Recent Trends in the Incidence, Treatment, and Outcomes of Patients with STEMI and NSTEMI
Article Outline
Abstract
Background
Despite the widespread use of electrocardiographic changes to characterize patients presenting with acute myocardial infarction, little is known about recent trends in the incidence rates, treatment, and outcomes of patients admitted for acute myocardial infarction further classified according to the presence of ST-segment elevation. The objectives of this population-based study were to examine recent trends in the incidence and death rates associated with the 2 major types of acute myocardial infarction in residents of a large central Massachusetts metropolitan area.
Methods
We reviewed the medical records of 5383 residents of the Worcester (MA) metropolitan area hospitalized for either ST-segment elevation acute myocardial infarction (STEMI) or non-ST-segment acute myocardial infarction (NSTEMI) between 1997 and 2005 at 11 greater Worcester medical centers.
Results
The incidence rates (per 100,000) of STEMI decreased appreciably (121 to 77), whereas the incidence rates of NSTEMI increased slightly (126 to 132) between 1997 and 2005. Although in-hospital and 30-day case-fatality rates remained stable in both groups, 1-year postdischarge death rates decreased between 1997 and 2005 for patients with STEMI and NSTEMI.
Conclusions
The results of this study demonstrate recent decreases in the magnitude of STEMI, slight increases in the incidence rates of NSTEMI, and decreases in long-term mortality in patients with STEMI and NSTEMI. Our findings suggest that acute myocardial infarction prevention and treatment efforts have resulted in favorable decreases in the frequency of STEMI and death rates from the major types of acute myocardial infarction.
Keywords: Acute myocardial infarction, Trends in incidence and prognosis
The acute coronary syndrome model espoused by the American College of Cardiology places unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI) at increasingly severe points along a disease continuum.1, 2 Clinical trial and registry data have supported this conceptual model by showing that individuals with NSTEMI and STEMI have differing short-term prognoses and responses to therapies.3, 4
Given the aging of the US population, and increasing population burden of obesity and diabetes, the characteristics of patients hospitalized with acute myocardial infarction have changed during recent years.5, 6 Moreover, increasing use of high-sensitivity biomarkers to define NSTEMI has resulted in the reclassification of many individuals previously diagnosed with unstable angina.7 Concomitantly, improved hospital treatments have reduced acute myocardial infarction-associated morbidity and in-hospital mortality.6, 8
While several community and more select population-based studies have provided information about trends in the magnitude, management, and outcomes of patients hospitalized with acute myocardial infarction,9, 10, 11, 12 few have examined trends in the incidence rates, hospital treatment, and prognosis of individuals experiencing STEMI and NSTEMI during a contemporary period when high-sensitivity biomarkers were introduced. The objectives of our study were to describe changes in the magnitude of, and outcomes associated with, STEMI and NSTEMI in residents of central Massachusetts.
Methods
The Worcester Heart Attack Study is an ongoing population-based investigation examining long-term trends in the incidence rates, in-hospital, and post-discharge case-fatality rates (CFRs) of greater Worcester (MA) (2000 census
=478,000) residents hospitalized with acute myocardial infarction at all metropolitan Worcester medical centers. In brief, the medical records of greater Worcester residents admitted to all 11 hospitals throughout central Massachusetts with a discharge diagnosis of acute myocardial infarction and related coronary disease rubrics were individually reviewed and validated according to pre-established diagnostic criteria.6, 13, 14 The 5 years under study included 1997, 1999, 2001, 2003, and 2005.
Classification of Acute Myocardial Infarction
A diagnosis of STEMI was made when new ST-segment elevation was present at the J point in 2 or more contiguous leads. A diagnosis of NSTEMI was accepted when, in the absence of ST-segment elevation, ischemic ST-segment or T-wave changes were present for at least 24 hours with positive cardiac enzymes or a typical clinical presentation, or both. From 2003 on, in the absence of electrocardiographic abnormalities, a diagnosis of NSTEMI was accepted when elevation in various cardiac biomarker assays, including troponin, was accompanied by typical clinical presentation. Trained nurse and physician study personnel reviewed all baseline and serial electrocardiograms (ECGs), and quality control activities were routinely conducted with respect to ECG interpretation and abstraction of data from hospital medical records. Computer systems at all area hospitals also over-read all ECGs and they were reviewed by study personnel.
Troponin assays were infrequently used before 2003 and were not considered in the diagnosis of acute myocardial infarction at that time. In contrast, troponin was commonly measured from 2003 on and was incorporated into the diagnostic criteria for acute myocardial infarction in 2003. Ninety-seven percent of patients with troponin had concomitant measures of total creatinine kinase or its isoenzyme subfraction.
Data Collection
Trained physicians and nurses abstracted demographic and clinical data from the medical records of greater Worcester residents with confirmed acute myocardial infarction. Abstracted information included patient's age, sex, medical history, acute myocardial infarction order (initial vs prior) and type (Q wave vs non-Q wave), physiologic factors, length of hospital stay, time interval between patient-reported acute symptom onset and emergency department arrival, hospital-associated delay to receipt of a percutaneous coronary intervention (PCI), and discharge status.15 Information about the use of important cardiac medications, coronary angiography, PCI, and coronary artery bypass graft surgery was collected.6, 13, 14 Development of various clinical complications during hospitalization was defined according to standardized criteria.6, 13, 14 Survival status after hospital discharge was determined through a review of medical records and search of death certificates. Some form of follow-up after hospital discharge was obtained for the vast majority (>99%) of discharged patients.
Data Analysis
Differences in the characteristics of patients hospitalized for STEMI and NSTEMI were examined through the use of chi-squared tests for discrete variables and t tests for continuous variables. The prognosis of patients with acute myocardial infarction was examined by calculating in-hospital, 30-day, and 1-year CFRs separately for patients with STEMI and NSTEMI.
Analyses were initially performed for all patients with confirmed acute myocardial infarction, and then repeated for patients with an initial myocardial infarction only (n=3494); the latter analyses were carried out for purposes of determining whether the presence of a prior myocardial infarction would change observed trends in our principal study outcomes. We accounted for the effect of potentially confounding demographic and clinical covariates in examining changes over time in hospital and postdischarge CFRs by means of a logistic multiple regression approach. Multivariable adjusted odds ratios for in-hospital, 30-day, and 1-year CFRs were calculated, together with 95% confidence intervals, controlling for differences in several clinical and demographic factors (age, sex, history of atrial fibrillation, heart failure, angina, diabetes mellitus, stroke, estimated glomerular filtration rate, acute myocardial infarction type, and presenting systolic blood pressure) separately for patients with STEMI and NSTEMI. In our regression models we did not control for the use of adjunctive medical therapy because the timing of medication administration could not be determined from our methods of data abstraction, nor could we account for confounding by treatment indication given the study's nonrandomized nature.
The incidence rates of STEMI and NSTEMI were calculated in a standard manner using 2000 census data for the greater Worcester population. We carried out intercensal extrapolations in constructing population denominators for purposes of calculating annual incidence rates of STEMI and NSTEMI. We also carried out a series of regression analyses for purposes of examining changes over time in the odds of developing STEMI and NSTEMI while controlling for the covariates described previously.
Results
Characteristics of Study Patients
A total of 5383 greater Worcester residents were hospitalized with confirmed acute myocardial infarction during the 5 biennial study years (Table 1). Individuals hospitalized for STEMI were more likely to be younger, male, and were less likely to have a prior history of several comorbidities in comparison with patients with NSTEMI. Patients with STEMI were also more likely to undergo cardiac catheterization or PCI and to be treated with aspirin, beta-blockers, and either an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) during hospitalization. Patients with STEMI were more likely to develop a Q-wave myocardial infarction, have a shorter prehospital and PCI-related delay, a higher body mass index and estimated glomerular filtration rate, a lower initial systolic blood pressure, and a higher initial diastolic blood pressure.
Table 1. Characteristics of Patients Hospitalized With Acute Myocardial Infarction (AMI)
| Variable⁎ | NSTEMI (n=3314) | STEMI (n=2071) | P Value |
|---|---|---|---|
| Demographics | |||
| Age (mean, years)+SD | 73.4+13.2 | 67.1+14.5 | <.001 |
| <65 | 822(24.8) | 874(42.2) | — |
| 65-74 | 719(21.7) | 470(22.7) | — |
| >75 | 1773(53.5) | 727(35.1) | — |
| Male (%) | 1771(53.4) | 1254(60.6) | <.001 |
| White race (%) | 2970(92.3) | 1862(92.9) | .43 |
| Medical history (%) | |||
| Atrial fibrillation | 536(16.2) | 153(7.4) | <.001 |
| Angina | 793(23.9) | 366(17.7) | <.001 |
| Diabetes | 1211(36.5) | 551(26.6) | <.001 |
| Heart failure | 1020(30.8) | 227(13.4) | <.001 |
| Stroke | 448(13.5) | 188(9.1) | <.001 |
| In-hospital treatment (%) | |||
| Aspirin | 2975(89.8) | 1948(94.1) | <.001 |
| Beta-blockers | 2795(84.3) | 1858(89.7) | <.001 |
| Angiotensin-converting enzyme inhibitor or angiotensin receptor blocker | 1973(59.4) | 1309(63.2) | .007 |
| Lipid-lowering medication | 1716(51.8) | 1121(54.1) | .09 |
| Cardiac catheterization | 1406(42.6) | 1339(64.7) | <.001 |
| Percutaneous intervention | 754(22.8) | 946(45.7) | <.001 |
| Coronary artery bypass grafting | 192(5.8) | 124(6.0) | .79 |
| Physiologic parameters (mean+SD) | |||
| Body mass index (kg/m2) | 27.2+6.1 | 27.7+5.9 | .004 |
| Ejection fraction (%) | 45.6+14.5 | 45.1+12.9 | .34 |
| eGFR (mL/min/m2) | 55.7+25.6 | 66.4+32.4 | <.001 |
| Systolic blood pressure (mm Hg) | 144.2+34.3 | 139.5+33.3 | <.001 |
| Diastolic blood pressure (mm Hg) | 76.4+20.7 | 78.8+21.4 | <.001 |
| Glucose (mg/dL) | 186.0+138.4 | 180.4+129.0 | .15 |
| Total cholesterol (mg/dL) | 179.8+53.9 | 182.2+48.1 | .25 |
| AMI associated features (%) | |||
| Initial† | 1974(59.6) | 1520(73.4) | <.001 |
| Q wave | 319(9.6) | 1030(49.7) | <.001 |
| Hospital-associated delays | |||
| Prehospital (median hours, IQR) | 2.3(1.1-5.0) | 1.8(1.0-3.8) | <.001 |
| PCI-related (median hours, IQR) | 32.9(17.3-69.2) | 3.5(2.2-22.3) | <.001 |
⁎Variables presented as proportions (%), means |
†First AMI |
Trends in Hospital Incidence Rates
The incidence rates (per 100,000 population) of STEMI decreased appreciably between 1997 and 2005 (121 to 77; P <.05) (Figure 1). After adjusting for several demographic and clinical factors that could affect the likelihood of developing STEMI, the multivariable-adjusted odds of developing STEMI decreased from 2001 to 2005 relative to the referent year of 1997 (Table 2).
Figure 1.
Incidence rates for ST-segment elevation acute myocardial infarction (STEMI) and non-ST-segment elevation acute myocardial infarction (NSTEMI) by study year.
Table 2. Odds of Developing ST-segment Elevation Myocardial Infarction (STEMI) and Non-ST-segment Elevation Myocardial Infarction (NSTEMI) by Study Year
| Study Year | All Patients | All Patients | ||||
|---|---|---|---|---|---|---|
| STEMI (n=2071) | Age- and Sex-adjusted Odds of Developing STEMI⁎ (95% CI) | Fully Adjusted Odds of Developing STEMI† (95% CI) | NSTEMI (n=3314) | Age- and Sex-adjusted Odds of Developing NSTEMI⁎ (95% CI) | Fully Adjusted Odds of Developing NSTEMI† (95% CI) | |
| 1997 | 477(45.0) | 1.0 | 1.0 | 582(55.0) | 1.0 | 1.0 |
| 1999 | 493(48.0) | 1.13(0.95-1.35) | 1.09(0.87-1.36) | 534(52.0) | 0.89(0.74-1.06) | 0.92(0.74-1.15) |
| 2001 | 443(35.8) | 0.70(0.59-0.83) | 0.76(0.62-0.94) | 796(64.2) | 1.43(1.20-1.70) | 1.31(1.07-1.62) |
| 2003 | 368(31.8) | 0.58(0.48-0.69) | 0.63(0.51-0.78) | 789(68.2) | 1.74(1.46-2.08) | 1.60(1.29-1.98) |
| 2005 | 290(32.1) | 0.59(0.48-0.71) | 0.65(0.52-0.82) | 613(67.9) | 1.71(1.41-2.06) | 1.53(1.22-1.92) |
⁎1997 |
†Adjusted for age, sex, history of atrial fibrillation, angina, diabetes mellitus, heart failure or stroke, eGFR, AMI type (Q wave vs non-Q wave), and order (initial vs prior), presenting level of systolic blood pressure. |
A slight increase in the incidence rates of NSTEMI was observed between 1997 and 2005 (126 to 132) (Figure 1). A significant increase in the NSTEMI incidence rates occurred in 2001, after which point NSTEMI incidence rates decreased. The multivariable-adjusted odds of NSTEMI remained relatively stable between 1997 and 1999, after which point the odds of developing NSTEMI increased (Table 2).
Hospital Treatment Practices
Overall, there were slight, but statistically significant, differences between our 2 primary comparison groups in the proportion of patients receiving ACE inhibitors/ARBs (62% vs 56%), aspirin (94% vs 90%), and beta-blockers (90% vs 84%) during hospitalization. On the other hand, there were marked differences in the proportion of patients undergoing cardiac catheterization (65% vs 43%), PCI (46% vs 23%), and thrombolytic therapy (26% vs 1%) in patients with STEMI versus NSTEMI.
Patients with STEMI were increasingly more likely to be prescribed each of the effective cardiac medications examined, with the exception of thrombolytic therapy, and were increasingly more likely to undergo cardiac catheterization or PCI (Table 3) over time. Similar patterns, albeit at lower utilization rates, were observed in patients with NSTEMI. There were, however, notable differences in treatment utilization trends. A greater increase in the hospital use of beta-blockers was noted among patients with NSTEMI over time, whereas a greater increase in the use of ACEI/ARBs, cardiac catheterization, and PCI was noted in patients with STEMI.
Table 3. Changing Trends in Hospital Treatment Practices
| Medication | ST-segment Elevation AMI (%) | Non-ST-segment Elevation AMI (%) |
|---|---|---|
| Aspirin | ||
| 1997 | 446(93.5) | 515(88.5) |
| 1999 | 469(95.1) | 481(90.0) |
| 2001 | 400(90.3) | 688(86.4) |
| 2003 | 356(96.7) | 714(90.5) |
| 2005 | 277(95.5) | 577(94.1) |
| % change (1997-2005) | +3.0 | +7.2 |
| Beta-blockers | ||
| 1997 | 420(88.1) | 439(75.4) |
| 1999 | 429(87.0) | 412(77.2) |
| 2001 | 392(88.5) | 653(82.0) |
| 2003 | 344(93.5) | 708(89.7) |
| 2005 | 273(94.1) | 583(95.1) |
| % change (1997-2005) | +6.8 | +26.1 |
| Lipid-lowering therapy | ||
| 1997 | 117(24.5) | 119(20.5) |
| 1999 | 207(42.0) | 209(39.1) |
| 2001 | 289(65.2) | 415(52.1) |
| 2003 | 307(83.4) | 569(72.1) |
| 2005 | 201(69.3) | 404(65.9) |
| % change (1997-2005) | +182.9 | +221.5 |
| ACE inhibitors/ARBs | ||
| 1997 | 246(51.6) | 282(48.5) |
| 1999 | 258(52.3) | 260(48.7) |
| 2001 | 283(63.9) | 444(55.8) |
| 2003 | 284(77.2) | 506(64.1) |
| 2005 | 216(74.5) | 368(60.0) |
| % change (1997-2005) | +44.4 | +23.7 |
| Thrombolytics | ||
| 1997 | 199(41.7) | 22(3.8) |
| 1999 | 191(38.7) | 9(1.7) |
| 2001 | 114(26.0) | 15(1.9) |
| 2003 | 34(9.2) | 6(0.8) |
| 2005 | 5(1.7) | 2(0.3) |
| % change (1997-2005) | −95.9 | −92.1 |
| Cardiac catheterization | ||
| 1997 | 238(49.9) | 185(31.8) |
| 1999 | 270(54.8) | 173(33.0) |
| 2001 | 299(67.5) | 324(40.7) |
| 2003 | 286(77.7) | 372(47.2) |
| 2005 | 246(84.8) | 352(57.4) |
| % change (1997-2005) | +34.9 | +25.6 |
| Percutaneous coronary intervention | ||
| 1997 | 113(23.7) | 50(8.6) |
| 1999 | 168(34.1) | 62(11.9) |
| 2001 | 202(45.6) | 160(20.1) |
| 2003 | 247(67.1) | 240(30.4) |
| 2005 | 216(74.5) | 242(39.5) |
| % change (1997-2005) | +214.3 | +359.3 |
| CABG | ||
| 1997 | 24(5.0) | 37(6.4) |
| 1999 | 30(6.1) | 24(4.6) |
| 2001 | 37(8.4) | 68(8.5) |
| 2003 | 23(6.3) | 39(4.9) |
| 2005 | 10(3.5) | 24(3.9) |
| % change (1997-2005) | −30.0 | −39.1 |
In-hospital, 30-Day, and 1-Year Death Rates
Although a greater proportion of patients with NSTEMI developed atrial fibrillation and heart failure while hospitalized (Table 4), in-hospital CFRs were similar for patients with STEMI and NSTEMI (Figure 2). The in-hospital and 30-day death rates for patients with STEMI remained relatively stable between 1997 and 2005 (Table 5). In-hospital death rates decreased only slightly in patients presenting with NSTEMI. Results were quantitatively similar for models evaluating 30-day death rates.
Table 4. Changing Trends in Various Hospital Outcomes for Patients with ST-segment (STEMI) and Non-ST-segment (NSTEMI) Elevation Myocardial Infarction
| Year | n | Atrial Fibrillation | Heart Failure | Cardiogenic Shock | ||||
|---|---|---|---|---|---|---|---|---|
| % Developing | Adjusted OR⁎ (95% CI) | % Developing | Adjusted OR⁎ (95% CI) | % Developing | Adjusted OR⁎ (95% CI) | |||
| STEMI | ||||||||
| 1997 | 477 | 11.7 | 1.0 | 25.8 | 1.0 | 8.8 | 1.0 | |
| 1999 | 493 | 14.0 | 1.13(0.74-1.74) | 29.4 | 1.20(0.86-1.68) | 7.9 | 0.93(0.55-1.60) | |
| 2001 | 443 | 21.9 | 1.84(1.23-2.77) | 31.8 | 1.25(0.90-1.76) | 9.9 | 1.14(0.68-1.91) | |
| 2003 | 368 | 20.9 | 2.02(1.33-3.08) | 31.8 | 1.39(0.99-1.97) | 6.8 | 0.71(0.40-1.28) | |
| 2005 | 290 | 16.9 | 1.53(0.97-2.44) | 29.7 | 1.21(0.83-1.77) | 8.6 | 1.09(0.61-1.95) | |
| NSTEMI | ||||||||
| 1997 | 582 | 13.4 | 1.0 | 36.9 | 1.0 | 5.5 | 1.0 | |
| 1999 | 534 | 17.4 | 1.19(0.81-1.75) | 43.8 | 1.21(0.90-1.63) | 5.1 | 1.04(0.55-1.96) | |
| 2001 | 796 | 20.0 | 1.43(1.02-2.02) | 41.1 | 1.06(0.80-1.39) | 4.0 | 0.80(0.44-1.47) | |
| 2003 | 789 | 23.3 | 1.69(1.21-2.37) | 45.1 | 1.31(1.00-1.72) | 2.8 | 0.58(0.31-1.10) | |
| 2005 | 613 | 25.1 | 1.96(1.38-2.79) | 41.8 | 0.99(0.75-1.33) | 4.1 | 0.85(0.45-1.60) | |
⁎Adjusted for age, sex, history of atrial fibrillation, heart failure, stroke, angina, diabetes mellitus, estimated glomerular filtration rate, AMI type (Q wave vs non Q wave), presenting systolic blood pressure. |
Figure 2.
In-hospital, 30 days, and 1-year case-fatality rates for ST-segment elevation acute myocardial infarction (STEMI) and non-ST-segment elevation acute myocardial infarction (NSTEMI) by study year.
Table 5. Changing Trends in Hospital, 30-Day, and 1-year Case Fatality Rates (CFRs) for Patients with ST-segment (STEMI) and Non-ST-segment (NSTEMI) Elevation Myocardial Infarction
| Year | Hospital CFRs | 30 Day Post Admission CFR | 1-year Post Discharge CFRs | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| n (%) | Age and Sex-adjusted OR (95% CI) | Multivariable Adjusted OR (95% CI)⁎ | n (%) | Age and Sex-adjusted OR (95% CI) | Multivariable Adjusted OR (95% CI)⁎ | n (%)† | Age and Sex-adjusted OR (95% CI) | Multivariable Adjusted OR (95% CI)⁎ | ||
| STEMI | ||||||||||
| 1997 | 477(11.1) | 1.0 | 1.0 | 477(13.2) | 1.0 | 1.0 | 424(10.6) | 1.0 | 1.0 | |
| 1999 | 493(9.9) | 0.95(0.65-1.40) | 0.82(0.50-1.35) | 493(13.0) | 0.95(0.65-1.40) | 0.96(0.61-1.51) | 444(14.0) | 1.25(0.92-1.69) | 1.07(0.74-1.54) | |
| 2001 | 443(13.5) | 1.21(0.83-1.77) | 1.08(0.68-1.72) | 443(15.8) | 1.21(0.83-1.77) | 1.12(0.72-1.74) | 383(15.4) | 1.05(0.79-1.39) | 0.98(0.70-1.36) | |
| 2003 | 368(8.4) | 0.73(0.47-1.14) | 0.66(0.39-1.12) | 368(10.0) | 0.73(0.47-1.14) | 0.67(0.40-1.10) | 337(8.3) | 1.04(0.79-1.37) | 0.88(0.64-1.23) | |
| 2005 | 289(9.7) | 0.88(0.55-1.39) | 0.81(0.47-1.41) | 289(11.4) | 0.88(0.55-1.39) | 0.78(0.46-1.33) | 261(8.4) | 0.63(0.46-0.86) | 0.50(0.35-0.72) | |
| NSTEMI | ||||||||||
| 1997 | 582(12.9) | 1.0 | 1.0 | 582(16.0) | 1.0 | 1.0 | 507(23.1) | 1.0 | 1.0 | |
| 1999 | 534(13.1) | 0.99(0.70-1.41) | 0.98(0.64-1.49) | 534(17.0) | 1.04(0.75-1.44) | 0.93(0.64-1.37) | 464(27.6) | 1.55(0.91-2.10) | 1.47(0.91-2.40) | |
| 2001 | 796(10.9) | 0.78(0.56-1.08) | 0.75(0.50-1.11) | 796(16.5) | 0.95(0.70-1.27) | 0.88(0.62-1.25) | 709(26.1) | 1.55(1.00-2.40) | 1.62(1.00-2.63) | |
| 2003 | 789(8.9) | 0.61(0.43-0.87) | 0.62(0.41-0.93) | 789(13.7) | 0.75(0.55-1.03) | 0.71(0.50-1.02) | 719(25.6) | 0.74(0.44-1.24) | 0.80(0.46-1.39) | |
| 2005 | 613(9.5) | 0.64(0.44-0.92) | 0.65(0.43-0.99) | 613(14.0) | 0.75(0.54-1.03) | 0.69(0.47-1.01) | 555(18.7) | 0.82(0.47-1.44) | 0.80(0.44-1.46) | |
⁎Adjusted for age, sex, history of atrial fibrillation, heart failure, stroke, angina, diabetes mellitus, estimated glomerular filtration rate, AMI type (Q wave vs non Q wave), presenting systolic blood pressure. |
†Hospital survivors only. |
In examining all-cause death rates during the first year after hospital discharge for patients with STEMI and NSTEMI, encouraging decreases in 1-year death rates were observed in both patient groups (Table 5; P for trend <.005). In multivariable-adjusted models, the odds of dying during the first year after discharge decreased steadily among patients with STEMI between 1997 and 2005. By 2005, the odds of dying within 1 year after discharge was 50% lower among STEMI patients in comparison with those admitted in 1997; a nonsignificant and inconsistent trend toward lower odds of dying within 1 year of hospitalization was noted among patients with NSTEMI.
Discussion
Trends in Hospitalization Rates
Hospitalization rates for acute myocardial infarction have remained largely stable or slightly increased over time in the US population.6, 16, 17 Our results provide relatively recent insights into these trends by suggesting that recent decreases in hospitalization for STEMI have been counter-balanced by slight increases in hospitalization for NSTEMI.
Improved coronary risk factor awareness and treatment practices may have contributed to the decreases in the incidence of STEMI observed in the present study.18 That a similar decrease was not observed in the incidence of NSTEMI may reflect a greater benefit of primary prevention measures for those at risk for STEMI. Alternatively, changes in the prevalence of emerging cardiovascular risk factors, such as diabetes and obesity, or changing demographic characteristics of patients hospitalized with acute myocardial infarction, may have differentially promoted the development of NSTEMI.5, 19
The most likely explanation for our findings, however, is that the observed decrease in the frequency of patients hospitalized with STEMI is part of a larger trend toward fewer patients with electrocardiographically diagnosed acute myocardial infarction. Indeed, the Framingham investigators have reported an approximate 50% decrease in the frequency of electrocardiographically diagnosed cases of acute myocardial infarction over a 40-year period.20 In our cohort, only 40% of NSTEMI cases diagnosed since 2003 had evidence of ECG abnormalities. These data suggest that had high-sensitivity cardiac biomarkers, particularly troponin, not been introduced into the greater Worcester community during recent years, the number of NSTEMI cases may have decreased over time.
Hospital Treatment Practices
Despite being considerably older, and having a higher prevalence of cardiovascular comorbidities, patients with NSTEMI were less likely to receive effective cardiac medications and to undergo cardiac catheterization or PCI during their hospitalization than were patients with STEMI. However, prescription of these medications and procedures increased significantly, with the exception of thrombolytic therapy and coronary artery bypass surgery, over the years under study among both patient groups.
Reasons for these differences are unclear because indications for the use of aspirin, beta-blockers, lipid-lowering agents, and ACEI/ARBs are generally similar, irrespective of acute myocardial infarction subtype. Although the guidelines for treatment of STEMI and NSTEMI differ with respect to timing of cardiac catheterization and PCI,21 data support the in-hospital use of these procedures in patients with NSTEMI.22 Thus, patterns in the use of cardiac catheterization and PCI cannot be explained solely on the basis of differential indications. In our analysis, no disease-level factors could be identified to explain why differences in the use of effective cardiac medications, cardiac catheterization, and PCI persisted between the study groups over time.
Patient, provider, and hospital level factors, however, may offer greater insights into the treatment disparities observed in our investigation. Because NSTEMI patients were generally older and more likely to have significant comorbidities present, providers may have been less aggressive in managing NSTEMI patients due to concerns about adverse effects.23, 24 Older patients may also have been less likely to agree to undergo invasive procedures or take multiple medications.19, 25 Hospital-based initiatives may have contributed to differences in treatment practices observed between our respective comparison groups. Further investigation into these areas is warranted, particularly because the number of older patients with NSTEMI appears to be increasing.
In-hospital, 30-Day, and 1-Year Death Rates
It is notable that in-hospital death rates in our study were higher for both NSTEMI and STEMI than has been reported elsewhere.26 This likely relates to differences in age as well as to the number and severity of comorbidities in patients participating in our community-based study relative to patients eligible for participation in randomized controlled trials.26 Use of more restrictive inclusion criteria, particularly upper age limits, may partially explain why clinical trials have not demonstrated similar death rates for NSTEMI and STEMI.
Mortality from NSTEMI remained significantly higher than STEMI at both 30 days and 1 year. The higher long-term death rates observed in patients discharged after NSTEMI may have resulted from the fact that patients with NSTEMI were older and had a greater burden of cardiovascular comorbidities. Under-utilization of effective cardiac medications and PCI, as well as greater delays in the time to receipt of PCI in patients with NSTEMI, may also have contributed to differences in the post-discharge death rates observed in these patients.27
Our results are consistent with the notion that differences in mortality in patients hospitalized with STEMI and NSTEMI strongly relate to patients' clinical characteristics and less so to the presence (or absence) of ST-segment elevation.28 The significant influence of heart failure, atrial fibrillation, diabetes, and kidney function on the outcomes assessed in our study also suggests that clinicians might further impact hospital and long-term death rates in patients with acute myocardial infarction by improving the treatment of these and other modifiable factors.28
Despite increasing rates of atrial fibrillation and heart failure over time, and an increasingly older patient population, 1-year death rates decreased for all greater Worcester residents discharged after acute myocardial infarction between 1997 and 2005. This finding is consistent with prior data that have demonstrated declining long-term CFRs for both NSTEMI and STEMI.26 Although we did not control for differences in hospital treatment practices between study groups, nor was information available about the use of cardiac medications after hospital discharge, we have previously demonstrated increasing application of effective cardiac medications in greater Worcester residents hospitalized for acute myocardial infarction.6 Increasing use of these therapies, and reductions in prehospital delay to PCI among patients with both STEMI and NSTEMI, may have contributed to the improved 1-year survival rates noted.29
Study Limitations
Although trends in the incidence and death rates for STEMI and NSTEMI may have been affected by the use of coronary interventional procedures and medical therapies, we did not adjust for differences in the management of these patients. Our study was underpowered to examine differences between patients with NSTEMI with diagnostic ECG changes from those without such changes. An electrocardiographic core laboratory was not employed, perhaps resulting in some misclassification of acute myocardial infarction. The number of deaths during several time periods was relatively small, limiting any inferences that might be drawn.
Conclusions
The incidence rates of STEMI decreased significantly between 1997 and 2005. Incidence rates of NSTEMI increased slightly during this period, likely as a result of high-sensitivity biomarker introduction. Encouraging trends were noted in the postdischarge death rates for both STEMI and NSTEMI at 1 year, suggesting that acute myocardial infarction treatment practices have likely improved the long-term outlook for all patients hospitalized with acute myocardial infarction. Increased attention needs to be directed to secondary prevention practices in the hospital and post-discharge management of patients hospitalized with NSTEMI because the proportion of NSTEMI patients receiving effective cardiac therapies lags behind those with STEMI.
Acknowledgments
We wish to acknowledge all persons involved in the review of data for this project as well as to our collaborators at all greater Worcester hospitals.
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Funding: National Institutes of Health (RO1 HL35434).
Conflict of Interest: There are no conflicts of interest to report for any of the authors.
Authorship: All authors had access to the data and had a role in writing this manuscript.
PII: S0002-9343(10)00736-9
doi:10.1016/j.amjmed.2010.07.023
© 2011 Elsevier Inc. All rights reserved.
