Myocarditis describes inflammation of the myocardium in the absence of acute or chronic ischaemia. This absence of ischaemia is the key differentiating factor between itself and ACS. A lack of ischaemia means that myocytes are not injured as seen in ACS (due to the ischaemia).
🦠 Pathophysiology and causative agents
It’s pathogenesis is not clear and there are innumerable causes of myocarditis.
There are both infective causes and non-infective causes of myocarditis. First, let’s take a look at the infectious causes:
Infectious causes
Viral causes
- Coxsackie B
- HIV
- Adenovirus
- Parvovirus B19
- Enteroviruses
- Hepatitis C
Many more…
Bacterial causes
- Diphtheria
- Clostridial spp.
- Borellia burgdorferi
- Brucella
- Treponema pallidum
Many more…
Fungal causes
- Aspergillus mainly
Protozoal causes
- Trypanosoma cruzi which causes Chagas’ disease.
- Toxoplasmosis
Non-infectious causes
Drugs/toxins
Anthracyclines such as doxorubicin
Hypersensitivity
Antibiotics such as penicillins, cephalosporins, sulfonamides.
Thiazide diuretics
Antiepileptics
Many more…
Systemic disorders
Autoimmune conditions - such as SLE, sarcoidosis, scleroderma
IBD
Collagen-vascular diseases
Thyrotoxicosis
Many more…
⚠️ Risk factors
- HIV - patients with HIV are at very high risk of developing myocarditis.
- Viral infection - patients often have a viral prodrome of fever, myalgias, respiratory symptoms, gastroenteritis about 2-3 weeks preceding their presentation of myocarditis.
- Autoimmune disorders - as mentioned above.
- Peri-partum/post-partum female
- Recently vaccinated - the smallpox vaccine and COVID-19 vaccine has rare cases of myocarditis presenting shortly after vaccination.
- <50 years old - the stereotypical presentation is a young patient with recent flu-like illness. A younger patient is also less likely to have an ACS so that is why the suspicion for myocarditis would be higher than in an elderly patient.
😷 Presentation
As mentioned previously, it is usually a young patient with an acute history
- Chest pain
- Viral prodrome - 2-3 weeks prior. As mentioned above.
- Arrhythmias - in the acute phase of the disease especially.
- Tachypnoea - more common in children and infants with myocarditis.
- Dyspnoea
- Orthopnoea
- Tachycardia
- Fatigue
- S3 gallop
- Hepatomegaly
- Elevated JVP
🔍 Investigations
- ECG - as with anyone presenting with chest pain. With myocarditis we may see:
- Non-specific ST-segment changes
- T-wave changes
- Bloods
- Serum CK - elevated.
- Serum CK-MB - CK-MB is 1 of 3 forms of creatine kinase. It is found mostly in the myocardium. It will also be elevated with myocarditis.
- Cardiac enzymes such as TnT and TnI - also elevated.
- Serum BNP - elevated due to ventricular distension (due to CHF 2º to myocarditis).
- 2D echocardiogram - shows left ventricular motion abnormalities and ventricular dilation.
- CXR - should be ordered with any patient presenting with shortness of breath. Often we may see bilateral pulmonary infiltrates when there is CHF involved.
- Cardiac MRI - can be used to confirm the diagnosis by showing the presence and extent of inflammation.
🏆 The gold-standard test is an endomyocardial biopsy via cardiac catheterisation but this is an invasive test and has associates risks.
🧰 Management
Treatment generally involves management of underlying cause + supportive therapies.
Supportive therapies may include:
- Corticosteroids - if autoimmune or hypersensitivity in aetiology.
- Methylprednisolone
- Antibiotics - if bacterial in aetiology.
- LV systolic dysfunction - we can give an ACEI or ARB as 1st line.
- Captopril/enalapril/lisinopril - ACEI.
- Candesartan or valsartan - ARB.
- Sacubitril-valsartan - 2nd line. Sacubitril is a neprilysin inhibitor (neprilysin degrades natriuretic peptides, by inhibiting it we increase natriuresis).
- Heart failure management
🚨 Complications
- Heart failure
- Arrhythmias
- Dilated cardiomyopathy