The true character of lipid rich plaque by intravascular imaging: message from pathologist to cardiologist

Abstract

Purpose: Vascular imaging, such as intravascular ultrasound (IVUS), optical coherence tomography (OCT) and coronary angioscopy (CAS), becomes widespread to characterize the coronary artery plaques. Most of the cardiologists believe that these imaging devices could detect atherosclerotic plaque component; therefore it is possible to diagnose the vulnerable plaque. However, lack of histopathological validation study may lead misinterpretation of these imaging. We have compared intravascular imaging with histopathology of coronary plaques by our autopsy cases and evaluated the histological character of imaging-basis lipid rich plaque (LRP) and thin cap fibroatheroma (TCFA). Methods: Freshly harvested 55 coronary arteries from 20 hearts with non-cardiac death were examined ex-vivo vascular imaging including IVUS, OCT and CAS within 6 hours after death. These arteries were imaged with IVUS and >70 mm length of intimal lesions were identified as focal plaque. OCT-basis LRP were defined by signal-poor regions with fibrous cap thickness <300μm. TCFA was defined as LRP with fibrous cap thickness <65μm. CAS examinations were performed for each focal plaque to evaluate plaque color and all focal plaques were graded as either white or yellow. The border characteristic of yellow plaque was also assessed as sharp or diffuse. Results: Forty plaques (19%) were matched with the OCT-basis LRP and 17 plaques (8%) with TCFA in 211 OCT-observed focal plaques. OCT-basis LRP were highly associated with lipid deposition within plaques (85%). However, 41% of those plaques demonstrated extracellular lipid accumulation without necrotic debris, cholesterin crystals, and massive inflammation, which are known as fibro-fatty plaque. Furthermore, false-positive diagnoses of OCT-basis LRP included micro-calcification, hemosiderin deposition, or organized thrombus by their histology. The sensitivity for detecting LRP by OCT was 58%. Of CAS-observed 180 plaques, 64 plaques (35%) were categorized as yellow plaques. Only 24 plaques out of 64 yellow plaques (37.5%) contained necrotic debris by histology. Most yellow plaques with sharp border contained superficial calcium deposition without lipid accumulation. Other yellow plaques demonstrated superficial extracelluler lipid deposition or foam cells infiltration over fibrous plaque, which are known as pathological intimal thickening or intimal xanthoma. Conclusion: Atherosclerotic plaques of coronary artery are heterogeneous. We need to keep in mild that vascular imaging modalities have a limitation in detecting vulnerable plaque.