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OBJECTIVE: Virtual Histology Intravascular Ultrasound (VH™ IVUS) is valuable for estimating minimal lumen diameter (MLD) and plaque characterization. The clinical use of IVUS in the carotid arteries is not well characterized. To evaluate carotid plaque morphology, we performed VH™ IVUS in patients with known carotid artery stenosis and correlated to embolic potential associated with CAS.
METHODS: From July 2010, patients were prospectively enrolled in an IRB-approved study to undergo IVUS prior to an elective carotid stenting procedure. Hospital records were reviewed for co-morbidities, carotid/arch anatomy, preoperative carotid duplex velocity measurements, and incidence of postoperative microemboli. Comparison of pre- and postoperative diffusion-weighted MR images was used to identify number of new microemboli. IVUS-derived MLD and vessel wall plaque characteristics were collected. A paired two-tailed T-test was used to correlate MLD with duplex-estimated stenosis and Pearson correlations were used to look at relationships between plaque characteristics and demographics with frequency of postoperative microemboli.
RESULTS: 24 patients were prospectively enrolled during the study period with severe carotid artery stenosis (average ICA/CCA ratio 4.5). Notable co-morbidities included hyperlipidemia (80%), diabetes (48%), and CAD with reversibility on P-thal (44%). Fourteen patients had type 1 arches and eight of the patients were symptomatic (preoperative stroke or TIA). Two patients received longer stents for better coverages of disease segments after IVUS evaluation. MLD correlated with preoperative duplex ICA/CCA ratio (p=<0.001). Diabetes correlated with incidence of a moderate number of microembolic lesions (p=0.007, R=-0.529). Absence of lesion calcification on preoperative ultrasound correlated with incidence of fewer microemboli (p=0.001, R=-0.612). Age also correlated with incidence of microemboli, with patients over 80 years of age having a higher incidence (p=.045, R=.529). Percentage of IVUS-derived necrotic core approached significant correlation with incidence of microemboli (p=0.081, R=0.372).
CONCLUSION: We demonstrate that carotid IVUS is clinically feasible, can facilitates device selection, and guide stent placement. Preoperative duplex measurements correlated with IVUS MLD confirming the fidelity of the technique. Moreover, carotid IVUS demonstrates that patients with necrotic plaque cores show trends of significance with incidence of microemboli and calcification is a significant predictor of embolic potential.