Author + information
- Matthew D. Solomon, MD, PhD∗ (, )
- Thomas K. Leong, MPH,
- Jamal S. Rana, MD, PhD,
- Yaping Xu, MD, MPH and
- Alan S. Go, MD
- ↵∗Division of Research, Kaiser Permanente Northern California, 2000 Broadway, Oakland, California 94611
Recent substantial reductions in acute myocardial infarction (AMI) rates have been reported in various patient populations (1). Within the same health care delivery system, we extended an earlier analysis from 1999 to 2008 to examine whether these reductions have persisted into the most recent era overall, and by type of AMI (ST-segment elevation myocardial infarction [STEMI] and non−ST-segment elevation myocardial infarction [NSTEMI]), age, sex, and status of diabetes mellitus (DM).
We identified patients who were older than age 18 years and who were hospitalized for AMI between 2008 and 2014 at Kaiser Permanente Northern California (KPNC), an integrated health care delivery system caring for >3.8 million persons. Using administrative claims data, AMI was defined as a primary discharge diagnosis of AMI (International Classification of Diseases-9th Revision [ICD-9] code 410.x), or an elevated troponin I level with either a primary discharge diagnosis of unstable angina (UA) (ICD-9 code 411.x), or a primary discharge diagnosis of coronary artery disease (ICD code-9 414.0) plus a secondary discharge diagnosis of UA (ICD-9 code 411.x). Incidence per 100,000 person-years was calculated for AMI, and separately for STEMI (ICD-9 codes 410.0-6x, 410.8x) and NSTEMI (ICD-9 codes 410.7x, 410.9x). Events identified by abnormal troponin I with diagnosis codes for UA were classified as NSTEMI. Results were stratified by age, sex, and DM status. Temporal trends were examined using Poisson regression.
We identified 29,087 patients from 2008 to 2014 with AMI (32,661 AMI events) among 3,966,248 patients aged older than 18 years enrolled for ≥1 full calendar year within KPNC during the study period. Overall, 22,684 patients presented with ≥1 NSTEMI (total of 25,602 NSTEMI events) and 6,937 presented with ≥1 STEMI (total of 7,059 STEMI events). STEMI patients were younger (64.5 ± 13.5 years for STEMI; 68.6 ± 13.5 years for NSTEMI), were disproportionately men (69% of STEMI, 61% of NSTEMI), and had lower rates of DM (23% for STEMI, 36% for NSTEMI). Between 2008 and 2014, rates (per 100,000 person-years) declined for overall AMI (225 to 173), NSTEMI (177 to 136), and STEMI (47 to 37) (p < 0.01) (Figure 1).
Among DM patients, AMI rates were substantially higher compared with those without DM, but similar percentage decreases were observed in both groups (21% reduction from 2008 to 2014 for DM patients; 26% reduction for non-DM patients) (Figure 1). AMI rates were significantly higher for men than women, but rates also declined similarly in both sexes (Figure 1). AMI rates increased with advancing age, but percentage decreases across our study period were similar across all ages, although they were slightly larger among the oldest patients (rates for overall AMI per 100,000 person-years from 2008 to 2014 declined from 35 to 24, 256 to 187, 538 to 392, 990 to 685, and 1,641 to 1,098, with percentage declines of 31.4%, 27.0%, 27.1%, 30.8%, and 33.1% for patients aged younger than 50 years, patients 50 to 64, 65 to 74, 75 to 84, and 85 years or older, respectively).
In a large, community-based population, AMI incidence declined from 2008 to 2014, continuing a trend observed from 1999 to 2008 (1). Reductions were consistent across age, sex, and DM subgroups. However, although previous declines were driven primarily by fewer STEMIs, the driving force since 2008 was fewer NSTEMIs. We observed similar percentage declines between STEMI and NSTEMI rates during our 7-year study period, but the magnitude of the decline in STEMIs was much smaller compared with 1999 to 2008 when STEMIs fell markedly (1). Despite excellent primary and secondary prevention efforts (2), STEMI rates may have reached a relative plateau compared with large previous declines.
Several recent studies have documented declines in AMI in the United States and other countries across demographics and DM status (3–5). Ours is the first to stratify AMI rates by type of MI, demographics, and DM, and we report the most recent temporal trends to date. In contrast to recent reports (3), we observed AMI declines among younger patients (younger than 50 years), although the magnitude was modest because the absolute reduction in AMIs was concentrated in older patients (50 years or older). Rates of AMI in our population were lower than those observed in Medicare (5) and international populations (4), perhaps reflecting differences in lifestyle habits, genetic predisposition, and primary and secondary prevention efforts (2).
Our results may not fully generalize to other settings, geographic regions, or to uninsured patients. Although there can be misclassification in identifying AMI using administrative diagnostic codes, a previous validation effort (1) showed excellent positive predictive value for the presence of AMI and AMI type. Because there was systematic use of troponin I testing and no documented changes in coding practices across participating hospitals, our results were unlikely confounded by testing or coding practices.
Overall, our findings showed that AMI rates have continued to decline since 2008 within a large, community-based population, overall and in key patient subgroups, which supports ongoing primary and secondary prevention efforts.
Please note: This study was sponsored by a research grant from Genentech, South San Francisco, California. The sponsor reviewed the manuscript before submission but did not have any role in the decision to submit the manuscript for publication. Dr. Solomon has received research funding from Genentech and Abbott Vascular. Dr. Xu is an employee of Genentech and owns stocks in Roche. Dr. Go has received research grants through his institution from AstraZeneca, Sanofi, and Abbott Vascular. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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