Among patients with myocardial infarction, women are more likely than men to present without chest pain or discomfort, and are more likely to die from the event, according to a report in the Feb. 22/29 issue of JAMA.

However, these sex-based differences are most pronounced at younger ages; they become attenuated and nearly disappear with increasing age, said Dr. John G. Canto of the Watson Clinic and Lakeland (Fla.) Regional Medical Center and his associates.

The investigators studied sex-related and age-related differences in MI patients using the "large and clinically rich" database of the National Registry of Myocardial Infarction. The industry-sponsored NRMI contains hospital data on over 2 million patients with confirmed MI treated at 1,977 hospitals across the country between 1994 and 2006.

Dr. Canto and his colleagues analyzed NRMI data on 1,143,513 of these MI patients, of whom 42% were women. For this study, chest pain/discomfort was defined as "any symptom of chest discomfort, sensation, or pressure, or tightness; or arm, neck, or jaw pain ... preceding a diagnosis of acute MI."

Overall, 35.4% of the study subjects presented without chest pain. The proportion was significantly higher among women (42.0%) than men (30.7%), the researchers said (JAMA 2012;307:813-22).

However, this difference decreased in a linear fashion with increasing patient age. For MI patients younger than 45 years, the odds ratio was 1.30; at 45-54 years, it was 1.26; at 55-64 years, it was 1.24; at 65-74 years, it was 1.13; and at 75 years and older, it was 1.03, or practically negligible.

Mortality followed a similar trend within those age groups, but went further in the opposite direction, to a reversal in the oldest patients. The adjusted odds ratio of mortality in women presenting with no chest pain, compared with men presenting with no chest pain, was 1.18 for those younger than age 45, 1.13 for those age 45-54, 1.02 for patients age 55-64, 0.91 at age 65-74, and 0.81 in the patients age 75 and older.

Comorbidity and clinical characteristics clearly accounted for most of the excess mortality in patients who did not have chest pain. These patients were more likely than those with chest pain to have diabetes, to have delayed seeking medical attention at the onset of MI, to present with Killip class III or IV heart failure, and to have non–ST-elevation MI.

Differences in treatment accounted for only a modest amount of the excess mortality in patients who did not have chest pain. These patients were less likely to receive any reperfusion therapies, such as fibrinolysis or percutaneous coronary intervention, and were less likely to receive aspirin, antiplatelet agents, heparin, or beta-blockers during hospitalization. But that was considered a relatively small contributor to their excess mortality.

The reasons for these sex- and age-based differences in symptoms remain unknown. "It is plausible, or even likely, that the pathophysiology or pathobiology of higher mortality observed in younger women also accounts for the apparent differences in MI symptom presentation in this premenopausal or middle-aged group," Dr. Canto and his associates said.