Sex-Specific Time Trends in Very Elderly Patients (Aged ≧80 Years) Hospitalized with Myocardial Infarction

The world population is rapidly aging. For instance, by 2050 the proportion of very elderly individuals in the United States will represent approximately a two-fold increase from 2010 [1]. This projected change in population age structure has already begun, and it is believed that women may be at more of a disadvantage than men since the magnitude of age-related increases in prevalence of leading medical conditions like coronary heart disease is greater in women [2]. Compounding these issues, the very elderly are relatively understudied with regard to cardiovascular disease, and practice findings suggest that the very old and women generally receive lower-quality cardiovascular care than their younger or male counterparts [2]. Since myocardial infarction (MI) occupies a central role in the assessment of the burden of heart disease, this study aimed to assess nationwide sex-specific trends in the percentage of persons hospitalized with MI who were aged ≥80 years over the last decade.

Data were obtained from the Nationwide Inpatient Sample (NIS), developed as part of the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality (AHRQ). NIS is designed to approximate a stratified 20% sample of all non-Federal, short-term, general and specialty hospitals serving adults in the United States. The sampling strategy selects hospitals within states that have State Inpatient Databases (SID) according to defined strata based on ownership, bed size, teaching status, urban/rural location and region. All discharges from sampled hospitals for the calendar year are then selected for inclusion into NIS. To allow extrapolation for national estimates, both hospital and discharge weights are provided. Detailed information on the design of the NIS is available at http://www.hcup-us.ahrq.gov. From 1997 to 2006, NIS captured discharge level information on primary and secondary diagnoses and procedures, discharge vital status and demographics on several million discharges per year from hospitals in 22 (1997) to 38 (2006) states. Data elements that could directly or indirectly identify individuals were excluded; we thus considered all discharges to be independent. The unit of analysis was the discharge rather than the individual. A unique hospital identifier allows for linkage of discharge data to an NIS data set with hospital characteristics.

To analyze MI hospitalization percentages, we identified all discharges for which an ICD9-CM code of 410.xx (acute myocardial infarction) was listed as the primary diagnosis. This approach has been utilized by other studies and was taken to specifically focus on patients who presented with acute myocardial ischemia and not those patients who had MI secondary to surgery, hypotension or other events after hospitalization [3]. Total number of MI was obtained by summing across codes. The 95% confidence intervals (95% CI) were approximated using Monte Carlo simulation strategy. For patients who had more than one reported code of 410.xx, only the first reported code was used. All patients with a diagnosis of MI were included regardless of whether they were alive or dead at the time of discharge.

The percentage of MI hospitalizations among men and women in the sample were computed over the 10-year study period (1997–2006). Age standardization was subsequently performed using the 2000 standard US population. Race was not adjusted for given the large amount of missing data on this variable (25%). We tested for significant trends in hospitalization percentage over years using linear logistic regression. To test for curvilinear trends, we included year as a continuous variable together with the quadratic term to the regression models. The p values for assessing sex differences in hospitalizations across the 10-year study period were computed using contrasts (Z-tests) under the regression model. All data analyses were conducted using SAS (version 9.1; SAS Institute Inc, Cary, N.C., USA). Statistical hypotheses were tested with p < 0.05 as the level of statistical significance.

The descriptive summary statistics are given in table 1. For simplicity, these descriptive tables only show the results for the years 1997 and 2006. These results are generally comparable across variables, but it can be noted that over the decade the median age went up by 1 year from 84 to 85 years, and there was an almost 6% point drop in those persons categorized as being of White race.

Overall, the absolute number of MI hospitalizations generally decreased from 732,170 to 674,988, but the percentage of the MI hospitalizations in the very elderly rose over the study period (table 2). The corresponding plot of percentage MI hospitalizations by year in the very elderly is shown in figure 1. The proportion increased significantly in a roughly linear fashion in both sexes across the decade. The proportion of very elderly men rose from 14.2% in 1997 to 17.05% in 2006, a 2.84% increase (linear trend: p < 0.01). The proportion of very elderly women also increased from 31.01% in 1997 to 35.95% in 2006, representing a 4.95% boost in frequency (linear trend: p < 0.001). The percent change across the decade was significantly greater in females than in males overall (ratio = 1.74, approximate 95% CI 1.26–2.23, p = 0.03).

Overall, this analysis found that across the last decade there was a modest yet significant increase in the proportion of hospitalized patients aged 80 years and above, in the United States. Of note, the increase in the proportion of very elderly women among the patients hospitalized with MI was about twice as large as that of very elderly men hospitalized with MI. At first glance, the approximately 3% rise for very elderly men and 5% rise for very elderly women over the 10-year period, although statistically significant, may not seem impressive. However, when put in the context of what appears to be diminishing absolute numbers of MI hospitalization in the overall population, established disparities in cardiovascular care unfavorable to women [4], the relentless aging of the US population [5], known poorer clinical outcomes after MI in the very elderly [2] and a recognized underutilization of proven vascular risk reduction treatments in the very-elderly age group [6], the findings could be of growing public health importance.

It is unlikely that these findings are due to better recognition of cardiovascular symptoms and risk factors by patients, or better detection of cardiovascular disease by providers [7] since conceivably any boost in recognition or diagnosis would also have applied to other patients, and yet, as noted, overall MI hospitalization numbers decreased. A more likely explanation would be that with superior medicines and their more timely and widespread use [8], relatively younger patients are now much older when they experience their first or recurrent MI, thereby postponing MI hospitalization well into their golden years [9]. Similarly, the comparatively greater longevity and delayed incidence of first MI in women versus men [5] may be contributing to the steeper rise in the proportion of the former hospitalized with MI. It is also possible that the undertreatment of cardiovascular risk factors observed among relatively younger women compared to men might also play a role in this disparate increase [4].

These findings underscore the need for healthcare providers and policy makers to prepare for a continued and probable exponential rise in the proportion MI hospitalization among the very elderly and women in years to come, and to identify ways to optimize clinical outcomes in these relatively underinvestigated and undertreated demographic groups [6]. Intensification of efforts at screening for and treating vascular risk factors may be warranted [6]. Furthermore, researchers and research-funding agencies may also need to boost research in this population to ensure that treatments being instituted actually carry a favorable risk-benefit ratio and that the more aggressive proven treatments applied to younger patients are not simply being blindly extended to this age group with uncertain or dire consequences.

This study has limitations. Initial MI hospitalizations could not be distinguished from recurrent ones, and although we included all MI-pertinent diagnostic codes, MI diagnoses were not validated using standardized criteria. Also, these data are not necessarily applicable to other countries, especially since regional variability in MI characteristics are known to occur [10]. The study was strengthened by hospital-based MI diagnoses and nationwide scope, and unlike many community-based studies was not limited by upper age limits, or inclusion of persons of only one race or sex.

From 1997 to 2006, the proportion of individuals hospitalized with MI in the United States who were very elderly women, rose at almost twice the rate of similarly aged men. These trends are probably similar in many developed nations and will likely exacerbate in years to come given the aging global population, necessitating enhanced efforts in vascular risk factor management among the very elderly, especially women.

B.O. received support from the University of California, Los Angeles, Resource Centers for Minority Aging Research Center for Health Improvement of Minority Elderly (RCMAR/CHIME) under NIH/NIA Grant P30-AG021684.