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Stents - a reality check

The advent of stents has revolutionised the practice of interventional cardiology, says Dr. B. CHANDRASEKAR.

Fighting fit... Future developments in stent technology hold promise.

THE incidence of coronary artery disease (disease of the coronary arteries) in our country is on the rise. The coronary arteries are blood vessels that supply blood to the heart. It is estimated that by the beginning of the next decade, coronary artery disease (commonly presenting itself as chest pain on exertion, heart attack, and other manifestations) will become the leading cause of mortality in India, accounting for nearly a third of all deaths in both women and men. Added to this, will be an incremental rise in disability associated with the disease, resulting in considerable impairment in the quality of life of those affected.

Angioplasty and stents

One of the proven options for treatment of coronary artery disease is angioplasty.

Angioplasty is a minimally invasive procedure performed under local anaesthesia that aims to clear obstructions (blockages) to blood flow in the coronary arteries, without requiring the patient to be submitted to a bypass surgery. The relative ease of the procedure, speedy, and virtually painless, recovery, and an early return to work make the procedure attractive. To overcome some of the limitations associated with the procedure and to improve its outcome further, "stents" were introduced as an adjunctive therapy.

Stents are hollow, cylindrical metallic structures that outwardly resemble the spring in a jotter ball-point pen. They are made from high-grade stainless steel, tantalum, nitinol, or cobalt/platinum. Once placed at the desired site during an angioplasty, they remain permanently in place in the blood vessel.

What do stents achieve?

The advent of stents has revolutionised the practice of interventional cardiology. Stents have had a welcoming impact on both the immediate and long-term success of angioplasty. First, they function as a scaffold, acting as a brace to the blood vessel and preventing the blood vessel from collapsing on itself, as may sometimes occur during angioplasty. This not only results in less risk to the patient, but is also reassuring to the interventional cardiologist in that any emergency complication is unlikely when the patient leaves the hospital.

Second, because of the permanent stable framework they provide, stents also prevent the treated blood vessel from gradually shrinking in diameter with time. This has helped, to a certain extent, to reduce the problem of recurrence of narrowing ("restenosis") after an angioplasty. For a patient this means that if a stent is used, there will be less need for a repeat procedure in the near future.

Drawbacks and prevention

Although stents have decreased the incidence of recurrence of narrowing after an angioplasty, this drawback is still seen in some patients undergoing the procedure. About 10 to 15 per cent of patients may require a repeat procedure in the first six months following stent placement. Recurrence of narrowing is infrequent beyond that time.

A certain group of patients has a higher probability of developing recurrence of narrowing. This emphasises the importance of proper selection of patients who are advised to undergo angioplasty and stent placement.

As of now, there is no clear answer to the question of prevention of recurrence of narrowing following stent placement. Several experimental strategies are under evaluation. Intravascular radiation appears to hold some promise, but this therapy brings with it many complex issues that require to be addressed. The use of agents such as anti-cancer drugs, agents targeting crucial cell enzymes, and gene therapy is being evaluated.

The future

The refinement of stent technology continues to evolve. In the days to come, in addition to providing mechanical support to the vessel wall, stents will also carry agents (chemicals or genetic material). These so-called "smart stents" will deliver these agents directly to the site of angioplasty. Stents capable of releasing radioactivity have shown both beneficial effects and important shortcomings in early clinical trials, emphasising the need for further research. Stents made of bio-degradable material, which disintegrate in two years after placement are also under evaluation.

Although recurrence of narrowing is an issue, with proper patient selection, more than 85 per cent of patients undergoing stent placement can be expected to have a very favourable outcome without the need for any further procedure or bypass surgery. Future developments in stent technology are likely to allow more patients to undergo angioplasty successfully.

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