Assessment of plaque composition by intravascular ultrasound and near-infrared spectroscopy: from PROSPECT I to PROSPECT II.

Atherosclerosis is the main cause of coronary artery disease (CAD), which is today the leading cause of death worldwide and will continue to be the first in the world in 2030. Vulnerable coronary plaques are usually characterized by a high content of necrotic core, a thin inflamed fibrous cap (intense accumulation of macrophages) and scarce presence of smooth muscle cells. None of these characteristics can be estimated by coronary angiography, which on the contrary underestimates the magnitude of atherosclerotic burden, particularly in earlier stage disease when positive vascular remodeling may allow "normal" lumen caliber despite substantial vascular wall plaque. The recognition of the ubiquity of substantial but non-flow limiting lesions that may be at high risk for subsequent plaque rupture has resulted in a paradigm shift in thinking about the pathophysiology of CAD, with the focus no longer solely on the degree of arterial luminal narrowing. This growing need for more information about coronary atherosclerosis in order to identify patients and lesions at risk for complications during PCI and for future adverse cardiac events has been the primary impetus for the development of novel intracoronary imaging methods able to detect plaque composition, in particular presence of a necrotic core/lipid pool, such as intravascular ultrasound virtual histology and near-infrared spectroscopy. These imaging technologies and their clinical and clinical/research applications are discussed in detail.