The influence of cardiac autonomic activity on the QT-variability index in able-bodied and incomplete spinal cord injured individuals

Hisham Sharif, Lisa M. Cotie, Michael F. La Fountaine, David S. Ditor

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Objectives: To investigate, via autonomic blockade, if the QT-variability index (QTVI) is a measure of cardiac autonomic regulation in able-bodied (AB) and incomplete spinal cord injured (SCI) individuals. Methods: Four SCI (41.6. ±. 13.4. years; C4-C7, AIS B-D, 13.4. ±. 13.4. years post injury) and 4 AB (33.0. ±. 7.8. years) individuals were tested. QTVI was determined from electrocardiographic readings obtained during supine rest and cardiovascular (CV) stress, with and without autonomic blockade. CV stress was induced by 40° head-up tilt, the hand submerged in 10. °C water and the jaw clenched. Autonomic blockade was achieved with metoprolol (β-blockade) and atropine (cholinergic blockade). Results: There was no group. ×. condition interaction for QTVI, although there was a significant main effect for condition. After collapsing across groups, QTVI increased with CV stress (p. =. 0.01) and decreased with subsequent β-blockade (p. =. 0.04), suggesting that during CV stress, QTVI is reflective of cardiac sympathetic activity. During supine rest, β-blockade did not change QTVI (p. =. 0.24), however, cholinergic blockade increased QTVI (p. <. 0.001), suggesting that during rest, QTVI is inversely related to cardiac parasympathetic regulation. Conclusion: During times of CV stress, QTVI reflects cardiac sympathetic activity, while during resting conditions, QTVI is inversely related to cardiac parasympathetic activity. These relationships persist after autonomically incomplete SCI.

Original languageEnglish
Pages (from-to)46-52
Number of pages7
JournalAutonomic Neuroscience: Basic and Clinical
Volume190
DOIs
StatePublished - 1 Jul 2015
Externally publishedYes

Keywords

  • Autonomic blockade
  • QTVI
  • Spinal cord injury

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