Heart Disease, Not Bypass Surgery, to Blame for Cognitive Declines

by Aalok Mehta

October 26, 2009

A person’s underlying heart disease, and not surgery, appears to cause the cognitive declines routinely seen in those who have undergone bypass operations, a recent study shows.

For years, patients and some members of the medical community have expressed reservations about surgeries involving heart-lung machines, in which the heart is temporarily stopped and a machine takes over its duties. The assumption was that long-term cognitive changes were related to “pumphead” syndrome—a bout of temporary memory less, vision trouble and slurred speech often observed following a bypass procedure.

A 2001 study reported in the New England Journal of Medicine bolstered that fear when it found that 42 percent of patients showed cognitive declines in the five years following a surgery involving a heart-lung machine.

But the new study, which appears in the August 2009 issue of Annals of Thoracic Surgery, found that similar cognitive declines occur in most patients with cardiovascular disease, regardless of whether they opted for surgery or drugs to treat their conditions.

 “In the past, everyone has blamed bypass pumps,” says study lead investigator Ola Selnes, a professor of cognitive neuroscience at Johns Hopkins School of Medicine. “They say it’s all because of the pumps. But that argument does not hold up anymore.”

The findings suggest that doctors need to learn much more about how cardiovascular disease affects the tiny blood vessels of the brain. It also provides crucial information for patients considering the procedure, which is increasingly being used on older and sicker people, including those in their 80s.

Under control

The question of what causes this cognitive decline remained unresolved for so long because no one had conducted a study comparing the appropriate groups of patients, according to Selnes and his co-authors. “Many many studies have attempted to quantify changes in cognition after the use of bypass pump,” Selnes says. “The problem is, the methods they have used to quantify have not been correct. It all stems from the fact that they did not use control groups.”

So for their study, the Johns Hopkins researchers attempted to cover all the bases. They administered routine tests of verbal and visual memory to 326 people with cardiovascular disease in three distinct groups. Only 159 of these underwent bypass surgery; 75 had an alternative procedure known as “off pump bypass,” in which their heart was kept beating during the operation, and the remainder chose to use arterial stents and drugs to control their conditions instead of surgery. In addition to those comparisons, the researchers also included a group of 69 people with no heart problems and no risk factors for heart disease.

Over the course of six years, all three of the groups with heart disease showed significant cognitive declines, compared with the healthy group. “There is no difference in terms of longitudinal decline in cognitive performance between the bypass group and the medication group,” Selnes says. “The groups with heart disease start out lower at baseline, and they trend toward a little more decline.”

Selnes adds that the study is only a first step. Although it implies that the cardiovascular disease is directly affecting the brain in some way, probably by causing changes in blood vessels, no one knows for sure exactly what is happening or how to stop it.

The study also did not look at short-term consequences of heart surgery, as the first tests weren’t administered until months afterward. If there are short-term consequences, “they are likely to be transient,” Selnes says. “By three months, the patients are pretty much back to normal.”

More evidence of underlying causes

The findings make sense to other experts in the field. People with cardiac disease are at a much higher risk of strokes, including small ones that often go undetected, says Jose Biller, a professor of neurology at Loyola University. Most of these people have disease that affects many of the body’s blood vessels, he says. “By and large [their cognitive impairments] are likely due to atherosclerosis,” or hardening of the arteries.

Also lending some support is Biller’s recently updated and revised review article, which was originally published in MedLink Neurology in June 2008 and which outlines rates of neurological complications resulting from cardiac surgeries. These were not just limited to bypass operations but included aortic surgeries, catherizations, valve replacements, transplants and other processes.

In almost all cases, complications could be traced directly to events that occurred during the surgery—such as a bubble of air causing a stroke or blood pressure irregularities. Strokes occurred in 1 percent to 5 percent of heart surgeries, depending on the type of operation and the age and health of the patient, but most were detected within two days. Other neurological symptoms were “often temporary, not permanent impairments.”

Some of the symptoms, meanwhile, may be the result of undetected conditions. “In an ideal world, everyone would have a neurological examination prior to surgical intervention,” Biller says. “Except that you have to understand—these are often emergency surgeries.

“We are not emphasizing the risks but ensuring that the complications are known, so we can understand how to prevent them,” he adds. “These are life-saving interventions that improve quality of life—the accomplishments of cardiac surgery have been incredible.”

The Johns Hopkins study was funded in part by the Dana Foundation. Guy McKhann, a scientific consultant for the Dana Foundation, was one of the paper’s co-authors.