Risk stratification remains central to implement appropriate therapeutic measures for patients with NSTEMI. The ECG provides rapid risk assessment for patients presenting with chest pain that permits their allocation to appropriate management algorithms to improve the outcomes

1. Cardiovascular Section, Department of Medicine, University of Oklahoma
Health Science Center, Oklahoma City, Oklahoma; Duke Clinical Research
Institute, Duke University Medical Center, Durham, North Carolina; and
Department of Medicine, Brigham and Women’s Hospital, Harvard Medical
School, Boston, Massachusetts.
(Am J Cardiol 2014;113:256e261)

2. INTRODUCTION
• Risk stratification remains central to
implement appropriate therapeutic measures
for patients with NSTEMI.
• The ECG provides rapid risk assessment for
patients presenting with chest pain that
permits their allocation to appropriate
management algorithms to improve the
outcomes.

3. • Patients diagnosed with NSTEMI constitute a
heterogeneous group with several variations of 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.

4. • 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.

5. 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.

6. • 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 PCI 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

7. • 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 ≥ 0.5mV 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 ≥ 0.2mV in men or ≥ 0.15mV in women in leads V2 to V3 and/ or
≥ 0.1 mV in other leads, and lasting <20 minutes, within the first 24 hours
of presentation.

8. • The ECG was considered to have no ischemic changes if the first
ECG had not revealed ST-segment depression, transient ST-segment
elevation, or T-wave inversion.
• If a patient had simultaneous ECG findings, grouping was done such
that if the ECG showed transient ST-segment elevation and other
findings, it was assigned to the transient ST-segment elevation
group.
• If the ECG 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.

9. • 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).

10. • 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

11. • 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)

12. RESULTS
• A total of 175,556 patients were entered into the
present analysis from 485 sites from January
2007 to september 2011 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%).

17. Discussion
• The present analysis of the ACTION Registry-GWTG has
provided important insight regarding the clinical
characteristics, in-hospital treatment, and outcomes of
patients presenting with NSTEMI when stratified by the
presenting ECG findings.
• The present study represents the largest and most recent
evaluation of patients with NSTEMI according to the
presenting ECG findings from hospitals throughout the
United States.
• In our study, the most common finding on the presenting
ECG for patients with NSTEMI was no ischemic changes
(60.2%) followed by ST-segment depression (22.9%), T-
wave inversion (14%), and transient ST-segment elevation
(2.9%).

18. • Of the 4 subgroups analyzed, patients with ST-segment
depression found on the ECG were the oldest, had the
highest incidence of co-morbidities, and the highest in-
hospital mortality.
• High-risk angiographic findings, including left main,
proximal left anterior descending, and 3-vessel CAD also
had the highest prevalence in this group. Also, these
patients underwent coronary artery bypass grafting most
often.
• These findings complement previous data showing that
patients presenting with ST-segment depression constitute
the highest risk group among patients with NSTEMI.
• Savonitto et al reported a higher short-term incidence of
death or MI in patients with ACS presenting with ST-
segment depression compared with those presenting with
T-wave inversion.

19. • In the present analysis, patients with ST-segment
depression had remarkably higher in-hospital mortality
compared with those with no ischemic changes. Patients
presenting with ST-segment depression have also been
shown to have worse cardiovascular outcomes in long-term
analyses.
• Despite being a high-risk population, these patients were
not the group that underwent cardiac catheterization most
frequently.
• These findings corroborate data from previous analyses of
patients with NSTEMI showing an inverse relation with the
risk status of the patient and the rate of coronary
angiography, despite data showing that an invasive strategy
is of benefit.
• The current practice patterns in this high-risk group
probably represent an opportunity for improvement.

20. • Transient ST-segment elevation was the least frequent
finding on the ECG (2.9%), and these patients constituted a
distinct group of younger patients with fewer co-
morbidities.
• Additionally, these patients were treated more aggressively,
with a higher proportion undergoing coronary angiography
and revascularization.
• In everyday practice, these patients pose a therapeutic
challenge, because the optimal management has been less
well-defined and might be judged as high-risk acute
coronary syndrome.
• It is likely that this ECG finding has been perceived to be a
high-risk feature similar to STEMI and thus leading to a
more aggressive therapeutic approach in this patient
subgroup.

21. • In their prospective observational study, Meisel et al reported an
incidence of such patients of 15.1%, with better clinical outcomes
when these patients underwent reperfusion therapy compared
with patients presenting with persistent STEMI.
• Similar prognostic implications were observed in the present
analysis, although with a much lower prevalence of patients with
transient ST-segment elevation.
• In their comparison of patients with ACS with transient ST-segment
depression and those with transient ST-segment elevation who
underwent continuous ECG monitoring, Drew et al reported that
transient ST-segment elevation occurred almost as frequently as
transient ST-segment depression.
• They also found SVD to be significantly (p = 0.0007) more frequent
in the transient ST-segment elevation group (46%) compared with
the transient ST-segment depression group (22%).

22. • Meisel et al found a frequency of Single Vessel CAD of 60% in patients with
transient ST-segment elevation.
• Our study revealed a higher frequency of Single Vessel CAD in patients
with transient ST-segment elevation (33.4%) compared with the other ECG
subgroups.
• The 2 other groups, the T-wave inversion group and no ischemic findings
group, seemed to have an intermediate burden of co-morbidities, in-
hospital cardiovascular events, and angiographic findings.
• Our study showed that those with no ischemic changes constituted most
(60.2%) of the patients with NSTEMI.
• Also, a lower proportion of those with no ischemic changes underwent
diagnostic coronary angiography within 24 hours compared with the other
groups. Similarly, a lower proportion of these patients underwent
percutaneous coronary intervention or coronary artery bypass grafting
compared with the other groups.

23. • Although the ACC /AHA guidelines for the treatment of patients with
NSTEMI have suggested that the signs and symptoms of ACS in patients
presenting with ST-segment deviations and/or T-wave inversion
(combined with other clinical and objective findings) have a greater
likelihood of being secondary to CAD and a lower likelihood for patients
presenting with no ischemic changes, our study showed that compared
with no ischemic changes.
• Patients with NSTEMI presenting with T-wave inversion had the lowest
adjusted in-hospital mortality using the ACTION Registry-GWTG in-hospital
mortality model (odds ratio 0.91, 95% confidence interval 0.83 to 0.99; p ¼
0.026)
• The prognostic significance of troponin in patients with acute coronary
syndrome is well known, and a recent analysis of the ACTION Registry-
GWTG has established that the peak troponin level possesses independent
prognostic implications.
• When analyzed in the present study, the quartile of peak troponin levels
correlated well with overall mortality and with mortality across all 4 ECG
subgroups.

24. • The present analysis represents observational
data that in themselves have inherent limitations.
• First, the ECG results reported by the sites were
not confirmed by a core laboratory.
• However, these results reflect routine practice in
which ECG are interpreted by the treating
physician without confirmation by a core
laboratory.
• Other limitations include the lack of details on
the findings of the ECGs performed after the
initial ECG limited details on the angiographic
findings, and limited details on nonfatal ischemic
outcomes occurring during the hospitalization.

25. 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.