Bypass surgery and memory

Temporary changes in memory and thinking skills are common after bypass surgery. Don't blame the heart-lung bypass pump.

Coronary artery bypass surgery offers a new lease on life for upwards of half a million Americans a year. Rerouting blood flow around cholesterol-clogged or blocked arteries brings extra oxygen and nutrients to regions of the heart that hadn't been getting their fair share. This eases angina, the chest pain that appears when the demand for oxygenated blood exceeds the supply. Bypass surgery also helps extend life in people with congestive heart failure and other serious conditions.

Given the disruption to the body — the traditional approach requires splitting the breastbone, stopping the heart, and using a pump to oxygenate and circulate blood — it's amazing that most people come through bypass surgery with only some scars as a long-term reminder. This isn't to say the operation is a walk in the park. For every 100 Americans who undergo it, 1 to 2 die within a month, and 2 to 3 have a stroke.

Some people experience a more subtle side effect: They just don't feel the same after bypass surgery. They get confused more easily, feel they aren't thinking as clearly as they were before the operation, or have trouble concentrating, remembering things, or solving problems. Pump-head, the slang term some doctors once privately used for this post-bypass mental fog, suggested a possible cause: the heart-lung bypass pump.

Pumping blood through the heart-lung machine may harm fragile blood cells and thus create clots. It may provoke a riot of inflammation, which could harm the brain. Handling and clamping the aorta, the large, curved artery that emerges from the left ventricle, can shake free a shower of atherosclerotic plaque, and these bits of debris can block blood vessels in the brain.

Brain problems after bypass spurred the development of beating-heart bypass, which circumvents the need for a machine to circulate blood. Introduced in 1995, and sometimes marketed as the "executive bypass" for people who couldn't afford to slow down mentally, off-pump surgery now accounts for about 20% of bypass operations.

Three reviews take the spotlight off the heart-lung pump. One indicates that pump-head might better be called cholesterol-clogged-artery-head. The other two show that off-pump bypass isn't all it has been cracked up to be.

Controversial effects

Just how common post-bypass mental changes are, how long they last, and what causes them has never been crystal clear.

At one end of the spectrum is a headline-grabbing study from Duke University Medical Center, published in 2001. It indicated that fully half of people undergoing bypass surgery developed memory or thinking problems in the days following it, and that these problems were usually still evident five years later.

At the other end of the spectrum are studies showing no long-term effects. Here's one example: Researchers followed 232 sets of twins for more than 10 years. One of each set had undergone bypass surgery. Overall, there were no differences in mental function in the bypass and nonbypass groups. Interestingly, those who underwent bypass at a younger age (63–70 years) actually did better on tests of mental performance than their twins who hadn't had a bypass.

Two Johns Hopkins researchers who have been at the forefront of this field reviewed the evidence on short-term and long-term mental changes after bypass surgery. They found that short-term confusion, memory loss, and poorer problem solving and information processing are common after bypass surgery, but are usually temporary and reversible. Most people return to their pre-bypass level of function between 3 and 12 weeks after surgery.

Long-term changes occur, too, but these are usually mild and tend to affect things such as how fast you can solve problems or process information. The authors suggest that these changes probably arise from changes in the brain caused by atherosclerosis, the same thing that led to the need for bypass surgery. They also acknowledge that it isn't possible right now to determine whether these late changes are caused by bypass surgery, normal aging, the slow development of Alzheimer's disease, the mini-strokes of vascular dementia, or other causes. Their report appeared in the May 2005 Annals of Neurology.

It will take one or more large, randomized trials comparing long-term changes in memory and thinking skills among people undergoing bypass surgery, those with heart disease but no surgery, and those without heart disease to tease out how much of this can be attributed to bypass surgery, heart disease, and aging.

Off-pump equivalence?

Is off-pump bypass better for the brain than bypass using a heart-lung machine? A team of Canadian researchers tried to answer this question by pooling the data from 37 trials comparing the two operations. The combined results showed no clear differences in short- and long-term mental function. Their paper appeared in the January 2005 issue of Anesthesiology.

The American Heart Association (AHA) said much the same thing in a scientific statement published in June 2005. Heart surgeons, cardiologists, anesthesiologists, and neurologists assembled by the AHA reviewed evidence from dozens of studies. They concluded that, overall, on-pump and off-pump bypass surgery are equally effective. Off-pump bypass might help reduce the chances of short-term memory and thinking problems, but in the long run there don't seem to be differences between the two types of surgery.

What it means for you

If you need to have bypass surgery down the road, expect some fogginess for a short time afterward. Not everyone experiences this, but it's good to be prepared.

What about long-term changes? These do occur, but whether they are from bypass surgery, cholesterol-narrowed arteries, or aging isn't clear. They certainly aren't inevitable, and you may be able to stave them off. In a small study from Germany, careful attention to blood pressure, cholesterol, smoking, and exercise virtually eliminated significant declines in mental function over a five-year period after bypass surgery.

The main messages from these studies on post-bypass brain changes are reassuring. They also reinforce the point that the surgeon you choose is more important than the type of surgery. For the best outcome, find a surgeon who has done many bypasses and who will be frank about what you might gain from bypass surgery as well as about the downsides of the operation. Talk with him or her about your particular risk for cognitive problems and what you can do to minimize them.