The influence of the presenting electrocardiographic (ECG) findings on the treatment and outcomes of patients with non–ST-segment elevation myocardial infarction (NSTEMI) has not been studied in contemporary practice. We analyzed the clinical characteristics, in-hospital management, and in-hospital outcomes of patients with NSTEMI in the Acute Coronary Treatment and Intervention Outcomes Network Registry–Get With The Guidelines (ACTION Registry-GWTG) according to the presenting ECG findings. A total of 175,556 patients from 485 sites from January 2007 to September 2011 were stratified by the ECG findings on presentation: ST depression (n = 40,146, 22.9%), T-wave inversions (n = 24,627, 14%), transient ST-segment elevation (n = 5,050, 2.9%), and no ischemic changes (n = 105,733, 60.2%). Patients presenting with ST-segment depression were the oldest and had the greatest prevalence of major cardiac risk factors. Coronary angiography was performed most frequently in the transient ST-segment elevation group, followed by the T-wave inversion, ST-segment depression, and no ischemic changes groups. The angiogram revealed that patients with ST-segment depression had more left main, proximal left anterior descending, and 3-vessel coronary artery disease and underwent coronary artery bypass grafting most often. In contrast, patients with transient ST-segment elevation had 1-vessel CAD and underwent percutaneous coronary intervention the most. The unadjusted mortality was highest in the ST-segment depression group, followed by the no ischemic changes, transient ST-segment elevation, and T-wave inversion group. Adjusted mortality using the ACTION Registry-GWTG in-hospital mortality model with the no ischemic changes group as the reference showed that in-hospital mortality was similar in the transient ST-segment elevation (odds ratio 1.15, 95% confidence interval 0.97 to 1.37; p = 0.10), higher in the ST-segment depression group (odds ratio 1.46, 95% confidence interval 1.37 to 1.54; p <0.0001), and lower in the T-wave inversion group (odds ratio 0.91, 95% confidence interval 0.83 to 0.99; p = 0.026). In conclusion, the clinical and angiographic characteristics and treatment and outcomes of patients with NSTEMI differed substantially according to the presenting ECG findings. Patients with ST-segment depression have a greater burden of co-morbidities and coronary atherosclerosis and have a greater risk of adjusted in-hospital mortality compared with the other groups. These findings highlight the importance of integrating the presenting ECG findings into the risk stratification algorithm for patients with NSTEMI.
Risk stratification remains central to implement appropriate therapeutic measures for patients with non–ST-segment elevation myocardial infarction (NSTEMI). The electrocardiogram provides rapid risk assessment for patients presenting with chest pain that permits their allocation to appropriate management algorithms to improve the outcomes. Patients diagnosed with NSTEMI constitute a heterogeneous group with several variations of electrocardiographic (ECG) findings at presentation, including ST-segment depression, T-wave inversions, transient ST-segment elevation, or no ischemic changes. From previous studies, ST-segment depression has been considered to be a high-risk ECG finding in patients with NSTEMI with an increased risk of early and long-term cardiovascular events, who often benefit from early invasive management. However, the clinical characteristics, outcomes, and treatment of patients presenting with transient ST-segment elevation have been less well defined. It has been suggested that intensive medical therapy and early angiography are acceptable treatment options for these patients. Limited data are available on the characteristics and treatment of patients with NSTEMI presenting with no ischemic changes. A comparison between these 4 ECG subgroups in NSTEMI has not been previously performed, especially in contemporary practice. Such a comparison would help better characterize, and give additional insight to, the appropriate treatment of patients with NSTEMI according to the ECG findings. Thus, we performed an analysis of the National Cardiovascular Data Registry Acute Coronary Treatment and Intervention Outcomes Network Registry–Get With The Guidelines (ACTION Registry-GWTG) in patients with NSTEMI according to the presenting ECG findings.
Methods
The National Cardiovascular Data Registry’s ACTION Registry-GWTG is a voluntary registry that receives data on consecutive patients with ST-segment elevation myocardial infarction (STEMI) and NSTEMI that began enrollment on January 1, 2007. Patients were eligible for inclusion in the ACTION Registry-GWTG if they had presented within 24 hours from the onset of ischemic symptoms and received a primary diagnosis of NSTEMI or STEMI. The individual institutional review board of each hospital approved participation in the ACTION Registry–GWTG. Informed consent was not required because the data were abstracted anonymously. De-identified data were extracted from the existing medical records by trained data collectors at each center. The trained data collection personnel performed data collection by individual chart review using a web-based case form. Data quality was maintained using various mechanisms, including point-of-entry and quarterly data quality checks and query reconciliation. Random site audits by trained nurse abstractors were used to maximize the completeness and accuracy of all records submitted. A total of 349,557 patients were identified in the ACTION Registry–GWTG from 664 sites from January 2007 to September 2011. Patients presenting with STEMI (n = 136,940), patients with partial data (n = 20,786), patients arriving to sites without percutaneous coronary intervention capabilities (n = 8,328), patients transferred to other facilities (n = 6,788), and patients with missing ECG findings (n = 1,159) were excluded. Included in the present analysis were 175,556 patients from 485 sites.
The presenting ECG findings were documented within 24 hours of arrival to the reporting hospital. The 4 subgroups constituted the NSTEMI group in the ACTION Registry–GWTG data form: ST-segment depression, T-wave inversions, transient ST-segment elevation, and no ischemic changes. ST-segment depression was defined as new, or presumed new, horizontal or downsloping ST-segment depression ≥0.5 mV in 2 contiguous leads below the isoelectric line on the electrocardiogram. T-wave inversion was defined as new, or presumed new, T-wave inversion of ≥0.1 mV in 2 contiguous leads with a prominent R wave or R/S ratio >1 within the first 24 hours of presentation. Transient ST-segment elevation was defined as new, or presumed new, ST-segment elevation at the J -point in 2 contiguous ECG leads with the cutoff points of ≥0.2 mV in men or ≥0.15 mV in women in leads V 2 to V 3 and/or ≥0.1 mV in other leads, and lasting <20 minutes, within the first 24 hours of presentation. The electrocardiogram was considered to have no ischemic changes if the first electrocardiogram had not revealed ST-segment depression, transient ST-segment elevation, or T-wave inversion. Before the third quarter of 2008, the data collection form allowed simultaneous reporting of simultaneous ECG findings. If a patient had simultaneous ECG findings, grouping was done such that if the electrocardiogram showed transient ST-segment elevation and other findings, it was assigned to the transient ST-segment elevation group. If the electrocardiogram revealed ST-segment depression and T-wave inversion (but not transient ST-segment elevation), it was assigned to the ST-segment depression group. Of the 1,844 patients categorized as having transient ST-segment elevation, 335 also had ST-segment depression, 215 also had T-wave inversion, and 80 also had both ST-segment depression and T-wave inversion. Of the 10,743 patients categorized as having ST-segment depression, 1,924 also had T-wave inversion.
The demographics, co-morbidities, and in-hospital procedures and mortality were compared across the 4 ECG categories. Continuous variables are presented as the median and interquartile range and categorical variables as percentages. All continuous variables were compared using the Kruskal-Wallis tests, and all categorical variables were compared using chi-square tests. To estimate the relative risks of the ECG findings on in-hospital mortality, we used the logistic generalized estimating equation method with the exchangeable working correlation matrix to account for within-hospital clustering, because patients at the same hospital are more likely to have similar outcomes relative to patients at other hospitals (i.e., within-center correlation for outcome). The logistic generalized estimating equation method outputs odds ratios similar to those from ordinary logistic regression analysis, but the variances have been adjusted for the correlation of mortality within the hospital. Using the no ischemic changes group as the reference, odds ratios for mortality were calculated for the other 3 groups. The model included covariates from the validated ACTION Registry-GWTG in-hospital mortality model. Also, to evaluate the relation between peak troponin and in-hospital mortality, we categorized the peak troponin ratio (greatest recorded troponin value within the first 24 hours/local laboratory troponin upper limit of normal value) into quartiles. For the overall cohort and each ECG subgroup, the unadjusted in-hospital mortality in each peak troponin ratio quartile was reported. Furthermore, linear trends of in-hospital mortality across the quartiles and the interaction between the ECG subgroups and the quartiles were tested using logistic regression analysis. Patients who died within 24 hours (n = 1,166) and patients without a peak troponin level recorded (n = 7,472; i.e., only baseline troponin values were recorded; thus, the peak value could not be ascertained) were excluded from the present analysis. All analyses were performed using Statistical Analysis Systems software, version 9.2 (SAS Institute, Cary, NC).
Results
A total of 175,556 patients were entered into the present analysis and grouped according to the presenting ECG findings: ST-segment depression (n = 40,146, 22.9%), T-wave inversion (n = 24,627, 14%), transient ST-segment elevation (n = 5,050, 2.9%), and no ischemic changes (n = 105,733, 60.2%). The baseline characteristics and in-hospital outcomes and treatment of the patients are listed in Tables 1 and 2 .
| Baseline Characteristics | Transient ST-Segment Elevation (n = 5,050) | ST-Segment Depression (n = 40,146) | T-Wave Inversion (n = 24,627) | No Ischemic Changes (n = 105,733) |
|---|---|---|---|---|
| Age (yrs) | 62 (52–73) | 68 (58–78) | 65 (55–76) | 67 (56–78) |
| Male gender | 65.1 | 62.7 | 58.5 | 61.7 |
| Current or recent smoker | 37.5 | 30.0 | 33.7 | 29.2 |
| Hypertension ∗ | 70 | 78.1 | 76.8 | 76.9 |
| Dyslipidemia † | 58.9 | 63.9 | 62.2 | 63.4 |
| ESRD | 1.5 | 3.4 | 3.0 | 3.1 |
| Chronic lung disease | 13.6 | 17.5 | 16.0 | 17.4 |
| Diabetes mellitus | 28.5 | 36.7 | 33.3 | 36.0 |
| Previous MI | 24.0 | 29.0 | 27.7 | 29.4 |
| Previous CHF | 9.2 | 17.2 | 14.6 | 17.7 |
| Previous PCI | 21.0 | 25.1 | 24.2 | 26.5 |
| Previous CABG | 12.3 | 22.0 | 17.2 | 18.6 |
| Atrial fibrillation or atrial flutter | 5.6 | 10.2 | 6.7 | 9.6 |
| Previous stroke | 7.0 | 10.4 | 9.4 | 9.6 |
| PAD | 8.4 | 14.8 | 11.6 | 11.8 |
| Signs of CHF on presentation | 12.6 | 22.7 | 18.2 | 19.4 |
| Cardiac arrest | 2.1 | 2.5 | 0.7 | 1.2 |
| Weight (kg) | 84.1 (71.4–98.7) | 82.1 (69.9–97) | 82 (69.5–97) | 84 (70.5–99) |
| Systolic blood pressure (mm Hg) | 144 (125–164) | 146 (124–168) | 147 (127–167) | 146 (126–166) |
| HR (beats/min) | 80 (68–95) | 86 (72–102) | 80 (69–95) | 83 (70–98) |
| Baseline creatinine (mg/dl) | 1 (0.9–1.2) | 1.1 (0.9–1.4) | 1 (0.9–1.3) | 1.1 (0.9–1.4) |
| Baseline troponin × ULN | 1.8 (0.4–11) | 2.1 (0.5–11.2) | 2.9 (0.7–14.4) | 2.1 (0.5–10.7) |
∗ Hypertension was defined as a history of hypertension diagnosed and treated with medication, diet, and/or exercise; previous documentation of blood pressure >140 mm Hg systolic and/or >90 mm Hg diastolic for patients without diabetes or chronic kidney disease or previous documentation of blood pressure >130 mm Hg systolic or >80 mm Hg diastolic on ≥2 occasions for patients with diabetes or chronic kidney disease; or currently receiving pharmacologic therapy for the treatment of hypertension.
† Dyslipidemia was defined as total cholesterol >200 mg/dl (5.18 mmol/L); low-density lipoprotein ≥130 mg/dl (3.37 mmol/L); or high-density lipoprotein <40 mg/dl (1.04 mmol/L).
| In-Hospital Characteristic | Transient ST-Segment Elevation (n = 5,050) | ST-Segment Depression (n = 40,146) | T-Wave Inversion (n = 24,627) | No Ischemic Changes (n = 105,733) |
|---|---|---|---|---|
| Acute medications | ||||
| Aspirin | 98.1 | 97.2 | 97.5 | 96.4 |
| Clopidogrel | 69.6 | 59.7 | 59.5 | 53.7 |
| β Blocker | 91.6 | 90.0 | 90.0 | 87.0 |
| ACE inhibitor/ARB | 49.8 | 47.6 | 48.8 | 46.6 |
| Statin | 66.1 | 62.4 | 63.9 | 59.0 |
| GP IIb-IIIa inhibitor | 49.6 | 38.6 | 37.4 | 29.0 |
| Anticoagulant | 90.1 | 89.3 | 89.4 | 86.0 |
| Invasive procedures | ||||
| Diagnostic catheterization | 90.4 | 80.5 | 83.4 | 78.6 |
| No. of diseased vessels | ||||
| 1 | 33.5 | 23.1 | 29.0 | 28.5 |
| 2 | 28.8 | 28.8 | 29.2 | 28.7 |
| 3 | 29.6 | 42.7 | 33.2 | 32.5 |
| Left main | 7.6 | 15.3 | 9.3 | 9.7 |
| Proximal LAD | 36.3 | 41.3 | 37.0 | 34.6 |
| PCI | 61.0 | 48.5 | 51.0 | 46.1 |
| CABG | 11.1 | 15.2 | 11.6 | 9.8 |
| In-hospital outcomes | ||||
| Death | 3.1 | 5.7 | 2.7 | 3.5 |
| Cardiogenic shock | 3.3 | 4.3 | 2.1 | 2.3 |
| Suspected bleeding | 3.5 | 5.6 | 4.1 | 3.7 |
| Peak cardiac marker values | ||||
| Peak troponin × ULN | 36.5 (8.9–148) | 33.3 (8.3–142.5) | 24.3 (6.2–95.0) | 22.8 (6.0–91.8) |
| Peak CK-MB | 6.9 (2.5–18.9) | 5.4 (1.9–16.0) | 3.5 (1.4–10.3) | 3.7 (1.5–10.3) |
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