Prognostic Value of Coronary CT
The majority of acute coronary syndromes (ACSs) are the result of a complication in an atherosclerotic plaque that had not caused a reduction in the blood stream prior to the episode. The presence of a stenosis, even if appreciable, does not necessarily lead to ischemia in the area supplied by the stenotic vessel. Even the presence of a complete obstruction does not automatically imply that the area downstream will become necrotic. Therefore, the stenosis is, in itself, of little diagnostic value in the assessment of perfusion or of contractile function; in other words, the anatomic aspect is often irrelevant with respect to the functional one. In two-thirds of ACS patients, however, there is fragmentation of the plaque. Those plaques that are highly likely to deteriorate are called “vulnerable plaques” and their histopathological characteristics are well-visualized with intravascular ultrasound (IVUS) imaging. About three-quarters of plaques complicated by rupture involve 50% of the vessel diameter, and in approximately half of the cases more than 75%. In two-thirds, the lipidic core occupies > 25% of the volume of the lesion, and in 80% of cases it expands to occupy > 50% of the thickness of the vessel wall. Most vulnerable plaques (95%) are located in the proximal segments of the epicardial branches and only rarely in the distal vessels. Furthermore, the necrotic core in ruptured lesions is significantly larger (2–22 mm in length, average 9 mm) than in the intact vulnerable plaque, suggesting that progressive enlargement of the necrotic core is associated with a higher probability of rupture. Indeed, when the area of the necrotic core exceeds a critical threshold (25% of the plaque area) the plaque is vulnerable to rupture. It has also been shown that the necrotic cores associated with plaque rupture occupy > 60° of the vessel circumference.
KeywordsCoronary Artery Calcium Coronary Artery Calcium Score Plaque Rupture Necrotic Core Vulnerable Plaque
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