Relationship Between the Smoking Index and the Extent of Coronary Artery Involvement in Patients With Acute Myocardial Infarction and a History of Smoking: A Complementary Evaluation Using the SYNTAX I Score

Introduction: Smoking is a major modifiable risk factor for acute myocardial infarction (AMI); however, the relationship between cumulative smoking exposure and the extent of coronary artery disease (CAD) remains under investigation. Objective: To evaluate the association between cumulative smoking exposure (smoking index) and the extent of coronary involvement in AMI events with documented smoking history and coronary angiography, and to examine its relationship with the SYNTAX I score as a complementary analysis. Methods: This was an observational, analytical, cross-sectional study based on a retrospective review of medical records from the Hemodynamics Service at Hospital Centenario Miguel Hidalgo (December 2022–December 2025). Of 400 initial records, 390 AMI events were retained; the primary analysis included 388 events with coronary angiography from 370 individuals. The smoking exposure analysis included 253 events from 244 individuals with a documented smoking history. Spearman correlations with bootstrap confidence intervals (95% CI) clustered by individual and logistic regression models adjusted for age, sex, hypertension, diabetes, and dyslipidemia, with clustered standard errors by individual, were performed. Results: Among the 388 AMI events, mean age was 62.8 ± 12.2 years; 273 (70.4%) occurred in men, 187 (48.2%) had multivessel disease, and 102 (26.3%) had three-vessel disease. Among the 253 events with a smoking history, the median smoking index was 19.5 pack-years (IQR 5.0–40.0). For every 10 pack-years, the adjusted odds ratio (OR) was 0.975 (95% CI: 0.875–1.085; p = 0.640) for multivessel disease and 0.954 (95% CI: 0.813–1.120; p = 0.568) for three-vessel disease. The correlation with the number of diseased vessels was −0.093 (95% CI: −0.216 to 0.032); with the SYNTAX I score, available in 135 events from 132 individuals, it was −0.108 (95% CI: −0.276 to 0.066). Sensitivity analyses yielded the same overall interpretation. Conclusions: No statistically conclusive evidence of an association was found between the smoking index and multivessel or three-vessel coronary disease in this population. The selective availability of SYNTAX I scores limits the interpretation of coronary anatomical complexity; therefore, this analysis is complementary and cannot be generalized to the entire study population. These findings do not demonstrate the absence of an effect, a protective effect of smoking, or causal mechanisms underlying AMI.