Coronary Artery Bypass Grafting (CABG): A Patient Guide

Coronary Arteries

Coronary arteries are usually visible on the surface of the heart and supply the heart muscle (‘myocardium’) with blood. The coronary arteries originate from the beginning of the aorta. The left coronary artery supplies the left ventricle and the septum of the heart with blood and divides early into two main branches: the left anterior descending artery (LAD) and the circumflex artery. The LAD supplies blood to the front and side of the left ventricle and the septum while the circumflex artery covers the side and back wall of the left ventricle. The right coronary artery distributes blood to the right ventricle, parts of the left ventricle, the septum and the electrical conduction system of the heart. Both coronary arteries give rise to several branches which vary significantly in size and importance.

Coronary Artery Disease

Coronary arteries develop narrowings (‘stenoses’) through thickening of their wall. The diagnosis of coronary artery disease is usually confirmed by coronary angiogram.
Significant coronary stenoses result in impaired blood flow, and therefore reduced supply of oxygen to the myocardium. Impaired blood supply is also called ischaemia. Symptoms of myocardial ischaemia include angina and shortness of breath.

Angina is often experienced as tightness or pain in the chest which may travel into the jaw or left arm. These symptoms tend to worsen during physical exertion.

Sudden occlusion of a coronary artery causes severe ischaemia resulting in myocardial infarction. This can cause death of a part of the myocardium. A myocardial infarction is often experienced as sudden crushing pain in the chest. Occasionally, myocardial infarctions occur without symptoms (‘silent’). Silent myocardial infarctions are more common in diabetes and women.

Coronary artery disease may affect one, two or all three main coronary arteries.
 
Treatment of coronary artery disease 

The method of treating coronary artery disease depends on its complexity, its symptoms and the fitness of the patient. Coronary artery disease is sometimes managed with medication alone. The majority of patients, however, will need some form of invasive treatment such as percutaneous coronary intervention (PCI) or Coronary Artery Bypass Grafting (CABG).
 
PCI is a non-surgical procedure performed by a specialist interventional cardiologist. It involves visualising the coronary arteries with an angiogram, inflating the stenoses with a balloon and inserting a stent to keep the stenotic area open. PCI is sometimes performed during acute myocardial infarction. It is also effective in patients with angina. 
 
CABG is performed to treat angina, to prevent heart failure and to reduce the risk of a myocardial infarction that can cause death. CABG is a surgical procedure that uses arteries and veins of the patient as grafts to by-pass stenoses in the coronary arteries. The most commonly used grafts are the  internal mammary artery (from inside the chest wall), the great saphenous vein (from the leg), and the radial artery(from the inner aspect of the forearm).
Arteries are more durable than veins provided they are used to treat coronary arteries with tight stenoses particularly the left coronary artery. The terms single, double, triple or quadruple bypass refer to the number of connections (’anastomoses’) the surgeons performs between the grafts and the coronary arteries.
 
CABG or PCI?  

A great body of work has been developed aiming to decide which patients benefit from PCI and which should be undergoing CABG. The most well known clinical trial in this field is SYNTAX. There are published international guidelines which support our decision making in treating coronary artery disease.  Generally speaking, patients with complex coronary artery disease that involves the LAD artery have better long term outcomes with CABG. Patients with diabetes gain additional benefits from surgery. Each patient should, of course, be assessed as an individual before the best treatment is decided. Numerous parameters, such as age and fitness, will be taken into consideration.

Techniques of CABG

Most surgeons perform CABG by connecting the patient’s circulation to a cardio-pulmonary bypass (CPB) machine. This is known as ‘on-CPB’ or ‘on-pump’ CABG. The CPB machine takes over the function of the heart and lungs for the duration of the main operation. It pumps blood and uses a gas exchange device to add oxygen and remove Carbon Dioxide from the blood.

During an on-pump operation, the heart is stopped, through the infusion of a solution high in potassium (K+), and the surgeon performs the anastomoses in a still and bloodless field. Once the grafts have been sewn, the heart is allowed to start beating again before the CPB is fully discontinued and the operation is completed.

‘On-pump’ is the commonest technique for performing CABG worldwide as it creates very good conditions for the formation of graft connections. Downsides include the need to manipulate and insert cannulae into the aorta and bleeding after the operation due to damage of blood cells.

CABG can also be performed without using CPB. This technique is known as ‘beating heart’ or ‘off-pump’ coronary surgery. During ‘off-pump’ CABG the heart continues to beat and the lungs continue to provide oxygenation. Areas of the coronary arteries that receive a bypass graft are kept relatively still with a mechanical stabiliser while the surgeon performs the connections.

The main advantage of the off-pump technique is that it avoids excessive manipulation of the aorta. It is also associated with less bleeding that on-pump CABG. It is, however, a technically more demanding technique that requires specific training by the surgeon and the team. There is evidence that off-pump is advantageous in high risk patients when performed by an experienced surgeon.

Arteries vs Veins

Arteries are vessels that carry blood away from the heart and towards organs and tissues. Arteries are subjected to blood pressure that is much higher than in veins. The left internal mammary artery (LIMA) is the commonest type of graft used in CABG surgery. The LIMA is associated with excellent durability when used in CABG as over 90% of LIMA grafts remain patent at 10 years and beyond following surgery. Other arterial grafts include the right Internal Mammary Artery (RIMA) and the radial artery.

Veins return blood towards the heart at low pressure. The great saphenous vein (GSV) is readily accessible on the inside of the leg and has been used extensively as a graft in cardiac surgery. While the GSV is a very good choice, there is some evidence that the radial artery and the RIMA are likely to last longer when they are used to graft the left coronary artery.

Preferred technique for CABG

Mr Asimakopoulos has extensive experience of both techniques and tailors the operation to the individual requirements of each patient to optimise the outcome as much as possible. He has performed over 1,300 off-pump CABG procedures with excellent results. The survival rate of his patients after CABG is 99%, including high risk and emergency operations.

He favours the use of more than one arterial graft for stenoses of the left coronary artery and  often uses both the LIMA and Radial Artery to perform two or more anastomoses.

References for further reading:

2023 ESC Guidelines for the management of acute coronary syndromes: Developed by the task force on the management of acute coronary syndromes of the European Society of Cardiology (ESC) https://academic.oup.com/eurheartj/article/44/38/3720/7243210

2024 ESC Guidelines for the management of chronic coronary syndromes https://scts.org/_userfiles/pages/files/vrints_european_heart_journal_2024.pdf