Pediatric Fulminant Myocarditis in Japan: A Retrospective Nationwide Database Study of Hospital Volume, Management Practices, and Mortality

OBJECTIVES Pediatric fulminant myocarditis is a subset of pediatric acute myocarditis associated with critical illness. We aimed to compare mortality and other outcomes such as length of hospital stay between pediatric fulminant myocarditis and nonfulminant myocarditis. For the subgroup of patients with fulminant myocarditis, we also aimed to describe the current management practices and evaluate the impact of clinically relevant factors, including hospital case volume, on mortality. DESIGN Retrospective observational study using the Diagnosis Procedure Combination database from April 2012 to March 2018. SETTING Over 1,000 acute care hospitals in Japan. PATIENTS Patients with acute myocarditis less than 18 years old, including patients with fulminant myocarditis (i.e., those who received at least one of the following by day 7 of hospitalization: inotropes/vasopressors, mechanical circulatory support, or cardiopulmonary resuscitation). INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Multivariable logistic regression analysis was conducted to investigate the association between clinically relevant factors and in-hospital mortality of patients with fulminant myocarditis. Furthermore, post hoc propensity score analyses (propensity score-adjusted, propensity score-matched, and inverse probability of treatment-weighted analyses) were performed to confirm the effect of hospital case volume on in-hospital mortality. In total, 866 pediatric patients with acute myocarditis were included, and 382 (44.1%) were categorized as fulminant myocarditis. In-hospital mortality for those with fulminant myocarditis was 24.1%. fulminant myocarditis was associated with 41.3-fold greater odds of mortality than nonfulminant myocarditis (95% CI, 14.7-115.9; p < 0.001). In the subgroup of patients with fulminant myocarditis, a higher in-hospital mortality was significantly associated with younger age (≤ 5 yr; odds ratio, 3.41; 95% CI, 1.75-6.64) and the need for either mechanical ventilation (odds ratio, 2.39; 95% CI, 1.03-5.57), cardiopulmonary resuscitation (odds ratio, 10.63; 95% CI, 5.52-20.49), or renal replacement therapy (odds ratio, 2.53; 95% CI, 1.09-5.87) by day 7. A lower in-hospital mortality rate was significantly associated with treatment at hospitals in the highest pediatric fulminant myocarditis case volume tertile (≥ 6 cases in 6 yr; odds ratio, 0.30; 95% CI, 0.13-0.68) compared with treatment at hospitals in the lowest tertile (1-2 cases in 6 yr). Post hoc propensity score analyses consistently supported the primary results. CONCLUSIONS In-hospital mortality of pediatric fulminant myocarditis in Japan remains high. Treatment at hospitals in the highest pediatric fulminant myocarditis case volume tertile (≥ 6 cases in 6 yr) was associated with a 70% relative reduction in odds of in-hospital mortality compared with treatment at hospitals in the lowest tertile (1-2 cases in 6 yr). The reasons for such differences need further study.