Successful coronary bypass surgery goes back just 30 years.
Before surgeons hit on the idea of taking a piece of vein from the leg and sewing it into the coronary circulation, the outlook for people with advanced heart disease was grim. Drugs could be used to relieve the chest pain (angina) that was an early warning the coronary arteries were becoming blocked. But as blood flow to the heart muscle gradually deteriorated, patients found themselves on a one-way street to a potentially fatal heart attack.
Since those first experimental coronary artery bypass grafts (CABGs), surgeons have left no stone unturned in their search for new and better ways to undo the arterial damage done by our unhealthy diets and lifestyles. Not content with simply bypassing blocks in blood vessels, they have pushed them out of the way with balloons - percutaneous transluminal coronary angioplasty (PTCA) - drilled through them with lasers and, most recently, turned to keyhole surgery to improve results, speed recovery and, hopefully, cut costs.
In 1982, around 7,000 people in the UK underwent coronary bypass surgery. Ten years later, the Society of Cardiothoracic Surgeons reported 306 CABGs and 202 PTCAs per million population, adding up to 28,000 procedures a year. Based on data from the UK, Europe and Australia, the British Cardiac Society recommended a realistic national target for 1996-97 of 1,000 interventions per million population, with a ratio of six CABGs to four PTCAs.
Success rate Comparative trials of CABG and PTCA have consistently shown similar risks of subsequent death and heart attack, but patients with PTCA are more likely to need a further procedure in the first year after treatment, and their angina is less likely to totally clear up.
A key meta-analysis of 3,371 patients followed up over 2.7 years showed that 4.6 per cent of CABG and 4.4 per cent of PTCA patients died during followup.
But 17.8 per cent of PTCA patients required additional CABG within a year, though subsequently this figure fell to 2 per cent per year. In the first year of follow-up, a third of PTCA patients and only 3 per cent of CABG patients required a further intervention (PTCA or CABG). These results have been much debated.
Patients were carefully selected, so that those with the most serious disease got CABG, and problems arising from bypass operations tend to occur several years after surgery, outside the follow-up of the trial. So CABG may have looked better than it is.
Large trials comparing the outcome of CABG and minimally invasive coronary artery bypass grafting (MICABG) have not been done. But evidence suggests MICABG most suits patients with isolated narrowing near the top of the left coronary artery. They would not normally be referred for CABG and would be treated with PTCA. But a small retrospective study has compared the outcome of CABG, MICABG and PTCA in one such group.
There were no differences in mortality or morbidity between the three (28 patients in all), though one MICABG patient had to switch to conventional CABG because of anatomical difficulties.MICABG and PTCA patients needed less time in hospital than those who had CABG (2.7, 2.6 and 4.8 days respectively).
What can go wrong?
The greater need for further treatment in the short term following PTCA compared with CABG is largely due to restenosis of treated areas, as the arterial wall attempts to repair itself after being stretched and disrupted and the resulting scar tissue protrudes into the blood vessel and impairs blood flow once more.
Research has shown that this risk of restenosis can be reduced if a small piece of tubing, called a stent, is left in the coronary artery after PTCA to hold the arterial wall in place and keep the vessel open. Studies show that stents can reduce the need for repeat angioplasty by 30-50 per cent, and the main drawback - clot formation around the device - can be minimised with anti-clotting agents. These have reduced the incidence of this complication from as much as 10 per cent to less than 1 per cent.
CABG is not without its failures. The need for operations to be redone increases after about five to eight years, with higher risks.
The main problems with MICABG were largely due to surgeons improvising technically and with instruments. Results have improved as practice has been established.
Cost-effectiveness Initial savings associated with PTCA compared with CABG are largely offset by subsequent increased need for further intervention with the less invasive procedure. A comparison of CABG and PTCA in the UK showed that, in a two-year follow-up of 1,011 patients, CABG cost£1,050 (range£621-£1,479) a patient more than PTCA.
The initial average cost of treating a patient with PTCA was just over half that of CABG, but after two years this rose to 80 per cent. Follow-up is continuing for 10 years.
A more recent US analysis showed the cost-effectiveness of PTCA over CABG limited to patients with less serious coronary disease. In a study of nearly 1,000 patients, the initial mean cost of angioplasty was 65 per cent that of surgery ($21,113 versus $32,347), and patients returned to work five weeks earlier than with CABG.
At five years the gap had narrowed, so the cost of angioplasty was 95 per cent of that of CABG. At this stage, surgeons who had performed PTCA instead of CABG on patients with two diseased coronary vessels had saved over $5,500 per patient. But those who had chosen PTCA for patients with three-vessel disease were nearly $1,500 out of pocket.
All three techniques are likely to have a future role, depending on the nature of the disease, age and general health of the patient, and cost and availability of facilities and expertise.
The coronary circulation
The heart needs a blood supply like any other part of the body, and a network of coronary arteries and cardiac veins criss-cross the surface of the heart carrying blood to and from the heart muscle (myocardium). The key players in the coronary circulation are the left and right coronary arteries which get their blood from the base of the aorta - the circulation's main trunk route from the heart to the rest of the body. The left coronary artery (LCA) supplies blood to the upper part of the heart's most important chamber, the left ventricle, and the right coronary artery (RCA) supplies the lower part of the left and the whole of the right ventricle.
Left and right coronary arteries branch into smaller and smaller blood vessels as they spread across the heart.
The precise pattern of coronary blood vessels varies from person to person. But, in two-thirds of people, the RCA is dominant, in 15 per cent the LCA is dominant, and in about 20 per cent the two systems are equally important.
When is an operation needed?
Narrowing (stenosis) or blockage in the larger parts of the coronary circulation are more serious than those in the smaller vessels. Thus, the most common indication for coronary artery bypass graft is severe narrowing of the main stem of the left coronary artery, with blocked right coronary artery. Similarly, severe narrowing of an early part of the LCA or multiple blockage of branches further down the blood vessel also take a high priority for CABG.
A triple, quadruple or more extensive bypass refers to the number of blocks bypassed. Thus a triple bypass may be carried out on a single, seriously diseased coronary artery or dotted around several blood vessels. Percutaneous transluminal coronary angioplasty is generally used in less severe cases involving smaller areas of damage to a coronary artery.
How are the operations done?
Bypass surgery involves taking a piece of the saphenous vein in the leg and using it to re-route the blood supply to the myocardium around the diseased part of the coronary vessel. This usually means attaching one end directly to the aorta and the other to a point beyond the blockage in the coronary artery, so that blood can flow freely. To work on the aorta it is necessary to stop blood flowing through it and put the patient on a heartlung machine while surgery is carried out.
PTCA is a much less invasive procedure, usually carried out under local anaesthetic by a cardiologist rather than by a surgeon. Using an x-ray monitor to show the way, a guide catheter is inserted into an artery in the groin or arm and manoeuvred into place inside the diseased part of the coronary artery. A tiny balloon is then inflated to push the blockage back against the walls of the blood vessel, slightly stretching it, so that the blood supply is improved. Other devices, including a small, mechanically driven shaver, a diamond-shaped burr, or a laser have been used to improve coronary blood flow instead of a balloon, but PTCA is the most established alternative to bypass surgery.
First described in 1994, minimally invasive (keyhole) bypass surgery is increasingly popular. Over 1,400 patients in 60 centres have had successful operations.
6A much smaller incision is made in the chest than for conventional bypass surgery and the diseased vessel bypassed by joining the left internal mammary artery to the LCA beyond the point at which it is damaged. The need is removed for patients to be put on heartlung bypass machines, and recovery is faster.
1 Pocock S, Henderson R, Rickards A et al. Meta-analysis of randomised trials comparing coronary angioplasty with bypass surgery. Lancet 1995; 346(8984): 1184-89.
2 King R, Reece T, Hurst J et al. Minimally invasive coronary artery bypass grafting decreases hospital stay and cost. Ann Surg 1997; 225(6): 805-09.
3 Corr L. The future of interventional cardiology. Lancet 1996; 348(suppl 1): s23-s26.
4 Sculpher M, Seed P, Henderson R et al. Health service costs of coronary angioplasty and coronary artery bypass surgery: the Randomised Intervention Treatment of Angina (RITA) trial. Lancet 1994; 344(8927): 927-30.
5 Hlatky M, Rogers W, Johnstone I et al. Medical care costs and quality of life after randomization to coronary angioplasty or coronary bypass surgery. Bypass angioplasty revascularization investigation (BARI) investigators. New England J of Medicine 1997; 336(21): 9299.
6 Mariani M, Boonstra P, Grandjean J. Minimally invasive coronary surgery: fad or future? Br Med J 1998; 316(7125): 88.