Coronary artery bypass graft (CABG) surgery represents one of the most complex surgeries performed. The procedure typically requires a few hours to complete and involves multiple steps. A variety of techniques exist for the steps in bypass surgery, from the choice of graft vessels, to the use of a machine to breathe for the patient, to the use of the clamp or clampless procedure. Regardless of the steps involved or the different techniques used, the goal remains the same to bypass blockages in the coronary arteries and restore healthy blood flow to the heart.
Before the actual placement of bypass grafts begins, the surgeon and her surgical team prep the patient, gain chest access, and administer the required medications. After completing these steps, the surgeon or her assistant begins the process of retrieving the vessels that the surgeon will use to create the grafts and bypass the blocked coronary arteries.
Choosing the proper graft vessel represents a critical step in the CABG procedure. As previously mentioned, a surgeon can retrieve the internal mammary artery (IMA) and the surrounding tissue from the chest wall for use as a bypass vessel. Once the surgeon has isolated the IMA, she typically leaves it attached to the subclavian artery and then connects it to the target artery. The surgeon may otherwise choose to remove the IMA from the subclavian artery and attached to the aorta and a coronary artery. This is known as a free graft. If the surgeon chooses to use the saphenous vein in the leg, it is taken by making a long incision down the leg. Following retrieval, the surgeon closes the leg wound and opens the chest for surgery. The radial artery, because it lies deep within the forearm, requires a more involved process when a surgeon chooses it for grafting. In this procedure, the surgeon takes great care to preserve the surrounding nerves and arteries. Because of the rate of success, some surgeons feel that the radial artery is the second arterial graft of choice, next to the internal mammary arteries.
Once the surgeon determines the proper location on the coronary artery to place the bypass graft vessel, the surgeon follows several steps to make the connection. The coronary artery (target vessel) is cut at a point away from the blockage. The surgeon then connects the bypass vessel to the side of the target vessel. The surgeon makes a hole in aorta, to which the bypass vessel is connected, thereby completing the graft. The surgeon repeats the process for each of the remaining grafts. Once the surgeon completes all the grafts, the surgical team checks the flow to assure that the grafts supply sufficient blood to the heart.
Cardiopulmonary bypass (CPB), known colloquially as an on-pump procedure, requires the surgeon to stop the heart for the bypass surgery. The surgeon arrests, or stops, the heart and fills it with a solution called cardioplegia to keep it still. During this time and throughout the procedure, a pump takes over the function of the heart (cardio) and lungs (pulmonary).
To accomplish CPB, the surgical team inserts a tube into the aorta to carry oxygenated blood from the bypass machine to the aorta for circulation to the rest of the body. Tubes are also inserted into the major veins that bring blood back to the right atrium of the heart, thereby circumventing the heart. The blood from these major veins goes from the patient to the machine, which oxygenates the blood and adjusts its temperature. The bypass machine then returns the oxygenated blood to the body through the aortic tube.
During cardiopulmonary bypass, aortic clamps are used to restrict blood flow from the area where the surgeon will place the grafts. These clamps remain closed on the aorta until the grafts are in place.
Following placement of the grafts, the surgeon takes the patient off bypass. The blood is warmed, the lungs inflated, and respiration restored. The surgeon then removes the tubes. The patient is slowly transitioned to bring the blood back into the body and the heart is restarted to resume circulation of the blood.
Off-pump surgery differs from on-pump surgery in that the surgeon does not stop the heart and does not utilize a bypass machine. During off-pump procedures, the heart continues to function, supplying the body with oxygenated blood. Surgeons utilize off-pump techniques because some in the medical community believe that CPB places patients at a higher risk of experiencing certain complications. Off-pump techniques provide a less invasive alternative to the more traditional on-pump procedure, although the trade-off is that off-pump procedures are technically more complicated procedures. The complexity of the procedure makes it much more difficult and susceptible to surgeon error.
Like the off-pump procedure, surgeons developed clampless bypass surgery to further reduce complications associated with manipulation of the aorta during bypass procedures. As in off-pump bypass, clampless bypass does not require the heart to be stopped nor does it utilize a bypass machine. The heart continues to beat and supply the body with oxygenated blood throughout the procedure.As its name suggests, the most significant difference in the clampless technique is the elimination of the clamps used to squeeze the aorta to isolate an area of it from blood flow. This is accomplished through the use of mechanical connectors that provide a graft connection much like sutures but can be used on the aorta without the need of a clamp to restrict blood flow.
Both on-pump and off-pump bypass procedures offer advantages and disadvantages. While off-pump may seek to reduce the risk of cardiopulmonary bypass, on-pump avoids the technical challenge of placing bypass grafts on a beating heart. Ultimately, both share the same goal, to effectively utilize bypass grafts to restore blood flow to the heart.
