For the many thousands who suffer from angina and heart failure, it is an attractive alternative to open-heart surgery; a tiny balloon is pushed into the large artery in the groin and guided up to the diseased coronary artery. When the balloon is inflated it flattens the blockage against the walls of the vessel, restoring a good flow of blood to the heart.
Angioplasty has one big drawback: in about 30 per cent of cases the blockage recurs within six months. It is a problem that has dogged the technique for 20 years. Only one device, the stent, has shown any promise in curbing the high reblockage rate. Now results from the first scientifically controlled trial of stenting versus conventional angioplasty have confirmed that a stent halves the chances of an artery becoming quickly reblocked.
The stent is a tiny mesh tube that is inserted into a blood vessel after it has been unblocked by an angioplasty balloon. Once in place, the stent acts as a mini-scaffold, propping the walls apart and increasing the flow of blood. The procedure is much the same as angioplasty, except that the stent is inserted around the angioplasty balloon. When the balloon is inflated, the stent expands to hold open the narrowed blood vessel and is left in place.
The 'Benestent' trial in 1992, named after Belgium and the Netherlands, where the study began, soon involved 520 patients in nine European countries. The patients, closely matched for the type and severity of their coronary artery disease, were randomly divided into two groups: one had angioplasty and a stent implanted; the other had angioplasty alone. When the coronary arteries of all the patients were examined six months later, only 17 per cent of the stent group had suffered reblockage compared with 34 per cent of the angioplasty group.
Stents were first used in human coronary arteries in 1987. Since then they have proved useful for dealing with threatened collapse of an artery, a complication met in about 5 per cent of angioplasties and which results in emergency bypass surgery in a third of patients. Stents have cut the incidence of sudden collapse to less than 1 per cent.
Cardiologists expect a big increase in the use of stents once the findings of the trial are published shortly in the New England Journal of Medicine. Dr Anthony Rickards, consultant cardiologist at the Royal Brompton National Heart and Lung Hospital, London, who entered several patients in the Benestent trial, said: 'Stenting is as good as angioplasty when you look at mortality and complications. It is better than angioplasty when you look at the reblockage rate. That is really what comes out of the trial.'
But he pointed out that the halving of the reblockage rate may not translate exactly. He estimates that stenting will reduce the need to redo an angioplasty, or go on to surgery, from 30 per cent to 20 per cent.
Not every patient is suitable for stenting. Dr Rickards estimates about a third of the 12,000 patients who undergo angioplasty in the UK each year could be candidates, and warns against any headlong rush into stenting. 'I think it is a worry. If you take the Benestent trial at its face value, you might end up doing more harm than good,' he says.
Sub-acute thrombosis is the sudden blockage of the artery by a blood clot. In stent patients this occasionally happens four to five days after the implant. Blood platelets stick readily to the metal surface of the stent, triggering the clotting process. Clot-busting drugs need to be given rapidly. In the Benestent trial, this sort of thrombosis was kept to a minimum by giving patients a combination of three anti-coagulant (blood-thinning) drugs just before stent implantation and for three to six months afterwards.
In the trial, nine patients in the stent group (3 per cent) suffered a sub-acute thrombosis and two died; in the angioplasty group, seven (2.7 per cent) suffered sub-acute thrombosis and one died. But Dr Rickards believes the trial was too small to be sure of this finding.
Dr Ulrich Sigwart, director of the Department of Invasive Cardiology at the Royal Brompton Hospital and in 1986 the first person to implant a stent in a human coronary artery, is also cautious: 'We have to make sure it is a controlled stenting explosion.' He believes stenting will soon replace half of all conventional angioplasties, and is planning to train cardiologists.
The growing enthusiasm for stenting among UK heart specialists is highlighted by statistics from the British Cardiovascular Intervention Society. Only 13 coronary stents were implanted in 1990, most to salvage an artery that had collapsed after angioplasty. In 1992, the latest year for which figures are available, the total was 316, with over half of these (179) being implanted in place of standard angioplasty.
Dr Charles Ilsley, consultant cardiologist at Harefields Hospital, Middlesex, opposes heavy promotion by stent manufacturers to encourage routine first-time use of stents in place of conventional angioplasty. The probable extra risk of sub-acute thrombosis with stenting means it should be restricted to cases in which conventional angioplasty has produced a poor result, he says.
He said if he were an angina patient given the option of a stent, he would want to know the implant was being carried out by a cardiologist who had done at least 500 angioplasties, and that standby coronary surgery facilities were available in case of emergency: 'This used to be a routine requirement for angioplasty. Not now. They're getting braver with other peoples' lives.' Despite these concerns, Dr Ilsley welcomed the 'era of stenting' because of its value in selected patients. Wider use of the technique should wait until the next generation of stent removed the threat of sub-acute thrombosis, he argued.
It could be a short wait. Just a few weeks ago, Dr Sigwart implanted in the first UK patient a stent coated with heparin, the clot-inhibiting drug. This patient is one of several hundred recruited for the Benestent 2 trial, which aims to find out if patients given the coated stent have a lower rate of sub-acute thrombosis than those given an ordinary stent. The heparin is slowly released from the stent, inhibiting the formation of clot during the dangerous first few weeks before the stent becomes buried within the artery walls.
It is hoped that by inhibiting clotting directly from inside the artery, thrombosis will be more effectively prevented and there will be no need for heavy anti-coagulant therapy that caused bleeding complications in almost one-tenth of patients in the first Benestent trial. Dr Sigwart is optimistic about the success of the new stent, as it produced a sub-acute thrombosis rate close to zero in pigs.
Dr Rickards is also impressed. 'It is conceivable that if a heparin-coated stent never causes sub-acute thrombosis, and if small amounts of thrombosis are responsible for restenosis, you develop the perfect stent. It will then replace angioplasty. That's the potential.
'In the UK, we are doing about 10,000 to 12,000 coronary angioplasties a year. But if you take 10,000 as the mark, then about 3,000 of these patients are going to need a second operation in the first few months after the angioplasty. By using coronary stenting you probably save about 1,000 of those procedures. That translates into a saving of about pounds 3m a year, and that's a lot of money.'
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