Coronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure performed to relieve angina and reduce the risk of death from coronary artery disease. Arteries or veins from elsewhere in the patient’s body are grafted to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation supplying the myocardium (heart muscle). This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass; techniques are available to perform CABG on a beating heart, so-called “off-pump” surgery.
Terminology
There are many variations on terminology, in which one or more of ‘artery’, ‘bypass’ or ‘graft’ is left out. The most frequently used acronym for this type of surgery is CABG (pronounced ‘cabbage’), pluralized as CABGs (pronounced ‘cabbages’). More recently the term aortocoronary bypass (ACB) has come into popular use. CAGS (Coronary Artery Graft Surgery, pronounced phonetically) should not be confused with Coronary Angiography (CAG).
Arteriosclerosis is a common arterial disorder characterized by thickening, loss of elasticity, and calcification of arterial walls, resulting in a decreased blood supply.
Atherosclerosis is a common arterial disorder characterized by yellowish plaques of cholesterol, lipids, and cellular debris in the inner layer of the walls of large and medium-sized arteries
Number of Bypasses
The terms single bypass, double bypass, triple bypass, quadruple bypass and quintuple bypass refer to the number of coronary arteries bypassed in the procedure. In other words, a double bypass means two coronary arteries are bypassed (e.g. the left anterior descending (LAD) coronary artery and right coronary artery (RCA)); a triple bypass means three vessels are bypassed (e.g. LAD, RCA, left circumflex artery (LCX)); a quadruple bypass means four vessels are bypassed (e.g. LAD, RCA, LCX, first diagonal artery of the LAD) while quintuple means five. Less commonly more than four coronary arteries may be bypassed.
A greater number of bypasses does not imply a person is “sicker,” nor does a lesser number imply a person is “healthier.” A person with a large amount of coronary artery disease (CAD) may receive fewer bypass grafts owing to the lack of suitable “target” vessels. A coronary artery may be unsuitable for bypass grafting if it is small (< 1 mm or < 1.5 mm depending on surgeon preference), heavily calcified (meaning the artery does not have a section free of CAD) or intramyocardial (the coronary artery is located within the heart muscle rather than on the surface of the heart). Similarly, a person with a single stenosis (“narrowing”) of the left main coronary artery requires only two bypasses (to the LAD and the LCX). However, a left main lesion places a person at the highest risk for death from a cardiac cause.
The surgeon reviews the coronary angiogram prior to surgery and identifies the lesions (or “blockages”) in the coronary arteries. The surgeon will estimate the number of bypass grafts prior to surgery, but the final decision is made in the operating room upon examination of the heart.
What is Coronary artery bypass grafting?
Coronary artery bypass grafting (CABG) has conventionally been an operation that requires the use of the heart lung machine. For selected patients, surgeons have designed an innovative way to bypass blocked arteries on the heart without the use of the heart-lung machine … this operation is called “off-pump coronary artery bypass grafting” or “OPCAB”. Although indications for performing this procedure are more limited, and long-term results compared with conventional CABG are unknown, there are some patients who may benefit from this procedure.
The principals of OPCAB are in some ways similar to that of CABG … namely, that an artery from behind the breast bone and/or veins from the legs are used to “bypass” blood around coronary artery blockages. OPCAB is different from CABG in that the heart-lung machine is not used … this means that the special catheters and “cannulae” that are placed in and around the heart for a conventional CABG operation are not used … the heart continues to pump blood to the rest of the body, and surgeons must operate on a “beating heart”.
An advantage of OPCAB over conventional CABG is that it may eliminate some of the risks associated with using the heart-lung machine. In most patients these risks are very, very small … but in some older patients with significant atherosclerotic disease of their aorta, poor kidney function, or significant lung disease … these risks may be more considerable, and OPCAB might be a reasonable and safer approach than conventional CABG. There are many more variables that determine whether or not a patient would be an acceptable candidate for OPCAB … these issues are best discussed with your surgeon.
A disadvantage of OPCAB is that because the heart is not stopped, surgeons must perform delicate suturing on a “beating heart”. Consequently, stabilizing devices have been developed to help limit the motion of the heart as surgeons operate.
The operation itself is similar to the CABG operation described above. General anesthesia is induced, and the patient is asleep for the entire course of the operation. The surgeon opens the chest by dividing the breast bone or sternum. An artery behind the sternum, the left internal mammary artery (LIMA), is taken down and one end prepared for bypass grafting. If more than one coronary artery will be bypassed, saphenous vein from the leg is removed and prepared for the additional bypasses.
A stabilizing device is now placed on the surface of the heart, limiting the motion of the beating heart. The coronary arteries are opened beyond the sites of the blockage, and the open ends of the LIMA and vein grafts are sewn to the openings in the coronary arteries. These are called the “distal” anastamoses. Because the “inflow” through the LIMA is left intact, as soon as the LIMA anastamosis is completed, blood flow is established to that region of the heart. A vein graft however, is harvested as a “free graft” and has no “inflow” … therefore, after the “distal” vein graft anastamosis is constructed, the other end of the vein graft is sewn to the aorta (the main artery leaving the heart) in order to establish “inflow”. These are called the “proximal” anastamoses. At this point in the operation, blood flow has now been established beyond all the blocked arteries, and the heart has effectively been “bypassed”.
Drainage catheters are placed around the heart … these are usually removed after 24hr. Temporary pacing wires to regulate the patient’s heart rate, are sewn to the surface of the heart … these are removed before the patient goes home. The sternum and incisions are closed, and the patient is transported to the Cardiac Post-Anesthesia Care Unit, a specialized unit caring exclusively for open-heart surgery patients. Patients generally awaken from anesthesia 4-6hr after the operation. The following morning all drainage catheters and monitoring lines are usually removed, and patients are transferred to a standard hospital room in the cardiac recovery wing of the hospital. Patients undergoing an OPCAB are usually hospitalized for 3-4 days following surgery.
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