Thrombolytic therapy and secular trends (1985-1995) in long-term survival following acute myocardial infarction: the Minnesota Heart Survey
Both short-term and long-term survival of acute myocardial infarction (AMI) patients have improved remarkably during the 1980s and 1990s. We investigated the contribution of greater utilization of thrombolytic therapy to these secular trends, and compared the survival trends among AMI patients who received thrombolytic therapy to survival trends among their counterparts who did not. The sample included 4,515 patients aged 30-74 years (2743 men, 1772 women) who were discharged from Minneapolis-St. Paul hospitals in 1985, 1990, or 1995 and determined to have had a definite AMI by the study criteria. Age-adjusted three-year mortality following hospitalized AMI decreased significantly over that period from 30% in 1985 to 25% in 1990 to 20% in 1995, with no evidence of heterogeneity of the secular trend by gender. The regression-derived hazard ratio of death - adjusted for age, gender, and history of MI - was 0.61 (95% CI: 0.52,0.71) for AMI patients in 1995 as compared with their counterparts in 1985. The frequency of administration of thrombolytic therapy increased dramatically from 1985 to 1990 (13% to 28%) but did not increase further in 1995 (27%). We estimated the contribution of more frequent administration of thrombolytic therapy to the time trend by modeling an indicator variable for thrombolytic therapy use and computing the percentage decrease in the coefficient for the “year effect” (1995 vs 1985). According to this method, only 11% of the secular trend in AMI mortality could be attributed to greater use of thrombolytic therapy. There was no statistical evidence of differential secular trend by thrombolytic therapy status (p=0.57). However, the estimated reduction in three-year mortality (1995 vs 1985) was larger among AMI patients who did not receive thrombolytic therapy treatment (31% to 22%) than among their counterparts who received that therapy (21% to 16%). Although more frequent use of thrombolytic therapy accounted for some of the favorable trend in AMI survival, other components of AMI care and secondary prevention measures appear to have played an important role.