News Release

Risk factors for stroke after heart surgery identified

Peer-Reviewed Publication

American Heart Association

DALLAS, Aug. 10 -- A new study helps identify which individuals may have the highest risk of stroke following heart surgery. Reporting in today's Circulation: Journal of the American Heart Association, researchers found that heart surgery patients who had previously had a stroke faced the highest risk. They had a 14-times higher risk of having a new stroke during or after surgery.

"Stroke is one of the most devastating complications of heart surgery," says Charles W. Hogue Jr., M.D., associate professor of anesthesiology and chief of cardio-thoracic anesthesia at Washington University and Barnes-Jewish Hospital in St. Louis, Mo.

Stroke incidence is as high as 5 percent in individuals undergoing bypass surgery, almost 9 percent in bypass patients age 75 or older and nearly 16 percent in patients with pre-existing disease involving blood flow in the brain or those undergoing heart valve surgery, according to Hogue. Bypass surgery involves rerouting blood flow around blocked blood vessels.

The purpose of the study was to help physicians better assess the risks of surgery as well as to identify ways to reduce the risk of post-operative stroke. In this study the post-operative strokes occurred in 48 of the patients, or 1.8 percent. "It must be emphasized that stroke happens in a low percentage of patients," Hogue says. "The benefits of heart surgery, for most patients, outweigh the risks. The surgery prolongs life."

The new research challenges several misconceptions that have persisted about post-surgical stroke, says Hogue. Unlike earlier studies, this one separated the 'early strokes' that occurred immediately after surgery when the patient was just waking up from the anesthesia from 'delayed strokes' that occurred later on. Sixty-five percent of the strokes occurred hours or even days after surgery in patients whose post-operative recovery had been uneventful. However, the early strokes, which occurred immediately following surgery, were more deadly than delayed strokes. The death rate was 41 percent for early strokes and 13 percent for delayed strokes.

Hogue says the study was unique because patients underwent ultrasound to determine if there was plaque buildup in their aortic artery before surgery. "Aortic atherosclerosis is a recognized risk factor for stroke -- both for surgical and non-surgical patients. Because we were better able to adjust for this risk factor, other risk factors may take on a new meaning," he says.

Although age was not a risk factor for these strokes, atherosclerosis -- which causes plaque build-ups that block blood flow in an artery -- was a risk factor. Gender was also identified as a significant risk factor. After heart surgery, female patients had triple the risk of stroke as men. This particular risk factor surprised Hogue. In general, men have a similar risk for stroke as women, but in this study the women had a higher rate of stroke following heart surgery. This was true even when age and medical conditions such as diabetes, high blood pressure and others were taken into account. The women in the study also had a higher death rate from stroke than the men, which is also true in the general population.

Having diabetes tripled the risk of post-operative stroke. Patients with a combination of atrial fibrillation and low cardiac output (volume of blood pumped) doubled their risk of stroke. Atrial fibrillation is a condition where the two upper chambers of the heart quiver instead of beating effectively. Blood isn't pumped completely out of them when the heart beats, which allows blood to pool and possibly clot. The clot can enter the circulatory system where it encounters a narrowed artery and obstructs blood flow. Interestingly, researchers say, atrial fibrillation alone was not a risk factor for post-operative stroke, although it is a major risk factor for stroke in the general population.

"Atrial fibrillation has also been identified as a risk factor for stroke after cardiac surgery," says Hogue. "However, in this study it was only a risk factor when it occurred along with low cardiac output state -- reduced blood flow from the heart."

Researchers also cited the duration of surgery as a risk factor for new stroke -- the longer the procedure the greater the risk. The reason was unclear, but Hogue says it may be because a longer time in surgery results in the patient spending more time on a heart-lung machine.

The risk of a stroke during or after heart surgery doubled in patients with aortic atherosclerosis, a build-up of fatty plaque that reduces or blocks the flow of blood from the heart to the main artery of the body.

Although this study identifies the same six risk factors as did earlier research, it was the first to use a large database of case histories to clearly establish the risk factors, says Hogue. The researchers examined the records of 1,900 men and 1,072 women age 50 and over who had undergone heart surgery at Barnes-Jewish Hospital from January 1990 through August 1996. All of the patients had either bypass surgery, valve surgery or both.

Co-authors were Suzan F. Murphy, R.N., B.S.N.; Kenneth B. Schechtman, Ph.D.; and Victor G. Davila-Roman, M.D.

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Media advisory: Dr. Hogue can be reached at 314-362-6584. (Please do not publish these numbers.)


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