Impact of Recanalization, Reperfusion, and Collateral Flow on Clinical Efficacy

Abstract

The goal of acute stroke therapy is reperfusion of salvageable ischemic tissue. Acute stroke trials have typically focused on inclusion of patients who present within a short time after the onset of symptoms. The assumption underlying this approach is that the time from symptom onset is a surrogate for the volume of salvageable tissue. It has been estimated that in patients with a large vessel occlusion presenting with acute ischemic stroke, about 120 million neurons die each hour.1 However, more recent data support the concept that the rate at which ischemic neurons become irreversibly injured after stroke onset is actually highly variable and depends on numerous factors, including the site of occlusion and the extent of collateral circulation. It seems that some patients lose neurons at an alarmingly high rate and that even very early reperfusion may be futile. In contrast, there seems to be a subgroup of stroke patients in whom irreversible ischemic injury evolves over many hours. These patients may be ideal candidates for reperfusion therapies administered at late time points. Although there has been controversy regarding the accuracy of acute diffusion-weighted imaging (DWI) for identification of irreversible ischemic injury, recent clinical and laboratory studies have confirmed that permanent and complete tissue salvage in regions of early DWI positivity is limited to no more than a few milliliters of tissue in the vast majority of large artery infarcts.2,3 Reports of large volume reversal may …