Menon BK, Qazi E, Nambiar V, Foster LD, Yeatts SD, Liebeskind D, et al. for the IMS III Investigators. Differential Effect of Baseline Computed Tomographic Angiography Collaterals on Clinical Outcome in Patients Enrolled in the Interventional Management of Stroke III Trial. Stroke. 2015
There has been increasing evidence that leptomeningeal collaterals play a significant role in determining outcomes during acute ischemic stroke. Collaterals maintain blood flow to the brain that would otherwise rapidly die during an acute ischemic stroke. Previously, collaterals were evaluated using catheter angiography or inferred using perfusion imaging. With the advent of non-invasive CT angiography, it has become possible to visualize collateral status in acute ischemic stroke patients. The authors of this study performed an interesting analysis in light of recent positive endovascular treatment trials like ESCAPE and applied CTA based collateral scoring to the IMS III cohort of patients.
Of the 656 patients who were enrolled in the IMS III study, 306 patients underwent baseline CTA. After exclusion, 185 patients who had intracranial M1 MCA +/- intracranial ICA occlusions were analyzed to ascertain collateral status using three separate scoring systems. Of the 185 patients analyzed, 126 patients were in the endovascular therapy arm and 59 patients were in the IV tPA arm. In multivariable modeling, the three collateral scores were each significant predictors of 90 day mRS 0-2 within their respective models (p-values <0.01 for all scores) while the effect of type of treatment (IV tPA alone vs. endovascular therapy) was not significant (all p values > 0.05). Analysis looking at secondary clinical outcomes included 90 day mrS 0-1 which showed statistically significant difference in rate of good clinical outcome between treatment types, favoring endovascular therapy, noted in patients with intermediate collateral status (p<0.05).
Further analysis of the IMS-III cohort of patient’s show that collateral status influence outcomes and those with intermediate collaterals seem to benefit the most from endovascular therapy. With the ESCAPE trial, collateral status was used as an inclusion criteria (patients with poor collaterals being excluded from the trial) and outcomes improved significantly in the endovascular group vs the IV tPA group. MR-CLEAN which was a study that did not use collateral status as an inclusion criteria did not have as significant overall good outcomes as the other published endovascular trials. Possibly because they included patients with poor collaterals, who don’t benefit from either endovascular or IV tPA treatments as the infarct grows too rapidly for recanalization to have an effect. Had IMS-III recruited patients based on collateral status as in ESCAPE, we may have had a positive trial three years earlier. As we continue to understand the pathophysiological reasons for the success of the recent endovascular trials, we should continue to fine tune and further explore therapy to maximize our chance of success. Future studies that look at augmenting collaterals during acute ischemic stroke would not only improve the results of these therapies but early initiation of these therapies (in the ambulance) may have neuroprotective effects that should be explored.