Intravascular Detection of the Vulnerable Plaque

Abstract

C oronary heart disease (CHD) remains the leading cause of death in the United States, and an estimated 1.4 million Americans have a heart attack each year. Over the past 2 decades, the concept of the "vulnerable plaque" (VP) being responsible for the majority of acute coronary syndromes (ACS) has become widely accepted. Coincidentally, there has been rapid expansion of coronary imaging modalities, both invasive and noninvasive, seeking the ability to detect high-risk plaques before their disruption and formation of occlusive thrombus. Histological characteristics of the plaques that are vulnerable to rupture are thin fibrous cap (Ͻ65 m), large lipid pool, and activated macrophages near the fibrous cap, all of which can be detected with highresolution coronary imaging. 1 Cellular mechanisms associated with plaque instability include inflammation, reduced collagen synthesis, local overexpression of collagenase, and smooth muscle cell apoptosis. These pathological processes can alter the plaque surface and its mechanical properties, which also have been targets of recent research. Noninvasive tests, such as CT and MRI are limited by low resolution and are unable to visualize most of the features of VP. At present, only intravascular modalities can potentially distinguish VP from benign types of plaques. In this review, we focus on the recent data from the various types of intravascular modalities currently available or in development and compare their advantages and limitations. Invasive Imaging TechniquesCoronary plaque develops eccentrically, and increasing plaque volume induces positive remodeling of the vessel, resulting in external elastic membrane expansion and preservation of luminal area. Coronary angiography only visualizes the coronary lumen and does not provide any information about the characteristics of the arterial wall and its contents. For this reason, coronary angiography has failed as a diagnostic modality for detection of VP, which often causes only modest luminal narrowing.Various histological plaque components have been targeted as potential candidates for plaque vulnerability. These candidate features and comparisons of the invasive imaging modalities are listed in the Table. 2 The characteristic architecture of a thin-cap fibroatheroma (TCFA) overlying a lipid pool has promoted further enhancements in high-resolution imaging modalities, including integrated backscatter intravascular ultrasound (IB-IVUS), virtual histology IVUS (VH-IVUS), optical coherence tomography (OCT), and intravascular MRI (IV-MRI). Plaque composition also affects the response of the vessel wall to pulsatile changes in blood pressure, and the mechanical strain patterns can be measured with elastography and palpography. The cholesterol-rich lipid core underlying the fibrous cap is identifiable by angioscopically detected color changes reflected on the plaque surface and by the unique absorption of energy of its cholesterol crystals, leading to the development of Raman spectroscopy (RS) and near-infrared spectroscopy (NIR...

Parameter estimation of atherosclerotic tissue optical properties from three-dimensional intravascular optical coherence tomography

“…[1][2][3][4][5][6][7][8][9][10][11][12] With regard to atherosclerotic plaques, IVOCT has demonstrated an ability to differentiate lipid, calcium, and fibrous tissue 13,14 and to quantify microscopic features such as macrophage content. 9 We have previously reported on IVOCT image analysis relating to segmentation, quantification, and visualization of plaques, stents, and other vessel wall components.…”

Ultrafast laser ablation for targeted atherosclerotic plaque removal

“…We also demonstrated OCT imaging of the ablated volume which provided high contrast images of the gas bubble resulting from ablation. The use of OCT in conjunction with plaque ablation is convenient because IV-OCT devices already provide clinicians a high-resolution tool for plaque recognition and characterization 15 . The results showed that pulse energies below 4 J provided axially isolated ablation volumes, such that ablation targeted deeper than 20 m rarely caused surface damage.…”

High-Risk Stents Harboring Neoatherosclerosis

“…NIRS can provide a semiquantitative measure of lipid burden (so-called lipid-core burden index). NIRS is Food and Drug Administration approved for the detection of lipid-core plaques, and it is under active investigation for the detection of vulnerable plaques 11 and plaques at risk of periprocedural myocardial infarction. 12 To date, however, limited information on NIRS' ability to detect neoatherosclerosis is available.…”