Atherosclerotic plaque composition assessed by virtual histology intravascular ultrasound and cerebral embolization after carotid stenting

Objective

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 obtained with an IVUS catheter that is advanced through the lesion after a filter has been placed distally, 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 artery stenting (CAS).

Methods

During a 10-month period, 24 patients undergoing CAS procedures using a filter device for embolic protection were prospectively evaluated. All patients underwent VH-IVUS exams at the time of the 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 correlation 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 within 30 days. Seventeen patients (71%) demonstrated new acute cerebral emboli in DW-MRI. Of these, all revealed ipsilateral lesions and 12 (50%) had contralateral lesions. For the entire study group, the median number of ipsilateral DW-MRI lesions was 1 (range, 0 to 3), and TCD MES counts were 227 (interquartile range, 143-315). Volumetric VH-IVUS analysis revealed that there was a trend for larger median dense calcium volume in patients with ipsilateral subclinical cerebral embolism detected with DW-MRI (33.2 ± 24.5 mm³ vs 11.4 ± 6.1 mm³; P = .08). Scatter plots of plaque components revealed statistically significant correlation between fibrofatty plaque volume (Spearman r = 0.49; P = .016) and number of new ipsilateral lesions in DW-MRI. Degree of cerebral embolization during CAS measured with TCD correlated with plaque burden, necrotic core, fibrofatty, and fibrous volumes.

Conclusions

Plaque composition, as determined by VH-IVUS, only weakly correlates with the degree of cerebral embolization after carotid stenting. Specifically, there is a trend for larger dense calcium volume in patients with distal embolization. Of note, the proportion of necrotic core, which has traditionally been considered the main component of a vulnerable or unstable plaque, is not definitely associated with subclinical cerebral embolization after CAS when a filter device for embolic protection is used. The role of VH-IVUS in evaluating plaque composition during CAS remains unestablished and warrants further investigation.