Coronary artery bypass graft surgery (CABG) is a procedure used to treat coronary artery disease in certain circumstances. Coronary artery disease (CAD) is the narrowing of the coronary arteries (the blood vessels that supply oxygen and nutrients to the heart muscle), caused by a buildup of fatty material within the walls of the arteries.
This buildup causes the inside of the arteries to become rough and narrowed, limiting the supply of oxygen-rich blood to the heart muscle.
One way to treat the blocked or narrowed arteries is to bypass the blocked portion of the coronary artery with another piece of blood vessel. Blood vessels, or grafts, may be pieces of a vein that are then grafted above and below the blocked area of a coronary artery, allowing blood to flow around the obstruction. Veins are usually taken from the leg, but arteries from the chest may also be used to create a bypass graft.
One end of the graft is attached above the blockage and the other end is attached below the blockage. Thus, the blood is rerouted around, or bypasses, the blockage through the new graft to reach the heart muscle.
This bypass of the blocked coronary artery can be done by performing coronary artery bypass surgery.
Traditionally, in order to bypass the blocked coronary artery in this manner, the chest is opened in the operating room and the heart is stopped for a time so that the surgeon can perform the bypass. In order to open the chest, the breastbone (sternum) is cut in half and spread apart.
Once the heart is exposed, tubes are inserted into the heart so that the blood can be pumped through the body during the surgery by a cardiopulmonary bypass machine (heart-lung machine). The bypass machine is necessary to pump blood while the heart is stopped and kept still in order for the surgeon to perform the bypass operation.
While the traditional "open heart" procedure is still performed and often preferred in many situations, newer, less invasive techniques have been developed to bypass blocked coronary arteries.
"Off-pump" procedures, in which the heart does not have to be stopped, were developed in the 1990's. Other minimally-invasive procedures, such as key-hole surgery (performed through very small incisions) and robotic procedures (performed with the aid of a moving mechanical device), are also in development.
Other related procedures that may be used to assess and/or treat the heart include resting or exercise electrocardiogram (ECG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest x-ray, computed tomography (CT scan) of the chest, echocardiography, electrophysiological studies, magnetic resonance imaging (MRI) of the heart, myocardial perfusion scans, percutaneous transluminal coronary angioplasty (PTCA), radionuclide angiography, and ultrafast CT scan.
Coronary arteries of the heart
To better understand how coronary artery disease affects the heart, a review of basic heart anatomy and function follows.
The heart is basically a pump. The heart is made up of specialized muscle tissue, called the myocardium.
The heart's primary function is to pump blood throughout the body, so that the body's tissues can receive oxygen and nutrients and have waste substances taken away.
Like any pump, the heart requires fuel in order to work. The myocardium requires oxygen and nutrients, just like any other tissue in the body.
However, the blood that passes through the heart's chambers is only passing through on its trip through the body - this blood does not give oxygen and nutrients to the myocardium. The myocardium receives its oxygen and nutrients from the coronary arteries. The coronary arteries lie on the outside of the heart and supply oxygenated blood to the heart tissue.
When the heart tissue does not receive an adequate blood supply, it cannot function as well as it should. If the myocardium's blood supply is decreased for a length of time, a condition called ischemia may develop.
Ischemia can decrease the heart's pumping ability, because the heart muscle is weakened due to a lack of food and oxygen.
For many years, coronary artery disease (CAD) was commonly called "hardening of the arteries" and was not easily treated. However, in the last 30 years, many advances have been made in the diagnosis and treatment of cardiac diseases.