Mechanical Thrombectomy for Isolated M2 Occlusions: A Post Hoc Analysis of the STAR,SWIFT, and SWIFT PRIME Studies

BACKGROUND AND PURPOSE:Mechanical thrombectomy is beneficial for patients with acute ischemic stroke and a proximal anterior occlusion, but it is unclear if these results can be extrapolated to patients with an M2 occlusion. The purpose of this study was to examine the technical aspects, safety, and outcomes of mechanical thrombectomy with a stent retriever in patients with an isolated M2 occlusion who were included in 3 large multicenter prospective studies.MATERIALS AND METHODS:We included patients from the Solitaire Flow Restoration Thrombectomy for Acute Revascularization (STAR), Solitaire With the Intention For Thrombectomy (SWIFT), and Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment (SWIFT PRIME) studies, 3 large multicenter prospective studies on thrombectomy for ischemic stroke. We compared outcomes and technical details of patients with an M2 with those with an M1 occlusion. All patients were treated with a stent retriever. Imaging data and outcomes were scored by an independent core laboratory. Successful reperfusion was defined as modified Thrombolysis in Cerebral Infarction score of 2b/3.RESULTS:We included 50 patients with an M2 and 249 patients with an M1 occlusion. Patients with an M2 occlusion were older (mean age, 71 versus 67 years; P = .04) and had a lower NIHSS score (median, 13 versus 17; P < .001) compared with those with an M1 occlusion. Procedural time was nonsignificantly shorter in patients with an M2 occlusion (median, 29 versus 35 minutes; P = .41). The average number of passes with a stent retriever was also nonsignificantly lower in patients with an M2 occlusion (mean, 1.4 versus 1.7; P = .07). There were no significant differences in successful reperfusion (85% versus 82%, P = .82), symptomatic intracerebral hemorrhages (2% versus 2%, P = 1.0), device-related serious adverse events (6% versus 4%, P = .46), or modified Rankin Scale score 0–2 at follow-up (60% versus 56%, P = .64).CONCLUSIONS:Endovascular reperfusion therapy appears to be feasible in selected patients with ischemic stroke and an M2 occlusion.

Recent data have shown that mechanical thrombectomy (MT) with a stent retriever is safe and improves functional outcome in patients with acute ischemic stroke and an occlusion of the anterior circulation.^1–5 It is unclear, however, if these results can be extrapolated to patients with an occlusion of the second segment of the middle cerebral artery (M2 occlusion). Because of its distal location, smaller diameter, and thinner walls, MT of the M2 segment is technically more challenging and may be associated with a higher risk of periprocedural complications. The potential benefit of reperfusion may also be different, in part because M2 occlusions generally respond better to IV thrombolysis.⁶The number of patients with an M2 occlusion in the thrombectomy trials was small. The Multicenter Randomized Clinical trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands (MR CLEAN) protocol did allow recruitment of these patients, but <8% of included patients had an isolated M2 occlusion.¹ In the Endovascular Revascularization With Solitaire Device Versus Best Medical Therapy in Anterior Circulation Stroke Within 8 Hours (REVASCAT), Endovascular Treatment for Small Core Proximal Occlusion Ischemic Stroke (ESCAPE), and Extending the Time for Thrombolysis in Emergency Neurological Deficits–Intra-Arterial (EXTEND-IA), only 10, 6, and 4 patients with an isolated M2 occlusion were treated with MT, respectively.^2,4,5 The Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment (SWIFT PRIME) protocol excluded M2 occlusions, but there were some protocol violations.³ Thus far, none of these studies has specifically examined the subgroup of M2 occlusions. The aim of our study was to examine the technical aspects, safety, and outcomes of MT with a stent retriever in patients with an isolated M2 occlusion who were included in 3 large multicenter prospective studies.