What cardiac toxicities can pembrolizumab (Keytruda) cause, and how should they be monitored and managed?

Pembrolizumab Cardiac Toxicity

Pembrolizumab can cause rare but potentially fatal cardiac toxicities, most notably myocarditis, which occurs in approximately 0.1% of patients but carries high mortality due to refractory arrhythmias and cardiogenic shock. 1

Spectrum of Cardiac Toxicities

Pembrolizumab-induced cardiovascular complications include:

• Myocarditis (most serious and life-threatening)
• Pericarditis and pericardial effusions
• Arrhythmias and conduction abnormalities (including heart block and cardiac arrest)
• Impaired ventricular function with heart failure
• Cardiomyopathy and myocardial fibrosis
• Vasculitis
• Venous thromboembolism
• Rare cases of acute coronary syndrome 1

The pathophysiology involves lymphocytic infiltration of the myocardium and cardiac conduction system, confirmed on myocardial biopsies. 1

Timing and Clinical Presentation

Median onset is 6 weeks (range: 2-54 weeks), though cases have been reported as early as 3 days and as late as 4,050 days after initiation. 1, 2 The median time to diagnosis across case series is approximately 25 days. 2

Key Clinical Features to Monitor:

• Progressive fatigue, weakness, or myalgias
• Palpitations or chest pain
• Presyncope or syncope
• Dyspnea or shortness of breath
• Peripheral edema
• Severe presentations: cardiogenic shock or sudden death 1

Critical pitfall: Symptoms are frequently masked by or overlap with other immune-related adverse events, particularly myositis (occurs in 43.3% of myocarditis cases), pneumonitis, and hypothyroidism. 1, 2 Always consider concurrent myositis when evaluating suspected cardiac toxicity.

Monitoring Strategy

Baseline Assessment:

• Cardiac history and examination
• Baseline troponin, creatine kinase (CK), and liver enzymes
• Baseline ECG
• Consider baseline echocardiogram in high-risk patients 3

During Treatment:

Monitor cardiac biomarkers (troponin, CK), ECG, and clinical symptoms at each visit. 2 The FDA label mandates evaluation of liver enzymes, creatinine, and thyroid function at baseline and periodically during treatment. 3

Diagnostic Workup When Suspected:

1. Immediate laboratory tests:

   • Troponin (often markedly elevated, e.g., >500 ng/L)
   • CK and CK-MB (frequently >3,000 U/L in myocarditis with myositis)
   • Liver transaminases 4, 2

2. ECG: Look for ST-segment changes, conduction abnormalities (fascicular blocks, AV blocks), or arrhythmias 4, 2

3. Echocardiography: Assess ventricular function and wall motion abnormalities 2

4. Cardiac MRI: Gold standard for confirming myocarditis (shows edema, inflammation, fibrosis) 2

5. Endomyocardial biopsy: Definitive diagnosis showing lymphocytic infiltration with myocyte necrosis, particularly when diagnosis is uncertain or treatment response is poor 4

Management Algorithm

Immediate Actions:

1. Permanently discontinue pembrolizumab 1, 3
2. Hospitalize immediately - this is an oncologic emergency requiring ICU-level care for severe cases 5
3. Initiate high-dose corticosteroids immediately:
   • Methylprednisolone 1-2 mg/kg/day IV or equivalent
   • Do not wait for confirmatory testing if clinical suspicion is high 4, 5

Escalation for Steroid-Refractory Cases:

1. Add intravenous immunoglobulin (IVIG) if inadequate response to steroids within 24-48 hours 4, 5, 6

2. Consider plasma exchange for fulminant cases not responding to steroids and IVIG, particularly when concurrent myositis is present 6

Supportive Care:

• Hemodynamic support with vasopressors/inotropes as needed
• Intra-aortic balloon pump for cardiogenic shock 5
• Continuous cardiac monitoring for arrhythmias
• Treat arrhythmias and heart failure per standard protocols 1

Steroid Taper:

After clinical improvement and biomarker normalization, taper prednisone slowly over weeks to months to prevent relapse. 4

Prognosis and Risk Factors

Mortality is high at approximately 26.8% despite treatment, with death typically from refractory arrhythmias or cardiogenic shock. 1, 2 However, 72.2% of patients recover with prompt recognition and aggressive immunosuppression. 2

Risk is increased with combination therapy: CTLA-4 plus PD-1/PD-L1 inhibitors show cardiovascular complications in 0.28% versus 0.06% with anti-PD-1 monotherapy. 1

Special consideration: Patients with thymic neoplasms (thymoma) are at particularly high risk for fulminant immune-related adverse events, including myocarditis, due to abnormal thymic physiology. These patients require heightened vigilance and lower threshold for aggressive intervention. 6

Key Clinical Pearls

• Maintain high index of suspicion - cardiac toxicity is rare but rapidly fatal if missed
• Screen for concurrent myositis - check CK in all suspected cases, as 43% have overlapping myositis 2
• Do not delay treatment - start high-dose steroids immediately when myocarditis is suspected; waiting for confirmatory testing increases mortality
• Multidisciplinary approach is mandatory - involve cardiology immediately for any suspected cardiac toxicity 5
• Grade ≥3 adverse events occur in approximately 31% of treated patients in real-world practice, with treatment discontinuation being common 7

1, 3, 4, 2, 5, 6