how to differentiate between acute myocarditis and stemi
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myocarditis AND "acute coronary syndrome"
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2025 ESC acute myocarditis guideline differentiate ST elevation myocardial infarction cardiac MRI
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https://www.escardio.org/guidelines/clinical-practice-guidel…
Acute myocarditis can closely mimic STEMI. Treat any patient with ongoing ischemic chest pain and diagnostic ST elevation as a STEMI until coronary occlusion is excluded. Do not delay emergency reperfusion assessment because a viral prodrome or suspected myocarditis is present.
| Feature | Acute myocarditis | STEMI due to acute coronary occlusion |
|---|---|---|
| Typical context | Often recent viral-type illness, fever, myalgia, fatigue; may occur in younger patients without coronary risk factors | Often older patient or coronary risk factors, but can occur at any age |
| Chest pain | Can be infarct-like, pleuritic, or positional, especially if concurrent pericarditis | Classically heavy, constricting, persistent ischemic pain, often with diaphoresis/nausea |
| ECG | ST elevation may be diffuse or nonterritorial; PR depression can suggest myopericarditis; ST-T changes may evolve | Regional ST elevation in a coronary territory with reciprocal ST depression, evolving Q waves or T-wave inversion |
| Troponin | Often elevated, sometimes markedly | Elevated with a rise/fall pattern. Level alone cannot reliably distinguish it from myocarditis |
| Echo | May be normal, show global dysfunction, or regional abnormalities that do not respect one coronary territory; possible pericardial effusion | Regional wall-motion abnormality corresponding to the affected coronary artery |
| Coronary angiography / CT coronary angiography | No acute obstructive culprit lesion, though myocarditis and CAD can coexist | Acute culprit coronary thrombotic occlusion or critical stenosis |
| Cardiac MRI | Myocardial edema plus typically patchy subepicardial or mid-wall late gadolinium enhancement, often inferolateral | Ischemic injury follows a vascular territory, with subendocardial to transmural late gadolinium enhancement and regional edema |
| Other clues | Arrhythmias, conduction block, heart failure out of proportion to ECG findings | Hemodynamic instability, malignant ventricular arrhythmias, or cardiogenic shock can occur in large infarcts |
Practical diagnostic approach
- Immediate ECG and serial ECGs, plus high-sensitivity troponin and bedside echocardiography.
- If the presentation or ECG meets STEMI criteria, activate the acute coronary pathway. Myocarditis is an established STEMI mimic, but it cannot be safely assumed at presentation.
- Urgent invasive coronary angiography is generally required for an ACS-like presentation to rule out obstructive coronary disease. Fuster and Hurst specifically notes that angiography remains necessary in myocarditis presenting like acute coronary syndrome.
- If coronary arteries are nonobstructive and the diagnosis remains uncertain, perform cardiac MRI promptly. It is usually the best discriminator between myocarditis, infarction with nonobstructive coronary arteries, and takotsubo syndrome.
ECG cautions
- Diffuse ST elevation and PR depression favor pericardial involvement, but neither excludes STEMI.
- Reciprocal ST depression and a clear territorial distribution favor STEMI, but myocarditis can occasionally be focal and territorial-looking.
- A normal or nondiagnostic ECG does not exclude myocarditis.
- Troponin elevation confirms myocardial injury, not its cause.
Key MRI distinction
- Myocarditis: edema with nonischemic injury pattern, usually subepicardial or mid-myocardial, patchy, and not confined to a single coronary artery distribution.
- STEMI: subendocardial injury, often progressing to transmural enhancement, in the distribution of an occluded coronary artery.
Textbook sources identify myocarditis as a condition that can mimic ST-elevation MI and emphasize coronary angiography for ACS-like presentations: Goldman-Cecil Medicine, Table 58-2; Fuster and Hurst’s The Heart, “Myocarditis as an ACS Mimicker”; Braunwald’s Heart Disease, “Cardiac Imaging.” The 2025 ESC myocarditis guideline is the current major guideline reference.
Bottom line: You differentiate definitively mainly with coronary anatomy plus cardiac MRI, not by symptoms, ECG, or troponin alone.
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