3):225-30. PubMed ID: 22364647.
    Abstract:
    INTRODUCTION: We postulated that it may be easier to identify earliest Q onset and latest T offset when the median beats from 12 leads are separated vertically by 5 to 10 mm (ungrouped superimposed median beat [SMB] method) rather than when their baselines closely (but rarely perfectly) overlap (grouped SMB method). METHODS: Three readers manually adjudicated annotations placed by an automated algorithm, using grouped (gSMB) and ungrouped (uSMB) methods in 2658 electrocardiograms (ECGs) recorded in 38 subjects in a crossover design thorough QT study at predose and 6 time points postdosing with placebo or moxifloxacin. RESULTS: Placebo-subtracted, moxifloxacin-induced QTcF prolongation was comparable with both methods. Maximum QTcF prolongation was seen at 2 hours--10.5 milliseconds (90% confidence interval, 7.9-13.1 milliseconds) with gSMB and 12.9 milliseconds (90% confidence interval, 9.9-15.8 milliseconds) by uSMB. Both methods showed good agreement; mean QT was 4 milliseconds greater by uSMB. Interreader variability of absolute differences in QT measurements was 1 millisecond lower with the uSMB method (6.8 ± 5.7 milliseconds by gSMB and 5.9 ± 4.5 milliseconds by uSMB). CONCLUSION: Mean QT was 4 milliseconds longer, and interreader variability, 1 millisecond lower with uSMB. Otherwise, both methods were comparable and detected the moxifloxacin effect.
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