Context Observational studies of acute myocardial perfusion imaging in emergency
department (ED) patients with chest pain have suggested high sensitivity and
negative predictive value for acute cardiac ischemia, but use of this method
has not been prospectively tested.
Objective To assess whether incorporating acute resting perfusion imaging into
an ED evaluation strategy for patients with suspected acute ischemia but no
initial electrocardiogram (ECG) changes diagnostic of acute ischemia improves
clinical decision making for initial ED triage.
Design, Setting, and Patients Prospective, randomized controlled trial conducted at 7 academic medical
centers and community hospitals between July 1997 and May 1999 among 2475
adult ED patients with chest pain or other symptoms suggestive of acute cardiac
ischemia and with normal or nondiagnostic initial ECG results.
Intervention Patients were randomly assigned to receive either the usual ED evaluation
strategy (n = 1260) or the usual strategy supplemented with results from acute
resting myocardial perfusion imaging using single-photon emission computed
tomography with injection of 20 to 30 mCi of Tc-99m sestamibi (n = 1215),
interpreted in real time by local staff physicians and with results provided
to the ED physician for incorporation into clinical decision making.
Main Outcome Measure Appropriateness of triage decision either to admit to hospital/observation
or to discharge directly home from the ED.
Results Among patients with acute cardiac ischemia (ie, acute myocardial infarction
[MI] or unstable angina; n = 329), there were no differences in ED triage
decisions between those receiving standard evaluation and those whose evaluation
was supplemented by a sestamibi scan. Among patients with acute MI (n = 56),
97% vs 96% were hospitalized (relative risk [RR], 1.00; 95% confidence interval
[CI], 0.89-1.12), and among those with unstable angina (n = 273), 83% vs 81%
were hospitalized (RR, 0.98; 95% CI, 0.87-1.10). However, among patients without
acute cardiac ischemia (n = 2146), hospitalization was 52% with usual care
vs 42% with sestamibi imaging (RR, 0.84; 95% CI, 0.77-0.92).
Conclusions Sestamibi perfusion imaging improves ED triage decision making for patients
with symptoms suggestive of acute cardiac ischemia without obvious abnormalities
on initial ECG. In this study, unnecessary hospitalizations were reduced among
patients without acute ischemia, without reducing appropriate admission for
patients with acute ischemia.
Each year in the United States, more than 6 million patients present
to emergency departments (EDs) with chest pain or other symptoms suggestive
of acute cardiac ischemia (ie, either acute myocardial infarction [MI] or
unstable angina pectoris).1 The majority of
these patients are admitted to the hospital or to an observation unit, because
the initial clinical examination, electrocardiogram (ECG) results, and initial
cardiac enzyme levels are insufficient to eliminate the possibility of acute
infarction or unstable angina.1-4 Nevertheless,
most patients without obvious ischemic ECG changes who are hospitalized or
observed in special units ultimately prove not to have acute ischemia.2,4-6 Moreover,
among patients discharged directly from the ED, an important minority actually
have acute ischemia, leading to unfavorable outcomes.6-8
Since the predominant pathophysiology of acute cardiac ischemia is a
reduction in coronary blood flow, myocardial perfusion imaging in the ED setting
is conceptually attractive. The feasibility of imaging in this setting was
established over 20 years ago using thallium 201,9 but
its use in the real-time ED setting was impractical. The logistics of the
use of newer technetium Tc 99m–based perfusion agents are more suitable
for use in the ED.10 The technetium Tc 99m
label is associated with generally higher-quality images, and there is minimal
redistribution after initial injection. Thus, imaging may occur at a later
time point after injection, with the resulting image reflecting myocardial
blood flow at the time of injection. Several observational studies have demonstrated
a very high negative predictive value of acute perfusion imaging using technetium
Tc 99m–labeled isotopes in confirming the absence of acute infarction
or subsequent cardiac events.11-15 No
previous study has prospectively tested the impact of an imaging vs a nonimaging
strategy.16 Therefore, we conducted a randomized
trial to determine whether incorporating myocardial perfusion imaging into
an ED evaluation protocol for patients with symptoms suggestive of acute cardiac
ischemia would improve clinical decision making.
This trial was designed to compare the clinical effectiveness of 2 ED
evaluation strategies for patients suspected of having acute cardiac ischemia
but without diagnostic initial ECG changes of acute ischemia: the usual care
strategy (the standard clinical evaluation strategy used in each hospital's
ED), and the scan strategy (the same standard clinical evaluation strategy
but also incorporating results derived from immediate resting single-photon
emission computed tomography [SPECT] myocardial perfusion imaging with technetium
Tc 99m sestamibi). The study protocol was approved by the institutional review
boards of all participating centers.
Between July 1997 and May 1999, all potentially eligible patients (defined
as any initial clinical suspicion of acute ischemia) were screened at the
EDs of 7 diverse hospitals during daytime hours. Eligible ED patients who
consented were immediately randomized, using simple unrestricted randomization,
by means of a central computerized telephone randomization system. Screened
patients who were ineligible, and eligible patients who did not consent to
participate, were entered anonymously into a registry for comparison with
For patients randomized to the scan strategy, injection of 20 to 30
mCi of technetium Tc 99m sestamibi (DuPont Pharmaceuticals, Wilmington, Del)
was performed in the ED, generally by a nuclear medicine technologist, as
soon as possible after randomization. SPECT imaging was performed beginning
30 to 60 minutes later in the nuclear cardiology laboratory, with images acquired
in the gated SPECT mode for simultaneous evaluation of resting perfusion and
systolic left ventricular function.17 The images
were interpreted on site in real time by the appropriate staff physicians
at each site, with results reported immediately to the responsible physician.
Based on all available results, a triage decision was made by the physician
to hospitalize the patient (to an observation unit, ward, telemetry unit,
or cardiac care unit [CCU]) or to discharge the patient directly home. The
decision-making physician was not directed by protocol to admit or discharge
the patient based on certain scan results; rather, imaging results were given
to the physicians who then incorporated the data into the information base
they used to make a clinical decision regarding their patient's disposition.
Included were all patients 30 years of age or older (unless there was
a history of recent cocaine use, in which case they were required to be 18
years or older) who had chest pain or any other symptoms suggestive of acute
cardiac ischemia (eg, shortness of breath) and, according to the evaluating
ED physician, an ECG either normal or nondiagnostic for acute ischemia or
infarction. To be included, patients' symptoms were required to be ongoing
or to have resolved no longer than 3 hours prior to consent. Excluded were
patients with a history of MI, since such patients will most often have an
abnormal resting perfusion pattern. Written informed consent was obtained
from all patients.
Acute Sestamibi Perfusion Imaging
Gated SPECT images were obtained using acquisition and processing parameters
standard at each study site. Images were classified as normal (no obvious
perfusion abnormalities with normal regional and global ventricular function),
abnormal (definite perfusion abnormality and/or regional or global function),
or equivocal (images that did not clearly fit into the other categories).
Physicians were advised to consider equivocal results as mildly abnormal,
based on a previous study showing that patients with equivocal scans in this
setting have a slightly higher event rate than patients with normal scans.12
For characterization of final diagnosis (acute cardiac ischemia or not),
all patients had follow-up ECGs, measurement of cardiac enzyme levels, and
protocol-specified follow-up stress testing with perfusion or echocardiographic
imaging. For patients initially admitted, this was usually accomplished during
the observation or hospitalization period. For all ED patients initially discharged
directly home, a return visit to the study site 24 to 36 hours later was made
for follow-up biomarker measurements, ECGs, and stress testing. The confirmed
diagnosis was assigned by the site principal investigator based on all available
data, including enzymatic, ECG, and stress testing data, as well as cardiac
catheterization data when available; principal investigators were blinded
to the randomization assignment and to initial scan result for patients randomized
to the scan strategy. For all patients whose final diagnosis was MI, for the
majority of patients whose final diagnosis was unstable angina, and for an
equal and randomly chosen group of patients whose final diagnosis was not
acute ischemia, medical records were reviewed at the coordinating center by
an independent investigator who was blinded to the original confirmed diagnosis
assignment. This independent assignment of confirmed diagnosis was concordant
in 98% of cases. Patients were contacted at 30 days following initial ED presentation
to determine vital status and the occurrence of other cardiac events and procedures;
follow-up was 99% complete.
The primary end point of the trial was the appropriateness of initial
ED triage decision, assuming that patients with acute infarction or unstable
angina should have been hospitalized (to a CCU, telemetry unit, ward, or chest
pain unit), and that patients without acute ischemia (ie, those with negative
serial enzyme test results, no evolutionary ECG changes on serial testing,
and a negative follow-up stress test result) ideally should not have been
hospitalized or admitted for observation.
The study was designed to have 80% power to detect a reduction (10%
to 3%) in ED discharges to home for patients ultimately diagnosed with acute
cardiac ischemia, and to have 80% power to detect a reduction in unnecessary
admissions for patients without acute ischemia from a 45% unnecessary admission
rate to 39%, ie, an absolute risk reduction of 6% and a relative risk reduction
of 15%. A data and safety monitoring board reviewed results at an interim
time point, to ensure that triage was not unfavorably affected by the intervention.
Patient characteristics were compared using the t test for continuous variables, and the Pearson χ2 test
or Fisher exact test for dichotomous variables. P<.05
was used to determine statistical significance. Trial data were analyzed based
on an intent-to-treat strategy. The effect of imaging on ED triage was analyzed
by computing the relative risk (RR) and the 95% confidence intervals (CIs)
for hospitalization vs discharge to home, using the Cochran-Mantel-Haenszel
method to adjust for hospital differences. Odds ratios for the effect of imaging
on admission were computed for different subgroups using logistic regression
analyses, including terms for the treatment effect, subgroup effect, the interaction
between treatment and subgroup, and terms for hospital effects to adjust for
possible hospital differences for factors that were not directly hospital
related (ie, hospital volume). Possible interactions between patient and site
subgroups and the effect of the scan strategy on admission rate were analyzed
using Wald χ2 testing from results of logistic regression analysis.
With the exception of the site stratifications, all P values
were adjusted for site effects. To facilitate interpretation of these results,
the adjusted odds ratios from these analyses were converted to RRs using the
method of Zhang and Yu,18 in which the strata-specific
admission rates for the nonacute cardiac ischemia usual care groups were used
as the control prevalence. All analyses were performed using SAS v8.0 (SAS
Institute Inc, Cary, NC).
During 20 months of recruitment, 7955 patients were screened for inclusion
(Figure 1), on the basis of presenting
symptoms suspicious for acute ischemia. Of these, 2908 consecutive patients
met all study eligibility criteria and were eligible for consent, of whom
2475 patients (85%) consented to participate and were randomized to 1 of the
2 ED evaluation strategies. Of the 5047 protocol- or consent-ineligible patients,
exclusion was most often because of either an ECG diagnostic for acute ischemia
or infarction (34%) or a history of prior infarction (27%). Other less common
reasons for ineligibility included: resolution of symptoms more than 3 hours
prior to presentation (10%), patient became unstable in the ED (4%), evaluating
physician or primary physician refused enrollment (3%), patient previously
enrolled in the study (2%), and patient unable to sign informed consent appropriately
(2%). Among eligible patients, those who were protocol-eligible but did not
sign informed consent were older than those consenting (mean [SD] age, 57
 vs 53  years; P = .001) and were slightly
more often women (55% vs 49%; P = .03).
Among randomized patients, 1260 were randomized to usual care and 1215
were randomized to the strategy incorporating sestamibi perfusion imaging.
Baseline characteristics for the groups are shown in Table 1. Other than the slight difference in proportion of women
between groups, there were no significant clinical or demographic differences
Overall confirmed diagnoses of acute cardiac ischemia were made in 13%
of patients: 2% had acute MI, while 11% had unstable angina. Diagnoses other
than acute cardiac ischemia were confirmed for 87% overall of patients in
each group (Table 1).
Patients randomized to the scan strategy had a lower rate of hospital
admission than patients randomized to usual care (47.5% vs 56.1%, respectively;
RR, 0.87; 95% CI, 0.81-0.93; P<.001), and a higher
rate of direct discharge home from the ED (Table 2). The increase in direct discharges home from the ED in
the scan strategy group was predominantly due to a reduction in admission
to a telemetry unit or ward, or to a chest pain unit. Despite fewer admissions
in the group randomized to the imaging strategy, there were no outcome differences
30 days after ED presentation between patients receiving usual ED care and
those receiving sestamibi imaging (Table
3). Thus, similar outcomes were observed with fewer hospital admissions
in the group randomized to the imaging strategy.
The median time from ED presentation to admission or discharge home
for patients in the usual care group was 4.7 hours (interquartile range, 3.4-6.4
hours), and for those randomized to the scan strategy, 5.3 hours (interquartile
range, 4.0-7.0 hours) (P<.001).
Impact on Triage for Patients With Acute Cardiac Ischemia
The impact of ED sestamibi imaging on hospitalization for patients with
acute cardiac ischemia is shown in Table
4. Among all patients with acute ischemia, there was no difference
in the appropriate hospitalization rate of approximately 85%. For patients
with acute infarction, there was also no difference in the hospitalization
rate, appropriately high at 96% overall: one such patient in each group was
inappropriately sent home from the ED. Follow-up testing showed the inappropriately
discharged patient in the usual care group to have an inferior wall infarction
with an inferior wall motion abnormality. The inappropriately discharged patient
in the sestamibi group had a normal sestamibi scan in the ED, as well as normal
results of echocardiography and follow-up stress perfusion testing, but had
positive enzyme test results on follow-up.
Among those with unstable angina, there also was no difference in the
appropriate admission rate between the 2 groups, nor were there differences
in specific in-hospital locations for admitted ED patients (Table 4).
Impact on Triage for Patients Without Acute Cardiac Ischemia
Among the 2146 patients whose final confirmed diagnosis was not acute
cardiac ischemia, 52% of patients randomized to usual care were hospitalized,
who, retrospectively, could be classified as unnecessary admissions (Table 5). In the sestamibi scan group,
this unnecessary admission rate was reduced to 42%, a 10% absolute reduction,
and a 20% relative change (RR, 0.84, 95% CI, 0.77-0.92, P<.001). Results were similar when the location of admission triage
from the ED to hospital was subcategorized as CCU, telemetry ward, or chest
The reduction in hospitalization of patients without acute ischemia
who had sestamibi scans occurred at 6 of the 7 study hospitals, the exception
being 1 site with a very low baseline admission rate that followed a prolonged
As shown in Table 6, perfusion
imaging increased direct ED discharges to home in patients without acute ischemia
in both men and women, in both younger and older patients, and in both those
with and without risk factors for coronary disease. The effect of incorporating
perfusion imaging into the evaluation strategy on increasing direct ED discharges
to home was similar at sites with an established chest pain center protocol
compared with those sites without such a protocol, and was also similar in
patients whose initial evaluation included a troponin I value compared with
those without an initial value. There were trends toward greater effect of
imaging for patients without a history of coronary disease and in those with
chest pain as their primary presenting symptom.
Relation of Sestamibi Imaging Results to Clinical Outcomes
Among the 1215 patients randomized to the scan strategy, the imaging
results were related to the risk of an adverse outcome. Among patients with
normal, equivocal, or abnormal scan results, the risk of acute MI was 0.6%,
0.8%, and 10.3%, respectively (RR for equivocal or abnormal vs normal scan,
6.61; 95% CI, 2.47-17.67; P<.001). A similar relationship
was observed between scan findings and any cardiovascular event at 30 days,
defined as acute MI, death, or revascularization. Among patients with normal,
equivocal, and abnormal scan results, the risk of a cardiac event defined
as such was 3.0%, 6.1%, and 20.5%, respectively (RR for equivocal or abnormal
vs normal scan, 3.83; 95% CI, 2.36-6.21; P<.001).
This trial indicates that incorporating results from acute resting perfusion
imaging with technetium Tc 99m sestamibi into an ED evaluation strategy for
patients with suspected acute cardiac ischemia improves triage decision making.
Specifically, unnecessary hospitalization of patients without acute cardiac
ischemia was reduced, without affecting appropriate hospitalization of patients
with acute ischemia. Accordingly, the reduction in hospital admission related
to the use of perfusion imaging was associated with unchanged 30-day clinical
Although several observational studies11-15,19 supported
the incorporation of perfusion imaging into an ED evaluation strategy, these
studies examined the prognostic value of imaging results but did not examine
the impact of imaging on ED triage decision making. Thus, this "effectiveness"
trial was designed to determine how imaging would affect ED triage decisions
when incorporated into usual care at a diverse group of hospitals, including
academic medical centers, urban public teaching hospitals, and moderate to
large community hospitals. The inclusion criteria were designed to capture
all low- to moderate-risk patients with possible acute cardiac ischemia in
whom the triage decision regarding admission or direct discharge to home is
often difficult.1-3 At
each site, the SPECT perfusion images were read on site and in real time by
the usual interpreting physician.
The rates of acute infarction (2%) and unstable angina (12%) among study
patients are lower than those observed in previous studies evaluating imaging
or other technologies in this setting.12-15 This
is likely a result of the broader inclusion criteria of this trial, allowing
inclusion of patients with any symptoms suggestive of acute ischemia. Other
studies with higher proportions of patients who prove to have acute infarction
have used narrower inclusion criteria, studying only patients with angina-like
chest pain and nondiagnostic ECGs,12 or patients
for whom the decision to hospitalize had already been made.15 The
inclusion criteria in this trial were designed so that trial results would
be applicable to the broad array of ED patients presenting with possible acute
Few ED diagnostic technologies or evaluation strategies for acute ischemia
have been rigorously tested in controlled clinical trials.1 Predictive
instruments for acute cardiac ischemia or infarction have improved triage
effectiveness in some trials20-22 but
not others.23 Controlled trials have also addressed
the use of an "accelerated diagnostic protocol" or a chest pain evaluation
unit as a means to create uniform, efficient evaluations for such patients,
and have shown shorter lengths of stay, fewer standard hospital admissions,
and lower resource utilization with similar outcomes.24,25
In these studies of accelerated protocols or observation units, the
majority of patients were ultimately diagnosed as not having acute ischemia.24,25 The results of the present trial
suggest that incorporating perfusion imaging into such ED evaluation strategies
should afford the possibility of determining the presence or absence of acute
ischemia even earlier in the ED evaluation process, facilitating an earlier
triage decision and diminishing the need for observation in a chest pain unit
or a similar pathway. In this regard, Kontos et al14 reported
that resting perfusion imaging with sestamibi was 92% sensitive for detecting
acute infarction in studies performed early in the ED, whereas initial measurement
of troponin I levels in the ED had only 39% sensitivity. In that study, the
sensitivity of troponin I levels became similar to that of sestamibi imaging
within the first 24 hours,14,26 consistent
with its known release kinetics after myocardial injury.27 Others
reported that optimal sensitivity and prognostic value of levels of troponins
T or I are not achieved until 18 hours after symptom onset.28,29
The finding that 42% of patients ultimately found to be without acute
ischemia in the scan group were admitted to the hospital suggests that even
further improvement in ED triage decision-making is possible. Such improvement
may result from further confidence in imaging results with increasing familiarity,
or may require a combination of imaging results with other probability estimates.
Future studies should address which populations benefit most from incorporating
imaging into the evaluation process, and whether there is a threshold of probability,
as might be provided by a predictive instrument, above or below which imaging
or any other technology is not needed. Patients who had a perfusion image
performed but were still admitted may also have had false-positive images,
potentially resulting from diaphragmatic or breast attenuation, or motion
Whether the data from this trial can be applied to smaller or more rural
hospitals is not clear, as such institutions were not represented in this
trial. However, the trial results are potentially generalizable to hospitals
with on-site imaging facilities, since hospitals with little or no experience
in using perfusion imaging in the ED demonstrated a similarly favorable triage
effect as those with some experience (Table
5). The safety of increasing direct discharges to home from the
ED by incorporation of a resting perfusion imaging strategy as seen in the
current study presumes incorporation of a follow-up evaluation after ED discharge.
In the current study, follow-up stress testing was directed per protocol.
This study was conducted during expanded daytime hours, and thus whether the
data generalize to use during nighttime hours cannot be determined with certainty.
In summary, incorporating acute resting sestamibi myocardial perfusion
imaging into an ED evaluation strategy for patients with symptoms suggestive
of acute cardiac ischemia reduced unnecessary hospitalizations among patients
without acute ischemia (ie, improved the specificity of the admitting decision),
without reducing appropriate admission of patients with acute ischemia (maintained
sensitivity), thereby improving the overall clinical effectiveness of the
ED triage process.
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