Aetiology of ischaemic heart disease.

There is evidence from population studies of strong positive associations between smoking, arterial pressure and serum cholesterol concentration and risk of ischaemic heart disease, and these appear to be independent of one another, but the evidence from unifactorial trials of risk factor reduction is less impressive. For smoking, there is no good experimental evidence that cessation reduces the risk of IHD, but there are good observational data to show that those who choose to cease have a lower mortality from IHD, and all causes of death, compared with those who continue to smoke. For arterial pressure, none of the randomized controlled trials has shown any benefit from a reduction in arterial pressure in relation to IHD, although the same studies have shown that risk of stroke is reduced substantially. The best trial evidence for risk factor reduction is seen for serum cholesterol, and in all three major placebo control trials, reduction was associated with a corresponding decrease in the incidence of IHD; for each 1% decrease in serum cholesterol concentration there was a 3% reduction in risk of IHD. However, total mortality was unchanged, and in the case of the WHO Co-Operative Study there was a statistically significant excess of deaths in the treatment group. The use of drugs in the primary prevention of IHD is a matter of judgement based on the risk of disease, the efficacy of the treatment and side effects.