Acute Myocardial Infarction

HEART STENTS

Heart Stents by Dr VP Nair

DR V P Nair 

PBM, MBBS, MRCP-UK, MRCP- Ireland, MRCGP (UK), FAMS (Cardiology-Singapore), FRCP- Edinburgh, FRCGP- UK, FRCPI, FRCP (London), FCCP (USA), FACC (USA) FESC (Europe), FSCAI (USA)

Cardiologist Interventional

Mt, Elizabeth Hospital Orchard, 3 Mount Elizabeth #16-08 Singapore 228510

Mt. Elizabeth Hospital Novena, 38 Irrawady Road #07-35 Singapore 329563 

In the late 1970s, doctors began using balloon angioplasty to treat narrowed coronary arteries. During this procedure, a very thin, long, balloon-tipped tube, called balloon catheter, is inserted into the affected (blocked or narrowed) artery through either the groin(femoral artery) or the  wrist( radial artery) and is moved to the site of the blockage with the help from a special  X-ray scanning in the catherisation laboratory. The balloon at the tip of the catheter is then inflated to compress the blockage and restore blood flow. And then it’s deflated to allow the catheter and balloon to be removed. The whole process is aided by a specialised thin wire and guiding catheter. 

Because no new support is left at the site of the blockage during balloon angioplasty, in a small percentage of cases, the artery will resume its previous shape or even collapse after the balloon is deflated. About 30% of all coronary arteries treated with balloon angioplasty are affected by restenosis.

To help solve these problems, doctors developed small stents (special laser cut tubes) which could be mounted on the balloon section of the catheter and inserted into a blood vessel. During a stenting procedure, the stent expands when the balloon is inflated, locks into place, and forms a permanent scaffold to hold the coronary artery open, after the balloon is deflated and removed.

In the 1986, French researchers implanted the first stent into a human coronary artery. In 1994, the FDA approved the first heart stent for the use in the U.S.

First-generation stents were made of bare metal called BMS or bare metal stent. Although bare-metal stents almost eliminated the risk of the artery collapsing, they only modestly reduced the risk of restenosis. About 25% of all coronary arteries treated with bare-metal stents would close up again, usually within the time lapse of six months to one year.

With the help of bio-medical engineers, doctors and companies began testing stents which were coated with drugs that interrupted the process of restenosis. These are called DES or drug-eluting stents which are now widely used all over the world. 

In clinical trials, drug-eluting stents dramatically reduced the rate of restenosis to less than 10%. Drug-eluting stents also reduced the need for repeat procedures in patients with diabetes, a condition associated with an increased risk of restenosis.

Despite these benefits, there were concerns that drug-eluting stents were associated with a rare but serious complication namely late in-stent thrombosis, in which a blood clot forms inside the stent one or more years after it's implanted. Because this complication can be fatal, it is extremely important that patients with drug-eluting stents take aspirin (100mg cardiprin) and an anticlotting drug such as Plavix (Clopidogrel) 300mg tab loading dose and 75mg daily or Effient (Prasugrel) 60mg loading dose and 10mg daily or Ticagrelor (Brilinta) 90mg 2 tablet loading dose & 1 tablet twice a day as prescribed. It should be continued regularly for at least for one year. It should not be stopped without doctor's approval. Some even continue the medications for many years, such as three years or more.

INNOVATIONS IN HEART STENTS

Due to concerns such as late in-stent thrombosis, the use of drug-eluting stents declined in late 2006. But many cardiologists believed that fears were overblown. They also began to re-examine whether drug-eluting stents were significantly more effective than the older bare-metal stents, especially in patients with blockages that were deemed to have a low risk of restenosis.

In December 2006, the FDA held a public meeting on the issue of late in-stent thrombosis. While concluding that more information was needed, the agency approved drug-eluting stents, when used as directed, DES were not associated with an increased risk of heart attack or death. Subsequent research studies confirmed the safety and effectiveness of drug-eluting stents, prompting continued development of new stent technologies.

In recent years, the usage of drug-eluting stents has steadily increased, and the global market for heart stents is expected to exceed $8 billion by the year 2015.

Many new second- and third-generation stent designs are under development, in clinical trials, or have been approved for use outside the U.S. These include:

A stent with a covering that delivers an anti-restenosis drug over a period of several months and then essentially becomes a bare-metal stent, a stent that is absorbed by the body and disappears after it has done its work, a stent which uses a bio-engineered coating to quickly create a thin, all-natural layer inside the artery. Drug-eluting balloons are also in use in selected cases. 

Other technologies include development including platinum-coated stainless steel stents, diamond carbon-coated stents, and gene therapy/antibody-coated stents.

Bio-absorbable vascular scaffolds (BVS) are special types of stents which will be absorbed in a few months. In this type of stents, the need for long term anti-platelets medications such as Plavix or Brilinta are markedly shortened to 6 months to 1 year. 

In my practise, more than 95% of stents used are now drug-eluting types or bio-absorbable vascular scaffolds. 

CORONARY HEART DISEASE