Out‐of‐Hospital Cardiac Arrest: Does a History of Myocarditis/Perimyocarditis Affect the Outcome? A Swedish Nationwide Study

BACKGROUND: Acute myocarditis/perimyocarditis presents with a variable prognosis ranging from complete recovery to end-stage heart failure (HF), sudden cardiac arrest, and death. The relationship between a prior history of myocarditis/perimyocarditis and outcomes in out-of-hospital cardiac arrest remains unclear. METHODS AND RESULTS: Using the SCRR (Swedish Cardiopulmonary Resuscitation Registry), we analyzed 54 568 cases of out-of-hospital cardiac arrest from 2010 to 2020 where cardiopulmonary resuscitation was attempted. Patients with a history of myocarditis/perimyocarditis were compared with those without in terms of characteristics and survival. Four hundred ninety-eight patients (0.9%) had a history of myocarditis/perimyocarditis. These patients were predominantly men (73.8%), had an average age of 68 years, displayed a higher prevalence of cardiovascular comorbidities, and more frequently displayed shockable initial rhythms (28.7% versus 23.1%). Prior myocarditis/pericarditis did not correlate with worse short-term (odds ratio [OR], 0.91 [95% CI, 0.61-1.33]) or long-term survival (hazard ratio [HR], 1.01 [95% CI, 0.91-1.13]). Patients with myocarditis/perimyocarditis with concomitant HF showed worse long-term survival in unadjusted analyses. Adjusted analyses confirmed that absence of HF was linked to improved short-term survival (OR, 1.46 [95% CI, 1.32-1.62]), whereas prevalence of HF was a predictor for worsened long-term survival (HR, 0.91 [95% CI, 0.91-0.95]) after out-of-hospital cardiac arrest. Analyses were adjusted for myocarditis/perimyocarditis, sex, age, HF, time to cardiopulmonary resuscitation start, and initial rhythm. CONCLUSIONS: Prior myocarditis/perimyocarditis per se did not contribute to a worsened outcome following out-of-hospital cardiac arrest. However, the presence of concomitant HF was linked to unfavorable short- and long-term outcomes.