Definitions and Methodology for the Grayscale and Radiofrequency Intravascular Ultrasound and Coronary Angiographic Analyses

Objectives In a prospective study of the natural history of coronary atherosclerosis using angiography and grayscale and radiofrequency intravascular ultrasound (IVUS)–virtual histology (VH), larger plaque burden, smaller luminal area, and plaque composition thin-cap fibroatheroma emerged as independent predictors of future adverse cardiovascular events. Background The methodology for IVUS-VH classification for an in vivo natural history study and the prospective image mapping by angiography and grayscale and IVUS-VH have not been established. Methods All culprit and nonculprit lesions (defined as ≥30% angiographic visual diameter stenoses) were analyzed. Three epicardial vessels as well as all ≥1.5-mm-diameter side branches were divided into 29 CASS (Coronary Artery Surgery Study) segments. Each CASS segment was then subdivided into 1.5-mm-long subsegments, and dimensions were analyzed. All grayscale and IVUS-VH slices from the proximal 6 to 8 cm of the 3 coronary arteries were analyzed, with lesions defined as having more than 3 consecutive slices with ≥40% plaque burden categorized as: 1) VH thin-cap fibroatheroma; 2) thick-cap fibroatheroma; 3) pathological intimal thickening; 4) fibrotic plaque; or 5) fibrocalcific plaque. The locations of angiographic and grayscale and IVUS-VH lesions were recorded in relation to the corresponding coronary artery ostium and nearby side branches. Results The 3-year cumulative rate of major adverse cardiovascular events was 20.4%. Events were adjudicated to culprit lesions in 12.9% of patients and to nonculprit lesions in 11.6%. On multivariate analysis, nonculprit lesions associated with recurrent events were characterized by a plaque burden ≥70% (hazard ratio: 5.03; 95% confidence interval: 2.51 to 10.11; p < 0.0001), a minimal luminal area ≤4.0 mm2 (hazard ratio: 3.21; 95% confidence interval: 1.61 to 6.42; p = 0.001), and IVUS-VH phenotype of a thin-cap fibroatheroma (hazard ratio: 3.35; 95% confidence interval: 1.77 to 6.36; p < 0.001). Conclusions Three-vessel multimodality coronary artery imaging was feasible and allowed the identification of lesion-level predictors for future events in this natural history study.