Background: Neutrophil-to-lymphocyte ratio (NLR) is an easy-to-use inflammatory biomarker. Baseline NLR is independently associated with incident cardiovascular events and all-cause mortality. However, whether this applies to acute myocarditis (AM) has not been evaluated. Objectives: The present study aimed to investigate the prognostic value of NLR in patients with AM. Methods: A total of 1,150 consecutive patients with a diagnosis of AM admitted to 10 international tertiary referral cardiac centers were included in the study. The diagnosis was confirmed using cardiac magnetic resonance or endomyocardial biopsy. The primary outcome measure was a composite of all-cause mortality or heart transplantation. Patients were divided into 2 groups according to an NLR cutoff of 4 derived from spline regression analysis and 70:30 train-test split algorithm. Results: Patients with an NLR <4 were younger and more likely to present with chest pain, and those with an NLR ≥4 were more likely to present with breathlessness and have other comorbidities. Over a median follow-up of 228 weeks, a NLR ≥4 was associated with a worse prognosis (P < 0.0001). After adjustment for prognostic variables, NLR emerged as an independent predictor of outcome (HR: 3.03 [95% CI: 1.30-7.04]; P = 0.010). Elevated NLR remained associated with worse outcomes among patients with preserved ejection fraction at baseline, who are conventionally considered to be at lower risk of adverse events (P < 0.0001). Conclusions: In patients with AM, elevated NLR is associated with worse prognosis and may be valuable for stratifying patients, even those conventionally considered at low risk.
