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The Coronary Artery Bypass Surgery

Coronary artery bypass surgery is also known as coronary artery bypass graft surgery (CABG) and more colloquially, heart bypass. It is a surgical procedure performed on patients with a coronary artery disease. The technique was introduced first in the late1960s. The surgery provides relief of angina, improves the heart muscle function and improves the blood supply to the myocardium (heart muscle).

The Procedure

Veins or arteries from other parts of the patient's body are grafted from the aorta to the coronary arteries, bypassing the coronary artery narrowness caused by atherosclerosis.

Most commonly, the sternum (breast bone) is cut down to the middle with a bone saw and the chest is opened up (a procedure known as median sternotomy). Depending on a number of factors, the surgeon may decide to place the patient on cardiopulmonary bypass ("on-pump") or use stabilizing devices to hold the heart still while sewing the anastomoses ("off-pump"). Blood vessels are harvested from elsewhere in the body for grafting. Sometimes artery end branches supplying tissues near the heart are rerouted to create the bypass.

Specifically, an artery is detached from the chest wall and the open end is then attached to the coronary artery below the blocked area.
A piece of a long vein in the leg may be taken. One end is sewn onto the large artery leaving the heart -- the aorta. The other end of the vein is attached or "grafted" to the coronary artery below the blocked area. Either way, blood can use this new path to flow freely to the heart muscle.

Successful grafts usually last upto 10-15 years. In general, CABG improves the chances of survival of patients who are at high risk (meaning those presenting with angina pain shown to be due to ischemic heart disease). The age of the patient at the time of CABG is critical. The younger patients with no complicating diseases have a high probability of greater longevity. The older patient can usually be expected to suffer further blockage of the coronary arteries.

Complications
Infection at incision sites
Deep vein thrombosis (DVT)
Nonunion or malunion of the sternum
Anesthetic complications such as malignant hyperthermia)
Myocardial infarction due to hypoperfusion, early graft occlusion, or graft failure
Acute renal failure due to hypoperfusion
Stroke during reperfusion
Stenosis of the graft, particularly of saphenous vein grafts
Keloid scarring
Chronic pain at incision sites
Postoperative stress-related illnesses such as constipation, chronic bracing, memory loss, trench mouth, and teeth grinding
Death due to myocardial infarction, stroke, renal failure, or sepsis

Conduits used for bypass

Typically, the left internal thoracic artery (LITA) and right internal thoracic artery are used for bypass. If additional bypasses are required, the great saphenous vein from the leg or the radial artery from the forearm is used.
Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. LITA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the arterial tree, the LITA need only be grafted at one end. The LITA is usually grafted to the left anterior descending coronary artery (LAD) because of it superior long-term patency when compared to saphenous vein grafts.
The LAD supplies the left ventricle, the part of the heart that pumps oxygenated blood around the body, and is the most important for survival. Alternatively, an artery such as the radial artery from the arm or gastroepiploic artery from the stomach, may be used in place of a vein.

Graft patency

Grafts can become diseased and may occlude in the months to years after bypass surgery is performed. Patency is a term used to describe the chances of a graft remaining open. A graft is considered patent if there is flow through the graft without any significant (>70% diameter) stenosis in the graft.
Graft patency is dependent on a number of factors, including the type of graft used (internal thoracic artery, radial artery, or great saphenous vein) and the size or the coronary artery that the graft is anastomosing with. The skill of the surgeon(s) performing the procedure is of course crucial.

In generally, the best patency rates are achieved with the left internal thoracic artery, when its proximal end is unchanged, with the distal end being anastomosed with the coronary artery.
Lesser patency rates can be expected with radial artery grafts and "free" internal thoracic artery grafts. Saphenous vein grafts have worse patency rates, but are more available, as the patients can have multiple segments of the saphenous vein used to bypass different arteries.

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