- 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.