Synonyms: CABG; bypass grafting; triple bypass; quadruple bypass

This is one of two procedures for coronary artery disease, the other being percutaneous transluminal coronary angioplasty (PTCA). The patient will already have had a clinical diagnosis of ischaemic heart disease (IHD), confirmed by coronary angiography to delineate the obstruction. If PTCA is feasible, it is usually performed at the time of coronary angiography. Coronary artery bypass grafting (CABG) may be performed as a primary procedure, after failed PTCA or as a repeat procedure.

Benefits of treatment

3 major randomised controlled trials compared CABG with medical therapy. They are the:

1. Coronary Artery Surgery Study (CASS)
2. The Veterans Administration (VA) Co-operative Study
3. The European Coronary Surgery Study (ECSS)

A meta-analysis of these 3 studies showed that in high- and medium-risk patients there was definite benefit from CABG but not in low-risk patients.¹ The risk reduction was greater in patients with left main artery disease than in those with disease in 3 vessels or 1 or 2 vessels. Other studies have found similar benefits of CABG over percutaneous coronary intervention (PCI), especially in patients with multivessel disease or left main stem (LMS) disease.^2,3 The benefits of CABG were most pronounced in patients in the highest risk categories. A more recent collaborative analysis reported similar long-term mortality after CABG or PCI in patients with multivessel disease.⁴ The authors further concluded that CABG might be better in patients with diabetes mellitus (DM) and those aged over 65, as there was lower mortality in these subgroups. SIGN states that benefits of surgery tend to be lost if surgery is delayed. The NHS is taking great steps to reduce time from first referral for exercise testing to surgery with considerable political pressure. The National Service Framework (NSF) sets targets for waiting times but these are dependent upon the degree of urgency. It is necessary to stratify urgency as deaths are often in the early stages of waiting.⁵

Choice of re-vascularisation procedure

• Short, discrete, non-calcified lesions on straight, unbranched arteries are often amenable to PTCA but longer, calcified lesions in tortuous vessels, or involving major bifurcations, and chronic occlusions are more likely to require CABG.
• PTCA is the treatment of choice for single or two-vessel disease unless it includes the proximal left anterior descending (LAD) artery. It can also be used as first choice if a previous CABG shows re-stenosis.
• CABG is the procedure of choice for LMS disease with >50% stenosis, two-vessel disease that includes the LAD and triple-vessel disease.⁶
• CABG also has advantages over PTCA if there is left ventricular (LV) dysfunction or a strongly positive exercise test.

Epidemiology

Around 28,000 CABG operations are performed in the UK each year. There is considerable geographical variation in terms of numbers of operations and referral rates between primary care centres.

Surgical technique

• The operation is usually performed through a mid-sternal incision.
• Veins may be harvested from the saphenous vein in the legs but arteries are also transplanted into place and these give better long-term outcomes.
• The most commonly-used arteries are the internal thoracic (internal mammary) but the gastro-epiploic, inferior epigastric or radial arteries are also used.
• Endoscopic vein harvesting is associated with a more adverse outcome compared with direct vision graft harvesting.⁷
• Over 75% of patients have at least 3 grafts and at least 1 is usually an artery.
• 10 years after CABG, 83% of internal thoracic artery grafts are patent but only 41% of saphenous vein grafts.⁸
• Those who receive only saphenous vein grafts have 1.6 times the death rate over 10 years compared with those who receive at least 1 internal thoracic artery.
• It is possible to use a smaller incision in a technique called minimally invasive direct coronary artery bypass (MIDCAB) with a more lateral approach. Minimal access surgery is where a small incision is made directly over the artery to be bypassed. "port access surgery" is where a series of small cuts are made in the chest. These new techniques are still being evaluated and are not yet available routinely.
• Most surgeons prefer cardioplegia with cardiopulmonary bypass.
• Sometimes surgeons operate on a beating heart, performing delicate anastomoses on a moving target (usually the case for MIDCAB and port access).⁹
• Operating without cardioplegia is said to reduce the risk of complications following surgery but this is disputed.¹⁰ The results of long-term survival rates are promising (median 23 years for surgery involving the LAD coronary artery).¹¹
• As with so many procedures, the evidence is that results are best when operators perform a significant number per year and in a unit with a reasonably high workload. The NSF suggests that each surgeon should perform at least 50 operations a year and that a unit should perform at least 400 cases per year by at least 3 trained surgeons. SIGN suggests a much higher figure of 250 operations per year by a trained surgeon.

Off-pump coronary artery bypass grafting

• A surgical technique which has been used increasingly since the 1990s is off-pump coronary artery bypass grafting (OPCAB).
• Its benefits include shorter procedure times and reduced complications, although these have not been consistently demonstrated.^12,13
• When first used, OPCAB was usually only undertaken in those with a single vessel disease - now multivessel OPCAB is feasible.
• The European System for Cardiac Operative Risk Evaluation (EuroSCORE) formula is a scoring method which can predict early and mid-term mortality for patients undergoing CABG. It may have a role to play in determining patient risk for those undergoing OPCAB.¹⁴

Outcomes

• CABG significantly improves symptoms of angina and quality of life, and exercise capacity and reduces the need for anti-anginal therapy compared with medical treatment.¹⁵
• Over 75% of patients are free of ischaemic events at 5 years and nearly 50% at 10 years.¹⁶
• There is less limitation of physical activity.
• At 10 years the benefit of CABG over medical therapy is lost in those who had only saphenous vein grafts but, after arterial grafts, it remains.
• Survival is improved, with the greatest relative benefit going to those with LMS stenosis of >50%. Patients with angina triple-vessel disease or two-vessel disease including proximal LAD stenosis also survive longer but those with two-vessel disease excluding proximal LAD stenosis, or with single vessel disease, gain no survival advantage.
• Patients with abnormal LV function or strongly positive exercise tests derive greater absolute survival benefit from coronary artery bypass surgery than from medical therapy.
• Women undergoing CABG have worse outcomes compared to men, which is thought to be the result of greater co-morbidity, smaller coronary arteries and older age. However despite this, long-term survival does not differ between genders.¹⁷

• Significant LMS stenosis of 50% or more
• Triple-vessel disease
• Two-vessel disease including a significant proximal LAD stenosis
• Impaired LV function or strongly positive exercise test

The operative mortality rate is around 1 to 3% but varies according to case type.

Both operative mortality and outcome are more likely to be adverse in the following:

• Increasing age
• Smoking
• Being female¹⁸ (the reason for this is debated but is probably multifactorial as mentioned above)
• Diabetes
• Overweight or obesity¹⁹
• Being short
• Other illness
• LMS disease, poor LV function and multivessel disease
• If the operation was an emergency for unstable angina or shortly after myocardial infarction (MI)

Complications

• MI occurs in 2% with probably rather more cases of diffuse myocardial damage
• Acute kidney injury
• Low output states requiring supportive measures
• Ventricular arrhythmias like broad complex tachycardia
• Stroke occurs in 2% but a third show impairment on psychometric testing. Reducing handling of the aorta may reduce embolism. The problem is that patients needing CABG are at risk of cardiovascular disease in general and it has been suggested that pre-operative investigation of cerebrovascular disease should be undertaken.²⁰ This includes looking for carotid artery stenosis - the risk of peri-operative stroke being higher in those who have symptomatic stenoses.²¹
• Damage to other organs is rare in elective surgery, but the risk increases with bypass time and increasing age
• Clopidogrel is much used with PTCA but should be avoided around CABG (stop 7 days before operation). It increases the need for substantial transfusion and also the need for re-operation to secure haemostasis.^22,23 Aspirin should be stopped 3 to 7 days before surgery, as stopping it 2 days or less before operation increases the need for transfusion.²⁴ It is usually started the day after surgery. During surgery with cardiopulmonary bypass (CPB), heparin is used. Patients who have had CPB seem to have an increased resistance to aspirin compared with those who were not operated on using CPB. This is probably because CPB causes an increased turnover of platelets.²⁵
• Cognitive decline has been reported in various studies following CABG. However, some of these studies have been criticised on the basis of no consensus on how best to measure pre-operative cognition. Most changes in cognition are thought to be mild and to reverse within the first few months after surgery.²⁶ Intraoperative cerebral oxygen desaturation predicts both cognitive decline and longer inpatient stay following CABG.²⁷

Follow-up

Attention must be paid to secondary prevention of IHD. Stopping smoking is essential if it has not been done already.²⁸ Long-term aspirin is essential, as is the use of an angiotensin-converting enzyme inhibitor (ACEI)/angiotensin receptor blocking (ARB) agent and beta blockers. Statins should be used to get optimum cholesterol levels. Control of blood pressure and any diabetes should be optimised. Encourage exercise within reason and a healthy diet.