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Chapter 25

Cardiac Disease in the Tropics

Living in the tropics does not prevent all the cardiac diseases which are, or used to be, common in nontropical countries. On the contrary, there are some fading in importance in many parts of the world but still common throughout the tropical countries. In addition, there are cardiac conditions which are virtually only seen in the tropics and there are others more familiar, which have a different natural history or have not yet become as important to tropical epidemiologists (or patients) as they are elsewhere. For example, coronary artery disease is not at present a major cause of morbidity and mortality in the tropics. For nontropical people something in their lifestyle has changed during the long process of becoming industrialized and westernized: many "unfortunate" peoples are fortunate - so far- to have avoided ischemic heart disease but, as urbanization continues, the differences may be blurred. On the other hand, essential hypertension is a major cause of death throughout the tropics, absent in only a few communities while of major importance in many others. Congenital heart disease occurs everywhere, although there are individual geographic variations which need further study. Rheumatic heart disease remains the commonest form of heart disease in children and young adults in most tropical and developing countries. In 1997 WHO estimated at least 12 million people were affected, resulting in 500,000 deaths every year and millions of repeated hospital admissions (in Ethiopia, 55% of all patients with cardiovascular disease). Moreover, it seems to be increasing; yet acute rheumatic fever is seldom seen.

Conversely, there are tropical cardiomyopathies that are seldom found in nontropical countries. Is this because of a difference in diet, a local medicine, or some chemical in the smoke of cooking fires? Maybe it is the lack of some nutritional essentials which causes this variation in the pattern of cardiac disease? Endemic cardiomyopathy (Keshan disease) has been associated in China with a clear selenium deficiency because in some areas the soil has extremely low selenium content. Less obvious selenium deficiency has also been associated with other cardiovascular disease. Perhaps the origin is genetic: the identification of the genes for familial hypertrophic cardiomyopathy strengthens the possibility that other cardiomyopathies may also be genetic? Or, maybe certain cardiomyopathies are due to a virus or associated with a parasite by an as yet unrecognized link? A great deal is known about some of these tropical cardiac diseases, while others are still only at the stage of description, and some are without any firmly identified cause which would account for either their occurrence or specific distribution. A few may develop in short-term visitors to the tropics, becoming a diagnostic challenge after they have returned to more temporate climes; others only occur in indigenous people. Time will tell whether social "progress" will cause a statistical change from one cardiac cause of death in certain tropical populations to a different westernized alternative. Hopefully we may learn on the way and all will benefit.

Those tropical cardiac diseases which are known to be caused by parasites (e.g., Chagas' disease, hookworm anemia, amebiasis), or by bacteria, virus, or nutrition (e.g., beriberi, kwashiorkor, AIDS, and syphilis), are discussed more fully in the appropriate chapters.

This chapter deals with the many aspects of common and uncommon cardiac diseases in the tropics, and particularly with the primary tropical cardiomyopathies, including endomyocardial fibrosis, subvalvular aneurysm, idiopathic cardiomegaly, and puerperal cardiomegaly, as well as idiopathic aortitis and tuberculous aortitis. Many of these conditions are by no means rare in some tropical countries, and some are almost as common as rheumatic heart disease.

Congenital Heart Disease

Detailed, up-to-date-to-date prevalence figures are unavailable for much of the tropics. Statistics are distorted, because the early mortality of infants in countries without facilities to treat congenital heart disease leads to a relatively low prevalence in the children and adults who survive. There is little reason, however, to suggest that there is a real difference unless there are obvious factors, such as altitude. Recent statistics are not always available. In 1987 a South African autopsy study found congenital heart disease in 2% of autopsies. A 1979 study of black South African children found an incidence of 3.9 per 1,000 live births. In 1975 in Uganda, at autopsy, the incidence was 3.7%, in the Philippines 5%, and in India about 10%. Earlier studies found a very similar incidence; for example, in South Africa in 1964, Schrire described a similar incidence of congenital heart disease in the white, Cape-colored, and Bantu populations. In Uganda and in Jamaica in the 1960s the distribution of congenital heart disease was similar to populations living in temperate zones. From necropsy studies in 1960 the pattern of congenital heart disease amongst the Chinese of Singapore did not differ from published series from elsewhere. In certain areas, however, there are significant differences; in Peru those living above 3500-5000 meters have an 18-30 times greater incidence of patent ductus arteriosus than their fellow countrymen living on the coast. This results from persistence of the fetal type of muscularized arterioles in the lungs, which causes continued right ventricular dominance. This is an example of a normal developmental change being modified by the environment.

Pulmonary Hypertension

Pulmonary arterial hypertension occurs in a variety of tropical disorders that are not usually considered in temperate climates (e.g. schistosomiasis), and although industrial pollution is a factor of importance in developed urban areas everywhere, there are also other forms of domestic pollution; burning cow dung in poorly ventilated housing causes pulmonary hypertension in northern India and in the African highlands. In Central America (Guyana, Panama, Honduras, Surinam, and some Caribbean Islands) the practice of smoking tobacco leaves cured by mineral oil formerly caused severe pulmonary hypertension and cor pulmonale, because the lipid vapor condensed in droplets in the lung and caused severe fibrotic lipid pneumonia known as black fat tobacco disease (Fig. 25.1). Fortunately this method of curing has virtually ceased, but this is an important example because no doubt there are still similar, perhaps poorly recognized problems elsewhere, such as the silicosis caused by the domestic grinding of corn between stones.

Fig. 25.1 Pulmonary hypertension arising from lipid pneumonia - the so-called black fat tobacco disease. (Courtesy of Dr. George Miller, Port of Spain, Trinidad).

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