Reproducibility of the QT-variability index in individuals with spinal cord injury.

PURPOSE

To examine the day-to-day reproducibility of the QT-variability index (QTVI) and the QT-apex variability index (QTaVI) in individuals with spinal cord injury (SCI).

METHODS

Ten individuals with SCI participated in the current study (C2-T10; AIS A-D; 8.6 ± 7.8 years post-injury). On two occasions, with a 10-day interval, a 10-minute resting electrocardiogram was obtained from each participant. The QTVI and QTaVI were analyzed from 256 electrocardiographic beats from all participants, and a separate analysis was performed on those with injuries above the 4th thoracic level. An intraclass correlation coefficient (ICC) test was performed to measure day-to-day reproducibility of these measures and a Bland-Altman test was performed on all participants in order to examine the skewness of the measures.

RESULTS

The reproducibility values were found to be high for both the QTVI (all participants: R=0.892; above T4: R=0.893) and the QTaVI (all participants: R=0.908; above T4: R=0.915). In addition, the reproducibility of QTVI and QTaVI did not appear to be skewed as indicated by Bland-Altman plots.

CONCLUSION

Both the QTVI and the QTaVI may be used as reproducible means of assessing cardiac autonomic function in individuals with SCI. Further, a reduction in cardiac sympathetic regulation after high thoracic and cervical level SCI does not appear to influence the day-to-day reproducibility of these measures.