The decline in coronary heart disease; did it fall or was it pushed?

Three linked studies assess the decline in mortality from coronary heart disease and its determinants in three European countries.1 2 3 National comparisons on this subject anticipate the Olympics. Who fell first? Furthest? Fastest? Started late? Why?4

Three decades ago, mortality from coronary heart disease in the United States, which had been high since the second world war, was found to be falling. The reasons were obscure. Cardiovascular risk factors had been studied in circumscribed cohorts, not in populations repeatedly sampled over time. Measurements were inadequately standardised.5 The effect of treatment was unknown, but it seemed unlikely to be so much greater in the US than in countries not experiencing a decline in mortality. In 1978 the US National Heart Lung and Blood Institute convened a conference to clarify what was known.6 Reinforcing existing surveillance, the report also inspired new initiatives: the Atherosclerosis Risk in Communities (ARIC) study in the US and the World Health Organization MONICA project (MONItoring trends and determinants in CArdiovascular disease).7 8

Observing that mortality in the population was the product of coronary event rates and their case fatality, MONICA hypothesised that a decrease in event rates was driven by a commensurate change in cardiovascular risk factors, and that case fatality was reduced by improvements in coronary care.8 Its protocol was followed across 37 populations in 21 countries. Collaborators monitored and validated 10 year population trends in non-fatal myocardial infarction, coronary mortality, coronary care, and risk factors.

MONICA’s final results were reported at the turn of the century.8 9 10 11 12 On average, two thirds of the decline in mortality was attributed to falling event rates and one third to falling case fatality.9 In most populations, event rates and risk factors were falling, but when trends in 10 year coronary event rates were plotted against trends in risk factors they showed a poor fit, although the correlation improved when a four year time lag was introduced.10 Across populations case fatality, mortality, and event rates all decreased greatly as coronary care improved.11 In contrast, ARIC showed that the recent US decline in mortality went with a minimal change in event rates and a greater fall in case fatality.12

Reports since MONICA extend into the new millennium of medical interventions.1 2 3 The Danish study by Schmidt and colleagues (doi:10.1136/bmj.e356) shows a 25 year decline (1984-2008) in both the incidence of those first episodes of myocardial infarction that involved hospital admission and the associated mortality, even though mortality was exacerbated by comorbidities.1 The study by Bandosz and colleagues (doi:10.1136/bmj.d8136) used the IMPACT model to assess how changes in treatments and risk factors have contributed to the decline in mortality in Poland since adoption of a market economy.2 The authors conclude that about 37% of the decline was attributable to treatments and about 54% to changes in risk factors, although confidence intervals were wide. The third study by Smolina and colleagues (doi:10.1136/bmj.d8059) shows a continuing decline in myocardial infarction and case fatality in England, with a hint of levelling off in the youngest age group.3 All three studies suggest that the recent decline is associated with the effects of evidence based treatments in primary prevention, coronary care, and secondary prevention.

Are other factors contributing to the decline? The IMPACT model and the INTERHEART study imply that there is little need for additional factors.2 13 MONICA could not exclude them.10 Classic risk factors for heart disease are not the sole determinants of risk, otherwise risk scores would not need to be recalibrated according to the population studied. In prevention, coronary risk is multiplicative, so interventions that affect one or two modifiable risk factors disproportionately benefit overall risk. Other and unknown factors are of secondary importance but difficult to dismiss. For example, diet does not operate exclusively through blood cholesterol. Similarly, it is difficult to believe that big reductions in coronary case fatality over decades are determined exclusively by drugs—perhaps patients are now fitter and coronary episodes less severe.

Are prevention policies correct and governments in control? Many countries did not have prevention policies until after their decline in mortality from coronary heart disease began. Ensuring that effective treatments are prescribed is less challenging than changing people’s lifestyles. Fortunately, taking exercise, refraining from smoking, and eating a varied diet are no longer considered punishment, but enjoyable. People are resistant to rapid cuts in salt consumption and total fat—it is easier to substitute the type of fat. Fish are scarce and expensive. There is a hard core of nicotine addicts. Obesity and diabetes are increasing. But atherogenic lifestyles are unsustainable in terms of world food and energy resources.

Governmental effectiveness cannot be tested in a controlled trial. One indicator is the ability of the health department to counteract vested interests, such as those of the tobacco industry and manufacturers of processed foods, thereby knocking out the props that hold disease rates up. In Poland the decline in coronary heart disease began with the change from a socialist command economy, which subsidised animal fats, to a market economy, where fruit and vegetables were more competitively priced.2 In the early 1980s, the then European common market had no mandate to consider human health when subsidising production of animal fats and tobacco. Britain had no coronary prevention policies. Now the European Commission and British health departments have relevant policies in place.

As the world population ages and becomes more industrialised and urbanised, the decline in coronary mortality is predominantly in rich nations, while rates increase in dozens of others.14 Can these countries learn from us, or must they repeat our mistakes? Standardisation of population risk factor measurements—led by the former MONICA Data Centre in Helsinki (www.ehes.info/)—facilitates comparison, prediction, and possible action. Better data from countries where coronary disease is increasing are needed, but motivation and resources may be scarce.