How to mend the heart but spare the mind

Content provided by the Faculty of the Harvard Medical School

How to mend the heart but spare the mind

Minimal manipulation of the heart and blood vessels may be the way to limit brain damage from coronary artery bypass.

Fixing broken hearts is something that modern medicine does remarkably well. But another pretty important organ, the brain, sometimes pays a steep price for these cardiac marvels.

Improved equipment and techniques have lowered the risk for stroke after coronary artery bypass surgery to less than 3%.

But lingering "cognitive deficits" remain a problem, particularly after coronary artery bypass. Months — even years — after their operations, many bypass patients can't focus, remember things, or work through problems.

Getting a handle on how often this happens is difficult — partly because it's difficult to define cognitive deficit. One study that's often cited found that five years after surgery, almost half (42%) of bypass patients were cognitively impaired to some degree.

How bypass surgery may cause brain damage

Off-pump bypass

During many heart operations, surgeons stop the patient's heart, partly because it's easier to operate on a heart that isn't moving. Patients are hooked up to a heart-lung machine that circulates the blood and restocks it with oxygen.

But doctors have suspected that blood cells may get damaged when they go through the heart-lung machines. Even slight damage could stir up inflammation and cause blood clots to form. Those clots — even small ones — could cause scattered blockages, called emboli, in brain vessels. Depending on their size and location emboli may cause subtle problems with thinking and attention.

Around the mid-1990s, surgeons started performing off-pump bypass, which involves operating on the heart while it's still beating. The hope was that by eliminating the need for the heart-lung machine, the off-pump operation would result in fewer emboli and lower rates of cognitive deficit.

Dozens of studies have been done, some positive, some negative, some in between. It's safe to say that off-pump hasn't emerged the hands-down winner. A British study published in June 2006 is a good example of the mixed signals. It concluded that conventional and off-pump bypass were equivalent in terms of grafted blood vessels staying open and some quality of life measures. But the off-pump patients did do a bit better on neurocognitive tests.

It's been argued that off-pump operations would make the biggest difference for older, high-risk patients, but a study published in 2006 in the journal Circulation found otherwise. Danish investigators enrolled high-risk patients whose average age was 76. Three months after surgery, 4 of the 54 patients (7.4%) who had off-pump surgery were cognitively impaired, versus 5 of 51 (9.8%) who had undergone a conventional bypass. That amounts to a statistical tie.

Do not disturb signs

Most evidence points to emboli as being the main cause of brain damage after bypass. Some experts believe just moving the heart a little can release "showers of microemboli" into the bloodstream. The same may be true for the aorta and other large blood vessels.

If that's the case, then the solution to post-bypass brain "fog" may lie in techniques that minimize manipulation of the heart and aorta. Some surgeons already use ultrasound scans of the aorta to avoid atherosclerotic plaques that might generate brain-damaging emboli. Eventually, we may see the development of scanning technology that will detect blood clots as they form.

Patient selection also needs to improve. Some people may already be on the brink of cognitive decline before bypass surgery; emboli from the bypass operation just tips them over the edge. Sophisticated brain scans and other tests might rule out bypass for some vulnerable people and might help others to weigh the risks more accurately.

Last updated:	September 05, 2008