Karissa C Arthur, MD
@KCArthurMD
Middle cerebral artery M2 segment occlusions represent about one-sixth of large vessel occlusions in the United States, though were underrepresented in early time window mechanical thrombectomy (MT) trials. However, data from several of these trials suggest that MT for M2 occlusions is safe with low risk of intracerebral hemorrhage and has similar clinical outcomes and mortality to M1 occlusions. Given the paucity of data on the safety and feasibility of MT for M2 occlusions, Jumaa et al. sought to evaluate the STRATIS registry to compare MT safety, rate of good clinical outcomes, and time dependence of MT benefit between M2 and M1 occlusions.
The STATIS registry is a prospective, multicenter, nonrandomized, observational study that evaluated the use of the Solitaire stent retriever in large vessel occlusions. It consists of 1,000 patients aged 18 or older with confirmed anterior circulation large vessel occlusions at 55 centers between August 2014 and June 2016. This subgroup analysis compared patients with M1 occlusions to those with M2 occlusions in terms of baseline characteristics, baseline National Institutes of Health Stroke Scale (NIHSS) and Modified Rankin Scale (mRS), IV recombinant tissue plasminogen activator (tPA) use, and workflow and procedural characteristics. Outcomes included good functional outcome (mRS of 0 to 2 at 90 days), successful reperfusion (modified Thrombolysis in Cerebral Infarction [mTICI] ≥ 2b), as well as safety outcomes such as symptomatic intracranial hemorrhage, worsening of NIHSS ≥4 within 24 hours, or vessel perforation during MT. The authors also dichotomized the M2 group into 90-day mRS score of 0-2 versus 0-1 to identify factors that influenced clinical outcome.
A total of 984 patients were included, of which 538 (54.7%) had M1 and 170 (17.3%) had M2 occlusions. Results showed that baseline demographics did not differ significantly between groups. The M2 occlusion group had a significantly lower baseline NIHSS (15.7±5.0 versus 17.3±5.5, P≤0.001) and higher ASPECTS score (8.7±1.4 versus 8.2±1.4, p < 0.001). There was no significant difference in IV r-tPA use between the two groups (63% versus 66%, P=0.38). Arrival to groin puncture time was longer in the M2 population (89.5±46.8 versus 78.3±50.2 minutes, P=0.02), but arrival to revascularization, onset to arrival, and onset to groin puncture time was similar between groups. Procedural characteristics, including mean number of passes and rates of reperfusion, were similar between the two groups. Rates of good functional outcome and mortality were similar between the two groups, though patients in the M2 group had a significantly higher rate of symptomatic intracranial hemorrhage (4% versus 1%, P=0.01). The authors also found that in patients with M2 occlusion with mRS score 0-1 at 90 days, factors that contributed to functional outcome included hypertension (OR, 0.09 [95% CI, 0.02–0.49], P=0.005), prestroke mRS (OR, 0.41 [95% CI, 0.19–0.91], P=0.03), baseline NIHSS (OR, 0.88 [95% CI, 0.80–0.97], P=0.008), and groin puncture to revascularization time (OR, 0.97 [95% CI, 0.95–0.99], P=0.002).
Overall, this subgroup analysis of the STRATIS registry showed that MT for M2 occlusions had similar rates of good functional outcome, successful reperfusion, and mortality compared with M1 occlusions. However, the M2 population had significantly more symptomatic intracerebral hemorrhage. The authors hypothesize that the distal location of the occlusion, with narrower diameter and thinner walls, may lead to increased risk of intracranial hemorrhage. While they did find that there was longer arrival to groin puncture times, perhaps representing a hesitancy to treat compared to more proximal occlusions, there was no difference in the association of time on good functional outcome.
There were several limitations to this study. There was no medical management arm, and, therefore, it is unclear if MT is superior to medical management only. Patients who presented with symptom onset >8 hours prior to treatment were not included, and, therefore, data cannot be applied to a later time window. In addition, the primary device used was Solitaire, and, therefore, techniques cannot be commented on, and it is possible that other techniques are better suited for M2 occlusions. Lower stroke severity in the M2 occlusion group, lack of 24-hour imaging, and lack of data on the dominance of the M2 divisions are also limitations. Further research is necessary to evaluate the benefit of MT for M2 occlusions, especially in a later time window.
