What is the role of plaque rupture in the pathophysiology of coronary artery atherosclerosis?

Updated: Apr 09, 2021
  • Author: Sandy N Shah, DO, MBA, FACC, FACP, FACOI; Chief Editor: Yasmine S Ali, MD, MSCI, FACC, FACP  more...
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Answer

Denudation of the overlying endothelium or rupture of the protective fibrous cap may result in exposure of the thrombogenic contents of the core of the plaque to the circulating blood. This exposure constitutes an advanced or complicated lesion. The plaque rupture occurs due to weakening of the fibrous cap. Inflammatory cells localize to the shoulder region of the vulnerable plaque. T lymphocytes elaborate interferon gamma, an important cytokine that impairs vascular smooth muscle cell proliferation and collagen synthesis. Furthermore, activated macrophages produce matrix metalloproteinases that degrade collagen.

These mechanisms explain the predisposition to plaque rupture and highlight the role of inflammation in the genesis of the complications of the fibrous atheromatous plaque. A plaque rupture may result in thrombus formation, partial or complete occlusion of the blood vessel, and progression of the atherosclerotic lesion due to organization of the thrombus and incorporation within the plaque.

Plaque rupture is the main event that causes acute presentations. However, severely obstructive coronary atheromas do not usually cause ACS and MI. In fact, most of the atheromas that cause ACS are less than 50% occlusive, as demonstrated by coronary arteriography. Atheromas with smaller obstruction experience greater wall tension, which changes in direct proportion to their radii.

Most plaque ruptures occur because of disruption of the fibrous cap, which allows contact between the highly thrombogenic lipid core and the blood. These modestly obstructive plaques, which have a greater burden of soft lipid core and thinner fibrous caps with chemoactive cellular infiltration near the shoulder region, are called vulnerable plaques. The amount of collagen in the fibrous cap depends on the balance between synthesis and destruction of intercellular matrix and inflammatory cell activation.

T cells that accumulate at sites of plaque rupture and thrombosis produce the cytokine interferon gamma, which inhibits collagen synthesis. Already-formed collagen is degraded by macrophages that produce proteolytic enzymes and by matrix metalloproteinases (MMPs), particularly MMP-1, MMP-13, MMP-3, and MMP-9. The MMPs are induced by macrophage- and SMC-derived cytokines such as IL-1, tumor necrosis factor (TNF), and CD154 or TNF-alpha. Authorities postulate that lipid lowering stabilizes the vulnerable plaques by modulating the activity of the macrophage-derived MMPs.


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