Myocarditis

• Myocarditis is an inflammatory disorder of the cardiac muscle characterized by infiltration of the myocardium by immune cells, and myocyte necrosis.
  
• The inflammation may be focal or diffuse.
  
  
  
  • Any or all cardiac chambers may be involved.
    
  • It may result in regional or global contractile impairment, chamber stiffening, or conduction system disease.
    
  • Clinical manifestation are highly variable depending upon the region of involvement, and include chest pain, acute heart failure, or cardiac arrhythmias.
  
  
• Viral illnesses (coxsackievirus, parvovirus, and human herpes virus 6) are the most common causes of myocarditis in the United States.
  
• Diphtheria is the most common bacterial cause worldwide.

Presentation

Pericarditis

Classic presentation

• Chest pain: sharp, pleuritic, and worse with recumbency (95%).
  
• Pericardial friction rub heard over the left sternal border (15–30%).
  
• ECG changes: diffuse ST elevations, PR depression in the lateral leads.
  
• Pericardial effusion.

Critical presentation

• Hemodynamic instability secondary to cardiac tamponade.
  
• Patients may complain of chest pain and dyspnea.
  
• Heart sounds may be muffled.
  
• Jugular venous distension.
  
• ECG demonstrating electrical alternans.
  
• Large effusion with diastolic right ventricular collapse on bedside echocardiogram.

Myocarditis

Classic presentation

• Chest pain that may mimic cardiac ischemia.
  
• Heart failure: dyspnea, fatigue, orthopnea, exercise intolerance.

Critical presentation

• Fulminant decompensated heart failure.
  
• Dysrhythmias, including complete heart block.
  
• Syncope and sudden cardiac death.

Diagnosis and evaluation

Pericarditis

• Acute pericarditis is largely a clinical diagnosis.
  
• Two of the following four criteria should be met:
  
  
  
  • Classic chest pain (sharp, pleuritic, and worse with recumbency).
    
  • Pericardial friction rub.
    
  • ECG changes with new diffuse ST elevation or PR depression in the lateral leads (Table 26.2; Figure 26.1).
    
    
    
    • The ST elevations associated with pericarditis can be differentiated from those seen with ST elevation myocardial infarction.
      
      
      
      • ST elevations in pericarditis rarely exceed 5 mm.
        
      • ST elevations are diffuse rather than in a vascular distribution.
        
      • Reciprocal ST depression and PR elevation should only be seen in leads aVR and V1.
        
      • Associated temporal changes, such as hyperacute T-waves or Q-waves, are not typically seen in pericarditis.
    
    
  • Pericardial effusion (Figure 26.2):
    
    
    
    • Presence of effusion confirms the diagnosis, though absence does not exclude it.
  
  
• Chest radiograph: enlarged cardiac silhouette if effusion is present.
  
• Inflammatory markers: leukocytes may be normal or elevated, ESR is usually elevated although it is not specific.
  
• Cardiac markers: may be elevated in myocarditis or postinfarction pericarditis.
  
• Echocardiogram:
  
  
  
  • Normal wall motion.
    
  • Evaluate for coexisting effusion; effusion size can be estimated by the distance between the epicardium and the pericardium (<0.5 cm = small effusion; 0.5–2 cm = moderate effusion; >2 cm = large effusion).
    
  • Presence of a large effusion on a bedside echocardiogram with RV collapse during diastole should prompt consideration of impending tamponade.

Table 26.2. ECG manifestations of acute pericarditis

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