Acute myocardial infarction or acute myocarditis? Discharge registry-based study of likelihood and associated features in hospitalised patients

OBJECTIVE: To evaluate the likelihood of and patient features associated with acute myocardial infarction (AMI) versus acute myocarditis in different population segments. DESIGN: Nationwide, multihospital observational retrospective registry study of 9.6 years in Finland. PARTICIPANTS: All consecutive patients aged ≥18 years hospitalised with a primary diagnosis of AMI (n=89 399) or acute myocarditis (n=2131) in 22 hospitals with a coronary catheterisation laboratory. PRIMARY OUTCOME MEASURES: Likelihood of AMI versus acute myocarditis and associated patient features. RESULTS: Men were over-represented in patients with AMI (59.8%) and in patients with acute myocarditis (76.1%). Age distributions of AMI and acute myocarditis were opposite as a majority of patients with myocarditis were aged 18–29 years, while the number of patients with AMI increased gradually up to 80 years of age. Patients aged 18–29 years were more likely to have acute myocarditis as the cause of hospitalisation (relative risk (RR)=11.4; 95% CI 7.6 to 16.1 for myocarditis, p<0.0001), but after 30 years of age the likelihood of infarction was higher with exponentially increasing RR for AMI. In youngest patients (18–29 years), the likelihood of AMI was higher in women, but men had higher odds for AMI after 40 years of age. Overall, men had OR of 1.97 (95% CI 1.74 to 2.23, p<0.0001) for AMI versus myocarditis when compared with women. Hypercholesterolaemia, chronic coronary artery disease, diabetes and hypertension predicted AMI in multivariate analysis. Odds for myocarditis were significantly higher if the patient had an otolaryngeal infection (OR 18.13; 95% CI 8.96 to 36.67, p<0.0001). CONCLUSIONS: Acute myocarditis is more common than AMI in hospitalised patients aged 18–29 years, but the risk of AMI increases exponentially thereafter. Hypercholesterolaemia, diabetes and hypertension predict AMI regardless of age and gender.