Endocardial Fibroelastosis: Causes, Symptoms, & Treatment

Endocardial fibroelastosis (EFE) is a condition in which collagen and elastic fibers accumulate on the inner lining of the heart, primarily the left ventricle, forming a thick layer that stiffens the chamber and impairs its ability to pump blood effectively.¹ It is primarily a disease of infants and young children, though it can persist into adulthood and, rarely, first present in adults. The condition can progress rapidly to heart failure, and its causes range from viral infections to genetic disorders to abnormal blood flow in a developing heart, which makes both diagnosis and management more complicated than they might first appear.

What Happens to the Heart Wall

The endocardium is the thin, smooth tissue lining the inside of the heart chambers. In EFE, this lining undergoes a dramatic transformation. Collagen and elastic fibers deposit either in patches or across the entire inner surface of the left ventricle, creating a new layer of dense, fibrous tissue. In the primary form of the disease, this process is typically diffuse and accompanied by dilation of the left ventricle, with changes to the papillary muscles (the small muscles that anchor the heart valve cords) and thickening along the edges of the mitral valve leaflets.²

This fibrotic layer is not just cosmetically different from normal endocardium. It is rigid. It restricts the ventricle’s ability to expand during filling and to contract during pumping. The result is a heart that is both overstretched in size and underperforming in function, a combination that leads directly to heart failure if left untreated.

Primary Versus Secondary EFE

Clinicians draw an important distinction between two forms. Primary EFE occurs in a heart that is structurally normal in other respects. The fibroelastotic thickening itself is the disease, and it leads to a dilated, poorly functioning left ventricle. Secondary EFE develops alongside another cardiac abnormality, most commonly congenital heart defects such as hypoplastic left heart syndrome (HLHS), where the left side of the heart is severely underdeveloped. In secondary EFE, the fibrous buildup is a response to the abnormal hemodynamics created by the underlying defect.

This distinction matters for treatment planning and prognosis. In the secondary form, addressing the underlying structural problem can sometimes halt the fibrotic process. In the primary form, treatment focuses on managing the heart failure itself, because there is no separate defect to fix.

Causes and Contributing Factors

EFE does not have a single cause. Several pathways can trigger the fibrotic buildup, and in many cases more than one factor may be at work simultaneously.

Viral Infection

One of the strongest lines of evidence ties EFE to viral infections of the heart muscle. A study examining heart tissue from 29 patients with confirmed EFE found viral genetic material in about 90% of samples. More than 70% tested positive for mumps virus, while roughly 28% showed adenovirus.³ The theory is that viral infection damages the endocardium or the heart muscle beneath it, provoking an inflammatory and fibrotic healing response that overshoots and lays down excessive scar tissue. The strong association with mumps is especially interesting historically: the incidence of primary EFE has declined in countries with widespread mumps vaccination, supporting the viral connection, though this correlation alone does not prove causation.

Abnormal Blood Flow During Development

In congenital heart disease, the mechanical forces acting on the endocardium are often far from normal. Research using a chick embryo model of HLHS found that reduced or disturbed flow through the left ventricle leads to a significant thickening of subendocardial fibrous tissue, with increased collagen deposits and expanded zones of oxygen deprivation in the heart muscle.⁴ When blood flow is inadequate, the endocardial cells experience abnormal shear stress and low oxygen levels, both of which can trigger the fibrotic cascade. This mechanism helps explain why EFE is so common in HLHS and other left-sided obstructive lesions.

Genetic and Metabolic Disorders

EFE also shows up alongside certain inherited conditions. Barth syndrome, an X-linked disorder that affects the mitochondria (the energy-producing structures in cells), is one example. This syndrome can cause a spectrum of heart problems in boys and male fetuses, including dilated cardiomyopathy and EFE.⁵ Familial cases of primary EFE also appear in the literature. In at least two families, multiple siblings developed the disease, with some surviving into their teens while others died in infancy.⁶ The genetics are still poorly mapped, but the familial clustering suggests that susceptibility can be inherited, even if no single “EFE gene” has been pinpointed.

How the Fibrosis Develops at the Cellular Level

For years, the mechanism behind EFE’s characteristic scar was unclear. Recent work has zeroed in on a process called endothelial-to-mesenchymal transition (EndMT). Normally, the cells lining the inside of the heart are endothelial cells: flat, smooth, and specialized for blood contact. In EndMT, these cells lose their endothelial identity and transform into mesenchymal cells, which are fibroblast-like cells that produce collagen and other structural proteins. When this transformation goes wrong, the endocardium begins generating its own scar tissue from the inside out.

Research using both animal models and human EFE tissue has confirmed that the fibrogenic cells within EFE come directly from endocardial endothelial cells that have undergone this aberrant transition.⁷ Markers of active EndMT have been identified in tissue samples from patients with HLHS and from patients with other congenital heart defects, suggesting that this mechanism is not limited to one particular structural abnormality but is a common pathway through which EFE develops across different underlying conditions.⁸ The fibrotic tissue even infiltrates into the heart muscle itself, with double-stained cells confirming that EndMT-derived scar extends beyond the endocardial surface into the myocardium beneath it.⁸

Understanding EndMT as the driver matters because it opens the door, at least theoretically, to treatments that might block the fibrotic process before it becomes irreversible. That research is still in early stages, but identifying the mechanism is the first step.

Symptoms and Presentation

EFE typically presents in infancy, often within the first six months of life. The symptoms are those of heart failure in a baby: rapid breathing, poor feeding, excessive sweating during feeds, failure to gain weight, and irritability. In more severe cases, the child may show signs of congestive heart failure with fluid buildup, including swelling and an enlarged liver. The onset can be gradual, with parents noticing the baby seems unusually tired and feeds poorly, or it can be acute and fulminant, with the infant collapsing into severe heart failure over days.¹

On a chest X-ray, the heart appears enlarged. An electrocardiogram often shows signs of left ventricular strain or hypertrophy. These findings, though, are not specific to EFE; they appear in many forms of cardiomyopathy in children, which is partly why EFE has historically been underrecognized and sometimes lumped together with dilated cardiomyopathy in general.

How EFE Is Diagnosed

Echocardiography is the primary imaging tool. In EFE, the echocardiogram typically shows a dilated left ventricle with poor contractile function and, critically, an abnormally bright (echogenic) endocardial surface. The fractional shortening, a measure of how much the ventricle squeezes with each beat, is reduced. In one documented case, fractional shortening was measured at just over 11%, far below the normal range.⁹ Though that finding comes from a veterinary case, the echocardiographic pattern of increased endocardial brightness with reduced function is the hallmark in humans as well.

Cardiac magnetic resonance imaging (MRI) can add important detail, particularly in older children and adults, by characterizing the extent and distribution of fibrosis. In some cases, cardiac MRI is the tool that raises the suspicion of EFE in a patient who was previously thought to have an unspecified cardiomyopathy. However, definitive diagnosis still often requires endomyocardial biopsy, in which a small tissue sample is taken from the heart’s inner wall and examined under a microscope.¹⁰ The biopsy reveals the characteristic dense collagen and elastic fiber deposits that confirm the diagnosis.

Detecting and Grading EFE Before Birth

In fetuses with aortic stenosis and evolving HLHS, it is now possible to detect and grade EFE on prenatal echocardiography. A study of 74 fetuses who underwent in-utero aortic valvuloplasty found that EFE could be graded reliably into three severity levels. Fetuses with the mildest EFE (grade 1) had higher left ventricular pressures and less globular ventricles, while those with more severe EFE (grades 2 and 3) had worse ventricular growth over the remainder of pregnancy. Incorporating EFE severity into scoring systems improved the ability to predict which babies would achieve a biventricular circulation after birth, rather than requiring single-ventricle palliation.¹¹

This prenatal grading has real clinical utility. When a fetal intervention like balloon valvuloplasty is being considered, the degree of EFE helps the medical team counsel parents about likely outcomes. A fetus with mild EFE is more likely to end up with a functioning two-ventricle heart; one with severe EFE is more likely to need the staged surgical pathway designed for single-ventricle physiology. Having this information before delivery allows families and surgical teams to plan more effectively.

Medical Treatment

There is no drug that reverses established EFE. Medical management is directed at controlling the heart failure that results from the stiff, poorly contracting ventricle. The standard approach borrows heavily from heart failure treatment in general: improving the heart’s pumping force, reducing fluid overload, and controlling symptoms.

A case report illustrates the typical acute management in a child presenting with sudden heart failure caused by EFE. The child was treated with supplemental oxygen, sedation to reduce cardiac demand, a digitalis glycoside (cedilanid) to strengthen heart contractions, and furosemide to pull off excess fluid. After stabilization, the child was maintained on low-dose oral digoxin and showed no recurrence of heart failure during nine months of follow-up.¹² Digoxin, a drug that has been used in pediatric heart failure for decades, remains a mainstay, along with diuretics and afterload-reducing agents like ACE inhibitors.

The challenge is that these medications manage symptoms but do not address the underlying fibrotic process. If the heart continues to deteriorate despite optimal medical therapy, the conversation shifts to mechanical support or transplantation.

Surgical Options

For patients whose heart failure cannot be controlled medically, surgical options exist but vary depending on the clinical scenario.

In adults with EFE who develop restrictive physiology, meaning the ventricle cannot fill properly because the thickened endocardium is too stiff, surgical resection of the affected tissue is one option. A reported case involved a 50-year-old man with hypereosinophilic syndrome and EFE who underwent surgical removal of the fibrotic endocardium along with mitral valve replacement. The procedure successfully relieved the restrictive physiology and improved the ventricle’s ability to expand and fill.¹³ This kind of surgery is rare and technically demanding, but it demonstrates that the fibrotic layer can be physically removed in selected cases.

For infants and young children with severe, refractory heart failure, mechanical circulatory support devices can serve as a bridge to heart transplantation. A series of seven small children supported with ventricular assist devices included two with EFE. All were in the most severe functional class and dependent on intravenous medications to keep the heart pumping. Six of the seven children were successfully bridged to transplantation.¹⁴ Heart transplantation remains the definitive treatment for end-stage EFE when no other option works, though the limited availability of donor hearts for small children is a persistent bottleneck.

Survival and Prognosis

Prognosis depends heavily on the severity of heart dysfunction at diagnosis and how quickly treatment begins. A retrospective study of 52 patients with confirmed EFE found actuarial survival rates of about 93% at six months, 83% at one year, and 77% at four years. The strongest predictors of a worse outcome were a lower cardiac index and a lower ejection fraction at the time of initial assessment.¹⁵ In practical terms, babies who present earlier with more severely compromised hearts are at higher risk.

That said, many children with primary EFE do survive the acute phase, especially with modern heart failure management. Some children treated in infancy become symptom-free and appear clinically well within a few years, which naturally leads to the question of whether they are truly “cured.”

The Problem With Apparent Recovery

One of the more sobering findings in EFE research is that clinical improvement does not always mean the heart has returned to normal. A study followed eight patients with the dilated form of primary EFE who had their heart failure treated successfully and remained free of symptoms for at least three years. When these patients were re-evaluated with cardiac catheterization, six of the eight still had a dilated left ventricle with reduced ejection fraction and elevated filling pressures, despite feeling well and showing some improvement on their electrocardiograms. The average ejection fraction in these patients was about 32%, essentially unchanged from the roughly 36% measured years earlier. Even among those whose electrical patterns on the ECG had reverted toward normal, some had high filling pressures.¹⁶

The implication is that a child who looks and feels well may still have a heart that is structurally and functionally compromised. This subclinical disease could explain cases of sudden death or unexpected clinical deterioration in older patients who were thought to have been cured of childhood EFE. It also argues strongly for long-term cardiac follow-up even in patients who appear to have fully recovered, because the fibrotic endocardium does not simply dissolve once symptoms improve.

Not every child follows this pattern. Among the familial cases studied in two separate families, surviving sisters reached ages as old as 17 with no symptoms and showed progressive decreases in left ventricular hypertrophy over time.⁶ Genuine recovery does happen, but distinguishing it from the more common pattern of silent persistence requires ongoing monitoring rather than assumption.

Why EFE Remains Underrecognized

Part of the difficulty with EFE is that it looks like other conditions on initial assessment. A baby in heart failure with a dilated, poorly functioning left ventricle could have any number of forms of cardiomyopathy. The echocardiographic clue of increased endocardial brightness can be subtle, and not all echocardiographers routinely look for it. Cardiac MRI, which can identify fibrosis more precisely, is not always performed in infants because of the logistical challenges of imaging a very small, sick child. Endomyocardial biopsy, while definitive, is invasive and carries risks in tiny patients.

There is also a conceptual problem. For decades, EFE was treated more as a pathological curiosity than a distinct clinical entity. Many cases were simply labeled as idiopathic dilated cardiomyopathy. The identification of EndMT as a unifying cellular mechanism and the growing recognition that EFE can be graded prenatally and factored into surgical decision-making have renewed interest in the condition. Still, awareness among general practitioners and even some pediatric cardiologists lags behind the research, which means some cases are likely diagnosed late or missed entirely. For a condition where early, aggressive heart failure management can make the difference between survival and death, delayed recognition carries real consequences.

EFE in Adults

Although EFE is overwhelmingly a pediatric diagnosis, it does occasionally present or persist into adulthood. Adults who had subclinical EFE as infants may come to attention decades later with unexplained heart failure or restricted heart function. When cardiac MRI or biopsy reveals the characteristic fibrotic endocardium, the diagnosis becomes clear in retrospect.¹⁰ Adults can also develop secondary EFE in association with hypereosinophilic syndrome, in which an abnormal overproduction of certain white blood cells damages the endocardium and triggers fibrosis.¹³

The management principles in adults parallel those in children: treat the heart failure, investigate and address any underlying cause, and consider surgical resection or transplantation when medical therapy fails. The prognosis in adult-onset cases depends heavily on the underlying condition driving the fibrosis and how much damage has already occurred by the time the diagnosis is made.

1
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2
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3
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4
PubMed Central. Endocardial Fibroelastosis is Secondary to Hemodynamic Alterations in the Chick Embryonic Model of Hypoplastic Left Heart Syndrome
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PubMed Central. Barth syndrome: an X-linked cause of fetal cardiomyopathy and stillbirth
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10
Archivos de Cardiología de México. Young male with long-term impaired ejection fraction – endocardial fibroelastosis: The importance of cardiac magnetic resonance
11
PubMed. Assessment of left ventricular endocardial fibroelastosis in fetuses with aortic stenosis and evolving hypoplastic left heart syndrome
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PubMed Central. Pediatric acute heart failure caused by endocardial fibroelastosis mimicking dilated cardiomyopathy: A case report
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PubMed Central. Surgical management of adult endocardial fibroelastosis
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