Association between smoking burden and one-year mortality in ST-elevation and non-ST-elevation myocardial infarction: insights from a regional cohort

Introduction : Cigarette smoking is a major modifiable risk factor for cardiovascular disease and acute myocardial infarction (MI). The prognostic impact of cumulative smoking exposure (pack-years) on post-MI outcomes remains uncertain. The controversial “smoker’s paradox” suggesting better short-term prognosis in smokers has been largely attributed to younger age and fewer comorbidities. Prior studies frequently failed to quantify smoking intensity, stratify by MI subtype (STEMI vs. NSTEMI), or adequately adjust for confounders such as age and renal function. Aim : This study examined whether cumulative smoking burden is independently associated with one-year all-cause mortality after MI. Materials and methods : In this retrospective cohort study from a tertiary center in Western Iran (December 2019–August 2020), 1,019 confirmed MI patients were classified as never-smokers (0 pack-years), moderate smokers (≤15 pack-years), and heavy smokers (>15 pack-years). Cox proportional hazards models (crude, age-adjusted, and fully adjusted for age, sex, diabetes, hypertension, BMI, lipids, eGFR, reperfusion therapy, and systolic blood pressure) estimated hazard ratios for one-year mortality. Proportional hazards assumptions were confirmed (Schoenfeld residuals p >0.05). Bias was minimized through multivariable adjustment and sensitivity analyses. Results : Smokers were younger, predominantly male, and had fewer comorbidities. In STEMI, heavy smokers exhibited lower crude mortality than never-smokers, but this vanished after adjustment. No differences emerged across smoking categories in NSTEMI. Age and reduced eGFR consistently predicted mortality in both subtypes. Conclusions : Cumulative smoking burden showed no independent association with one-year post-MI mortality. The smoker’s paradox is explained by confounding, especially age and renal function. Smoking cessation remains essential for secondary prevention.