Understanding balloon angioplasty

This article was contributed to The Star (Malaysia) and published on the 15th of January 2006. It was cotributed on behalf of the Federation of Private Medical Practitioners Associations Malaysia. Please note our standard disclaimer.

An angioplasty (angio = blood vessel; plasty = repair) is the common term given to a whole range of percutaneous (done via a puncture through the skin) treatment of coronary artery disease. Balloon angioplasty then is repair of heart arteries, using the balloon and other devices, done via a puncture through the skin, into an artery, under local anaesthetic.

The proper medical name is actually PERCUTANEOUS (puncture through the skin) CORONARY (of the heart) INTERVENTIONS, or PCI for short. This term includes plain old balloon angioplasty – POBA (treatment using only the balloon) and angioplasty with coronary devices, for example, stents, cutting balloons, atherectomies (cutting away atheroma plaques) and others.

Just to recall some earlier articles: coronary artery disease (CAD) is caused by cholesterol accumulation (atheroma) in the coronary artery wall. It can be silent and only detected after a medical check-up, present itself as angina-type chest pains (typical or atypical), heart attacks, sudden cardiac arrest, and heart failure. Balloon angioplasty is an effective and minimally invasive way to clear away the cholesterol blockages.

What is balloon angioplasty?

In 1965, Dr Mason Sones, an American cardiologist working in Cleveland, performed the first coronary angiogram. This discovery was important because prior to 1965, it was believed that any attempt to instrumentate the arteries of the heart would result in death of the patient. Dr Sones showed us that this was possible, and safe.

With the coronary angiogram, we also have a road map of the patient’s heart arteries and the blockages that need fixing.

Dr Andreas Gruentzig, a Swiss cardiologist, carried this idea a little further by showing that it was safe to work inside the heart artery by performing the first angioplasty in 1977, clearing a severe blockage in the left front artery of a Swiss man (who was awake and talking). This feat was revolutionary. Balloon angioplasty was born.

In angioplasty and PCI, under local anaesthetic, a hollow rubber tubing, called the guiding catheter, is first positioned at the mouth (ostia) of the target coronary artery. Through this catheter, a very soft, floppy guidewire (0.014 inches in diameter) is gently negotiated into the target artery, and across the blockage, under the guidance of X-ray fluoroscopy. With the guidewire safely across the target blockage, the appropriate sized balloon catheter is then threaded into the guiding catheter with the guidewire as the monorail track.

The size and length of the balloon catheter selected depends on the size of the artery and length of the blockage. The balloon catheter has radio-opaque markers so that its exact position can be easily tracked. Once the balloon catheter is nicely across the target blockage, it is inflated with an inflation device, with hydrostatic pressures of about 6-8 barrs.

A recent cholesterol blockage is usually soft as margarine, so it is easily squashed and plastered to the artery wall, thus clearing the blockage. Old or longstanding blockages can be very hard.

Plain old balloon angioplasty (POBA) is almost always followed by coronary stent implantation (the reason for this will be made known later). POBA has an average procedural success rate of 85-95%, depending on the type of blockage, and also the experience of the operator.

Some centres boast a success rate of 97%. The risk of complications is about 4% and the risk of death from the procedure is about 1%. Again, complications and risks are very much dependant on the lesion, the centre doing the procedure and also the experience of the operator. We encourage all operators and institutions to keep a logbook (report card) of their experience so that their patient outcomes can be known, not just borrowing Western numbers as their own.

Problems with plain old balloon angioplasty (POBA)

There are three major problems associated with POBA. The first being coronary artery dissection, a dreaded complication of POBA. When hydrostatic pressures of the magnitude of 6-8 barrs are applied to the wall of the coronary artery in an attempt to clear the blockage, the normal three-layered arterial wall may crack (the inner layer with the cholesterol plaque may peel off from the middle layer). Should this happen, it may impede blood flow, causing an acute heart attack and possibly death.

This can occur in about 4-10% of POBA. Should this occur, an emergency coronary artery bypass surgery is required to save the patient. Currently, this complication is effectively treated with the coronary stent.

The second major problem is angioplasty re-narrowing (restenosis). This means that after a complete clearing of the blockage, over the next three to six months, the blockage recurs, to the original degree or even more.

The third major problem with POBA is total artery blockage of such long duration (chronic total occlusion) that it is hard as rock and the soft guidewire cannot traverse it, therefore causing POBA to fail.

Comparing medical therapy, PCI and bypass surgery

The big advantage of angioplasty over medical therapy is that with a preceding angiogram, the exact extent of artery blockage is known, and life threatening narrowings can be dealt with either by angioplasty, or by-pass surgery.

Of course, angioplasty also relieves chest pains better, when compared to medical therapy. The big advantage of angioplasty over bypass surgery is that it is minimally invasive, avoids general anaesthetics and the heart lung machine. POBA allows for rapid discharge (sometimes same day discharge) and the patient can return to work sooner. It can be repeated as often as necessary, quite unlike by-pass surgery.

Of course, it is of lower risk too. Indications for angioplasty include any significant narrowing in the heart arteries. The operative word here is “significant”. Not all narrowings in the heart arteries are significant. Less than 50% narrowings are not significant. Narrowings that do not cause anginal type chest pains (refer to first article in the series), or narrowings where the patient’s stress ECG is normal, are generally considered to be non-significant.

We do not encourage angioplasty in non-significant narrowing because it does not help the patient and there is a very real danger of re-narrowing, and complications from angioplasty.

Angioplasty re-narrowing (restenosis)

Probably the biggest let-down with balloon angioplasty is re-narrowing (restenosis). Having done a successful POBA, the cardiologist is faced with a 30-60% chance of the blockage re-occurring at the treated site. This reoccurrence following successful angioplasty is due to scar tissue (not cholesterol accumulation) forming over the site of the balloon trauma (the pressure exerted on the wall), almost like keloids forming following surgery.

Since the artery treated is about 2-3 mm in diameter, there is not much room to accommodate the scar tissue, therefore the re-narrowing of the artery. The main factors influencing re-narrowing include the size of the treated artery, the type of cholesterol blockage treated, the operator’s experience, the presence or absence of diabetes, and cigarette smoking, among others. The effective treatment to lessen re-narrowing is the coronary stent.

Coronary stents

A. The bare-metal stent or BMS for short

In the early days of POBA, various devices were introduced in quick succession to complement and improve upon POBA. All the devices, and there were many, are now reserved for special niche indications and not for routine use, except for coronary stents, and maybe, intravascular ultrasound. Some of the devices have gone totally off the market because of potential harm to the patient, for example, laser angioplasty.

A coronary stent is a thin, tubular wiremesh of surgical grade stainless steel (nowadays, some stents are made of composite materials), that is crimped onto a balloon catheter, so that where the balloon catheter goes, the stent can follow, all riding on the guidewire as a monorail track.

Once over the target lesion, the balloon is inflated, and with it, the stent too. Once fully expanded to its full size, the balloon is deflated and withdrawn while the stent is left behind, stuck to the artery wall.

Over the next one to two months, scar tissue will grow over the stent and cover it. But because, the artery passage can be fully widened with the stent, the scar tissue has more room to grow, and so there is less re-narrowing.

Extensive laboratory and also in-man use has proven these stents to be safe and effective. Its use is so widespread and popular now that newer and better stents have come into the market.

The original type of bare-metal stainless steel stents, had a re-narrowing rate of about 20-30%, better than POBA re-narrowing rates of 30-60%, but still unacceptably high, especially in the diabetic patients. Stents, however, were very useful to treat artery dissection, which sometimes complicates POBA. It is important to note that BMS is relatively cheap. Like all devices there are problems. The problem with BMS is the risk of acute stent thrombosis (blood clotting in the stent), often due to failure to take certain blood thinning medications, or procedural technical problems. Of course there is also the problem of a 20-30% risk of re-narrowing, for which reason, the drug-eluting stents were invented.

B. The drug-eluting stents (medicated stents) or DES for short

These stents were recently introduced into the market (as late as 2002) to combat the POBA and BMS problem of re-narrowing. The DES is a stainless steel stent coated with a polymer, onto which a drug is bonded. It reduces re-narrowing on the stent coating, lessening scar tissue formation.

Currently, there are two medicated stents that are FDA and CE mark approved – the Cypher stent which contains the drug sirolimus, and the Taxus stent which contains the drug paclitaxel. There are a few other DES that are CE mark-approved but not yet FDA-approved.

The biggest benefit of DES is a very low re-narrowing rate (less than 5%). In diabetes, this re-narrowing rate may be about 10%, making this a major advancement in the treatment for CAD.

Although there were initial worries about their safety, over time and wider usage, they have both been proven to be very safe and effective. As more and more DES are implanted, they pose a serious threat to coronary artery bypass surgery. To date, more then 4.5 million DES have been implanted, despite the fact that DES are expensive, costing an average US$2,500 (RM9,250) each.

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