Cardiovascular disease risk after spinal cord injury: The role of autonomic dysfunction

Cardiovascular disease (CVD) is the leading cause for mortality and morbidity after spinal cord injury (SCI) with an earlier onset and more rapid progression compared to the general population. Lifestyle changes after injury have been suggested to be the main contributor to CVD risk, but I proposed that the issue is more complicated. Although less well-known, autonomic function is affected by SCI, in addition to motor and sensory dysfunction. Cardiovascular autonomic dysfunction is a particular concern in individuals with high lesions (above T5) due to the possible disruption of descending spinal sympathetic pathways to the heart and main vascular resistance bed. In this thesis, I propose that cardiovascular autonomic impairment plays a role in the elevated CVD risk. The thesis starts with an evaluation of the prevalence and progression of cardiovascular dysfunction after SCI. Then, the contribution of autonomic dysfunction on CVD risk is investigated. In addition, markers for obesity-related CVD risk specific to individuals with SCI and ECG markers for cardiac arrhythmias in relation to autonomic impairments are explored. Prevalence of cardiovascular dysfunction was found not to improve over time after injury and it was highest in those with lesions above T5. The second study showed that autonomic dysfunction contributes to overall CVD risk and specifically to glucose intolerance, either directly or through an interaction with physical activity levels. The data showed that waist circumference is the best marker for obesity considering ability to detect adiposity and CVD risk, and practicality of use. A specific cut-off for waist circumference was found to be lower compared to the general recommendations. The final study showed increased values for the ECG markers Tpeak-Tend variability, P-wave variability and QTVI, only in those with impairments to descending cardiac sympathetic pathways. The ECG characteristics may be indicative of susceptibility to cardiac arrhythmia related to autonomic dysfunction. Implications of these findings are that management of cardiovascular autonomic dysfunction should remain a priority into the chronic phase of injury, not merely due the direct impact on quality of life, but also due to its contribution to the elevated cardiovascular disease risk after SCI.