Trends from 1992 to 2009 are shown by age group and for all ages.
Shroff GR, Heubner BM, Herzog CA. Incidence of Acute Coronary Syndrome in the General Medicare Population, 1992 to 2009A Real-World Perspective. JAMA Intern Med. 2014;174(10):1689-1690. doi:10.1001/jamainternmed.2014.3446
We examined temporal trends in the incidence of acute coronary syndrome (ACS) among US Medicare beneficiaries.
We searched the 5% Medicare database (about 1.8 million patients per cohort year) to identify patients hospitalized with ACS from 1992 to 2009. Our cohort included Medicare patients at least 65 years old continuously enrolled with Parts A and B coverage and not enrolled in a health maintenance organization, excluding those with end-stage renal disease. We included claims for the following diagnostic codes (International Classification of Diseases, Ninth Revision, Clinical Modification): 410 (excluding 410.x2), acute myocardial infarction (AMI); and 411, unstable angina. Incidence was defined as the percentage of patients with at least 1 ACS inpatient claim in each cohort year.
Between 1992 and 2009, the proportion of patients aged 65 to 74 years decreased from 56% to 50%, while the proportion older than 84 years increased from 11% to 15%. However, the proportions of women (60% to 58%) and white patients (88% to 87%) remained relatively constant. The annual unadjusted incidence of ACS was about 2.4% to 2.5% until 2002 and then steadily declined to about 1.7% in 2009 (Figure, A). The incidence of unstable angina steadily declined (from 1.5% in 1997 to 0.6% in 2009; Figure, B), but that of AMI remained constant, about 1.2% to 1.4%, throughout the study period (Figure, C). This trend was similar for all age, sex, and race groups except patients older than 84 years, in whom the ACS incidence initially increased, from 2.8% in 1992 to 3.4% in 2002, and then declined to 2.6% by 2009.
Trends in AMI incidence have been studied in various populations. Yeh et al1 evaluated a community-based cohort of patients with AMI, who demonstrated a marked reduction in incidence, adjusted for age and sex, from 2000 to 2008 from 274 to 208 cases per 100 000 patient-years, which was driven by a decreased incidence of ST-segment elevation myocardial infarction. Using data from the National Health Service in England, Smolina et al2 reported a decrease in age-standardized AMI rates from 2002 to 2010 by about 33% in men and 31% in women. In contrast, Wong et al,3 evaluating national data from Australia, reported an increase in age- and sex-adjusted incidence from 1993 to 2010 from 215 to 251 cases per 100 000 person-years.
Our Medicare population differs significantly from the US community-based sample evaluated by Yeh et al1 owing to higher proportions of older and female patients. Moreover, unlike other investigators studying Medicare patients (eg, Chen et al4 and Wang et al5), we determined the cumulative incidence of ACS, not just AMI, for nearly 2 decades. This study illustrates the disproportionate reduction in the incidence of unstable angina relative to AMI in the most recent decade. Our study is limited, however, by our use of administrative data, which are subject to appropriate coding, and our lack of clinical data.
In conclusion, the declining incidence of ACS from 2002 to 2009 demonstrates that improvement in cardiovascular outcomes extends to Medicare beneficiaries, probably reflecting better implementation of preventive strategies. This parallels a simultaneous reduction in US mortality rates associated with cardiovascular and coronary heart disease.6 However, our findings indicate that the AMI incidence among Medicare patients is higher than community-based estimates and has declined only modestly in nearly 2 decades, deserving additional attention. Importantly, the trend of declining ACS incidence was driven primarily by a reduction in unstable angina diagnoses, probably reflecting more frequent diagnosis of AMI relative to unstable angina due to expanded use of more sensitive cardiac biomarkers and changing definitions of AMI. These observations have important clinical and economic implications for this vulnerable patient population.
Corresponding Author: Charles A. Herzog, MD, Chronic Disease Research Group, Minneapolis Medical Research Foundation, 914 S Eighth St, Ste S4.100, Minneapolis, MN 55404 (firstname.lastname@example.org).
Published Online: August 11, 2014. doi:10.1001/jamainternmed.2014.3446.
Author Contributions: Dr Herzog had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Herzog.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Shroff.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Heubner.
Obtained funding: Herzog.
Study supervision: Herzog.
Conflict of Interest Disclosures: Dr Herzog has ownership interest in Johnson & Johnson. No other disclosures are reported.
Funding/Support: This study was supported by a research contract with Ortho-McNeil Janssen Scientific Affairs, LLC.
Role of the Sponsors: Before submission for peer review, the manuscript was reviewed by the sponsor. Comments were sent to the authors, who are solely responsible for the final version. The analysis, interpretation, and reporting of these data are the responsibility of the authors. The funding source had no role in the design and conduct of the study, the collection or management of data, the preparation or approval of the manuscript, or the decision to submit the manuscript for publication.
Additional Contributions: We thank Delaney Berrini, BS, and Nan Booth, MSW, MPH, ELS, paid employees of the Chronic Disease Research Group, Minneapolis Medical Research Foundation, for manuscript preparation and manuscript editing, respectively.