Acute Stroke Treatment With Mechanical Thrombectomy
What are the effects of mechanical thrombectomy (MT) for acute ischemic stroke in patients with evidence of diffusion-weighted imaging (DWI) hyperintensities on magnetic resonance imaging (MRI)?
The authors used data from a prospective registry of acute ischemic stroke patients treated with MT at two comprehensive stroke centers between January 2012 and August 2015. Patients treated with MT for an occlusion of the internal carotid artery or proximal middle cerebral artery and who had a DWI-ASPECTS score of ≤6 were included. DWI-ASPECTS is a technique to grade the extent of presumed brain infarction seen on MRI (DWI hyperintensities are thought to represent infarction). The score ranges from 0-10 with higher numbers indicating less infarct. The DWI-ASPECTS score was calculated by a neuroradiologist, blinded to the results of MT treatment. Clinical and demographic information was abstracted from patient charts. The MT treatment was not standardized; some patients received general anesthesia and others conscious sedation.
The primary outcome of the study was the percentage of patients who had a good functional outcome, defined by a modified Rankin scale (mRS) score of 0-2 at 90 days. (The mRS is a measure of disability ranging from 0-6, with 0 indicating no functional deficits and 6 indicating death.) The 90-day outcome measure was ascertained by nurses, blinded to DWI-ASPECTS score, via in-person or telephone interviews or after consultation with the patient’s primary care physician. Hemorrhagic complications were also evaluated.
During the study period, 854 patients were treated with MT and 218 were eligible for this analysis. About two-thirds of the patients had good recanalization after MT and the median time to reperfusion was 310 minutes. There was no difference in clinical or demographic factors, or DWI-ASPECTS score between patients who were recanalized with MT and those who were not. The patients who were successfully recanalized had better functional outcome at 90 days than those who were not recanalized (odds ratio for 1 point improvement in mRS, 2.38; 95% confidence interval [CI], 1.40-4.02). After adjustment for prognostic factors, patients who were recanalized continued to have better 90-day functional outcomes (mRS ≤2; adjusted risk ratio, 3.00; 95% CI, 1.71-5.29). Additionally, patients who were recanalized had lower mortality (22.6% vs. 39.1%; p = 0.013). There was no difference in hemorrhagic complications between patients who were reperfused and those who were not.
When outcomes were evaluated by stratifying DWI-ASPECTS groups, there was no association between successful reperfusion and functional outcome, mortality, or hemorrhagic complications in patients with a DWI-ASPECTS score of 0-4.
In patients with evidence of DWI changes on MRI (DWI-ASPECTS ≤6), MT with successful recanalization is associated with improved functional outcome.
A large component of eligibility for thrombolysis in acute ischemic stroke patients has traditionally been determined by duration of symptoms, along with computed tomography (CT) imaging findings. When there is evidence of extensive infarction on CT, patients are generally not eligible for thrombolysis. MRI with DWI is more sensitive than CT to evaluate for ischemia; and there has been debate in the stroke community about offering MT to patients with evidence of infarct on MRI, even if they present within an eligible time window, as reperfusing ischemic tissue is associated with hemorrhagic complications.
The results of this study are informative and suggest that for patients with DWI-ASPECTS scores of ≤6, recanalization with MT is not only safe, but effective. It is reassuring that despite the DWI changes seen on MRI, MT was not associated with an increased risk of intracerebral hemorrhage. Traditionally, DWI changes on MRI were thought to represent irreversible infarction; however, the finding from this study supports other data that suggest early DWI changes can be reversed with successful reperfusion. The subgroup analysis suggesting that patients with DWI-ASPECTS scores of 0-4 do not benefit from MT demonstrates that there may be a threshold effect and that extensive ischemic changes cannot be reversed with recanalization.
This is a registry from two centers and these findings need to be verified in a trial. Additionally, reperfusion occurred just after 5 hours in most patients in this study. Increased time from onset to reperfusion is likely to temper the beneficial effects of MT. While prethrombolysis MRI is more commonly being used to evaluate acute stroke patients at large stroke centers, it is difficult for most hospitals to perform these hyperacute MRIs.
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