Background and Purpose—Studies have established a relation between recanalization and improved clinical outcome in acute ischemic stroke patients; however, intra-arterial clot size has not been routinely assessed. The aim of the study was to determine the impact of intra-arterial thrombus burden on intra-arterial treatment (IAT) and clinical outcome.

Methods—A retrospective review of our IAT stroke database included procedure time, recanalization, symptomatic intracranial hemorrhage, poor outcome (modified Rankin Scale score 4 at discharge), and mortality. The modified Thrombolysis in Myocardial Infarction thrombus grade was dichotomized into grades 0 to 3 (no clot or moderate thrombus, <2 vessel diameters) versus grade 4 (large thrombus, >2 vessel diameters).

Results—Data were collected on 135 patients with thrombus grading. The baseline median National Institutes of Health Stroke Scale score was higher in patients of grade 4 compared with grades 0 to 3 (19 vs 17, P=0.012). Grade 4 thrombi required longer (median, range) times for IAT (113, 37 to 415 minutes vs 74, 22 to 215 minutes, respectively; P<0.001) and higher rates of mechanical clot disruption (wire, angioplasty, snare, stent, or Merci retriever) compared with grades 0 to 3 (76% vs 53%, P=0.005). There were no differences in rates of symptomatic intracranial hemorrhage (6.6% vs 4.1%, P=0.701) or recanalization (50% vs 61%, P=0.216) in grade 4 versus grades 0 to 3. Multivariate analysis adjusted for age, baseline National Institutes of Health Stroke Scale score, and artery of involvement showed that grade 4 thrombi were independently associated with poor outcome (odds ratio=2.4; 95% CI, 1.06 to 5.57; P=0.036) and mortality (odds ratio=4.0; 95% CI, 1.2 to 13.2; P=0.023).

Conclusions—High thrombus grade as measured by the modified Thrombolysis in Myocardial Infarction criteria may be a risk factor that contributes to poor clinical outcome.