myocarditis

Introduction

myocarditis should be especially considered in the differential of chest pain, arrythmias, exercise intolerance or syncope in adolescents and young adults
can be mistaken for asthma in children
more prevalent in young people, with a median age between 20 and 40 years and affects males more than females with 75-84% of acute cases being male
in the elderly it is more commonly associated with medications such as ICIs and clozapine
the inflammatory myo-pericarditis syndrome (IMPS) is a newly introduced umbrella term encompassing the full spectrum of inflammatory myocardial (myocarditis) and pericardial (pericarditis) diseases, including those overlapping both conditions.

Aetiology

viral
- Coxsackie virus
- Parvovirus B19
- COVID-19 coronavirus (2019-nCoV / SARS-CoV-2)
- adenovirus
- EBV / glandular fever / infectious mononucleosis
- HIV / AIDS - particularly common in the late stages of HIV infection
- hepatitis C virus
- influenza
- rubella
- polio
bacterial, protozoal or fungal infections (usually only in the immunocompromised)
- brucellosis
- diphtheria
- gonococcus
- H. influenzae
- Lyme disease
- cholera
- toxoplasmosis
- mycoplasma
- aspergillus
- toxic shock syndrome
- various parasites
- NB. the most common cause worldwide is Chagas disease, which is endemic to Central and South America that results from infection with the protozoan Trypanosoma cruzi
immune conditions:
- following certain mRNA vaccines
  - appears to be due to induced production of CXCL10 by macrophages which in turn causes T cells to produce increased levels of IFN-gamma resulting in increased local neutrophil activity and inflammation ¹⁾
  - this appears to be blocked by genistein, a mild estrogen-like substance derived from soybeans which has anti-inflammatory activity and the ability to counter marijuana-induced damage to blood vessels and heart tissue
- sarcoidosis
- scleroderma
- Kawasaki disease
- systemic lupus erythematosus (SLE)
medications
- clozapine
- chemotherapy for cancers especially immune checkpoint inhibitors (ICI)
drugs and toxins
- ethanol (alcohol and alcohol withdrawal)
- cocaine
- carbon monoxide poisoning (CO)
- snakebite and envenomation
- heavy metals - copper, iron poisoning
- arsenic
as part of pericarditis
electrocution / electrical injury
radiation injury
giant cell myocarditis
rare causes:
- Idiopathic Hypereosinophilic Syndrome-Related Myocarditis
  - usually associated with either:
    - toxic reaction to a drug eg. DRESS syndrome
    - the consequence of certain types of parasite and protozoan infections
    - the result of excessively high levels of activated blood eosinophils due to a wide range of other causes including eosinophilic leukaemia,
      - see eosinophilia
- Isolated Right Ventricular Lymphocytic Myocarditis

as per 2025 ESC Guidelines for the management of myocarditis and pericarditis: Developed by the task force for the management of myocarditis and pericarditis of the European Society of Cardiology (ESC)
during the acute stage of myocarditis, patients are advised to rest completely, since exercise has been associated with arrhythmias and sudden cardiac death
patients Rx with immune checkpoint inhibitors (ICI) who develop suspected myocarditis - immediately cease ICI and start high dose steroids
- diagnostic triage within 24hrs is advised for these patients to stop the inflammatory process and stabilise the patient
patients with sarcoid myocarditis should be considered for implantable cardiac defibrillator (ICD) to prevent sudden cardiac death if:
- sustained VT / VF or aborted cardiac arrest, or,
- LVEF < 35%
combined immunosuppressive Rx is generally recommended for those with giant cell myocarditis (GCM)
- endomyocardial biopsy should be considered for suspected GCM if unexplained new onset heart failure with normal or dilated LV and new ventricular arrhythmias, 2nd or 3rd degree HB, or failure to respond to usual care within 1-2wks
all patients should have follow up within 6 months including Holter, echo, cardiac MRI
long term follow up is recommended for those with complicated myocarditis to identify a potential progression and new complications

Clinical features

may present with either:
- ischaemic sounding chest pain but may be sharp or stabbing and may radiate through to the back or to arm(s)
- features of pericarditis
- palpitations
- exercise intolerance or features of heart failure
- syncope
- sudden death
ECG may show dynamic changes, arrhythmias or heart blocks (none of which pathognomonic, and approx. half are normal)
- most commonly, there is a sinus tachycardia with non-specific ST or T wave changes
- new T wave inversion develops within 48hrs in ~half of patients ²⁾
- if pericarditis is also present (ie. myopericarditis) then ECG changes of this may also be present
- presence of Q waves, a widened QRS complex, prolongation of the QT interval, high degree AV nodal blockade, and ventricular tachyarrhythmias are associated with a poor prognosis when seen on ECG in people with myocarditis, while ST elevation with a typical early repolarization pattern is associated with a better prognosis. ³⁾
serial troponin rise

DDx

is it something other than myocarditis? see the adult patient with chest pain in the ED
if it is myocarditis, what is the cause - see above under aetiology

Mx in ED

usual bloods including FBE, U&E, Ca, Mg, PO4, LFTs, CRP and serial troponins (plus consider HCG, D-Dimer and TSH if appropriate)
cardiac monitor
CXR
Rx arrhythmias or heart blocks as per usual
consult with cardiology
consider viral serology - HIV / AIDS, hepatitis C virus (lyme disease if appropriate)
echocardiography
Rx the cause where possible
consider cardiac MRI
consider endomyocardial biopsy
- high risk myocarditis
- haemodynamic instability
- intermediate risk myocarditis not responding to conventional Rx to detect a specific histologic subtype and presence of viral genome

¹⁾

2025: Inhibition of CXCL10 and IFN-γ ameliorates myocarditis in preclinical models of SARS-CoV-2 mRNA vaccination

²⁾ , ³⁾

2019: Diagnostic and prognostic role of electrocardiogram in acute myocarditis: A comprehensive review. Carmelo Buttà et al.

Table of Contents

myocarditis

Introduction

Aetiology

Clinical features

DDx

Mx in ED