How should pembrolizumab (Keytruda)-induced myocarditis be managed?

Management of Pembrolizumab (Keytruda)-Induced Myocarditis

Immediately discontinue pembrolizumab permanently and initiate high-dose corticosteroids (methylprednisolone 1000 mg/day IV or 1-2 mg/kg/day) upon suspicion or confirmation of myocarditis, as this is a life-threatening emergency requiring intensive monitoring and aggressive immunosuppression. 1

Initial Recognition and Diagnostic Workup

Clinical Presentation

• Suspect myocarditis with any new cardiovascular symptoms including dyspnea, chest pain, myalgia, fatigue, or palpitations, particularly within the first 34 days of treatment (though onset can occur at any time) 1
• High-risk features include concomitant myositis/myasthenia gravis (occurs in 42% of severe cases), diabetes, or combination ICI therapy 1
• Arrhythmias and conduction abnormalities are common presentations and can be the mode of death even with preserved ejection fraction 1

Immediate Diagnostic Testing

Perform comprehensive cardiac evaluation promptly 1:

• ECG and continuous telemetry monitoring for arrhythmias, conduction abnormalities, QTc prolongation, or ST-T wave changes 1
• Cardiac biomarkers: Troponin (>99th percentile institutional normal is significant), creatine kinase, BNP or NT-pro-BNP 1
• Inflammatory markers: C-reactive protein, erythrocyte sedimentation rate, complete blood count 1
• Echocardiogram with global longitudinal strain to assess ventricular function and wall motion abnormalities 1
• Cardiac MRI when feasible for tissue characterization and confirmation of myocardial inflammation 1
• Endomyocardial biopsy should be considered if diagnosis is highly suspected with otherwise negative workup 1
• Viral titers to exclude infectious causes 1

Immediate Management

Drug Discontinuation

• Permanently discontinue pembrolizumab for any clinical myocarditis (Grade 3-4) 1
• Hold pembrolizumab for Grade 3 cardiac toxicity (moderately abnormal testing with symptoms during mild activity, BNP >500 pg/mL, troponin >99th percentile) until stabilized 1

Immunosuppressive Therapy

For confirmed or highly suspected myocarditis:

• Initiate high-dose IV methylprednisolone 1000 mg/day followed by oral prednisone 1 mg/kg/day immediately 1
• Alternative dosing: methylprednisolone 1-2 mg/kg IV for at least several days 1
• Continue corticosteroids until resolution of symptoms and normalization of troponin, left ventricular systolic function, and conduction abnormalities 1
• Taper steroids slowly over at least 4-6 weeks after improvement to Grade ≤1 1

For steroid-refractory or high-grade myocarditis with hemodynamic instability:

• Add additional immunosuppressive agents 1:
  • Antithymocyte globulin
  • Infliximab (avoid in patients with heart failure) 1
  • Mycophenolate mofetil 1
  • Abatacept 1
• Consider these agents if no improvement after 2 days of high-dose steroids or if symptoms worsen 1

Supportive Cardiac Care

• Admit to intensive care unit with continuous telemetry monitoring 1
• Provide guideline-directed medical therapy for heart failure if cardiomyopathy develops (ACE inhibitors/ARBs, beta-blockers) 1
• Manage arrhythmias with appropriate antiarrhythmic therapy and consider temporary or permanent pacemaker for symptomatic heart block 1, 2, 3
• Hemodynamic support as needed, including inotropes, vasopressors, or intra-aortic balloon pump for severe cases 4

Severity-Based Management Algorithm

Grade 1 (Abnormal biomarkers/ECG, asymptomatic)

• Continue close observation with serial cardiac biomarkers and ECG 1
• Establish baseline for comparison during therapy 1

Grade 2 (Mild symptoms, abnormal screening tests)

• Optimize management of underlying cardiac conditions and risk factors 1
• Consider withholding pembrolizumab and monitor closely 1

Grade 3 (Moderate symptoms with mild activity)

• Withhold pembrolizumab until stabilized 1
• Consider corticosteroids if myocarditis suspected (case-by-case basis) 1
• Consult cardiology urgently to discuss risk/benefit of continuing therapy and starting immunosuppression 1

Grade 4 (Severe decompensation, life-threatening)

• Permanently discontinue pembrolizumab 1
• Initiate high-dose corticosteroids immediately (methylprednisolone 1-2 mg/kg IV) 1
• Add additional immunosuppressive agents for severe refractory cases 1
• Provide intensive supportive care including treatment of heart failure and arrhythmias 1

Critical Pitfalls and Considerations

Early Recognition

• Myocarditis symptoms are nonspecific (myalgia, dyspnea, chest pain) and can mimic pneumonitis or other immune-related adverse events 1
• Mortality remains high (23%) even with rapid intervention, with conduction abnormalities being the primary mode of death 1
• Troponin elevation may be the earliest marker and should prompt immediate evaluation 5
• 64% of severe cases occur after only 1-2 doses of pembrolizumab 1

Concomitant Conditions

• Screen for concurrent myositis (check creatine kinase) and myasthenia gravis, which occur in 42% of severe myocarditis cases 1, 2, 6
• Evaluate for hepatitis if transaminases are elevated to distinguish from immune-mediated hepatitis 1

Rechallenge Considerations

• ICI therapy should be permanently discontinued with any clinical myocarditis 1
• Rechallenge requires multidisciplinary discussion considering cancer status, severity of cardiotoxicity, regression with immunosuppression, and patient preference 1
• If rechallenge necessary, consider anti-PD-1 monotherapy with very close cardiovascular surveillance 1
• One case report documented successful rechallenge in mild myocarditis without left ventricular dysfunction, but this requires exceptional circumstances and intensive monitoring 7

Steroid Tapering

• Taper very slowly over 6 weeks or more to prevent relapse 1
• Relapses during steroid tapering have been reported 1
• Continue corticosteroids until complete normalization of troponin, ventricular function, and conduction abnormalities 1

Long-term Management

• Continue cardiac monitoring even after resolution, as late complications can occur 1
• Maintain guideline-directed heart failure therapy indefinitely if cardiomyopathy developed 1