Women under 75 more likely than men to die of heart attacks, say scientists

Women under age 75 who suffer heart attacks are almost twice as likely to die in the hospital following the seizure than are men under age 75, according to a Yale study published in the Oct. 12 issue of the American Medical Association's Archives of Internal Medicine. Conversely, the study shows that women who are 75 years of age or older have a significantly lower risk of death than men in the same age group.

The researchers studied data from the medical records of 1,025 patients who met accepted criteria for myocardial infarction. "When examining sex differences in outcomes from heart attacks, findings have been conflicting," says Viola Vaccarino, assistant professor of epidemiology and public health at the School of Medicine, who led the study. "Averaging the risks over a broad age range may have obscured the higher risk for women in the younger age group."

She added that further investigations are needed to confirm the findings in larger populations, and determine the reasons for the relatively poor prognosis after heart attacks for younger female patients.

The study was based on the Myocardial Infarction Project II (MIP II), a database developed by the Connecticut Peer Review Organization and 15 Connecticut hospitals to help improve the quality of health care for heart attack patients. Trained nurses and medical record technicians studied the medical records of patients who suffered myocardial infarctions in 1992 and 1993 to obtain information on the patients' demographics, medical history, clinical characteristics on admission, treatments and hospital mortality.

"We found that, overall, women of all ages had a 40 percent higher hospital mortality than men, but that simple age adjustment eliminated the sex differences in mortality rate, as previous studies have shown," says Vaccarino. "However, when the sample was subdivided into two age groups, women younger than 75 years old showed twice as high mortality as men of the same age, while older women showed no difference in mortality," explains the Yale professor, who collaborated on the study with Drs. Ralph I. Horwitz and Harlan M. Krumholz of the School of Medicine, and Dr. Thomas P. Meehan, Marcia K. Petrillo and Dr. Martha J. Radford of the Connecticut Peer Review Organization.

The researchers then took the study a step further. After taking into account sex differences in coexisting illness, clinical severity of the heart attack and hospital treatments, they found that the higher mortality persisted for women under age 75 (although somewhat less dramatically at only 49 percent higher), while women 75 or older actually showed a 46 percent lower mortality rate than men. In addition, the study showed that there is no "threshold effect," which means that higher risk did not occur suddenly at age 65 or 70. Instead, the researchers discovered that the younger the women, the higher their risk of death after a heart attack compared with men.

Because of the protective effect of estrogen in premenopausal women, myocardial infarction is much less common than in men up to about age 75, according to Vaccarino. Women who have a heart attack before then may be genetically predisposed to early onset or more severe heart disease, and may represent "a distinct group in terms of risk factors and pathophysiology, with a particularly aggressive course for the disease," she says, noting that another explanation could be a delay in detection of coronary heart disease in younger women and less frequent referrals for treatment.

"When examining sex differences in outcomes of myocardial infarction, it may not be sufficient to adjust for age alone, but future studies should also consider the interaction between sex and age," she adds.