Myocarditis Incidence, Complications and Mortality in Sweden: A Retrospective Registry Study From 2000-2014

Objectives: Investigate trends in incidence and prognosis of myocarditis in Sweden during 2000-2014. Background: Myocarditis is an inflammatory heart disease, with scarce data concerning incidence and prognosis. Methods: : Linking Swedish National Patient and Cause of Death Register, we identified individuals ≥16 years with first-time diagnosis of myocarditis during 2000-2014. Reference population, matched for age and birth year (n=16 622) was selected from the Swedish Total Population Register. Results: Among the 8 679 cases, (75% men, 64% <50 years), incidence rate/100 000 inhabitants rose from 6.3 to 8.6, mostly in men and those <50 years. Incident heart failure/dilated cardiomyopathy occurred in 6.2% within 1 year after index hospitalization and in 10.2% during 2000-2014, predominantly in those ≥50 years (12.1% within 1 year, 20.8% during 2000-2014). In all, 8.1% died within 1 year, 0.9% (<50 years) and 20.8% (≥50 years). Hazard ratios (adjusted for age, sex) for 1-year mortality comparing cases and controls were 4.00 (95% confidence interval 1.37-11.70), 4.48 (2.57-7.82), 4.57 (3.31-6.31) and 3.93 (3.39-4.57) for individuals aged <30, 30-<50, 50-<70, and ≥70 years, respectively. Conclusion: The incidence of myocarditis during 2000-2014 increased, predominantly in younger men. One-year mortality in the young was low, but fourfold higher compared with reference population.