Coronary Artery Bypass Graft (CABG )


Coronary artery bypass grafting (CABG) is a type of surgery called revascularization (re-VAS-kyu-lar-i-ZA-shun), used to improve blood flow to the heart in people with severe coronary artery disease (CAD).

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CAD occurs when the arteries that supply blood to the heart muscle (the coronary arteries) become blocked due to the buildup of a material called plaque (plak) on the inside of the blood vessels. If the blockage is severe, chest pain (also called angina), shortness of breath, and, in some cases, heart attack can occur.

CABG is one treatment for CAD. During CABG, a healthy artery or vein from another part of the body is connected, or grafted, to the blocked coronary artery. The grafted artery or vein bypasses (that is, it goes around) the blocked portion of the coronary artery. This new passage routes oxygen-rich blood around the blockage to the heart muscle. As many as four major blocked coronary arteries can be bypassed during one surgery.




Overview
CABG is the most common type of open-heart surgery in the United States, with more than 500,000 surgeries performed each year. Doctors called cardiothoracic (KAR-de-o-tho-RAS-ik) surgeons perform this surgery.

CABG isn’t used for everyone with CAD. Many people with CAD can be treated by other means, such as lifestyle changes, medicines, and another revascularization procedure called angioplasty.

CABG may be an option if you have severe blockages in the large coronary arteries that supply a major part of the heart muscle with blood—especially if the heart’s pumping action has already been weakened.

CABG may also be an option if you have blockages in the heart that can’t be treated with angioplasty. In these situations, CABG is considered more effective than other types of treatment.

If you’re a candidate for CABG, the goals of having the surgery are to:

  • Improve your quality of life and decrease angina and other symptoms of CAD
  • Resume a more active lifestyle
  • Improve the pumping action of the heart if it has been damaged by a heart attack
  • Lower the chances of a heart attack (in some patients, such as those with diabetes)
  • Improve your chance of survival
Repeat surgery may be needed if grafted arteries or veins become blocked, or if new blockages develop in arteries that weren’t blocked before. Taking medicines as prescribed and making lifestyle changes that your doctor recommends can lower the chance of a graft becoming blocked.

In people who are candidates for the surgery, the results are usually excellent, with 85 percent of people having significantly reduced symptoms, less risk for future heart attacks, and a decreased chance of dying within 10 years following the surgery.




During the last three decades careful studies have clearly shown that coronary artery bypass surgery relieves angina pectoris and other symptoms caused by coronary artery disease and, for some patients, prolongs their lives. However, coronary artery bypass surgery alone does not remove the metabolic causes of coronary artery disease and even after successful operation the occurrence of new obstructions may cause problems as the years ago by. These new obstructions may develop either in the patient’s own coronary arteries (progression of native coronary artery disease) or in bypass grafts, particularly in saphenous vein grafts.


Saphenous vein graft




Within a decade of the development of bypass surgery it became apparent that obstructions could develop in saphenous vein to coronary bypass grafts and that the likelihood of obstructions developing was related to time. Within 5 years of surgery approximately 20% of saphenous vein grafts developed partial or total obstructions, and between 5 and 10 years after operation these processes continued to progress such that by 10 years after operation almost half of saphenous vein grafts were either totally obstructed or showed some angiographic evidence of pathologic changes .

Since those early days of bypass surgery progress has been made in the treatment of patients with vein grafts that decreases the rate of vein graft failure. Taking aspirin early after operation increases the percentage of grafts that are functioning well a year after surgery and, more recently, treatment with HMG-CoA reductase inhibitors, also known as "statin" type drugs, has been shown to have long term benefit. However, the failure of vein grafts over the long term remains a significant problem effecting outcomes after bypass surgery and it is the single greatest cause of the need for repeat surgery for bypass grafting .

Internal thoracic artery (ITA, also called mammary artery) graft
(bypass graft using left and/or right internal thoracic artery from the chest wall)


Distal end of ITA attached to LAD
Fortunately there have been other bypass grafts available that are resistant to a late failure - internal thoracic (mammary) artery grafts. Internal thoracic artery (ITA) grafts were used from the beginning of bypass surgery although at relatively few centers during the early years.

Most commonly the left ITA was left attached at its origin from the left subclavian artery and the distal end was dissected away from the chest wall, swung over, and its distal end was attached with sutures to the side of the left anterior descending (LAD) coronary artery.


Multiple vein bypass graft


In the most common situation the left ITA was used as a graft to the LAD coronary artery and saphenous vein grafts were used from the aorta to the other coronary vessels. Studies of angiograms performed after bypass surgery have shown that not only did the LITA to LAD graft have a more than 90% chance of functioning well early after operation, but that these grafts continued to function well for many years and that even 20 years after operation the development of obstructions in these grafts is extremely uncommon (Ref 1).

Long-term follow-up studies done at The Cleveland Clinic Foundation during the 1980s show that not only is the LITA-LAD graft likely to stay functioning over the years but also, that graft has an important long-term effect on clinical outcomes. Over time, patients with a LITA-LAD graft are less likely to die or to need a reoperation when compared with patients who received only vein grafts (Ref. 3). Since these studies have been completed the LITA-LAD graft has become a standard part of operations for coronary bypass grafting.

There are two internal thoracic arteries, one on either side of the sternum (breast bone) and more extensive use of ITA grafts can be accomplished by using the right ITA as an in situ graft (left attached to the right subclavian artery), as a "free" graft from the aorta to the coronary artery, or attached to the left ITA as a composite graft.


ITA as in situ graft ITA as "free" graft ITA as composite graft

Despite the logic that more extensive ITA grafting would be an advantage over the use of only one ITA graft it has only recently been shown by long-term follow-up studies from The Cleveland Clinic Foundation that bilateral ITA grafts further decrease the long-term risks of death and reoperation when compared to patients receiving only one ITA graft (Ref 4). The use of both ITAs as bypass grafts is a more complicated operation and there are some patients where this strategy is not appropriate. However, two ITA grafts do produce better outcomes than just one ITA graft for many patients.


Gastroepiploic graft

Because of the success of ITA grafts, surgeons have search for other arterial bypass grafts. The gastroepiploic artery (GEA) is a branch of the blood supply to the stomach (an organ with a very rich blood supply) that has been used as a bypass graft usually to the right coronary artery. This is a technically difficult operation to perform and it has not become a popular bypass graft but it has a high likelihood of good long-term functioning when used in the proper situation and in some patients represents a significant advantage over vein grafts.

Radial artery graft
(bypass graft using artery from inner forearm)


Radial artery graft


The radial artery was used as a bypass graft in the early years of coronary surgery but its use was abandoned for a number of years because of the occurrence of graft occlusions. In the past few years, its use was revived because of the hope that new methods of preparation and drug treatment with antispasm agents might improve the long-term results. The advantage of radial artery grafts is that they are easy to prepare. The hope is that they will be resistant to the development of atherosclerosis, a problem that has plagued vein grafts. However, the long-term (more than 10 years) of outcomes of radial artery grafts are as yet unknown.

Our data indicates that the long-term results of radial artery grafts are not as good as those for ITA grafts, in particular we have seen more early graft failures. In fact, radial artery graft patency was not better than for saphenous vein grafts. We continue to recommend and use radial artery grafts, particularly for young patients with hyperlipidemia (high cholesterol or triglycerides) who have a relatively high risk of vein graft failure because of the occurrence of vein graft atherosclerosis. In patients who are 70 years or older we use radial artery grafts more cautiously, mainly when alternative grafts are not available. In addition, a radial graft needs a severe blockage or stenosis in the native artery to be grafted, to have a better chance to be promoted and to stay open.(Ref.5)


Total revascularization
It is very clear that the internal thoracic arteries are the best bypass grafts that we have. Because not all patients can be completed treated with just the internal thoracic arteries, the search continues to go on for other arterial bypass conduits and/or total arterial revascularization.

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