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.