What are the symptoms and laboratory findings of myocarditis?

Myocarditis: Clinical Symptoms and Laboratory Findings

Myocarditis presents with a triad of cardiac symptoms, elevated cardiac troponin, and abnormal cardiac testing (ECG, echocardiography, or cardiac MRI), with chest pain being the most common symptom occurring in 82-95% of adult patients. 1, 2

Clinical Symptoms

Cardinal Presenting Symptoms

• Chest pain is the predominant symptom, occurring in 82-95% of adult patients with acute myocarditis, often mimicking acute coronary syndrome with angina-like quality 3, 2
• Dyspnea presents in 19-49% of cases, ranging from mild exertional breathlessness to acute heart failure 1, 3, 2
• Fever is among the most common symptoms, particularly with viral myocarditis including COVID-19 1, 3
• Cough frequently accompanies viral myocarditis, especially in respiratory viral infections 1, 3

Additional Cardiac Symptoms

• Palpitations from supraventricular or ventricular tachyarrhythmias are common 1, 3
• Syncope occurs in 5-7% of patients, often related to arrhythmias or hemodynamic compromise 1, 3, 2
• Postexertional fatigue is a characteristic symptom that may persist long-term 1, 3
• Nonspecific chest discomfort beyond typical angina, including pressure sensations 1, 3

Temporal Pattern and Severity Spectrum

• Recent viral illness with gastrointestinal or upper respiratory symptoms often precedes cardiac symptoms by days to weeks 3
• Symptoms typically evolve over days to weeks during the inflammatory phase 1, 3
• Resolution within 3 months occurs in many cases, though persistence beyond 12 months has been documented indicating chronic myocarditis 1, 3
• Acute congestive heart failure with or without cardiogenic shock can occur 1
• Cardiogenic shock develops in 27% of COVID-19-associated myocarditis cases 3, 4

Laboratory Findings

Cardiac Biomarkers

• Elevated cardiac troponin (preferably using a high-sensitivity assay) above the 99th percentile upper reference limit is a defining feature of myocarditis 1, 3
• Troponin elevation is required for diagnosis but correlates poorly with the degree of systolic dysfunction 4
• Creatine kinase may also be elevated, indicating myocyte necrosis 1

Electrocardiographic Findings

• Diffuse T-wave inversion without reciprocal changes 1, 3
• ST-segment elevation without reciprocal ST-segment depression, mimicking acute myocardial infarction 1
• Prolongation of the QRS complex duration 1
• Supraventricular and ventricular tachyarrhythmias are common 1
• Bradyarrhythmias and intraventricular conduction delays, including advanced atrioventricular block 1, 3

Echocardiographic Findings

• Left ventricular wall motion abnormalities in a noncoronary distribution 1, 3
• Wall thickening may be present 2
• Systolic dysfunction ranging from subclinical abnormal strain patterns to overt heart failure 4
• Right ventricular dysfunction is common, with fractional area change <35% 4

Cardiac MRI Findings (Definitive Diagnosis)

• Nonischemic late gadolinium enhancement (LGE) pattern, typically subepicardial or mid-myocardial rather than endocardial 1, 4, 5
• Prolonged native T1 relaxation times (>2 standard deviations above local reference mean) indicating inflammation/edema 1, 4, 5
• Prolonged T2 relaxation times (>2 standard deviations above local reference mean) indicating myocardial edema 1, 4, 5
• Elevated extracellular volume (ECV) >30% suggesting interstitial/extracellular space involvement 4
• Updated Lake Louise Criteria requires at least one T2-based criterion and at least one T1-based criterion for high specificity diagnosis 5

Diagnostic Certainty Levels

The American College of Cardiology categorizes myocarditis into three levels of diagnostic certainty 1:

Possible Myocarditis

• Cardiac symptoms present 1
• Elevated cardiac troponin 1
• Abnormal ECG and/or echocardiographic findings 1
• But either CMR/biopsy not performed or shows no acute myocarditis 1

Probable Myocarditis

• All features of possible myocarditis present 1
• Follow-up CMR and/or biopsy within 6 months demonstrates abnormalities consistent with previous myocarditis 1

Definite Myocarditis

• All features of possible myocarditis present 1
• CMR and/or biopsy performed at time of acute illness demonstrates findings consistent with active myocarditis 1

Critical Diagnostic Pitfalls

• Symptom intensity does not correlate with ejection fraction severity - patients may have severely reduced LVEF with minimal symptoms or vice versa 4
• Cardiac biomarkers correlate poorly with the degree of systolic dysfunction - elevated troponin does not predict severity of ventricular dysfunction 4
• Flow-limiting coronary artery disease must be excluded, ideally in men older than 50 years and women older than 55 years 1
• CMR has lower sensitivity for chronic myocarditis (>14 days from symptom onset), with diagnostic accuracy dropping from 81% in acute cases to 45% in chronic cases 5
• Multiple etiologies may coexist, making it challenging to identify a specific underlying cause 1