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CORONARY COMPUTED TOMOGRAPHY
355
quality. As the temporal resolution of the newer
generation CT scanners improve, strict heart rate
control has become less critical. Patients in atrial
fi brillation (which makes gating more diffi cult) are
usually excluded, but this restriction is less stringent
with the newer, faster CT scanners. If functional data
is desired, a cine data set can be obtained with cer-
tain acquisition protocols that permit the assessment
of global and regional left ventricular function in
the hope that this information may add diagnostic
and prognostic value to information on the coronary
arterial tree.
The patient is typically out of the ED for 30
minutes, of which approximately 20 minutes is
for patient preparation and image acquisition. The
remaining time is for transportation. Besides cardiac
dysrhythmias, other important exclusion criteria
include elevation in serum creatinine or other con-
cerns for contrast-induced nephropathy, allergy to
iodinated contrast, pregnancy, and unwillingness to
withhold use of metformin for 48 hours after the
contrast administration. The radiation dose deliv-
ered by CT angiography has been estimated to be
approximately 10–20 mSieverts per examination,
but this is decreasing with newer generation scan-
ners and employment of dose-saving techniques
(such as lower tube voltage for thinner patients,
minimizing the scan range, and EKG-tube current
modulation).
25,26
This compares to approximately 12
mSieverts of radiation exposure with nuclear isotope
(i.e. sestamibi) utilization.
The cross-sectional or transaxial images obtained
(called source images) are reviewed by CT readers,
typically general or cardiac radiologists or cardi-
ologists. These source images are reconstructed into
multi-planar reformations (MPR) that are oriented
into three standard planes (coronal, sagittal, and
axial), and can be manipulated and viewed by the
user into any obliquity. A maximum intensity projec-
tion (MIP) image can be reconstructed using larger
slice thickness to produce better contrast differentia-
tion between the contrast and noncontrast enhanced
structures. Three-dimensional volume-rendered tech-
niques (VRT) can provide visually pleasing images
that graphically demonstrate the location of lesions.
The reader typically comments fi rst on whether the
study is interpretable, meaning that all 17 segments
of the coronary arterial system, as described by the
AHA, are clearly visualized. Due to the blooming
left anterior descending, circumfl ex, and right) can be
estimated. Plaque can be identifi ed as calcifi ed (hard),
noncalcifi ed (soft), or mixed. Both the intra- and ext-
racardiac contents of the entire thoracic cavity are
visualized and additional noncardiac or “incidental”
fi ndings outside the coronary vascular tree may be
discovered.
21
Image acquisition and interpretation
The CT image is constructed from an X-ray source that
rotates around the patient to be imaged, and a detec-
tor array that is positioned on the opposite side. In a
multidetector CT scanner, a detector array may con-
tain many rows of detectors or sensors. As a patient
is passed through the X-ray source and these sensors,
multiple cross sectional images (slices) are obtained.
They are then reorganized by computers to create
three-dimensional reconstructions of the anatomic area
of interest. Based on the generation of the scanner, these
source images typically contain 16, 64, or 128 parallel
cross sections. Modern CT scanners provide isotropic
or near-isotropic spatial resolution of 0.4–0.5 mm,
with a temporal resolution of 83–250 milliseconds.
This allows visualization of the complete coronary tree
in a single breath hold over several heart beats.
22
To visualize the coronary arterial tree, an initial
test bolus of approximately 10–20 ml of intravenous
imaging contrast is given to determine timing, fol-
lowed by a full bolus of 80–100 ml (depending on
the scan range). While most imaging protocols inject
contrast, some acquisition protocols obtain a non-
contrast CT fi rst to calculate a calcium (Agatston)
score. A calcium score is measured in Hounsfi eld
units, and if high, suggests the presence of advanced
coronary artery disease. Due to the blooming arti-
fact from calcifi cation, a high calcium score can sug-
gest that the scan will be more diffi cult to interpret.
23
Sublingual nitrates are usually administered to maxi-
mally dilatate the coronary vessels.
24
EKG gating
allows the CT angiography to be timed to the car-
diac cycle to provide motion-free images. Due to the
limited temporal resolution of certain CT scanners,
slower heart rates are needed to achieve the desired
motion-free images. Thus, for 64-slice CT scanners
or older generation scanners, oral or intravenous
beta-blockers are often administered to patients with
heart rates above 65 beats per minute (bpm), with
a goal heart rate below 60 bpm for optimal image
CHAPTER 25
356
and incidental intra-and extracardiac fi ndings as well
(see Figure 25-1 for examples).
21
Scientifi c basis for the use of CCT in ED populations
The utility of the CCT to rule out ACS rests on
evidence that ACS usually occurs in the context of
coronary artery disease.
36,37
Hence, a test that dem-
onstrates that a patient has no or minimal coronary
artery disease decreases the likelihood that this
patient is suffering from ACS. The original research
on CCT compared its ability to identify lesions in
the coronary arteries to coronary arteriography,
and compared its sensitivity and specifi city to this
criterion (gold) standard. The ability of the CCT to
detect both plaque and stenosis was measured. Test
characteristics such as sensitivity or specifi city were
reported either by the number of coronary artery
segments or by the number of patients evaluated cor-
rectly. For the fi nding of CA stenosis by evaluable
segment, both individual studies and meta-analyses
suggest sensitivities of 80–95% and even higher, with
specifi cities around 90–95%.
10,28–35,38,39
However, the
percentage of CA segments that can be evaluated
vary from 80–100% depending on the generation
of the scanner.
40–43
For the fi nding of CA stenosis
on a per patient analysis, ranges for sensitivities are
95–100%, with specifi cities of 84–100%.
35,41,44,45
The sensitivity of CCT for fi nding both CA plaque
and stenosis varies by whether plaque is calcifi ed
or not, the size of the CA being examined, and the
and beam-hardening artifacts, a high burden of coro-
nary artery calcifi cation makes the degree of luminal
obstruction diffi cult to interpret, as do prior open or
percutaneous (i.e., coronary stent) revascularization
procedures. For this reason, patients with a history
of coronary artery bypass graft surgery or percuta-
neous coronary interventions with stenting are often
excluded. Other causes of uninterpretable coronary
artery segments involve technical issues, such as respi-
ratory or motion artifacts.
27
A typical report will comment on which if any of
the four main coronary arteries (CA) contain plaque,
and how much of their lumen is obstructed. Luminal
obstruction may be reported quantitatively or quali-
tatively. Qualitative description of luminal obstruc-
tion is typically preferred, but may vary signifi cantly
depending on the CT reader and local institutional
protocol for interpretation. Depending on CCT inter-
preter or author, a plaque burden considered “mild”
may be reported as causing luminal narrowing of
between 1% and 25%, or sometimes up to 40%.
The term “moderate” severity may be used either for
lesions obstructing from 26–50% or from 41–70% of
the CA lumen. The term “severe” has been applied by
some interpreters for any luminal narrowing greater
than 50%, but is usually reserved for lesions caus-
ing greater than 70% obstruction. This high grade or
“severe” obstruction is also referred to as “signifi cant
stenosis.” Complete or total occlusion is reported
when no contrast appears to traverse a lesion.
28–35
A
fi nal report may describe wall motion abnormality
Figure 25.1 Images of CCT CAS: Source Images, multiplanar
reformat; 3D image all with pathology. CT images of the
right coronary artery (RCA) show high-grade stenosis
of a noncalcifi ed plaque in its mid segment (arrow).
A. Multi-planar reformation (MPR) image in the axial
view. B. Maximum intensity projection (MIP) image with
also calcifi cation in the right coronary cusp, as well as
mild calcifi ed plaques in the proximal RCA, left main and
proximal left anterior descending artery but no signifi cant
stenosis. C. 3D-volume rendering technique (VRT) image.
Courtesy of Quynh Truong, MD, Massachusetts General
Hospital, Boston, MA.
CORONARY COMPUTED TOMOGRAPHY
357
typically death, acute MI, or a coronary artery revas-
cularization procedure. Patients with no or nonob-
structing plaque are shown to be free of MACE events
for at least 2 weeks and up to 12 months.
47,52
The
change in ED length of stay varies by study, but there
is some suggestion that time in the ED decreased.
52,54
This literature suggests that patients with a nega-
tive biomarker 8 hours after onset of symptoms, a
non-diagnostic initial EKG, a low TIMI score, and
no or mild coronary artery disease on CCT can be
safely discharged from the ED. Patients with severe
or total obstruction should receive additional cardiac
risk-stratifi cation testing per institutional guidelines.
The best approach for patients with CCTs displaying
moderate stenosis remains unclear.
47,52,53
Unresolved issues regarding CCT in ED populations
It appears that CCT offers a unique and accurate
ability to provide information on the status of an ED
patient’s CAs in real time. It has a good to excellent
sensitivity and predictive negative value both to diag-
nose ACS and to predict major adverse cardiac events.
Why, then, is it not the perfect test? Unresolved issues
revolve around the degree to which it changes pro-
viders’ decisions, and how it compares to traditional
cardiac risk stratifi cation tests used in the past. In
particular, its cost effectiveness has been called into
question.
55,56
The few articles that exist suggest that CCT has the
ability to change clinicians’ decisions, and to avoid
admissions in patients who do not have ACS.
57,58
In
studies that have compared the ability of the CCT
to cardiac nuclear imaging to reach the correct
clinical diagnosis, the sensitivities of these tests are
comparable.
47,59
Limited data also suggest that the
CCT can change clinical diagnoses from ACS to other
diagnoses and possibly lead to discharge from the ED
in 20–40% of patients.
57,58
The cost effectiveness of
CCT may vary by gender and by its cost.
50,60
In sev-
eral studies, it appears to be as or more cost effective
than alternative diagnostic strategies.
29,47,54
However,
these studies were conducted at single sites, and most
involved modest study population sizes. Conclusions
also vary a great deal depending on the value chosen
for input variables.
50,60
While they suggest that CCT
may indeed be comparable to or better than alter-
native imaging strategies and be cost effective, large
multicenter trials are needed.
55,56
generation of scanner used.
34,41
Newer generation
scanners provide higher sensitivity.
41,46
Since a scan
that accurately characterizes 16 of the 17 CA seg-
ments but misses a stenosis in the 17th would affect
patient care, per patient data may be more relevant
to clinicians, particularly since studies vary on how
they include unevaluable segments in a per patient
analysis. Since stenosis has not been ruled out in
a patient with even only one unevaluable segment,
patients with these indeterminate scans often receive
another risk stratifi cation test such as a cardiac
nuclear-imaging test.
Once it was established that CCT measured CA
plaque and stenosis reliably compared to coronary
arteriograpy, a number of studies examined the clini-
cal usefulness of this information. These studies dem-
onstrate the ability of the CCT to diagnose ACS in
undifferentiated ED population with sensitivities from
0.83–l.00 and specifi cities from 0.74–1.00.
28–30,33,35,47–49
Summary estimates from pooled data suggest sensitivi-
ties of 0.95 and specifi cities of 0.90.
27,41
Furthermore,
the extent of plaque adds to the diagnosis of ACS and
contributes diagnostic information beyond that of tra-
ditional risk factors or clinical estimates of the prob-
ability of ACS.
29,30
The most recent published studies have examined
how well CCT results predict short and long-term
safety in patients discharged from an ED. Patients
studied were typically at low or moderate risk for
ACS; in fact, it has been demonstrated that the CCT
is most helpful in patients with low or medium pretest
probabilities of ACS, and has less value in those with
high pretest probabilities.
50,51
While the defi nition of
low or moderate risk varies, patients in these stud-
ies are typically those with nondiagnostic ED evalua-
tions, including normal initial troponin measurements
and nonischemic EKGs.
52
Risk-stratifi cation scores,
such as the TIMI risk score indicating low risk for
subsequent adverse events, have been used for patient
selection as well. Depending on the availability of
the scan and interpreters, the CCT is obtained from
the ED or from an observation unit or medical fl oor.
Patients with no or non-obstructing plaque, typically
occluding less than 50% of any CA lumen (i.e., no
stenosis), are discharged without any further cardiac
testing. Their calcifi cation score is often used for deci-
sion making as well.
47,52,53
Study populations were followed for the develop-
ment of Major Adverse Cardiac Events (MACE),
CHAPTER 25
358
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1993. Am J Emerg Med. 1996;14(4):341–345.
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guidelines for the clinical use of cardiac radionuclide
imaging--Executive Summary: A report of the American
College of Cardiology/American Heart Association task
With respect to the test’s accuracy, while false neg-
ative tests do occur, they are relatively few, and the
negative predictive value of CCT is high. Sensitivity
and specifi city depend on which plaque or stenosis
criterion is used to defi ne a “positive” or abnormal
CCT. The major concerns that have been raised are
around the issue of false positives. These are patients
who have signifi cant stenosis on CT, but do not
turn out to have an ACS event. In these cases, the
visualized stenosis did not represent a thrombosis
related to a culprit lesion or vulnerable atheroscle-
rotic plaque. For example, in one study, a higher
number of coronary arteriograms is associated with
use of the CCT.
47
A second area of concern revolves
around radiation doses. Modeling studies suggest
that the lifetime risk of cancer from CCT is signifi -
cant, particularly in women and the young.
61
Newer
data suggest a decreasing dose of radiation with
newer generation scanners.
25
Finally, reactions to IV
contrast and contrast-related renal failure have been
raised as potential issues.
62
Section IV: Decision making
The advantages of CCT are that it can be performed •
and interpreted relatively quickly, and a result
demonstrating absent or only minimal CA plaque
has been associated with lack of ACS and a good
prognosis.
To date, there is minimal published data to show •
how much it changes provider decisions, and how
it compares to other available testing.
Issues of risk, especially with regard to radiation, •
need to be considered.
The specifi c population in which it will be used •
needs to be clearly defi ned.
The authors would like to acknowledge Quynh
Truong, MD, for her advice on technical issues involv-
ing CCT.
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pain. J Am Coll Cardiol. 2007;49(8):863–871.
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Diagnostic accuracy of noninvasive coronary angiogra-
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Rubinshtein R, Halon DA, Gaspar T, et al. Usefulness 49
of 64-slice cardiac computed tomographic angiog-
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patients with chest pain of uncertain origin. Circulation.
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SECTION SIX
Cardiac Surgery Complications
363
Cardiovascular Problems in Emergency Medicine: A discussion-based review, First Edition.
Edited by Shamai A. Grossman and Peter Rosen.
© 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.
Postcardiac Surgery Emergencies
Jonathan Anderson
1
& Shamai Grossman
2
1
Instructor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center,
Boston, Massachusetts, USA
2
Director, Cardiac Emergency Center and Clinical Decision Unit, Beth Israel Deaconess
Medical Center, Assistant Professor of Medicine, Harvard Medical School,
Boston, Massachusetts, USA
26
Section I: Case presentation
A 57-year-old man was brought to the emergency
department (ED) by EMS. The paramedics reported
that they found the man sitting on a sidewalk a couple
of blocks from his apartment. He was diaphoretic,
and felt too weak to walk home. A passerby had
noticed him, and called 911. On scene, the patient
had a blood pressure of 85mmHg/palpation, and a
fi nger-stick glucose of 227 mg/dl. They noted him to
be tachycardic with an irregular rhythm at a rate of
about 150 beats/min. He denied chest pain or dys-
pnea, and was transported to the ED immediately;
they did not have time to perform an EKG en route,
but did establish IV access in one arm, and started a
normal saline drip.
The patient appeared fl ushed and diaphoretic. The
initial vital signs were: temperature 37.8ºC (100.1ºF)
orally, heart rate 156 beats/min (irregular), blood
pressure 83/52 mmHg, respiratory rate of 18 breaths/
min, and oxygen saturation 98% on room air. On
physical examination there was a fresh surgical scar,
a median sternotomy. The patient stated, “I was just
released from the hospital yesterday. I had heart sur-
gery last week, but I felt great this morning so I went
for a walk to the donut store.” He further complained
about palpitations, weakness, and lightheadedness
that started suddenly about 30 minutes prior. He
stated he was discharged on “a bunch of pills” that he
has been taking faithfully. He again denied chest pain
and dyspnea. The review of systems revealed low-
grade fevers, which the patient noted he had since
surgery. He stated that aside from the heart condition,
high blood pressure, and high blood sugars he had no
other medical problems, no allergies, and had only
had the one surgery in his life.
The patient was an obese male who appeared to
be his stated age. He was in mild distress, but was
lying nearly supine on the gurney. Pertinent fi ndings
included an irregularly irregular and tachycardic car-
diac rate. There were no murmurs or rubs. The lungs
were clear to auscultation. The sternal incision had
some mild erythema extending 1 cm from the incision
over the inferior one-third of its length. The abdomen
was nontender. The remainder of the physical exami-
nation was normal.
A second peripheral IV was established, and blood
was sent for complete blood count, chemistries, cul-
tures, and cardiac enzymes. A portable chest X-ray
study and a urinalysis were ordered. An EKG revealed
atrial fi brillation with a rate of 152 beats/min, a nor-
mal axis, normal intervals, and no ST changes. After
a 500 cc normal saline bolus, the patients’ vital signs
improved to a heart rate of 145 beats/min (irregular)
and blood pressure of 104/65 mmHg. The decision
was made to attempt pharmaceutical control of the
patient’s heart rate. After 5 mg of IV metoprolol, the
CHAPTER 26
364
This is not work aversion; one cannot care for
another surgeon’s postoperative problems as suc-
cessfully as when you are taking care of your own
complications.
Dr. Amal Mattu: I think most surgeons would be
amenable to transfer, especially when it’s after a com-
plicated surgery. Assuming this patient had bypass
surgery, I can’t imagine a cardiothoracic surgeon who
would say anything other than, “Yes, defi nitely trans-
fer him back to us so we can take care of him.”
PR: Before talking about transfer, however, we need
to discuss what interventions would be important
while the patient is in the ED. I am a little surprised
to hear that he was given a beta-blocker with a blood
pressure as low as that reported.
AM: I am also a bit surprised. Even though metoprolol
is beta-one specifi c, because of the negative inotropic
effect, I would be very hesitant to give a beta-blocker
to someone who is already hypotensive. If I did use
metoprolol, I would start out with even lower doses
than were used in this case. Some might argue for
using esmolol instead, since it is titratable, but I’d
still be hesitant even with esmolol, because if your
patient deteriorates and you turn off the esmolol, its
effects may linger for about 15 more minutes. I would
prefer diltiazem, because in my experience, premedi-
cating with calcium can be very helpful in avoiding
hypotension. In addition, if the patient does drop
his blood pressure further, you can always give the
calcium afterward to reverse the vasodilatatory effect
without reversing the chronotropic effect. Other
alternatives might be digoxin, if you’re not in a rush,
or even amiodarone. Although I think amiodarone is
often overused, I’ve had success utilizing it in patients
with this scenario of borderline or low blood pres-
sure plus rapid atrial fi brillation. The fi nal option
is cardioversion, which is particularly useful in the
unstable patient in rapid atrial fi brillation. However,
before any interventions, I would want to know what
comprised this patient’s daily “bunch of pills.” This
list might direct me toward using a medication that
he is already taking, such as a beta-blocker, calcium
channel blocker, or amiodarone.
SG: Would you consider not intervening with this
patient’s rhythm at all, and instead try to treat the
underlying etiology of his atrial fi brillation, such as
treating what’s likely an infectious process?
patient’s vitals were unchanged. An additional 5 mg of
IV metoprolol was administered, with reduction of the
rate to 95 beats/min, and improvement of the blood
pressure to 110/70 mmHg. The patient noted that his
subjective malaise and weakness felt improved.
The patient’s laboratory studies showed a white blood
cell count of 18,000 cells/mm
3
with a slight left-shift,
a blood sugar of 230 mg/dl, and a creatinine of
1.3 mg/dl. The chest X-ray study showed sternal wires
from the median sternostomy, and some widening of
the mediastinum. The urinalysis was normal. An ini-
tial diagnosis of mediastinitis was made, the patient
was started on broad spectrum antibiotics, and was
admitted to the cardiac surgery service.
Section II: Case discussion
Dr Peter Rosen: Was the patient’s cardiac surgery per-
formed at your medical center, or is he new to your
hospital?
Dr Shamai Grossman: The surgery was at an outside
hospital.
PR: Let’s discuss this case from both vantage points.
Clearly, if the surgery was performed at your hospital,
then you are going to have an easier time evaluating
this patient because you will have access to his records.
You will be able to fi nd out what the surgery was,
what the postoperative course was, and you should
be able to contact the surgical service that cared for
him expeditiously. If he is new to your hospital, then
that’s a problem; you don’t have easy access to any
of these materials, and you will have to retrieve them.
While he may be able to tell you which hospital he is
from, he may not know the details of his surgery. I am
amazed at the number of times patients don’t get back
to the hospital where they were recently admitted, even
though it would clearly be preferable for them to be
cared for in that institution. I can understand the con-
straints upon the EMS system, but an extra 10 minutes
of transit time could make hours of difference in the
evaluation of a patient.
SG: Would you attempt to transfer this patient after
stabilization in the emergency department?
PR: Absolutely. I am a fi rm believer that surgeons
should take care of their own postoperative patients.