Two recent University studies raise possibilities for a genetic link to cognitive disabilities after coronary bypass surgery.
The studies, presented Monday at the annual meeting of the Society for Cardiovascular Anesthesiologists, may lead to explanations for cognitive dysfunction in coronary bypass patients. One establishes a more concrete link between dysfunction and surgery, while the other suggests that a gene variant may predispose patients to risk factors for cardiovascular disease at an earlier age than normal.
Dr. Mark Newman, chief of cardiothoracic anesthesia, presented both studies.
In the first study, researchers examined 313 bypass patients both six weeks and five years after surgery. Almost one third of patients experienced cognitive difficulties.
One theory to explain the finding is that the heart-lung machine used to keep blood flowing during surgery-while the heart is stopped-contributes to the cognitive dysfunction. "While we have known for some time that the heart-lung machine is probably a cause, we don't know for certain exactly what the mechanism is," said Newman in a press release.
Duke Han, a research technician in anesthesiology, said another possible explanation for surgery's effect on cognitive abilities is that coronary bypass surgery "shakes things up." This allows emboli-tiny air bubbles or fatty deposits-to move into the brain and block blood flow.
Newman is currently working on surgical techniques to prevent negative effects on the brain. One project cools the body with ice to slow metabolism, thereby decreasing the brain's demand for oxygen. Another involves the use of drugs to increase oxygen levels, thus compensating for possible oxygen deprivation.
Newman is also exploring the possibility that there is a relationship between the APO gene and bypass surgery's connection to cognitive dysfunction. There are three variants of the APO gene, which codes for the APO protein: E-2, E-3 and E-4. The protein is involved in lipid transport. People with cognitive dysfunction caused by bypass surgery may have the APOE-4 gene, a risk factor for Alzheimer's disease.
There appears to be a connection between APOE-4 and abnormal brain healing processes. "People with APOE-4 do not recover well from head trauma, coma, stroke or intercerebral hemorrhage," said Ann Saunders, assistant research professor of neurology.
"All the work [on APOE-4] has been in the rest of the body, not the brain," Saunders said.
In the second study-which involved 576 coronary bypass patients-researchers found that surgical patients with the APOE-4 gene were more likely to be affected by cognitive disfunction at a young age than others. People with the E-4 type are at risk for cholesterol build-up and are, in turn, at a greater risk for heart disease.
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