Cardiac Diagnostic Testing: What Bedside Nurses Need to Know

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Cardiac Diagnostic Testing:
What Bedside Nurses
Need to Know
LUPE M. RAMOS, MSN, NP-C, ACNP
Coronary artery disease affects more than 385 000 persons annually and continues to be a leading cause
of death in the United States. Recently, the number of available noninvasive cardiac diagnostic tests has
increased substantially. Nurses should be knowledgeable about available noninvasive cardiac diagnostic
testing. The common noninvasive cardiac diagnostic testing procedures used to diagnose coronary heart
disease are transthoracic echocardiography, stress testing (exercise, pharmacological, and nuclear), multidetector computed tomography, coronary artery calcium scoring (with electron beam computed tomography or computed tomographic angiography), and cardiac magnetic resonance imaging. Objectives include
(1) describing available methods for noninvasive assessment of coronary artery disease, (2) identifying
which populations each test is most appropriate for, (3) discussing advantages and limitations of each
method of testing, (4) identifying nursing considerations when caring for patients undergoing various
methods of testing, and (5) describing outcome findings of various methods. (Critical Care Nurse. 2014;
34[3]:16-28)
C
oronary heart disease costs the United States $108.9 billion each year.1 Between
1999 and 2009, rates for death due to cardiovascular disease declined, yet coronary
heart disease continues to be the leading cause of death in the United States, with 1
American experiencing a coronary event every 34 seconds.2 Of those persons who die
suddenly of coronary heart disease, 50% of men and 64% of women have had no previous signs or symptoms.2 Accurate assessment and risk stratification of patients with coronary
heart disease are crucial in identifying patients at greatest risk for coronary events. Thus, clinicians
must be knowledgeable about the many forms of cardiac diagnostic testing available.
Although considered the gold standard for visualization of coronary heart disease, coronary angiography is invasive and expensive and involves a risk for acute myocardial infarction, stroke, arrhythmias,
CNE Continuing Nursing Education
This article has been designated for CNE credit. A closed-book, multiple-choice examination follows
this article, which tests your knowledge of the following objectives:
1. Discuss common noninvasive cardiac diagnostic tests
2. Interpret results of noninvasive cardiac diagnostic tests
3. Describe nursing considerations for care of patients undergoing noninvasive cardiac diagnostic testing
©2014 American Association of Critical-Care Nurses doi: http://dx.doi.org/10.4037/ccn2014361
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Table 1
Framingham risk category definitionsa
No. of risk factors present
10-Year absolute risk for
coronary heart disease, %
Low
0-1
<10
Moderate
2+
<10
Moderately high
2+
10-20
Presence of diabetes mellitus in a patient
older than 40 years, peripheral arterial
disease, or other coronary risk equivalent
>20
Risk category
High
a Based
on information from the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high
blood cholesterol in adults (Adult Treatment Panel III) final report.9
and bleeding.3 This imaging method is not considered a
first-line diagnostic study in patients at low risk for heart
disease.4 Cardiac imaging studies are costly and when used
inappropriately can be harmful to patients by exposing
them to unnecessary radiation and medications. In addition, unprecedented outside scrutiny by patients, increased
emphasis on transparency, and pay-for-performance
policies have required clinicians to be even more judicious
in choosing the most appropriate, least invasive test for
a patient’s condition.
Appropriate use of cardiac procedures has received
much attention recently in media coverage of cases in
which patients underwent procedures that were deemed
medically unnecessary.5 In addition, a recent article6 in
the New England Journal of Medicine indicated that only
one-third of patients at low risk for coronary heart disease
who had elective diagnostic angiography had obstructive
coronary artery disease. Because of these findings, the
authors6 concluded that better strategies for risk stratification are needed.
In 2005 the American College of Cardiology Foundation began to develop appropriate use criteria. The goal
was to assist cardiology professionals in deciding when
and how often to do an imaging test or procedure. The
ultimate goal is to improve patient care and health outcomes in a cost-effective manner.4,7 Adoption of appropriate use criteria has been somewhat slow because of
confusion over the method with which the criteria were
formulated, application of the criteria to clinical care,
and use of the labels uncertain and inappropriate in
describing indications for testing.8 Clinicians are hopeful, however, that new terminology published in 2013
will lead to increased use of appropriate use criteria.8
Because of the numerous advances and improvements
in cardiac imaging, nurses should know about the vast
array of diagnostic testing that a patient may undergo.
Nurses play a key role in the safe administration of these
tests by educating patients about the indication for testing and explaining the results.
In this article, I review common noninvasive cardiac
diagnostic tests, specifically those used in diagnosing
coronary heart disease. Emphasis is placed on how each
test is administered, what information is provided by
the results, and what nurses need to know when caring
for patients who have the tests.
Risk-Factor Assessment
For patients who have never had a diagnosis of coronary heart disease, a risk stratification method such as
the Framingham Risk Score is useful in identifying
patients’ 10-year risk for a major coronary event.9 The
Framingham Risk Score is based on a patient’s sex, level
of total cholesterol, level of high-density lipoprotein,
systolic blood pressure, history of cigarette smoking,
and age.9 Depending on the score, a patient is assigned
to a low-, intermediate-, or high-risk category (Table 1).
Author
Lupe Ramos is a nurse practitioner in cardiac services at St Joseph Hospital in Orange, California.
Corresponding author: Lupe Ramos, 1416 N Olive St, Santa Ana, CA 92706 (e-mail: [email protected]).
To purchase electronic or print reprints, contact the American Association of Critical-Care Nurses, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 899-1712 or (949)
362-2050 (ext 532); fax, (949) 362-2049; e-mail, [email protected]
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Intermediate risk may be further categorized as moderate and moderately high.9,10 The Framingham Risk Score
is useful in helping both patients and clinicians identify
appropriate lifestyle modifications in an attempt at primary prevention of coronary heart disease.
For patients in the intermediate- to high-risk categories,
the concern is how to approach the patients about diagnostic testing. The American College of Cardiology
Foundation and the American Heart Association have
issued guidelines to assist clinicians in selecting tests.
I address these guidelines in the subsequent sections.
Methods of risk-factor assessment include advanced
lipid assessment, level of C-reactive protein, carotid
intima-media thickness, and ankle-brachial index; however, in this article, I focus on the noninvasive imaging
studies most often used in practice.
Transthoracic Echocardiography
Echocardiography is one of the most frequently used
noninvasive cardiovascular diagnostic tests.11 The procedure provides high-quality imaging and hemodynamic
data in a safe, quick, and painless manner and requires
little preparation of patients (unless done by the transesophageal approach). The imaging can be done by using
a transthoracic or a transesophageal probe that emits ultrasound waves directed at cardiac structures. In transthoracic echocardiography, a probe is placed externally over
the chest wall.
The Framingham Risk Score can help
If they are
both patients and clinicians identify
able, patients
appropriate lifestyle modifications to
are asked to
prevent coronary heart disease.
lie on their left
side for better visualization of cardiac structures. Continuous electrocardiographic (ECG) monitoring is used to
time events to the cardiac cycle. Transducer gel is placed
on the chest wall to facilitate ultrasound transmission.
The sound waves are interpreted by the ultrasound
machine to reconstruct images of the heart.12
Transthoracic echocardiography is done with M-mode,
and either 2- or 3-dimensional imaging. M-mode provides
a 1-dimensional view and is used for fine measurements.
Two-dimensional imaging is the standard mode and is
used for cross-sections of the heart moving in real time.
Three-dimensional imaging is becoming more common
and offers the benefit of eliminating some of the artifacts
associated with 2-dimensional imaging. Doppler imaging is used to assess the speed and direction of blood as
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Table 2
Definitions of sensitivity and specificity
Sensitivity
Can be thought of as a true-positive rate
If the results of a test with high sensitivity for
detection of a disease are negative, the disease
almost certainly is not present
Specificity
Can be thought of as a true-negative rate
If the results of a test with a high specificity for
detection of a disease are positive, the disease
almost certainly is present
it moves through cardiac structures and is particularly
useful for identifying the severity of valve disease, flow
across a ventricular septal defect, and severity of pulmonary hypertension.12
Transthoracic echocardiography is useful in assessing
conditions such as dyspnea, syncope, angina without elevation in cardiac enzymes or changes in ECG findings,
sustained ventricular or supraventricular tachycardia,
suspected valve disease, and cerebrovascular events.12 It
is also used to evaluate ventricular systolic and diastolic
function, abnormalities in regional wall motion, hemodynamic changes, and presence of pericardial effusions
with or without cardiac tamponade.12
Transthoracic echocardiography allows visualization
of areas of hyperkinesia, hypokinesia, akinesia, and dyskinesia and imaging of aneurysmal segments.11 This procedure is an accurate diagnostic tool for detecting and
localizing acute myocardial infarction and is helpful in
detecting complications of acute myocardial infarction
such as ventricular free wall rupture and rupture of the
papillary muscle.11 Normal motion of the left ventricular
wall during an episode of acute chest pain usually indicates that no myocardial infarction has occurred.3
Although useful for diagnosing impending myocardial infarction and for assessing left ventricular function in patients after myocardial infarction, resting
echocardiography alone does not have high sensitivity
or specificity for the diagnosis of coronary heart disease
in patients who do not have ischemia or infarction13
(Table 2). The guidelines of the American College of
Cardiology Foundation and the American Heart Association for cardiovascular risk assessment recommend
echocardiography for detection of left ventricular
hypertrophy in adults who have no signs or symptoms
of heart disease who have hypertension.13 Echocardiography is not routinely recommended for patients who
do not have hypertension.13
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Table 3
Contraindications to stress testinga
Absolute
Congestive heart failure
Uncontrolled cardiac
arrhythmias
Severe aortic stenosis
Unstable angina
Myocardial infarction
within the past 2 days
Acute pulmonary embolus
Myocarditis
Severe pulmonary
hypertension
Relative
Known obstruction of the left
coronary artery
Tachyarrythmias with
uncontrolled ventricular rate
Hypertrophic obstructive
cardiomyopathy
Hypertension greater than
200/110 mm Hg
Acute illness such as anemia
Electrolyte imbalance
Uncontrolled hyperthyroidism
Aortic dissection
a Based
on information from Fletcher et al.15
Table 4
Indications for terminating exercise testinga
Absolute
Relative
Acute myocardial infarction
Moderate to severe angina
Symptomatic decrease in systolic
blood pressure despite an
increase in workload
Arrhythmias such as second- or
third-degree atrioventricular
block, ventricular tachycardia,
frequent premature ventricular
contractions, atrial fibrillation
with rapid ventricular response
Signs of poor perfusion including
pallor, cyanosis, or cold,
clammy skin
Severe dyspnea
Ataxia, vertigo, visual or gait
problems, or confusion
Stress Testing
Stress testing is one of the most commonly used methods of noninvasive assessment of coronary artery disease.
Stress testing involves the use of exercise (for patients
who are physically able) or drugs such as vasodilators
and dobutamine (for patients who are physically unable
to exercise) to increase myocardial demand and is used
to determine the presence of ischemia. Assessment data
are collected by using continuous ECG monitoring,
echocardiography, nuclear imaging, or various combinations of these 3 methods.
Exercise Stress Testing
Strenuous exercise increases heart rate, stroke volume,
and cardiac output and activates the sympathetic nervous system, resulting in vasoconstriction of most vasculature except that of the exercising muscle and cerebral
and coronary vessels.14 Release of norepinephrine and
increased levels of renin result in increased cardiac contractility. During exercise, coronary blood flow increases.
Obstructive coronary artery disease prohibits adequate
coronary blood flow to the affected area of the myocardium
and ischemia occurs.15 Exercise stress testing is therefore
a useful way to assess for evidence of myocardial ischemia
and exercise capacity.
Exercise stress testing often involves use of a treadmill
or bicycle ergometer.14 In order to participate in an exercise
stress test, patients must be alert and oriented and have
adequate coordination. Advanced age, poor functional
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Decrease in systolic
blood pressure greater
than 10 mm Hg from
baseline blood pressure, despite an
increase in workload,
in the absence of signs
and symptoms
Increasing angina
Hypertensive response
(systolic blood
pressure >260 mm Hg,
diastolic blood
pressure >115 mm Hg)
Fatigue, shortness of
breath, wheezing, leg
cramps, or claudication
Patient requests to stop
a Based
on information from Henzlova et al.18
capacity, poor balance, joint or back pain, and generalized deconditioning are typically contraindications to
treadmill testing16; in these instances, pharmacological
testing may be used (Table 3).
Before stress testing begins, Advanced Cardiac Life
Support equipment should be on standby. Leads are
placed on the patient for 12-lead ECG, and baseline values are obtained. Baseline vital signs are assessed along
with the patient’s history and list of medications. Medications such as digoxin, calcium channel blockers, and
-blockers may produce ST-segment depression or prevent the patient from reaching the target heart rate.15 If
safe to do so, administration of these medications should
be stopped 24 to 48 hours before the stress test is done.
Nursing considerations before treadmill testing
include explaining the procedure to the patient and
informing him or her of what to expect during the test,
including signs and symptoms that warrant termination
of the test (Table 4) and possible complications.15 Because
of the risk for aspiration, patients should not take anything by mouth for 4 hours before the test, but they may
take routine medications with small amounts of water.15
Patients should wear comfortable clothing and shoes
and must be able to walk briskly up an incline. The skin
should be cleansed where the ECG electrodes will be
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applied to ensure good contact. If pharmacological testing is being done, intravenous access is obtained, preferably in the antecubital fossa. Intravenous access is not
required for treadmill testing done without use of
vasodilators or dobutamine.
Various protocols for exercise stress testing exist, but
much of the reported data are based on the Bruce protocol.17 With the Bruce protocol, both the speed and the
grade of the treadmill are increased every 3 minutes
through each of 7 stages, for a total of 21 minutes of exercise; the goal is to reach at least 85% of the target heart rate
(220 minus age).18 Three key parameters are monitored
during an exercise stress test: the patient’s subjective clinical response (eg, dyspnea, dizziness, chest pain), hemodynamic response (eg, tachyarrhythmia, bradyarrhythmia,
or marked hypotension or hypertension), and ECG
changes (horizontal or downsloping ST-segment depression >1 mm).15 Continuous ECG monitoring is done
throughout the testing and for 6 to 8 minutes after exercise
is completed (or longer if the patient is symptomatic).15
Echocardiography may be used as an adjunct to
treadmill or pharmacological stress testing and is indicated for symptomatic patients who have abnormal ECG
findings at rest, such as findings indicative of left bundle
branch block, use of a pacemaker, left ventricular hypertrophy, or use of digoxin.13 If echocardiography is used,
echocardiogAdenosine is useful in pharmacological
raphy is done
stress testing because it can increase
at the start of
blood flow in normal coronary arteries
the stress testwith little or no change in the flow in
ing and immestenotic arteries.
diately after
exercise is completed (preferably <1 minute).15 In pharmacological stress tests, echocardiographic images are
obtained at baseline, time of peak dobutamine infusion,
and during recovery.15 Echocardiographic evidence of
segmental and global left ventricular dysfunction is
indicative of ischemia.
Exercise stress testing is useful for detecting obstructive coronary disease in patients at high risk for the disease and for risk stratification of patients after myocardial
infarction.18 It is also helpful in assessing risk in patients
with chronic stable coronary artery disease and in patients
at low risk for acute coronary syndrome who are not
having active chest pain or heart failure.18 Exercise stress
testing is also sometimes used for preoperative evaluation of patients undergoing noncardiac surgery.18 It is
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not recommended as a method of risk assessment in
asymptomatic patients who have low or intermediate
risk for a coronary event.13
The mean sensitivity of exercise stress testing for detection of coronary artery disease is 68%, and the specificity
is 77% (in a meta-analysis of a findings obtained predominantly in men).15,19 If echocardiography is added,
stress testing has a sensitivity of 81% and a specificity of
92%, and if nuclear imaging is added, it has a sensitivity
of 88% and a specificity of 90%.19 Compared with men,
women have an increased risk for false-positives, with a
sensitivity of 31% to 71% and a specificity of 66% to 78%.19
The difference between the sexes may be due to more
frequent ST-T wave changes in women at rest, lower
ECG voltage, and hormone-related factors.20
Pharmacological Stress Testing
Pharmacological stress testing is indicated for patients
who are unable to exercise on a treadmill. Cardiac
vasodilators such as adenosine, dipyridamole, and
regadenoson and the positive inotrope dobutamine are
common agents used in pharmacological stress testing
(Table 5).
Adenosine Adenosine antagonizes -adrenergic
receptors, resulting in vasodilatation and a decrease in
heart rate. Adenosine is useful in pharmacological stress
testing because it can increase blood flow in normal
coronary arteries with little or no change in the flow in
stenotic arteries.15 Stenotic arteries visualized with
adenosine and a radiopharmaceutical show less uptake
of the radioactive drug than normal arteries do.15
In addition to the nursing considerations associated
with exercise stress testing mentioned earlier, nurses
caring for a patient undergoing pharmacological stress
testing must ensure that the patient has not had any
theophylline or dipyridamole 48 hours before the test
and no caffeine-containing products 24 hours before
the test, because these drugs competitively block the
effects of adenosine.15 An intravenous catheter with a
Y-connector is required for injection of the adenosine
and the radiopharmaceutical. Typically the adenosine is
administered intravenously via an infusion pump at a dose
of 140 μg/kg per minute for 6 minutes.21 A radiopharmaceutical such as thallous chloride Tl 201 is injected after
the first 3 minutes of the adenosine infusion21 (see section
on nuclear testing). Patients may experience flushing, shortness of breath, nausea, and even chest pain that is not
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Table 5
Medication
Dose
Pharmacological agents used in stress testinga
Adverse effects
Contraindications
Nursing
considerations
Adenosine
140 μg/kg per minute for
6 minutes
Flushing, shortness
of breath, nausea,
chest pain
Second- or third-degree AVB,
sick sinus syndrome without a pacemaker, ventricular
tachycardia, bronchospastic
disease
NPO after midnight
Off theophylline for 48 hours
Off caffeine for 24 hours
Can cause hypotension
Short half-life
Dipyridamole
0.14 mg/kg per minute for
4 minutes
Chest pain, ECG
changes, headache,
dizziness
Second- or third-degree AVB,
bronchospastic disease
Has longer half-life than adenosine
Give aminophylline 50-250 mg
slow IVP for 1-2 minutes if
adverse reaction occurs
Dobutamine
Initiated at 10 μg/kg per
minute and increased
every 3 minutes to a
maximum dose of
50 μg/kg per minute
until THR is achieved
Feeling of shakiness,
nausea
NPO after midnight
Uncontrolled hypertension,
Off -blockers for 48 hours
atrial fibrillation, tachyarrhythmias, recent myocar- If severe adverse effects, may
give short-acting -blocker
dial infarction, unstable
angina
Regadenoson
Single bolus of 400-μg,
10-second infusion
Chest discomfort,
headache, abdominal pain, flushing,
dyspnea, dizziness
Second- or third-degree AVB,
sick sinus syndrome without a pacemaker, bronchospasm, SBP < 90 mm Hg
Has a longer half-life than
adenosine
Has mild effect on blood pressure
Off dipyridamole, aminophylline,
or caffeine for 48 hours
If severe reaction, can give
aminophylline 50-250 mg IVP
for 1-2 minutes
Abbreviations: AVB, atrioventricular block; ECG, electrocardiogram; IVP, intravenous bolus; NPO, nothing by mouth; SBP, systolic blood pressure; THR, target
heart rate.
a Adapted
from Henzlova et al.18
necessarily indicative of coronary heart disease. ECG
recordings and blood pressure measurements are taken
every minute during the testing and for 3 to 5 minutes
during the recovery phase.
Adenosine should be avoided in patients with bronchoconstrictive or bronchospastic lung disease because
of the risk for bronchospasm. It also should not be given
to patients who have second- or third-degree atrioventricular block, sick sinus syndrome, symptomatic bradycardia (except in patients with a functioning pacemaker),
or ventricular tachycardia. Because adenosine has a short
half-life, adverse signs and symptoms typically resolve
shortly after the infusion has ended.22 The sensitivity of
adenosine stress testing with echocardiology for detecting
coronary artery disease is 62% to 79%, and the specificity
is 88% to 93%.23 Because use of vasodilators does not
require that a target heart rate be reached, vasodilators are
useful in patients who have chronotropic incompetence
(inability of the heart rate to increase with increased
activity) or depend on a pacemaker.16
Dipyridamole Dipyridamole (Persantine) is another
vasodilator that may be used for stress nuclear imaging.
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It stimulates production of prostacyclin, a potent inhibitor
of platelet aggregation and vasodilatation. It also inhibits
uptake of adenosine and increases local concentrations
of adenosine.22 Dipyridamole is administered intravenously at 0.14 mg/kg per minute for 4 minutes.22 A
radiopharmaceutical is injected 3 to 5 minutes after the
dipyridamole infusion. Like adenosine, dipyridamole
should be avoided in patients with bronchospastic lung
disease. Adverse effects include chest pain, ECG changes,
headache, and dizziness.22 Dipyridamole has a longer
half-life than does adenosine, and adverse signs and
symptoms may last for 15 to 30 minutes after the infusion
is complete.22 If an emergency occurs, aminophylline
should be given slowly at a dose of 50 to 250 mg as an
intravenous bolus 1 to 2 minutes.24
Regadenoson Regadenoson (Lexiscan) is another
drug that may be used for myocardial perfusion imaging.
Some evidence25 suggests that patients subjectively feel
better after a regadenoson stress test than after an adenosine stress test. Regadenoson is more cardioselective for
adenosine receptors than is adenosine and is administered
as a single rapid bolus of 0.4 mg over 10 seconds and then
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Table 6
Adrenergic receptors and associated
therapeutic response
Receptor
Response
1
Vasoconstriction, bronchoconstriction
2
Vasoconstriction, platelet aggregation
1
Increased contractility,
increased heart rate
2
Vasodilatation, bronchodilatation
an immediate 5-mL bolus.22 The radiopharmaceutical
for imaging myocardial perfusion is administered 10 to
20 seconds after the bolus.26 Regadenoson is contraindicated in patients with second- or third-degree heart
block and in patients with sinus node dysfunction who
do not have a functioning pacemaker. Use of dipyridamole
should be stopped 48 hours before regadenoson is
injected, and patients should not ingest any theophylline
or caffeine-containing products for at least 12 hours
before the stress test.
Dobutamine Dobutamine is another pharmacological stressor useful in patients who are unable to physically exercise and have contraindications to use of
vasodilators, such as chronic obstructive pulmonary
disorder. Dobutamine is often used in conjunction with
echocardiography but may also be used with nuclear
imaging. Dobutamine is primarily a 1-inotrope but also
has some 2- and 1-agonist properties (Table 6). The
drug increases heart rate and myocardial contractility,
leading to
Nuclear stress testing is useful for detecting increases in
coronary
coronary artery disease in asymptomatic
adults with a strong family history of coro- blood flow
and myocarnary artery disease or diabetes mellitus
dial oxygen
and in adults who have a coronary artery
demand withcalcium score >400.
out causing
bronchoconstriction as the vasodilators can. During
pharmacological stress testing, dobutamine is infused
intravenously at a rate of 10 μg/kg per minute and
increased by 10 μg/kg per minute every 3 minutes to a
maximum dose of 50 μg/kg per minute until the target
heart rate is achieved.27 A radiopharmaceutical may be
injected once the target heart rate has been achieved.
Patients may feel shaky or nauseated during dobutamine
administration. Patients with uncontrolled hypertension,
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atrial fibrillation, or tachyarrhythmia should not receive
dobutamine.27 Atropine may be administered at a dose of
0.25 to 0.5 mg if the patient is having difficulty achieving
the maximum heart rate.27
Nuclear Stress Testing
Both exercise and pharmacological stress testing can
be used in combination with intravenous injection of a
radiopharmaceutical such as thallous chloride Tl 201 or
technetium sestamibi Tc 99m (Cardiolite).22 These agents
are distributed into the myocardial tissue proportionally
to the flow of blood. In nuclear stress testing, also called
myocardial perfusion imaging, a radiopharmaceutical is
injected first, before peak exercise stress or peak pharmacological vasodilatation. Then 15 to 20 minutes later, a
rest scan is done. After the rest scan, the stressing agent
and a second injection of the radiopharmaceutical are
injected. Then after 30 to 60 minutes, a stress scan is
done for comparison with the rest scan. Vessels that dilate
take up more of the radiopharmaceutical than do diseased vessels. This lack of uptake is known as a perfusion
defect. A reversible perfusion defect indicates ischemia
and will occur during stress but will normalize when the
heart is at rest.22 A nonreversible or fixed defect (evidence
of decreased uptake of radiopharmaceutical on both
rest and stress images) suggests a scar or hibernating
myocardium.22 Hibernating myocardium is defined as an
area of dysfunctional myocardium that improves once
perfusion is reestablished. Contraindications to nuclear
stress testing include the general contraindications for
any stress test and the medications mentioned earlier.
Some scanners may have a weight requirement, making
nuclear stress testing an inappropriate technique for
patients who weigh more than 135 to 158 kg (300-350 lb).
Nuclear stress testing is useful for detecting coronary
artery disease in asymptomatic adults with a strong family history of coronary artery disease or diabetes mellitus
and in adults who have a coronary artery calcium (CAC)
score greater than 400.13 It has no benefit in asymptomatic patients who have low or intermediate risk for
heart disease.13
Computed Tomography
Another method of noninvasive diagnostic testing is
computed tomography (CT). Historically, CT techniques
for visualizing coronary arteries have been difficult,
because of the constant motion of the heart during the
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cardiac cycle and respiratory motion produced by the rising and falling diaphragm during inspiration and expiration.28 With the advent of multidetector CT (MDCT),
improvements in spatial and temporal resolution have
improved visualization of the coronary arteries, making
this imaging method more reliable for detecting coronary artery disease.28 With MDCT, an arm with an x-ray
tube located within a moveable platform (a gantry)
rotates around a patient with 165-ms or faster imaging
at 3.0-mm intervals.29 X-rays are taken on a detector
array and converted to images.30 Each detector array
consists of an alignment of narrow rows or channels.
Most arrays have 64 or more rows. The greater the number of rows, the shorter are the scan time and duration
of exposure to radiation.30 MDCT testing is conducted
during a single breath hold.28 Patients’ cooperation and
ability to understand and follow directions are paramount to the success of this method.
ECG gating is used, and images are acquired solely
during a specific part of the cardiac cycle. With MDCT,
images are obtained during end systole and mid diastole
when the heart motion is the least.28 In an effort to improve
image quality, -blockers or calcium channel blockers
are often administered before the procedure to decrease
heart rate and reduce or eliminate ectopy. Because of the
adverse impact of motion on the quality of the images,
patients with atrial fibrillation are not candidates for
this imaging technique.28 Sublingual nitroglycerin may
also be given to dilate the coronary arteries and improve
visualization. In order to avoid a risk for profound hypotension, nurses must ensure that patients have not used
phosphodiesterase inhibitors (eg, sildenafil, tadalafil,
and vardenafil) within the previous 24 hours. Pacer and
implantable cardioverter defibrillator wires, artificial
valves, and surgical clips can be a source of artifacts and
can make the images uninterpretable.31 CT can be used
for CAC scoring and with angiography.
CAC Scoring
The atherosclerotic process involves deposition of
calcium in the coronary arteries. Any calcium deposition
in the coronary arteries is considered abnormal. CAC
screening is useful as an adjunct method for predicting
risk for coronary artery disease in asymptomatic patients
beyond traditional risk-factor stratification. The 2010
guidelines13 of the American College of Cardiology Foundation and the American Heart Association recommend
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CAC screening as a reasonable method for risk assessment
in patients who are asymptomatic and have a 10% to 20%
10-year Framingham risk for a coronary event (intermediate risk). CAC screening may also be reasonable for
patients who are at low to intermediate risk (6% to 10%
10-year risk for a coronary event).13 According to the
guidelines, patients who are asymptomatic and at low risk
should not undergo CAC measurement for cardiovascular risk assessment.13 Use of CAC scoring may be reasonable, however, in asymptomatic patients who are more
than 40 years old and have diabetes mellitus (high risk).13
Electron Beam CT
One method of CAC screening includes electron
beam CT (EBCT). In EBCT, an electron beam rotates
around the patient who is supine on the table with the
arms extended
over the head or In EBCT, a computerized scoring
at the side. The
algorithm is used to generate a calcium
beam is directed score, which provides a measurement
at a stationary
of the area and density of the calcium
tungsten target
deposition in the coronary tree.
that lies beneath
the patient. EBCT allows the acquisition of 1.5- to 3-mm
sections with an exposure time of 50 to 100 ms during a
single breath hold. No intravenous contrast material is
used, and the patient does not need to avoid ingesting
anything by mouth beforehand. The procedure requires
approximately 10 to 15 minutes. Patients usually experience little to no discomfort, and the CT tube is typically
much larger than that of a traditional magnetic resonance imaging (MRI) device, so claustrophobia is not
much of a concern. Patients may be asked to remove
metal objects near the chest, such as jewelry or underwire bras, because these objects may produce artifacts
in the images. EBCT requires less radiation than does
MDCT; however, radiation from CAC screening is associated with a small but measurable increase in the risk
for cancer.32
In EBCT, a computerized scoring algorithm is used to
generate a calcium score, which provides a measurement
of the area and density of the calcium deposition in the
coronary tree. The most commonly used score is the
Agatston score. Patients who have a score of 10 or less
are considered at low risk. Scores of 11 to 399 indicate
intermediate risk, and patients with a CAC score greater
than 400 are at very high risk.33 In a systematic review33
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23
CASE STUDY
M
s Whitney, a 37-year-old woman with a
history of hypertension and hyperlipidemia, has her cardiovascular conditions
medically managed by her primary care provider. Her
blood pressure is currently 128/78 mm Hg; she is taking olmesartan 10 mg twice a day and nebivilol 5 mg/d.
Her lipid profile is as follows: total cholesterol 170
mg/dL (4.40 mmol/L; desirable <100 [2.60]), triglycerides 128 mg/dL (1.45 mmol/L; desirable <150
[<1.69]), low-density lipoproteins 78 mg/dL (2.02
mmol/L; desirable <70 [<1.81]), and high-density
lipoproteins 30 mg/dL (0.78 mmol/L; desirable >50
[>1.3] in women). She takes rosuvastatin 10 mg once a
day and omega-3-acid ethyl esters (Lovaza) 1 g/d. Other
medications include aspirin 81 mg/d and escitalopram
10 mg/d. Her body mass index (calculated as weight in
kilograms divided by height in meters squared) is 23.
She is physically active and does 45 minutes of aerobic
exercise daily, does not smoke, and describes herself as
a social drinker. She works as a pharmaceutical representative. She has a family history of coronary artery
disease on her father’s side, and she has a 42-year-old
brother who has coronary calcification. Although she
currently has no indications of coronary artery disease,
she was referred for further evaluation because she was
concerned about her risk for a heart attack.
Ms Whitney had electron beam computed tomography through a heart and vascular screening program at
her local hospital to determine her coronary artery calcium score. The score was greater than 2000, which is in
the 99th percentile. The cardiologist recommended that
Ms Whitney have treadmill stress echocardiography. During the stress test, she had exercise-induced hypokinesis
of the distal anterior septal region, no ST-segment depression, and some vague chest discomfort. Ms Whitney later
had coronary angiography. The findings indicated that
she had nonobstructive coronary atherosclerosis with
severe coronary calcification, although she had no evidence of obstructive disease. No percutaneous coronary
intervention was indicated at this time. Medical therapy
was maximized, and she was referred for advanced cholesterol assessment and endocrine screening because of
the unusually high coronary calcification revealed by both
electron beam computed tomography and angiography.
of CAC screening with standard EBCT, the range of sensitivities for detecting coronary artery disease were 68%
to 97%, and specificities were 52.6% to 94%.
blockage), moderate (50%-60% blockage), and severe
(>70% blockage).35 CTA is also useful in evaluating patency
of coronary bypass grafts, detecting coronary anomalies,
evaluating coronary aneurysms and cardiac masses, and
assessing complex congenital heart disease.28 This method
is considered superior to catheter angiography for imaging
the aorta and pulmonary arteries.34 CTA is less useful in
evaluating patients who have received percutaneous
stents because the stents can cause artifacts.28
Most CTAs are performed with MDCT because of
the high spatial and temporal resolution of the latter.34
Patients undergoing CTA should have nothing by mouth
for 3 hours before the study and should avoid ingesting
caffeine 24 hours before the study because caffeine can
elevate heart rate. Nurses should assess patients for adequate hydration because dehydration increases the risk
for contrast-induced nephropathy (CIN).35 Vital signs
are assessed before the procedure, and a large-bore
intravenous catheter is placed. Because iodinated contrast medium is administered via injection at a rate of
CT Angiography
CAC scoring by EBCT and MDCT is limited: noncalcified plaque cannot be visualized, and the degree of
luminal stenosis cannot be determined. CT angiography
(CTA) is an excellent technique in which ECG gating and
administration of intravenous contrast material are used
to visualize and measure calcified areas of coronary
plaque and luminal stenosis.34 Although considered
inferior to cardiac catheterization, CTA can provide
visualization of small, tortuous arteries (as small as 1
mm in diameter).34 Coronary CTA can provide valuable
information on distribution, severity, morphology, and
composition of coronary arterial plaque, along with
prognostic information on the severity of both obstructive (>50% blockage) and nonobstructive (<50% blockage) disease.28 Stenosis is usually reported as mild (<50%
24
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www.ccnonline.org
5 mL/s, a 20-gauge or larger cannula should be placed
in the cephalic or medial cubital vein.35 The patient is
positioned in the CT scanner with the arms above the
head, and ECG leads are applied. Patients are asked to
hold their breath at various intervals during the test,
and during injection of the contrast medium, they may
experience a sensation of flushing, warmth, or a metallic
taste in the mouth.22
Risks of CTA include allergic reactions (anaphylactic
or idiosyncratic) and CIN because iodinated contrast
medium is toxic to renal tubular cells. An allergic reaction is the most frequent form of a reaction to contrast
material and may, on occasion, be fatal.35 Patients at
greater risk for reactions include those with asthma, a
history of reaction to contrast material, and renal disease.35 Patients who are more than 75 years old or who
have congestive heart failure, diabetes, or multiple
myeloma are at increased risk for CIN.36
CIN is defined as an increase in the serum level of
creatinine of at least 25% from baseline after administration of iodinated contrast material.35 The incidence of
CIN is 3.3% to 8% in patients without preexisting renal
dysfunction.36 Nurses who provide care for patients undergoing CTA should assess baseline renal function. Patients
with a glomerular filtration rate greater than 60 mL/min
per 1.73 m2 are considered at low risk for CIN, those
with a rate of 30 to 60 mL/min per 1.73 m2 are considered at intermediate risk, and patients with a rate less
than 30 mL/min per 1.73 m2 are considered at high risk.35
Patients at intermediate or greater risk should have nephrotoxic medications discontinued 2 days before CTA, and
those considered at high risk should avoid iodinated
contrast material altogether unless CTA is absolutely
necessary.35 All patients taking metformin should discontinue the medication on the day of the imaging and
for 48 hours after the administration of contrast material
because of the risk for lactic acidosis.35 Patients should
be assessed for adequate hydration, and oral intake of
fluids should be encouraged within the 12 hours before
CTA. Patients at greatest risk may benefit from intravenous hydration before the imaging. A reaction to contrast material within the preceding 24 hours is a relative
contraindication to CTA.35 After the procedure, patients
should be advised to increase oral intake of fluids, or fluids
may be administered intravenously. Follow-up measurements of serum creatinine should be obtained 48 hours
after CTA for patients at intermediate or high risk for CIN.35
www.ccnonline.org
One drawback to CTA is that patients must be in sinus
rhythm. Intravenous -blockers may be administered to
lower the patient’s heart rate to less than 70/min but
may be contraindicated in patients with asthma, severe
aortic stenosis, second- or third-degree atrioventricular
block, or severe left ventricular dysfunction. The degree
of stenosis may be difficult to assess in heavily calcified
vessels, and if marked blockage is detected, the patient
will still have to undergo invasive coronary angiography
for intervention.37 The radiation dose associated with
CTA is also higher than that associated with invasive
coronary angiography.
Compared with invasive coronary angiography,
CTA has a 92% sensitivity and a 95% specificity.28 Its
high negative predictive value of 97% to 99% makes it a
useful test for asymptomatic patients who have an
intermediate Framingham Risk Score of 10% to 20%.28
Coronary CTA is not recommended as a method of risk
assessment in
asymptomatic Contrast-induced nephropathy is defined
adults.13 It is, as an increase in the serum level of
however, rea- creatinine of at least 25% from baseline
after administration of iodinated contrast
sonable to
material.
consider for
patients with
intermediate risk for coronary heart disease or for
patients who are symptomatic or who have inconclusive results from pharmacological stress testing or are
unable to undergo nuclear myocardial perfusion imaging or echocardiography.13
Cardiac MRI
In cardiac MRI, a static magnet, pulsed radiofrequency energy, and gradient magnetic fields are used to
image the body. These studies can be performed with
patients at rest or during the intravenous administration
of a pharmacological stress agent such as dobutamine.
Cardiac MRI may be useful for assessment or detection
of dynamic cardiac anatomy and ventricular function,
cardiomyopathies and fibrosis, myocardial ischemia and
viability through the use of pharmacological agents, perfusion abnormalities at rest or during pharmacologically
induced stress, cardiac masses or pericardial disease,
valvular disease, and complex congenital and coronary
anomalies.38 It is not recommended for cardiovascular
risk assessment in patients who do not have symptoms
of coronary heart disease.13
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25
Cardiac MRI has several advantages.39 Patients are
not exposed to ionizing radiation, radioactive isotopes,
or iodinated contrast material unless the imaging is done
in conjunction with a stress test. Images can be obtained
without regard to a patient’s body size. The imaging
method can be used to assess cardiovascular anatomy
and structure, determine myocardial viability, measure
wall motion, visualize myocardial perfusion, and define
the course and orientation of coronary arteries. Also,
cardiac MRI has high temporal and spatial resolution.
It is particularly useful in patients who have allergic
reactions to contrast material or have chronic kidney
disease in whom exposure to contrast material would be
problematic.40 Disadvantages include cost and lack of
widespread availability; most cardiac MRI is done at
specialized centers.
Nursing considerations include assessment of patients
for metal objects that are contraindicated in any MRI,
such as neural stimulators, aneurysm clips, cochlear
implants, metal fragments in the eye, and infusion pumps.
Patients who have received coronary stents should not
have MRI within the first 6 weeks after placement of the
stent. Pacemakers, internal cardioverter defibrillators,
and hemodynamic support devices such as intra-aortic
balloon pumps or left ventricular assist devices are contraindications to MRI, although some newer versions
of these devices are considered MRI compatible. Patients
should remove all jewelry and hairpins. Tattoos may
heat up slightly but are not considered contraindications
to the imaging.40
Intravenous access is required for infusion of the
radiopharmaceutical. During the procedure, patients
have continuous monitoring of ECG findings and vital
signs, including oxygen saturation. Patients lie supine on
a flat table in a tunnel-like apparatus. Because of the loud
knocking noise made by the MRI scanner, patients wear
headsets to protect their ears and may be given a mild
anxiolytic. Patients can communicate via an intercom
system and are asked to hold their breath for 10 to 20
seconds several times during the imaging. The procedure lasts 1 to 2 hours. Cardiac MRI may be especially
difficult for patients who are claustrophobic.
Conclusion
Advances in noninvasive cardiac imaging techniques
most likely will continue during the next several years.
Although coronary angiography remains the gold standard
26
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Vol 34, No. 3, JUNE 2014
for coronary artery assessment, newly emerging techniques
most likely will begin to play a larger role in patient
assessment and offer potential for increased accuracy
and patient satisfaction in a noninvasive approach. Nurses
must be knowledgeable about the various techniques
available in order to offer patients education and guidance
(Table 7—available online at www.ccnonline.org). CCN
Financial Disclosures
None reported.
Now that you’ve read the article, create or contribute to an online discussion
about this topic using eLetters. Just visit www.ccnonline.org and select the article you want to comment on. In the full-text or PDF view of the article, click
“Responses” in the middle column and then “Submit a response.”
To learn more about cardiac monitoring, read “National Survey
of Cardiologists’ Standard of Practice for Continuous ST-Segment
Monitoring” by Sandau et al in the American Journal of Critical
Care, March 2010;19:112-123. Available at www.ajcconline.org.
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