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Heart surgery--particularly coronary artery bypass graft (CABG)
surgery*--is one of the most common surgical procedures in the United States,
with more than 650,000 CABG surgeries performed each year. Advances in surgical
techniques have made heart surgery safer--even for patients formerly not
considered candidates for surgery, including older patients and those with other
diseases such as kidney disease and diabetes. Nevertheless, the risk of harmful
effects on the brain following heart surgery continues to be a concern.
*Coronary artery bypass grafting is a procedure that uses sections of blood
vessels from other parts of the body to bypass--or go around--blockages in the
coronary arteries, the vessels that supply the heart muscle with oxygen-rich
blood. This restores good blood flow to the heart muscle.
What brain-related problems can occur after heart surgery?
The most common problems related to the brain and cognition (ability to
think) that can occur after cardiac bypass surgery include:
- Stroke -- This occurs in 1 percent to 5 percent of patients.
- Delirium -- Delirium is a state of mental confusion. It occurs in
10 percent to 30 percent of patients and may be related to the use of
anesthesia.
- Short-term deficits -- These are primarily problems with memory,
attention and concentration, and can occur in 33 percent to 83 percent of
patients. They generally improve over time.
Long-term deficits in mental functioning--such as an inability to process
complex problems, follow directions or plan actions--also may occur, although
they are often subtle. The person may express these deficits by being
short-tempered or easily frustrated. He or she also may be depressed or have
mood swings.
Neurological complications are less common following other cardiac
procedures, such as angiography, in which complications occur in less than 1
percent of cases.
How does heart surgery affect the brain?
Experts believe there are several factors that may contribute to problems
with mental functioning following heart surgery:
- During heart surgery, the patient's body temperature is lowered
(hypothermia), which allows the heart to remain stopped longer without
damage. Lowering body temperature also has a protective benefit to the
brain. Some researchers believe the brain's protection may be decreased if
the body is warmed too quickly after heart surgery, placing sensitive brain
tissue at risk for damage.
Who is at risk for neurological complications?
There are certain factors that can increase a person's risk for developing
neurological complications after heart surgery. These risk factors include age,
having previously had a stroke or TIA ("mini-stroke") and the presence
of other medical conditions, including:
- Atherosclerosis (hardening of the arteries)
- Chronic kidney failure
- Diabetes
- High blood pressure
- Carotid artery disease (narrowing of the blood vessels going to the brain)
- Peripheral vascular disease (problems with the blood vessels that go to
the arms and legs)
What can be done to protect the brain during heart surgery?
An initial step in helping to protect the brain during heart surgery is to
identify patients with the risk factors listed above and then treating them with
medication or by adjusting the surgical procedure, when possible. Advances in
surgical techniques have reduced manipulation of the aorta, reducing the risk
that particles of plaque will become dislodged. There are additional strategies
being developed to reduce the occurrence of neurological complications following
heart surgery.
What does the future hold?
Surgeons at The Cleveland Clinic Heart Center continue to investigate new
techniques to reduce the neurological risk of heart surgery. A new intra-aortic
filtering system--called the Embol-X system--is now undergoing final testing at
the Clinic..
The filtering device, which includes a tiny mesh screen, is placed within the
aorta during surgery. The filter allows for normal blood flow, but traps
loosened pieces of plaque and other debris. The filter remains in place until
the patient is taken off of cardiopulmonary bypass (heart-lung machine), after
which the filter is removed from the body. In initial studies, the filter was
successful in capturing particles in more than 95 percent of cases.
Researchers at The Clinic also are studying the use of certain drugs--called
neuroprotectants--that may help protect the brain against brief periods of
oxygen loss, which occurs during coronary artery bypass procedures.
One therapy currently being studied involves keeping magnesium levels above
the normal range during surgery. Magnesium is a mineral needed by every cell in
the body, as it is necessary for more than 300 biochemical reactions. Magnesium
helps to maintain normal muscle and nerve function, keep heart rhythm steady and
bones strong.
Magnesium appears to block the pathway that allows dangerous levels of
calcium to enter oxygen-deprived brain cells. Magnesium also might decrease
brain cell damage due to inflammation (swelling and irritation).
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