Table 1. Case Definition Criteria for Myocarditis Following Immunization^a.

Suspected case	Probable case	Confirmed case
Dyspnea, palpitations, or chest pain of probable cardiac origin, with either one of the following: ECG abnormalities beyond normal variants, not documented previously, including: ST-segment/T-wave abnormalities Paroxysmal or sustained atrial or ventricular arrhythmias AV nodal conduction delays or intraventricular conduction defects Continuous ambulatory ECG monitoring that detects frequent atrial or ventricular ectopy Focal or diffuse depressed LV function of indeterminate age identified by an imaging study	Meets criteria for suspected myocarditis, in the absence of other likely cause of symptoms, in addition to one of the following: Elevated cardiac enzymes (troponin-I, troponin-T, or creatine kinase-MB) New-onset or increased degree of severity of focal or diffuse depressed LV function by imaging Abnormal imaging findings indicating myocardial inflammation (cardiac MRI with gadolinium, gallium-67 scanning, antimyosin antibody scanning)	Histopathologic evidence of myocarditis by endomyocardial biopsy or autopsy

Abbreviations: ECG, electrocardiography; LV, left ventricular; MRI, magnetic resonance imaging.

^aThis definition was originally developed to evaluate cardiac events after smallpox vaccine. The definition is currently being reviewed by the international Brighton Collaboration for application to COVID-19 vaccine.