Scoping Review on True and Relative Bradycardia in Trauma: How to Approach Bradycardia in Traumatic Brain Injury

Brain-heart interactions have garnered considerable interest in the landscape of traumatic brain injury (TBI). This scoping review focused on bradycardia caused by high intracranial pressure (ICP), brainstem injury, autonomic imbalance, hypothalamic-pituitary-adrenal axis disruption, or massive bleeding. The latter condition is attributed to a physiological phenomenon called relative bradycardia (RB). True bradycardia results from underlying physiological or pathological cardiac disorders, whereas RB has different definitions and implications in medical and surgical settings. The former reflects pulse-temperature dissociation, while the latter reflects pulse-pressure dissociation. However, it can reflect an abnormal neurological response called the Cushing reflex. Therefore, bradycardia may indicate imminent shock after TBI associated with torso injuries or high ICP following severe isolated TBI. RB is underrecognized and underappreciated in emergency settings. This review investigated whether RB affects patient survival and neurological function. Physicians should approach patients presenting with RB with a high index of suspicion and timely management.