The smokers' MI paradox

OB/GYN News, Nov 15, 2001 by Sally Koch Kubetin

Smokers seem to have better clinical outcomes following an acute MI than nonsmokers do. Now cardiovascular epidemiologists have an explanation for this so-called smokers' paradox.

New data suggest a twofold explanation: Compared with nonsmokers, smokers are relatively younger at the time of their first MI and have a lower incidence of anterior MIs, which tend to be larger and more severe infarctions, Sarah R. Kermgard reported at the annual meeting of the American College of Cardiology.

She reviewed data from four of the Thrombolysis in Myocardial Infarction trials involving a total of 1,179 active smokers and 1,232 nonsmokers with acute MI. Univariate analysis demonstrated the smokers' paradox at work: 30-day mortality was 6.22% in nonsmokers, compared with 2.57% among smokers. The smokers also had a lower rate of intracranial hemorrhage: 0.71%, less than half the 1.51% rate in nonsmokers.

But the smokers were also significantly younger, with a mean age at the time of their MI of 54.4 years, compared with 62.4 years for nonsmokers. Moreover, angiographic data indicated that only 16.5% of smokers had triple-vessel disease, compared with 21.5% of nonsmokers. Smokers also had a significantly lower incidence of MIs attributed to left anterior descending coronary lesions, noted Ms. Kermgard, formerly of the University of California, San Francisco.

After differences in age and infarct artery location were corrected for in a multivariate analysis, there were no longer any significant differences between smokers and nonsmokers in terms of mortality or intracranial hemorrhage risk.