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Cognitive Decline After Bypass Surgery Predicts 5-Year Cognitive Decline

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Duke Health News 919-660-1306

DURHAM, N.C. -- While coronary artery bypass graft surgery
has saved the lives of millions of Americans since its
inception decades ago, physicians have long noticed a nagging
problem – many patients, while restored to good health, have
noticed declines in their cognitive abilities.

In the largest study of its kind, Duke University Medical
Center researchers have now measured this loss and shown that
five years after surgery, more than one-third of the patients
will have measurable cognitive decline. It has been generally
accepted that

many bypass patients exhibit some cognitive defects shortly
after surgery and improve over the ensuing months, and now the
long-term effects of the surgery on cognition are becoming
better understood.

The researchers gave 261 heart surgery patients the same
battery of standardized tests of cognition at different
intervals during a five-year period and discovered that 53
percent had measurable declines at discharge from the hospital,
36 percent had measurable

declines six weeks after surgery, and 24 percent had
measurable declines at six months. However, by five years after
surgery, 42 percent had measurable declines.

In the study, the researchers tested such cognitive
abilities as short-term memory, attention, concentration,
language comprehension, abstraction and spatial
orientation.

The results of the Duke study, which was supported by grants
from the National Heart, Lung and Blood Institute and the
American Heart Association, were published Feb. 8 in The New
England Journal of Medicine. Dr. Mark Newman, chief of
cardiothoracic anesthesia at Duke, led the multi-disciplinary
study of heart surgery patients treated at Duke University
Hospital.

"Little is more devastating to patient and family than for
the patient to have a successful operation that prolongs life,
but diminishes the quality of that prolonged life," Newman
said. "Our results confirm long-term persistence of cognitive
dysfunction and the importance preventing these deficits. They
will also help us design strategies to make an already safe
procedure even safer."

In addition to demonstrating the cognitive declines, the
researchers also found that three factors were important
determinants of the five-year decline: age, level of education
and the level of cognitive decline at discharge.

"The older the patient, the higher the probability of
suffering decline," Newman said. "Age is an important factor,
especially since we can safely operate on an older population
of patients. Also, the more educated a patient is, the smaller
the decline. While we don't know the exact reasons for this, it
seems that education confers more of a cognitive 'reserve,' so
the loss is not noticed as much."

This study did not compare the study participants with
similar people who did not undergo surgery. While studies have
shown that cognitive function has been shown to decline
gradually with age, the researchers pointed out that study
participants who suffered cognitive declines showed a decline
more than two times that demonstrated by 5,888 Medicare
patients in a recent five-year study.

Coronary artery bypass grafting (CABG) surgery is a surgical
procedure performed more than 600,000 times a year in the
United States. Typically, surgeons use pieces of blood vessels
from other parts of the body to "bypass" clogs in coronary
arteries, and thereby restoring blood flow to the heart.

The researchers say it is likely that many factors are
behind the cognitive declines, although they believe that the
heart-lung bypass machine commonly used in CABG surgery is an
important culprit. This machine essentially pumps and
oxygenates the blood for the body while surgeons operate on the
stopped heart.

"While we have known for some time that the heart-lung
machine is probably a cause, we don't know for certain how it
might affect cognition," Newman said. "It is likely that tiny
emboli, or clots, are formed and go to the brain. Other
factors, such as inflammation and the lowered blood pressures,
could play a part as well. There needs to be further
investigation into operative neuroprotection to allow us to
reduce the short- and long-term consequences of cognitive
decline after surgery."

The Duke team is investigating many strategies to better
understand this phenomenon of cognitive decline with the hope
of developing new strategies to protect the brain. These
include:

-- Using minimally invasive techniques, surgeons are now
operating on beating hearts, meaning that the heart-lung
machine is not needed. Preliminary results are encouraging,
although the long-term effects are not yet known.

-- Duke researchers have found that temperature has an
effect on cognitive decline. During surgery, the heart-lung
machine cools the blood to lessen the metabolic needs of the
body during the procedure. Duke studies have shown that
patients who are rewarmed more slowly after surgery tend to do
better on cognitive tests.

-- Duke researchers also have found a genetic component to
the decline. Patients with the E-4 variant of the APOE gene
(which has also been linked to early onset Alzheimer's disease)
tend to do worse than patients with other variants of the
gene.

Other Duke members of the team are: Jerry Kirchner, Barbara
Phillips-Bute, Vincent Gaver, Dr. Hilary Grocott, Dr. Robert
Jones, Dr. Daniel Mark, Dr. Jerry Reves and James Blumenthal.
All are members of the Duke Neurological Outcome Research Group
and the Cardiothoracic Anesthesiology Research Endeavors
group.

Note to editors: Dr. Mark Newman is available at (919)
681-5458. A photo of Newman is available at
http://photo1.dukenews.duke.edu/Duke_News_Service/Newman02.jpg.

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