1. This is acute or chronic inflammation of the myocardium – and may present similarly to MI.

Epidemiology

1. More freq in children & young adults. Post-mortem studies suggest it is a major cause of sudden unexpected death in adults, implicated in ~20% of those aged <40 years.

Causes

Infection – lots of candidates all rare except for viral

1. Viral:
   1. Coxsackievirus, enteroviruses, adenovirus, HIV, EBV, CMV, Hep A&C, influenza, HSV, RSV, measles, mumps, rubella and parvoviruses, vaccinia, Herpes/varicella zoster…
2. Bacterial:
   1. Brucella, gonococcus and meningococcus, H influenzae, mycobacterium, Strep. spp, salmonella, Staph. spp, Mycoplasma, Trep. pallidum, C. diphtheria and V. cholerae.
3. Spirochetal:
   1. e.g. Lyme disease (borrelia) and leptospira
4. Fungal:
   1. e.g. Actinomyces, aspergillus, candida, cryptococcus, histoplasma.
5. Protozoal:
   1. e.g. Toxoplasma gondii and Trypanosoma cruzi
6. Parasitic:
   1. e.g. Ascaris, schistosoma
7. Rickettsial:
   1. e.g. Q fever (Coxiella burnetti)

Immune Mediated

1. Autoantigens:
   1. Chagas’ Disease (most common worldwide), Sarcoidosis, SLE, Rh F., **Scleroderma, Chlamydia pneumoniae, Churg-Strauss syndrome, Giant-cell myocarditis, IBD, IDDM, Kawasaki’s, Myasthenia gravis, polymyositis, thyrotoxicosis, Wegener’s granulomatosis.
2. Allergens:
   1. Drugs (acetazolamide, amitriptyline, cefaclor, colchicine, frusemide, isoniazid, lidocaine, methyldopa, penicillin, phenytoin, tetracycline, thiazides and tetanus toxoid).
3. Alloantigens:
   1. Heart-transplant rejection

Toxic Myocarditis

1. Drugs:
   1. Ethanol, cytotoxic antibiotics (anthracyclines, e.g. doxorubicin), amphetamines, cocaine, cyclophosphamide, fluorouracil, lithium, interlukin-2 and trastuzumab.
2. Heavy metal poisoning:
   1. lead, copper, iron
3. Physical agents:
   1. Electric shock, hyperpyrexia, radiation
4. Others:
   1. arsenic, insect stings and bites, phosphorus, carbon monoxide and inhalants

Symptoms and signs:

1. From asymptomatic with ECG abnormalities to severe heart failure. Patients commonly complain of flu-like prodrome, fever, fatigue, dyspnoea, chest pain and palpitations. There may be a tachycardia, soft S1, S4 gallop, and signs of heart failure.

Investigations

1. ECG:
   1. ↑HR, ↑ or ↓ST, ↓T waves, atrial arrhythmias, transient AV block.
2. CXR.
   1. Cardiomegaly common. Echo. For cardiac fn.
3. Bloods:
   1. FBC, U&E, CK, Trop, ESR or CRP, LFT, serology, autoantibodies. Myocardial biopsy:_ limited sensitivity <70%.
4. Antimyosin scintigraphy

Management:

1. Treat underlying cause. Pharm. support. Mechanical support (ECMO, ventricular assist devices). Steroids/immunodepressants Rx for autoimmune causes. Ongoing trials on antiviral agents/viral vaccines. Cardiac monitoring. CCU/ICU. May need transplantation.

Prognosis:

1. Most mort in first 72-96hrs. 95% survival if mech. support not reqd for first 72hrs. Commonly progresses to chronic HF or dilated cardiomyopathy. Better prognosis in children.