Signs and Symptoms of Myocarditis
Myocarditis typically presents with chest pain, dyspnea, fever, and palpitations, though the clinical presentation is highly variable and can range from subtle symptoms to fulminant heart failure requiring mechanical support.
Cardinal Symptoms
The most common presenting symptoms include 1, 2:
- Chest pain (most frequent presentation, often mimicking acute coronary syndrome)
- Dyspnea (shortness of breath)
- Fever (particularly in infectious/viral myocarditis)
- Palpitations (may indicate underlying arrhythmias)
- Fatigue (including post-exertional fatigue)
- Syncope (loss of consciousness)
A critical pitfall: Symptoms may be non-specific or even absent in some athletes undergoing screening, making diagnosis challenging 2. Some patients present only with fatigue, which can easily be missed 2.
Prodromal Features
Many patients report a preceding viral illness with coryzal symptoms (upper respiratory infection) or diarrhea in the days to weeks before cardiac symptoms develop 2. This history is particularly important when evaluating chest pain in young, otherwise healthy individuals.
Electrocardiographic Abnormalities
ECG findings are variable but commonly include 2:
- Frequent and/or complex ventricular arrhythmias
- Supraventricular arrhythmias
- ST-segment alterations
- T-wave inversions
- Left bundle branch block (LBBB)
- Atrioventricular block
- Low QRS voltages (particularly with pericardial effusion)
Laboratory Markers
Elevated cardiac troponin (preferably high-sensitivity assay) above the 99th percentile is a defining feature 1. Additional biomarkers include:
- Elevated inflammatory markers (C-reactive protein)
- Elevated natriuretic peptides (BNP/NT-proBNP)
Severity Spectrum and Clinical Presentations
The disease exists on a spectrum 1, 3:
Mild/Uncomplicated
- Chest discomfort with preserved ventricular function
- Normal hemodynamics
- Minimal symptoms
Moderate
- Heart failure symptoms
- Left ventricular systolic dysfunction (occurs in ~25% of cases) 3
- Arrhythmias requiring monitoring
Fulminant
- Cardiogenic shock (27% of COVID-19-associated cases) 1
- Distributive shock (12% of COVID-19-associated cases) 1
- Requires mechanical circulatory support
- Mortality 1-7% depending on etiology 3
Important caveat: Symptom intensity does NOT correlate well with left ventricular ejection fraction or biomarker levels 1. A patient with mild symptoms may still have significant myocardial dysfunction on imaging.
Imaging Findings
While not strictly "signs," cardiac magnetic resonance (CMR) findings are now central to diagnosis 1:
- Increased native T1 signal (fibrosis or inflammation)
- Increased T2 signal (inflammation or edema)
- Non-ischemic late gadolinium enhancement (LGE)
- Regional wall motion abnormalities (classically segmental rather than global)
Duration of Symptoms
Symptoms typically resolve within 3 months but can persist beyond 12 months in some patients 1. This prolonged symptom duration should prompt continued monitoring and delayed return to activity.
High-Risk Warning Signs
Immediate recognition of these features is critical 2, 3:
- Syncope or presyncope
- Sustained ventricular arrhythmias
- Heart failure symptoms (orthopnea, paroxysmal nocturnal dyspnea)
- Hemodynamic instability
- Severe left ventricular dysfunction
The risk of sudden cardiac death does not always correlate with severity of inflammation or troponin levels 2, making clinical vigilance essential even in seemingly mild cases.