Our study reveals a marked reduction in hospital-level 30-day RSMRs in the United States from 1995 through 2006. In this period, the average hospital-specific 30-day RSMR decreased approximately 3%, a nearly one-sixth relative reduction in short-term mortality. Moreover, we observed a reduction in crude mortality that occurred during a period in which the AMI population had an increase in age and comorbid conditions. Among Medicare beneficiaries, for every 33 patients admitted in 2006 compared with 1995, there was 1 additional patient alive at 30 days. Moreover, the variability of hospitals’ 30-day mortality rates was reduced. Moreover, the variability of hospitals’ 30-day mortality rates was reduced, while the overall change in 30-day mortality for non-AMI admissions did not change substantially.
The reduction in hospital-level heterogeneity in 30-day mortality is consistent with the hypothesis that quality improvement efforts contributed to this reduction. In the mid 1990s there were 39 hospitals at the high end of the mortality distribution, with RSMRs exceeding 24% (99th percentile) in the poorest-performing hospitals. By 2006 there was no hospital in this group, and the worst 1% of hospitals had a 30-day RSMR of 19.5%. The change resulted from a shift in the entire spectrum of performance among hospitals and a decrease in the variation in performance.
In 1997, Braunwald13
described 2 distinct eras of innovation that reduced mortality for patients with AMI. The first era, beginning in the 1960s, was initiated by the introduction of cardiac care units and defibrillation. The second era, starting in the 1980s, began with the publication of studies revealing that interventional and pharmacological strategies could markedly reduce the risk of AMI.
In 1992, Jencks and Wilensky9
heralded a new era of quality improvement within the Health Care Financing Administration in which efforts to improve care for Medicare beneficiaries shifted from a focus on individual errors to the strong support of efforts to improve mainstream care by monitoring performance and instituting systems to elevate practice, with particular emphasis on initiatives targeting high-impact conditions such as AMI. This most recent era of change also reveals a marked improvement in outcomes and a decrease in variation across the spectrum of institutions. Mortality rates following AMI have concurrently decreased, coinciding with major efforts to improve the quality of AMI care. Such improvement efforts have identified gaps in treatment and are aimed at better realizing the benefits of medical advances by delivering the appropriate treatments to eligible patients.
Our findings are consistent with some other, more limited reports of trends in outcomes of patients with AMI, although their focus is on patient outcomes and none includes a hospital-level analysis. Masoudi et al,14
based on data from 4 states, reported that compared with results in 1992-1993, pa-tients in 2000-2001 had a 13% lower adjusted risk of 1-year mortality. Rosamond et al,15
using data from the Atherosclerosis Risk in Communities study, reported that from 1987 through 1994, the 4 communities in the study experienced an annual reduction in mortality of approximately 5%. Investigators studying Worcester, Massachusetts, reported a decrease in in-hospital mortality from 1975-1995.16
Industry-sponsored registries also have noted reductions in mortality rates, although they reflect on the sites that enrolled and the cases that they provided6,10,11
and as such are not necessarily representative of practices at all institutions. However, to our knowledge, our report is the first to provide a national perspective on hospital performance over this recent period.
A limitation of this study is that it cannot prove what caused the observed changes. Through statistical adjustment, we can reduce the possibility that changes in the patient population accounted for the change. The shift in performance and the narrowing of variability is consistent with a role for quality, but other factors may have contributed. Moreover, much of the quality efforts focused on process measures and not on overall short-term outcomes, though many such improvements would be expected to affect 30-day mortality. For example, in 1992-1993, only about 60% of Medicare beneficiaries with AMI received aspirin within 2 days of admission,17
whereas the rate now exceeds 90%. In addition, the period was associated with notable technological advances, including the introduction of new medications and a marked increase in the use of procedures.
The changing definition of AMI also could have influenced the pattern of hospital mortality. Troponin testing came into widespread use at the end of the 1990s. Most studies suggest that the introduction of troponin assays has increased the number of cases qualifying for this diagnosis and that the added cases have a relatively higher risk of adverse outcomes. An analysis of a Medicare cohort indicated that older persons with AMI diagnosed using only troponin assay have a similar or slightly higher risk for short-term mortality compared with those diagnosed using creatine kinase assay.18
That study is consistent with our finding of increased mortality rates around the time that troponin tests were introduced, which was followed again by gradual decreases. An Atherosclerosis Risk in Communities (ARIC) study, based on medical chart review of AMI cases between 1987 and 2002, found that severity decreased over time, but the severity measures in that study, such as shock during the admission, could have been influenced by quality of care.19
Roger et al20
found that the new AMI criteria, when applied in chart review to patients presenting with an elevated troponin level, would increase the number of AMIs and reduce risk, but interestingly, physicians considered only half of the patients who met only the troponin criterion to have had an AMI, perhaps resulting in higher risk among those coded as having an AMI. The application of clinical judgment to the diagnosis may account for the absence of an increase in hospitalization rates after the new definition was introduced.
During the study period, the enrollment in Medicare managed care varied within hospitals and regions. The effect of this variation is difficult to gauge. Our focus on patients admitted with AMI, controlling for age and comorbidity, likely mitigates bias introduced by variation in managed care populations and differences in the baseline health of these populations.
Another limitation is the use of administrative claims data. As such, there is no information about medications or process measures. However, the Medicare database is the only truly national source of information that can be used to address trends in mortality with a standardized period of follow-up. A recent administrative claims-based model produced estimates of hospital-level RSMRs in close approximation to estimates that would have been produced with a medical record–based model,2
and the predictive values of the variables in the models have remained relatively constant over time. Also, the codes for AMI have a high sensitivity and specificity for the identification of patients admitted with this condition.21
The use of the Medicare administrative data also allowed a focus on 30-day outcomes rather than in-hospital events, which would have overestimated the improvement in hospital performance over time.
A change in coding practices for the concomitant conditions also could have affected the results. However, the ob-served mortality demonstrated a reduction over time, suggesting that the RSMR finding was not simply a result of risk adjustment. In addition, chart review has revealed increases in age and comorbidity over time in AMI cohorts, suggesting that this trend does not merely reflect changes in coding.14
Lastly, the association of the comorbid conditions and 30-day mortality has not changed over the period, suggesting that the same type of conditions are being coded.2
Lastly, this study is limited to Medicare patients and cannot represent trends in younger populations of patients with AMI. Unfortunately, we lack national data on younger patients that would include 30 days of follow-up. Nevertheless, Medicare patients represent more than half of all patients with AMI.