Endomyocardial fibrosis (EMF) is a severe form of heart disease that primarily affects the inner lining of the heart (endocardium) and the underlying muscle (myocardium). Classified as a restrictive cardiomyopathy, the heart chambers become stiff and cannot properly relax and fill with blood between beats. EMF is rare in developed nations but is a significant global health concern due to its high prevalence in specific tropical and subtropical regions. The progressive nature of the disease often leads to advanced heart failure and a poor outlook, particularly among children and young adults.
The Mechanism of Endomyocardial Fibrosis
The pathological process of endomyocardial fibrosis begins with an inflammatory phase targeting the inner layers of the heart. This initial stage, which may last for several weeks or months, involves an infiltration of inflammatory cells, often including a high number of eosinophils (a type of white blood cell). This acute inflammation damages the subendocardium, the tissue beneath the heart’s inner lining.
Following the inflammatory period, the body responds by laying down excessive collagen and fibrous tissue in a process called fibrosis. This scarring typically starts in the ventricular apex (the tip of the lower heart chambers) and spreads toward the heart valves. The accumulation of this dense, non-compliant scar tissue causes the endocardium to thicken significantly, leading to a loss of elasticity.
The stiffening and thickening of the heart walls produce restrictive physiology, the hallmark of EMF. The rigid ventricles cannot expand fully to accommodate blood returning from the body and lungs, leading to impaired filling during diastole (the relaxation phase). This diastolic dysfunction causes blood to back up into the atria and venous circulation, elevating systemic pressures.
In many cases, the scarring extends to involve the papillary muscles and chordae tendineae, structures that anchor the heart valves. This involvement tethers the valve leaflets, preventing proper closure and causing severe regurgitation (backward flow of blood), particularly in the mitral and tricuspid valves. The fibrosis also often results in obliteration of the ventricular apices and creates a surface prone to blood clot formation inside the heart chambers.
Geographic Prevalence and Proposed Causes
Endomyocardial fibrosis exhibits a highly localized geographic distribution, primarily affecting populations in tropical and subtropical belts near the equator. The disease is endemic in parts of equatorial Africa (Uganda and Nigeria) and is frequently reported in South America and South Asia (Brazil and India). This regional specificity means EMF is a leading cause of heart failure in young adults within these affected areas.
The precise cause of EMF remains unknown, but its clustering in specific, often low-income, rural regions suggests a complex interplay of environmental, infectious, and nutritional factors. One prominent hypothesis involves infectious agents, particularly parasitic infections common in these areas, such as schistosomiasis or filariasis. These infections may trigger a sustained immune response, including high levels of eosinophils, which release toxic proteins that damage the endocardium.
Environmental exposure to certain toxins has also been investigated as a possible trigger. Studies in India have explored the link between EMF and high intake of the mineral cerium, sometimes present in soil and consumed through food crops. Nutritional deficiencies, such as a lack of protein or certain trace elements like magnesium, are also considered potential co-factors that might increase susceptibility to the disease.
The combination of poverty, poor sanitation, and environmental and infectious risk factors highlights the socio-economic dimension of EMF. While a genetic predisposition has been suggested, the strong environmental link indicates that external factors are the primary drivers of the disease. The decline in incidence in some areas following improvements in living standards further supports the role of these non-genetic factors.
Recognizing the Signs and Confirmation
The clinical presentation of endomyocardial fibrosis depends on which side of the heart is predominantly affected by the scarring, though it typically manifests as chronic heart failure symptoms. When fibrosis involves the right ventricle, patients often experience signs of systemic venous congestion. This leads to symptoms such as fluid accumulation in the abdomen (ascites) and swelling of the legs and feet (peripheral edema).
If the left ventricle is the primary site of damage, the reduced capacity to pump blood forward from the lungs results in shortness of breath, particularly during exertion, and difficulty breathing when lying flat. Fatigue and weakness are common regardless of the side affected, as the heart struggles to meet the body’s demands. The progressive nature of the disease can also lead to severe weight loss and muscle wasting.
Diagnosis relies heavily on non-invasive imaging, with echocardiography being the primary tool. An echocardiogram clearly visualizes the characteristic features of EMF, including abnormal thickening of the endocardium and obliteration of the ventricular apex by fibrous tissue. This method also assesses the severity of atrioventricular valve regurgitation caused by tethering of the valve structures.
Cardiac magnetic resonance imaging (MRI) provides detailed anatomical information, confirming the presence and extent of fibrosis and differentiating it from other restrictive cardiomyopathies. Blood tests may reveal evidence of prior inflammation, such as an elevated eosinophil count, but these are not definitive for diagnosis. In advanced cases, diagnosis relies on imaging findings coupled with the distinct clinical picture of restrictive heart failure in a patient from an endemic region.
Treatment and Long-Term Outlook
The management of endomyocardial fibrosis is complex and often begins with medical therapy aimed at controlling heart failure symptoms. Diuretics are prescribed to manage fluid retention and congestion resulting from restricted heart filling. Other heart failure medications, such as ACE inhibitors or beta-blockers, may provide symptomatic relief, though their effectiveness is limited by the underlying mechanical restriction.
Given the high risk of blood clot formation on the scarred endocardial surface, anticoagulation therapy is necessary for many patients to prevent thromboembolic events like stroke. Immunosuppressive drugs are generally not useful for patients presenting in the late fibrotic stage, as the active inflammatory period has typically passed. Medical management alone often provides only temporary relief as the disease progresses.
For patients with advanced disease and severe symptoms, the definitive treatment is surgical intervention, specifically an endocardiectomy. This procedure involves surgically scraping away the thick, fibrotic tissue from the inner lining of the ventricle to improve its ability to fill. The surgery is often performed in conjunction with the repair or replacement of the damaged mitral or tricuspid valves.
The long-term outlook for individuals with EMF is guarded, with survival rates dependent on the stage of the disease at diagnosis and the success of surgical treatment. Without effective intervention, the prognosis is poor, and many patients succumb to progressive heart failure or sudden cardiac death within a few years. Successful endocardiectomy can significantly improve symptoms and function, with some studies reporting a survival rate of approximately 70% at five years post-surgery.