Patients in clinical trials of fibrinolytic agents have been shown to be younger, less often female, and to have lower risk characteristics and a better outcome compared with unselected patients with ST-elevation myocardial infarction. However, a direct comparison of patients treated with fibrinolytic agents and not enrolled versus those enrolled in a trial, including a large number of patients, has not been performed.

Prospective data from the Swedish Register of Cardiac Intensive Care on patients admitted with acute myocardial infarction treated with thrombolytic agents in 60 Swedish hospitals were linked to data on trial participants in the ASsessment of Safety and Efficacy of a New Thrombolytic (ASSENT)-2 trial of fibrinolytic agents. Baseline characteristics, treatments, and long-term outcome were evaluated in 729 trial participants (A2), 2048 nonparticipants at trial hospitals (non-A2), and 964 nonparticipants at other hospitals (non-A2-Hosp).

Nontrial patients compared with A2 patients were older and had higher risk characteristics and more early complications, although the treatments were similar. Patients at highest risk of death were the least likely to be enrolled in the trial. The 1-year mortality rate was 8.8% versus 20.3% and 19.0% (P < .001 for both) among A2 compared with non-A2 and non-A2-Hosp patients, respectively. After adjustment for a number of risk factors, the 1-year mortality rate was still twice as high in nontrial compared with A2 patients.

The adjusted 1-year mortality rate was twice as high in patients treated with fibrinolytic agents and not enrolled in a clinical trial compared with those enrolled. One major reason for the difference in outcome appeared to be the selection of less critically ill patients to the trial.