Sex differences in early ventricular fibrillation among patients with fulminant myocarditis in a nationwide registry

Background Fulminant myocarditis is a rare but life-threatening condition frequently complicated by malignant ventricular arrhythmias. Data on sex differences in early ventricular fibrillation (VF) in fulminant presentation are limited. Methods We conducted a retrospective nationwide multicentre cohort study using the Japanese Registry of Fulminant Myocarditis between 2012 and 2017. Fulminant presentation was defined as prodromal symptoms within 4 weeks and the need for catecholamines and/or mechanical circulatory support within 14 days of admission. The primary endpoint was VF within 30 days after admission. We estimated the 30-day cumulative incidence of VF and used Fine-Gray competing-risk regression (death as the competing event) to evaluate the association with sex. Results Among 696 patients (40% female), VF within 30 days occurred in 120 (17%). Female patients had a higher 30-day incidence of VF than male patients (22% vs 14%; p=0.006). In multivariable complete-case analysis adjusting for age, left ventricular ejection fraction on admission, estimated glomerular filtration rate and peak creatine kinase, female sex was associated with 30-day VF (subdistribution HR, 1.58; 95% CI 1.09 to WHAT IS ALREADY KNOWN ON THIS TOPIC2.28; p=0.016). Ninety-day all-cause mortality was 36% in female patients and 34% in male patients (p=0.732). Conclusions In a nationwide registry of fulminant myocarditis, female sex was associated with a higher risk of early VF, whereas there was no clear evidence of a sex difference in 90-day all-cause mortality. Incorporating sex into early risk assessment may help tailor acute monitoring and management strategies in this high-risk condition.