Relative bradycardia in patients with moderate-to-severe COVID-19: a retrospective cohort study

Coronavirus-related disease (COVID-19) can result in relative bradycardia; however, there are no reports on relative bradycardia in patients with moderate-to-severe COVID-19 who require oxygen. We retrospectively investigated 45 patients with moderate-to-severe COVID-19 and examined the relationship between heart rate and body temperature at the time of initiating oxygen or mechanical ventilation. For three consecutive days after initiating oxygen therapy, body temperature (day's highest temperature), heart rate, and other vital signs were measured simultaneously. We checked for relative bradycardia and analyzed the differences between patients with moderate COVID-19 (oxygen requirement ≤ 5 L/min) and those with severe COVID-19 (oxygen requirement ≥ 5 L/min). Of the 45 patients, 28 and 17 had moderate and severe COVID-19, respectively. The heart rate increased with increasing body temperature, and almost all patients satisfied the criteria of relative bradycardia. In Spearman's rank correlation analysis, body temperature was significantly correlated with heart rate (ρ = 0.483, p = 0.012) in moderately ill patients but not in severely ill patients (ρ = 0.261, p = 0.297). Multiple regression analysis revealed that the severity of COVID-19 and body temperature were independent predictors of heart rate. The predicted change in heart rate was 6.0 beats/min for each 1 °C rise in body temperature. Relative bradycardia was suggested to be a characteristic finding in patients with moderate-to-severe COVID-19 who require oxygen. Additionally, severely ill patients were more likely to develop relative bradycardia than moderately ill patients. Focusing on the relationship between heart rate and body temperature might help clinicians diagnose this disease in patients with worsening respiratory failure.