Futile Recanalization in Mechanical Embolectomy Trials

Abstract

See related article, pages 953–960. It is well known that clot burden is likely a major determinant of vessel recanalization rates with the volume of thrombus to be dissolved by fibrinolytic agents much larger in the intracranial carotid artery than in the middle cerebral artery. So, the more distal the occlusion is located, the higher the likelihood of recanalization. This statement seems to be true for intravenous thrombolysis as demonstrated in several transcranial Doppler studies showing that the probability of complete recanalization at 2 hours of tissue plasminogen activator (tPA) bolus is 44%, 29%, and 10% in the distal middle cerebral artery, proximal middle cerebral artery, and terminal internal carotid artery, respectively.1 However, a differential treatment response according to clot size and location has not been demonstrated in patients with stroke undergoing mechanical embolectomy. Several methodological, technical, and pathophysiological differences preclude the translation of this “clot-burden effect” of intravenous tPA therapy into mechanical revascularization trials. In this issue of Stroke, Shi et al2 retrospectively analyzed the pooled data of patients with middle cerebral artery strokes from the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) and Multi MERCI trials. Patients were dichotomized into 2 groups: middle cerebral artery M1 occlusions and isolated M2 occlusions. Baseline characteristics, revascularization rates, hemorrhage rates, complications, outcomes, and mortality were evaluated for both groups. The authors observed that patients with isolated M2 occlusions were revascularized at a higher rate (82.1% versus 60%), required fewer number of passes, and were associated with a trend of a shorter median procedure time than patients with M1 occlusions. However, no statistically significant differences were …