Fungal myocarditis

Article written and reviewed by Dr Luca Moretti

Fungal myocarditis is an invasive infection of the myocardium caused by yeasts, molds or dimorphic fungi. In most cases it does not arise as isolated cardiac disease, but as a localization of disseminated fungal infection or by extension from the endocardium, pericardium, prosthetic material or contiguous tissues. The heart may contain extensive microabscesses without specific symptoms, which is why many historical series derive from autopsy studies.

The term encompasses different mechanisms. Candida tends to disseminate hematogenously and form microabscesses; Aspergillus invades blood vessels and causes thrombosis, hemorrhagic infarctions and necrosis; Cryptococcus often accompanies disseminated disease; Mucorales and endemic fungi cause patterns related to immune status and exposure. Treatment therefore cannot be selected on the basis of the generic label of fungal infection alone.

Neutropenia, leukemia, hematopoietic or solid-organ transplantation, corticosteroids, advanced AIDS, major burns and immunomodulatory therapies increase susceptibility. Venous catheters, parenteral nutrition, cardiac surgery, prosthetic material, broad-spectrum antibiotics and prolonged intensive-care stays particularly favor candidemia and endocarditis; the risk profile guides probability but does not replace microbiological demonstration.

Distinguishing fungal disease from bacterial myocarditis is urgent because drugs, duration and surgical requirements differ; persistent fever despite antibiotics, pulmonary nodules, cerebral or cutaneous lesions, endophthalmitis, candidemia and new emboli should raise suspicion of a fungal cause. Conversely, respiratory or urinary colonization does not prove invasive fungal disease and may lead to unnecessary toxic treatment.

Management belongs to a multidisciplinary team integrating infectious diseases, cardiology, microbiology, hematology or transplant medicine, imaging and cardiac surgery; early treatment can be lifesaving, but diagnostic sampling must preserve specimens for species identification and susceptibility testing. In an era of azole resistance and emerging Candida species, identifying the fungus has immediate consequences.

Etiology, Pathogenesis and Pathophysiology

Candida albicans and non- albicans species enter the bloodstream through damaged mucosa, catheters or the gastrointestinal tract; adhesion, biofilm formation and dissemination allow implantation in myocardium, endocardium and devices. Microabscesses may be multiple and invisible on echocardiography; the infiltrate depends on neutrophils, so in a neutropenic host a large yeast burden may be associated with an attenuated inflammatory response.

Aspergillus is generally acquired by inhalation. From the pulmonary site, hyphae invade arteries and disseminate to the brain, heart, kidneys and other organs. In the myocardium, angioinvasion causes thrombosis, ischemia, hemorrhage and abscesses; injury may involve the coronary arteries and conduction system. Negative blood cultures are common because hyphae do not circulate like readily cultivable candidemia.

Mucorales share marked vascular invasiveness, particularly in diabetic ketoacidosis, neutropenia, iron overload or immunosuppression; necrosis reduces drug penetration and makes debridement important when anatomically feasible. Histologic distinction from Aspergillus should be confirmed microbiologically because hyphal appearance in tissue may be distorted and susceptibility profiles differ.

Cryptococcus neoformans and C. gattii predominantly affect the lungs and central nervous system, but heavy dissemination may reach the myocardium, especially in immunocompromised patients; encapsulated cells and granulomas can be identified in tissue. Cardiac localization mandates a search for meningitis even in the absence of neurologic symptoms because the induction regimen depends on central nervous system involvement.

Histoplasma, Coccidioides and other dimorphic fungi may cause granulomas, pericarditis and disseminated disease; geographic exposure remains essential even years after travel because immunosuppression may reactivate latent infection. An immune-mediated pericardial effusion in histoplasmosis is not equivalent to disseminated myocardial invasion and does not automatically receive the same treatment.

Extension from fungal endocarditis may produce annular abscesses, fistulas, pseudoaneurysms and septal infiltration; prosthetic valves, devices and intravenous drug use increase risk. In this setting, elevated troponin may reflect coronary embolism or periannular destruction in addition to myocarditis, and anatomic definition influences surgery.

The immune response contributes both to control and to injury; neutrophils and macrophages limit yeasts and hyphae, but mediator release amplifies edema and contractile depression. During neutrophil recovery, apparent inflammatory worsening may occur; it must be distinguished from fungal progression using pathogen burden, imaging and perfusion rather than assuming that every deterioration represents an immune-reconstitution syndrome.

Necrosis and fibrosis create an arrhythmic substrate, whereas abscesses near the conduction system cause block; fungal infarctions and coronary involvement generate regional abnormalities. Global dysfunction may ultimately result from diffuse invasion, septic shock and treatment toxicity, mechanisms that often coexist in the same patient.

Antifungal selective pressure changes etiology. Azole prophylaxis reduces some infections but favors breakthrough disease due to resistant strains or uncovered molds; echinocandins may select different species and resistance patterns. Previous therapy must be reported to the laboratory because a fungus emerging during prophylaxis is not automatically treated by increasing the dose of the same agent.

Biofilm on catheters and prosthetic material contains cells with phenotypes and susceptibilities different from planktonic growth; a favorable minimum inhibitory concentration does not guarantee eradication of infected material. This discrepancy between laboratory susceptibility and the infected site explains persistent candidemia and relapses after apparently adequate courses, making source control a biological component of treatment.

Clinical Manifestations

Persistent or recurrent fever is the most common signal, but it may be absent during profound neutropenia or corticosteroid therapy; dyspnea, chest pain, hypotension, palpitations and syncope are nonspecific. Rising troponin, new ventricular dysfunction or conduction block during invasive fungal disease makes myocardial involvement plausible without excluding ischemia, sepsis or drug toxicity.

Cardiac candidiasis may present with persistent candidemia, emboli, endophthalmitis, skin lesions, renal failure and signs of endocarditis. Isolated microabscesses do not necessarily produce vegetations and may escape echocardiographic detection; slow bloodstream clearance requires a search for catheters, thrombophlebitis, prosthetic material, valves, ocular involvement and deep foci.

Disseminated aspergillosis often combines pulmonary nodules or cavitations, pleuritic pain, hemoptysis, cerebral lesions, splenic or renal infarctions and cutaneous involvement; the heart may be affected by embolization or hematogenous spread. Neurologic deficits and chest pain must be evaluated in parallel because anticoagulation and surgery change radically in the presence of hemorrhagic lesions.

Myocarditis may assume an infarct-like phenotype with ST-segment elevation and regional abnormalities; angioinvasion, embolism from a vegetation and atherothrombosis remain competing and sometimes concomitant diagnoses. Coronary anatomy is investigated when indicated because attributing the presentation to inflammation may delay revascularization or source control.

Arrhythmias include atrial fibrillation, ventricular tachycardia and ventricular fibrillation; septal infiltration may cause atrioventricular block. Electrolyte disturbances from amphotericin B, renal failure and azole interactions add a second proarrhythmic risk; telemetry must therefore accompany both the disease and its treatment.

Heart failure may be left-sided, right-sided or biventricular, with pericardial effusion and mixed shock; preserved ejection fraction does not exclude focal abscesses or conduction-system abnormalities. Serial echocardiography is more informative than a single examination, especially when the hemodynamic condition changes rapidly.

Extracardiac disease guides the likely fungus and often provides the best diagnostic site; lung and paranasal sinus involvement suggests molds, meningitis and antigenemia suggest cryptococcosis, and skin or retinal lesions may reveal dissemination. The presentation is not exclusive, however, and species identification remains necessary before de-escalation.

In premature neonates and pediatric patients, signs may be limited to instability, apnea, thrombocytopenia or respiratory deterioration. Catheters, parenteral nutrition and candidemia increase probability; antifungal dose, formulation and toxicity require pediatric expertise and are not mechanically extrapolated from adults.

In transplant recipients, cardiac involvement may be confused with rejection, graft dysfunction or toxicity; increasing corticosteroids in response to a biopsy interpreted as inflammation, without appropriate stains and cultures, may accelerate fungal disease. Advance coordination between pathologist and microbiologist allows fresh tissue to be preserved and rejection and organisms to be sought simultaneously.

Investigations and Diagnosis

Diagnosis integrates host probability, microbiology, imaging and tissue findings; multiple blood cultures are obtained before treatment when possible, but sensitivity is modest in deep fungal disease and very low for Aspergillus. A positive culture is identified to species level and undergoes susceptibility testing when indicated, particularly after previous azole exposure or treatment failure.

Beta-D-glucan supports the diagnosis of some invasive fungal diseases but is nonspecific and may yield false-positive results after blood products, dialysis, medical materials or contamination. Serum or bronchoalveolar-lavage galactomannan performs best in defined hematologic and transplant populations; mold-active prophylaxis and neutropenia modify sensitivity. Neither marker localizes infection to the myocardium.

Cryptococcal antigen, urinary antigens for endemic fungi and PCR are used in specific scenarios. A result must be interpreted according to prevalence and cross-reactivity: Histoplasma and Blastomyces antigens, for example, may cross-react; molecular diagnostics do not replace culture when susceptibility testing is needed.

Echocardiography assesses function, effusion, vegetations, periannular abscesses and prosthetic material; transesophageal echocardiography increases sensitivity for endocarditis and complications. Intramyocardial microabscesses may nevertheless fall below its resolution; computed tomography and positron emission tomography define disseminated foci, whereas cardiac magnetic resonance characterizes edema, necrosis, masses and scar without identifying the fungal species.

Tissue diagnosis requires hematoxylin-eosin, Grocott-Gomori and PAS stains in addition to culture and molecular methods; tissue should not be entirely fixed in formalin: a sterile portion must reach the microbiology laboratory. Morphology, branching angle and pigmentation provide clues, but species and resistance cannot be inferred with certainty from histology alone.

Endomyocardial biopsy is considered in severe or unresolved diagnostic presentations when direct evidence would change treatment; thrombocytopenia, hemodynamic instability and focal disease reduce safety and yield. A pulmonary, cutaneous, lymph-node or other extracardiac biopsy may be preferable if it documents the same disseminated process with lower risk.

ECG, troponin, natriuretic peptides, lactate, renal and liver function and electrolytes describe severity and treatment tolerability; troponin may rise because of sepsis, coronary embolism or renal failure and does not measure fungal burden. Parallel trajectories of cardiac and microbiological biomarkers help distinguish myocardial recovery from infection control.

The differential diagnosis includes bacterial endocarditis with abscess, viral myocarditis, neoplastic infiltration, myocardial infarction, drug toxicity, rejection and granulomatous disease. A patient may have more than one cause simultaneously, especially after transplantation; response to an antifungal drug alone does not confirm the diagnosis if antibiotics, immunosuppression and supportive therapy were also changed.

Radiologic interpretation takes immune timing into account. During neutrophil recovery, nodules and tracer uptake may increase despite effective therapy, whereas cavitation may represent lesion demarcation. In the myocardium, persistent edema does not distinguish fungal viability from repair; a decision that therapy has failed requires microbiology, drug exposure and multiorgan evolution, not the isolated diameter of a lesion.

Antifungal susceptibility testing is prioritized for emerging species, treatment failures, azole exposure and healthcare-associated transmission settings; identification by MALDI-TOF or sequencing corrects errors from phenotypic methods. Distinguishing Candida auris also has isolation and infection-control implications extending beyond care of the individual patient.

Treatment and Prognosis

Therapy is started promptly when the probability of invasive fungal disease is high, after adequate samples have been collected. Species, site, clinical stability, immune status, previous prophylaxis, renal and liver function guide selection; dosing must achieve therapeutic exposure and is adjusted for weight, interactions, absorption and extracorporeal support.

In invasive candidiasis, an echinocandin is often the initial treatment, with step-down to fluconazole only in stable patients with a susceptible isolate and documented bloodstream clearance. Endocarditis, prosthetic material and deep foci may require liposomal amphotericin B with or without flucytosine or high-dose echinocandin therapy, surgery and prolonged suppression. Myocarditis without endocarditis is individualized according to extent and response.

For invasive aspergillosis, voriconazole is an established primary therapy; isavuconazole or liposomal amphotericin B is selected according to interactions, resistance, tolerability and site. Therapeutic drug monitoring is important for several azoles; echinocandin monotherapy is not standard primary treatment for invasive aspergillosis.

Mucormycosis requires early liposomal amphotericin B, metabolic control, reduction of immunosuppression and surgery of necrotic tissue when possible; posaconazole or isavuconazole have defined roles according to phase and response. Voriconazole does not cover Mucorales, and isolated empiric use may allow progression.

Disseminated or central nervous system cryptococcosis requires fungicidal induction, generally with amphotericin B and flucytosine, followed by consolidation and maintenance with fluconazole. Raised intracranial pressure is treated actively. Cardiac involvement does not reduce the need to search for and treat neurologic disease.

Endemic mycoses are treated with azoles or amphotericin B according to severity, organs involved and immune status; localized inflammatory pericarditis and dissemination with yeast in the myocardium are not equivalent. Remote residence in an endemic area is considered before starting immunosuppression for presumed granulomatous myocarditis.

Source control includes removal of infected catheters, drainage, debridement and surgery on valves or prosthetic material when indicated. Biofilm protects the fungus and may render apparently active systemic therapy insufficient; surgical timing balances embolic risk, anatomic destruction, neutropenia and the possibility of hematologic recovery.

Cardiac therapy supports output, congestion and rhythm without interfering with antifungal treatment. Azoles inhibit metabolic enzymes and interact with antiarrhythmic drugs, anticoagulants, immunosuppressants and oncologic therapies; amphotericin B causes nephrotoxicity and potassium and magnesium loss. ECG, drug concentrations and electrolytes are part of causal care.

Prognosis remains poor in disseminated forms, especially with persistent neutropenia, cerebral involvement, angioinvasion, shock or delayed therapy; microbiological clearance, immune recovery and source control improve outcome. Treatment duration is often prolonged and is guided by clinical and radiologic resolution rather than a fixed number of days.

Therapeutic drug monitoring of azoles addresses variability in absorption, metabolism, interactions and extracorporeal support; insufficient concentration may explain progression without true resistance, whereas a high level increases neurotoxicity, hepatotoxicity and electrical risk. Sample timing relative to the dose and target concentration are interpreted according to the drug and site, avoiding adjustments based on a nonstandardized sample.

Immune reconstitution is therapeutic but must be calibrated; recovery of neutrophils, control of HIV and reduction of corticosteroids improve clearance, whereas abrupt withdrawal may trigger rejection or an inflammatory syndrome. Granulocyte growth factors and transfusions are assessed within the hematologic context and are not considered substitutes for active antifungal therapy.

Complications

Shock may be septic, cardiogenic or mixed; serial echocardiography, perfusion, lactate and response to fluids prevent overloading an infiltrated ventricle or undertreating vasoplegia. In potentially reversible forms, temporary mechanical circulatory support is discussed together with the hematologic prognosis and degree of infection control.

Abscesses, necrosis and pseudoaneurysms may rupture into the pericardium or cardiac chambers, causing tamponade, fistula or embolization. Drug therapy alone does not reconstruct destroyed tissue; repeated imaging and cardiac-surgical consultation become urgent when a new murmur, conduction block, pain or instability appears.

Fungal vegetations and emboli are often large and may reach the brain, spleen, kidneys, limbs and coronary arteries. Anticoagulation does not sterilize the focus and may be dangerous in hemorrhagic cerebral infarction or mycotic aneurysms; antithrombotic decisions depend on the documented lesion rather than the generic label of endocarditis.

Arrhythmias and conduction blocks result from inflammation, ischemia, scar and electrolyte abnormalities. Temporary pacing may be necessary, but a permanent intravascular device during active fungemia adds a surface for biofilm; timing of implantation is agreed upon after microbiological control and assessment of reversibility.

Relapse may emerge months after an apparent response, especially with retained prosthetic material, persistent immunosuppression or inadequate tissue penetration. Some patients require chronic antifungal suppression; fever, new emboli or rising biomarkers require cultures and imaging rather than automatic extension of the same drug.

Antifungal toxicity may limit lifesaving therapy; renal failure, hepatitis, cytopenias, neurotoxicity, phototoxicity and QT abnormalities require prevention and adjustment. Substitution must preserve coverage of the species and infected site, avoiding untreated intervals in a rapidly progressive disease.

After cure, fibrosis and valvular injury may leave heart failure, arrhythmias and reduced functional capacity. Cardiology follow-up continues even when cultures and antigens become negative, while infectious-disease follow-up assesses relapse and prophylaxis during future periods of immunosuppression; resumption of chemotherapy or transplantation is planned around both risks.

Prevention combines catheter hygiene, antibiotic stewardship, environmental mold control, prophylaxis in high-risk groups and resistance surveillance. There is no single strategy for every immunocompromised patient: duration of neutropenia, type of transplant, graft-versus-host disease and local epidemiology determine the likely pathogen; every breakthrough case is also analyzed as a possible failure in the care process.