Myocarditis

• When the heart is involved in an inflammatory process, often caused by an infectious agent, myocarditis is said to be present
• Inflammation may involve the myocytes, interstitium, vascular elements &/or pericardium
• Characterised by isolated pockets of inflamed & necrotic myocardial cells
• Myocardial involvement may be local or diffuse, but the myocardial lesions are generally randomly distributed in the heart & thus the clinical consequences are dependent on the size & number of lesions and the location of the lesions; a small single lesion residing in the conductive tissue may result in a fatal arrhythmia
• May be chronic or acute
• Usually of sudden onset
• Symptoms include fever, malaise, anorexia, leucocytosis, chest pain, ventricular failure, shock, sudden death

Aetiologies of Myocarditis

§ Occurs secondary to:

:i) viral [measles, mumps, influenza]

ii) bacterial [diphtheria]

iii) fungal [aspergillosis]

iv) protozoan [toxoplasmosis, trypanosoma]

v) roundworm [trichinosis]

vi) rheumatic fever

vii) serum sickness

viii) chemical agent [lead]

ix) collagen disease

x) radiation

xi) metabolic [uremia]

§ Infectious agents cause myocarditis by 3 mechanisms:

1. invasion of myocardium

2. production of myocardial toxin e.g. diphtheria

3. immunologically mediated myocardial damage e.g. rheumatic fever

§ Often seen 2° acute pericarditis or acute endocarditis

§ In western countries is usually virus is origin

§ Identification of the specific causative agent usually rest on associated extracardiac signs & symptoms since the cardiovascular signs & symptoms are usually non specific

Relationship of myocarditis to cardiomyopathy

• Outcome after viral myocarditis is variable
• Usually the event is entirely self-limited & often unrecognised
• Myocardial involvement is subclinical in most acute infectious diseases
• Myocardial involvement may only be inferred from ECG changes [T-wave flattening, heart blocks]
• Overt myocarditis results in acute CCF
• Unrecognised myocarditis may be a source of arrhythmias
• May see chest pain associated with normal coronaries
• Viral myocarditis may culminate in dilated cardiomyopathy 2° to viral-mediated immunological cardiac damage

cardiomyopathy

• any disease that affects the heart

• greatly enlarged heart with no evidence of valvular disease, hypertension or CAD

Rheumatic fever:

• systemic inflammatory disorder
• characterised by joint pain, fever, cardiac dysfunction
• acute streptococcal infection —> delayed formation of immune complexes between streptococci—streptococcal Ab—complement —> immune complexes deposit in joints & small myocardial blood vessels —> tissue destruction
• usually damage to pericardium & myocardium is reversible but damage to endocardium (including valves) is permanent.

Diphtheria

• myocardial involvement occurs in 1/4 of cases
• most common cause of death in this infection
• cardiac damage due to liberation by the diphtheria of a toxin that inhibits protein synthesis