Heart rate changes associated with autonomic dysreflexia in daily life of individuals with chronic spinal cord injury

Objective: To characterize heart rate (HR) changes during autonomic dysreflexia (AD) in daily life for individuals with chronic spinal cord injury (SCI). Design: Data analysis of two prospective clinical studies and one cross-sectional study. Setting: Single-center study. Participants: Forty-five individuals (including 8 females) with a chronic SCI at or above the sixth thoracic spinal segment with confirmed AD, and a median age and time since injury of 43 years (interquartile range [IQR] 36 - 50) and 17 years (IQR 6 - 23) respectively, were included for analysis. Interventions: Not applicable. Main outcome measure: Any systolic blood pressure (SBP) increase > 20mmHg from baseline from a 24-hour ambulatory surveillance period was identified and categorized as either confirmed (i.e. known AD trigger), unknown (i.e. no diary entry), and unlikely (i.e. potential physical activity driven SBP increase). SBP-associated HR changes were categorized as either unchanged, increased or decreased compared to baseline. Results: A total of 797 episodes of SBP increase above AD threshold were identified and classified as confirmed (n = 250, 31.4%), unknown (n = 472, 59.2%) or unlikely (n = 75, 9.4%). Median SBP changes and median SBP-related HR changes were 37 mmHg and -8 bpm, 28 mmHg and -6 bpm, or 30 mmHg and -4 bpm for confirmed, unknown, or unlikely episodes, respectively. HR-decrease/increase ratio was 3:1 for confirmed and unknown, and 1.5:1 for unlikely episodes. HR changes resulting in brady-/tachycardia were 34.4% / 2.8% for confirmed, 39.6% / 3.4% unknown, and 26.7% / 9.3% for unlikely episodes, respectively. Conclusions: Our findings suggest that the majority of confirmed AD episodes are associated with a HR decrease. Further improvements, such as more precise participant diaries combined with the use of 24-hour Holter electrocardiogram and wearable-sensors-derived measures of physical activity could provide a better, more detailed characterization of HR changes during AD.