The Clinical Significance of Relative Bradycardia.

Introduction: Relative bradycardia is a poorly understood paradoxical phenomenon that refers to a clinical sign whereby the pulse rate is lower than expected for a given body temperature.

Objective: To provide an overview and describe infectious and noninfectious causes of relative bradycardia.

Methods: PubMed and Medline databases were searched using individual and Medical Subject Headings terms including relative bradycardia, fever, pulse-temperature dissociation and pulsetemperature deficit in human studies published from inception to October 2, 2016. The causes and incidence of relative bradycardia were reviewed.

Results: Relative bradycardia is found in a wide variety of infectious and noninfectious diseases. The pathogenesis remains poorly understood with proposed mechanisms including release of inflammatory cytokines, increased vagal tone, direct pathogenic effect on the myocardium, and electrolyte abnormalities. The incidence of this sign varies widely, which may be attributable to multiple factors, including population size, time course for measuring pulse and temperature, and lack of a consistent definition used. The fact that this sign is not consistently identified in case series suggests that relative bradycardia is caused by mechanisms presumably involving or influenced by pathogen and host factors.

Conclusions: Relative bradycardia is a sensitive but nonspecific clinical sign that may be an important bedside tool for narrowing the differential diagnosis of potential infectious and noninfectious etiologies. Recognizing this relationship may assist the clinician by providing bedside clinical clues into potential etiologies of disease, particularly in the setting of infectious diseases and in circumstances when other stigma of disease is absent.