Cardiovascular monitoring of a city over 30 years

This lecture on population studies was given in memory and honour of the late Professor Frederick Epstein. It relates to studies performed in Göteborg, Sweden. The main topics discussed in the presentation are: Coronary heart disease and stroke incidence according to the MONICA Project. Risk factors with special emphasis on relative and population attributable risk. Incidence and mortality of coronary heart disease in hospital and out of hospital. Quantitative aspects on treatment and prevention of myocardial infarction. The analysis was based upon a Myocardial Infarction Register which started in 1970, cross-sectional and prospective population studies primarily among men which started in 1963, cross-sectional studies among men and women based upon population studies (the MONICA Project) as well as studies of myocardial infarction. We have also been involved in many intervention trials in primary and secondary prevention regarding physical training, beta-blockers, thrombolytics, aspirin, anti-arrhythmics, ACE-inhibitors and lipid lowering drugs. In the Primary Prevention Study it was found during a 16 years' follow-up that the coronary heart disease risk was related to entry level of serum cholesterol both among those who had signs of coronary heart disease or angina pectoris, as well as among those with no such previous coronary heart disease events at entry. For each cholesterol level, the risk was about seven times higher among those who had had a myocardial infarction compared to those without any coronary heart disease event at entry. In those with angina the risk was about three to four times higher. An example shows how important it is to take the so-called 'regression dilution bias' into account, which results in steeper risk factor-incidence curves. The concept of 'population attributable risk' is also discussed. It is a general finding that the many with moderate elevations of risk factors contribute to most disease events. This is true for smoking, serum cholesterol, blood pressure etc. Results from various prospective studies have repeatedly demonstrated three main risk factors for coronary heart disease: cholesterol, high blood pressure and smoking, and they explain more than 90% of infarct cases in the middle-aged population. Other risk factors, including psychological, are, however, also of some importance and they are discussed briefly. The Göteborg population studies started in 1963. The data to 1990 show that among men there has been a decline in serum cholesterol and blood pressure, which has resulted in a decline in risk for coronary heart disease of 37%, well compatible with the registered decline of 30-40% in coronary heart disease incidence among men aged 45-54 years. Simultaneously, there has been a marked decline, especially among men, of 28-day fatality among hospitalized patients, but because most deaths occur outside hospital the decline in incidence has had greater importance for overall coronary heart disease mortality. Several studies have demonstrated the importance of stopping smoking, at least after myocardial infarction. Other interventions after a myocardial infarction are also important for the outcome, which has improved considerably over the last 20 years. In the general population in whom there is no sign of coronary heart disease, it is important to reduce risk factors among the many with moderate risk, by stopping smoking and changing diet.