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ability to synchronize with the patient’sECG,
or “ECG-gating,” also allows assessment of
systolic function. Of note, SPECT MPI currently
delivers the most ionizing radiation of all
the stress imaging modalities (average effective
dose 16.8 mSv, depen ding on radionuclide and
protocol used)
16
although recent studies have
been successful at decreasing radiation without
sacrificing test accuracy.
17
PET has been proven
to be more accurate than SPECT (87%
vs. 71% respectively), likely due to better pictures resulting from improved spatial resolution
andbettercorrectionofsofttissueattenuation
artifact.
18
Compared to MPI with SPECT, it has
a higher sensitivity,
18
alowerdosimetry,16and is
performed much more quickly, but its higher
cost and lower availability limit its use. Nuclear
MPIs are effective tests for risk-stratification;
negative tests are associated with a 1–2% per
year cardiac event (death or MI) rate if pharmacologic SPECT was used and a < 1% per
year event rate if exercise SPECT was used,
19
while a negative myocardial perfusion PET
scan is associated with a 0.09% per year cardiac
event rate.
20
Stress Echocardiogram – The stress “echo”
uses ultrasonography to assess cardiac activity.
While it does not identify specific coronary
stenoses, it detects ischemia as new or worsening
wall motion abnormalities, decreased wall
thickening, or compensatory hyperkinesis in
response to cardiac stress. It is logical then, that
this test has a rather weak positive predictive
value (5–53% in a recent meta-analysis).
13
Its
negative predictive value is fairly high however
(89–100%),
13
with a < 1%peryearcardiacevent
rate in patients with a normal exercise echocardiogram
21
and 1.2% per year event rate for
normal pharmacologic stress echo.
22
The stress
echo also p rovides information on cardiac structure and function, and can concurrently assess
for signs to indicate other etiologies of chest pain
such as pulmonary embolism, or pericardial
effusion. Limitations are those of standard echocardiography, including poor acoustic windows
in patients who are obese or have obstructive
lung disease. The use of contrast enhancement
can help ameliorate these poor views, and a
negative contrast-enhanced stress echo has been
associated with a 0.8% per year ACS rate in
recent studies.
23
Stress Cardiovascular Magnetic Resonance
Imaging – Stress Cardiovascular Magnetic Reson-
ance Imaging (CMR) is also a type of MPI and is
one of the newer imaging modalities for evaluation of chest pain and detection of CAD.
Coupling pharmacologic stress via adenosine or
dobutamine with gadolinium-enhanced magnetic
resonance imaging, stress CMR provides a great
deal of information due to its excellent spatial
resolution and soft-tissue differentiation capabilities. In patients presenting with chest pain, it
detects CAD with a reported sensitivity of 96%
and specificity of 83%,
24
with an NPV of 100%.
25
It provides anatomic, functional, and prognostic
information, and as a part of an accelerated diagnostic protocol that includes both OU admission
and monitoring with stress CMR, this modality
decreases medical costs without increasing
adverse events, when compared to standard inpatient admission.
26
Computed Tomography Coronary Angiog-
raphy – Computed Tomography Coronary Angi-
ography (CTCAs) are included in this chapter
because they are used in OUs for CAD diagnosis.
The standard CTCA is not a n actu al stress test,
although protocols for “stress myocardial CT
perfusion” are currently being developed and
tested to ad d a functional assessment to what is
now primarily anatomic.
27
CTCAs utilize multislice scanners and intravenous contrast to produce 3D images of the heart and coronary vessels
with resolution that allows measurement of stenosis severity. CTCAs are quick and have been
proven to have high sensit ivity and specifici ty,
with negative predictive values of 94–100%.
28,29
In addition to the standard negatives asso ciated
with contrasted CTs, the image quality of the
CTCA is limited by elevated heart rate s and the
test must often be administered with betablockers in order to achieve slower rates for optimal images.
30
Despite its disadvantages, studies
have demonstrated its utility in disposition of
chest pain patients; use of CTCA is associated
with decreased admission rates from the ED,
shorter lengths of stay, and higher detection of
CAD when compared with standard “rule-out”
protocols.
31
TestinginWomen
Cardiovascular testing in women can be challenging for a variety of reasons. Women with
Stress Testing
029
20:44:19
coronary disease generally have more diffuse, less
obstructive CAD than their male counterparts.
32
They often present later in life and therefore have,
at baseline, decreased exercise capacities that
hinder test performance.
33
They are more likely
to have baseline ST-segment and T-wave anomalies that might confuse ETT interpretation, they
are more subject to soft-tissue attenuation artifact
in nuclear studies and poor acoustic windows
during echocardiography due to breast tissue,
they have smaller cardiac chambers which can
affect interpretation of nuclear imaging,
33
and
their chest pain is more frequently atypical,
affecting pretest risk stratification and conduction
of the tests themselves. It is therefore important
for providers to be aware of differences in test
accuracy in the female population.
The ETT remains the initial test of choice in
intermediate-risk women presenting with chest
pain, with an average sensitivity and specificity of
61% and 70%, respectively.
34
Occurrence of ST
depressions seems to have less prognostic value in
women than men,
35
but exercise capacity and
chronotropic response remain helpful indicators
of future risk in women.
36,37
Stress echo sensitivity
is similar to that in men, but specificity is higher in
women (80% vs. 56% in men).
38
For SPECT, sensi-
tivity and specificity are both approximately 88%.
39
CTCA has been shown to have a comparable sensitivity between men and women, 96% vs. 90%,
both with excellent NPVs (100% and 99%, respectively).
40
The high spatial resolution of CMR mitigates issues such as breast attenuation and small
cardiac chamber size; a recent study found no difference in its prognostic value between men and
women, and actually demonstrated an impressive
annual major adverse cardiac event rate of only
0.3% in women who had negative stress CMR.
41
Of note, the WOMEN trial recently found that
even in females with high exercise tolerance, the
mere report of more frequent chest pain was
associated with a higher risk of abnormal findings
on exercise testing.
42
This study has not yet been
repeated, but providers should be on guard and
consider frequency of chest pain when determining pretest probability.
Patient Characteristics
Patients undergoing stress testing in OUs
should be patients at least 18 years of age, with
negative cardiac biomarkers, a negative or nondiagnostic ECG, and no ongoing or worsening
chest pain after 6–8 hours of monitoring.
10
It is
important to note the absolute contraindications
to stress testing: recent acute MI (within
48 hours), u nstable angina not stabilized by
medical therapy, uncontrolled arrhythmias
causing hemodynamic instability or symptoms,
severe aortic ste nosis, uncontrolled heart failure,
and presence or suspicion of acute pulmonary
embolism, myocarditis, pericarditis, and aortic
dissection. Specific contraindications to the
variousstresstestmodalities are included in
Table 26.3.
Management
In preparation for stress testing, patients should
be made NPO (nil per os) 4–6hourspriorto
the test, should not smoke or use nicotine
replacement, and should not be given anything
containing caffeine during their stay (no caffeine
in the prior 12–24 hours is ideal). Patient home
medications should generally be continued;
although nitrates, beta-blockers, and nondihydropyridine calcium chan nel blockers may affect
exercise respon se and therefore test accuracy.
Depending on the reason for their use, consider
holding these medicines until after exercise
testing. Diabetic patients should not take oral
antihyperglycemics until after testing, and
patients on insulin should generally take onehalf of their usual dose and eat a light meal
2–4 hours prior to testing, although treatment
can be tailored according to blood glucose monitoring in the unit. Patients who have taken theophylline or aminophylline in the prior 24 hours
are excluded from pharmacologic stress testing
with adenosine, dipyridamole, or regadenoson
due to decreased efficacy of the agents in testing.
If outside of that time frame, these medications
should be held until after the test has been
completed.
Outcome
In the setting of short-stay CPU/OUs, stress
testing has one main purpose: to risk
stratify patients with regards to CAD in order
to determine appropriateness of discharge or
guide referrals for more intense and urgent
management.
Kami M. Hu and Amal Mattu
029
20:44:19
Table 26.3 Stress Test Characteristics
Test Diagnostic
Performance
Advantages Disadvantages Prognostic Value
(Annual Cardiac Event Rate
After Negative Test)
Stress
Electrocardiogram
(ECG)
Sensitivity: 70%
Specificity: 77%
10
NPV: 89–100%
PPV: 0–77%
12
Inexpensive
Widely available
Quick (15–30 min)
Provides information about
exercise capacity and prognosis
No radiation exposure
Does not identify culprit arteries,
severity of stenosis or extent of
ischemia (therefore less useful after
prior MI or revascularization)
Decreased accuracy in females
42
Cannot use in patients on digoxin
or with various baseline ECG
abnormalities, or paced rhythms
10
Based on DTS risk:
44
Low risk: 0.9%
Medium risk: 1.7%
High Risk: 4.4%
*Cardiac event = Cardiac death
or MI
Stress Echo
cardiogram
Sensitivity: 86%
Specificity:
81%
14, 20
NPV: 89–100%
PPV: 5–53%
12
Accuracy:
84–87%
45, 46
Fairly quick (< 60 min)
No radiation exposure
Can be used in patients unable to
exercise
Can be used in patients with
baseline ECG abnormalities
May diagnose other etiologies of
chest pain
Diagnostic views may be limited by
operator skill, patient body habitus,
or tachycardia
Requires specialist interpretation
Labor intensive
Pharmacologic stress
negative: 1.2%
22
Exercise stress negative:
< 1%
21
*Cardiac event = MI, cardiac
death, revascularization
21
(+anginal hospitalization)
22
Nuclear myocardial
perfusion imaging:
Single-photon
emission computed
tomography
Sensitivity:
82–88%
Specificity:
61–74%
10
Accuracy: 71%
18
Can be used in patients unable to
exercise
Can be used in patients with
baseline ECG abnormalities
Length of time for test (2–6 hours)
On average, the most radiation
exposure of any stress test
(16.8mSv)
15
Pharmacologic stress
negative: 1–2%
Exercise stress negative:
< 1%
19
*Cardiac event = MI or death
029
20:44:19
Nuclear myocardial
perfusion imaging
Positron emission
tomography (PET)
Sensitivity:
84–96%
Specificity:
81–93%
47
Accuracy: 87%
18
Fairly quick (< 60 min)
Higher accuracy and less radiation
than SPECT
18
Can be used in patients unable to
exercise
Can be used in patients with
baseline ECG abnormalities
Radiation exposure (avg. 6.1mSv)
48
Expensive, less widely available
Difficult to perform with exercise
stress
Negative 82Rb-PET: 0.09%
20
*Cardiac event = MI, cardiac
death, revascularization
Stress cardiac
magnetic resonance
imaging
(CMR)
Sensitivity:
96–100%
Specificity:
83–91%
NPV:100%
24,25
PPV: 67%
24
Fairly quick (< 60 min)
Offers anatomic, functional, and
prognostic information
No ionizing radiation
Expensive, less widely available
Contraindicated in patients with
renal failure, specific metallic
devices, claustrophobia
Limited in patients who are unable
to breath-hold, or with arrhythmias
Negative stress: 1.5%
49
*Cardiac event = MI, death,
revascularization, ischemic
hospitalization
Computed
tomography
coronary
angiography
(CTCA)
Sensitivity:
96–99%
Specificity:85–86%
NPV:93–95%
PPV: 92–96%
28,29
Very quick (~5 min)
Offers anatomic and prognostic
information
Can also assess for pulmonary
embolism and aortic dissection (the
“triple rule out”)
No functional assessment
Requires slow heart rate for optimal
images
Radiation exposure (avg. 3.7mSv)
15
Contraindicated in patients with
contrast allergy or renal failure
Risk of contrast-induced
nephropathy
Nonobstructive CAD:
1.4%
Negative for CAD:
0.17%
50
and 99.7%
survival at 2.3yrs
51
*Cardiac event: MI,
revascularization, all-cause
mortality
NPV = negative predictive value, PPV = positive predictive value, DTS = Duke treadmill score, MI = myocardial infarction, mSV = milliseiverts, CAD = coronary artery disease
133
029
20:44:19
Conclusion
Each stress test provides a di fferent array of
information, with a different risk-benefit profile
and a different overall worth that is specific to
the patient being tested, depending on his or
her pretest probability . A standard exercise
ECG (quick, low-risk, a nd inexpensive) though
imperfect is nevertheless very helpful at decreasing the likelihood that obstructive CAD is the
etiology for a patient’ s chest pain. The negative
predictive value of any test is diminished, however, in patients with high pretest probability.
Functional testing or testing that concomitantly
offers possibl e therapeutic intervention, such as
coronary angiography, is more appropriate in
this population.
Stress testing is useful for CAD diagnosis,
functional assessment, and prognosis/riskstratification. In the context of observation
medicine, its utilization has been proven to lower
cost burden without increasing adverse events
when compared to standard inpatient admissions
for ACS rule-outs. Providers should be careful,
however, about adhering to protocols that subject
patients to knee-jerk testing that is not tailored to
their individual circumstances or needs. Evidence
shows that the majority of low risk chest pain
patients in OUs undergo stress tests despite very
low pretest probabilities, and when abnormal test
results occur, they rarely require action.
43
It is the
provider’s responsibility to tailor the test to the
individual patient, to weigh the risks and benefits,
and to withhold stress testing in patients who do
not require it. This provider-directed imaging
strategy has been proven to lower costs without
changes in length of stay or increase in 30-day
ACS
8
and is more aligned with the physician’s
duty to the patients in his care.
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Kami M. Hu and Amal Mattu
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Subpart IVB
Chapter
27
Clinical – Respiratory
Asthma
Eric Anderson, MD, MBA, FACEP, FAAEM
Introduction
The exact definition of asthma varies by medical
discipline. Generally speaking, for emergency
physicians, asthma can be considered a chronic
condition of recurrent hyper-responsiveness of
airways characterized by inflammation and airflow obstruction.
1
Medical treatment strategies
involve reducing or preventing airway inflammation and obstruction with anti-inflammatory and
bronchodilator medicines. Patient education strategies involve general education about asthma, recognizing and treating exacerbations before they
become severe, avoidance of known asthma triggers, and importance of medication compliance.
Asthma is a condition commonly encountered
in emergency medicine. Approximately 1.8% of
annual emergency department (ED) visits are
due to asthma.
2
The condition affects approximately 7–10% of U.S. adults, which represents
approximately 22 million Americans.
3,4
Preva-
lence statistics are similar in Canada.
5
There are
approximately 2 million annual ED visits for
asthma. There are approximately 500,000 hospital
admissions annually for asthma in the United
States. Asthma prevalence increased in the 1980s
and 1990s, and was noted to plateau in the mid
2000s. Death rates have decreased as well, from
5637 in 1995 to 3816 in 2004.
6,7,8
Though death
rates have decreased, they remain high in certain
demographic groups: women 2.3 and African
Americans 3.4 per 10,000 people with current
asthma.
6
The death rate for the general population
is less than 2 per 10,000 population.
6
Overall hos-
pitalization rate in the United States in 2005 was
10.3 hospitalizations per 10,000 adults and 19 hospitalizations per 10,000 children.
9
Canada has
similar statistics with estimated deaths in 1995 of
400–500 and a death rate in 2004 of 268, which
works out to an overall death rate of about 1 per
100,000 Canadian population.
10
Disposition of Asthma Patients
Presenting to Emergency
Departments
Of patients that present to the ED for evaluation
of asthma, most are ddischarged home. In a
study of asthma care in U.S. EDs by Tsai et al.,
79% of asthma patients were discharged home,
16% were admitted to the general medical ward
or to the observation unit (OU), 2% were admitted to the intensive care unit (icu), and 3% other
(left against medical advice or unknown). Only
3% of asthma patients had pneumonia.
4
A Canadian study yielded a similar high discharge
rate: 90% of patients were discharged and 7% were
admitted.
3
Ginde et al. reviewed asthma care and
found a discharge rate of 85–90%.
2
Cost of Care for Asthma
The approximate annual cost of asthma care in the
United States is 18 billion dollars.
11
This cost
estimate does not include lost wages from time
away from work or cost to patients for medications and follow-up care. Cost of medications was
found to be an important barrier to care according
to approximately 50% of patients.
12
Asthma is the
main cause of missed school days for children.
13
Patients with asthma have 17 mean work days
missed annually.
14
OU care of asthma has been
shown to be cost-effective when compared to
inpatient costs.
13
Inclusion and Exclusion Criteria
for Observation Unit
Presentations of asthma to the ED generally are
broken into broad categories: mild, moderate,
severe, and life threatening. Table 27.1 lists the
various categories of asthma severity as well as
the diagnostic criteria for each category. For the
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20:58:41
purpose of this chapter, the moderate and severe
categories will be discussed. Mild exacerbations
are generally treated at home or the physician’s
office. Life-threatening asthma clearly needs to be
admitted if not immediately intubated. Patients
suitable for the OU are those who have shown
improvement during ED treatment, however, the
patient or the physician feel that the patient needs
more time for medications to take effect or additional treatment. Inclusion and exclusion criteria
should be developed for OUs treating patients
with asthma. Table 27.2 illustrates general guidelines, inclusion criteria, and exclusion criteria for
asthma patients being considered for OUs. OU
patients should be discharged within the time
constraints of the OU. Whatever the time constraints of your unit, patients should be expected
to improve to the point of discharge within that
allowed time frame. Patients who are expected
to take more than the allowed time in the OU
should be hospitalized from the ED. The OU
should not be used to decide which patients need
an ICU versus medical bed. Most OUs are not
considered mini-IC Us and ICU potential patients
should remain in the ED until a decision is firmly
made about admission to the ICU versus the
medical floor.
Treatment in Observation Unit
OU treatment consists of inhaled beta agonists at
prescribed intervals, usually every 1–4 hours,
inhaled anticholinergic medications, intravenous
(IV) or oral steroids, and supplemental oxygen as
needed. The opportunity should be taken during
the OU stay for asthma education about the
prevention of exacerbations and treatment by
nurses or asthma educators, pamphlets or video
tapes. Smoking cessation education should also
occur at this time in applicable patients. Periodic
assessments by nursing and/or physician staff
should occur to determine response to treatment.
Response to treatment should be measured by
several subjective and objective criteria. Objective
criteria about patient response to treatment
include the following: improvement in PEFR or
FEV1 to > 70% of predicted or back to patient’s
historical discharge values, improvement of vital
signs, and improvement of pulse oxygen saturation
readings. Auscultation of wheezes is not a reliable
indicator of pulmonary status. However, pulmonary auscultation in combination with physician
clinical judgment and the patient’s opinion of their
clinical status are useful guides in disposition decisions. Some patients will indicate that they are
always discharged with a mild wheeze and that
they feel well enough to go home. In these cases,
review of the evolution of objective parameters
(PEFR, FEV1, vital signs, and pulse oxygen saturation) will guide in disposition decisions.
Medications
There are several classes of therapeutic agents used
in the treatment of asthma. OU treatment will be
an extension and continuation of treatment initiated in the ED. Inhaled short-acting beta adrenergic agonists cause bronchodilation by stimulation
of the enzyme adenyl cyclase, which changes intracellular adenosine triphosphate (ATP) to cyclic
adenosine monophosphate (cAMP). This causes
intracellular calcium to bind to cell membranes,
Table 27.1 Asthma Severity
Ability to
Speak
Physical
Activity
Pulse PEFR pCO
2
Mild Speaks in
sentences
Activity causes
SOB
< 100 > 70% predicted < 42
Moderate Short phrases Limited activity 100–120 40–69% predicted < 42
Severe Words SOB at rest > 120 < 40% predicted > 42
Life
threatening
Cannot speak
due to work of
breathing
Tolerates no
activity
Bradycardia < 25% predicted
if patient can
perform test
> 42, ABG usually not
needed due to
imminent respiratory
arrest
SOB = shortness of breath
PEFR = peak expiratory flow rate
ABG = arterial blood gas
Adapted from References:
15,16
Eric Anderson
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20:58:41
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