Cardiovascular · Topic 27 of 48

Myocarditis

Cardiovascular · myocardial and pericardial disease

Myocarditis

Troponin and heart failure in a young patient with clean coronaries. Confirm with cardiac MRI; stabilize fulminant cases with inotropes and mechanical support.

Key numbers

Unexplained troponin, no cardiac risk factors1–4 wk after viral illness

No strenuous exercise for 3–6 months3–6 months

01 · Look forUnexplained troponin, no cardiac risk factors

Suspect myocarditis when a patient without cardiac risk factors develops heart failure, arrhythmia or chest pain with elevated troponin, often 1–4 weeks after a viral or nonspecific illness.

02 · Defined byCardiac MRI confirms the diagnosis

Cardiac MRI is the key noninvasive test: updated Lake Louise criteria need at least one T2-based marker of edema plus one T1-based marker of injury (raised T1, extracellular volume or late gadolinium enhancement).

03 · DoFulminant: inotropes and mechanical support

Fulminant myocarditis presents in cardiogenic shock: admit to the ICU, refer to a heart failure center, and support with diuresis, inotropes and mechanical circulatory support (IABP, LVAD) or transplant if needed.

Causes & risk factors

Why it happens

Viral, drug, toxin and autoimmune causesCauses: viruses (parvovirus B19, HHV-6, enteroviruses such as coxsackie B, influenza, SARS-CoV-2), drugs (clozapine, immune checkpoint inhibitors, anthracyclines, penicillins), cocaine and alcohol, sarcoidosis and autoimmune disease; many are idiopathic.

Presentation

What you'll see

Heart block suggests Lyme, giant cell or sarcoidThe ECG is nonspecific (ST–T changes, sometimes ST elevation, tachyarrhythmias); heart block points to Lyme carditis, giant cell myocarditis or cardiac sarcoidosis.

Do right now

In this order

First moves

Fulminant: inotropes and mechanical support

→

Exclude coronary disease with angiography or CT

→

Cardiac MRI confirms the diagnosis

→

Biopsy for shock, ventricular arrhythmia or heart block

Why each step

Fulminant: inotropes and mechanical supportFulminant myocarditis presents in cardiogenic shock: admit to the ICU, refer to a heart failure center, and support with diuresis, inotropes and mechanical circulatory support (IABP, LVAD) or transplant if needed.

Exclude coronary disease with angiography or CTMyocarditis mimics MI — troponin release, ST changes and regional wall-motion abnormalities — so order coronary angiography or coronary CT to exclude obstructive coronary artery disease.

Cardiac MRI confirms the diagnosisCardiac MRI is the key noninvasive test: updated Lake Louise criteria need at least one T2-based marker of edema plus one T1-based marker of injury (raised T1, extracellular volume or late gadolinium enhancement).

Biopsy for shock, ventricular arrhythmia or heart blockEndomyocardial biopsy is the gold standard but patchy disease makes it insensitive; do it for fulminant heart failure, ventricular arrhythmias, high-grade heart block or suspected giant cell myocarditis, when results change treatment.

Management

Orders

Start guideline-directed HF therapy once stableOnce hemodynamically stable, treat reduced ejection fraction with guideline-directed therapy: ARNI or ACE inhibitor/ARB, evidence-based beta-blocker, mineralocorticoid antagonist and SGLT2 inhibitor.

Checkpoint-inhibitor myocarditis: stop drug, high-dose steroidsImmune checkpoint inhibitor myocarditis: stop the checkpoint inhibitor and give high-dose glucocorticoids, adding abatacept, alemtuzumab or antithymocyte globulin for severe or steroid-refractory cases.

Giant cell myocarditis: steroids plus calcineurin inhibitorGiant cell myocarditis presents with shock, refractory ventricular arrhythmias or complete heart block; glucocorticoids plus a calcineurin inhibitor (cyclosporine or tacrolimus) improve survival.

Hypersensitivity myocarditis: stop the drug, give steroidsHypersensitivity (eosinophilic) myocarditis — suggested by rash and peripheral eosinophilia — is treated by stopping the causative drug immediately and giving glucocorticoids.

Red flags & don'ts

Avoid harm

Avoid NSAIDs when ejection fraction is reduced avoidNSAIDs or colchicine may treat chest pain from associated pericardial inflammation, but avoid NSAIDs when the left ventricular ejection fraction is significantly reduced.

The rules

Know these

No routine immunosuppression for viral myocarditisViral myocarditis is treated supportively; reserve immunosuppression for giant cell, eosinophilic, sarcoid, autoimmune, checkpoint-inhibitor or biopsy-proven virus-negative disease, after excluding infection (TB myocarditis worsens with glucocorticoids).

Myocarditis or acute MI?

Commonly confused

Typical patient	No cardiac risk factors, recent viral illness
Troponin and ST changes	Can be present — mimics MI
Coronary angiography or CT	No obstructive culprit lesion
Late gadolinium enhancement on MRI	Subepicardial or mid-wall

Teach & follow up

Patient education

No strenuous exercise for 3–6 monthsRestrict strenuous and competitive activity for 3–6 months in symptomatic myocarditis; return to play depends on clinical course, resolution on MRI, Holter arrhythmia burden and exercise testing.

More detail

Reference

Show 7 reference facts

Lyme carditis is treated with oral doxycycline, amoxicillin or cefuroxime, or IV ceftriaxone; heart block may need temporary pacing.

Myocarditis after mRNA COVID-19 vaccination is very rare, occurs mostly in adolescent and young adult males within a week of the dose, and is usually mild.

High-sensitivity troponin has a reported sensitivity of 64–100% for acute myocarditis; CK isoenzymes are not used for diagnosis.

Pulsus alternans signals severe LV systolic dysfunction, and low QRS voltage may reflect severe myocardial edema or dysfunction.

The 2024 ACC pathway stages myocarditis A (at risk) to D (severe, needing ICU care and mechanical support); stages C–D get serial troponin, MRI and echo follow-up.

Myocarditis that does not resolve over months becomes chronic and can progress to dilated cardiomyopathy; sudden cardiac death can be the first presentation.

Consider genetic testing with recurrent myocarditis or pericarditis, persistent troponin elevation, a family history, or severe ventricular arrhythmia.

Pearl

Troponin up, coronaries clean, young patient after a viral illness: think myocarditis and get the cardiac MRI.

Sources · Merck Manual Professional — Myocarditis (reviewed Apr 2026) · Drazner MH et al. 2024 ACC Expert Consensus Decision Pathway on the Diagnosis and Management of Myocarditis. J Am Coll Cardiol 2025;85:391–431 · Ferreira VM et al. Cardiovascular MRI in nonischemic myocardial inflammation: expert recommendations (updated Lake Louise criteria). J Am Coll Cardiol 2018;72:3158–3176 — Europe PMC abstract · Ganatra S et al. 2025 ACC Concise Clinical Guidance: cardiovascular adverse effects of targeted oncology therapies (BTK, immune checkpoint and VEGF inhibitors). J Am Coll Cardiol 2026;87:654–682 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).