Younger women hospitalized with an acute myocardial infarction (MI) have a poorer prognosis than men. Whether this is true for patients with acute ST-segment elevation MI (STEMI) and non-STEMI (NSTEMI) is not extensively studied. Using the MarketScan 2004 to 2007 Commercial and Medicare supplemental admission databases, we assessed gender differences in in-hospital mortality according to age in 91,088 patients (35,899 with STEMI, 55,189 with NSTEMI) who were 18 to 89 years old and had acute MI as their primary diagnosis. Patients with STEMI had significantly higher in-hospital mortality than those with NSTEMI (4.35% vs 3.53%, p <0.0001). Compared to men women were older, had higher co-morbidity scores, and were less likely to undergo revascularization during hospitalization in the STEMI and NSTEMI populations. In patients with STEMI the unadjusted women-to-men odds ratio for in-hospital mortality was 2.29 (95% confidence interval 1.48 to 3.55) for the 18- to 49-year age group, 1.68 (1.28 to 2.21) for 50 to 59, 1.48 (1.17 to 1.88) for 60 to 69, 1.28 (1.06 to 1.57) for 70 to 79, and 1.01 (0.83 to 1.23) for 80 to 89. Corresponding unadjusted odds ratios were 1.51 (0.87 to 2.61), 1.46 (1.11 to 1.92), 1.29 (1.04 to 1.61), 0.83 (0.70 to 0.99) and 0.82 (0.70 to 0.94) for patients with NSTEMI. After adjustment for potential confounding factors, excess risk for in-hospital mortality in younger women versus their men counterparts (<60 years old) persisted in STEMI. In patients with NSTEMI the difference between younger women and younger men was not statistically significant; however, older women (≥70 years old) had better survival than men. In conclusion, higher risk of in-hospital mortality in younger women compared to younger men is more evident in patients with STEMI.
During the previous 2 decades studies have consistently shown that younger women hospitalized with an acute myocardial infarction (AMI) have a poorer prognosis than their men peers, whereas older women (≥70 or ≥75 years old) have similar or better outcomes compared to older men. Previous studies examining the gender difference on mortality after AMI have included acute ST-segment elevation MI (STEMI) and acute non-STEMI (NSTEMI), events that differ in pathophysiology, clinical presentation, initial management, and prognosis. Gender differences in in-hospital mortality appear to differ for these 2 types of AMI. Studies have shown that in STEMI in-hospital mortality is higher for women than for men, but in NSTEMI women seem to have similar or even better outcomes than men. Researchers, however, have yet to determine whether there are age-specific gender-based differences in in-hospital mortality in STEMI and NSTEMI as have been found in the overall AMI population. Accordingly, we used the Thomson Reuters MarketScan 2004 to 2007 Commercial and Medicare supplemental inpatient admission databases (Thomson Reuters, Ann Arbor, Michigan) to examine gender differences for in-hospital mortality across age groups by type of AMI after adjustment for sociodemographic and clinical characteristics.
Methods
The MarketScan 2004 to 2007 inpatient admission databases included information from approximately 40 privately insured employers including state governments. Databases included >2.4 billion service records representing commercially insured employees, retirees, and dependents from >100 geographically diverse health insurance plans in all 50 United States and the District of Columbia. These databases contain patient demographics, dates of service, length of hospital stay, primary and up to 14 secondary hospital discharge codes, primary and up to 14 secondary procedure codes, and other variables. The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) was used for hospital discharge codes. ICD-9-CM and Current Procedure Terminology-4 (CPT-4) codes were used for procedure codes.
From 2004 through 2007, 91,609 patients (101,031 hospitalizations) 18 to 89 years old who had an AMI as their primary diagnosis were included in the inpatient admission databases. If a patient had >1 hospitalization for AMI from 2004 through 2007, the first hospitalization was included in the analysis. We excluded 521 patients who had a hospital length of stay >30 days. Thus, 91,088 patients (35,899 with STEMI, 55,189 with NSTEMI) who had AMI as a primary diagnosis were included in this analysis.
STEMI was identified using ICD-9-CM codes 410.01, 410.11, 410.21, 410.31, 410.41, 410.51, 410.61, and 410.81 and NSTEMI was identified by 410.71. This method has been used to identify STEMI and NSTEMI in other studies. Using ICD-9-CM codes for the secondary diagnoses we identified co-morbidities of heart failure (402.01, 402.11, 402.91, 404.01, 404.03, 404.11, 404.13, 404.91, 404.93, and 428.xx), hypertension (401 to 405), diabetes (250), hyperlipidemia (272), kidney disease (403 to 404, 582 to 583, 585 to 587), and cancer (140 to 280) and complications of cardiac shock (785.51), stroke (430 to 438), ventricular tachycardia (427.1), ventricular fibrillation (427.41 or 427.42), atrial tachycardia (427.0), and atrial fibrillation (427.31 or 427.32). CPT-4 codes 92980 to 92982, 92984, and 92995 to 92996 and ICD-9-CM codes 00.66 and 36.01 to 36.09 were used to identify patients who underwent percutaneous coronary intervention, and CPT-4 codes 33510 to 33519, 33521 to 33523, and 33533 to 33536 and ICD-9-CM codes 36.10 to 36.19 were used to identify patients who underwent coronary artery bypass grafting surgery.
We used zip codes and the 2000 United States Census to classify economic status. Income for a zip code was characterized as low, middle, or high using tertiles of household income level derived from the census; patients living in that zip code were classified accordingly. Insurance status was categorized as capitated plan (health maintenance organization and point of service with capitation) or noncapitated plan (basic or major medical, comprehensive, exclusive provider organization, point of service without capitation, preferred provider organization, and consumer-driven health plan). Hospitals were classified as urban if they were included in a metropolitan statistical area and rural if they were not. The Charlson co-morbidity index, which measures the likelihood of death or serious disability in the subsequent year and was derived from up to 18 co-morbidities, was included in the multivariable regression analysis as a measurement of co-morbidity burden. This index has been used as an adjusting variable in AMI population.
Categorical data were reported as frequency and percentage and compared by chi-square test. Continuous variables were expressed as mean ± SD and compared using unpaired t test. Breslow-Day test was used to assess whether there was an interaction between age group (in years, 18 to 49, 50 to 59, 60 to 69, 70 to 79, and 80 to 89) and gender for all characteristics and in-hospital mortality. All comparisons were presented in terms of odds ratios in women compared to that in men in addition to 95% confidence intervals. We used a series of multivariate regression models to determine the gender difference in in-hospital mortality according to age in the 2 populations. The significance of interaction between gender and age groups was assessed using the Wald test and type III analysis. The first model, which included gender as a sole variable, was used to calculate the unadjusted odds ratio for women (vs men) for in-hospital mortality and its 95% confidence interval. The second model added age, and the interaction term between gender and age was added in the third model. The fourth model adjusted for other demographic factors (insurance status, region, economic status, and urban/rural), disease severity (Charlson co-morbidity index), and 3 dummy variables for year of discharge (2005, 2006, and 2007, with 2004 used as the reference category). All tests of statistical significance were 2-tailed and a p value <0.05 was considered statistically significant. All statistical analyses were performed using SAS 9.1.3 (SAS Institute, Cary, North Carolina).
Results
Of the 91,088 patients, 60,065 (65.9%) were men and 31,023 (34.1%) were women. There were 28.9% women in the STEMI group and 37.4% women in the NSTEMI group (p <0.0001). As can be calculated from Table 1 , STEMI accounted for a smaller percentage of AMI in women than in men (33.5% vs 42.5%, p <0.0001). Mean age was older in patients with NSTEMI than in those with STEMI (66.1 vs 61.2 years, p <0.0001).
| Variable | STEMI | NSTEMI | ||||
|---|---|---|---|---|---|---|
| Overall (n = 35,899) | Women (n = 10,387) | Men (n = 25,512) | Overall (n = 55,189) | Women (n = 20,636) | Men (n = 34,553) | |
| Age (years), mean ± SD | 61.2 ± 12.2 | 65.5 ± 13.3 | 59.5 ± 11.8 † | 66.1 ± 13.1 | 69.0 ± 13.3 | 64.4 ± 13.0 † |
| Charlson co-morbidity index | 1.76 ± 1.3 | 1.93 ± 1.4 | 1.69 ± 1.2 † | 2.13 ± 1.5 | 2.22 ± 1.5 | 2.07 ± 1.5 † |
| Urban | 89.6% | 89.6% | 89.6% | 89.1% | 89.3% | 89.0% |
| Region | ||||||
| Northeast | 7.5% | 7.5% | 7.5% | 8.3% | 8.1% | 8.4% |
| Central north | 33.2% | 34.8% | 32.6% | 37.1% | 38.9% | 36.0% |
| South | 40.3% | 37.6% | 41.5% | 36.5% | 33.9% | 38.1% |
| West | 19.0% | 20.1% | 18.5% | 18.1% | 19.0% | 17.5% |
| Capitated insurance ⁎ | 17.6% | 19.2% | 17.0% † | 18.8% | 19.2% | 18.5% |
| Economic status | ||||||
| Low | 34.3% | 33.7% | 34.6% | 32.8% | 32.5% | 32.9% |
| Middle | 33.8% | 34.5% | 33.4% | 33.3% | 32.9% | 33.5% |
| High | 31.9% | 31.8% | 32.0% | 34.0% | 34.7% | 33.6% |
| Year | ||||||
| 2004 | 21.2% | 21.7% | 21.0% † | 20.5% | 20.5% | 20.5% † |
| 2005 | 27.0% | 30.0% | 25.8% | 27.7% | 29.0% | 27.0% |
| 2006 | 21.5% | 21.3% | 21.6% | 21.5% | 21.2% | 21.6% |
| 2007 | 30.3% | 27.2% | 31.6% | 30.2% | 29.3% | 30.8% |
⁎ Capitated insurance includes health maintenance organization and point of service with capitation; noncapitated insurance includes basic/major medical, comprehensive, exclusive provider organization, point of service, preferred provider organization, and consumer-driven health plan.
Women were older than men at admission in the STEMI group (mean age 65.5 ± 13.3 vs 59.5 ± 11.8 years, p <0.0001) and NSTEMI group (69.0 ± 13.3 vs 64.4 ± 13.0 years, p <0.0001). Sixty-four percent of women with STEMI but only 46% of their men counterparts were ≥60 years old; the corresponding percentages by gender (for ≥60 years of age) in the NSTEMI group were 73% versus 62% (p <0.0001 for the 2 comparisons; Table 2 ).
| Age Group (years) | STEMI | NSTEMI | ||||
|---|---|---|---|---|---|---|
| Overall (n = 35,899) | Women (n = 10,387) | Men (n = 25,512) | Overall (n = 55,189) | Women (n = 20,636) | Men (n = 34,553) | |
| 18–49 | 6,262 (17.4%) | 1,333 (12.8%) | 4,929 (19.3%) | 6,082 (11.0%) | 1,770 (8.6%) | 4,312 (12.5%) |
| 50–59 | 11,380 (31.7%) | 2,452 (23.6%) | 8,928 (35.0%) | 12,656 (22.9%) | 3,700 (17.9%) | 8,956 (25.9%) |
| 60–69 | 8,753 (24.4%) | 2,271 (21.9%) | 6,482 (25.4%) | 12,867 (23.3%) | 4,295 (20.8%) | 8,572 (24.8%) |
| 70–79 | 5,710 (15.9%) | 2,325 (22.4%) | 3,385 (13.3%) | 12,317 (22.3%) | 5,128 (24.8%) | 7,189 (20.8%) |
| 80–89 | 3,794 (10.6%) | 2,006 (19.3%) | 1,788 (7.0%) | 11,267 (20.4%) | 5,743 (27.8%) | 5,524 (16.0%) |
Women were more likely than men to have heart failure but less likely to have hyperlipidemia ( Supplemental Tables 1 and 2 ) and they had significantly higher co-morbidity scores in the 2 populations ( Table 1 ). Younger women were more likely than younger men to have diabetes, obesity, heart failure, cancer, stroke, and other co-morbidities but less likely to have hyperlipidemia ( Supplemental Tables 1 and 2 ). Differences by gender for co-morbidities generally decreased with increasing age, with women 80 to 89 years old less likely than men to have cancer and kidney disease.
Women were less likely to undergo revascularization (percutaneous coronary intervention or coronary artery bypass grafting surgery) than men during hospitalization in the 2 populations (p <0.0001 for all comparisons). The younger the age of the patients, the greater the gender difference for percutaneous coronary intervention. In contrast, the older the age of the patients, the greater the gender difference for coronary artery bypass grafting surgery ( Table 3 ).
| Variable | Women | Men | Age Group (years), OR (95% CI) | Overall OR (age adjusted) | ||||
|---|---|---|---|---|---|---|---|---|
| 18–49 | 50–59 | 60–69 | 70–79 | 80–89 | ||||
| ST-segment elevation myocardial infarction | ||||||||
| Patients | 10,387 | 25,512 | 1,333/4,929 | 2,452/8,928 | 2,271/6,482 | 2,325/3,385 | 2,006/1,788 | 10,387/25,512 |
| Percutaneous coronary intervention | 64.9% | 75.0% | 0.67 (0.58–0.78) | 0.70 (0.63–0.77) | 0.83 (0.75–0.93) | 0.84 (0.75–0.93) | 0.87 (0.76–0.98) | 0.78 (0.74–0.83) |
| Coronary artery bypass grafting | 7.1% | 10.6% | 0.83 (0.65–1.07) | 0.81 (0.69–0.96) | 0.59 (0.50–0.69) | 0.63 (0.53–0.74) | 0.37 (0.27–0.51) | 0.66 (0.60–0.73) |
| Ventricular tachycardia | 4.4% | 7.1% | 0.73 (0.56–0.95) | 0.70 (0.58–0.85) | 0.67 (0.53–0.83) | 0.55 (0.43–0.70) | 0.57 (0.40–0.81) | 0.65 (0.58–0.72) |
| Atrial tachycardia | 0.7% | 0.6% | 0.44 (0.13–1.47) | 1.53 (0.94–2.49) | 1.02 (0.56–1.89) | 1.55 (0.78–3.06) | 0.97 (0.43–2.21) | 1.17 (0.87–1.59) |
| Ventricular fibrillation | 3.2% | 4.4% | 1.22 (0.92–1.60) | 0.79 (0.63–0.99) | 0.79 (0.61–1.03) | 0.59 (0.43–0.81) | 0.44 (0.29–0.67) | 0.78 (0.68–0.91) |
| Atrial fibrillation | 8.1% | 6.8% | 0.95 (0.65–1.40) | 0.70 (0.55–0.89) | 0.74 (0.61–0.90) | 0.95 (0.81–1.12) | 1.02 (0.86–1.22) | 0.88 (0.79–0.97) |
| Cardiogenic shock | 6.1% | 4.6% | 1.30 (0.95–1.78) | 1.20 (0.97–1.49) | 1.19 (0.96–1.46) | 1.20 (0.97–1.48) | 1.10 (0.86–1.41) | 1.19 (1.07–1.33) |
| Non–ST-segment elevation myocardial infarction | ||||||||
| Patients | 20,636 | 34,553 | 1,770/4,312 | 3,700/8,956 | 4,295/8,572 | 5,128/7,189 | 5,743/5,524 | 20,636/34,553 |
| Percutaneous coronary intervention | 33.0% | 44.9% | 0.55 (0.50–0.62) | 0.61 (0.56–0.66) | 0.72 (0.67–0.78) | 0.82 (0.76–0.89) | 0.82 (0.75–0.90) | 0.71 (0.68–0.74) |
| Coronary artery bypass grafting | 7.4% | 13.2% | 0.63 (0.52–0.77) | 0.55 (0.49–0.62) | 0.60 (0.53–0.67) | 0.62 (0.55–0.70) | 0.51 (0.42–0.61) | 0.54 (0.51–0.58) |
| Ventricular tachycardia | 2.1% | 4.2% | 0.92 (0.68–1.26) | 0.51 (0.40–0.66) | 0.50 (0.40–0.62) | 0.46 (0.37–0.57) | 0.37 (0.29–0.48) | 0.50 (0.44–0.56) |
| Atrial tachycardia | 1.1% | 0.8% | 1.09 (0.57–2.11) | 1.56 (1.04–2.36) | 1.14 (0.79–1.66) | 1.38 (0.96–1.98) | 1.24 (0.86–1.79) | 1.29 (1.07–1.56) |
| Ventricular fibrillation | 0.7% | 1.3% | 0.76 (0.44–1.32) | 0.59 (0.40–0.86) | 0.59 (0.40–0.86) | 0.54 (0.37–0.80) | 0.44 (0.26–0.73) | 0.57 (0.47–0.69) |
| Atrial fibrillation | 11.5% | 10.5% | 0.68 (0.45–1.03) | 0.84 (0.70–1.00) | 0.75 (0.66–0.86) | 0.93 (0.85–1.03) | 0.98 (0.89–1.07) | 0.90 (0.84–0.96) |
| Cardiogenic shock | 1.4% | 1.6% | 1.26 (0.70–2.26) | 0.88 (0.62–1.24) | 0.90 (0.66–1.21) | 0.85 (0.65–1.12) | 0.75 (0.56–1.01) | 0.86 (0.74–1.00) |
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