Endocardial fibroelastosis

Article written and reviewed by Dr Luca Moretti

Endocardial fibroelastosis is an abnormality characterized by accumulation of collagen and elastic fibers in the endocardium, which becomes thickened, whitish, and poorly compliant. It predominantly affects the left ventricle in the fetal and infant heart, although distribution and extent may vary. It is primarily a pathologic phenotype and a mode of response to different insults, not a single etiologic diagnosis. Recognition of thickening is therefore the starting point for determining which heart disease produced it and how much it contributes to dysfunction.

The traditional distinction between primary and secondary forms indicates, respectively, the absence or presence of an obvious structural malformation. A form defined as primary may nevertheless be associated with a genetic or metabolic cardiomyopathy or a recognizable immune context; the term does not mean that an unknown cause has been definitively established. Morphologically, there are presentations with a dilated, dysfunctional left ventricle and presentations with a small or hypoplastic cavity, often associated with left-sided obstructive lesions. The two presentations share endocardial thickening but pose different hemodynamic and therapeutic problems.

Most diagnoses concern fetuses, neonates, and young children. Frequency estimates depend on the population observed and on the use of echocardiographic, histologic, or clinical criteria; series of explanted hearts inevitably select severe disease. The term is also used for a finding associated with congenital heart disease or cardiomyopathy, making independent epidemiologic counting difficult. Its clinical importance derives from the possibility of impairing filling, growth, and recovery of the left ventricle even after treatment of the obstruction or initial cause.

Etiology, pathogenesis, and pathophysiology

In the immature heart, flow, loading, and cavity development are closely linked. Significant left ventricular outflow obstruction increases ventricular workload and may alter subendocardial perfusion and function; reduced effective flow through the ventricle in turn changes growth stimuli. Fetal aortic stenosis may therefore be accompanied by dysfunction, mitral regurgitation, and fibroelastosis, with possible progression toward hypoplasia of left-sided structures. The relationship is not purely linear: once the wall becomes stiff, it contributes to limiting filling and development, perpetuating the problem that favored its formation.

Fibroelastosis may also occur in cardiomyopathies not associated with a major malformation. Genetic and metabolic causes should be considered according to phenotype, family history, and extracardiac manifestations; the endocardial finding does not identify a single gene or a universal inheritance pattern. Historical reports of families with possible X-linked transmission document a possibility, not a rule for all cases. Disorders of mitochondrial function, metabolism, or myocardial structure may produce a dysfunctional heart in which fibroelastosis represents part of the remodeling process.

Coronary abnormalities, particularly anomalous origin of the left coronary artery from the pulmonary artery, should be excluded when an infant presents with left ventricular dysfunction, mitral regurgitation, and a hyperechoic endocardium. In this setting, ischemia may involve myocardium and papillary muscles and produce abnormalities that are incorrectly attributed to a primary cardiomyopathy. The distinction has immediate consequences because restoration of coronary perfusion addresses a specific causal mechanism. Endocardial thickening must therefore not become a label that stops the anatomic investigation.

An immune-mediated form has been described in association with maternal anti-Ro/SSA and anti-La/SSB autoantibodies. Cardiac injury may include fibroelastosis with or without atrioventricular block, so a normal fetal rhythm does not completely exclude this possibility. The mother may not have a previously diagnosed autoimmune disease. However, maternal antibody positivity alone does not prove that every fetal echocardiographic finding has that cause: fetal evolution, other manifestations, anatomy, and alternative diagnoses must be integrated. Myocardial inflammatory processes should also be distinguished from the simple presence of a fibroelastic scar.

Lesion formation involves expansion of the extracellular matrix and altered behavior of endocardial cells. Experimental studies have assigned a role to endothelial-to-mesenchymal transition, in which cells with endothelial characteristics acquire mesenchymal properties and contribute to fibrous tissue. Abnormal flow and growth signals may favor this process. The model clarifies a possible link between hemodynamics and fibrogenesis, but it does not demonstrate that all clinical forms have an identical mechanism or that experimental modulation of a biologic pathway already constitutes an effective therapy in children.

The fibroelastic lining increases stiffness and limits diastolic expansion. The ventricle may require high atrial pressures to accommodate a relatively modest volume; increased pulmonary venous pressure causes congestion and increases right ventricular load. When myocardial injury coexists, contractility decreases and stroke volume falls further. Mitral regurgitation may result from geometric abnormalities, papillary-muscle ischemia, or involvement of the apparatus and amplifies atrial volume overload. Function should therefore be evaluated as the combined result of endocardium, myocardium, valves, and loading conditions.

In a borderline left ventricle, the central issue is the functional capacity of the chamber. An increase in volume after a procedure does not guarantee that the chamber can fill at acceptable pressures and support the systemic circulation. Mitral inflow, compliance, systolic function, outflow, aortic valve, and arch all need to be considered. Fibroelastosis may limit the potential for recovery even when dimensions appear favorable; conversely, a single unfavorable anatomic index does not necessarily describe every developmental possibility. This relationship explains the need for serial, integrated assessment in ventricular recruitment pathways.

Fetal and postnatal circulations impose different conditions. Before birth, flow distribution and communication between circuits can partly compensate for left-sided limitation; after birth, changes in resistance and closure of fetal pathways make the need for adequate systemic output apparent. In coronary abnormalities, the change in pulmonary pressures instead modifies myocardial perfusion. Age and timing of deterioration therefore provide information about mechanism and should not be interpreted as mere demographic characteristics.

Clinical manifestations

During fetal life, suspicion may arise from endocardial hyperechogenicity, altered ventricular shape or function, aortic stenosis, mitral regurgitation, and abnormal flow patterns. Effusions and fetal hydrops indicate major hemodynamic compromise and require specialist evaluation of the entire circulation. An isolated hyperechoic area is not equivalent to diffuse fibroelastosis: site, extent, continuity with the endocardial lining, and functional consequences are decisive. Evolution across serial examinations may be more informative than signal intensity alone.

In the neonate, critical obstructive heart disease may present with hypoperfusion, tachypnea, feeding difficulty, oliguria, and acidosis as the postnatal circulation changes. The presentation may initially be confused with sepsis or respiratory disease; absence of a loud murmur does not exclude severe obstruction, particularly when output is low. The priority is to recognize critical physiology and define the anatomy, because treatment of generic heart failure does not correct a circulation dependent on specific flows or communications.

In an infant with the dilated form, heart failure is often expressed during feeding: fatigue, sweating, frequent pauses, tachypnea, and poor weight gain. Spontaneous reduction in caloric intake combines with increased energy expenditure and creates progressive nutritional imbalance. Hepatomegaly, persistent tachycardia, and signs of congestion are more informative than peripheral edema, which may be absent. Irritability or crying during feeding may also accompany ischemia in coronary disease, making contextual interpretation important.

In older children, reduced exercise tolerance, fatigue, chest pain, palpitations, and syncope may reveal persistent dysfunction. The course depends on the cause and previous procedures: residual obstruction, significant regurgitation, or an arrhythmia may explain deterioration more directly than endocardial thickness. Assessment should reconstruct growth, usual activity, hospitalizations, and previous responses, because a child may adapt by reducing exercise and appear minimally symptomatic at rest despite limited reserve.

Family history looks for cardiomyopathies, sudden or infant death, consanguinity, and neuromuscular or metabolic manifestations; maternal history considers autoimmunity, antibodies, and pregnancy course. Physical examination integrates perfusion, pulses, blood pressure, saturation, rhythm, murmurs, liver size, and growth. Dysmorphic features, hypotonia, or involvement of other organs may point toward a syndromic cause. Their value derives from the overall pattern and does not justify diagnosing a specific genetic disease from clinical appearance alone.

Investigations and diagnosis

Echocardiography should describe fibroelastosis within a complete anatomic study. Endocardial thickness and distribution, chamber size and geometry, systolic and diastolic function, the mitral valve, aortic valve, outflow tract, and arch are assessed. Pediatric measurements should be indexed to size and age using appropriate reference values; serial comparisons should maintain consistent methods. Hyperechogenicity also depends on settings and insonation angle and should not be used in isolation as a quantitative measure of fibrosis.

In fetuses with aortic stenosis evolving toward left heart hypoplasia, grading systems for endocardial echogenicity have been studied to add prognostic information. The study by McElhinney and colleagues in 74 fetuses showed the feasibility of graded assessment and associations with functional parameters and circulatory outcome. However, the finding concerns a selected population and does not provide a general etiologic criterion or a universal operability threshold. The degree of fibroelastosis must be integrated with ventricular pressure and function, mitral flow, outflow, and dimensional trends.

Flow assessment defines the functional consequence of the lesion. Mitral filling, regurgitation, flow through the outflow tract and arch, interatrial communications, and pulmonary venous behavior help establish whether the left heart can receive and forward blood without excessive pressures. After a procedure, a reduced gradient across the valve alone does not demonstrate ventricular recovery. A chamber that remains stiff may maintain high atrial pressures and congestion even after an anatomic obstruction has been reduced.

Assessment of the coronary arteries is essential in forms with left ventricular dilatation and dysfunction. Origin and proximal course, flow direction, and indirect signs of ischemia should be documented, without considering an apparently normal image in a single view sufficient. If echocardiography does not resolve the question and suspicion remains significant, the most appropriate anatomic method is used according to clinical condition and center expertise. The distinction between primary cardiomyopathy and anomalous coronary origin changes treatment and cannot be based solely on the presence or absence of Q waves.

Cardiac magnetic resonance imaging may define volumes, function, and distribution of the endocardial abnormality, showing subendocardial enhancement and contributing to myocardial characterization. In young children, examination duration, need for sedation, and hemodynamic stability must be considered. Added value is greatest when it answers a question that changes strategy; it should not delay treatment of a critical obstruction that has already been clearly documented. Enhancement must also be interpreted in context, because a subendocardial distribution may have different mechanisms, including ischemia.

ECG, any prolonged monitoring, troponin, and natriuretic peptides assess rhythm, injury, and hemodynamic stress but do not by themselves confirm fibroelastosis. The ECG may provide clues to ischemia or conduction disorders and contribute to suspicion of a coronary or immune-mediated cause. Renal and liver function, electrolytes, and metabolic assessment are adapted to severity and phenotype. In neonates with low output, trends in lactate, urine output, and perfusion contribute to monitoring response without replacing anatomic definition.

Genetic and metabolic evaluation begins with family history, age at presentation, cardiac morphology, and extracardiac findings. An appropriate panel or broader testing may be useful when hereditary cardiomyopathy is suspected, but results require specialist interpretation. A variant of uncertain significance should not alone guide an irreversible decision or predictive screening as though it were pathogenic. When robust, a molecular diagnosis may modify prognosis, family assessment, and the possibility of treating a specific metabolic cause.

Testing for maternal anti-Ro/SSA and anti-La/SSB antibodies is relevant when the fetal or neonatal presentation suggests immune-mediated injury, even without atrioventricular block. Positivity should be contextualized and does not make investigation for structural and coronary abnormalities unnecessary. If myocarditis is suspected, the pathway follows severity and whether tissue characterization would change treatment; active inflammation should not be inferred from a hyperechoic lining alone. The distinction between an ongoing process and a sequela is particularly important before considering immunosuppression.

Histologic confirmation documents thickening rich in collagen and elastic fibers and may be obtained from surgical tissue or an explanted heart. It confirms the phenotype but does not necessarily identify its cause. An isolated endomyocardial biopsy has sampling limitations and should be justified by a clinical question, not merely by the desire to label an already convincing finding. Explant analyses provide valuable information on advanced disease but do not permit inference of the frequency or prognosis of all children with fibroelastosis.

The diagnostic synthesis should state anatomy, function, and documented or suspected cause, distinguishing dilated cardiomyopathy with fibroelastosis from a borderline ventricle with inflow or outflow obstruction. When the choice between circulatory strategies remains uncertain, multidisciplinary assessment integrates serial imaging and, when appropriate, invasive hemodynamics. The decisive question is whether the ventricle can sustain the intended circulation at tolerable filling pressures, not whether it independently exceeds a dimensional threshold or shows a particular degree of echocardiographic brightness.

Treatment and prognosis

Treatment is directed first toward the causal heart disease. Critical stenosis, a coronary abnormality, and a metabolic cardiomyopathy require different interventions even when the endocardium looks similar. In an unstable neonate, respiratory and circulatory stabilization must be coordinated with the physiology of the lesions present; indiscriminate administration of vasodilators or diuretics may be inappropriate if flow dependence and degree of obstruction are not known. Management therefore belongs within a pediatric cardiology and cardiac surgery pathway capable of integrating anatomy and intensive support.

In forms with heart failure, diuretics reduce congestion, while other drugs are selected according to systolic function, blood pressure, perfusion, and age. Doses and monitoring must be pediatric and updated with growth and renal function; adult regimens should not be transferred automatically. Residual obstruction or a poorly compliant cavity may limit tolerance of reductions in preload or afterload. Clinical response should therefore be assessed from breathing, feeding, urine output, perfusion, and growth in addition to echocardiography.

Nutritional support is part of treatment for infant heart failure. The child may expend more energy and take in less milk because feeding increases respiratory and cardiac work; simply advising greater intake does not correct this imbalance. Caloric density, meal method and duration, and any enteral support should be adapted to fluid balance and tolerance. Serial growth monitoring establishes whether the strategy is rebuilding reserves or whether congestion, low output, and feeding difficulties persist and require revision of treatment.

Correction of a coronary abnormality aims to restore adequate perfusion; correction of left-sided obstruction reduces pathologic load and may favor recovery and growth. Improvement, however, depends on myocardial viability, valve function, and the degree of residual stiffness. After a technically successful procedure, persistently elevated filling pressures do not necessarily imply an uncorrected stenosis: they may reflect endomyocardial injury. Follow-up should therefore measure functional outcome, not only patency of the treated segment.

Fetal aortic valvuloplasty is considered in highly specialized centers for selected fetuses with critical stenosis and progression toward left heart hypoplasia. The aim is to alter flow and development, but technical success and a postnatal biventricular circulation are not synonymous. Fibroelastosis may contribute to limiting recovery, and the procedure does not directly remove it. Selection, maternal-fetal risks, and likelihood of benefit require dedicated discussion; results from selected series do not justify offering intervention to every fetus with a hyperechoic endocardium.

Endocardial resection may be incorporated into strategies for recruitment of a borderline left ventricle. The program includes treatment of inflow or outflow obstructions and management of flows to stimulate the chamber, sometimes through a staged pathway after initial single-ventricle palliation. In selected strategies, restriction of the interatrial communication increases the proportion of pulmonary venous return that crosses the mitral valve and left ventricle: the goal is to promote filling and growth while maintaining tolerable atrial pressures. If the chamber is too stiff or inflow remains obstructed, the same increase in flow may produce pulmonary venous hypertension rather than useful recruitment.
Surveillance must therefore compare increases in volume, flows, function, and signs of congestion. In the series by Emani and colleagues, the combined strategy achieved a native biventricular circulation in 12 patients, all with restriction at the atrial septum; however, the observational design does not isolate the effect of each component. Fibroelastosis resection should be interpreted within this pathway, not as a procedure capable by itself of guaranteeing ventricular recovery.

Persistence of an obstructive load may favor an incomplete result and recurrence of the lesion. A 2025 retrospective study in patients with critical aortic stenosis and fibroelastosis associated more complete elimination of outflow obstruction with a lower risk of recurrence. The observation supports the importance of treating the underlying physiology but is subject to selection and does not establish a mandatory procedure for every patient. Surgical choice considers the aortic valve, outflow tract, dimensions, growth potential, and future costs of different reconstructions.

In immune-mediated forms, treatment is defined within the context of maternal-fetal disease and any inflammatory activity, without assuming that corticosteroids can reverse all already-organized fibroelastosis. Likewise, experimental findings on fibrogenesis pathways do not justify routine antifibrotic therapy. Any specific metabolic or genetic treatment depends on a documented diagnosis. Etiologic precision therefore serves to identify real therapeutic opportunities and avoid treating an anatomic finding with a single empirical regimen.

In children with refractory heart failure, mechanical circulatory support and transplantation are assessed before multiorgan injury and nutritional deterioration make the pathway impracticable. Age, weight, anatomy, right ventricular function, recovery potential, and extracardiac disease influence candidacy and support selection. A device may serve as a bridge to recovery or transplantation, with different risks and goals. Anticoagulation follows the presence of a device, documented thrombus, and other clinical factors; it is not prescribed automatically to every child with a thickened endocardium.

Prognosis depends on the cause and the ventricle's ability to sustain the required workload. Some dilated forms may recover function, whereas others progress to end-stage heart failure; in borderline ventricles, outcome should be judged by the sustainability of the circulation achieved, not only by increased volume. Follow-up includes growth, feeding, neurodevelopment, rhythm, filling, regurgitation, and residual obstructions. Imaging is adapted to age and clinical questions, with serial echocardiography as the reference and other modalities used when they add decisive information.

The causal diagnosis also guides family assessment. A relevant pathogenic variant may indicate family screening and reproductive counseling; a maternal anti-Ro/SSA association requires specialist planning for subsequent pregnancies. In the absence of a defined cause, the family should receive a clear description of what is known and which checks are useful, without assigning a precise hereditary risk that has not been demonstrated. Transition to adult care in survivors with residual heart disease should preserve the anatomic and procedural history because it conditions interpretation of future problems.

Complications

Low cardiac output may progress to shock with oliguria, acidosis, and multiorgan compromise; in the fetus, deterioration may manifest as hydrops. Severity depends on the combination of anatomy, function, and loading conditions, not on isolated endocardial echogenicity. In the infant, pulmonary congestion and mitral regurgitation may increase respiratory work and further reduce feeding. The cycle between heart failure and malnutrition reduces reserve for infections and interventions and requires combined management.

Arrhythmias may worsen perfusion or signal major myocardial injury. Atrioventricular block associated with maternal autoantibodies represents a distinct mechanism, although it may coexist with fibroelastosis; rhythm control does not guarantee normalization of ventricular function. Persistent tachycardia, bradycardia, or syncope therefore require specific characterization. Risk stratification follows cause, function, and the patient's electrical history, without inferring device indications from the endocardial finding alone.

Intracardiac thrombosis may occur in severely dysfunctional chambers, particularly with additional stasis factors or devices, and may be complicated by embolization. However, risk is not an obligatory feature of every form and should be balanced against bleeding before antithrombotic therapy is started. Mechanical support introduces its own protocols and additional risks. In a stable child without thrombus, the decision cannot be transferred automatically from series of end-stage heart failure or extracorporeal support.

After correction or recruitment, diastolic dysfunction, regurgitation, and residual obstructions may persist; fibroelastosis may recur and require further procedures. A chamber that has increased in size may still have excessive filling pressures and fail to sustain an adequate biventricular circulation. Deterioration therefore requires reassessment of the entire strategy rather than merely measurement of endocardial thickness. The need for reintervention depends on functional consequences and anatomy, not on recurrence of hyperechogenicity alone.

Complications of care include hypotension, electrolyte disturbances, renal dysfunction, bleeding, and infections according to the treatments used. Prolonged hospitalization and severe disease may interfere with growth and development, making continuous nutritional and neurodevelopmental follow-up useful. A child who fails to grow requires integrated reassessment of caloric intake, congestion, perfusion, and drug tolerance. Family support and shared recognition of warning signs help maintain continuity among intensive care, rehabilitation, and long-term follow-up.