The central autonomic input (both sympathetic and parasympathetic) is crucial for the cardiovascular control; therefore SCI can interfere with its function (Henrich 1982; Lehmann et al 1987). Bradycardia, defined as a heart rate of less than 60 beats per minute (bpm), is one common cardiovascular complication that is often lesion-dependent but unique to each SCI. Generally, higher-level injuries along the spinal cord result in a greater degree of cardiovascular impairment; investigators have also reported a higher incidence of bradycardia in persons with tetraplegia than in persons with paraplegia (Mirkowski et al. 2015; Dixit 1995; Biering-Sørensen et al. 2017). The relationship between injury completeness and resulting cardiovascular dysregulation is less well understood; no clear association has yet been established, even though researchers have reported ECG abnormalities in the SCI population compared with the nondisabled population (West et al. 2013; Prakash et al. 2002).
We would like to emphasize that bradycardia and other dysrhythmias, particularly atrial fibrillation, may also occur during episodes of AD in individuals with high level SCI and may require immediate pharmacological intervention (Pine 1991; Forrest 1991). Current pharmacological management of bradycardia in SCI patients involves the use of different agents including phosphodiesterase inhibitors (e.g. aminophylline, theophylline) and chronotropic agents (e.g. atropine, epinephrine, and norepinephrine) (Mirkowski et al. 2015). Implanting cardiac pacemakers for bradycardia is typically reserved for those who do not respond to pharmacologic treatment (Evans et al. 2014; Franga et al. 2006; Ruiz-Arango et al. 2006; Sadaka et al. 2010; Wood et al. 2014).