Chapter 20

Intravascular imaging continues to play a vital role in advancing our understanding of the pathophysiology of coronary artery disease (CAD) and in the development of novel cardiovascular drugs1,2 and device therapies.3,4 Gray-scale intravascular ultrasound (IVUS) was introduced more than 20 years ago and has been an integral component of the clinical decision-making process in the catheterization laboratory. Contemporary percutaneous coronary intervention (PCI) techniques mostly derived from initial IVUS observations showing that high-pressure balloon inflation was required to adequately appose metallic stents to the vessel wall and prevent thrombosis.5 Intravascular imaging has also evolved with time. IVUS technologies have added features such as tissue characterization by means of radiofrequency data (RFD) analysis to facilitate evaluation of the atherosclerotic plaque. This technique allows a more sophisticated assessment of changes in plaque characteristics over time beyond simplistic measurements of plaque dimensions.6 However, the relative poor image resolution of IVUS and physical limitations of sound have hampered a broader clinical and research application of intravascular imaging. The recent introduction of infrared light-based imaging technologies such as optical coherence tomography (OCT), which offers image resolution 10 times that of IVUS, has allowed interventional cardiologists to explore the vascular microenvironment for the first time and is expected to fuel a new wave of device, drug, and technique developments. These intravascular imaging technologies and their clinical and research applications are discussed in more detail below.

Coronary x-ray angiography has retained the gold standard status in coronary imaging for more than 4 decades. Angiography depicts arteries as a planar silhouette of the contrast-filled lumen and provides a quick roadmap of the coronary circulation. Importantly, angiography does not provide visualization of the vessel wall and is not suitable for assessment of atherosclerosis. Essentially, angiography provides assessment of lumen dimensions and is used to localize and estimate the severity of obstructive coronary disease. Angiographic disease assessment is based on the comparison of the stenotic segment with the adjacent, “normal-appearing“ coronary, which is often an incorrect assumption because of the diffuse nature of atherosclerosis as shown by pathologic and IVUS studies.7 Angiography image interpretation is flawed by large inter- and intraobserver variability and usually underestimates the severity of the disease and vessel dimensions. Although quantitative coronary angiography (QCA) has reduced visual errors, the ability of arteries to enlarge to compensate for plaque growth makes angiography an unreliable method of assessing atherosclerosis burden.8 Vessel foreshortening and overlapping side branches, particularly in disease involving bifurcations, are important practical limitations of angiography and QCA. Despite the use of multiple views, characterization of eccentric lesions by angiography remains a challenge. Finally, angiographic assessment of balloon angioplasty results is hampered by the presence of contrast filled dissection and intra-plaque channels, and determination of proper stent apposition is not possible. Three-dimensional angiography at the time of the contrast injection may provide an accurate and precise assessment of the luminogram. This may address some of the limitations of conventional angiography but still ...

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