Past, Present and Future of Cardiovascular Epidemiology and Prevention in the U.S.A.

Concern about rising coronary heart disease (CHD) death rates and awareness of international differences in CHD and stroke mortality led to early epidemiological studies including Framingham Heart, Seven Countries and NI-HON-SAN studies. Elevated blood cholesterol and blood pressure, cigarette smoking and diet were identified as risk factors, predominantly in men. Clinical trials demonstrated the feasibility and efficacy of lowering risk factors through pharmacologic and behavioral interventions. The continuing decline in CHD mortality began in the late 1960's and is attributable to healthier lifestyles and improved medical management. Current epidemiological studies include more women and diverse populations and expand potential risk factors and outcomes to include obesity, diabetes, hemostatic and psychosocial factors, physical inactivity and genes, as well as markers of pre-clinical atherosclerosis, ischemia, and cardiac dysfunction. CVD prevention encompasses national education programs, community interventions and high risk approaches. In the future new insights are expected on the interplay of genetic susceptibility and non-genetic risk and protective factors and on precipitants of clinical events. Advances in treatment and wider use of preventive measures should reduce or delay CVD especially among low socio-economic groups, the elderly and survivors of an event. National goals for lower rates of CHD, stroke and risk factors have been set for the year 2000. J Epidemiol,1996 ; 6 : S203-S207.

States collaborating in the Pooling project were in Albany, Chicago Western Electric Company, Chicago Peoples Gas Company, Framingham, Tecumseh, Los Angeles and Minnesota. The Pooling Project established the importance of cholesterol, blood pressure and smoking as risk factors for white middle aged men 2). Since the mid 1960's multiple regression analyses have provided estimates of the probability of developing CHD and stroke based on composite risk factor profiles which use information on sex, age, blood pressure, cholesterol, cigarette smoking, glucose intolerance, left ventricular hypertrophy, family history and prevalent heart disease. An important lesson was that several moderately elevated risk factors increase risk as much or more than a single high risk factor does.
International differences in death rates from heart disease and stroke had a major influence on the design and implementation of epidemiological studies in the 1950's and 1960's 3). The Seven Countries Study pioneered international comparisons of lifestyles, especially diet, and showed that fat content of diets and serum cholesterol levels were correlated with heart disease rates in men in ecologic analyses. Several other studies enrolled cohorts in countries with substantially different CVD death rates. The NI-HON-SAN study used the opportunity provided by migrants from Japan to Honolulu or San Francisco to explore behavioral and environmental factors related to heart disease and stroke in more genetically homogeneous populations. Details of this study are presented in this volume. Comparisons with the Japanese population and with the Framingham cohort were envisaged when the Honolulu Heart Program, the Puerto Rico and Yugoslavia studies were implemented, however, the latter two are no longer active. International comparisons showed that although the major risk factors were the same, they did not account completely for the differences in CVD morbidity and mortality among these populations.
While it was known by the late 1960's that incidence of CVD could be predicted for groups of people, it was not certain that incidence could be reduced by lowering risk factors that were amenable to change. Primary prevention trials to answer this question included the High Blood Pressure Detection and Follow-up Program (HDFP) 4), The Multiple Risk Factor Intervention Trial (MRFIT) 5) and the Lipid Research Clinics Coronary Primary Prevention Trial (LRC-CPPT) 6). These randomized controlled trials enrolled thousands of middle-aged subjects; men and women in HDFP, men only in MRFIT and LRC-CPPT. Endpoints were total mortality, CVD and CHD deaths and nonfatal myocardial infarction. Follow-up over periods of 5 or more years showed that levels of blood pressure, cholesterol and rates of cigarette smoking could be reduced by hygienic measures or drug treatment, and that end points could be reduced. The positive results of these trials published in the 1970's and 1980's have been major and continuing influences on medical practice and on the behavior of individuals. Clinical guidelines for treating high blood pressure and elevated levels of cholesterol through hygienic and pharmacologic means have been disseminated and accompanied by national education programs 7,8).
The Conference on the Decline in Coronary Disease Mortality in 1978, established the reality of the downward trend which began in the mid 1960's, and concluded that reasons for the decline were unclear though both primary prevention and better medical care had contributed. The conference also pointed out the need for new knowledge and for monitoring trends in mortality, morbidity and risk factors. A working group on heart disease epidemiology subsequently set the direction for the next generation of studies which were implemented beginning in 1984.
THE PRESENT 1984PRESENT -1996 Needs and opportunities for research identified by the working group included; community surveillance to monitor trends in incidence of fatal and nonfatal CHD and their relation to changing risk factors; longitudinal studies of the development of and trends in risk factors over the entire age range; and clinical trials of reduced salt intake and weight reduction. They commented on the need for better measurements or more information on physical activity, psychosocial characteristics, cigarette smoking, occupational exposures and water hardness. They also recommended studies of the quality of medical care, evaluation of interventions for CVD, as well as training programs for epidemiologists and biostatisticians.
Individual investigators initiated and continued epidemiological and prevention studies throughout the period and were responsible for many innovative approaches. A few examples in addition to those mentioned above and below are the Nurses Health Study, the Minnesota Heart Survey, the Bogalusa and Muscatine Studies, the Charleston, Evans County, Worcester, and San-Antonio Heart Studies, the College Alumni and the Physicians Health Studies.
The major new epidemiologic investigations initiated by the National Heart Lung and Blood Institute were; Coronary Artery Risk Development in Young Adults (CARDIA), Atherosclerosis Risk in Communities (ARIC), the Cardiovascular Health Study (CHS) in people over 65 years of age, the National Growth and Health Study, the Strong Heart Study in American Indians, the Insulin Resistance Atherosclerosis Study (IRAS) and most recently the Family Heart Study and the Family Blood Pressure Program s) These studies extend studies predominantly of middle aged white men, to include young adults, the elderly, minority populations and women. They, as well as studies continuing from the past, have broken new ground in detecting and confirming risk factors such as lipids and lipoproteins, clotting and fibrinolytic factors, and the amount and distribution of body fat. Evidence on the role of low birth weight, insulin, hyperhomocysteinemia is accruing as is information on potential protective factors including vitamin E, flavonoids, other antioxidants, hormone replacement therapy and moderate alcohol consumption. The efficacy of aspirin for primary and secondary prevention has been demonstrated for men and is under investigation in women.
Current . Information from these and other ongoing clinical trials and epidemiologic studies has been or soon will be published in the medical literature. Three community-based prevention research demonstration studies were completed recently. In the Stanford Five City Project, the Minnesota and the Pawtucket Heart Health Programs, educational interventions were conducted using mass media, community organizations and environmental strategies. Changes in knowledge, risk factors, morbidity and mortality were the goals and evaluation of processes and results were essential components of these studies. Short-term benefits on CVD risk were detected in treatment compared with control communities and were in addition to those experienced by the US population in general.
The earliest of the national education programs, Detection, Evaluation and Treatment of High Blood Pressure and the National Cholesterol Education Program were initiated in 1972 and 1985 respectively7,8). Their countinuing success guided the newer programs on Smoking, Obesity and Physical Activity, and the Heart Attack Alert Program which were inititated recently.
Major advances resulting from research in epidemiology and prevention in the present period include; increased understanding and recognitiuon of new CVD risk factors in general, and in previously understudied populations; use of new non-invasive technologies to detect and measure pre-clinical atherosclerosis, silent ischemia, and cardiac dysfunction; development of community surveillance and intervention strategies; and demonstration of the efficacy of primary and secondary prevention approaches.

THE FUTURE
Recommendations for future research made in 1994 by the Epidemiology and Prevention Task Force include for epidemi-ology: clarifying relationships among subclinical atherosclerosis, CVD risk factors and clinical CVD; identifying precipitants of acute events; and monitoring and increasing knowledge of etiology and prevention of heart failure, cardiomyopathies and vascular disease of the kidney 10). The Task Force also recommended comparisons of CVD morbidity, disability and mortality in the U.S. and other countries, with assessment of lifestyles, geographic, socioeconomic, racial and ethnic characteristics as determinants of differences in CVD. The report states environmental and genetic factors influencing key risk factors should be identified; the interaction of gentic susceptibility and environmental determinants of CVD should be investigated; interrelationships of lifestyles, hormone metabolism and psychosocial factors should be studied in women, as should relationships of socio-economic status to CVD risk in men and women. Observations on blood pressure, amount and distribution of body fat are needed from childhood through adult ages to identify determinants and effects on CVD of levels and changes over the life span. Research is recommended on the determinants and precursors of CVD at older ages. Risk factors considered in need of further study include nutritional components, physical activity, diabetes, insulin, glucose metabolism, weight gain, obesity, thrombosis, platelet function, inflammation and psychosocial factors; relationships between these and other risk factors, atherosclerosis and CVD require elucidation.
Recommendations for research on prevention of CVD include research on methods for translating knowledge about modifying lifestyles and management of risk factors into public awareness, policy and practice. Specifically the Task Force recommended developing more effective methods for modifying blood lipids, preventing high blood pressure, obesity and diabetes mellitus and eliminating smoking. Ways should be found to reduce CVD -related limitations on function and quality of life by influencing social settings and psychological variables. Approaches to secondary prevention that were suggested involve physician education, clinical research and dissemination of information about effective strategies against disease progression and death. The Task Force recommended evaluation of interventions in older people, in women, minorities, groups with low socio-economic status, children and adolescents. They also cited needs for better understanding of etiology and prevention of congenital heart disease, for more effective methods for preventing rheumatic heart disease and for treating Kawasaki disease.
Many of these investigations are underway in ongoing observational and intervention studies which will be presenting results in the next several years 11). Longitudinal population based research studies continue to be necessary along with surveillance to monitor trends in prevalence, incidence and risk factors, as well as mortality, case fatality and medical care. The dramatic changes over time in death rates for CHD in the U.S.  Reduce coronary heart disease deaths to no more than 100 per 100,000 people.
Reduce stroke deaths to no more than 20 per 100,000 people.
Increase to at least 50 percent the proportion of people with high blood pressure whose blood pressure is under control.  are shown in Figure 1. Comparable information on morbidity and a wider range of CVD is needed for the future. Studies of economic costs, quality and availability of care are relatively new directions in epidemiology and ones requiring development and testing of methods.
Randomised clinical trials are needed to provide definitive answers about promising new preventive and therapeutic approaches such as preventing hypertension, raising HDL-cholesterol and lowering homocysteine levels, and also to identify any adverse effects of interventions which may otherwise escape detection. Populations participating in clinical trials and community interventions will be more diverse and research is needed to enhance participation and retention of those who are hard to recruit.
On the national level, specific goals have been set in "Healthy People 2000" National Health Promotion and Disease Prevention Objectives 12). The challenge for CHD is to reduce the death rate to no more than 100 per 100,000 people, and for stroke to reduce the death rate to no more than 20 per 100,000 people. Assuming recent rates of decline continue, the goal for CHD should be attainable but the decline in stroke mortality appears to be slowing down. Approaches to reaching the objectives for CVD are indicated by the goals for reducing cholesterol, controlling high blood pressure, reducing the prevalence and initiation of cigarette smoking and reducing the prevalence of overweight by reducing dietary fat intake and increasing physical activity. The targets for these risk factors are shown in Figure 2. Although trends are generally encouraging, obesity is increasing. Improvements in other risk factors have been less in some subgroups than in others 13).
This brief overview of accomplishments, opportunities and challenges for epidemiology and prevention of CVD in the U.S.A. indicates that future improvements in cardiovascular and general health are necessary and possible if current knowledge and proven strategies are combined with unprecedented opportunities to develop and apply new knowledge for the benefit of individual patients, families and populations.