Coronary stents are tiny expandable mesh tubes used to help restore blood flow in narrowed heart arteries. These arteries can become narrowed by plaque, a buildup of fat, cholesterol, calcium, and other materials. When blood flow is reduced, the heart muscle may not get enough oxygen, causing chest pain or increasing the risk of a heart attack.
Stents matter because they provide a mechanical way to prop an artery open after it has been widened.
A stent is usually delivered during a procedure called angioplasty using a thin balloon catheter. The catheter carries the collapsed stent to the narrowed area, where the balloon inflates and presses the stent outward against the artery wall. After the balloon is deflated and removed, the stent stays in place to hold the vessel open.
Many modern stents also release medication that helps reduce scar tissue growth inside the artery.
Key Facts
- A coronary stent is a small metal mesh tube that supports a narrowed coronary artery.
- Angioplasty uses a balloon catheter to widen the artery before or during stent expansion.
- Blood flow rate can increase when vessel diameter increases because resistance decreases strongly with radius.
- Poiseuille relationship: R = 8ηL/(πr^4), so small increases in radius can greatly reduce resistance.
- Pressure difference drives flow through a vessel: Q = ΔP/R.
- Drug-eluting stents release medicine to lower the chance of restenosis, which is re-narrowing of the artery.
Vocabulary
- Coronary artery
- A blood vessel that supplies oxygen-rich blood to the heart muscle.
- Plaque
- A buildup of fatty and fibrous material inside an artery that can narrow the vessel.
- Stent
- A small expandable tube placed in a vessel to help keep it open.
- Balloon catheter
- A thin tube with an inflatable balloon at its tip used to expand a narrowed artery and deploy a stent.
- Restenosis
- The re-narrowing of a treated artery after a procedure such as angioplasty or stent placement.
Common Mistakes to Avoid
- Thinking the stent removes plaque, which is wrong because the stent usually compresses plaque against the artery wall rather than extracting it.
- Assuming the balloon stays in the artery, which is wrong because the balloon catheter is deflated and removed after the stent expands.
- Ignoring the r^4 effect in blood flow, which is wrong because a small increase in artery radius can cause a large decrease in flow resistance.
- Believing all stents are identical, which is wrong because some are bare-metal stents and others are drug-eluting stents with medication coatings.
Practice Questions
- 1 A narrowed artery has a radius of 1.0 mm before treatment and 2.0 mm after stent placement. Using R proportional to 1/r^4, by what factor does the resistance decrease?
- 2 If the pressure difference across a vessel is 80 mmHg and the resistance is 20 arbitrary units, what is the flow rate Q using Q = ΔP/R?
- 3 Explain why a stent can improve oxygen delivery to heart muscle even though it does not remove the plaque from the artery.