The use of EKG to evaluate low-risk chest pain in the emergency department
Alexander Leung1,3, Gaurav Puri, M.D.2, Vincent Ho, M.D.2, Steven Rhee, M.D.2
1 – MD Candidate 2015, Faculty of Medicine, University of Toronto, Toronto, Ontario,
Canada, M5S 1A8
2 – Department of Emergency Medicine, St. Joseph’s Health Center, Toronto, Ontario,
Canada, M6R 1B5
3 – To whom correspondence may be addressed. Email:
alexander.leung@mail.utoronto.ca
1
Background: Chest pain is a common chief complaint to emergency departments (ED)
across Canada. Most often these patients have low-risk chest pain where incidence of
life-threatening conditions such as acute coronary syndrome (ACS) is minimal. With
that, the development of a strategy to assess low-risk chest pain could improve and
accelerate patient care.
Objective: To determine whether findings of a normal electrocardiogram (EKG) can rule
out ACS in young patients presenting with chest pain classified as low-risk in the ED.
Methods: A retrospective chart review of patients presenting to the ED with low-risk
chest pain defined as patients between the ages between 16 and 40 in a medical center
during a 1-year period from April 2011 to March 2012.
Results: Medical charts from a total of 1019 patients between the ages of 16 and 40
with a chief complaint of chest pain were identified. The EKG had sensitivity and
specificity values of 71% and 65% respectively. The positive predictive value and
negative predictive value were 14% and 97% respectively. Post-hoc subgroup analysis
to assess EKG findings and ACS by age groups 16-20, 21-30 and 31-40 years of age
was performed, and the sensitivities and specificities were calculated. For the 16-20
years of age group, the sensitivity and specificity were 80% and 77% respectively; for
the 21-30 years of age group, the sensitivity and specificity were 50% and 64%; for the
31-40 years of age group, the sensitivity and specificity were 77% and 64%.
2
Conclusion: The use of EKG alone to exclude ACS is not recommended in patients
presenting with low-risk chest pain.
3
Annually, approximately 500 000 Canadians present to emergency departments
(ED) with chest pain, a symptom that raises concern of acute coronary syndrome
(ACS). The diagnoses which ACS encompasses include unstable angina, ST-segment
elevation myocardial infarction and non-ST segment elevation myocardial infarction.1
These patients undergo a lengthy assessment in the ED or as hospital inpatients to rule
out an acute myocardial infarction (AMI). This often involves testing two samples of
blood collected at least 6 hours apart for biomarkers of myocardial necrosis, most
frequently troponin.2 Of these patients, it is estimated that 20% are ultimately admitted
with a diagnosis of acute coronary syndrome.1,3 Therefore, the majority of patients
presenting with chest pain complaints do not have ACS.4,5 Moreover, the evaluation of
patients may involve diagnostic tests which in retrospect may have been misleading,
thereby contributing to unnecessary inpatient hospitalizations and prolonged treatment.6
Diagnostic evaluation of chest pain in the ED remains a constant challenge to
physicians. In response, extensive research has been focused on developing strategies
to risk-stratify chest pain patients with the likelihood for ACS. However, the majority of
these studies often involve patient populations above the age of 40.7-11 Consequently,
evidence-based strategies for the management of chest pain in younger patients in the
ED is limited. Particular interest in this specific patient population is warranted,
considering the increased potential years of life lost. 4% to 8% of patients diagnosed
with ACS and 14% of chest pain visits to the ED are from patients younger than 40
years of age.10,12 In general, patients in this age group present with chest pain where
the incidence of life-threatening ACS is minimal. Furthermore, ACSs in younger patients
4
have different clinical presentations, receive earlier treatment and have a more
favorable outcome relative to older patients.12 As such, for the purposes of this study, an
age under 40 would be used as an objective and efficient measure to risk-stratify
patients presenting with chest-pain into a ‘low-risk chest pain’ category where risk of
ACS is low. This method could be rapidly applied to accelerate patient care, especially
in the environment of the ED. Therefore, the aim is to develop a strategy to rapidly
identify ACS in patients with low-risk chest pain.6
Previous studies have shown that patients presenting to the ED with chest pain
and have normal electrocardiogram (EKG) findings have lower rates of cardiac
complications and mortality.13 However, in a general ED setting, Turnipseed et al.14
have shown that normal EKG findings do not exclude ACS in patients with chest pain.
The study population was predominantly over 40 years of age.14 By narrowing the
patient population, we hypothesized that patients presenting to the ED with low-risk
chest pain who have a normal EKG finding would have a low rate of ACS diagnosis.
Therefore, a normal EKG finding could be used as a test to exclude the diagnosis of
ACS in a low-risk chest pain patient presenting to the ED.
Methods
Study Design
5
We conducted a retrospective chart review on patients at St. Joseph’s Health Center
(SJHC). Inclusion criteria for this study were patients admitted to the ED with a chief
complaint of chest pain between the ages of 16 and 40, irrespective of previous medical
treatments or history, within a 1-year period from 1 April 2011 to 31 March 2012. The
initial ED EKG interpretation by the attending physician and the first troponin value were
collected. The EKG findings were then classified under “normal” or “abnormal”
categories using pre-defined criteria, and troponin results were used to determine ACS
diagnosis. Patients without an EKG or troponin test results were excluded from the
study. There was no re-interpretation of any clinical findings. The study was approved
by the SJHC research ethics board.
Study Setting and Population
All patients charts were reviewed at SJHC, a community hospital setting with an annual
visit volume of approximately 100 000, and a catchment population over 500 000. It
should be noted that patients with significant ST-segment elevation on the EKG during
ambulance transportation were automatically re-directed to a designated regional
hospital with cardiovascular intervention labs. Since this population of patients
bypassed the hospital, they were excluded from the study.
Study Protocol
Patient charts were screened for inclusion criteria followed by a review for exclusion
criteria by the study co-investigators. For the study, a chief complaint of chest pain was
ascertained by first identifying the presenting complaint on the nursing triage note. This
finding was compared to the chief complaint on the emergency registration outpatient
6
record, as identified by the attending physician. If the two records were consistent, the
patient was classified as having a chief complaint of chest pain. Conversely, if there was
a discrepancy, the chief complaint recorded on the outpatient record was used for data
collection. The initial EKG findings on presentation to ED were documented into the ED
record by the ED physician. From there, two patient groups were generated: patients
with “normal” EKG findings and patients with “abnormal” EKG findings. The other
clinical data recorded were age, troponin I levels, cardiac stress testing results and
discharge diagnosis.
Criteria for “normal” EKG findings included: (1) heart rate of 55-105 beats/min
and normal sinus rhythm or sinus arrhythmia, (2) normal sinus rhythm with left axis
deviation up to -30°, (3) sinus rhythm with normal variant RSR’ patterns in leads V1 or
V2, (4) normal QRS interval and ST segment, and (5) normal T-wave morphology. All
other patterns were excluded and categorized as “abnormal,” which included any of:
potentially pathologic Q waves, ST-T wave abnormalities, premature ventricular
contractions, premature atrial contractions, ectopic and pacemaker rhythms, abnormal
changes in voltage, and heart block. These criteria are consistent with the EKG criteria
used by Turnipseed et al.14 For the study, only the original EKG interpretation by the ED
physician was used. Likewise, there was no reinterpretation of clinical findings. With the
collected data, an outcome of ACS was defined by at least one of the following findings:
(1) elevation in troponin I, (2) ST-segment elevation consistent with ST-segment
elevation myocardial infarction, or (3) a positive result in cardiac stress testing. For the
troponin I tests (Cardiac Troponin I by Siemens Inc., NY, USA), a value ≥0.07 μg/L (99th
percentile of normals with <10% variance) was used to define myocardial injury. Cardiac
7
stress testing was defined as a modified Bruce exercise treadmill test (Quinton Q-Stress
by Cardiac Science, WI, USA) ordered directly from the ED.
Data Analysis
Out of the study population, the total numbers for normal and abnormal EKG findings,
and positive and negative ACS diagnostic results were collected and cross-tabulated.
These cross-tabulations were used to calculate sensitivity, specificity, positive predictive
value (PPV) and negative predictive value (NPV). All values were multiplied by 100 to
yield a percentage. For patients stratified by age, comparisons were made for
sensitivity, specificity, PPV and NPV with the use of the χ2 test for associations.
Microsoft Excel 2007 was used for analysis (Microsoft Corp., WA, USA).
Results
Records of 1019 patients, aged 16 to 40 years old, who met the inclusion criteria
and were admitted to the ED during the study period (1 April 2011 to 31 March 2012) for
chest pain at SJHC were selected. From those patients, 153 were excluded according
to the exclusion criteria, resulting in 866 study participants. The mean and median ages
for the sample population were 30 and 31 respectively. There were 79 persons within
the ages of 16 to 20, 324 persons within the ages of 21 to 30, and 463 persons within
the ages of 31 to 40. Patient demographics are summarized in Table 1.
In the total study group, 541 (62.5%) patients had a “normal” EKG finding and 62
(7.16%) patients had a positive finding diagnostic of ACS. As seen in table 2, which
8
describes the tests performed to diagnose ACS, patients with ACS either had a positive
troponin I value or EKG finding of ST-elevation myocardial infarction. The frequency of
ACS in the study population was 7.2%. Of the people with ACS, 18 persons (29.0%)
had a diagnosis of ACS with a “normal” initial EKG and a positive troponin I result. The
remaining 44 people with ACS had an “abnormal” EKG, of whom 7 met criteria for STsegment elevation MI and were corroborated by positive troponin I values. Finally, 281
(32.5%) subjects had “abnormal” EKG findings and were found not to have ACS
through troponin I testing (Table 3).
Therefore, the EKG had sensitivity and specificity values of 71.0% and 65.0%
respectively. The PPV and NPV were 13.5% and 96.7% respectively (Table 3). Posthoc analysis by dividing the total patient population into subgroups defined by the ages
16-20, 21-30 and 31-40 years was conducted. The statistical measures were calculated
and summarized in Table 4. The EKG sensitivities were: 16-20 year olds, 80.0% (95%
confidence interval [CI], 16.4% to 21.6%); 21-30 year olds, 50.0% (95% CI, 46.7% to
53.3%), 31-40 year olds, 76.7% (95% CI, 73.9% to 79.6%). These differences were not
statistically significant. Similarly, there were no significant differences in the specificity,
PPV and NPV of the EKGs between the groups.
Table 1: Demographics for study population (n =
866)
Age
Mean (and SD), years
Median, years
30 (6.7)
31
Gender
Male
Female
347
519
9
Subgroups
No. ages 16-20 years
No. ages 21-30 years
No. ages 31-40 years
79
324
463
Table 2: Diagnosis of ACS by study criteria (n = 62)
Positive troponin I
Positive EKG finding of ST-elevation
myocardial infarction (STEMI)
Positive stress test
55
7
0
Note: ACS = acute coronary syndrome, EKG =
electrocardiogram, STEMI = ST-elevation myocardial infarction
Table 3: Overall accuracy of ACS diagnosis with “normal” EKG findings
Diagnosis; no. of patients
EKG Finding
ACS
No ACS
Total no. of
patients
Abnormal
Normal
44
18
281
523
325
541
Total no. of patients
62
804
866
Sensitivity 71.0% (44/62), 95% confidence interval (CI) 67.9%-74.0%
Specificity 65.0% (523/804), 95% CI 61.9%-68.2%
Positive predictive value 13.5% (44/325), 95% CI 11.3%-15.8%
Negative predictive value 96.7% (523/541), 95% CI 95.4%-97.9%
Table 4: Subgroup Analysis; Sensitivity, specificity, PPV and NPV of the EKG in
detection of ACS by age group
Age range of subgroups (years)
Parameters
16-20
21-30
31-40
Sensitivity
80.0 (4/5), 77.3-82.7
50.0 (7/14), 46.7-53.3
76.7 (33/43), 73.9-79.6
Specificity
77.0 (57/74), 74.2-79.8
63.9 (198/310), 60.7-67.1
63.8 (268/420), 60.6-67.0
PPV
19.0 (4/21), 16.4-21.6
5.9 (7/119), 4.3-7.4
63.8 (268/420), 60.6-67.0
NPV
98.3 (57/58), 97.4-99.1
96.6 (198/205), 95.4-97.8
96.4 (268/278), 95.2-97.6
10
Data expressed as a percentage (95% CI), calculations provided in brackets. None of the differences
were statistically significant (χ2 test for association, P<0.05)
Discussion
The use of EKG to diagnose ACS in patients with low-risk chest pain is a practical tool
within the ED, an environment where providing efficient care with limited resources and
time is essential. EKGs can be performed cheaply and rapidly at the time of patient
presentation to the ED, and without the lengthy waits usually associated with cardiac
biomarkers. Furthermore, when compared to findings of ischemia on EKG, a normal
EKG has been shown to be associated with a lower 30-day risk for cardiac
complications and mortality.13 In the midst of advances in medical technology,
physicians have numerous strategies available to assess chest pain in patients and
identify ACS. This may make it tempting for ED physicians to perform additional tests to
ensure a definitive exclusion of ACS. However, since chest pain in low-risk patients
have diagnostic etiologies which are by and large benign, this "more is better" approach
is not entirely acceptable in a time of escalating healthcare costs.6 Taken together,
maximizing the clinical value of the EKG in the ED could significantly improve
healthcare resource utilization.
We hypothesized that patients between the ages of 16 to 40 years presenting to
the ED with chest pain would have the diagnosis of ACS ruled out if the initial EKG on
presentation was normal. The overall sensitivity of the EKG in this young study
population with low-risk chest pain was 71.0%. Of the 62 patients diagnosed with ACS,
44 had abnormal findings on the EKG and 18 had a normal EKG. This result
11
demonstrates that in a study population with low-risk chest pain a normal initial EKG is
associated with a lower frequency of ACS compared to those with abnormal EKG
findings. In spite of this, the sensitivity of the EKG in the overall study group was low.
From there, we proposed that the sensitivities of EKGs might improve with age
stratification: the younger a patient was with chest pain, the more likely ACS could be
excluded with normal EKGs. This improvement would also be seen with the specificity,
PPV and NPV values. However, our results demonstrate that the ability of EKG to rule
out ACS does not improve with younger age. There was no similar improvement in any
of the other statistical parameters either. As such, this significant type II error rate
severely restricts the value of a normal EKG in excluding the diagnosis of ACS.
These results are consistent with previous studies on the effectiveness of normal
EKG findings to diagnose or exclude the diagnosis of ACS in a general ED population.
Zalenski, R.J et al.15 showed that acute myocardial infarction (AMI) patients who had
normal EKGs on presentation did not have significantly lower complication rates than do
those with positive EKGs. They found that both groups had similar rates of hospital
complications and intensive procedures. Similarly, Turnipseed, S.D. et al.14 and Singer
et al.16 showed that in cases of suspected ACS, irrespective of the presence of chest
pain at that moment or the duration of symptoms from onset respectively, obtaining a
normal EKG finding does not reliably exclude ACS. Welch et al.17 showed that patients
with AMI presenting with normal EKGs had a mortality rate of 5.7% versus 11.5% for
those with diagnostic EKGs. The authors concluded that although patients with AMI
presenting with normal EKGs have more favorable mortality rates, they were still high.
In all the aforementioned studies, however, the mean age of the study population was
12
over 50 years, a cohort which could be considered as a higher risk population for
ACS.14-17 Nevertheless, all the studies build upon the notion that normal EKGs cannot
be used to rule out ACS in any patient population, and our data is consistent with that
conclusion.14,15
The study by Singer et al.16 used the NPV of normal EKG findings to rule out
AMI. For symptoms which lasted 0 to 3 hours from onset, the NPV of the EKG in the
detection of AMI was 93.2% (95% CI, 97.4-96.1). Yet, the authors concluded that even
if NPV was 100% many patients with normal EKG findings may still require admission to
reliably exclude ACS. Reaching the same judgment, this study had a similar NPV of
96.7% (95% CI, 95.4-97.9). Lastly, given the life-threatening and legal implications of
ACS misdiagnosis, the risks associated with failure to diagnose cannot be ignored.18
Even with the practical advantages, the EKG by itself does not fulfill the demand for a
highly sensitive clinical test to exclude a diagnosis of ACS in patients with chest pain.
Limitations
This study has several limitations. Our patient population was identified at only one
community hospital, and as a result, the study size was relatively small. The study also
focused on patients presenting with a chief complaint of chest pain. However, the
classic symptom of chest pain may not present in all cases of ACS, especially in young
women.19,20 In addition, patients with ST-segment elevation during ambulance
transportation were not included the study. Secondly, the definition of ‘low-risk’ chest
pain varies widely6. As such, the criteria of age (16-40 years) used in this study to
13
describe low-risk chest pain may not be sufficient when, for instance, other known
cardiac risk factors and medical history could have been collected and utilized.8,14
In terms of diagnostic tests, EKG findings were not re-interpreted by emergency
physicians and this may have impacted the accuracy of the results. Also, only the initial
ED EKG was used in the study. Due to limitations in acquiring patient data, our
definition of ACS did not include results from imaging studies including
echocardiography, coronary angiograms, or CT and magnetic resonance angiography,
which are more definitive tests for ACS.22 Beyond ACS, troponin values are also
elevated in a variety of other clinical situations, which could lead to over-diagnosis of
ACS.23 Lastly, patients with misdiagnosed ACS may have been included in this study.
Conclusion
This study has demonstrated that in patients 16 to 40 years old with a chief complaint of
chest pain, a normal electrocardiogram is not sensitive enough to reliably rule out acute
coronary syndrome.
Acknowledgements
A.L. would like to thank the Comprehensive Research Experience for Medical Students
(CREMS) Programs and the Jones, Janes and Howard O. Bursary Fund for providing
the summer scholarship for this project.
Conflicts of Interest
The authors have no conflicts of interest to declare.
14
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