RU
ENThe histopathological status of an atherosclerotic plaque can not only be quantified but also tracked over time by using a parameter calculated from optical coherence tomography (OCT) images, researchers from the Chinese PLA General Hospital in Beijing, China, have found.
Called the index of plaque attenuation (IPA), the parameter is a measure of a tissue's optical properties. Using the IPA, the researchers were able to identify increasingly pathologic stages of atherosclerotic plaques, from fibrous and fibrocalcific to thick- and thin-cap fibroatheromas. They were also able to determine the likely stability of the plaques.
IPA values reflect the dynamic progression of coronary atherosclerotic plaques and show a significant positive correlation with their histological classification, explained study investigator and associate physician, Shanshan Zhou, MD, here at the European Society of Cardiology (ESC) Congress 2024 on September 1.
Distinct variations were observed across different stages and types of plaques, she noted, and macrophage infiltration was a major contributor to higher IPA values.
"The translational perspective is that maybe we can provide qualitative data to help physicians assess coronary lesions more rapidly, accurately, and consistently," Zhou explained. This real-time imaging could enable clinical tracking of coronary plaque grading, she suggested during the "Smaller Trials and Other Studies on Atherosclerosis" late-breaking research session at the congress.
Study Information
The study builds on previous knowledge that OCT can differentiate altered tissue structures and organization that is reflected in its optical properties or attenuation coefficient. According to Zhou, these changes may not be visible with conventional imaging techniques.
She explained that a higher attenuation coefficient indicated tissue instability, areas of dead cells (necrotic cores), and macrophage infiltration. Conversely, lower attenuation values indicated calcification and fibrous tissue.
To quantify and comprehensively characterize coronary atherosclerotic plaques using OCT attenuation imaging, the team at the Chinese PLA General Hospital used 10 autopsied human hearts. The hearts had been snap-frozen in liquid nitrogen after removal and stored at −80°C. They took 21 sections of the coronary arteries from 30 vessels within these hearts and prepared 359 blocks of tissue for histological examination. Of these, 288 were suitable for both histological and OCT examination.
IPA values were calculated from the OCT images as the ratio of the number of pixels in the image greater than a certain threshold (ie, between 8 and 12 mm−1) to the total number of pixels present, then multiplied by 1000.
Plaques were classified histologically according to American Heart Association criteria published in 1995, where types I-II lesions showed increasing infiltration of fat and other molecules, and types IV-VI showed increasing formation of atheroma and fibrotic lesions.
Plaques were considered "significant" if they were fibrous, had pathologic intimal thickening, were fibrocalcific, a fibroatheroma, or a thin-cap fibroatheroma.
Key Results
Results showed that the IPA value was significantly correlated with the pathological staging of plaques, with an IPA value of 10 found to be the most optimal for detecting advanced plaques. The area under the receiver operating characteristic (AUROC) curve was 0.844 (P < .001).
Combining the IPA10 with the percentage of stenosis seen in the coronary artery sample allowed for an even more accurate identification of advanced plaques, with an AUROC value of 0.088 (P < .001) and corresponding sensitivity and specificity values of 91.4% and 80.8%, respectively, as well as positive and negative predictive values of 79.1% and 92.2%, respectively.
Zhou pointed out that notable variations in IPA values were observed among different types of plaques. AUROC values were 0.88 for significant plaques as a group, 0.81 for fibrous/fibrocalcific plaques, 0.89 for thick-cap fibroatheromas, and 0.97 for thin-cap fibroatheromas. All were significant (all P < .001).
Moreover, in advanced plaques, high optical attenuation was associated with high-risk features, indicating the possibility of instability and an increased likelihood of rupture. This included the infiltration of lipids and, most importantly, macrophages.
Looking more closely at macrophage-infiltrated lesions revealed that the IPA values were different depending on the type of plaques being studied. More importantly, the IPA value increased with the pathological staging of the plaque, from 264 for fibrous plaques, 548 for atheromatous plaques, and 676 for thin-cap atheromatous plaques.
