Atherosclerosis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Atherosclerosis is a disease affecting arterial blood vessels. It is a chronic inflammatory response in the walls of arteries, in large part due to the deposition of lipoproteins (plasma proteins that carry cholesterol and triglycerides). It is commonly referred to as a "hardening" or "furring" of the arteries. It is caused by the formation of multiple plaques within the arteries.
Pathologically, the atheromatous plaque is divided into three distinct components:
- The atheroma ("lump of porridge", from Athera, porridge in Greek,) is the nodular accumulation of a soft, flaky, yellowish material at the center of large plaques, composed of macrophages nearest the lumen of the artery.
- Underlying areas of cholesterol crystals.
- Calcification at the outer base of older/more advanced lesions.
The following terms are similar, yet distinct, in both spelling and meaning, and can be easily confused: arteriosclerosis, arteriolosclerosis and atherosclerosis. Arteriosclerosis is a general term describing any hardening (and loss of elasticity) of medium or large arteries (in Greek, "Arterio" meaning artery and "sclerosis" meaning hardening), arteriolosclerosis is atherosclerosis mainly affecting the arterioles (small arteries), atherosclerosis is a hardening of an artery specifically due to an atheromatous plaque. Therefore, atherosclerosis is a form of arteriosclerosis.
Atherosclerosis causes two main problems. First, the atheromatous plaques, though long compensated for by artery enlargement, see IMT, eventually lead to plaque ruptures and stenosis (narrowing) of the artery and, therefore, an insufficient blood supply to the organ it feeds. Alternatively, if the compensating artery enlargement process is excessive, then a net aneurysm results.
These complications are chronic, slowly progressing and cumulative. Most commonly, soft plaque suddenly ruptures (see vulnerable plaque), causing the formation of a thrombus that will rapidly slow or stop blood flow, e.g. 5 minutes, leading to death of the tissues fed by the artery. This catastrophic event is called an infarction. One of the most common recognized scenarios is called coronary thrombosis of a coronary artery causing myocardial infarction (a heart attack). Another common scenario in very advanced disease is claudication from insufficient blood supply to the legs, typically due to a combination of both stenosis and aneurysmal segments narrowed with clots. Since atherosclerosis is a body wide process, similar events also occur in the arteries to the brain, intestines, kidneys, legs, etc.
Pathophysiology
Atherogenesis is the developmental process of atheromatous plaques. It is characterized by a remodeling of arteries involving the concomitant accumulation of fatty substances called plaques. One recent theory suggests that for unknown reasons, leukocytes such as monocytes or basophils begin to attack the endothelium of the artery lumen in cardiac muscle. The ensuing inflammation leads to formation of atheromatous plaques in the arterial tunica intima, a region of the vessel wall located between the endothelium and the tunica media and tunica adventitia. The bulk of these lesions are made of excess fat, collagen, and elastin. Initially, as the plaques grow only wall thickening occurs without any narrowing, stenosis of the artery opening, called the lumen; stenosis is a late event which may never occur and is often the result of repeated plaque rupture and healing responses, not the just atherosclerosis process by itself.
Diagnosis
History and Symptoms
According to United States data for the year 2004, for about 65% of men and 47% of women, the first symptom of atherosclerotic cardiovascular disease is heart attack or sudden cardiac death (death within one hour of onset of the symptom).
Laboratory Findings
Cardiac stress testing, traditionally the most commonly performed non-invasive testing method for blood flow limitations generally only detects lumen narrowing of ~75% or greater, although some physicians advocate that nuclear stress methods can detect as little as 50%.