Diagnosing Myocarditis in the ED

Myocarditis is a rare but can’t-miss cause of chest pain, arrhythmia, and new heart failure in the ED. The 2024 ACC pathway frames suspected myocarditis as a structured diagnostic problem: recognize the syndrome, order the right initial tests, and involve cardiology early because normal early studies do not exclude it.

Recognizing Suspected Myocarditis

• Three syndrome presentation: Suspect myocarditis when the presentation clusters around one of three syndromes: chest pain, arrhythmia, or heart failure/cardiogenic shock.
• High-yield historical clues: Recent viral illness, autoimmune disease, prior myocarditis, cardiotoxin exposure, or a family history of cardiomyopathy or sudden death all raise the pretest probability.
• Chest pain phenotype: Myocarditis can look like STEMI or pericarditis, with troponin elevation and inflammatory markers adding support, but ACS still has to be ruled out first.
• Arrhythmic warning signs: Palpitations, presyncope, syncope, tachydysrhythmias, bradydysrhythmias, and even sudden death all fit the myocarditis spectrum, a distinction we get into in the episode.
• Advanced disease signal: New or worsening heart failure with hemodynamic instability should move myocarditis higher on the differential, especially when the story does not fit routine ischemia.

ED Workup and Early Management

• Core ED diagnostics: Initial workup starts with CBC, BMP, troponin, ECG, and echocardiography, because the diagnosis is usually built from pattern recognition rather than a single test.
• Normal test caveat: A normal troponin or normal ECG does not rule out myocarditis, making bedside suspicion and repeat reassessment more important than false reassurance.
• ECG pattern range: ECG findings range from nonspecific ST-T changes to pericarditis patterns, brady- or tachydysrhythmias, and even STEMI mimics that may still warrant cath lab evaluation.
• Echo bedside targets: Echocardiography should look for left ventricular dysfunction, pericardial effusion, wall motion abnormalities, and diastolic dysfunction. We walk through what matters most on the bedside study in the episode.
• Specialty testing pathway: Cardiac MRI with T1/T2 mapping and endomyocardial biopsy are the major confirmatory tests, but they are usually inpatient decisions made with cardiology.
• Treat the syndrome first: Early management is supportive and presentation-driven: treat arrhythmias, heart failure, shock, sepsis, and possible ACS while cardiology helps guide disposition and disease-specific therapy.

References:

1. Drazner MH, et al. 2024 ACC Expert Consensus Decision Pathway on Strategies and Criteria for the Diagnosis and Management of Myocarditis: A Report of the American College of Cardiology Solution Set Oversight Committee. J Am Coll Cardiol. 2025 Feb 4;85(4):391-431. PMID: 39665703.
2. Lasica R, et al. Update on Myocarditis: From Etiology and Clinical Picture to Modern Diagnostics and Methods of Treatment. Diagnostics (Basel). 2023 Sep 28;13(19):3073. PMID: 37835816