Slow-flow Phenomenon During Carotid Artery Intervention with Embolic Protection Devices: Predictors and Clinical Outcome

Objectives: The purpose of this research was to define the predictors of the "slow-reflow" phenomenon during carotid artery intervention with filter-type embolic protection devices (EPDs) and to determine its prognostic significance.

Background: During carotid artery intervention using filter-type EPDs, we have observed cases in which there is angiographic evidence of a significant reduction in antegrade flow in the internal carotid artery proximal to the filter device, termed "slow-flow." The predictors of this phenomenon and its prognostic significance are unknown.

Methods: Using a single-center prospective carotid intervention registry, patients with slow-flow were compared to patients with normal flow during carotid intervention with respect to clinical, procedural, and lesion characteristics, and the 30-day incidence of death and stroke.

Results: A total of 414 patients underwent 453 carotid artery interventions using EPDs. Slow-flow occurred in 42 patients (10.1%) undergoing 42 carotid interventions (9.3%), and most commonly occurred after post-stent balloon dilatation (71.4%). Multivariate logistic regression analysis identified the following predictors of slow-flow: recent history (<6 months) of stroke or transient ischemic attack (odds ratio [OR] 2.8, 95% confidence interval [CI] 1.4 to 5.6, p = 0.004), increased stent diameter (OR 1.4, 95% CI 1.02 to 1.94, p = 0.044), and increased patient age (OR 1.05, 95% CI 1.01 to 1.09, p = 0.025). Among patients with slow-flow, the 30-day incidence of stroke or death was 9.5% compared to 2.9% in patients with normal flow (chi-square = 4.73, p = 0.03). This difference was driven by the disparity in the 30-day incidence of stroke (9.5% vs. 1.7%).

Conclusions: Slow-flow during carotid intervention with EPDs is a frequent event that is associated with an excess risk of periprocedural stroke. The association of the phenomenon with clinically symptomatic carotid lesions and use of larger stent diameters suggests that embolization of vulnerable plaque elements may play a pathogenic role.