from its surrounding
adipose tissue (yellow). The tube visible at the bottom is the
aortic cannula, which returns blood from the
heart–lung machine. The tube above it (obscured by the
surgeon on the right) is the
venous cannula, which receives blood from the body. The patient's
heart is stopped and the
aorta is cross-clamped. The patient's head (not seen) is at the bottom.
Preoperative examination and strategy Routine preoperative examination aims to check the status of systems and organs besides the heart. The examination typically includes a chest X-ray to check the lungs, a
complete blood count, and kidney and liver function tests. Physical examination to determine the quality of the grafts or the safety of removing them, such as
varicosities in the legs, or the
Allen test in the arm is performed to be sure that blood supply to the arm will not be critically disturbed. A patient taking anticoagulants—
aspirin,
clopidogrel,
ticagrelol and others—will stop taking them several days before, to prevent excessive bleeding during and after the operation. Warfarin is also stopped for the same reason and the patient starts taking
heparin products after the
INR falls below 2.0. After the angiogram is reviewed by the surgical team, targets are selected (that is, which native arteries will be bypassed and where the anastomosis should be placed). Ideally, all major lesions in significant vessels should be addressed. Most commonly, the left internal thoracic artery (LITA; formerly, left internal mammary artery, LIMA) is anastomosed to the left anterior descending artery (LAD) because the LAD is the most significant artery of the heart and supplies blood to a larger portion of myocardium than other arteries. A conduit can be used to graft one or more native arteries. In the latter case, an end-to-side anastomosis is performed. In the former, using a sequential anastomosis, a graft can then deliver blood to two or more native vessels of the heart. Also, the proximal part of a conduit can be anastomosed to the side of another conduit. It is preferred not to harvest too much conduit because it might necessitate re-operation.
With cardiopulmonary bypass machine (on-pump) The intubated patient is brought to the
operating theater. Lines (e.g., peripheral IV cannulae, central lines such as internal jugular cannulae) are inserted for drug administration and monitoring. A description of a traditional CABG follows. ; Harvesting An
incision in the sternum is made while
vessels are being
harvested, either from the arms or chest or from the leg, usually from the internal mammary artery or the saphenous vein. The LITA is harvested through the sternotomy. There are two common ways of mobilizing the LITA: the pedicle (i.e., a pedicle consisting of the artery plus surrounding fat and veins) and the skeletonized (i.e., freed of other tissues). Before the LITA is divided in its more distal part, the anticoagulant heparin is administered to the patient via a peripheral line, to prevent clots. ; Catheterization and establishment of cardiopulmonary bypass After harvesting, the
pericardium—the sac that surrounds the heart—is opened and stay sutures are placed to keep it open.
Purse string sutures are placed in the aorta to prepare the insertions of the cannula into the aorta, and a catheter which
temporarily arrests the heart using a solution high in potassium. Another purse string is placed in the right atrium for the venous cannula. Once the cannulas and the catheter are placed, cardiopulmonary bypass (CPB) is commenced. Deoxygenated blood arriving to the heart from veins is forwarded to the CPB machine to get oxygenated, then delivered to the aorta to keep the rest of the body saturated. The blood is often cooled to to slow
metabolism and minimize the demand for oxygen. A clamp is placed on the aorta between the cardioplegic catheter and aortic cannula, so that the flow of cardioplegic solution may be controlled by adjusting the clamp. Within minutes, the heart stops beating. ; Anastomosis (grafting) With the heart still, the tip of the heart is taken out of pericardium so that native arteries lying on the posterior side of the heart are accessible. Usually, distal anastomoses are constructed first (first to the right coronary system, then to the circumflex) and then the sequential anastomosis if necessary. Surgeons check the anastomosis for patency (whether it is sufficiently open) or leaking. They then insert the graft within the pericardium, sometimes attached to the cardioplegic catheter. The anastomosis of the LIMA to the LAD is usually the last distal anastomosis to be constructed; while it is being constructed the blood rewarming process starts (by the CPB). After the anastomosis is completed and checked for leaks, the proximal anastomoses of the conduits, if any, are next. They can be done either with the clamp still on, or after removing the aortic clamp and isolating a small segment of the aorta by placing a partial clamp. That said, aortas burdened by plaques might be damaged or release atheromatous debris by being overhandled. ; Weaning from cardiopulmonary bypass and closure After the proximal anastomoses are done, the clamp is removed and the aorta and conduits de-aired. Pacing wires, which supply a current to assist the heartbeat, might be placed. If the heart and other systems are functioning, CPB is discontinued and cannulae are removed.
Protamine is administered to reverse the effect of the anticoagulant heparin. After possible bleeding sites are checked,
chest tubes are placed and the sternum is closed.
Off-pump Off-pump coronary artery bypass (OPCAB) surgery avoids using the CPB machine by stabilizing small segments of the heart at a time. The surgical team and anesthesiologists must coordinate and take great care to not manipulate the heart too much, lest they compromise the stability of blood flow. Compromise should be detected immediately and appropriate action taken. Keeping a healthy heartbeat may involve maneuvers like placing atrial wires to protect from
bradycardia, or by placing stitches or incisions into the pericardium to help exposure. Snares and tapes are used to facilitate exposure. The aim is to avoid distal ischemia caused by blockage of the vessel supplying distal portions of the left ventricle, so usually LITA to LAD is the first to be anastomosed and others follow. For the anastomosis, a fine tube blowing humidified CO2 keeps the surgical field clean of blood. Also, a shunt might be used so the blood can travel past the site of anastomosis. After the distal anastomoses are completed, proximal anastomoses to the aorta are constructed with a partially closed aortic clamp. The rest of the process is similar to on-pump CABG.
Alternative approaches and special situations When CABG is performed as an emergency because of a myocardial infarction, the highest priority is to salvage the struggling myocardium. Before operation, an
intra-aortic balloon pump (IABP) might be inserted to relieve some of the burden of pumping blood, effectively reducing the amount of oxygen needed by myocardium. During operation, the standard practice is to place the patient on CPB as soon as possible and revascularize the heart with three saphenous veins. A calcified aorta also poses a problem because it is very dangerous to clamp. In this case, the operation can be done as an off-pump CAB using both
inferior mesenteric arteries (IMA) or Y, T and sequential grafts. Deep arrest may be induced with
hypothermia, lowering the temperature of the body to slightly above . In cases where a significant artery is totally blocked, it may be possible to remove the plaque and use the same hole in the artery to perform an anastomosis. This technique is called endarterectomy and is usually performed at the right coronary system. Re-operations of CABG (another CABG operation after a previous one) pose difficulties. The heart may be positioned too close to the sternum and thus at risk when cutting the sternum again, so an
oscillating saw is used. The heart may be covered with strong adhesions to adjusting structures. Doctors must decide whether aging grafts should be replaced. Manipulation of vein grafts is avoided because it risks dislodgement of plaque.
Minimally invasive direct coronary artery bypass (MIDCAB) strives to avoid a large incision in the sternum. It utilizes off-pump techniques to place a graft, usually of the LIMA at the LAD. The LIMA is freed through an
incision between the left ribs (thoractomy), or even using an endoscope placed in the left chest. Robot-assisted coronary revascularization, which is not yet widely used, avoids the sternum incision to prevent infections and bleeding. Both conduit harvesting and the anastomosis are performed with the aid of a robot, through a thoracotomy. Usually, the procedure is combined with
hybrid coronary revascularization, in which methods of CABG and PCI are both employed. Anastomosis of the LIMA to the LAD is performed in the operating theater and other lesions are treated with PCI—either at the operating room immediately following the anastomosis, or several days later. File:Coronary Artery Bypass Surgery.jpg|Coronary artery bypass graft File:Coronary Artery Bypass Graft, Single Bypass.jpg|Coronary artery bypass graft, single bypass File:Coronary Artery Bypass Graft, Double Bypass.jpg|Coronary artery bypass graft, double bypass. File:Coronary Artery Bypass Graft, Triple Bypass.jpg|Coronary artery bypass graft, triple bypass File:Coronary Artery Bypass Graft, Quadruple Bypass.jpg|Coronary artery bypass graft, quadruple bypass == Post-operative care ==