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Hypertension and Atheroma

There are isolated communities where (at present) blood pressure does not rise with age (e.g. among the Masai of Kenya and Tanzania, the Orang Asli of Malaysia, the New Guinea Highlanders, the Brazilian Indians, and the Bushmen of the Kalahari). In general, however, idiopathic hypertension is increasing in prevalence in much of the tropics, and is estimated by WHO to affect 20% of the adult population. Racial, dietary, and economic status all may play a part, but similar trends in black and Polynesian Americans raise the question of a genetic contribution. Hypertension (and diabetes) are common in those who come from the Pacific Islands and live on a different diet in Hawaii, suggesting that nutrition is also a contributory factor.

Recent research (Tackett et al, 1994) has suggested that the arteries of black Americans do not relax quickly after constriction caused by stress or drugs. Their arterial lining does not release nitric oxide, which normally stimulates relaxation. However, personal experience of angiography in Africans, in West, Central, East and southern Africa, has not suggested unusual arterial constriction when compared to similar examinations in other races; maybe there are many causes, as is so often the case.

Secondary arterial hypertension caused by renal disease is not an important factor, even in areas of schistosomiasis (which affects the kidneys late in the disease). In children and young adults hypertension may be caused by aortitis, with involvement of the renal arteries.

Ischemic Heart Disease

The frequency of coronary atherosclerosis varies greatly throughout the tropics, reflecting genetic as well as dietary diversity. Although ischemic heart disease is not a significant problem amongst agricultural workers in much of black Africa, the pattern of urbanization with dietary changes and affluence is leading to an increased prevalence. Wherever there are significant alterations of traditional diets, with rising consumption of refined carbohydrate (sugars) and fat, there is an alarming increase in diabetes and coronary disease. The most striking examples are in the Polynesian people of Hawaii and the Republic of Nauru and elsewhere in the Western Pacific, and among the Yuma Indians of Arizona, but similar changes have occurred in the Asian and mixed race populations of Southern Africa. If, as has been suggested, viral or other infections play a part in the development of atherosclerosis, this, too, may be changing in the tropics. In a few generations, coronary artery disease may become common everywhere because many other causal factors are already becoming more prevalent.

Endomyocardial Fibrosis

Synonyms

Endomyocardial fibrosis. EMF. Davies' disease. Idiopathic mural endocarditis. Obliterative cardiomyopathy. Eosinophilic carditis. Tropical endomyocarditis. Restrictive cardiomyopathy. Sp: Fibrosis endocardiaca. Fr. Elastomyofibrose endocardiaque. Ger. Endokard-fibro-elastose Syndrom.

Definition

Endomyocardial fibrosis (EMF) is a progressive cardiac disease which is most common in children and young adults. It is characterized by swelling of the endocardial connective tissue, with accumulation of acid mucopolysaccharides in the endocardium followed by scarring and fibrosis. It may affect one or both ventricles primarily, and the other cardiac chambers to a lesser extent. It is a cardiac disease, not accompanied by lesions in any other part of the body (except when there is embolization).

Geographic Distribution

Endomyocardial fibrosis was initially observed in West African troops during the Second World War; it has since been recognized, in East and West Africa and occasionally in the Sudan and Mali. In Egypt it is a little atypical and is uncommon. It is inexplicably rare in some parts of Africa, e.g., Zimbabwe. It is seen also in Brazil, Colombia, Venezuela, New Guinea, southern India, and Sri Lanka, and occasionally in other parts of Southeast Asia and Central Africa. It is more common in lower socio-economic groups, but short-term visitors to an endemic area may acquire the disease. A few cases have been seen in the United States and England. In temperate zones, hypereosinophilic cardiopathies can be very similar, but, unlike EMF, these occur particularly in middle-aged males, with females less frequently affected.

Etiology

At the present time (2000) suggestions regarding the etiology are still speculative, as no single cause can account for the occurence of EMF in different endemic areas. However, there are some clues. Patients seen early in the course of the disease in West Africa have hypereosinophilia, fever, puffiness of the face, and urticaria. Sporadic cases of Löffler's disease are also associated with these clinical features and there is much to suggest that the two disorders are similar: however, eosinophilia is not seen in EMF in East Africa (although it is still a feature of Löffler's disease there). The precursor of the allergic state is uncertain: in West Africa, one possibility is loiasis (see Chap. 26). Twenty-three cases of EMF have occurred in Caucasians who lived in Africa; most had filariasis and severe eosinophilia. Loiasis is limited to the rain forests of West Africa, so this explanation is not valid for East Africa; nevertheless, if Europeans can acquire the disease after only a short stay, it seems likely that a parasite or other infection could play an initial role. Although it is possible to produce similar lesions in dogs and rats by administering corticosteroids, it seems clear that an immune defect is not the sole cause. Still uncertain is the part played by the many toxic herbs and mixtures which are such an important aspect of traditional medicinal therapy. Some are inhaled, others ingested or given as enemas. Some are known to have a steroidal effect. Variation in local practice may account for the geographical differences in EMF.

Pathology

The atria may be dilated but the heart is not increased in weight. The endocardial fibrosis that penetrates the myocardium begins at the cardiac apex as surface plaques of white tissue on the inflow portion of the right or left, or sometimes both ventricles (Fig. 25.4). The disease tends to be dominant on one side, but both ventricles are involved in 47% of cases and the atria in about 50%, although this is not always clinically apparent. In Egypt it seems to affect only the right side of the heart, with the calcification and fibrosis extending to the right ventricular outflow tract, with pericardial inflammatory reaction. Wherever it occurs, the papillary muscles become scarred and the tethering effect (Figs. 25.4A, 25.5), together with fibrosis of the posterior wall, results in tricuspid or mitral incompetence. In 68% of patients, the posterior mitral leaflet is involved and may be reduced to little more than a fibrous ridge, permitting mitral regurgitation which does not always produce the typical murmur on auscultation. The valve leaflets otherwise remain intrinsically normal unless there is bacterial or rheumatic infection. The latter does occur in 16% of cases, sometimes simultaneously with EMF, and can affect different leaflets of the same valve. Gradually, obliteration of the ventricular apex occurs which, with cicatrization, reduces the volume and alters the shape of the affected ventricular chamber.

In the later stages of right ventricular disease, tricuspid incompetence causes a very large "paper-thin" right atrium, with massive thrombi in the atrial appendage. These sometimes extend into the superior vena cava or the veins draining into it. The right ventricle becomes contracted and distorted, with a hypertrophied, dilated outflow tract. In left-sided involvement, the left atrium is enlarged, unless partially protected by the low flow rates of biventricular disease. The right coronary artery is displaced by the bulging of the atrioventricular groove, but the coronary lumen is not compromised on either side.

When the heart is examined at autopsy, endomyocardial fibrosis is easily recognized by the pearly white fibrous tissue from which the chordae tendineae seem to arise as white rigid columns. The fibrosis is not only endomyocardial but extends deeply into the cardiac muscle. Intracardiac thrombi are almost always present.

The microscopic changes within the heart depend on the stage of the disease. In the early stages there is swelling of the endocardial connective tissue, an accumulation of acid mucopolysaccharides, and some overlying platelets and fibrin covering the endothelium. This progresses to the endomyocardial scar; there may be foci of fibrinoid degeneration or scar tissue in the endocardium, but, later, there is dense collagen on the surface which extends to a variable degree into the myocardium. The scar tissue is hyalinized and sometimes focally calcified. The edge of the scar merges into a layer of granulation tissue, with dilated blood vessels and a mild chronic inflammatory infiltrate. Deep within the ventricular wall there is often diffuse and extensive change; the myofibrils become granular and vacuolated with enlarged nuclei. Not all areas of necrosis are contiguous with the endomyocardial fibrosis. Aschoff nodes are not seen (unless there is rheumatic carditis also), nor is there amyloid, fatty, or glycogen infiltration. A unique lesion is a focal "fibrinoid" degeneration of the endocardial connective tissue, but the cause of this and its role in pathogenesis is not clear.

Accompanying EMF there is very frequently a pericardial effusion, particularly in pure right-sided EMF. The effusion is serous and has a high protein content. It is seldom sufficient to cause clinical recognition, but may be seen on ultrasonography. Some patients may have a history of recent pericarditis. Lesions do not occur elsewhere in the body in EMF except as complications. Valvular incompetence can lead to heart failure; emboli to the systemic circulation occur in a small percentage of patients, but pulmonary emboli are more frequent. Death results from cardiac failure in the majority of patients. Rheumatic heart disease may accompany EMF and infectious endocarditis is a rare complication, often terminal.

....

Fig. 25.4 A, B. Two hearts showing EMF. A There are white plaques extending from the mitral valve to the cardiac apex (A) and climbing to the outflow portion. Note the tethered papillary muscle (M). B Biventricular EMF. There is a large dilated atrium (RA), and an almost obliterated right ventricle with external deformity at apex. In the left ventricle the papillary muscle (M) is enveloped in a plaque that has obliterated the left ventricular apex. T Thrombus.

Fig. 25.5. Early EMF showing papillary muscles drawn closer together by organizing thrombus in the left ventricular inflow tract and apex. (From Rose 1995).

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