Endomyocardial fibrosis (EMF) is a rare disease in North America but common in the tropical and subtropical regions of the developing world. It is characterized by fibrosis of the left ventricular and right ventricular endocardium which cause restrictive cardiomyopathy. In endemic areas of Africa, endomyocardial fibrosis is an important cause of heart failure accounting for up to 20% of the cases. Currently, the exact etiology and pathogenesis of the disease remain unknown. However, its pathology resembles conditions such as eosinophilic cardiomyopathy and hypereosinophilic syndrome. As a result, EMF is sometimes considered part of a single disease process that also includes Loffler endocarditis (eosinophilic endomyocardial fibrosis).
The exact cause of the fibrotic process of EMF remains currently unknown. Nonetheless, multiple factors have been proposed.
It has been recognized that EMF is similar to the fibrotic stage of Loffler endocarditis, as severe chronic eosinophilia has been known to cause endomyocardial damage and fibrosis. Even though there is a resemblance between the two conditions, eosinophilia is not always seen in patients with EMF.
Due to the geographical location of the disease, several infectious pathogens have been considered; these include Plasmodium species, Microfilaria, Schistosoma, Helminths, arboviruses, and Toxoplasma. Nonetheless, there has been no correlation with a single organism in EMF.
Cerium is a chemical element and has been found in increased quantities in affected areas. As a result, it has been hypothesized to be a risk factor for developing EMF. Cerium can contaminate soil and as well as food items.
Anti-myosin antibodies have been detected in some patients with EMF. Nonetheless, anti-myosin antibodies are also present in several conditions such as rheumatic heart disease, Dressler syndrome, and post-cardiac transplant rejection. So the presence of this marker is non-specific.
A familial component has been proposed but it is currently unclear whether this is a result of a genetic or environmental cause or a combination of both.
Endomyocardial fibrosis is most prevalent in the tropical regions of Africa, Asia, and South America. It is a disease that mainly affects young adults of lower socioeconomic status. A study in Uganda indicated a bimodal peak at 10 and 30 years of age. Studies on gender distribution have been mixed, and currently, there is no specific data on gender predisposition.
EMF involves both the right and left ventricle in 50% of cases. Forty percent of cases have solely the left ventricle involved, and in the remaining 10% of cases, the right ventricle is involved. The hallmark characteristic of the condition is the fibrotic obliteration of the affected ventricle. The underlying process produces focal or diffuse endocardial thickening and fibrosis which leads to restrictive physiology. Endomyocardial fibrosis involves the apices of the right and left ventricle. In the left ventricle, the fibrosis typically extends from the apex to the posterior leaflet of the mitral valve, sparing the anterior mitral valve leaflet and the left ventricular outflow tract. Furthermore, the fibrosis in some cases can involve the papillary muscles and chordae tendineae resulting in atrioventricular valve regurgitation and distortion. In advanced stages, endocardial calcific deposits and thrombus formation can occur. This process does not involve the epicardium, and coronary artery obstruction is very uncommon. There is no involvement of the extracardiac organs.
Histology typically demonstrates fibrotic thickening of the endocardium due to acellular collage tissue deposition with the proliferation of fibrous tissue in the underlying myocardium.
The clinical presentation of EMF depends on the cardiac chamber involved and its severity. The initial phase of the illness is the acute carditis phase, characterized by a febrile illness and in severe cases cardiogenic shock. Those who survive the acute illness progress into sub-acute and chronic phase. Majority of patients present during the chronic burnt out phase. Therefore, at presentation most patients present with advanced complications such as heart failure, arrhythmias and/or thromboembolic disease.
Patients with predominantly right ventricular involvement present with ascites, hepatomegaly, lower extremity edema, elevated jugular venous pressure and tricuspid regurgitation. Giant V waves and a rapid Y decent can be seen in right ventricular involvement. In patients with left ventricular involvement, dyspnea is the predominant symptom. Fatigue, cachexia, and orthopnea are also commonly present. Mitral regurgitation can occur due to the fibrotic involvement of the chordae tendineae and posterior mitral valve leaflet. In addition, findings of pulmonary hypertension and S3, S4 gallop are also frequently present.
In advanced stages of EMF, low-voltage QRS complexes and nonspecific ST and T wave abnormalities are observed. Also, atrioventricular blocks, intraventricular conduction delay, and right or left bundle branch blocks are frequently seen. Left atrial enlargement and atrial arrhythmias occur in advanced cases of left sides EMF.
Echocardiography is the diagnostic modality of choice when making the diagnosis of a classical presentation of EMF. Via this modality, the pathological hallmarks of the disease such as apical obliteration and endocardial surface thrombi may be seen. Microbubble contrast aids in enhancing the left ventricular cavity and allowing better imaging quality for diagnosis. Furthermore, atrioventricular valve abnormalities and restrictive filling pattern can be identified. In right-sided EMF, obliteration of the trabecular aspect of the right ventricular cavity is noted. With further disease advancement, there is a reduction of the right ventricular cavity volume and worsening tricuspid regurgitation due to tricuspid annular dilatation. Spontaneous echo contrast and right atrial thrombi are also commonly seen. In left-sided EMF, the ventricular apex is also obliterated causing restricted movement of the apex due to fibrosis. The basal portion of the ventricle becomes hypercontractile as a compensatory mechanism. Fibrotic involvement of the posterior mitral valve leaflet can cause severe eccentric mitral regurgitation. In both left and right sided EMF, the atria are enlarged.
Transmitral inflow using Doppler echocardiography, the duration of deceleration time and isovolumetric relaxation time are all consistent with a restrictive filling pattern. In early diastole, there is brisk filling with very poor filling observed in the rest of diastole. Also, in a large number of patients decreased flow propagation velocity (vp) has been demonstrated.
On cardiac catheterization, the left ventricular tracing typically shows a dip and plateau pattern which is consistent with restrictive ventricular filling. Elevated Left ventricular end diastolic pressure is also commonly observed. Left ventricular angiography reveals characteristic obliteration of the apex of the involved ventricle.
Electron Beam Computed Tomography Scanning
Obliteration of the apex and inflow tract if present can be demonstrated. In addition, the fibrosis can be visualized by a band of low attenuation within the endocardium.
Cardiovascular Magnetic Resonance Imaging
Imaging with late gadolinium enhancement can highlight myocardial fibrosis. Contrast-enhanced MRI has become a more frequent diagnostic modality in the non-invasive diagnosis of endomyocardial fibrosis.
Various degrees of cardiomegaly from mild to severe, atrial enlargement and pulmonary vascular congestion can be identified. Occasionally endomyocardial calcification can be seen.
In some cases, eosinophilia can be seen. Hypoalbuminemia is also commonly present due to protein-losing enteropathy.
Medical care currently remains very challenging as one-third to one-half of patients with advanced disease die within 2 years. Atrial fibrillation is a poor prognostic factor; however rate control strategies can offer patients symptomatic relief. A limited role exists for immunosuppressive therapies as the majority of the patients present long after any possible period of myocarditis. Symptomatic therapy can be provided with diuretic therapy. These patients could benefit to some degree from ACE inhibitors and beta-blockers. Anticoagulation is recommended in patients who have a thrombus identified by imaging. Surgery in the correct setting can increase survival and especially in patients with advanced heart failure. The most commonly used approach is endocardectomy combined with valvular replacement when indicated. It is to be noted that the mortality rate for surgery can approach 15% to 20%.
The prognosis for EMF is poor as the incidence of sudden cardiac death due to arrhythmia, thromboembolic disease, and end-stage heart failure is very high. As a result, the mean survival rate is approximately 2 years.