Evaluation of plaque composition using iMap-intravascular ultrasound predicts thin-cap fibroatheroma determined by optical coherence tomography

Abstract

Purpose: The iMap-intravascular ultrasound (iMap-IVUS), a novel radiofrequency intracoronary imaging system, can generate objective and quantitative information about coronary plaque compositions. The aim of this study was to determine whether iMap-IVUS can detect Thin-Cap Fibroatheroma (TCFA), which is a primary type of vulnerable plaque, as determined by Optical Coherence Tomography (OCT). Methods: Seventy nine culprit plaques in 70 patients with stable and 9 with unstable angina pectoris were analyzed using iMap-IVUS and OCT. Quantitative volumetric grayscale and iMap-IVUS analysis was performed across the entire lesion segment, and cross-sectional area analysis was performed to evaluate vessel remodeling. Plaque compositions were classified using iMap-IVUS as fibrotic, lipidic, necrotic and calcified, which are expressed as absolute amounts and as a percentage of plaque volume. We defined OCT-derived TCFA as lipid-rich plaque with a <65-μm thick fibrous cap. Patients were divided into 2 groups according to the presence (TCFA group, n=33) or absence (non-TCFA group, n=46) of TCFA. Results: The vessel volume, lumen volume, and plaque volume were significantly greater, and the prevalence of positive remodeling was significantly higher in the TCFA, than in the non-TCFA group. The absolute and percent necrotic volume (62.6±34.6 vs. 30.0±27.8 mm3, p<0.001, and 42±14 vs. 30±13%, p=0.001, respectively) and the absolute lipidic volume (14.0±5.8 vs. 8.6±5.5 mm3, p<0.001) were significantly greater, and the percent fibrotic volume (46±14 vs. 59±14%, p=0.001) were significantly smaller in TCFA compared with non-TCFA group. Fibrous cap thickness measured by OCT correlated negatively with vessel volume (r= -0.44, p<0.001), lumen volume (r= -0.26, p=0.032), plaque volume (r= -0.44, p<0.001), absolute and percent necrotic volume (r= -0.56, p<0.001, and r= -0.50, p<0.001, respectively), absolute lipidic volume (r= -0.49, p<0.001), and positively with percent fibrotic volume (r=0.50, p<0.001). Multivariate logistic regression analysis showed that absolute necrotic volume was the only independent predictor of the TCFA (odds raio, 1.033; 95% CI, 1.013–1.054; p=0.001). The area under the receiver-operator characteristic curve for absolute necrotic volume predicting the TCFA was 0.80. The optimal cut-off value of absolute necrotic volume for predicting the TCFA was 32.9 mm3 (sensitivity 73%, specificity 69%). Conclusions: Coronary plaque with a greater necrotic volume assessed by iMap-IVUS is closely associated with TCFA determined by OCT.