Infectious myocarditis is caused by pathogens that directly invade the myocardium or trigger a harmful immune response. The severity of the clinical picture depends on both the aggressiveness of the pathogen and the host's immune response.
Viral Myocarditis
Viral myocarditis is the most common form and often presents after a systemic viral infection. The viruses involved are:
Enteroviruses (Coxsackievirus B): frequently cause acute myocarditis with direct myocyte injury and possible progression to fulminant forms.
Parvovirus B19: implicated in subacute and chronic cases, often with a tendency toward myocardial fibrosis.
Adenovirus: common in children, may be associated with significant ventricular dysfunction.
Cytomegalovirus (CMV) and Epstein-Barr Virus (EBV): more frequent in immunocompromised patients.
SARS-CoV-2: associated with myocarditis with microvascular injury and a hyperinflammatory state.
Distinctive feature: many viral forms present an initial flu-like syndrome, followed by cardiac symptoms such as chest pain, palpitations, or dyspnea.
Bacterial Myocarditis
Bacterial myocarditis mainly arises from bacteremia with cardiac dissemination of the pathogen. The most frequently involved organisms include:
Staphylococcus aureus: may cause necrotizing myocarditis with microabscess formation.
Mycobacterium tuberculosis: often associated with pericardial effusion and a chronic progression.
Borrelia burgdorferi (Lyme disease): typically responsible for transient atrioventricular blocks.
Distinctive feature: bacterial myocarditis is more frequently suppurative, with a risk of microabscess formation or localized fibrosis.
Fungal Myocarditis
A rare form, typically associated with immunosuppression. The main etiologies include:
Candida spp.: frequent in candidemia, with possible endocardial involvement.
Aspergillus spp.: may cause ischemic lesions due to mycotic embolization.
Distinctive feature: often associated with multiorgan involvement and signs of septic embolization.
Parasitic Myocarditis
Occurs predominantly in endemic areas or immunocompromised patients. The main cause is:
Trypanosoma cruzi (Chagas disease): can evolve into a progressive dilated cardiomyopathy.
Distinctive feature: the chronic form may result in apical ventricular aneurysms and AV conduction disturbances.
Non-Infectious Myocarditis
Non-infectious myocarditis results from immunological or toxic reactions. Myocardial injury is predominantly mediated by inflammation rather than by direct pathogen invasion.
Eosinophilic Myocarditis
This form is characterized by eosinophilic myocardial infiltration, detectable through endomyocardial biopsy. It may result from various conditions:
Substance abuse: alcohol (alcoholic dilated cardiomyopathy), cocaine and amphetamines (vasospastic and direct toxic effects).
Distinctive feature: toxic myocarditis may present with dose-dependent cardiac injury or idiosyncratic reactions, often with parallel systemic involvement (hepatotoxicity, neurotoxicity).
Idiopathic Myocarditis
A diagnosis of exclusion, when no specific cause is identified. Some forms may have an as yet unidentified autoimmune basis.
Distinctive feature: may present with rapidly progressive ventricular dysfunction and partial response to steroids.
Complications of Myocarditis
Myocarditis can lead to cardiovascular complications of varying severity. The main ones include:
Heart failure: in the case of severe ventricular dysfunction.
Arrhythmias: AV blocks, ventricular tachycardia, atrial fibrillation.
Dilated cardiomyopathy: possible chronic outcome of myocarditis.
Cardiogenic shock: in fulminant forms.
Need for heart transplantation: in patients with irreversible myocardial injury.
