Under (back) pressure: Better collateral flow may facilitate clot removal in ischemic stroke: A systematic review and meta-analysis

Background: Collateral status may facilitate clot removal and affect rates of successful reperfusion following endovascular therapy (EVT) for acute ischemic stroke (AIS). Methods: Following the PRISMA guidelines, a systematic literature review of the English language literature was conducted using PubMed, Scopus, Web of Science, and Embase. Papers which focused on collateral status and patients treated with EVT for AIS were included in our analysis. Outcomes of interest included collateral score grading, rates of successful reperfusion defined as thrombolysis in cerebral infarction (TICI) score 2b-3 and onset to revascularization time. We calculated pooled odds ratio (OR) or mean difference (MD) and their corresponding 95% confidence intervals (CI) based on collateral status. Results: 16 studies, with 6073 patients, were included in our analysis. Among the included studies, there were six different collateral grading scales, which were dichotomized into “good to moderate” and “poor” collaterals. Odds of successful reperfusion were significantly higher among patients with good to moderate collateral circulation compared to those with poor collaterals (OR = 1.61; 95% CI = 1.24 to 2.09; P-value < 0.001); however, there was heterogeneity among included studies (I2= 5 4%; P-value = 0.008). Onset to revascularization time was comparable between patients with good to moderate collateral circulation compared to those with poor collaterals (MD = 3.91 min; 95% CI = −8.71 to 16.53; P-value = 0.544); however, there was heterogeneity among included studies (I2= 60%; P-value = 0.014). Conclusions: The presence of good collaterals may increase the odds of achieving successful reperfusion following EVT for AIS. Improved collateral flow was associated with improved angiographic outcomes, although future work is needed to determine if a causal relationship exists.