Coronary Artery Bypass Grafting (CABG)/ Heart Bypass Surgery

• What is coronary artery bypass surgery?
• When is CAGB surgery used?
• Pre-Operative preparation
• Details of the operation
• Success rates
• Risks
• Recovery
• Alternative treatments to surgery

Coronary Artery Bypass Grafting "CABG" (often pronounced ‘cabbage’) is a major cardiac operation performed to treat ischaemic heart diseases. Ischaemic heart disease is very common in Australia and usually manifests as angina symptoms or may lead to heart attacks. CABG surgery is quite a common operation and tends to produce favourable outcomes in most patients.

CABG surgery has been performed since the 1950s. It really took off following the introduction of a mechanical heart-lung machine in 1953. This machine revolutionised cardiac surgery, allowing the heart to be stopped during surgical manipulation, whilst the heart-lung machine continued to do all the work of the heart. Today CABG surgery is often still performed using this traditional method. More recently however CABG surgery has been performed on a beating heart without the need for bypass!

CABG surgery involves using a vessel from your leg, wrist or inner chest to attach to the coronary vessels on the outside of your heart. Much like a detour on the road, this allows blood to get to the remainder of the heart muscle by bypassing the blockage. Usually an incision is made down the centre of the chest and an open operation performed. Minimal invasion techniques using scopes and other devices are also available.

In general, CABG surgery is quite safe and most patients make a reasonable recovery. Like all operations there are risks including bleeding, infection, pain and more serious consequences such as stroke, heart attack or even death. However CABG surgery is frequently life saving if you have severe disease of the coronary vessels. Medical treatments and angioplasty are alternative therapies but only suitable for some patients.

What is coronary artery bypass surgery?

Coronary Artery Bypass Grafting "CABG" surgery is the most common major cardiac surgery performed in Western countries. Cardiothoracic surgeons perform the operation by opening the chest and using healthy vessels from the arm, leg or chest to bypass diseased coronary arteries. This is similar to forming a detour route to bypass a blockage on the road.

CABG is a type of treatment used for ischaemic heart diseases. In this condition atherosclerosis leads to plaque formation and blockage of the coronary arteries, the key vessels supplying the heart muscle. The heart has two main coronary arteries (called the right and left) which form several branches on the heart’s surface. The arteries give the heart muscle the oxygen and nutrients it requires to pump blood all around the body. If you look carefully at the image, you can see small vessels on the surface of the heart. These represent the coronary arteries.

When part of these vessels becomes blocked, ischaemia (damage due to reduced oxygen) develops in the muscle. This can cause symptoms of angina pectoris (recurrent episodes of chest pain) or even lead to a heart attack. Some patients (especially those with diabetes mellitus) can develop ischaemic damage without even knowing it. This is what we call silent infarcts. Your doctor may notice ischaemic changes or disease of the coronary arteries incidentally when performing investigations such as ECG / EKG.

If coronary artery disease is suspected your doctor will perform other investigations such as an exercise stress test, angiogram (threading a catheter through a vessel of your leg to the heart and injecting a dye into your coronary arteries) or echocardiogram (ultrasound of the heart) to determine the degree of obstruction.

If coronary heart disease (CHD) is identified a number of different treatment options are available including medications, angioplasty (insertion of stents) or CABG surgery. These treatments all improve the blood supply to the heart and will help prevent further symptoms or heart attacks. Your doctor can discuss which of these treatments is best for you.

When is CABG surgery used?

CABG surgery is one of three different treatment modalities for coronary artery disease. The decision for surgery is largely based on your symptoms and severity of disease. Studies have shown that the following patients benefit from CABG surgery over the alternative treatment options:

• Patients with persistent symptoms of angina despite medical therapy or who cannot tolerate medical therapy. This group of patients is the most common indication.
• Patients with disease of the left main coronary artery. The left coronary artery supplies most of the heart muscle including the main pumping chamber, the left ventricle. Blockage of this vessel can have severe consequences.
• Patients with triple vessel disease, meaning that 3 big vessels (the left anterior descending, right coronary and circumflex arteries) have blockages from atherosclerotic plaques. The left ventricle also has reduced contractile function.
• Patients with two vessel disease, one of which includes the left anterior descending near its origin. If this important vessel is blocked close to its beginning, a large area of heart muscle will not get sufficient blood supply.

Your doctor will look at your angiogram to decide which vessels need grafting. During this investigation x-rays are taken of the dye within the coronary vessels. The doctor can therefore see any areas of vessel that are narrowed more than half their diameter, which will be suitable for grafting. When you hear people saying a double, triple, or quadruple bypass, they are talking about the number of coronary vessels grafted during surgery.

Pre-operative preparation

Prior to your operation your surgeon will explain the reasons for the operation, how it is performed and the common and most serious risks associated with the operation (discussed below). You will have to sign a written consent form that proves you agree to have the operation and accept the risks explained to you. You will also have to say whether you consent to a blood transfusion. As cardiac surgery is major surgery and can be associated with bleeding, the doctors need your permission to administer blood products if you require them during your operation. Many CABG operations are performed electively meaning that you will be pre-booked for the operation and come into hospital the night before the surgery. 

Prior to surgery you will have to have a number of investigations which may include:

• Electrocardiogram (ECG)– An electrical tracing of the heart which can help diagnoses ischaemic heart disease and helps to tell how fit your heart is for surgery.
• Echocardiogram– An ultrasound of the heart performed either through the chest or using a tube down the oesophagus. This test shows how each chamber of the heart is working and can help the surgeon to decide if any additional procedures need to be performed. If your heart is pumping poorly you may need a ‘balloon pump’ inserted into the aorta (large artery descending in the abdomen) via the femoral artery in the groin. This helps the heart fill so it can better cope with surgery. Occasionally your doctor may also decide that a valve within your heart also needs repair or replacement at the time of surgery.
• Carotid Doppler- This is an ultrasound examinations of the vessels in the neck. It determines whether you have a blockage in the main artery in the neck which determines your risk of stroke during cardiac surgery. If there is a significant blockage you may require a carotid endarterectomy procedure (where the carotid artery is opened and atherosclerotic material removed) prior to cardiac surgery.
• Chest x-ray– Routine pre-operative investigation.
• Blood tests- Including a full blood count, electrolytes, liver function tests (LFT) and coagulation factors. These tell the doctor how well the systems in your body are working and how fit you are for surgery. A sample of blood for cross-matching is also taken. This means the laboratory tests your blood to identify antigens and determine which blood samples are compatible in case blood is needed during your surgery.
• Urine sample- To exclude infection.
• Nasal swab- To exclude Methicillin resistant Staphylococcus Aureus (MRSA) carriage. If this is present a course of antibiotics may be needed prior to surgery to ensure other areas of the body are not infected with this resistant bacteria.
• Hepatitis C, hepatitis B and HIV serology- As there is a lot of blood involved in cardiac surgery, there is a high risk of needlestick injury for cardiac surgeons. These tests are therefore performed as a protective measure for theatre staff.

As forementioned, you will usually be admitted the night before your surgery. If you have severe stenosis of your vessels you may need to take aspirin (a blood thinner) until a day before the surgery. This reduces your risk of further ischaemia. However, in most other cases any blood thinning medications will be ceased a week prior to surgery to reduce your risk of bleeding. Your doctor will discuss with you how to manage your medications. Your doctor will also prescribe a nasal smear called mupiricin to take 2 days prior and 3 days after your surgery. This is an antibiotic drug which kills the bugs you carry in your nose. It is important to use this drug twice daily to reduce your risk of wound infection from breathing on the wound. You will also need to wash with a special chlorhexidine wash the night before and morning of your surgery. In addition you will need to fast (usually from midnight) the night before your surgery. This means no food or drink for several hours before your surgery to ensure your stomach is empty and to minimise the risk of aspiration.

CABG surgery does not cure your disease. It is important that before and after your surgery you take measures to reduce your cardiovascular risk. This involves:

• Quitting smoking- This should be done pre-operatively to reduce the progression of disease. Some surgeons may even refuse to operate on patients who continue to smoke. With appropriate motivation it is possible for you to quit. Your doctor can refer you to several support groups to help you in this process and can even prescribe some medications (such as Zyban) to reduce cravings. It is very important to quit smoking as smoking can damage all vessels in the body as well as the lungs and heart.
• Maintaining a healthy weight- You may need to cut down on fats, cholesterol and increase your exercise.
• Reducing excessive alcohol intake- Excess alcohol prior to surgery damages your liver and inhibits the production of clotting factors. This may predispose to bleeding.
• Reducing high blood pressure– This can be done by reducing salt in your diet and performing regular exercise. You should have your blood pressure monitored regularly by your GP and take any medications as prescribed.

Details of the operation

CABG operations are performed by specialised cardiac surgeons. For the procedure you will be under a general anaesthetic, meaning you will not fell or remember anything of the operation. The anaethetist will insert several ‘lines’ or ‘tubes’ into the arms, chest and neck to measure blood pressures and to allow administration of drugs and fluids. You will also have a urinary catheter inserted into your bladder. The operation is performed by making a large incision down the midline of your chest, through the sternum (breastbone). Simultaneously another surgeon will dissect a vein from the leg or an artery from the wrist. Depending on the number of grafts you need you may have vessels removed from the wrist, inner leg or inside of the chest.

CABG surgery can be performed the traditional method (on-pump using the bypass machine) or off-pump where the heart is operated on whilst it is still beating. Both methods produce similar long term results and the method is more dependent on the surgeon’s choice, skill and expertise. If the former method is used, after the grafts are prepared, the heart will be connected to heart lung machine (cardio-pulmonary bypass machine) by a series of tubes. A big tube is connected to the aorta to provide the arterial supply and other cannulae are attached to the big veins leading to the heart. The bypass machine allows all blood to be redirected from the heart and lungs so that a bloodless field can be created for the surgeon. The bypass machine cleans, filters and warms the blood before it is returned to your body. The body temperature is cooled to reduce the metabolic demands of the heart. The heart is stopped using a specialised cardioplegia solution.

The surgeon then starts to connect the grafted vessels to the coronary arteries. The grafts are connected distal (after) the blockage to allow blood to divert around the obstruction and supply the rest of the heart. The vessel from inside the chest (internal mammary artery) is usually used to connect to the descending branch of the left coronary artery. The other grafts are then attached from the aorta to other obstructed vessels. Very small stitches are used to secure the vessels. Occasionally the surgeon may perform other procedures such as replacing a valve at the time of surgery. This depends on your underlying disease and should be discussed with your surgeon. After grafting is completed you are slowly weaned of bypass and the heart is restarted.

A similar method is used if the procedure is performed off-pump except there will be no insertion of tubes or use of the heart-lung machine. The surgeon will still stitch the grafts to the vessels but will do so whilst the heart continues to beat. The area of heart been grafted is stabilised using special equipment. After grafting is complete the surgeon will check for any bleeding and make sure the grafts are functioning. The pericardium (capsule surrounding the heart), sternum and skin will be closed up. The sternum is closed using permanent wires through the bone. Usually drains will be inserted to remove any fluid or blood post operatively. Pacing leads may be connected to the heart through the skin also. These help the heart beat regularly following the operation. CABG surgery usually takes 4-5 hours. You will wake up in the intensive care unit (ICU) with a large cut down your chest (and leg or arm) with a number of tubes coming out your body (as described above). There will also be several monitors around you. It is likely that you will feel very drowsy for the first day or so after the surgery due to the anaesthetic. You will normally be extubated (have the tube down your throat removed) a day after surgery. The chest drains are usually removed a day or two after surgery. Following ICU you will be transferred to a surgical ward where you will stay for approximately one week, depending on your condition. You will receive several medications and start physiotherapy during this period.

Success rates

Although major surgery, the results of CABG surgery are promising. Approximately 90% of patients will have relief of symptoms of angina without requiring ongoing medications. The procedure itself is considered relatively safe with a mortality less than 1% if you have normal heart function. Grafts using the internal mammary artery tend to remain patent for a long time but about half of venous grafts become occluded by ten years. Repeat CABG surgery is occasionally necessary, usually at least ten years following the initial surgery. This may be due to obstruction of an existing graft or due to new disease in another vessel. This re-emphasises the importance of controlling your cardiovascular risk factors after your operation. If repeat surgery is necessary the risks of mortality are higher (approximately 5 to 10%) and it is less likely that your symptoms will be resolved.

Risks of CABG surgery

Like all operations or procedures, CABG surgery carries some risks of complications. It is a major surgery, however often cannot be avoided if you have severe heart disease. You should be aware of the various possible risks of surgery. You should discuss these with your doctor as they can give you a better idea of YOUR risk depending on YOUR age, other medical conditions and heart function. Some risks of CABG surgery include:

• Mortality/death- The overall mortality of CABG is quoted at approximately 3-4%. This may be higher if you are elderly or have complex medical problems. Interestingly the overall mortality is higher in women as they tend to get heart disease at a later age (due to the effects of female hormones). Women are therefore at greater risk of neurologic and cardiac complications.
• Bleeding- This is a relatively high risk of bleeding during cardiac surgery as manipulation of the major blood vessels is involved. Approximately 5% of patients may require reexploration due to bleeding. Blood transfusions is required in up to a third of patients which is associated with inherent risks of transfusion reactions and acquisition of blood-borne infections (less than one in a million chance).
• Stroke or myocardial infarction– Both carry a risk of approximately 1-2%.
• Infection- Infection of chest or leg wounds or pneumonia (chest infection) can occur in up to 5% of patients. Measures including antibiotic treatment during the operation and careful skin preparation are designed to reduce the risk of infection.
• Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE)- These are risks of all surgery. Immobilisation can predispose to clots in the legs that can occasionally break off and go to the lungs (PE). You will be prescribed blood thinner medications and wear pressure stockings to reduce this risk.
• Reduction in renal function- Approximately 5% of patients will develop some reduction in renal function. However, only a very small number will go on to require dialysis.

Recovery

Heart surgery is major surgery so it can take several weeks to months for you to recover. You will have the sutures removed from your leg and chest wounds approximately 7-10 days following your operation. Your sternal wound takes quite a bit longer to heal. It takes about 6 weeks for the sternum to unite and approximately 12 weeks for full bone strength to return. You should avoid lifting heavy objects (above 5kg) and using your arms to support your body weight during this period. Your physiotherapist can teach you safe ways to move your body. It is recommended you do not drive for 5-6 weeks following your operation. It usually takes approximately 3 months before you can return to manual work or sporting activities. It is important that you have somebody at home to help you throughout this recovery period. After discharge from hospital you will be booked to see your cardiologist and cardiothoracic surgeon. This allows them to monitor how you are coping after the operation and ensure no complications have arisen.

Alternative treatments to surgery

As previously mentioned, angioplasty and medical therapy are alternative treatments for coronary heart disease. Both angioplasty and CABG surgery produce similar long term outcomes in terms of mortality, heart attack and strokes. However, percutanous stenting is associated with greater rates of repeated revascularisation treatments so CABG may be preferred in patients with significant coronary disease. The indications for CABG discussed above are those with documented improvements in mortality and prognosis. Note that the appropriate mode of treatment depends on a number of factors. Your doctor will be able to decide the best treatment for you based on your symptoms, pathology and general health.

References

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