Background: Influenza virus infection can lead to acute cardiovascular events, but the relationship between influenza-induced inflammation and cardiac dysfunction remains unclear. This study evaluated whether the severity of inflammation was associated with cardiac impairment, as assessed by echocardiography, in hospitalized patients with influenza.

Methods: In this prospective cohort study conducted in Denmark across three influenza seasons (2021-2022, 2022-2023, and 2023-2024), consecutive hospitalized patients with laboratory-confirmed influenza underwent protocolized echocardiography. Associations between C-reactive protein (CRP) levels and measures of cardiac function were assessed using multivariable models.

Results: Among 241 patients (median age, 73.2 years; IQR, 58.3-82.8; 53% female), 54% had left ventricular (LV) systolic dysfunction (ejection fraction < 50% or global longitudinal strain < 16%), 15% had signs of elevated LV filling pressure (E/e´ ≥ 14), 29% had right ventricular (RV) systolic dysfunction (tricuspid annular plane systolic excursion [TAPSE] < 1.7 cm or RV free wall strain < 20%), and 31% had pulmonary hypertension (RV systolic pressure [RVSP] > 40 mmHg). CRP showed a significant nonlinear association with E/e´, RVSP, and TAPSE. E/e´ and TAPSE worsened with higher CRP up to 100 mg/L, plateauing thereafter, whereas RVSP worsened at CRP levels > 100 mg/L.

Conclusions: Cardiac dysfunction was observed in more than half of all examined hospitalized patients with influenza. Higher levels of inflammation were independently associated with elevated LV filling pressure, pulmonary hypertension, and RV dysfunction, supporting a potential link between influenza infection and cardiac impairment.