Brain Damage After Bypass Surgery Most Likely Due to
the Coronary Artery Disease
Heart-lung machines that pump blood and supply the
body with oxygen during surgery do not cause postoperative long-term
brain deficits
Aug.
4, 2009 The long-term memory loss and
cognitive problems sometimes experienced by bypass surgery patients are
due to the coronary artery disease itself and not the effects of having
used a heart-lung machine, say brain scientists and cardiac surgeons at
John Hopkins.
Researchers say their latest findings explain study
results presented last year, which showed that the heart-lung machines
used to pump blood and supply the body with oxygen while the heart is
stopped during surgery did not cause postoperative long-term brain
deficits.
"Our results hammer home the message that
heart-lung machines are not to be blamed for cognitive declines observed
years later in people who have had bypass surgery," says lead study
investigator
Ola A. Selnes, Ph.D., a professor in the Division of Cognitive
Neuroscience in the neurology department at the Johns Hopkins University
School of Medicine.
The new results stand in contrast to the impact of
heart-lung machines on so-called "pumphead" syndrome, the temporary
memory loss, vision and slurred speech observed right after surgery in
many heart bypass patients.
According to another of the study's investigators,
William A. Baumgartner, M.D., former cardiac surgeon in charge at
The Johns Hopkins Hospital, the short-term syndrome led many surgeons
and patients alike to assume that long-term losses must also be due to
use of heart-lung machines, an assumption proven wrong by the latest
evidence.
"Now we can assure these people that the disease,
not the machine itself, is the cause of the problem," says Baumgartner,
vice dean for clinical affairs and the Vincent L. Gott Professor in
Cardiac Surgery at the Johns Hopkins University School of Medicine and
its Heart and Vascular Institute.
Neurologists on the study team say the results
highlight the need for further research into the long-term consequences
of cardiovascular disease on the brain, and the brain's complex network
of tiny blood vessels.
About Coronary Artery
Bypass Surgery
Also called: Bypass surgery, CABG,
Coronary artery bypass graft
If you have
coronary artery disease (CAD), the arteries that supply
blood and oxygen to the heart muscle become hardened and
narrowed. If lifestyle changes and medicines don't help, your
doctor may recommend coronary artery bypass surgery.
The surgery uses a piece of a vein from the
leg or artery from the chest or wrist. The surgeon attaches this
to the coronary artery above and below the narrowed area or
blockage. This allows blood to bypass the blockage. Some people
need more than one bypass.
You may need bypass surgery for various
reasons. Another procedure for CAD,
angioplasty, may not have widened the artery enough. In some
cases, the angioplasty tube can't reach the blockage.
A bypass also can close again. This happens
in more than 10 percent of bypass surgeries, usually after 10 or
more years.
"Neuroscientists do not yet have good measures on
heart disease and how the burden of this disease impacts brain
function," says study senior investigator and neurologist
Guy McKhann, M.D., a professor at Johns Hopkins, who next plans
brain imaging studies to look at changes before and after heart bypass
surgery to determine if there are any early, even predictive signs of
cognitive problems, and if surgery could fix them.
McKhann notes that previous studies have found some
50 percent of patients awaiting heart bypass surgery already have some
early indication of brain damage.
"If we can eventually figure out how heart disease
and declines in brain function are linked over the long term, then it is
feasible to think that we can diagnose problems earlier and, ultimately,
intervene and prevent, or even lessen, these cognitive problems," says
McKhann.
During heart bypass surgery, more formally known as
coronary artery bypass grafting, or CABG, blood vessels from other parts
of the body are removed and re-attached to the heart to restore open
blood flow when the natural blood supply becomes constrained from
coronary arteries that are diseased and blocked. Patients often spend an
hour or more connected to a heart-lung machine during the surgery.
Results of the new study, published in the August
2009 issue of Annals of Thoracic Surgery, showed no differences in brain
impairment in those who had heart bypass surgery, including a group of
75 heart patients who had so-called off-pump bypass surgery, and another
group of 99 heart patients who opted for drugs and arterial stents to
keep their blood vessels open instead of bypass, with none requiring use
of a heart-lung device.
But all 326 patients in the three groups were found
to have experienced significant cognitive decline over the six-year
study period on 16 different scores of verbal and visual memory when
compared to 69 heart-healthy people who had no known risk factors for
coronary artery disease.
The study, on heart patients from the
Baltimore-Washington, D.C., region, is believed to be the first
controlled study of its kind directly looking at the underlying causes
of brain impairment, a phenomenon seen since the 1960s, when the CABG
procedure was first introduced.
Adding to patients' fears was a 2001 report by
researchers elsewhere, which found that 42 percent of heart bypass
patients experienced some long-term cognitive impairment.
McKhann says CABG has "really evolved" along with
heart disease treatment since the heart bypass machines and restorative
procedure were first introduced, with procedure volumes peaking in the
1990s, but dropping afterwards, as physicians and patients began opting
for less-invasive procedures. According to the latest estimates from the
American Heart Association, roughly 469,000 CABG procedures were
performed in the United States in 2005 on some 261,000 patients.
He points out that the procedure remains in
widespread practice as patients considered safe to have the CABG
procedure are getting older and sicker. People as old as 80, he says,
are now candidates for CABG.
"With these new data, patients can now more
accurately and confidently weigh the risks and benefits of bypass
surgery against off-pump surgery or even more conservative options,"
says McKhann.
All study participants underwent an hour-long
series of cognitive tests five times and during regularly scheduled
annual study visits. In one test of verbal memory, patients had to
memorize 15 words in a specific order and within 30 minutes. In another
test of visual memory, patients had to trace on paper a complex diagram,
which was then taken away, and then redraw the diagram from scratch.
Funding support for this study was provided by the
U.S. National Institute of Neurological Disorders and Stroke, a member
of the U.S. National Institutes of Health, and the Dana Foundation.
Besides McKhann, Baumgartner, and Selnes, other
researchers involved in this study, conducted from 1997 through 2008,
were Maura Grega, M.S.N.; Maryanne Bailey, M.P.H.; Luu D. Pham, M.Sc.;
and Scott Zeger, Ph.D.
Aug.
4, 2009 The long-term memory loss and
cognitive problems sometimes experienced by bypass surgery patients are
due to the coronary artery disease itself and not the effects of having
used a heart-lung machine, say brain scientists and cardiac surgeons at
John Hopkins.