Coronary Artery Bypass Grafting

The coronary arteries are the blood vessels which supply oxygen rich blood and nutrients to the muscles of the heart. These vessels arise directly from the aorta. Aging, diabetes, obesity and high cholesterol are all risk factors for the build up of plaque in the walls of these vessels which can cause significant obstruction to blood flow leading to coronary artery disease (CAD). This reduction in blood flow manifests with chest pain and can progress to a heart attack in the event of complete obstruction of the vessel.

Coronary Artery Bypass Grafting, often referred to as CABG (pronounced as cabbage), is a surgery of the heart where arteries or veins from other parts of the body are utilised to bypass the blocked coronary artery to restore blood supply to the heart. Every year around 1000 CABGs are performed per million individuals in the United States of America with excellent outcomes.

Goals of CABG Surgery

• To alleviate symptoms
• To prevent the occurrence of a heart attack
• To prevent recurrence of a heart attack
• To restore blood supply to a damaged heart to improve pumping efficiency
• To improve survival
• To improve quality of life

The other procedure used for treating CAD and heart attacks is Percutaneous Coronary Intervention (PCI) which is non invasive and involves inserting a stent into the obstructed vessel to reopen it. While PCI is being done more commonly across the world, CABG has the advantage of being able to achieve complete restoration of blood flow and longer duration of symptom free survival. CABG is performed by a Cardiac Surgeon and PCI is performed by a Cardiologist.

Indications for CABG Surgery

• The presence of severe CAD involving multiple coronary arteries.
• A significant obstruction in the left main artery (the coronary artery generally supplying the majority of the heart muscle)
• In the event of a Heart Attack as an emergency procedure
• Situations when PCI is difficult to perform or not feasible.

Often, a patient may undergo both PCI and CABG of different vessels depending on the pattern of CAD and the severity.

Investigations prior to procedure

• Electrocardiogram (ECG): This is a test to record the electrical activity of the heart and can reveal the presence of a current or previous heart attack. Several structural heart diseases can also be identified along with any abnormalities of the rate and rhythm of the heart.
• Stress ECG: This test records the ECG during exertion to the heart which is achieved thorough walking or running on a treadmill or by using certain medications. Changes in the ECG pattern may suggest the presence of CAD
• Chest X ray: This is done as a preliminary imaging of the chest to look at the structure of the heart and to identify any lung disease.
• Coronary angiography: This is a very important test where a small catheter is inserted through a nick in the groin or arm vessels and pushed all the way up to the coronary vessels. Contrast dye is injected to visualise them. An obstruction show up as a filling defect in the concerned vessel. This test allows identifying the pattern of CAD and the extent of block.
• Echocardiogram: This is an imaging tool to visualise the structure and function of the heart. Areas of absent blood supply can also be identified from abnormal movement of the heart wall.
• Routine investigations including complete blood counts and electrolyte levels are also performed.

Procedure of CABG

There are three major types of CABG all of which are performed under general anaesthesia. They generally take from 3 to 6 hours depending on the number of vessels to be operated on and their structural variations. The following are the different types of CABG

• Traditional CABG :This is done through open heart surgery after cutting through the chest wall and sternum (breast bone) to expose the heart. The heart is then stopped for the duration of the surgery while the patient is connected to a heart-lung machine. The heart lung machine takes over the role of pumping blood to the body and of oxygenating the blood. After the bypass graft is in place, the heart is restarted and the chest wall is closed.
• Off-Pump CABG :This is similar to traditional CABG in that the chest wall is opened by cutting through the sternum. However, as the name suggests, the heart lung machine is not used to pump blood and the heart is allowed to continue beating. This is also called beating heart bypass grafting.
• Minimally Invasive Direct CABG:This type of CABG does not involve cutting open the sternum. Instead, several small cuts are made in the chest wall to allow the passage of cameras and surgical instruments into the chest. These are used to perform the grafting. This type can be done only in select individuals with  single vessel abnormality on the front of the heart.

Graft Vessel Selection for CABG

The vessel used to bypass the obstructed coronary artery is generally taken from the patient’ chest, arm or leg. Both arteries and veins can be used.

Arterial Grafts: These have the advantage of being less likely to get blocked over time. The most commonly used graft is the internal mammary artery (aka internal thoracic artery) which runs on either side of the sternum within the chest wall. Due to its close proximity to the heart, the left artery is frequently used for grafting. The radial artery in the fore arm is also used.

Venous Grafts: The most commonly used vein is the saphenous vein which runs superficially on the inner aspect of the leg is used. These are more prone for obstruction over time with need for a repeat CABG.

Complications of CABG

• Bleeding during the procedure and from the graft insertion site during recovery
• Infection of the operation site wound
• Risks from anaesthesia and sedative medications
• Stroke from reduced blood supply to the brain
• Life threatening arrhythmias (abnormal heart rhythms) which can rarely lead to cardiac arrest and death

Post-CABG Recovery

In the Hospital:As traditional CABG involves open heart surgery, complete recovery can take 6 to 12 weeks. The first few days following the procedure are spent in an Intensive Care Unit (ICU) with provision for continuous cardiac monitoring and frequent measurement of vital signs. Chest drains would be left in place to allow for draining of secretions. This is to facilitate patient recovery, prevent post CABG infection and monitor for complications. After the ICU, a few days are spent in a step down unit or the ward before being discharged home.

At Home:Instructions for caring for the operation wound are provided upon discharge along with instructions on medications and follow up visit. Generally, individuals can return to work after 6 weeks, begin driving after 3 to 8 weeks and resume sexual activity after 4 weeks. Regular follow up and compliance to medications is necessary for long term success of the graft

Follow Up and Monitoring after CABG

• Investigations: Tests such as ECG, stress test and Echo are done to monitor the heart
• Medications: Drugs to control the heart rate and blood pressure, lower cholesterol and prevent formation of blood clots are recommended.
• Life style modification: To maintain the benefit of the surgery, it is important to take certain precautions such as eating a healthy diet, quitting smoking, decreasing stress levels and regular physical exercise.
• Cardiac Rehab: This refers to a medical y supervised program where a team approach is utilised to provide information on healthy lifestyle, exercise training  and counselling about maintaining a healthy diet and the importance of regular medical follow up and medication compliance.

Prognosis after CABG

CABGs have had excellent outcomes. Most people remain free of symptoms for up to 10 to 15 years with proper care and are able to live longer with a good quality of life.

References:

• Coronary Artery Bypass Grafting | National Heart, Lung, and Blood Institute (NHLBI) [Internet]. [cited 2018 Aug 28]
• Harris R, Croce B, Tian DH. Coronary artery bypass grafting. Ann Cardiothorac Surg. 2013 Jul;2(4):579.