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Explanations for the 'smoker's paradox' in cardiac resuscitation

Nature Reviews Cardiology volume 11, page 553 (2014)Cite this article

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In her Research Highlight (Cardiac resuscitation: The 'smoker's paradox' after in-hospital cardiac arrest. Nat. Rev. Cardiol. 11, 374; 2014),1 Alexandra Roberts focuses on the large observational analysis by Gupta and colleagues on in-hospital cardiac arrest.2 According to this analysis, smokers have higher survival rates and better neurological outcome after in-hospital cardiac arrest than nonsmokers.2 The finding was explained by the investigators as an effect of ischaemic preconditioning,3 whereby tobacco smoke causes regular hypoxic effects4 leading to frequent minor ischaemia and subsequent reperfusion.1,2,3,5,6 As a result, the tissue becomes preconditioned to reperfusion.2,3,6 Preconditioning mitigates the paradoxically harmful effects of reperfusion on the tissue, which occur as a result of cardiac resuscitation after major ischaemia or cardiac arrest.1,2,3,5,6

Although the phenomenon of ischaemic preconditioning is a possible explanation for the smoker's paradox, at least two alternative explanations exist. First, in the analysis by Gupta and colleagues, significantly more smokers had a primary diagnosis of acute myocardial infarction than nonsmokers (14.8% vs 9.1%; P <0.001).2 Although the researchers adjusted for this factor in the statistical analysis, the indirect effects were not considered. A primary diagnosis of acute myocardial infarction means that the patient is usually first treated in the emergency room or the cardiac catheterization laboratory, and subsequently transferred to an intensive care ward. In these locations, defibrillators are available and patients are constantly monitored (that is, time to defibrillation is usually short). As a consequence, survival and neurological outcome are better among these patients. This difference is likely to have at least partially contributed to the observed smoker's paradox.

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References

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  1. Department of Internal Medicine, University Hospital, University of Basel, Am Petersgraben 4, Basel, 4031, Switzerland

    Rainer Spiegel

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  1. Rainer Spiegel
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Correspondence to Rainer Spiegel.

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Spiegel, R. Explanations for the 'smoker's paradox' in cardiac resuscitation. Nat Rev Cardiol 11, 553 (2014). https://doi.org/10.1038/nrcardio.2014.73-c1

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