Paradoxical Effect of Smoking in the Spanish Population With Acute Myocardial Infarction or Unstable Angina
From the Intensive Care Unit (Dr. Ruiz-Bailén), Critical Care and Emergency Department, Hospital de Poniente, El Ejido, Almería.
Objectives: The paradoxical effect of smoking after acute myocardial infarction (AMI) is aphenomenon 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 theparadoxical 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. Tobaccosmokers 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, nostatistically significant difference in mortality was found.
* acute myocardial infarction
* cigarette smoking
* unstable angina
The association between smoking and heart disease was first suspected in the early 20th century. Subsequently, the direct relationship between smoking and development of coronary artery disease was confirmed. Smoking is associated witha higher incidence of acute myocardial infarction (AMI) and a higher incidence of death due to coronary artery disease. There is a clear dose-effect relationship that is minimized or eliminated after giving up smoking.Tobacco smoking is a predictive, independent variable for coronary atherosclerosis, AMI, and sudden death.
There are multiple causes of this poor prognosis in smokers including,particularly, the following: (1) induction of states of hypercoagulability, as shown in human and animal studies that demonstrate that tobacco exposure increases fibrinogen levels and causes platelet aggregation, which in turn may enhance development of atherosclerosis and increase coronary artery occlusion in earlier stages of atheromatous disease by promoting platelet aggregation and thrombosis ;(2) nicotine-induced catecholamine release leads to increased heart rate, BP, and even arrhythmogenic effect ; and (3) induction of coronary artery vasoconstriction and reduction in oxygen delivery due to increased carbon monoxide levels
In view of the above, it would seem to be logical that tobacco smokers will have higher mortality rates than nonsmokers after AMI. However, this hypothesis hasnot been demonstrated. Rather, there is evidence that smokers with AMI have lower mortality, a finding known as the paradoxical effect of smoking. Many explanations have been proposed for the more favorable prognosis of smokers after AMI including, particularly, the following: (1) smokers are younger and less seriously ill, or have fewer comorbid conditions; (2) smokers have fewer cardiovascularrisk factors; (3) coronary artery lesions are smaller; (4) there is greater myocardial preconditioning and/or greater coronary artery reperfusion, either spontaneous or due to greater efficacy of the thrombolysis acting on a thrombus, during the early phases of coronary atherosclerosis; (5) prehospital mortality is possibly higher in smokers; and (6) sudden withdrawal of smoking could have a...