Overview

Endocardial fibroelastosis (EFE) is a rare but severe cardiac condition observed in infants. It is characterised by abnormal overgrowth and thickening of the inner lining of the heart with fibroelastic tissue.

Modern technologies such as foetal echocardiography are paramount in identifying this condition during pregnancy. Detection before birth enables early prognostication and supports clinicians in developing a well-considered, multidisciplinary management plan. This article reviews current approaches to the prenatal diagnosis of EFE, with particular focus on the use of echocardiography. It also explores the clinical value of these diagnostic approaches and considers the outcomes of patients who were successfully diagnosed prenatally.

Introduction

The thickening that occurs in EFE effectively impairs the heart's normal contractile function. This loss of compliance and contractility in the myocardium reduces the heart's ability to pump blood efficiently around the body.¹ EFE may lead to congestive heart failure and, if left unmanaged, can become fatal.

The condition can develop in one of two ways and is therefore classified as either primary or secondary EFE. Primary EFE arises independently, for example through genetic mutations. Secondary EFE, as the name implies, develops as a consequence of other underlying stresses, such as structural heart defects, infections, or the transfer of maternal antibodies.²

Echocardiography: Theory

Performed by foetal cardiology specialists, echocardiography is the cornerstone of prenatal diagnosis. It is a safe, non-invasive procedure that uses ultrasound waves to produce real-time moving images of the foetal heart during pregnancy. Whilst a standard obstetric ultrasound assesses overall foetal growth and development, foetal echocardiography is specifically directed at cardiac anatomy and function. The principal data recorded includes:

• Heart structure: The size, shape, and wall thickness of the cardiac chambers
• Blood flow: Doppler imaging to assess how blood travels between chambers
• Heart function: Measurements of pumping strength and filling efficiency

Foetal echocardiography is particularly useful for identifying conditions such as EFE. The test is typically performed between 18 and 24 weeks of gestation, although it may be carried out earlier if there is a significant risk of cardiac disease or a known family history of EFE.

When evaluating a foetus for EFE, clinicians look for specific echocardiographic signs. The first is a structural finding: a bright, thickened appearance of the inner cardiac lining, sometimes described as having a specular or echogenic quality.³ This is known as increased echogenicity. In addition, EFE can reduce the contractile strength of the ventricles, impairing the heart's ability to pump blood adequately. Doppler studies are used to assess blood movement within the heart, with particular attention to the E/A ratio. A low E/A ratio indicates ventricular stiffness and reduced diastolic compliance.⁴

Echocardiography: Clinical Value

Because EFE can deteriorate rapidly, echocardiography plays an important role not only in initial diagnosis but also in ongoing monitoring throughout pregnancy. It enables early detection, informs clinical decision-making, helps differentiate EFE from other conditions that may mimic its appearance (such as hypertrophic cardiomyopathy), and supports delivery planning. Its clinical role can be understood across four key areas.

1. Early Detection Enables Better Planning

A key advantage of foetal echocardiography is its ability to identify problems early. Since EFE tends to worsen progressively, early detection gives clinicians additional time to counsel families, plan delivery at a centre equipped to manage serious neonatal cardiac conditions, and monitor for major complications such as foetal hydrops, a condition in which fluid accumulates throughout the foetal body as a result of cardiac failure.

2. Grading Severity: Mild Versus Severe EFE

Not all cases of EFE are alike. Echocardiography helps assess disease severity by evaluating:

• Degree of endocardial thickening: The extent of echogenicity and the thickness of the inner cardiac layer
• Chamber enlargement: Severe EFE is often associated with marked dilatation of the left ventricle
• Cardiac function: Reduced ejection fraction and diminished wall motion are indicators of significant disease

Grading severity is clinically important because mild cases may remain stable and require only close monitoring, whereas severe cases may necessitate urgent intervention or intensive postnatal care.

3. Guiding Treatment Decisions

Echocardiography is also essential for planning treatment. In cases where EFE arises secondary to structural abnormalities, such as aortic valve obstruction, targeted interventions may improve outcomes. One such procedure is foetal aortic valvuloplasty, in which a small balloon catheter is introduced through the mother's abdomen into the foetal heart. The balloon is used to widen a stenotic aortic valve, restoring blood flow to the left heart and reducing pressure on the cardiac wall, which may slow the progression of EFE. Although such procedures are complex and performed in only a small number of specialist centres globally, echocardiography is indispensable for identifying suitable candidates and guiding the intervention.

4. Monitoring Disease Progression Throughout Pregnancy

EFE is a dynamic condition. The degree of endocardial thickening, chamber size, and cardiac function can change considerably as pregnancy progresses. Serial echocardiographic assessments allow clinicians to monitor changes in ventricular function and wall motion over time, identify emerging complications, and determine the optimal timing and mode of delivery. For example, if the condition deteriorates significantly, early delivery may be recommended to enable immediate postnatal care in a neonatal intensive care unit.

Fetal Outcomes

EFE has a significant influence on neonatal outcomes. Severity is often assessed echocardiographically using a grading scale based on the degree of endocardial echogenicity and the extent of myocardial thickening.

EFE Grading System (0 to 3 Scale)

• Grade 0 to 1 (Mild): Mild echogenicity of the endocardium with minimal myocardial involvement. Associated with favourable outcomes when treatment is initiated promptly
• Grade 2 to 3 (Moderate to Severe): Marked endocardial thickening, extensive echogenicity, and significantly reduced myocardial function. Associated with a higher risk of cardiac failure and poorer prognosis

Clinical Scenarios

EFE Associated with Hypoplastic Left Heart Syndrome (HLHS)

Hypoplastic left heart syndrome (HLHS) is a congenital cardiac defect in which the left-sided structures of the heart are underdeveloped. EFE frequently develops as a secondary response to the abnormal haemodynamics and pressure changes associated with this condition.

In a study of 72 foetuses with evolving HLHS, approximately one-third demonstrated echocardiographic evidence of EFE.⁵ Survival rates remained high (approximately 91%) with appropriate specialist care, regardless of the presence of EFE or associated coronary abnormalities. Mild EFE was associated with better recovery of cardiac function, particularly in cases where foetal cardiac intervention was performed. These findings suggest that early echocardiographic detection of mild EFE can help identify candidates suitable for foetal intervention and may improve postnatal outcomes.

Right-Sided EFE and Diastolic Function

EFE can also affect the right ventricle, particularly in conditions associated with elevated right-sided cardiac pressures. One study found that foetuses with mild right-sided EFE demonstrated better diastolic function and higher survival rates compared to those with severe disease involvement.⁶ This suggests that disease severity, rather than laterality, is the more important determinant of prognosis.

EFE Associated with Maternal Autoimmune Conditions

In some cases, maternal autoantibodies (anti-Ro and anti-La) cross the placenta and cause cardiac injury in the foetus, potentially resulting in EFE, conduction abnormalities, and impaired cardiac function.

In a case series of four neonates affected by maternal antibody transfer, three presented with moderate to severe EFE, and only one survived postnatally.⁷ Severe cases were characterised by progressively declining ventricular function, valvular regurgitation, and early-onset cardiac failure. These findings underscore the importance of foetal echocardiographic surveillance in pregnancies complicated by known maternal autoimmune disease, as early detection facilitates timely and targeted clinical intervention.

Summary

Endocardial fibroelastosis (EFE) is a rare but potentially life-threatening cardiac condition in which the inner lining of the heart becomes abnormally thickened. Foetal echocardiography is the primary tool for prenatal identification, enabling early diagnosis, severity grading, and ongoing monitoring throughout gestation. It also aids in differentiating EFE from other conditions with a similar appearance and supports treatment planning, including foetal interventions where appropriate. Evidence suggests that even in the context of complex associated conditions such as HLHS, survival rates can be as high as 91% with timely specialist care. Early detection and coordinated multidisciplinary management are central to optimising both foetal and neonatal outcomes.