Rates of acute myocardial infarction (AMI) hospitalizations for elderly Medicare patients decreased during the previous decade. However, trends in population rates of AMI hospitalizations for all adults by subgroups have not been described. Using data from a large all-payer administrative database of hospitalizations, we calculated annual AMI hospitalization rates from 2001 through 2007. Trend analysis was performed across age, gender, and ethnicity categories using survey regression. Overall rate decreased from 314 to 222 AMI hospitalizations per 100,000 patients from 2001 through 2007, representing a 29.2% decrease. Significant decreases were observed in AMI hospitalization rate for each group by age categories (p <0.001) and by gender (p <0.001). When stratified by ethnicity and gender, age-adjusted AMI hospitalization rates in white men and women decreased by 30.8% and 31.4%, whereas black men and women had significantly slower rates of decrease of 13.6% and 12.6%, respectively. In conclusion, although the overall rate of AMI hospitalizations decreased from 2001 through 2007, the observed decrease was smaller for black patients compared to white patients across all age groups studied.
Recent studies have reported substantial decreases in acute myocardial infarction (AMI) hospitalization rates in older Medicare fee-for-service patients and in studies with data collected within a single state. Despite the impact of AMI on the inpatient health care system, it is not known whether recent trends in the Medicare fee-for-service population are generalizable to younger patients and other subgroups. Although previous work has demonstrated there may be ethnicity- and gender-based disparities in early mortality for MI, it is not known whether these differences are present in AMI hospitalization trends in younger populations. Characterizing differences in AMI hospitalization rates in a larger group of patients stratified by age, gender, and ethnicity may highlight areas of relative progress and help guide decisions on optimal allocation of resources in prevention strategies. AMI hospitalization trends from a large national database may also provide hypothesis-generating insights on the benefits of recent improvements in primary and secondary prevention in cardiovascular disease. The National Inpatient Sample (NIS) from the Healthcare Cost and Utilization Project (HCUP) is an all-payer administrative database of hospitalization. The HCUP includes information from Medicare, Medicaid, active and retired military insurance, private insurers, and the uninsured, which provides a more representative sample of patients. The NIS includes 41 states, which accounts for approximately 94% of the United States population. For this study, we examined recent AMI hospitalization rates from 2001 through 2007 in using an all-payer database and compared AMI trends among age, gender, and ethnicity subgroups.
Methods
The NIS from the HCUP is a longitudinal hospital inpatient database containing all discharge data from >1,000 hospitals in 41 states, approximating a 20% stratified sample of United States community hospitals. The NIS captures incident and recurrent AMI hospitalizations. Data include discharge-level data files with trend weights and data elements consistently defined across data years ( http://www.hcup-us.ahrq.gov/db/nation/nis/nistrends.jsp ). Using NIS data in the HCUP from 2001 through 2007, we selected the following fields for analysis: age, gender, ethnicity, discharge status, length of stay, in-hospital death, principal diagnosis codes to identify AMI hospitalization, state of hospitalization, and universal discharge weights that can be used to estimate the total number of events or admissions of the hospital. A hospitalization was classified as an AMI hospitalization if the primary discharge diagnosis was 410.xx, excluding 410.x2, based on the International Classification of Diseases, Ninth Revision, Clinical Modification . We included only primary discharge diagnoses of AMI because nonprimary diagnoses may not reflect an acute process or does not reflect the reason for admission.
The 2000 Census data with annual intercensal survey adjustments were used to calculate each subgroup population of subjects at risk for AMI to calculate population-based overall and AMI rates ( http://www.census.gov/popest/states/ ). Corresponding numbers of patients were calculated for subgroups stratified by state, age groups, gender, and ethnicity in separate years from these data.
All discharges from hospitals in the HCUP-NIS from 2001 through 2007 were initially included (n = 55,402,296). We then excluded discharges with missing data on patient age, gender, length of stay, and in-hospital death (n = 194,331, 0.4%); discharges in which patients were <18 years old (n = 9,735,028, 17.3%); discharges in which patients were discharged alive and on the same day of the admission because they were unlikely to have acute disease (n = 832,472, 1.8%); and discharges in which patients were transferred in from another hospital (n = 155,008, 3.5%), leaving a cohort of 43,272,788 discharges. To examine the trend stratifying by ethnicity in white and black patients, we limited to the 21 states that reported ethnicity data during each year in the study and excluded discharges in which the patients’ ethnicity was neither white nor black, which resulted in a study cohort of 22,713,429 discharges.
AMI hospitalization rate was expressed as number of AMI hospitalizations divided by number of corresponding census-based patients within a given group. First we examined the distribution of AMI patients’ characteristics related to age (<45, 45 to <55, 55 to <65, 65 to <75, and ≥75 years old), gender (men and women), and ethnicity (white and black). Second, we examined AMI hospitalization rates stratified by subgroups of age, gender, and ethnicity. We also calculated overall hospitalization rates stratified by subgroups of age, gender, and ethnicity to provide a comparison for trends observed in AMI hospitalizations. Third, we calculated age-adjusted AMI hospitalization rates in subgroups determined by a combination of gender and ethnicity. Linear trend of adjusted rates over different year was calculated using Poisson regression analyses. All rates were calculated per 100,000 patients based on population information from the census summary data. All statistical analyses of hospitalization rates were conducted with SAS 9.2 (SAS Institute, Cary, North Carolina).
Results
There were 2,179,509 AMI hospitalizations from 2001 through 2007 in the study sample. Overall rate decreased from 314 AMI hospitalizations per 100,000 patients to 222 AMI hospitalizations per 100,000 patients, representing a 29.2% decrease. The decrease in AMI hospitalizations occurred in the setting of a 5.2% decrease in the population-based rate of hospitalizations in the same dataset. There was a significant decrease (with relative decreases in percentages) over the study period in AMI hospitalization rate for each group by age category: <45 years of age (24.6%), 45 to <55 years of age (26.7%), 55 to <65 years of age (34.0%), 65 to <75 years of age (34.8%), and ≥75 years (32.4%, p <0.001 for each age category; Table 1 ). Similarly, significant decreases were seen across gender and ethnicity (p <0.001; Table 1 ).
| Description | Year | p Value for Trend | Absolute Change | Relative Change | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | ||||
| All | 314 | 285 | 268 | 248 | 245 | 229 | 222 | <0.0001 | 92 | 29.2 |
| Age categories (years) | ||||||||||
| <45 | 30 | 27 | 27 | 22 | 24 | 23 | 23 | <0.0001 | 7 | 24.6 |
| 45–<55 | 219 | 191 | 191 | 164 | 165 | 166 | 160 | <0.0001 | 59 | 26.7 |
| 55–<65 | 465 | 416 | 392 | 337 | 337 | 319 | 307 | <0.0001 | 158 | 34.0 |
| 65–<75 | 812 | 734 | 662 | 623 | 578 | 539 | 530 | <0.0001 | 282 | 34.8 |
| ≥75 | 1,598 | 1,461 | 1,337 | 1,298 | 1,269 | 1,140 | 1,080 | <0.0001 | 518 | 32.4 |
| Gender | ||||||||||
| Men | 375 | 338 | 317 | 292 | 289 | 273 | 265 | <0.0001 | 109 | 29.2 |
| Women | 257 | 236 | 221 | 207 | 202 | 187 | 181 | <0.0001 | 76 | 29.5 |
| Ethnicity | ||||||||||
| White | 326 | 292 | 273 | 252 | 254 | 234 | 226 | <0.0001 | 100 | 30.8 |
| Black | 231 | 240 | 232 | 219 | 179 | 194 | 199 | <0.0001 | 32 | 13.7 |
Absolute decreases in AMI hospitalization rate were greater in older patients compared to younger patients. For example, the absolute change was 518 AMI hospitalizations per 100,000 patients for patients >75 years old compared to 7 AMI hospitalizations per 100,000 patients for patients <45 years old. Rates in men and women decreased 109 and 76 AMI hospitalizations per 100,000 patients and there was a significant higher percent decrease in men compared to women (p <0.01). In addition, white adults had a greater absolute decrease compared to black adults (100 vs 32 AMI hospitalizations per 100,000 patients); however, linear decrease trends were not significant between white and black patients (p = 0.2).
Relative decreases in AMI hospitalization rates in white and in black patients were 30.8% and 13.7%, respectively. Although the overall decrease in AMI hospitalization rates in black patients was significant from 2001 through 2007, there was an upward trend from 2001 through 2002 and from 2005 through 2007.
Table 2 lists AMI hospitalization rates stratified by gender and ethnicity in different age groups for patients from a subgroup of states reporting ethnicity data in all years from 2001 through 2007. In the <45-year-old group, only white men demonstrated a significant decrease in AMI hospitalization rates. White women had minimally lower rates, whereas black men and women showed a slight increase, although these changes did not reach significance. In all other age groups, every category by ethnicity and gender showed a significant decrease in AMI hospitalization rates (p <0.01).
| Description | Year | Overall p Value | Absolute Change | Relative Change | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | ||||
| All | 314 | 285 | 268 | 248 | 245 | 229 | 222 | <0.0001 | 29.2 | 92 |
| Age <45 years | ||||||||||
| White men | 45 | 38 | 38 | 30 | 34 | 31 | 30 | <0.0001 | 32.2 | 14 |
| White women | 13 | 12 | 12 | 11 | 10 | 11 | 10 | 0.0080 | 22.7 | 3 |
| Black men | 45 | 47 | 45 | 40 | 38 | 43 | 45 | 0.5894 | −0.7 | 0 |
| Black women | 25 | 28 | 26 | 24 | 23 | 21 | 25 | 0.2192 | −0.4 | 0 |
| Age 45–<55 years | ||||||||||
| White men | 334 | 283 | 282 | 245 | 248 | 248 | 234 | <0.0001 | 30.2 | 101 |
| White women | 100 | 84 | 86 | 71 | 78 | 74 | 75 | <0.0001 | 25.4 | 25 |
| Black men | 304 | 332 | 324 | 276 | 240 | 253 | 266 | <0.0001 | 12.7 | 39 |
| Black women | 185 | 186 | 177 | 163 | 133 | 153 | 155 | 0.0013 | 16.3 | 30 |
| Age 55–<65 years | ||||||||||
| White men | 675 | 589 | 554 | 481 | 489 | 460 | 427 | <0.0001 | 36.8 | 248 |
| White women | 260 | 227 | 224 | 187 | 190 | 174 | 173 | <0.0001 | 33.5 | 87 |
| Black men | 642 | 680 | 589 | 505 | 420 | 447 | 507 | <0.0001 | 21.0 | 135 |
| Black women | 386 | 412 | 350 | 319 | 310 | 303 | 299 | <0.0001 | 22.6 | 87 |
| Age 65–<75 years | ||||||||||
| White men | 1,092 | 968 | 862 | 805 | 771 | 713 | 701 | <0.0001 | 35.8 | 391 |
| White women | 575 | 519 | 465 | 441 | 416 | 373 | 365 | <0.0001 | 36.6 | 210 |
| Black men | 961 | 904 | 898 | 905 | 695 | 668 | 709 | <0.0001 | 26.2 | 252 |
| Black women | 711 | 753 | 722 | 643 | 472 | 578 | 543 | <0.0001 | 23.6 | 167 |
| Age ≥75 years | ||||||||||
| White men | 1,954 | 1,767 | 1,575 | 1,550 | 1,526 | 1,350 | 1,295 | <0.0001 | 33.7 | 659 |
| White women | 1,421 | 1,298 | 1,193 | 1,136 | 1,149 | 1,017 | 954 | <0.0001 | 32.9 | 468 |
| Black men | 1,419 | 1,383 | 1,422 | 1,390 | 1,014 | 1,089 | 1,011 | <0.0001 | 28.8 | 408 |
| Black women | 1,259 | 1,252 | 1,273 | 1,331 | 956 | 1,069 | 1,021 | 0.0048 | 18.9 | 237 |
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