From the Guidelines
Relative bradycardia in typhoid fever is primarily caused by the direct effects of Salmonella Typhi endotoxins on the cardiovascular system, leading to vasodilation, decreased peripheral vascular resistance, and a blunted heart rate response to hypotension. The mechanisms underlying this phenomenon include the direct inhibitory effect of endotoxins on the sinoatrial node, autonomic nervous system dysfunction with altered vagal tone, and myocarditis that may develop during the infection 1. Additionally, cytokines released during the inflammatory response to Salmonella Typhi can affect cardiac pacemaker function. The relative bradycardia typically manifests as a heart rate increase of less than 10 beats per minute for each 1°C rise in temperature, compared to the expected 18-20 beats per minute increase seen in other febrile illnesses. Some key points to consider in the context of relative bradycardia in typhoid fever include:
- The clinical presentation of typhoid fever, which often includes insidious onset of sustained fever, headache, malaise, anorexia, relative bradycardia, constipation or diarrhea, and nonproductive cough 1
- The importance of Faget's sign, a diagnostic clue for typhoid fever characterized by a heart rate increase of less than 10 beats per minute for each 1°C rise in temperature
- The potential for relative bradycardia to occur in other infections, such as brucellosis, leptospirosis, and certain viral infections, highlighting the need for a thorough diagnostic workup in patients presenting with this clinical sign.
From the Research
Mechanisms of Relative Bradycardia in Typhoid Fever
The mechanisms leading to relative bradycardia in typhoid fever are not fully understood, but several factors have been proposed:
- Release of inflammatory cytokines 2
- Increased vagal tone 2
- Direct pathogenic effect on the myocardium 2
- Electrolyte abnormalities 2
Underlying Causes
Relative bradycardia is often associated with infectious diseases, including typhoid fever, Legionnaire's disease, and pneumonia caused by Chlamydia sp. 3. The exact mechanisms underlying relative bradycardia in these diseases are unknown, but it is thought to be related to the intracellular location of the pathogens 3.
Clinical Significance
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 2. In typhoid fever, relative bradycardia has been observed in several cases, including a case report of a 25-year-old male who presented with syncope due to relative bradycardia 4.
Cardiac Status in Typhoid Fever
Cardiac status in typhoid fever has been evaluated in several studies, including a study of 50 adult patients with culture-proved typhoid fever 5. The study found that various types of ECG abnormalities were observed in 22 patients, and transaminases were significantly raised in some patients. However, the relationship between elevated enzyme levels, severity of disease, and ECG changes was not clear 5.