Endovascular Thrombectomy for Acute Ischemic Stroke
What is the relationship between endovascular mechanical thrombectomy (stroke treatment) and clinical outcomes among patients with acute ischemic stroke?
A systematic review was done to identify potential multicenter randomized clinical trials through August 2015. Studies were included in the meta-analysis if they met the following criteria: enrolled adults, compared endovascular stroke treatment with intravenous (IV) tissue plasminogen activator (tPA), and reported functional outcome using the modified Rankin scale (mRS). The mRS is a 7-point (0-6) ordinal scale that measures functional status. Studies that did not include IV tPA in the control group were excluded. Standard measures were used to assess for bias in the published trials. The primary outcome was mRS score at 90 days (measured by proportional odds ratio [OR]), although functional independence (mRS 0-2), 90-day all-cause mortality, and symptomatic intracerebral hemorrhage were also evaluated. The authors also looked for patient, imaging, or treatment characteristics that were associated with improved functional outcome at 90 days.
Data from eight trials encompassing a total of 2,423 patients were included. Fifty-four percent of the patients were treated with endovascular therapy. The average time from stroke onset to endovascular treatment was 3.8 hours (standard deviation 1.2 hours). Endovascular treatment was associated with an increase in the odds of a good functional outcome (OR, 1.56; 95% confidence interval [CI], 1.14-2.13). Patients treated with endovascular therapy were 12% more likely to be functionally independent at 90 days (mRS 0-2) (OR, 1.71; 95% CI, 1.18-2.49), leading to a number needed to treat of eight. There was no difference in the rates of symptomatic intracranial hemorrhage (OR, 1.12; 95% CI, 0.77-1.63) or all-cause mortality (OR, 0.87; 95% CI, 0.68-1.12). As there was heterogeneity (I2 = 75.4%) in the outcome of functional improvement, subgroup analyses were done to evaluate the efficacy of endovascular versus standard treatment. Imaging confirmed proximal artery occlusion (OR, 2.24; 95% CI, 1.72-2.90), combined IV tPA and endovascular treatment (OR, 2.07; 95% CI, 1.46-2.92), and the use of contemporary stent retriever devices (OR, 2.39; 95% CI, 1.88-3.04) were associated with improved functional outcome. Age, stroke severity (as measured by the National Institutes of Health Stroke Scale), and time to randomization were not associated with improved outcomes.
In patients with acute ischemic stroke, endovascular therapy when compared with standard treatment, including IV tPA, is associated with improved functional outcomes and no increased risk of mortality or symptomatic intracerebral hemorrhage.
Initial randomized trials of endovascular stroke treatment did not show a benefit; however, recently published studies have shown an association between endovascular treatment and improved functional outcome. This meta-analysis is valuable because it pools studies to get a better estimate of the true benefit of this therapy. The improved functional outcomes with endovascular treatment are achieved without an increased risk of bleeding or mortality. Factors that were associated with improved outcomes include use of contemporary stent retriever devices, which are associated with better recanalization, and confirmation of a large vessel occlusion on computed tomography angiography or magnetic resonance angiography prior to treatment. While the results of these trials and this meta-analysis will change practice, some caution is warranted. Four of the trials were halted in interim analyses after the MR CLEAN trial was published. This may lead to an overestimation of effect size. Time to treatment, one of the most important factors in outcome, was not captured in this meta-analysis. Despite these limitations, the number needed to treat of eight to achieve functional independence means that endovascular treatment for acute ischemic stroke patients with large vessel occlusion has rapidly become the standard of care.
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