August 31, 2009

Is there long-term brain damage after heart bypass surgery?

Brain scientists and cardiac surgeons at Johns Hopkins have evidence from 227 heart bypass surgery patients that the long-term memory losses and cognitive problems they experience are due to the underlying coronary artery disease itself and not to ill aftereffects from having used a heart-lung machine.

Researchers say that their latest findings explain study results presented last year that showed 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,” said lead study investigator Ola A. Selnes, a professor of cognitive neuroscience in the Neurology Department at the School of Medicine.

The new results stand in contrast to the impact of heart-lung machines on so-called “pumphead” syndrome of temporary memory loss, impaired vision and slurred speech observed right after surgery in many heart bypass patients. According to another of the study’s investigators, William A. Baumgartner, 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 the use of heart-lung machines, an assumption proved wrong by the latest evidence.

“Now we can assure these people that the disease, not the machine itself, is the cause of the problem,” said Baumgartner, vice dean for clinical affairs and the Vincent L. Gott Professor in Cardiac Surgery at the 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.

“Neuroscientists do not yet have good measures on heart disease and how the burden of this disease impacts brain function,” said study senior investigator and neurologist Guy McKhann, a professor at Johns Hopkins.

McKhann 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. He 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 decline 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,” McKhann said.

During heart bypass surgery, more formally known as coronary artery bypass grafting, blood vessels from other parts of the body are removed and reattached 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 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.

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 coronary artery bypass grafting procedure was first introduced.

Adding to patients’ fears was a 2001 report by researchers elsewhere that found that 42 percent of heart bypass patients experienced some long-term cognitive impairment.

McKhann says that 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 afterward 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.

McKhann points out that the procedure remains in widespread practice as patients considered safe for having 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,” McKhann said.

All study participants underwent an hourlong series of cognitive tests five times during regularly scheduled annual study visits. In one test of verbal memory, patients had to memorize 15 words in a specific order within 30 minutes. In a test of visual memory, patients had to trace on paper a complex diagram and then redraw it after the diagram was taken away.

Funding support for this study was provided by the National Institute of Neurological Disorders and Stroke and by the Dana Foundation.

In addition to McKhann, Baumgartner and Selnes, researchers involved in this study, conducted from 1997 through 2008, were Maura Grega, Maryanne Bailey, Luu D. Pham and Scott Zeger, all of Johns Hopkins.

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