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Arterial Coronary Artery Bypass Grafts
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 (bypass graft using saphenous vein from the leg)
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 cardiac 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 a cardiac
bypass surgery 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 cardiac 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)
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.
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 . 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.
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 artery (GEA)
(bypass using artery from the stomach) 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) 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.
Radial artery graft
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.
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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