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Case 018: Acute Myocarditis - Viral Prodrome with Heart Failure

Presentation

A 14-year-old previously healthy male presents with 3 days of progressive fatigue, decreased appetite, and mild abdominal pain. He had a "stomach bug" with vomiting and diarrhea 2 weeks ago that resolved.

Vital Signs: - Heart rate: 130 bpm - Blood pressure: 88/60 mmHg - Respiratory rate: 28 - SpO2: 94% on room air - Temperature: 37.2°C

Exam: - Appears ill, pale, and diaphoretic - JVD present - Tachycardia, gallop rhythm (S3), no murmur - Lungs with bibasilar crackles - Liver palpable 3 cm below costal margin - Cool extremities, capillary refill 4 seconds

Initial Workup

Labs: - Troponin I: 2.8 ng/mL (markedly elevated) - BNP: 1,850 pg/mL (elevated) - CRP: 4.2 mg/dL - WBC: 9,800 - BMP: Creatinine 1.1 (baseline 0.6) - AST/ALT: 180/210 (elevated)

ECG: - Sinus tachycardia - Low voltage QRS - Non-specific ST-T changes diffusely - Frequent PVCs

Chest X-ray: - Cardiomegaly - Pulmonary venous congestion - Small bilateral pleural effusions

Clinical Reasoning

Question 1: What is the most likely diagnosis?

Answer **Acute viral myocarditis with cardiogenic shock** Key features: - Viral prodrome 2 weeks prior (classic timing for myocarditis) - Signs of heart failure (JVD, gallop, hepatomegaly, pulmonary edema) - Cardiogenic shock (hypotension, poor perfusion, end-organ dysfunction) - Markedly elevated troponin (myocyte injury) - Elevated BNP (ventricular strain) The presentation differs from pericarditis - here the primary problem is **pump failure**, not pericardial inflammation.

Question 2: What additional test would confirm the diagnosis?

Answer **Echocardiogram** is the most important next test. Expected findings in acute myocarditis: - Decreased LV systolic function (low EF) - LV dilation - Possible regional wall motion abnormalities - May show RV involvement - May see small pericardial effusion **CMR (Cardiac MRI)** is the gold standard for diagnosing myocarditis (Lake Louise criteria) but is not first-line in unstable patients.

Question 3: What is the initial management?

Answer **Immediate priorities for cardiogenic shock:** 1. **ICU admission** - close hemodynamic monitoring 2. **Cardiology consultation** - STAT 3. **Hemodynamic support:** - If persistent hypotension: consider inotropes (milrinone, dobutamine) - Avoid aggressive fluid resuscitation (already in heart failure) - May need mechanical support (ECMO) if deteriorating 4. **Diuretics** - cautiously for pulmonary congestion 5. **Arrhythmia monitoring** - high risk for VT/VF 6. **Avoid NSAIDs** - may increase myocardial injury **NOT indicated initially:** - Immunosuppression (not proven beneficial in viral myocarditis) - IVIG (may consider in specific cases, but not routine)

Question 4: What is the prognosis?

Answer **Variable, but often favorable with support:** - **~50-60%** recover normal LV function - **~20-30%** develop dilated cardiomyopathy (DCM) - **~10-20%** die or require transplant **Poor prognostic factors:** - Fulminant presentation with hemodynamic collapse - Persistent LV dysfunction at 1 month - Giant cell myocarditis (rare, requires biopsy) - Arrhythmias (sustained VT) **Good prognostic factor:** - Paradoxically, fulminant myocarditis with rapid onset may have better long-term outcomes than subacute presentations (if the patient survives the acute phase)

Key Teaching Points

  1. Myocarditis mimics many conditions - consider in any child with unexplained heart failure, arrhythmias, or chest pain after viral illness

  2. Viral prodrome 1-4 weeks prior is classic history - always ask about recent illness

  3. Troponin + BNP are key biomarkers - troponin indicates myocyte injury, BNP indicates ventricular strain

  4. Echo before MRI in unstable patients - echo is faster and available at bedside

  5. Avoid NSAIDs in myocarditis - associated with increased mortality in animal studies

  6. Mechanical support may be lifesaving - ECMO bridge to recovery or transplant

References

  • Ammirati E, et al. Fulminant Versus Acute Nonfulminant Myocarditis. JACC. 2019;74(3):299-311. PMID: 30846341
  • Law YM, et al. Diagnosis and Management of Myocarditis in Children. Circulation. 2021;144(6):e123-e135. PMID: 34229446