The use of EKG to exclude a diagnosis of acute coronary syndrome in a
population with low-risk chest pain
Background: Chest pain is a common chief complaint to emergency departments (ED)
across Canada. These patients often have low-risk chest pain where incidence of acute
coronary syndrome (ACS) is minimal. 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 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.
1
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%.
Conclusion: The use of EKG alone to exclude ACS is not recommended in patients
presenting with low-risk chest pain
Annually, approximately 500 000 Canadians present to emergency departments
(ED) with chest pain, a symptom that raises concern of acute coronary syndrome
(ACS). ACS encompasses unstable angina, ST-segment elevation myocardial infarction
and non-ST segment elevation myocardial infarction.1 These patients undergo a lengthy
assessment in the ED to rule out an acute myocardial infarction (AMI). This often
involves testing two samples of blood collected 6 hours apart for biomarkers of
myocardial necrosis, most frequently troponin.2 It is estimated that 20% of these
patients 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 In addition, patients may undergo diagnostic tests which in retrospect may have
2
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. Extensive research has 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 Accordingly, 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 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, ACS in younger patients have different clinical
presentations, receive earlier treatment and have a more favorable outcome relative to
older patients.12 Therefore, an age under 40 is 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.
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 would have a low rate of ACS diagnosis. Therefore,
3
a normal EKG could be used to exclude the diagnosis of ACS in a low-risk chest pain
patient presenting to the ED.
Methods
Study Design
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 the first troponin result was used to determine
ACS diagnosis. Patients without an EKG or troponin test result 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
4
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. A chief complaint of chest pain was ascertained by
first identifying the presenting complaint on the nursing triage note. This was compared
to the chief complaint recorded by the attending physician on the emergency
registration outpatient record. If the two records were consistent, the patient had 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 the ED were documented by the ED physician. From there, two
patient groups were generated: patients with “normal” EKG findings and patients with
“abnormal” EKG findings. Other clinical data recorded were age, sex, troponin I levels,
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, left
ventricular hypertrophy, low voltage, and heart block. These criteria are consistent with
5
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 an
elevation in troponin I level ≥0.07 μg/L (Cardiac Troponin I by Siemens Inc., NY, USA;
99th percentile of normal with <10% variance).
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 presented 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 patients. Mean and median ages for the
study 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.
6
541 (62.5%) patients had a “normal” EKG finding and 62 (7.16%) patients had a
finding diagnostic of ACS, a positive troponin I value. The frequency of ACS in the study
population was 7.2%. Of the patients with ACS, 18 persons (29.0%) had a diagnosis of
ACS with a “normal” initial EKG and a positive troponin I result. 44 patients with ACS
had an “abnormal” EKG and elevated troponin I values. Lastly, 281 (32.5%) persons
had “abnormal” EKG findings and were found not to have ACS through troponin I testing
(Table 2).
Therefore, the EKG had sensitivity and specificity values of 71.0% (95%
confidence interval [CI], 57.9% to 81.4%) and 65.0% (95% CI, 61.6% to 68.3%)
respectively. The PPV and NPV were 13.5% (95% CI, 10.1% to 17.9%) and 96.7%
(95% CI, 94.7% to 98.0%), respectively (Table 2). Post-hoc analysis was completed by
dividing the total patient population into subgroups defined by the ages 16-20, 21-30
and 31-40 years. The statistical measures were calculated and summarized in Table 3.
The EKG sensitivities were: 16-20 year olds, 80.0% (95% CI, 29.9% to 98.9%); 21-30
year olds, 50.0% (95% CI, 24.0% to 76.0%), 31-40 year olds, 76.7% (95% CI, 61.0% to
87.7%). 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
7
Gender
Male
Female
347
519
Subgroups
No. ages 16-20 years
No. ages 21-30 years
No. ages 31-40 years
79
324
463
Table 2: 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) 57.9%-81.4%
Specificity 65.0% (523/804), 95% CI 61.6%-68.3%
Positive predictive value 13.5% (44/325), 95% CI 10.1%-17.9%
Negative predictive value 96.7% (523/541), 95% CI 94.7%-98.0%
Table 3: 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), 29.9-98.9
50.0 (7/14), 24.0-76.0
76.7 (33/43), 61.0-87.7
Specificity
77.0 (57/74), 65.5-85.7
63.9 (198/310), 58.2-69.2
63.8 (268/420), 59.0-68.4
PPV
19.0 (4/21), 6.29-42.6
5.90 (7/119), 2.60-12.2
17.8 (33/152), 12.8-24.3
NPV
98.3 (57/58), 89.5-99.9
96.6 (198/205), 92.8-98.5
96.4 (268/278), 93.3-98.2
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
8
EKGs can be performed cheaply and rapidly at the time of patient presentation.
The test also lacks the lengthy waits usually associated with cardiac biomarkers. These
practical qualities are especially important in the ED, an environment where providing
efficient care with limited resources and time is essential. For common presenting
complaints like chest pain, the ability to quickly rule out life-threatening ACS would be
extremely valuable.
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 diagnoses which are by and
large benign, this "more is better" approach is not entirely acceptable in a time of
escalating healthcare costs.6 Hence, given its low cost and practical advantages,
studying whether a normal EKG can be used to exclude ACS in patients with low-risk
chest pain is warranted.
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 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 EKG
findings while 18 had normal findings. This result demonstrates that in a study
population with low-risk chest pain defined by ages between 16-40, a normal initial EKG
is associated with a lower frequency of ACS compared to those with abnormal EKG
findings. Despite this result, 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
9
stratification: the younger a patient with chest pain, the more likely ACS could be
excluded with normal EKGs. This improvement would also be seen in 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
other statistical parameters as well. 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 exclude the diagnosis of ACS in a general ED population. Zalenski et
al.15 showed that patients diagnosed with AMI who had normal EKGs on presentation
did not have significantly lower complication rates than did those with positive EKGs.
They found that both groups had similar rates of hospital complications and intensive
procedures. Similarly, Turnipseed 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, obtaining a normal EKG finding does not reliably
exclude ACS. In the aforementioned studies, however, the mean age of the study
population was over 50 years, a cohort which is at higher risk for ACS.14-17
Nevertheless, 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
Singer et al.16 used the NPV of normal EKG findings to rule out AMI. For
symptoms that lasted 0 to 3 hours from onset, the NPV of the EKG in the detection of
AMI was 93.2% (95% CI, 87.4-96.1). This study had a similar NPV of 96.7% (95% CI,
94.7-98.0). Despite the finding, Singer et al. concluded that many patients with a normal
10
EKG would still require admission to reliably exclude ACS. Specifically, patients with
high-risk unstable angina may present with normal EKG findings.16 Lastly, given the lifethreatening and legal implications of ACS misdiagnosis, the risks associated with failure
to diagnose cannot be ignored.18 Even with the practical advantages, the EKG alone
does not fulfill the demand for a highly sensitive clinical test to exclude a diagnosis of
ACS in patients with low-risk chest pain.
Limitations
This study has several limitations. Our patient population was identified at 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 widely.6 The criteria of age (16-40 years) used in this study to define low-risk
chest pain may not be sufficient when 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 in the study
and this may have impacted the accuracy and precision of the results. Due to limitations
in acquiring patient data, our definition of ACS did not include results from imaging
studies including echocardiography or coronary angiograms, which are more definitive
tests for ACS.22 Also, the elapsed time between chest pain presentation and the initial
11
troponin result was not included, and only the first troponin value was used. As a result,
the troponin values used in the study may have been obtained before serum levels rose
to detectable levels. This would lead to an underestimation of ACS. 23 Troponin values
can also be elevated in a variety of other clinical conditions which present with chest
pain, including myocarditis and pulmonary embolus.24 Since these causes of chest pain
were not excluded in the study, this would lead to over-diagnosis of ACS. 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 at the emergency department, 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.
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