Cardiac Effects of Recurring Autonomic Dysreflexia

Persons with a spinal cord injury (SCI) above the sixth thoracic vertebrae commonly experience autonomic dysreflexia (AD), 90 percent of individuals with this level of injury are susceptible to AD which is associated with an increase in sympathetic nerve activity. Left untreated AD causes a paroxysmal rise in blood pressure that may result in seizures, heart attack, or even death. This project investigates how AD affects QT interval, RR interval, P wave height, heart rate, and QRS width both during an event and long term to help identify potential cardiac risks for individuals with SCI who experience chronic AD. Sympathetic tone has been shown to influence QT interval changes that can be indicative of an increased risk of arrhythmia, which can be exacerbated by recurring episodes of AD. A rat spinal cord injury model at the T3 level undergoing colorectal distention (CRD) was used to induce AD. Electrophysiological recordings from an implanted ECG sensor and noninvasive skin nerve activity (SKNA) sensor array during normal baseline and three trials of CRD were collected on days 5, 7, 9, 11, 14, 16, 19, and 21 post-SCI. Custom MATLAB algorithms were used to identify the QRS complex and T-peaks from the implant ECG signal. QT interval measurements were taken for 2 minutes of baseline and for 2 minutes after the initiation of each CRD trial. Corrected QT interval (QTc) was calculated using normalized Bazett’s formula to account for the impact of heart rate on QT interval. It was found that the rats’ susceptibility and reaction to AD events varied between subacute (5-14 days) and chronic phases of SCI. During the chronic phase the incidence of AD events increased during regular occurrences of CRD as indicated by above-threshold (≥15 mmHg) blood pressure spikes. AD events also resulted in increased QT interval short term variability marking an increased risk of arrythmias. Baseline P-wave height and QTc interval were also increased while QRS complex width decreased resulting in potentially detrimental cardiac effects. This rat model showed that humans who experience recurrent AD during the chronic phase of SCI may be at increased risk for arrythmia.