When the arteries that supply blood to the heart become narrowed or blocked, the heart muscle may not receive enough oxygen-rich blood. This condition, known as coronary artery disease (CAD), can cause chest pain, shortness of breath and reduced exercise tolerance. In more serious cases, it can increase the risk of a heart attack.
One treatment option for significant coronary artery blockages is coronary artery bypass grafting (CABG). Instead of removing the blockage itself, CABG creates a new route for blood to flow around the narrowed or blocked section of the coronary artery.
If you are looking for a broader overview of the procedure, you can also explore our guide to Coronary Artery Bypass Grafting (CABG).
What happens when a coronary artery becomes blocked?
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Coronary arteries carry oxygen-rich blood to the heart muscle. Over time, fatty deposits, cholesterol and other substances can build up inside the artery wall, forming atherosclerotic plaque.
As plaque accumulates, the artery can become progressively narrower. A severely narrowed artery may restrict blood flow, particularly when the heart needs more oxygen during physical activity.
If a plaque ruptures and a blood clot forms on top of it, the artery can become suddenly blocked. This can cause an acute coronary syndrome, including a heart attack.
The effect of a blockage depends not only on how narrow the artery is, but also on its location, how many coronary arteries are affected, the development of alternative blood-flow pathways and the amount of heart muscle at risk.
Does every blocked coronary artery require CABG?
No. This is an important distinction. Finding a blockage on a coronary angiogram does not automatically mean that bypass surgery is required. Some blockages can be managed with medicines, lifestyle changes or a catheter-based procedure such as angioplasty and stent placement.
CABG is considered when the overall pattern of coronary artery disease suggests that surgical revascularization is likely to provide a greater benefit than medical treatment or PCI for that particular patient. Doctors consider factors such as:
- How many coronary arteries are significantly narrowed
- Where the blockages are located
- How complex the coronary artery disease is
- Whether the left main coronary artery is affected
- Whether the patient has diabetes
- Heart pumping function
- Symptoms and their effect on daily life
- Whether angioplasty and stenting are technically suitable
- The patient's overall health and surgical risk
When is CABG commonly considered for blocked arteries?
CABG becomes particularly important when coronary artery disease is extensive or complex and bypass surgery is expected to provide an advantage over other treatment options.
Multiple coronary arteries are significantly blocked
When several major coronary arteries have significant disease, treating every blockage with stents may be technically difficult or may require multiple procedures. CABG can create several bypasses during one operation, allowing blood to reach different areas of the heart beyond their respective blockages.
For patients with complex multivessel coronary disease who are suitable candidates for both PCI and CABG, contemporary European guidance notes evidence favouring CABG in certain groups, particularly patients with diabetes.
The left main coronary artery is affected
The left main coronary artery supplies blood to a large portion of the heart through its major branches. Significant disease in this artery can therefore have serious consequences.
Surgical revascularization is recommended in patients with significant left main coronary artery disease when appropriate, although selected patients with suitable anatomy may also be considered for PCI. The decision depends on anatomical complexity and the patient's overall clinical situation.
The disease is complex or difficult to treat with stents
Some blockages are difficult to treat with PCI because of their location, length, calcification or involvement of multiple branches. In these situations, CABG may offer a more complete and durable way of restoring blood flow to the affected areas.
The patient has diabetes and multivessel disease
Diabetes can affect multiple coronary arteries and is an important factor when choosing a revascularization strategy. For appropriate patients with diabetes and multivessel coronary artery disease, guidelines generally favour surgical revascularization when the patient is a suitable surgical candidate.
How does CABG bypass a blocked artery?
The goal of CABG is not to physically remove the plaque from the coronary artery. Instead, the surgeon creates a new pathway around the blockage.
A healthy blood vessel is taken from another part of the body. Depending on the patient's anatomy and the number of bypasses required, surgeons may use an artery from the chest or arm, or a vein from the leg. One end of the graft is connected to a source of blood flow, while the other end is connected to the coronary artery beyond the blockage.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Blood can then travel through the graft and reach the heart muscle without having to pass through the severely narrowed section of the original coronary artery.
Why doesn't CABG simply remove the blockage?
Coronary artery plaque develops within the walls of the arteries and can affect long segments or multiple branches. Surgically removing plaque from the coronary arteries is not the standard approach for treating widespread coronary artery disease.
Bypass surgery takes a different approach: rather than trying to clear every diseased section, it provides an alternative route for blood flow. This is especially useful when several important vessels are affected or when the blockages are located in areas that are difficult to treat safely with a stent.
What determines how many bypasses are needed?
The number of bypasses depends on the patient's coronary anatomy rather than simply the number of blockages seen on a scan. A person may have several areas of narrowing within one coronary artery, while another patient may have significant disease affecting several different arteries.
During treatment planning, the cardiac team studies the coronary angiogram to determine which vessels have significant disease and which areas of the heart need improved blood supply.
As a result, terms such as single bypass, double bypass, triple bypass or quadruple bypass describe the number of grafts created rather than simply the number of blockages.
What symptoms may suggest that blocked arteries are affecting the heart?
Significant coronary artery disease can cause symptoms when the heart muscle does not receive enough oxygen. Common symptoms include:
- Pressure, tightness or discomfort in the chest
- Shortness of breath during physical activity
- Unusual tiredness or reduced exercise capacity
- Discomfort spreading to the arm, shoulder, neck, jaw or back
- Sweating, nausea or light-headedness during episodes of chest discomfort
How are blocked coronary arteries diagnosed before CABG?
Doctors use a combination of clinical assessment and investigations to understand the extent of coronary artery disease. Coronary angiography is particularly important when revascularization is being considered. It provides detailed images of the coronary arteries and helps identify the location and severity of blockages.
Other tests may include:
- Electrocardiography (ECG)
- Echocardiography
- Blood tests
- Stress testing in selected patients
- Coronary CT angiography in appropriate situations
What happens if the blockage is treated with a stent instead?
PCI, commonly called angioplasty and stenting, is another way to restore blood flow through a blocked coronary artery. During PCI, a catheter is guided into the coronary artery and a balloon may be used to open the narrowed area. A stent is then placed to help keep the artery open.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
PCI can be an excellent treatment for many types of coronary blockage, but it is not equally suitable for every pattern of disease. CABG may be favoured when disease is extensive or complex, when several vessels are involved or when the overall evidence suggests that surgery offers a better long-term revascularization strategy.
What happens to the blocked artery after CABG?
The original blocked artery usually remains in place. CABG does not remove the underlying coronary artery disease. Instead, the graft provides another route for blood to reach the heart muscle beyond the obstructed section.
This distinction is important because coronary artery disease can continue to progress elsewhere. Even after successful bypass surgery, long-term treatment remains important to reduce the risk of further artery disease and protect the bypass grafts.
Does CABG completely cure coronary artery disease?
CABG can significantly improve blood flow and, in appropriately selected patients, relieve angina and provide important long-term benefits. But it does not permanently eliminate the underlying process that caused the coronary arteries to become diseased.
Think of CABG as creating a new route around an existing roadblock. The roadblock may remain, and other roads can develop problems in the future. Long-term cardiovascular care is therefore still necessary after surgery.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
The Bottom Line
CABG is a surgical way of restoring blood flow when coronary arteries are significantly narrowed or blocked. Rather than removing the blockage, the surgeon creates a new pathway using a blood vessel from another part of the body, allowing blood to reach the heart muscle beyond the diseased section.
However, a blocked coronary artery does not automatically mean that bypass surgery is necessary. Some patients can be effectively treated with medication or PCI, while CABG may be more appropriate when disease is extensive, involves several important arteries, affects the left main coronary artery, or has a pattern for which surgery is expected to provide greater benefit.
The most appropriate treatment depends on the patient's complete coronary anatomy, heart function, symptoms, other medical conditions and long-term goals. When the choice between CABG and another treatment is not straightforward, a multidisciplinary Heart Team can help determine which revascularization strategy is most appropriate.
