Atherosclerotic Plaque Composition and Cerebral Embolization After Carotid Stenting

Background: Previous studies have investigated the predictive value of clinical and morphologic parameters for distal embolization during carotid interventions. The composition of the atherosclerotic plaque using virtual histology intravascular ultrasound (VH IVUS) imaging at the intervention site has not been evaluated as a marker for cerebral embolization. The purpose of this study was to assess the relationship between atherosclerotic plaque composition determined with VH IVUS and the occurrence of cerebral embolization after carotid angioplasty and stenting (CAS).
Methods: During a 10-month period, 24 patients undergoing CAS procedures using a filter device for embolic protection (Accunet filter, Abbott Vascular, Santa Clara, CA) were prospectively evaluated. All patients underwent VH IVUS exams prior to intervention, transcranial Doppler (TCD) monitoring during CAS and pre- and 24 hour postprocedural diffusion-weighted magnetic resonance imaging (DW-MRI) exams. Using VH-IVUS, plaque components were characterized as fibrotic, fibrofatty, dense calcium, and necrotic core. The frequency of Doppler-detected microembolic signals (MES) during CAS and the incidence and location of acute, postprocedural embolic lesions detected with DW-MRI were assessed to determine cerebral embolization. Univariate and linear regression analyses were used to assess the association between plaque composition and frequency of cerebral embolization.
Results: No periprocedural transient ischemic attacks, strokes or deaths occurred at 30 days. Fourteen patients (58%) demonstrated new acute cerebral emboli in DW-MRI. Of these, all revealed ipsilateral lesions and 8 (32%) had also contralateral lesions. For the entire study group, the median number of DW-MRI lesions was 2 (range, 0 to 173) and the TCD MES counts were 222 (interquartile range, 152-322) .Of the plaque components, only dense calcium was significantly associated with cerebral embolization as determined by DW-MRI. The proportion of dense calcium was significantly larger in patients with cerebral embolization (5.7±2.2% vs. 1.2±0.3%, P=.04). Findings on postprocedural DW-MRI did not correlate with the proportion of fibrotic, fibrofatty and necrotic core. Degree of cerebral embolization during CAS measured with TCD did not correlate with plaque composition.
Conclusions: Plaque composition, as determined by VH IVUS, correlates with the degree of cerebral embolization after carotid stenting but not during the intervention. Specifically, the proportion of dense calcium is strongly associated with the occurrence of cerebral embolization after CAS. Of note, the proportion of necrotic core, which has traditionally defined the presence of a vulnerable or unstable plaque, does not correlate with the degree of distal embolization after CAS when a filter device for embolic protection is used. Optimal management and strategies to prevent distal embolization after CAS of lesions with significant dense calcium warrant further investigation.