Comparison of QT-interval and variability index methodologies in individuals with spinal cord injury
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STUDY DESIGN: Within-group comparison. OBJECTIVES: Individuals with spinal cord injury (SCI) demonstrate an elevated risk for cardiac arrhythmias as indicated by an elevated QT-variability index (QTVI). The methodology measuring the QTVI, however, is not standardized, and therefore the purpose of this investigation is to determine whether the threshold and tangent methods of QT-interval measurement, as well as the electrocardiographic (ECG) epoch duration, influence the QTVI in individuals with SCI. SETTING: Ontario, Canada. METHODS: Ten minutes of resting ECG data were collected and analyzed from 14 individuals with SCI (C2-L3; ASIA Impairment Scale (AIS) A-D; 11.5±9.4 years post injury). The QTVI was analyzed via the threshold and tangent methods of QT-interval measurement, as well as from 1-, 5- and 10-min ECG epochs. RESULTS: The threshold method produced significantly higher QTVI values compared with the tangent method. The QTVI from a 1-min epoch was significantly higher compared with that from 5- and 10-min epochs. The QTVI values acquired from the threshold method were shown to have higher reproducibility compared with those from the tangent method. There were no differences in QTVI values between participants with lesions above and below T1, as shown by both methods of QT-interval measurement. CONCLUSION: The method of QT-interval measurement and the length of ECG epoch influence QTVI values in individuals with SCI. The methodology of QTVI analysis must be standardized in studies involving SCI individuals to reduce the variability accounted by methodological inconsistency.
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