Critical stenosis in atherosclerotic plaques
Critical stenosis is a narrowing of about 70 to 80% of an artery's lumen, where blood flow falls significantly and ischaemia (too little oxygen for the tissue) becomes likely.
Remember
Plaques are usually clinically silent (they cause no symptoms) for years. In a slowly growing plaque, symptoms usually start when the lumen is about 70 to 80% narrowed, because flow then falls significantly and the tissue becomes short of oxygen during exercise.
An atherosclerotic plaque is a fatty deposit that builds up in the wall of an artery. Most plaques cause no symptoms, because for a long time the artery still delivers enough blood. Early on, the wall can also expand outwards as the plaque grows, which keeps the lumen (the channel blood flows through) open and can mask the severity of the disease.
Stenosis is a narrowing of the lumen. A narrowed artery has less ability to increase its flow when it is needed. Once about 70 to 80% of the lumen is narrowed, blood flow falls significantly. At rest, a narrowed artery may still supply enough blood. When the muscle or heart has to work harder, it needs more oxygen than the narrowed artery can supply. The tissue then becomes short of oxygen, which is called ischaemia.
The symptoms depend on which artery is affected. In the leg arteries the result can be intermittent claudication, a cramping pain on walking that eases with rest. In the coronary arteries the result can be angina, chest pain from ischaemic heart muscle. Once the person rests, the demand lowers again and the pain eases.
The 70 to 80% figure is approximate. The exact threshold varies with the tissue's oxygen demand, the artery, the patient and how narrowing is measured, and some leg-artery sources quote a range of 50 to 70%. The 70 to 80% figure describes slow narrowing; if a plaque ruptures, an artery can be blocked suddenly at a lower degree of narrowing.
Key facts
- Silent phase
- most plaques cause no symptoms, because the artery can still deliver enough blood for a long time.
- Usual threshold
- blood flow falls significantly once the lumen is narrowed by about 70 to 80%.
- Legs
- narrowing shows as intermittent claudication, a cramping pain on walking that eases with rest.
- Heart
- narrowing of the coronary arteries shows as angina, chest pain from ischaemic heart muscle.
- Not total blockage
- a slowly narrowing artery causes symptoms well before the lumen has closed.
- Variation
- how much narrowing is needed depends on the artery, the patient and the tissue's oxygen demand.
Exam traps
- Complete blockage of an artery is not needed for ischaemia, because a slowly narrowing artery causes it well before the lumen closes. Total blockage is usually a later or sudden event.
- A very severe narrowing of 90 to 95% is not the point at which ischaemia first becomes likely, because blood flow is already significantly reduced at about 70 to 80%, well before the lumen is nearly closed.
- Claudication pain does not come from stretching of the arterial wall, because it comes from ischaemic muscle: a fixed stenosis limits the extra blood flow that exercise needs.
Read the full notes
Tested in 6 SimpleMed+ questions
Practice it in Pathology, with the answer and a full explanation after every question.
Practice these questions