Women more likely than men to have a stroke after heart surgery

By Jim Dryden

May 4, 2001

Researchers have found that women who have cardiac surgery have a significantly greater risk for stroke than men having the same operation.

Investigators from the School of Medicine and Duke University showed that, even after considering other risk factors such as age, diabetes and hypertension, stroke risk is higher for women. They reported their findings in the May 1 issue of Circulation, the journal of the American Heart Association.

"Being female was independent of any other risk factor," said Charles W. Hogue Jr., M.D., the paper's first author. "There seems to be something about being a woman that predisposes a patient to a higher risk for stroke after heart surgery."

Hogue, associate professor of anesthesiology, analyzed clinical information from the Society of Thoracic Surgery (STS) National Cardiac Surgery Database. The database contains information about patient risk factors and surgical outcomes. About 60 percent of the centers that perform heart surgery in North America submit information.

"It's a very large national database that includes not only big academic centers like ours but also smaller community hospitals," said Victor G. D‡vila-Rom‡n, M.D., the paper's corresponding author and associate professor of medicine, anesthesiology and radiology. "With its size and the number and types of centers involved, the STS database provides a representative sample of what goes on in hospitals around the country."

Hogue, D‡vila-Rom‡n and their colleagues analyzed data on 416,347 patients who had heart surgery in 1996 or 1997. Of those patients, 32 percent were women. In the days following heart surgery, 3.8 percent of the women suffered some type of neurological event --a stroke, transient ischemic attack or coma. Only 2.4 percent of the men had similar neurological problems. So the risk was 1.6 times greater for the women.

In addition, the death rate after surgery was higher for women than for men --5.7 percent versus 3.5 percent. Among the patients who suffered strokes, the rates were 32 percent versus 28 percent. When the investigators used statistical techniques to control for risk factors such as high blood pressure, age, diabetes and smoking, they still found women to be at increased risk.

"Not only are women more likely than men to have a neurological event after heart surgery, but when they do, they are more likely to die in the 30 days following surgery," Hogue said. "That higher risk is not explained by any currently known risk factors."

The researchers studied patients undergoing cardiac bypass surgery, valve repair or replacement surgery and combined bypass and valve surgery. For every type of surgery, women had a significantly greater risk for stroke or other postoperative neurological event. They also had higher death rates following surgery than their male counterparts. The 30-day mortality rate for women undergoing combined bypass and valve surgery was 11.4 percent compared with only 6.4 percent for men.

"It seems clear that women have a higher incidence of neurological events after cardiac surgery, higher mortality rates and longer hospital stays," D‡vila-Rom‡n said. "Post-operative stroke is a devastating complication for both men and women. It is associated with significant suffering for patients and their families and results in high health-care costs.

"Our challenge is to identify the causes of the strokes and to devise aggressive strategies to prevent them from occurring."

D‡vila-Rom‡n and Hogue hypothesize that decreased levels of the hormone estrogen may contribute to the risk for women. Most female heart surgery patients are operated on 10-15 years after they go through menopause.

Estrogen is believed to help protect women from heart disease prior to menopause, and some research has shown that the hormone also protects brain cells from injury. Men have less estrogen in their systems than pre-menopausal women, but they do make some by converting a portion of their male hormone, androgen, into estrogen. In that way, men can maintain some level of estrogen throughout life. But once women go through menopause, their estrogen levels decrease to practically immeasurable concentrations.

"Unfortunately, the STS data do not reveal which women were on hormone replacement therapy," Hogue said. "But when we looked at our own data from Barnes-Jewish Hospital in St. Louis, we found that fewer than 10 percent of the women who came for heart surgery were taking estrogen at that time."

Hogue, D‡vila-Rom‡n and their colleagues are comparing the use of estrogen administered at the time of cardiac surgery with those not given the therapy. The study is being conducted at various hospitals affiliated with the University and BJC HealthCare.