Coronary Artery Bypass Graft (cont.)
How is CABG surgery done?
The cardiac surgeon makes an incision down the middle of the chest and then
saws through the breastbone (sternum). This procedure is called a median
(middle) sternotomy (cutting of the sternum). The heart is cooled with iced salt
water, while a preservative solution is injected into the heart arteries. This
process minimizes damage caused by reduced blood flow during surgery and is
referred to as "cardioplegia." Before bypass surgery can take place, a
cardiopulmonary bypass must be established. Plastic tubes are placed in the
right atrium to channel venous blood out of the body for passage through a
plastic sheeting (membrane oxygenator) in the heart lung machine. The oxygenated
blood is then returned to the body. The main aorta is clamped off (cross
clamped) during CABG surgery to maintain a bloodless field and to allow bypasses
to be connected to the aorta.
The most commonly used vessel for the bypass is the saphenous vein from the
leg. Bypass grafting involves sewing the graft vessels to the coronary arteries
beyond the narrowing or blockage. The other end of this vein is attached to the
aorta. Chest wall arteries, particularly the left internal mammary artery, have
been increasingly used as bypass grafts. This artery is separated from the chest
wall and usually connected to the left anterior descending artery and/or one of
its major branches beyond the blockage. The major advantage of using internal
mammary arteries is that they tend to remain open longer than venous grafts. Ten
years after CABG surgery, only 66% of vein grafts are open compared to 90% of
internal mammary arteries. However, artery grafts are of limited length, and can
only be used to bypass diseases located near the beginning (proximal) of the
coronary arteries. Using internal mammary arteries may prolong CABG surgery
because of the extra time needed to separate them from the chest wall.
Therefore, internal mammary arteries may not be used for emergency CABG surgery
when time is critical to restore coronary artery blood flow.
CABG surgery takes about four hours to complete. The aorta is clamped off for
about 60 minutes and the body is supported by cardiopulmonary bypass for about
90 minutes. The use of 3 (triple), 4 (quadruple), or 5 (quintuple) bypasses are
now routine. At the end of surgery, the sternum is wired together with stainless
steel and the chest incision is sewn closed. Plastic tubes (chest tubes) are
left in place to allow drainage of any remaining blood from the space around the
heart (mediastinum). About 5% of patients require exploration within the first
24 hours because of continued bleeding after surgery. Chest tubes are usually
removed the day after surgery. The breathing tube is usually removed shortly
after surgery. Patients usually get out of bed and are transferred out of
intensive care the day after surgery. Up to 25% of patients develop heart rhythm
disturbances within the first three or four days after CABG surgery. These rhythm
disturbances are usually temporary atrial fibrillation, and are felt to be
related to surgical trauma to the heart. Most of these arrhythmias respond to
standard medical therapy that can be weaned one month after surgery. The average
length of stay in the hospital for CABG surgery has been reduced from as long as
a week to only three to four days in most patients. Many young patients can even be
discharged home after two days.
A new advance for many patients is the ability to do CABG with out going on
cardiopulmonary bypass ("off pump"), with the heart still beating. This
significantly minimizes the occasional memory defects and other complications
that may be seen after CABG, and is a significant advance.
Next: How do patients recover after CABG surgery? »
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