EPIDEMIOLOGIC REVIEWS

Copyright © 1990 by The Johns Hopkins University School of Hygiene and Public Health All rights reserved

Vol. 12, 1990 Printed in U.S.A.

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE MORTALITY, MORBIDITY, AND RISK FACTORS ROBERT BEAGLEHOLE BACKGROUND

Coronary heart disease is the leading cause of death in western industrialized countries, responsible typically for 30 percent of all deaths each year (1). Coronary heart disease is also an increasingly important cause of death in less developed countries, many of which are still burdened by infectious disease epidemics (2). Trends in coronary heart disease mortality are of major public health importance, both because of their impact on the overall health status of populations and because of the insights these trends can provide for the control of noncommunicable diseases in general. Attention was first drawn to the national decline in coronary heart disease mortality in the United States in 1975 (3). Since then, the international trends in coronary heart disease have generated a large amount of interest (4-6), and many studies, including large-scale collaborative studies, have been initiated in an attempt to explain the trends. In simple terms, a decline (or increase) in coronary heart disease mortality could be due to a decline (or increase) in either incidence or case fatality. In turn, incidence could fall (or rise) as a direct consequence of the success (or failure) of primary pre-

ventive efforts; case fatality could fall (or rise) as a consequence of secondary preventive efforts or a change in the natural history. Regrettably, the real world of cardiovascular epidemiology is complex, and 15 years after the first paper describing the decline in the United States, explanations for the trends in coronary heart disease mortality are still surprisingly tentative. This paper reviews the recent international data on trends in coronary heart disease mortality and morbidity and risk factor levels and assesses the possible explanations for the changes in mortality rates. The implications of the trends and the associated investigations for the prevention and control of coronary heart disease and other noncommunicable diseases are discussed. TRENDS IN CORONARY HEART DISEASE MORTALITY

International trends

Routine national mortality data have provided important information about the epidemic of coronary heart disease. The value of these data has been questioned, initially by epidemiologists and more recently by nonepidemiologists (7). There is, however, compelling evidence to indicate that, in general, the trends revealed by rouFrom the Department of Community Health, tine death statistics in developed countries School of Medicine, University of Auckland, Private are real and cannot be explained by trends Bag, Auckland, New Zealand. (Reprint requests to in diagnostic fashions, certification pracProf. Robert Beaglehole at this address.) This work was supported in part by the National tices, or classification procedures (1). Heart Foundation of New Zealand and the Medical Within-country comparisons are more seResearch Council of New Zealand. Dr. A. Lopez, cure; between-country comparisons are less Global Epidemiological Surveillance, World Health Organization, Geneva, Switzerland, provided the mor- secure because of the possibility of systemtality data. The author thanks Drs. R. Bonita and R. atic differences in some or all of these facJackson for comments on an earlier draft and Ms. E. tors. More confident between-country comMcCullagh for technical assistance with the manuparisons can be made using the broader script.

BEAGLEHOLE

category of all heart diseases; trends in this category mirror the trends in coronary heart disease mortality (1). Furthermore, trends in all cardiovascular disease and in total mortality, show similar patterns. Trends in age-standardized coronary heart disease mortality in eight selected countries since 1970 are shown in figures 1 and 2 for men and women aged 40-69 years, based on data collated and provided by the

World Health Organization (8). The period since 1970 covers two revisions of the International Classification of Diseases, the Eighth Revision introduced between 1968 and 1970 and the Ninth Revision introduced in 1979 or 1980, except in Finland and Sweden, which used the Eighth Revision throughout the period. In both revisions, coronary heart disease refers to codes 410-414; in all countries except the United

800-1

Sa

Finland

600-

Hungary England and Wales New Zealand

400-

Poland Sweden USA

200-

Japan

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Year FIGURE 1. Age-standardized coronary heart disease mortality rates in selected countries, 1970-1986, among men aged 40-69 years. 250

Hungary New Zealand England and Wales Finland USA Poland Sweden Japan

~I

1

1

1

1

1

1

1

1

1

1

1

1~

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Year FIGURE 2. Age-standardized coronary heart disease mortality rates in selected countries, 1970-1986, among women aged 40-69 years.

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

States, the change to the Ninth Revision had only a minor impact on mortality trends (8). Several patterns are apparent, particularly in men. In countries such as the United States, Finland, and New Zealand, where death rates increased from the 1950s until the mid- to late 1960s, there has since been a consistent decline. The decline has been particularly marked in the United States, with death rates falling by over 50 percent since 1970. England and Wales and Sweden followed a similar pattern, although with a more recent onset and smaller decline. In Poland and Hungary, death rates were initially low but have increased consistently since 1970. In Japan, death rates have been low and have declined throughout the entire period. In the 1980s, in contrast to the 1970s, coronary heart disease mortality trends have been downward in all countries except in eastern Europe (9). In women, coronary heart disease rates are substantially lower than in men in all countries and there is much less variability between countries; death rates in women in most countries, except in eastern Europe, have been declining consistently since the early 1950s. The within-country trends in mortality generally follow the same pattern in men and women; the trends since 1970 are summarized in table 1. The male to female ratio for coronary heart disease mortality varies by country from less than threefold to almost fivefold.

TABLE 2

International trends in male to female ratio of coronary heart disease age-standardized mortality rates among men and women aged 40-69 years, 1970 and 1986 Finland United States New Zealand England and Wales Sweden Hungary Poland Japan

1970

1986

4.4 2.9 3.1 3.7 3.3 2.6 3.9 2.2

4.6 2.8 3.1 3.3 4.3 3.1 4.2 2.8

Between 1970 and 1986, the ratio increased in five of the eight countries (table 2), reflecting the greater rate of decline, or slower rate of increase, in women. The trends in mortality in relative terms have, in general, been greater in younger people, irrespective of whether the mortality rates are increasing or decreasing. However, smaller relative declines in the elderly have a much greater impact on the absolute number of coronary disease events in a population. The recent trends in coronary heart disease mortality in eastern Europe are of particular concern. Total mortality increased in the Soviet Union between 1967/ 1970 and 1988 as a result of the increase in cardiovascular disease and particularly coronary heart disease (10). Marked increases have occurred in Poland, Hungary, Bulgaria and Czechoslovakia, Romania, and the German Democratic Republic, especially in men (8). In most of these countries, there have also been recent increases in TABLE 1 male death rates from all cardiovascular International trends in coronary heart disease: diseases and in total death rates. A striking percent change in age-standardized mortality rates in and rapid increase in coronary heart dismen and women aged 40-69 years, 1970-1986 ease mortality occurred in Singapore in Men Women the 1960s and 1970s (11); the rapidity of this change bodes ill for less developed Finland -27.5 -30.6 United States -52.2 -50.4 countries. New Zealand -32.2 -30.7 In Japan, coronary heart disease mortalEngland and Wales -13.9 -4.7 ity rates increased until about 1970, albeit Sweden -7.2 -27.7 Hungary +38.6 +14.0 to a low level; since then, the rates have Poland +78.5 +65.9 declined (12). These trends are of great Japan -43.6 -56.6 interest, particularly in view of the appar-

BEAGLEHOLE

ent recent adverse changes in dietary habits in segments of the Japanese population (13, 14). The validity of Japanese death certificate diagnoses for coronary heart disease have been questioned. In fact, coronary heart disease detection rates at autopsy increased between 1961-1972 and 19721983, suggesting that the decline in coronary heart disease mortality is real (15). The fall in coronary heart disease mortality rates in Japan has been accompanied by a consistent decline in all cardiovascular disease and total mortality rates (12). Within-country trends Recognition of the coronary heart disease mortality decline in the United States led to detailed investigation of the trends by age, sex, ethnicity, geographic locality, and socioeconomic status. Although early investigators reported that the decline in mortality was a universal and uniform phenomenon (3, 16), further studies have identified marked variations in both the onset and extent of the decline by spatial, demographic, and social factors (17). Within the United States, the decline began in California, perhaps as early as the mid1950s, although in most states the decline began between 1960 and 1965 (18). A diffusion-like process has occurred; rates in states in the west and northeast began to decline before states in the southeast. The order of decline was similar in men and women and by age group (18). In the period 1968-1975, the annual rate of decline in the United States was similar in white men, and in blacks, although it was lower in white women. Since 1975, the secular trends in rates of decline have diverged, with the decline continuing at the same rate in white men; the decline was approximately half as steep for the other three race-sex groups (19). This divergence is a strong indication that the factors responsible for the decline are unequally distributed by demographic group in the United States. There is now impressive and consistent evidence, both from nationwide studies and

within-population studies, that the decline in coronary heart disease has been greatest in higher social class groups defined in either occupational or educational terms (20-24). This differential decline has led to a widening in the social inequalities of health status within populations (17, 21). The most obvious explanation for this trend is that higher social class people have more freedom and flexibility to implement changes in health behavior (17). Specifically, during the last two decades, smoking has become less common in higher social classes, particularly among older men, in countries that have seen a decline in mortality (25). It is also possible that the social class pattern of coronary heart disease is generated at least in part by differences in hemostatic mechanisms, which in turn may be due to social class differences in smoking habits (26). The evidence on dietary trends is less persuasive. Dietary patterns are different by educational status, with more educated people having a diet more closely approximating the recommended diet (27). However, aggregate data from the United Kingdom do not suggest that social class trends in diet account for the social class trends in coronary heart disease (28). An examination of international trends in coronary heart disease mortality raises several important and largely unresolved questions concerning the marked variation in between-country coronary heart disease mortality rates and trends. Information on secular trends in coronary atheroma would be of assistance in assessing the mortality trends. Unfortunately, the data are limited and inconsistent. A study from New Orleans suggests that atherosclerotic plaques in routine autopsy material on young men were less common in the 1970s than in earlier decades (29); similar trends were found in the Honolulu cohort (30). Mayo Clinic data, however, suggest that there was no change in arterial disease in the period 1950-1979 (31). Variation in subject selection may account for these inconsistencies. Unfortunately, no trend data are available on thrombus formation, the

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

other important component of coronary arterial disease. Because of the limited data on arterial disease trends, interpretation of the mortality trends must be based on data on trends in the clinical manifestations and outcome of coronary heart disease.

onary heart disease mortality in the period 1968-1970 and 1980-1982 can be attributed to the decline in out-of-hospital death rates (40). Of particular importance is whether the decline in out-of-hospital deaths occurs in people free of previous clinical coronary TRENDS IN EVENT RATES artery disease, that is, whether it represents A central question is whether coronary a decline in incidence of coronary disease heart disease incidence rates or case fatality or a decline in recurrence rates. A decline have been changing. The two major multi- in incidence would testify to the influence center collaborative studies established ex- of primary prevention; a decline in recurpressly to examine this question are still in rence rates would suggest an important role the data collection phase (32, 33); infor- for secondary prevention. The evidence on mation is, however, available from smaller this critical point is limited and mixed. Swedish data indicate that less than 20 scale studies. percent of people who died from coronary Mortality rates heart disease had experienced a previous There are consistent data from at least clinically apparent coronary event prior to six studies that validate the within-country death (41). In New Zealand, 30 percent of trends in coronary heart disease mortality sudden death patients had a history of a rates (table 3). For example, death certifi- previous myocardial infarction, and a furcate diagnoses of coronary heart disease ther 25 percent had been on treatment for have been found to be highly sensitive and either hypertension or angina (42). In specific in the United States (34, 35), Western Australia in 1970-1971,25 percent Australia (36), and New Zealand (37). Al- of acute myocardial infarction patients had though it remains possible that some of the had a previous episode, and over two-thirds increase in the coronary heart disease epi- had a past history of cardiovascular disease demic in the 1940s and 1950s was due to or diabetes (40). In young men who died changes in certification practices, the de- from coronary heart disease in Allegheny cline cannot be ascribed to these factors. County, Pennsylvania, 40 percent had a Between-country comparisons of coronary history of heart disease (34). heart disease death certificate data are less There is thus reasonably consistent evifrequent. A comparison between Australia dence that only a minority of out-ofand New Zealand indicated that variation hospital deaths take place among persons in general practitioner certification prac- who have a history of a major coronary tices could not explain the higher reported event which might have led to effective death rate in New Zealand (38). Most of secondary preventive intervention. A larger the decline in coronary heart disease mor- proportion of out-of-hospital deaths occur tality has occurred in out-of-hospital in people who have a medical history for deaths ("sudden deaths"). For example, in which effective secondary prevention is less Minneapolis-St. Paul, Minnesota, in the effective. It is thus likely that the decline period 1970-1985, the out-of-hospital mor- in out-of-hospital deaths represents in large tality rates declined by over two-thirds in part a decline in the incidence of sudden men, in contrast to a 43 percent decline in coronary death. in-hospital death rates (39), and much of the total decline in coronary heart disease Myocardial infarction rates mortality (60-70 percent) occurred in outIn contrast to the consistency of findings of-hospital deaths. In Perth, Western on the importance of the decline in out-ofAustralia, 80 percent of the decline in corhospital coronary deaths, the trends in

TABLE 3

Trends in coronary heart disease (CHD) mortality and morbidity: selected populations Country/study (reference no.) United States Allegheny Co., PA (34)

Population

Time period

CHD mortality

Sudden deaths

White men 35-44 years

1970-1986

55% decline

Minnesota Heart Survey (39)

Total population 30-74 years

1970-1986

Worcester Heart Attack Study (47)

Community-wide

1975-1984

52% decline in men 58% decline in women No data

Total population 25-64 years

1970-1985

50% decline

Total population 25-69 years

1979-1985

14% decline in men and women

No data

Total population 25-64 years

1974-1986

50% decline in men Decline in women until 1981

50-59 years

1970-1984

Increase in men until 1979 No change in women

Australia Perth (40)

Hunter Region, NSW (44) New Zealand Auckland (42)

Sweden Gothenburg (41)

Myocardial infarction

Case fatality Short term

Long term

66% decline, especially incidence 68% decline in men 58% decline in women 44% decline

No data

No data

No data

No change

Fell in men

No data

27% decline in both incidence and recurrence

Fell

No change

35% decline in men and women

Decline in incidence: 18% in men, 32% in women Decline: 26% in men, 4% in women

No change

No change

Increase in men

No data

28% decline in men 10% decline in women

No change

No change

No change

Increase in men until 1979 No change in women

No change in

No change

Decline in 19681977

Q

men

Increase in women

I

O M

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

myocardial infarction rates are less clear (table 3). In Minnesota, definite myocardial infarction attack rates increased in both men and women between 1970 and 1985 (39). In Australia, definite myocardial infarction rates have declined in both Perth (43) and Newcastle (44). In Perth, the decline has been primarily in the incidence of myocardial infarction (43). In Auckland, New Zealand, there has been a nonsignificant decline in myocardial infarction rates in men, but no evidence of a change in women (42). There are several possible reasons for the variation in myocardial infarction rates. In the United States, the hospital reimbursement system implemented in 1983-1984 has increased the financial incentive for hospitals to identify and document every acute myocardial infarction, with a consequent diagnostic shift from chronic coronary heart disease to acute coronary heart disease codes (45). Changes in routine cardiac enzyme tests toward more sensitive assays, and an increase in elective diagnostic and acute coronary artery therapeutic procedures, may also increase the diagnosis of acute myocardial infarctions (46). Adjustment for these factors reduced, but did not eliminate, the increase in myocardial infarction discharge rates in Minnesota in the period 1980-1985 (46).

New Zealand, in the period 1974-1981 (49), where diagnostic fashions and therapeutic procedures have apparently changed less; there is some evidence of an earlier decline in long-term case fatality in Auckland (50). In Perth, Australia, there was no improvement in 28-day or 1-year survival between 1971 and 1979 (51). In Gothenburg, Sweden, there was a decline in mortality after hospital discharge for myocardial infarction in the early part of the period 19681969 to 1977 (52), although the trend was then stable through 1985 (41). TRENDS IN POPULATION RISK FACTOR LEVELS

The major modifiable determinant of population coronary heart disease levels is the risk factor status of the population. There are surprisingly little secular crosssectional data on risk factor levels either by country or region (table 4). The most extensive data come from the United States. At the national level, declines have been reported in systolic blood pressure and blood total cholesterol levels and, particularly in men, in self-reported current smoking rates (53). The difficulty in standardizing blood pressure and cholesterol measurements over time means that trends in these variables must be interpreted cautiously. The trends in self-reported smokCASE FATALITY TRENDS ing rates are more secure, despite underreporting, because they are supported by total Trends in case fatality following myocarconsumption trends and ultimately by lung dial infarction, particularly in in-hospital cancer mortality trends. case fatality, are highly dependent on denominator changes. Changes in admission The best within-population data from policy or diagnostic criteria could easily the United States come from the increase the proportion of milder cases hos- Minnesota comparison of the 1973 Lipid pitalized, and it would not be surprising Research Clinics Prevalence Survey data if hospital case fatality fell as a conse- with Minnesota Heart Survey data from quence. Perhaps for this reason, hospital 1980-1982 and 1985-1987 (39). The Lipid case fatality fell substantially in the 1970s Research Clinics study population methods in Minnesota (39) and Worcester, Massa- were not strictly comparable with the later chusetts (47), and in Melbourne, Australia two surveys, although adjustments for (48) (table 3). In contrast, there was no methodological differences were made. decline in definite myocardial infarction Smoking rates declined in absolute terms case fatality over 28 days, 1 year, or 3 years by 10 percent in both men and women aged in community-based studies in Auckland, 25-59 years from 42 percent to 32 percent

BEAGLEHOLE TABLE 4

Trends in coronary heart disease risk factors in selected populations Country/study (reference no.)

United States Minnesota Heart Survey, 1973-1986 (39) Australia 1980-1983 (54) New Zealand Auckland, 1982-1987 (55) Sweden Gothenburg, 1970-1979 (41)

Serum total cholesterol

Blood pressure*

Cigarette smoking

Decline 4% in men and 5% in women

DBP fell 2 mmHg in men and women

Decline in men and women

No change

DBP fell 2 mmHg

Decline

Decline 1% in men and women

No change

Decline in men and women

Decline 6% in men and 10% in women

SBP and DBP decline in men and women

Decline in men Increase in women

* Abbreviations: DBP, diastolic blood pressure; SBP, systolic blood pressure.

and 38 percent to 28 percent, respectively, although the mean number of cigarettes smoked by smokers increased. Total cholesterol levels decreased by approximately 4 percent and blood pressure levels improved from the early 1970s to 1980 but changed little through 1986. Body mass index progressively increased throughout the period in both men and women (39). Nationwide data from two prevalence studies in Australia in 1980 and 1983 found small reductions in cigarette smoking rates and in diastolic blood pressure levels but no change in systolic blood pressure or total cholesterol levels and an increase in body mass index (54). These trends require very cautious interpretation because of sampling differences, relatively high nonresponse rates, and changes in methods between surveys. Again, the most secure trends are with cigarette smoking, since other national survey data show consistent findings. In Auckland, New Zealand, smoking rates have declined markedly in the period 19821987 (particularly in men), but total blood cholesterol declined by only 1 percent; there were no consistent trends in either blood pressure or body mass index levels (55). In Gothenburg, Sweden, in 50-year-old men examined in 1963, 1973, and 1983, favorable trends occurred in smoking rates

throughout the period, and since 1973, in total cholesterol and blood pressure levels (41). Between 1973 and 1983, there was a decrease of about 30 percent in multivariate logistic risk for major coronary heart disease events (41). Of particular interest are data on population risk factor levels from eastern European countries. Smoking rates, particularly in men, and blood pressure levels are high in eastern Europe (56). There is also limited evidence from Poland (57) and the German Democratic Republic (58) that risk factor levels, particularly levels of blood total cholesterol, have increased since the 1970s, although in both countries smoking rates have fallen. The percentage of energy from dietary fat increased dramatically in Poland between 1950 and 1980 (57). Nationwide data for Japan indicate that since 1956 the intake of cholesterol and saturated fatty acids have increased remarkably; body mass index levels have increased but blood pressure levels and smoking rates have declined (13). Similar trends are reported from a rural community in northeast Japan (14). An ecologic examination of the relation of changes in nutrition, smoking, and alcohol consumption to international trends in coronary heart disease found that in almost all of the countries with major falls

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

or rises in mortality there are corresponding decreases or increases in animal fat consumption (59). The prevalence of smoking is declining among men and remains unchanged among women in most countries, suggesting that differences in the rate of change between countries or between the sexes are not related to differences in the change of smoking habits. However, it is likely that the mortality changes within countries, particularly in men, are influenced by changes in smoking. The impact of these risk factor trends on coronary heart disease mortality is likely to be considerable. The Australian risk factor trends are estimated to account for up to half the decrease in mortality in people aged 40-49 years (54). In New Zealand, favorable national trends in food and tobacco consumption were estimated to account for up to 50 percent of the decline in mortality between 1968 and 1981 (60). Similar estimates were derived for the impact of risk factor trends in the United States (61). The role of trends in cigarette smoking in the United States decline has been stressed (62). Although it is noteworthy that in US veterans, coronary heart disease mortality rates declined at a faster rate in nonsmokers, the attributable amount of the decline is primarily in the cigarette smoking group because of the high prevalence of smoking and the high rate of disease in smokers (63). It appears likely that the apparent deterioration in risk factor status in eastern Europe is one cause of the rising coronary heart disease mortality rates in eastern Europe.

of a variety of interventions designed to reduce the consequences of the acute ischemic episode. A complementary strategy has been the high-risk approach to primary prevention, which has focused on the identification and treatment of people at particularly high risk of coronary heart disease. It is not surprising that considerable credit for the decline has been attributed to advances in medical care. At the first Conference on the Decline in Coronary Heart Disease Mortality, it was stated that changes in coronary heart disease care have probably had an impact on this decline (4). The difficulty in estimating the size of this contribution was recognized as was the limitation of the potential of acute coronary care, because the majority of deaths occur out of hospital. Since this conference, two estimates of the impact of medical care have suggested that approximately 40 percent of the decline in the United States between 1968 and 1976 (61), and in New Zealand between 1968 and 1981 (65), could be attributed to improvements in medical care. The New Zealand estimate now appears optimistic, and, in particular, the contribution attributed to improvements in blood pressure treatment may have been overestimated. At the 1986 conference it was stated that "the evidence suggests that medical care is playing a larger role in reducing coronary heart disease mortality now than in the early years of the decline" (5). In fact, the evidence to support this statement is exceedingly weak. There is no doubt that patterns of medical and surgical management of coronary heart disease and its risk T H E INFLUENCE OF MEDICAL CARE factors have changed dramatically over the The primary response to the epidemic of last two decades. However, the data to recoronary heart disease in all countries has late these changes to trends in mortality at been at the tertiary prevention level; that the population level are sparse. In the abis, a large proportion of the available re- sence of convincing declines in case fatalsources have been directed at the treatment ity, it appears unlikely that tertiary prevenof the acute attack, rather than to primary tion has had a significant impact on prevention utilizing the population strategy mortality trends. Regrettably, there has (64). Hence, the emphasis given to the de- been no increase in our ability to assess the velopment of coronary care units and mo- influence of medical care over the last bile life support units, and the introduction decade.

10

BEAGLEHOLE

Some general points can, however, be made. In the United States, the rate of increase in the epidemic slowed in the late 1950s and early 1960s before the decline began. This change occurred well before the major changes in medical care of clinical coronary heart disease; for example, the first coronary care unit was introduced in the United States only in the mid-1960s (61) and coronary artery surgery did not become widespread until the mid-1970s (66). The focus on medical care has concentrated on the potential beneficial effect of modern medical care. It has also been suggested that removal of deleterious medical care interventions in the mid-1960s might also have been an important influence on mortality trends (67). For example, reduction in bed rest post-myocardial infarction might be one factor responsible for improvements in hospital case fatality. The major factor that limits the potential role of medical care in reducing coronary mortality is the natural history of the disease. Most deaths occur out of hospital (68) and most of these deaths still occur in people without major clinical manifestations of the disease. There is also little possibility that the high-risk approach to the control of risk factors has had a major impact; the treatment of hypertension has only a disappointingly small impact on coronary heart disease mortality and widespread management of hypercholesterolemia is a very recent phenomena (69). The secondary prevention of smoking in highrisk patients could potentially have a considerable impact, because the positive, albeit small, impact of physicians' advice has been demonstrated (70) and the importance of the risk factor has long been recognized. It remains extremely difficult to assess the population impact of medical intervention. Indeed, the impact at the clinical level is often not assessed appropriately with well-designed randomized controlled trials. Analytic techniques for estimating population impact, even when controlled trial data are available, are still rudimentary.

MONITORING STUDIES

Two major multicenter collaborative and prospective studies have been established to investigate trends in cardiovascular disease: the World Health Organization MONICA Project (Monitoring Trends and Determinants in Cardiovascular Disease) (32) and the US National Heart, Lung and Blood Institute ARIC Study (Atherosclerosis Risk in Communities) (33). Planning for the MONICA Project began in 1979 using the experience of the earlier World Health Organization myocardial infarction and cerebrovascular registers. The primary objective of the MONICA Project is to measure in middle-aged people the trends in coronary heart disease and stroke mortality and morbidity and to assess the extent to which these trends are explained by trends in the major cardiovascular risk factors and in medical care. The detailed hypotheses under investigation and the organization of the study have been described (32), together with baseline mortality and crosssectional risk factor data from most of the 39 centers in 26 countries (71, 72). The coordinating and quality control aspects are supported by the World Health Organization, but each MONICA center is responsible for its own funding. A major problem facing the Project has been its lack of resources; much less attention than is desirable has been devoted to quality control activities. Great emphasis is placed on internal quality control so as to ensure that reliable within-center trend data are available for cross-national comparisons over time, even if less confidence can be placed in the between-center comparisons of absolute event rates (particularly stroke rates) and risk factor levels (71). The standardization of measurement of event rates over time and in widely varying social and cultural evnironments is proving difficult. Particularly problematic is the measurement of incident events because of the variation in medical records, postmortem rates, and interview procedures (71). It is possible that only a minority of the

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

MONICA centers will produce data on trends in both incident and recurrent events. The core MONICA risk factor surveys are restricted to measurement of blood cholesterol, blood pressure, cigarette smoking, and weight and height, on the assumption that most of the impact of primary prevention will operate through these factors. Optional studies focus on nutrition, exercise, and psychosocial factors. The planned 10-year data collection phase of the MONICA Project has just passed its half-way mark; it could be up to another 10 years before the definitive collaborative MONICA data are published, although shorter term trend data from some MONICA centers have already been published (42, 43). Despite these problems, the achievements of the Project have been considerable. Although it is too early for Project data to be used to examine the major study hypotheses, the mortality and risk factor data have confirmed the existence of major between-center variations (71, 72). Less tangibly, but ultimately perhaps of even more importance, the MONICA Project has had a major worldwide impact on stimulating cardiovascular disease epidemiologic research and prevention activities. The ARIC Study is a prospective investigation of the etiology and natural history of atherosclerosis and the etiology of clinical atherosclerotic disease in four communities (33). The main focus of the study is the identification of new risk factors of ultrasonographically defined atherosclerosis and its progression and clinical sequelae. A subsidiary aim is to measure variations in cardiovascular risk factors, medical care, and disease by race, sex, place, and time. The study has cohort and community surveillance components. The community surveillance component is directly related to the desire to measure coronary heart disease incidence differences by race and geographic location and is based on the earlier Community Cardiovascular Surveillance Program. Surveillance for coronary heart disease will involve review of hospitaliza-

11

tions and deaths among residents aged 3574 years of the four study communities. Regrettably, the number of study centers and their relatively small populations means that the power of this study to investigate coronary heart disease mortality trends is extremely limited (73). DISCUSSION AND CONCLUSION

Even in the absence of long-term data from the MONICA and ARIC studies, it is still possible to draw several conclusions from the published studies. 1) The reported coronary heart disease mortality declines are real and it is likely that trends in countries with increasing rates are also valid. 2) Until recently, coronary heart disease was an epidemic disease only in the western industrialized countries. Internationally, disease patterns are now diverging. In particular, pronounced declines in mortality have occurred in affluent countries and mortality has increased in some less affluent industrialized countries (notably eastern European countries) and has grown extremely rapidly in some newly developed countries (for example, Singapore). 3) An important emerging feature of the ongoing research has been the recognition, in contrast to the early interpretations, that the trends have also been diverging within countries. There is unequivocable evidence that within countries the greatest decline has occurred in the higher social classes. This divergence has led to an increase in the social inequalities of health status within countries. 4) The major part of the decline in mortality rates has occurred in out-of-hospital ("sudden") deaths; much of this decline has been in incident cases. No data are available on the components of deaths that have contributed to the increased mortality rates in eastern Europe. 5) Definite myocardial infarction trends are not consistent, perhaps at least in part because of changes in admission policies and enzyme tests and, in the United States, in hospital reimbursement systems. Never-

12

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theless, there is evidence that incidence rates have declined in some centers. 6) Hospital case fatality has declined in a number of centers and this trend is not fully explained by the admission of milder cases; trends in long-term case fatality are generally stable, although further analyses are required that adjust for disease severity. 7) The impact of medical care on mortality trends remains difficult to quantify with confidence, although on balance it appears to be only of secondary importance. 8) Population risk factor levels have in general declined, especially cigarette smoking, and beneficial dietary changes have occurred. In eastern Europe, limited data suggest that population risk factor levels are worsening. In Japan, adverse dietary changes have occurred but are, as yet, insufficient in amount or duration to influence national mortality rates. 9) A reasonable judgement is that risk factor trends, particularly in diet and smoking, are the most important causes of the trends in mortality. The continued high population level of these risk factors justifies continued and intensified public health action. Despite the downturn in mortality, coronary heart disease remains the leading cause of death in most countries. Coronary heart disease proportionate mortality has fallen over the last two decades but coronary heart disease still accounts for approximately 30 percent of all deaths each year. Furthermore, as the population ages, and in particular as the post-World War II baby boom generation ages, the absolute number of coronary heart disease events and deaths will increase by the year 2000. Unprecedented reduction in risk factor levels will be required to offset these demographic effects on the absolute burden of coronary heart disease (74). The diverging social trends in mortality within countries have important implications for all preventive programs, especially cardiovascular prevention. The effect of traditional health promotion programs on increasing social inequalities is a reflection

of their focus on individual patterns of behavior, and in particular on consumption habits, for example, of tobacco and food (17). As higher social class people, particularly white men, change their habits, pressure is exerted on other social groups to increase their consumption of unhealthy products. For example, young women have become the focus of attention of the tobacco and alcohol industries. Regrettably, this pattern is repeated on an international scale, with multinational tobacco companies exploiting the potentially huge markets in less developed countries (75). The new health promotion, as expressed in the Ottawa Charter (76), has the potential to avoid the deleterious effects of traditional individually focused programs. With its emphasis on public policy and the creation of healthy environments, the new health promotion could exert a positive influence on the production and availability of healthy products and facilitate healthy behavioral options. The achievement of a healthier environment will ensure that improvements in health of some segments of the population are not at the expense of others. Coronary heart disease is the first major noncommunicable disease for which community-wide prevention programs have been developed. Although specific programs have focused on the prevention of lung cancer and stroke, the approach to coronary heart disease, because of its multifactoral origin, has been unique. It took at least two decades to accumulate the epidemiologic knowledge necessary for the development of coronary heart disease prevention and control programs. It is clear that for other important noncommunicable diseases, epidemiologic knowledge is still insufficient for effective preventive programs. There is a need for cost-efficient and robust surveillance systems for a wide range of epidemic noncommunicable diseases (77). It is likely that, as with coronary heart disease, other mass diseases of western industrialized countries also have their origin

INTERNATIONAL TRENDS IN CORONARY HEART DISEASE

in the environment and in the way people live and eat (78). It is also likely that a rise and fall in these epidemic diseases will reflect changes in their incidence, rather than being due to the impact of medical care. Our relative ignorance concerning the changes in coronary heart disease incidence, case fatality, and population risk factor levels should alert us to the need to document these aspects of the other emerging epidemic noncommunicable diseases. Explaining time trends is difficult and will always be tentative. The lesson from coronary heart disease is that resources devoted to monitoring disease and risk factor trends are absolutely central to rational explanations of time trends. In turn, these data are essential for determining and targeting specific intervention programs and in monitoring their success or failure. REFERENCES

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