| Summary: | Introduction: Myocarditis is a frequent cause of sudden cardiac death (SCD) in young individuals (<35 years), but the frequency of myocarditis in middle-aged (35-65 years) and older SCD victims (>65 years) is unclear. Objective: We aimed to investigate the prevalence and characteristics of myocarditis-related sudden death in the general population. Methods: Our study population is drawn from the Fingesture study, which has prospectively collected all out-of-hospital SCD cases from Northern Finland (population ~700,000) since 1998. As required by Finnish law, all sudden deaths undergo a medicolegal autopsy. All out-of-hospital sudden death cases in the community with a verified cardiac cause of death at autopsy are included in the Fingesture study. By 2017, the Fingesture study had collected data on 5,869 SCD victims. Results: In total, 60 SCD victims had evidence of acute myocarditis at autopsy (1.0% of all SCD cases). The mean age of SCD victims with myocarditis was 55.9±18.2, which was significantly lower than among the rest SCD victims (65.0±12.3; p<0.001). Myocarditis cases were also more often female in comparison to the rest SCD cases (33.3% vs. 21.0%; p=0.02). The proportion of myocarditis was highest among young (<35 years) SCD cases (n=6/73; 8.2%), and the proportion decreased in middle aged (35-65 years) (n=34/2,948; 1.2%) and older (>65 years) SCD cases (n=20/2,848; 0.7%) (p<0.001), although the absolute number was higher. The most common diagnosis was undetermined acute myocarditis (n=42/60; 70%) followed by infective myocarditis (n=10/60; 16.7%) and pericarditis (n=5/60; 8.3%). In addition, two SCD cases had sarcoidosis and one had giant cell myocarditis. Five SCD cases due to myocarditis (8.3%) occurred during physical exercise. Conclusions: Myocarditis is a rare cause of SCD in the general population. Although the relative proportion of myocarditis was highest among young SCD victims, the absolute number was highest among middle-aged SCD victims.
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