Myocarditis

Myocarditis: Inflammation of the myocardium of the heart, usually due to infection via a virus in developed countries. However other causes, especially in developing countries, range from bacteria to Chagas Disease to scorpion bites. Various drugs reactions, including even acetaminophen, have been reported to also cause myocarditis.

Etiology: As many cases are asymptomatic, the true incidence is unknown. The average at presentation is 42.

Clinical Presentation:  The patient presentation of myocarditis is diverse which reflects the variable histology of the disease with inflammation being local or diffuse. Rapid progress to heart failure is a feared complication of myocarditis.  Sudden cardiac death due to ventricular fibrillation or tachycardia is another grave concern. Although pericarditis is most associated with chest pain, myocarditis may also cause a similar presentation. 

Signs: The patient might appear fluid overloaded. Also a S3 and sometimes a S4 gallop might be noted. The murmur of tricuspid or mitral regurgitation might also be heard due to ventricular dilation.

Differential Diagnosis: Acute Coronary Syndrome, Congestive Heart Failure, Aortic Dissection, Pneumonia.

Diagnoses: While diagnoses may only be confirmed via endomycocardial biopsy, chest radiographs, electrocardiography, radionuclide ventriculography, and cardiovascular MRI are all useful tools in assessing for myocarditis. Cardiac Troponin I has a sensitivity of 35% but a specificity of 90%.

Treatment: With only a mild presentation, most patients recover well with only supportive treatment. More severe presentations require detection and treatment of arrhythmias, careful fluid balance, and supplemental oxygen.


Imaging Findings

CXR:
- Cardiomegaly on PA projection
- Pulmonary edema may be seen in acute myocarditis

Cardiac gated CTA: 
- Myocarditis typically presents with new onset dilated cardiomyopathy
- LV dilation and global hypokinesis on multiphase cine reconstructions
- Dilated cardiomyopathy secondary to ischemia is on differential; normal coronary arteries would help rule out ischemic etiology
- Good assessment of systolic function; can quantify LV volume, EF, end-diastolic wall thickness

Cardiac MR: 
- Overall gold standard in imaging diagnosis of myocarditis
- By Lake Louise Consensus Criteria, in the setting of clinically suspected myocarditis, CMR findings are consistent with myocardial inflammation, if at least 2 of the following criteria are present: 

  1. Regional or global myocardial signal intensity increase in T2-weighted images (indicative of edema in acute myocarditis)
  2. Increased global myocardial early gadolinium enhancement ratio between myocardium and skeletal muscle in gadolinium-enhanced T1-weighted images; 

    • Calculate ratio by dividing myocardial enhancement by skeletal muscle enhancement
    • Less than 2.5 ratio is normal
    • Greater than 4.0 ratio is diagnostic of myocarditis 
  3. There is at least 1 focal lesion with nonischemic regional distribution in inversion recovery-prepared gadolinium-enhanced T1-weighted images (“late gadolinium enhancement,” "delayed enhancement")

    • Delayed enhancement marker of myocardial inflammation
    • In myocarditis, delayed enhancement is typically subepicardial, in inferolateral wall
    • May also see mid-wall hyperenhancement in non-coronary distribution
    • This distribution differentiates from ischemic hyperenhancement, which is subendocardial

- SSFP white blood cine provides good assessment of systolic function; can quantify LV volume, EF, end-diastolic wall thickness


Echocardiogram
- Can help exclude ischemic valvular causes of new dilated cardiomyopathy
- Good serial exam for assessing degree of systolic dysfunction and recovery of function

Nuclear medicine
- Antimyosin scintigraphy (myocardial inflammation) and gallium scanning (myocardial infiltration) have high sensitivity but low specificity for myocarditis 


 

Case #1. The delayed enhancement of subepicardial and midwall myocardium is classic for myocarditis.