What is a stent?

Image | AOPA

When you have coronary artery disease, blockages made up of plaque narrow down or completely block the coronary arteries, reducing the blood supply (ischaemia) or causing a heart attack. To prevent this damage, we can insert a stent to push the blockage out of the way and get blood flow back.

A stent is a tiny expandable metal mesh that pushes the plaque out of the way and restores blood flow to the heart muscle. After the angiogram has been performed demonstrating a blockage, one of the options is to put in a stent. In certain hospitals, this is performed in the same procedure as the angiogram.

The plaque is pushed into the walls of the coronary artery (the blood vessel), and blood flows through the middle of the stent. The process of intervening on a coronary artery (such as putting in a stent), is called percutaneous coronary intervention, or PCI. Following the angiogram, a thin wire is inserted through the blockage. Use the wire as a rail, the stent is then positioned in the blockage and expanded using a balloon.

A stent is a foreign body to the body, and as such the body can react by either trying to overgrow it (in-stent restenosis) or form blood clots on it (stent thrombosis). Once a stent has been inserted, it is permanent and cannot be removed. The body will grow a thin lining of vessel wall over a stent. If a new blockage develops inside a previous stent, then a new stent is inserted inside the old one.

There are three types of stents currently available:

Bare metal stents (BMS)

Bare metal stents are as described – a metal scaffold only. These were the first type of stents created. Although they are still effective, overall they have declined in use over the past few years.

The main problem with bare metal stents is called in-stent restenosis (ISR), meaning the stent can re-narrow over time. The blood vessel reacts to the metal being pushed against it, and in response the body attempts to grow a lining over the stent. A thin lining is actually beneficial and smoothens the vessel, however sometimes a thick aggressive lining can develop causing significant narrowing. In-stent restenosis usually takes many months to years to occur, and gradually causes ischaemia.

Generally, patients are on two types of blood thinning tablet (aspirin and one other) for at least one month after a bare metal stent. 

It is critical that you do not stop your blood thinning medications for any reason without speaking to your cardiologist.

Drug eluting stents (DES)

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To counter this problem of in-stent restenosis (ISR), stent manufacturers started incorporating a special drug onto the metal itself. This drug was designed to slowly leak out over months after the stent was inserted, preventing any overgrowth of the blood vessel wall.

The main issue here is stent thrombosis, or blood clots developing on the stent and blocking the blood vessel. Because the vessel wall does not grow over the stent, the raw metal is exposed to the blood flowing through. As it is a foreign body, blood can start to clot as it passes over it. Stent thrombosis can occur immediately, within minutes, or much later, over months. If a clot develops, then the stent can block off and you could have a heart attack, which in this case is often life threatening.

Overall, drug eluting stents are becoming increasingly popular, particularly as newer generations of technology have significantly reduced stent thrombosis while still preventing in stent restenosis.

To prevent stent thrombosis, patients need to be on two types of blood thinning tablet (aspirin and one other) for at least twelve months after a drug eluting stent. This duration may be altered on a per-patient basis, so clarify this with your cardiologist.

It is critical that you do not stop your blood thinning medications for any reason without speaking to your cardiologist.

Bioabsorbable stents (BAS)

Sometimes called bioresorbable vascular scaffolds (BVS), these stents are not made of metal; instead, they are made of a biodegradable substance called polylactide. A tiny bit of platinum is attached to each end to act as a marker to assist with placement when we use X-rays.

These scaffolds also release a drug (like the above drug eluting stent) over several months. The difference here is that over a 2-3 year period, after the body has grown a new vessel lining, the entire stent dissolves, leaving only the platinum markers behind. Theoretically, this allows for the coronary artery to heal without the metal being in the way, and restore the normal curve and function of the vessel.

These stents are relatively new and longer term studies are in process to prove their benefit.

Making the choice

The choice of which type of stent should go in is individualised; studies have shown benefits in certain groups of patients, or with certain types of blockages. Patients who may have a tendency toward bleeding, or those on strong blood thinners already for other conditions, may be more suited toward a bare metal stent due to the shorter duration of blood thinning tablets.

The duration is also variable; it is important to listen carefully to your cardiologist about the specific time interval they discuss with you about the blood thinning tablets – too short, and you could be putting your stent at risk of blocking and yourself at risk of a heart attack. Too long, and you could be exposing yourself to a bleeding issue.

It is critical that you do not stop your blood thinning medications for any reason without speaking to your cardiologist.

 

 

 

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