Background: Influenza infection has been associated with multiple cardiac complications including acute heart failure and myocardial infarction. The FluHeart study aims to uncover the potential effect of influenza infection on cardiac structure and function as assessed by echocardiography during hospitalization.

Methods: This prospective cohort study included hospitalized influenza patients of the 2021-2022 influenza season. Participants underwent echocardiography using a prespecified protocol. Participants were successfully matched 1:1:1 on age, sex, and heart failure status with controls from the general population and controls hospitalized with COVID-19.

Results: This interim analysis involved 108 participants (36 influenza patients, 36 general population controls, and 36 COVID-19 patients). Mean age was 72 ± 18 years and 58% were male. Median time from admission to echocardiography was 1 day (IQI: 1:1) for influenza patients. The prevalence of left ventricular (LV) dysfunction was 75%, and right ventricular (RV) dysfunction was observed in 20% of influenza patients. N-terminal pro-brain natriuretic peptide levels were elevated ≥ 300 pg/mL in 62%, and 19% exhibited myocardial injury with elevated high-sensitivity troponin I levels. RV tricuspid annular plane systolic excursion and LV early diastolic peak mitral inflow to early diastolic tissue velocity were significantly worse in influenza patients compared to general population controls. Echocardiographic measures did not significantly differ between patients hospitalized with influenza and COVID-19.

Conclusion: In this interim analysis of the FluHeart study, both RV and LV function measures were significantly impaired in hospitalized influenza patients compared with matched general population controls. The extent of impairment resembled that observed in hospitalized COVID-19 patients.