Environmental Exposure and Long-Term Mortality After Coronary Artery Bypass Grafting: A Multicenter Cohort Study...

Background: Ambient air pollution is an established cardiovascular risk factor; however, its impact on long-term outcomes after coronary artery bypass grafting (CABG) remains insufficiently defined. We aimed to evaluate whether chronic exposure to air pollutants may influence long-term mortality following surgical revascularization. Methods: In this multicenter retrospective cohort study, 1033 consecutive patients undergoing CABG with BIMA (bilateral internal mammary arteries) grafting were analyzed with a median follow-up of 8.1 years. Individual exposure to nitrogen dioxide (NO₂), particulate matter ≤10 μm (PM₁₀), and ≤2.5 μm (PM_2.5) was estimated based on residential data. Multivariable Cox proportional hazards models were used to assess associations with long-term mortality. Model performance was evaluated using receiver operating characteristic (ROC) analysis, while incremental prognostic value was quantified using net reclassification improvement (NRI) and integrated discrimination improvement (IDI). Kaplan-Meier analyses were performed using data-driven thresholds and model-based risk stratification. Results: During follow-up, 220 deaths (21.1%) occurred. In multivariable analysis, both NO₂ and PM₁₀ were associated with increased mortality (NO₂: HR 2.70 per 10 μg/m³, 95% CI 2.03-3.59; PM₁₀: HR 2.73 per 10 μg/m³, 95% CI 1.94-3.83; both p < 0.001), whereas PM_2.5 was not significant. The clinical model demonstrated moderate discrimination (AUC 0.73), which improved significantly after inclusion of pollution variables (AUC 0.84; ΔAUC 0.11). Reclassification analysis showed substantial improvement (NRI 0.42, p < 0.001; IDI 0.11, p < 0.001). Kaplan-Meier analysis confirmed enhanced risk stratification, with a hazard ratio of 2.70 for the clinical model and 7.02 for the combined clinical and pollution model (both p < 0.001). Conclusions: In this retrospective cohort of patients undergoing CABG with BIMA grafting, higher long-term residential exposure to NO₂ and PM₁₀ was associated with greater all-cause mortality after adjustment for measured clinical and procedural factors. These findings support further investigation of environmental exposure as a prognostic marker in surgically treated coronary disease, pending external validation and more granular control for contextual confounding. These findings suggest that environmental exposure may represent a relevant component of long-term risk stratification, although confirmation in large-volume cohorts is required.