Coronary artery bypass surgery offers a new lease on life for upwards of half a million Americans a year. Rerouting blood flow around clogged or blocked arteries brings 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. But the operation isn't perfect. 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 get confused more easily, have memory trouble, or feel they aren't thinking as clearly as they were before the operation. A possible cause: the heart-lung bypass pump.
Pumping blood through the heart-lung machine may harm blood cells and thus create clots. It may provoke inflammation, which could harm the brain. Handling and clamping the aorta 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. 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.
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 study from Duke University Medical Center, published in 2001. It indicated that 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
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. They also acknowledge that it isn't possible right now to determine whether these changes are caused by bypass surgery, normal aging, the slow development of Alzheimer's disease, the mini-strokes of vascular dementia, or other causes.
It will take one or more large, randomized trials to tease out how much of this can be attributed to bypass surgery, heart disease, and aging.
Is off-pump bypass better for the brain than on-pump bypass? Heart surgeons, cardiologists, anesthesiologists, and neurologists assembled by the American Heart Association (AHA) reviewed evidence from dozens of studies to try to answer this question. 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.
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.
February 2006 update