Relative importance of improved hospital treatment and primary prevention. Results from 20 years of the Myocardial Infarction Register, Göteborg, Sweden

OBJECTIVE: To analyse to what extent declines in incidence and mortality of coronary artery disease can be attributed to improved hospital and post-hospital treatment in contrast to how much is due to primary prevention. DESIGN: A register for non-fatal and fatal myocardial infarction and sudden coronary death registered in in-hospital as well as out-of-hospital events between 1975 and 1994. SETTING: City of Göteborg, Sweden, with 450,000 inhabitants. RESULTS: Seventy-one per cent of the decline in attacks could be attributed to a decline in first infarctions. Of the decrease in coronary deaths, 63% was due to a decline in out-of-hospital mortality. Previous registrations for myocardial infarction were considerably more common amongst people who died in hospital (29%) than amongst those who died out-of-hospital (11-16%) or who survived an infarction (11-13%). Out-of-hospital resuscitation contributed to about half of the reduction in out-of-hospital mortality. Thus, most of the decline in incidence and about half of the decline in sudden coronary deaths was due to primary preventive measures. Population data on risk factors indicate a decline of 37% between 1963 and 1995 in coronary risk amongst consecutive cohorts of 50-year-old men in the community. CONCLUSION: Out-of-hospital resuscitation, treatment in coronary care units and post-infarct treatment improved considerably, but changes in primary risk factors were also of major importance for the decline in incidence and mortality.