Myocarditis

Patient: 26M with chest pain and dyspnea 10 days after a flu-like illness. Troponin 6.8, BNP 2400. ECG: diffuse ST elevation without reciprocal changes. Echo: EF 30%, global hypokinesis. No coronary disease on angiography.

Key findings: Acute viral myocarditis with new-onset HFrEF. Clean coronaries exclude ACS. Diffuse ST changes (not territorial) + recent viral prodrome + young patient = classic presentation.

Management:

• Cardiac MRI, Lake Louise criteria: T2 edema + LGE in non-coronary distribution (mid-wall/epicardial) confirms myocarditis
• GDMT for HFrEF: ACEi/ARB, beta-blocker (once stable), MRA if EF ≤ 35%
• Telemetry monitoring, arrhythmia risk highest in acute phase (VT/VF)
• NO NSAIDs (worsen inflammation and remodeling in myocarditis)
• Repeat echo at 3-6 months, most viral myocarditis recovers EF (60-70% normalize)

Teaching point: Do NOT place an ICD during acute myocarditis even if EF ≤ 35%. Most patients recover EF, wait ≥ 3-6 months and reassess. LifeVest (wearable defibrillator) is a bridge if high arrhythmia risk.

Patient: 32F with 2 days of progressive dyspnea, now in cardiogenic shock. HR 120, BP 72/48, cool extremities, lactate 6.2. Echo: EF 10%, global severe hypokinesis. Troponin 42. No prior cardiac history.

Key findings: Fulminant myocarditis, rapid-onset cardiogenic shock in a previously healthy patient. Paradoxically, fulminant myocarditis has BETTER long-term prognosis than acute myocarditis if the patient survives the acute phase (stronger immune response → better viral clearance).

Management:

• ICU, vasopressors/inotropes (dobutamine 5 mcg/kg/min + norepinephrine for MAP ≥ 65)
• Early mechanical circulatory support: Impella or VA-ECMO if refractory to inotropes
• Endomyocardial biopsy, rule out giant cell myocarditis (requires immunosuppression) or eosinophilic myocarditis
• Avoid beta-blockers acutely in cardiogenic shock (can worsen hemodynamics)
• If giant cell myocarditis on biopsy: high-dose steroids + cyclosporine (without immunosuppression, mortality > 80%)

Teaching point: Fulminant myocarditis is a "bridge to recovery" disease, patients who survive the acute phase often recover near-normal EF. Aggressive mechanical support (ECMO/Impella) saves lives. Biopsy is critical to exclude giant cell myocarditis.

Patient: 58M on pembrolizumab for melanoma × 3 cycles. New fatigue, dyspnea, palpitations. Troponin 2.4 (was normal at baseline). ECG: new conduction delay, PR prolongation. Echo: EF 45% (was 60%).

Key findings: Immune checkpoint inhibitor (ICI) myocarditis, occurs in 1-2% of ICI-treated patients but mortality is 25-50%. Can present with conduction abnormalities, arrhythmias, or HF. Often coexists with myositis and myasthenia gravis.

Management:

• Hold pembrolizumab immediately (permanently discontinue, do not rechallenge)
• High-dose methylprednisolone 1g IV daily × 3-5 days → prednisone 1 mg/kg with slow taper
• If steroid-refractory: add mycophenolate, infliximab, or abatacept
• Continuous telemetry, high-grade AV block and VT are common and often fatal
• Check CK (concurrent myositis), anti-AChR antibodies (concurrent MG), and cardiac MRI

Teaching point: ICI myocarditis is the most lethal irAE, early troponin monitoring and a low threshold for holding therapy saves lives. Conduction abnormalities (PR prolongation, BBB) may be the first sign before EF drops.