Can fever cause tachycardia in patients?

Does Fever Cause Tachycardia?

Yes, fever directly causes tachycardia through a well-established physiological mechanism, with heart rate increasing approximately 10 beats per minute for every 1°C rise in temperature, though this relationship is more complex than simple linear correlation. 1, 2

Physiological Mechanism

• Fever induces sinus tachycardia as a compensatory response to maintain cardiac output when myocardial performance is impaired during the febrile state 3
• The tachycardic response serves to preserve adequate cardiac output despite decreased left ventricular stroke work and stroke volume during fever 3
• When fever resolves, stroke volume index increases by 23-27% and left ventricular stroke work index increases by 37-38%, demonstrating that fever actively impairs cardiac performance 3

Expected Heart Rate Changes

• In neonates and infants, the upper normal limit for heart rate is 166 beats/min in the first week and 179 beats/min in the first month, with fever being one of the most frequent causes of sinus tachycardia 1
• The traditional teaching of 10 beats/minute increase per °C elevation applies during the febrile state, but this relationship changes dramatically during antipyretic treatment 2
• During pharmacological temperature reduction with antipyretics, heart rate decreases by an average of 21.1 beats/minute per °C reduction in fever—more than double the expected rate 2

Clinical Implications and Pitfalls

• Critical warning: Persistent tachycardia after fever reduction with antipyretics should not be dismissed as fever-related and warrants investigation for other causes including sepsis, myocarditis, or other serious bacterial infections 1
• Tachycardia that is disproportionate to the level of fever suggests myocarditis, particularly when accompanied by gallop rhythm, T wave changes, or conduction disturbances 1
• In COVID-19 patients, persistent sinus tachycardia that cannot be explained by the degree of hypoxia, hypotension, fever, or anemia indicates acute cardiovascular involvement requiring further evaluation 1

Conditions Where Fever-Associated Tachycardia Has Special Significance

• In postural orthostatic tachycardia syndrome (POTS) diagnosis, fever must be excluded as a cause of sinus tachycardia before confirming the diagnosis, as fever is a physiological explanation that negates POTS criteria 1
• In pediatric septic shock, the inflammatory triad of fever, tachycardia, and vasodilation is common even in benign infections, requiring assessment of additional signs like altered mental status and perfusion abnormalities to identify serious illness 1
• After bariatric surgery, the combination of fever and tachycardia (≥110 bpm) is a significant predictor of anastomotic leak or staple line leak requiring urgent surgical evaluation 1

Diagnostic Approach When Fever and Tachycardia Coexist

• Measure heart rate over two respiratory cycles in awake patients to establish accurate baseline 1
• Assess for disproportionate tachycardia by comparing heart rate to fever magnitude and clinical context 1
• Exclude other causes of tachycardia including pain, dehydration, anemia, hyperthyroidism, infection beyond simple fever, and medications 1
• In children given antipyretics, persistent tachycardia after temperature reduction has poor diagnostic value for serious bacterial infection, while persistent tachypnea remains significant 4

Rare but Important Arrhythmic Complications

• Fever can unmask Brugada syndrome, triggering polymorphic ventricular tachycardia even with normal QTc intervals 5, 6
• In COVID-19 patients, fever may trigger life-threatening ventricular arrhythmias with normal left ventricular function and normal QTc, requiring aggressive fever control and continuous monitoring 5
• Acute rheumatic fever causes sinus tachycardia and PR prolongation commonly, though complete heart block and ventricular arrhythmias are rare 1