Myocardial Involvement Is Just as Common in Patients Hospitalised for Influenza as in Those Hospitalised for...

The possibility of myocardial involvement is well recognised with Covid-19 infection but less so with influenza. We designed this study to explore the frequency of elevated biomarkers and new clinical cardiac diagnoses in patients hospitalised with influenza or Covid-19.

This was a retrospective cohort study of all adults hospitalised from April 2015 to March 2023 with either influenza or Covid-19 in 29 hospitals in Ontario. We used multivariable regression with generalised estimating equations to compare troponin and natriuretic peptide levels and new cardiac diagnoses during the index hospitalisations.

The 25,200 patients with Covid-19 were younger (67 vs 72 years) and more likely to be men (56% vs 47%), and fewer had prior cardiovascular disease (7% vs 13%) than the 8569 patients with influenza (all P < 0.001). Although more likely to have their troponin (84.2% vs 78.7%; P < 0.001) or natriuretic peptides (21.6% vs 12.7%; P < 0.001) measured, patients with Covid-19 were not more likely to have elevated levels compared with influenza patients: 42.7% vs 39.8% for troponin (adjusted risk ratio [aRR] 1.07, 95% CI 0.99-1.15), and 72.3% vs 81.7% for natriuretic peptides (aRR 0.93, 95% CI 0.87-0.99). The frequency of new clinical diagnoses of heart failure (2.4% vs, 2.6%, aRR 1.18, 95% CI 0.79-1.77) or new atrial fibrillation (3.4% vs 5.2%, aRR 0.89, 95% CI 0.79-1.77) did not differ between those with Covid-19 or influenza.

The frequencies of elevated troponins (two-fifths) and natriuretic peptides (three-fourths) were similar in patients hospitalised with influenza and Covid-19 who had biomarkers measured, but the frequencies of clinically recognised diagnoses were low.