OBJECTIVES

Three intravascular ultrasound (IVUS) signatures have been associated with coronary artery disease instability: echo attenuation, an intraplaque echolucent zone, and spotty calcification. The aim of this study was to investigate the substrates responsible for these IVUS signatures in a relatively large series of post-mortem human coronary samples.

BACKGROUND

The exact mechanisms and pathological correlates underlying echo attenuation, an intraplaque echolucent zone, and spotty calcification remain poorly understood.

METHODS

IVUS was compared with near-infrared spectroscopic detection of lipid core plaque and histopathology in 2,294 vessel segments from 151 coronary specimens from 62 patients at necropsy using the modified American Heart Association classification.

RESULTS

IVUS detected echo-attenuated plaques in 18.3% of segments, echolucent plaques in 10.5% of segments, and spotty calcification in 14.4% of segments. Histopathologically, 91.4% of echo-attenuated plaques corresponded to either a fibroatheroma (FA) with a necrotic core (NC) or pathological intimal thickening with a lipid pool; almost all segments with superficial echo attenuation indicated the presence of an FA with an advanced NC. Echolucent plaques indicated the presence of a relatively smaller lipid or NC compared with echo-attenuated plaques (thickness: 0.51 mm [interquartile range (IQR): 0.35 to 0.64 mm] vs. 0.70 mm [IQR: 0.54 to 0.92 mm] [p < 0.001]; arc: 74.5° [IQR: 59.0° to 101.0°] vs. 90° [IQR: 70.0° to 112.0°] [p < 0.001]), although 82.8% of superficial echolucent zones indicated an NC-containing FA. IVUS spotty calcification, especially when superficial in location (72.6%), was often associated with an FA with calcium deposits and had smaller arcs of calcium in the setting of FA compared with fibrocalcific plaques (37.5° [IQR: 23.0° to 53.0°] vs. 59.0° [IQR: 46.0° to 69.0°]; p < 0.001). Comparisons between IVUS and near-infrared spectroscopy revealed that echo-attenuated plaques contained the highest probability of near-infrared spectroscopy-derived lipid core plaque, followed by echolucent plaques and spotty calcifications.

CONCLUSIONS

This study demonstrated that echo-attenuated plaque, especially superficial echo attenuation, was the most reliable IVUS signature for identifying a high-risk plaque (i.e., an FA containing a large NC).