Coronary Artery Bypass Surgery (CABG): How Bypass Surgery Restores Blood Flow to the Heart

Coronary artery disease can produce narrowing in one or more arteries supplying the heart muscle. Medication can reduce symptoms and cardiovascular risk, while angioplasty and stenting can open selected narrowed segments from inside the artery.

But some patterns of coronary disease are better approached by creating an entirely new route for blood to reach the heart muscle.

That is the principle behind coronary artery bypass grafting (CABG).

Instead of removing the underlying blockage, CABG uses a blood vessel taken from another part of the body to create a pathway around the diseased section of a coronary artery. Blood can then reach the heart muscle beyond the obstruction through the new graft.

The operation is particularly important when coronary disease is extensive, anatomically complex, or when the expected balance between surgical bypass and catheter-based treatment favours CABG.

What is CABG?

CABG is a surgical procedure used to restore blood flow to areas of heart muscle supplied by significantly diseased coronary arteries.

A surgeon connects a healthy blood vessel to the coronary artery beyond the obstructed segment.

The new vessel acts as a bypass.

The original coronary artery may remain narrowed, but blood has an alternative route to reach the myocardium.

This is fundamentally different from angioplasty and stenting.

With PCI, the cardiologist works inside the diseased coronary artery and treats the obstructing lesion.

With CABG, the surgeon creates a new pathway around the diseased segment.

Harrison’s describes this distinction as important: PCI targets individual culprit lesions, whereas a bypass graft can provide a conduit around the diseased segment and potentially future culprit lesions proximal to the graft connection.

Why would someone need a bypass rather than a stent?

A coronary blockage does not automatically mean that bypass surgery is required.

The decision depends on several factors, including:

• how many coronary arteries are diseased
• where the blockages are located
• how complex the lesions are
• the patient’s left ventricular function
• whether diabetes is present
• whether the anatomy is suitable for PCI
• the expected completeness of revascularisation
• other medical conditions
• the risks associated with surgery

Harrison’s describes symptoms, coronary anatomy and ventricular function as major factors in CABG selection.

Bailey & Love similarly frames the decision around two separate questions: whether coronary revascularisation is appropriate and, if so, whether CABG or PCI is the more appropriate method for that individual patient.

This is why a coronary angiogram alone does not determine the treatment.

The entire clinical picture matters.

When is CABG considered?

CABG can be considered when coronary revascularisation is appropriate and the anatomy or clinical circumstances make surgical bypass suitable.

One important indication is persistent limiting angina despite appropriate medical therapy.

Revascularisation may also be considered when the coronary anatomy places the patient at sufficiently high risk that revascularisation can provide a prognostic benefit.

Harrison’s identifies severe or extensive coronary disease, including important patterns of left-main and multivessel disease, among circumstances in which CABG may have a role.

The decision becomes particularly important in patients with:

• left-main coronary disease
• extensive multivessel disease
• certain patterns of diabetes with multivessel disease
• significant coronary disease with impaired left ventricular function
• coronary anatomy unsuitable for PCI
• recurrent disease after previous PCI in selected circumstances

The exact indications used in modern practice depend on contemporary guidelines and the individual patient’s anatomy and risk profile. Harrison’s 20th edition is a useful clinical foundation but was published in 2018, so current guideline thresholds should be verified separately when making an individual treatment decision.

What happens during CABG?

Traditional CABG is performed through a median sternotomy, providing the surgical team access to the heart.

The operation may use cardiopulmonary bypass (CPB).

CPB temporarily takes over the circulation and oxygenation of blood, allowing the surgeon to operate on a relatively still and bloodless heart.

Bailey & Love describes CPB as a complex process involving the surgeon, anaesthetist and perfusionist, with complications related to anticoagulation, blood exposure to the artificial circuit, inflammation and organ-system effects.

Once the heart is adequately exposed and protected, the surgeon prepares the coronary targets and connects the grafts to the coronary arteries beyond the obstructive lesions.

After the grafts have been completed and cardiac function is adequate, circulation is gradually returned to the patient’s own heart and CPB is discontinued.

The chest is then closed and the patient is transferred to intensive care for postoperative monitoring.

Where do the bypass grafts come from?

One of the defining features of CABG is that the surgeon needs a suitable blood vessel to use as a conduit.

The major sources include:

Internal thoracic artery

The internal mammary artery—also called the internal thoracic artery—is one of the most important arterial conduits used in CABG.

The left internal mammary artery (LIMA) is particularly important for bypassing the left anterior descending artery (LAD).

Harrison’s describes internal mammary and radial artery grafting as preferred arterial approaches, with the saphenous vein used when additional conduits are required.

Bailey & Love also describes the increasing recognition of the value of the internal mammary artery in coronary bypass surgery.

Radial artery

The radial artery from the forearm can also be used as an arterial graft.

Its use depends on the patient’s anatomy, suitability of the vessel and the surgeon’s strategy for achieving complete revascularisation.

Saphenous vein

A section of the saphenous vein, usually obtained from the leg, can be used to construct a bypass conduit.

It can provide additional grafts when several coronary targets need to be bypassed.

The choice and combination of conduits are individualised according to the coronary targets and patient factors.

What does “double bypass” or “triple bypass” mean?

Patients sometimes hear terms such as:

• single bypass
• double bypass
• triple bypass
• quadruple bypass

These terms generally refer to the number of coronary bypass grafts created, not the number of coronary arteries that are completely blocked.

For example, a “triple bypass” means that three bypass grafts have been constructed.

The number of grafts required depends on the number and location of significant coronary lesions and which vessels can be successfully bypassed.

The goal is not simply to create as many grafts as possible.

The goal is to achieve an appropriate and sufficiently complete revascularisation strategy.

On-pump vs off-pump CABG

CABG does not always require conventional cardiopulmonary bypass.

On-pump CABG

In conventional CABG, CPB supports circulation while the surgeon operates on a controlled surgical field.

This allows the surgeon to work on a relatively still heart.

Off-pump CABG

Off-pump coronary artery bypass (OPCAB) is performed on the beating heart without using conventional CPB.

Special stabilisation devices are used to reduce movement at the area where the surgeon is creating the coronary anastomosis.

Bailey & Love describes off-pump surgery as avoiding some of the physiological stress associated with CPB and reducing, to some extent, manipulation of the aorta. However, it also notes concerns about performing precise anastomoses on a beating heart and that evidence has not established universal superiority of one approach.

Harrison’s similarly notes that minimally invasive or off-pump approaches can reduce morbidity and shorten convalescence in selected patients.

The decision therefore depends on the patient’s coronary anatomy, surgical plan and the expertise of the treating team.

Can CABG be performed through a smaller incision?

Selected patients may be suitable for minimally invasive approaches.

Bailey & Love describes minimally invasive direct coronary artery bypass (MIDCAB), in which a strategically placed smaller incision can allow the internal mammary artery to be connected to the LAD without conventional full sternotomy.

Another approach is hybrid coronary revascularisation, in which minimally invasive bypass—often LIMA-to-LAD—is combined with PCI for other coronary lesions.

These approaches are not appropriate for every patient.

Extensive multivessel disease may still require conventional surgical exposure and multiple bypass grafts.

What are the risks of CABG?

CABG is major cardiac surgery and carries substantially greater physiological stress than catheter-based PCI.

Potential complications include:

• bleeding and need for blood transfusion
• myocardial infarction
• stroke
• atrial or other cardiac arrhythmias
• infection
• wound complications
• kidney injury
• respiratory complications
• neurological complications
• complications associated with cardiopulmonary bypass
• graft occlusion
• postoperative heart failure
• death

Cardiopulmonary bypass itself can contribute to inflammatory, coagulation and organ-system complications. Bailey & Love lists bleeding disorders, infection, embolic complications, myocardial depression, neurological dysfunction, pulmonary injury and systemic organ dysfunction among potential CPB complications.

The patient’s individual risk can be considerably different from another patient’s.

Risk increases with factors such as significant ventricular dysfunction, major comorbidities, advanced age, urgent surgery and reoperation. Harrison’s specifically notes the relationship between these factors and perioperative risk.

What happens after CABG?

After surgery, patients generally spend an initial period in intensive care.

The early postoperative period focuses on:

• cardiovascular monitoring
• respiratory support
• bleeding assessment
• rhythm monitoring
• fluid and kidney function
• pain control
• prevention of infection
• gradual mobilisation

The recovery process then progresses from intensive monitoring to ward-based care and eventually rehabilitation at home or through a cardiac rehabilitation programme.

The chest incision requires time to heal, and recovery from a sternotomy is considerably longer than recovery from a catheter-based PCI procedure.

Patients may initially experience:

• chest or wound discomfort
• fatigue
• reduced exercise tolerance
• sleep disturbance
• appetite changes
• temporary mood changes

These symptoms do not necessarily indicate that the bypass has failed.

Recovery should be assessed in the context of the entire operation and the patient’s preoperative condition.

How effective is CABG for angina?

CABG can substantially improve angina when the bypass successfully restores blood flow to the affected myocardium.

Bailey & Love reports that when revascularisation is complete, more than 90% of patients have relief or improvement of anginal symptoms at one year, with the proportion decreasing over longer follow-up as native coronary and graft disease progresses.

Harrison’s similarly reports substantial improvement in angina following complete revascularisation.

However, CABG does not permanently eliminate atherosclerosis.

The patient can still develop disease in:

• native coronary arteries
• saphenous vein grafts
• other arterial grafts
• previously less-diseased coronary segments

Long-term cardiovascular risk-factor management therefore remains essential.

How long do bypass grafts last?

Different grafts have different long-term patency characteristics.

Arterial grafts generally have better long-term durability than saphenous vein grafts.

Harrison’s reports substantially higher long-term patency for internal mammary and radial artery grafts compared with saphenous vein grafts.

Saphenous vein grafts are vulnerable to progressive disease and occlusion over time.

This does not mean that every vein graft will fail.

It means that graft surveillance and aggressive management of cardiovascular risk factors remain important after surgery.

Can a bypass graft become blocked?

Yes.

A bypass graft can narrow or become completely occluded.

The mechanisms differ according to the time after surgery.

Early graft failure can involve technical problems or thrombosis, while later vein-graft disease can involve progressive atherosclerotic changes.

Symptoms may return if a graft becomes significantly narrowed or if disease develops elsewhere.

Recurrent chest pain after CABG therefore needs proper assessment rather than being automatically attributed to the previous surgery.

What happens if angina returns after CABG?

Recurrent symptoms can have several causes.

They may result from:

• progression of disease in a native coronary artery
• narrowing of a bypass graft
• occlusion of a graft
• disease in a coronary territory that was not previously bypassed
• a non-cardiac cause of chest pain

Evaluation may involve clinical assessment, ECG, stress testing, echocardiography, CT coronary angiography or invasive coronary angiography depending on the circumstances.

The appropriate test depends on the patient’s symptoms, risk profile and previous coronary anatomy.

CABG vs angioplasty and stenting

The difference can be simplified as follows:

The table should not be interpreted as saying that one treatment is universally preferable.

The choice is patient-specific.

Harrison’s emphasises the importance of considering left ventricular function, diabetes, lesion complexity and coronary anatomy when selecting between PCI and CABG.

In complex cases, a multidisciplinary Heart Team approach involving interventional cardiology, cardiac surgery and the patient is particularly useful.

CABG in patients with diabetes

Diabetes is an important consideration when choosing a revascularisation strategy.

Patients with diabetes can have extensive and diffuse coronary disease, and CABG has demonstrated important benefits in selected patients with diabetes and multivessel coronary disease.

Harrison’s describes evidence supporting CABG over PCI in selected patients with diabetes and multivessel ischemic heart disease.

But diabetes alone does not automatically mean that CABG is required.

The number and location of diseased vessels, lesion complexity, ventricular function, surgical risk and the feasibility of PCI all remain relevant.

CABG when heart function is reduced

Some patients requiring CABG have reduced left ventricular function.

Chronic coronary disease can sometimes leave portions of myocardium with reduced contractility despite preserved cellular viability. This is commonly described as hibernating myocardium.

Revascularisation can restore blood flow to viable but chronically underperfused myocardium.

Harrison’s discusses CABG in ischemic cardiomyopathy with multivessel disease and notes evidence supporting revascularisation particularly in patients with ongoing angina and left ventricular dysfunction.

However, reduced ejection fraction also increases operative risk.

This is one reason CABG decisions in patients with advanced ventricular dysfunction require particularly careful assessment.

Is CABG an emergency operation?

Not usually.

CABG can be performed urgently in selected clinical situations, but many patients undergo planned surgery after detailed assessment and preparation.

The timing becomes especially important after an acute coronary syndrome.

Bailey & Love notes that the optimal timing differs between PCI and CABG and that CABG may be performed after a period of medical stabilisation when circumstances allow.

Emergency surgery may be required in selected patients when coronary anatomy cannot be adequately treated with PCI or when mechanical complications or other serious problems require surgical treatment.

Life after CABG

CABG is not the end of coronary disease management.

The operation creates new routes for coronary blood flow, but it does not eliminate the underlying biological process that caused atherosclerosis.

Long-term management may include:

• antiplatelet therapy
• lipid-lowering treatment
• blood-pressure control
• diabetes management
• smoking cessation
• regular physical activity
• healthy dietary habits
• weight management where appropriate
• cardiac rehabilitation
• follow-up with the treating cardiovascular team

These measures help protect both native coronary arteries and bypass grafts.

Harrison’s specifically highlights treatment of cardiovascular risk factors, particularly dyslipidemia, as important for maintaining graft patency and improving outcomes.

Questions to ask the cardiac surgeon

Before planned CABG, patients may want to ask:

1. How many coronary arteries require bypass?
2. Which coronary vessels will be bypassed?
3. Which grafts are planned—internal mammary, radial artery or saphenous vein?
4. Why is CABG being recommended instead of PCI?
5. Could PCI reasonably achieve complete revascularisation in my case?
6. Will the operation use cardiopulmonary bypass?
7. Am I a candidate for an off-pump or minimally invasive approach?
8. What are my individual surgical risks?
9. How long should I expect to remain in hospital?
10. What will my cardiac rehabilitation and long-term medication plan involve?

The key point

CABG works by creating a new route for blood to reach heart muscle beyond a diseased coronary artery.

The operation can use arterial conduits such as the internal thoracic or radial artery and venous conduits such as the saphenous vein.

Unlike PCI, which focuses on treating individual coronary lesions, CABG can provide bypasses to multiple coronary targets and is particularly important in selected patients with extensive or complex coronary disease.

But CABG is major surgery, and the decision involves balancing the potential benefits of revascularisation against operative risk.

For patients in whom both PCI and CABG are technically possible, the choice should consider coronary anatomy, ventricular function, diabetes and other clinical factors, together with the patient’s preferences and the expertise of the treating team.

Written and Reviewed By Dr. Munaf Ahmad Ansari

Medical information note: This article is written for information purpose only. Individual treatment decisions should be based on contemporary clinical guidelines and assessment by an appropriately qualified medical team.