Relative bradycardia in infectious diseases.

Relative bradycardia in infectious diseases is a poorly defined term. No exact and useful definition exists and the underlying mechanisms are unknown. Despite this, the term is often used in the literature and in clinical practice both as a clinical sign for an individual patient and as a characteristic feature of certain specific diseases. In this study a definition of relative bradycardia as a clinical sign in an individual patient and a definition of relative bradycardia as a characteristic feature of a specific disease were established based on a reference population comprising 673 patients with various infectious diseases. Relative bradycardia as a clinical sign in an individual patient held no predictive value regarding the likely type of infection. Relative bradycardia as a characteristic feature of specific disease was found for typhoid fever (P = 0.003), Legionnaire's disease (P = 0.005), and pneumonia caused by Chlamydia sp. (P = 0.0005), but not for mycoplasma pneumonia. It was not found for other pulmonary infections, infections caused by other Salmonella sp., other extracellular Gram-negative infections, or viral infections. Thus, relative bradycardia as a clinical sign has no predictive value for obtaining a tentative diagnosis, but relative bradycardia as a feature of specific disease is seen in typhoid fever, Legionnaire's disease, and pneumonia caused by Chlamydia sp. It seems that relative bradycardia as a feature of specific disease only occurs in diseases caused by organisms that are both Gram-negative and intracellular.