Severe Type:

Significant symptoms (e.g., fatigue, palpitations, chest pain) triggered by daily activities without hemodynamic changes; elevated myocardial biomarkers (Cardiac troponin, creatine kinase, Creatine kinase myocardial band, Aspartate aminotransferase，natriuretic peptides); new ECG changes; structural and functional myocardial abnormalities on echocardiography or MRI.

Critical Type:

Intolerable symptoms (e.g., respiratory dysfunction, heart failure, cardiogenic shock) at rest or minimal activity, with hemodynamic instability; significantly elevated myocardial biomarkers (Cardiac troponin, creatine kinase, Creatine kinase myocardial band, Aspartate aminotransferase, natriuretic peptides); severe myocardial structural and functional abnormalities on echocardiography or MRI; new severe arrhythmias on ECG .

Subclinical Myocardial Injury: All three of the following criteria must be met:

1. No clinical symptoms triggered by daily activities;
2. Only mild elevation of Cardiac troponin levels without elevation of other myocardial injury biomarkers;
3. No abnormalities detected in other auxiliary examinations.

Mild Type: The following conditions must be met for diagnosis:

1. Daily activities may cause mild, nonspecific symptoms such as fatigue or shortness of breath;
2. Mild elevation of myocardial injury biomarkers (Cardiac troponin, creatine kinase, Creatine kinase myocardial band, Aspartate aminotransferase，natriuretic peptides);
3. Mild abnormalities on ECG, including new-onset sinus tachycardia, atrial arrhythmias, or nonspecific ST-T changes;
4. No structural or functional abnormalities of the myocardium detected by echocardiography or cardiac MRI.

Blood samples will be collected at baseline and at follow-up time points (3 days, 7 days, and before discharge). Traditional myocardial injury biomarkers, iron metabolism-related biomarkers, and immunological biomarkers will be tested.

By monitoring the dynamic changes in biomarker combinations at different time points (baseline, day 3, day 7, and before discharge), this study aims to evaluate the differences between the severe/critical group and the mild/subclinical myocardial injury group, and investigate their correlation with disease severity. Independent sample t-tests will be used to assess the differences between the two groups, assuming a moderate effect size (Cohen's d = 0.7) for biomarkers between the severe/critical and subclinical/mild immune checkpoint inhibitor-related myocarditis patients. If significant differences (p < 0.10) in biomarkers are observed between the groups, these differences will serve as key indicators for stratified management of disease severity.

The severity assessment model, constructed based on biomarker combinations, was evaluated for its predictive performance using indicators such as the ROC curve and AUC value. The model demonstrated a predictive performance with an AUC > 0.75 at different time points, indicating a high predictive ability and validating its practical application in clinical risk stratification.

The rate of death occurring within the hospital during a patient's stay.

The 3-month survival rate will be defined as the proportion of patients alive 3 months after enrollment in the study.