Aims: To investigate the effect of different lead exclusion criteria for the manual measurement of QT dispersion (QTd).
Methods: Simultaneous 12-lead ECGs from three groups of 25 subjects were studied; healthy normal subjects (Nor), subjects with a myocardial infarction (MI), and subjects with arrhythmias (Arrhy). Leads were excluded with: 1) small absolute T wave amplitudes; 2) small relative T wave amplitudes; 3) small and/or large relative QT measurements. QTd was calculated as the QT range, and assessed for its ability to differentiate between the normal and pathological groups.
Results: With exclusion of no leads or low absolute amplitude T waves (< 50 V) significant differences were observed only between Nor and MI groups (p < 0.05). Significant differences between normal and both pathological groups were observed when excluding the lead with the smallest amplitude T wave or shortest QT (p < 0.05), or when two leads of either type were excluded (p < 0.005). There was good agreement between leads excluded by amplitude or QT (p < 0.01).
Conclusion: Lead exclusion for QTd is important. Exclusion of the two smallest amplitude or two shortest QT leads from each subject produced the greatest differences between the normal and pathological groups.
Langley P, di Bernardo D, Murray A. Effect of lead exclusion for the manual measurement of QT dispersion. PACE 2001;24:75-81.
Dr. Philip Langley, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-1370.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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