There are no data on population-based epidemiological changes in acute myocarditis in Europe. Our aim was to evaluate temporal trends in incidence, clinical features and outcomes of hospital treated acute myocarditis (AM) in Spain from 2003 to 2015.
We conducted a retrospective longitudinal study using information of all hospital discharges of the Spanish National Health System. All episodes with a discharge diagnosis of AM from January 1, 2003 to December 31, 2015 were included. The risk-standardized in-hospital mortality ratio (RSMR) was calculated using a multilevel risk adjustment model developed by the Medicare and Medicaid Services. Temporal trends for in-hospital mortality were modelled using Poisson regression analysis.
A total of 11,147 episodes of AM were analysed, most of them idiopathic (94.7%). The rate of AM discharges increased along the period, from 13 to 30/million inhabitants/year (2003 to 2015), and this increase was statistically significant when weighted by age and sex (incidence rate ratio, IRR 1.06,95%CI 1.04-1.08,p=0.001). In-hospital crude mortality rate was 3.1%, diminishing significantly along 2003 to 2015 (IRR 0.95,95%CI 0.92-0.99,p=0.02). RSMR also significantly diminished along the period (IRR 0.95,95%CI 0.92-0.99,p=0.01). Renal failure (OR 7.03,5.38-9.18,p=0.001), liver disease (OR 4.61,2.59-8.21,p=0.001), pneumonia (OR 4.13,2.75-6.20,p=0.001) and heart failure (OR 1.91,95%CI 1.47-2.47,p=0.001), were the strongest independent factors associated with in-hospital mortality.
AM is an uncommon entity, although hospital discharges have increased in Spain along the study period. Most of AM were idiopathic. Adjusted mortality was low and seemed to decrease from 2003 to 2015, suggesting an improvement in AM management.

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