Abstract
Although rupture of thin-cap fibroatheroma (TCFA) underlies most myocardial infarctions, reliable TCFA identification remains challenging. Virtual-histology intravascular ultrasound (VH-IVUS) and optical coherence tomography (OCT) can assess tissue composition and classify plaques. However, direct comparisons between VH-IVUS and OCT are lacking and it remains unknown whether combining these modalities improves TCFA identification. Two hundred fifty-eight regions-of-interest were obtained from autopsied human hearts, with plaque composition and classification assessed by histology and compared with coregistered ex vivo VH-IVUS and OCT. Sixty-seven regions-of-interest were classified as fibroatheroma on histology, with 22 meeting criteria for TCFA. On VH-IVUS, plaque (10.91±4.82 versus 8.42±4.57 mm(2); P=0.01) and necrotic core areas (1.59±0.99 versus 1.03±0.85 mm(2); P=0.02) were increased in TCFA versus other fibroatheroma. On OCT, although minimal fibrous cap thickness was similar (71.8±44.1 μm versus 72.6±32.4; P=0.30), the number of continuous frames with fibrous cap thickness ≤85 μm was higher in TCFA (6.5 [1.75-11.0] versus 2.0 [0.0-7.0]; P=0.03). Maximum lipid arc on OCT was an excellent discriminator of fibroatheroma (area under the curve, 0.92; 95% confidence interval, 0.87-0.97) and TCFA (area under the curve, 0.86; 95% confidence interval, 0.81-0.92), with lipid arc ≥80° the optimal cut-off value. Using existing criteria, the sensitivity, specificity, and diagnostic accuracy for TCFA identification was 63.6%, 78.1%, and 76.5% for VH-IVUS and 72.7%, 79.8%, and 79.0% for OCT. Combining VH-defined fibroatheroma and fibrous cap thickness ≤85 μm over 3 continuous frames improved TCFA identification, with diagnostic accuracy of 89.0%. Both VH-IVUS and OCT can reliably identify TCFA, although OCT accuracy may be improved using lipid arc ≥80° and fibrous cap thickness ≤85 μm over 3 continuous frames. Combined VH-IVUS/OCT imaging markedly improved TCFA identification.
Highlights
Rupture of thin-cap fibroatheroma (TCFA) underlies most myocardial infarctions, reliable TCFA identification remains challenging
VH-IVUS and optical coherence tomography (OCT) image sets were matched to coregistered histological ROI by an experienced intravascular imaging investigator, blinded to final histological plaque classification
Of the ROI classified as fibroatheroma, 22 met the criteria for TCFA (8.5% of total ROI) with mean fibrous cap thickness (FCT) on histology being 43.0±16.8 μm
Summary
Ex Vivo ImagingThe study protocol was approved by the Cambridgeshire Research and Ethics Committee (Ref. 07/H0306/123) and consent obtained from relatives. Arteries were harvested from human hearts during autopsy in consultation with a senior pathologist. Hearts were excluded if coronary artery thrombosis was the suspected cause of death. All vessels were stored immediately in phosphate-buffered saline at 4°C and imaged within 48 hours of death. The left anterior descending artery (n=14) was dissected and excised, including ≈40 mm of surrounding tissue to maintain overall structural integrity.[4] Side branches were ligated and a guide catheter sutured into the left coronary ostium. Vessels were imaged under pressure–perfusion at 100 mm Hg before histological processing. OCT data were acquired by DragonFly C7 catheters (St. Jude Medical) using 25.0 mm/s automated pullback. All imaging data were digitally stored and exported for offline analysis
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