Direct comparison of virtual-histology intravascular ultrasound and optical coherence tomography imaging for identification of thin-cap fibroatheroma

Abstract

Background 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.

Methods and Results 258 regions-of-interest (ROI) were obtained from autopsied human hearts, with plaque composition and classification assessed by histology and compared with co-registered ex vivo VH-IVUS and OCT. 67 ROI were classified as fibroatheroma on histology, with 22 meeting criteria for TCFA. On VH-IVUS plaque (10.91±4.82 vs. 8.42±4.57mm2 , p=0.01) and necrotic core areas (1.59±0.99 vs. 1.03±0.85mm2 , p=0.02) were increased in TCFA vs. other fibroatheroma. On OCT, although minimal fibrous cap thickness (FCT) was similar (71.8±44.1µm vs. 72.6±32.4, p=0.30), the number of continuous frames with FCT≤85µm was higher in TCFA (6.5 [1.75-11.0] vs. 2.0 [0.0-7.0], p=0.03). Maximum lipid arc on OCT was an excellent discriminator of fibroatheroma (AUC 0.92, 95%CI 0.87-0.97) and TCFA (AUC 0.86, 95%CI 0.81-0.92), with lipid arc≥80° the optimal cutoff value. Using existing criteria, the sensitivity, specificity and diagnostic accuracy for TCFA identification was 63.6%, 78.1%, 76.5% for VH-IVUS and 72.7%, 79.8% and 79.0% for OCT. Combining VH-defined fibroatheroma and FCT≤85µm over 3 continuous frames improved TCFA identification, with diagnostic accuracy of 89.0%.

Conclusions VH-IVUS and OCT can both reliably identify TCFA, although OCT accuracy may be improved using lipid arc≥80° and FCT≤85µm over 3 continuous frames. Combined VHIVUS/OCT imaging markedly improved TCFA identification.