Endomyocardial fibrosis

Article written and reviewed by Dr Luca Moretti

Endomyocardial fibrosis is a cardiomyopathy characterized by fibrous thickening of the endocardium and subendocardial myocardium, predominantly in the apical and inflow regions of one or both ventricles. Cavity retraction, alteration of the atrioventricular apparatus, and reduced compliance produce a combination of restrictive physiology and valvular insufficiency. Global systolic function may remain relatively preserved even when forward output is low, because the problem includes loss of useful ventricular volume and increased pressures required for filling.

The term is used mainly for the disease described in tropical areas, whose etiology remains incompletely defined. It should not be confused with any myocardial scar or with the fibrotic phase of Loeffler endocarditis. These conditions may share some morphologic features, but it has not been demonstrated that every case of endemic endomyocardial fibrosis derives from a hypereosinophilic syndrome. Specifying the context avoids inferring an indication for corticosteroids or hematologic therapy from imaging resemblance alone.

Its geographic distribution includes foci in sub-Saharan Africa, Asia, and Latin America, with major differences even among neighboring communities and changes over time. Children, adolescents, and young adults may be affected, but the disease is also recognized later in life and outside endemic areas. In a 2008 echocardiographic study of 1,063 residents of a rural community in Mozambique, the observed prevalence was 19.8%; this finding documents the importance of that particular focus and does not represent the prevalence of the entire continent. Late diagnosis and limited access to cardiac surgery heavily influence outcomes in the most affected populations.

Etiology, pathogenesis, and pathophysiology

The etiology is probably multifactorial, but no single hypothesis explains the distribution, susceptibility, and course of the disease. Environmental conditions, nutritional status, infections, immune response, and specific exposures have been investigated, often through associative observations. Concentration in disadvantaged communities identifies an important epidemiologic context without establishing a single causative agent. Eosinophilia has also been proposed as a pathogenetic step, but it is neither constant nor sufficiently documented in every patient. Biologic hypotheses must therefore be distinguished from actually demonstrated therapeutic targets.

The established lesion consists of dense fibrous tissue lining the inner ventricular surface and may extend into adjacent myocardium. Distribution favors the apices and inflow regions, with relative sparing of the outflow tracts in many typical forms. Adherent thrombi may overlie the lesion and, as they organize, contribute to cavity deformation. Histology of an advanced lesion documents the scar well but may no longer preserve signs of the process that initiated it. Absence of a specific infiltrate at this stage does not retrospectively resolve the etiology.

Apical obliteration reduces the volume available for filling and alters ventricular geometry. In the right ventricle, apical retraction may leave a small functional cavity with marked atrial dilatation; in the left ventricle, shortening and narrowing of the chamber limit output even without severe impairment of contractility in the residual myocardium. The fibrotic wall also creates increasing resistance to distention. These two mechanisms, loss of volume and increased stiffness, explain why assessment cannot be limited to ejection fraction.

Involvement of papillary muscles, chordae, and the ventricular surface of the leaflets causes adherence and retraction of the subvalvular apparatus. The mitral or tricuspid valve can no longer coapt normally, and regurgitation develops, often severe. The defect adds atrial volume overload and reduces forward output; at the same time, a valve that appears mobile in some portions may be functionally impaired by tethering of others. Distinguishing leaflet disease from deformation of the supporting apparatus is essential for understanding the mechanism and planning repair.

Diastolic restriction produces relatively rapid early filling, driven by high atrial pressure, followed by abrupt limitation when the cavity reaches the volume permitted by the stiff wall. End-diastolic pressure rises and filling reserve during exercise falls. A small increase in volume may worsen congestion, whereas excessive volume removal may reduce output. The patient therefore lives within a narrow hemodynamic range in which heart rate, rhythm, volume status, and function of the opposite ventricle become particularly important.

In predominantly right-sided forms, increased atrial pressure is transmitted to the venous system and liver, causing ascites and systemic congestion. Effective pulmonary flow may be limited by the small cavity and tricuspid regurgitation, so peripheral findings may be disproportionate to pulmonary congestion. In left-sided forms, high atrial pressures and mitral regurgitation cause pulmonary venous hypertension; if persistent, they increase right ventricular load. Biventricular forms combine both mechanisms and may impair output without marked ventricular dilatation.

Atrial dilatation favors arrhythmias and stasis, while the abnormal endocardial surface and poorly perfused regions favor thrombosis. Thrombus may cover fibrosis and increase the apparent obliteration. Loss of atrial contraction during atrial fibrillation and reduced diastolic time during tachycardia may precipitate heart failure. Thrombotic risk therefore derives from anatomy, rhythm, and flow, with a weight that varies among patients and cannot be inferred from the mere presence of an endocardial plaque.

Clinical manifestations

The disease may remain minimally symptomatic in early stages and be identified during an examination performed for a murmur or during screening. As hemodynamic reserve decreases, fatigue, exertional dyspnea, palpitations, and impaired growth in children appear. Progression is not necessarily uniform: periods of apparent stability may be interrupted by arrhythmias, infections, anemia, or other conditions that increase output requirements. Clinical deterioration should therefore be interpreted by looking both for anatomic progression and for a correctable precipitating factor.

In right-sided disease, ascites may be the dominant sign, associated with hepatomegaly, jugular venous distention, and edema of variable degree. The relative paucity of respiratory symptoms may initially suggest hepatic or abdominal disease. A prominent venous pulse, signs of tricuspid regurgitation, and a markedly dilated right atrium help reconstruct the cardiac cause. Ascitic fluid and liver tests may contribute to assessment, but diagnosis requires connection with cardiac hemodynamics and anatomy.

In left-sided forms, dyspnea and orthopnea predominate, with possible pulmonary congestion and signs of mitral insufficiency. Low output may present as fatigue, cold extremities, and reduced exercise tolerance even when resting blood pressure is maintained. In biventricular disease, systemic and pulmonary congestion coexist and may produce major nutritional deterioration. Murmur intensity alone does not measure the severity of regurgitation because it also depends on pressure gradients, output, and loading conditions.

Palpitations and an irregular pulse may indicate atrial fibrillation or other tachyarrhythmias; presyncope and syncope require evaluation of rhythm and output. Embolic events may present with neurologic deficits, peripheral ischemia, or visceral symptoms; in right-sided lesions, thrombus may embolize to the pulmonary circulation. Onset and event location should be reconstructed, because not every episode of abdominal pain in a patient with ascites is congestive and not every respiratory deterioration is caused by filling pressures.

History includes geographic origin and residence, age at onset, family history, previous episodes of eosinophilia, and treatments, without turning geography into a sufficient diagnostic criterion. Physical examination assesses growth and nutritional status, perfusion, venous pressure, liver, ascites, edema, and valvular signs. Comparison with usual functional capacity is useful for recognizing deterioration that may be gradual and underestimated by the patient. In children, spontaneous reduction in activity may mask severity until more obvious signs appear.

Investigations and diagnosis

Echocardiography is the diagnostic cornerstone. It should describe endocardial thickening, plaque distribution, apices, functional cavities, thrombi, atria, and the atrioventricular apparatus. Foreshortening of apical views may simulate volume loss or conceal a lesion; the anatomic apex must therefore be sought in multiple planes. A small right ventricle with a large atrium should not automatically be interpreted as congenital heart disease: apical retraction and adherence of the tricuspid apparatus suggest a different mechanism. Echocardiographic contrast may be useful when the endocardial border or a thrombus is not clearly distinguishable.

Doppler assessment evaluates regurgitation, filling flows, annular function, and estimated pulmonary pressures. Functional severity results from integration of restriction, forward stroke volume, and valve disease; ejection fraction alone may underestimate it. Echocardiographic criteria combining major and minor findings and an extent/severity score have been proposed and have also been used in epidemiologic studies. Their application should respect the original definitions without converting a single nonspecific sign into a certain diagnosis.

Major echocardiographic criteria of the Mocumbi system, as reproduced in the 2025 EACVI/DICSBC document:

• Endomyocardial plaques thicker than 2 mm: 2 points.
• Thin endomyocardial plaques, 1 mm or less in thickness, in more than one ventricular wall: 3 points.
• Obliteration of the right or left ventricular apex: 4 points.
• Thrombi or spontaneous echo contrast in the absence of severe ventricular dysfunction: 4 points.
• Retraction of the right ventricular apex with a characteristic notch: 4 points.
• Atrioventricular dysfunction due to adherence of the valvular apparatus to the wall: 1 to 4 points according to severity.

Minor echocardiographic criteria of the same system:

• Thin endomyocardial plaque limited to one ventricular wall: 1 point.
• Restrictive filling pattern across the mitral or tricuspid valve: 2 points.
• Diastolic opening of the pulmonary valve: 2 points.
• Diffuse thickening of the anterior mitral leaflet: 1 point.
• Dilated atrium with a normal-sized ventricle: 2 points.
• M-shaped motion of the interventricular septum and flat posterior wall: 1 point.
• Increased echogenicity of the moderator band or other intraventricular bands: 1 point.

In the proposed system, a definite diagnosis requires at least two major criteria or one major criterion associated with two minor criteria. The score classifies disease as mild below 8 points, moderate from 8 to 15, and severe above 15. The classification promotes reproducible description and comparison among populations; it is not an autonomous algorithm for deciding on surgery. A patient with major symptoms and valve disease must be assessed according to individual anatomy and hemodynamics, while a high score alone does not resolve questions of reversibility and operative risk.

Cardiac magnetic resonance imaging defines volumes, distribution of fibrosis, thrombi, and residual myocardium. Subendocardial late enhancement may outline the pathologic lining of the cavities; when thrombus overlies the fibrosis, stratification among myocardium, enhanced fibrotic layer, and minimally or nonenhancing thrombotic material may produce the so-called double-V appearance. The sign is useful in the appropriate context, but its absence does not exclude the disease. Description of extent and relationships with the subvalvular apparatus is often more useful than a simple diagnostic label, particularly before surgical discussion.

Tissue characterization distinguishes scar from a possible inflammatory component or recent thrombus within the limitations of the technique. Late enhancement indicates expansion of the extracellular space and does not by itself demonstrate inflammatory activity. Presence of edema, injury biomarkers, or significant eosinophilia instead requires etiologic reassessment because it may identify a different or superimposed condition amenable to causal treatment. During follow-up, imaging should be compared with function, symptoms, and therapies, avoiding interpretation of small technical differences as biologic progression.

ECG and rhythm monitoring look for electrical signs of atrial enlargement, atrial fibrillation, and other abnormalities; chest radiography and laboratory tests contribute to assessment of congestion and organ consequences. Complete blood count with differential, renal and liver function, electrolytes, and natriuretic peptides define the clinical context, but there is no blood marker specific for endomyocardial fibrosis. Persistent eosinophilia requires its own diagnostic work-up and should not be considered automatic confirmation of the endemic form. Likewise, normal inflammatory tests are compatible with a hemodynamically severe scar.

The differential diagnosis with apical hypertrophy is based on recognizing thickened myocardium versus a cavity occupied by fibrosis and thrombus; CMR can resolve an equivocal echocardiogram. In post-infarction thrombi, scar distribution and wall-motion abnormalities more often follow a coronary territory. Trabeculations and recesses of noncompaction should be distinguished from masses obliterating the cavity. In right-sided disease, Ebstein anomaly has abnormal tricuspid insertion, unlike acquired adherence of the apparatus to a fibrotic wall.

Comparison with constrictive pericarditis requires attention to respiratory variation in flows, ventricular interdependence, annular velocities, and pericardial anatomy. The presence of ascites or a restrictive filling pattern alone does not distinguish the two conditions. In constriction, pericardial restraint accentuates competition between the ventricles during respiration; in endomyocardial restriction, the main limitation lies within the wall and cavity. This difference directs the search for respiratory septal shift and reciprocal changes in filling. Significant valve disease, atrial fibrillation, and mixed conditions may, however, make the findings less interpretable.
In complex cases, catheterization with simultaneous ventricular pressure analysis and their relationship to respiration can clarify the mechanism together with imaging. A dip-and-plateau pattern is not exclusive to constriction. Invasive study is also considered when pulmonary pressures, resistance, output, or risk must be defined before intervention.

Biopsy is not mandatory when anatomy and context are typical and the result would not change management. Focal distribution limits sensitivity, and thrombi or a deformed cavity may increase procedural difficulty. Sampling becomes more relevant when it is necessary to distinguish an active treatable disease or an alternative diagnosis. Tissue obtained during surgery should be examined to define fibrosis, organized thrombosis, and possible specific components, remembering that the terminal phase may not preserve enough information about the initial cause.

Treatment and prognosis

No pharmacologic therapy has been demonstrated to remove established endomyocardial fibrosis. Medical treatment aims to control congestion, arrhythmias, and thromboembolism and to maintain functional status, while any anatomic correction requires surgical assessment. Corticosteroids, antiparasitic drugs, or hematologic therapies are indicated when a specific cause is documented or strongly supported, not for the fibrotic appearance alone. Experimental hypotheses concerning mechanisms of fibrogenesis should not be presented as clinically validated treatments.

Decongestion uses diuretics titrated according to weight, symptoms, venous pressure, perfusion, renal function, and electrolytes. In a small, stiff ventricle, excessive preload reduction may lower output despite improving edema and ascites. Sodium and fluid management should be adapted to the clinical picture, avoiding indiscriminate restrictions that worsen nutritional status. Refractory ascites requires reassessment of the hemodynamic burden and possibilities for correction; any drainage procedures address the symptom, not the cardiac mechanism maintaining it.

Atrial fibrillation may be particularly poorly tolerated because of loss of atrial contribution and changes in filling time. The choice between rhythm and rate control considers arrhythmia duration, atrial size, probability of maintaining sinus rhythm, and hemodynamic conditions. An excessively high rate reduces filling, whereas excessive slowing may reduce output when stroke volume cannot change much. Drugs and doses should be evaluated against this physiology, not merely the number of beats per minute.

Anticoagulation is considered in the presence of thrombi, previous emboli attributable to the heart, atrial fibrillation, and other defined indications. Bleeding risk may be increased by hepatic congestion, renal failure, malnutrition, and monitoring difficulties. Choice should therefore include feasibility and continuity of care, especially in areas with limited healthcare access. An isolated fibrous plaque does not by itself constitute a universal indication; in treated patients, duration and intensity are reassessed according to the source and clinical evolution.

Surgery, when necessary, combines endocardiectomy with mitral or tricuspid repair or replacement. The goal is to recover useful cavity volume and improve filling and forward flow while simultaneously addressing regurgitation. Valve replacement alone may leave major restriction if the cavity remains obliterated; conversely, endocardial resection without correction of an irreversibly deformed apparatus may fail to resolve congestion. Extension into the myocardium, the possibility of finding a dissection plane, and function of the residual ventricle affect the result.

Selection considers symptoms, univentricular or biventricular distribution, regurgitation, pulmonary pressures, renal and liver function, nutritional status, and technical risk. Assessment before advanced organ damage may preserve opportunities that diminish in patients with cachexia and severe biventricular failure. Surgical series suggest benefit in selected patients but are influenced by center experience and selection and do not provide a universal threshold for intervention. Prosthesis choice also takes into account the possibility of reliable anticoagulation and, in young patients, long-term consequences.

In patients who cannot be corrected or who have refractory heart failure, transplantation may be considered in selected settings after assessment of associated disease and extracardiac injury. Mechanical support is also conditioned by small cavities, distorted anatomy, and right ventricular involvement, which may make strategies used in dilated cardiomyopathy less straightforward. Planning should therefore precede terminal deterioration when realistic advanced-treatment options exist. Where such resources are unavailable, symptom and complication control remains essential.

Prognosis varies with extent, stage at diagnosis, arrhythmias, thrombosis, and access to correction. Outcomes from advanced hospital cohorts do not automatically describe the course of a mild lesion identified by screening. Follow-up assesses functional capacity, growth in children, congestion, rhythm, regurgitation, and volumes, while keeping echocardiographic acquisitions comparable. After surgery, residual function, prosthesis or repair, and possible recurrence of lesions are monitored. Stable symptoms do not exclude gradual deterioration if the patient has spontaneously reduced activity.

Complications

Advanced heart failure may cause chronic hepatic congestion, renal failure, and malnutrition. High venous pressure and low output act together, reducing tolerance of diuretics and increasing procedural risk. In left-sided disease, pulmonary hypertension and right ventricular overload may turn predominantly unilateral involvement into a functionally biventricular problem. Severity of extracardiac injury then becomes a determinant of both the feasibility of correction and spontaneous prognosis.

Thromboembolic complications include stroke and visceral or peripheral ischemia from left-sided sources, pulmonary embolism from right-sided sources, and additional events related to atrial fibrillation. A laminated thrombus may be minimally mobile yet contribute to cavity reduction; a recent component may behave differently. After an event, the source and antithrombotic protection should be reassessed while also considering bleeding risk in the affected territory. Disappearance of the mass alone does not guarantee elimination of the anatomic conditions that favored its formation.

Atrial arrhythmias are favored by dilatation and may precipitate congestion; ventricular arrhythmias and conduction disturbances require individual assessment of the substrate and function. Valvular insufficiency may become the main source of instability even when fibrosis shows no clear progression on imaging. These mechanisms help explain clinical deterioration without major changes in endocardial thickness and prevent use of a single anatomic parameter as an indicator of the entire disease.

After endocardiectomy and valve surgery, restriction, regurgitation, ventricular dysfunction, and thrombotic risk may persist, in addition to complications intrinsic to prostheses. Bleeding, electrolyte abnormalities, and worsening renal function may complicate medical therapy. Rehabilitation and nutritional recovery should be integrated with cardiac follow-up because anatomic improvement does not immediately restore muscle capacity and independence. In young patients, continuity of follow-up should accompany growth, transition to adult care, and planning for conditions that increase circulatory load, including a future pregnancy.