Abstract 1930: 3D Volumetric Carotid Plaque Imaging by Cardiovascular MRI Solves the Mystery of the ‘Percent Stenosis Paradox’

Morphologic characteristics of plaque composition have been proposed to explain the apparent paradox of improved clinical events despite no or minimal reduction in % stenosis with statins. CMR can distinguish underlying features that determine plaque ‘vulnerability’. We hypothesize that in statin-naive pts with high-grade carotid artery stenosis, there will be a high degree of correlation in the relationship between the ‘unstable’ lipid pool and ‘stable’ fibrous plaque by 3D CMR, yet may be independent of 2D %stenosis. Representing 530-two mm contiguous CMR (1.5T GE) in vivo slices of advanced (mean 61±24% stenosis) carotid disease, 26 complete bilateral human (age: 66±14yrs) plaques were analyzed for 3D volumetric extent of vascular wall: lipid pool, fibrous cap, matrix and minima/maxima of each. All were related to fasting lipid levels relative to %stenosis via QPlaque (Medis, The Netherlands). Plaque morphology determined by T1, T2/PD CMR. In all, 25/26 in vivo plaques were imaged. Mean resolution: 1x1x2mm. The mg/dL range of LDL-C was 63–186, HDL-C: 28–59 and TG: 81–213. Lipid pool represented 15±4% while fibrous plaque represented 5±15% of total vessel wall. Total Cholesterol (Chol T ) and LDL-C were inversely related to minimum vessel wall thickness (r=−0.5 and −0.6, respectively, p<0.05, for both) while only Chol T was related to fibrous cap (r=0.6, p<0.01). The Chol T /LDL-C ratio was highly related to minimum fibrous plaque thickness (r=0.8, p<0.001). The 3D lipid pool was the only fraction highly correlated (>0.6) with triglycerides (r=0.6, p<0.01). A linear regression relating fibrous cap: vessel wall ratio to non-HDL cholesterol and Chol T was highly correlated (r=0.6, 0.7, respectively, p<0.01 for both) but was independent of in vivo % stenosis (r=0.1). Relating %stenosis to any lipid fraction or ratio showed no relationship. Percent stenosis provides relatively little information about vulnerability of de novo , statin-naive carotid plaques. As most current imaging studies concentrate on plaque stenosis, a more appropriate focus on plaque composition provides a more robust quantifiable volumetric metric and may be more indicative of the underlying pathology by high-resolution 3D CMR. This research has received full or partial funding support from the American Heart Association, AHA National Center.