Meta-analysis of the Smoker's Paradox in Acute Ischemic Stroke Patients Receiving Intravenous Thrombolysis or Endovascular Treatment.

Introduction: The existence of the smoker's paradox is controversial and potential mechanisms have not been explained. We aimed to explore the association between cigarette smoking and functional outcome at 3 months in patients with acute ischemic stroke who were treated with intravenous thrombolysis (IVT) or endovascular treatment (EVT).
Methods: This meta-analysis was conducted in accordance with the PRISMA guidelines. Studies exploring the association between smoking and good functional outcome (modified Rankin Scale score ≤ 2) following IVT or EVT were searched via the databases of PubMed, Embase, and the Cochrane Library from inception to August 8, 2018. Information on the characteristics of included studies was independently extracted by two investigators. Data were pooled using a random-effects or fixed-effects meta-analysis according to the heterogeneity of included studies.
Results: Among 20 identified studies, 15 reported functional outcomes following IVT, and five reported functional outcomes following EVT. Unadjusted analyses showed that smoking increased the odds of good functional outcomes with a pooled odds ratio (OR) of 1.48 (95% confidence interval [CI]: 1.36-1.60) after IVT and 2.10 (95% CI: 1.47-3.20) after EVT. Of IVT studies, only eight reported outcomes adjusted for covariates and none of the EVT studies reported adjusted outcomes. After adjustment, the relation between smoking and good functional outcome following IVT lost statistical significance (OR 1.14 [95% CI: 0.81-1.59]).
Conclusion: Our meta-analysis suggested that smoking was not associated with good functional outcome (mRS ≤ 2) at 3 months in patients with acute ischemic stroke who were treated with intravenous thrombolysis.
Implications: The existence of the smoker's paradox is controversial. A previous letter by Plas et al. published in 2013 reported a positive result for the association between smoking and good functional outcome at 3 months in acute ischemic stroke patients who received intravenous thrombolysis (IVT). However, a major limitation of their meta-analysis was that the process of data synthesis was based on unadjusted data. Therefore, we conducted this meta-analysis to investigate the association based on adjusted data and a larger sample size. Our meta-analysis suggested that smoking was not associated with good functional outcome after adjusting for covariates.
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