Bypass Surgery Doesn't Harm Cognitive Ability
New study finds heart procedure free of lasting deficits
MONDAY, April 25, 2005 (HealthDay News) -- Coronary artery bypass surgery doesn't appear to impair a patient's memory or the ability to process and respond to information clearly, quickly, and effectively, a large-scale review of recent research suggests.
Researchers from Johns Hopkins University now say that although some patients may experience declines in mental skills and motor speed immediately after surgery, such negative side effects will usually subside within a matter of months.
"A small subset of patients -- mostly those who are very old and with risk factors for vascular disease -- may suffer transient cognitive decline after surgery," said Dr. Ola A. Selnes, a Hopkins professor of neurology and study co-author. But "this cognitive decline is generally mild and reversible by three months."
The findings were published online in the April 25 issue of the Annals of Neurology.
Selnes and a Hopkins colleague -- neurology professor Dr. Guy M. McKhann -- analyzed the findings of dozens of prior studies that explored the impact that heart bypass surgery can have on both short-term and long-term cognitive function.
Heart bypass surgery was first successfully performed in 1953 as a means to restore proper blood flow to the hearts of patients whose arteries have become clogged or clotted due to the build up of plaque. If left untreated, such blockages can ultimately provoke the onset of both chest pain -- in the form of angina -- and heart attacks.
Typically, the procedure involves the extraction of a blood vessel from the patient's leg or chest. One end of the vessel is then attached to the patient's coronary artery below the blocked juncture, while the other end is linked to the aorta -- the heart's largest artery, according to the American Heart Association.
Currently, more than half a million coronary bypass surgeries are performed each year in the United States.
Yet although the surgery itself is now firmly entrenched in the medical mainstream, coming to a consensus on its impact has not been so easy. The study authors caution that no clear and uniform research method has been established to assess the surgery's influence on cognitive functioning. This can make a review of past studies a frustrating comparison of apples and oranges.
Different studies analyzed different surgical techniques, Selnes and McKhann noted. Some focused on the track record of the more conventional "on-pump" bypass procedure, which involves full heart stoppage and mechanical heartbeat assistance. Others, however, targeted the relatively new technique of "off-pump" bypass, in which the surgeon operates on an unassisted beating heart.
In addition, the reviewed studies did not always look at the same type of heart patient pool -- with wide apparent differences in the mental health, disease history, and age of the men and women undergoing cardiac surgery.
Nevertheless, a careful study-by-study breakdown revealed that bypass surgery does seem to have a short-term negative impact on basic cognitive functions such as perception, recognition, and the ability to remember, reason, imagine, and process information, the authors said.
In particular, Selnes and McKhann confirmed the long-held notion that post-bypass patients tend to experience some short-term memory and visual-spatial problems.
However, they found these declines are often mild and reversible -- in some instances as short as two weeks.
While the investigators did find evidence of longer-term decline in the speedy execution of motor skills -- enduring as much as five years post-surgery -- they concluded that it is not clear whether such decline is the result of the heart surgery itself or rather due to other mitigating factors.
In addition, they concluded that the available research also cannot as yet specifically distinguish between heart bypass surgery and a range of other surgical procedures in terms of how one or the other might harm long-term cognition.
The researchers further pointed out that as bypass surgery has become more common, the patient pool has aged. They noted that this raises the possibility that longer-term cognitive problems may not be the result of the surgery itself or the use of anesthesia during the operation, but rather a function of the normal aging process or the development of Alzheimer's disease or other chronic neurological illnesses.
While the authors cited a need for more in-depth research into these questions, they concluded that bypass surgery appears to be an increasingly safe procedure with minimal long-term cognitive impact.
"We're talking about issues of memory -- issues related to judgment, language function, speed of doing things -- which all fall into a complex web of cognitive functions," said McKhann. "And we don't think there is very good evidence that there are long-term effects or delayed effects on these cognitive functions from coronary surgery."
McKhann also noted that he and Selnes uncovered additional evidence suggesting that even short-term cognition issues might not be a function of the bypass surgery itself, but rather symptomatic of heart disease in general.
"People who have heart surgery really aren't different -- aren't experiencing any greater problems -- than those people who have coronary heart disease but who do not have surgery," he said. "And those people who have short-term problems appear to be getting better faster than we would have thought."
Dr. Robert Lowery, chief of cardiothoracic surgery at SUNY (State University of New York) Downstate Medical Center in New York City, expressed a great deal of enthusiasm about the Hopkins review.
"I think it really gives all of us a chance to breathe a sigh of relief," he said. "Although we know there can be complications with cardio-bypass surgery, there has been some untoward negative publicity -- and a little bit of hysteria -- with regards to the negative effects. So this corroborates what many of us have seen over the years -- that millions of peoples' lives have been saved by heart bypass surgery."
For more on coronary artery bypass surgery, visit the American Heart Association.