Women more likely than men to have a stroke after heart surgery
St. Louis, May 1, 2001 – Researchers have found that women who undergo cardiac surgery have a significantly greater risk of stroke after surgery than men having the same operation. Investigators from Washington University School of Medicine in St. Louis and Duke University showed that, even after considering other risk factors such as age, diabetes and hypertension, stroke risk is higher for women. They report 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," says 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, an associate professor of anesthesiology at the School of Medicine, 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," says Victor G. Dávila-Román, M.D., the paper’s corresponding author and an associate professor of medicine, anesthesiology and radiology at the School of Medicine. "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, Dávila-Román and 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 (TIA) or coma. Only 2.4 percent of the men had similar neurological problems following surgery. 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. That higher risk is not explained by any currently known risk factors," Hogue says.
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 of a 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. "The number of patients in this study is so large, and the STS database is so representative that our findings have great statistical power. It seems clear that women have a higher incidence of neurological events after cardiac surgery, higher mortality rates and longer hospital stays," Dávila-Román says. "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."
Dávila-Román and Hogue hypothesize that decreased levels of the hormone estrogen may contribute to the elevated risk for women. Most female heart surgery patients are operated on 10 to 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, called 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 says. "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, Dávila-Román and 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 Washington University and the BJC HealthCare system.
This research was supported with funding from the Cardiovascular Imaging and Clinical Research Core Laboratory at Washington University School of Medicine in St. Louis.
For more information, refer to Hogue CW, Barzilai B, Pieper KS, Coombs LP, DeLong ER, Kouchoukos NT, Dávila-Román VG. Sex differences in neurological outcomes and mortality after cardiac surgery. Circulation vol. 103 May 1, 2001.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.