Coronary artery bypass surgery, alsocoronary artery bypass graft (CABG, pronounced "cabbage") 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
 
Three coronary artery bypass grafts, a LIMA to LAD and two saphenous vein grafts – one to the right coronary artery (RCA) system and one to the obtuse marginal (OM) system.
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.
 
Indications for CABG
Several alternative treatments for coronary artery disease exist. They include:

• Medical management (anti-anginal medications plus statins, antihypertensives, smoking cessation, tight blood sugar control in diabetics)
• Percutaneous coronary intervention (PCI)

Controversy
The value of coronary artery bypass surgery in rescuing someone having a heart attack (by immediately alleviating an obstruction) is clearly defined in multiple studies, but studies have failed to find benefit for bypass surgery vs. medical therapy in stable angina patients. The artery bypass can temporarily alleviate chest pain, but does not increase longevity. The "vast majority of heart attacks do not originate with obstructions that narrow arteries.
Loss of mental function is a common complication of bypass surgery, and should influence procedure cost benefit considerations. One published study using MRI imaging just after coronary bypass surgery found significant brain damage in 51% of patients.
Several factors may contribute to immediate cognitive decline. The heart-lung blood circulation system and the surgery itself release a variety of debris, including bits of blood cells, tubing, and plaques. For example, when surgeons clamp and connect the aorta to tubing, resulting emboli block blood flow and cause mini strokes. Other heart surgery factors related to mental damage may be events of hypoxia, high or low body temperature, abnormal blood pressure, irregular heart rhythms, and fever after surgery^.
A safer and more permanent and successful way to prevent heart attacks in patients at high risk is to exercise, give up smoking, take "drugs to get blood pressure under control and drive cholesterol levels down to prevent blood clotting". Longer term, behavioral and medication treatment may be the only way to avoid vascular related loss of mental function
 
Procedure (simplified)
 
Coronary artery bypass surgery during mobilization (freeing) of the right coronary artery from its surrounding tissue, adipose tissue (yellow). The tube visible at the bottom is the aortic cannula (returns blood from the HLM). The tube above it (obscured by the surgeon on the right) is the venous cannula (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.

1. The patient is brought to the operating room and moved on to the operating table.
2. An anaesthetist places a variety of intravenous lines and injects a painkilling agent (usually fentanyl) followed within minutes by an induction agent (usually propofol) to render the patient unconscious.
3. An endotracheal tube is inserted and secured by the anaesthetist and mechanical ventilation is started. General anaesthesia is maintained by a continuous very slow injection of Propofol.
4. The chest is opened via a median sternotomy and the heart is examined by the surgeon.
5. The bypass grafts are harvested – frequent conduits are the internal thoracic arteries, radial arteries and saphenous veins. When harvesting is done, the patient is given heparin to prevent the blood from clotting.
6. In the case of "off-pump" surgery, the surgeon places devices to stabilize the heart.
7. If the case is "on-pump", the surgeon sutures cannulae into the heart and instructs the perfusionist to start cardiopulmonary bypass (CPB). Once CPB is established, the surgeon places the aortic cross-clamp across the aorta and instructs the perfusionist to deliver cardioplegia (a special potassium-mixture, cooled) to stop the heart and slow its metabolism. Usually the patient's machine-circulated blood is cooled to around 84 °F (29 °C)
8. One end of each graft is sewn on to the coronary arteries beyond the blockages and the other end is attached to the aorta.
9. The heart is restarted; or in "off-pump" surgery, the stabilizing devices are removed. In cases where the aorta is partially occluded by a C-shaped clamp, the heart is restarted and suturing of the grafts to the aorta is done in this partially occluded section of the aorta while the heart is beating.
10. Protamine is given to reverse the effects of heparin.
11. Chest tubes are placed in the mediastinal and pleural space to drain blood from around the heart and lungs.
12. The sternum is wired together and the incisions are sutured closed.
13. The patient is moved to the intensive care unit (ICU) to recover.
14. Nurses in the ICU focus on recovering the patient by monitoring blood pressure, urine output and respiratory status as the patient is monitored for bleeding through the chest tubes. If there is chest tube clogging, complications such as cardiac tamponade, pneumothorax or death can ensue. Thus nurses closely monitor the chest tubes and under take methods to prevent clogging so bleeding can be monitored and complications can be prevented.
15. After awakening and stabilizing in the ICU (approximately one day), the person is transferred to the cardiac surgery ward until ready to go home (approximately four days).

Minimally invasive CABG
Alternate methods of minimally invasive coronary artery bypass surgery have been developed. Off-pump coronary artery bypass (OPCAB) is a technique of performing bypass surgery without the use of cardiopulmonary bypass (the heart-lung machine). Further refinements to OPCAB have resulted in minimally invasive direct coronary artery bypass surgery (MIDCAB), a technique of performing bypass surgery through a 5 to 10 cm incision.
 
Conduits used for bypass
 
The choice of conduits is highly dependent upon the particular surgeon and institution. Typically, the left internal thoracic artery (LITA) (previously referred to as left internal mammary artery or LIMA) is grafted to the left anterior descending artery and a combination of other arteries and veins is used for other coronary arteries. The right internal thoracic artery (RITA), the great saphenous vein from the leg and the radial artery from the forearm are frequently used; in the U.S., these vessels are usually harvested endoscopically, using a technique known as endoscopic vessel harvesting (EVH). The right gastroepiploic artery from the stomach is infrequently used given the difficult mobilization from the abdomen.
CABG associated

• Postperfusion syndrome (pumphead), a transient neurocognitive impairment associated with cardiopulmonary bypass. Some research shows the incidence is initially decreased by off-pump coronary artery bypass, but with no difference beyond three months after surgery. A neurocognitive decline over time has been demonstrated in people with coronary artery disease regardless of treatment (OPCAB, conventional CABG or medical management). However, a 2009 research study suggests that longer term (over 5 years) cognitive decline is not caused by CABG but is rather a consequence of vascular disease.
• Nonunion of the sternum; internal thoracic artery harvesting devascularizes the sternum increasing risk.
• Myocardial infarction due to embolism, hypoperfusion, or graft failure.
• Late graft stenosis, particularly of saphenous vein grafts due to atherosclerosis causing recurrent angina or myocardial infarction.
• Acute renal failure due to embolism or hypoperfusion.
• Stroke, secondary to embolism or hypoperfusion.
• Vasoplegic syndrome, secondary to cardiopulmonary bypass and hypothermia
• Grafts last 8 – 15 years, and then need to be replaced.
• Pneumothorax: An air collection around the lung that compresses the lung
• Hemothorax: Blood in the space around the lungs
• Pericardial Tamponade: Blood collection around the heart that compresses the heart and causes poor body and brain perfusion. Chest tubes are placed around the heart and lung to prevent this. If the chest tubes become clogged in the early post operative period when bleeding is ongoing this can lead to pericardial tamponade, pneumothorax or hemothorax.
• Pleural Effusion: Fluid in the space around the lungs. This can lead to hypoxia which can slow recovery.

General cardiac surgery

• Post-operative atrial fibrillation: An arrhythmia that sometimes occurs after cardiac surgery.

General surgical

• Infection at incision sites or sepsis.
• Deep vein thrombosis (DVT)
• Anesthetic complications such as malignant hyperthermia.
• Keloid scarring
• Chronic pain at incision sites
• Chronic stress related illnesses
• Death