Safety and Efficacy of MCA-M2 Thrombectomy in Delayed Time Window: A Propensity Score Analysis From the STAR Registry

Mechanical thrombectomy of middle cerebral artery M2 segment occlusion of the middle cerebral artery has reported safety and efficacy in recent post-hoc and observational studies. However, there is no known benefit of mechanical thrombectomy for patients with M2 segment occlusions in the delayed time window (>6 hours).

The Stroke Thrombectomy and Aneurysm Registry (STAR) is a prospective, multicenter, nonrandomized observational study registry for acute ischemic stroke thrombectomy and aneurysm treatment. We analyzed all patients who underwent mechanical thrombectomy within the late time window (>6 hours from symptom onset) involving isolated M2 occlusions. We used propensity score matching to select a comparison group of patients who underwent mechanical thrombectomy for M1 occlusion in the same time window.

Of 1083 consecutive patients analyzed, propensity matching yielded 180 well matched M1 and M2 pairs. Baseline demographics were well balanced between the groups (M1 and M2). Alberta stroke program early CT score (7.6±1.7 versus 8.3±1.5; P<0.001) was higher in the M2 group. There was a trend towards less complete recanalization (Thrombolysis in Cerebral Infarction 3) 46.1% versus 39.9% (P=0.053) in the middle cerebral artery M2 segment cohort. However, successful recanalization (Thrombolysis in Cerebral Infarction 2b-3) was better in middle cerebral artery M2 segment cohort (85% versus 90.5%; P=0.053). Postprocedural asymptomatic hemorrhage rates were similar (29.4% versus 27.8%; P=0.816), but symptomatic hemorrhage rates were higher in the M1 group (7.2% versus 2.2%; P=0.047). Rates of good clinical outcome (modified Rankin scale 0-2) were similar at final follow-up (43.9% versus 46.7%; P=0.672). The overall mortality was also similar between the cohorts (12.8% versus 13.9%; P=0.877).

In our analysis of the Stroke Thrombectomy and Aneurysm Registry, M2 occlusions not only achieved similar rates of recanalization and good functional outcome compared with M1 occlusions in a delayed time window (6-24 hours from last normal) but also had less symptomatic intracranial hemorrhage.