Does the Merci Retriever Work?

Abstract

Section Editors: Geoffrey A. Donnan MD, FRACP Stephen M. Davis MD, FRACP Technically, it works. And remarkably so. The Merci Retriever is a mechanical embolectomy device designed to reopen occluded vessels by extracting occlusive thrombi from the cerebral vasculature. In the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) trial (parts I and II combined), among 151 patients enrolled in the intention-to-treat group; partial or complete recanalization by use of the device alone was achieved in 46%.1 This rate substantially exceeded that in the prespecified comparator group—patients enrolled in the control arm of the Prolyse in Acute Cerebral Thromboembolism (PROACT-II) trial (18%). The associated probability value of <0.0001 indicates a less than 1 in 10 000 chance that this result occurred by chance. The Merci Retriever indeed works. And it works well where we most need it to work: on proximal occlusions for which there was previously no good therapy. Proximal carotid terminus and M1 middle cerebral artery thrombi respond poorly to IV or intra-arterial fibrinolytic therapy, likely attributable in large part to the sheer volume of the clot burden requiring enzymatic digestion. The average volume of carotid terminus thrombi (0.4 ml) is more than an order of magnitude larger than that of M2 middle cerebral artery division thrombi …