Association of clinical trial participation after myocardial infarction with socioeconomic status, clinical characteristics, and outcomes

Aims To investigate whether participants in clinical trials after myocardial infarction (MI) are representable for the post-MI population concerning characteristics, secondary prevention, and prognosis. Methods and results Cohort study on 31 792 attendants to 1-year revisits after MI throughout Sweden (n = 2941 clinical trial participants) between 2008 and 2013 identified in the Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART). Individual-level data on socioeconomic status (SES) (disposable income, educational level, and marital status) and outcomes (first recurrent non-fatal MI, coronary heart disease death, fatal or non-fatal stroke until study end 2018) were linked from other national registries. Trial participants were more likely to be men [risk ratio 1.09; 95% confidence interval (CI) 1.07–1.11], and married (1.07; 1.04–1.10), have a highest-quintile income (1.42; 1.36–1.48), and post-secondary education (1.25; 1.18–1.33), while less likely to have a history of MI (0.88; 0.80–0.97), be persistent smokers (0.83; 0.75–0.92) and have left ventricular dysfunction (0.59; 0.44–0.79) compared to non-participants. During a mean 6.7-year follow-up, 5206 outcome events occurred. Risk was lower in trial participants (hazard ratio 0.80; 95% CI 0.72–0.89), also after adjusting for clinical characteristics and post-MI therapies (0.85; 0.77–0.94) and additionally for SES (0.88; 0.79–0.97). Conclusions Clinical trial participants post-MI are more often male, have higher SES, a more advantageous risk profile, and better prognosis. Additional unmeasured participation bias was implied. Questionable external validity of post-MI trials highlights the importance of complementary studies using real-world data.