Sparse data are available describing recent trends in the magnitude, clinical features, treatment practices, and outcomes of comparatively young adults hospitalized with acute myocardial infarction (AMI). The objectives of this population-based study were to describe 3 decade-long trends (1975 to 2005) in these end points in adults <55 years old who were hospitalized with an initial AMI. The study population consisted of 1,703 residents of the Worcester (Massachusetts) metropolitan area 25 to 54 years of age who were hospitalized with initial AMIs at all central Massachusetts medical centers during 15 annual periods from 1975 through 2005. Overall hospital incidence rate (per 100,000 residents) of initial AMI in our study population was 66 (95% confidence interval 63 to 69) and incidence rates of AMI decreased inconsistently over time. Patients hospitalized during the most recent study years were more likely to have important cardiovascular risk factors and co-morbidities present but were less likely to have developed heart failure during their index hospitalization. In-hospital and 30-day death rates decreased by approximately 50% (p = 0.04) during the years under study concomitant with increasing use of effective cardiac therapies. In conclusion, the results of this community-wide investigation provide insights into the magnitude, changing characteristics, and short-term outcomes of comparatively young patients hospitalized with a first AMI. Decreasing odds of developing or dying from an initial AMI during the 30 years under study likely reflect increased primary and secondary prevention and treatment efforts.
The Worcester Heart Attack Study (WHAS) has been conducting surveillance of acute myocardial infarction (AMI) in adult residents of the Worcester (Massachusetts) metropolitan area for the previous 3 decades. Using data from this ongoing study of central Massachusetts residents, we examined 30-year trends (1975 to 2005) in disease incidence rates, patient characteristics, hospital treatment practices, and short-term outcomes in comparatively young adults who had been hospitalized for AMI at all greater Worcester medical centers. In light of regional data highlighting the increasing prevalence of obesity and diabetes in young greater Worcester residents, we hypothesized that we would observe increasing incidence rates of initial AMI. We also hypothesized that better monitoring and treatment of comparatively young adults hospitalized with AMI over time would be associated with favorable decreases in complication and mortality rates after AMI.
Methods
The study population consisted of greater Worcester residents 25 to 54 years of age who were hospitalized with a discharge diagnosis of AMI at all medical centers in the Worcester metropolitan area during 15 individual study years from 1975 through 2005. Sixteen hospitals were originally included in this investigation but fewer hospitals (n = 11) have been included in recent years because of hospital closures or conversion to long-term care or rehabilitation facilities. We restricted the present sample to adults 25 to 54 years of age who were hospitalized with an independently validated initial AMI because we were interested in describing the clinical epidemiology of AMI in a comparatively young population and examining the occurrence of initial (incident) acute coronary events. Based on careful review of previous and current hospital medical records, diagnostic test results, and electrocardiograms by trained nurse and physician abstractors, patients with a clinical history of MI were excluded. In total 1,703 patients meeting these criteria were hospitalized with an initial AMI during the following study years: 1975 (n = 131), 1978 (n = 128), 1981 (n = 129), 1984 (n = 77), 1986 (n = 92), 1988 (n = 75), 1990 (n = 77), 1991 (n = 118), 1993 (n = 116), 1995 (n = 128), 1997 (n = 124), 1999 (n = 129), 2001 (n = 147), 2003 (n = 130), and 2005 (n = 102). These years were selected because of funding availability and for purposes of examining trends in our principal study outcomes on an approximate alternating yearly basis.
The details of this study have been extensively described. In brief, potentially eligible patients were identified through a review of computerized hospital databases of patients with discharge diagnoses consistent with the possible presence of AMI. Medical records of residents of the Worcester metropolitan area (2000 census 478,000) were reviewed in a standardized manner, and diagnosis of AMI was confirmed according to pre-established criteria. Beginning in 2003, troponin assays were incorporated into the diagnostic criteria for AMI. Trained study physicians and nurses abstracted information from hospital medical records on a patient’s demographic characteristics, presenting symptoms, medical history, clinical and laboratory findings, receipt of cardiac treatments, length of hospital stay, prehospital delay, hospital discharge, and 30-day postadmission survival status. Heart failure, cardiogenic shock, atrial fibrillation, and stroke were defined by information contained in hospital charts and characterized according to established criteria previously used in this ongoing surveillance study. Follow-up information after hospital discharge was obtained for >99% of discharged patients.
Incidence rates of initial AMI were calculated in a standard manner using census and intercensus estimates of the greater Worcester population. Chi-square tests for categorical variables and analysis of variance for continuous variables were used to examine potentially changing trends in various demographic and clinical factors. Short-term outcomes in each period were examined by calculating in-hospital and 30-day case-fatality rates and trends in these end points were examined through use of chi-square tests for trends. Logistic regression modeling was used to assess the significance of 30-year trends in short-term death rates while controlling for several potentially confounding demographic, medical history, and clinical characteristics of prognostic importance. Because length of stay decreased markedly over the study period, we included duration of hospital stay in our regression models. The committee for the protection of human subjects at the University of Massachusetts Medical School approved this study.
Results
Demographic, clinical, and treatment characteristics of the study sample are presented in Table 1 . Approximately 1 in every 5 of all greater Worcester residents hospitalized with an initial AMI at all area hospitals from 1975 through 2005 was 25 to 54 years old. Overall incidence rate of AMI during the 30-year period under study was 66 per 100,000 (95% confidence interval 63 to 69) in patients 25 to 54 years old. Incidence rates of initial AMI in patients <55 years old decreased over the first 10 years of our study and then remained relatively flat thereafter ( Figure 1 ).
| Period | ||||
|---|---|---|---|---|
| Characteristic | Total Population (n = 1,703) | 1975–1978 (n = 259) | 1990–1991 (n = 195) | 2005 (n = 102) |
| Age (years), mean ± SD | 46.7 ± 6.0 | 47.0 ± 5.9 | 45.4 ± 6.5 | 47.8 ± 5.3 |
| Age (years) | ||||
| <40 | 12.1% | 10.8% | 17.4% | 7.8% |
| 40–44 | 18.9% | 15.8% | 21.0% | 17.7% |
| 45–50 | 29.9% | 31.3% | 31.8% | 27.5% |
| 50–54 | 39.1% | 42.1% | 29.7% | 47.1% |
| Men | 79.2% | 78.4% | 81.5% | 70.6% |
| White | 88.7% | 90.4% | 86.2% | 89.2% |
| Medical history | ||||
| Angina pectoris | 10.3% | 12.4% | 10.3% | 6.9% |
| Diabetes mellitus | 14.7% | 14.7% | 9.2% | 13.7% |
| Hypertension | 38.1% | 34.0% | 38.5% | 47.1% |
| Stroke | 1.8% | 1.5% | 1.0% | 0% |
| Heart failure | 1.6% | 1.5% | 0.5% | 4.9% |
| Current smoker ⁎ | 51.1% | — | — | 48.0% |
| Total cholesterol (mg/dl), mean ± SD | 219.2 ± 56.0 | 242.4 ± 56.3 | 222.9 ± 45.4 | 193.0 ± 55.9 |
| Prehospital delay (hours), median † | 1.8 | — | 1.7 | 1.5 |
| Length of stay (days), mean ± SD | 8.8 ± 7.6 | 17.3 ± 8.3 | 8.7 ± 5.9 | 4.0 ± 4.7 |
| Q-wave acute myocardial infarction | 60.7% | 75.3% | 66.7% | 32.4% |
| In-hospital therapies | ||||
| Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers ‡ | 44.6% | — | 14.9% | 69.6% |
| Aspirin | 69.8% | 20.1% | 88.7% | 98.0% |
| β Blockers | 73.6% | 23.6% | 86.7% | 96.1% |
| Calcium channel blockers ⁎ | 27.9% | — | 44.6% | 9.8% |
| Lipid-lowering agents † | 37.4% | — | 9.7% | 64.7% |
| Thrombolytics † | 32.2% | — | 42.6% | 2.9% |
| Cardiac catheterization | 48.7% | 4.6% | 39.5% | 92.2% |
| Percutaneous coronary intervention ⁎ | 37.3% | — | 11.3% | 78.4% |
| Coronary artery bypass graft surgery | 3.2% | 0% | 2.1% | 2.9% |
For ease of analysis and interpretation, we aggregated the individual study years into selected groupings (1975/1978, earliest; 1990/1991, middle; 2005, most recent) for purposes of examining changing trends in characteristics of patients hospitalized with AMI ( Table 1 ). In examining changing trends in the prevalence of obesity during the most recent years under study, the proportion of patients presenting with a body mass index ≥30 kg/m 2 increased markedly over a relatively short period (40% in 2001, 49% in 2005). Because we began collecting information on type of AMI (ST-segment elevation and non–ST-segment elevation) in 1997, we examined nearly decade-long trends in incidence rates of ST-segment elevation AMI from 1997 through 2005. Although incidence rates of ST-elevation AMI decreased in patients of all ages hospitalized with AMI in our study (121 to 77), there was an increase in the proportion of patients diagnosed with ST-segment elevation AMI in patients <55 years of age (30% in 1997, 38% in 2005, p for trend <0.05).
There was a marked and steady increase in use of effective medical therapies and revascularization procedures during the years under study (p <0.001 for all comparisons). Although outpatient use of effective cardiac therapies remained low throughout the study period, we observed a considerable increase in the proportion of hospitalized patients who were prescribed these medications before hospital admission. In 1975, 16% of hospitalized patients reported being on aspirin and only 9% reported long-term use of a β blocker before hospitalization for AMI. These percentages increased steadily over time, reaching 20% and 13%, respectively, in 2005. Similarly, in examining the previous use of ≥2 effective cardiac medications (e.g., aspirin, β blockers, angiotensin-converting enzyme inhibitors, lipid-lowering agents) before a patient’s index hospitalization, the percentage of patients receiving any 2 of these 4 effective cardiac therapies increased steadily over time (p <0.001; Figure 2 ).
Incidence rates of heart failure decreased significantly from 1975 through 2005 in young patients hospitalized with an initial AMI (p for trend <0.001; Table 2 ). Although we did not observe a decrease in incidence rates of atrial fibrillation, cardiogenic shock, and stroke during the years under study, the frequency of these complications during hospitalization for AMI remained relatively low (5.2%, 3.1%, and 0.5% overall, respectively).
| Study Period | Heart Failure | Atrial Fibrillation | Cardiogenic Shock | Stroke |
|---|---|---|---|---|
| 1975–1978 | 19.7% | 4.3% | 2.3% | 0% |
| 1981–1984 | 21.8% | 4.4% | 2.9% | 0% |
| 1986–1988 | 13.8% | 5.4% | 1.8% | 1.8% |
| 1990–1991 | 19% | 5.6% | 3.1% | 0% |
| 1993–1995 | 14.3% | 5.7% | 4.5% | 0% |
| 1997–1999 | 14.2% | 6.3% | 4.4% | 0.8% |
| 2001–2003 | 11.9% | 4.7% | 2.5% | 0.7% |
| 2005 | 5.9% | 2.0% | 2.0% | 1.0% |
Short-term mortality in young patients admitted with an initial AMI decreased significantly over the 30-year study period ( Table 3 ). To more systematically examine trends in short-term death rates, we carried out a series of multivariable-adjusted regression analyses and simultaneously controlled for several potentially confounding prognostic factors ( Table 4 ). Results of this analysis were consistent with results of our univariate analyses, showing marked decreases in hospital and 30-day postadmission death rates over the study period.
| Study Period | In-Hospital Death Rates | 30-Day Death Rates |
|---|---|---|
| 1975–1978 | 5.4% | 6.6% |
| 1981–1984 | 4.4% | 4.4% |
| 1986–1988 | 3.0% | 3.6% |
| 1990–1991 | 1.0% | 1.0% |
| 1993–1995 | 1.2% | 1.6% |
| 1997–1999 | 3.2% | 3.6% |
| 2001–2003 | 2.5% | 2.9% |
| 2005 | 2.9% | 2.9% |
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