Acute myocarditis (AM) is an inflammatory disorder characterized by a sudden onset of myocardial injury, affecting four to 14 per 100000 individuals each year worldwide, with reported mortality at approximately 1%–7%.1

This condition presents with a wide range of clinical manifestations, from mild symptoms to severe cardiac complications, including heart failure (HF), refractory arrhythmias, and cardiogenic shock.2

Previous studies have revealed that approximately 75% of patients hospitalized with myocarditis have an uncomplicated course with negligible mortality. In contrast, those presenting with acute HF or ventricular arrhythmias have an in-hospital mortality or heart transplantation rate of about 12%. Hemodynamic instability occurs in 2%–9% of patients, often requiring inotropic support or mechanical circulatory assistance, and is associated with a 60-day mortality or transplantation rate around 28%.1

In fact, the Italian multicenter Lombardy registry, including 443 patients with AM, found that cardiac death and heart transplantation occurred almost exclusively in patients with a complicated presentation, defined by left ventricular ejection fraction <50%, sustained ventricular arrhythmias, or hemodynamic instability at admission. These patients had a cardiac mortality or heart transplantation rate of 10.4% at 30 days, and 14.7% at 5 years, whereas no such events occurred in patients with uncomplicated AM. Severe hemodynamic compromise at presentation was the strongest predictor of adverse outcomes.3

Nevertheless, important knowledge deficits continue to exist concerning optimal monitoring strategies as well as robust risk stratification frameworks.4

While close follow-up is essential for high-risk patients, prolonged hospital surveillance of those at very low residual risk may unnecessarily increase patient anxiety and healthcare resource utilization.

In this regard, Vilela et al. designed a prospective observational single-center study, published in this issue of the Journal, which included 158 patients admitted with AM between 2007 and 2022 and followed at a tertiary Cardiology center (mean follow-up [FUP] of 6±4.3 years).5 In this cohort, 3.6% of patients experienced severe complications, such as cardiogenic shock or arrhythmic storm. However, only a fulminant presentation at the time of the index admission was significantly associated with mortality, raising the question of whether patients with less severe disease require prolonged FUP.

With regard to risk stratification, in this cohort, late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) was detected in almost all patients and this finding was not a predictor of mortality.5

Likewise, Rees et al. retrospectively reviewed 196 patients with AM diagnosed by CMR and clinical criteria. Reduced left ventricular ejection fraction (<40%) was observed in nine patients, while LGE was present in 174. After a median FUP of 4.6 years, no cardiac deaths occurred. Overall, CMR-diagnosed AM showed a favorable medium-term prognosis, with severe dysfunction and intensive care unit admission being uncommon.6

Nonetheless, Palmisano et al., in a prospective multicenter study of 105 patients with MRI-confirmed AM, evaluated serial CMR at baseline (6 days after symptom onset), short-term (36 days), and long-term FUP (392 days), with 5-year major adverse cardiovascular events (MACE) assessment. MACE occurred in 28.5% of patients. Active disease persisted in 91% at short-term and 61.5% at long-term FUP. A lateral LGE pattern was associated with better prognosis, whereas higher scar burden, elevated native T1 (short-term), and abnormal T2 mapping (long-term) independently predicted adverse outcomes. Overall, CMR enabled longitudinal assessment of myocardial healing, and persistent inflammation beyond one year was associated with worse outcomes and chronic disease progression.7

Regarding the risk of chronic active myocarditis (CAM) and chronic HF after AM, Li et al. recently published the results of a multicenter retrospective study including 483 patients with biopsy- or CMR-confirmed myocarditis. Predictive models for CAM and chronic HF were developed. The CAM model (including renal replacement therapy, extracorporeal membrane oxygenation, lactate dehydrogenase, cardiac troponin I, left atrial size, and hospital stay) showed excellent discrimination (AUC 0.881), and the chronic HF model (including resuscitation/defibrillation, inflammatory and myocardial injury markers, and ventricular size) also performed well (AUC 0.872), with both models undergoing internal and external validation. A cardiac troponin I threshold of 10000 pg/mL was associated with significantly increased risks of CAM and HF, and CAM was associated with a markedly higher risk of subsequent CHF (HR 9.43).8

Furthermore, Tomás et al. conducted a systematic review and meta-analysis showing that a positive genetic test was found in 27.3% of patients with AM, with patients frequently having family history of cardiovascular disease (53.3%).9 Genetic carriers had a fourfold increased risk of recurrent AM (RR 4.02, p<0.001), with common variants involving TTN, DSP, PKP2, MYH7, BAG3, RBM20, DSG2, TNNT2, and SCN5A genes. These findings highlight the importance of refining genetic testing criteria in AM to better identify high-risk patients who may benefit from closer surveillance. Moreover, LGE on CMR (81.2%) indicated a higher genetic burden and worse risk profile.9

A recent systematic review and meta-analysis of 19 observational studies (3954 patients) found that major arrhythmic events occurred in 28% of patients after complicated AM over a median follow-up of 24 months. Sustained ventricular tachycardia was the most frequent event (22%), while sudden cardiac death was uncommon (1%). High-grade atrioventricular block, major arrhythmic events at presentation, and fulminant myocarditis independently predicted recurrent arrhythmic events, whereas male sex was associated with lower risk. These findings emphasize the need for improved risk stratification to identify patients at increased arrhythmic risk and guide long-term management.10

As wearable technologies with ECG capabilities become increasingly ubiquitous, they are likely to play a growing role in arrhythmia surveillance. Continuous longitudinal data from these devices may improve risk stratification and facilitate more personalized long-term follow-up strategies after AM.

In conclusion, robust risk stratification strategies that integrate clinical presentation at admission with multimodality assessment are needed to support clinical decision-making and avoid unnecessarily prolonged follow-up in low-risk patients after acute myocarditis.