What is the management approach for influenza patients with elevated Creatine Phosphokinase-MB (CPK MB) levels indicating cardiac involvement?

Management of Elevated CPK-MB in Influenza Patients

All influenza patients with elevated CPK-MB indicating cardiac involvement should receive immediate ECG and echocardiography, antiviral therapy with oseltamivir, and close hemodynamic monitoring with consideration for ICU transfer if cardiac dysfunction is present. 1

Initial Cardiac Assessment

When influenza patients present with elevated CPK-MB, this signals potential myocardial involvement requiring urgent evaluation:

• Obtain an ECG immediately to assess for ST-segment changes, Q waves, low-voltage QRS complexes with electrical alternans (suggesting pericardial effusion), or conduction abnormalities like complete left bundle branch block 1, 2
• Perform echocardiography to evaluate for myocarditis (global wall motion abnormalities, reduced left ventricular function), pericardial effusion, or cardiac tamponade 3, 4, 2
• Check troponin levels in addition to CPK-MB to confirm myocardial injury 1
• Assess vital signs closely including blood pressure for hypotension, heart rate for tachycardia, and evaluate for pulsus paradoxus if tamponade is suspected 3

Critical timing consideration: Cardiac involvement typically develops 4-7 days after initial influenza symptoms, with worsening dyspnea being the most common presenting cardiac symptom 2

Antiviral Therapy

Initiate oseltamivir immediately regardless of symptom duration when cardiac complications are present:

• Dosing: 75 mg orally twice daily for 5 days in adults 1, 5
• Dose adjustment: Reduce to 75 mg once daily if creatinine clearance <30 mL/min 6
• Even if the patient presents beyond the typical 48-hour window, antiviral therapy should still be given when serious complications like myocarditis are present 5, 3

Hemodynamic Support and Monitoring

Assess for volume depletion and cardiac complications, providing intravenous fluids as clinically indicated 1, 5

• Monitor vital signs at least twice daily (more frequently if severe): temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation 1, 6
• Provide oxygen therapy if hypoxic, targeting PaO2 >8 kPa and SaO2 ≥92% 1, 7
• Consider catecholamine support for patients with cardiogenic shock or severe hemodynamic compromise 8

ICU/HDU Transfer Criteria

Transfer to intensive care should be considered for patients with:

• Cardiogenic shock or persistent hypotension (systolic BP <90 mmHg) 1
• Severe cardiac dysfunction on echocardiography with clinical decompensation 4, 8
• Cardiac tamponade requiring emergent pericardiocentesis 3
• Fulminant myocarditis presentation 4, 2
• CURB-65 score of 4 or 5 if concurrent pneumonia is present 1

Additional Investigations

Beyond cardiac workup, obtain:

• Full blood count (may show leucocytosis with left shift) 1
• Urea, creatinine, and electrolytes 1
• Liver function tests 1
• Chest radiograph to assess for pneumonia or cardiomegaly 1
• Arterial blood gases if SaO2 <92% or features of severe illness 1

Common Pitfalls to Avoid

Do not dismiss cardiac symptoms as simple viral myalgias - worsening dyspnea, chest pain, or persistent weakness beyond typical flu symptoms warrant cardiac evaluation 2

Do not delay echocardiography if clinical suspicion exists - cardiac tamponade can develop rapidly and requires emergent intervention 3

Do not withhold oseltamivir based on symptom duration when serious cardiac complications are present - the standard 48-hour window is less relevant in complicated influenza 3, 8

Prognosis and Follow-up

• Left ventricular function may normalize in up to 50% of myocarditis cases with supportive therapy 4
• Mortality remains significant in fulminant presentations despite aggressive support 4, 2
• Arrange cardiology follow-up for all patients with documented cardiac involvement to assess recovery of ventricular function 8