Objectives: The paradoxical effect of smoking after acute myocardial infarction (AMI) is a phenomenon consisting of a reduction in the mortality of smokers compared to nonsmokers. However, it is not known whether the benefit of this reduction in mortality is due to smoking itself or to other covariables. Despite acceptance of the paradoxical effect of smoking in AMI, it is not known whether a similar phenomenon occurs in unstable angina. The objective of this study was to investigate the paradoxical effect of smoking in AMI and unstable angina, and to study specifically whether smoking is an independent prognostic variable.
Methods and results: The study population was selected from the multicentric ARIAM (Análisis del Retraso en el Infarto Agudo de Miocardio [analysis of delay in AMI]) Register, a register of 29,532 patients with a diagnosis of unstable angina or AMI. Tobacco smokers were younger, presented fewer cardiovascular risk factors such as diabetes or hypertension, fewer previous infarcts, a lower Killip and Kimball class, and a lower crude and adjusted mortality in AMI (odds ratio, 0.774; 95% confidence interval, 0.660 to 0.909; p = 0.002). Smokers with unstable angina were younger, with less hypertension or diabetes. In the multivariate analysis, no statistically significant difference in mortality was found.
Conclusions: The reduced mortality observed in smokers with AMI during their stay in the ICU cannot be explained solely by clinical covariables such as age, sex, other cardiovascular factors, Killip and Kimball class, or treatment received. Therefore, smoking may have a direct beneficial effect on reduced mortality in the AMI population. The lower mortality rates found in smokers with unstable angina are not supported by the multivariate analysis. In this case, the difference in mortality can be explained by the other covariables.