Of the 916 380 patients included in the analysis, approximately 10% of women and 25% of men throughout the study period were younger than 65 years (). For both men and women, the overall risk factor profile worsened over time, with proportionally more patients having a history of diabetes, hypertension, hyperlipidemia, and congestive heart failure, whereas the prevalence of STEMI decreased, as previously reported.19
Irrespective of age, women more often had a history of hypertension than men, whereas men more often had a history of MI or previous revascularization. For other characteristics, however, sex differences were more marked among younger patients. Specifically, women younger than 55 years were more likely than men of similar age to have Medicaid insurance, a history of diabetes, heart failure or stroke, and a higher Killip class on admission; sex differences in these factors were less pronounced among older patients ( and ). Furthermore, for diabetes, hypertension, and Killip class, the sex differences tended to be less pronounced in later years, which suggests that worsening trends for these factors were less marked in women. The sex difference in previous revascularization decreased over time among patients younger than 65 years but not among older patients. In addition, STEMI became less common in women younger than 65 years than in men of similar age in later years, whereas there was no difference in STEMI prevalence among older patients throughout the study period. Time trends in aspirin use in the first 24 hours were similar in women and men, irrespective of age, as they were for β-blockers among older patients. However, in 1994-1995, the use of β-blockers was less among women younger than 65 years than in their male counterparts; this gap decreased progressively in later years.
Distribution of the study sample according to age and study period. A, Men; B, women.
Women were less likely than men to undergo coronary catheterization and revascularization procedures during admission; sex differences in procedure use were more pronounced among older patients. However, no difference was seen over time in the sex-related risk ratios for these procedures. Over time, there was a slight increase in the representation of hospitals of larger size, with larger MI volume, and with capability for invasive cardiac procedures. These changes followed similar trends over time by sex and age.
The length of hospital stay decreased over time more in younger than in older patients but in a similar fashion in women and men within age strata. Between 1994 and 2006, the total hospital time in patients younger than 65 years decreased 37.9% (−2.5 days) in men and 35.1% (−2.6 days) in women. Among patients 65 years or older, it decreased 25.0% (−1.9 days) in men and 25.6% in women (−2.0 days). No significant interaction was seen among sex, age, and year, which suggests that the total days in the hospital decreased in a similar fashion by sex and age.
Between 1994 and 2006, hospital mortality rates decreased more in women than in men in virtually all age groups (). The rate reduction in 2004-2006 relative to the rate in 1994-1995 was particularly pronounced among women younger than 75 years. It was largest in women younger than 55 years (52.9%) and lowest in men younger than 55 years (33.3%). Among patients younger than 55 years, the excess mortality for women was 44.0% larger in 1994-1995 than it was in 2004-2006 (an OR of 1.93 vs an OR of 1.34; ). Even when considered in absolute terms, the decrease in the mortality difference by sex was largest in younger patients, even though older patients had a larger absolute mortality decrease given their higher mortality rates. Among patients younger than 55 years, the absolute rate of decrease was 3 times higher in women (2.7%) than in men (0.9%). Both in absolute () and relative () terms, the sex difference in mortality decrease became lower in older patients (P=.004 for the interaction among sex, age, and year). As a result, the excess mortality in younger women compared with men decreased progressively over time ( and ).
Hospital Mortality Rates in Patients Classified According to Sex, Age, and Admission Year
Unadjusted and Adjusted Female-to-Male Odds Ratios (95% Confidence Intervals) for Hospital Mortality According to Age and Admission Year
Figure 2 Unadjusted and adjusted odds ratios (ORs) for death during hospitalization for myocardial infarction in women compared with men, according to age and study period. The unadjusted ORs (A) were derived from the model that included sex; age (5 groups); study (more ...)
Adjustment for comorbidity and clinical characteristics on admission accounted for a large part of the excess mortality of younger women compared with younger men in the entire period by lowering the female-to-male ORs in the younger age groups in each study year (). It also substantially explained the differential mortality trends over time by bringing the OR for 1994-1995 closer to the OR for 2004-2006 () and making the interaction among sex, age, and year no longer significant (P=.34). Overall, time changes in comorbidity and clinical features explained 93% of the changes in mortality in younger women relative to men, as shown by the decrease in the ORs (1994-1995 vs 2004-2006) from 1.44 to 1.03 (). In contrast, treatment did not explain further the differential mortality trends over time, although it somewhat lowered the mortality difference between women and men in all years ( and ). Further adjustment for hospital characteristics had no impact on the women-to-men estimates (). When the analysis was restricted to only hospitals that participated in the NRMI for the entire study period, results were similar, which suggests that variations in hospital participation in the NRMI had no substantial impact on our results. Finally, when analyses were restricted to patients without a previous history of MI (n=680 995; 74%), the results remained substantially unchanged, which suggests that our results are not driven by better recognition or treatment of previous MI events. In this subgroup, time changes in comorbidity and clinical features explained 91% of the changes in mortality in younger women relative to men.