Objectives: Intermediate echogenic plaque without acoustic shadow on intravascular ultrasound (IVUS) imaging has been recognized as fibrous plaque. Such echogenic plaque with ultrasonic attenuation may have higher risk for distal flow disturbance (slow flow/no-reflow) during percutaneous coronary intervention. However, histological evaluation of plaque with ultrasonic attenuation has not been performed. This study evaluated the histological characteristics of plaque with ultrasonic attenuation assessed by IVUS.
Methods: By using IVUS, 36 samples of human cadaveric coronary arterial echogenic plaque (percentage plaque area > 40%) without calcium were selected, and classified into the attenuation group; plaque with ultrasonic attenuation, and the non-attenuation group; plaque without attenuation. These plaques were classified for fibrous, fibrofatty, calcium, and necrotic core areas by histological examination.
Results: True fibrous plaque was found in 91.7% of the non-attenuation group, but only 68.0% of the attenuation group (p < 0.01) . On the other hand, the percentage fibrofatty and necrotic core plaque areas in the attenuation group were significant larger than those in the non-attenuation group (fibrofatty: 16.3 +/- 13.8% vs. 2.7 +/- 3.1%, p < 0.01; necrotic core: 13.0 +/- 19.4% vs. 3.9 +/- 8.0%, p = 0.03). CONCLUSIONS. Plaque with ultrasonic attenuation contains more fibrofatty tissue and necrotic core compared to fibrous plaque without attenuation.