What is arterial stenosis?
Arteries transport oxygenated blood to different tissues and organs of the body. This is essential for metabolic activities and sustaining life functions. Any narrowing of an artery will hamper the flow of blood and depending on the extent of the narrowing, known as stenosis, the artery may be partially or completely occluded (blocked).
Narrowing of an artery may not cause obvious signs and symptoms in the initial stages. If sufficient oxygenated blood is able to reach the target organs and tissues, the narrowing may go unnoticed for long periods of time. Diagnostic investigations like an angiogram may be the only way to identify the narrowing of an artery.
As the condition progresses, the flow of blood will be hampered to a degree that affects the oxygen supply to the target tissue. It is usually at this stage that the first signs and symptoms become evident. A sudden occlusion of an artery (blocked artery) can lead to a host of life threatening illnesses, including a myocardial infarction (heart attack), stroke or pulmonary embolism. However, slow and progressive narrowing may remain unnoticed for weeks, months or years.
Effects of Narrowing Artery
Narrowing may cause hypoxia, where there is little oxygen reaching the target tissue, or anoxia, where there is no oxygen reaching the target area. Initially this may result in ischemia and eventually lead to an infarct where there is death of tissue.
The extent of the tissue damage depends on the area as many sites have collateral supplies of arterial blood. Single artery stenosis may therefore remain unnoticed if there is sufficient collateral blood supply. However, multiple artery stenotic lesions affecting the blood supply to a a specific site will produce signs and symptoms sooner and impair recovery.
In addition, the effects of hypoxia or anoxia on different tissues in the body varies, where at some sites it take minutes to cause cell death, while at other sites, this can persist for hours before death occurs.
For example, cell death due to anoxia may occur within :
- 5 to8 minutes for brain tissue
- 30 minutes to 2 hours for heart muscle or kidney tissue
- several hours for skin and connective tissue
Causes of Artery Narrowing
A narrowing may be due to pathology within the artery, in the artery wall or from outside of the artery.
Atherosclerosis is the most common cause of arterial narrowing. The formation of atheromatous plaques within the wall of the artery bulges into the lumen and partially reduces blood flow to target organs. Atherosclerosis is progressive – it develops slowly over time. If left untreated, the plaque can grow to a size that significantly impairs the flow of blood. In addition, rupture of the plaque and the formation of a blood clot may then completely occlude the artery.
An embolus or thrombus may occur suddenly and the signs and symptoms of the occlusion may be evident within seconds or minutes, depending on the site. Depending on the size of the embolus or thrombus, the flow of blood may be partially or completely blocked.
Atherosclerosis develops within the wall of the artery while an embolus or thrombus develops inside the lumen of the artery. Atherosclerosis is more likely to affect large to medium sized arteries whereas and embolus or thrombus tends to cause a significant blockage in medium to small arteries.
Other causes of narrowing (stenosis) includes :
- Mass pressing against the artery as is the cases with a neighboring tumor, fluid filled cyst or the pregnant uterus. In pregnancy, the narrowing is temporary and is relieved upon change of position.
- Infection causes inflammation and thereby swelling of the arterial wall.
- Non-infectious causes of inflammation (vasculitis) also causes swelling of the arterial wall.
- Congenital anomalies like fibromuscular dysplasia where there is irregular thickening of the walls of arteries.
- Spasm affects smaller arteries where sudden and persistent contraction of the muscular layer of the artery wall may cause significant narrowing of the artery. Example : coronary artery spasm in angina.
- Valve stenosis occurs when the valve within an artery, like the aortic valve, becomes diseased and therefore cannot open fully thereby causing a narrowing within the artery.