(With India’s increasing heart disease burden, the number of people requiring stents is going up. Why is a stent recommended? And how do you make a decision about stents? A cardiologist from Mumbai’s Jaslok Hospital explains)
People who suffer from blockages in the heart arteries might be offered angioplasty and stent implantation. The decision of stenting is based on severity of lesion, location of blockage in the heart artery and symptoms of the patient. The stent is usually inserted in the artery once it is widened by the inflated balloon, a process called angioplasty. After angioplasty, preventing and re-narrowing helps when the stent supports the walls of the artery. The procedure is done through a small hole in the groin artery or the forearm artery.
How is it Done?
After a small needle prick in the groin or forearm, the area is anesthetised. A hollow tube catheter is then advanced till the starting of the artery. The stent, which is placed at the tip of the catheter is mounted on a balloon. To hold it open and improve blood flow to the heart the stent stays in the artery permanently.
At the blockage, the balloon is inflated and the stent expands and locks into place inside the artery.
Once the stent is in place, the balloon catheter is removed and more images (angiograms) are taken to see how well blood flows through the newly widened artery.
Once placed, the stent is fixed for the lifetime and doesn’t move. After the stent placement, the doctor is likely to prescribe treatment with ‘blood-thinning’ medications called anti-platelets.
What is a Stent?
Stents are small expandable tubes used to treat narrowed or weakened arteries in the body. In patients with coronary artery disease (CAD), stents are used to open narrowed arteries and help reduce symptoms such as chest pain (angina) or to help treat a heart attack. These types of stents are commonly called heart stents, but they are also referred to as cardiac or coronary stents.
Usually made of metal mesh, heart stents are implanted in narrowed coronary arteries during a procedure called a percutaneous coronary intervention (PCI). Stents help prevent the artery from becoming blocked again (recoiling).
There are currently three types of stents available:
- Bare Metal Stent (BMS)
- Drug Eluting Stent (DES)
- Bioresorbable Vascular Scaffold (BVS)
Bare Metal Stents
These are the oldest stents available and were first used in clinical practice in 1986. Bare metal stents (BMS) are usually stainless steel and have no special coating of the drug. They act as scaffolding to keep the arteries open after balloon dilatation. However, sometimes an overgrowth of scar tissue in the arterial lining increases the risk of re-blockage. This is the major drawback of BMS over drug coated stents. Over time the use of these stents has reduced drastically.
In present times, the only clinical indication of use of BMS is in patients who are planned for some major surgery in near future or have suspected intolerance to blood thinning medicines (anti-platelet agents). Sometimes it is used as an alternative to Drug Eluting Stents (explained below) in patients who cannot afford DES.
2. Drug Eluting Stent (DES)
Drug Eluting Stents (DES) are coated with medication that is released (eluted) to help prevent the growth of scar tissue in the artery lining. These were first used in 1999 and were one of the major discoveries for treating patients with blockages in heart arteries. These stents help the artery remain smooth and open, ensuring good blood flow and reduces the chances of re-narrowing of the artery or restenosis. However, it also leads to a higher chance of blood clots (stent thrombosis).
Over the last few years, many drugs have been tried on the surface of the stents. This drug is slowly released in the surrounding tissue and prevents new tissue growth inside the stent. The maximum chance of this is in the first few months of the stent placement. Hence, most of the stents are coated with drug in such a manner that the drug is slowly released for the next few months. Due to a relatively slower healing process, patients implanted with DES must strictly follow their doctor's recommendation on blood thinning medicines to help reduce risk of stent thrombosis.
3. Bioresorbable Vascular Scaffold
The Bio-Vascular Scaffold (BVS) is a drug eluting stent on a dissolvable type of scaffold platform which is supposed to be absorbed by the body over time. The concept is that over few months, the artery remodels itself and the metallic scaffold of any stent is no longer required. In the year 2011, the BVS came with a big bang and was used worldwide. Although the initial results were promising, in long run, they performed worse than conventional DES which are now the standard stents used. The company themselves withdrew it from the market in 2017.
There is limited role of Bare Metal Stents. And although the dissolvable stents theoretically were promising, it couldn’t be converted into benefit for the patients. There are many trials ongoing for BVS with better designs to improve the outcomes in patients. However as of today, Drug Eluting Stents are the preferred stents.
(Dr Rahul Chhabria is a Consultant Cardiologist at Jaslok Hospital and Research Centre.)
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