Impact of atrial fibrillation on patients hospitalized for acute myocarditis: Insights from a nationally-representative United States cohort.

Background: Atrial fibrillation (AF) is associated with increased all-cause mortality in the general population. However, the impact of AF on the in-hospital outcomes of acute myocarditis (AM) patients is not well characterized.

Methods: Patients (age ≥ 18 years) with a primary diagnosis of AM in the National Inpatient Sample from 2007 to 2014 were included, using the ICD-9-CM diagnostic codes. We compared the in-hospital outcomes between the AF group and propensity score-matched control group without AF.

Results: AF was reported in 602 (9%) of the AM patients. Compared to those without AF, AM patients with AF experienced higher in-hospital mortality (odds ratio [OR] 1.7, 95% confidence interval [CI] 1.1-2.7, P = 0.02). AF was associated with higher risk of cardiogenic shock (OR 1.9, 95% CI 1.3-2.8, P < 0.001), cardiac tamponade (OR 5.6, 95% CI 1.2-25.3, P = 0.002) and acute kidney injury (OR 1.6, 95% CI 1.1-2.1, P = 0.02). Furthermore, patients with AF were more likely to have non-routine hospital discharge (31.6% vs 38.4% P = 0.02), longer length of stay and higher cost of hospitalization.

Conclusions: AF was associated with increased risk of in-hospital mortality and complications in patients admitted to the hospital with acute myocarditis.