Making heart surgery more brain-friendly

Surgeons at University Hospitals of Cleveland have demonstrated that the risk of brain damage associated with the use of the heart lung machine can be significantly reduced by modifying the traditional placement of cannulas (tubing) for returning blood flow to the patient. The findings were presented last month at the American Heart Association’s annual Scientific Sessions conference in Chicago, Ill.

The neurological problems associated with bypass surgery have been widely reported. As much as 6 percent to 10 percent of bypass patients will experience memory loss, visual changes, or even stroke. Surgeons believe these outcomes are partly due to “debris” lining the aorta that may break off during surgery–under pressure exerted by the heart-lung bypass machine (which keeps blood flowing to the brain).

Alan Markowitz, MD, and a team of researchers at The Research Institute of University Hospitals of Cleveland and Case Western Reserve University studied the patterns of blood flow to the brain on the heart-lung machine and the risk of stroke from debris released into the aorta, the conventional site of blood return flow to the patient.

Under the standard approach, surgeons place a cannula into the ascending aorta, forcing blood to flow through the aorta and upwards to the brain. Dr. Markowitz’s team selected a different blood vessel. They placed the cannula into the axillary artery, a branch of the aortic arch providing direct blood flow to the right side of the brain. This innovative approach significantly reduced the flow of emboli (debris) to the brain.

“Axillary perfusion appears to deflect debris away from the brain and markedly limits postoperative neurological complications,” Dr. Markowitz says. He has used this approach (to cannulate the axillary artery instead of the aorta) in several hundred adult heart surgery patients who were at higher risk for stroke. The results showed a very low incidence of stroke in this high-risk patient population.

“Our clinical experience with such a low stroke rate in these high-risk patients stimulated us to go back to the lab to work out the reason, and we were able to prove our hypothesis,” Dr. Markowitz says.

In the laboratory, the research team conducted studies on dogs after modifying the aortic arch to mimic the human anatomy. Their results were gratifying. “We tracked microscopic emboli using fluorescent markers,” says Dr. Markowitz. “The placement of the cannula in the axillary artery resulted in a 75 percent decrease in the number of emboli flowing to the right side of the brain, and a 45 percent decrease in the number of emboli flowing to the left side of the brain.”

Dr. Markowitz presented his findings in the American Heart Association’s “Stroke Risk and Reduction” section. His presentation was entitled, “Axillary Artery Cannulation for Cardiopulmonary Bypass Reduces Cerebral Microemboli.”