Hazard function and secular trends in the risk of recurrent acute myocardial infarction: 30 years of follow-up of more than 775,000 incidents.

BACKGROUND: The incidence of a first acute myocardial infarction (AMI) has fallen considerably during the last decades. However, no previous studies have analyzed the underlying hazards function of experiencing a recurrent AMI, and none has analyzed the change of risk for a recurrent AMI over the last 3 decades. METHODS AND
RESULTS: The study was based on the Swedish national myocardial infarction register. The register contained more than 1 million AMI events. After exclusion of events occurring in subjects younger than 20 or older than 84 years and events with uncertain first AMI status, 775 901 events occurring between 1972 and 2001 remained for analysis. During the study period, the risk of a new event among survivors of a previous AMI decreased sharply during the first 2 years after the previous event, had its minimum after 5 years, and then increased slowly again. The risk for a recurrent AMI during the first year after a previous event was fairly stable over the years until the late 1970s and then decreased by 36% in women and 40% in men until the late 1990s, irrespective of age and AMI number, mirroring the incidence decrease over the years for primary events.
CONCLUSIONS: The risk of a recurrent AMI event was highly dependent on time from the previous event, a novel finding which may affect risk scoring. There were strong secular trends toward diminishing risk for a recurrent AMI in recent years, even when other outcome affecting variables were taken into account.