CAD is by far the most common cause of heart disease, resulting from the narrowing of coronary arteries ('stenosis') caused by deposition of atherosclerotic plaque. Coronary artery stenosis may be asymptomatic or may lead to angina, a chest pain that may be severe enough to restrict or prevent exertion. A critical reduction of the blood supply to the heart may result in MI or death.
CAD causes about 2,100 deaths annually per million of the population in England and Wales (about 110,000 deaths in total), 1 of the highest rates in the world. CAD is also the cause of considerable morbidity and loss of ability to lead a normal life. Approximately 1.4 million people in England and Wales suffer from angina, the most common form of such morbidity.
Stenotic lesions are categorised as A, B1, B2 and C. A denotes a relatively short (less than 10 mm) and easily accessible lesion. C denotes lesions that: are relatively long (greater than 20 mm); may be less accessible, tortuous and/or have side branches; and may be totally occluded.
CAD may affect 1 or more arteries, which may be of different calibres. Occlusion may be partial or total.
The symptoms and health risks that are associated with a stenosed artery may be treated medically – by modification of risk factors (for example, smoking, hyperlipidaemia, obesity and hyperglycaemia) and/or by drug treatment (for example, beta-adrenergic blockers, nitrates, calcium channel blockers, antiplatelet agents and statins).
If these medical treatments fail or are inappropriate, 2 invasive therapies are available. The first, coronary artery bypass grafting (CABG), involves major cardiac surgery. The second, so-called balloon angioplasty, or percutaneous transluminal coronary angioplasty (PTCA), involves a non-surgical widening from within the artery using a balloon catheter. When inflated, the balloon increases the calibre of the artery.
Recently, most PTCA procedures have involved the use of stents. Stents are thin wire-mesh structures that act as permanent prosthetic linings to keep the artery inflated and maintain its patency. PCI is a generic term to encompass PTCA with or without adjunct techniques such as stenting.
For disease in a single artery, PCI with a stent has been the more frequent treatment; for disease in 2 arteries, patient numbers for PCI with a stent and CABG have been similar; and for more than 2 affected arteries, CABG has been used much more frequently.
The major problem with PCI is restenosis of the artery, which has 3 main causes. The first, recoil of the artery, happens when the balloon is deflated. It usually occurs immediately or within 24 hours of completion of the procedure, and may require emergency CABG. Stents essentially eliminate recoil of the artery. The 2 subsequent problems, mostly arising during the first 6 months, are contraction of the adventitia secondary to an injury reaction (3 to 6 months), and proliferation of smooth muscle cells within the arterial wall (4 to 6 months). A repeat procedure is consequently required in approximately 20% of patients with simple lesions. This rate of reintervention is much higher (up to 50%) for arteries of small calibre, saphenous vein grafts, long lesions, total occlusions and in people with diabetes.
Recent advances in stent technology have reduced some of the problems of restenosis, as well as lowering the cost of stents. In addition, the use of antiplatelet drugs and other therapeutic strategies to prevent thrombosis have improved long-term outcomes.
One of the main criteria for assessing the clinical effectiveness of PTCA with stents compared with standard PTCA (without stents) is the ability to reduce the incidence of subsequent attacks of angina as well as major adverse coronary events (MACE), which include death, MI and the need for further revascularisation procedures (CABG or repeat PCI).
Patients for whom both a CABG and a PCI involving stenting are appropriate techniques would, other things being equal, choose PCI in almost all cases, even though the chances of restenosis are greater. This is because the procedure is less invasive, has a lower chance of death during the operation, and involves a much shorter and less painful recuperation time.
Approximately 39,000 PCI procedures were undertaken in the UK in 2001, equating to 663 per million of the population – a rate that had increased at an average of 14% per year over the previous 10 years. The rate for the UK remains below that of the European Union (EU) average, which exceeds 1,000 per million of the population.
In the UK, the proportion of PCI procedures using stents rose steeply between 1993 and 1999, from below 10% to nearly 80%. It has continued to increase, although more slowly, to about 85% in 2001.
The number of CABG procedures performed each year in the UK has increased from 15,700 in 1991 to 24,700 in 1999 to 2000, or from 292 to 464 per million of the population. The rate of increase has slowed since the first half of the 1990s.
The National Service Framework for Coronary heart Disease target, set in March 2000 for revascularisations (PCIs and CABGs), is at least 1,500 per million of the population (750 for each type of intervention). At current growth rates, the combined target will be reached by about 2005.