Myocarditis

Etiologies:
1) Infectious – most commonly Viral (coxsackie B, echovirus, adenovirus, influenza, HIV, CMV, EBV, Hep B and C), also bacterial (e.g. staph, strep, TB, many more), spirochetes (syphilis, lyme), fungal, protozoal (Chaga’s disease, Toxoplasmosis).

2) Noninfectious
a. Toxins  – Anthracyclines, Cocaine, Methamphetamines, Alcohol, Heavy metals, Cytoxan, etc
b. Hypersensitivity – many antibiotics, Dobutamine (due to the carrier), many more
c.  Systemic Disorders – Sarcoidosis, Collagen Vascular Diseases, Wegener’s, Thyrotoxicosis, Hypereosinophilic Syndrome, Celiac Disease, Acute Rheumatic Fever
d. Idiopathic – including Giant Cell Myocarditis (usually fulminant and often fatal)

Clinical Manifestations:

• Highly variable! Majority of pts with viral myocarditis have subclinical and benign courses, but can sometimes present with fulminant course (as in our patient). 
• If symptomatic, patients will have preceding viral prodrome, then present with signs/symptoms of heart failure, +/- chest pain (usually with concomitant pericarditis), +/- various arrhythmias (sinus tachycardia most common, but also PACs/PVCs, ventricular arrhythmias and sudden cardiac death).
• Diagnostic clues: Signs of CHF, possibly a pericardial friction rub, EKG showing nonspecific ST changes and sometimes low voltages (due to myocardial edema), sometimes signs of pericarditis (i.e. diffuse ST elevations),  and can have frank ST elevations and Q waves from myocardial necrosis as well as conduction abnormalities.  Labs will show elevated cardiac enzymes, again due to myocardial necrosis.
• Echocardiogram is perhaps the most valuable test, and usually shows global dysfunction but can be regional/segmental as well.
• Coronary angiogram has a role mainly in ruling out ischemia as an etiology. 
• Cardiac MRI is being used more and more and is good at detecting myocardial damage and edema which can point you towards myocarditis.

Indications for Endomyocardial Biopsy (2007 AHA Guidelines)
There are multiple scenarios when you should consider a myocardial biopsy, but the two strongest recommendations are in the following scenarios:
1.  New onset CHF of duration < 2 weeks associated with hemodynamic compromise
2.  New onset CHF of duration 2 weeks-3 months associated with a dilated LV and new ventricular arrhythmias, 2nd or 3rd degree AV block, or failure to respond to usual care within 1-2 weeks.

So essentially, consider a biopsy for patients with new onset heart failure rapid clinical deterioration or significant arrhythmias.  Main benefit is to detect certain types of myocarditis which will respond to immunosuppression.  Problems with myocardial biopsies include relatively low sensitivity (so multiple biopsies from different sites are usually taken) and inter-rater variability in interpretation of pathologists. 

Prognosis and Therapy: 
1) Lymphocytic (Viral) Myocarditis – prognosis is variable, but many patients will spontaneously recover.  The benefit of immunosuppression and IVIG is unclear, again since many patients recover on their own.  There is possible benefit to antiviral therapy and a RCT is currently underway looking at Interferon-beta.
2) Giant Cell Myocarditis – rare and frequently fatal, important to recognize because there is a benefit to immunosuppression (steroids, cyclosporine, anti-T-cell antibodies).
3) Eosinophilic Myocarditis – tx: remove offending agent is the most important step, also benefit to steroids.
4) Sarcoid Myocarditis – tx: steroids
So as you can see, there is a benefit to steroids in several types of myocarditis although less clear in the most common type (lymphocytic).

(Chanu Rhee MD, 11/30/10)