Distal Protection Device-Induced Slow- or Stop-Flow Phenomenon During Carotid Stenting and the Use of Aspiration to Decrease Periprocedural Events

The phenomenon of slow flow (significant reduction in antegrade flow in the internal carotid artery [ICA]) or stop flow (cessation of antegrade flow in the ICA) during carotid artery stenting (CAS) caused by distal embolic protection devices (EPDs), specifically the Angioguard XP filter, was evaluated in the article by Sorimachi et al. (12) in this issue of WORLD NEUROSURGERY. Although this is not a well-discussed topic in the literature, it could have very important implications with respect to the acceptance of CAS because this acceptance depends on the equivalent effectiveness of CAS when compared to its operative counterpart, carotid endarterectomy, in preventing periprocedural stroke. CAS has been criticized for its higher periprocedural event rates when compared to carotid endarterectomy. These events mainly occur during stent placement and angioplasty, although they have been shown to occur up to 18 hours after the procedure (13). The use of a distal EPD can potentially reduce the incidence of intracranial embolization observed during CAS, decreasing periprocedural event rates. The literature includes multiple studies that show lower stroke rates with distal EPDs as well as studies that show no statistical difference when they are used, such as the Stent-Protected Angioplasty versus Carotid Endarterectomy (SPACE) trial (5). However, the most recent trial published, the Carotid Revascularization Endarterectomy vs. Stenting Trial (CREST), which was a multicenter randomized North American trial that compared the efficacy of carotid endarterectomy with that of CAS, performed with the aid of an EPD in the prevention of stroke, myocardial infarction, and death in symptomatic and asymptomatic patients, showing a very low 30-day composite rate of stroke and death for symptomatic (6.1%) and asymptomatic (3.8%) CAS patients (3). Other studies have looked at the slow-flow phenomenon during CAS, such as Casserly et al. (4), who used multivariate logistic regression analysis to evaluate 71 CAS procedures. Their analysis showed that increased age, history of transient ischemic attack or stroke within 6 months of the procedure, and large stent diameter were predictive of slow flow during CAS. Slow flow was noted predominantly after balloon dilatation, although 25% of the cases occurred after stent deployment (4). The underlying etiology of slow flow is uncertain, but it is known that once the filter is retrieved, normal flow is restored. This isolates the filter as the problem and, thus, likely the occlusion of the pores of the filter as the reason for the slow-flow state. Histopathologic analysis of the filter debris has shown amorphous material derived from the core of atherosclerotic plaque (1). This correlates with the findings of slow flow being related to stent deployment and balloon angioplasty, as well as symptomatic lesions and increased stent diameter being independent predictors of slow-flow states. Casserly et al. (4) found that the 30-day incidence of stroke and/or death among patients with slow flow was 9.5%, compared to 2.9% in patients with normal flow. All the strokes occurred the same day as the procedure and were noted after retrieval of thefilter. These risk factors of slowflow have also been shown to be general risk factors of neurologic events associated with CAS. The CREST trial showed that patients older than age 79 years had higher 30-day stroke and death rates (11.9%) (8). Both the CREST (3) and the Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy (SAPPHIRE)