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The correct identification of thin-cap fibroatheromas (TCFAs) with optical coherence tomography (OCT) is crucial. Superficial macrophage infiltration and tangential light drop-out are known to cause “false TCFAs.” We identify several additional false TCFA mechanisms and quantify the frequency of true and false TCFAs in cadaver hearts.
Human coronary arteries from 10 cadaver hearts were imaged with OCT. TCFA and thick-cap fibroatheroma (ThKFA) were identified by 3 expert readers as diffusely shadowed regions with bright fibrous caps (< 65 μm for TCFA) in OCT images. OCT images were compared with histology.
Of 44 OCT TCFAs, only 15 (34%) were confirmed by histology, while 7 were ThKFAs with deeper lipid cores, and 22 were false TCFAs without lipid cores. Of 19 OCT ThKFAs: only 10 were confirmed by histology and 7 were false ThKFAs without lipid cores. The appearance of false TCFAs and ThKFAs was due to superficial macrophage infiltration (17), tangential light drop-out (3), calcium (6), proteoglycans (3), loose connective tissue (4) and cellular fibrous tissue (5). Additionally, 60% of true TCFAs and ThKFAs exhibited bright streaks (see figure) between the fibrous cap and necrotic core due to a large gradient in optical index of refraction.
False TCFAs are due to excessive light scattering away from the OCT catheter creating the false appearance of lipid beneath the fibrous cap. Further, a new OCT marker for TCFA, a bright streak between the fibrous cap and necrotic core, could improve accuracy of identification.