Interaction between income and education in predicting long-term survival after acute myocardial infarction

Abstract

Background Population-based data on the impact of socioeconomic status (SES) on long-term survival after myocardial infarction (Ml) are lacking. We evaluated the association of income and education with all-cause mortality and cardiac mortality post-MI and assessed income-by-education interaction. Design Prospective cohort study. Methods Between February 1992 and February 1993, 1521 consecutive patients aged 65 years or less (19% women) discharged from all hospitals in central Israel after incident acute MI were enrolled and followed up through December 2005. Data on SES indicators, cardiovascular risk factors, MI characteristics and severity, comorbidities, and acute treatment were assessed at baseline. Results Low SES, as defined by income and education, was associated with older age, female sex, and higher prevalence of risk factors and comorbidities. Further, low SES patients presented with more severe disease and received fewer cardiac procedures and medications. During follow-up, 427 patients died. Income and education strongly interacted ( P = 0.003). The hazard ratio for death associated with income (below average vs. average/above average) was considerably higher for less educated (≤12 years) patients [2.64, 95% confidence interval (CI): 1.92–3.63] than for more educated (≥12 years) patients (1.53, 95% CI: 1.02–2.29). Adjustment for various prognostic indicators attenuated these estimates, yet excess risk persisted for the less educated group (hazard ratio = 1.58, 95% CI: 1.13–2.21). Similar patterns were noted for cardiac mortality. Conclusion Among patients with incident MI, low SES is related to higher risk profile and poorer treatment. Low income is associated with a large increase in mortality risk when accompanied by low education, suggesting a double jeopardy phenomenon.